Molecular weight chemical properties affected

Among others, chain flexibility/rigidity, crystallinity, hydrophilicity/hydrophobicity, molecular weight, chemical property, biodegradability, thermal property, mechanical property, and electrochemical property of polymers are considered to affect the performance of membranes most strongly. Moreover, these properties are often mutually interrelated. 

The rates of adsorption and chain scission are affected by physicochemical properties of the substrate, such as the molecular weight, chemical composition, crystallinity, and surface area, and also by the inherent characteristics of the enzyme which can be measured in terms of its activity, stability, concentration, amino acid composition, and conformation. Moreover, environmental conditions such as pH and temperature also influence the activity of enzymes. The presence of stabilizers, activators, or inhibitors released from the polymer during the degradation process or additives that are leached out may also affect enzyme activity. Chemical modification of biopolymers may also affect the rate of enzymatic resorption since, depending on the degree of chemical modification, it may prevent the enzyme from recognizing the polymeric substrate. The rate of enzymatic resorption is limited by an enzyme saturation point. Beyond this enzyme concentration, no further increase in the rate of resorption is observed even when more enzyme is added. 

Electrical Properties. Erom a chemical standpoint, HDPE is a saturated aUphatic hydrocarbon and hence a good insulator. Its electrical characteristics are given in Table 1. Because polymer density and molecular weight affect electrical properties only slightly, HDPE is widely used for wire and cable insulation. 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

Similar molecular weight poly(DMA-co-EPl), 1750 daltons, ca. 13 repeat units, and poly(TMDAB-co-DCB), 1500 daltons, ca. 11 repeat units were compared. The two condensation polymers appeared to be about equally effective in preventing the swelling of Wyoming bento-nite. Any small differences are probably due to repeat unit chemical structure differences rather than the small variations in polymer molecular weight. The presence of the hydroxyl group and the smaller N - N distance in poly(DMA-co-EPl) could affect polymer conforma-tion in solution, geometry of the polymer - clay complex, and surface properties of the polymer - clay complex as compared to poly(TMDAB-co-DCB). 

Polymerization processes represent an extremely important aspect of the chemical processing industry. Since many of the properties of polymeric materials are markedly affected by their average molecular weight and their molecular weight distribution, the design of reactors for polymerization processes offers many opportunities for the use of the principles presented earlier in this chapter. 

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