13C‐NMR of ABS in the solid state. Characterization and relaxation studies

Abstract

Abstract13C‐NMR spectra of bulk acrylonitrile‐butadiene‐styrene (ABS) resin are reported. The styrene‐co‐acrylonitrile (SAN) carbons can be observed selectively by using high‐power proton decoupling, cross polarization, and magic angle spinning (MAS). The polybutadiene (PBd) carbons can be observed selectively by using low‐power proton decoupling, with or without MAS. Methods and conditions for using 13C‐NMR to quantify the amount of PBd in solid ABS resins are developed. The 13C‐NMR results and results from iodine monochloride titrations for PBd content are in good agreement. Resonances of PBd in ABS in the solid state are assigned on the basis of triad sequences of cis, trans, and vinyl‐1,2 geometric isomers of butadiene. Computational methods are set forth for measuring directly from the 13C‐NMR spectra the percent of cis, trans, and vinyl‐1,2 isomers in PBd in the ABS resin. The NMR measurement of PBd microstructure appears to be preferable to infrared (IR) determinations. Relaxation parameters (T1 and NOE) are reported for PBd in bulk ABS as a function of temperature and are analyzed in terms of a distribution of rotational correlation times. These relaxation parameters are similar to those of nongrafted PBd and indicate that the local motions in grafted and nongrafted PBd are similar.