Transparent graft copolymers based on acrylate soft phases

Abstract

The invention relates to graft copolymersbased on non-cross-linked acrylate soft phases from which styrenic monomers are graftedwith a defined micro-structure, having a high transparency, toughness and weather resistance (UV-stability), a process for their preparation and their use, and also to polymer blends comprising said graft copolymers and styrenic polymers, and shaped articles produced therefrom and their use.

Claims

1. A graft copolymer B, built up from: (B1) 15 to 45 wt.-%, based on the graft copolymer B, of a non-cross-linked graft substrate polymer B1 having a glass transition temperature T.sub.G below 25 C. (DSC, heating rate: 5K/min), consisting of polymerized units derived from monomers B11, B12, and optionally B13: (B11) from 95 to 99.5 wt.-%, based on the total weight of B11, B12, and B13, of at least one C.sub.1-C.sub.10-alkyl acrylate; (B12) from 0.5 to 5 wt.-%, based on the total weight of B11, B12 and B13, of at least one monomer (=(meth)acrylate) of the formula (I)
H.sub.2CCR.sup.1COOR.sup.2X(I), wherein R.sup.1H or CH.sub.3, R.sup.2C.sub.1-C.sub.4-alkanediyl, XNH.sub.2, OH or ##STR00005## and (B13) from 0 to 4.5 wt.-%, based on the total weight of B11, B12, and B13, of at least one other copolymerizable, monoethylenically unsaturated monomer; and (B2) 55 to 85 wt.-%, based on the graft copolymer B, of at least one polymer B2 having a glass transition temperature T.sub.G above 25 C., grafted (in the form of branches) from the graft substrate polymer (B1), where polymer B2 consists of polymerized units derived from monomers B21 and optional comonomers B22: (B21) from 65 to 100 wt.-% of at least one vinylaromatic monomer and/or of a C.sub.1-C.sub.8-alkyl-(meth)acrylate; and (B22) from 0 to 35 wt.-% of at least one other monofunctional comonomer; where components B1 and B2 give 100 wt.-% in total, and wherein the graft substrate polymer B1 has a gel content (non-soluble fraction in toluene) below 5 wt.-%, based on the total amount of B1; the polymerized units derived from monomer B12 are chemically modified by moieties of the formula (II) H.sub.2CCR.sup.1CO (II) (R.sup.1H or CH.sub.3) which are covalently bound to the functional groups X; and the double bond of the moiety of formula (II) is the active site from which polymerized units derived from monomer B21 and optionally comonomer B22 are grafted.

2. The graft copolymer B according to claim 1 having a transmittance T of at least 75% (determined according to ASTM D1003) and a haze coefficient below 10% (determined according to ASTM D1003-95).

3. The graft copolymer B according to claim 1, wherein monomer B11 is ethyl acrylate, 2-ethylhexyl acrylate, n-butyl acrylate, or mixtures thereof.

4. The graft copolymer B according to claim 1, wherein monomer B12 of the formula (I) is hydroxyethyl acrylate (HEA), glycidyl methacrylate (GMA), (2-hydroxyethyl) methacrylate (HEMA), or hydroxypropylmethacrylate.

5. The graft copolymer B according to claim 1, wherein monomer B21 is styrene, -methylstyrene, or a mixture of styrene or -methylstyrene with methyl methacrylate.

6. The graft copolymer B according to claim 1, wherein comonomer B22 is maleic anhydride or acrylonitrile.

7. The graft copolymer B according to claim 1, wherein polymer B2 has been built up from styrene, or from a mixture consisting of 65 to 85 wt.-% styrene and 15 to 35 wt.-% acrylonitrile, maleic anhydride, or methyl methacrylate.

8. The graft copolymer B according to claim 1, wherein monomer B13 is not present.

9. The graft copolymer B according to claim 1 built up from: (B1) 20 to 40 wt.-% of graft substrate polymer B1; and (B2) 60 to 80 wt.-% of polymer B2.

