Diacetylene copolymer

Sundar and Keller have reported the synthesis of linear boron-silicon-diacetylene polymers (31) (Fig. 21) using phenylboron dichloride (PBD) as the source for boron.50 The compositions of the thermally stable boron-silicon-diacetylene copolymers 31a-d are summarized in Figure 21. These polymers were observed to possess exceptional thermooxidative stabilities. 

Figure 21 The linear (boron-silicon-diacetylene) copolymers (31a-d) with their respective compositions. (Adapted from ref. 50.)...

As utilized in the synthesis of PPV-based polymers, soluble precursor routes have been developed for the synthesis of various heterocyclic Jt-conjugated polymers. The two most widely employed of these methods for heterocycle formation, shown in Scheme 66, center around ring closure of pre-polymers containing diacetylene 65 or 1,4-diketone units 66 [335-339]. The synthesis of heterocyclic structures from 1,4-diketones has been a known transformation in organic chemistry for decades. While once mainly used for monomer preparation through various cyclizations, it is now being employed to make heterocycle-containing polymers and copolymers [340-342]. 

Some of the copolymers composed of diacetylene should be mentioned, even though they may not fit exactly the definition of polydiacetylenes. 

The negative expansivity along the chain direction (a[j) seems to be a universal phenomenon with planar zigzag chains as it is exhibited by a variety of polymers of different chemical compositions, i.e. PE [37,38,60], ethylene tetrafluoroethylene alternating copolymer [61], PET [36], nylon 6 [39, 40], poly (vinyl alcohol) [62] and poly diacetylene... 

Figure 15.8 The general structure of the (boron-silicon-diacetylene) copolymers of Sundar et al. (top) and the compositions of the representative polymers (bottom)...

The approach that was adopted [66-69] was to prepare a series of urethane-diacetylene copolymers in which polydiacetylene units are incorporated into segmented copolyurethanes. It was shown in Section 8.1.1 that large strain-induced Raman band shifts can be obtained during the deformation of polydiacetylene single crystal fibers [8-12]. In fact, it is found that the largest shift measured so far (—20cm"V% strain) is for the C=C triple bond stretching band of polydiacetylenes (Table 8.1). 

Figve 8.8 Schematic representation of the solid-state topochemical polymerization of the diacetylene-urethane hard s ments (a) linear segmented block copolymer (b) cross-polymerized material (after [67])... 

Figwc8.9 Full Raman spectrum for the cross-polymerized diacetylene-urethane copolymer (after [67,68])... 

Figure8.10 (a)Shiftofthe2090cm Raman band with strain for the cross-polymerized urethane-diacetylene copolymer (after [68]) (b) dependence of the peak position of the 2090cm Raman band upon strain , t loading unloading, o, reloading (after [68])...

A series of polyaryleneethynyiene copolymers (—Ar-—(2 C—Ar —C=C—) , where Ar = 3-hexylthiophene, 3,4-dinitrothiophene, or selenophene and Ar = 3-hexylthiophene, 2,5-pyridyl, or 1,4-phenylene units were prepared by Pd(0)-catalyzed coupling of the 2,5-dihalothiophene and the appropriate diacetylene [54]. These materials had MW > 10, were soluble, and exhibited large third-order nonlinear optical susceptibilities and strong fluorescence. Several were n-dopable. 

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