Crystallinity factors affecting

If a polymer molecule has a sufficiently regular structure it may be capable of some degree of crystallisation. The factors affecting regularity will be discussed in the next chapter but it may be said that crystallisation is limited to certain linear or slightly branched polymers with a high structural regularity. Well-known examples of crystalline polymers are polyethylene, acetal resins and polytetrafluoroethylene. 

X = alkyl, H, halogen, etc. They are usually colourless, crystalline compounds with mp in the range 0-100° for X = H and 50-200° for X = halogen. Synthetic routes, and factors affecting the stability of the adducts have already been discussed (p. 165 and p. 198). In cases where diborane undergoes unsymmetrical cleavage (e.g. with NH3) alternative routes must be devised ... 

Kerr, G.T. (1955) Chemistry of crystalline aluminosilicates 1. Factors affecting the formation of zeolite A. 

Numerous factors affect various mechanical properties of polymers, including molecular weight, processing, extent and distribution of crystallinity, composition of polymer, and use temperature. 

Selected factors affecting crystallinity regarding Tg and Tm are described in Chapter 2. Here we discuss the influence of crystallinity on the mechanical properties of polymers. For thermoplastics the relation between the degree of crystallinity and the physical nature is shown in Table 5.1. The general lack of difference in physical nature shown by largely crystalline polymers at... 

To evaluate the factors affecting the structural stability of some crystalline materials that are potential hosts for radioactive wastes, the crystal structures of a series of 3+p5 xv5+o compounds, where A is lanthanum or a member of the rare-earth series, were determined. The end-member phosphates (APO4) have the monoclinic Monazite structure (P2 /n) for A La, Ce-Gd, and the tetragonal Zircon structure (l4]/amd) for A Tb - Lu. The corresponding vanadates have the Monazite structure only for LaVO, and the Zircon structure for A = Ce - Lu. When the end members are iso-structural, e.g., LaPO /LaVO, Monazite, YbPC /YbVOA,... 

Polymorphism is the ability of a molecule to take more than one crystalline form depending on its arrangement within the crystal lattice. In lipids, differences in hydrocarbon chain packing and variations in the angle of tilt of the hydrocarbon chain packing differentiate polymorphic forms. The crystallization behavior of TAG, including crystallization rate, crystal size, morphology, and total crystallinity, are affected by polymorphism. The molecular structure of the TAG and several external factors like temperature, pressure, rate of crystalhzation, impurities, and shear rate influence polymorphism (5). 

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. 

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. 

Han, M., Morino, S., and Ichimura, K. Factors affecting in-plane and out-of-plane photoorientation of azobenzene side chains attached to liquid crystalline polymers induced by irradiation with linearly polarized light. Macromolecules 33, 6360 (2000). 

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