Combined Solid-State NMR And Quantum Chemical Calculation Studies Of Microstructure, Hydrogen Bond And Segmental Motion In Polymers

In this thesis, combined quantum chemical calculation and solid-state NMR techniques were used to study the microstructure and hydrogen bond interaction in a series of crystalline and amorphous polymers, as well as segmental dynamics in polymer blends. This thesis basically consists of the following four parts:1. Studies on the chemical shifts of two types of crystalline polymers, isotactic and syndiotactic polypropylene (iPP/sPP). By analyzing the influence of different initial configurations, conformations and optimizing methods to quantum chemical calculation results, we obtained an effective method to accurately calculate NMR chemical shift in crystalline polymer. We also discussed the successes and shortcomings in elucidating the 13C chemical shifts of PP with different tacticities usingγ-gauche effect. We studied the merits and drawbacks, as well as the optimization of experimental parameters of two newly developed NMR techniques (SUPER and RAI) for recoupling the chemical shift anisotropy. The CSA powder lineshapes of iPP were successfully obtained, which were also compared with quantum chemical calculation results. It was found that the results of quantum chemical calculation are in good accordance with NMR experimental results.2. Combined quantum chemical calculations and solid-state NMR experiments were used to investigate the complex hydrogen bonds and their influence to 13C chemical shifts in three types of polyvinyl alcohol (PVA) with different tacticities. We have succecesfully elucidated the nature of methine triplets of 13C NMR spectrum in PVA and explored the influence of the intermolecular hydrogen bonds between PVA and water on the chemical shifts. Quantum chemical calculation is able to predict the 13C NMR spectrum of iPVA well. For sPVA, because the used structural model was highly syndiotactic while the experimental sample is slightly syndiotactic, thus the theoretical prediction was a little different with the NMR result. Plenty of structural models with different configurations and conformations were built for aPVA, and quantum chemical calculation partly clarified the origin of the methine triplets. Our results show that we should not only take into account intramolecular but also intermolecular hydrogen bonds when studing the origin of the triplets, and intramolecular hydrogen bond can be only formed at certain particular configurations and conformations. Through a series of quantum chemical calculation results, some basic rules of chemical shift distribution of methine carbons in PVA were summarized: (1) In case of only one hydrogen bond, when the hydroxyl group in PVA is proton acceptor, the peak of methine carbons moves toward low field, and when the hydroxyl group in PVA is proton acceptor, the peak of methine carbons moves towards high field; 2) when the hydroxyl group in PVA is involved in an intramolecular hydrogen bond and an intermolecular hydrogen bond, the peak of methine carbons moves towards low field; (3) when multiple intermolecular hydrogen bonds is formed between different PVA chains, the peak of methine carbons moves towards high field, and when multiple intermolecular hydrogen bonds is formed between PVA and water, the peak of methine carbons moves towards low field. Variable-temperature 13C CP/MAS and SUPER solid-state NMR experimental results further confirmed the conclusion obtained from quantum chemical calculation.3. On the basis of recently developed continuous phase modulation techniques for homonuclear decoupling among protons, we proposed two new high resolution solid-state 1H NMR techniques:DF-CRAMPS and DQ-CRAMPS, which are used to obtain mobile and rigid proton signals in organic solids. These techniques were then used to study various types of complex hydrogen bond structures in polyacrylic acid (PAA). We have obtained high resolution'H NMR spectra and correctly assigned the NMR peaks associated with hydrogen bonds according to experimental and quantum chemical calculation results. Several new hydrogen bond structures were found for the first time in PAA.4. Studies on the hydrogen bonds and segmental motion in poly-4-vinylphenol/polyethylene oxide (PVPh/PEO) blends. Through high resolution 2D solid-stae NMR techniques including 2D 1H-1H spin exchange experiment and 13C-1H separated-local-field NMR experiment, we revealed the hydrogen bond interaction between the phenolic hydroxyl in PVPh and PEO as well as molecular mobility of different components in PVPh/PEO blends; we also found an interchain cooperation motion in compatible blends resulting from interchain weak interaction.