Poly crack formation

It is obvious from Fig. 12 that crack formation does not start at emergent imperfections which has been confirmed by transmission electron microscopy (see Sect. IV.b.)59. The scanning electron micrographs of poly-DSP and poly-P2VB44) crystals are quite different. The difference may be reflected by a crystal volume change during polymerization in which the DSP crystals shrink while the P2VB crystals expand. 

Figure 5.307 shows that the stress-cracking resistance of polycarbonate compared to poly-a-oleflns (PAO) depends strongly on the viscosity of the poly-a-olefins. The higher the PAO viscosity, the lower is the tendency to stress-crack formation. 

Acidic chloroaluminate ionic liquids are excellent media for polymer cracking reactions. With the huge quantities of polymers that need to be disposed of each year the ability to break them down into useful compounds for new synthesis or to use as liquid fuels is extremely important. While certain polymers such as poly(methyl methacrylate) are easily cracked into their constituent monomers that can be reused, the majority of polymers are extremely difficult to crack into useful organic compounds. However, merely dissolving polyethylene in acidic chloroaluminate ionic liquids containing a proton source results in the formation of a mixture of alkenes and cyclic alkenes [48], The key compounds produced are shown in Figure 10.10. 

The conventional fabrication process for poly(tetrafluoro-p-xylylene) (Par-ylene F) is difficult, involving many process steps, and is more expensive than that for Parylene N. Typically, this process first involves the formation of a dimer, l,l,2,2,9,9,10,10-octafluoro[2.2]paracyclophane. The dimers are cracked at 720-730°C to get the monomer TFPX. 

The thermooxidative degradation and SiOx film formation of poly(vinyl imidazole-co-vinyl trimethoxysilane) on copper was investigated. Thermal degradation of the copolymer was catalysed by copper in the film and at the substrate surface. Copper in the copolymer film contributed to the formation of a copper-containing SiOx film during thermal degradation. Copper oxides in the film interacted with the SiOx film to form a copper-rich phase near the film defects and cracks (142). 

Siripurapu et al. [60] studied the continuous foaming of highly crystalHne poly (vinyUdene fluoride) (PVDF) at 175 °C with 2 wt% of SCCO2, which resulted in a foam structure with a heterogeneous cell size distribution and a low cell density, attributed to the low solubility of CO2 in the polymer and therefore tittle CO2 available for bubble formation. A further restriction is the semi-crystaUine structure of PVDE. As the temperature falls below the crystallization occurs, which expels CO2 into the amorphous domains and may lead to cracking of the cell walls and therefore formation of discrete particles. Improvements in the foam characteris-... 

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