10. A process for the preparation of the graft copolymer B according to claim 1, which comprises the following steps: (i) free radical aqueous emulsion polymerization of monomers B11, B12, and optionally B13 in presence of an initiator PI-1; (ii) chemical modification of graft substrate polymer B1 obtained in step (i) by reaction of the functional groups X with (meth)acrylic acid, its acid chloride, its acid anhydride, or its salts in presence of a base and a polymerization inhibitor; (iii) grafting monomer B21 and optional comonomer B22 from graft substrate polymer B1 obtained in step (ii) by free radical emulsion or solution polymerization in presence of an initiator PI-2; where the initiators PI-1 and PI-2 can be the same or different compounds, and wherein step i) is performed in the presence of 0.85 to 2 wt.-% of at least one chain transfer agent, based on the total amount of monomers B11, B12, and B13; step ii) is performed in aqueous emulsion or in an organic solvent, the amount of graft substrate polymer B1 is 20 to 75 wt.-%, based on the total reaction medium, and the amount of (meth)acrylic acid or its said derivatives is 10 to 20 wt.-%, relative to B1; and in step iii): the amount of initiator PI-2 is 0.1 to 3 wt. % relative to the total content of monomers B21 and B22; and monomer B21 and, if present, comonomer B22, and optionally the initiator PI-2 are fed continuously to the reaction mixture over 8 to 20 hours at a temperature of from 50 to 100 C.

11. The process according to claim 10, wherein in step i) the chain transfer agent is added stepwise in two or more portions.

12. The process according to claim 10, wherein in step iii) the monomer, and optional initiator, feed is over 10 to 18 hours.

13. A process for the preparation of the graft copolymer B according to claim 1, which comprises the following steps: (i-s) free radical solution polymerization of monomers B11, B12, and optionally B13 in presence of an initiator PI-1; (ii) chemical modification of graft substrate polymer B1 obtained in step (i) by reaction of the functional groups X with (meth)acrylic acid, its acid chloride, its acid anhydride, or its salts in presence of a base and a polymerization inhibitor; (iii) grafting monomer B21 and optional comonomer B22 from graft substrate polymer B1 obtained in step (ii) by free radical solution polymerization in presence of an initiator PI-2; where the initiators PI-1 and PI-2 can be the same or different compounds, and wherein step i) is performed in the presence of 0.85 to 2 wt.-% of at least one chain transfer agent, based on the total amount of monomers B11, B12, and B13; step ii) is performed in aqueous emulsion or in an organic solvent, the amount of graft substrate polymer B1 is 20 to 75 wt.-%, based on the total reaction medium, and the amount of (meth)acrylic acid or its said derivatives is 10 to 20 wt.-%, relative to B1; and in step iii): the amount of initiator PI-2 is 0.1 to 3 wt.-% relative to the total content of monomers B21 and B22; and monomer B21 and, if present, comonomer B22, and optionally the initiator PI-2 are fed continuously to the reaction mixture over 8 to 20 hours at a temperature of from 50 to 100 C., wherein in all steps (i-s), (ii), and (iii) an organic solvent is used as reaction medium.

14. A graft copolymer B obtained by the process according to claim 10.

15. A molding composition comprising at least one graft copolymer B according to claim 1, and optionally additives and/or auxiliaries C.

16. The molding composition according to claim 15, further comprising at least one thermoplastic polymer A having a glass transition temperature above 25 C.

17. The molding composition according to claim 16, wherein the thermoplastic polymer A is selected from standard polystyrene (GPPS, homopolystyrene), styrene-acrylonitrile copolymers (SAN), -methylstyrene-acrylonitrile copolymers (AMSAN), styrene-maleic anhydride copolymers (SMSA), and styrene-methyl methacrylate copolymers (SMMA).

18. The molding composition according to claim 16, comprising: 5 to 60 wt.-% of at least one graft copolymer B, 30 to 95 wt.-% of at least one thermoplastic polymer A, and 0 to 10 wt.-% of additives and/or auxiliaries C, wherein the sum of the amounts of components A, B, and, if present, C, makes 100 wt.-%.

19. A shaped article comprising the molding composition according to claim 15.

20. The molding composition according to claim 15 for the production of a household item, an electronic component, household equipment, garden equipment, medical-technology equipment, a motor-vehicle component, and a bodywork part.

