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A series of high molecular weight poly(N-isopropylacrylamide) (PNIPAM)s with low polydispersity (Mn= 7.0 × 104to 10.2× 104g 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)3Lewis 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 × 104to 4.0 × 104g mol–1, PDI = 1.2–1.3) having different isotacticity [meso diad (m) = 45–72%)] reported earlier by us (Rayet al. Polym. J.2005, 37, 234) showed that Tgof PNIPAM decreases with increase in its meso diad content (m%) and decrease in its molecular weight. [ABSTRACT FROM AUTHOR]