Poly(N-vinylcaprolactam) microgel particles grafted with amphiphilic chains

Grafted temperature-sensitive poly(N-vinylcaprolactam), PVCL, microgel, par ticles have been prepared. The grafting has been accomplished using an amph iphilic macromonomer consisting of a hydrocarbon segment and a poly(ethylen e oxide), PEG, segment. The water-soluble amphiphilic macromonomer has been synthesized and utilized in two different cases. In the first case, the gr afted particles were prepared using macromonomers as reactive emulgators in emulsion copolymerization. In the second case the PVCL particles were firs t synthesized in an emulsion stabilized with SDS, and then, the microgel pa rticles swollen with monomers were postmodified with amphiphilic macromonom ers. Properties of the grafted nanoparticles in water were investigated by static and dynamic Light scattering, as well as by H-1 NMR relaxation and d iffusion measurements. All the polymers show the LCST behavior typical to P VCL, and they collapse upon heating. For the particles prepared in one step in an emulsion stabilized by the macromonomer, the collapse was discontinu ous and took place in a very narrow temperature range. When the particles w ere prepared in two steps, the grafts were observed to change the particle size as well as the critical temperature of the collapse. In the latter cas e the thermal transition was much more gradual than in the former one. This is probably due to a difference in the number of electric charges in the p olymer particles, originating from the initiator and SDS.