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Cyclic ketene acetals (CKAs) possess unique features in two aspects. On one hand, after the addition of a radical on the alkene, CKAs can undergo ring‐opening via radical rearrangement, enabling polyester preparation based on chain‐growth polymerization. On the other hand, the alkene connected with two electron‐donating oxygens in a strained form exhibit unique reactivities, resulting in complex reactions in the presence of electron deficient compounds. In this investigation, fundamental studies on CKA radical ring‐opening polymerization and charge‐mediated reactions were performed. Alternating copolymers of CKA and maleimides, or maleates, were prepared and characterized. Quantum chemistry modeling from the perspectives of reaction kinetics and thermodynamics enabled an in‐depth mechanistic study on the side reactions between CKA and maleic anhydride or itaconic anhydride, inspiring the techniques to minimize those side reactions in competition with radical copolymerization. After purifying the anhydride monomers with sublimation, the copolymerization with CKA successfully occurred. The anhydride containing polyester structures with an alternating sequence were confirmed with comprehensive characterizations. Facile post‐functionalization with an alcohol was performed, resulting in carboxylate containing polyesters. [ABSTRACT FROM AUTHOR]

The phase behavior of block copolymers (BCPs) at the water‐oil interface is influenced by the segmental interaction parameter (χ ${\chi }$) and chain architecture. We synthesized a series of star block copolymers (s‐BCPs) having polystyrene (PS) as core and poly(2‐vinylpyridine) (P2VP) as corona. The interaction parameters of block‐block (χ ${\chi }$ PS‐P2VP) and block‐solvent (χ ${\chi }$ P2VP‐solvent) were varied by adjusting the pH of the aqueous solution. Lowering pH increased the fraction of quaternized‐P2VP (Q‐P2VP) with enhanced hydrophilicity. By transferring the equilibrated interfacial assemblies, morphologies ranging from bicontinuous films at pH of 7 and 3.1 to nanoporous and nanotubular structure at pH of 0.65 were observed. The nanoporous films formed hexagonally packed pores in s‐BCP matrix, while nanotubes comprised Q‐P2VP as corona and PS as core. Control over pore size, d‐spacing between pores, and nanotube diameters was achieved by varying polymer concentration, molecular weight, volume fraction and arm number of s‐BCPs. Large‐scale nanoporous films were obtained by freeze‐drying emulsions. Remarkably, the morphologies of linear BCPs were inverted, forming hexagonal‐packed rigid spherical micelles with Q‐P2VP as core and PS as corona in multilayer. This work provides insights of phase behaviors of BCP at fluids interface and offer a facile approach to prepare nanoporous film with well‐controlled pore structure. [ABSTRACT FROM AUTHOR]

One of the important challenges in designing robust alkaline anion exchange membranes is the difficulty associated with the chemical stability of covalently bound cationic units. Here, a systematic study exploring alkaline stabilities of polymerizable hexyltrimethylammonium cations is presented, where the hexyl chain is linked to a phenyl ring through a direct carbon‐carbon, phenyl ether, or benzyl ether functionality. For this work, small molecule model compounds, styrenic monomer analogs, and their homopolymers are synthesized. Alkaline stabilities of the small molecule cations and their homopolymers are compared to alkaline stability of benzyltrimethylammonium (BTMA) cation and its homopolymer poly(BTMA), respectively. All the hexyl‐tethered cations and their homopolymers are significantly more stable under strongly alkaline conditions (2 m KOD at 80 °C). Moreover, ether‐linked cations show comparable stability to the direct carbon‐carbon linked cation. Via 1H NMR analyses, possible degradation mechanisms are investigated for each small molecule cation. Findings of this study strongly suggest that the alkaline stability is dictated by the steric hindrance around the β‐hydrogen. This study expands beyond the limits of general knowledge on alkaline stability of alkyl‐tethered ammonium cations via the Hofmann elimination route, highlights important design parameters for stable ammonium cations, and demonstrates accessible directly polymerizable alkaline stable ammonium cations. [ABSTRACT FROM AUTHOR]

Ionic conductivity in a polymeric fuel cell requires water uptake. Previous theoretical studies of water uptake used idealized parameters. We report a parameter-free prediction of the water-swelling behavior of a model fuel cell membrane. The model polymers, poly(methyl-butylene)-block-poly(vinylbenzyl-trimethylamine), form lamellar domains that absorb water in humid air. We use the Scheutjens-Fleer methodology to predict the resulting change in lamellar structure and compare with x-ray scattering. The results suggest locally uniform water distributions. However, under conditions where a PVBTMA and water mixture phase-separate, the two phases arrange into stripes with a dilute stripe sandwiched between two concentrated stripes. A small amount of water enhances conductivity most when it is partitioned into such channels, improving fuel-cell performance. [ABSTRACT FROM AUTHOR]

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 (AEMs) are a promising class of materials for applications that require selective ion transport, such as fuel cells, water purification, and electrolysis devices. Studies of structure--morphology--property relationships of ion-exchange membranes revealed that block copolymers exhibit improved ion conductivity and mechanical properties due to their microphase-separated morphologies with well-defined ionic domains. While most studies focused on symmetric diblock or triblock copolymers, here, the first example of a midblock quaternized pentablock AEM is presented. A symmetric ABCBA pentablock copolymer was functionalized to obtain a midblock brominated polymer. Solution cast films were then quaternized to obtain AEMs with resulting ion exchange capacities (IEC) ranging from 0.4 to 0.9 mmol/g. Despite the relatively low IEC, the polymers were highly conductive (up to 60 mS/cm Br- at 90 °C and 95%RH) with low water absorption (<25 wt %) and maintained adequate mechanical properties in both dry and hydrated conditions. X-ray scattering and transmission electron microscopy (TEM) revealed formation of cylindrical non-ionic domains in a connected ionic phase. [ABSTRACT FROM AUTHOR]

