Atypical Transition Temperature Dependence of Poly(N-isopropylacrylamide) and Poly(N-isopropylacrylamide-co-acrylamide) Nanocomposites on the Content of Exfoliated Montmorillonites

Exfoliated montmorillonite (MMT)/poly(N-isopropylacrylamide) (PNIPAAm) and MMT/poly(N-isopropylacrylamide-co-acrylamide) [P(NIPAAm-co-AAm)] nanocomposites were fabricated by soap-free emulsion polymerization. Interestingly, as the content of MMT was increased from 0 to 10 wt%, the glass transition temperature of MMT/PNIPAAm was decreased from 145 to 122 degrees C, whereas that of the MMT/P(NIPAAm-co-AAm) increased from 95 to 153 degrees C. Although the lower critical solution temperature (LCST) of 32 degrees C for the MMT/PNIPAAm nanocomposites in aqueous solutions was slightly increased with the content of MMT, that of the MMT/P(NIPAAm-co-AAm) was decreased from 70 to 65 degrees C. A mechanism that the hydrogen bonds between the amide groups of PNIPAAm. were interfered by the exfoliated MMT nano-platelets for the MMT/PNIPAAm nanocomposites and the preferred absorption of acrylamide units to the MMT nanoplatelets rather than N-isopropylacrylamide in the MMT/P(NIPAAm-co-AAm) nanocomposites was suggested to interpret these unusual transition behavior. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 524-530, 2009