Atom transfer radical polymerization of (meth)acrylates and their novel block copolymers with vinyl acetate

Homopolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) by atom transfer radical polymerization (ATRP) were carried out at 90 °C using methyl-2-bromopropionate (MBP) as initiator, copper halide (CuX, X=Cl, Br) as catalyst, 2,2^′-bipyridine (bpy) or N,N,N^′,N^′,N^″-pentamethyldiethylenetriamine (PMDETA) as ligand in 1-butanol (less polar and containing OH) and acetonitrile (more polar) solvents. It was found that with CuCl/bpy catalyst ATRP of MA and MMA in 1-butanol proceeded faster than that in acetonitrile. The rate of ATRP of MA and MMA in acetonitrile and 1-butanol was comparable when CuCl/PMDETA used as catalyst system. The number-average molecular weights increased with conversion and polydispersities were low . The ATRP of MA and MMA with vinyl acetate telomer having trichloromethyl end group (PVAc-CCl₃) were also used to synthesize new block copolymers. The structures and molecular weight of synthesized PVAc-b-PMA and PVAc-b-PMMA were characterized by ¹H NMR, FTIR spectroscopy and gel permeation chromatography (GPC) and shown that the block copolymers were novel.     

Synthesis of poly(methyl methacrylate-co-styrene)-block-polysulfide-block-poly(methyl methacrylate-co-styrene) copolymers by free radical polymerization combined with oxidative coupling

Poly(methyl methacrylate-co-styrene)-block-polysulfide-block-poly(methyl methacrylate-co-styrene) triblock copolymers were synthesized for the first time by the free radical copolymerization of methyl methacrylate (MMA) and styrene (St) in the presence of a thiocol oligomer as a chain transfer agent, followed by chemical oxidation of the remaining SH-end groups. The apparent chain transfer constant of the thiocol SH groups in the copolymerization reaction was estimated from the rate of consumption of the thiol groups versus the overall rate of consumption of the monomers (C_T = 1.28). Based on this value, the chain transfer constant of the thiocol SH groups in St polymerization was calculated . The triblock copolymers synthesized were characterized by SEC and ¹H NMR measurements.     

Synthesis and characterizations of well-defined dendrimer-like copolymers with the second and third generation based on polystyrene and poly(l-lactide)

Dendrimer-like copolymers with two and three generations, (polystyrene)₃-b-(poly(l-lactide))₆ (PSt₃-b-PLLA₆) and PSt₃-b-PLLA₆-b-PSt₁₂ have been successfully prepared using core-first method. The first step of this synthesis is the preparation of three-armed PSt by atom transfer radical polymerization (ATRP) of St using 1,1,1-tri(methylene-α-bromoisobutyryl)propane as initiator. Terminal divergence of the polymers obtained was achieved by the reaction of terminal bromines with branching agent, 2,2-dimethyl-1,3-dioxolane-4-methanol. After deprotection, the polymer with six terminal hydroxyl groups was used in the ring-opening polymerization of LLA. The dendrimer-like copolymer with PLLA as a second generation diverged continuously by the reaction of 6 terminal hydroxyl groups with branching agent, 2,2-bis(methylene-α-bromoisobutyryl)propionyl chloride. The resultant polymer with 12 terminal bromines was used as macroinitiator in the ATRP of St to produce the target dendrimer-like copolymer, PSt₃-b-PLLA₆-b-PSt₁₂. The structures of polymers obtained from each step were confirmed by their ¹H NMR spectra and GPC measurements. DSC results show one for the three-armed PSt, , and for the dendrimer-like copolymer with two generations, C(PSt(PLLA)₂)₃, and , and for the copolymer with three generations, C(PSt(PLLA(PSt)₂)₂)₃.     

Comb copolymers of polystyrene-poly(tert-butyl (meth)acrylate) prepared by combination of nitroxide mediated polymerization and photoinduced iniferter technique

Comb copolymers consisting of polystyrene backbone and poly(tert-butyl (meth)acrylate) side chains were synthesized by combination of nitroxide (TEMPO)-mediated polymerization (NMP) and photoinduced grafting from macro-iniferters. First, poly(chloromethylstyrene), PCMS, with the degree of polymerization and two random poly(styrene-co-chloromethylstyrene) copolymers, P(S-co-CMS), with similar but different content (8 and 14 mol%) of CMS units, were synthesized by NMP. In the second step the CMS units both in the homopolymer and the copolymers were converted to N,N-diethyldithiocarbamyl groups (DC) yielding photosensitive multifunctional macro-iniferters. Finally, tert-butyl methacrylate tBuMA was grafted from the synthesized polymer backbones by iniferter technique under UV-irradiation yielding copolymers polystyrene-graft-poly(tert-butyl methacrylate) PS-g-P(tBuMA). Grafting initiated by the macro-iniferters containing ∼6-11 DC initiating sites per macromolecule proceeded by pseudo-living polymerization mechanism, i.e., the number-average molecular weight increased with conversion and the SEC traces were unimodal. In contrast, photo-polymerization initiated by highly functionalized polystyrene backbone was poorly controlled. Hydrolysis of loosely grafted copolymers PS-g-P(tBuMA) afforded amphiphilic copolymers polystyrene-graft-poly(methacrylic acid). Molecular parameters of the synthesized graft copolymers in dilute THF solutions were determined by scattering (DLS, SLS, SAXS) and viscometric measurements.     

Crystal structure and vibrational properties of new luminescent hosts K3YF6 and K3GdF6

The luminescence hosts K₃YF₆ and K₃GdF₆ were obtained in a single-crystal form. Their crystal structure was determined from single-crystal X-ray diffraction data. Both crystals adopt monoclinic system with space group P2₁/n, Z=2. Lattice parameters for K₃YF₆ are refined to the following values , , , β=90.65(3) and for K₃GdF₆, , , β=90.80(3). The vibrational analysis, IR and Raman spectroscopy at room temperature, was applied to these compounds in order to study the site symmetry of Y³⁺ and Gd³⁺ ions.     

