FUNCTIONALIZED POLYGLYCINE-POLY(ALKYLENIMINE) COPOLYMERS, THEIR PREPARATION AND USE FOR PREPARING ACTIVE INGREDIENT FORMULATIONS AND SPECIAL-EFFECT SUBSTANCE FORMULATIONS

Abstract

The invention relates to copolymers that contain structural units of the formula (I), of the formula (II) and optionally of the formula (III) NR.sup.1CHR.sup.3CHR.sup.4 (I), NHCOCHR.sup.7 (II), NHCHR.sup.9CHR.sup.10 (III), or structural units of the formula (IV), of the formula (V) and optionally of the formula (VI) NR.sup.1CHR.sup.3CHR.sup.4CHR.sup.5 (IV), NHCOCHR.sup.7CHR.sup.8 (V), NHCHR.sup.9CHR.sup.10CHR.sup.11 (VI), wherein R.sup.1 is a residue of the formula COR.sup.2, of the formula CONHR.sup.2 or of the formula CH.sub.2CH(OH)R.sup.12, R.sup.3, R.sup.4, R.sup.5, R.sup.7, R.sup.8, R.sup.9, R.sup.10 and R.sup.11 independently of each other represent hydrogen, methyl, ethyl, propyl or butyl, and R.sup.2 and R.sup.12 represent hydrogen or selected organic residues. These copolymers are characterized by good degradability and can be used, for example, for preparing active ingredient formulations.

Claims

1. Copolymers containing 10 to 95 mol % of structural units of the formula (I), 5 to 90 mol % of structural units of the formula (II) and 0 to 20 mol % of structural units of the formula (III)
NR.sup.1CHR.sup.3CHR.sup.4(I),
NHCOCHR.sup.7(II),
NHCHR.sup.9CHR.sup.10(III), or copolymers containing 10 to 95 mol % of structural units of the formula (IV), 5 to 90 mol % of structural units of the formula (V) and 0 to 20 mol % of structural units of the formula (VI)
NR.sup.1CHR.sup.3CHR.sup.4CHR.sup.5(IV),
NHCOCHR.sup.7CHR.sup.8(V),
NHCHR.sup.9CHR.sup.10CHR.sup.11(VI), wherein R.sup.1 is a radical of the formula COR.sup.2, of the formula CONHR.sup.2 or of the formula CH.sub.2CH(OH)R.sup.12, R.sup.3, R.sup.4, R.sup.5, R.sup.7, R.sup.8, R.sup.9, R.sup.10 and R.sup.11 independently of one another are hydrogen, methyl, ethyl, propyl or butyl, R.sup.2 is selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, aralkyl, C.sub.mH.sub.2mX or (C.sub.nH.sub.2nO).sub.o(C.sub.pH.sub.2pO).sub.qR.sup.6, R.sup.6 is hydrogen or C.sub.1-C.sub.6 alkyl, R.sup.12 is selected from the group consisting of hydrogen, alkyl, alkenyl, cycloalkyl, aryl or aralkyl, X is selected from the group consisting of hydroxyl, alkoxy, carboxyl, carboxylic acid ester, sulfuric acid ester, sulfonic acid ester or carbamic acid ester, m is an integer from 1 to 18, n and p independently of one another are integers from 2 to 4, where n is not equal to p, and and q independently of one another are integers from 0 to 60, at least one of o or q not being equal to 0, the percentages being based on the total amount of the structural units of the formula (I), (II) and (III) or of the formula (IV), (V) and (VI).

2. Copolymers according to claim 1, wherein these contain 20 to 90 mol % of structural units of the formula (I), 10 to 80 mol % of structural units of the formula (II) and 0 to 20 mol % of structural units of the formula (III).

3. Copolymers according to claim 1, wherein R.sup.1 is a radical of the formula COR.sup.2.

4. Copolymers according to claim 1, wherein R.sup.2 is C.sub.1-C.sub.18-alkyl, preferably C.sub.1-C.sub.6-alkyl, and very preferred C.sub.1-C.sub.2-alkyl.

5. Copolymers according to claim 1, wherein n=2 and p=3.

6. Process for the preparation of the copolymers according to claim 1 comprising the steps of i) reacting a polyalkyleneimine containing recurring structural units of formula (Ia) or of formula (IVa) with an oxidizing agent, thereby obtaining a copolymer containing the structural units of formula (Ia) and of formula (II) or containing the structural units of formula (IVa) and of formula (V)
NHCR.sup.3HCR.sup.4H(Ia),
NHCOCR.sup.7H(II),
NHCR.sup.3HCR.sup.4HCR.sup.5H(IVa),
NHCOCR.sup.7HCR.sup.8H(V), wherein R.sup.3, R.sup.4, R.sup.5, R.sup.7 and R.sup.8 have the meaning defined in claim 1, and ii) reacting the copolymer of step i) with an acyl derivative of the formula (VII) or with an isocyanate of the formula (VIII) or with an epoxide of the formula (IX) to give a copolymer according to claim 1
R.sup.2COR.sup.13(VII),
R.sup.2NCO (VIII), ##STR00002## wherein R.sup.2 and R.sup.12 have the meaning defined in claim 1, and R.sup.13 represents a leaving group, in particular fluorine, chlorine, bromine, iodine or an activated carboxylic acid.

7. Process for the preparation of the copolymers according to claim 1 comprising the steps of iii) partial hydrolysis of a polyoxazoline containing recurring structural units of formula (I) or a polyoxazine containing recurring structural units of formula (IV)
NR.sup.1CHR.sup.3CHR.sup.4(I),
NR.sup.1CHR.sup.3CHR.sup.4CHR.sup.5(IV), to a copolymer comprising the recurring structural units of the formula (I) and the formula (III) or the formula (IV) and the formula (VI)
NHCHR.sup.9CHR.sup.10(III),
NHCHR.sup.9CHR.sup.10CHR.sup.11(VI), wherein R.sup.1, R.sup.3, R.sup.4, R.sup.5, R.sup.9, R.sup.10 and R.sup.11 have the meaning defined in claim 1, and iv) reacting the copolymer from step iii) with an oxidizing agent, thereby obtaining a copolymer containing the structural units of formula (I), of formula (II) and optionally of formula (III) or containing the structural units of formula (IV), of formula (V) and optionally of formula (VI)
NHCOCHR.sup.7(II),
NHCOCHR.sup.7CHR.sup.8(V), wherein R.sup.7 and R.sup.8 have the meaning defined in claim 1.

8. Process according to claim 6, wherein the oxidizing agent used is a peroxide, a hydroperoxide or a percarboxylic acid, preferably hydrogen peroxide.

