Influence of Zwitterions on Thermomechanical Properties and Morphology of Acrylic Copolymers: Implications for Electroactive Applications

Abstract

n-Butyl acrylate-based zwitterionomers and ionomers containing 3- [[2-(methacryloyloxy)ethyl](dimethyl)ammonio]-1-propanesulfonate (SBMA) and 2-[butyl(dimethyl)amino]ethyl methacrylate methanesulfonate (BDMAEMA MS), respectively, were synthesized using conventional free radical polymerization. Size-exclusion chromatography confirmed the molecular weights of the copolymers exceeded the critical molecular weight between entanglements (M e ) for poly(n-butyl acrylate). Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and atomic force microscopy (AFM) revealed that zwitterionomers promoted more welldefined microphase separation than cationic analogues. Dynamic mechanical analyses (DMA) of the copolymers showed a rubbery plateau region due to physical cross-links between charges for zwitterionomers only. Since SBMA and BDMAEMA MS have very similar chemical structures, we attributed improved microphase separation and superior elastomeric performance of the zwitterionomers to stronger association between covalently tethered charged pairs.

Structures and Synthesis of Zwitterionic Polymers

“…Although known at least since the late 1950s [9][10][11], they have been considered to be rather exotic compounds for long. They found a certain interest as ionomers [12][13][14][15], for fibres due to strong interactions with charged dye stuffs [16][17][18], and as rheology modifiers in aqueous solutions [19], due to their great tolerance to highly saline environments [5]. Continuously increasing interest in polyzwitterions has risen only since the 1980s, when they were recognized as analogs of important biological structures, such as phospholipids that are the major constituents of cell membranes [20][21][22][23][24][25].…”

“…RDRP techniques offer direct access to polymers bearing zwitterionic groups with previously unthinkable features, such as predefined molar masses and narrow molar mass distributions [163,[182][183][184][185][186][187][188][189] as well as well-defined functional end groups [61,166,182,[190][191][192][193][194][195][196][197][198][199][200][201][202][203][204][205][206][207][208]. Moreover, complex architectures, such as block copolymers [14,[46][47][48]166,167,169,173,187,, graft copolymers [164,213,237,[241][242][243][244]…”

Zwitterionic copolymer self-assembly for fouling resistant, high flux membranes with size-based small molecule selectivity

“…Typical dipole moments of sulfobetaine-type zwitterions are ~18.7-27.6 D [50], whereas water is only 1.9 D. Due to the presence of permanent dipoles and large electrostatic attractions, antiparallel arrangement of dipoles is theoretically predicted to be the most energetically favorable, and the formation of tubular (channels) or lamellar (disk-like) structures are suggested to be strongly favored, as opposed to spheres [34,51]. Studies on the self-assembly of zwitterionic amphiphilic copolymers indicate that zwitterions form clusters ~1-5 nm in size, as measured by small angle X-ray studies and solid state NMR, but do not report morphology [52][53][54][55][56][57][58]. The self-assembly is driven by the strong dipole-dipole interactions between the zwitterionic groups, as well as the differences in χ parameter between the hydrophobic and zwitterionic repeat units [52][53][54][55][56][57][58][59].…”

Thermoresponsive Double Network Hydrogels with Exceptional Compressive Mechanical Properties

“…[14] Their zwitterionic charge results in not only high hydration, [15] but also the potential to improve mechanical properties through physical intra- and inter-chain electrostatic interactions. [16] …”