Mechanistic aspects on molecular structure formation of polymeric networks from diisocyanates with amidine compounds

Polymeric networks are produced by step‐growth polyaddition and co‐polyaddition reactions of 1‐ethylimidazoline in combination with various diisocyanates. Five aromatic, two aliphatic diisocyanates and a polyurethane prepolymer are used as particular reactant in N,N‐dimethylformamide as solvent at room temperature. Obviously, 1‐ethylimidazoline can serve as trifunctional monomer, which enables a crosslinking reaction with diisocyanates. Molecular structure elements of the polymeric networks were studied by solid state 13C‐NMR spectroscopy revealing that detailed molecular structure formations are determined whether aromatic or aliphatic diisocyanates are used. Quantum chemical calculations were used as supporting method to elucidate the complex reaction cascades. Hence, it can be shown that beside 3:1 stoichiometric structures 2:1 based structures are formed as well. These structures are observed as kinetically controlled products only when aromatic diisocyanate monomers are used. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 977–985     

Synthesis of the Functional Hydrogels: Poly(N-isopropylacrylamide) Threaded onto the PEG Backbones Via RAFT

Functional poly(N-isopropylacrylamide) (PNIPAM) hydrogels were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization of NIPAM in the presence of four-arm poly(ethylene glycol) (4A-PEG) as backbone and 4-cyanopentanoic acid dithiobenzoate functional α -cyclodextrin threaded onto the PEG as chain transfer reagent (CTA).The structure of the hydrogels was characterized in detail with FTIR techniques. The analytical results demonstrated that α -cyclodextrin remains in as-obtained hydrogels. The swelling behavior was investigated and the functional hydrogels (functional gels) showed accelerated shrinking kinetics and higher swelling ratio comparing with conventional hydrogel (CG). It could be attributed to the presence of dangling chains. The hydrogel exhibited rapid swelling and deswelling kinetics. In principle, the hydrogel might find a number of applications including an on-off system and drug delivery systems.     

Synthesis of polymer with defined fluorescent end groups via reversible addition fragmentation transfer polymerization for characterizing the conformations of polymer chains in solutions

A new type of chain transfer agent used in reversible addition fragmentation chain transfer (RAFT) polymerization named 9‐anthracenylmethyl (4‐cyano‐4‐(N‐carbazylcarbodithioate) pentanoate) (ACCP) was synthesized with a total yield over 75% by the incorporation of both fluorescent donor and acceptor chromophores. Polymerization of heterotelechelic α,ω end‐labeled dye‐functionalized polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(n‐butyl methacrylate) (PBMA) with adjustable molecular weights and narrow polydispersity could be conducted by a one‐pot procedure through RAFT polymerization with this bischromophore chain transfer agent. The polymerizations demonstrated “living” controlled characteristics. By taking advantage of the characteristic fluorescence resonance energy transfer (FRET) response between the polymer chain terminals, the variation of chain dimensions in solution from the dilute region to the semidilute region can be monitored by changes in the ratio of the fluorescence intensities of the carbazolyl group to the anthryl group, which lends itself to potential applications in characterizing chain dimensions in solutions for thermodynamic or dynamic studies. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2413–2420     

Radical Alliances: Solutions and Opportunities for Organic Synthesis

The present account discusses in detail various mechanistic features of the degenerative radical addition‐transfer of xanthates and related thiocarbonylthio congeners and makes a comparison with the more classical Kharasch reactions to which it is similar in certain aspects. The xanthate group reacts reversibly with the ‘active’ radicals in the medium and is able to store them in a somewhat inactive form. This increases their effective lifetime in the medium and, at the same time, lowers their absolute concentration while regulating their relative concentration. These properties translate into a powerful carbon–carbon bond forming process, especially as regards intermolecular additions to electronically unbiased (‘unactivated’) alkenes. Most functional groups are tolerated, in particular polar functions that often require protection with other chemistries. This broad versatility is illustrated by examples where the xanthate addition to the alkene is combined with other, more classical reactions to provide a convergent, rapid access to a wide range of useful structures. Emphasis has been placed on the synthesis of open chain and more complex carbocycles, as well as on the transfer of chirality. These ‘radical alliances’ include organosilicon chemistry, the Diels–Alder cycloaddition and cheletropic extrusion of sulfur dioxide, the Claisen sigmatropic rearrangement, and the Horner–Wadsworth–Emmons (HWE) condensation.     

Facile synthesis of graft copolymers containing rigid poly(dialkyl fumarate) branches by macromonomer method

Graft copolymers show microphase separated structure as seen in block copolymers and have lower intrinsic viscosity than block copolymers because of a branching structure. Therefore, considering molding processability, especially for polymers containing rigid segments, graft copolymers are useful architectures. In this work, graft copolymers containing rigid poly(diisopropyl fumarate) (PDiPF) branches were synthesized by full free‐radical polymerization process. First, synthesis of PDiPF macromonomers by addition‐fragmentation chain transfer (AFCT) was investigated. 2,2‐Dimethyl‐4‐methylene‐pentanedioic acid dimethyl ester was found to be an efficient AFCT agent for diisopropyl fumarate (DiPF) polymerization because of the suppression of undesired primary radical termination, which significantly took place when common AFCT agent, methyl 2‐(bromomethyl)acrylate, was used. Copolymerization of PDiPF macromonomer with ethyl acrylate accomplished the generation of the graft copolymer having flexible poly(ethyl acrylate) backbone and rigid PDiPF branches. The graft copolymer showed a microphase separated structure, high transparency, and characteristic thermal properties to PDiPF and poly(ethyl acrylate). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2474–2480     

Enantioselective Organocatalytic Aza-Michael Additions of Phthalimide Derivatives to α,β-Unsaturated Aldehydes

Phthalimide derivatives as nitrogen nucleophiles with α,β‐unsaturated aldehydes for asymmetric aza‐Michael additions have been reported. The reactions proceed smoothly to afford corresponding Michael adducts in good yields (up to 98%) and enantioselectivities (up to 95% ee).     

Synthesis of New Pyrimidine,Quinazoline and Diazatricyclo Derivatives by Multicomponent Reaction and Evaluation of Their Biological Activity

Abstract

A series of new pyrimidine and quinazoline derivatives was synthesized by a Biginelli-like reaction of urea/thiourea, aldehyde, and ketone in the presence of hydrochloric acid as a catalyst. In a similar way, some novel diazatricyclo derivatives were obtained via a Biginelli-like reaction followed by an intramolecular Michael-type addition. The yields of products were reasonable after recrystallization from ethanol. All newly synthesized compounds were characterized using IR and NMR (¹H and ¹³C) spectroscopy and elemental analysis. The antibacterial activity of these compounds was investigated against Staphylococcus aureus (RTCC, 1885), and Escherichia Coli (ATCC, 35922).

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Electrophilic and Nucleophilic Addition of Alkanethiols to 2-Vinyloxyethylmethacrylate

Under acid- or base-catalyzed conditions, thiols add regio- and chemos-electively either to vinyloxy or methacrylate group of vinyloxyalkyl-methacrylates to give polyfunctional methacrylates or polyfunctional vinyl ethers, respectively.