Controlled Anionic Block Copolymerization with N , N ‐Dialkylacrylamide as a Second Block

Summary: 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) (PDAlAAm) 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 LiCl and ZnEt 2 on the mode of the anionic homopolymerization of N , N ‐dialkylacrylamide 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 ‐diethylacrylamide)] 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. Temperature dependence of the scattering intensity of various poly[(2‐vinylpyridine)‐ block ‐( N , N ‐diethylacrylamide)] block copolymers. image Temperature dependence of the scattering intensity of various poly[(2‐vinylpyridine)‐ block ‐( N , N ‐diethylacrylamide)] block copolymers.