Characterization of structural heterogeneity of polyurethane coatings

The thermal analysis techniques-Differential Scanning Calorimetry and Therm oStimulated Current-have been used to characterize a polyurethane high soli d coating. The glass transition temperature, as determined by DSC, is 60 de greesC. Below this glass transition temperature, an alpha (sub) dielectric relaxation mode has been observed; it corresponds to cooperative movements precursor of the glass transition. The alpha (ss) dielectric relaxation mod e, located at approximate to T-g has been attributed to movements of soft s equences of the amorphous phase liberated at the glass transition temperatu re. The analysis of the fine structure shows that they are constituted of e lementary processes characterized by relaxation times following a compensat ion law. Above T-g, the alpha (hs) dielectric relaxation of hard sequences has been shown. It corresponds to hard sequences hydrogen bonded in polyure thane. (C) 2001 John Wiley & Sons, Inc.