Glass transition temperature amorphous polymers

PVC is an amorphous polymer (glass transition temperature = 220 °F, 105 °C). As a result, it has good clarity. Another important characteristic is that it can be extruded either as a rigid material or as a flexible material by adding a plasticizer to the polymer. Rigid films can be metallized and punched into sequins for dressmaking applications. Flexible films are used to overwrap clothing and other textile products. 

Properties. One of the characteristic properties of the polyphosphazene backbone is high chain dexibility which allows mobility of the chains even at quite low temperatures. Glass-transition temperatures down to —105° C are known with some alkoxy substituents. Symmetrically substituted alkoxy and aryloxy polymers often exhibit melting transitions if the substituents allow packing of the chains, but mixed-substituent polymers are amorphous. Thus the mixed substitution pattern is deUberately used for the synthesis of various phosphazene elastomers. On the other hand, as with many other flexible-chain polymers, glass-transition temperatures above 100°C can be obtained with bulky substituents on the phosphazene backbone. 

A second class of polarizers uses dichroism to produce linearly polarized light. Techniques to produce dichroic polarizing sheets were pioneered by Land [52], These are made by dissolving a strongly dichroic, small molecule into an amorphous, transparent polymer. The dichroic molecules are then oriented by a uniaxial stretching of the polymer matrix. Since this is accomplished below the polymers glass transition temperature, this ori-... 

Figure 3.5. Microhardness H as a function of temperature for four amorphous polymers. Glass transition values are denoted by arrows. (From Ania etal, 1989.)...

For amorphous polymers, the viscosity at a given temperature is a function of the and of the material. For many polymers, the Williams-Landry-Ferry (WLF) equation provides a good estimate of melt viscosity where -qj is melt viscosity, polymer viscosity at 7g, T is the melt temperature, the polymer glass-transition temperature, and b and/ are parameters ... 

EVA (ethylene vinyl acetate) is a copolymer which is available in various compositions of ethylene and vinyl acetate. At a content of 50 vinyl acetate or more the crystallinity has been vanished completely. Give qualitatively the nitrogen permeability at room temperature for a copolymer with 10%, 50% and 90% vinyl acetate respectively and indicate the character of the polymer in terms of rubbery and glassy, crystalline and amorphous (The glass transition temperatures of the pure polymers polyethylene and polyvinyl acetate are given in table II - 5). 

Gwyther, 1. and Manners, 1. (2009) Diblock copolymers with amorphous, high glass transition temperature, organometallic block synthesis, characterisation and self-assembly of polystyiene-i -poly(ferrocenylisopropyl-methylsilane) in the bulk state. Polymer 50, 5384—5389... 

Irregularities such as branch points, comonomer units, and cross-links lead to amorphous polymers. They do not have true melting points but instead have glass transition temperatures at which the rigid and glasslike material becomes a viscous liquid as the temperature is raised. 

Molecular Weight. The values of the mechanical properties of polymers increase as the molecular weight increases. However, beyond some critical molecular weight, often about 100,000 to 200,000 for amorphous polymers, the increase in property values is slight and levels off asymptotically. As an example, the glass-transition temperature of a polymer usually follows the relationship... 

Polycarbonates are an unusual and extremely useful class of polymers. The vast majority of polycarbonates are based on bisphenol A [80-05-7] (BPA) and sold under the trade names Lexan (GE), Makrolon (Bayer), CaUbre (Dow), and Panlite (Idemitsu). BPA polycarbonates [25037-45-0] having glass-transition temperatures in the range of 145—155°C, are widely regarded for optical clarity and exceptional impact resistance and ductiUty at room temperature and below. Other properties, such as modulus, dielectric strength, or tensile strength are comparable to other amorphous thermoplastics at similar temperatures below their respective glass-transition temperatures, T. Whereas below their Ts most amorphous polymers are stiff and britde, polycarbonates retain their ductiUty. 

As-polymerized PVDC does not have a well-defined glass-transition temperature because of its high crystallinity. However, a sample can be melted at 210°C and quenched rapidly to an amorphous state at <—20°C. The amorphous polymer has a glass-transition temperature of — 17°C as shown by dilatometry (70). Glass-transition temperature values of —19 to — 11°C, depending on both method of measurement and sample preparation, have been determined. 

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