All-aromatic high-performance block-copolymers

Abstract

The invention is directed to a method for the preparation of a liquid crystal block copolymer, comprising melt polycondensation of a melt comprising at least two non-latent aromatic monomers and a latent aromatic monomer.

Claims

1. A method for the preparation of a liquid crystal block copolymer, comprising melt polycondensation of a melt comprising at least two non-latent aromatic monomers and a latent aromatic monomer.

2. The method of claim 1, wherein the copolymer comprises a polyester and/or a polyamide and said latent and non-latent aromatic monomers are each according to the formula HO.sub.2CArX, including salts and derivatives thereof, wherein Ar is an aromatic group and each X is OH or NH.sub.2.

3. The method of claim 1, wherein the latent aromatic monomer comprises a six-member aromatic group that comprises an electron withdrawing group at a meta, ortho, and/or para position of the six-member aromatic group.

4. The method of claim 1, wherein the lowest pK.sub.a value of the latent aromatic monomer is at least 0.5 pH units lower than the lower pK.sub.a values of the non-latent aromatic monomers.

5. The method of claim 1, wherein the non-latent aromatic monomers have a structure according to HO.sub.2CArX, including salts and derivatives thereof, wherein each X is OH or NH.sub.2 and Ar is selected from the group consisting of ##STR00009##

6. The method of claim 1, wherein the latent aromatic monomer has a structure according to HO.sub.2CArX, including salts and derivatives thereof, wherein each X is OH or NH.sub.2 and Ar is selected from the group consisting of ##STR00010##

7. The method of claim 1, wherein the latent monomer comprises one or more compounds selected from the groups consisting of ##STR00011## and salts and derivatives thereof, wherein X is OH or NH.sub.2.

8. The method of claim 1, wherein the melt further comprises end-cap compounds.

9. A liquid crystal block copolymer comprising blocks A and B comprising non-latent aromatic monomers and a latent aromatic monomer obtainable by the method of claim 1.

10. The liquid crystal block copolymer of claim 9, wherein the A blocks comprise more latent monomer than non-latent monomer and B blocks comprise more non-latent monomer than latent monomer.

11. The liquid crystal block copolymer of claim 9, further comprising an end-cap compound.

12. The liquid crystal block copolymer of claim 9, wherein the liquid crystal block copolymer is a liquid crystal ABA-triblock copolymer.

13. The liquid crystal block copolymer of claim 9, having two glass transition temperatures.

14. A liquid shape memory material for a recoverable deformation upon the application of an external thermal stimulus which comprises the crystal block copolymer of claim 9.

15. The method of claim 5, wherein each X is OH or NH.sub.2 and Ar is selected from the group consisting of ##STR00012##

16. The method of claim 8, wherein the melt further comprises a nucleophilic end-cap compound and an electrophilic end-cap compound.

17. The method of claim 16, wherein the nucleophilic end-cap compound has the structure ArX, including salts and derivatives thereof, and the electrophilic end-cap compound has the structure ArCO.sub.2H, including salts and derivatives thereof, wherein Ar is an aromatic group.

18. The method of claim 17, wherein said Ar comprises the aromatic group that is also present in the latent aromatic monomer or in the non-latent aromatic monomer.

19. The liquid crystal block copolymer of claim 11, wherein said end-caps are reactive end-caps.

Description

EXAMPLE 1

(1) 4-Hydroxybenzoic acid (4-HBA) and acetic anhydride were purchased from Aldrich (Zwijndrecht, The Netherlands). 6-Hydroxy-2-naphthoic acid (HNA) was purchased from Ueno Fine Chemicals Ltd and potassium acetate was purchased from Acros Organics (Geel, Belgium). 4-Phenylethynylphthalic anhydride (PEPA) was obtained from Hangzhou Chempro Tech Co., Ltd. The synthesis of the reactive end-groups, i.e. N-(4-carboxyphenyl)-4-phenylethynylphthalimide (PE-COOH) and N-(4-acetoxyphenyl)-4-phenylethynylphthalimide (PE-OAc) were prepared as described in Knijnenberger et al., Macromolecules 2006, 39, 6936-6943.

