Polymer glass formation temperature effects

Mixtures of poly(vinylidene fluoride) with poly (methyl methacrylate) and with poly (ethyl methacrylate) form compatible blends. As evidence of compatibility, single glass transition temperatures are observed for the mixtures, and transparency is observed over a broad range of composition. These criteria, in combination, are acceptable evidence for true molecular intermixing (1, 19). These systems are particularly interesting in view of Bohns (1) review, in which he concludes that a compatible mixture of one crystalline polymer with any other polymer is unlikely except in the remotely possible case of mixed crystal formation. In the present case, the crystalline PVdF is effectively dissolved into the amorphous methacrylate polymer melt, and the dissolved, now amorphous, PVdF behaves as a plasticizer for the glassy methacrylate polymers. 

We have previously stressed that network formation rapidly increases viscosity and causes gelation. Cross linking after that point increases the apparent glass transition temperature. Figure 11 illustrates the effect of degree of cross linking on the dynamic modulus of a thermoplastic and a cross-linked polymer. The point at which modulus drops off rapidly is approximately the glass transition temperature. 

The nanodispersion of Si and O throughout the polyimide polymer matrix leads to the formation of a protective silica layer on the polyimide surface when the material reacts with AO [15]. Our data indicates that upon AO exposure, the organic material in the polymer surface erodes, while the atomic oxygen reacts with the nanodispersed POSS to form a silica layer. Therefore, when POSS is copolymerized to form POSS-PI, it imparts remarkable AO resistance, and does so with minor effects in the storage modulus, glass transition temperature, and coefficient of thermal expansion [15]. 

From these values, one may calculate and compare the effective glass transition temperature of the resin as a function of diluent concentration. Gordon et a1. have recently derived an expression relating the glass temperature of a polymer-plasticizer mixture to the glass temperatures of the components on the basis of the configurational entropy theory of glass formation (4). 

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