Lithiated Thiaacetals as Initiators for Living Anionic Polymerization of Diene Elastomers: Polymerization and Compounding

Polybutadiene and poly(butadiene-co-styrene) elastomers were prepared in high conversions using 2-lithio-2- methyl-1,3-dithiane as the initiator. Polymers were readily prepared with a polydispersity index (PDI) of 1.05 to 1.26 and a Mn of up to 208 kg/mol. The replacement of the 2-methyl substituent with phenyl, trimethylsilyl or 4-dimethylamino phenyl also gave active initiators that incorporated at the head of the chain. However, initiation rates appeared to vary somewhat with the structure of the initiators. The polymerizations obtained are in all cases controlled and apparently living with the live chain ends capable of further reactions. The initiators could be generated prior to addition to the polymerization mixture or by an in-situ procedure. Model studies gave evidence that the dithiane chain end can be opened under cure conditions and react with unsaturation present in the polymer chain. Several of the product polymers were found to impart improved hysteresis to carbon and silica-filled rubbery vulcanizates possibly through an endlinking mechanism.