Very soft, non-sticky and transparent styrenic thermoplastic elastomer composition

Abstract

Thermoplastic elastomer compositions can be used for medical skin contact applications, comprising: a) 90.9 to 69.0 wt.-% star-shaped block copolymer A with 4 arms of the general structure [S.sub.1—(S/B).sub.k—(S/B).sub.I—(S/B).sub.m—S.sub.2].sub.n—X, where S.sub.1 and S.sub.2 are vinylaro-matic hard polymer and S/B are soft random vinylaromatic/diene copolymer blocks; X is a coupling center; and b) 9.1 to 31.0 wt.-% of a plasticizer B: b1) a mixture of mineral oil B1 and cyclohexane 1,2-dicarboxylic acid C.sub.8 to C.sub.10 dialkyl ester B2; or b2) a mixture of mineral oil B1 and vegetable oil B3.

Claims

1. A thermoplastic elastomer composition comprising components a), b), and c): a) 90.9 to 69.0 wt.-% of at least one star-shaped block copolymer A of the structure
[S.sub.1−(S/B).sub.k−(S/B).sub.l−(S/B).sub.m−S.sub.2].sub.n−X  (I), where S.sub.1 and S.sub.2 are polymer blocks made from at least one vinylaromatic monomer and S/B are random copolymer blocks made from at least one vinylaromatic monomer and at least one diene forming a soft phase; X is a coupling center derived from a polyfunctional coupling agent; b) 9.1 to 31.0 wt.-% of a plasticizer B; and c) 0 to 2.0 wt.-% of further additives C; wherein the sum of components a), b), and c) is 100 wt.-%; the arms S.sub.1−(S/B).sub.k−(S/B).sub.m−(S/B).sub.m−S.sub.2 are identical; the proportion of the blocks S.sub.1 and S.sub.2 (forming a hard phase), based on the entire block copolymer A, is from 24 to 40 wt.-%; the vinylaromatic monomer/diene (=S/B) ratio of all of the blocks (S/B) is from 1/0.45 to 1/2.5; the S/B-ratio of the blocks (S/B).sub.k, (S/B).sub.l and (S/B).sub.m is different from each other; the S/B-ratio of the blocks (S/B).sub.k and (S/B).sub.m is lower than the S/B-ratio of the block(s) (S/B).sub.l; the weight ratio of blocks S.sub.2/S.sub.1 is from 0.1 to 0.8; and the weight average molar mass M.sub.w (determined by GPC according to ISO 16014-3:2012) of the block copolymer A is from 220000 to 450000 g/mol; n is a natural number from 1 to 8; k and m are 1; and l is a natural number of at least 1; and the plasticizer B is b1) a mixture composed of mineral oil B1 and at least one cyclohexane 1,2-dicarboxylic acid C.sub.8 to C.sub.10 dialkyl ester B2; or b2) a mixture composed of mineral oil B1 and at least one vegetable oil B3 having an iodine value (g/100 g) of no more than 130.

2. The thermoplastic elastomer composition according to claim 1, wherein the plasticizer in plasticizer mixture b1) or b2) the weight ratio of component B1 to component B2 or B1 to B3 is 80:20 to 40:60.

3. The thermoplastic elastomer composition according to claim 1, wherein the plasticizer B is mixture b2).

4. The thermoplastic elastomer composition according to claim 1, wherein the vegetable oil B3 is selected from the group consisting of: rapeseed oil, sunflower oil, grape seed oil, palm oil, olive oil, coconut oil, palm kernel oil, cocoa butter, jojoba oil, cottonseed oil, corn oil, wheat germ oil, soybean oil, peanut oil, castor oil, sesame oil, and rice brain oil.

5. The thermoplastic elastomer composition according to claim 1, wherein the vegetable oil B3 is rapeseed oil.

6. The thermoplastic elastomer composition according to claim 1, which melt mass flow index (measured on a polymer melt at 200° C. and 5 kg load according to ISO 1133-1:2011) is in the range of from 8 to 16 cm.sup.3/10 min.

7. The thermoplastic elastomer composition according to claim 1 comprising 9.1 to 20.0 wt.-% of plasticizer B (component b)) and the Mw of block copolymer A is 250000 to 320000 g/mol.

8. The thermoplastic elastomer composition according to claim 1 comprising more than 20 wt.-% of plasticizer B (component b)) and the Mw of block copolymer A is 325000 to 410000 g/mol.

