Cross-linking of macromolecules

After one-year exposure to low ozone doses, excess ageing of rabbits was observed. Ozone can affect the ageing process due to the dependence of this process on irreversible cross-linking of macromolecules. Lipoperoxidation can also play a role in this process. 

The above analysis shows that wear resistance of pol3miers and copolymers of different molecular structure depends largely on the nature of the triboengineering processes leading to destruction and cross-linking of macromolecules. These processes display, as a rule, a competitive behavior and the structure of the dominating product depends on the pol3Tuer material and its friction characteristics. 

Introduction of Cl into a thermoplastic composition changes the kinetics of its thermal destruction processes. This is expressed in variations of the thermal resistance temperatures (Tt) and destruction initiation (Td) recorded by DTA. Tt and Td for the PE-based compositions shift to the region of lower temperatures by, correspondingly 1-50°C and 5-20°C. The activation energy (Ta) and macromolecular destruction found by DTA also diminish. Compositions based on HOPE show a reduction of Ta from 266 to 100-150kJ/mole, and the more efficient the antioxidizing effect of Cl towards HDPE the lower the Eg,. This is probably because the lower amount of oxide compounds in the polymer volume retards cross-linking of macromolecules and results in reduction. 

Jellinek and co-workers [14, 15] studied the effect of NO on films of linear polyurethane synthesised from tetramethylene glycol and hexamethylene diisocyanate. It was found that the degradation of polyurethanes is accompanied by cross-linking of macromolecules, and that the degree of degradation and yield (weight percentage)... 

This scheme expresses the degradation accompanied by cross-linking of macromolecules, the consumption of NH groups of the polymer, as well as the release of CO upon degradation. 

This synthesis is not accompanied by the destruction or cross-linking of macromolecules. 

Measurements of the concentrations of radical R separately in gel fractions [53] are represented in Table 4.1. The concentrations at late stages of photolysis become invariable, i.e., radicals are localised in the cross-links of macromolecules. The estimations on the basis of ESR spectra [53] show that one cross-link accounts for... 

T> Tg, for irradiation above the melting range, the whole sample exists in the molten (amorphous) state. Cross-linking of macromolecules by irradiation also yields a stabilization of this phase after cooling down to room temperature (i.e., any crystallization is prevented, and no lamellar structures are visible in TEM). 

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