Search

The length of pendant side chains in charged, random, comb‐shaped polymers dictates the nature of their short‐range ordering. Random copolymers, and terpolymer, of 4‐vinylpyridine (4VP), styrene, and isoprene were synthesized and subsequently fully quaternized with 1‐alkylbromides having varying number of carbons on the alkyl group ranging from 2 to 8. Evaluation by wide angle X‐ray scattering revealed that dipole–dipole attraction facilitates the formation of ionomer cluster morphology in samples with two carbons on the pendant side chain, whereas for samples with four or more carbons on the pendant side chains, side‐chain sterics was dominant resulting in periodic backbone spacing. Copolymers with isoprene, having flexible backbones, favor the formation of ionomer cluster morphology while styrene copolymers having rigid backbones disfavor the formation of ionomer clusters. An "in‐line" dipole model was developed to predict the separation distance at which both ionomer cluster and backbone–backbone morphologies could coexist. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1325–1336 [ABSTRACT FROM AUTHOR]

Anion exchange membranes (AEM) are polymer electrolytes that facilitate ion transport in alkaline fuel cells and electrochemical devices. Fabrication of mechanically durable AEMs with high ionic conductivity is a challenge. Here, a copolymer of isoprene and vinylbenzyl trimethylammonium and a terpolymer of isoprene, vinylbenzyl trimethylammonium and styrene were crosslinked by various methods, and properties, including conductivity and mechanical strength, were investigated at dry and saturated conditions. Polymer chemistry and degree of crosslinking significantly influenced conductivity, swelling, and mechanical properties. The terpolymer had a higher proportion of vinylbenzyl trimethylammonium units increasing the ion exchange capacity (IEC), but membranes could still be rendered insoluble by crosslinking. The higher IEC of the terpolymer resulted in higher chloride conductivity, 20-75 mS/cm at 50°C and 95%RH, compared to 4-17 mS/cm for the copolymer at the same conditions. At dry conditions films were stiff, having Young's moduli between 100-740 MPa, but hydration caused severe softening, reducing moduli by 1-2 orders of magnitude. The severe softening effect of hydration was confirmed by dynamic mechanical analysis. The AEMs studied did not have adequate mechanical durability at hydrated conditions, additional work is needed to determine polymer chemistries and crosslinking methods that will produce robust AEMs for long-term use in fuel cells and electrochemical devices. [ABSTRACT FROM AUTHOR]

A systematic comparison between graft poly( l-lactide) copolymers with different topologies and their ability to form stereocomplexes with poly( D-lactide) (PDLA) is performed. Comb and hyperbranched copolymers based on functional poly(ethylene glycol) and poly( l-lactide) with molecular weights in the range of 2000-90 000 g mol−1 and moderate molecular weight distributions ( Mw/ Mn = 1.08-1.37) are prepared via the combination of anionic and ring-opening polymerization. Two 'topological isomers,' a linear poly(ethylene oxide)/poly(glycerol) (PEG/PG) copolymer and a branched PEG/PG copolymer are used as backbone polymers. Furthermore, the stereocomplex formation between PDLA and the hyperbranched and comb copolymers containing poly( l-lactide) arms is studied. Stereocomplex formation is confirmed by DSC as well as by Fourier transform IR (FTIR) and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Front Cover: Instead of using traditional chemical crosslinking, flexible and rubbery poly(lactic acid) can be created by controlling the crystallization process. The stereo complex crystals formed are the “physical crosslinks”. This slide is used to demonstrate the relative crystallization kinetics and the morphology formed for two chemically identical but physically different co‐crystallizing PLA based blends. Further details can be found in the article by S. R. Rathi, D. Ng, E. B. Coughlin,* S. L. Hsu,* C. S. Golub, G. H. Ling, and M. J. Tzivanis on page 320. [ABSTRACT FROM AUTHOR]

Abstract: Recent developments in single-site catalysis (SSC) have led to many interesting discoveries in ethylene and α-olefin copolymerizations. Here, we report the synthesis of, and polymerizations with, supported piano-stool catalysts and their related analogues. CpTiCl3, Cp*TiCl3, TMSCpTiCl3, and (TMS)2CpTiCl3 were covalently bound to a poly(styrene-r-4-hydroxystyrene) copolymer, affording macroligated catalysts. Ethylene/1-octene and ethylene/styrene copolymerizations with each of these supported catalysts were attempted with cocatalysts including methyl aluminoxane, B(C6F5)3, [Ph3C][B(C6F5)4], and [PhN(CH3)2H][B(C6F5)4]. To determine the effects that the macroligand and the substituents on the cyclopentadienyl ring have on polymer yield and activity, comonomer incorporation, polymer composition, molecular weight, polydispersity index, melting point, and crystallization behavior were investigated. We discovered that the catalysts have vastly different, yet interesting, effects on ethylene/1-octene (EO) and ethylene/styrene (ES) copolymerizations. For ethylene/1-octene copolymers, the activity of the supported catalysts and the amount of 1-octene incorporated into the copolymer is dependent upon the substituents on the cyclopentadienyl ring. The formation of EO copolymers using supported aryloxy-based cyclopentadienyl complexes can also be used as additional evidence for the presence of the tethered aryloxy moiety. The copolymer composition and the thermal properties of these copolymers were also studied. Ethylene/styrene copolymerizations produced polymers with varying characteristics specific to the catalyst employed for the polymerizations. Polymers synthesized with the supported CpTiCl3 and TMSCpTiCl3 displayed both polyethylene and syndiotactic polystyrene melting points. Conversely, polymers synthesized with the supported Cp*TiCl3 displayed only a polyethylene melting point, while polymers prepared with the supported (TMS)2CpTiCl3 displayed only a syndiotactic polystyrene melting point. These findings suggest that copolymerization of ethylene and styrene is not possible with these catalysts. Analysis of the homopolymerizations of styrene and ethylene with Cp*TiCl3 and (TMS)2CpTiCl3, respectively, shows significantly lower activities, leading to preferential polymerization of the more active monomer during copolymerization. [Copyright &y& Elsevier]

Abstract: Proton conducting polymers and copolymers containing tethered benzimidazole moieties spanning a wide range of glass transition temperatures (2–113 °C) have been prepared. Conductivity versus temperature plots of the homopolymers display the competing effects of mobility and charge carrier density. Consistent with literature reports, T g values of benzimidazole-containing polymers increased over the parent polymer, however, successful reduction of T g was accomplished by copolymerizing a benzimidazole functional acrylate monomer (B5A) with poly(ethylene glycol) methyl ether acrylate (PEGMEA). The reduction in T g is thought to occur through disruption of intermolecular forces between benzimidazole units. Evaluation of conductivity as a function of temperature by ac impedance methods indicate that decreasing T g through copolymerization results in conductivity increases over the low and intermediate temperature range (40–160 °C). Copolymer T g decreases with increasing PEGMEA content, and conductivity at 40 °C can be increased by nearly 2.5 orders of magnitude over B5A homopolymer. However, conductivity at high temperatures (>160 °C) decreases due to charge carrier dilution by the addition of PEGMEA. [Copyright &y& Elsevier]