The use of 1H NMR spectroscopy to analyze the number-average molecular weight of a methoxy poly(ethylene glycol) (MPEG) and an acetate derivative of this MPEG is described. These analyses illustrate NMR principles associated with the chemical shift differences of protons in different environments, NMR integration, and the effect of the natural abundance of 13C carbons in a polymer and the resulting low but predictable intensity of the satellite peaks due to 13C–1H spin–spin coupling. Also included in this discussion is an example of end-group analysis of the product of an acetylation reaction. In the discussion of the acetylation product, an 1H NMR spectrum of a crude product mixture where the small peaks due to end groups can be seen along with a set of impurities due to catalyst, solvents, and byproducts is included because, in practice, chemists often first see these sorts of spectra.Keywords: Analytical Chemistry; Inquiry-Based/Discovery Learning; Isotopes; NMR Spectroscopy; Organic Chemistry; Polymer Chemistry; Second-Year Undergraduate; Spectroscopy;

This describes the preparation of a recyclable organo photoredox catalyst that efficiently carries out light-mediated radical polymerizations of acrylates. This PIB-bound 10-phenylphenothiazine organic photoredox catalyst can be easily separated from the polymer product and reused via a facile biphasic separation process for 3 cycles with no significant loss of catalytic activity.

Soluble poly(4-alkylstyrene) containing 4-methyl-, 4-tert-butyl, 4-dodecyl-, and 4-octadecylstyrene were formed either with monomers containing dyes-, ligands, or catalysts or with 5–10 mol% of 4-chloromethylstyrene and studied as supports for ligands or catalysts. Studies with dye-labeled polymers showed that polymers containing longer alkyl groups alone or at ca. 10 mol% loading are highly soluble in heptane can be used to separate and recycle organo- and transition metal catalysts.

Polyisobutylene (PIB)-bound azo dyes were prepared from aryl amine terminated polyisobutylene oligomers and used to form palladacycle precatalysts that can be used for catalytic carbon–carbon cross coupling reactions. The catalysts so formed were recyclable using thermomorphic heptane–DMF solutions that are monophasic at 80 °C and biphasic at room temperature. Under these conditions, the Pd catalyst can be recycled but some Pd leaches into the product solution. Using a low melting polyethylene oligomer as a solvent in place of the volatile heptane solvent reduces this leaching by roughly an order of magnitude. Further modification that involves using a second polyisobutylene (PIB)-bound phosphine ligand both increases the activity of the colloidal Pd catalyst and decreases the total Pd leaching by almost two orders of magnitude with 99.88% of the Pd being recovered. In this case, the Pd content in the solution of the product was ca. 0.3 ppm. These two modifications together lead to a much more sustainable strategy for the use of Pd colloidal catalysts in catalytic cross coupling chemistry.

4-Dodecylstyrene was copolymerized with 4–15 mol% of styrene monomers containing functional groups to synthesize polystyrene-like, alkane phase-selectively soluble polymer supports. Comparison studies of substituted polystyrenes containing dansyl groups showed that dodecyl groups significantly increase the phase selective solubility of a dodecyl-substituted polystyrene analog in the heptane phase of a heptane–acetonitrile mixture versus the phase selective solubility of poly(4-tert-butylstyrene) in this same solvent mixture. Coupling of a 4-dimethylaminopyridine (DMAP) derivative to poly(4-dodecylstyrene) (C12PS) formed a (C12PS)-supported DMAP organocatalyst. This C12PS-bound DMAP catalyst had activity like that of other polymer-supported DMAP catalysts and was fully recyclable in a variety of acylation reactions. Catalyst recycling was effected using a biphasic liquid–liquid separation step after a monophasic reaction. By using a C12PS-supported DMAP catalyst that contained dansyl groups, we were able to show that the C12PS-bound DMAP organocatalyst could be recycled as many as 20 times with catalyst leaching that was as low as 0.002% of the starting catalyst per cycle.

A series of N-heterocyclic carbene (NHC) Ag(I) complexes have been prepared and used to study the dynamics of NHC ligand exchange in these Ag(I) complexes. These studies used solution-state variable-temperature (VT) 13C NMR spectroscopy and the temperature-dependent changes in 13C–107/109Ag coupling to determine activation energies for the ligand exchange process. The effects of concentration, bridging anions, and additives on the exchange process have been studied. The experimental activation energies for the NHC ligand exchange processes of these silver complexes are also compared with DFT calculations. The results are consistent with an associative mechanism for the Ag(I)–NHC exchange process.

Polymers like poly(N-isopropylacrylamide) (PNIPAM) exhibit lower critical solution temperature (LCST) behavior. A variety of reports have shown that brush grafts of PNIPAM on surfaces exhibit similar temperature responsiveness. We recently described an alternative synthetic approach to such surfaces that affords surfaces with similar LCST-like behavior. We also noted how such surfaces’ wettability can change in response to the identity and concentration of solutes. Here we show that this synthetic procedure can be extended to glass surfaces and to more complex surfaces present in porous glass frits. Functionalized glass surfaces exhibit solute-dependent wetting behavior analogous to that previously reported. We further show that the resulting responsive nanocomposite grafts on such frits exhibit “smart” responsive permeability with a greater than 1000-fold difference in permeability to water versus aqueous solutions of sodium sulfate. This “smart” permeability is ascribed to the solute-dependent wettability behavior of the responsive PNIPAM component of the nanocomposite graft, which is sensitive both to the identity and concentration of the solute anion and to temperature.

Phosphines are important as catalysts or reagents in synthesis but must be separated from products after a reaction. This report shows that polyisobutylene (PIB)-bound alkyldiaryl- and triarylphosphines are useful as catalysts in addition and allylic amination reactions or as reagents in aza-Wittig and Mitsunobu reactions. Heptane solutions of such phosphines and their oxidized byproducts can be easily separated from polar solutions of organic products, and PIB-phosphine oxides formed during a reaction can readily be reduced to PIB-phosphines for reuse.