Segmented polyurethanes functionalized with azo group

In this study poly (urethane-urea)s (PUU) and polyurethanes (PU) containing segments from azobenzene derivatives, which present photoisomerization or fluorescence emission, were studied. PUU based on polyethylene glycol (PEG), polycaprolactone (PCL) or an equimolar mixture of PEG/PCL, called as PEG-PUU, PCL-PUU or PEG/PCL-PUU, respectively, were synthesized using the two-step route by using 4,4'-diphenylmethane diisocyanate (MDI) and 4,4'-diaminoazobenzene (DAAB) as a chain extender. PUU were characterized according to their composition, molar mass, thermal, dynamic-mechanical, spectrophotometric properties, self-assembly in solution and photoisomerization kinetics. PUUs presented photoisomerization as the DAAB precursor, and the isomerization kinetics was affected by PUU self-assembly in N,N-dimethylformamide (DMF). The relaxation spectrum of PUU in the solid state presenting different azobenzene configurations (cis or trans), as well as the diameter of PUU particles in DMF proved the photoresponsive character of these polymers. Polyurethanes containing segments derived from 2,2'-dihydroxyazobenzene (DHAB) were also synthesized by the two-step route. The hydroxyls of DHAB interact with the azo group by hydrogen bonds, stabilizing the molecular structure, preventing trans-cis isomerization and decreasing the reactivity of hydroxyls towards isocyanate. As a strategy for the incorporation of DHAB in the polymer chain, the PU-diol oligomer based on DHAB, MDI and 1,4'-butanediol (BD) was synthesized The segmented polyurethane, PCLDHAB, was synthesized using PCL-diol and PU-diol as polyols, MDI and BD. PU were characterized with respect to structure and composition, molar mass, thermal, dynamic-mechanical, spectrophotometric properties, self-assembly in solution, and fluorescence emission. PCLDHAB was flexible and semi-crystalline polyurethane with heterogeneous amorphous phase. Similarly to DHAB, the segments containing the azo group in the PU did not show trans-cis isomerization, but did fluoresce. The absorption and emission spectra of PU showed differences in relation to the spectra for DHAB due to changes in the chemical environment associated with the composition in the polymer chains and also the aggregation in solution. The DHAB has different conformers, and this characteristic was preserved in the PU chains, however with changes in the proportionsbetween the conformers. While DHAB emits in two regions of the UV-vis spectrum, PUs emit in three regions. This work demonstrated that the combination of chain segments with different characteristics in PU and PUU is a simple and efficient strategy for obtaining amphiphilic, photoresponsive materials and with properties that can be modulated by the composition (AU)