Chain dimensions Thermoplastics

The less simple polymers (like the epoxies, the polyesters and the formaldehyde-based resins) are networks each chain is cross-linked in many places to other chains, so that, if stretched out, the array would look like a piece of Belgian lace, somehow woven in three dimensions. These are the thermosets if heated, the structure softens but it does not melt the cross-links prevent viscous flow. Thermosets are usually a bit stiffer than amorphous thermoplastics because of the cross-links, but they cannot easily be crystallised or oriented, so there is less scope for changing their properties by processing. 

Swift heavy ion beams with extremely high LETs are used to degrade strongly polymer chains within tracks over a range of a few tens of micrometers. After irradiation, the top surface of bulk thermoplastics such as polyethyleneterephtalate, polycarbonate, polyvinylidene fluoride or polyimide materials as well as thin films made of the same material are subsequently etched by a wet chemical treatment that reveals pores of which the shape, surface density and dimensions can be controlled by choosing appropriate conditions. High aspect ratio cylindrical or conical traces of diameter ranging from a few nanometers to some... 

Cross-linkage consists of joints between chains which occur in three dimensions. Cross-linkage usually again is reflected in physical properties, increasing, for example, polymer rigidity. In general, thermoplastic materials have linear and branched chains whereas thermosets are cross-linked. 

Polymers are frequently classified in terms of bonding in one dimension versus bonding in two or three dimensions. Bonding in one dimension results in linear polymers with single-strand chains. Bonding in two or three dimensions results in cross-linked polymers having infinite sheets or three-dimensional networks. Linear polymers are produced by addition polymerization if the reactant has only one double bond or by condensation polymerization if the reactant or reactants each have two reactive sites. Such polymers are usually soluble in suitable solvents. Since they also tend to soften when heated, they are called thermoplastic polymers. Cross-linked polymers may be produced by addition polymerization if the reactant has more than one double bond, or by condensation polymerization if the reactant or reactants each have more than two reactive sites. Such network polymers are usually insoluble and Infusible and are called thermosetting polymers. 

Some polymers, such as polyethylene, polystyrene, and polypropylene, have chainlike molecules. These polymers usuaUy soften when heated and are sometimes caUed thermoplastic polymers. Other polymers are made up of networks instead of chains. Some of the network polymers have long chains with short chains (cross links) fastening two or more chains together, and others, such as Bakehte, have networks that are bonded in two or three dimensions. These polymers are sometimes called thermosetting because they are usuahy formed at high temperatures. 

The thermal transitions and the relaxation processes observed in multiblock terpolymers allow to evaluate their phase morphology. At room temperature, these polymers are composed of three phases hard, soft, and strongly expanded interphase. The two latter phases are amorphous and form a matrix (continuous phase), whereas the hard (crystalline) phase is the dispersed phase. The thermal transition and relaxation processes occurring in the interphase of the multiblock copolymers are not detected by the DSC and DMTA methods. The incorporation of the third short block into the copolymer chain causes an increase in the volume of the interphase. This facilitates the establishment of the processes occurring in this phase at various temperatures. Moreover, it enables the evaluation of the influence of the dimension and composition of this phase on the polymer properties. (About the number of phases in poly(ether ester) thermoplastic elastomers, see also Chapter 6.)... 

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