9. The thermoplastic elastomer composition according to claim 1, wherein n is a natural number from 3 to 5.

10. The thermoplastic elastomer composition according to claim 1, wherein X is a coupling center derived from epoxidized linseed oil or epoxidized soybean oil.

11. The thermoplastic elastomer composition according to claim 1, wherein Mw of the polymer block S.sub.1 is in the range of from 22900 to 54000 g/mol, and Mw of the polymer block S.sub.2 is in the range of from 5000 to 12000 g/mol.

12. The thermoplastic elastomer composition according to claim 1, wherein the weight ratio of blocks S.sub.2/S.sub.1 of block copolymer A is from 0.1 to 0.6.

13. The thermoplastic elastomer composition according to claim 1, wherein the S/B-ratio of the copolymer block (S/B).sub.k is from 0.5 to 1.0; the S/B-ratio of the copolymer block(s) (S/B).sub.l is from 0.5 to 1.2; and the S/B-ratio of the copolymer block (S/B).sub.m is from 0.3 to 0.8.

14. The thermoplastic elastomer composition according to claim 1, wherein the weight average molar mass M.sub.w of the copolymer blocks (S/B).sub.k, (S/B).sub.l and (S/B).sub.m is different from each other; Mw (S/B).sub.k is in the range of from 16500 to 40000 g/mol; Mw (S/B).sub.l is in the range of from 25800 to 60800 g/mol; and Mw (S/B).sub.m is in the range of from 14300 to 33800 g/mol.

15. A process for the preparation of a thermoplastic elastomer composition according to claim 1, wherein component a) is introduced continuously into an extruder and then component b) and optionally further components c) are metered in.

16. A process for the preparation of a thermoplastic elastomer composition according to claim 1, wherein component b) and optional component c)—as such or in solution—are added into a solution of block copolymer A, then to homogenize the liquids, and subsequently to free the product from the solvent.

17. A shaped article produced from the thermoplastic elastomer composition according to claim 1.

18. A star-shaped block copolymer A of the structure
[S.sub.1−(S/B).sub.k−(S/B).sub.l−(S/B).sub.m−(S/B).sub.m−S.sub.2].sub.n−X  (I), wherein: S.sub.1 and S.sub.2 are polymer blocks made from at least one vinylaromatic monomer and S/B are random copolymer blocks made from at least one vinylaromatic monomer and at least one diene forming a soft phase; X is a coupling center derived from a polyfunctional coupling agent; the arms S.sub.1−(S/B).sub.k−(S/B).sub.m−(S/B).sub.m−S.sub.2 are identical; the proportion of the blocks S.sub.1 and S.sub.2 (forming a hard phase), based on the entire block copolymer A, is from 24 to 40 wt.-%; the vinylaromatic monomer/diene (=S/B) ratio of all of the blocks (S/B) is from 1/0.45 to 1/2.5; the S/B-ratio of the blocks (S/B).sub.k, (S/B).sub.l, and (S/B).sub.m is different from each other; the S/B-ratio of the blocks (S/B).sub.k and (S/B).sub.m is lower than the S/B-ratio of the block(s) (S/B).sub.l; the weight ratio of blocks S.sub.2/S.sub.1 is from 0.1 to 0.8; the weight average molar mass M.sub.w (determined by GPC according to ISO 16014-3:2012) of the block copolymer A is from 220000 to 450000 g/mol; n is a natural number from 1 to 8; k and m are 1; and l is a natural number of at least 1.

19. A process for the preparation of block copolymer A of formula (I) according to claim 18 characterized by i) a single initiation; ii) first addition and polymerization of vinyl aromatic monomer; iii) at least 3 times addition and polymerization of vinyl aromatic monomer and diene mixture; iv) second addition and polymerization of vinyl aromatic monomer; and v) a coupling step after the addition and polymerization of the vinylaromatic monomers of the last polymer block.

20. The shaped article of claim 17, wherein the shaped article is a medical article.

21. The shaped article of claim 20, wherein the medical article is for skin contact applications or intravenous applications.

