Preparation Of Poly(Styrene-b-lactide) By"Living"/Controlled Radical Polymerization

Controlled/living radical polymerization (CRP) combines the advantages of living polymerization and free radical polymerization. It is one of the most important research area in polymer science. We can utilize this technology synthesis polymer which has exact molecular weight, fine structures and narrow polydispersitie. The react condition of CRP is not rigorous as living polymerization but similar to traditional free radical polymerization. It can be executed in monomers, solution, emulsion and suspension. Nitroxide-mediated radical polymerization(NMP), reversible addition-fragmentation chain transfer(RAFT) and atom transfer radical polymerization(ATRP) are the most reportorially in recent years among the methods of "living" free radical polymerization.Our works and main results are summarized as following:(1) NMP for block copolymer poly(styrene-b-lactide)(PS-b-PLA). Firstly, styrene was polymerized by NMP polymerization using AIBN/HTEMPO at125℃and polystyrene with hydroxyl end group (PS-OH) was obtained. AIBN/HTEMPO system was successful at controlling the polymerization of styrene. Dependence of the number-averafe molecular weight (Mn) on conversion is a diagonal line, molecular weight distributing (MWD) is less than1.3. Then use PS-OH as macro-initiator and for the ring-opening polymerization of lactide (LA), it was catalyzed by stannous octoate (Sn(Oct)2). We characterized this polymer using1H nuclear magnetic resonance (1H-NMR), fourier transfer infrared spectrum(FT-IR) gel permeation chromatography (GPC) to confirm both the structure and molecular weight.(2) ATRP for block copolymer PS-b-PLA. Firstly, LA was polymerized by ring-opening polymerization using1-pentanol as initiator and Sn(Oct)2as catalyzer. The obtained polylactide has a hydroxyl end group (PLA-OH). Then PLA-OH reacts to2-bromoisobutyryl bromide to transform PLA-Br. The polymerization of styrene was initiated by PLA-Br and catalyzed by CuBr/PMDETA. Block copolymer PLA-b-PS was prepared by this atom transfer radical polymerization. The kinetics curve of polymerization of styrene was a line that can confirm the reaction was under control. We characterized the product using GPC,1H-NMR and FT-IR.(3) RAFT for block copolymer PS-b-PLA. S-1-Dodecyl-S’-(α,α’-dimethyl-α’’-ceticacid) trithiocarbonate was synthesized by by phase transfer method. The struetureof this TTCA was characterized by1H-NMR and FT-IR. Macro RAFT agentPLA-TTCA was obtained by esterification between PLA-OH and TTCA usingDCC/DMAP as dehydrating agent. Then styrene was polymerized by RAFpolymerization using AIBN/PLA-TTCA at70℃. We characterized the copolymerusing GPC,1H-NMR and FT-IR. The relationship between Mnand conversion ofstyrene is a linear relation, and MWD of the copolymer is narrow. This can confirm thepolymerization of styrene was under control.