Description

EXAMPLES

(1) Materials

(2) Toluene, THF, cyclohexane, methanol, acrylic acid, trimethylamine, and triethylenetetramine are supplied by VWR chemicals as chromatography grades and are used without any further purification. Ethanol and Triphenyl phosphine are supplied by Merck Millipore and used without further purification. Aluminum oxide (activated, basic, Brockmann Grade I, 58 angstroms) was purchased from Alfa Aesar and was used as received.

(3) DGEBA was supplied by BASF SE and was used without any further purification. Styrene and methyl methacrylate are supplied by VWR chemicals. The inhibitor is removed by adsorptive filtration using an aluminum oxide column.

(4) Benzoyl peroxide (BPO) and azoisobutyronitrile (AIBN) are purchased from VWR chemicals and purified by recrystallization from ethanol and methanol respectively.

(5) Methods for Characterization

(6) SEC analysis is performed with an Agilent 1100 Series HPLC system, equipped with UV (254 nm) detector and RI detector (Agilent 1100 series). The following column set from Agilent is used: PL gel 5 m guard column (507.5 mm), 2 PL gel 5 m Mixed-C columns (3007.5 mm). The analysis is performed using THF as solvent for the sample dissolution as well as for elution solvent. The samples are dissolved at 1 mg/mL concentration and the flow rate is fixed at 1 mL/min. A polystyrene standard set from Polymer Standard Service PSS is used for calibration.

(7) HPLC analysis is performed with an Agilent 1100 Series HPLC system, using a Nucleosil 100-5 OH (2504.6 mm) column. An evaporative light scattering detector PL-ELS 2100 from Agilent is used.

(8) 1H NMR analysis is recorded on a Bruker advance 300 NMR spectrometer (frequency at 300.38 MHz) in CDCl.sub.3 at 298.1 K. Chemical shifts are reported in units (ppm) relative to the remaining resonances of the solvent at 7.26 ppm.

(9) NMR analysis is used to determine the hard phase content in the graft copolymer by integration of the corresponding hard and soft phase peaks.

(10) The molar percentage of hard phase is calculated as follows:

(11) $\mathrm{mol}.{\%}_{\mathrm{hard}\mathrm{phase}}=\frac{\begin{array}{c}{\mathrm{Int}}_{\left(\mathrm{hard}\mathrm{phase}\mathrm{peak}\right)}\\ \mathrm{number}H\end{array}}{\frac{{\mathrm{Int}}_{\left(\mathrm{soft}\mathrm{phase}\mathrm{peak}\right)}}{\mathrm{number}H}+\frac{{\mathrm{Int}}_{\left(\mathrm{hard}\mathrm{phase}\mathrm{peak}\right)}}{\mathrm{number}H}}$$\mathrm{wt}.{\%}_{\mathrm{hard}\mathrm{phase}}=\frac{\frac{\mathrm{mol}.{\%}_{\mathrm{hard}\mathrm{phase}}}{M_{\mathrm{hard}\mathrm{phase}}}}{\frac{1-\mathrm{mol}.{\%}_{\mathrm{hard}\mathrm{phase}}}{M_{\mathrm{soft}\mathrm{phase}}}+\frac{\mathrm{mol}.{\%}_{\mathrm{hard}\mathrm{phase}}}{M_{\mathrm{soft}\mathrm{phase}}}}$

(12) The analysis is used to quantify the number of olefinic groups remaining on the grafted backbone after graft copolymerization. The grafting yield can therefore be defined as:

(13) $\left(\mathrm{grafting}\right)=\frac{\mathrm{mol}.\%\mathrm{of}\mathrm{olefinic}\mathrm{after}\mathrm{grafting}}{\mathrm{mol}.\%\mathrm{of}\mathrm{olefinic}\mathrm{before}\mathrm{grafting}}$

(14) Film casting from solvent: The dried graft copolymer is dissolved in toluene (3 wt.-% solution). The solution is cast in a petri dish and the solvent is allowed to evaporate at room temperature for minimum 24 h. The obtained film of the graft copolymer is removed from the petri dish by dipping. Then, the film is dried in a vacuum oven for a minimum of 24 h. The films are used for mechanical testing, optical measurements and TEM analysis.

(15) Mechanical properties: Tensile strength, elongation and E modulus are determined of the samples are measured using a Zwick Roell Z 2.5 device.

