Asymmetric polydiacetylenes with irreversible thermochromic properties

Asymmetric polydiacetylenes of general formula I are described, in which: - R = CH3-(CH2)p-, - R' = -(CH2)p-OH, - m is a whole number having the value 2, 4, 9, - p is a whole number having the value 1, 2, 3, 4, - n is a whole number greater than 20. The said polymers have the property of changing colour irreversibly when they exceed a threshold temperature, which is different for each one; because of this they can be used as indicators to indicate that the aforesaid temperature threshold has been exceeded. These polymers have absorption spectra in the ultraviolet or visible range with characteristic peaks at values between 570 and 650 nm. The absorption maximum is irreversibly displaced towards low wavelengths when the abovementioned temperature threshold is exceeded. The aforesaid compounds are obtained by polymerisation of the corresponding monomers converted into the solid state if liquid, cooling them to a temperature below their melting point and subsequently irradiating with radiation having a wavelength of not more than 254 nm.