Well-defined polyvinylpyridine-block-polystyrene diblock copolymers via RAFT aqueous-alcoholic dispersion polymerization: synthesis and isoporous thin film morphology

In this work, the synthesis and characterization of polyvinylpyridine-polystyrene (PVP-b-PS) diblock copolymers via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization is presented. A series of poly(4-vinylpyridine) (P4VP) and poly(2-vinylpyridine) (P2VP) homopolymers were prepared by RAFT bulk polymerization at 80 degrees C using either a carboxylic acid functionalized trithiocarbonate or a non-functionalized trithiocarbonate RAFT agent. The P4VP and P2VP macroRAFT agents acted as stabilizers in the subsequent RAFT-mediated polymerization-induced self-assembly (PISA), when they were chain extended via RAFT aqueous-alcoholic dispersion polymerization of styrene at 70 degrees C. Following this protocol, high styrene conversions between 86-99% were achieved, leading to a series of well-defined, high molecular weight PVP-b-PS diblock copolymers with narrow molecular weight distributions as confirmed by proton nuclear magnetic resonance (H-1 NMR) spectroscopy and gel permeation chromatography (GPC). The bulk and surface morphologies of the diblock copolymers were investigated via transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The solution-cast and spin-coated thin films of the P4VP-b-PS and P2VP-b-PS diblock copolymers exhibited microphase-separated structures with spherical or cylindrical order according to their compositions. Spin-coated PVP-b-PS diblock copolymer films with weight fractions of the minority PVP block ranging from 17-24% were converted into porous surfaces by a controlled alignment and swelling strategy, exploiting the distinct selectivities of different solvents for the individual blocks.