9. Process according to claim 6, wherein the polyalkyleneimine used in step i) is obtained by acidic hydrolysis of a poly(oxazoline) or of a poly(oxazine).

10. Use of the copolymers according to claim 1 for the manufacture of formulations comprising pharmaceutical or agrochemical active ingredients.

11. Use of the copolymers according to claim 1 for applications in the field of active ingredient delivery.

12. Particles comprising copolymers according to claim 1.

13. Particles according to claim 12, wherein these are present as nanoparticles having a mean diameter D.sub.50 of less than 1 m, preferably of 20 to 500 nm.

14. Particles according to at claim 12, wherein these contain pharmaceutical or agrochemical active ingredients.

Description

MATERIALS

[0142] All chemicals and solvents were purchased from commercial suppliers and used without further purification unless otherwise stated. 2-Ethyl-2-oxazoline (EtOx, 99+%), triethylamine (NEt.sub.3, 99.7%), and EtOx were purchased from Acros Organics. 2-Ethyl-2-oxazoline was dried over calcium hydride and distilled under argon atmosphere. Methyl tosylate (MeOTs, 98%), n-decanoyl chloride (98%), and proteinase K were obtained from Sigma Aldrich. Methyl tosylate was dried over barium oxide and distilled under argon atmosphere. Hydrochloric acid (37%) was obtained from Fisher Chemicals. Aqueous hydrogen peroxide solution (30% w/w) was obtained from Carl Roth. Acetyl chloride (approximately 90%) was obtained from Merck Schuchardt. Propionyl chloride (>98.0%), n-butyryl chloride (>98.0%), valeroyl chloride (>98.0%), n-hexanoyl chloride (>98.0%), n-heptanoyl chloride (>98.0%), n-octanoyl chloride (>99.0%), and n-nonanoyl chloride (>95.0%) were purchased from Tokyo Chemical Industry (TCI). Amberlite IRA-67 was obtained from Merck and was washed several times with deionized water before use. N, N-dimethylformamide (DMF) and acetonitrile were dried in a solvent purification system (MB-SPS-800 from M Braun). Phosphate buffered saline (PBS) was obtained from Biowest.

[0143] Performance of Measurements

[0144] Proton (.sup.1H) nuclear magnetic resonance (NMR) spectra were measured on a Bruker AC 300 MHz or a Bruker AC 400 MHz spectrometer. Correlation spectroscopic (COSY) NMR, heteronuclear single quantum correlation spectroscopic (HSQC) NMR, heteronuclear multiple bond correlation (HMBC) NMR spectra, and DOSY NMR spectra were recorded on a Bruker AC 400 MHz spectrometer. Measurements were performed at room temperature using either D.sub.2O, d.sub.4-methanol, or deuterated chloroform as solvents. Chemical shifts (6) are reported in parts per million (ppm) relative to the remaining non-deuterated solvent resonance signal. Infrared (IR) spectroscopy was performed on a Shimadzu IRAffinity-1 CE system equipped with a Quest ATR single reflectance diamond crystal cuvette for extended range measurements.

[0145] Size exclusion chromatography (SEC) was performed using two different setups. Measurements in N,N-dimethylacetamide (DMAc) were performed using an Agilent 1200-series system equipped with a PSS degasser, a G1310A pump, a G1329A autosampler, a Techlab oven, a G1362A refractive index detector (RID), and a PSS GRAM-guard/30/1000 column (10 m particle size). DMAc containing 0.21 wt % LiCl was used as the eluent. The flow rate was 1 ml min.sup.1 and the oven temperature was 40 C. Polystyrene (PS) standards ranging from 400 to 1,000,000 g mol.sup.1 were used to calculate molar masses. Measurements in chloroform were performed using a Shimadzu system (Shimadzu Corp., Kyoto, Japan) equipped with an SCL-10A VP system controller, a SIL-10AD VP autosampler, an LC-10AD VP pump, an RID-10A RI detector, a CTO-10A VP oven, and a PSS SDV guard/lin S column (5 mm particle size). A mixture of chloroform/isopropanol/triethylamine (94/2/4 vol %) was used as eluent. The flow rate was 1 ml min.sup.1 and the oven temperature was 40 C. PS standards from 400 to 100,000 g mol-1 were used to calibrate the system.

[0146] Thermogravimetric analysis (TGA) was performed using a Netzsch TG 209 F1 Iris from 20 to 580 C. at a heating rate of 20 K min.sup.1 under N2 atmosphere. Decomposition temperatures (T.sub.d) were determined at 95% of the original mass.

[0147] Differential scanning calorimetry (DSC) measurements were performed using a Netzsch DSC 204 F1 Phoenix under N2 atmosphere from 100 to 160 C., 100 to 150 C., 190 to 100 C., and 190 to 140 C., respectively. Three heating runs were recorded for each measurement. The first and second runs were performed at a heating rate of 20 K min.sup.1 and the third run was performed at a heating rate of 10 K min.sup.1. The cooling rate between the first and second runs was set to 20 K min.sup.1 and between the second and third runs to 10 K min.sup.1. Glass transition temperatures (T.sub.g, inflection points) and melting temperatures (T.sub.m) were determined from the third heating run. Thermograms were analyzed using Netzsch Proteus Thermal Analysis 4.6.1 software, which applies the smoothing option to analyze the T.sub.g value when necessary.

General Synthesis Methods

Synthesis of poly(2-ethyl-2-oxazoline), PEtOx

[0148] PEtOx was synthesized by cationic ring opening polymerization (CROP) of EtOx. In a scale-up batch method, MeOTs (124 g, 0.665 mol) and EtOx (3965 g, 40.00 mol, 60.2 equiv.) were dissolved under argon atmosphere in dry MeCN (5860 ml) in a 10 L Normag reactor to achieve a monomer-to-initiator ratio [M]:[I] of 60:1. After a reaction time of 6.5 h under reflux conditions, the polymerization was terminated with 270 ml of deionized water. After removal of aliquots for determination of monomer conversion (99.7%) by .sup.1H NMR spectroscopy, the solvent was removed under reduced pressure, the residue was dissolved in dichloromethane (20 L) and washed with saturated aqueous sodium hydrogen carbonate solution (10 L) and aqueous sodium chloride solution (210LI). The organic phase was dried over a mixture of sodium sulfate (15 kg) and magnesium sulfate (4 kg) and the solvent was removed under reduced pressure. The product was finally dried in vacuo for 14 days (yield: 3848 g) and analyzed by .sup.1H NMR spectroscopy (300 MHz, D.sub.2O) and SEC. M.sub.n,theor.=6000 g mol-1; M.sub.n,NMR=6300 g mol.sup.1; DP=60.

