Thermally degradable block copolymers

The thermostability of siloxane-silazane copolymers of both random and block structure is found to be much higher (i.e. 100-200°C) with respect to polysiloxanes. This effect is brought about by introducing only a few silazane entities into the polymer chain. The reasons for the effect are not clear and the mechanism of thermal degradation of polysilazoxanes will require further experimental studies. 

In a series of publications Berlin et al. 87-90) describe block copolymers with poly-azophenylene units which are extremely stable with respect to both thermal and oxidative degradation. From an emulsion polymerization of isoprene initiated by the... 

Macromolecular structures such as star copolymers have been synthesized in the search for polymers with new mechanical and thermal properties and new degradation profiles. Fig. 7 shows a schematic representation of four-armed homo- and block copolymers. 

The copolymerization of ethylene and chlorotrifluoroethylene is performed as a free radical suspension process in aqueous media at low temperatures. Lowering the temperature reduces the number of ethylene blocks in the polymer backbone that are susceptible to thermal degradation. A commercial polymer with an overall CTEE-to-ethylene ratio of 1 1 contains ethylene blocks and CTFE blocks in the proportion lower than 10 mol% each [85], Reaction pressure is adjusted to give the desired copolymer ratio [86]. Typical pressures during the process are on the order of 3.5 MPa... 

However, the question whether the mesostructure obtained after heat treatment is a hexagonal or a lamellar one remains unclear. Si and CP-MAS NMR studies have been performed to investigate the thermal degradation of the block copolymer within the mesostmctured silica upon heat treatment in air at different temperatures ranging from 20 to 600 °C. The NMR spectrum... 

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