Crystalline polymers basic principles

Order and Mobility are two basic principles of mother nature. The two extremes are realized in the perfect order of crystals with their lack of mobility and in the high mobility of liquids and their lack of order. Both properties are combined in liquid crystalline phases based on the selforganization of formanisotropic molecules. Their importance became more and more visible during the last years in Material science they are a basis of new materials, in Life science they are important for many structure associated functions of biological systems. The main contribution of Polymer science to thermotropic and lyotropic liquid crystals as well as to biomembrane models consists in the fact that macromolecules can stabilize organized systems and at the same time retain mobility. The synthesis, structure, properties and phototunctionalization of polymeric amphiphiles in monolayers and multilayers will be discussed. 

For many polymers, crystal growth can take place either from the melt or from dilute solution to yield single crystals. Crystal formations in polymers were studied intensively almost from the time of recognition of their existence in macromolecules. As a result, certain basic principles were established (1) The melt crystallization process is a first-order phase transition (see Section 1.4.5). (2) Crystallization from a molten polymer follows the general mathematical formulation for the kinetics of a phase change.Equilibrium conditions, however, are seldom if ever attained and complete crystallinity is not reached. 

This book covers a wide range of topics and addresses different disciplines in the field. The chapters are arranged as a learning scheme for the professional, from basic science to applied engineering. The first few chapters summarize the syntheses of various polyester, polyester-amide, and polyimide liquid crystalline polymers. The science and origins of liquid crystal formation are revealed. Next, we introduce the characterizations of these materials by their different chemical and physical aspects. To help the reader, the principles of material characterizations are also discussed. 

High-resolution NMR in the solid state of matter has been developed fairly recently. Since this technique can detect the local structure of molecules via chemical shift and magnetic relaxation, it has been possible to obtain detailed information on chain conformation as well as chain dynamics of macromolecules not only in the crystalline state but also in the non-crystalline, glassy or rubbery state. This chapter gives a brief description of the basic principles of solid-state high-resolution NMR as well as its recent application to crystalline polymers. 

The basic thermodynamic, kinetic, and structural principles which govern the crystallization behavior of polymers have been developed so far. These principles can now be applied to give an understanding of the properties of semicrystalline polymers. There is a continuing interest in understanding the properties of crystalline polymers in terms of structure. Because of the non-equilibrium character of the... 

Abstract This chapter describes polymers that undergo a temperature-induced phase transition in aqueous solution providing an important basis for smart materials. Different types of temperature-responsive polymers, including shape-memory materials, hquid crystalline materials and responsive polymer solutions are briefly introduced. Subsequently this chapter will focus on thermoresponsive polymer solutions. At first, the basic principles of the upper and lower critical temperature polymer phase transitions will be discussed, followed by an overview and discussion of important aspects of various key types of such temperature-responsive polymers. Finally, selected potential apphcations of thermoresponsive polymer solutions will be described. 

Crystallization analysis fractionation (CRYSTAF) provides the same information as TREF but is much faster, as it uses only the dissolution process to accomplish the separation. The basic principle is that material with a low-level of crystallinity dissolves in a solvent at a lower temperature than material with a higher level. It also avoids the use of a column and thus the peak broadening that occurs there and requires no support. However, CRYSTAF involves very small quantities of material and is therefore not useful as a preparative technique. The sample is placed in a small sample vial equipped with a stirrer and a sampling line with a filter that prevents crystals from leaving. The vial is placed in an oven whose temperature is gradually increased. Samples are collected at small temperature intervals by nitrogen pressurization, and the polymer concentration is detected by an IR sensor. A cumulative curve of polymer concentration versus temperature of crystallization is obtained. Taking the derivative, a TREF-type curve can be obtained, and for conversion to CCD the calibration procedure is the same as in TREF. 

The conformation assumed by polymer chains in the crystalline state depends on the configuration of the stereoisomeric centers present along the chains, and is defined by two basic principles [1,2,23-25]. 

Recently, new interesting phenomena that control the mode of packing of polymers have been found, and it has been shown that the basic principles of polymer crystallography are, in some cases, violated. In particular, (1) an atactic polymer can crystallize this is, for instance, the case of polyacrylonitrile [107] (2) in a crystalline polymer the chains can be nonparallel for instance, the structure of the yform of iPP is characterized by the packing of nearly perpendicular chains [108, 109] (3) the principle of entropy-driven phase formation may be violated and the high local symmetry of the chains is lost in the limit-ordered crystkhne lattice of polymers (symmetry breaking). 

Volume 1 is devoted to fundamental principles of polymer blends and is divided into eight chapters. These chapters cover the basic thermodynamic principles defining the miscible, immiscible, or compatible nature of amorphous, semi-crystal-hne and Uquid crystalline polymer blends, and temperature and composition dependent phase separation in polymer blends. They are detailed below and build upon each other. 

Typical materials that exhibit liquid crystalline behaviour are made up of long, thin molecules. Hence in principle polymers ought to show the basic requirement for liquid crystal behaviour. Conventional polymers, however, are too flexible and tend to adopt random coil configurations in the melt. They are thus not sufficiently anisotropic to exhibit a mesophase. 

Starting from an analysis of the conformation of a polymer chain in the liquid (amorphous) and crystalline (ordered) states, it has been possible to develop the basic thermodynamic, kinetic, and stmctural principles that govern the crystallization... 

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