NMR investigations into heterogeneous structures of thermosensitive microgel particles

The intern al properties of submicron poly(N-isopropylmethacrylamide) la te x particles were investigated as a function of the methylene bisacrylamide (MBA) concentration used as a crosslinker. Two experimental approaches were performed. First, quasi-electric light scattering measurements provided th e size variation of the particles as a function of temperature, from which the swelling capacity of the particles as a function of MBA were estimated. In addition, the broadening and lowering effects of the volume phase trans ition temperature were detected from the turbidity of the solutions versus the MBA concentration. Second, observations of the transverse relaxation of protons gave evidence for heterogeneous structures inside the particles; s everal structural parts were discriminated from one another from different proton mobilities detected through magnetic relaxation rates. Corresponding to the concentration gradients of the crosslinker, the internal particle s tructures were looser and looser from the core to the shell. The state of t he gelation of the polymer particles was governed by the initial amount of the crosslinker introduced into the latex recipe. (C) 2000 John Wiley & Son s, Inc.