Morphology, polymer

Polymers are macromolecules formed by joining a large number of small molecules, or mono- 

Fibers Polyethylene, polyester, nylon, acetate, polyacrylonitrile, polybenzobisthiazole, polypropylene, acrylic, aramid 

Filins, packaging Polyethylene, polyester, polypropylene, polycarbonate, polyimide, fluoropolymers, polyurethanes, poly(vinyl chloride) 

Engineering resins Polyoxymethylene, polyester, nylon, polyethersulfone, poly(phenylene sulfide), acrylonitrile-butadiene-styrene, polystyrene 

Structural organization of a solid polymer can be characterized by three principal supramolecular parameters the content of the amorphous phase, the degree of chain orientation in this phase, and the degree of crystallinity in semicrystalline polymers. These parameters depend to a large extent on its processing history, and on the glass transition (Tg) and melting temperature (Tm). 

Chain orientation Drawing orients the polymer chains, changes the sample morphology and can influence the rate of degradation in two ways  

Orienting chains increases the intermolecular interactions, while at the same time decreasing the free volume and segmental mobility. Most of the orientation experiments have been performed with semicrystalline polymers (iPP or HDPE). 

Reproduced with permission from Handbook of Polymer Science and Technology, Ed., N.P. Cheremisinoff, Marcel Dekker, New York, NY, USA, 1989. Copyright Marcel Dekker, 1989. 

The general morphology of crystalline polymers is now well known and understood and has been described by Geil [2], Keller [3], Wunderlich [4], Grubb [5,6], Uhlmann [7] and Bassett [8,9]. The text by Bassett [8] is a good overview 

Recall that increasing the tensile or shear stress will (1) first stretch the chains in an amorphous region of a polymer sample, (2) then order the polymer chains, and (3) then induce crystallinity in regions of the polymer. These changes will affect chemical reactivity because molecular diffusion is slower in ordered and cystalline phases compared to amorphous phases consequently, intermolecular reaction rates, such as those in the autooxidation cycle, will be slower in ordered polymers. 

Crosslinking can also affect photodegradation rates by locking the polymer structure and preventing lamellar unfolding. The consequence is to prevent separation of photoproduced radicals, which favors radical-radical combination. Crosslinked systems therefore generally have smaller quantum yields of degradation relative to non-crossUnked systems.  

It was pointed out in the previous chapter that the geometric arrangement of the atoms in polymer chains can exert a significant influence on the properties of the bulk polymer. To appreciate why this is so, the subject of polymer morphology, the structural arrangement of the chains in the polymer, is introduced here. 

The arrangement of individual polymers in a material is broken down to general regions amorphous (unstructured) and crystalline. This chapter covers the types of crystallinity in 

Fundamental Principles of Polymeric Materials, TTiird Edition. Christopher S. Biazel and Stephen L. Rosen. 2012 John Wiley Sons, Ine. Published 2012 by John Wil Sons, Ine. 

Poly(methyl methacrylate) Poly(vinyl chloride) 

Styrene-butadiene rubber Ethylene-vinyl acetate Styrene-butadiene copolymers 

The chemical composition of macromolecules is important in determination of properties. 

electron and optical scattering techniques and a range of other analytical tools are commonly applied to determine the structure of polymers. X-ray diffraction, for example, permits the determination of interatomic ordering and chain packing. The morphology of polymers is determined by a wide range of optical and electron microscopy techniques, which are the major subject of this text. Finally, there are many other analytical techniques that provide important information regarding polymer structure. 

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D. C. Bassett, Principles of Polymer Morphology, Cambridge University Press, 1981. 

Mention may also be made of an application in which careful control of polymer morphology has led to the production of novel materials. By treatment of solutions of high-density polyethylene, products are obtained with a celluloselike morphology and which are known as, fibrides or synthetic wood pulp. They are used for finishing paper and special boards to impart such features as sealability and improved wet strength. They are also reported to be used for such diverse applications as tile adhesives, thixotropic agents, battery separators and teabags ... 

