Controlled Anionic Block Copolymerization withN,N-Dialkylacrylamide as a Second Block

Novel well-defined block copolymers composed of polystyrene, poly(2-vinylpyridine), poly(ethylene oxide), or poly(tert-butyl methacrylate) as the first block and poly-(N,N-dialkylacrylamide) (PDA1AAm) as the second block were synthesized by ligated anionic polymerization. The latter was carried out in tetrahydrofuran (THF) initiated by 1,1-diphenyloligostyryllithium in the presence of ZnEt 2 and LiCl. At first the role of the additives LiCI and ZnEt 2 on the mode of the anionic homopolymerization of N,N-dialkyl-acrylamide was investigated. Polymerization in the presence of ZnEt 2 resulted in syndiotactic polymers with narrow molecular weight distribution only. In the presence of both additives, the reaction mixture became heterogeneous with a high degree of isotacticity of the polymers. Despite the fact that the polymerizations were performed in heterogeneous phase, the DAlAAm monomers were polymerized in a quantitative yield. The efficiency of the first block of active sites was always higher than 0.71. Preliminary studies using dynamic light scattering of aqueous hydrochloric acid solutions of poly [(2-vinylpyridine)-block-(N,N-diethylacryl-amide)] block copolymers at different temperatures and at pH 2 showed that above 45 °C, micelle-like aggregates were formed. The heating and cooling cycles were reversible but showed hysteresis, which was obviously due to the isotactic structure of the poly(N,N-diethylacrylamide) block.