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ABSTRACT:Sol-gel transitions of a series of fractionated low-density polyethylenes in cyclohexane--{:arbondisulfide were studied. Gelation temperatures increased with polymer concentration as well as molecular weight. Experimental data were analyzed by a theory proposed by Takahashi, Sakai and Kato for the gel-melting temperature of branched polymers. This theory was found to apply well to the experimental data. The results of our study suggest that the size of the crystalline junction is independent of the molecular weight of fractionated samples.KEY WORDS Sol-Gel Transition I Gel I Gel-Melting Temperature Polyethylene I Branched Polyethylene I Low Density Polyethylene I It is well known that polyethylene withstands chemical reagents and is soluble in organic solvents only at elevated temperatures. This is a very good property of polyethylene but one which makes it difficult to measure molecular weight and solution properties. A few years ago, Nita Das and Palit reported that low density polyethylene was soluble near room temperature in binary mixtures of organic solvents such as xylene-carbondisulfide, cyclohexane-carbondisulfide, cyclohexane-trichloroethylene and cyclohexane-cyclohexanone systems.1 Their experiments were followed over a wide range of concentrations in our laboratory; we found that solutions of low density polyethylene in cyclohexane-carbondisulfide were converted to gels on cooling and the gels reverted to solutions when were warmed near room temperature. 2 · 3 Moreover, we found from X-ray diffraction patterns that the gels were crystalline. Our experimental results showed that gel-formation temperature depended on the molecular weight of the polymer as well as the concentration of the solution. Recently, Takahashi, Sakai, and Kato carried out similar experiments using three unfractionated branched polyethylenes and proposed a new theory for treating the gelmelting temperature of a branched polymer. 4 Their treatment is useful for estimating the size of a crystalline junction in the gel. In this study, gelation temperatures were measured for a series of fractionated low density polyethylene in cyclohexane-carbondisulfide and compared with the theory of Takahashi, Sakai, and Kato.