DETERMINATION OF CRITICAL MOLECULAR-WEIGHT FOR ENTANGLED MACROMOLECULES USING THE TENSILE-STRENGTH DATA

The multivariable power dependence of polymer properties on molecular characteristics (Dobkowski, 1981) has been applied to molecular weight dependence of tensile strength, and the known equation of Flory (1945 ) has been extended taking polydispersity of polymers into account. Co nstant parameters of the relevant regression equations have been calcu lated using experimental data on tensile strength and molecular weight averages M(n) and M(w) of polystyrene (PS) and polycarbonate (PC). Th en, the critical molecular weight for entanglements M(c) has been obta ined from the following relationship: A = K sigma(infinity)M(c), where A and sigma(infinity) are parameters of the extended Flory equation f or the tensile strength, and the constant K = 2 is assumed for linear polymers. It has been found that M(c) of injection and compression mou lded PS is equal to 34000 and 37350 g/mole, respectively, while M(c) o f injection moulded PC equals to 5000 g/mole. The values of M(c) calcu lated From the polymer tensile strength are consistent with published data obtained by other methods and with the computer modeling calculat ions. Branched polymers have only qualitatively been discussed. Dimens ionless equations have been proposed for tensile strength characterist ics for polymer materials. The described procedure can be suggested as applicable to various polymers for the determination of their M(c) va lues. However, more experimental data on another polymer materials wil l be necessary to support hitherto obtained results.