Synthesis and characterization of well-defined diblock copolymers of poly(N-isopropylacrylamide) and poly(vinyl acetate)

Abstract

In this study the synthesis of well-defined diblock copolymers of poly(Nisopropylacrylamide) (PNIPAM) and poly(vinyl acetate) (PVA) was performed for the first time by macromolecular design via interchange of xanthates (MADIX) process. In the first stage, methyl (isopropoxycarbonothioyl)sulfanyl acetate (MIPCTSA) was used as chain transfer agent to obtain PVA macro-chain transfer agent. Then, under the same reaction conditions N-isopropylacrylamide (NIPAM) was introduced as the second monomer and block copolymers were synthesized by using PVA macro-chain transfer agent. Characterizations of the obtained homopolymers and block copolymers were done. 1H NMR spectroscopy confirmed the presence of both blocks in the copolymer structure, with the expected composition based on the feed ratio. Kinetic study showed a linear relationship between conversion and reaction time at early stages. Fourier Transform Infrared (FTIR) Spectroscopy showed the characteristic absorptions of both polymer sequences. The Size Exclusion Chromatography (SEC) data were investigated as relative values in spite of the encountered problems. The Differential Scanning Calorimetry (DSC) analysis showed the two glass transition temperature (Tg) values belonging to PVA and PNIPAM blocks. The Tg values were closer to each other with respect to the original values of homopolymers, which indicated that both polymer sequences were well distributed in each other. Scanning Electron Microscopy (ESEM) characterization showed that the composition of the samples influenced the general morphology and density of the block copolymers. Atomic Force Microscopy (AFM) results showed homogeneously distributed phases, which was a very good indication of the block copolymer structure.