“Rounding” of the sulfur living polymerization transition under spatial confinement

Abstract

“Rounding” effects and other specific changes of liquid sulfur’s polymerization transition are studied using Raman scattering in the case of fluid’s spatial confinement in nanonoporous sol-gel glasses. Specifically, in this paper we demonstrate the smearing or “rounding” of the monomer↔polymer transition caused by geometrical confinement of the liquid, a phenomenon that is in marked contrast to ordinary (bulk) liquid sulfur, where the polymerization transition is quite sharp, bearing a close resemblance to a second-order-type transition. In noticeable agreement with recent theories of living polymerizations, the limited growth of polymeric species brings about a diminishing of the strength of the transition as evidenced in the temperature dependence of many physical properties. The careful determination of the extent of polymerization by analyzing Raman spectra made it possible to recalculate the magnitude of certain thermodynamic parameters changes across the polymerization transition. As a result, the temperature dependence of the equilibrium constants for the initiation and propagation step of polymerization and the number average chain length of polymeric species have been reconsidered. A comparison between the temperature dependence of these quantities for the case of bulk (unconfined) and the corresponding ones for the case of confined liquid has been advanced in the framework of recent mean-field models of living equilibrium polymerization.