Synthesis of Linear Poly(Ethyleneimine), PEI

[0149] The synthesis of PEI was performed by an adapted procedure based on previously published methods (Van Kuringen, H. P.; Lenoir, J.; Adriaens, E.; Bender, J.; De Geest, B. G.; Hoogenboom, R. Partial hydrolysis of poly(2-ethyl-2-oxazoline) and potential implications for biomedical applications? Macromol. Biosci. 2012, 12, 1114-1123; Tauhardt, L.; Kempe, K.; Knop, K.; Altunta, E.; Jager, M.; Schubert, S.; Fischer, D.; Schubert, U. S. Linear polyethyleneimine: Optimized synthesis and characterizationOn the way to pharmagrade batches. Macromol. Chem. Phys. 2011, 212, 1918-1924). PEtOx (80.0 g, 12.5 mmol) was dissolved in aqueous hydrochloric acid (6 M, 600 mL) and heated to 90 C. for 24 h. Volatiles were removed under reduced pressure and the residue was dissolved in deionized water (1600 mL). Aqueous NaOH (3 M, 300 mL) was added in portions to achieve a pH of 10, resulting in precipitation of the polymer. The polymer was then filtered off and purified by recrystallization in water (800 mL). PEI was obtained as a white solid (yield: 47.5 g).

[0150] .sup.1H NMR (300 MHz, CD.sub.3OD): degree of hydrolysis (DH)=99%.

Synthesis of poly(ethyleneimine-stat-glycine), oxPEI

[0151] The synthesis of oxPEI was performed according to an adapted method of Englert et al. (Englert, C.; Hartlieb, M.; Bellstedt, P.; Kempe, K.; Yang, C.; Chu, S. K.; Ke, X.; Garcia, J. M.; Ono, R. J.; Fevre, M.; Wojtecki, R. J.; Schubert, U. S.; Yang, Y. Y.; Hedrick, J. L. Enhancing the biocompatibility and biodegradability of linear poly(ethylene imine) through controlled oxidation. Macromolecules 2015, 48, 7420-7427). PEI (45.0 g, 17.0 mmol) was dissolved in methanol (1100 ml) with stirring and aqueous hydrogen peroxide solution (72 ml, 30% w/w, 0.7 equiv. per amine unit) was added dropwise. After stirring at room temperature for 3 days, the solvent was removed under reduced pressure and the product was dried in vacuo at room temperature for 7 days and at 70 C. for 1 day. oxPEI was obtained as a brown solid (yield: 29.1 g).

[0152] .sup.1H NMR (300 MHz, D.sub.2O): degree of oxidation (DO)=54%.

General Synthesis Procedure for poly(2-n-alkyl-2-oxazoline-stat-glycin)es, dPAOx

[0153] oxPEI was predried under vacuum for 2 h at 70 C. and then dissolved in dry DMF (6 ml per g polymer) under argon atmosphere. Triethylamine (4 equiv. per amine unit) was added, followed by dropwise addition of acyl chloride solutions (3 equiv. per amine unit) in dry DMF (6 mL per g polymer). During this process, the mixture was cooled in an ice bath. Additional dry DMF (6 mL per g of polymer) was used to rinse residues from the flask walls. After reaching room temperature, the reaction mixture was stirred for an additional 24 hours. Purification was adjusted depending on the solubility of the products. Details on the preparation of individual dPAOx can be found in the experimental section below.

[0154] Determination of the Degree of Hydrolysis

[0155] The degree of hydrolysis DH was calculated according to equation (1) from the integrals of the .sup.1H NMR spectra of PEI. Here, D means the integral of the methylene groups of the ethyleneimine units and A means the integral of the methyl groups of the remaining EtOx units.

[00001]$\begin{array}{cc}\mathrm{DH}=\frac{D}{D+\frac{4}{3}A}.Math.100\%& \left(1\right)\end{array}$

[0156] Determination of the Degree of Oxidation

[0157] The degree of oxidation DO was calculated from the integrals of the polymer backbone signals of the .sup.1H NMR spectra of oxPEI according to equation (2). Here, F means the integral of the methylene group of the glycine units, A means the integral of the methyl groups of the remaining EtOx units and D means the integral of the methylene groups of the ethyleneimine units.

[00002]$\begin{array}{cc}\mathrm{DO}=\frac{2\left(F-\frac{4}{3}A\right)}{\left(F-\frac{4}{3}A\right)+D}.Math.100\%& \left(2\right)\end{array}$

[0158] Performance of Titration

[0159] Titrations for the determination of the remaining amino groups were carried out with an auto-mated Metrohm OMNIS Titrator equipped with a Metrohm Ecotrode plus pH electrode. All measurements were performed in a dynamic titration mode that adapted the titration speed to the change in pH during the titration. A typical measurement was performed as follows: The polymer was dissolved in deionized water to give a polymer solution of 10 mL with a concentration of 1 mg mL.sup.1. The polymer solution was acidified by adding a concentrated aqueous HCl solution dropwise to achieve a pH of 2. The solution was then titrated to a pH of 12 with stirring against aqueous 0.1 M sodium hydroxide solution. The equivalence points were determined from the first derivative of the titration curve.

[0160] Performance of Degradation Studies

[0161] For degradation under acidic conditions, the polymer (20 mg) was dissolved in 6 mol L.sup.1 HCl (2 ml) and stirred for 48 h at 90 C. The reaction mixture was neutralized with aqueous sodium hydroxide solution and the water was removed under reduced pressure.

[0162] For degradation under enzymatic conditions, dPMeOx (20 mg) and proteinase K (10 mg) were dissolved in PBS buffer solution and incubated at 37 C. for 30 days. Water was then removed under reduced pressure. Both products were analyzed by NMR spectroscopy.

Preparation Example H1: Synthesis of poly(2-methyl-2-oxazoline-stat-glycine), dPMeOx

[0163] dPMeOx was prepared according to the general procedure using 3.2 g (1.0 mmol) oxPEI, 16 ml (11.6 g, 115 mmol, 4.1 equiv. per amine unit) triethylamine, and 6 ml (6.6 g, 84 mmol, 3.0 equiv. per amine unit) acetyl chloride. The reaction mixture was precipitated by direct immersion in ice-cold diethyl ether (about 80 C., 700 ml). The residue was dissolved in DMF (70 ml) and the precipitation was repeated twice. The crude product was dissolved in deionized water, Amberlite IRA-67 ion exchange resin was added and the mixture was stirred for 1.5 h at room temperature. Subsequently, Amberlite IRA-67 was filtered off and water was removed under reduced pressure. The crude product was dissolved in methanol and precipitated twice in ice-cold diethyl ether (about 80 C.). The product was dissolved in methanol and dried under reduced pressure. The residue was dissolved in deionized water and freeze-dried. To remove all remaining impurities, the product was dissolved in deionized water and stirred with Amberlite IRA-67 Ion Exchange Resin for an additional 4 h. Amberlite IRA-67 was filtered off and the product dried under reduced pressure. Dissolution in deionized water and freeze drying gave dPMeOx as a brown solid (yield: 1.9 g).

