Preparation of novel syndiotactic poly(vinyl alcohol) microspheres through the low-temperature suspension copolymerization or vinyl pivalate and vinyl acetate and heterogeneous saponification

Syndiotactic poly (vinyl alcohol) (PVA)/poly(vinyl pivalate/vinyl acetate) [P(VPi/VAc)] microspheres, with a skin-core structure, were prepared through the heterogeneous saponification of copolymers of vinyl pivalate (VPi) and vinyl acetate (VAc). For the preparation of P(VPi/VAc) microspheres with various particle sizes and a uniform particle size distribution (which are promising precursors of syndiotactic PVA embolie materials to be introduced through catheters for the management of gastrointestinal bleeders, arteriovenous malformations, hemangiomas, and traumatic rupture of blood vessels), VPi and VAc were suspension-copolymerized at 30°C with a room-temperature initiator, 2,2'-azobis(2,4-dimethylvaleronitrile). The effects of the polymerization conditions were investigated in terms of the size and size distribution of the suspension particles. P(VPi/VAc) microspheres, with various syndiotactic dyad (s-dyad) contents, were produced through the control of the monomer feed ratio. In addition, monodisperse P(VPi/VAc) particles of various particle diameters were obtained by the separation and sieving of the polymerization product. Monodisperse P(VPi/VAc) microspheres of various particle sizes were partially saponified in the heterogeneous system, and the effects of the particle size and particle size distribution on the saponification rate were investigated in terms of the tacticity and the saponification time and temperature. Novel skin-core PVA/P(VPi/VAc) microspheres of various s-dyad contents and degrees of saponification were successfully produced through the control of the various polymerization and saponification parameters.