Using Triethylborane to Manipulate Reactivity Ratios in Epoxide-Anhydride Copolymerization: Application to the Synthesis of Polyethers with Degradable Ester Functions.

Vamshi K Chidara,Yves Gnanou,Xiaoshuang Feng

doi:10.3390/molecules27020466

Abstract

The anionic ring-opening copolymerization (ROCOP) of epoxides, namely of ethylene oxide (EO), with anhydrides (AH) generally produces strictly alternating copolymers. With triethylborane (TEB)-assisted ROCOP of EO with AH, statistical copolymers of high molar mass including ether and ester units could be obtained. In the presence of TEB, the reactivity ratio of EO (rEO), which is normally equal to 0 in its absence, could be progressively raised to values lower than 1 or higher than 1. Conditions were even found to obtain rEO equal or close to 1. Samples of P(EO-co-ester) with minimal compositional drift could be synthesized; upon basic degradation of their ester linkages, these samples afforded poly(ethylene oxide) (PEO) diol samples of narrow molar mass distribution. In other cases where rEO were lower or higher than 1, the PEO diol samples eventually isolated after degradation exhibited a broader distribution of molar masses because of the compositional drift of initial P(EO-co-ester) samples.

Highlights

During copolymerization, comonomers are inserted in the chain at a rate and in a sequence order that is dictated by two factors that are the monomers’ reactivity ratios and the composition of the initial monomer mixture
Depending upon the feeding ratio of anhydrides to epoxides, either tapered block poly(ester-b-carbonate) copolymers or random poly(ester-co-carbonate) copolymers were eventually obtained. In this investigation, which is related to the copolymerization of ethylene oxide (EO) with anhydrides and to the influence of TEB, we first carried out a blank reaction by mixing 100 eq of EO
We checked that no reaction occurred when tetrabutylammonium chloride (TBACl) was not added to the reaction mixture, confirming that TEB by itself cannot initiate copolymerization

Summary

Introduction

Comonomers are inserted in the chain at a rate and in a sequence order that is dictated by two factors that are the monomers’ reactivity ratios and the composition of the initial monomer mixture. Frey’s group reported the anionic copolymerization of two different monomers characterized by a large difference in their reactivity ratios that resulted in the formation of block-like tapered copolymers [3,4]. Wurm’s group reported the anionic copolymerization of aziridines and ethylene oxide (EO), which afforded blocky structures because of the large difference in the reactivity ratios of the two monomers [5]. William’s group achieved the control of polymer composition through the use of a catalyst that switched from the copolymerization of epoxides with various comonomers to the homopolymerization of ε-caprolactone, resulting in the formation of multiblock copolymers [6]. Frey’s group reported that i-Bu3 Al and double metal cyanide catalysts, when used to copolymerize ethylene oxide and propylene oxide, produce in the first case blocky structures and in the second statistical copolymers [7]

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Conclusion