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

Abstract

ABSTRACT:Gel-melting temperatures (T~) of ethylene-propylene random copolymer gels formed in n-hexane and n-octane were measured as a function of polymer concentration. The copolymers were heterogeneous in both composition and molecular weight. T~ obeyed well the thermodynamic theory derived by Takahashi, in which gel--->sol transition was treated as melting of crystalline junctions with fringed micelle-type morphology: Plots of 1/T~ vs. In V2N according to the theory were scaled on a common straight line when copolymers had similar propylene contents (PC), where V2 is the volume fraction of the copolymer in the gel and Nis the weight-average degree of polymerization. Quantitative analysis of the theory, including measurements of dilute solution properties, led to the results that average size of crystalline junction ( in number of ethylene units per crystalline sequence was ca. 11 for copolymers with PC= 22 wt%, 9 for PC= 26 and 27wt%, and 5 for PC=49wt%, and thus ( decreased with increasing PC. The junction sizes ( were reasonable order as compared with those estimated from X-ray diffractions.

Study of Polyolefin Gel in Organic Solvents IX. Ethylene Sequence Distribution of Ethylene–Propylene Random Copolymer and Crystalline Junction Size in Its Thermoreversible Gel

“…against In V 2 N for each sample, the crystalline junction size ( was determined from the intercept and slope of each straight line according to the method described in the previous study. 4 Values of ( thus determined are summarized in Table II, together with data reported previously. 4 As expected above, values of ( show nearly the same magnitude for the samples with similar PC as shown in Table II, independently of differences in gelation solvents.…”

“…4 Values of ( thus determined are summarized in Table II, together with data reported previously. 4 As expected above, values of ( show nearly the same magnitude for the samples with similar PC as shown in Table II, independently of differences in gelation solvents. That is, the following average values of ( are obtained: ( 11 for the samples with PC= 22 wt¾; ( 9 for the samples with PC=26 and 27wt%; and ( 5 for the sample with PC= 49 wt%, as listed in the last column of Table II.…”

“…4 of this series, EP copolymers in organic solvents (such as carbon disulfide, toluene, cyclopentane, n-hexane, and n-octane) were found to convert to thermally reversible gels when the solutions were cooled below ca. -40°C.…”

“…The discussion regarding correlation between the crystallizable ethylene sequence length in the primary structure of an EP chain and the ethylene sequence length ( in the higher structure such as a crystalline junction point has never been carried out for BP-organic solvent gels. From the above-mentioned viewpoint, the size of crystalline junction ( in an EP copolymer gel is estimated successively from the previous study 4 with the aid of the Takahashi theory using another solvents. Then, ( is compared with crystallizable ethylene sequence length which can be estimated statistically from the sequence distribution curve of ethylene units.…”

Study of Ethylene−Propylene Copolymer Thermoreversible Gels

“…The propensity of ethylene−propylene (EP) random copolymers to form thermoreversible gels has been investigated in a variety of organic solvents . A number of studies have been published on EP copolymer gels. − These studies mainly focused on the influence of polymer concentration, molecular mass, ethylene content, and solvent type on the gel-melting temperature. The data obtained from these studies were also used to determine the average size of the crystalline junctions or crystallites formed by crystallizable ethylene sequences along EP copolymer chains.…”