TEMPERATURE-DEPENDENCE OF THE ELASTIC-MODULUS OF CRYSTALLINE REGIONS OF ISOTACTIC POLY(4-METHYL-1-PENTENE)

The elastic modulus E(l) of crystalline regions of isotactic poly(4-methyl-l-pentene) (P4M1P) in the direction parallel to the chain axis and its temperature dependence were investigated by x-ray diffraction. E(l) values for the (001) and (007) planes of P4M1P agreed well at 4.1 GPa at room temperature. This small E(l) value could be attributed both to the contracted helical conformation (7/2 helix) and to a large cross-sectional area of P4M1P in the crystalline regions. Though the lattice distortion of the first kind increased and partial destruction of crystallites occurred with increasing stress, the stress-strain curve for the crystal lattice was linear up to 80 MPa. However, the E(l) value remained unchanged up to 150-degrees-C. The lattice spacing for the (007) plane increased monotonously with increasing temperature, with a thermal expansion coefficient of 0.9 x 10(-4) K-1. These phenomena were in contrast with the temperature dependence of E(l) values of various polymers previously reported, in which E(l) decreased in the temperature region where the thermal expansion coefficient changed. It is considered for P4M1P that the axial thermal molecular motions which cause the decrement of E(l) do not take place and that the deformation mechanism of the chain molecules remains unchanged in the crystalline regions over the temperature and stress range studied.