(2) Synthesis of Latent Monomer N-(3-hydroxyphenyl)trimellitimide (IM)

(3) A 500 mL flask equipped with a mechanical stirrer and reflux condenser was charged with 250 mL glacial acetic acid and trimellitic anhydride (0.1 mol, 21.01 g). The mixture was heated to 120 C. and when all solids were dissolved, 3-aminophenol (0.1 mol, 10.91 g) was added. A thick suspension formed almost immediately and this reaction mixture was refluxed for 4 h at 120 C. After cooling the reaction mixture, the precipitated product was isolated by filtration and washed with acetic acid (2) and ethanol (2). The off-white N-(3-hydroxyphenyl)trimellitimide (IM) was dried under vacuum at 140 C. for 24 h. Yield: 24.06 g. (0.085 mol, 85%); m.p. 304 C. (DSC). FTIR: the characteristic absorption peaks of imide groups were observed at 1777, 1715, 1383 and 725 cm.sup.1; the broad band around 3500 cm.sup.1 can be assigned to the phenolic hydroxyl group and carboxyl group. .sup.1H NMR (DMSO-d.sub.6, 400 MHz): 6.82-6.90 (m, 3H), 7.30 (t, 1H, J=8.2 Hz), 8.06 (d, 1H, J=7.7 Hz), 8.29 (s, 1H), 8.40 (dd, 1H, J=7.8, 1.1 Hz), 9.77 (s, 1H), 13.60 (s, 1H). .sup.13C NMR (DMSO-d.sub.6, 100 MHz): 114.30, 115.20, 117.73, 123.32, 123.66, 129.45, 131.93, 132.55, 134.80, 135.34, 136.32, 157.59, 165.74, 166.13, 166.15. MS m/z (relative intensity): 283.05 (100%) (M.sup.+), 239 (20.7), 120 (30.6), 103.05 (27.8), 92 (46.1), 75 (32.1).

(4) Synthesis of LC Poly(Esterimide)s and Reactive Oligomers.

(5) A series of LC poly(esterimide)s based on IM, HBA and HNA as described in table 1 (entries 1-9) were synthesized using standard melt condensation techniques. The samples were labeled xxIM according to the feed ratio of IM in the polymerization, e.g. 22IM refers to a IM/HBA/HNA molar ratio of 0.22/0.51/0.27. An all ester-based reference polymer, with a HBA/HNA molar ratio of 0.73/0.27, was synthesized according to an identical procedure but without IM and labeled 0IM.

(6) TABLE-US-00001 TABLE 1 IM HBA HNA Sample mol % mol % mol % 0IM 0 73 27 22IM 22 51 27 29IM 29 44 27 37IM 37 36 27 44IM 44 29 27 51IM 51 22 27 58IM 58 15 27 65IM 65 8 27 73IM 73 0 27 22IM-9K 22 51 27 22IM-5K 22 51 27

EXAMPLE 2

(7) As a representative example, the synthesis of a 9000 g/mol block copolymer comprising reactive end-caps with a IM/HBA/HNA molar ratio of 0.22/0.51/0.27, 22IM-9K is described.

(8) IM (0.22 mol, 61.988 g), HBA (0.51 mol, 70.533 g), HNA (0.27 mol, 50.809 g), PE-OAc (0.0187 mol, 7.137 g), PE-COOH (0.0187 mol, 6.873 g), and potassium acetate (0.1 mmol, 10 mg) were charged to a 500 mL three-neck round-bottom flask. The flask was equipped with a nitrogen gas inlet, an overhead mechanical stirrer, and a reflux condenser. The reactor was purged with nitrogen for 30 min prior to the start of the reaction and a slow nitrogen flow was maintained throughout the duration of the synthetic procedure. Acetic anhydride (113 mL, 1.2 mol) was added for the in-situ acetylation of the monomers. The reaction mixture was slowly stirred under a nitrogen atmosphere and heated to 140 C. to allow acetylation to take place. After a 1 h isothermal hold, the temperature of the reaction mixture was slowly increased to 310 C. using a heating rate of 1 C. min.sup.1. During this process acetic acid was collected as the polycondensation by-product. At 310 C. the nitrogen flow was stopped and a vacuum was applied to remove the residual acetic acid and other low molecular weight side products. The reaction flask was allowed to cool down overnight under a nitrogen flow and the final product was removed from the flask and processed into a powder. A solid-state post-condensation step was performed at 260 C. for 24 h under vacuum in order to remove all volatiles and ensure full polymerization. Yields for these syntheses were generally above 95%. The high molecular weight parent polymers were prepared under identical conditions but without PE-OAc and PE-COOH end-cap compounds.

EXAMPLE 3

(9) Melt pressed thin films were prepared using standard melt pressing techniques. Post-condensed LC polyesterimide powder, prepared as described in examples 1 and 2, was placed between two Kapton films and consolidated in a preheated Joos hot press at 320 C. for 20 min with 5 kN force. The thermoset films were prepared from reactive oligomer powder under similar conditions but cured at 370 C. for 45 min

(10) Post-Treatment.

(11) In order to understand the effect of post-treatment on properties such as the glass transition temperature (T.sub.g) and storage modulus (E), the thermoset films were heated from 25 C. to the predetermined temperature at a heating rate of 2 C. min.sup.1.

