Isotactic polystyrene samples crystallized from concentrated solutions (> 10% by weight) in the thermodynamically good solvent toluene display a lamellar thickness L = (170 ± 15) Å at room temperature, as determined by neutron scattering investigation. This thickness is about twice the value reported for samples crystallized in poor solvents. The results may be interpreted in terms of a substantially smaller melting enthalpy of the polymer in toluene, producing a proportionally inverse increase of the thickness L?c of the central, crystalline portion of the lamellae. In turn, we suggest that the overall thickness L of the lamellae increases more than proportionally with L?c, due to the need of accomodating in the amorphous zone increasing amounts of polymer containing steric defects. The decrease of the melting enthalpy is also qualitatively consistent with growth rate results. The half-peak width of the Bragg diffraction peaks suggests that the crystalline fraction of the lamellar thickness is about 50%, in approximate agreement with results obtained by Overbergh, Berghmans and Reynaers (J. Polym. Sci., Polym. Phys. Ed. 14, 1177 (1976)) from bulk-crystallized samples showing about the same values of L and L?c as observed by us
Isotactic polystyrene: An unusually large lamellar thickness as an effect of a thermodynamically good solvent
LUZZATI S;
1990
Abstract
Isotactic polystyrene samples crystallized from concentrated solutions (> 10% by weight) in the thermodynamically good solvent toluene display a lamellar thickness L = (170 ± 15) Å at room temperature, as determined by neutron scattering investigation. This thickness is about twice the value reported for samples crystallized in poor solvents. The results may be interpreted in terms of a substantially smaller melting enthalpy of the polymer in toluene, producing a proportionally inverse increase of the thickness L?c of the central, crystalline portion of the lamellae. In turn, we suggest that the overall thickness L of the lamellae increases more than proportionally with L?c, due to the need of accomodating in the amorphous zone increasing amounts of polymer containing steric defects. The decrease of the melting enthalpy is also qualitatively consistent with growth rate results. The half-peak width of the Bragg diffraction peaks suggests that the crystalline fraction of the lamellar thickness is about 50%, in approximate agreement with results obtained by Overbergh, Berghmans and Reynaers (J. Polym. Sci., Polym. Phys. Ed. 14, 1177 (1976)) from bulk-crystallized samples showing about the same values of L and L?c as observed by usI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
