No abstract

Poly (1-vinyluracil) has now been prepared with complete repression of cyclopolymerization via -radiationinitiated polymerization using the following techniques: (a) polymerization at low temperature, (b) polymerization at high concentrations of monomer, (c) polymerization in the solid state, (d) polymerization of negatively charged monomers, and (e) polymerization of monomers containing bulky substituents. As the temperature was reduced from 0 to -78°the extent of cyclopolymerizations decreased from 20% to 0% in solution. At 0°, high concentrations of negatively charged 1-vinyluracil also led to 0% cyclopolymerization. In the solid state, polymerization occurred at 40°without any cyclopolymerization. At very high doses, some cross-linking was observed. Polymerization of 6-methyl-1-vinyluracil at 250 in solution led to the completely noncyclopolymerized polymer. The polymers were amorphous by X-ray diffraction, and the 100-MHz nmr spectra at 170°in DMSO-t/6 suggested that the poly(l-vinyluracils) varied in their degree of syndiotacticity. The ultraviolet hypochromism at 264 µ was found to vary widely with the tacticity.