Organocatalyzed ring-opening copolymerization of α-bromo-γ-butyrolactone with ε-caprolactone for the synthesis of functional aliphatic polyesters – pre-polymers for graft copolymerization

Diphenyl phosphate (DPP) was exploited as an organocatalyst to synthesize copolymers by ring-opening polymerization with α-bromo-γ-butyrolactone (αBrγBL) and ε-caprolactone (εCL) as monomers and polyethylene glycol (PEG) as initiator. The conversion rates of monomers and molecular weights of copolymers synthesized under different conditions were determined by 1H-NMR. The 1H-NMR results showed that the copolymers of αBrγBL and εCL initiated by PEG (PEGCB) were successfully synthesized and the conversions of εCL were relatively high (>70%), while the conversions of αBrγBL were relatively low (<26%). The highest molar ratio of αBrγBL to εCL units in these copolymers is 0.17, when the copolymerization was carried out at 100℃ for 17h.

The bromine atoms hanged on the chain of the copolymers PEGCB provide a good opportunity to construct graft copolymers via atom transfer radical polymerization (ATRP). The subsequent grafting of 2-(dimethylamino)ethyl methacrylate (DMAEMA) was conducted by using PEGCB3 as macroinitiator, CuBr/N,N’,N’,N”,N”- pentamethyldiethylenetriamine (PMDETA) as catalysts and toluene/anisole as solvents via ATRP. According to the analysis of 1H-NMR, the grafting efficiency, grafting ratio and grafting frequency were 22.4%, 160.7% and 1133.8, respectively.