Strategy for Scalable Comb Block Polyolefin Synthesis. Efficient Graft of Isotactic Polypropylene to a Commercial Broad Molecular Weight Distribution, Hyperbranched, Ethylene Methylacrylate Copolymer

• Published in: Macromolecules 2020-08, Vol.53 (15), p.6353-6368
• Main Authors: Brant, Patrick, Lu, Jiemin, Shivokhin, Maksim, Yakovlev, Sergey, Kang, Shuhui, Welke, Bethany, Raney, Melissa, Throckmorton, Joseph, Rapp, Jennifer, Wang, Hao, Yablon, Dalia
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.0c00828

Judicious selection and use of a readily available, reactive polyolefin backbone can facilitate scalable comb block construction. This can be further assisted by appropriate grafting chemistry. In this work, alcohol-terminated isotactic polypropylene (iPP-OH) is grafted to commercially available hyperbranched, very broad molecular weight distribution ethylene methyl acrylate copolymer (EMA; 20.9 wt % methylacrylate; melting peak 80 °C). iPP-OH (melting peak 135 °C; number average molecular weight 16 kDa/mole) is synthesized from vinyl-terminated isotactic polypropylene (vt-iPP) macromonomer by oxidative hydroboration in 75% yield based on initial vt-iPP mass charged and >95% yield based on the consumption of vinyl termini. This product is in turn grafted efficiently onto the EMA via the transesterification of less than 2% of the MA groups to yield comb block copolymers (EMA-cb-iPP). Two graft products containing 24 and 38 wt % iPP were prepared, with grafting efficiency determined to be greater than 80 and 95%, respectively, based on alcohol consumption (1H NMR and 13C NMR). Efficient grafting of iPP-OH to EMA and the hyperbranched nature of EMA and comb block products were further affirmed by GPC equipped with multiple detectors, including an infrared detector capable of differentiating polyethylene from polypropylene. Scanning transmission electron microscopy and atomic force microscopy, along with small-angle X-ray scattering, of the EMA-cb-iPP products show that, in spite of the structural complexity of the EMA, these products readily self-assemble into uniformly finely textured morphology of phase-separated EMA and iPP of the order 50–100 nm. These blocks act to compatibilize blends of EMA and iPP and disperse well into iPP. It is believed that the synthetic strategy illustrated hereinespecially the use of a commercially available reactive polyolefin to, from, or through which to graftwill encourage pursuit of economically viable and scalable comb block synthetic strategies for new material applications.