Linear and crosslinked polyanhydrides can be made using photoinitiated thiol-ene chemistry, a simple and effective method of making crosslinked structures that have surface degradation characteristics.

The synthesis of diacrylated poly(b-amino ester) crosslinkers, obtained from the oligomerization of di(ethylene glycol) diacrylate (DEGDA) and piperazine (PIPz), and their use in hydrogels are reported. In particular, the poly(b-amino ester) crosslinkers were used to study swelling and degradation properties of hydrogels made of N-vinylpyrrolidone and 2-hydroxy ethyl methacrylate. Poly(b-amino ester) crosslinkers with two different molecular weights (800 and 3000 g mol À1 ) and hydrogels with 1 and 3% crosslinker were studied. Swelling and degradation of the gels were monitored in phosphate buffered saline (pH ¼ 7.4) at 37 C. The swelling and degradation characteristics of the poly(b-amino ester) crosslinked hydrogels were then compared to hydrogels crosslinked with poly(ethylene glycol) diacrylate (PEGDA) of similar molecular weights. It was found that both swelling and degradation were faster in the poly(b-amino ester) crosslinked hydrogels, particularly for the highest molecular weight poly(b-amino ester) crosslinker.

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 g values 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.