Poly preventing crystallization

The amorphous polyesters are becoming increasingly important for one-component 100% solid moisture-curing adhesives. These materials are usually viscous, amorphous liquids. Poly(2-methylpropane adipate), an example of an amorphous polyester, is a liquid even at a molecular weight of 2000. The amorphous polyesters are usually asymmetrical in structure. In the poly(2-methylpropane adipate) example, the pendant methyl group would be expected to interfere with chain packing, thereby preventing crystallization [27]. 

The two structures appear very similar. Poly( 1,2-propylene adipate) has the same basic structure as poly(ethylene adipate), except for a pendant methyl group. This pendant methyl group on the poly( 1,2-propylene adipate) makes a large difference, however. Poly( 1,2-propylene adipate) has no crystalline melting point. Trappe theorizes that the pendant methyl prevents chain packing and therefore, prevents crystallization [42]. 

Poly(vinylidene chloride) latices can be easily prepared by the same methods but have few uses because they do not form films. Copolymers of high VDC content are film-forming when freshly prepared but soon crystallize and lose this desirable characteristic. Because crystallinity in the final product is very often desirable, eg, in barrier coatings, a significant developmental problem has been to prevent crystallization in the latex during storage and to induce rapid... 

Pijpers et al. (2002) have shown the utility of using fast scan rates to prevent crystallization of poly(ethylene terephthalate) (PET). In Fig. 2.85 during cooling at 100°C/min, no crystallization occurs, only vitrification. On reheating PET at 10°C/min, devitrification is observed, followed by extensive cold crystallization near 150 C. This is followed by melting at 23(>-260°C. However, on the first heating of PET at lOO C/min, cold crystallization is nearly eliminated and the subsequent melting is quite small. 

Silver [7440-22-4]—The coloi additive silvei (EEC No. E 174) is a crystaUine powdei of high purity silver prepared by die reaction of silver nitrate with ferrous sulfate in the presence of nitric, phosphoric, and sulfuric acids. Poly(vinyl alcohol) is used to prevent the agglomeration of crystals and the formation of amorphous silver. 

Stretch-oriented poly(vinyl alcohol) films which contain iodine are essential light polarizing components in today s liquid crystal displays (LCDs). They do, however, suffer from the inherent diffusion and sublimation problems of iodine and its chemical aggressiveness. The latter also prevents realization of new LCD... 

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