Fractions of both linear polyethylene and ethylene-butene copolymers were found to form thermally reversible gels when crystallized from quiescent p-xylene solutions. For linear polyethylene, gels were observed over the molecular weight range from 1.26 x 10('3) to 1.62 x 10('6). The maximum polymer concentration required for gelation to occur was found to depend on the molecular weight and the crystallization temperature. For linear polyethylene solutions cooled rapidly to 22(DEGREES)C, this concentration was found to range from 2.0% (wt./vol.) for the low molecular weight fractions to 0.3% for the highest molecular weight. The concentration required for gelation to occur was found to increase greatly for crystallization at 86(DEGREES). Linear polyethylene fractions were observed to form gels at substantially lower concentrations than ethylenebutene copolymer fractions of comparable molecular weight. / Studies of the crystallite thickness and accompanying thermodynamic properties demonstrated that the gels were composed of lamellar crystallites very similar in nature to those shown to be characteristic of crystallization from dilute solutions (0.08%). / Polarized light microscopy studies revealed in all the gels studied large supermolecular structures up to 100 microns in length. The concentration where adjacent supermolecular structures begin to exhibit substantial overlap was found to correspond to the minimum concentration required for gel formation. These morphological studies of ethylene-butene copolymers and linear polyethylene fractions when crystallized from relatively dilute solutions were shown to provide interesting parallels with similar studies on bulk crystallized samples. / In conclusion, this work showed thermally reversible gelation to be a more general aspect of polymer crystallization than had been thought previously. / Source: Dissertation Abstracts International, Volume: 42-10, Section: B, page: 4077. / Thesis (Ph.D.)--The Florida State University, 1981.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_74667 |
| Contributors | EDWARDS, CHARLES O'NEIL., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 168 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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