David F Lawson

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

Abstract 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...

Effect of ester structure on flammability in poly(organophosphazenes)

Abstract The relationship between ester structure and flammability was studied for a series of organophosphazene ester polymers and oligomers. Aliphatic esters showed lowest oxygen index ( OI ) values, ranging from 16 to 26. Thermogravimetric and pyrolyzate analyses suggested that this low range was due to both volatility and ready fragmentation to hydrocarbons. Non-halogenated aryloxyphosphazenes showed moderately high OI values in the range of 25–33, and flammability was similar for both polymers and corresponding oligomers. Highest OI s were found in halogenated derivatives, presumably owing to chemical inertness and stability. Differences in flammability among organophosphazene esters are rationalized in terms of degradation mechanisms followed by individual structures and the resulting fuels which are formed.