Morphology amorphous polymers

Amorphous Polymer - Amorphous polymers are polymers having noncrystalline or amorphous supramolecular structure or morphology. Amorphous polymers may have some molecular order but usually are substantially less ordered than crystalline polymers and, subsequently, have inferior mechanical properties. 

Polymers can be divided into two groups morphologically amorphous polymers and crystalline polymers. Amorphous polymers lack sufficient regularity in packing of the chains to produce the sharp x-ray diffraction pattern characteristic of highly crystalline polymers. The term crystalline polymer is actually a misnomer since no polymer is 100% crystalline, containing both crystalline domains and amorphous domains. Therefore, a more correct yet seldom used designation is semicrystalline polymer. 

Polymers with differing morphologies respond differentiy to fillers (qv) and reinforcements. In crystalline resins, heat distortion temperature (HDT) increases as the aspect ratio and amount of filler and reinforcement are increased. In fact, glass reinforcement can result in the HDT approaching the melting point. Amorphous polymers are much less affected. Addition of fillers, however, intermpts amorphous polymer molecules physical interactions, and certain properties, such as impact strength, are reduced. 

In addition to temperature and concentration, diffusion in polymers can be influenced by the penetrant size, polymer molecular weight, and polymer morphology factors such as crystallinity and cross-linking density. These factors render the prediction of the penetrant diffusion coefficient a rather complex task. However, in simpler systems such as non-cross-linked amorphous polymers, theories have been developed to predict the mutual diffusion coefficient with various degrees of success [12-19], Among these, the most notable are the free volume theories [12,17], In the following subsection, these free volume based theories are introduced to illustrate the principles involved. 

The volume inside the semicrystalline polymers can be divided between the crystallized and amorphous parts of the polymer. The crystalline part usually forms a complicated network in the matrix of the amorphous polymer. A visualization of a single-polymer crystallite done [111] by the Atomic Force Microscopy (AFM) is shown in Fig. 9. The most common morphology observable in the semicrystalline polymer is that of a spherulitic microstructure [112], where the crystalline lamellae grows more or less radially from the central nucleus in all directions. The different crystal lamellae can nucleate separately... 

Biercuk MJ, Llaguno MC, Radosavljevic M, Hyun JK, Johnson AT (2002). Morphological and mechanical properties of carbon-nanotube-reinforced semicrystalline and amorphous polymer composites. Appl. Phys. Lett. 80 2767-2769. 

D. Axelson For the polyethylenes, at least, there is a major effect of morphology on linewidth. This is going to make more difficult a detailed description of the dynamics of the low frequency motion relative to a completely amorphous polymer. 

The close connection that exists between polymer morphology and mechanical properties stimulated extensive research in this field. In amorphous polymers, elastic neutron scattering led to important results. Using mixtures of conventional and deuterated macromolecules, the mean square radius of gyration < > of several amorphous polymers in bulk has been determined (237). This... 

If crystallization is carried out from concentrated solutions, multilamellar aggregates are formed. In particular, melt crystallization of polyethylene gives bunched-up lamellae with an overall spherical symmetry. The space between the lamellae contains uncrystallized amorphous polymer. These objects are called spherulites, and their radii grow linearly with time, in spite of their intricate morphological features [9]. Another remarkable feature of spheruhtes formed by linear polyethylene is that they are gigantically chiral, although the molecules are achiral. 

Sometimes, small structural differences in morphology of polymer samples can be isolated by using a double subtraction technique. For example, with polyethylene terephthalate) PET, differences in the amorphous phase of the melt-quenched polymer and solution-cast polymer can be isolated by first subtracting out the contribution due to the trans isomer and then subtracting the two difference spectra from each other 214). (Fig. 16) shows the resultingdifference spectrum obtained after the second subtraction. Obviously the two amorphous structures are different from each other. 

Melting temperatures of as-polymerized powders are high, i.e., 198— 205°C. As-polymerized PVDC does not have a well-defined glass-transition temperature because of its high crystallinity. The amorphous polymer has a glass-transition temperature of — 17°C. Once melted, PVDC does not regain its as-polymerized morphology when subsequently crystallized. 

Morphology is the order or arrangement of the polymer structure. The possible order between a molecule or molecule segment and its neighbors can vary from a very ordered highly crystalline polymeric structure to an amorphous structure (i.e., a structure in greatest disorder or random). The possible range of order and disorder is clearly depicted on the left side of Fig. 1.14. For example, a purely amorphous polymer is formed only by the non-... 

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