A Practical Guide to Understanding the NMR of Polymers

PETER A. MIRAU is Senior Research Scientist in the Nonmetallic Materials Division (Polymer Branch) at the Air Force Research Laboratories in Dayton, Ohio.

1. Introduction to NMR.1.1 Introduction.1.2 Basic Principles of NMR.1.2.1 Introduction.1.2.2 Magnetic Resonance.1.2.3 The Rotation Reference Frame.1.2.4 The Bloch Equations.1.2.5 Pulsed NMR.1.2.6 The Fourier Transform.1.2.7 The Product Operator Formalism.1.3 Chemical Shifts and Polymer Structure.1.3.1 Molecular Structure and Chemical Shifts.1.3.1.1 Chemical Structure Effects.1.3.1.2 Inductive Effects.1.3.1.3 Anisotropic Shielding.1.3.1.4 Chemical Exchange.1.3.2 Proton Chemical Shifts.1.3.3 Carbon Chemical Shifts.1.3.4 Other Nuclei.1.3.4.1 Fluorine.1.3.4.2 Silicon.1.3.4.3 Phosphorus.1.3.4.4 Nitrogen.1.4 Spin-Spin Coupling.1.4.1 Introductions.1.4.2 Nomenclature for Spin-Spin Coupling.1.4.3 Spin-Spin Coupling Patterns.1.4.3.1 Strong Coupling.1.4.3.2 Scalar Coupling and nD NMR.1.4.4 Proton-Proton Coupling.1.4.5 Proton-Carbon Coupling.1.4.6 Other Nuclei.1.4.6.1 Fluorine Couplings.1.4.6.2 Phosphorous Couplings.1.4.6.3 Silicon Couplings.1.4.6.4 Nitrogen Couplings.1.4.7 Homonuclear Couplings in Insensitive Nuclei.1.5 NMR Relaxation.1.5.1 Introduction.1.5.2 Relaxation Mechanisms.1.5.2.1 Dipole-Dipole Interactions.1.5.2.2 Quadrupolar Interactions.1.5.2.3 Chemical Shift Anisotropy.1.5.2.4 Paramagnetic Relaxation.1.5.2.5 Other relaxation Mechanisms.1.5.3 Spin-Lattice Relaxation.1.5.3.1 Heteronuclear Spin-Lattice Relaxation.1.5.3.2 Homonuclear Spin-Lattice Relaxation.1.5.4 Spin-Spin Relaxation.1.5.5 The Nuclear Overhauser Effect.1.5.5.1 Heteronuclear Nuclear Overhauser Effects.1.5.5.2 Homonuclear Nuclear Overhauser Effects.1.6 Solid State NMR.1.6.1 Chemical Shift Anisotropy.1.6.2 Magic-Angle Sample Spinning.1.6.3 Dipolar Broadening and Decoupling.1.6.4 Cross Polarization.1.6.5 Quadrupolar NMR.1.7 Multidimensional NMR.1.7.1 Magnetization Transfer in nD NMR.1.7.1.1 Through-Bond Magnetization Transfer.1.7.1.2 Through-Space Magnetization Transfer.1.7.2 Solution 2D NMR Experiments.1.7.2.1 COSY.1.7.2.2 TOCSY.1.7.2.3 Heteronuclear Multiple Quantum Coherences.1.7.2.4 2D Exchange NMR.1.7.2.5 J-Resolved NMR.1.7.3 Solid-State 2D NMR Experiments.1.7.3.1 2D Exchange NMR.1.7.3.2 Wideline Separation Spectroscopy.1.7.3.3 Heteronuclear Correlation.2. Experimental Methods.2.1 Introduction.2.2 The NMR Spectrometer.2.2.1 The Magnet.2.2.2 Shim Coils.2.2.3 RF Console.2.2.4 NMR Probes.2.2.5 Computer.2.3 Tuning the NMR Spectrometer.2.3.1 Adjusting the Homogeneity.2.3.2 Adjusting the Gain.2.3.3 Tuning the Probe.2.3.4 Adjusting the Pulse Widths.2.4 Solution NMR Methods.2.4.1 Sample Preparation.2.4.2 Data Acquisition.2.4.3 Decoupling.2.4.4 Data Processing.2.4.4.1 Baseline Corrections.2.4.4.2 Digital Resolution and Zero-Filling.2.4.4.3 Window Functions.2.4.4.4 Phasing.2.4.4.5 Quadrature Detection.2.4.4.6 Referencing.2.4.5 Quantitative NMR.2.4.6 Sensitivity Enhancement.2.4.7 Spectra Editing.2.5 Solid-State NMR Methods.2.5.1 Magic-Angle Sample Spinning.2.5.2 Gross Polarization.2.5.3 Decoupling.2.5.4 