The measurements of residual dipolar couplings in elastomer system is desirable, because they reflect the hindrance to molecular motions by the cross-linking, topological constraints and the external factors like mechanical stress. Dipolar-encoded longitudinal magnetization nuclear magnetic resonance (NMR) decay curves, double-quantum and triple-quantum NMR buildup intensities for measuring the residual dipolar couplings, and the associated dynamic order parameters are introduced. It is shown that in the short excitation time regime the effective dipolar network is simplified. In the limit of this model based on localized dipolar couplings, the spin response to two-dimensional pulse sequences used to record multiple-quantum (MQ) NMR coherences was evaluated for longitudinal magnetization, double-, and triple-quantum coherences of methylene, and methyl protons in synthetic 1,4-cis-polyisoprene. The dynamic order parameters can be evaluated from this NMR response using a classical scale-invariant polymer model. These dynamic order parameters were measured for a cross-link series of synthetic polyisoprene and correlated with the cross-link density. The decay rates of the Hahn-echo amplitudes reflecting residual dipolar couplings as well as effects of molecular motion are also measured for the same cross-link series. The contribution of molecular motions to the transverse relaxation can be separated from the residual dipolar couplings using a train of magic echoes. The sensitivity of these transverse relaxation rates to the cross-link density is compared to that of residual dipolar couplings. The NMR time scale is shorter for the dipolar-encoded longitudinal magnetization and MQ experiments as compared to transverse relaxation experiments leading to an increased sensitivity to cross-link density of the former approaches.

The microphase composition of poly(butylene terephthalate)-block-poly(tetramethylene oxide) multiblock (PBT-block-PTMO) copolymers with varying content of PTMO soft block and varying block length was studied by 1 H NMR transverse magnetization relaxation (T2 relaxation) and 1 H 2D DQ NMR experiments under fast MAS. The 2D NMR method showed the existence of the molecular scale mixing of PBT and PTMO blocks. The 1 H and previously obtained 13 C NMR relaxation data provided detailed information on the microphase composition. The content of soft domains (i.e., viscoelastic material which is composed of the soft block and mixed PBT) and hard domains (i.e., crystalline PBT and immobilized PBT chain portions at the crystal-amorphous PBT interface) depends largely on temperature. It was shown that about 15-25% of PBT in the samples is soft due to molecular mixing with PTMO. The results suggest that at 40 °C the mixed phase is composed of approximately one PBT chain unit per eight PTMO chain units. The PBT crystallinity in the copolymers slightly increases with increasing length of the soft block, since this causes increase of the average length of PBT blocks. The content of crystalline PBT is nearly constant for samples with hard blocks containing more than five monomer units and decreases for shorter PBT block lengths. An increase in the content of PTMO with the same block length causes a significant increase in chain mobility in the soft domains. Apparently, the content of the mixed phase and the density of physical/topological junctions at the PBT/PTMO interphase largely affect the molecular mobility in the soft domains.

Selected applications of spatially resolved NMR are presented, which demonstrate the use of the method for investigating applied topics relevant to polymer and materials science. Examples are given for imaging of rigid, soft, and fluid matter. They include characterization and interpretation of electrical aging in poly(ethylene), cross-link density at the interface of covulcanized elastomer sheets, and cross-filtration in hollow-fiber filter modules. A novel NMR dectector, the NMR-MOUSE, has been developed for process and quality control by relaxation measurements. Its use for non-destructive determination of the glass-transition temperature by room temperature measurements on elastomer samples is demonstrated.

Summary: Information about segmental mobility in thermoplastic elastomers was obtained using static 1H double quantum (DQ) NMR experiments in combination with homo‐ and heteronuclear dipolar filters, e.g. 13C editing of 1H DQ buildup curves. Block copolymers of poly(butylene terephthalate) (PBT) as hard blocks and poly(tetramethylene oxide) (PTMO) as soft blocks (PBT‐block‐PTMO) were investigated by varying composition and block length. By simulation of the DQ buildup curves, residual dipolar couplings and with this the average order parameter were deduced for the mobile PTMO blocks which are sensitive to the segmental mobility responsible for the viscoelastic properties of thermoplastic elastomers. A strong correlation exists between residual dipolar coupling and composition. Furthermore, the average order parameter correlates linearly with the amount of PTMO in a PTMO‐rich phase as determined in previous studies. Additionally, 1H transverse magnetization relaxation measurements revealed a direct correlation between the effective T2 relaxation time of the soft domain and the composition of the thermoplastic elastomers.

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