Dark polymerization of acrylamide induced by tyrosine-containing peptide.

We proposed a novel photoinitiation system composed of photosensitizer and tyrosine-containing peptide, which could initiate radical photopolymerization of acrylamide in water in air. And, when the irradiation was extinguished, the formula with purged nitrogen kept polymerizing in the dark for a long time. The highlight of this system stems from the fact that after low-intensity irradiation as brief as 2 or 5 min, the generated radicals have long lifetime, allowing polymerization propagation in the dark to result in high molecular weight and high conversion. The dark polymerization might be ascribed to the protonation and the steric hindrance of polyacrylamide macroradicals, endowed by the tyrosine-containing peptide, preventing the biradical termination. And these behaviors of the investigated peptides were related to the location of the tyrosine residue on polypeptide chain. In addition, this novel photoinitiator can't initiate dark polymerization of other water-soluble monomers, but can initiate dark copolymerization of acrylamide with these monomers, further indicating that the hydrogen bonding between acrylamide and polypeptide might be the key factor for dark polymerization. This novel system has potential applications in the preparation of biohydrogels. [ABSTRACT FROM AUTHOR]