химический каталог




Компьютерное материаловедение полимеров

Автор А.А.Аскадский, В.И.Кондращенко

interaction and polar groups upon formation of one or another surface properly of organic liquids and polymers. At the same time performance of such a quantitative analysis would permit to regulate the chemical structure of a substance in order to impart necessary surface properties to it.

For calculation of surface tension of organic liquids Expression (382) was obtained which accounts for chemical structure of a liquid and, thus, allowing to evaluate contribution of particular polar groups and specific intermolecular interaction into the value of y,. For example, the contribution of hydrogen bonds into the value of fi for alcohols and acids is as great as 72 %, whereas for lormamide it equals only 33 %.

A similar expression for calculation of surface tension for polymers yi has the form (389) A disadvantage of those equations is a necessity to take into consideration a particular material belonging to a certain group of substances depending on the presence of hydrocarbon, ester, alcohol, acid, amide, nitrite etc. groups. It is taken into account by different meanings of Aj in equation (382) on calculationof y, for liquids and of Cj in equation (389) on calculation of yp for polymers. These drawbacks are absent in formulas obtained for determination of surface tension of liquids and polymers issuing from their chemical structure only. The value of surface tension for organic liquids is calculated according to Equation (396), whereas for polar and non-polar polymers according to Equations (399) and (400) respectively. These formulas possess a high predictive capability (see Table 46 for liquids, Table 47 for polymers) and as distinct from Equation (372) allow to connect the value of surface tension to the solubility parameter of the substance or to cohesion energy density (402) For copolymers the surface tension is better calculated according to Expression (411") via surface tensions of homopolymers.

512

Summary

Summary

513

Chapter XIV Miscibility of Polymers

The problem of miscibilily is one of the most important for polymers That is due to the fact (tat new polymer materials are developed, as a rule, not by way of synthesis of new polymers but mosUy by mixing of the existing ones. In die course of this not only mixed compositions are created where the components are present in comparable quantities, but also microadditions of polymers are introduced, surface of components is modified, etc. Under such circumstances new problems arise, such as microphase separation, skill of control of microphase composition and dimensions, etc.

One of possible approaches to the problem of miscibility prediction of polymers is based on the idea of "solubility" of one polymer in another and application of Equation (345) for obtaining the irascibility criterion of polymers aimed at evaluation of polymer solubility. As a result of analysis performed forthe case of total incompatibility between polymers when one homopolymerdoes not "solve" in another, and the second one does not solve in the first, that criterion has the form (412) and (413). Under partial irascibility when one homopolymerdoes not "solve" in another, but the second one docs "solve" in the first, or vice versa, the irascibility criterion is given by inequalities (417) and (418). Under absolute miscibility of polymers when the first and die second polymers solve in one anoUicr the corresponding criterion lias die form (419) and (420). Taking as examples systems with partial (one polymer is polystyrene, another is poly vinylmetliyl ether) and absolute (one polymer is polystyrene, another is poly-2, 6-dimethyI-1.4-phenyleneoxide) miscibility a high predictive capability of the criterion obtained lias been shown in the whole range of ratios between mixture components (Figs.99.101). It should be noted that the discussed approach has an advantage over several other approaches in that it does not require an introduction of "fitting" parameters, but only a knowledge of chemical structure of the components.

Chapter XV

Influence of End Groups upon Properties of Polymers

Much attention is paid to evaluation of the role of a polymer molecular mass and the role of end groups connected to it in formation of polymer properties This problem is especially important under analysis of action of the molecular mass upon the properties of growing chains when the number n of links in a molecular chain is small. The proposed relations between polymer properties and ils molecular mass are. as a mle, of empirical nature and do not permit to determine the action of particular atomic groups, type of intermolecular interaction and relative volume of end groups upon die polymer properties. Such an evaluation performed for four polymers - polymethylmetacrylate, polystyrene, polyeUiyleneterephdialate and polycarbonate - allowed to find out some important regularities in variation of Van-der-{ Waals volume, molar refraction, molar cohesion energy, solubility parameter,

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