Phase‐equilibrium behavior of vinyl chloride/n‐butane and its application in determination of vinyl chloride heterogeneous polymerization kinetics

Studies of the phase‐equilibrium behavior of vinyl chloride (VCM)/ n ‐butane mixtures and the kinetics of VCM heterogeneous polymerization, using n ‐butane as a reaction medium, were carried out using a 1‐ L glass autoclave. The vapor composition was measured by gas chromatography, showing that the vapor pressure of the VCM/ n ‐butane mixture was located above the line connecting the points for pure VCM and n ‐butane. The concentration of VCM in the vapor phase was greater than that in the corresponding liquid phase. It was confirmed that the presence of poly(vinyl chloride) (PVC) resin had no significant influences on the phase equilibrium of VCM/ n ‐butane mixtures. Thus, the phase‐equilibrium equations were applied to determine the conversion of VCM during heterogeneous polymerization. The conversions calculated from the variations of vapor pressure or composition agreed with those determined by the weighing method. The conversion–time and polymerization rate–time curves obtained for VCM heterogeneous polymerization showed that the polymerization accelerated at low initiator concentration, but the polymerization rate decreased with an increase of conversion at relatively high initiator concentrations. The chain‐transfer reaction to n ‐butane was confirmed by a decrease of the molecular weight and broadening of the molecular weight distribution of PVC.