Polymer Morphology and Mechanical Properties

The fundamental difference between polymers and other materials is the high molecular weight of chain polymers. If we consider the alkane series, there is a progressive 

To a synthetic chemist the concept of a polymer is rather different. The term is often used to describe molecules formed from quite small numbers of monomers units but which resist crystallization and purification owing to the range of chain lengths present. Such materials will normally form brittle solids which are either amorphous or have a low level of crystalline order. 

As prepared by the method of Shirakawa et al. 2 3), polyacetylene is a free-standing film. On closer examination, its density is found to be around 0.4gem-3, only about 30% of the value (1.16 gem-3) predicted from X-ray analysis, and electron microscopy reveals complex morphologies. 

The materials used in most current research are irregular mats of highly crystalline fibrils with diameters of around 10 nm, so that the films are characterised by a very high surface area (around 60 m2 g-1), a problem in some potential applications and an asset in others. The morphology of polyacetylene is sensitive to the conditions of preparation and to ageing and was the subject of much heated discussion in the early development of polyacetylene. 

During a normal polymerization of acetylene, in addition to the film which forms on the reactor wall, there is also a gel which forms on the solution surface, plus powder which forms in the bulk solution. According to Karasz et al.359), the globular 

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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... 

Not applicable for PUs, but what about us I would gladly wave back when it is cold outside. Numerous studies had been made on the influence of temperature on the PUs deformation. A series of model MDI based PUs were characterized by Crawford et al [220] before, and after varying degrees of strain aging to study the effect of strain on the polymer morphology and mechanical properties. The segmented materials were synthesized by using the one-shot technique. The molar ratios of the model polymers were varied. 

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