Diacetylenes, molecular structures

Influence of subphase temperature, pH, and molecular structure of the lipids on their phase behavior can easily be studied by means of this method. The effect of chain length and structure of polymerizable and natural lecithins is illustrated in Figure 5. At 30°C distearoyllecithin is still fully in the condensed state (33), whereas butadiene lecithin (4), which carries the same numEer of C-atoms per alkyl chain, is already completely in the expanded state (34). Although diacetylene lecithin (6) bears 26 C-atoms per chain, it forms both an expanded and a condensed phase at 30°C. The reason for these marked differences is the disturbance of the packing of the hydrophobic side chains by the double and triple bonds of the polymerizable lipids. At 2°C, however, all three lecithins are in the condensed state. Chapman (27) reports about the surface pressure area isotherms of two homologs of (6) containing 23 and 25 C-atoms per chain. These compounds exhibit expanded phases even at subphase temperatures as low as 7°C. 

Orchard B, Tripathy S (1986) Molecular-structure and electronic property modification of poly(diacetylenes). Macromolecules 19 1844—1850... 

The arrangement shown in Figure 1(a) presupposes an extended conformation of the diacetylene molecule. For monomers with bulky end groups, the flexibility of the monomer molecule can result in a compact molecular structure in the crystal. The sidegroups then impede the reaction, in contrast to the situation in reactive monomers where the sidegroup interactions bring the diacetylene moieties into the desired reactive contact. 

The following molecular structure data were used to calculate the values of the G-function of diacetylene ... 

If the diacetylene moiety is introduced into phospholipids or similar double-layered membrane and/or micelle/vesicle-forming molecular structures, these special forms of orgemisation may be polymerized as well providing a solid-like arrcungement of the reactive groups is attained. Vesicles and micelles of polydiacetylenes have been prepared in a great variety following this principle (12,16). 

IPUDO (for the molecular structure see Tab. 9.2) is an example of a symmetrically substituted diacetylene. For the monomer as well as polymer crystals, non-centrosymmetrical orthorhombic crystal structures can be found already at room temperature [84]. The c-axis is the polar axis of the monomer crystal. IPUDO can only be polymerized by y radiation ( °Co). For 85% polymerized crystals pyroelectric properties were observed only in b direction. The permittivity of IPUDO is highly anisotropic, with maximum values of 8.5 for the... 

If the diacetylene is solid-state polymerized, dissolved and respread on the subphase, a monolayer is produced with much lower 11 and viscosity than the corresponding surface polymerized material. This illustrates the fact that in some cases polymer properties can be strongly influenced by the polymerization mode, and if specific material parameters are required, it may be an advantage to use one polymerization technique in preference to another. However, in contrast, almost identical U-A behaviour has been reported for structure (10) with n = 12, m = 8 when polymerized on the subphase surface (UV irradiation for 1 h at a surface pressure of 10 mN m under a nitrogen atmosphere), and when prepolymerized in solution (using 2,2 -azoisobutyronitrile in toluene at 60 for 20 h) [27]. This emphasises the difficulty in predicting polymer properties each material system will exhibit characteristic behaviour, depending not solely on the molecular structure, but also on primary factors such as the mode of polymerization and the specific experimental conditions. 

Using the above strategy for the preparation of layered compounds the next step for the preparation of a layered diacetylene was to design a second molecular structure containing the diacetylene and necessary functionality for its incorporation into the layered hydrogen bonded network [15]. A reasonable choice is diacetylene 2 which contains the pyridine functionality, a functionality well known to hydrogen bond to carboxylic acids forming supramolecular networks [16]. 

Because supramolecular structural features, such as the close contact of the diacetylenes, are extremely difficult to predict from a given molecular structure, they... 

In some cases, chemical substituents can bring about unusual monotropic liquid crystalline phases which only exist upon heating or cooling. The diphenyl-diacetylenes are examples in this category [22]. Early theoretical connections between molecular electronic structure and orientational order... 

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