Photoisomerization of Triazine-stilbene Fluorescent Brighteners in Solution and in their Copolymers with Styrene

Bleaching of polymeric materials can be achieved by blending or surface treatment with fluorescent brighteners, FBs [1]. In both cases the FB migrates with time, and the degree of whiteness decreases. The introduction of polymerizable groups into the FB makes it applicable in the copolymerization process with vinyl monomers, resulting in the formation of covalent bonds in the polymer molecule. Fluorescent brighteners based on triazine-stilbene are well known as effective compounds for attaining high degrees of whiteness. They are substances with excellent brightening properties and are easy to produce. About 80% of the FBs produced are derived from stilbene [2]. The triazine-stilbene FBs are mainly used for whitening of cotton and polyamide textiles [3] as well as paper [4], There exists extensive literature on FBs containing different amino and alkoxy derivatives in the triazine ring [2, 5], The synthesis of some triazine-stilbene FBs containing different polymerizable groups is reported in [6-9], and investigation of their copolymers with acrylonitrile or styrene in [10-12]. In solution these FBs have low light resistance because they can exist in two stereoisomeric forms: eisand trans. Exposure to light cause trans-cis isomerization with shift of the absorption maxima and formation of an equilibrium mixture. Isomerization to the m f o r m results in a loss of fluorescence [13],