Controlling the swelling characteristics of temperature-sensitive cellulose ether hydrogels

Novel temperature-sensitive hydrogels; have been synthesized by chemically crosslinking cellulose ethers; hydroxypropyl cellulose, methyl cellulose and hydroxypropylmethyl celluloses. These gels are highly swollen at low temperatures, gradually deswelling as temperature rises, usually sharply over a limited temperature range. Linear polymer type, crosslink density and ionic content have been varied in order to determine the effects of controllable network parameters on the important properties (degree of swelling, transition temperature and sharpness of transition) of the gels obtained. The transition temperature itself is about that of the observed linear polymer lower critical solution temperature (LCST). Producing gels from increasingly hydrophilic cellulose ethers raises the transition temperature and increases the swelling degree at comparable crosslink densities. However, decreasing crosslinking has little effect on swelling above the transition temperature. In contrast, increasing ionic content increases swelling at all temperatures. The transition temperature is not affected by the degree of crosslinking, but increases with increasing ionic content. The volume transition of the hydroxypropyl cellulose gel is significantly sharper than for the other gels. Crosslinking and ionic content have little effect on transition sharpness. The trends observed with cellulose ether gels are consistent with those observed in gels produced by conventional copolymerization/crosslinking synthesis methods, though some differences are noted.