In the present study, a mathematical model is developed to numerically predict nonisothermal batch suspension polymerization of vinyl chloride. Free volume theory was used to consider diffusion‐controlled reactions. Model predictions were validated against field data obtained in a pilot scale stirred tank reactor. Variable temperature trajectory was considered during the course of the reaction to improve productivity by reducing the polymerization time for a certain conversion. Variable temperature during the course of the polymerization was successfully implemented by considering the predefined K value. By using variable temperatures during the course of the reaction, the density of the short branches per 1,000 monomer units as a criterion for structure defect remained relatively unchanged. Maximum reduction in reaction time relative to the isothermal case with the same K value and final conversion was 44% for the best temperature trajectory. J. VINYL ADDIT. TECHNOL., 22:470–478, 2016. © 2015 Society of Plastics Engineers

Among the properties required for producing PVC resin of good quality, the particle morphology (size, primary particles, agglomerates, skins, pores, etc.) plays an important role in processing and performance of products. Three main physical transitions are involved in self-structuring the grains of suspension PVC: nucleation, aggregation and growth. All of these processes are affected by many physical transitions and chemical phenomena that are inter-related and many are complex functions of polymerization conditions (i.e., agitation, temperature, stabilizers, etc.). Because of this multiscale complexity, the relationships between suspension polymerization conditions and morphology have yet to be well-understood. In spite of all these difficulties, a literature survey of the available research nevertheless provides a comprehensive and descriptive insight into mechanisms governing PVC particle formation accounting for the effect of the process variables.

Vinyl chloride suspension polymerization using different temperature trajectories was carried out in a pilot scale batch reactor. Detailed understanding of the conversion at which the primary particles become motionless (Xm) and the key effects of Xm on morphology development of PVC grains were provided. Motionless conversion is estimated for poly(vinyl chloride) (PVC) grains prepared with different temperature trajectories by cold plasticizer absorption measurements. The porosity of PVC grains (prepared isothermally and nonisothermally) shows a maximum at a certain conversion that is considered motionless conversion. With increasing monomer conversion, the cold plasticizer uptake decreases dramatically with conversions greater than motionless conversion until the monomer phase is completely exhausted (Xf) and continues to slightly decrease after Xf. The decrease in cold plasticizer absorption is more pronounced for PVC grains produced nonisothermally by lower initial temperature. The results obtained by scanning electron microscopy and Brabender® plastography showed that the changes in internal structure and fusion behavior of PVC grains after Xm would be much lower when early aggregates of primary particles are formed. Scanning electron microscopy photographs indicate that applying the variable temperature with negative slope accelerates networking between the primary particles inside the polymerizing monomer droplets. The Brabender® plastograph measurements indicate a lower time and temperature of fusion and a higher degree of gelation for nonisothermally produced resin in which the temperature trajectory follows a greater negative slope. J. VINYL ADDIT. TECHNOL., 24:84–92, 2018. © 2015 Society of Plastics Engineers

Molecular and morphological properties of suspension poly(vinyl chloride) produced by nonisothermal polymerization was experimentally investigated in a pilot-scale reactor. Although molecular weight and polydispersity index of the nonisothermally produced poly(vinyl chloride) is almost the same as the equivalent isothermal polymerization, there are differences in morphological characteristics. The cold plasticizer absorption of the resin produced nonisothermally is greater than that of the equivalent isothermal product. Scanning electron microscopy showed that nonisothermally produced particles are more regularly shaped, with a smoother surface, and had greater porosity compared with the product of isothermal polymerization reaction. Applying temperature trajectory produces particles with slightly wider particle size distribution relative to the particles produced isothermally. The evolution of particles with conversion is characterized by processing images obtained by scanning electron microscope. Applying a variable temperature trajectory accelerates the formation of a three-dimensional skeleton of primary particles relative to the isothermally produced particles. J. VINYL ADDIT. TECHNOL., 23:267-274, 2017.

Thermal stability of poly(vinyl chloride) (PVC) produced using continuous dosages of a fast initiator method was investigated in terms of morphological and microstructural characteristics. The results were compared with the properties of the PVC prepared by conventional polymerization method. The Brabender V R Plastograph and DSC results showed a lower fusion time, higher stable time, and greater degree of fusion for PVC obtained by polymerization using initiator continuous dosage method. Also, chemical analysis indicated that the PVC produced under an initiator continuous dosage system have lower structural defects, that is, branch numbers, internal double bonds, labile chlorine, and tacticity index, thereby improving the thermal stability of PVC resin. The results obtained from dehydrochlorination and thermogravimetry analysis confirm the improvement of thermal stability of PVC chains synthesized with continuous dosages of a fast initiator. Moreover, it was found that the concentration of microstructural defects and the dehydrochlorination rates of the PVC samples prepared by both processes increase with monomer conversion, particularly after critical conversion. V C 2016 Wiley Periodicals, Inc. J.Appl. Polym. Sci. 2017, 134, 44480.