This disclosure relates to fluorescent brighteners.  More particularly the disclosure relates to fluorescent brighteners, methods of preparing the fluorescent brighteners, compositions comprising the fluorescent brighteners, in particular polymer compositions comprising the fluorescent brighteners, and uses thereof. 
Fluorescent brighteners, also known as fluorescent whitening agents, fluorescent whiteners, optical brighteners, and optical whiteners, are additives that alter the visual properties of polymers.  Fluorescent brighteners are colorless to weakly colored organic compounds.  When in solution, applied to a substrate, or combined with a polymer, they absorb primarily ultraviolet light in the 300 to 400 nanometer (nm) range.  Most of the absorbed energy is then re-emitted as visible violet-to-blue fluorescent light in the 400 to 500 nm range.  Fluorescent brighteners thus help to mask inherent yellowness in discolored polymers and impart unique, robust color to specialty plastic products. 
There are very few fluorescent brighteners exhibiting high Tg values.  In addition, many fluorescent brighteners decompose at temperatures commonly used to process polymers.  One high Tg fluorescent brightener is 2,2′-(2,5-thiophenediyl) bis[5-(1,1-dimethylethyl)]-benzoxazole, (CAS No. [ 7128-64-5]) available from Ciba under the trade name UVITEX®-OB.  Nonetheless, there remains a need in the art for fluorescent brighteners that have a high Tg to enable their use in a wide variety of polymers, especially thermoplastic polymers.