Polymerization shrinkage and change of refractive index have been studied on thin sample layers during photopolymerization. By using laser interferometry and special substrates it was possible to determine both parameters simultaneously. The monomer studied was bis(2-hydroxyethyl)bisphenol A dimethacrylate (HEBDM). Once the refractive index and the shrinkage were known, the double-bond conversion could be calculated using the Lorentz-Lorenz equation. It has been found that shrinkage proceeds linearly with conversion until vitrification of the system sets in. From that moment shrinkage cannot keep up with conversion and lags behind. The described model can also be used to predict changes of thickness and refractive index upon further relaxation.
Посилання на статтю:
Time-resolved determination of volume shrinkage and refractive index change of thin polymer films during photopolymerization / J. de Boer*, R. J. Visser and G. P. Melis // Polymer. – 1992. – Vol 33. – P. 1123-1126.