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SYNOPSISTriboelectrification of small polymer particles ( < 10 microns) in which various functional groups are introduced by addition of substituted comonomers is studied. The particles are produced by suspension polymerization and mechanical crushing of larger particles. The effect of the different production methods on the particle is described. The particles produced by the polymerization method have a spherical shape with a smooth surface, and those produced by the crushing method have an irregular shape. Studies show that particles that have easily ionizable functional groups are charged more effectively. It is believed the iontransfer route is the dominant mechanism in the triboelectrification charging of the particle. The magnitude of charge becomes saturated after 0.5% addition of substituted comonomers in the particle. The particles produced by the polymerization method have a tendency to be charged effectively compared with those produced by the crushing method. I NTRO DUCT1 0 NThe triboelectrification of polymer particles is an important component for the process of electrophotography and for electrostatic paint application. Micron-sized polymer particles have attracted great interest from informational industries, especially in the field of the electrophotography. Triboelectrification is one of many very important properties for the toner particle. In spite of the importance of the triboelectrification property, only a few have reported the relationship between the sign and magnitude of the charge and the chemical structure of the particle material. A small number of reports do show limited qualitative rankings of various material~.'-~ We report triboelectrical charging data of micronsized polymer particles in which various chemical functional groups are introduced. The particles are produced by suspension polymerization and the me-

ABSTRACT:Sol-gel transition and the structure ofisotactic polypropylene (itPP) gels formed from toluene and o-xylene solutions were studied. Weight-average molecular weight range of samples used is from 25.8 x Hf to 50.1 x !If. A thermo-reversible gel was formed from a semi-dilute solution on cooling. Gel-melting temperature was measured and its dependency on polymer concentration as well as molecular weight was investigated.increased gradually with increasing polymer concentration and obeyed Eldridge-Ferry's type of plot: the reciprocal absolute gelmelting temperature had a linear relationship to the logarithm of volume fraction of polymer, while molecular weight dependency of was little. In a gel, many spherulites were observed, the spherulites were bound with crystalline ties, and a three-dimensional network structure was observed. In this crystalline network, a polymer solution was confined. It is concluded that the formation of spherulites and crystalline ties is conducive to gelation.

An ethylene-propylene random copolymer (EP) in carbon disulfide, toluene, and cyclopentane was found to convert to a thermoreversible gel at the temperature lower than ca. woe. Sol<=±gel transition temperatures were measured as a function of polymer concentration using several samples with different propylene contents (PC) and molecular weights. PC varies from 22 to 49wt%. The sol--.gel and gel-->sol transition temperatures, where thermal hysteresis was present for each sample, lowered considerably with increasing PC, regardless of differences in molecular weights. The gel-melting behavior was investigated with the aid of the Takahashi theory which is based upon a conjecture that junction points of a gel are fringed micelle crystallites. The theory was well applicable to the present systems. A common linear relation was found to hold between liT;, and In V2N when the samples had similar PC, where is the observed gel-melting temperature, v2 is the volume fraction (concentration) of the polymer in the gel, and N is the weight-average degree of polymerization. Further, results of X-ray diffraction, differential scanning calorimetry, and microscopic observation showed that gelation took place through crystallization and that junction points of an EP gel were made up of microcrystallites such as fringed micelles, particularly for a sample with high content of propylene.

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