Volumetric properties, glass transition

The volumetric, elastic and dynamic properties of internally and externally plasticised PVC were studied and compared with those of unplasticised PVC. The glass transition temperature for the plasticised samples was markedly lowered and this decrease was more important for the externally plasticised ones. The positions of the loss peaks from dielectric alpha-relaxation measurements confirmed the higher efficiency of the external plasticisation. However, the shape of the dielectric alpha-relaxation function was altered only for the internally plasticised samples. The plasticisation effect was linked with a decrease in the intensity of the beta-relaxation process but no important changes in the activation energy of this process were observed. The results were discussed. 47 refs. 

These dimers are of interest because they serve as model compounds for a new class of phenolic materials, the polybenzoxazines, whose synthesis and characterization has been described by Ishida and coworkers.146-149 These polybenzoxazine resins were found to have a number of unusual, but commercially favorable, properties, in particular a near-zero shrinkage or volumetric expansion upon curing (polymerization) as well as low water absorption. In addition, the resins have high glass-transition temperatures even though they have been shown to have low crosslink densities. Explanations for these properties have been hypothesised in terms of favorable hydrogenbonding interactions.150... 

Glass transition The glass transition is a reversible change in an amorphous polymer between a viscous rubbery condition and a hard brittie condition. This property can be measured by a number of different properties, such as optical and volumetric. 

Plasticizers and oils, which can be incorporated in extremely large quantities into certain elastomer compounds, are commercially important for two main reasons. They depress the glass transition temperature and hence improve the working temperature range of an elastomer selected on the basis of other properties. Secondly, they allow the incorporation of more diluent filler than the surface adsorption properties of the polymer would normally allow, hence reducing the volumetric cost of the compound. 

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