The effect of hydroxyspiro‐orthocarbonates on the cationic photopolymerization of an epoxy resin and on the mechanical properties of the final polymer

Abstract It is well known that bicyclic compounds like spiro‐orthocarbonates (SOCs) have the ability to reduce or eliminate the shrinkage produced during polymerization. In the work reported, four different SOCs were prepared, two of them with one and two hydroxyl groups, respectively, another with two alkoxy groups and one reference compound without substituents. It was found that the SOCs with hydroxyl groups increased the photopolymerization rate and conversion of an epoxycycloaliphatic monomer, while the compound with butoxy groups had an antagonistic effect, reducing both photopolymerization rate and conversion, due to the basic character of the ether groups. The reference compound did not display accelerating effects but it did increase slightly the conversion. Dynamic mechanical analysis revealed that the SOC with two hydroxyl groups increased the values of storage modulus of the obtained polymer in comparison with the polymer from pristine monomer. This may be due to the multifunctionality of this compound that induced a higher level of crosslinking, while the SOC with one hydroxyl group had the opposite effect, decreasing the viscoelastic property values of the polymer due to chain‐transfer reactions originated by the hydroxyl groups. The SOC with two hydroxyl groups was the more efficient of the studied compounds in reducing the shrinkage of the cured polyether. Copyright © 2011 Society of Chemical Industry