Polymerization-induced self-assembly of PVAc-b-PVDF block copolymersvia RAFT dispersion polymerization of vinylidene fluoride in dimethyl carbonate
Résumé
Polymerization-induced self-assembly of PVAc-b-PVDF block copolymers (BCPs) in dimethyl carbonate (DMC) was performed and studied using vinylidene fluoride (VDF) RAFT dispersion polymerization protocols in DMC in the presence of PVAc macromolecular chain transfer agents (macro-CTAs). The polymerizations were conducted at 73 °C in DMC using three PVAc macro-CTAs of different molar masses and targeting various DPPVDF. The relatively high frequency of head-to-head (HH) additions in VAc polymerization and the much lower reactivity of the resulting PVAc chains terminated with a–CH(OAc)–CH2–SC(S) OCH2CH3group (PVAcT–XA, where XA stands for the xanthate end-group) compared to their regularly terminated analogs (PVAcH–XA) leads to an accumulation of PVAcT–XA chains during polymerization. These PVAcT–XA reactivate slower than PVAcH–XA in the presence of PVDF• radicals. In addition, RAFT polymerization of VDF is prone to the same chain defect problem and to non-negligible transfer to DMC. In consequence, RAFT dispersion polymerization of VDF in the presence of PVAc macro-CTAs afforded PVAc-b-PVDF BCPs (contaminated with starting unreacted PVAc and PVDF homopolymers formed viatransfer to DMC). These phenomena were studied using 1H and 19F NMR spectroscopy and size exclusion chromatography. Nevertheless, the VDF RAFT dispersion polymerization in DMC experiments resulted in self-assembled BCP morphologies in the form of crystalline (1–5μm) ovoidal flakes.These flakes stack on top of each other and form star-like structures. The structures are thought to formby epitaxial growth of the PVDF crystals and interparticle interpenetration crystallization. Although they are formed under polymerization-induced self-assembly conditions, the morphologies of these BCP structures are governed by the crystallization of PVDF.