MOLECULAR DESIGN FOR NOVEL STIMULI-SENSITIVE GELS

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Poly(siloxyethylene glycol) (PSEG), which consists of alternating oligo(dimethylsiloxane) and oligo(ethylene glycol) (OEG) units in the main chain was synthesized through polycondensation reactions between oligosiloxane having two diethylamino groups and OEG. The molecular weight of the polymer was in the range of 3,500 to 17,700 g/mol with monomodal molecular weight distribution. The glass transition temperature of the polymer thus obtained was controlled by changing the silicon content in the polymer. Actually, with increasing Si content, the Tg of the polymer decreased from -53℃(PEG) to -100℃. PSEG having a silicon content of less than 15 wt% was soluble in aqueous media. With increasing solution temperature, phase separation occurred and the solution become turbid. The temperature at the phase separation is known as a lower critical solution temperature(LCST). The LCST was controlled by the silicon content in the polymer. The hydrolytic stabilities of the PSEG in aqueous solution were also examined.Poly(silamine), which consists of alternating ethylene diamine and 3-silapentane, was also prepared via anionic polyaddition reaction of ethylenediamine with divinylsilane in the presence of lithium alkylamide. Poly(silamine) hydrogel exhibits a discontinuous volume phase transition and rubber elasticity transition in respond to pH change for the protonation of amine units in the main chain. It also has been revealed that the rubber elasticity transition is controlled by the anion for the strong interaction between poly(silamine) and anions. The results suggest that the stiffness of poly(silamine) hydrogel decreases with its swelling.