Large-scale synthesis of arborescent polystyrenes

A method was developed for the large (100 g) scale synthesis of arborescent polystyrenes using acetyl coupling sites. Successive generations of dendritic graft polymers were obtained from cycles of polystyrene substrate acetylation with acetyl chloride and coupling in the presence of LiCl with "living" polystyryllithium chains capped with 2-vinylpyridine units. The grafting yield for the synthesis of a generation zero (GO or comb-branched) arborescent polystyrene under the conditions previously reported for the 10 g scale reactions decreased from 95 to 75% when scaled up to 100 g. The lowered yield was linked to side chain dimerization and deactivation of the macroanions. The modified 100 g scale procedure, using end-capping of the polystyryllithium with 1,1-diphenylethylene and the addition of 3-6 equivalents per living end of 2-vinylpyridine as a dilute solution, eliminated side chain dimerization and provided grafting yields of up to 95%. The large-scale procedure developed was applied to the synthesis of arborescent polystyrenes of generations up to G2 with low polydispersity indices (M_w/M_n ≤ 1.04) and molecular weights increasing in an approximately geometric fashion for each cycle.