Nanostructured amphiphilic segmented networks based on poly(1,3-dioxolane) (PDXL) and poly(methyl methacrylate) (PMMA) have been synthesized by radical copolymerization of α,ω-diacrylate PDXL with methyl methacrylate (MMA). The corresponding polymer blends have been prepared by the radical polymerization of MMA in the presence of α,ω-dihydroxy-PDXL. The multiphase behavior of the segmented networks and polymer blends have been compared by making use of solid-state 13C CP/MAS NMR spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetrical analysis (TGA). For the network structures, the combined analysis of the proton spin−lattice relaxation times (T 1H) and proton spin-lock relaxation times (T 1 ρ H) revealed small PDXL domain sizes between 1 and 20 nm. DSC and DMA analysis also showed the forced compatibility of the network components. In the case of the polymer blends, the phase morphology strongly depends on the PDXL weight fraction. For blends with PDXL fractions higher than 20 wt %, T 1H relaxometry, DSC, and DMA analysis evidenced the presence of a heterogeneous phase morphology (domain sizes > 20 nm) that allows for the crystallization of the PDXL-rich domains.

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The fracture behavior of two different types of extruded polyamide 6 (PA6)/maleic anhydride grafted ethylene−propylene (EPM-g-MA) blends is examined by magnetic resonance imaging (MRI). TEM micrographs demonstrate a clear difference in morphology:  where one blend type contains pure rubber particles dispersed in the PA6 matrix, the other type contains PA6 occlusions within the rubber particles and is significantly more tough. MRI experiments on notched specimens of both blend types under critical load reveal a gradual increase of rubber cavitation toward the crack tip which can be quantified on the basis of the localized proton spin density. A clear relation is observed between the toughness and the dimensions of the plastic zone:  the toughest blend has a significant more extended plastic zone ahead of the crack tip. The enhanced toughness of the blends with occlusions can be attributed to a more pronounced delocalization of energy, which is suggested to result from a different deformation mechanism in which the load bearing capacity of the rubbery chains plays an important role.

NMR imaging is applied to study the crack growth resistance of polymers, being an important toughness parameter of which the understanding is still incomplete. A dedicated stretching device was developed to keep notched materials under load during the NMR measurements allowing to visualize the near crack tip damage behavior in polymers. Two polymers were investigated:  ABS, a blend of poly(styrene-co-acrylonitrile) with 28 wt % polybutadiene, and a block copolymer poly(butylene terephthalate)/poly(tetramethylene oxide) (PBT/PTMO). MRI investigations were performed on loaded specimens with a crack grown under critical conditions as well as on unloaded specimens. Numerous damage bands appear in the images of strained ABS which converge toward the crack tip and remain present upon unloading. Image contrast is demonstrated to arise from a reduced material density in these damage bands. The material density near the crack tip is reduced to about one-fourth of the normal density. Obviously severe crazing and rubber particle cavitation occurs at the crack tip. For the PBT/PTMO block copolymer a more continuous distribution of stress induced material response is observed that disappears almost completely upon unloading. Here image contrast mainly arises from a reduction of chain mobility in soft domains due to stress induced chain orientation.

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