Effects of vinyl ethers upon radical polymerizations

Various vinyl ethers have been examined as additives during radical polymer izations initiated by azobisisobutyronitrile at 60 degrees C; the monomers were methyl methacrylate (MMA), styrene (STY) and acrylonitrile (AN). For M MA and STY, the vinyl ethers were incorporated to only small extents but th ey caused reductions in rate of polymerization and chain length of the resu lting polymer; the effects can be attributed to the low reactivities in gro wth reactions of radicals to which a vinyl ether unit was last added. Copol ymerization of the vinyl ethers with AN was more evident but, in many cases , it was accompanied by increased rate of consumption of AN and increased c hain length of the polymer. These changes can be explained in terms of a ph ysical effect which can be likened to that believed to be responsible for t he gel effect. It is considered that polymer radicals are rather tightly co iled in an indifferent solvent so that the normal bimolecular termination i s impeded.