Polyanhydride Networks from Thiol-Ene Polymerizations

Thiol−ene photopolymerization was used in the synthesis of elastomeric polyanhydrides. Side reactions involving the addition of thiol to the anhydride were observed but take place at a much slower rate than photoinitiated thiol−ene polymerization. The thermomechanical properties, including the glass transition temperature (T_g) as well as tensile and compressive modulus, of the cross-linked material were studied using dynamic mechanical analysis. T_gvalues ranged from −15 to approximately −50 °C and were dependent on the degree of cross-linking. The Young’s and compressive modulus measurements confirm that these types of networks are a soft rubber-like material at room and body temperature and become softer as the cross-linking density is reduced. The hydrophobicity/hydrophilicity of these networks was analyzed by water contact angle measurements. The polyanhydrides were moderately hydrophobic, with water contact angle averages ranging from 82° to 92°. This hydrophobicity, coupled with the high reactivity of the anhydride groups, results in the material eroding via the surface erosion mechanism.