title: Maltopentaose-conjugated CTA for RAFT polymerization generating nanostructured bioresource-block copolymer.
abstract: 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 (Mal5) in dry methanol at room temperature and subsequent N-protected reaction with acetic anhydride, producing a stable oligosaccharide-building block, such as Mal5 with an azidopentyl group (Mal5-N3). The azido group was hydrogenated using platinum dioxide (PtO2) as a catalyst to give Mal5 with aminopentyl group (Mal5-NH2), which was then reacted with CTA molecules bearing activated ester moieties. These reactions produced Mal5-modified macro-CTAs (Mal5-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 Mal5-hybrid amphiphilic block copolymers (BCPs), such as Mal5-polystyrene (2) and Mal5-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 °C. The featured results were observed for 2 (ϕMal5 = 0.14) and 3 (ϕMal5 = 0.16) at temperatures above 100 °C, where ϕMal5 denotes the volume fraction of the Mal5 unit in the BCP sample. For both BCP samples, the primary scattering peaks q* were clearly observed together with the higher-ordered scattering peaks √2q* and √3q*. Thus, these Mal5-hybrid amphiphilic BCP samples have a body centered cubic (BCC) phase morphology. The domain spacing (d) values of the BCC morphology for 2 (ϕMal5 = 0.14) and 3 (ϕMal5 = 0.16) were 10.4 and 9.55 nm, respectively, which were determined using Bragg's relation (d = 2π/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.
authors.affiliation: Department of Polymer Science and Engineering, Graduate School of Science and Engineering, Yamagata University , Jonan 4-3-16, Yonezawa 992-8510, Japan.
authors.forename: Daichi
authors.initials: D
authors.lastname: Togashi
authors.forename: Issei
authors.initials: I
authors.lastname: Otsuka
authors.forename: Redouane
authors.initials: R
authors.lastname: Borsali
authors.forename: Koichi
authors.initials: K
authors.lastname: Takeda
authors.forename: Kazushi
authors.initials: K
authors.lastname: Enomoto
authors.forename: Seigou
authors.initials: S
authors.lastname: Kawaguchi
authors.forename: Atsushi
authors.initials: A
authors.lastname: Narumi
mesh_terms: D008970:Molecular Weight; D049329:Nanostructures / Q000737:chemistry*; D009844:Oligosaccharides / Q000737:chemistry*; D058105:Polymerization; D011108:Polymers / Q000737:chemistry*; D019904:Polymethyl Methacrylate / Q000737:chemistry; D053838:Scattering, Small Angle; D020058:Styrene / Q000737:chemistry; D013696:Temperature
chemical_list: D009844:Oligosaccharides; D011108:Polymers; C019193:maltopentaose; D020058:Styrene; D019904:Polymethyl Methacrylate