No abstract

The synthesis of aromatic polyphosphonates based on the step polymerization of various bisphenols and dichlorophenyl phosphine oxide was investigated. The effect of catalyst, type, concentration, and polymerization time were systematically varied to obtain high molecular weight polymers. Very high molecular weight tough, ductile materials with a high degree of optical clarity were synthesized. In contrast with the aromatic polycarbonates, the refractive index was increased from 1.58 to 1.60 (for the bisphenol A-based system) and 1.64 for a biphenol-based system. The latter was still an amorphous soluble polymer as a result of the non-coplanar nature of the phenyl phosphine oxide bond, unlike the analogous polycarbonate. Hydrolytically stable meltprocessable cumyl phenol end-capped polyphosphonates were successfully achieved for the first time. Rheological studies show that these end-capped systems are melt-stable at 200°C, whereas the systems of initially higher molecular weight but without any well-defined end capping clearly degraded quickly probably as a result of an acidcatalyzed hydrolysis process. Extensive high char yields were produced upon pyrolysis in either nitrogen or air, suggesting good fire resistance.

The influence of chemical structure on the important properties of composite matrix resins is being systematically investigated. This study addresses the relationships between pendent side chain structures, viscosity and curing shrinkage. In particular, viscosity is known to be greatly influenced by intermolecular interactions, such as hydrogen bonding, and free volume effects. In order to establish the relative importance of these factors, analogues of BIS-GMA were synthesized in which the pendent hydroxyl groups were replaced by trimethyl siloxyl, and by dimethyl, isopropyl siloxyl groups. The viscosities were determined with a cone and plate viscometer and curing shrinkages were determined gravimetrically. They were compared to previously determined values for BIS-GMA and its methyl and hydrogen substituted analogues. The high viscosity of BIS-GMA is drastically reduced by replacement of the hydroxyl group, or its substitution by silylation. The relatively smaller effects produced by varying the bulk of the substituted side chains indicates that the main effect on viscosity is due to the presence or absence of hydrogen bonding. Conversely, increasing the bulk of the side chain substituent has less effect on viscosity, but significantly reduces the curing shrinkage. Changes in curing shrinkages were explained in terms of effects of free volumes associated with the monomers.

Several novel dimethacrylates have been developed as alternative matrix materials for dental composite applications. For the cured bulk polymers the equilibrium water uptake, reduction of glass transition temperatures (Tgs) by water sorption, refractive indices and the surface hardness have been determined. The properties were then compared with those of the control Bis-GMA. These properties correlated well with the structures of the polymers. Polar groups were found to increase the water sorption and thus reduce surface hardness.

A number of new aryl phosphorus-containing polymers were found to be miscible with the commercially significant bisphenol A-based poly(hydroxy ether)s (PHE) over the entire composition range by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) measurements of the blends. Both the FTIR and CP-MAS 31 P NMR results suggested extensive hydrogen-bonding interactions between hydroxyl groups and the phosphonyl groups. Specifically, the poly(arylene thioether diphenylphenylphosphine oxide) and phosphorus-containing polyimides were also miscible with PHE, again emphasizing the importance of phosphonyl groups for generating miscible polymer blends. In contrast, a structurally similar commercial polyimide, Ultem, was not miscible with PHE. These results suggested that the miscibility was induced mainly by hydrogen bonding between phosphonyl and hydroxyl groups, rather than other sites such as carbonyl or ether oxygen atoms and the hydroxyl groups. Furthermore, the measurements of proton spin-lattice relaxation times in the rotating frame (T 1F) showed that the phosphorus-containing polyimide/PHE blends were homogeneous even at about a 4 nm scale.