Understanding the structure–property relationships and the phenomena responsible for ion conduction is one of the keys in the design of novel ionomers with improved properties. In this report, the morphology and the mechanism of ion exchange in a model anion exchange membrane (AEM), poly(vinyl benzyl trimethyl ammonium bromide)-block-poly(methylbutylene) ([PVBTMA][Br]-b-PMB), is investigated with small angle X-ray scattering, high-resolution thermogravimetry, modulated differential scanning calorimetry, dynamic mechanical analysis, and broadband electrical spectroscopy. The hyper-morphology of the material consists of hydrophilic domains characterized by stacked sides of [PVBTMA][Br] which are sandwiched between “spaghetti-like” hydrophobic cylindrical parallel domains of the PMB block. The most important interactions in the hydrophilic domains occur between the dipoles of ammonium bromide ion pairs in the side chains of adjacent chains. A reordering of the ion pair dipoles is responsible for a disorder–order transition (Tδ) at high temperature, observed here for the first time in AEMs, which results in a dramatic decrease of the ionic conductivity. The overall mechanism of long range charge transfer, deduced from a congruent picture of all of the results, involves two distinct ion conduction pathways. In these pathways, hydration and the motion of the ionic side groups are crucial to the conductivity of the AEM. Unlike the typical perfluorinated sulfonated proton-conducting polymer, the segmental motion of the backbone is negligible. [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]

The crystallization behavior of two chemically identical but physically different co-crystallizing poly( l-lactic acid) (PLLA)-based blends is studied. The first set studied involves an all- l unit polymer (PLLA) co-crystallizing with a PDLA-miscible soft polyether-PDLA triblock copoly­mer, where d refers to the d isomer. The second set studied involves homopolymer blends of PLLA/miscible soft polyether/PDLA with compositions identical to the first set. Crystallization is performed under isothermal and non-isothermal crystallization conditions and the crystallization kinetics, crystal perfection, and the blend morphology are investigated. It is clear that the stereocomplex crystallization is significantly slower in the triblock copolymer blends in comparison with the homopolymer blends. Furthermore, based on diffraction, spectroscopic, and thermal data, it is found that the stereocomplex crystals formed in the homopolymer blends achieve higher order and perfection, with a melting temperature 15-20 °C higher than those formed in the triblock blends. [ABSTRACT FROM AUTHOR]

ABSTRACT This short review is meant to provide the reader with highlights in anion exchange membrane research, describe current needs in the field, and point out promising directions for future work. Anion exchange membranes (AEMs) provide one possible route to low platinum or platinum-free fuel cells with the potential for facile oxidation of complex fuels beyond hydrogen and methanol. AEMs and related stable cationic polymers also have applications in energy storage and other electrochemical technologies such as water electrolyzers and redox flow batteries. While anion exchange membranes have been known for a long time in water treatment applications, materials for electrochemical technology with robust mechanical properties in thin film format have only recently become more widely available. High hydroxide and bicarbonate anion conductivity have been demonstrated in a range of AEM formats, but intrinsic stability of the polymers and demonstration of long device lifetime remain major roadblocks. Novel approaches to stable materials have focused on new types of cations that employ delocalization and steric shielding of the positive center to mitigate nucleophilic attack by hydroxide. A number of promising polymer backbones and membrane architectures have been identified, but limited device testing and a lack of understanding of the degradation mechanisms in operating devices is slowing progress on engineered systems with alkaline fuel cell technology. Our objective is to spur more research in this area to develop fuel cell systems that approach the costs of inexpensive batteries for large-scale applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1727-1735, 2013 [ABSTRACT FROM AUTHOR]

Block copolymers of polystyrene- b-poly(vinyl benzyl trimethylammonium tetrafluoroborate) (PS- b-[PVBTMA][BF4]) were synthesized by sequential monomer addition using atom transfer radical polymerization. Membranes of the block copolymers were prepared by drop casting from dimethylformamide. Initial evaluation of the microphase separation in these PS- b-[PVBTMA][BF4] materials via SAXS revealed the formation of spherical, cylindrical, and lamellar morphologies. Block copolymers of polystyrene- b-poly(vinyl benzyl trimethylammonium hydroxide) (PS- b-[PVBTMA][OH]) were prepared as polymeric alkaline anion exchange membranes materials by ion exchange from PS- b-[PVBTMA][BF4] with hydroxide in order to investigate the relationship between morphology and ionic conductivity. Studies of humidity [relative humidity (RH)]-dependent conductivity at 80 °C showed that the conductivity increases with increasing humidity. Moreover, the investigation of the temperature-dependent conductivity at RH = 50, 70, and 90% showed a significant effect of grain boundaries in the membranes against the formation of continuous conductive channels, which is an important requirement for achieving high ion conductivity. © 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1751-1760, 2013 [ABSTRACT FROM AUTHOR]

ABSTRACT The synthesis and characterization of a photocleavable block copolymer containing an ortho-nitrobenzyl (ONB) linker between poly(methyl methacrylate) and poly( d-lactide) blocks is presented here. The block copolymers were synthesized via atom transfer radical polymerization (ATRP) of MMA followed by ring-opening polymerization (ROP) of d-Lactide and ROP of d-lactide followed by ATRP of MMA from a difunctional photoresponsive ONB initiator, respectively. The challenges and limitations during synthesis of the photocleavable block copolymers using the difunctional photoresponsive ONB initiator are discussed. The photocleavage of the copolymers occurs under mild conditions by simple irradiation with 302 nm wavelength UV light (Relative intensity at 7.6 cm: 1500 μW/cm2) for several hours. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4309-4316 [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]