NOVEL CHARACTERISTICS OF POLYSTYRENE MICROSPHERES PREPARED BY MICROEMULSION POLYMERIZATION

Tap kinds of styrene microemulsion systems were polymerized to prepare polystyrene microspheres (micro-PS), one emulsified by sodium dodecyl sulfate (SDS) and coemulsified by 1-pentanol and the other emulsified by octylphenoxypoly(ethoxyethanol) (OP-10). Micro-PS possessed an ess entially atactic configuration hom H-1-NMR measurement. Comparison of LR spectra showed some conformational differences between micro-PS and ordinary atactic PS (o-PS). Each polystyrene microsphere contains onl y about three macromolecular chains iso-called pauci-chain microsphere s!? which adopt a special conformation: individual chains are highly c ompact, while the whole structure of the microsphere is relatively loo se in comparison with a random-coil chain in a multichain system. Ther e were apparent differences in thermal behaviors between micro-PS and o-PS during the DSC scan. Micro-PS displayed two exotherms near 107 an d 157 degrees C during the first scan. In the subsequent scan, both ex otherms disappeared and only one glass transition similar to o-PS was shown. The first exotherm might be due to the sintering of polystyrene microspheres with small particle sizes. From wide-angle X-ray diffrac tion (WAXD) and polarizing optical microscopy (POM) studies, the secon d exotherm could be ascribed to the relatively compact conformation of polystyrene chains and the consequently formed slightly ordered regio ns inside micro-PS during the heating process. The special conformatio n was the driving force leading to its novel thermal behaviors. This i s perhaps the first report that polystyrene from direct free radical p olymerization has the ability to form some kind of ordered structure.