Polydiacetylene formation

The sensors discussed so far are based on ligands covalently bound to the polymer backbone. Other methods of detection - often referred to as mix and detect methods - work by simple noncovalent incorporation of the polymer with the ligand of interest. Reichert et al. generated liposomes of polydiacetylene with sialic acid for the same purpose of detection as Charych s surface-bound polymers, but realized that covalent functionalization of the polymer was not necessary [17]. Through simple mixing of the lipid-bound sialic acid with the polymer before sonication and liposome formation, they were able to form a functional colorimetric recognition system (Fig. 8). 

Kim J-M, Lee J-S, Lee J-S, Woo S-Y, Ahn DJ. Unique effects of cyclodextrins on the formation and colorimetric transition of polydiacetylene vesicles. Macromol Chem Phys 2005 206 2299-2306. 

Many authors have investigated the photoconductivity of the polydiacetylenes [142-171], The main problem discussed concerns the nature of the initial act of the photoeffect. At first, most authors considered the exciton formation to occur at the beginning with consequent dissociation on the free carriers. Then it was shown the broad band existence for directions along the chains. The unification of the excitonic and band model of the free charge carrier generation was developed [146-150],... 

The following is an attempt to summarize the structural data which have been accumulated recently and to critically review the present state of knowledge on the formation and structural properties of polydiacetylenes and to point out some directions of future developments in the field. Other aspects have been reviewed recently and the photopolymerization and reaction kinetics as well as the... 

Although interesting within the framework of polymer physics and material science this would not be sufficient to attract so many workers from areas outside of conventional polymer research. Additional interest arouse because of the unusual structure of the polymers obtained via solid-state polymerization of diacetylenes and because of the mechanistic features related to its formation. Polydiacetylenes exhibit a fully conjugated and planar backbone in the crystalline state and are thus considered the prototype study object as far as the nature and physical behavior of polyconjugated macromolecules are concerned Theoretical discussions of the electronic structure of these polymers (2) lead to a description in terms of a wide band one-dimensional semiconductor... 

Although there has been a lot of interest in the PDAs due to their unique chemical, optical, and electronic properties, no method is available yet that is generally applicable to the formation of polydiacetylene films possessing suf-ficiendy high quality for technological applications, i.e., electronic and photonic devices, due to the insolubility of many polydiacetylenes. There is a continuous search for techniques to increase the processibility and quality of PDA film. Paley et al. reported a novel technique to obtain high-quality thin PDA films. They used photodeposition technique from monomer solutions onto UV trans-... 

Fig. 5.15 The formation of mechanism of the helical PDA(polydiacetylene) chain in the Lcoi liquid crystal state. Reproduced from Ref. [76] by permission of The Royal Society of Chemistry...

Scheme 10.1. The formation of polydiacetylene polymer from the diacetylenic monomers using 1,4 addition via UV irradiation at wavelength 254 nm. For clarity, only three monomers are shown.

However, the development of experimental observations of intramolecular singlet fission calls the 2Ag-mediated model into question (Fig. 2). In a pair of transient absorption studies on isolated chains of polydiacetylene (1), Lanzani et al. conclusively demonstrated intramolecular singlet fission, observing rapid (<200-fs) formation of triplet excitons accompanied by loss of the spectral signature of Due to... 

Fig. 2 Polyenes and the 2 state, (a) Schematic representation of the singlet 2Ag state in a polyene, showing its equivalent description either as a triplet-triplet or as soliton-antisoliton pair. Adapted from ref. 33. (b) Polyene-type structures discussed in the text. 1 Polydiacetylene [34,35], 2 Poly(diethyldipropargylmalonate) 136], 3 Poly(3-dodecylthienyl-enevinylene) [37], 4 Polyibenzodithiophene thiophene dioxide) [38]. R-groups denote solubilizing chains, (c) Models of singlet fission in polyenes, mediated by formation of 2Ag (left) or directly from IBu (right).

Fourier transform near-infrared spectroscopy had been used to determine traces of hydroxy and carboxy functional groups and water in polyesters. Bowden and co-workers [25] monitored the degradation of PVC using Raman microline focus spectrometry. They demonstrated that PVC decomposition is accompanied by the formation of modal polyene chains containing 11-12 or 13-19 double bonds. Bloor [26] has discussed the Fourier transform Raman spectroscopy of polydiacetylenes. Koenig [27] discusses results obtained by the application of infrared and Raman spectroscopy to polymers. 

Despite their potential importance, there are few spectroscopic studies of polymerizable surfactants. The only well-characterized polymerized surfactants are the polydiacetylenic fatty acids. The polymerization mechanism (1,4 addition) was only recently discovered as a result of studies on crystals of non-surfactant monomers which become brightly colored on polymerization [1], indicating the formation of polymer concurrent with a solid-solid phase transition. Several groups, particularly that of Ringsdorf, have pioneered the study of polydiacetylenic fatty acids [2-5]. A significant amount of spectroscopic work has been done on non-surfactant polydiacetylenes [6-9]. In addition, Lando and co-workers have used electron diffraction from mono- and bilayers of fatty acids to establish the conformation of the diacetylene backbone chains in this ordered surfactant system [10,11], and others have performed Raman spectroscopy on Langmuir-Blodgett films of similar surfactants [12]. This provides one with a powerful "basis set" of information from which to study other polydiacetylenic systems. 

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