ESR imaging and FTIR study of thermally treated poly(acrylonitrile-butadiene-styrene) (ABS) containing a hindered amine stabilizer: Effect of polymer morphology, and butadiene and stabilizer content

Abstract

Electron spin resonance imaging (ESRI) was applied to the study of thermal degradation at 393 K of poly(acrylonitrile-butadiene-styrene) (ABS) prepared by emulsion polymerization and containing 25% wt butadiene (ABS-25B). The polymer was doped with 1 or 2% wt Tinuvin 770 as the hindered amine stabilizer (HAS). The spatial distribution of the HAS-derived nitroxide radicals, obtained by 1D ESRI, was initially homogeneous, but became heterogeneous through sample depth with increasing treatment time, t. The spatial variation of ESR line shaping with sample depth was visualized by 2D spectral-spatial ESRI. ESR spectra along the sample depth, obtained by nondestructive (“virtual”) slicing of the 2D images, were used to deduce the relative intensity of nitroxide radicals present in two dynamically distinct sites; the sites were assigned to butadiene-rich (fast component) and SAN-rich domains (slow component), respectively. 1D and 2D ESRI allowed the determination of the extent of degradation within morphologically-distinct domains as a function of sample depth and treatment time. The results from the ESRI experiments were substantiated by attenuated total reflectance (ATR)-FTIR spectroscopy of the outer layer (500 μm thick) of the polymer. Both techniques indicated faster degradation of polymer samples that contained the higher HAS content, 2% wt. Comparison with the results obtained for a parallel study of ABS prepared by mass polymerization and containing 10% wt butadiene (ABS-10B) indicated clearly that the rate of degradation of the polymer prepared by emulsion polymerization (ABS-25B) is significantly reduced. This result can be explained by the formation of cross-linked “composite” networks during emulsion polymerization, which leads to greater thermal stability.