Polyme morphology

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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