CHARACTERIZATION OF SEMI-CRYSTALLINE RANDOM COPOLYMERS BY SMALL-ANGLE NEUTRON-SCATTERING

A new method is introduced to determine the degree of partitioning of noncrystallizable comonomer units (B units) between the two phases of a semicrystalline random copolymer. The method is based on the comparison of the intensities of small-angle neutron and x-ray scattering (SANS and SAXS, respectively). By this technique two quantities can be evaluated: the difference DELTA p of the mass densities between the crystalline and the disordered regions, and the concentration fluctuations of the B units in the two phases. It is found that SANS is very sensitive to the presence of small amounts of B units if their scattering length is sufficiently different from that of the A units. The cpability of the method was proved by measurements on chlorinated polyethylene and on 1,3,5-trioxane-1,3-dioxolane copolymers. Both copolymers are distinguished by a random distribution of the co-units. The results show that even at relatively low concentrations CHI //B of the comonomer units a remarkable fraction of the B units is incorporated into the crystalline A phase and that this fraction rises if CHI //B is increased.