Preparation Example H2: Synthesis of poly(2-ethyl-2-oxazoline-stat-glycine), dPEtOx

[0164] dPEtOx was prepared according to the general procedure using 3.2 g (1.0 mmol) oxPEI, 16 ml (11.6 g, 115 mmol, 3.8 equiv. per amine unit) triethylamine, and 7.5 ml (8.0 g, 86 mmol, 2.9 equiv. per amine unit) propionyl chloride. Triethylammonium chloride formed during the reaction was filtered off and the solution precipitated in ice-cold diethyl ether (1000 ml, 80 C.). The residue was dissolved in DMF (50 ml) and precipitated again in ice-cold diethyl ether (500 ml). The crude product was dissolved in deionized water, Amberlite IRA-67 ion exchange resin was added, and the mixture was stirred for 1.5 h. Subsequently, Amberlite IRA-67 was then filtered off and water was removed under reduced pressure. The residue was dissolved twice in methanol (30 ml) and precipitated in ice-cold diethyl ether (about 80 C.). The product was dissolved in methanol and dried under reduced pressure, dissolved in deionized water and freeze-dried. The product was redissolved in deionized water and stirred with Amberlite IRA-67 ion-exchange resin for 4 h. Amberlite IRA-67 was filtered off and water was removed under reduced pressure. The product was redissolved in deionized water and freeze-dried. dPEtOx was obtained as a brown solid (yield: 1.0 g).

Preparation Example H3: Synthesis of poly(2-n-propyl-2-oxazoline-stat-glycine), dPPropOx

[0165] dPPropOx was prepared according to the general procedure using 3.2 g (1.0 mmol) oxPEI, 16 ml (11.6 g, 115 mmol, 3.8 equiv. per amine unit) triethylamine, and 8.5 ml (8.8 g, 82 mmol, 2.7 equiv. per amine unit) butyryl chloride. The precipitated triethylammonium salt was filtered off after the reaction and the filtrate was concentrated under reduced pressure. The residue was dissolved in chloroform (200 ml) and washed with saturated aqueous sodium hydrogen carbonate solution (3500 ml) and aqueous sodium chloride solution (3500 ml). The organic phase was dried over sodium sulfate, filtered and volatiles were removed under reduced pressure. Drying in vacuo overnight yielded the polymer as a brown, highly viscous liquid (yield: 6.7 g).

Preparation Example H4: Synthesis of poly(2-n-butyl-2-oxazoline-stat-glycine), dPButOx

[0166] dPButOx was prepared according to the general procedure using 3.0 g (0.96 mmol) oxPEI, 15 ml (10.9 g, 108 mmol, 3.9 equiv. per amine unit) triethylamine, and 9.5 ml (9.7 g, 80 mmol, 2.9 equiv. per amine unit) valeroyl chloride. Triethylammonium chloride was removed by filtration. Volatiles were removed under reduced pressure, the residue was dissolved in chloroform (50 ml), and washed with saturated aqueous sodium hydrogen carbonate solution (320 ml) and aqueous sodium chloride solution (320 ml). The organic phase was dried over sodium sulfate, filitrated and concentrated under reduced pressure. The procedure was repeated twice until all triethylammonium salt impurities were removed. After removal of the solvent and drying in vacuo overnight, the product was obtained as a brown, highly viscous liquid (yield: 5.7 g).

Preparation Example H5: Synthesis of poly(2-n-pentyl-2-oxazoline-stat-glycine), dPPentOx

[0167] dPPentOx was prepared according to the general procedure using 2.7 g (0.88 mmol) oxPEI, 13 ml (9.4 g, 93 mmol, 3.6 equiv. per amine) triethylamine, and 10 ml (9.6 g, 72 mmol, 2.8 equiv. per amine) hexanoyl chloride. Triethyl ammonium chloride was filtered off and volatiles were removed under reduced pressure. The crude product was dissolved in chloroform (100 ml) and washed with saturated aqueous sodium bicarbonate solution (340 ml) and aqueous sodium chloride solution (440 ml). To remove the remaining triethyl ammonium chloride and DMF impurities, the organic phase was diluted with chloroform (100 ml) and washed again with saturated aqueous sodium hydrogen carbonate solution (3500 ml) and aqueous sodium chloride solution (3500 ml). The organic phase was dried over sodium sulfate, filtered, and the solvent was removed under reduced pressure. After drying under vacuum overnight, the product was obtained as a brown, highly viscous liquid (yield: 6.5 g).

Preparation Example H6: Synthesis of poly(2-n-hexyl-2-oxazoline-stat-glycine), dPHexOx

[0168] dPHexOx was prepared according to the general procedure using 2.1 g (0.88 mmol) oxPEI, 10.5 ml (7.6 g, 75 mmol, 3.8 equiv. per amine unit) triethylamine, and 8.5 ml (8.2 g, 55 mmol, 2.8 equiv. per amine unit) heptanoyl chloride. The precipitated triethylammonium salt was filtered off and the was filtrate concentrated under reduced pressure. The residue was dissolved in chloroform (200 ml) and washed with saturated aqueous sodium hydrogen carbonate solution (3500 ml) and aqueous sodium chloride solution (3500 ml). The organic phase was dried over sodium sulfate, filtered and solvent was removed under reduced pressure. After drying overnight, dPHexOx was obtained as a brown, highly viscous liquid (yield: 7.6 g).

Preparation Example H7: Synthesis of poly(2-n-heptyl-2-oxazoline-stat-glycine), dPHeptOx

[0169] dPHeptOx was prepared according to the general procedure using 2.0 g (0.65 mmol) oxPEI, 10 ml (7.3 g, 72 mmol, 3.8 equiv. per amine unit) triethylamine, and 9 ml (8.6 g, 53 mmol, 2.8 equiv. per amine unit) octanoyl chloride. Triethyl ammonium chloride was filtered off and the filtrate was concentrated under reduced pressure. The residue was dissolved in chloroform (200 ml) and extracted with saturated aqueous sodium hydrogen carbonate solution (3500 ml) and aqueous sodium chloride solution (3500 ml). The organic phase was dried over sodium sulfate and filtered. Removal of the solvent and drying overnight gave the product as a brown, highly viscous liquid (yield: 7.4 g).

