Acid-labile, thermoresponsive (meth)acrylamide polymers with pendant cyclic acetal moieties

Acid-labile, thermoresponsive polymers with pendant six-membered cyclic acetal groups were prepared by radical polymerization of two monomers, N-(2,2-dimethyl-1,3-dioxan-5-yl) methacrylamide (NDMM) and N-(2,2-dimethyl-1,3-dioxan-5-yl) acrylamide (NDMA). The aqueous solution properties of the polymers, PNDMM and PNDMA, were studied by turbidimetry, H-1 NMR, fluorescence, and DSC measurements. It is found that both polymers show sensitive and reversible phase transitions with distinct lower critical solution temperatures (LCST). Below their LCSTs, there are still some polymer aggregates as evidenced by measurements of pyrene excitation spectra and urea effects on the cloud points (CP) of polymers. The salting effect of six inorganic sodium salts on the phase transition behavior of PNDMM was investigated by turbidimetric approach. The salting-out to salting-in effect is in the order of SO42- > F- > Cl- > Br- > I- > SCN-, following the Hofmeister's series. pH-dependent hydrolysis of PNDMM and PNDMA was studied by turbidimetric and H-1 NMR methods. They are both pH-sensitive and their hydrolysis rates significantly increase with decreasing pH value. The CP of PNDMM gradually increases with the acid-triggered hydrolysis of the acetal groups and the hydrolyzed polymer with similar to 30% hydrolysis degree does not show thermally induced phase transition. (c) 2008 Wiley Periodicals, Inc.