Polymerized ionic-liquids (PILs) are promising materials whose ionic properties can be tuned based on their chemistry. By incorporating PILs into block copolymer (BCP) structures, it is possible to provide complementary functionality (i.e., structural stability) and transport tunability to ionconducting materials. In this study, we describe the selfassembly and conductivity of novel poly(styrene-blockhistamine methacrylamide) diblock copolymers (PS-b-PHMA) and the resulting PS-b-PIL derivatives obtained after treatment with trifluoroacetic acid (TFA). These materials selfassemble into ordered BCP structures with tunable domain sizes as demonstrated by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). PS-b-PHMA membranes show conductivities up to 2 × 10 −4 S/cm at room temperature, which increase by an order of magnitude in the presence of acid. In addition, both PHMA-and PIL-based membranes exhibit lower water uptake (λ = 4−6 and 8−10, respectively) in comparison with most proton conducting membranes reported elsewhere. The low water content in these membranes translates into a stronger effect of morphology on transport behavior, resulting in a measurable increase in ion conductivity as a function of conducting channel size.
A semicrystalline polyethylene (PE) macroinitiator was prepared by copolymerizing ethylene and an inititating monomer (5-norbornen-2-yl-2'-bromo-2'-methyl propanoate) (3) using [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)isobutanamidato]-Ni(eta1-CH2Ph)(PMe3) (1) and Ni(COD)2 (bis(1,5-cyclooctadiene)-nickel) (2). Although 3 decomposes Ni(COD)2, if the initiating species (1/2) are exposed to ethylene for a period of time, t1, and then 3 is introduced for another period of time, t2, the polymerization takes place in a controlled manner. Variations in temperature, pressure, and [3] afford a great deal of control over the composition and architecture of the PE macroinitiator. Subsequent grafting with methyl methacrylate (MMA) yields PE-graft-PMMA with narrow polydispersities and increasing PMMA content at longer reaction times. Because the products are semicrystalline materials with high melting points, they are anticipated to function as blend compatibilizers for linear polyethylene.
Abstract:The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum's acid is shown to be effectively copolymerized with polyethylene using a nickel R-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum's acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization.
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