Diacetylene monolayers, polymerization

Day, D. and J.B. Lando. 1980. Morphology of crystalline diacetylene monolayers polymerized at the gas-water interface. Macromolecules 13 1478. 

Monolayer Polymerization. Polymerization of the highly ori-ented monomer films can simply be achieved by UV irradiation under nitrogen (Figure 8.). The polymerization of the diacetylene monomers (2, 5-9) is a topochemical reaction (32,38) that only takes place, if the monomers are perfectly orderecTT i.e. in the crystalline state or in oriented mono- (32) or multilayers (39) and leads to the formation of conjugated Tlue and red colorecT polymer backbones (Eqn. I.). 

Convincing evidence for phase separation was obtained from the photopolymerization behavior of 6 in the mixed 6/DSPE monolayer films. Photopolymerization of diacetylenes is a topotactic process which requires the proper alignment of the 1,3-diyne moieties [35]. Thus diacetylenes typically polymerize rapidly in the solid state but not in solution. Polymerization is triggered by ultraviolet irradiation and proceeds via a 1,4-addition mechanism yielding a conjugated ene-yne backbone (Fig. 5). The reaction can be followed by the growth of the visible absorption band of the polymer. 

LB films have also been prepared from simple (20, for example) [165] and functionalized (21, for example) [166] amphiphatic diacetylenes. Two different approaches were pursued. In the first approach, diacetylenes were polymerized as monolayers and subsequently transferred to substrates to generate LB films. In the second approach, LB films were formed from monomeric diacetylenes and were subsequently polymerized. Strong absorption of polydiacetylenes in... 

Diacetylene monolayer photopolymerization was found to be topochemical it only occurred in the two-dimensional solid state of the surfactants. Polymerized diacetylenes, both in monolayers and in LB films, were found to be rather rigid and prone to cracking [160]. This undesirable property somewhat limits the exploitation of polymerized diacetylene LB films for potential electronic applications. 

Okawa and Aono [50] demonstrated under ambient conditions a diacetylen chain polymerization induced in a self assembled monolayer of 10,12-nonacosadiyonic acid on graphite. First an artificial defect was created with the STM tip by applying a positively pulsed sample bias, the polymerization of a single diacetylene monolayer chain was initiated at another surface location with a negative voltage pulse. After progression of the chain reaction, the polymer chain was terminated at the artificial defect site. 

Muniz-Miranda M, Giorgetti E, Margheri G, Del Rosso T, Sottini S, Giusti A, Alloisio M (2005) SERS investigation on the polymerization of carbazolyl-diacetylene monolayers on gold surfaces. Macromol Symp 230 67-70... 

Langmuir-Blodgett films may have value in many applied areas of traditional interest to the industrial chemist, such as adhesion, encapsulation, and catalysis. The permeability characteristics of monolayer assemblies may also find application as synthetic membranes for ultrafine filtration, gas separation, and reverse osmosis. For example, Albrecht et al. (44) proved the eflSciency of polymeric diacetylene monolayers on semipermeable supports in reducing the flow of CH4. One interesting possibility lies in using LB monolayers as lubricants in magnetic tape technology. Unpublished reports have indicated that frictional coeflScients can be reduced markedly when the tape is coated with a few monolayers. In applications such as those listed previously, difiSculties may well be encountered with the mechanical stability of the films. To date, relatively little research has been carried out in this area. 

That this is, in principle, possible was shown for polymerized diacetylene monolayers, the red-orange color of which was visible with the naked eye Day, D. and Ringsdorf H. (1978) J. Potym. Sci. Polym. Lett. Ed., 16, 205. 

The use of monolayers to achieve the supramolecular structural parameters for a topochemical polymerization is a powerful strategy that will undoubtedly prove to be useful for the preparation of sensors (35) and devices (36) that exploit the diacetylene-conjugated polymeric backbone (Fig. 6). 

Monolayer and Multilayer Polymerization A reaction scheme for the polymerization of a diacetylene monolayer is shown in Figure 2. In the following work the lithium salt was studied and the surface pressure during polymerization was 10 dynes/cm. 

Photopolymerization reactions of monolayers have become of interest (note Chapter XV). Lando and co-workers have studied the UV polymerization of 16-heptadecenoic acid [311] and vinyl stearate [312] monolayers. Particularly interesting is the UV polymerization of long-chain diacetylenes. As illustrated in Fig. IV-30, a zipperlike process can occur if the molecular orientation in the film is just right (e.g., polymerization does not occur readily in the neat liquid) (see Refs. 313-315). 