22. An elastic and flexible molding produced from the thermoplastic elastomer composition according to claim 1.

Description

EXAMPLES

(1) Plasticizer B:

(2) B1 Winog® 70, a commercially available medical white oil

(3) B2 Hexamoll® (DINCH) from BASF SE, Germany

(4) B3 Rapeseed oil, Agri-pure® AP-60 from Cargill

(5) Block Copolymer A1

(6) A star-shaped block copolymer A of the structure [S.sub.1—(S/B).sub.k—(S/B).sub.l—(S/B).sub.m—S.sub.2].sub.n—X was prepared by sequential anionic polymerization of styrene (monomers S1 to S5) and butadiene (monomers B1 to B3) (cp. Table 1), and subsequent coupling using epoxidized soybean oil. 25670 ml of cyclohexane were used as initial charge (ic) and titrated to the end point at 45° C. with 1.6 ml of sec-butyllithium (BuLi ic), and cooled to 45° C. before adding the volume of a 1.4 M sec-butyllithium initiator solution as mentioned in Table 2, (BuLi) for initiation, and the volume of a 0.3304 M potassium tert-amyl alcoholate (PTA) randomizer solution as mentioned in Table 2. Next, the initiator mixture was then admixed and the mixture was cooled to 40° C. In a next step, 1350 gram styrene (S1) was added and the polymerization reaction was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture). In a next step, 570 gram butadiene (B1) and 415 gram styrene (S2) were added simultaneously and the polymerization reaction was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture).

(7) In a next step, again 800 gram butadiene (B2) and 720 gram styrene (S3) were added simultaneously and the polymerization reaction was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture). In a next step, again 535 gram butadiene (B3) and 310 gram styrene (S4) were added simultaneously and the polymerization reaction was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture). In a next step, 300 gram styrene (S5) was added and the polymerization reaction was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture).

(8) Finally, the amount of Edenol® D82 as mentioned in Table 2, dissolved in 10 mL cyclohexane, was added at a temperature between 45 and 55° C. as coupling agent and allowed to react for 10 minutes. Finally, 5 ml of isopropanol was added and the mixture was stirred during 10 min. Next, the mixture was acidified with 10 mL destilled water and 5 min of CO.sub.2 gas stream (0.1 kg/h) while stirring. Finally, 0.135 wt.-% phm*Irganox 1010, 0.180 wt.-% phm*Irgaphos 168 and 0.135 wt.-% phm*Sumilizer GS were added.

(9) *phm=‘per hundred parts by weight of monomer’ (wt.-% of component (initiator, coupling agent etc.) is calculated on the total mass of the monomers).

(10) TABLE-US-00001 TABLE 1 Block copolymer A (composition and sequence of addition) 5.sup.th 1st 2nd block 3rd block 4th block block block S.sub.1 (S/B).sub.k (S/B).sub.l (S/B).sub.m S.sub.2 S1 B1 S2 B2 S3 B3 S4 S5 wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% 27.0 11.4 8.3 16.0 14.4 10.7 6.2 6.0

(11) Block copolymers A1 to A8 of different weight average molar masses M.sub.w were obtained in accordance with the preparation as hereinbefore described (cp. Table 1) by use of the appropriate amount of BuLi, PTA and Edenol (cp. Table 2).

(12) Table 2 shows further the determined Shore A hardness of S-TPE compositions comprising one of the block copolymers A1 to A8 and different amounts of plasticizer B (mixture of B1/B2 or B1/B3 used in highest B1/B2 or B1/B3-ratio in which no bleeding occurs, cp. Table 4).

(13) TABLE-US-00002 TABLE 2 PTA M.sub.peak Plasti- Shore A BuLi random- before M.sub.w after cizer ASTM 1.4M izer Edenol coupling coupling B* D2240 Polymer mL mL mL g/mol g/mol phm (15 sec) A1 42.26 5.12 6.53 100240 252950 10 70 A2 37.72 4.57 5.83 112310 296540 15 64 A3 34.68 4.20 5.36 122150 290270 20 58 A4 33.01 4.00 5.10 128310 318020 25 50 A5 31.20 3.78 4.82 135770 352430 30 45 A6 28.46 3.45 4.40 148820 390720 35 43 A7 28.45 3.44 4.40 148870 367850 40 40 A8 26.78 3.24 4.14 158190 403480 45 38
Block Copolymer C1 (Comparative Compound)

