Glass factors affecting

The size of the group attached to the main chain carbon atom can influence the glass transition point. For example, in polytetrafluoroethylene, which differs from polyethylene in having fluorine instead of hydrogen atoms attached to the backbone, the size of the fluorine atoms requires the molecule to take up a twisted zigzag configuration with the fluorine atoms packed tightly around the chain. In this case steric factors affect the inherent flexibility of the chain. 

Chemical structure factors affect the melting point and glass transition temperature in much the same manner. A good empirical rale for many polymers is (142-144)... 

Que Hee, S.S., Sutherland, R.G., McKinlay, K.S., and Sara, J.G. Factors affecting the volatility of DDT, dieldrin, and dimethylamine salt of (2,4-dichlorophenoxy)acetic acid (2,4-D) from leaf and glass surfaces. Bull Environ. Contam. Toxicol, 13(3) 284-290, 1975. 

B. S. Chang, R. M. Beauvais, A. Dong, and J. F. Carpenter, Physical factors affecting the storage stability of freeze-dried interleukin-1 receptor antagonist glass transition and protein conformation. Arch. Biochem. Biophys. 557 249-258 (1996). 

Most of the earlier studies on the immobilization of enzymes were directed towards the attachment of the enzymes to water-insoluble polymeric supports such as cellulose dextran derivatives, polyacrylamide and porous glass Diffusion problems and steric hindrance are two main factors affecting the application of such supports. The introduction of soluble polymers for immobilization purposes overcomes these difficulties to a greater extent. These soluble enzyme derivatives were synthesized in order to increase the effective molecular size of parent en mes this would rmit the use of ultrafiltration without any los of the enzyme. O NeiD etal. immobilized the enzyme chymotrypsin on soluble dextran for... 

Factors Affecting the Glass Transition of Polymers Problem Sets... 

In this chapter we study the characteristics that determine the crystallinity of polymers, crystalline morphology, and the factors affecting the crystallization and melting of polymers. We describe the amorphous state, focusing on the glass transition, a fundamental property for defining the mechanical behavior of polymers. The entire description refers exclusively to synthetic polymers. 

The influence of factors such as chemical structure, molecular weight, cross-linking and plasticizers in the glass transition of polymers can be related to the changes that they provoke on the free volume fraction, which, as we already know, reaches a critical value at the glass transition temperature. The factors affecting the glass transition can be classified into two types (1) molecular factors, i.e., those related to the chemical structure of the polymer chain, and (2) external or controllable factors. 

We have approached the subject in such a way that the book will meet the requirements of the beginner in the study of viscoelastic properties of polymers as well as those of the experienced worker in other type of materials. With this in mind. Chapters 1 and 2 are introductory and discuss aspects related to chemical diversity, topology, molecular heterodispersity, and states of aggregation of polymers (glassy, crystalline, and rubbery states) to familiarize those who are not acquainted with polymers with molecular parameters that condition the marked viscoelastic behavior of these materials. Chapters 1 and 2 also discuss melting processes and glass transition, and factors affecting them. 

The line-widths of e.s.r. absorptions in solution may be as narrow as a few milligauss (Hausser, 1964) in this respect, solution studies have a considerable advantage over studies in viscous media or glasses, where lines are broadened by anisotropic interactions. Carrington (1963) has discussed some of the factors affecting line-shape and width in solution. 

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