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

Abstract

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.

Ring-opening polymerization of γ-lactones and copolymerization with other cyclic monomers

“…α-Bromo-γ-butyrolactone (αBrγBL), a commercial functional γBL derivative, was copolymerized with other heterocyclic monomers including εCL, trimethylene carbonate (TMC), and 2-allyloxymethyl-2-ethyltrimethylene carbonate (AOMEC) [76,77]. The ROCP proceeded in bulk at RT with DPP or MSA (Scheme 2a) [77].…”

“…Both poly(TMC-co-αBrγBL) and triblock copolymer were used as macroinitiators for single electron transfer living radical polymerization (SET-LRP) of methyl acrylates, the dispersed αBrγBL site along the polymer chain being the initiating sites. The "graft from" polymerization proceeded with good control and nearly complete initiation, resulting in well-defined poly(methyl acrylate) graftedcopolymers with degradable polymers based on αBrγBL and εCL [76]. In the same vein, amphiphilic triblock copolymers were synthesized starting from HO-PEG-OH.…”

Chemoselective and controlled ring-opening copolymerization of biorenewable α-methylene-δ-valerolactone with ε-caprolactone toward functional copolyesters

“…4 The functional groups on the polyester backbone provide opportunities to further adjust the drug release kinetics and in vivo degradation behaviors as well as the conjugation of bioactive molecules, such as drugs, peptides, and proteins. [5][6][7][8][9][10] A variety of functional aliphatic polyesters containing different reactive groups have been successfully prepared, including halogen groups, [11][12][13][14] hydroxyl groups, 15,16 amino groups, 17 carboxylic groups, 18 and carbon-carbon double bonds. 19,20 Although it is possible to directly introduce functional groups into the backbone of commercial polyesters, such a post-modification strategy suffers from harsh conditions, possible chain scission and racemization.…”

“…4 The functional groups on the polyester backbone provide opportunities to further adjust the drug release kinetics and in vivo degradation behaviors as well as the conjugation of bioactive molecules, such as drugs, peptides, and proteins. 5–10 A variety of functional aliphatic polyesters containing different reactive groups have been successfully prepared, including halogen groups, 11–14 hydroxyl groups, 15,16 amino groups, 17 carboxylic groups, 18 and carbon–carbon double bonds. 19,20…”