Poly , inherent

Another type of synthetic polymer-based chiral stationary phase is formed when chiral catalyst are used to initiate the polymerisation. In the case of poly(methyl methacrylate) polymers, introduced by Okamoto, the chiraUty of the polymer arises from the heUcity of the polymer and not from any inherent chirahty of the individual monomeric subunits (109). Columns of this type (eg, Chiralpak OT) are available from Chiral Technologies, Inc., or J. T. Baker Inc. 

The many commercially attractive properties of acetal resins are due in large part to the inherent high crystallinity of the base polymers. Values reported for percentage crystallinity (x ray, density) range from 60 to 77%. The lower values are typical of copolymer. Poly oxymethylene most commonly crystallizes in a hexagonal unit cell (9) with the polymer chains in a 9/5 helix (10,11). An orthorhombic unit cell has also been reported (9). The oxyethylene units in copolymers of trioxane and ethylene oxide can be incorporated in the crystal lattice (12). The nominal value of the melting point of homopolymer is 175°C, that of the copolymer is 165°C. Other thermal properties, which depend substantially on the crystallization or melting of the polymer, are Hsted in Table 1. See also reference 13. 

In addition to carbon and glass fibers ia composites, aramid and polyimide fibers are also used ia conjunction with epoxy resias. Safety requirements by the U.S. Federal Aeronautics Administration (FAA) have led to the development of flame- and heat-resistant seals and stmctural components ia civiUan aircraft cabias. Wool blend fabrics containing aramids, poly(phenylene sulfide), EDF, and other inherently flame-resistant fibers and fabrics containing only these highly heat- and flame-resistant fibers are the types most frequently used ia these appHcations. 

Poly(vinyl chloride). PVC is one of the most important and versatile commodity polymers (Table 4). It is inherently flame retardant and chemically resistant and has found numerous and varied appHcations, principally because of its low price and capacity for being modified. Without modification, processibiUty, heat stabiUty, impact strength, and appearance all are poor. Thermal stabilizers, lubricants, plasticizers, impact modifiers, and other additives transform PVC into a very versatile polymer (257,258). 

Other typical pyrotechnic fuels include charcoal, sulfur, boron, siUcon, and synthetic polymers such as poly(vinyl alcohol) and poly(vinyl chloride). Extensive use has been made of natural products such as starches and gums, and the use of these materials continues to be substantial in the fireworks industry. MiUtary pyrotechnics have moved away from the use of natural products due to the inherent variabiUty in these materials depending on climatic conditions during the growth of the plants from which the compounds are derived. 

Plasticizers. Plasticizers are materials that soften and flexibilize inherently rigid, and even britde polymers. Organic esters are widely used as plasticizers in polymers (97,98). These esters include the benzoats, phthalates, terephthalates, and trimeUitates, and aUphatic dibasic acid esters. Eor example, triethylene glycol bis(2-ethylbutyrate) [95-08-9] is a plasticizer for poly(vinyl butyral) [63148-65-2] which is used in laminated safety glass (see Vinyl POLYMERS, poly(vinyl acetals)). Di(2-ethyUiexyl)phthalate [117-81-7] (DOP) is a preeminent plasticizer. Variation of acid and/or alcohol component(s) modifies the efficacy of the resultant ester as a plasticizer. In phthalate plasticizers, molecular sizes of the alcohol moiety can be varied from methyl to tridecyl to control permanence, compatibiUty, and efficiency branched (eg, 2-ethylhexyl, isodecyl) for rapid absorption and fusion linear (C6—Cll) for low temperature flexibiUty and low volatility and aromatic (benzyl) for solvating. Terephthalates are recognized for their migration resistance, and trimeUitates for their low volatility in plasticizer appHcations. 

As previously mentioned, some urethanes can biodegrade easily by hydrolysis, while others are very resistant to hydrolysis. The purpose of this section is to provide some guidelines to aid the scientist in designing the desired hydrolytic stability of the urethane adhesive. For hydrolysis of a urethane to occur, water must diffuse into the bulk polymer, followed by hydrolysis of the weak link within the urethane adhesive. The two most common sites of attack are the urethane soft segment (polyol) and/or the urethane linkages. Urethanes made from PPG polyols, PTMEG, and poly(butadiene) polyols all have a backbone inherently resistant to hydrolysis. They are usually the first choice for adhesives that will be exposed to moisture. Polyester polyols and polycarbonates may be prone to hydrolytic attack, but this problem can be controlled to some degree by the proper choice of polyol. 

As reported in Table 5 and in other recent publications [399,491 ], polymers with very low Tg are expected when the inherent skeletal flexibihty of poly-phosphazenes is coupled with fluorinated alcohols of low dimensions and/or of high chain mobility. In fact, the Tg values for POPs substituted with fluorinated alcohols vary between -50 °C and -90 °C, confirming the extreme chain mobility of these polymers and the existence in them of very low torsional energy barriers. 

Even though poly(ortho esters) contain hydrolytically labile Linkages, they are highly hydrophobic materiads and for this reason are very stable and can be stored without careful exclusion of moisture. However, the ortho ester linkage in the polymer is inherently thermally unstable and at elevated temperatures is believed to dissociate into an alcohol and a ketene acetal (33). A possible mechanism for the thermal degradation is shown below. This thermal degradation is similar to that observed with polyurethanes (34). 

The thermal properties of tyrosine-derived poly(iminocarbonates) were also investigated. Based on analysis by DSC and thermogravi-metric analysis, all poly(iminocarbonates) decompose between 140 and 220 C. The thermal decomposition is due to the inherent instability of the iminocarbonate bond above 150°C and is not related to the presence of tyrosine derivatives in the polymer backbone. The molecular structure of the monomer has no significant influence on the degradation temperature as indicated by the fact that poly(BPA.-iminocarbonate) also decomposed at about 170 C, while the structurally analogous poly(BPA-carbonate) is thermally stable up to 350 C. 

From the characteristics of the methods, it would appear that FD-MS can profitably be applied to poly-mer/additive dissolutions (without precipitation of the polymer or separation of the additive components). The FD approach was considered to be too difficult and fraught with inherent complications to be of routine use in the characterisation of anionic surfactants. The technique does, however, have a niche application in the area of nonpolar compound classes such as hydrocarbons and lubricants, compounds which are difficult to study using other mass-spectrometry ionisation techniques. 

Inherent Viscosities of Poly(Methyl Vinylsalicylates) Polymer inh... 

Similar studies have been conducted on poly(vinyl chloride) (PVC) to assign different IR signatures obtained from different stereo-configurational isomers. The sensitivity of the vC-Cl bond on the stereochemical environment has been utilized using IR spectroscopy. The characteristic vibrations of the vC-Cl bonds are inherently tied in to the configuration as well as the conformation of the... 

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