Mono vinyl aromatic conjugated diene block copolymer and polymer composition comprising said block copolymer and a mono vinylarene acrylate copolymer

Abstract

The present invention relates to novel block copolymers comprising at least one mono vinyl aromatic monomer (also referred to as mono vinylarene) and at least one conjugated diene monomer, in particular to styrene butadiene block copolymers (SBC), with a defined block structure. The invention further relates to polymer blends which comprise at least one block copolymer and at least one mono vinylarene acrylate copolymer, in particular a styrene-methyl methacrylate copolymer. Related methods for preparation and articles prepared from the polymer blends are also provided.

Claims

1. A block copolymer comprising at least one mono vinyl aromatic monomer and at least one conjugated diene monomer, wherein the block copolymer comprises at least a first and a second homo block of a mono vinyl aromatic monomer and, between these vinyl aromatic blocks, at least one homo block of a conjugated diene and at least one random block of at least one mono vinyl aromatic monomer and at least one conjugated diene, wherein the block copolymer comprises from 20 to 50% by weight of conjugated diene monomer, based on the total block copolymer, wherein the block copolymer has a star shaped structure and wherein the block copolymer is obtained by a process that comprises the steps of forming by sequential anionic polymerization and coupling at least one branch with the block sequence S1-S2-B1-S3/B2-S4 and/or S2-B1-S3/B2-S4, wherein S represents homo blocks of mono vinyl aromatic monomer, B represents homo blocks of conjugated diene, and S/B represents a random block consisting of vinyl aromatic monomer and conjugated diene, where at least the polymerization step of the random block S/B takes place in the presence of a potassium salt as randomizer.

2. The block copolymer according to claim 1, wherein the at least one mono vinyl aromatic monomer is styrene and the at least one conjugated diene is 1,3-butadiene.

3. The block copolymer according to claim 1, wherein the molar mass of the at least one homo block of a conjugated diene monomer is in the range of 1,000 to 3,500 g/mol.

4. The block copolymer according to claim 1, wherein the molar mass of the second block of a mono vinyl aromatic monomer is in the range of 1,000 to 10,000 g/mol.

5. A polymer composition comprising a block copolymer, which comprises at least one mono vinyl aromatic monomer and at least one conjugated diene monomer according to claim 1 and at least one mono vinylarene acrylate copolymer, wherein the polymer composition comprises from 6 to 31% by weight, based on the total composition, of conjugated diene units.

6. The polymer composition according to claim 5 wherein the polymer composition comprises from 12 to 15% by weight, based on the total composition, of conjugated diene units.

7. The polymer composition according to claim 5, wherein the at least one mono vinylarene acrylate copolymer is a styrene methyl methacrylate copolymer.

8. The process for preparing a block copolymer according to claim 1, wherein in the sequential anionic polymerization the molar ratio of anionic polymerization initiator to potassium salt is from 10:1 to 100:1.

9. A process for preparing a polymer composition according to claim 7 comprising the step of mixing the polymer components and optionally additives.

10. A molding comprising a polymer composition according to claim 5.

11. The molding according to claim 10, wherein the molding is selected from household items, electronic components, household equipment, garden equipment, medical-technology equipment, motor-vehicle components, and bodywork parts.

Description

EXAMPLE I

Preparation of Styrene Butadiene Block Copolymers (SBC)

Examples 1 To 5

(1) Linear styrene butadiene block copolymers (SBC) of the structure S1-S2-B1-(S3/B2).sub.1-(S3/B2).sub.2-(S3/B2).sub.3-S4 (polymer chain 1) and S2-B1-(S3/B2).sub.1-(S3/B2).sub.2-(S3/B2).sub.3-S4 (polymer chain 2) were obtained by sequential anionic polymerization of styrene and butadiene in cyclohexane as solvent at from 60 to 90° C. The ratio of the initiator BuLi (BuLi1) of polymer chain 1 to initiator BuLi (BuLi2) of polymer chain 2 was 1:2.3. The polymer chains 1 and 2 were coupled using Dehysol D82. Thus, the following SBC block copolymer was obtained:

(2) $\hspace{1em}\begin{array}{cc}1x& S1\text{-}S2\text{-}B1\text{-}S3\text{/}B2\text{-}S4\\ 2,3x& S2\text{-}B1\text{-}S3\text{/}B2\text{-}S4\end{array}\setminus /$

