Characterization of n-butyl acrylate centered triads in poly(n-butyl acrylate-co-carbon monoxide-co-ethylene) by isotopic labeling and two dimensional NMR

Abstract

Poly(n-butylacrylate-co-carbon monoxide-co-ethylene) (polyEBC) samples prepared from C-13-labeled monomer, n-butyl acrylate, were characterized using two dimensional (2D) pulsed field gradient (PFG) 750 MHz NMR spectroscopy. To elucidate the complex structure of the terpolymer, 2D-H-1/C-13-heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) experiments were conducted by selectively exciting the enhanced resonances in the spectra of two polymer samples, one polymer resulting from synthesis with 1-C-13-n-butylacrylate monomer and a second polymer obtained from a synthesis with 2-C-13-n-butylacrylate monomer. High-resolution 2D-NMR combined with C-13-labeling of the polymer greatly simplifies the 2D-NMR spectra, selectively enhances the weak peaks from low occurrence B-centered triad structures, and aids in their resonance assignments. In all experiments, the sample temperature was 120degreesC, to ensure a homogeneous solution and sufficient molecular mobility.