POST-MODIFICATION OF THERMOSENSITIVE MICROGELS IN BLEACH

Abstract

<p>N-chloramide containing and primary amine-containing microgels were prepared by post-modification of thermosensitive microgels in alkaline bleach. The objective of this project was to develop simple strategies for preparation of functionalized microgels.</p> <p>N-chlorination of linear poly(N-isopropylacrylamide) (PNIPAM) in bleach at high pH resulted in a novel N-chloramide containing copolymer: poly(NIPAM-co-NIPAMCl). The chlorinated PNIPAM showed controlled phase transition temperature and oxidative ability. The N-chlorination of linear PNIPAM inspired the preparation of N-chloramide containing PNIPAM microgels in a similar way. The phase transition temperature of the resulted chlorinated microgels, which corresponds to the extent of N-chlorination, was affected by the reaction temperature and salt concentration. The reaction between the chlorinated microgels and glutathione is proposed as diffusion controlled.</p> <p>The N-chlorination of poly(N-isopropylmethacrylamide) (PNIPMAM) microgels in bleach was restricted, in comparison with PNIPAM microgels. The active chlorine content of chlorinated PNIPMAM microgels was about one-tenth of that of chlorinated PNIPAM microgels under the same N-chlorination condition. It is proposed that the high stability of PNIPMAM in bleach is a result of the electron-donating effect of methyl groups on PNIPMAM backbone. Hence, core-shell microgels with PNIPAM cores and poly(NIPAM-co-NIPMAM) shells showed improved colloidal stability after N-chlorination because the shell was less chlorinated and served as a steric stabilizer.</p> <p>Finally, primary amine-containing microgels were prepared via Hofmann rearrangement of copolymers of methacrylamide, which decomposed to give amines, and NIPMAM, which did not react. The method was further extended to give amphoteric microgels by including acrylic acid in the starting microgels. Although other approaches to aminated and amphoteric microgels have been developed, this approach is particularly attractive because of the ease of the reaction and the ability to control the microgel isoelectric points.</p>