We report a new class
of organoaluminum-based initiator for anionic
ring-opening polymerization of epoxides that is simple to synthesize
from readily available precursors. The resultant organometallic initiator
was the triethylaluminum adduct of (2-dibenzylamino)ethoxydiethylaluminum
(TAxEDA) [(AlEt3)·(O(AlEt2)CH2CH2N(Bn)2)], which was isolated by direct
crystallization from the reaction medium and then compositionally
and structurally characterized by NMR spectroscopy and XRD. We studied
the reactivity and versatility of the new initiator through the polymerization
of propylene oxide, butylene oxide, epichlorohydrin, and allyl glycidyl
ether into homopolymer, statistical copolymer, and block copolymer
architectures with heterobifunctional end-groups consisting of dibenzylamine
and hydroxyl functionalities. The TAxEDA-initiated polymerizations
were consistent with a controlled, living, anionic mechanism that
was tolerant of chemical functionality and exhibited no chain transfer
to monomer that limits the traditional anionic ring-opening polymerization
of substituted epoxides.
The structural and electrical properties of electronic-type-separated (metallic and semiconducting) single wall carbon nanotube (SWCNT) thin-films have been investigated after irradiation with 150 keV 11B+ and 150 keV 31P+ with fluences ranging from 1012 to 1015 ions/cm2. Raman spectroscopy results indicate that the ratio of the Raman D to G′ band peak intensities (D/G′) is a more sensitive indicator of SWCNT structural modification induced by ion irradiation by one order of magnitude compared to the ratio of the Raman D to G band peak intensities (D/G). The increase in sheet resistance (Rs) of the thin-films follows a similar trend as the D/G′ ratio, suggesting that the radiation induced variation in bulk electrical transport for both electronic-types is equal and related to localized defect generation. The characterization results for the various samples are compared based on the displacement damage dose (DDD) imparted to the sample, which is material and damage source independent. Therefore, it is possible to extend the analysis to include data from irradiation of transferred CVD-graphene films on SiO2/Si substrates using 35 keV C+ ions, and compare the observed changes at equivalent levels of ion irradiation-induced damage to that observed in the SWCNT thin-film samples. Ultimately, a model is developed for the prediction of the radiation response of nanostructured carbon materials based on the DDD for any incident ion with low-energy recoil spectra. The model is also related to the defect concentration, and subsequently the effective defect-to-defect length, and yields a maximum defect concentration (minimum defect-to-defect length) above which the bulk electrical transport properties in SWCNT thin-films and large graphene-based electronic devices rapidly degrade when exposed to harsh environments.
Lower critical solution behavior in binary blends of hydrophobic polyethers with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf 2 N]) exhibited a difference in lower critical solution temperature (LCST) greater than 80 °C between structurally homologous poly(isopropyl glycidyl ether) (PiPGE) and poly(n-butyl glycidyl ether) (PnBGE). Replacement of the acidic hydrogen on the imidazolium ring with a methyl group (i.e., 2,3-dimethyl-1-hexylimidazolium bis(trifluoromethylsulfonyl)imide ([hmmim][Tf 2 N])) significantly reduced the LCST of both the PnBGE/ionic liquid (IL) mixture and the PiPGE/IL mixture. Differing degrees of hydrogen bonding between the polymer and the cation cannot alone explain the observed behavior. Similar hydrogen bonding between the [hmim] + cation and both polymers from molecular dynamics simulations was consistent with this conclusion. However, stronger [hmim] + cation tail/polymer alkyl side-chain interactions for PnBGE, with consequently stronger cation/anion interactions, point to solvophobic interactions as the basis for the large LCST difference between the PnBGE/[hmim][Tf 2 N] and PiPGE/[hmim][Tf 2 N] blends.
The ability to disperse and, hence, manipulate single-walled carbon nanotubes is critical for their use in organic photovoltaic devices, either as a transparent electrode or as an electron acceptor material. We present data to quantify the physical interaction of single wall carbon nanotubes (SWCNTs) with two soluble phenylene vinylene conjugated polymers, poly[2'-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] and poly(2,5-di(hexyloxy)cyanoterephthalylidene). We provide static quenching constants, associated with polymer-SWCNT complexation, as a weight percent ratio of polymer to nanotubes for different solvent and polymer concentration conditions. Optimization of conditions for nanotube dispersion using a given polymer can now be predicted, and furthermore, we can describe a technique allowing for enhanced relative comparisons of polymer materials for nanotube dispersion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.