PIPERAZINE COPOLYMERS FOR MEDICAL IMPLANT APPLICATIONS

Piperazine copolymers were investigated for possible use in medical implant applications with special reference to the replacement of the cornea of the eye. Initial work involved the study of the thermal stability of the polymers which is important in sterilization procedures; their stability toward long-wave ultraviolet and visible radiation; and blood coagulation tests. The thermal stability of piperazine copolyamides was studied by both programmed and isothermal techniques. Experiments were carried out with the block copolymers of terephthaloyl trans-2,5-imethylpiperazine/isophthaloyl trans-2,5-dimethylpiperazine; terephthaloyl trans-2,5-dimethylpiperazine/sebacyl trans-2,5-dimethylpiperazine; and isophthaloyl trans-2,5-dimethylpiperazine/sebacyl trans-2,5-dimethylpiperazine. In contrast to the previously studied homo polymers, the activation energies (range 185 to 256 kJ/mole), rates of volatilization and half-life values are influenced by the molecular weights of the block copolymers. In general, the data indicate a random degradation process during isothermal heating in a vacuum between 336°C and 440°C. The exception is the block copolymer of isophthaloyl trans-2,5-dimethylpiperazine/sebacyl trans-2,5-dimethylpiperazine which shows the completing effect of hydrolytic processes. Film samples of the polymers that have been irradiated up to 160 h by a long wave ultraviolet lamp (having an energy peak close to 360 nm with virtually no radiation shorter than 300 nm) showed no changes in the ultraviolet and visible spectra and no gelation occurred. These results are important since polymer films that are to be considered for cornea replacement must exhibit good stability to long wave ultraviolet and visible radiation. Initial data on blood coagulation tests indicate that the polymers considerably increase the coagulation times of human blood when glass is used as a standard. © 1969.