SELECTIVE CATALYTIC HYDROGENATION OF SBS BLOCK COPOLYMER WITH METALLOCENE CATALYST ACCELERATED BY METHYL BENZOATE

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The selective catalytic hydrogenation of living styrene-butadiene copolymer (SBS) prepared in the presence of metallocene catalyst modified by methyl benzoate was studied. The effects of factors,such as number-average molecular weight (Mn) of SBS,on the hydrogenation degree of the copolymers under different experimental conditions were discussed. The results show that when the ratio of Ti to 100 g dry copolymer is in the range of 0. 15 ～ 0. 3 mmol,adding methyl benzoate in a special mode can significantly improve the activity of titanocene catalyst. The hydrogenation degree of both SBS basic copolymers with Mn of 6. 5 × 104 and 5. 5 × 104 respectively are 97. 0% after reaction for 180 min in the case of using metallocene catalyst not modified by methyl benzoate. On the other hand,the hydrogenation degree of the same SBS samples is ≥ 98. 0% after reaction for 60 ～ 120 min under the condition of using the modified metallocene catalyst. In contrast with the similar researches reported before,our experiments could shorten the hydrogenation time by 60 ～ 120 min. When the ratio of Ti to 100g dry copolymer falls in the range of 0. 15 ～ 0. 3 mmol,the hydrogenation degree of the SBS basic copolymer is affected by magnitude of the Mn. For 30 min after the reaction,the hydrogenation degree of SBS copolymer with Mn of 5. 5 × 104 is ≥97. 0% whereas that of the copolymer with Mn of 6. 5 × 104 is 90. 0% . The disparity in hydrogenation degree between the two SBS copolymers is gradually diminished as the hydrogenation process proceeds and becomes unobvious after reaction for 180 min. In such a case the hydrogenation degree of both SBS basic copolymers are ≥ 98% . The effect of every influential factor on the hydrogenation degree of the SBS copolymers is elucidated in terms of the hydrogenation mechanism.