Crystal structures, polymers crystalline phase

In the section on structure and fundamental properties of SPS, Chapter 9 summarizes the polymorphic behavior of this polymer, the structure of the different forms, and the crystallization and melting behavior. Chapter 10 describes co-crystals and nanoporous crystalline phases of SPS regarding preparation, structure, properties, and new interesting applications, for example, molecular sensors. The section concludes with Chapter 11 on selected topics of crystallization thermodynamics and kinetics of SPS. 

The compatibilization largely affects the phase morphology of the blends and the interfacial properties, thus it may significantly influence the crystallization behavior of the polymer components and the structure of crystalline phases. In the next paragraphs some examples of blends compatibilized by means of different methods will be presented, with focus on the morphological aspects, phase interaction phenomena, and crystallization behavior. 

This effect of M can be explained as being due to the crystalline phase in the o semi-crystalline polymer. The presence of this crystalline phase reduces the molecular mobility. The crystalline structure is not something static, but it is perfected on annealing. The longer the reaction at a high temperature, the more perfect the crystalline phase, and the more the molecular mobility is restricted. After melting this starts all over again and the lower the M the faster is this crystallization process, o... 

Classical X-ray diffraction and scattering is carried out in the subarea of wide-angle X-ray scattering (WAXS). The corresponding scattering patterns yield information on the arrangement of polymer-chain segments (e.g., orientation of the amorphous phase, crystalline structure, size of crystals, crystal distortions, WAXS crystallinity). 

In addition to the crystal forms, X-ray scattering studies indicate that when unoriented PEN fiber was drawn at 120 °C ( 7 g), a mesophase is generated. In this form, the molecular chains are in registry with each other in the meridional direction but not fully crystallized in the equatorial direction. This conclusion was based on the presence of additional meridional peaks not accounted for by the crystal structure obtained by X-ray scattering. The mesophase is a intermediate phase and its existence is strongly dependent upon the processing conditions consequently, it could have implications with respect to the properties of commercially produced fibers and films, since it appears to be stable and not easily converted to the crystalline form, even at elevated temperature [25, 26], The mesophase structures of PET, PEN and poly(ethylene naphthalate bibenzoate) were compared by Carr et al. [27], The phase behavior of PEN and PEN blends with other polymers has also been studied [28-32],... 

As a consequence of this almost perfect alignment of molecule structures, such polyamides are able to orientate in solution and to form liquid crystalline phases (see Sect. 1.3.4). Out of these solutions one obtains fibers of poly(p-phenylene terephthalamide) (PPTA) having 5-10-fold higher values for stiffness and strength as the all-mefa linked polymers. In addition, PPTA crystallizes, whereupon the fibers achieve an extraordinary temperature resistance in a nitrogen atmosphere they decompose at temperatures above 550 °C without melting. 

Liquid Crystalline Polymers. One class of polymers that requires some special attention from a structural standpoint is liquid crystalline polymers, or LCPs. Liquid crystalline polymers are nonisotropic materials that are composed of long molecules parallel to each other in large clusters and that have properties intermediate between those of crystalline solids and liquids. Because they are neither completely liquids nor solids, LCPs are called mesophase (intermediate phase) materials. These mesophase materials have liquid-like properties, so that they can flow but under certain conditions, they also have long-range order and crystal structures. Because they are liquid-like, LCPs have a translational degree of freedom that most solid crystals we have described so far do not have. That is, crystals have three-dimensional order, whereas LCPs have only one- or two-dimensional order. Nevertheless, they are called crystals, and we shall treat them as such in this section. 

In semi-crystalline polymers the interaction of the matrix and the tiller changes both the structure and the crystallinity of the interphase. The changes induced by the interaction in bulk properties are reflected by increased nucleation or by the formation of a transcrystalline layer on the surface of anisotropic particles [48]. The structure of the interphase, however, differs drastically from that of the matrix polymer [49,50]. Because of the preferred adsorption of large molecules, the dimensions of crystalline units can change, and usually decrease. Preferential adsorption of large molecules has also been proved by GPC measurements after separation of adsorbed and non-attached molecules of the matrix [49,50]. Decreased mobility of the chains affects also the kinetics of crystallization. Kinetic hindrance leads to the development of small, imperfect crystallites, forming a crystalline phase of low heat of fusion [51]. 

The second group involves polymers with three-dimensional ordering of side branches (e.g., those forming Mj-phaseXTable 5). On X-ray patterns of these polymers 3-4 narrow reflexes at wide angles are observed. As a rule, the authors define this type of structure as crystalline, or ascribe a smectic type of structure, characteristic for ordered smectics in SE or SH phases. The heats of transition from anisotropic state to isotropic melt are usually small and do not exceed the heats of transition smectic liquid crystal — isotropic melt . The similarity of structural parameters of three-dimensionally ordered smectics and that of crystalline polymers of the type here considered, make their correct identification quite a difficult task. 

The potential for novel phase behaviour in rod-coil block copolymers is illustrated by the recent work of Thomas and co-workers on poly(hexyl iso-cyanate)(PHIC)-PS rod-coil diblock copolymers (Chen etal. 1996). PHIC, which adopts a helical conformation in the solid state, has a long persistence length (50-60 A) (Bur and Fetters 1976) and can form lyotropic liquid crystal phases in solution (Aharoni 1980). The polymer studied by Thomas and co-workers has a short PS block attached to a long PHIC block. A number of morphologies were reported—wavy lamellar, zigzag and arrowhead structures—where the rod block is tilted with respect to the layers, and there are different alternations of tilt between domains (Chen et al. 1996) (Fig. 2.37). These structures are analogous to tilted smectic thermotropic liquid crystalline phases (Chen et al. 1996). 

---