Evaluation of Process Variables on the Suspension Polymerization of Vinyl Pivalate.

Poly(vinyl pivalate) − PVPi is a poly(vinyl ester) that presents interesting characteristics that lead to the production of embolic agents, such as poly(vinyl alcohol) (PVA), with high level of sindiotacticity in contrast to the one synthesized from poly(vinyl acetate), for example. This work aims the study of the influence of process variables, such as stirring speed, amount of initiator, and suspending agent concentration on the suspension polymerization reaction of vinyl pivalate. Also, it has the objective of studying the way these parameters can influence the properties of the polymeric particles formation. For this purpose, the reaction system was evaluated using 550, 750, 950, and 1150 rpm as stirring speed, fraction of initiator in the range from 0.3 to 0.5 wt.%, and 0.5, 1.0, 1.5, 2.0, and 2.5 g L⁻¹ of suspending agent. All samples were characterized by classical gravimetric measurements, proton nuclear magnetic resonance (¹H‐NMR), gel permeation chromatography (GPC), and scanning electron microscopy (SEM). ¹H‐NMR measurements confirmed the synthesis of poly(vinyl pivalate). SEM images have suggested the formation of particles with spherical morphology, exhibiting average diameters of 200, 122, 86, and 79 µm related to the stirring speed of 550, 750, 950 e 1150 rpm, respectively. It was also observed that the polymers had average molar mass of 6.7 · 10⁵, 4.8 · 10⁵, and 4.4 · 10⁵ g mol⁻¹ when 0.3, 0.4, and 0.5 wt.% of benzoyl peroxide (BPO) was employed, respectively. The global conversion achieved was ca. 90% in all conditions. [ABSTRACT FROM AUTHOR]