Maltopentaose-Conjugated CTA for RAFT Polymerization Generating Nanostructured Bioresource-Block Copolymer

摘要

We now describe the synthesis of a new family of oligosaccharide-conjugated functional molecules, which act as chain transfer agents (CTAs) for the reversible addition-fragmentation chain transfer (RAFT) polymerization. The synthesis was started from the catalyst-free direct N-glycosyl reaction of 5-azidopentylamine onto maltopentaose (Mal(5)) in dry methanol at room temperature and subsequent N-protected reaction with acetic anhydride, producing a stable oligosaccharide-building block, such as Mal(5) with an azidopentyl group (Mal(5)-N-3). The azido group was hydrogenated using platinum dioxide (PtO2) as a catalyst to give Mal(5) with aminopentyl group (Mal(5)-NH2), which was then reacted with CTA molecules bearing activated ester moieties. These reactions produced Mal(5)-modified macro-CTAs (Mal(5)-CTAs, 1), which were used for the RAFT polymerizations of styrene (St) and methyl methacrylate (MMA) in DMF. The polymerizations were performed using the [M](0)/[1](0) values ranging from 50 to 600, affording the Mal(5)-hybrid amphiphilic block copolymers (BCPs), such as Mal(5)-polystyrene (2) and Mal(5)-poly(methyl methacrylate) (3), with a quantitative end-functionality and the controlled molecular weights between 4310 and 20 300 g mol(-1). The small-angle X-ray scattering (SAXS) measurements were accomplished for 2 and 3 to ensure their abilities to form phase separated structures in their bulk states with the increasing temperatures from 30 to 190 degrees C. The featured results were observed for 2 (phi(Mal5) = 0.14) and 3 (phi(Mal5) = 0.16) at temperatures above 100 degrees C, where phi(Mal5) denotes the volume fraction of the Mal(5) unit in the BCP sample. For both BCP samples, the primary scattering peaks q* were clearly observed together with the higher-ordered scattering peaks root 2q* and root 3q*. Thus, these Mal(5)-hybrid amphiphilic BCP samples have a body centered cubic (BCC) phase morphology. The domain spacing (d) values of the BCC morphology for 2 (phi(Mal5) = 0.14) and 3 (phi(Mal5) = 0.16) were 10.4 and 9.55 nm, respectively, which were determined using Braggs relation (d = 2 pi/q*). The present RAFT agents were shown to eventually provide the phase separated structural polymeric materials in which 5.4 nm bioresource-spherical domains were periodically arrayed at the interval of about 10 nm.