Block copolymers composed of Poly (N-isopropyl acrylamide) (PNiPAAm) and PEO were prepared by using the redox initiation. The reaction between oxidizing agent and -$CH_2OH$ groups of poly (ethylene oxide) (PEO) were generated macromolecular free radicals and polymerization was proceeded by addition of NiPAAm monomers.
The aqueous solutions of the block copolymers exhibited thermal phase transition. The thermal phase transition temperatures of PNiPAAm homopolymer was observed at 32℃. But the phase transition temperatures of the block copolymers in aqueous solution are higher than that of PNiPAAm homopolymer and the phase transition temperature increases with PEO content. The aqueous solution of block copolymers exhibited LCST at high content of PEO, and thermal phase transition temperatures were 34~36℃. It is shown that the thermal phase transition of PNiPAAm solution is not affected by PEO homopolymer in aqueous solution but the thermal phase transition behaviors of aqueous block copolymer solutions are significantly affected by PEO block.
The hydrogels composed of PEO, PNiPAAm, and cross-linker, α, -diacrylated PEO ω-(DAPEO) and N,N``-methylene-bisacrylamide (MBAAm) were synthesized by using the same method. The thermoshrinking of these hydrogels were observed on higher temperature and wider temperature range than PNiPAAm hydrogel. The molecular interactions between PNiPAAm and PEO of the dried hydrogels were studied by Fourier transform infrared (FTIR) spectroscopy and the morphology of the dried hydrogels was studied scanning electron microscopy (SEM). As the result of FTIR and SEM studies, the hydrogels cross-linked by DAPEO were more influenced by PEO chain during the dehydration process than hydrogels cross-linked by MBAAm.
The copolymers of PNiPAAm grafted onto sodium alginate (SA) were prepared by redox initiation. The graft copolymers showed higher phase transition temperatures than PNiPAAm homopolymer. The graft copolymers that had relatively high S...