ASPECTS OF MISCIBILITY IN POLYMER SYSTEMS: HYDROGEN BONDING IN POLYMER BLENDS (PVC, POLYCAPROLACTONE)

The importance of hydrogen bonding interactions in promoting miscibility in polymer-polymer blends has been demonstrated. Hydrogen bonding is considered to be responsible for the large number of compatible blends involving poly(vinyl chloride), poly(caprolactone), and several water-soluble polymers. This research has been undertaken to understand the structural requirements for hydrogen bonding in polymer blends, with the goal of providing molecular explanations for the phase behavior of selected polymer-polymer systems, and a basis for predicting phase behavior of new systems. The method of analysis has been infrared spectroscopy; the locations of the absorption frequencies of potentially hydrogen bonded groups (hydroxyl and carbonyl absorptions) were monitored on carefully selected probe molecules. The intensities of the bonded and nonbonded peaks were compared to measure the percentage of bonded groups, while the amount of shift (from nonbonded absorptions) was used to determine hydrogen bond strength.^ Mixtures of low molecular weight monofunctional probes incorporated into a variety of polymer matices were studied in order to determine the effect of molecular size and geometry on the strength of a hydrogen bonding interaction. Cyclic base probes were found to interact more strongly than straight chain molecules; probe geometry was not significant in mixtures of monofunctional acid probes. Results of these studies were also used to rank polymer matices in terms of their potential to interact with another polymer.^ The interaction of oligomeric probes with several polymers was also investigated. These materials were ideally large enough to interact with matrix as would a polymer, but small enough to preclude intramolecular hydrogen bonding and phase separation. However, probe-probe interactions were found to dominate in these blends; the strength of these interactions was usually a function of the polymer dielectric constant. Thus, the number and strength of self-associations which had to be broken to achieve miscibility were important. Also, the effect of weaker non-specific interactions, such as dipole-dipole, was significant.^ Changes in subtle variables, including polymer tacticity, functional group concentration, and matrix molecular weight, were also studied.