(14) Linear block copolymer C1 of the structure S.sub.1—(B.sub.1/S.sub.2)—(B.sub.2/S.sub.3)—(B.sub.3/S.sub.4)—S.sub.5 (cp. Table 3) was prepared by sequential anionic polymerization of styrene (monomers S1 to S5) and butadiene (monomers B1 to B3), and subsequent terminating using 15 mL isopropanol. Linear block copolymer C1 was prepared in a manner similar to that as described for block copolymer A above, except of the coupling step, and further that 17970 mL cyclohexane was used as a solvent, in each case 960 g of styrene were used for the terminal blocks S, a mixture of 660 g of styrene and 700 g of butadiene for the random soft block (B.sub.1/S.sub.2), a mixture of 852 g of styrene and 904 g of butadiene for the random soft block (B.sub.2/S.sub.3) and a mixture of 468 g of styrene and 496 g of butadiene for the random soft block (B.sub.3/S.sub.4). The polymerisation was initiated using 37.59 mL of a 1.4 M sec-butyllithium solution and 4.49 mL of a 0.304 M potassium tert-amyl alcoholate (PTA) solution. After termination of the polymerization, the mixture was acidified with 10 mL destilled water and 5 min of CO.sub.2 gas stream (0.1 kg/h) while stirring. Finally, 12 gram Irganox 1010, 16.2 gram Irgaphos 168 and 12 gram Sumilizer GS were added.

(15) Mw: 141930 g/mol

(16) Shore A (ASTM D2240 (15 sec)): 84

(17) TABLE-US-00003 TABLE 3 Block copolymer C (composition and sequence of addition) 5.sup.th 1st 2nd block 3rd block 4th block block lni 1 block S.sub.1 (B.sub.1/S.sub.2) (B.sub.2/S.sub.3) (B.sub.3/S.sub.4) S.sub.2 SBC BuLi1 S1 B1 S2 B2 S3 B3 S4 S5 (1.4M) wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% (phm*) Cl 16.0 11.7 11.0 15.1 14.2 8.3 7.8 16.0
Preparation of S-TPE Compositions

(18) In a stirred vessel to a cyclohexane solution (polymer content 27.8 wt.-%) of one of the obtained stabilized block copolymers A1 to A8 or block copolymer C1, 0 to 45 phm of plasticizer B (based on 100 parts by weight (phm) of the total monomer weight used during the synthesis of block-copolymer A) were added and homogeneously mixed at 60° C. Each solution was subsequently degassed and the S-TPE compositions for further testing (cp. Tables 2, 4 and 5) were obtained.

(19) Bleeding Tests

(20) The samples with different plasticizer concentrations and plasticizer compositions (cp. Table 4) were compression molded to plates and cut into pieces (3 cm×3 cm). Next, the samples were stored on absorption paper under a load of 5 kg and at 35° C. After 1 week, the bleeding of the plasticizer B into the absorption paper was assessed according to next scale:

(21) 0=No bleeding (=non-sticky)

(22) 1=Bleeding stains onto the absorption paper

(23) 2=Bleeding stains onto the absorption paper+greasy polymer sample

(24) Table 4 shows that the oil-uptake without bleeding can be increased by use of the inventive S-TPE compositions comprising block copolymer A (cp. inventive samples 27 and 28 with a total plasticizer B concentration of 40 phm). Even with a total oil concentration of 45 phm a bleeding score of 0 can be achieved.

(25) TABLE-US-00004 TABLE 4 Bleed- Bleed- ing ing Block Block Fraction Fraction Fraction score score Plasti- co- co- of B1 of B3 of B2 block block cizer poly- poly- (wt.-%), (wt.-%) (wt.-%) co- co- B** mer mer based based based polymer polymer No. (phm) C A on B on B on B C A 1 10 C1 A1 100 1 1 2 80 20 0 0 3 80 20 0 0 4 60 40 0 0 5 60 40 0 0 6 40 60 0 0 7 40 60 0 0 8 20 C1 A4 100 2 2 9 80 20 0 0 10 80 20 2 0 11 60 40 0 0 12 60 40 0 0 13 40 60 0 0 14 40 60 0 0 15 30 C1 A5 100 2 2 16 80 20 2 2 17 80 20 2 2 18 60 40 0 0 19 60 40 0 0 20 40 60 0 0 21 40 60 0 0 22 40 C1 A7 100 2 2 23 80 20 2 2 24 80 20 2 2 25 60 40 2 2 26 60 40 2 2 27 40 60 1 0 28 40 60 1 0 29 45 C1 A8 100 2 2 30 80 20 2 2 31 80 20 2 2 32 60 40 2 2 33 60 40 2 2 34 40 60 2 1 35 40 60 2 0 **total plasticizer B concentration (phm) on top of total weight of monomers of block copolymer A or C
Mechanical Properties

