Polymer, chemical physics thermal polymerization

Polymeric addition compounds (16) of furan and ethylene, where n is a whole number from 1 to 50, have been prepared (58) by addition of >2 mole furan to 1 mole ethylene at 120 °C to 250 °C and high pressures followed by fractional extraction of the solid product formed. These polymers have interesting physical and chemical properties. They appear to be highly crystalline on analysis by X-ray. As a consequence, the polymers show good thermal stability, which increases directly with molecular weight. The presence of ether bridges makes possible conversion (Scheme 4) to other compounds that retain the double hydrocarbon chain (ladder) structure and may bear various func-... 

It has been reported that silver ion-exchanged zeolites exhibit antibacterial activity [32]. The mechanism of antibacterial action of the zeolite is initiated when moisture or liquid film comes into contact with the ion exchange material and silver ions are exchanged with sodium (Na) or other cations from the environment [33]. The released silver ions attach to the bacteria by forming chelate complexes with deoxyribonucleic acid, which blocks the transport processes in the cell [34]. The use of zeolite as a filler in polymeric materials has been reported in the literature and it has been proved that they enhance the antibacterial activity of the polymer [35]. Furthermore, the effect of zeolite content on the physical and thermal properties of the polymer was also examined [35] increasing the silver/zeolite ratio in the polymer led to an increased antimicrobial activity (due to the higher silver ion concentration), but depending upon the application the zeolite content may influence physical, thermal and/or chemical properties of the polymeric material. 

This transformation process represents the line of demarcation separating the thermosets from the thermoplastic polymers. Crystalline thermoplastic polymers are capable of a degree of crystalline cross-linking but there is little, if any, of the chemical cross-linking that occurs during the thermosetting reaction. The important beneficial factor here lies in the inherent enhancement of thermoset resins in their physical, electrical, thermal, and chemical properties due to that chemical cross-linking polymerization reaction which, in turn, also contributes to their ability to maintain and retain these enhanced properties when exposed to severe environmental conditions. 

The need to develop superior polymeric materials with an excellent combination of chemical, physical, and mechanical properties with ease of processability has triggered research on semifluorinated polymers. Incorporation of fluorine in polymers imparts many interesting properties. Ruorine and perfluoro-alkyl groups in polymers enhance processability and increase thermal stability, reduce water absorption and dielectric constant, and enhance gas permeability. All of these superior properties of perfluorinated polymers result from many unique properties of fluorine. The highest electronegativity of fluorine and the high bond strength and low polarizability of C-F bonds cause many of these properties. 

Polymer Suiface Modifications The growing need of polymeric materials with specific properties for sophisticated applications has led to the development of new polymer surfaces, which can be created by traditional polymerization processes or by the modification of existing surfaces. Surface modification of polymers is used to improve their chemical, physical, mechanical, and tribological properties. Many techniques have been applied to produce the desired surface properties, ranging from thermal treatments, chemical and electrochemical modifications, metallization, and electrical treatments, to plasma treatments and particle beam irradiation techniques. The literature shows that SIMS is a method of choice to characterize the results of such treatments. Hereafter we introduce some examples taken from published studies. 

DTA is a widely used tool for studying and characterizing polymers. Figure 31-7 illustrates the types of physical and chemical changes in polymeric materials that can be studied by differential thermal methods. Note that thermal transitions for a polymer often take place over an extended temperature range because even a pure polymer is a mixture of homologs and not a single chemical species. 

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