(12) Characterization

(13) The thermal properties of the LC poly(esterimide)s are summarized in table 2.

(14) The thermal stability of the LC polymers and cured thermosets were evaluated using dynamic thermogravimetric analysis (TGA) at a heating rate of 10 C. min.sup.1. High decomposition values (T.sub.d.sup.5%450 C.) and high char yields (65 wt %) were found, indicating that the dynamic thermal stability of this polymer series is comparable to that of commercially available high-performance polymers such as bismaleimide (BMI) and bisnadimide (PMR15). The char yield of the LC poly(esterimide)s is higher than that of 0IM (54 wt %), which results from the excellent thermal stability of the imide-based moiety (IM).

(15) The thermal behavior of the LC polymers and reactive oligomers was investigated using differential scanning calorimetry (DSC). FIG. 3 depicts the first and second heating scans of the polymers using a heating rate of 20 C. min.sup.1. With regard to 0IM, no glass transition temperature (T.sub.g) but a crystal-to-nematic transition (T.sub.K-N) at 283 C. is observed. All LC poly(esterimide)s show high T.sub.g's at 210-230 C.

(16) In order to explore the thermomechanical properties of the LC poly(esterimide)s, the storage modulus (E) and loss modulus (E) as function of temperature were studied using dynamic mechanical thermal analysis (DMTA). The thin films as prepared in Example 3 were used for these DMTA experiments and the results are provided in FIGS. 4, 5 and 6 as well as in table 2.

(17) In FIG. 4, results of the DMTA analysis of the LC poly(esterimide)s 22IM-73IM melt pressed films are provided. Storage modulus (E) and loss modulus (E) as function of temperature for 0IM (A, B), the polymers with [IM]51 mol % (C, D) and the polymers with [IM]58 mol % (E, F). Heating rate 2 C. min.sup.1/nitrogen atmosphere and a frequency of 1 Hz.

(18) In FIG. 5, results of the DMTA analysis of the LC poly(esterimide)s comprising reactive end-caps (22IM-5K and 22IM-9K) as well as the LC poly(esterimide)s 22IM as comparison are provided. Storage moduli (E) (A) and loss moduli (E) (B) as function of temperature for the 22IM parent polymer and cured thermoset films thereof. Heating rate 2 C. min.sup.1/nitrogen atmosphere and a frequency of 1 Hz.

(19) In FIG. 6, results of the DMTA analysis of the LC poly(esterimide)s comprising reactive end-caps 22IM-5K after post-processing are provided. Storage moduli (E) (A) and loss moduli (E) (B) for 22IM-5K films after different post-treatment temperatures are shown. Heating rate 2 C. min.sup.1/nitrogen atmosphere and a frequency of 1 Hz. The films were post-treated from 25 C. to the predetermined temperatures with a heating rate 2 C. min.sup.1/nitrogen atmosphere and immediately cooled down to 25 C. (cooling rate 3 C. min.sup.1).

(20) TABLE-US-00002 TABLE 2 T.sub.K-N T.sub.g1 ( C.) T.sub.g2 ( C.) T.sub.g1 ( C.) T.sub.g2 ( C.) E at 25 C. T.sub.d.sup.5% Char yield Sample ( C.).sup.a DSC.sup.b DSC.sup.b DMTA.sup.c DMTA.sup.c (GPa) ( C.).sup.d (wt %).sup.e 0IM 280 111 5 480 54 22IM 280 120 222 124 200 6 450 63 29IM 300 119 229 124 220 6 449 65 37IM 310 121 226 129 221 7 447 65 44IM 300 221 139 219 8 445 63 51IM 300 225 143 216 7 448 65 58IM 290 233 224 5 453 64 65IM 290 234 230 5 448 65 73IM 300 235 228 5 446 66 22IM-9K 280 118 250 123 225 8 458 63 22IM-5K 270 118 254 127 243 10 458 64 .sup.aT.sub.K-N values were obtained from a hot-stage optical microscopy study. Heating rate 50 C. min.sup.1/air atmosphere. .sup.bT.sub.g values were obtained from the second heating scan of DSC experiments. Heating rate 20 C. min.sup.1/nitrogen atmosphere. .sup.cTg data were obtained from DMTA experiments using melt pressed films, defined by the maximum of the loss modulus (E) peak. Heating rate 2 C. min.sup.1/nitrogen atmosphere and a frequency of 1 Hz. .sup.dThermal stability was evaluated using dynamic TGA. The sample was isothermal held at 370 C. for 1 h. before the actual measurement. Heating rate 10 C. min1/nitrogen atmosphere. .sup.eChar yield at 600 C.