Separations of commercial polyolefins, which often involve mixtures of linear and branched polyethylenes, can be very challenging to optimize as species with similar hydrodynamic sizes or solubility often co-elute using various chromatographic methods. To better understand the effects of polyolefin structure on the dilute solution properties of polyolefins, a family of short-chain branched polyolefins with control of alkyl branch frequency and branch length were synthesized by ring-opening metathesis polymerization (ROMP) of 1-alkyl-<i>trans</i>-cyclooctene monomers. Quantitative post-polymerization hydrogenation generates the final branched polyolefins with ideal head-to-tail addition of monomer, resulting in a fixed branch frequency and branch length across the molar mass distribution.<br/>A series of linear polyolefins with comparable molar masses, but varied short-chain branch length, were analyzed by high temperature size exclusion chromatography with infrared, refractive index, viscometric, and multi-angle light scattering detectors to quantify molar mass, molar mass distribution, intrinsic viscosity, radius of gyration, and degree of short-chain branching. A systematic decrease of intrinsic viscosity is observed with increasing branch length across the entire molar mass distribution. Polymer conformational constants, such as the contraction ratio and viscosity shielding ratio, were also determined and confirmed by offline small angle neutron scattering measurements (SANS). These values provide valuable information about the solution properties of these materials as a function of branch length. These short-chain branched polyolefins can serve as useful standards to calibrate the branching index factor as a function of molar mass so long-chain and short-chain branching distributions in polyolefins can be more accurately measured. Mixtures of the branched polymers at unknown compositions and variable branching frequency were also analyzed to determine if all species present could be identified and accurately quantified.

High temperature size exclusion chromatography measurements of polyolefins with precise control of branch frequency and branch length<br />

255th National Meeting (2018)

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