No abstract

No abstract

No 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.

A study was made to investigate an optimum condition for ruthenium tetraoxide staining of poly(butylene terephthalate) (PBT) with glass transition temperature as low as ca. 23 degrees C for TEM observation of melt-grown PBT crystals. The morphological study of ultrathin sections prepared based on optimum staining at 25 degrees C for 8 h revealed formation of fringed-micellar crystal nuclei in the early stage and folded-chain fringed-micellar crystals in the later stage of isothermal crystallization at 40 degrees C from melt. The fraction of chain-folded crystals increased with increasing crystallization temperature from the quantitative analysis of crystal thickness in comparison with the reported morphology using the replica method.