Critical and tricritical phenomena in ‘‘living’’ polymers

Publisher Website
Google Scholar
Abstract
The equilibrium polymerization of ‘‘living polymers’’ such as polytetrahydrofuran and poly-α-methylstyrene can be usefully described by the n=0 limit of the n vector model of magnetism. Nonclassical critical behavior is predicted near the ceiling temperature when the initiator concentration is sufficiently small. The small initiator concentration implies a small magnetic field in the n→0 vector model. The agreement of our theory with the limited experimental data available is good, and appears to confirm nonclassical critical behavior. Solutions of living polymers can be described by an annealed dilute n→0 vector model, and interesting new phase diagrams are predicted that include tricritical points analogous to those found in He3–He4 mixtures at very low temperature and in models of sulfur solutions and dilute ferromagnets. The relationship between the phase diagrams in these systems is elucidated.