The results are shown in Fig. 7. It can be noted
that the fraction of associated carbonyl groups
increases within the domain of miscibility up to
about 50wt% of PMMA and then begins to
decrease outside the domain of miscibility. It seems
that the miscibility is due to the presence of a
specific interaction of hydrogen-bonding type up to
about 50wt% of PMMA. An excess of PMMA in
comparison with PVC is unfavourable to this
interaction and leads to a phase separation as
observed by viscometric and DSC measurements.