Palladium complexes with meso-bioxazoline ligands for alternating styrene/CO copolymerisation: Counterion effect

Two sets of mono- and dicationic palladium complexes (8) and (10), having and as counterions, were synthesised. The interionic structure of the methyl-acetonitrile complexes [Pd((R,S)-Bn-Box)(CH₃)(NCCH₃)](X) (8) in solution, was investigated by pulsed-gradient spin-echo (PGSE) diffusion measurements and (¹H, ¹⁹F)-HOESY NMR spectroscopy. A high degree of ion-pairing was found in each complex. The HOESY spectra showed that the and anions take up selective positions, on the side of the complex remote from the benzyl groups, but close to the acetonitrile ligand, while the triflate is, partially, occupying a pseudo fifth coordination position on the side of the cation remote from the two benzyl-groups. The complexes 8 and 10 were used as catalyst precursors for the copolymerisation of styrene with carbon monoxide, producing syndiotactic copolymers, with the exception of complex 10a, that led to isotactic copolymers.     

Syntheses and characterization of two new zinc phosphites with 1D chains decorated by Zn-centered complexes

Two inorganic-organic hybrid solids, Zn₂(phen)(HPO₃)₂ (1) and Zn(phen)(HPO₃) (2), have been synthesized under solvothermal conditions in the presence of 1,10-phenanthroline (phen) ligands. Their structures were determined by single-crystal X-ray diffraction and further characterized by FTIR, elemental analysis, powder X-ray diffraction, thermogravimetric analysis and fluorescent spectra. Compound 1 crystallizes in the triclnic system, space group P-1, , , , α=75.609(1)°, β=79.145(2)°, γ=67.157(2)°, , Z=2. Compound 2 is monoclinic, C2/c, , , , β=94.175(4)°, , Z=8. Both structures consist of 1D chains constructed from strictly alternating ZnO₄ and HPO₃ polyhedra through sharing vertices. The chains are further decorated by Zn-centered complex architectures, [Zn(phen)]²⁺ for 1 and [Zn(phen)₂]²⁺ for 2. The 2D and 3D supramolecular arrays for 1 and 2 are stably stacked via strong π-π interactions of the phen groups, respectively.     

Synthesis and characterization of amphiphilic star copolymers of 2-(dimethylamino)ethyl methacrylate and methyl methacrylate: Effects of architecture and composition

Six amphiphilic star copolymers comprising hydrophilic units of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and hydrophobic units of methyl methacrylate (MMA) were prepared by the sequential group transfer polymerization (GTP) of the two comonomers and ethylene glycol dimethacrylate (EGDMA) cross-linker. Four star-block copolymers of different compositions, one miktoarm star, and one statistical copolymer star were synthesized. The molecular weights (MWs) and MW distributions of all the star copolymers and their linear homopolymer and copolymer precursors were characterized by gel permeation chromatography (GPC), while the compositions of the stars were determined by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Tetrahydrofuran (THF) solutions of all the star copolymers were characterized by static light scattering to determine the absolute weight-average MW () and the number of arms of the stars. The of the stars ranged between 359,000 and 565,000 g mol⁻¹, while their number of arms ranged between 39 and 120. The star copolymers were soluble in acidic water at pH 4 giving transparent or slightly opaque solutions, with the exception of the very hydrophobic DMAEMA₁₀-b-MMA₃₀-star, which gave a very opaque solution. Only the random copolymer star was completely dispersed in neutral water, giving a very opaque solution. The effective pKs of the copolymer stars were determined by hydrogen ion titration and were found to be in the range 6.5-7.6. The pHs of precipitation of the star copolymer solutions/dispersions were found to be between 8.8-10.1, except for the most hydrophobic DMAEMA_10-b-MMA₃₀-star, which gave a very opaque solution over the whole pH range.     

Colorimetric and ratiometric fluorescence sensing of fluoride ions based on competitive intra- and intermolecular proton transfer

Receptors 1 and 4 show fluoride ion selective changes in their absorbance and emission behaviours amongst F⁻, Cl⁻, Br⁻, I⁻, , CH₃COO⁻, , and anions. Fluoride ion mediated ‘ON-OFF-ON’ switching behaviour of 4 provides opportunities for ratiometric estimation of fluoride ions.     

Reactions of pyridyl donors with halogens and interhalogens: an X-ray diffraction and FT-Raman investigation

Three different N-donors L, namely N-ethyl-N′-3-pyridyl-imidazolidine-4,5-dione-2-thione (1), N,N′-bis(3-pyridylmethyl)-imidazolidine-4,5-dione-2-thione (2), and tetra-2-pyridyl-pyrazine (3), bearing one, two and four pyridyl substituents, respectively, have been reacted with halogens X₂ (X = Br, I) or interhalogens XY (X = I; Y = Cl, Br). CT σ-adducts L · nXY, bearing linear N?XY moieties (L = 3; X = I; Y = Br, I; n = 2), and salts containing the protonated cationic donors H_nLⁿ⁺ (L = 1 − 3; n = 1, 2, 4), counterbalanced by Cl⁻, Br⁻, , , , , I₂Br⁻, , or anions, have been isolated. Among the reactions products, (H1⁺)Cl⁻, (H1⁺)Br⁻, , , and 3 · 2IBr have been characterised by single-crystal X-ray diffraction. The nature of the products has been elucidated based on elemental analysis and FT-Raman spectroscopy supported by MP2 and DFT calculations.