Control of Molecular Weight and End-Functional Groups of Polyester from A₂ + B₂ Polycondensation via Cross-Metathesis of Cyclic Unsaturated Polyester with Difunctional Olefin

Abstract

As an approach to control the molecular weight and polymer end groups of polyester obtained by A 2 + B 2 polycondensation, we investigated cross-metathesis of cyclic polyesters containing carbon−carbon double bonds in the backbone with a symmetric olefin having two functional groups as an exchange reagent (ExR). Polycondensation of cis-2-butene-1,4-diol (1) and sebacoyl dichloride (4) did not selectively afford cyclic polyester, but when cisor trans-4-octene-1,8-diol, instead of 1, was reacted with 4 or isophthaloyl dichloride, we found that cyclic unsaturated polyesters were formed selectively. The obtained cyclic polyesters successfully underwent cross-metathesis reaction with cis-1,4-diacetoxy-2-butene (6) in the presence of second-generation Grubbs catalyst to afford linear polyester bearing acetoxy groups at both ends. The molecular weight of the linear polyester decreased with increasing amount of 6 regardless of the molecular weight of the starting cyclic polyester; the molecular weight of the resulting linear polyester was governed by the molar ratio of 6 to carbon−carbon double bonds in the cyclic ester. Cross-metathesis using other ExRs enabled the introduction of tert-butoxycarbonyl (Boc) amino, bromophenyl, and tert-butyl carboxylate groups at both ends of polyester.

Synthesis of Block Copolymers of Polyester and Polystyrene by Means of Cross-Metathesis of Cyclic Unsaturated Polyester and Atom Transfer Radical Polymerization

“…Accordingly, the cross-metathesis of cyclic PEs with PSt-1 hardly proceeded, probably because the Grubbs catalyst could not readily approach the CC bond in PSt-1 due to the sterically hindered PSt chains around it. The decrease in the molecular weight of cyclic PEs is presumably attributed to cross-metathesis between cyclic PEs with entropy change as the driving force; a similar decrease in the molecular weight of cyclic PEs was observed in the cross-metathesis of cyclic PEs with a small amount of low-molecular-weight ExR …”

“…We next conducted cross-metathesis of cyclic unsaturated PEs with the prepared macro-ExR (Scheme a). Cyclic PEs were synthesized according to our previous report …”

A Strategy toward Cyclic Topologies Based on the Dynamic Behavior of a Bis(hindered amino)disulfide Linker

“…Considering that a cyclization process is inevitable at some point during the synthesis of compounds with a cyclic topology and that this step is presumably the most difficult, we thought that using a spontaneous and selective cyclization would be ideal. In this work, we focus on the dynamic covalent chemistry of bis(2,2,6,6‐tetramethylpiperidin‐1‐yl)disulfide (BiTEMPS) and use it as the driving force to induce an ideal cyclization. We have previously reported that the BiTEMPS unit behaves as a stable covalently bound structure at room temperature, while it exchanges disulfide bonds above 80 °C .…”

Importance of a reversible reaction for the synthesis of telechelic polymers by means of polycondensation using an excess of one monomer

“…When a carbon–carbon double bond is present in the cyclic polymer and ExR, Ru-catalyzed metathesis can be used for the exchange reaction between the cyclic polymer and ExR. 7 A polystyrene- b -polyester- b -polystyrene triblock copolymer was synthesized by means of this approach. 8 For simple cyclic polyesters without carbon–carbon double bonds, an alkoxide-catalyzed ester–ester exchange reaction with a symmetrical ExR bearing the ester linkage provides access to telechelic polyesters.…”