(3) In the following the sequential polymerization of the blocks of the SBC block copolymers is described in detail (Example 5): S1: 4786 ml of cyclohexane and 6.7 ml (9.39 mmol) of a 1.4 molar sec-butyllithium solution (in n-hexane/cyclohexane) (BuLi1) as initiator were initially charged in a stirred reactor. The mixture had been titrated at 50° C. with about further 1.6 ml of 1.4 molar sec-butyllithium solution until a light red color appeared. The amount of 321.28 g (354 ml) styrene required to prepare the block S1 was metered in. The maximum temperature was 72.2° C. Sample 1 was taken (solid content 7.92%). S2: After all of the styrene had been consumed 15.4 ml (21.60 mmol) of a 1.4 molar sec-butyllithium solution (in n-hexane/cyclohexane) (BuLi2) and the amount of 379.04 g (418 ml) styrene required to prepare the block S2 was metered in. The maximum temperature was 74.9° C. Sample 2 was taken (solid content 15.80%). B1: After all of the styrene had been consumed an amount of 80 g (122 ml) butadiene required to prepare block B1 was added. The maximum temperature was 74.9° C. Sample 3 was taken (solid content 17.29%). S3/B2: After all of the butadiene had been consumed, 2.89 ml of potassium tert-amylate (KTA, potassium-2-methyl-butanolate) (solution of KTA with concentration of 5.76%/0,357 molar) was added as randomizer and three blocks S3/B2 were attached by adding three times a mixtures of 65.92 g (72.7 ml) styrene and 168.5 g (257 ml) butadiene. After each addition the polymerization was carried out at a maximum temperature of 79.3° C. The molar ratio of initiator/randomizer (Li/K) was 30/1. Sample 4 was taken (solid content 28.44%). S4: Finally the styrene block S4 was polymerized by addition of 116.16 g (128 ml) styrene. The maximum temperature was 71° C. Sample 5 was taken (solid content 30%). Coupling: The copolymers branches S1-S2-B1-(S3/B2).sub.1-(S3/B2).sub.2-(S3/B2).sub.3-S4 (polymer branch 1) and S2-B1-(S3/B2).sub.1-(S3/B2).sub.2-(S3/B2).sub.3-S4 (polymer branch 2) are coupled by adding Dehysol D82. The mixture was allowed to react under slow agitation for ten minutes.

(4) Finally the reaction mixture was terminated using isopropanol and acidified using 1% by weight CO.sub.2 and 0.5% by weight water. Irganox 1010 and Sumilizer GS were added in an amount of 0.2% by weight based on the polymer composition for stabilization.

(5) In all examples 1 to 5 the ratio of BuLi1:BuLi2 was 1:2.3 and the ratio of BuLi to randomizer KTA was 30:1.

(6) Examples 1 to 5 were carried out as described above using slightly different amounts of styrene and butadiene. The molar masses M.sub.n and weight percent of the different blocks are summarized in Table 1.

(7) TABLE-US-00001 TABLE 1 SBC block copolymers with random S/B-block Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 M M M M M [g/mol] wt-% [g/mol] wt-% [g/mol] wt-% [g/mol] wt-% [g/mol] wt-% S1 33,186 44.4 33,186 44.4 33,697 44.9 33697 44.9 34208 45.3 S2 11,504 15.3 11,504 15.4 11,865 15.8 11875 15.8 12237 16.2 B1 3,096 4.1 2,580 3.5 3,096 4.1 2580 3.4 2580 3.4 S3 6,096 8.2 7,023 9.4 6,096 8.1 6714 8.9 6387 8.5 of S3B2 B2 15,795 21.1 16,305 21.8 15,795 21.0 16305 21.7 16305 21.6 of S3B2 S4 5,058 6.8 41,29 5.5 4,545 6.1 3941 5.3 3750 5.0 Branch 1 74,735 74,727 75,094 75112 75467 Branch 2 41,549 41,541 41,397 41,415 41,259 Block 170,298 170,271 170,307 170,367 170,363 copolymer

(8) The calculated values of the molecular weights of the blocks were verified by GPC and melt flow index. The molecular weights of the synthesized SBC block copolymers were analyzed after each polymerization sequence using gel permeation chromatography (GPC) on polystyrene gel columns (Polymer Labs, mixed B type) with monodisperse polystyrene standards at room temperature using tetrahydrofuran as eluent.

