SOLUBLE POLYSTYRENE-BLOCK-POLY(P-PHENYLENE) BLOCK COPOLYMERS PREPARED FROM POLYSTYRENE-BLOCK-POLY(1,3-CYCLOHEXADIENE) PRECURSORS - STUDY OF THE AROMATIZATION PROCESS

Polystyrene-block-poly(p-phenylene) block copolymers were prepared from polystyrene-block-poly(1,3-cyclohexadiene) (PS-PCHD precursors. The PS-PCHD copolymers were initiated by sec-butyllithium in benzene. The aromatization of poly(1,3-cyclohexadiene) sequences was carried out by dehydrogenation with substituted quinones. Secondary reactions occur during this reaction leading to defects in the poly(p-phenylene) (PPP) sequences which limit the mean length of conjugated blocks at about 11-12 phenylene units. The defects result from the addition of hydroquinone ether groups to the chain. The influence of experimental conditions (nature of quinone, additives, temperature) on the aromatization yield and defect content is studied. The reaction with p-chloranil(a)) at 130-degrees-C gives the best results. The formation of aggregates during this reaction is observed and explains the final slow kinetics. The purified copolymers are partly aggregated into micelles with a PPP core. For a given polystyrene sequence the fraction of aggregated chains and the size of PPP core increases with the length of PPP sequences. Improvements of PPP blocks are expected by a better control of the aggregation process.