Nmr Studies Of The Ethylene Copolymer Chain Structure And Aggregation Structure

The relationship between the chain structures and the phase structures of several semicrystalline ethylene copolymers are studied by both solid and solution NMR spectroscopy. The copolymers used in this thesis are ethylene(E)-vinyl alcohol(V) copolymers(EVOH), ethylene(E)-vinyl acetate(VA) copolymers(EVA) and ethylene (E)-methyl acrylate(MA) copolymers(EMA). The main results include:1. A new assignment of I3C CP/MAS spectrum of EVOH was given by solution-state high-resolution and solid-state high-resolution 13C NMR. It was demonstrated that the triple splitting of the signal of methine carbon of the vinyl alcohol unit in 13C CP/MAS spectrum is caused by sequence distribution, tacticity, and both intra-and inter- molecular hydrogen-bonding interactions.2. The phase structure of EVOH copolymers with different comonomer contents was studied by variable temperature solid-state high-resolution 13C CP/MAS NMR spectroscopy. At 353K, which is about 20-30 degree higher than the Tg of the amorphous region of the samples, the splitting of about 2ppm caused by difference in phase structures was observed for both methine and methylene carbons. This result is helpful to both the assignment of the I3C CP/MAS NMR spectra of EVOH and the investigation of phase structure in detail.3. Due to the variation of crystal structure and the decrease of density of hydrogen bonding interaction, the melting temperature of EVOH decreases with the increase of the ethylene comonomer content in EVOH.4. Both one and two dimension variable-temperature high-resolution 'H NMR wereused to investigate the hydrogen bonding interaction of EVOH in DMSO solution. From the temperature dependence of chemical shift of hydroxyl proton, it was proved that the strength of hydrogen bonding varies with different sequence and tacticity. The strength of hydrogen bonding of different hydroxyl groups on polymer chains decreases as follows: EVE, mVVE, rVVE, mmVVV, mrVVV and rrVVV. A new phenomenon was observed about the temperature dependence of chemical shift of methin proton in EVOH, that is, due to the influence of hydrogen bonding interaction, the 'H signals of methine shift to lower field with the increase of temperature. From 2D NOESY spectrum, steady hydrogen bonding interactions between polymer chains and solvent is observed. At the same time, the inter- and intra- hydrogen bonding interactions between molecular chains are also visible in 2D NOESY spectrum.5. The phase structures and the crystalline structures of random EVA copolymers were studied by solid-state high-resolution I3C NMR. A distinguishable peak at 34ppm was observed for EVA28 and EVA40 by I3C CP/MAS NMR, which is attributed to the monoclinic signal in EVA crystal region. A bi-exponential 13C TI decay behavior of crystalline component was obtained by Torchia pulse program. Due to the changes in the thickness of the crystallite, the value of longer T] in crystal region decreases with the increase of VA content. With the experimental results of EMA sample, it was shown that the component with short TI comes mainly from the imperfect parts near the surface of crystals.6. The degree of crystallinity of EVA samples was obtained by solid wide-line proton NMR. It is shown that with the increase of VA content, the crystallinity of EVA almost decreases linearly.7. With solid-state wide-line proton NMR, we attempt to investigate the molecularmobility and chain structures of EVA sample under drawing. Compared with that of the non-drawn samples, the line-width of the drawn sample is broadened and the signal shift to lower field. It is shown that the molecular mobility decrease under traction. The change in chemical shift can be explained by the change of chain structure. The detail information is expected to be observed by solid-state high-resolution NMR.