NMR Study of Polyacrylamide Tacticity Synthesized by Precipitated Polymerization Method

In this study polyacrylamide was prepared in various molar ratio contents of ethylacetate and ethanol at 60ºC by free-radical precipitated polymerization method. Theassignment of all stereosequences at pentad level of methine, hexad level of methylene, and triad level of carbonyl carbons of the polyacrylamide were observedusing 13C nuclear magnetic resonance spectroscopy (13C NMR) in deuterium oxide atroom temperature. Bernoullian and 1st-order Markov statistics were used for all carbons and the results were compared with experimental data by statistical method. Itwas shown that Bernoullian statistics model fit slightly better than 1st-order Markov statistics model for the assigned sequences. The results indicated that correspondingvalues of the probability (Pm) and length average (Nm) of meso addition were 0.443 and1.698, respectively and no significant differences were observed by changing the molarratios of the two solvents. By heteronuclear multiple quantum coherence (HMQC) astwo-dimensional NMR spectroscopy, the methylene and methine groups were assignedby triad sequences in which isotactic contour was thoroughly isolated from syndiotactic and atactic contours. Therefore, isotactic triad sequence could only be calculated by 1H NMR. In other words, isotactic placement value was calculated byusing the integration of areas of methylene and methine protons (mm = 0.21) peaks.