Study of Polyolefin Gel in Organic Solvents VII. Thermoreversible Gelation of Ethylene-Propylene Random Copolymer in Carbon Disulfide, Toluene, and Cyclopentane

Abstract

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.

Study of Polyolefin Gel in Organic Solvents VIII. Size of Crystalline Junction and Structure of Ethylene-Propylene Random Copolymer Gel

“…So, the effect of propylene content on T~ is examined in the following section using the Takahashi theory. It was already found in the previous study 12 that the theory was applicable well to EP random copolymer-organic solvent gel systems.…”

“…32 Values of Xe are summarized in Table IV together with those determined from DSC measurements. 12 values from X-ray and DSC measurements shows approximately good agreement for each sample. In this respect, the present analysis of X-ray diffractions was carried out precisely.…”

“…-40 to -70°C. 12 T~ ofEP gel lowered considerably in comparison with that of iPP, LHDPE, LLDPE, or BLDPE gel as seen in Figure l(A). In that study, it was suggested from measurements of X-ray diffraction, atomic force microscope, and transmission electron microscope that fringed micelle-type junctions were formed in EP gels.…”

“…Moreover, melting behavior of the gels obeyed well the Takahashi theory, 13 • 14 in which junction point of a copolymer-diluent gel system is modelled as a fringed micelle morphology. As the Takahashi theory was found to be applicable to T~ of EP random copolymer gels, effect of the content of propylene units on T~ was examined qualitatively in the previous study 12 with the aid of the theory.…”

“…Values of ( in CS 2 , cyclopentane, and toluene which were used in the previous study 12 are calculated in this study, and are summarized in the same used here where the differences in molecular weights are not so large. It is well known that there are generally three models for the interfacial structure of lamellar crystals crystallized from the melt 2 4 : the regular model with the same thickness of lamellar height; the irregular model with different thicknesses of lamellar height; the switchboard model in which a non-ordered amorphous layer is present on each side of the lamellae.…”