Synthesis of Controllable Carboxylated Polystyrene Microspheres by Two-Step Dispersion Polymerization with Hydrocarbon Alcohols

Carboxylated polystyrene (PS) microspheres were synthesized by the two-step dispersion polymerization of styrene in hydrocarbon alcohols (CnH2n+1OH,n=1–5) in the presence of acrylic acid (AA) as a functional comonomer, 2,2′-azobis-(2-methylbutyronitrile) (AMBN) as the initiator and polyvinylpyrrolidone (PVP55) as the dispersant. The effects of solvent type, AA concentration, and first reaction time on the carboxyl content on the microsphere surfaces were investigated. The PS microspheres were characterized by scanning electron microscopy, infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography. The results showed that the first reaction time of the two-stage dispersion polymerization had a great influence on the nucleation process, and appropriately prolonging the first-step reaction time had a great influence on the surface carboxyl content. The effect of the solvent on the surface carboxyl content of PS microspheres was significant. With n-butanol as the solvent, the carboxyl group content on the surface of the microspheres reached 57.05 mg/g.

Vapor Pressures of Low-Volatile Esters of 2,4-D

The vapor pressures of the four most common commercial low-volatile esters and a reference high-volatile ester of 2,4-dichlorophenoxyacetic acid (2,4-D) were determined by gas-liquid chromatography. The order of increasing volatility and the vapor pressure of these esters in mm of Hg at 187 C are as follows: isooctyl—2.7; 2-ethylhexyl—3.0; butoxy ethanol—3.9; propylene glycol butyl ether—3.9; and the reference, isopropyl—16.7. Extrapolations to 25 C support this ranking at working temperatures. Commercial esters of 2,4-D derived from long-chain hydrocarbon alcohols are in the same volatility range as the commercial esters containing an ether linkage.