Glass transition temperature basic properties

Summary In this chapter, a discussion of the viscoelastic properties of selected polymeric materials is performed. The basic concepts of viscoelasticity, dealing with the fact that polymers above glass-transition temperature exhibit high entropic elasticity, are described at beginner level. The analysis of stress-strain for some polymeric materials is shortly described. Dielectric and dynamic mechanical behavior of aliphatic, cyclic saturated and aromatic substituted poly(methacrylate)s is well explained. An interesting approach of the relaxational processes is presented under the experience of the authors in these polymeric systems. The viscoelastic behavior of poly(itaconate)s with mono- and disubstitutions and the effect of the substituents and the functional groups is extensively discussed. The behavior of viscoelastic behavior of different poly(thiocarbonate)s is also analyzed. 

The method of additive properties has been applied to density, glass transition temperature, and many other polymer properties by Van Krevelen (2 ). The basic idea is that the properties of each chemical group in the polymer are nearly independent of the other groups. Because of this., each group can be assigned a contribution to the glass transition temperature, for example, and the Tg of a polymer is the sum of the contributions of all the groups. 

In this section, we will first provide a short discussion on some of the basics of the design of photorefractive polymers. Then we will review some of the basic physical properties such as photogeneration and transport in organic amorphous materials needed to develop and understand photorefractive polymers. We will describe the orientational photorefractive effect that is used in most of today s low glass transition temperature materials. Finally we will describe selected examples of photorefractive polymers and describe their optical and electrical properties. 

Physical properties of PHAs are determined by monomer units, which are predominantly responsible for the molecular interactions, the molecular weight, and the molecular weight distribution. In addition, different crystalline modifications and processing conditions have a considerable effect on the achievable property level of the samples. For this reason, only the basic material data are listed and compared the glass transition temperature (7 ), the equilibrium melting temperature of an infinite crystal (T ), the equilibrium heat of fusion (AH ), and the densities of the amorphous (yj and crystalline (yc) parts (Table 1). 

One of the most important bulk property variables of polymers is the glass transition temperature 7g, which must be well below the use temperature to allow the interdiffusion and entanglement of polymer chains when the particles get in contact, once the aqueous phase has been evaporated. Thus, the monomer(s) used have to be selected such that the desired is obtained. Useful tables showing Tg and other physical and chemical properties of homopolymers are available in the literature [66-68]. The well-known Fox equation [69] can be used to estimate the Tg of a copolymer as a function of monomer composition and TgS of the component monomers. It is important to take into account that polar polymers tend to hydroplasticize, reducing the in the film formation process [70]. Several commercial latexes are terpolymers that contain two of the monomers present in major amounts to grossly obtain the basic desired properties, with the third monomer present in a minor amount for fine tuning of a special property [71-73]. 

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