Wideline NMR.2.5.5 Solid-State Proton NMR.2.6 NMR Relaxation.2.6.1 NMR Relaxation in Solution.2.6.1.1 Spin-Lattice Relaxation.2.6.1.2 Spin-Spin Relaxation.2.6.1.3 Nuclear Overhauser Enhancements.2.6.2 Solid-State NMR Relaxation.2.6.2.1 Spin-Lattice Relaxation.2.6.2.2 Rotating-Frame Spin-Lattice Relaxation.2.7 Multidimensional NMR.2.7.1 Data Acquisition.2.7.1.1 Digital Resolution and Acquisition Times in nD NMR.2.7.1.2 Inverse Detection.2.7.1.3 Phase Cycling.2.7.1.4 Quadrature Detection.2.7.1.5 Pulsed Field Gradients.2.7.1.6 Decoupling.2.7.2 Data Processing.2.7.2.1 Apodization.2.7.2.2 Phasing.2.7.2.3 Baseline and t1 Noise.2.7.2.4 Linear Prediction and Zero-Filling.3. The Solution Characterization of Polymers.3.1 Introduction.3.1.1 Polymer Microstructure.3.1.1.1 Regioisomerism.3.1.1.2 Stereochemical Isomerism.3.1.1.3 Geometric Isomerism.3.1.1.4 Branching and Endgroups.3.1.1.5 Chain Architecture.3.1.1.6 Copolymers.3.1.2 Spectral Assignments in Polymers.3.1.2.1 Model Compounds and Polymers.3.1.2.2 Polymer Chain Statistics.3.1.2.3 Chemical Shift Calculations.3.1.2.4 The gamma-Gauche Effect.3.1.2.5 Spectral Editing.3.1.2.6 Multidimensional NMR.3.2 Stereochemical Characterization of Polymers.3.2.1 The Observation of Stereochemical Isomerism.3.2.2 Resonance Assignments for Stereosequences.3.2.2.1 Assignments of Stereosequences Using Model Compounds.3.2.2.2 Assignments of Stereosequences Using Polymerization Statistics.3.2.2.3 Assignments of Stereosequences Using Chemical Shift and Conformational Calculations.3.2.2.4 Assignments of Stereosequences Using nD NMR.3.3 Regioisomerism in Polymers.3.4 Defects in Polymers.3.4.1 Branching.3.4.2 Endgroups.3.5 Polymer Chain Architecture.3.6 Copolymer Characterization.3.6.1 Random Copolymers.3.6.2 Alternating Copolymers.3.6.3 Block Copolymers.3.7 The Solution Structure of Polymers.3.7.1 Polymer Chain Conformation.3.7.2 Intermolecular Interactions in Polymers.4. The Solid-State NMR of Polymers.4.1 Introduction.4.2 Chain Conformation in Polymers.4.2.1 Semicrystalline Polymers.4.2.1.1 Solid-State Phase Transitions.4.2.2 Amorphous Polymers.4.2.3 Elastomers.4.2.4 Reactivity and Curing in Polymers.4.3 Structure and Morphology in Polymers.4.3.1 Introduction.4.3.2 Spin Diffusion and Polymer Morphology.4.3.2.1 Spin Diffusion and Interfaces.4.3.2.2 Spin Diffusion and Coefficients.4.3.2.3 Polarization Gradients for Measuring Spin Diffusion.4.3.2.4 Proton Relaxation and Morphology.4.3.3 Semicrystalline Polymers.4.3.4 Block Copolymers.4.3.5 Multiphase Polymers.4.3.6 Polymer Blends.5. The Dynamics of Polymers.5.1 Introduction.5.2 Chain Motion of Polymers in Solution.5.2.1 Modeling the Molecular Dynamics of Polymers in Solution.5.2.2 Relaxation Measurements in Solution.5.2.3 NMR Relaxation Measurements in Solution.5.2.4 The Relaxation of Polymers in Solution.5.3 NMR Relaxation in the Solid State.5.3.1 Introduction.5.3.2 NMR Relaxation in Solid Polymers.5.3.3 Spin Exchange in Solid Polymers.5.3.4 Polymer Dynamics and Lineshapes.5.3.4.1 Wideline Deuterium NMR.5.3.4.2 Chemical Shift Anisotropy and Polymer Dynamics.5.3.4.3 Dipolar Lineshapes and Polymer Dynamics.