IR-SPECTROSCOPIC STUDY OF THE HYDROGEN-BONDS NETWORK IN COPOLYMERS OF METHYL-METHACRYLATE WITH METHACRYLIC-ACID

In copolymers of methyl methacrylate with 5-20% of methacrylic acid the hydrogen bonds network is a result of the equilibrium between network points of two types: carboxyl dimers and complexes of carboxyl groups with ester ones. Because of the high concentration of ester groups at high temperatures this equilibrium is completely displaced in the direction of -COO ... O = C(OCH3)- complexes formation. Temperature dependence of the frequency and intensity of the absorption band of the O-H vibration in these complexes is a result of the change of the length and strength of the H ... O bond because of the heat expansion of a copolymer. The formation of the hydrogen bond between carboxyl and ester groups is accompanied by the transition of the last one from the cis- into the trans-conformation and by the change of its orientation towards the main chain. Chemical crosslinks are mentioned to affect the conformation of the ester group in polydimethacrylates by the same way.