Synthesis and characterizations of well-defined dendrimer-like copolymers with the second and third generation based on polystyrene and poly( l-lactide)

Abstract

Dendrimer-like copolymers with two and three generations, (polystyrene) 3- b-(poly( l-lactide)) 6 (PSt 3- b-PLLA 6) and PSt 3- b-PLLA 6- b-PSt 12 have been successfully prepared using core-first method. The first step of this synthesis is the preparation of three-armed PSt by atom transfer radical polymerization (ATRP) of St using 1,1,1-tri(methylene-α-bromoisobutyryl)propane as initiator. Terminal divergence of the polymers obtained was achieved by the reaction of terminal bromines with branching agent, 2,2-dimethyl-1,3-dioxolane-4-methanol. After deprotection, the polymer with six terminal hydroxyl groups was used in the ring-opening polymerization of LLA. The dendrimer-like copolymer with PLLA as a second generation diverged continuously by the reaction of 6 terminal hydroxyl groups with branching agent, 2,2-bis(methylene-α-bromoisobutyryl)propionyl chloride. The resultant polymer with 12 terminal bromines was used as macroinitiator in the ATRP of St to produce the target dendrimer-like copolymer, PSt 3- b-PLLA 6- b-PSt 12. The structures of polymers obtained from each step were confirmed by their 1H NMR spectra and GPC measurements. DSC results show one T g PS = 102 ° C for the three-armed PSt, T g PLLA = 53 ° C , T c PLLA = 123 ° C and T m PLLA = 159 ° C for the dendrimer-like copolymer with two generations, C(PSt(PLLA) 2) 3, and T g PLLA = 53 ° C , T c PLLA = 114 ° C and T m PLLA = 166 ° C for the copolymer with three generations, C(PSt(PLLA(PSt) 2) 2) 3.