Effect of scission of hydrogen bonds by phenol on phase behaviour and physical properties of polydiacetylene gels: P(3BCMU) and P(4BCMU)

We report the effect of phenol on the phase behaviour and physical properties of polydiacetylene gels. Specifically, they are o -dichlorobenzene ( o -DCB) solution of poly[4,6-decadiyne-1,10-diol-bis(n-butoxycarbonylmethylurethane)], abbreviated as P(3BCMU), and toluene (Tol) solution of poly[5,7-dodecadiyne-1,12-diol-bis(n-butoxycarbonylmethylurethane)], abbreviated as P(4BCMU). The polymer concentration was 0.1 to 2 wt%, and the molar ratio z of phenol to the monomer unit of the polydiacetylenes was regulated within 20. The gel-to-sol transition temperatures T t were determined by measurements of shear modulus for the P (3 BCMU ) o- DCB system and by a falling ball method for the P(4BCMU)/Tol systems. T t decreased with increasing z and the systems with polymer concentration of 1 wt% turned into a sol at room temperature in the range of z ≳ 10. The temperature dependence of alternating-current (a.c.) conductivity σ ac at 1 kHz exhibited a maximum at a temperature ca. 20 K below the transition temperature. The value of σ ac decreased steeply at the electrical transition temperature T σ , which also decreased with increasing z . Ultra-violet and visible-light spectra for the P (3 BCMU ) o- DCB and P(4BCMU)/Tol systems shifted to the short-wavelength side with increasing z . The infra-red spectra indicate that the intramolecular hydrogen bonds between the NH and CO groups of the side groups are cleaved by phenol. These results indicate that the conjugated rod-like conformation is made unstable by phenol. To clarify the mechanism of crosslinks of the gel network, the crystallinity of concentrated P(3BCMU) gels was determined by wide-angle X-ray diffraction. No crystallinity was observed in the gels of C less than 30 wt%.