(16) Optical properties: Transmittance, clarity and haze coefficients are determined by using a Gardner Haze hard plus. The transmission is determined according to ASTM D1003 and the haze is determined according to ASTM D1003-95.

Example 1: Emulsion Polymerization of polybutylacrylate-co-glycidylmethacrylate (2 wt.-% GMA, 1 wt.-% TDM)

(17) The reaction vessel is charged with 151.52 g of demineralized water, 1.525 g of a 40 wt.-% sodium alkylsulfonate (C14 to C18) solution in water and 0.23 g sodium bicarbonate and subsequently evacuated and purge with nitrogen. After heating the reaction vessel to 59 C., 0.18 g potassium persulfate is added to the reaction mixture. A mixture of 2.04 g glycidylmethacrylate (GMA) and 100 g butyl acrylate is added within 210 min under constant stirring. After 30 min, 90 min and 150 min a portion of each 0.33 g tert-dodecylmercaptane is added. The post polymerization time is 60 min at a temperature of 61 C. A scaling factor of 20 was used. A diameter of 86 nm was determined by turbidity for the latex particles. The Gel content in Toluene is below 1 wt.-%.

(18) An aqueous solution containing 1 wt.-% of MgSO.sub.4 and 0.06 wt.-% of H.sub.2SO.sub.4 was prepared and heated up to 50 C. The prepared latex was poured in a minimum of 5 folds of the aqueous acidic solution, heated up to 90 C. to coagulate. The polymer was then filtered and dried in a vacuum oven for 24 h at 50 C.

Example 2: Emulsion Polymerization of polyethylacrylate-co-glycidylmethacrylate (2 wt.-% GMA, 1 wt.-% TDM)

(19) The reaction vessel is charged with 151.52 g of demineralized water, 1.525 g of a 40 wt.-% sodium alkylsulfonate (C14 to C18) solution in water and 0.23 g sodium bicarbonate and subsequently evacuated and purge with nitrogen. After heating the reaction vessel to 59 C., 0.18 g potassium persulfate is added to the reaction mixture. A mixture of 2.04 g Glycidylmethacrylat (GMA) and 100 g ethyl acrylate is added within 210 min under constant stirring. After 30 min, 90 min and 150 min a portion of each 0.33 g tertdodecylmercaptan is added. The post polymerization time is 60 min at a temperature of 61 C. A scaling factor of 20 was used.

(20) 5052 g of polymer latex was mixed with 5 I of demineralized water and 505 g of a 20.35 wt.-% magnesium sulfate solution was added at room temperature under constant stirring. The precipitated polymer was separated from the remaining solution and rinsed with water. The polymer was then dried in an oven for 24 h at 60 C.

Example 3: Modification of polybutylacrylate-co-glycidylmethacrylate backbone (2 wt. % GMA, 1 wt. % TDM)

(21) The product from example 1 (200 g) is dissolved in toluene (200 g) in a 1000 mL three neck round bottom flask equipped with a mechanical stirrer. The mixture is stirred at 150 rpm at room temperature. 0.4 g of 4-methoxyphenol (MEHQ) and 4 g of triphenylphosphine are dissolved in 40 g of acrylic acid and added and the reaction mixture under constant stirring. The reaction is heated up to 115 C. and kept for 24 h.

(22) The reaction mixture is allowed to cool down and precipitated in an excess of methanol (at least 5 folds). The methanol is removed and the polymer is re-dissolved in around 200 g of THF. The solution is then poured in minimum 5 folds of methanol and the polymer is dried at 40 C. under vacuum until constant weight.

(23) The yield of modification, measured by NMR is 100%.

Example 4: Modification of polyethylacrylate-co-glycidylmethacrylate backbone (2 wt. % GMA, 1 wt. % TDM)

(24) The product from example 2 (200 g) is dissolved in toluene (200 g) in a 1000 mL three neck round bottom flask equipped with a mechanical stirrer. The mixture is stirred at 150 rpm at room temperature. 0.4 g of 4-methoxyphenol (MEHQ) and 4 g of triphenylphosphine are dissolved in 40 g of acrylic acid and added and the reaction mixture under constant stirring. The reaction is heated up to 115 C. and kept for 24 h. The reaction mixture is cooled down and precipitated in an excess of a 70/30 vol/vol mixture of methanol/water (at least 5 folds). The methanol/water is removed and the polymer is re-dissolved in around 200 g of THF. The solution is then poured in minimum 5 folds of methanol/water and the polymer is dried at 40 C. under vacuum until constant weight.

