RESUMO
Enantiopure poly(lactic acid) (PLA) can form stereocomplexes when enantiomeric PLA chains are mixed in equivalent amounts. Such materials provide interesting features that might be suitable for numerous applications. Despite several advantages, the main drawback of PLA is its narrow window of processing, thus limiting its use for industrial applications. Reported herein are achiral iron complexes, that are highly active, productive, and stereoselective under mild reaction conditions for the ring-opening polymerization of lactide. The corresponding catalytic systems enable the production of stereoblock polymers with high molecular weights, allowing the formation of thermally stable and industrially relevant stereocomplexes.
RESUMO
Current techniques for intra-coronal bleaching of stained root-filled teeth employ oxidative bleaching with hydrogen peroxide. However, it has been shown that hydrogen peroxide and hydroxyl radicals, the by-products of the bleaching process, diffuse from the pulp chamber to the outer root surface. The control of such diffusion may be of importance in minimizing the risk of invasive cervical resorption (ICR) which has been linked to intracoronal bleaching. A novel reductive-oxidative bleaching process using a thiourea and hydrogen peroxide regimen is proposed as a more effective and safer bleaching protocol. Also, other clinical considerations during the intra-coronal bleaching of root-filled teeth are discussed.