Preparation of fluorinated polyesters by reversible addition–fragmentation chain transfer step-growth polymerization

Abstract

Fluorinated polyesters have demonstrated significant research value and application prospects, while their traditional synthetic strategies were restrained by harsh reaction conditions, low monomer activity, and limited polymer topology. Herein, we exploited reversible addition–fragmentation chain transfer (RAFT) step-growth polymerization to prepare fluorinated polyesters with tailor-made chemical compositions and correlated their thermal and surface properties with chemical structures. A model polymerization was first performed using the fluorinated bifunctional chain transfer agent (CTA) BDMAT_8F and N,N′-(1,4-phenylene)dimaleimide as the monomers, and the polymerization kinetics was monitored through nuclear magnetic resonance (NMR) spectroscopy and size exclusion chromatography (SEC), which suggested a step-growth polymerization mechanism. With this method, fluorinated polyesters with different chemical structures were synthesized by varying the molecular structures of the bifunctional CTA and the bismaleimide monomer. The chemical structure and molecular weight of the synthesized fluorinated polyesters were characterized by ¹H NMR, ¹⁹F NMR, and SEC, the thermal properties were characterized by thermogravimetric analyses and differential scanning calorimetry, and the surface properties were characterized by water contact angle (WCA) measurements. The glass transition temperature (T_g) of these fluorinated polyesters was correlated with their chemical structures, where a rigid backbone favored a high T_g, while a flexible pendant group decreased the T_g. However, neither the backbone rigidity nor the fluorine content had an obvious effect on the WCA of the fluorinated polyesters. Instead, the pendant group showed a significant influence on their WCA. The unique advantage of RAFT step-growth polymerization for preparing fluorinated polyesters was demonstrated by the preparation of a novel fluorinated polyester brush by grafting copolymerization of acryloylmorpholine through RAFT radical polymerization from an as-synthesized fluorinated polyester. Both the thermal and surface properties of this fluorinated polyester brush were strongly correlated with the properties of the poly(acryloylmorpholine) sidechains. This method has provided a new platform for the preparation of fluorinated polyesters and will provide new insight for tailoring the properties of polyesters.