A number of quasi-binary homopolymer blends have been investigated
with regard to their miscibility. The blends consisted of
poly(epichlorohydrin) (PEPC) mixed with a range of poly(methacrylate)
polymers:- poly(methyl methacrylate); poly(ethoxyethyl methacrylate);
poly(tetrahydrofurfuryl methacrylate) and poly(glycidyl methacrylate)
(PGMA). It was found that the state of mixing of the systems varied
with the structure of the ester side chain, embracing a number of
miscibility states. It has been postulated that the observed miscibility
in the system PGMA/PEPC is due to the presence of a small
specific interaction between the species.
A second category of blend investigated comprised of a homopolymer
(PEPC) and a random copolymer. In two cases the copolymers (styreneco-
methacrylonitrile; methyl methacrylate-co-methacrylonitrile) were
chosen such that the cohesive energy density of PEPC lay between
those of the comonomers. This led to the observation of a number
of miscibility states for the systems, depending upon the copolymer
composition. Analysis of these systems and similar examples in the
literature was conducted using the mean-field approach. A reasonable
accord between theory and experiment was found when the role of both
specific interactions and free-volume terms was negligible.
A third type of copolymer (glycidyl methacrylate-co-methyl
methacrylate) was found to be only partially miscible with PEPC.
This was due to the small GMA/PEPC interaction and the tendency of
the copolymer to diverge from the copolymerisation equation at high
GMA concentrations.
The experimental probe for miscibility has been the glass
transition temperature. This was determined using Differential
Thermal Analysis, Dynamic Mechanical Thermal Analysis and to a lesser
extent, Dielectric Relaxation.
The phenomenon of partial miscibility, in which phase composition
varies with overall blend composition, has been discussed. It has
been postulated that this widely observed behaviour is due to a
non-equilibrium phase separation process. The inadequacy of existing
relationshi in describing the variation of the glass transition
temperature of a miscible blend with composition has been highlighted.
Furthermore, the importance of the transition width as an indicator
of miscibility has been stressed