Chemical properties of deposited monolayers have been studied in various ways. The degree of ionization of a substituted coumarin film deposited on quartz was determined as a function of the pH of a solution in contact with the film, from which comparison with Gouy-Chapman theory (see Section V-2) could be made [151]. Several studies have been made of the UV-induced polymerization of monolayers (as well as of multilayers) of diacetylene amphiphiles (see Refs. 168, 169). Excitation energy transfer has been observed in a mixed monolayer of donor and acceptor molecules in stearic acid [170]. Electrical properties have been of interest, particularly the possibility that a suitably asymmetric film might be a unidirectional conductor, that is, a rectifier (see Refs. 171, 172). Optical properties of interest include the ability to make planar optical waveguides of thick LB films [173, 174]. 

Figure 12. STM image of a monolayer of C9(DIA)C8ISA 63 (a) before and (b) after photoinduced polymerization of the diacetylene units. Pictures taken from ref. [41].

Compression- and Shear-Induced Polymerization in Model Diacetylene-Containing Monolayers. 

Figure 9. VIS Multiplot of absorbance of a monolayer of diacetylene lipid (5) vs. polymerization time. Constant surface pressure 10 mN m l 20°C N2 atmosphere.

Domain formation in binary mixtures of a polymerizable lipid and non-polymerizable lipid is well established for diacetylenic lipids. The rigid diacetylenic unit facilitates the formation of enriched domains in the condensed phase of monolayers or the solid-analogous phase of bilayers. Since diacetylenes polymerize most readily in solid-like states, most studies have focused on conditions that favor domain formation. Only in the case of a mixture of a charged diacetylenic lipid and a zwitterionic PC was phase separation not observed. Ringsdorf and coworkers first reported the polymerization of a phase-separated two-dimensional assembly in 1981 [33], Monolayer films were prepared from mixtures consisting of a diacetylenicPC (6) (Fig. 5) and a nonpolymerizable distearoyl PE (DSPE). 

Condensed monolayer films of pure 6 polymerized rapidly, as did mixed 6/DSPE films of up to 75% DSPE, provided the monolayers were in the condensed state [33], In the liquid-expanded state, polymerization did not occur. In the condensed state, lateral diffusion of individual lipids within the monolayer is severely restricted compared to the liquid-like state. This precludes initiation of polymerization by diffusive encounter between excited-state and ground-state diacetylene lipids. In order for polymerization to occur in the condensed state, the film must be separated into domains consisting of either pure 6 or pure DSPE. A demonstration that the rates of photopolymerization for pure 6 and mixed 6/DSPE monolayers are equal would be a more stringent test for separate domains of the lipids, but no kinetic data have been reported for this system. 

Besides the polymerization of diacetylenes, butadienes and acrylates, the polycondensation behavior of long-chain ot-amino acids, diamines and diesters has been investigated in monolayers 52. ... 

Aqueous dispersions of polymerizable lipids and surfactants can be polymerized by UV irradiation (Fig. 18). In the case of diacetylenic lipids the transition from monomeric to polymeric bilayers can be observed visually and spectroscopically. This was first discussed by Hub, 9) and Chapman 20). As in monomolecular layers (3.2.2) short irradiation brings about the blue conformation of the poly(diacetylene) chain. In contrast, upon prolonged irradiation or upon heating blue vesicles above the phase transition temperature of the monomeric hydrated lipid the red form of the polymer is formed 23,120). The visible spectra of the red form in monolayers and liposomes are qualitatively identical (Fig. 19). 

Due to the topochemical restrictions of diacetylene polymerization, diacetylenic lipids are solely polymerizable in the solid—analogous phase. During the polyreaction an area contraction occurs leading to a denser packing of the alkyl chains. In addition to surface pressure/area isotherms the polymerization behavior of diacetylenic lipids containing mixed films give information about the miscibility of the components forming the monolayer ... 

Polymerization is induced with the STM tip. STM images of the monolayer of NCDA before and just after applying a positive pulsed bias voltage of 4Y are shown in Fig. 19. In Fig. 19a, a number of parallel lines corresponding to the diacetylene portions of NCDA molecules are observed. 

Polymeric Systems.—Absorption, fluorescence excitation, and emission spectra of soluble poly(diacetylene) at room and liquid nitrogen temperature has been recorded for different solvents. The excimer-to-monomer emission ratio for polystyrene depends upon the polymer molecular weight but is independent of the solvent. Monolayer films of the 27-carbon-chain-length alkyldiace-... 

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