Overview poly chain

An overview of the synthesis and characterization of a unique class of polymers with a phosphorus-nitrogen backbone Is presented, with a focus on poly(dichloro-phosphazene) as a common Intermediate for a wide variety of poly(organophosphazenes). Melt and solution polymerization techniques are Illustrated, Including the role of catalysts. The elucidation of chain structure and molecular weight by various dilute solution techniques Is considered. Factors which determine the properties of polymers derived from poly(dichlorophos-phazene) are discussed, with an emphasis on the role that the organic substituent can play In determining the final properties. 

Since the chemical structure and monomer composition of a specific polymer are the most important factors in determining the polymer s physical and material properties, a short recapitulation of typical representatives of microbially synthesized poly(hydroxyalkanoates) is presented in this section. A more detailed overview on this issue is available from References [19-21], but is not within our scope here. The monomer composition of PHAs depends on the nature of the carbon source and the microorganisms used. This way, numerous monomers have been introduced into PH A chains [3-9]. PHAs have been divided roughly into two classes [19]. 

Chemical breakdown usually involves oxidative chain reactions that cause embrittlement of semicrystalline polymers and discoloration of poly(vinyl chloride) and polymers with aromatic groups. The reactions are complicated by the presence of transient intermediates and by rates that depend on minute concentrations of molecular defects, impurities and additives. They also depend on several important piiysi-cal factors outlined in this brief overview of polyolefin degradation, two of these factors, the transfer of excitation energy and the transport of products and protectants, play a major role in stabilization processes. 

This section is concerned with polymers derived from open-chain phosphazenes, phospha(thia)zenes and related cross-linked materials. Cyclolinear and cyclomatrix materials as well as carbon-chain polymers with cyclophasphazene substituents are covered in Section 3. General and specific reviews have appeared including an overview of recent development in inorganic polymers including poly(phosphazenes), a comprehensive survey of hybrid siloxane-phosphazene systems, water-soluble phosphazenes and related hydrogels, a brief survey of polymerization reactions and mechanisms, and sulfur containing poly(phosphazenes). ... 

The discussion above has laid out the general principles of polymer chain fragmentation as derived from TOF-SIMS studies, and presented two important, illustrative examples polystyrenes and acrylics. The present section will deal with studies of other polymer systems, in less detail, to provide an overview of other systems that have been studied. Specifically, nylons, polyesters, and poly(dimethyl siloxanes) will be considered. In addition, polyesters will... 

For polymers, anisotropic friction 10) was observed on lamellar crystals II -13 as well as on extended-chain crystals obtained by friction transfer deposition 14). The anisotropic friction for lamellar crystals was explained by the occurrence of chain-folding oriented preferentially in planes parallel to the corresponding crystal face. For extended-chain crystals friction anisotropy observed parallel and perpendicular to the chain direction was interpreted by the interlocking asperity model. In this paper we give an overview regarding our nanotribological observations on oriented high density polyethylene (HDPE), poly(tetrafluoroethylene) (PTFE) and on crystals of polyethylene (PE) and transcrystallized poly(ethylene oxide) (PEO). 

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