Controlling the kinetic chain length of the crosslinks in photo-polymerized biodegradable networks

Biodegradable polymer networks were prepared by photo-initiated radical polymerization of methacrylate functionalized poly(d,l-lactide) oligomers. The kinetic chains formed in this radical polymerization are the multifunctional crosslinks of the networks. These chains are carbon–carbon chains that remain after degradation. If their molecular weight is too high these poly(methacrylic acid) chains can not be excreted by the kidneys. The effect of the photo-initiator concentration and the addition of 2-mercaptoethanol as a chain transfer agent on the molecular weight of the kinetic chains was investigated. It was found that both increasing the initiator concentration and adding 2-mercaptoethanol decrease the kinetic chain length. However, the effect of adding 2-mercaptoethanol was much larger. Some network properties such as the glass transition temperature and the swelling ratio in acetone are affected when the kinetic chain length is decreased.