Browsing by Author "Yoshio Okamoto"

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Effects of tacticity and molecular weight of poly(N -isopropylacrylamide) on its glass transition temperature
(2011) Chandra Sekhar Biswas; Vijay Kumar Patel; Niraj Kumar Vishwakarma; Vimal K. Tiwari; Biswajit Maiti; Pralay Maiti; Masami Kamigaito; Yoshio Okamoto; Biswajit Ray
A series of high molecular weight poly(N-isopropylacrylamide) (PNIPAM)s with low polydispersity (Mn = 7.0 × - 104 to 10.2× - 104 g mol-1, PDI = 1.23-1.35) having different isotacticity [meso diad (m) = 47-88%]] was successfully synthesized using the reversible addition-fragmentation chain transfer (RAFT) polymerization method in the presence of different concentrations of Y(OTf)3 Lewis acid. Measurement of the glass transition temperature (Tg) of this high molecular weight isotactic PNIPAM series and the low molecular weight PNIPAM series (Mn = 3.5 × - 104 to 4.0 × - 104 g mol-1, PDI = 1.2-1.3) having different isotacticity [meso diad (m) = 45-72%)] reported earlier by us (Ray et al. Polym. J. 2005, 37, 234) showed that Tg of PNIPAM decreases with increase in its meso diad content (m %) and decrease in its molecular weight. © 2011 American Chemical Society.
Study of the effect of isotacticity on some physical properties of poly(N-isopropylacrylamide)
(Springer Verlag, 2015) Chandra Sekhar Biswas; Kheyanath Mitra; Shikha Singh; Kalyan Ramesh; Nira Misra; Biswajit Maiti; Amiya Kumar Panda; Pralay Maiti; Masami Kamigaito; Yoshio Okamoto; Biswajit Ray
Some physical properties of high molecular weight linear poly(N-isopropylacrylamide)s (PNIPAM) having different isotacticities (m, meso dyad = 47, 62, 68, 81, and 88 %) have been studied. The solubility of these polymers in different solvents varied with their isotacticity. Thermal degradation of higher isotactic polymer started slightly earlier. Cloud point of these polymers in water gradually decreased with increase in m up to 68 %. Surface tension of these polymers in N,N-dimethylformamide (DMF) was slightly lower than DMF and almost independent of their isotacticity in the temperature range of 20–60 °C. But it decreased linearly with the increase in temperature. Moreover, for all polymers, it decreased very slightly with the increase in their concentrations in the range of 0.001–0.01 % (w/v). Viscosity of these polymers in DMF increased with (i) the increase in the concentration range of 1–5 % (w/v), (ii) the increase in their m values, and (iii) the decrease in the temperature in the range of 20–60 oC. © 2015, Springer-Verlag Berlin Heidelberg.