Hybrid Copolymerization via the Combination of Proton Transfer and Ring-opening Polymerization

Phosphazene base, t-BuP2, was employed to catalyze the proton transfer polymerization (PTP) of 2-hydroxyethyl acrylate (HEA), and PTP was further combined with ring-opening polymerization (ROP) to exploit a new type of hybrid copolymerization. The studies on homopolymerization showed that t-BuP2 was a particularly efficient catalyst for the polymerization of HEA at room temperature, giving an excellent monomer conversion. Throughout the polymerization, transesterification reactions were unavoidable, which increased the randomness in the structures of the resulting polymers. The studies on copolymerization showed that t-BuP2 could simultaneously catalyze the hybrid copolymerization via the combination of PTP and ROP at 25 °C. During copolymerization, HEA not only provided hydroxyl groups to initiate the ROP of e-caprolactone (CL) but also participated in the polymerization as a monomer for PTP. The copolymer composition was approximately equal to the feed ratio, demonstrating the possibility to adjust the polymeric structure by simply changing the monomer feed ratio. This copolymerization reaction provides a simple method for synthesizing degradable functional copolymers from commercially available materials. Hence, it is important not only in polymer chemistry but also in environmental and biomedical engineering.