(25) The yield of modification, measured by NMR is 71.2%.

Example 5: Grafting of MMA from Modified pBA-co-GMA Backbone

(26) The product from example 3 (7.88 g) is dissolved in toluene (93 g) in a 250 mL three round neck bottom flask equipped mechanical stirrer (150 rpm) and heated up to 85 C. A mixture of MMA (29.95 g), benzylmethacrylate (BMA) (1.58 g) and AIBN (0.47 g, 1.5 wt.-% relative to MMA and BMA) is added to the reaction mixture during 15 hours. The reaction is further continued for 10 h.

(27) After cooling down, the reaction mixture is precipitated in methanol, redissolved in THF (approximately 100 g) and poured in a minimum of 5 folds of methanol. After filtration the polymer is dried under vacuum at 50 C. for 24 h.

Example 6: Grafting of Styrene from Modified p-EA-co-GMA Backbone

(28) The product from example 4 (7.58 g) is dissolved in toluene (89 g) in a 250 mL three round neck bottom flask equipped mechanical stirrer (150 rpm) and heated up to 85 C. A mixture of styrene (30.33 g) and BPO (0.23 g, 1.125 wt.-%, relative to styrene) is added to the reaction mixture during 15 hours. The reaction is further continued for 10 h.

(29) After cooling down, the reaction mixture is precipitated in methanol, redissolved in THF (approximately 100 g) and poured in a minimum of 5 folds of methanol. After filtration the polymer is dried under vacuum at 50 C. for 24 h.

Example 7: Grafting of Styrene from Modified pBA-co-GMA Backbone

(30) A 250 mL reactor flask equipped with an anchor stirrer, a condenser and a nitrogen inlet was charged with 11 g of the product from example 3 pre-diluted in toluene (159.8 g) and heated up to 85 C. while stirring at 200 rpm. 0.35 g of dibenzoylperoxide was dissolved in 44 g of styrene and degassed with nitrogen for 15 minutes. This initiator in styrene solution was fed to the reaction mixture for 13.4 h by a piston pump with a rate of 55 L/min. After 24 h, the polymer mixture was allowed to cool down and the polymer was precipitated into methanol. After filtration, the polymer powder was dried in a vacuum oven at 60 C. for 15 h.

(31) TABLE-US-00001 TABLE 1 Preparation of Graft Copolymers B Dosing time (h) of Example Polymer Backbone used monomer 5 pBA-co-GMA- modified pBA-co-GMA 15 g-PMMA (2 wt.-% GMA, 1 wt.-% TDM) 6 p-EA-co- modified p-EA-co-GMA 15 GMA-g-PS (2 wt. %, 1 wt. % TDM) 7 pBA-co- modified pBA-co-GMA 13.4 GMA-g-PS (2 wt.-% GMA, 1 wt.-% TDM)

(32) TABLE-US-00002 TABLE 2 Mechanical and Optical Properties of Graft Copolymers B Young's Elongation Trans- Haze modulus at break mittance (%) (GPa) (%) (%) Conversion Example 5 8 1.24 14 93.5 88.6 Example 6 28 0.736 13.8 92 37.5 Example 7 12 0.44 80 92 59.9 Styrolux 1.5 1.5 160 89

(33) As shown in Table 2, the graft copolymers according to example 5 and Example 6 exhibit excellent transparency as well as mechanical properties. The tensile modulus of the film is 1.24 GPa and 0.74 GPa and the elongation at break is 14% and 13.8% (in comparison to Styrolux with a tensile modulus of 1.5 GPa). The transparency of the film, especially the transmittance (93.5%) is high compared to a transparent styrene-butadiene block co-polymer such as Styrolux with a transmittance of 89%. The graft copolymers according to example 7 show an excellent transparency as well as a good toughness (elongation at break 80%).

Example 8

(34) A molding composition is prepared from 50% by weight of the polymer from example 5 and 50% by weight of commercial SAN-copolymer (Luran).