Xanthate functionalized MPEGs as new macro-initiators for the catalyst-, solvent-, and PLA-free controlled synthesis of core-shell forming amphiphilic block copolymers

Abstract

In this paper, we describe a new simple and efficient synthetic protocol for the preparation of amphiphilic block copolymers on the basis of MPEG and PLA (MPEG-b-PLA). The proposed method consists of the preliminary modification of the terminal OH-group of MPEG using only carbon disulfide and KOH as reagents. It will be demonstrated that the resulting xanthate-functionalized MPEG (MPEGX) serves as a macro-initiator, thus allowing the ring-opening polymerization of D,l-lactide to be performed and the desirable block copolymers to be obtained in solvent-free and catalyst-free conditions. It will also be shown that this method is characterized by the lack of by-product (PLA) formation, which is almost unavoidable when traditional catalytic methods are applied. These circumstances, coupled with the low polydispersity (1.04) of the obtained product, demonstrate the precise control over a process realized under relatively soft conditions. Self-assembly of the purified copolymers into micelles and disassembly of the micelles caused by the degradation of the xanthate link is demonstrated using DLS measurements and GPC analysis, and peculiarities in the electronic structure of the xanthate derivatives responsible for the observed degradation effects are evaluated using DFT-based quantum chemical calculations.