Dispersion mechanisms amorphous polymers

There is little information on the mechanism or kinetics of formation of the amorphous polymer produced concurrently with the crystalline polymer. In general, polymerization rates and molecular weights are lower, but there is no clear relationship between rate of formation of amorphous polymer and catalyst composition. Catalysts from TiCl4, VOCI3 or VCI4 which tend to produce colloidally dispersed or appreciably soluble catalysts give higher amounts of amorphous polymer and in some instances little or no crystalline material is produced. There is a tendency with most catalysts for the amount of amorphous polymer to increase with increase in metal—alkyl concentration. 

Some recent examples demonstrating the molecular dispersion of rod polymer molecules in coil polymer matrices due to ionic interactions were given by Parker et al. (1996). These systems were based on three types of ionic PPTA s (Figure 5.4) and polar polymers, such as poly(4-vinylpyridine) (PVP), poly(vinyl chloride) (PVC), poly(ethylene oxide) (PEO), and poly(styrene-co-acrylonitrile) (S-AN). Due to the ionic-dipole interactions the rod-coil polymer pairs formed molecular composites as revealed by optical clarity, polarized microscopy, Tg measurements, as well as TEM observations. More significantly the molecular composites based on amorphous matrix polymers (e.g., PVP) were all transparent and showed no phase separation upon heating. Therefore they are melt-processible. As would expected, the mechanical properties of the molecular composites were... 

Previous studies on nanocomposites made with highly conductive nanoparticles and amorphous polymers have been reported (Jimenez and Jana, 2007 Mathur et al., 2008) such nanocomposites possessed a strain-to-failure of less than 5%. In a recent study (Vdlacorta et al., 2012), we have investigated the EM SE and electrical properties of heat-treated CNFs dispersed in a flexible linear low-density polyethylene (semiciystalhne) matrix. This chapter explores the effect of two other carbon-based modifiers on the EM SE of composites prepared by multiple melt-mixing routes with LLDPE for potential use in ductile/flexible EMC apphca-tions. Attention is also directed to the electrical and mechanical properties of such composites in relation with their electromagnetic shielding performance. 

Semicrystalline Polymers must have a polar crystalline phase to render them piezoelectric. The Morphology of such polymers consists of crystallites dispersed within amorphous regions, as shown in Figure la. The amorphous region has a glass-transition temperature that dictates the mechanical properties of the polymer, and the melting temperature of the crystallites dictates the upper limit of the use temperature. The degree of crystallinity in such poljnners depends... 

A characteristic feature of the crystalline or amorphous polymers under processed by vibratory milling, is that the process involves not only the formation of new surfaces by the mechanochemical mechanism of fracture, but also a continuous increase of the material specific surface, as due to mechano dispersion. 

In previous models of the interaction of water with hydrophilic polymers, it is generally hypothesized that the water molecules are either bonded to specific polymer chain sites or are freely dispersed homogeneously throughout the amorphous polymer matrix (Huang and Yang, 2005). However, based on the FT-IR analysis of the BIN-SMPU, the moisture absorption mechanism can be explained by the theory of dynamic combinatorial chemistry or constitutional dynamic chemistry proposed by Lehn (2007), which relies on the selection of the thermodynamically most stable product from an equilibrating mixture. 

When the nanocomposite matrix is semi-ciystalline, incorporation of [nano)particles such as CNTs frequently aims at modifying the crystallization behavior of the polymer in order to improve its properties like, for example, its mechanical performance, and/or to shorten processing cycle times. This way, high levels of mechanical reinforcement can be achieved at low CNT loadings due to the formation of a highly crystalline layer in the immediate vicinity of the CNT walls, ensuring effective interfacial stress transfer. In addition, dispersion of electrically conductive particles into a semi-crystalline [as well as amorphous) polymer matrix also leads to the production of conductive materials. 

Now let us consider the applicability of models developed for two-phase filled polymers for describing the mechanical behaviour of amorphous glassy and semicrystalline polymers. By the analogy with the dispersion theory of strength the composite (or in the considered case, amorphous polymer structure) shear yield stress X is given as follows [37] ... 

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