Rotations around torsional barriers induce changes in chain conformation. For conjugated systems like polydiacetylenes, flow-induced changes in chain conformation can have a profound influence on the photon absorption and electronic conductivity properties of the material [73]. Flow-induced changes in molecular conformation form the basis for several technically important processes, the best known examples are the production of oriented fibers by gel spinning [74], the compatibility enhancement [75] and the shear-induced modification of polymer morphology [76]. 

In semi-cristalline polymers, rate-enhancement under stress has been frequently observed, e.g. in UV-photooxidation of Kapron, natural silk [80], polycaprolactam and polyethylene terephthalate [81]. Quantitative interpretation is, however, difficult in these systems although the overall rate is determined by the level of applied stress, other stress-dependent factors like the rate of oxygen diffusion or change in polymer morphology could occur concurrently and supersede the elementary molecular steps [82, 83], Similar experiments in the fluid state showed unequivocally that flow-induced stresses can accelerate several types of reactions, the best studied being the hydrolysis of DNA [84] and of polyacrylamide [85]. In these examples, hydrolysis involves breaking of the ester O —PO and the amide N —CO bonds. The tensile stress stretches the chain, and therefore, facilitates the... 

Woodward AE (1988) Atlas of polymer morphology. Hanser, Munich... 

Bassett DC (1981) Principles of polymer morphology. Cambridge Univ Press, London... 

A history independent sorption in a glassy polymer is represented by Eqs. (l)-(3), however, due to the microcavitational nature of the hypothesized polymer morphological modification, the history dependency of the solubility is assumed to affect the Languimir term only ... 

Sorption curves obtained at activity and temperature conditions which have been experienced to be not able to alter the polymer morphology during the test, i.e. a = 0.60 and T = 75 °C, for as cast (A) and for samples previously equilibrated in more severe conditions, a = 0.99 and T = 75 °C (B), are shown in Fig. 13. According to the previous discussion, the diffusion coefficient, calculated by using the time at the intersection points between the initial linear behaviour and the equilibrium asymptote (a and b), for the damaged sample is lower than that of the undamaged one, since b > a. The morphological modification which increases the apparent solubility lowers, in fact, the effective diffusion coefficient. 

The incorporation of minute amounts of certain ions into lattice type inorganic ion exchanging films can induce changes in the polymer morphology that can be... 

An analysis of partition coefficient data and drug solubilities in PCL and silicone rubber has been used to show how the relative permeabilities in PCL vary with the lipophilicity of the drug (58,59). The permeabilities of copolymers of e-caprolactone and dl-lactic acid have also been measured and found to be relatively invariant for compositions up to 50% lactic acid (67). The permeability then decreases rapidly to that of the homopolymer of dl-lactic acid, which is 10 times smaller than the value of PCL. These results have been discussed in terms of the polymer morphologies. 

Advanced computational models are also developed to understand the formation of polymer microstructure and polymer morphology. Nonuniform compositional distribution in olefin copolymers can affect the chain solubility of highly crystalline polymers. When such compositional nonuniformity is present, hydrodynamic volume distribution measured by size exclusion chromatography does not match the exact copolymer molecular weight distribution. Therefore, it is necessary to calculate the hydrodynamic volume distribution from a copolymer kinetic model and to relate it to the copolymer molecular weight distribution. The finite molecular weight moment techniques that were developed for free radical homo- and co-polymerization processes can be used for such calculations [1,14,15]. 

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. 

A.E. Woodward, In E.H. Immergat (Ed.), Understanding Polymer Morphology, Hanser/Gardner Publisher, Ohio, USA, 1995. 

This book is divided up into sections. The first three chapters provide a background sections that follow contain chapters dealing with polymer chain analysis, polymer morphology and structure, polymer degradation, polymer product analysis and support techniques. These are listed in more detail in Chapter 1, which also expands more fully on our industrial perception of the requirements for competence and appreciation in all techniques and methods for polymer molecular characterization and analysis. We hope you find this book of value and its approach both unique and technically informative and useful. 

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