I-Ssuer Chuang

Synthesis and solid-state NMR structural characterization of polysiloxane-immobilized amine ligands and their metal complexes

Abstract Polysiloxane-immobilized amine and diamine ligand systems have been made by hydrolytic condensation of Si(OEt)4 with (EtO)3Si(CH2)3NH2 or (MeO)3Si(CH2)3NH(CH2)2NH2. The corresponding triamine ligand was made from the reaction of 3-chloropropylpolysiloxane with diethylenetriamine (H2NCH2CH2NHCH2CH2NH2); solid-state 13 C and 15 N nuclear magnetic resonance (NMR) spectra can identify the structure of the product of this reaction. 29 Si , 15 N , 13 C and 1 H NMR spectra are in general valuable for characterizing these polysiloxane structures, and provide evidence for the involvement of the amine ligands in hydrogen bonding with surface silanols. Together with results of classical elemental analysis, the NMR data indicate that a portion of the ligand groups are inaccessible to metal ions and remain uncoordinated when these materials are treated with aqueous solutions of divalent metal ions. 29 Si NMR spectra and elemental analysis reveal some details of the leaching of these polysiloxane materials, when they are treated with acids or metal ion solutions. Relaxation times, T1H, were measured, based on 29 Si and 13 C detection, on the polysiloxane-immobilized ligand systems. The T1H results suggest that the organofunctionalities in these systems are evenly distributed in the polysiloxane network.

Synthesis and solid-state NMR structural characterization of polysiloxane-immobilized phosphine-amine and phosphine-thiol ligand systems

Abstract Polysiloxane-immobilized phosphine ligand systems have been prepared by hydrolytic condensation of mixtures of Si(OEt)4 and (R′O)3Si(CH2)nPPh2 (n = 2, R′ = Me; n = 3, R′ = Et) Polysiloxane-immobilized phosphine-amine and phosphine-thiol ligand systems have been prepared by hydrolytic condensation of mixtures of Si(OEt)4, (R′O)3Si(CH2)nPPh2 (n = 2, R′ = Me; n = 3, R′ = Et) and (R′O)3Si(CH2)3X (X = NH2, R′= Et; X = NHCH2CH2NH2. R′ = Me) or (MeO)3Si(CH2)3SH. In the polysiloxane-immobilized phosphine-amine and phosphine-thiol systems two types of ligand groups are introduced into the polysiloxane matrix during the sol-gel process. Solid-state 13C, 31P and 29Si NMR spectroscopy was used to investigate the structures of the polysiloxane-immobilized ligand systems — e.g., to determine the presence of unhydrolyzed/uncondensed alkoxy groups, to determine the ratios of phosphine to phosphine oxide moieties, to determine details of the silicon-based backbone (relative populations of various types of RSi(-O-)3 and Si(-O-)4 moieties) and to establish domain homogeneity throughout a given material.

Synthesis and solid-state NMR structural characterization of polysiloxane-immobilized thiol and thiol-amine ligands

Abstract Thiol and thiol-amine ligand systems that are immobilized in a polysiloxane matrix have been synthesized via the sol-gel process by hydrolytic condensation of mixtures of Si(OEt)4 and (MeO)3Si(CH2)3SH, as well as (EtO)3Si(CH2)3NH2 or (MeO)3Si(CH2)3NH(CH2)2NH2 for thiol-amine systems. In these systems, most of the amine groups can be protonated by aqueous acid solution. Solid-state 29Si nuclear magnetic resonance (NMR) spectra confirm the fact that these materials, in analogy to polysiloxane-immobilized amine systems, undergo leaching of small oligomers containing ligand groups when they are treated with aqueous acid. 15N NMR spectra indicate that the amine groups in these systems may be involved in hydrogen bonding with silanols or with other ligand groups. 13C-detected and 29Si-detected T1H values were measured on the polysiloxane-immobilized thiol system, thiol-monoamine system and thiol-diamine system. The T1H results suggest that the ligand groups in these systems are evenly distributed in the polysiloxane networks.

Natural-abundance 15N cross-polarization/magic-angle spinning nuclear magnetic resonance study of urea-formaldehyde resins

High-quality natural-abundance 15N cross-polarization/magic-angle spinning (c.p.-m.a.s.) spectra of urea-formaldehyde (UF) resins were obtained by employing a large-volume (2.5 cm3) magic-angle spinning (m.a.s.) rotor. 15N c.p.-m.a.s. nuclear magnetic resonance (n.m.r.) spectroscopy can clearly distinguish dimethylene ether linkages from methylol groups for UF resins prepared under neutral or basic conditions, a weak point in 13C c.p.-m.a.s. strategies because of 14N broadening effects, and can detect the existence of tertiary amides and unreacted primary amides in UF resins. 15N c.p.-m.a.s. n.m.r. also establishes the fact that there are methylol aggregates that are spatially separated from some other structural moieties in UF resins and that the domain size of methylol aggregates diminishes with the concentration of methylol groups in UF resins. 15N c.p.-m.a.s. results also indicate that the formation of dimethylene ether linkages is least favourable at pH 9 and most favourable at pH 12 among the three pH values 7, 9 and 12.

NMR Characterization of Complex Organic Resins

Publisher Summary This chapter discusses the nuclear magnetic resonance (NMR) characterization of complex organic resins. The chapter defines organic resin as a macromolecular organic system synthesized by condensation polymerization of a specific set of monomers, with some diversity in the primary structure, including various degrees of crosslinking. The properties of solid polymers depends on their molecular structures, phase behavior, morphology, molecular order and molecular motions, and the end use of most complex organic polymer materials is in the solid state. Solid-state NMR provides a unique tool to probe the microstructures and dynamics of the materials down to the molecular levels with a wide range of dimensional scales accessible; therefore, this approach is powerful in the investigation of composite materials and of the compatibility in polymer blends. Recently, the solid-state version of 13C- 1H heteronuclear chemical shift correlation spectroscopy (HETCOR) has been applied successfully to study the polymer blend and the application of this approach can be expected to grow in popularity.

13C cross-polarization/magic-angle spinning nuclear magnetic resonance investigation of urea-formaldehyde resins made from N,N′-dimethylolurea or from paraformaldehyde

Abstract 13C cross-polarization/magic-angle spinning nuclear magnetic resonance spectroscopy has been used to investigate urea-formaldehyde (UF) resins prepared at room temperature from reaction mixtures containing N,N′-dimethylolurea or various pretreated paraformaldehyde agents as a source of CH2 groups. Resins prepared from reaction mixtures with various ‘equivalent’ formaldehyde-to-urea molar ratios and various pH values and reactant concentrations were examined. Structural changes in the UF resins that accompany variations in these parameters, and the dependence of the UF resin structures on the solubilities of N,N′-dimethylolurea or various pretreated paraformaldehyde agents in water are discussed along with the relative rates of various reactions at different pH values. Comparisons are made among the UF resins prepared from formalin, N,N′-dimethylolurea or various pretreated paraformaldehyde agents as a source of CH2 groups in the resins. Valuable information on the mechanisms and reactivities of various reactions in the complicated UF resin system was drawn from these comparisons.