Influence of side branch on the elastic modulus of ethylene-tetrafluoroethylene terpolymers

Influence of side branches on the storage modulus of ethylene-tetrafluoroethylene (ETFE) terpolymers has been investigated on the basis of dynamic mechanical analysis. The terpolymer containing short branches (CF3) has been found to behave in a different manner from the case of long branches (C4F9). The storage modulus was found to depend sensitively on the content of branches and also the degree of crystallinity in the case of terpolymer with long branches, while the modulus did not change very much for the sample with short branches even when the crystallinity was changed remarkably. The storage modulus of the terpolymer with long branches was found to behave similarly to that of ETFE copolymer without any branch. These differences were successfully interpreted on the basis of mechanical series model of crystalline and amorphous phases, where the modulus of the bulk sample is dependent sensitively on Young's modulus of the crystalline region. The short branches (CF3) are included in the crystal lattice and the crystal lattice is expanded with an increment of branch content, resulting in the remarkable decrease in Young's modulus of the crystal lattice. The long branches (C4F9) are on the other hand, excluded out of the crystal lattice and Young's modulus of the crystal region is not affected very much. This difference in Young's modulus of the crystal lattice reflects on the different behavior of the modulus of the bulk sample as mentioned above.