Photodegradable Hydrogels\nMade via RAFT

Abstract

The photodegradation kinetics of reversible addition–fragmentation\nchain transfer (RAFT) synthesized hydrogels were investigated and\ncompared to conventional free radical gels, using rheological monitoring.\nThe gel polymerizations were conducted on <i>N</i>-acryloylmorpholine\n(NAM) between parallel plates of a rheometer, in aqueous media and\nat ambient temperature using the redox couple ammonium persulfate\n(APS) and <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethane-1,2-diamine\n(TEMED). The gels synthesized by RAFT are believed to have a more\nhomogeneous network structure which is thought to be a contributing\nfactor to the faster degradation kinetics displayed by the RAFT gels\ncompared to conventional non-RAFT gels. Difunctional macro-RAFT agents\nwere used to prepare the gels which insert degradable points in backbone\nchains, as well as the cross-links, to give significantly faster degradation\nrates. RAFT also provided a platform to carry out a systematic study\nof the photodegradable gels and demonstrated a limitation of the system,\nwhich is the unavoidable attenuation of light intensity by the light\nactive components of the gel. This means that the concentration of\nphotodegradable cross-linker, a parameter which is varied in order\nto modulate the final storage modulus <i>G</i>′ of\nthe gel, will also have a consequence on the degradation kinetics.