The synthesis of extended and oriented very thin layers of polymers by solid-state polymerization of multilayers built up from monomolecular films of suitable monomers by means of the Langmuir-Blodgett (LB) technique has been felt to be a particular challenge for a long time. Attempts to make use of radiation-induced free radical polymerization of long-chain vinyl derivatives have been successful only in part (1–5).

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pol.1979.170170607

Polymerization of diacetylenes in multilayers

Prolonged storage (∼2 years) or gentle heating (50−80 °C) of crystalline 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) affords a highly conducting, bromine-doped poly(3,4-ethylenedioxythiophene) (PEDOT), as confirmed by solid-state NMR, FTIR, CV, and vis−NIR spectroscopies. The novel solid-state polymerization (SSP) does not occur for 2,5-dichloro-3,4-ethylenedioxythiophene (DCEDOT), and requires a much higher temperature (>130 °C) for 2,5-diiodo-3,4-ethylenedioxythiophene (DIEDOT). X-ray structural analysis of the above dihalothiophenes reveals short Hal···Hal distances between adjacent molecules in DBEDOT and DIEDOT, but not in DCEDOT. The polymerization may also occur in the melt but is significantly slower and leads to poorly conductive material. Detailed studies of the reaction were performed using ESR, DSC, microscopy, and gravimetric analyses. SSP starts on crystal defect sites; it is exothermic by 14 kcal/mol and requires activation energy of ∼26 kcal/mol (for DBEDOT). The temperature dependence...

Solid-State Synthesis of a Conducting Polythiophene via an Unprecedented Heterocyclic Coupling Reaction

Heptadeca-2,4-diine-1-ol and Heptadeca-2,4-diine-1-acid were synthesized and their polymerization behaviour in the solid state was investigated. Both compounds polymerize thermally below the melting point and photochemically under the action of uv-light to form polymers via 1,4-addition to the conjugated triple bonds with a backbone of conjugated double-and triple-bonds. The photoresponse spectra resemble the absorption spectra exhibiting maxima of photoreactivity in the absorption band of the conjugated triple bonds of the monomers.

Polymerization of mono- and multilayer forming diacetylenes

One of the challenges in polymer science has been to prepare large-polymer single crystals. We demonstrate a visible light-triggered quantitative topochemical polymerization reaction based on a conjugated dye molecule. Macroscopic-size, high-quality polymer single crystals are obtained. Polymerization is not limited to single crystals, but can also be achieved in highly concentrated solution or semicrystalline thin films. In addition, we show that the polymer decomposes to monomer upon thermolysis, which indicates that the polymerization-depolymerization process is reversible. The physical properties of the polymer crystals enable us to isolate single-polymer strands via mechanical exfoliation, which makes it possible to study individual, long polymer chains.

http://science.sciencemag.org/content/sci/343/6168/272.full.pdf

Single-Crystal Linear Polymers Through Visible Light–Triggered Topochemical Quantitative Polymerization

This article reviews the current state of art of photopolymerization of crystalline diacetylenes, although complementary information on thermal and γ-polymerization is also included whenever felt appropriate. Priority is given to an outline of recent achievements regarding reaction kinetics and energetics as well as to model considerations for both initiation and propagation of the polymer chain. It will be shown that at least for diacetylene-bis(p-toluenesulfonate) (TS) existing experimental data allow establishing a consistent picture of the polymerization process. After discussing recent works on photopolymerization in Langmuir-Blodgett-multilayer assemblies, including sensitization and self-sensitization effects, potential applications of the unusual optical, electrical, and reaction properties of diacetylenes are outlined.

R. Huber

Papers

ESR of a diacetylene polymer single crystal