Wh. Ming et al., NOVEL CHARACTERISTICS OF POLYSTYRENE MICROSPHERES PREPARED BY MICROEMULSION POLYMERIZATION, Macromolecules, 29(24), 1996, pp. 7678-7682
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.