Preparation Example H8: Synthesis of poly(2-n-octyl-2-oxazoline-stat-glycine), dPOctOx

[0170] dPOctOx was prepared according to the general procedure using 1.9 g (0.61 mmol) oxPEI, 9.5 ml (6.9 g, 68 mmol, 3.8 equiv. per amine unit) triethylamine, and 9.5 ml (8.9 g, 51 mmol, 2.8 equiv. per amine unit) nonanoyl chloride. Triethyl ammonium chloride formed during the reaction was filtered off and the filtrate was concentrated under reduced pressure. The residue was dissolved in chloroform (200 ml) and washed with saturated aqueous sodium hydrogen carbonate solution (3500 ml) and aqueous sodium chloride solution (3500 ml). The organic phase was dried over sodium sulfate, filtered, and the solvent was removed under reduced pressure. After drying overnight, the product was obtained as a brown, highly viscous liquid (yield: 7.5 g).

Preparation Example H9: Synthesis of poly(2-n-nonyl-2-oxazoline-stat-glycine), dPNonOx

[0171] dPNonOx was prepared according to the general procedure using 1.8 g (0.58 mmol) oxPEI, 9 ml (6.5 g, 65 mmol, 3.8 equiv. per amine unit) triethylamine, and 10 ml (9.2 g, 48 mmol, 2.8 equiv. per amine unit) decanoyl chloride. Precipitated triethylammonium chloride was removed by filtration and volatiles were removed under reduced pressure. The crude product was dissolved in chloroform (200 ml) and extracted with saturated aqueous sodium hydrogen carbonate solution (3500 ml) and aqueous sodium chloride solution (3500 ml). The organic phase was dried over sodium sulfate and filtered. After removal of the solvent under reduced pressure and drying under vacuum overnight, the product was obtained as a brown, highly viscous liquid (yield: 6.7 g).

Example C1: Characterization of the Polymers by .SUP.1.H-NMR Spectroscopy

[0172] The first step towards a dPAOx library was to synthesize a substantial amount of PEtOx as a well-defined starting material via CROP (compare General Synthesis Methods, Synthesis of PEtOx). To this end, a synthesis protocol was developed in a 10 L Normag reactor that yielded nearly 4 kg of PEtOx with a degree of polymerization (DP) of 60 and a narrow dispersity (D) of 1.14, as determined by SEC in DMAc. Since CROP was terminated by addition of water, the resulting PEtOx contained two isomeric end groups resulting from nucleophilic attack on the 2- or 5-positions of the oxazoline ring, but in both cases this resulted in hydroxyl end groups upon hydrolysis to linear poly(ethyleneimine) (PEI). The hydrolysis was carried out under acidic conditions (see general synthesis methods, synthesis of PEI). To obtain complete hydrolysis, the reaction was carried out overnight with an excess of 6 M HCl. The successful synthesis was confirmed by the .sup.1H NMR spectrum (compare FIG. 1), which clearly showed the disappearance of the signals assigned to the ethyl substituents of PEtOx. Moreover, a clear high-field shift of the backbone signal (compare C vs. D in FIG. 1) confirmed the formation of PEI. The degree of hydrolysis (DH) was determined to be 99%, calculated by the ratio of the integrals in the .sup.1H NMR spectrum (compare general synthetic methods, synthesis and characterization of dPAOx, equation (1)).

[0173] FIG. 1 shows .sup.1H NMR spectra (300 MHz, 300 K, D.sub.2O or MeOD) of PEtOx, PEI, oxPEI, and dPEtOx and the assignment of the signals to the schematic representations of the structures.

[0174] Next, PEI was prepared by oxidation of PEtOx using hydrogen peroxide as oxidant. The oxidation occurred in the polymer backbone and thus backbone amide groups were formed in a statistically distributed manner. The structure of the resulting oxPEI corresponds to the repeating unit of poly(glycine) adjacent to unaffected ethyleneimine units. Therefore, the polymer can also be referred to as a poly(ethyleneimine-stat-glycine) copolymer. With the aim of generating 50% of the amino groups by oxidation in PEI, 0.7 equivalents of hydrogen peroxide per amino group were used. The degree of oxidation (DO), determined by the integral ratio in the .sup.1H NMR spectrum as 54% (compare General Methods of Synthesis, Synthesis and Characterization of dPAOx, Eq. (2)), confirmed the successful synthesis. The methylene group signals assigned to the ethyleneimine (D) and glycine repeating units (F) occurred in close proximity in the .sup.1H NMR spectrum and partially overlapped each other. Coupling of these signals in the HMBC NMR spectrum confirmed the random distribution of the two different repeating units within the polymer. The NH proton signal E indicated the formation of an amide group, which confirmed the presence of glycine units as well.

[0175] Since the remaining amino groups can be further functionalized, the resulting oxPEI provided the platform for the synthesis of various degradable polymers. Here, subsequent reacylation with a homologous series of aliphatic acyl chlorides from acetyl chloride to n-decanoyl chloride was applied to reintroduce amide units equivalent to the N-acylethylenimine structures in PAOx. The resulting polymer structures resemble PAOx with additional, randomly distributed poly(glycine) units integrated into the polymer backbone. Therefore, they can also be considered as poly(2-n-alkyl-2-oxazoline-stat-glycine) copolymers or as degradable poly(2-n-alkyl-2-oxazoline) analogs due to the degradability of the glycine unit. Thus, the synthetic approach described allowed the preparation of a dPAOx library with the same chain length and DO, using only EtOx as a commercially available monomer.

[0176] Characterization of the purified dPAOx by .sup.1H NMR spectroscopy indicated a decrease in the signals attributed to the PEI repeating units, while signals attributed to the alkyl side chains confirmed their conversion to the corresponding N-acylethylenimine structures. As illustrated in FIG. 1 for dPEtOx, the corresponding signals (A and B) occurred at the same chemical shifts as in the non-degradable PEtOx starting material. The assignments were verified by COSY NMR, HSQC NMR, and HMBC NMR measurements.

