Diene Triblock Polymers with Styrene-Alpha-Methylstyrene Copolymer End Blocks

Abstract

Diene triblock copolymers with styrene-alpha-methylstyrene copolymer (SAMS) end blocks have been prepared by two procedures: (1) by preparing the center diene block in cyclohexane and then the end blocks in cyclohexane-THF mixture; (2) by preparing the triblock in alpha-methylstyrene itself as the solvent. Several variations of procedure (2) were used. When all the monomers were added in the reaction mixture at the same time and a dilithium initiator was used, the product was a tapered triblock. When styrene was withheld until the diene block was formed, the triblock was untapered. The triblock was also prepared by forming the end block first using s-butyllithium as the initiator. The diene monomer was then added to the reaction mixture to form the diblock. The reactive diblock was coupled to form a triblock and also a radial block. Triblock was also formed by adding more styrene monomer instead of coupling.

The polymers prepared with a diene content between 55 to 70 weight percent were thermoplastic elastomers. The properties of the polymers prepared by the several different procedures were comparable and also comparable to conventional styrene-diene block polymers with the exception that the softening temperature as measured by thermomechanical analysis was 20^ºC higher than that of the corresponding styrene-diene block polymers. The SAMS-based triblock polymers prepared with a diene content below 40% were clear impact resisting plastics. The Vicat softening points of the clear plastics samples were also about 30^ºC higher than those of similar polymers based on styrene and butadiene.