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

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• 作者：Daichi Togashi ; Issei Otsuka ; Redouane Borsali ; Koichi Takeda ; Kazushi Enomoto ; Seigou Kawaguchi ; Atsushi Narumi
• 刊名：Biomacromolecules
• 出版年：2014
• 出版时间：December 8, 2014
• 年：2014
• 卷：15
• 期：12
• 页码：4509-4519
• 全文大小：603K
• ISSN：1526-4602

文摘

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鈥揻ragmentation 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鈥?00 g mol^鈥?. 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 掳C. The featured results were observed for 2 (蠒_Mal5 = 0.14) and 3 (蠒_Mal5 = 0.16) at temperatures above 100 掳C, where 蠒_Mal5 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 鈭?q* and 鈭?q*. 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 (蠒_Mal5 = 0.14) and 3 (蠒_Mal5 = 0.16) were 10.4 and 9.55 nm, respectively, which were determined using Bragg鈥檚 relation (d = 2蟺/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.