Example C2: Characterization of the Polymers by IR-Spectroscopy

[0177] Further structural evidence was obtained by IR spectroscopy. FIG. 2 shows ATR-IR spectra of PEtOx, PEI, oxPEI, and dPEtOx in the range of wavenumbers from 1000 to 3500 cm.sup.1 including assignment of the major bands. The IR spectroscopy of PEtOx, PEI, poly(glycine) as well as oxPEI was previously described in the literature, which allowed easy assignment of vibrational bands. The band at 3213 cm.sup.1 in the PEI spectrum, assigned to the NH vibration of the amino group, was not observed for PEtOx but appeared after hydrolysis. The band decreased upon oxidation to oxPEI and almost disappeared after the following re-acylation step to dPEtOx, indicating almost complete functionalization of the amino groups. The vibrational band at 1628 cm.sup.1 in the PEtOx spectrum can be attributed to the amide I band, which is mainly due to the carbonyl valence vibration. The band disappeared almost completely during hydrolysis to PEI due to cleavage of the side chain carrying carbonyl groups. During oxidation to oxPEI and subsequent reacylation to dPEtOx, amide groups were reintroduced, leading to an increase in the carbonyl vibrational band. The amide II band at 1543 cm.sup.1, mainly caused by the NH bond deformation vibration, was not observed in PEtOx, which had only tertiary amide groups without NH bonds, showing the structural difference between PEtOx and dPEtOx. Signals of carboxylic acid derivatives due to possible degradation products are expected at about 1710 cm.sup.1. However, such signals could not be observed in the spectra of oxPEI or dPEtOx.

Example C3: Characterization of the Polymers by SEC

[0178] SEC analyses were limited due to solubility changes in the synthetic pathway as well as possible interactions of some polymers with the column material. However, all polymers dissolved in both CHCl.sub.3 and DMAc, with the exception of PEI, which was not soluble in these SEC solvents, and dPMeOx, which was soluble only in DMAc (compare Table 1).

[0179] In agreement with the theoretically expected molar masses, the signal of PEtOx appeared at the lowest elution volume in the polar eluent DMAc, while the hydrodynamic volume of oxPEI decreased significantly. Reacylation to dPEtOx shifted its signal to an intermediate elution volume and corresponding molar mass. However, comparison of the SEC elugrams of all dPAOx clearly indicated that significant changes in hydrophilicity due to increasing side-chain length should be considered, as these affected the hydrodynamic volumes of the polymers. This was particularly evident from the apparent higher molar mass of dPMeOx compared to dPEtOx, which can be attributed to the relative method used to determine the molar mass of SEC.

[0180] The increased hydrophobicity of dPAOx with longer side chains was indicated by a comparison of their SEC elugrams in the hydrophobic eluent CHCl.sub.3. Their signals shifted toward lower elution volumes with increasing side chain length. This is consistent with the trend expected for the theoretical molecular masses due to increased lipophilicity and thus increasing hydrodynamic volume within the homologous series. Nevertheless, the discrepancy between the M.sub.n values determined by SEC and the theoretical molecular masses increased with side-chain length, indicating an increasing difference between the hydrodynamic volumes of the dPAOx and SEC standards previously reported for PAOx.

TABLE-US-00001 TABLE 1 molar masses M.sub.n, dispersity values and thermal properties of PEtOx, PEI, oxPEI and dPAOx. M.sub.n SEC, CHCl.sub.3 SEC, DMAc thermal properties theor..sup.a M.sub.n .sup.b M.sub.n .sup.c T.sub.d .sup.d T.sub.g .sup.e T.sub.m .sup.f Polymer [g/mol] [g/mol] .sup.b [g/mol] .sup.c [ C.] [ C.] [ C.] PEtOx 6000 4000 1.29 10,900 1.14 351 54 PEI 2600 317 62 oxPEI 3100 330 1.75 1570 1.46 155 16 dPMeOx 4200 5420 3.35 170 105 dPEtOx 4600 470 1.95 3360 1.78 196 75 dPPropOx 5000 650 1.95 2880 1.77 154 24 dPButOx 5400 680 1.93 2560 1.54 175 36 dPPentOx 5800 830 1.79 1800 1.97 173 52 dPHexOx 6100 750 1.13 1850 2.05 194 71 dPHeptOx 6500 760 2.18 1920 1.85 194 9 dPOctOx 6900 1060 1.93 2020 1.93 200 18 dPNonOx 7300 890 2.20 2060 1.78 197 28 .sup.aReceived by calculation with theoretical monomer units. .sup.b Determined by SEC in CHCl.sub.3 (2 vol % isopropanol, 4 vol % triethylamine, PS calibration, RI detection). .sup.c Determined by SEC in DMAc (0.21 wt % LiCl, PS calibration, RI detection). .sup.d Decomposition temperature; determined by TGA at 95% of the original mass. .sup.e Glass transition temperature; determined by DSC using the third heating curve at 10K min.sup.1; inflection points are determined as T.sub.g values. .sup.f Melting temperature; determined by DSC using the third heating curve at 10K min.sup.1.

[0181] Among the synthesized dPAOx, only the polymers with the shortest side chains, namely dPMeOx and dPEtOx, were sufficiently hydrophilic to be soluble in water at room temperature. In contrast, degradable poly(2-n-butyl-2-oxazoline) analogs (dPButOx) and longer side chain analogs were hydrophobic and could only be dissolved in organic solvents. The degradable poly(2-n-propyl-2-oxazoline) analog (dPPropOx) showed intermediate solubility behavior. Only small amounts could be dissolved in water, which allowed the titration of amino groups in aqueous solution (see below). Nondegradable PAOx exhibit similar solubility characteristics. However, PEtOx and poly(2-n-propyl-2-oxazoline) (PPropOx) exhibit a lower critical solution temperature (LCST) in water, whereas this was not observed for dPEtOx or dPPropOx, possibly due to the formation of additional hydrogen bonds that can be formed by the amide hydrogen of the glycine moiety.

Example C4: Characterization of the Polymers by Titration

[0182] Titrations in aqueous solution were performed to determine the number of amino groups in the polymer backbone of PEI, oxPEI, and the water-soluble dPAOx, namely dPMeOx, dPEtOx, and dPPropOx. Although the titration of amino groups allowed a qualitative evaluation, an accurate quantitative analysis was not performed due to water residues in PEI and oxPEI that would affect the results. An overlay of the titration curves of PEI, oxPEI and dPMeOx is shown as an example in FIG. 3. FIG. 3 shows titration curves of PEI, oxPEI and dPMeOx (1 mg mL.sup.1) against 0.1 M NaOH and their first derivatives. The polymer solutions were acidified with concentrated HCl before titration. The individual curves are superimposed vertically for clarity and the corresponding pH values of the equivalence points are shown.

