Mark A. Arnould

Structural characterization of polyester copolymers by MALDI mass spectrometry

A polyester copolymer is produced by step-growth polymerization of neopentyl glycol (50 mol%), trimethylol propane (1%), terephthalic acid (45%) and adipic acid (5%) and its microstructure is characterized by gel permeation chromatography and matrix-assisted laser desorption ionization mass and tandem mass spectrometry. The combination of these analytical methods is shown to yield detailed insight about the composition, end groups, molecular weight, and sequence of the product.

Tandem mass spectrometry characteristics of polyester anions and cations formed by electrospray ionization

Electrospray ionization of polyesters composed of isophthalic acid and neopentyl glycol produces carboxylate anions in negative mode and mainly sodium ion adducts in positive mode. A tandem mass spectrometry (MS/MS) study of these ions in a quadrupole ion trap shows that the collisionally-activated dissociation pathways of the anions are simpler than those of the corresponding cations. Charge-remote fragmentations predominate in both cases, but the spectra obtained in negative mode are devoid of the complicating cation exchange observed in positive mode. MS/MS of the Na+ adducts gives rise to a greater number of fragments but not necessarily more structural information. In either positive or negative mode, polyester oligomers with different end groups fragment by similar mechanisms. The observed fragments are consistent with rearrangements initiated by the end groups. Single-stage ESI mass spectra are also more complex in positive mode because of extensive H/Na substitutions; this is also true for matrix-assisted laser desorption ionization mass spectra. Hence, formation and analysis of anions might be the method of choice for determining block length, end group structure and copolymer sequence, provided the polyester contains at least one carboxylic acid end group that is ionizable to anions.

Reaction of polymeric organolithium compounds with ethylene oxide in hydrocarbon solution: determination of extent of oligomerization

The functionalization of poly(styryl)lithium with excess ethylene oxide in benzene solution has been reexamined to determine if oligomerization of ethylene oxide occurs under normal conditions. No 13 C NMR peaks were observed at b = 69-70 and 72-73 ppm as expected for a chain end with two ethylene oxide units. These peaks were not observed even when 3.3 equivalents of 13 C-labeled ethylene oxide (98 atom % 13 C) was utilized. No peak corresponding to two ethylene oxide units at the chain end (at m/z 104n + 210 + 44 Daltons) was observed in the MALDI-TOF mass spectrum of the functionalization product. The main series of peaks (Ag + -cationized) appeared at m/z 104n + 210, corresponding to the expected C 4 H 9 and CH 2 CH 2 OH end groups with a number average degree of polymerization of n. A small peak ( ca. 3 %) corresponding to two ethylene oxide units at the chain end was observed in the mass spectrum of the functionalization product obtained using 10 equivalents of ethylene oxide.

Functionalization of Poly(styryllithium) with 1‐Butene Oxide

Functionalization of poly(styryllithium) with 1-butene oxide (BO) was studied in benzene at room temperature. The hydroxyl-functionalized polymer was characterized by size exclusion chromatography (SEC), titration, 1 H NMR, 13 C NMR, DEPT- 13 C NMR (distortionless enhancement by polarization transfer) spectroscopy, MALDI-TOF mass spectrometry and flash column chromatography. The ω-hydroxylated polystyrene was obtained in 99% yield with quantitative regioselectivity (addition to the methylene carbon of 1-butene oxide) to form the secondary alcohol without oligomerization. The amount of unfunctionalized polystyrene formed (<1%) was much less than that found for functionalization with propylene oxide (PO, 6-7%) consistent with reduced proton transfer from the ethyl group in BO versus the corresponding methyl group in PO