BF<Subscript>3</Subscript>OEt<Subscript>2</Subscript>-coinitiated cationic polymerization of cyclopentadiene in the presence of water at room temperature

The cationic polymerization of cyclopentadiene (CPD) with 1-(4-methoxyphenyl)ethanol (1)/BF₃OEt₂ initiating system in CH₂Cl₂:CH₃CN 4:1 (v/v) mixture at room temperature and in the presence of water ([H₂O]/[BF₃OEt₂] up to 8) is reported. The number-average molecular weights of obtained polymers increased in direct proportion to monomer conversion or initial monomer concentration (M _n ≤ 4,000 g mol⁻¹) in agreement with calculated values, and were inversely proportional to initiator concentration. Polymer MWDs were relatively narrow (M _w/M _n = 1.4–1.7) up to 60% of monomer conversion. It was also shown that regioselectivity of CPD polymerization with 1/BF₃OEt₂ initiating system did not depend significantly on water, monomer, or initiator concentration (1,4-structures content was nearly 60% in all cases).     

Novel triazole-based aluminum complex for ring-opening polymerization of lactones

Novel triazole-based aluminum complex {O,O′-[4,5-P(O)Ph₂tz]-AlMe₂ was studied as the catalyst for the ring-opening polymerization of caprolactone (ε-CL) in chlorobenzene. In the presence of methanol, isopropanol, and bifunctional poly(ethylene glycol), the catalytic system produced polymers with high conversion (81–85 %) but broader distribution (M _w/M _n = 1.5–1.8). The system of catalyst and benzyl alcohol produced relative monodisperse PCLs (M _w/M _n ~ 1.2) with defined molecular weight at 1/1ratio, 60 °C and an initial concentration of ε-CL equal to 0.5 mol/L.     

Ring-opening polymerization of (CH3)2Si[CpMo(CO)3]2, a molecule with an –Si(CH3)2– bridge between two cyclopentadienyl ligands

The (CH₃)₂Si[CpMo(CO)₃]₂ complex (1) was synthesized and used to explore ring-opening polymerization (ROP) as a method to prepare high molecular weight polymers containing Mo–Mo bonds along their backbones. Attempts to initiate ROP of 1 using n-BuLi or PtCl₂ did not yield any polymers. The X-ray crystal structure of 1 shows that the Si center is not strained, and it is suggested that no ROP occurred because 1 is less strained than other organometallic ROP monomers, such as the silicon-bridged ferrocenophanes. Thermal ROP (TROP) of 1 was successful and yielded a polymer (M _w = 210,000 g mol⁻¹) containing both Mo–Mo single bonds and Mo≡Mo triple bonds. When CO_(g) is passed over the polymer in the solid state, the Mo≡Mo triple bonds are converted to Mo–Mo single bonds. Attempts to increase the yield of the TROP polymer by increasing the reaction times led to polymer decomposition. The decomposition is likely caused by the weakness of the Mo–Mo bond, cleavage of which causes the polymer to degrade.     

Fe(III)-catalyzed AGET ATRP of styrene using triphenyl phosphine as ligand

Activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) is a new technique for conducting ATRP developed recently. In this work, an iron(III)-mediated AGET ATRP of styrene in bulk was carried out at 110 °C, using benzyl bromide as an initiator, oxidatively stable iron(III) chloride hexahydrate (FeCl₃·6H₂O) as a catalyst, triphenyl phosphine as a ligand, and ascorbic acid as a reducing agent. The polymerizations demonstrated the features of “living”/controlled free-radical polymerization, such as the number–average molecular weights increasing linearly with monomer conversion and narrow molecular weight distributions (M _w/M _n = 1.14–1.31).     

Thiohydroxamic esters

Summary N-Hydroxypyridine-2-thione derivativesIa-c and N-hydroxy-4-methylthiazole-2(3H)-thione derivativesIIa-b act as chain transfer agents in free radical polymerizations of methyl methacrylate (C _x =0.6–4.3), styrene (C _x =0.32–3.9), methyl acrylate (C _x =3.1–20), and vinyl acetate (C _x =9.7–80) at 60°C. Some retardation occurs with vinyl acetate and methyl acrylate.Ib also has the property of initiating the polymerization of methyl methacrylate photochemically, whileIIb acts as a thermal initiator. The chain transfer constants ofIIb make it particularly suitable for regulating molecular weight in batch polymerizations of methyl methacrylate and styrene.     

