SAXS investigation on the influence of oil dilution on morphological changes in a SBS block copolymer during the first draw cycle

Abstract

Spin-cast films of one pure SBS and two oil-extended SBS samples were observed during first cycle drawing in the synchrotron radiation beam at Hasylab. For evaluation, from a two-dimensional Vidicon scattering picture the scattering curve was extracted by intersecting perpendicular to the observed layer lines. Using a method described in a preceding paper [1], the scattering curve is analyzed by fitting to one-dimensional two-phase models. Essential for a fit with parameters of physical sense is the assumption of at least two components. One of these two main components is identified with fibrils containing PS cylinders, the axes of which are orientated parallel; the other is identified with fibrils containing cylinders transverse to the drawing direction.

For the mechanical properties of the thermoplastic rubber this splitting of cylinder orientation in the drawn state seems to be of some importance. Only the cylinders of the longitudinal component turn out to be rigid, while the cylinders of the transversal component appear to yield and even break.

The amount of cylinders allotted to each of the two components in the drawn state varies as a function of the diluent. An extrapolation of topological parameters back to the undrawn state indicates a possible reason, a fair variation of the cylindrical particle dimensions within a “lattice cell” of only slighly varying dimensions. While paraffinic mineral oil dilution causes the cylinders lengths to decrease, thus improving cylinder orientability within the pseudo lattice cell, aromatic oil dilution increases the particles diameters.

A remaining faint contribution to the scattering pattern that produces the layer lines is suggested not to be caused by a periodic structure, but by a single and precisely defined polybutadiene matrix length (“string”) between two PS cylinders with a considerable height variance.