Progress and challenges in the synthesis of sequence controlled polysaccharides

The sequence, length and substitution of a polysaccharide influence its physical and biological properties. Thus, sequence controlled polysaccharides are important targets to establish structure–properties correlations. Polymerization techniques and enzymatic methods have been optimized to obtain samples with well-defined substitution patterns and narrow molecular weight distribution. Chemical synthesis has granted access to polysaccharides with full control over the length. Here, we review the progress towards the synthesis of well-defined polysaccharides. For each class of polysaccharides, we discuss the available synthetic approaches and their current limitations.

Controlled and Efficient Polymerization of Methyl Methacrylate Catalyzed by Pyridinylidenaminophosphines Based Lewis Pairs

Developing different synthetic approaches to realize controlled or living polymerization are aspirational to achieve polymers with defined molecular weight, narrow molecular weight distribution and unambiguous structures by polymer chemists. Herein,...

Doping of Silicon by Phosphorus End-Terminated Polymers: source characterization and dopant diffusion in SiO2

A polystyrene homopolymer with a narrow molecular weight distribution (Mn = 2.3 ± 0.3 kg/mol, Ð = 1.05 ± 0.01) and end-terminated with a phosphorus containing moiety has been used...

Synthesis of thermo-sensitive polymer with super narrow molecular weight distribution: PET-RAFT polymerization of N-isopropyl acrylamide meditated by cross-linked zinc porphyrins with high active site loadings

To overcome aggregation of porphyrins and realize heterogeneous catalysis with high active site loadings, the twisted ZnTHP-Me2Si and layered ZnTHP-Ph2Si are synthesized through cross-linking zinc tetraphenylporphyrin (ZnTHP) respectively with dichlorodimethylsilane...

Living Chain-Walking (Co)Polymerization of Propylene and 1-Decene by Nickel α-Diimine Catalysts

Homo- and copolymers of propylene and 1-decene were synthesized by controlled chain-walking (co)polymerization using phenyl substituted α-diimine nickel complexes activated with modified methylaluminoxane (MMAO). This catalytic system was found to polymerize propylene in a living fashion to furnish high molecular weight ethylene-propylene (EP) copolymers. The copolymerizations proceeded to give high molecular weight P/1-decene copolymers with narrow molecular weight distribution (Mw/Mn ≈ 1.2), which indicated a living nature of copolymerization at room temperature. The random copolymerization results indicated the possibility of precise branched structure control, depending on the polymerization temperature and time.

Organocatalytic Ring-Opening Polymerization Strategies for Synthesis of Poly(phosphothioesters) with a Pendent Phenyl Group

A novel type of phosphothioester substrate, 2-phenyl-1,3,2-dioxaphospholane 2-sulfide (PTP), has been synthesized and subjected to ring-opening polymerization. DBU/thiourea served as an efficient cooperative organocatalyst for the synthesis of poly(PTP), delivering the polymer with a well-defined structure, a relatively narrow molecular-weight distribution (1.14–1.20), and high molecular weight (up to 45.2 kg/mol). The ring-opening polymerization process showed a controlled/living nature. In addition, diblock copolymers of PTP with rac-lactide with well-defined structures were also synthesized.

EFFECT OF REVERSIBLE ADDITION-FRAGMENTATION CHAIN TRANSFER EMULSION STYRENE–BUTADIENE RUBBER ON THE PROPERTIES OF SILICA COMPOUNDS

ABSTRACT In recent years, solution styrene–butadiene rubber (SSBR), which has a narrow molecular weight distribution, controllable microstructure, and chain end functionality, is mainly used as base rubber for passenger car tire tread compounds. However, SSBR has a lower molecular weight than that of emulsion SBR (ESBR) because it is difficult to increase the molecular weight of SSBR. In contrast, ESBR can easily increase the molecular weight; however, it has a broad molecular weight distribution. The reversible addition-fragmentation chain transfer (RAFT) polymerization technique is applicable to the emulsion polymerization. Polymers with narrow molecular weight distributions can be obtained by the RAFT polymerization because the RAFT agent prevents the coupling reaction of the growing chain radicals. In this case, ESBR having a narrow molecular weight distribution, which is an advantage of SSBR, and a high molecular weight, which is an advantage of ESBR, can be synthesized. Therefore, we synthesized RAFT ESBR and fabricated its compounds with silica filler. We confirmed that the physical properties of the RAFT ESBR silica compound are different from those of the ESBR silica compound. In addition to the narrow molecular weight distribution of the RAFT ESBR, the trithiocarbonyl group of the RAFT agent in the RAFT ESBR chain molecules affects the physical properties.