ABSTRACT:The variation of the pore structure of styrene-divinylbenzene (S-DVB) copolymer beads with the drying conditions was investigated. Macroporous S-DVB copolymer beads with various DVB contents were prepared in the presence of toluenecyclohexanol mixtures as a diluent. It was found that the pores of 10 1 -nm radius, corresponding to the interstices between the microspheres, collapse upon drying of the copolymers from toluene. The collapsed pores reexpand if the copolymers were dried from methanol. The collapse-reexpansion process of the pores was found to be reversible, indicating that the actual pore structure formed during the crosslinking copolymerization is memorized by the copolymer network. The magnitude of the pore structure variation increased on worsening the polymer-diluent interactions during the gel formation process due to the simultaneous increase in crosslink density distribution.

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Conventional expandable polystyrene (EPS) was modified by the preparation of copolymers containing 1.0, 2.5, and 5.0% ␣-methylstyrene. Increasing the glasstransition temperature of EPS was the aim of this work. Copolymeric expandable polystyrene (CEPS) samples were characterized with various techniques.1 H-NMR spectroscopy was used for the determination of the composition, and gel permeation chromatography was used for the determination of the molecular weights and molecular weight distributions. Differential scanning calorimetry showed that the glass-transition temperatures of the CEPS samples increased with increasing ␣-methylstyrene contents. The prevention of the collapse of the EPS cells was observed in scanning electron microscopy images of the inner portions and outer surfaces of the CEPS samples.

Commercially available diethyl, dicetyl, and dimyristyl peroxydicarbonate initiators are investigated in a commercial PVC suspension polymerization recipe. Diethyl peroxydicarbonate, which is formed in situ by the reaction of hydrogen peroxide, lime, and ethylchloroformate, produced PVC with less "fish-eyes", whereas it has the disadvantage of being toxic and gives inconsistent polymerization times, therefore the reactor efficiency decreases. Dicetyl and dimyristyl peroxydicarbonates are solid, less toxic materials easy to handle, therefore, when these initiators are used, consistency between batches is obtained. However, PVC with coarse particle sizes containing considerable amounts of "fish-eyes" is obtained, which eventually causes processing problems. It is found that particle coarsening occurs as a result of water soluble impurities of initiators, and "fish-eyes" occur as a result of morphological changes. When dicetyl and dimyristyl type initiators are used, the number of non-porous PVC particles increases. This structure heterogeneity causes formation of ungeltified spots, so-called "fisheyes", during processing. It is found that the non-porous particles are formed due to accumulation of an excessive amount of initiator in a single vinyl chloride monomer droplet.When the distribution of these solid initiators is homogenized by adding them in solution, the formation of non-porous particles is inhibited. However, the coarsening effect still remains, which could be eliminated by extraction of initiator solutions with water just before they are fed to the reactor. Extraction also decreases the amount of crust formation. ZUSAMMENFASSUNG Handelsiibliche Diethyl-, DicetyJ-und Dimyristylperoxydicarbonat-Initiatoren wurden in einem technischen PVC-SuspensionspolymerisationsprozeR verwendet. Diethylperoxydicarbonat, das aus Wasserstoffperoxid, Chlorameisenstiureethylester und Kalk in situ hergestellt wurde, fiihrte zu einem PVC mit wenigen ,,Fischaugen", jedoch erwiesen sich dessen Toxizitat und die ungleichmaRigen, den Reaktorwirkungsgrad herabsetzenden Polymerisationszeiten als nachteilig. Dicetyl-und Dimyristylperoxydicarbonat 0 1991 Hiithig & Wepf Verlag, Basel CCC 0003-3146/91/$04.00 99 C. Arslanalp, E. Erbay, T. BilgiG 0. T. Savayqisind weniger giftige, leicht handhabbare Feststoffe, die, als Initiator, verwendet zu wesentlich gleichmafligeren Produkten fiihren; man erhalt ein grobkorniges PVC, das jedoch relativ viele ,Fischaugen" enthalt, wodurch moglicherweise Verarbeitungsprobleme verursacht werden konnen. Es konnte gezeigt werden, da8 die Vergroberung der PVC-Partikel auf wasserldsliche Verunreinigungen im Initiator und das Auftreten von ,,Fischaugen" auf morphologische Veranderungen zuriickzufiihren sind. Bei Verwendung von Dicetyl-und Dimyristylperoxydicarbonat steigt die Anzahl der nicht-porosen PVC-Teilchen an. Diese Strukturinhomogenit&t fiihrt beim Verarbeiten zur Bildung von nicht erstarrenden Bereichen, den sogenannten ,,Fischaugen". Es konnte gezeigt werden, daf3 diese nicht-porosen Teilchen durc...