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

Dendrimer-like copolymers with two and three generations, (polystyrene)3-b-(poly(l-lactide))6 (PSt3-b-PLLA6) and PSt3-b-PLLA6-b-PSt12 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, PSt3-b-PLLA6-b-PSt12. The structures of polymers obtained from each step were confirmed by their 1H NMR spectra and GPC measurements. DSC results show one image for the three-armed PSt, image, image and image for the dendrimer-like copolymer with two generations, C(PSt(PLLA)2)3, and image, image and image for the copolymer with three generations, C(PSt(PLLA(PSt)2)2)3.