Masami Kamigaito

Stereospecific living radical polymerization: dual control of chain length and tacticity for precision polymer synthesis.

3.3.3. Ionic Bonding or Interaction 5141 3.3.4. Multiple Hydrogen Bonding Interactions 5142 4. Stereospecific Living Radical Polymerization 5143 4.1. Acrylamides and Methacrylamides 5143 4.2. Methacrylates and Acrylates 5146 4.3. Vinyl Esters, Vinyl Amides, and Vinyl Chloride 5148 4.4. Stereoblock and Stereogradient Polymers 5149 4.4.1. Stereoblock Polymers 5149 4.4.2. Stereogradient Polymers 5151 5. Conclusions 5151 6. Acknowledgments 5152 7. References 5152

AAB-Sequence Living Radical Chain Copolymerization of Naturally Occurring Limonene with Maleimide: An End-to-End Sequence-Regulated Copolymer

Sequence control in chain-growth polymerization is still one of the most challenging topics in synthetic polymer chemistry in contrast to natural macromolecules with completely sequence-regulated structures like proteins and DNA. Here, we report the quantitative and highly selective 1:2 sequence-regulated radical copolymerization of naturally occurring (+)-d-limonene (L) and a maleimide (M) in fluoroalcohol giving chiral copolymers with high glass transition temperatures (220-250 degrees C) originating from the specific rigid cyclic structures of the monomers. Furthermore, the combination with a reversible addition-fragmentation chain transfer (RAFT) agent (C-S) via the controlled/living radical polymerization resulted in end-to-end sequence-regulated copolymers [C-(M-M-L)(n)-M-S] with both highly sequenced chain ends and main-chain repeating units as well as controlled molecular weights.

Sequence-regulated vinyl copolymers by metal-catalysed step-growth radical polymerization.

Proteins and nucleic acids are sequence-regulated macromolecules with various properties originating from their perfectly sequenced primary structures. However, the sequence regulation of synthetic polymers, particularly vinyl polymers, has not been achieved and is one of the ultimate goals in polymer chemistry. In this study, we report a strategy to obtain sequence-regulated vinyl copolymers consisting of styrene, acrylate and vinyl chloride units using metal-catalysed step-growth radical polyaddition of designed monomers prepared from common vinyl monomer building blocks. Unprecedented ABCC-sequence-regulated copolymers with perfect vinyl chloride-styrene-acrylate-acrylate sequences were obtained by copper-catalysed step-growth radical polymerization of designed monomers possessing unconjugated C=C and reactive C-Cl bonds. This strategy may open a new route in the study of sequence-regulated synthetic polymers.

DESIGN OF INITIATORS FOR LIVING RADICAL POLYMERIZATION OF METHYL METHACRYLATE MEDIATED BY RUTHENIUM(II) COMPLEX

Abstract A series of initiators have been developed for living radical polymerization of methyl methacrylate (MMA) mediated by ruthenium(II) complexes [e.g., RuCl2(PPh3)3; PhC6H5]. These initiators include chloromethanes, α-chloroesters, α-chloroketones, and α-bromoesters, among which CCl3COCH3, CHCl2COPh, and H(MMA)2-Br are the best to give polymers with controlled molecular weights and very narrow MWDs ( M w M n = 1.1−1.2 ). The wide variation of the initiators therefore demonstrates the generality of our transition metal-mediated living radical polymerizations.

Living radical polymerization of methyl methacrylate with a zerovalent nickel complex, Ni(PPh3) 41

A zerovalent nickel complex, Ni(PPh 3 ) 4 , induced living radical polymerization of methyl methacrylate (MMA) in conjunction with an organic bromide as an initiator [R-Br: CCl 3 Br, (CH 3 ) 2 C(CO 2 Et)Br, (CH 3 ) 2 C(COPh)Br] in the presence of Al(Oi-Pr) 3 additive. The molecular weight distributions were narrow (M w /M n ∼ 1.2) throughout the reactions, and the number-average molecular weights (M n ) increased in direct proportion to monomer conversion. In contrast, the polymers obtained with CCl 4 in place of R-Br had broader MWDs (M w /M n > 2). The Al(Oi-Pr) 3 additive should be added for the smooth polymerizations of MMA to occur, similarly to those with a divalent nickel bromide, NiBr 2 (PPh 3 ) 2 . The Ni(PPh 3 ) 4 -mediated living polymerization apparently proceeds via the activation of the C-Br bond from the initiators R-Br, assisted by the redox reaction of the complex between Ni(0) and Ni(I) species.

Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization

Recent developments in polymerization reactions utilizing thiocarbonylthio compounds have highlighted the surprising versatility of these unique molecules. The increasing popularity of reversible addition–fragmentation chain transfer (RAFT) radical polymerization as a means of producing well‐defined, ‘controlled’ synthetic polymers is largely due to its simplicity of implementation and the availability of a wide range of compatible reagents. However, novel modes of thiocarbonylthio activation can expand the technique beyond the traditional system (i.e., employing a free radical initiator) pushing the applicability and use of thiocarbonylthio compounds even further than previously assumed. The primary advances seen in recent years are a revival in the direct photoactivation of thiocarbonylthio compounds, their activation via photoredox catalysis, and their use in cationic polymerizations. These synthetic approaches and their implications for the synthesis of controlled polymers represent a significant advance in polymer science, with potentially unforeseen benefits and possibilities for further developments still ahead. This Research News aims to highlight key works in this area while also clarifying the differences and similarities of each system.

Immobilized-type chiral packing materials for HPLC based on polysaccharide derivatives

The polysaccharide-based chiral packing materials (CPMs) for high-performance liquid chromatography (HPLC) have been recognized as the most powerful ones for the analyzing and preparative separating of the chiral compounds. These CPMs have been conventionally prepared by coating polysaccharide derivatives on a silica gel support. This means that the solvents, which swell or dissolve the derivatives on the silica gel and reduce the performance of the chiral columns, do not allow to be applied as components of the eluents. Therefore, the polysaccharide-based CPMs can be used with a rather limited number of eluents. In order to enhance the versatility of the eluent selection for more practical and economical chromatographic enantioseparations, the polysaccharide derivatives must be immobilized onto the silica gel. This review summarizes our latest studies on the development of the immobilized-type CPMs via the radical copolymerization and the polycondensation of the polysaccharide derivatives bearing small amounts of vinyl groups and alkoxysilyl groups, respectively.

Immobilization of Amphiphilic Polycations by Catechol Functionality for Antimicrobial Coatings

A new strategy for preparing antimicrobial surfaces by a simple dip-coating procedure is reported. Amphiphilic polycations with different mole ratios of monomers containing dodecyl quaternary ammonium, methoxyethyl, and catechol groups were synthesized by free-radical polymerization. The polymer coatings were prepared by immersing glass slides into a polymer solution and subsequent drying and heating. The quaternary ammonium side chains endow the coatings with potent antibacterial activity, the methoxyethyl side chains enable tuning the hydrophobic/hydrophilic balance, and the catachol groups promote immobilization of the polymers into films. The polymer-coated surfaces displayed bactericidal activity against Escherichia coli and Staphylococcus aureus in a dynamic contact assay and prevented the accumulation of viable E. coli, S. aureus, and Acinetobacter baumannii for up to 96 h. Atomic force microscopy (AFM) images of coating surfaces indicated that the surfaces exhibit virtually the same smoothness for all polymers except the most hydrophobic. The hydrophobic polymer without methoxyethyl side chains showed clear structuring into polymer domains, causing high surface roughness. Sum-frequency generation (SFG) vibrational spectroscopy characterization of the surface structures demonstrated that the dodecyl chains are predominantly localized at the surface-air interface of the coatings. SFG also showed that the phenyl groups of the catechols are oriented on the substrate surface. These results support our hypothesis that the adhesive or cross-linking functionality of catechol groups discourages polymer leaching, allowing the tuning of the amphiphilic balance by incorporating hydrophilic components into the polymer chains to gain potent biocidal activity.

Biomass-derived heat-resistant alicyclic hydrocarbon polymers: poly(terpenes) and their hydrogenated derivatives

Naturally-occurring terpenes, such as (−)-β-pinene and (−)-α-phellandrene, were cationically polymerized and subsequently hydrogenated into stable alicyclic hydrocarbon polymers with a rigid backbone. In contrast to the already known poly(terpenes), the hydrogenated poly(β-pinene) with a high molecular weight (Mw > 50 000) showed a high glass transition temperature (Tg = 130 °C) and degradation temperature (10% loss at > 400 °C), suggesting new promising biomass-derived materials for practical use.

Design and synthesis of self-degradable antibacterial polymers by simultaneous chain- and step-growth radical copolymerization

Self-degradable antimicrobial copolymers bearing cationic side chains and main-chain ester linkages were synthesized using the simultaneous chain- and step-growth radical polymerization of t-butyl acrylate and 3-butenyl 2-chloropropionate, followed by the transformation of t-butyl groups into primary ammonium salts. We prepared a series of copolymers with different structural features in terms of molecular weight, monomer composition, amine functionality, and side chain structures to examine the effect of polymer properties on their antimicrobial and hemolytic activities. The acrylate copolymers containing primary amine side chains displayed moderate antimicrobial activity against E. coli but were relatively hemolytic. The acrylate copolymer with quaternary ammonium groups and the acrylamide copolymers showed low or no antimicrobial and hemolytic activities. An acrylate copolymer with primary amine side chains degraded to lower molecular weight oligomers with lower antimicrobial activity in aqueous solution. This degradation was due to amidation of the ester groups of the polymer chains by the nucleophilic addition of primary amine groups in the side chains resulting in cleavage of the polymer main chain. The degradation mechanism was studied in detail by model reactions between amine compounds and precursor copolymers.