Studies On Ring-Opening Polymerization Of εCaprolactone Catalyzed By Bifunctional Phosphides

Poly (ε-caprolactone)(PCL) is an important class of biocompatible materials, which makes them interesting materials for a range of biomedical and commodity applications, including controlled drug release, tissue engineering, medical implants or environmentally friendly packaging materials. The ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and other cyclic esters provides an efficient and convenient route to the direct synthesis of these macromolecules. Typically, aluminum, tin salts, IVB metal or rare earth metal compounds are used as the catalysts for the polymerization of s-caprolactone (ε-CL). But its metallic residues and toxic issues can limit the development of PCL. Compared to traditional metal-catalyzed ROPs, organocatalysis processes can be performed under milder reaction conditions with controlled molar masses and narrow dispersities, furthermore the metal contaminant of the polymer products can be avoided to be removed prior to application as biomedical and pharmaceutical materials. This paper focused on the impact of organic small molecule system such as Br(?)nsted acids catalysts and bifunctional catalysts on the ring-opening polymerization of ε-CL.A series of phosphate acid catalyst and the reaction conditions were examined for polymerization of s-CL.1,1’-Bi-2-naphthol (BINOL)-based phosphoric acid was found to be an effective organocatalyst for ROP leading to polyesters at90℃. The overall conversion to poly (s-caprolactone) was99%and poly (s-caprolactone) with Mn of8369and polydispersity index of1.13was obtained at at [M]0/[I]0/[Cat.]0ratio of100/5/3. The controlled polymerization was indicated by (1) the linear relationships between number-average molar mass and monomer conversion, or (2) monomer-to-initiator ratio,(3) the number-average molecular weight of the polymer agreed with Mn,theo calculated from the initial ratios of [ε-CL]0/[BnOH]0and the monomer conversions. Bifunctional activation of the initiator/monomer systems, the paper focused on three different catalysts. The bifunctional catalysts could be used as electrophilic reagent for activation of the initiator/chain end, while using hydrogen bonds for activation of monomer to carry out effective and selective ROP of ε-CL. In addition, the present protocol provided an easy-to-handle, inexpensive and environmentally benign entry for the synthesis of biodegradable materials as well as polyesters for biomedical applications.