(26) The samples with different plasticizer concentrations and plasticizer compositions were compression molded to plates with 2 mm thickness at 200° C. Next, the tensile test bars, according to ISO 527-1A, were pneumatically pressed from this compression molded plates (>1 cm from the edges) and tempered for 24 hours at 23° C. Finally, the bars were subjected to a tensile test on a Zwick tensile tester (2.5 kN+500N) according to the ISO 527 procedure.

(27) The resulting E-modulus, stress at break and strain at break are given in Table 5 below.

(28) TABLE-US-00005 TABLE 5 Frac- Frac- Frac- tion tion tion Block of B1 of B3 of B2 co- Plasti- (wt.- (wt.- (wt.- E- Stress Strain poly- cizer %), %) %) mod- at at mer B** based based based ulus break break Sample A (phm) on B on B on B (MPa) (MPa) (%) A A3 15 80 20 4.7 12.4 881 B 80 20 5.1 12.2 841 C A4 20 80 20 3.4 11.9 912 D 80 20 3.2 12.8 918 E 60 40 3.8 11.3 924 F 60 40 3.3 13.1 948 G A5 30 20 80 2.16 4.75 1100 H 20 80 3.45 9.71 1230 I A7 40 20 80 1.49 2.29 1000 J 20 80 2.14 8.90 1340 K A8 45 20 80 2.12 4.02 1280 L 20 80 2.16 8.27 1360 ** otal plasticizer B concentration (phm) on top of total weight of monomers of block copolymer A or C

(29) Table 5 shows that the S-TPE compositions according to the invention have significantly improved mechanical properties while also having a very good softness as indicated by their shore A hardness (cp. Table 2), almost all values are between 60 and 40.

(30) Very good overall results, including the mechanical properties, are obtained with a composition comprising a plasticizer mixture B1/B3. S-TPE compositions comprising 15 to 20 phm of plasticizer B, in particular plasticizer b2) (mixture B1/B3), show a high stress at break (more than 11 MPa) and are very soft (Shore A hardness of 64 to 50).

(31) Compositions comprising 30 to 45 phm of plasticizer B, in particular plasticizer b2) (mixture B1/B3), show a good stress at break (often more than 8 MPa) and a high strain at break (often more than 1200%) and are extremely soft (Shore A hardness of 45 to 38).

(32) Optical Properties and Melt Volume Flow Rate

(33) Samples were prepared—as hereinbefore described—and tested for their optical properties. Additionally the MFI (200° C., 5 kg) of these samples was determined.

(34) Transparency, haze and clarity were measured on a BYK Haze-gard I according to ASTM D1003 on 2 mm compression molded plates which were produced at 200° C. under 40 bar during 10 min.

(35) The data obtained are shown in Table 6.

(36) TABLE-US-00006 TABLE 6 Fraction Fraction Fraction Plasti- of B1 of B3 of B2 MFI Block cizer (wt.-%), (wt.-%) (wt.-%) Trans- (cm.sup.3/ Sam- copolymer B** based based based parency Haze Clarity 10 ple A (phm) on B on B on B (%) (%) (%) min) A A3 15 80 20 91.3 7.8 54.0 11.9 B 80 20 91.0 7.9 80.5 10.7 C A4 20 80 20 91.8 5.8 77.6 7.4 D 80 20 91.1 8.9 75.0 8.7 E 60 40 91.1 8.9 75.0 8.3 F 60 40 87.3 11.9 83.0 10.2 G A5 30 20 80 90.6 19.2 77.6 15.4 H 20 80 91.1 12.1 74.6 4.1 I A7 40 20 80 89.8 29.4 50.8 16 J 20 80 90.7 24.1 67.4 14.9 K A8 45 20 80 91.8 12.7 77.6 15.8 L 20 80 91.0 14.0 78.1 12.7

(37) The data as shown in Table 6 prove that the compositions according to the invention have a high transparency. Moreover, the MFI values of the inventive samples obtained are such as to allow good processing, even when increasing amounts (cp. 40, 45 phm) of plasticizer are added.