Confined crystallization in lamellae forming poly(3-(2′-ethyl)hexylthiophene) (P3EHT) block copolymers

Charge transport in poly(3-alkylthiophene)s (P3AT)s is closely linked to the nanoscale organization of crystallites. Block copolymer morphologies provide an ideal platform to study crystallization as the chain ends are tethered at a known interface in a well-defined geometry. The impact of soft versus hard confinement on P3EHT crystallization was studied using poly(3-(2′-ethyl)hexylthiophene) (P3EHT) containing diblocks with both rubbery poly(methyl acrylate) (PMA) and glassy polystyrene (PS) blocks. Here, P3EHT's lower melting point relative to the commonly studied poly(3-hexylthiophene) (P3HT) facilitated its confined crystallization and makes it an ideal model system. While transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) revealed well-ordered lamellar morphologies both in the melt and post-crystallization for both sets of diblocks, the glassy blocks inhibit confined crystallization of P3EHT relative to rubbery matrix blocks. Analysis of aligned diblocks by both SAXS and wide angle X-ray scattering (WAXS) revealed that the P3EHT chain axis aligns perpendicular to domain interfaces, allowing preferential growth of the alkyl-chain and π–π stacking directions parallel to lamellae. Finally, it was shown that following diblock self-assembly in the melt, crystallite growth drives expansion of microdomains to match the P3EHT contour length. It was concluded that P3EHT chains adopted an extended conformation within confined crystallites due to the rigid nature of polythiophenes relative to flexible chain crystalline polymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 205–215     

Free-radical copolymerisation of acrylamides,acrylates, and α-olefins

We report the results of a joint theoretical and experimental investigation into the copolymerisation of acrylamides and acrylates with α-olefins in free-radical processes. The transition-state structures of models for free-radical homo- and copolymerisation involving acrylamide, methylacrylamide, methacrylate, methyl methacrylate, and ethylene have been determined using density functional theory. The reaction energies and barrier heights comport with the experimentally observed properties, including the prevalence of monomer alternation, the realised stereospecificity, and the reaction yield. Continuum solvation models have been applied to determine the sensitivity of the relative energies to the bulk solvent properties. Experimentally, a Lewis acid catalyst is demonstrated to increase the incorporation of nonpolar 1-alkenes in copolymerisations with polar acrylamides and acrylates. In the presence of the Lewis acid, scandium (III) trifluoromethanesulfonate, the copolymerisation of 1-hexene and acrylamide results in an 8.5 mol % incorporation, up from 3.9 mol % in the absence of the Lewis acid. Computations incorporating Mg²⁺ as a model Lewis acid elucidate the mechanism of this catalysis. In the addition of methacrylate to a methyl methacrylate radical terminated polymer, the Lewis acid binds to the carbonyls on both promoting isotactic addition, while for the addition of an alkene to the same polymer, the Lewis acid binds to the polymer, reducing the barrier for alkenyl addition inductively by withdrawing electron density. We have demonstrated the ability of computational studies to aid experimentalists in the synthesis of new copolymers with desired properties.     

Dispersion of single‐walled carbon nanotubes using nucleobase‐containing poly(acrylamide) polymers

Single‐walled carbon nanotubes (SWNTs) possess extraordinary properties, but suffer from poor solubility and a lack of purity. Of the possible routes available to solubilize and purify nanotube samples, the use of noncovalent functionalization is ideal as carbon nanotube properties are not deleteriously affected. A multitude of different dispersants have been investigated thus far, but of particular interest is deoxyribonucleic acid (DNA), which has previously been demonstrated to effectively separate metallic and semiconducting carbon nanotubes. Here, we investigate the ability of synthetic nucleobase‐containing poly(acrylamide) polymers to produce stable nanotube dispersions in organic solvents. Polymers bearing different nucleobase and backbone structures, as well as block copolymers with different block sequences were investigated. Polymer:SWNT mass ratios and solvent compositions were optimized for the nucleobase‐functionalized polymers, and semiconducting and metallic SWNT populations were identified by a combination of UV‐Vis‐NIR absorption, Raman, and fluorescence spectroscopy. These results demonstrate the capacity for synthetic DNA analogues to disperse SWNTs in organic media. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2611–2617