Structure of Crystalline Polymers

In contrast, in 1966, Colson and Eby assumed that the comonomer B could enter the crystalline phase of A, with the mole fraction Xg, and caused a lattice defect energy AHb (Colson and Eby 1966). They derived that 

Equation (10.19) fits well for the experimental results on the parallel system of copolymers with small comonomer units. 

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Thermal Properties. A typical dsc thermogram of an HPL/PVA blend (Fig. 4) shows a single Tg and Tm (10). Differences in the shape of the melting endotherms of PVA(96), (88), and (75) can be attributed to different degrees of crystallinity in the three polymers. Changes in crystalline structure of polymer blends usually result from polymer-polymer interactions in the amorphous phase. Such interactions result in a reduction of crystallinity, thereby reducing the enthalphy of the phase change (16,17). The observed reductions in melt endotherm area of HPL blends with PVA (> 0) may therefore indicate the existence of polymer-polymer interactions between the two types of macromolecules. 

As well known, the crystalline structure of polymers is generally characterized by a comparatively high proportion of defects compared with the case of low molecular weight substances these defects may be due either to chemical faults or may be simply attributed to the mechanism of crystallization. As a consequence, this means that most polymers can contain a small proportion of extraneous units in the crystal state. However, we will not consider as real cases of macromolecular isomorphism those having a concentration of either component below 5%. 

The crystalline structure of polymer composites depends strongly on their thermal history and their manufacturing process. To assess their crystal structure and degree of crystallinity, wide angle X-ray diffraction (WAXS) experiments are frequently performed. Figure 10.11 shows the room temperature diffraction patterns of different PEEK/... 

Based on the definition of plasticization the elongation should increase with increase in the plasticizer concentration. On the other hand, plasticizers are frequently capable of dissolving crystalline structures of polymers or separate elements of physical crosslinking, therefore excess of plasticizer may affect network and cause decrease in elongatiorr Figure 10.9 shows that gains in elongation may be substantial." ... 

Crystalline Structures of Polymers 10.3.1 Hierarchical Crystalline Structures... 

In this section, our recent investigation of LPE by solid-state NMR has been briefly reviewed. Through these studies solid-state NMR has been found to be very useful to studying the crystalline structure of polymers. Although we have been concerned only with LPE of very simple chemical structure, by use of different magnetic relaxation phenomena the developed spectroscopic technique will be applicable to other polymers of complex chemical structure. 

While much has been learned about the crystalline structure of polymers, the exact shape and structure of crystalline regions is still under intense study as increasing the degree of crystallinity leads to improved thermo-mechanical properties (Table 4.4). Relations between crystalline structure and mechanical response will be discussed in more detail later. The first interpretation of crystalline structure was suggested by x-ray diffraction studies and is known as the fringed micelle model . The Bragg... 

It is an X-ray diffraction technique that is often used to determine the crystalline structure of polymers. This technique specifically refers to the analysis of Bragg Peaks scattered to wide angles, which (by Bragg s law) imphes that they are caused... 

MODELS FOR THE CRYSTALLINE STRUCTURE OF POLYMERS 4.6.1 Fringed Micelle Model... 

The crystalline structures of polymers, CNCs and nanocomposites can be analyzed by X-ray diffrac-tograms, and from these graphics it is possible to determine the crystallinity index (X ). The most common method used to determine this valne is by the nse of Equation (13.1) defined by Segal et al. [101] ... 

The semi-crystalline structure of polymers is characterized by special features. Firstly, the crystallites are embedded in an amorphous matrix, resulting in a two-phase morphology. Secondly, most polymers form folded-chain crystals in which the chains fold back into the same crystallite. Thirdly, several crystallites stack up and form superstructures known as sphemlites [8], Fig. 1.2. Finally, chains wander from one crystallite to the next one, thereby connecting them to each other. The chain segment between two adjacent crystals is known as tie-molecule [9], Tie-molecules act as stress-transmitters [10-12]. Thus they play an important role in mechanical properties of semi-crystalline polymers. 

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