Studies of thermal oxidative degradation of polypropylene impact copolymer using the temperature rising elution fractionation method

Abstract

Thermal oxidative degradation of polypropylene impact copolymer has been studied with its fractions obtained using the temperature rising elution fractionation method. The fractions were analyzed using 13 C NMR, Fourier transform infrared and differential scanning calorimetry measurements, and the chemical structure, isotacticity, conformation and melting point were investigated. It is found that these fractions are composed of a homopolymer or a polymer blend of polypropylene, polyethylene and ethylene-propylene copolymer. The thermal oxidative degradation of each fraction was carried out at 130 • C, and the degradation progress was estimated by the change of molecular weight distribution (from gel permeation chromatography curves). The rate of degradation is found to be dominated by the content of tertiary C-H bonds (propylene unit) and the existence of 3 1 helix conformation corresponding to a crystalline polypropylene part in each fraction. The latter is more evident leading to the degradation reaction path with a lower activation energy.

Using Crystallisation Fractionation to Monitor Thermo‐Oxidative Degradation of Impact Poly(propylene) Copolymers

“…The FTIR and SEC results indicated a longer induction period and slower increase in carbonyl functionalities, as well as a slower decrease in $\overline {M} _{{\rm w}} $ for copolymer 4V. A longer induction period and slower degradation rates in impact PP copolymers with higher ethylene contents and isotacticity has been reported by a number of authors,20–22 whereas the opposite result was obtained by others 18, 23. The introduction of more stable ethylene units is believed to be the reason for the delayed onset and slower rate of oxidation in ICPP's of higher ethylene contents.…”

Fractionation and Analysis of an Impact Poly(propylene) Copolymer by TREF and SEC‐FTIR

“…Such bimodal molecular weight distributions indicate compositional heterogeneity due to the co‐elution of non‐identical products. This is often observed for the mid‐elution temperature fractions of ICPPs fractionated by TREF14, 26, 27 where semi‐crystalline EPCs and PP homopolymer co‐elute due to the isotacticity distribution found in PP 14, 28. PP homopolymer will not elute entirely at high temperatures, since PP fractions of lower isotacticity will become soluble within the same lower temperature range of the semi‐crystalline EPC phase of corresponding crystallisability.…”

Recent Advances in High-Temperature Fractionation of Polyolefins

“…3D-SEC-TREF is not only useful in understanding microstructure but also in analyzing the composition of polymer blends and final products. Nakatani and coworkers [34] studied the thermo-oxidative degradation of impact polypropylene. They collected eight TREF fractions and studied them by 13 C NMR, FTIR and DSC.…”