Photopolymerisation of Poly(tetra-methylene ether) glycol diacrylates and properties of the obtained networks

A series of poly(tetramethylene ether) glycol α,ω-diacrylates have been prepared from the corresponding hydroxy-terminated oligomers. The acrylation reaction, performed with acrylic acid in the presence of p-toluenesulfonic acid as a catalyst, allowed us to obtain oligomers with n in the range 250–2000 and an acrylic functionality close to 2. The n of the acrylated product was always lower than that of the starting oligomer, suggesting the occurrence of degradation reactions. These were attributed to an acidic hydrolytic attack on the oligomer chain. The oligomers were subjected to an ultra-violet light promoted curing process as thin films on glass substrates under N2 atmosphere. Complete acrylic double-bond conversion was obtained in all cases, with the exception of the oligomer with the lowest molecular weight. The thermal and mechanical properties of the networks were investigated by means of differential scanning calorimetry, thermomechanical analysis and dynamic mechanical thermal analysis (d.m.t.a.). Amorphous and rubbery materials were obtained with the exception of those from the oligomers of the highest molecular weight, which showed partial crystallinity. By means of thermal analysis and d.m.t.a., Tg values were measured and correlated to the molecular weights of the oligomers used. In particular, the Tg values, as a function of the crosslinking density, agreed with those calculated by the Nielsen equation. Moreover, equilibrium swelling measurements in water were performed. The results obtained are discussed on the basis of Flory's theory and interpreted in terms of the solubility parameters and the crosslinking densities of the networks.