Effects of Tacticity and Molecular Weight of Poly(N-isopropylacrylamide) on Its Glass Transition Temperature

A series of high molecular weight poly(N-isopropylacrylamide) (PNIPAM)s with low polydispersity (M_n = 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 (T_g) of this high molecular weight isotactic PNIPAM series and the low molecular weight PNIPAM series (M_n = 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 T_g of PNIPAM decreases with increase in its meso diad content (m %) and decrease in its molecular weight.