Phase transitions in ethylene oxide – methyl methacrylate block copolymers

Abstract

This thesis describes the methods of anionic polymerisation and characterisation of poly(ethylene oxide) - poly(methyl methacrylate) block copolymers. Several experimental techniques have been used to study the phase transitions in these block copolymers as well as the corresponding binary blends. These techniques have included the following: differential scanning calorimetry, optical microscopy, small angle light scattering, small angle and wide angle x-ray scattering. A major part of this work involved the design, construction and operation of the small angle light scattering technique. The isothermal crystallisation kinetics of both the block copolymers and blends with high percentages of ethylene oxide component were investigated. The phase behaviour of the block copolymers and the blends was also studied. This involved analysing melting point depression and glass d-ansition data as well as investigating the structural morphology of the polymer systems. The phase behaviour of the block copolymers and die blends containing intermediate component compositions was observed at temperatures below the melting point temperature of PEO. For two block copolymer systems containing 50% and 55% by weight ethylene oxide, the chemical joint within die block inhibited crystallisation directly from the melt. These block copolymers microphase separated at low temperatures forming microdomains rich in PEO. Upon heating, the PEO microdomains crystallised A phase diagram incorporating this behaviour as well as the phase behaviour of the blends is presented. The structure from the micron level and below of the phase separated and crystalline regions has also been deduced. A block copolymer containing 76% ethylene oxide by weight crystallised directly from the melt. The isothermal crystallisation mechanism was very similar to that of the corresponding blend, however, the rate of crystallisation was appreciably slower and the melting point reduced. Comparison of analysed data from several techniques has allowed the contributions to the isothermal crystallisation mechanism to be distinguished