BACKGROUND: Selection of polymers for two-phase partitioning bioreactors (TPPBs) has been focused primarily on predicting a polymer's affinity for the target molecule. Although the extent to which a polymer absorbs a solute is important, the rate of uptake/release must be sufficiently rapid such that a TPPB is not mass transfer limited. This work focused on developing a guide to identify combinations of polymer diffusivities and diffusional path lengths that will ensure a TPPB is not limited by substrate delivery.

A new method of exerting control over the dynamics and outcomes of radical-mediated polyolefin modifications is adapted for the dynamic vulcanization (DV) of polypropylene + poly(ethylene-co-octene) (PP+EOC) blends. Whereas the conventional peroxide-initiated DV of these blends produce extreme initial rates of EOC cross-linking and extensive PP matrix degradation, formulations containing nitroxyls that bear polymerizable functionality do not suffer from these limitations. Acryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl (AOTEMPO), used alone or in combination with a triacrylate monomer, is used to delay the onset of polymer modification, raise the cross-link density of dispersed elastomer phase, and mitigate changes to the molecular weight of the thermoplastic matrix. Brief demonstrations of the influence of AOTEMPO on dicumyl peroxide (DCP) modifications of each blend component are followed by careful studies of PP+EOC dynamic vulcanization. Dispersed phase size distributions and melt-state oscillatory rheometry reveal the effect of AOTEMPO on DV product architecture and morphology.

New chemistry for controlling the dynamics and yields of radical‐mediated polyolefin modifications is adapted to prepare impact‐resistant thermoplastic vulcanizates. Dynamic vulcanization of polypropylene (PP) + poly(ethylene‐co‐octene) (EOC) blends using small amounts of acryloyloxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (AOTEMPO) overcomes the limitations of conventional peroxide formulations, giving products with fine EOC particle dispersions, high PP matrix viscosities, and superior mechanical toughness. Guidelines for selecting starting materials and reagent concentrations are developed before assessing the merits of an AOTEMPO‐derived products relative to benchmark blend materials. Measurements of dispersed‐phase size distributions and melt‐state oscillatory shear rheological properties are combined with solid‐state impact resistance, flexural, and tensile data to identify the strengths and limitations of AOTEMPO chemistry with respect to impact‐toughening applications. POLYM. ENG. SCI., 58:1999–2007, 2018. © 2017 Society of Plastics Engineers