This study is concerned with the phase behaviour of partially miscible highly interacting poly
mer blends and thin films. In this context, ’highly interacting’ refers to a steep slope of ther
modynamic interaction with inverse temperature, such that a small temperature variation in
duces a substantial change in thermodynamic equilibrium or demixing. To this effect, three
polymer blends were selected and investigated as potential model systems, namely polycarbon
ate(PC)/poly(methyl methacrylate)(PMMA), chlorinated poly(vinyl chloride)(CPVC)/PMMA
and poly(α-methyl styrene-co-acrylonitrile) (PαMSAN)/PMMA blends.
PC/PMMA blends were found to exhibit a phase boundary below the glass transition tem
perature for reasonable component molecular masses, thus prevented a rigorous study of one
phase, equilibrium, region. Despite a systematic investigation of the effect of the degree of
CPVC chlorination, blends were found to demix at all conditions investigated, in contrast with
previous reports. We have therefore focused on the investigation of the phase behaviour of
PαMSAN/PMMA blends, on both sides of the phase diagram, employing small angle neutron
scattering (SANS), supplemented by spectroscopic ellipsometry and optical microscopy. The
effects of blend composition (φ), polymer mass (Mw) and tacticity were studied. Data analysis
was carried out with de Gennes Random Phase Approximation (RPA) and Cahn-Hilliard-Cook
(CHC) theories, establishing that thermodynamic interactions are largely independent of φ, but
change significantly with tacticity. By contrast with expectations from Flory-Huggins theory,
Mw is found to have minimal impact into blend behaviour. Locally correlated lattice (LCL)
theory provides variable insight into the various thermodynamic contributions to the free en
ergy of mixing. In order to apply the LCL theory, detailed thermal expansion measurements
were carried out by ellipsometry. The highly interactive nature of this blend was demonstrated by the precise formation of small scale spinodal decomposition structures, down to ∼35 nm, via thermal induced phase separation. Such dimensions are typically only accessed by block
copolymer ordering.
In a related study of the PC/PMMA blend, we attempted to reduce the of Mw of PC to design
accessible phase boundaries away from the glassy state. This led to the crystallisation of PC
in thin films, and specifically to the formation of banded spherulites in confinement whose
mechanism and kinetics were investigated. Overall this work provides significant new insight into the phase behaviour of model blends and
homopolymers and the role of molecular architecture that is relevant from both an academic
and industrial perspective.