| Abstract
| - Thermal properties of copolymers, poly(N-isopropylacrylamide) (PNIPA) grafted withdifferent amounts of poly(ethylene oxide) (PEO), were studied in aqueous solutions. A functional backbonecopolymer with Mw 1.8 × 105 was grafted by amino-terminated PEO (Mw 6000) in water at two differenttemperatures, 15 and 29 °C. The average number of PEO side chains increased from 6 to 7 with increasingreaction temperature. Above the lower critical solution temperature (LCST), the polymers form stablespherical aggregates observable by light scattering. In a viscous flow, however, the formation of aggregatesduring the collapse of the PNIPA chains was prevented, and small polymer spheres were detected. EPRexperiments showed that with increasing temperature an amphiphilic spin probe, 5-doxylstearic acid,diffused more easily out from the copolymer with more PEO grafts, this indicating that the hydrophilicside chains affect the size of the hydrophobic core in a collapsed copolymer. A polymer grafted in dioxane,which contained 10 PEO grafts, was used as a reference. A comparison of all the three graft copolymerssuggests that the conformation of PNIPA during the grafting affects the properties of the product polymers.
|
