Quantitative NMR Spectroscopy and Determination of Polymer Microstructure of Ethylene‐Styrene and Ethylene‐Isobutylene Co‐Polymers

Abstract

AbstractSummary: Quantitative 13C NMR spectroscopy is used to determine reactivity ratios and end group and branching frequency of ethylene‐styrene and ethylene‐isobutylene co‐polymers synthesized at a temperature T = 205 °C and pressure p = 1650 bar at different levels of co‐monomer fraction. In the forefront of the studies quantitative 13C NMR conditions have to be investigated. Optimum conditions are achieved using a relaxation agent Chromium(III) acetylacetonate (Cr(acac)3) at measurement temperature T = 100 °C and a delay time d1 = 7 s with a 90° pulse and inverse‐gated decoupling. The analysis of conversion dependence of co‐monomer content shows an increase in conversion with increasing co‐monomer content for the ethylene‐styrene co‐polymerization, whereas conversion decreases with rising isobutene fraction in the co‐polymer. Reactivity ratios for ethylene‐styrene as well as for ethylene‐isobutylene co‐polymerization system are determined with values rES = 0.09 ± 0.007 and rSE = 2.3 ± 7.0 and rEIB = 3.3 ± 0.6 and rIBE = 6.3 ± 4.2. Frequency on methyl end groups, end‐of‐chain contributions caused by transfer to propionic aldehyde and butyl branches are gained. For the ethylene‐styrene co‐polymer system a decrease in frequency is observed, whereas for the ethylene‐isobutylene co‐polymer system the opposite occurs. Influence of the co‐monomers on the polymerization reaction steps as transfer to chain transfer agent and backbiting reaction is discussed.