Living poly-α-methylstyrene near the polymerization line. II. Phase diagram in methylcyclohexane

We present the experimental determination of the liquid-liquid coexistence curve of living poly-α-methylstyrene (initiated by n-butyllithium) in methylcyclohexane. We measured the coexistence curve by measuring the phase separation temperatures of a set of samples of different mole fractions of the initial monomer, x*m. All the samples had the same ratio, r (=0.008), of the mole fraction of the initiator to the mole fraction of the monomer. We also measured the polymerization line by measuring the temperatures at which increases in viscosity signaled the onset of polymerization. The measured upper critical solution point for this system is at a temperature of 274±1 K and at x*m = 0.18 ± 0.02. At this x*m, the polymerization temperature Tp is 285 K, well above the critical temperature. Tp decreases as x*m decreases, so that the polymerization line meets the coexistence curve at about x*m = 0.12. We compare the predictions of a lattice model which is equivalent to the mean field limit of the dilute n→0 magnet model for constant r to the measured phase diagram and find good qualitative agreement. Better agreement might result if we could solve the model without taking the mean field limit. © 1993 American Institute of Physics.

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