Low-density polyethylene (LDPE) is produced commercially in a high pressure process which uses radical generators to initiate the polymerization. Peroxides, hydroperoxides, and azo compounds are commonly used in the process due to the weak oxygen-oxygen or nitrogen-carbon bonds present within them. By tailoring the substituents around these sensitive linkages, a range of initiation temperatures can be achieved, allowing for better control of the polymerization process. Sterically encumbered diphenylethane compounds, like 2,3-dimethyl-2,3-diphenylbutane, also possess weak linkages, and the scission of the central carbon-carbon bond produces radicals that are competent initiators for ethylene polymerization. However, the initiation temperature for this process is too high for most desired applications. While it is known that increasing the steric bulk present in these structures weakens the bond-strength of the central carbons, it is unclear how such changes effect polymerization behavior. A series of diphenylethane structures were synthesized to help address this question. This motif was rapidly accessed using a two-step procedure; first, a lanthanium catalyzed Grignard alkylation of the corresponding alkylphenones yielded tertiary alcohols; then the tertiary alcohols were stitched together to generate the central carbon-carbon bond using McMurry coupling conditions. This talk will discuss the synthesis of these molecules and will examine whether the initiation temperature for the radical-induced polymerization of ethylene using diphenylethane compounds can be lowered further by tuning the degree of steric congestion within their structure.

Carbon-carbon centered radical initiators for polymerization of unsaturated monomers.

ACS Spring Meeting 2021

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