Preparation of ultrahigh-molecular-weight syndiotactic poly(vinyl pivalate) monodisperse microspheres by low-temperature suspension polymerization of vinyl pivalate

The particle size distributions of poly(vinyl pivalate) (PVPi) produced from low-temperature suspension polymerization of vinyl pivalate (VPi) with 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (AMDMVN) as an initiator have been studied. By controlling various synthesis parameters, near-monodisperse PVPi microspheres from 100 to 400 μm were obtained that are expected to be precursors of near-monodisperse syndiotactic poly(vinyl alcohol) (PVA) microspheres for biomedical embolie applications. The mean particle diameter follows the relationship: the volume average diameter, D_vad ∝ Y^0.26[VPi]^0.52[AMDMVN]^-0.25[PVA] ^0.40T^-8.35Rpm^-0.67 where Y, [VPi], [AMDMVN], [PVA], T, and Rpm are the fractional conversion, concentrations of VPi, AMDMVN, and suspending agent, polymerization temperature, and agitation speed during the polymerization of VPi, respectively. The polydispersity of the particle size distribution of PVPi decreased with decreasing conversion, [AMDMVN], T, and Rpm and with increasing [VPi]. In the case of [PVA], optimization of the suspension stability led to a narrow particle size distribution. Ultrahigh-molecular- weights PVPi and PVA (number-average degrees of polymerization of PVPi (25,000-32,000) and PVA (14,000-17,500), of high syndiotactic diad content (63%), and of high ultimate conversion of VPi into PVPi (85-95%) were obtained by suspension polymerization at 10°C, followed by saponification.