Ring retention via pulsed plasma polymerization of heterocyclic aromatic compounds

Polymerization of two isomeric heterocyclic monomers, 3-methyl-1-vinylpyrazole and 1-allylimidazole, was investigated under pulsed plasma conditions. Large-scale, progressive variations in polymer compositions were observed with sequential changes in the plasma duty cycles employed, all other plasma variables being held constant. In particular, unusually linear polymers (by normal plasma polymerization standards) are achieved at exceptionally low average power inputs, employed when the pulsed plasma technique is operated at low duty cycles. With both monomers, a pronounced increased retention of their aromatic rings is observed in the plasma-synthesized polymers as the duty cycle employed during film formation is reduced. Overall, a higher ring retention is achieved with the imidazole, compared to the pyrazole, reflecting bond energy differences in these two isomers. This study also includes synthesis and spectral characterization of a conventionally prepared linear poly(3-methyl-1-vinylpyrazole) which was employed to assess the degree of ring retention in the plasma polymers. On the basis of the results of this study, it appears that relatively linear polymers of fairly complex molecules are readily synthesized using the low duty cycle pulsed plasma technique. according-ly, this approach is useful in extending the utility of plasma polymerizations which have heretofore tended to focus on synthesis of unique, relatively highly cross-linked materials. The pulsed technique provides synthesis of these polymers while maintaining the many inherent advantages of the plasma polymerization technique, including particularly the pinhole-free, conformal, and adhesive qualities of these films.