Aggregation phenomena in the suspension polymerization of VCM

Abstract

In the suspension polymerization of VCM, insoluble polymer particles are formed inside the monomer droplets. The growth and aggregation of these particles are responsible for important polymer properties, such as porosity. It is well established that the most characteristic polymer particles, the primary particles, are of a narrow distribution with a size (diameter) ranging from 0.10-0.20 vm. This work studied the formation of primary particles based on the aggregation phenomena that take place inside a monomer droplet. This was done by formulating a population balance equation, which was based on the following considerations: a) polymerization occurs in both the monomer and the polymer phases; b) there is continuous formation of the basic particles in the monomer phase; c) the growth of the polymer particles occurs as a result of both polymerization in the polymer phase and aggregation of the particles; d) the colloidal properties of the particles that are responsible for the aggregation phenomena were considered to be the net result of attraction and repulsion energies.It was shown that for particles carrying a constant charge it was not possible to predict the formation of primary particles of size 0.10-0.20 t~m. The particle size distribution had a mode diameter equal to the diameter of the basic particles. Consequently, the particle charge was allowed to vary in a way proportional to the particle radius raised to a power coefficient. For values of the coefficient greater than zero, i. e., when the particle charge increased during polymerization, the aggregation of the basic particles was efficient enough to result in the formation of large primary particles.

S-PVC Grain Morphology: A Review

“…It is known that the contribution of latter effect to the increase of porosity is greater. 7,57 Effect of Media Viscosity. The viscosity of the reaction media and the gel strength of the suspending agents (the formation of temperature-dependent gels in water, strength of which is a function of both structure and molecular mass of suspending agents) can also impact particle morphology.…”

“…Second, the steric stabilization contribution of primary particles, imparted by high concentration of the nonionic surfactant leads to a less dense packing of the primary particles and higher porosity. It is known that the contribution of latter effect to the increase of porosity is greater. , …”

Hydrogel Microspheres II. Precipitation Copolymerization of Acrylamide with Comonomers to Prepare Monodisperse Hydrogel Microspheres

“…The figure was drawn by refering to the scheme for the formation of poly(vinly chloride) granules. 10 According to Diamadopoulos, et al, 10 the poly( vinyl chloride) granules are formed by the combination of the following processes: a) the formation of polymer molecules due to solution polymerization; b) the separation of the polymer phase from the continuous phase with the formation of insoluble polymer particles (basic particles having a diameter around 20nm); c) the aggregation of the basic particles to form primary particles (diameter of 100-200 nm), and d) the aggregation of primary particles accompanying the growth of the particle volume due to the polymerization in the polymer phase. The size and individuality of the primary particles depend on their stability and the partition of monomer between continuous and polymer phases.…”