This work explores the process of water ageing of high-temperature high-pressure polymerized urethane dimethacrylate (UDMA) networks. UDMA samples polymerized under several pressures (0.1e300 MPa) and differing by the conversion degree of polymerization were aged in water at 37, 50 and 70 C and followed by gravimetry. Diffusion was observed to obey Fick's law. The diffusion coefficient and water maximal uptake were observed to be almost independent of polymerization pressure, consistently with analysis of Dynamic Vapor Sorption data suggesting that external polymerization pressure has no effect on polymer affinity with water. This was ascribed to the fact that all materials have the same cohesive energy, as confirmed by ultrasonic measurements of elastic moduli. Polymerization pressure (used to improve conversion degree and mechanical properties) would thus have a minor influence on water ageing that is mainly triggered by polymer chemistry. When elevating the polymerization pressure, there is hence no compromise between the optimization of thermo-mechanical properties and the resistance to water ageing.
a b s t r a c tThe hydrolytic degradation of fully cured polyester-urethane networks polymerized in the presence of several weight ratios of triacetin was monitored by the residual concentration in elastically active chains obtained from modulus and equilibrium solvent swelling measurements. The presence of triacetin does not change the water uptake but induces a lower rate of degradation. Comparisons were performed with networks in which triacetin was removed before ageing, and with networks in which polyester-urethane was first polymerized and then impregnated by triacetin. Data suggest that the presence of triacetin during polymerization induces the presence of elastically inactive chains such as dangling chains and loops, the hydrolysis of which does not change the elastic properties of the network. This explanation was checked from relaxation measurements by NMR and DMA, and by the analysis of the soluble fraction generated by hydrolysis.
This paper describes water absorption in polydicyclopentadiene (PDCPD) and more specially the impact of thermal oxidation on its behavior. Unaged PDCPD is found to be almost hydrophobic consistently with its non-polar structure. During thermal oxidation, hydrophilicity progressively increases with ageing time. This increase is linked with the buildup of polar products (mainly ketones, carboxylic acids, hydroperoxides, alcohols). Moreover, it appears that water absorption in PDCPD obeys to Flory Huggins law for all conditions considered here. In the meantime, water diffusivity seems to decrease when oxidation level increases. Finally, a mastercurve that links carbonyl concentration, water diffusivity and waterpolymer interaction parameter is proposed and allows changes of water resistance of PDCPD to be predicted.
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