ROLE OF STRUCTURAL HETEROGENEITIES ON SEGMENTAL ORIENTATION IN DEFORMED CHAINS - APPLICATION TO ALTERNATING COPOLYMERS

Effects of intrinsic structural and conformational properties on segme ntal orientation in uniaxially deformed copolymers are considered. Dep edence of segmental orientation on equilibrium values of bond angles, torsional states, and probability distribution of rotameric states is studied. Calculations are carried out for chains with independent as w ell as pairwise interdependent rotameric states for neighboring bonds using the matrix generation technique of rotational isomeric state for malism. Results invite attention to the importance of specific energy and geometry parameters in prescribing the level of molecular orientat ion in the two different components A and B of AB type copolymers. Res ults are interpreted with reference to polarized Fourier transform inf rared spectroscopy measurements in which the orientation of transition moment vectors is detected. The consequences of certain assumptions i n data interpretation such as the choice of cylindrically symmetric re ference axes along the chain contour are pointed out. The orientations of vectors along the backbone exhibit strong nonlinear dependence on the conformational characteristics of the component A or B to which th ey are appended. Thus, the bond vectors of the two monomeric units may exhibit quite distinct orientations, arising only from slight perturb ation in bond angles of one of the units. Vectors perpendicular to cha in backbone were less sensitive to monomeric structure. Calculations c arried out independently by Monte Carlo simulations showed that this m ethod yields an adequate qualitative description of the orientational behavior of chain segments while precise quantitative determination re quires the use of the exact matrix generation technique.