(9) The data concerning the pure SBC block copolymers are summarized in Table 2.

(10) TABLE-US-00002 TABLE 2 Physical data of pure SBC block copolymer Ex. 1 Ex. 1a Ex. 2 Ex. 3 Ex. 4 Ex. 5 Melt flow 11.58 7.24 35.46 15.78 8.8 7.88 rate [g/10 min] Mw 115.3 175.9 124.5 142.4 171.3 178.5 [kDalton] Refractive — 1.568 1.568 1.567 1.561 1.567 Index Lower Tg −67.6 −65.5 −64.4 −65.1 −64.2 −66.1 [° C.] Upper Tg 83.8 85.9 85.8 95.3 98.1 88.4 [° C.]

EXAMPLE II

Preparation of the SMMA/SBC Polymer Blends

(11) The obtained SBC block copolymers according to Example 5 were degassed using a twin screw extruder ZSK 25.

(12) 36% by weight of the SBC according to Example 5 were mixed with 64% by weight of a pelletized styrene methyl methacrylate (SMMA) product (NAS®30 of Styrolution). For that purpose pellets of the SBC block copolymer and pellets of the SMMA polymer components were first mixed in a tumble blender along with 1200 ppm by weight of processing stabilizers. The resulting blend was then fed into a single screw extruder with a 1.5 inch diameter and L to D ratio of 30:1. Barrel temperatures ranged from 218 to 232° C. Polymer exited the extruder through a strand die, then a water bath to cool the polymer alloy, before finally cutting the cooled strands into cylindrical pellets.

(13) As control sample a polymer blend using the commercial available SBC product BK19® and NAS® 30 was used. Said commercial SBC is a styrene butadiene copolymer comprising 30 to 40 wt-% of butadiene and encompass at least one tapered block. Said SBC product and the SBC/SMMA blend are described for example in WO2006/052623. The formulations are summarized in Table 3.

(14) TABLE-US-00003 TABLE 3 SMMA/SBC polymer blends compositions Control Example [wt-%] sample P5 SMMA_NAS ® 30 63.8 63.8 BK19 ® 36.1 SBC/Ex. 5 36.1 Irganox 1076 0.09 0.09 Sumilizer GS 0.03 0.03

EXAMPLE III

Physical Data of the Polymer Blends

(15) The melt flow rate, the mechanical properties and the optical properties were determined as described above. Analytical and mechanical data on injection-molded specimen of the examples 1 to 5 and control examples are summarized in the following Table 4.

(16) TABLE-US-00004 TABLE 4 Properties of SMMA/SBC polymer blends Control sample Example P5 Melt flow rate 5.20 5.27 [g/10 min] Vicat softening point 99.0 98.5 [° C.] Tensile modulus with extensiometer 2.151 1.984 [MPa] Tensile stress at yield with extensiometer 28.0 26.9 [MPa] Tensile strain at yield with extensiometer 4.3 4.3 [%] Tensile stress at break without 26.4 26.6 extensiometer [MPa] Tensile strain at break without 34.1 41.8 extensiometer [%] Pellet L* 84.4 79.1 Pellet a* −0.80 −1.11 Pellet b* 1.29 5.33 Clarity [%] 98.4 99.1 Haze [%] 2.39 1.57 Transmittance [%] 91.13 91.5

(17) It is shown that the inventive injection-molded specimen (Example P5) show better transmittance and lower haze in comparison to the control sample comprising the commercial SBC product BK19®. Further sufficient mechanical properties of the SBC/SMMA specimen, such as tensile modulus and tensile strain can be achieved by using the inventive SBC.

EXAMPLE IV

Test Methods

(18) The test physical and optical tests, which were used in order to characterize the SBC block copolymer and the polymer blends, were performed as follows:

(19) TABLE-US-00005 Test Identification Melt Flow Rate ASTM D-1238 Vicat Softening Point ASTM D-1525 Tensile Properties ASTM D-638 Transmittance; Haze ASTM D-1003

(20) The properties clarity, haze and transmittance were determined using haze-gard plus (BYK Gardner GmbH) (illuminate CIE-C). The clarity was determined on basis of ASTM D-1044.