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 × 10 4 to 10.2× 10 4 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 × 10 4 to 4.0 × 10 4 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.