Nature offers interesting examples of structures with a gradually changing composition that provides unique mechanical properties. Today, the transfer of biological principles to technical applications is gaining increasing attention. One prominent example of the transfer of biomimetic principles to materials science is the mussel byssus. Byssus threads possess gradually changing mechanical properties from soft to stiff in order to efficiently attach the mussel to the rock. This design is the basis for polymer gradient materials. Herein, we give a comprehensive overview of the most recent developments in the field of PGMs. In addition to basic terminology and definitions, selected highlights of PGMs are presented, followed by experimental techniques and characterization methods.magnified image

Ordered nanofiber arrays are a promising material platform for artificial adhesive structures, tissue engineering, wound dressing, sensor arrays, and self-cleaning surfaces. Their production via self-ordered porous alumina hard templates serving as shape-defining molds is well-established. However, their release requires the destruction of the hard templates, the fabrication of which is costly and time-consuming, by wet-chemical etching steps with acids or bases. We report the nondestructive mechanical extraction of arrays of cross-linked polyacrylate nanofibers from thus recyclable self-ordered nanoporous alumina hard templates. Silica replicas of the latter were synthesized using the extricated nanofiber arrays as secondary molds that could be mechanically detached from the molded material. The approach reported here, which can be combined with microstructuring, may pave the way for the high-throughput production of both functional nanofiber arrays and ordered nanoporous membranes consisting of a broad range of material systems.

Melt electrowriting (MEW), an additive manufacturing process, is established using polycaprolactone as the benchmark material. In this study, a thermoplastic elastomer, namely, poly(urea-siloxane), is synthesized and characterized to identify how different classes of polymers are compatible with MEW. This polyaddition polymer has reversible hydrogen bonding from the melt upon heating/cooling and highly resolved structures are achieved by MEW. The influence of applied voltage, temperature, and feeding pressure on printing outcomes behavior is optimized. Balancing these parameters, highly uniform and smooth-surfaced fibers with diameters ranging from 10 to 20 µm result. The quality of the 3D MEW scaffolds is excellent, with very accurate fiber stacking capacity-up to 50 layers with minimal defects and good fiber fusion between the layers. There is also minimal fiber sagging between the crossover points, which is a characteristic of thicker MEW scaffolds previously reported with other polymers. In summary, poly(urea-siloxane) demonstrates outstanding compatibility with the MEW process and represents a class of polymer-thermoplastic elastomers-that are, until now, untested with this approach.

SUMh4ARENew monomers are described for the synthesis of rod-like poly(l,4-phenyleneethynylene)s with long flexible aliphatic side chains. By palladium catalyzed polycondensation soluble polymers with melting points around 100 "C could be obtained. The molecular weight was estimated by GPC, VPO and elemental analysis: GPC showed a multimodale distribution with P, = 9-15. N M R spectra were found to be in agreement with the assumed polymer structure, but signals of the acetylenic carbons could not be detected. A broad, structureless absorption with a maximum at A = 410 nm is seen in the UV-VIS-spectra. The thermal decomposition of the substituted PPE's starts at about 400 "C and is comparable to that of unsubstituted PPE in air.*) Footnote added in proof: Very recently alkoxy groups were attached to PPV's, too (S. H.

The syntheses of polyenynes as model compounds for poly(diacety1ene)s (PDAs) are described. Variation of properties (UV-VIS, Raman, NMR and bond geometries) as a function of the chain length was investigated. After extrapolation to infinite chain length these data were compared to those for PDAs. From UV-VIS spectra a value of I = 551 nm (2.25eV) was calculated corresponding to the electronic transition of a single polyenyne chain. This energy is located at the low energy end of a yellow PDA solution spectrum. From Raman scattering v(,--,-) = 2108-2128cm-' and vCEc) = 1505-1532crn-' were calculated after extrapolation. Similarly sp-C ''C NMR data yielded a shift of 6 = 100ppm. These data are almost identical to data known for yellow PDA solutions. Bond geometries are almost identical to those of poly(diacety1ene)s and theoretical data.

This article describes the synthesis and thermal characterization of novel aryl‐substituted rod‐like homopolyimides. Synthetic aspects of monomer syntheses and one‐step polymer synthesis in m‐cresol are presented. Polyimides with rod‐like chain structure are based on monophenylated pyromellitic dianhydride (MPPMDA), diphenylated pyromellitic dianhydride (DPPMDA), and as rod‐like diamine units on phenylated para‐phenylene diamine and 1,1′‐binaphthyl‐4,4′‐diamine. As partial flexible units, which have the possibility to be converted into an extended chain conformation, commercially available 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 3,4′‐oxydianiline (3,4′‐ODA) were used. The polyimides were investigated with respect to solution properties and thermal behavior. © 1993 John Wiley & Sons, Inc.

A miniature small‐scale material processing and testing approach is developed as a screening method to evaluate polymer materials for fused deposition modeling (FDM). This method is suitable for a small material input of less than 10 g using a mini compounder in combination with an injection molding machine to manufacture short rods usable as FDM feedstock material. Compared with conventional continuous filament extrusion, where the amount of raw material required is around 1–5 kg, time and material consumption are both significantly reduced for the investigation of FDM filament materials or formulations. In order to demonstrate this method, three different polypropylene grades are processed into rods and compared to commercially available continuous filaments. In addition to warp deformation, interlayer bonding properties are also measured on test specimens punched out of FDM‐printed square tubes. The presented rod preparation and square tube printing offer fast and efficient material screening and optimization for new FDM material development.

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