Organic‐Inorganic Nanohybrids Obtained by Sequential Copolymerization of ε‐Caprolactone and L,L‐Lactide from Activated Clay Surface

Abstract

AbstractSummary: We report here on the controlled grafting of defined copolyester chains directly onto the activated surface of MMT nanoplatelets dispersed in apolar medium. More precisely, monomers such as CL and LA were copolymerized, in dilute solution, by the well‐known coordination‐insertion ring‐opening mechanism initiated directly from the clay platelets. This method is based on the use of MMT organo‐modified by ammonium cations bearing hydroxyl functions. Using a surfactant mixture that contains varying proportions of hydroxyl‐substituted alkyl ammonium and non‐functionalized alkylammonium cations for exchanging the initial Na+ counterions of the natural clay allows preparing organoclays with a tunable amount of hydroxyl functions on their surface. These hydroxyl functions can then easily be derivatized into aluminium alkoxides in order to initiate the polymerization directly from the surface of clay swollen in an organic solvent like toluene. The resulting activated organo‐clays proved to promote efficiently the block copolymerization of CL and LA in solution. The results demonstrate that adjusting the parameters allows to control the process. Indeed, the growing copolyester chains are effectively surface‐anchored onto the clay and their average length and grafting density can readily be modulated by the available amount of OH functions on the MMT platelets. These new organic‐inorganic nanohybrid materials present nearly exfoliated morphologies and the grafted copolymers display a semi‐crystalline and blocky structure as attested by DSC and NMR analyses, respectively.TEM photograph of the recovered nanohybrid based on poly[CL‐block‐LA] diblock copolyester grafted onto Cloisite®30B surface.magnified imageTEM photograph of the recovered nanohybrid based on poly[CL‐block‐LA] diblock copolyester grafted onto Cloisite®30B surface.