Narrowly distributed spherical microgel particles of poly(N isopropylacrylamide) (PNIPAM) were prepared by emulsion polymerization in water.The volume phase transition of the microgel particles was studied by static and dynamic laser light scattering.The results were compared with the coil to globule transition of individual long linear PNIPAM chains.The microgel particles have a higher transition temperature

but a less sharp phase transition in comparison with that of long linear chains.This difference has been attributed to both the short length and the broad length distribution of the subchains inside the microgels.A combination of static and dynamic laser light scattering results revealed that even in a highly collapsed state the microgel particles retained～70%of water and the density of the microgel networks increased from 0.021g/ml to ～0.3g/ml during the phase transition.The phase transition of the microgel particles is continuous

in cintrast to the discontinuous volume phase transition in bulk PNIPAM gels.The microgel particles are thermodynamically stable even at their collapsing limit.The behavior of microgel particles in comoared with that of individual PNIPAM chains.