Phase equilibria of modified ethylene glycol–maleic anhydride–phtalic anhydride polyester resins

Abstract

SYNOPSISThis paper describes the influence of a termination of ended carboxyl groups of ethylene glycol-maleic anhydride-phtalic anhydride polyesters with cyclohexanole on a position of phase interface of the unsaturated polyester-styrene system. At given temperatures, optimal molecular weights were determined for the achievement of maximal miscibility of this polymer with styrene. Simultaneously, a model implicit equation was proposed, which is based on the assumption that the dependence of the interaction parameter x on numberaverage molecular weights is similar to the dependence of the interaction parameter X on temperature. Solution of these implicit equations are isotherms in the phase diagram M,, -6'2 -Tcloude point. INTRODUCTIONUnsaturated polyester ( U P ) resins are solutions of unsaturated polyesters in reactive solvents, mainly styrene. Except for the method of initiation and cure, which has influence on the network density of the UP-styrene system, criteria of physical and chemical properties of cross-linked resins are, above all, the composition of synthetized polyesters, their molecular weight averages and distributions, and, further, generally known effects caused by the method of synthesis. A very important factor is also the content of the reactive solvents and remainder monomers. The choice of the polymerization degree at preparation of UPS and the contents of the reactive solvent is, however, also influenced by the required processing properties of UP before cross-linking. This is, above all, a question of requirements on optimal viscosity, reactivity, and emission of reactive solvents. Then, it is necessary to find UP behavior in the solution with styrene in connection with molecular weight and polydispersity. Phase equilibria and miscibility boundary conditions of the polyester-solvent system may be a limiting criterion of optimalization of UP properties. THEORYAccording to the generally known Flory-Huggins theory, the x parameter is considered to be independent of temperature, concentration of polymer in the solution, and its molecular In modifying the Flory-Huggins theories, this x parameter is considered mostly as function of temperature and concentration. In this paper, we assume that the X parameter is also a function of molecular weight. Flory assumed simplifying presumptions in his theory, such as, for example, identical size of polymer molecules, undisturbed interactions of polymer segments with solvent molecules, and accidental mixing of solvent molecules with polymer. Real systems are obviously different in these aspects connected to a change of energy at elementary contacts of solvent molecules ( 1 ) and polymer segments ( 2 ) . The change of energy at elementary mixing is where wll is an energy of contact type 1-1; w22 is an energy of contact type 2-2; w12 is an energy of contact type 1-2, which contributes to production of solution; w H is the enthalpic term of change of an interaction energy; w s is an enthropic term of change of an interaction energy dependencies on temperatur...