Norbert Reichelt

Course of degradation and build-up reactions in isotactic polypropylene during peroxide decomposition

In the investigation of the course of degradation and build-up reactions during the decomposition of the tert-butyl perbenzoate (TBPB) (at eight different concentrations) in isotactic polypropylene (iPP), it was found that, at the beginning of the peroxide decomposition at all investigated peroxide concentrations from 4.62–200 mmol/kg iPP, the degradation reactions of iPP prevailed. At the TBPB concentration of ≤37.0 mmol/kg iPP during the whole period of peroxide decomposition, degradation reactions leading to a lower of molecular mass of PP prevailed. But at higher peroxide concentrations of TBPB ≥74.4 mmol/kg iPP and at the later stage of peroxide decomposition, a predominance of the build-up reactions, that is, an increase the molecular mass, was observed. The degradation and build-up reactions were determined from the measurements of the melting-flow indexes of the peroxide-treated iPP samples. The reaction mechanism of the degradation and build-up reactions in iPP is discussed.

Modification of unsaturated polyesters by poly(ethylene glycol) end groups

This article reports on the modification of unsaturated polyesters by poly(ethylene glycol) end groups in order to influence the solution behavior in styrene and to modify mechanical properties of the cured resin. The synthesis was done by the reaction of a carboxyl-terminated unsaturated polyester with various poly(ethylene glycol) mono-methyl ethers of molecular weights from 350 to 2000 g/mol. The characterization and curing properties of the synthesized block copolymers are presented. The glass transition temperatures decrease with increasing length of the poly(ethylene glycol) end groups. The introduction of long poly(ethylene glycol) end groups (2000 g/mol) leads to a phase separated and partly crystalline block copolymer with a melting point of 48°C. The block copolymers can be easily diluted in styrene to create the curable resins. The mixtures containing the block copolymers with the short poly(ethylene glycol) end groups (350 and 550 g/mol) could be cured in a reasonably short time. Compared to commercial unsaturated polyesters the mechanical testing revealed that the tensile strength is decreasing while the elongation is increasing.

PARTIAL CROSSLINKING OF THE HETEROPHASIC ETHYLENE-PROPYLENE COPOLYMER IN THE SOLID PHASE

The influence of radical modification with peroxides under solid phase conditions on mechanical properties and the morphology of an heterophasic ethylene-propylene copolymer (HECO) were investigated. The extent of crosslinking and degradation was characterized by the melt flow index and extraction data. Influence of modification on dynamic viscoelasticity of HECO was also investigated. The morphology was studied by the transmission electron microscopy (TEM). Tensil and impact tests were performed on samples of the modified HECO. Crosslinking occurred in the dispersed EPR phase of HECO in the investigated peroxide concentration range. The extent of crosslinking and degradation was dependent on the type of peroxide as a result of the modification in the melt. The modification with higher peroxide concentrations led to the morphology close to the one of the unmodified HECO powder before and also after the extrusion step. The elongation at break of HECO increased at low peroxide concentrations. Improved impact strength at 23°C was attained. Loss of toughness at −20°C was found probably due to slight degradation of PP matrix and due to an inhomogeneous crosslinking of EPR in HECO.