Study of the Mechanical Properties of Dibenzyl-Based Polyurethane Containing a Molecularly Dispersed UV Absorber

Blends of certain polyurethanes based on 4,4′ -dibenzyl diisocyanate (DBDI) with 1,2-bis-[2-(2-hydroxy-5-methylphenyl)-5-benzotriazolyl]-ethane (BHMBE) as the UV absorber were prepared and their mechanical properties were studied during environmental exposure. Two methods were used to prepare the blends: the introduction of the UV absorber into the polymer solution, or the addition of the UV absorber to the melted prepolymer during the polyurethane synthesis. The latter method allows temporary chemical binding of the UV absorber to polyurethane chain as a result of the additional reaction of OH phenolic groups to the isocyanate end-capped prepolymer. A process was performed and the new urethane groups were broken releasing the absorber as a molecular-level dispersion in the polymer matrix. The improved photo-oxidative stability of dibenzyl diisocyanate-based polyurethane treated with the UV absorber, 1,2-bis-[2-(2-hydroxy-5-methylphenyl)-5-benzotriazolyl]-ethane (BHMBE) is discussed in relation to the chemical structure and the content of UV absorber.