[0183] FIG. 3 shows the evolution within the synthesis sequence. Acidification of the aqueous polymer solutions with concentrated HCl prior to the titrations resulted in the appearance of two equivalence points (EP) for amino group-containing polymers when titrated with dilute sodium hydroxide solution. The first EP corresponds to the neutralization of the excess HCl, while the second EP refers to the neutralization of the amino groups. The oxidation of PEI to oxPEI converted 54% of the amino units to amide units of the poly(glycine) units. The decreased number of amino groups was evident in the decreased distance between the two EPs during titration.

[0184] Only one EP was observed in the titration curves of dPMeOx and dPPropOx. This was due to the neutralization of HCl alone and confirmed the complete functionalization of the amino groups. Two EPs still appeared in the titration curve of dPEtOx, revealing incomplete reacylation. However, their proximity indicated that only a small number of amino groups remained, consistent with observations from IR spectroscopy.

Example C5: Characterization of the Polymers by TGA and DSC

[0185] The thermal properties of the polymers were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).

[0186] The dPAOx showed good thermal stability up to temperatures above 100 C. However, they are not as stable as their non-degradable PAOx analogues, which exhibit degradation temperatures (T.sub.d) up to above 300 C. The lower thermal stability of dPAOx may be attributed to the presence of additional degradable amide groups in the backbone.

[0187] FIG. 4 shows the DSC thermograms of PEtOx, PEI, oxPEI, and dPEtOx (N2, third heating curve, 10 K min.sup.1). The individual thermograms are superimposed vertically for clarity.

[0188] FIG. 5 shows the DSC thermograms of different dPAOx (N2, third heating run, 10 K min.sup.1). Again, the individual thermograms are superimposed vertically for better visualization. In the figure, the DSC thermograms of the C.sub.1-C.sub.9-alkyl-substituted derivatives of dPAOx (dPMeOx-dPNonOx) are shown.

[0189] FIG. 6 shows glass transition temperatures and melting temperatures of dPAOx compared with glass transition temperatures and melting temperatures of non-degradable PAOx from literature. Glass transitions were determined from inflection points. Data from the literature were taken from the following publications: Hoogenboom, R.; Fijten, M. W. M.; Thijs, H. M. L.; van Lankvelt, B. M.; Schubert, U. S. Microwave-assisted synthesis and properties of a series of poly(2-alkyl-2-oxazoline)s. Des. Monomers Polym. 2005, 8, 659-671. [0190] Rettler, E. F. J.; Kranenburg, J. M.; Lambermont-Thijs, H. M. L.; Hoogenboom, R.; Schubert, U. S. Thermal, mechanical, and surface properties of poly(2-N-alkyl-2-oxazoline)s. Macromol. Chem. Phys. 2010, 211, 2443-2448. [0191] Kempe, K.; Lobert, M.; Hoogenboom, R.; Schubert, U. S. Synthesis and characterization of a series of diverse poly(2-oxazoline)s. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 3829-3838. [0192] Beck, M.; Birnbrich, P.; Eicken, U.; Fischer, H.; Fristad, W. E.; Hase, B.; Krause, H.-J. Polyoxazolines on a lipid chemical basis. Angew. Makromol. Chem. 1994, 223, 217-233. [0193] Rodrguez-Parada, J. M.; Kaku, M.; Sogah, D. Y. Monolayers and Langmuir-Blodgett films of poly(AT-acylethylenimines) with hydrocarbon and fluorocarbon side chains. Macromolecules 1994, 27, 1571-1577.

[0194] An overlay of the DSC thermograms of PEtOx, PEI, oxPEI and dPEtOx in FIG. 4 shows the differences in the thermal behavior of the polymers within the synthesis sequence. With the exception of PEI, the polymers exhibited amorphous behavior. The PEI backbone has no side chains, allowing the main chains to be regularly packed, leading to the formation of crystallites with a melting temperature (T.sub.m) at 62 C. The introduction of randomly distributed amide groups by oxidation disrupted the packing, leading to an amorphous behavior of oxPEI. Similar to PEtOx, dPEtOx also exhibited amorphous behavior, both with glass transition temperature (T.sub.g) values above the T.sub.g of oxPEI due to the existence of side chains. dPEtOx exhibited the highest T.sub.g within the sequence due to both the irregularity of the polymer backbone due to the statistically distributed amide groups and N-acyl side chains.

[0195] From the DSC thermograms of the dPAOx polymers in FIG. 5, as well as from the relationships between the T.sub.g and T.sub.m values and the number of carbon atoms in the dPAOx side chain and the comparison with the T.sub.g and T.sub.m values of non-degradable PAOx in FIG. 6, the following information can be obtained.

[0196] Significant differences in thermal behavior were observed depending on the structure of the polymer side chain. Analogous to their PAOx counterparts, the dPAOx with short n-alkyl side chains exhibited amorphous properties up to the degradable poly-(2-n-hexyl-2-oxazoline) analog (dHexOx). The T.sub.g values decreased linearly with increasing side chain length with similar slope for both series, especially for dPAOx with longer side chains. Macromolecules with only short side chains can be packed more tightly, resulting in a stronger interaction between the amide dipoles, which slows down the relaxation of the backbone, leading to higher T.sub.g values. However, a gap was observed between the T.sub.g of dPEtOx at 75 C. and the T.sub.g of dPPropOx at 24 C. Consequently, the T.sub.g values of dPMeOx and dPEtOx were higher than the T.sub.g values of PMeOx and PEtOx, while all other dPAOx glass transition temperatures were at lower temperatures than their nondegradable PAOx analogs. According to their T.sub.g values above room temperature, dPMeOx and dPEtOx appeared macroscopically as solids, while dPPropOx and the dPAOx with longer side chains formed highly viscous liquids caused by their glass transitions below room temperature

[0197] Semicrystalline behavior was observed for the degradable poly(2-n-heptyl-2-oxazoline) (dPHeptOx), poly(2-n-octyl-2-oxazoline) (dPOctOx) and poly(2-n-nonyl-2-oxazoline) (dPNonOx) analogs. The semicrystalline properties, which occurred only for dPAOx with side chains of at least seven carbon atoms, can be attributed to side-chain crystallization analogous to PAOx. However, PAOx exhibits semicrystallinity even with shorter alkyl substituents. The difference can be attributed to the irregularity in the dPAOx backbone due to the additional, statistically distributed glycine units.

