Synthesis of benzoin end-chain functional macrophotoinitiator of poly(D,L-lactide) homopolymer and poly(ε-caprolactone)-poly(D,L-lactide) diblock copolymer by ROP and their use in photoinduced free radical promoted cationic copolymerization

Benzoin (B) end-chain functional macrophotoinitiator of poly(d,l-lactide) homopolymer (B-PDLLA) and poly(epsilon-caprolactone)-poly(d,l-lactide) (B-PCL-b-PDLLA) diblock copolymer with controlled molecular weights and low polydispersities have been synthesized via ring-opening polymerization (ROP). The ROP of d,l-lactide with benzoin as the initiator and tin octoate (Sn(Oct)(2)) as the catalyst in bulk at 130 A degrees C formed B-PDLLA polymer. B-PCL-b-PDLLA was synthesized by sequential ROP in two steps. Benzoin (B) end-chain functional macrophotoinitiator of poly(epsilon-caprolactone) (B-PCL) was first prepared via ROP of epsilon-caprolactone by using benzoin/Sn(Oct)(2) initiating system. The resultant hydroxyl-terminated B-PCL macrophotoinitiator was subsequently utilized as the macroinitiator in the second-step ROP of d,l-lactide to synthesize B-PCL-b-PDLLA. The H-1 NMR, FT-IR, GPC, UV, and fluorescence spectroscopic studies revealed that low-polydispersity poly(d,l-lactide) homopolymer and poly(epsilon-caprolactone)-poly(d,l-lactide) diblock copolymer with benzoin end-groups were obtained. These macrophotoinitiators were used as prepolymers in photoinitiated free radical promoted cationic polymerization for obtaining AB type di- and ABC type tri-block copolymers.