Morphology And Molecular Motions Of Polymeric Elastomers Under In-situ Stretching As Studied By Solid-state High-resolution NMR Spectroscopy

The morphology and molecular motion of 4 different elastomers, including natural rubber (NR), poly (ester ether) (PEE), ethylene-methyl acrylate (EMA) and ethylene-octene(POE) copolymers, have been systematically investigated by employing an "in-situ stretching" solid-state NMR technique. The main results include:1. A design of a set of devices for a 4 mm magic angle spinning (MAS) rotor by which "in-situ stretching" solid-state high-resolution NMR investigations of elastomers can be easily performed. A maximum and stable spinning rate of 7 kHz was attainable. Based on these devices, the application of the solid-state high-resolution NMR technique was extended and enabled the stretching behavior of elastomers to be investigated on a molecular level.2. 13C CP/MAS and DD/MAS spectra, as well as 13C Ti and 1H T2 relaxation times of the individual nuclei were measured for the first time of "in-situ stretched" NR samples. The high-resolution appearance of the NMR spectra suggests that a small amount of crystals do exist in unstretched NR samples at room temperature. A detailed spectral assignment of the crystalline part in the NMR spectrum of both the unstretched and the stretched samples are presented. It was found that the intensity of the crystalline component increases with increasing draw ratio {X). The strain-induced crystallization starts when X is about 2.0. Quantitative experiments suggest that an approximate linear relation between crystallinity and X exists for X in the range of 2.0 to 6.0. The maximum crystallinity obtained was 19.3%. Compared to non-filled samples, the ability of crystallization of the carbon black-filled NR samples was significantly smaller.3. The morphology and molecular motion of "in-situ stretched" PEE samples were studied by solid-state high-resolution 13C NMR techniques. Strain-induced crystallization of ploy(tetramethylene oxide) (PTMO) wasobserved for X.=2.0. The degree of crystallinity of PTMO and the lamellar thickness of the crystallites were found to increase with increasing X. The molecular motion at high frequency of amorphous PTMO was found to be almost independent on X, indicating that the strain-induced crystallization mainly occurs in the "pure" PTMO region. The thickness of the interfacial region between the amorphous and the crystalline phases of PTMO is about 1.1 nm. The corresponding interfacial region between the amorphous PTMO and the crystalline hard segment is about 3.1 nm.4. The relative content of the orthorhombic crystalline component in EMA samples exhibit a process of decreasing, and then increasing tendencies at lower Xs, and finally a great decreasing at the utmost ratio (b), while the contents of the monodinic components increase monotonously with s. 13C Ti and spin-diffusion experiments demonstrated that the thicknesses of the crystalline lamella decreases upon stretching, while the increase of the crystallinity is mainly due to the newly formed crystals. It was demonstrated further that the origin of the biexponential 13C Ti relaxation behavior of the crystalline region is due to the coexistence of an intermediate and an internal crystalline parts within the sample. The thickness of the intermediate crystalline region was found to be approximately 1.1 nm. The content of this intermediate fraction was found to increase with increasing X.5. The morphology and molecular motion of POE samples were found to be dependent on the octene content, conditions of crystallization and X. A comparablely high content of monodinic crystals was found in POE samples. With increasing octene content the degree of crystallinity was found to decrease while the ratio of monodinic and orthorhombic crystals (Mono/Orth) increases. All these results indicate that monodinic and orthorhombic crystals are inclined to form by realtively shorter and longer ethylene segments respectively. Moreover, the crystallinity increases with X at low X region. At higher s, the crystallinity, and the fraction of both monodinic and...