By employing solution serial reactors along with judicious choices of organometallic catalysts, bimodal comb block copolyolefins can be produced with bimodalities in molecular weight, in branching, and in composition distributions. A low molecular weight (MW) vinyl terminated polyolefin prepared in the first reactor along with its catalyst and unreacted olefin monomer was fed directly into the second reactor without purification and catalyst termination. A second olefin monomer and a second catalyst capable of incorporating macromers and of producing high MW were then added in the second reactor leading to the synthesis of bimodal comb block polyolefins. These comb block copolyolefins contain low MW linear polyolefins of mixed compositions and high MW comb branched polyolefins of a constant composition.<br/>Various bimodal PE-sb-aPP, or polyethylene-(side block)-atactic polypropylene, was thus prepared with propylene being the first-reactor monomer and ethylene being the second-reactor monomer with varying aPP comb arm MW, backbone MW, and comb arm number. Their bimodalities were confirmed by GPC-4D (Gel Permeation Chromatography-4 Detectors) and by extraction C13 NMR (Carbon 13 Nuclear Magnetic Resonance). The presence of these low MW linear polypropylene and poly(propylene-r-ethylene) may prevent the micelle formation of the high MW comb block PE-sb-aPP as evident by the devoid of micelles examined by bimodal AFM (atomic force microscopy), when the bimodal PE-sb-aPP was added into HDPE (high density polyethylene), iPP (isotactic polypropylene), and blends of HDPE and iPP. Without the micelle formation, the high MW PE-sb-aPP can be intimately entangled with HDPE and with iPP delivering extensional flow hardening, as measured by SER (Sentmanat Extensional Rheometer) rheometer, when the bimodal PE-sb-aPP was added at 5% or less. In addition to enhancing processabiity of PE, iPP, and PE/iPP blends, it was found that this bimodal PE-sb-aPP can compatibilize the immiscible blends of HDPE and iPP.

Bimodal comb block polyolefins by serial reactors

251st National Meeting (2016)

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