[0198] The T.sub.m values of dPHeptOx, dPOctOx, and dPNonOx were more than 100 C. lower than the T.sub.m values of the corresponding PAOx of about 150 C. The melting points increased with increasing side chain length of T.sub.m from 9 C. for dPHeptOx to a T.sub.m of 28 C. for dPNonOx, while the T.sub.m values of PAOx were independent of side chain length. Moreover, asymmetric triple melting peaks were observed for dPAOx with longer side chains, while the corresponding PAOx showed only one symmetric melting peak. The asymmetry became less pronounced with increasing side chain length. Similar asymmetric double melting peaks were previously observed for poly(2-n-butyl-2-oxazoline) as well as for other semicrystalline polymers such as poly(ethylene terephthalate), poly(ether ketone), poly(L-lactic acid) or chiral poly(2-oxazolines) and can be explained by recrystallization of the melt.

Example C6: Characterization of the Polymers by Degradation Studies by Means of Acidic Hydrolysis

[0199] An important advantage of dPAOx compared to PAOx is their ability to be potentially degradable due to the additional backbone amide groups. To confirm this, PEtOx, PEI, oxPEI, and the water-soluble dPAOx, namely dPMeOx, dPEtOx, and dPPropOx, were treated with 6 M HCl at 90 C. for 2 days. These conditions are similar to those used for the hydrolysis of PEtOx to PEI, in which no degradation of the PEtOx or PEI polymer backbone occurs.

[0200] FIG. 7 shows the superposition of the .sup.1H NMR spectra of PEtOx (left) and of dPEtOx (right) before (lower spectrum) and after (upper spectrum) treatment with HCl (400 MHz, 297 K, D.sub.2O, solvent signals suppressed). The individual spectra are superimposed vertically for clarity.

[0201] FIG. 7 shows the successful degradation of dPAOx polymers under these conditions. Before treatment with HCl, dPEtOx showed broad signals typical of polymers, while the signals of the degraded dPEtOx were sharp, as is commonly observed for small molecules.

[0202] The splitting of the EtOx side chain signals at 1.04 ppm and 2.16 ppm into a triplet and a quartet, respectively, indicated the cleavage of the side chain from the polymer backbone, yielding propionic acid. This did not necessarily confirm the degradation of the polymer chain itself and was also found for PEtOx upon treatment with HCl. However, while the spectra of PEtOx after treatment showed only the backbone signal of the remaining PEI, several sharp signals appeared upon chemical shifts of the former dPEtOx backbone. The singlet at 3.21 ppm can be attributed to the methylene unit of glycine formed upon degradation, while the two triplets at 3.91 ppm and 3.10 ppm can be attributed to the remaining ethyleneimine units. In addition, a sharp signal appeared at 8.45 ppm, which had already been reported for oxPEI after degradation and which could be due to additional degradation products. At the same time, the broad amide signal disappeared at about 8.0 ppm, indicating hydrolysis of the associated backbone amide groups.

[0203] Furthermore, DOSY NMR spectroscopy was used to confirm the degradation of dPAOx. FIG. 8 shows the superposition of the DOSY NMR spectra of PEtOx (left) and dPEtOx (right) before (upper spectrum) and after (lower spectrum) treatment with HCl (400 MHz, 297 K, D.sub.2O, solvent signals suppressed). The individual spectra are superimposed vertically for clarity. DOSY NMR spectroscopy allows fractionation of the .sup.1H NMR signals according to their diffusion coefficients. Before treatment with HCl, all PEtOx signals corresponded to the same diffusion coefficient and confirmed the covalent bonds between the individual groups. After hydrolysis, the cleaved propionic acid could be clearly distinguished from the undegraded PEI backbone because it had a higher diffusion coefficient due to its lower molecular mass. Before treatment with HCl, all dPEtOx signals showed the same diffusion coefficient. In contrast, the spectrum of the degraded dPEtOx showed signals with three different diffusion coefficients. The propionic acid signals formed were easy to identify because they showed the same diffusion coefficient as in the spectra of PEtOx after treatment. Therefore, the other two signals were attributed to degradation products of the former polymer backbone, for example glycine, which showed different diffusion behavior.

Example C7: Characterization of the Polymers by Degradation Studies by Means of Enzymatic Hydrolysis

[0204] Degradation studies were carried out under enzymatic conditions to confirm the degradability of the polymers under milder and biological conditions. Therefore, dPMeOx was treated with proteinase K at 37 C. in a PBS buffer solution for 30 days.

[0205] FIG. 9 shows the superposition of the .sup.1H NMR spectra of dPMeOx after treatment with proteinase K in PBS buffer (upper spectrum) and of glycine with proteinase K in PBS buffer (lower spectrum) (400 MHz, 297 K, D.sub.2O). The individual spectra are superimposed vertically for clarity.

[0206] The .sup.1H NMR spectrum of dPMeOx after treatment with proteinase K in FIG. 9 confirmed the partial degradation of the polymer. The sharp signal at 1.93 ppm showed the cleavage of the side chains, resulting in acetic acid in dPMeOx. The sharp signal at 8.46 ppm and the signal at 3.58 ppm were already observed for dPAOx degraded under acidic conditions, confirming the degradation of the polymer backbone. Superposition with a .sup.1H NMR spectrum of glycine in a proteinase K PBS buffer solution of the same concentration confirms the assignment of the latter signal to glycine.

[0207] However, the broad polymer signals of the methyl side chain, the dPMeOx backbone, and the backbone amide group can still be observed in the spectrum, indicating the slow degradation kinetics under the conditions of the experiment.

[0208] These experimental results confirm that a facile route of synthesis through polymer analog functionalizations to build a library of acidic and enzymatically degradable poly-(2-n-alkyl-2-oxazoline) analogs has been found. Copolymers were developed, which were prepared via consecutive hydrolysis of PEtOx, partial oxidation of the polymer backbone, and re-acylation of the remaining amino groups to re-introduce N-acylethylenimine units. Among the resulting dPAOx polymers, only dPMeOx and dPEtOx were water-soluble, while dPButOx and longer side-chain analogs showed hydrophobic properties.

[0209] In analogy to their non-degradable PAOx counterparts, a strong dependence of the thermal properties on the side chains was observed. dPAOx with n-alkyl side chains of up to six carbon atoms were amorphous. Similar to the shorter non-degradable PAOx, the T.sub.g values of the polymers decreased with increasing number of carbon atoms in the side chain.

[0210] Higher dPAOx homologs were semicrystalline and exhibited T.sub.m values that increased with the length of the n-alkyl side chains but remained below 30 C., making the novel materials attractive for a range of pharmaceutical applications, e.g., as PEG replacements.

[0211] The incorporation of glycine units facilitated the degradability of the dPAOx backbone under acidic and enzymatic conditions, highlighting their potential to be used as degradable PAOx analogues in biomedical or other applications.