Palygorskite as Efficient Catalyst for Ring-Opening Polymerization of E-Caprolactone

Fiber-like high-surface-area and natural nanostructure clay mineral palygorskite (or attapulgite, ATP) containing lots of hydroxyl groups is found to efficiently catalyze the ring-opening polymerization (ROP) of E-caprolactone (E-CL). The products are subsequently characterized by FTIR, H-1 NMR, GPC, DSC, SEM and XPS analysis. The results show that porous PCL with relatively high molecular weight is obtained. A mechanism is proposed to illustrate that E-CL is initiated by the constituent water in ATP and catalyzed by three active centers relate to hydroxyl groups on the surface of ATP. The ATP acts as a proton shuttle via its acidic hydrogen atoms and basic oxygen atoms. Moreover, there exists synergetic catalytic effect between the metal centers and Si centers.