Chain conformation of semicrystalline isotactic polystyrene by small-angle neutron scattering

Abstract

The results obtained from SANS (small-angle neutron scattering) measurements on isotactic polystyrene in the bulk-crystallized state are discussed. For tagged chain molecular weights ranging from 2.5 × 10⁵ to 7 × 10⁵, variations of the radius of gyration both as a function of crystallinity, x, and the molecular weight of deuterated species for IPS hydrogenated matrices of, respectively, M_w= 4 × 10⁵ and M_w= 1.7 × 10⁶ are examined. In the case of the matrix of lower molecular weight, there is found at x= 0.3 for the law R_g≈M^ν an exponent ν close to 0.78 with an appreciable increase in the dimensions on increasing crystallinity. Calculations performed on schematic models lead to the adoption in such a case of a conformation possessing a long crystallized sequence [along the (330) plane] with two linked amorphous wings. Experiments performed with the matrix of higher molecular weight reveal almost no variation in the radius of gyration even at the highest crystallinity. Accordingly, Flory's conformation seems to be a good model in such a situation. These results are corroborated by the dependences on q^–2 and the intensity levels measured in the intermediate range. Comparisons with amorphous samples confirm the proposed models. An attempt to explain these conformations is made by comparing the crystalline growth rates and the long relaxation times.