NMR Measurement of Identical Polymer Samples by Round Robin Method IV. Analysis of Composition and Monomer Sequence Distribution in Poly(methyl methacrylate-co-acrylonitrile) Leading to Determinations of Monomer Reactivity Ratios

Abstract

In order to assess the reliability of NMR measurement of polymers, 1H and 13C NMR data for three copolymers of methyl methacrylate (MMA) and acrylonitrile (AN) prepared with AIBN were collected from 46 spectrometers whose resonance frequencies for 1H NMR measurements ranging from 90 to 500 MHz. 1H and 13C NMR spectra were measured in nitrobenzene-d5 at 110°C and acetonitrile-d3 at 70°C, respectively. Standard deviations (σ’s) for chemical shift measurements of the 1H and 13C NMR signals were 0.003—0.008 ppm and 0.03—0.05 ppm, respectively. Compositions of the copolymers were determined from the relative intensities of the signals due to the OCH3 (MMA) and CH (AN) protons, and the σ values for the determinations were 3.7—9.5%. The compositions determined from 13C NMR (C=O for MMA unit, CN for AN unit) agreed well with those obtained from 1H NMR. Monomer reactivity ratios rij (i,j=1 or 2) for a penultimate model were determined from monomer feed ratios and triad fractions obtained from the C=O (MMA) and CH (AN) carbon signals. Most of the σ values for rij determinations were 5—14%. While r22 and r12 are nearly equivalent, r11 and r21 are significantly different from each other, indicating a possible existence of the penultimate-unit effect in the copolymerization of MMA and AN. Terminal model reactivity ratios, r1 and r2, determined formally from the compositions of three samples by Fineman-Ross method showed large σ values (22—24%).