Assembling semiconducting molecules by covalent attachment to a lamellar crystalline polymer substrate.

We have investigated the potential of polymers containing precisely spaced side-branches for thin film applications, particularly in the context of organic electronics. Upon crystallization, the side-branches were excluded from the crystalline core of a lamellar crystal. Thus, the surfaces of these crystals were covered by side-branches. By using carboxyl groups as side-branches, which allow for chemical reactions, we could functionalize the crystal with semiconducting molecules. Here, we compare properties of crystals differing in size: small nanocrystals and large single crystals. By assembling nanocrystals on a Langmuir trough, large areas could be covered by monolayers consisting of randomly arranged nanocrystals. Alternatively, we used a method based on local supersaturation to grow large area single crystals of the precisely side-branched polymer from solution. Attachment of the semiconducting molecules to the lamellar surface of large single crystals was possible, however, only after an appropriate annealing procedure. As a function of the duration of the grafting process, the morphology of the resulting layer of semiconducting molecules changed from patchy to compact.

Long-Chain Aliphatic Polymers To Bridge the Gap between Semicrystalline Polyolefins and Traditional Polycondensates.

Other than their established short-chain congeners, polycondensates based on long-chain difunctional monomers are often dominated by the long methylene sequences of the repeat units in their solid-state structures and properties. This places them between traditional polycondensates and polyethylenes. The availability of long-chain monomers as a key prerequisite has benefited much from advances in the catalytic conversion of plant oils, via biotechnological and purely chemical approaches, likewise. This has promoted studies of, among others, applications-relevant properties. A comprehensive account is given of long-chain monomer syntheses and the preparation and physical properties, morphologies, mechanical behavior, and degradability of long-chain polyester, polyamides, polyurethanes, polyureas, polyacetals, and polycarbonates.

Long-Spaced Polyketones from ADMET Copolymerizations as Ideal Models for Ethylene/CO Copolymers.

Long-spaced polyketones containing 0-52.6 ketone groups per 1000 methylene units were prepared by ADMET copolymerization of docosa-1,21-dien-11-one (1) with undeca-1,10-diene (2), followed by exhaustive hydrogenation. Melting point differences of 5-10 °C were found between these polyketones and their reported congeners from ethylene/CO copolymerizations with comparable CO contents, which were related to additional methyl branching occurring in insertion copolymerization. Consequently, ADMET-derived polyketones can act as defect-free model polyketones. Comparison with polymers containing the same degrees of other carbonyl functionalities (esters, carbonates) shows that the partial compensation of the disturbance of polyethylene crystallization goes along with the groups' polarity.

Precise Microstructure Self-Stabilized Polymer Nanocrystals.

Nanoparticles with a defined shape and surface chemistry result from an encoding of crystal size directly in the polymer microstructure. This is brought about by carboxy groups spaced precisely on every 21st or 45th carbon atom of linear polyethylene chains synthesized by acyclic diene metathesis polymerization (ADMET) of precisely branched, long-chain α,ω-dienes. These hydrophilic functional groups form a layer on the nanocrystal surface, which interacts with the aqueous dispersing medium and, thus, self-stabilizes the nanocrystals. The nanocrystal thickness is directly predeterminded by the length of the long-chain methylene spacer between the functional groups.

Which polyesters can mimic polyethylene?

Self-metathesis of erucic acid by [(PCy(3))(η-C-C(3)H(4)N(2)Mes(2))Cl(2)Ru = CHPh] (Grubbs second- generation catalyst) followed by catalytic hydrogenation and purification via the ester yields 1,26-hexacosanedioate (>99% purity). Polyesterification with 1,26-hexacosanediol, generated from the diester, affords polyester-26,26, which features a T(m) of 114 °C (T(c) = 92 °C, ΔH(m) = 160 J g(-1)). Ultralong-chain model polyesters-38,23 (T(m) = 109 °C) and -44,23 (T(m) = 111 °C), generated via multistep procedures including acyclic diene metathesis polymerization, underline that melting points of such aliphatic polyesters do not gradually increase with methylene sequence chain length. Available data suggest that to mimic linear polyethylenes thermal properties, even longer sequences, amounting to at least four times a fatty acid chain, fully incorporated in a linear fashion are required.