Synthesis of poly(vinyl alcohol) graft copolymers by living cationic polymerization in the presence of added bases I. Design and synthesis of poly(vinyl alcohol) graft copolymers with well-controlled poly(vinyl ether) grafts

A new method of synthesis of Poly(vinyl alcohol) (PVA) graft copolymers via living cationic polymerization was designed using a new coupling reagent, partially-hydrolyzed poly(vinyl acetate) (PVAc-OH). The living cationic pol ymerization of vinyl ethers was carried out in the presence of added bases, and the living propagating species were allowed to react with PVAc-OH, sel ectively. The graft copolymers contained well-controlled poly(vinyl ether) grafts with a very narrow molecular weight distribution. The PVAc main chai n was quantitatively converted to PVA by hydrolysis under mild alkaline con ditions. The resulting PVA graft copolymers could dissolve in not only wate r and DMSO, but also many organic solvents such as toluene and chloroform. The graft copolymers with poly(2-methoxyethyl vinyl ether) and/or poly(2-et hoxyethyl vinyl ether) turned out to exhibit the unique behavior of thermos ensitive phase separation in water. When the aqueous solution was warmed to the critical temperature, the clear solution changed to opaque in a rapid transition. On the other hand, at below room temperature, characteristic ph ysical gelation of main chain PVA was also observed gradually.