Spatial structures, polymeric systems

In the first case, that is with dipoles integral with the main chain, in the absence of an electric field the dipoles will be randomly disposed but will be fixed by the disposition of the main chain atoms. On application of an electric field complete dipole orientation is not possible because of spatial requirements imposed by the chain structure. Furthermore in the polymeric system the different molecules are coiled in different ways and the time for orientation will be dependent on the particular disposition. Thus whereas simple polar molecules have a sharply defined power loss maxima the power loss-frequency curve of polar polymers is broad, due to the dispersion of orientation times. 

Carboxylated polymers can be prepared by mechanical treatment of frozen polymer solutions in acrylic acid (Heinicke 1984). The reaction mechanism is based on the initiation of polymerization of the frozen monomer by free macroradicals formed during mechanolysis of the starting polymer. Depending on the type of polymer, mixed, grafted, and block polymers with a linear or spatial structure are obtained. What is important is that the solid-phase reaction runs with a relatively high rate. For instance, in the polyamide reactive system with acrylic acid, the tribochemical reaction leading to the copolymer is completed after a treatment time of 60 s. As a rule, the mechanical activation of polymers is mainly carried out in a dry state, because the structural imperfections appear most likely here. 

In the application of SANS to bulk polymeric systems, the anticipated developments in instrumentation and flux will provide the opportunity to extend the work of McLeish et n/., and probe polymer conformation under extrusion and in flow. Measurements as a function of position will enable complex spatial distributions of velocity and stress within an extruder to be mapped. Measurements with partial deuterium labelling will allow further development of the structure/rheology relationship in polymer processing. 

However, over the last decade, important advances have been made in IR micro-spectroscopy with a synchrotron source [16], which can provide new opportunities and motivation for the study of polymeric materials. The most utilized key synchrotron parameter for this community is the ability, thanks to the source brightness, to differentiate the chemical nature of the constituents in multicomponent polymeric systems. When the sizes of the different domains are in the range of the IR wavelength (micron scale), the spatial differentiation and study of each of these domains is possible using SR-FTIR micro-spectroscopy. Such analytical tools allow the study of various aspects related to the chemical composition, structure and morphology of the polymeric materials. Some of the areas that have benefited from synchrotron infrared over the last four years are reviewed in this section. 

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