Effect of Urea on Dynamic Relaxation Behaviour of Poly(2-hydroxyethyl methacrylate)

Abstract Effect of urea on the dynamic relaxation behaviour of poly(2-hydroxyethyl methacrylate) (PHEMA) was studied by means of a torsion pendulum in a temperature range from - 196°C to + 130°C. The incorporation of urea decreases the glass transition temperature of PHEMA, whereas the temperature of the secondary (β1) relaxation of the oxycarbonyl groups does not change appreciably; the extent of the low-temperature (γ) relaxation assigned to the hindered rotation of the hydroxyethyl side groups is reduced. In contradistinction to other low-molecular weight compounds urea does not give rise to a characteristic diluent dispersion in PHEMA. A decrease in the molecular mobility with increasing urea content manifests itself in an increase in the storage modulus below the temperature of the β1 dispersion (Tβ1 = 28°C) (antiplasticizing effect). The atypical effect of urea on the relaxation behaviour of PHEMA was tentatively assigned to a strong interaction of the components which is evidenced by densification of the system. The effect of water on the relaxation behaviour of the system PHEMA-urea is analogous to that assessed for PHEMA.