P-relaxations of conventional PMMA

3 INFLUENCE OF THE NATURE OF THE SOLVENT ON THE a AND p-RELAXATIONS OF CONVENTIONAL PMMA 

Thin polymer films are generally obtained by solution casting, in many applications, such as paints, varnishes, or adhesives. The properties of polymer films obtained from a solution differ from the original bulk properties, and this effect can have some significant consequences on the expected behavior of the final film. 

At 10 KHz, only one peak is detectable (whatever the sample) which is attributed to the a-relaxation. However, the peak is not symmetrical, with a broadening towards the lower temperatures, due to the contribution of the P-relaxation. At 100 Hz, two peaks are present, the major at lower temperature, corresponding to the p-relaxation and die minor at higher temperature, attributed to die a-relaxation. 

The results show that the temperature of the a-transition is significantly reduced for cast films compared to the bulk polymer, with a lower value for chloroform samples. The decrease of the a-transition temperature can be explained by the presence of residual solvent, inducing a plasticizing effect. On the contrary, an increase of the P-transition tempera- 

Toluene, THF and acetone are described as basic solvents. The residual solvent molecules can therefore only weakly interact with the acrylate groups. Interactions between chains are then favored and self-associations between PMMA chains appear. The rotation of the aery late groups becomes more difficult compared to the bulk PMMA, probably due to self-aggregation of some PMMA chains (even if the studied polymer is not stereoregular). 

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