The second virial coefficient A 2 and intrinsic viscosity [] were determined in methanol at 25.0 C for poly(Nisopropylacrylamide) (PNIPA) samples synthesized by living anionic polymerization in the range of weight-average molecular weight M w from 4:91 Â 10 3 to 7:23 Â 10 4 , which are called L samples, and also for those by radical polymerization in tert-butanol and benzene by the use of azobis(isobutyronitrile) as an initiator in the range of M w from 1:23 Â 10 4 to 7:83 Â 10 4 , which are called T and B samples, respectively. It is found for both A 2 and [] that their values for the three kinds of samples agree well with each other in the range of M w. 3 Â 10 4 but deviate from each other as M w is increased from 3 Â 10 4 , the value for the L sample being the largest and that for the B sample the smallest. The result is consistent with the fact that the average chain dimension is the largest for the L sample having no branch point and the smallest for the B sample having the largest number of branch points. From a simultaneous analysis of A 2 and [] for the L samples on the basis of the Kratky-Porod wormlike chain with excluded volume, the stiffness parameter À1 is estimated to be 18 Å , which is almost the same as those determined for typical flexible polymers. For the L samples, the cloud point was also determined in their aqueous solutions in the range of the weight fraction w of PNIPA from ca. 0.5 to ca. 10%. It is found that the cloud point in the range of w & 2% decreases from ca. 32 C to ca. 18 C as M w is decreased from 7:23 Â 10 4 to 5:47 Â 10 3. Such behavior may be regarded as arising from effects of hydrophobic chain end groups of the L samples.

The mean-square radius of gyration, second virial coefficient and intrinsic viscosity were determined in methanol at 25.0 1C for poly(N-isopropylacrylamide) (PNIPA) samples in the range of weight-average molecular weight M w from 1.04Â10 5 to 2.65Â10 6 , which were synthesized by aqueous redox polymerization using a redox catalyst consisting of ammonium persulfate and sodium metabisulfite. Analyses of the quantities showed that the samples have almost the same degree of branching as that of PNIPA samples previously synthesized by radical polymerization using azobis(isobutyronitrile) as an initiator in tert-butanol. The cloud point was also determined in aqueous solutions of two PNIPA samples with M w ¼1.04Â10 5 and 1.86Â10 5 and compared with the results of the previous samples. It was found that the cloud point is definitely higher for the present samples than for the previous ones, and, moreover, the M w dependences of the cloud point for the two kinds of samples are opposite to each other. As the two kinds of samples have almost the same stereochemical composition and degree of branching, such difference in the behavior of the cloud point is considered to arise from the difference in their chain-end groups.