ATTEMPTED SYNTHESIS OF MULTIBLOCK COPOLYMERS OF BUTADIENE, STYRENE, AND ALPHA-METHYLSTYRENE - EFFECT OF POLAR ADDITIVES ON COPOLYMERIZATIONS

Owing to the low T-g of polystyrene, the mechanic al properties of pol ystyrene-block-polybutadiene-block-polystyrene (SBS) thermoplastic ela stomers drop steeply above 60 degrees C. To overcome this behavior, ma ny research groups have considered the replacement of styrene (S) by a lpha-methylstyrene (MS). We also attempted the synthesis of copolymers with a central polybutadiene (poly B) block and rigid blocks consisti ng of polystyrene (poly S) and poly(alpha-methylstyrene) (poly MS) blo cks. Starting hom a dilithium initiator, difunctional poly B's with lo w 1,2 content (10%) were prepared and toluene was added. After additio n of a small amount of styrene, MS was added in the presence of a 15% (in vol) of THF at T less than or equal to -40 degrees C. The copolyme rs did not have the expected structure and poor mechanical properties resulted, which were, however, still measurable at 120 degrees C. Thes e results probably resulted from secondary reactions involving the MS carbanions. To identify these reactions and to control the polymer str ucture, the synthesis of multiblock copolymers was carried out with a monofunctional polybutadienyllithium to which were added successively S and MS (in a mixture of hexane and benzene as solvent). MS was added at low temperature in the presence of small amounts of THF or at room temperature after addition of TMEDA. These attempts were unsuccessful , the copolymer being always multimodal as a result of unwanted coupli ng reactions involving terminal double bonds. The synthesis of elastom ers using a coupling reaction of poly MS-poly S-poly B was also consid ered but the yield in poly B was low since termination reactions invol ving the polar additive occurred. (C) 1994 John Wiley and Sons, Inc.