Photodegradable Hydrogels Made via RAFT

The photodegradation kinetics of reversible addition fragmentation chain transfer (RAFT) synthesized hydrogels were investigated and compared to conventional free radical gels, using rheological monitoring. The gel polymerizations were conducted on N-acryloylmorpholine (NAM) between parallel plates of a rheometer, in aqueous media and at ambient temperature using the redox couple ammonium persulfate (APS) and N,N,N',N'-tetramethylethane-1,2-diamine (TEMED). The gels synthesized by RAFT are believed to have a more homogeneous network structure which is thought to be a contributing factor to the faster degradation kinetics displayed by the RAFT gels compared to conventional non-RAFT gels. Difunctional macro-RAFT agents were used to prepare the gels which insert degradable points in backbone chains, as well as the cross-links, to give significantly faster degradation rates. RAFT also provided a platform to carry out a systematic study of the photodegradable gels and demonstrated a limitation of the system, which is the unavoidable attenuation of light intensity by the light active components of the gel. This means that the concentration of photodegradable cross-linker, a parameter which is varied in order to modulate the final storage modulus G' of the gel, will also have a consequence on the degradation kinetics.