Structural aspects of suspension poly(vinyl chloride). Small-angle neutron scattering of rigid and plasticized suspension PVC

Abstract

A comprehensive SANS study on both rigid and plasticized suspension PVC demonstrates the presence of superstructural order in this polymer. Comparison of the experimental scattering invariant data with a tentative two-phase model points to specific penetration of the plasticizer in the noncrystalline regions of PVC. Thermal experiments manifest the gradual and thermoreversible melting of the crystalline regions at temperatures above 80-90 °C. Uniaxial deformation experiments on plasticized PVC confirm the existence of a heterogeneous network-structure in PVC where the crystalline tie-points act as physical cross-links. The observed anisotropic "butterfly" scattering pattern of a uniaxially stretched sample indicates the formation of concentration inhomogeneities as a consequence of the random distribution of the crystalline tie-points in plasticized PVC. The anistropy of the scattering pattern gradually disappears on heating, probably resulting from the increasing mobility of the plasticized interstitial medium.

Resolution effects and analysis of small-angle neutron scattering data

“…In this case the Porod plot shows the characteristic upturn at the low-q part of each setting. This has been observed for a granular PVC powders [17].…”

Heterogeneous structure of poly(vinyl chloride) as the origin of anomalous dynamical behavior

“…3-6, 8, 9͒ and SANS. 5,7 In order to characterize the correlation peaks in the simplest way, the contribution at very low Q-values, B(Q,T), may be subtracted. Furthermore, we subtract a flat background FBG.…”

“…A strong controversy on the ''crystalline'' nature of this polymer is still open. Evidences of heterogeneous morphology have been reported, [3][4][5][6][7][8][9] but a clear interpretation of the structure is lacking. 1,10,11 On the other hand, PVC undergoes a glass transition and displays dynamical properties like the ␣and ␤-relaxations characteristic for glassforming systems.…”

“…Since it couples directly to the density, neutron scattering is the appropriate tool in order to access such information. Concerning PVC structure, some experimental results obtained by small angle neutron scattering ͑SANS͒ have been reported, 5,7 but they correspond to only one temperature.…”

Analytical Methods

“…267 Interpretation of WAXS patterns of PVC seems to confirm that the crystalline phase has an orthorhombic cell formed by syndiotactic chains in the planar zig-zag configuration. 274,275 The degree of crystallinity increases with temperature of polymerization increasing and any thermal treatment during processing modifies crystallinity. 219,273 It was found that sample stretching does not modify WAXS peaks.…”