Polymer Compounding - Requirements

Compounding is a complex processing method for obtaining materials with expected properties (including melt flow index, oxidation induction time and mechanical properties) during processing. 

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Accelerator activators are chemicals required to initiate the acceleration of the curing process. They also improve the polymer compound quaUty. 

It has been common practice to blend plasticisers with certain polymers since the early days of the plastics industry when Alexander Parkes introduced Parkesine. When they were first used their function was primarily to act as spacers between the polymer molecules. Less energy was therefore required for molecular bond rotation and polymers became capable of flow at temperatures below their decomposition temperature. It was subsequently found that plasticisers could serve two additional purposes, to lower the melt viscosity and to change physical properties of the product such as to increase softness and flexibility and decrease the cold flex temperature (a measure of the temperature below which the polymer compound loses its flexibility). 

Polymer compounds vary considerably in the amount of heat required to bring them up to processing temperatures. These differences arise not so much as a result of differing processing temperatures but because of different specific heats. Crystalline polymers additionally have a latent heat of fusion of the crystalline structure which has to be taken into account. 

Although the polymer industry is often considered a bulk industry, the development and production of the different types, grades and compounds requires advanced technology and an appreciable amount of R D. In support of the industrial development phase, production control and quality management, the polymer industry needs to determine more than 60 elements in polymeric materials, in concentrations ranging from per cent down to ppt levels. 

Such studies, and others on an O-phosphonomannan155 and a tei-choic acid,168 relied on judicious comparisons (of shift) with signals of model compounds, and these are simpler than conventional, analytical procedures. For example, it is difficult to methylate alkali-labile O-phosphonomannans, and sialic acid and KDO-containing polymers would require difficultly available, O-methylated standards. In addition, periodate-oxidation analyses are restricted to polymers having fortuitously amenable, chemical structures. 

A clearer understanding of the structures of these polymers will require synthesis of model compounds for the triad and tetrad sequences. Only with such models can more confident assignments of the nmr spectra be made. Despite the tediousness of such syntheses we believe the postulate of syndioregic polymerization to be sufficiently interesting to warrant the effort and are presently working on the problem. 

Coated Sorbents. When collection and recovery of a specific substance cannot be achieved using charcoal, silica gel, or porous polymers, chemical sorption with a coated sorbent may be necessary. Compounds requiring this method of collection are usually too reactive or unstable to be collected and stored by other means. In this case, a specific stable derivative or unique product characteristic of the compound of interest is desired. 

Living polymers usually require special reagents to achieve termination. Any electrophilic reagent that reacts with the carbanion active center and also allows preparation of polymers with desired terminal functionalities can be used for this purpose.168,174,181 Hydrogen-terminated polymers can be produced by proton donors, whereas carbon dioxide results in a carboxylate end group. Terminal alcohol functionalities can be formed through reaction with ethylene oxide and carbonyl compounds. 

Full understanding of the stereospecific polymerization, especially of the asymmetric one, is one of the most fascinating problems in synthetic organic chemistry as well as in synthetic polymer chemistry. Requirement posed on the stereospedfic polymerization may be severer than that on the stereospedfic reaction of low molecular wdght compound, because any side reaction, if occurred, puts the structurally and stereochemically irregular units, which cannot be separated from the regular one, in the polymer molecule. 

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