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ℓ©C Solid-state nuclear magnetic resonance study of the miscibility of polymer blends

Authors Wang, Jian
Issue Date 1999
Summary Polymer blends have been extensively studied since the 1980s because they can provide a wide range of materials with different properties. Polymer-polymer miscibility is a crucial factor that influences the physical properties of the polymer blends. Numerous methods, such as thermal analysis, mechanical analysis, spectroscopy, microscopy, etc, have been employed to study the polymer-polymer miscibility. Among them, high-resolution solid-state NMR spectroscopy has proven to be a powerful method for characterizing the scale of the polymer-polymer miscibility. Detailed information about the miscibility, inter-molecular interaction, and morphology of polymer blends can be obtained through examining the parameters, i.e., the chemical shift and line width as well as the relaxation times. In this study, the DSC, FAIR and 13C solid-state NMR were adopted to investigate three polymer blend systems, 1. Poly (ethyl oxazoline) (PEOx) / Poly (4-vinylphenol) (PVPh) 2. Poly (4-vinylpyridine) (P4VP) / Poly (4-vinylphenol) (PVPh), 3. Polycaprolactone (PCL) / Poly (4-vinylphenol) (PVPh) The purpose of selecting these systems is to compare the effect of different chemical structure and physical properties on the miscibility of the blends. PEOx is an amorphous polymer with a glass transition temperature of 54°C. It contains amide carbonyl groups giving great potential of forming hydrogen bonds with the polymers containing proton-donating groups. P4VP is also an amorphous polymer with similar molecular structure to that of PVPh, but with the phenolic aromatic ring being replaced with a pyridine ring. The glass transition temperature of P4VP (153°C) is very close to that of PVPh (156[degrees C]). The nitrogen atom on the pyridine ring of P4VP can act as a proton acceptor. PCL is a semi-crystalline polymer with the glass transition temperature of -60°C, and with the melting temperature of 52°C. PCL has been known to be miscible with many polymers since the carbonyl group of the PCL can form specific inter-molecular interaction with a lot of other function groups. The key results of this work are summarized as following: 1. For the PEOx/PVPh blends, it is found that PEOx is miscible with PVPh as shown by the existence of a single composition-dependent glass transition temperature (Tg) in the whole composition range. FTIR results revealed that strong hydrogen bonding exists between the carbonyl groups of PEOx and the hydroxyl groups of PVPh. Observed from the 13C cross-polarization (CP) / magic angle spinning (MAS) / dipclar decoupling (DD) spectra of the blends, the chemical shifts of the carbonyl carbon of PEOx and the hydroxyl-substituted carbon of PVPh changed monotonously with composition change. This is indicative of a strong intermolecular hydrogen-bonding interaction between PEOx and PVPh, which is consistent with the DSC and FIIR results. The proton spin-lattice relaxation in both the laboratory frame, T1(H), and the rotating frame, T1p,(H), were studied as a function of the blend composition. The Ti(H) result was in good agreement with the thermal analysis, i.e., the blends are completely homogenous on the scale of 30-40 nm. The T1p(H) results further indicated that the blends are homogenous even on the scale of 2-3 nm. 2. For the P4VP/PVPh blends, DSC results indicate that P4VP and PVPh form complex during the sample preparation process. For all different compositions, the Tgs are much higher than that of the calculated weight-average values, which is indicative of even stronger inter-molecular interaction between the two components. FTIR studies reveal the existence of specific interaction via hydrogen bonding between the hydroxyl groups in PVPh and the nitrogen atom at the pyridine ring of P4VP. The results of the 13C CP/MAS/DD spectra showed a 2.9 ppm downfield shift for the hydroxyl-substituted carbon when the P4VP concentration increased to 70 %. This result could be ascribed to the formation of the intermolecular specific interaction between PVPh and P4VP. The T[subscritp 1] (H) result was in good agreement with the thermal analysis and the FTIR result, i.e., the blends are completely homogeneous on the scale of 25-30 nm. The results of T1p(H) further indicated that the blends were homogeneous on the scale of 2-3 nm. T[subscripe 1](H) and T[subscritp 1p](H) values of the blended samples are longer than that of the pure components, which revealed that the strong hydrogen bonding between P4VP and PVPh restricted the mobility of the polymer chains. 3. For the PCL/PVPh blends, DSC results indicated that PCL/PVPh blends were miscible in the whole composition range. FTIR results indicated that hydrogen bonding exists between the phenolic hydroxyl groups of PVPh and the carbonyl groups of PCL. Significant chemical shifts of the hydroxyl groups of PVPh and a new absorption band formed in the carbonyl group region of PCL supporting the idea of hydrogen bonding that formed in the blends. Slight downfield shifts of the hydroxyl-substituted carbon resonance of PVPh were observed from the solid-state 13C CP/MAS/DD spectra of PCL/PVPh blends, which reveal that specific inter-molecular interaction exists between the two components. The T1(H) result was in good agreement with the thermal analysis and FTIR result, i.e., the blends are completely homogeneous on the scale of 25-30 nm. A bi-exponential decay of PCL component was observed in the T1p(H) measurements, which indicates the spin-diffusion does not average out the whole relaxation process on the scale of T1p(H) measurements. It can be concluded from the T1(H) and T1p(H) measurements that the domain sizes of the PCL/PVPh blend are homogeneity on the scale of 30 nm, but are heterogeneity on the scale of 2-3 nm.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 1999
Language English
Format Thesis
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