Stable free radical polymerization of styrene with 4-sulphonate-2,2,6,6-tetramethylpiperidine-N-oxyl as mediators

The stable free radical polymerizations of styrene were investigated with five 4-sulphonate-2,2,6,6-tetramethylpiperidine-N-oxyl stable radicals as mediators and benzoyl peroxide (BPO) as initiators at 125 °C. The results indicated that the polymerizations proceeded in a “living”/controlled manner, i.e., the polymerization rates were first-order with respect to the monomer concentrations, molecular weights increased linearly with conversions and the molecular weight distributions were relatively low (M _w/M _n = 1.2–1.4), ¹H NMR analysis of the polymer chain-ends and successful chain extensions. The polymerization rates were faster than that of 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (OH-TEMPO) mediated ones. The effects of steric interference of different substitute groups at four-position of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), the molar ratios of stable radical to BPO and the temperature on the polymerizations were investigated.     

Polymerization of rac-lactide catalyzed by group 4 metal complexes containing chiral N atoms

The hydroxyl- and phenoxy-bridged dinuclear zirconium and hafnium complexes, 1 and 2, containing a chiral N atom in the N₂O₂ ligand (H₂L = 2-(((2-pyridylmethyl)(2-hydroxyphenyl)amino)methyl)-4,6-di(tert-butyl)phenol) were used as catalysts for the ring-opening polymerization of rac-lactide. Experiments prove that 1 and 2 are living and controlled catalytic systems with activity up to 3.25 g_pol mmol_ini ⁻¹ h⁻¹. The isotactic-rich polylactides in a narrow polydispersity (M _w/M _n = 1.01–1.13) were produced with enantiomeric complexes 1 and 2 (P _m = 0.65–0.73). The kinetic studies show a first-order dependency in both monomer and initiator. The initiation mechanism is discussed on the basis of the MALDI-TOF MS and ¹H NMR spectra of the rac-LA oligomer prepared by 1.     

Synthesis of star polymethyl acrylate by SET-LRP at ambient temperature

The star-shaped polymethyl acrylate (PMA) was synthesized by single electron transfer living radical polymerization (SET-LRP) at 30 °C in dimethyl sulfoxide, using 2,2-dibromomethyl-1,3-dibromopropane as the multifunctional initiator, Cu⁰ powder and tris-(2-dimethylamino ethyl)amine (Me₆-TREN) as catalyst. The structure of polymer was analyzed by ¹H NMR, and the results showed that the star-shaped PMA had perfect chain ends (–Br) retention. In addition, the polymerization proceeded smoothly and the time dependence of ln([M]₀/[M]) was linear, which could indicate a first order propagation rate with respect to both radicals and monomer concentration, the polymerization was the living polymerization. The M _n and M _w/M _n of polymer were being measured by Gel Permeation Chromatography. The k _p^app = 0.0367 h⁻¹ and the conversion was 36.3% at 16 h, meanwhile the M _n^GPC of the polymer was 13,300 and the M _w/M _n was 1.40.     

Radical polymerization of (phenylethynyl)styrenes and characterization of poly(phenylethynyl)styrenes as a thermally curable material

Summary The radical polymerizations of 2-, 3-, and 4-(phenylethynyl)styrenes (1a–c) and the copolymerizations of 1a–c (M₁) with styrene (M₂) were carried out using AIBN as the initiator in toluene at 60°C. The number-average molecular weights (M _ns) were extremely low for poly(2-phenylethynylstyrene) (2a) and poly[(phenylethynyl)styrene-co-styrene] (3a), and increased in the order of 2a, 3a << 2b, 3b < 2c, 3c. Monomer reactivity ratios were determined as r ₁= 1.80 and r ₂= 0.51 for 1a, r ₁= 1.72 and r ₂= 0.53 for 1b, and r ₁= 3.17 and r ₂= 0.24 for 1c. Polymers 2a–c and 3a–c underwent an exothermic reaction at elevated temperature to form organic solvent-insoluble polymers. Although the decomposition of 2a was observed from 200°C, 2b and 2c exhibited a high heat-resistance property in both nitrogen and air atmospheres, in particular, 2b showed no significant weight loss below 450°C. Received: 28 January 1998/Accepted: 5 March 1998     

Synthesis and Crystal Structures of Two New Coordination Polymers Based on Diphenic Acid

Two new metal coordination polymers [Zn(dpa)(bim)] _n and [Ni(dpa)(bpp)] _n , (H₂dpa = 3,4′-Biphenyl-dicarboxylic acid, bim = Benzimidazole and bpp = 1,3-Di (4-pyridyl)-propane) have been synthesized and structurally characterized by elemental analysis, IR and X-ray diffraction. Single-crystal X-ray analyses reveal that the 3,4′-diphenic acids act as bridging ligands, exhibiting three coordination modes to link metal ions: μ ₂–η ¹: η ¹, μ ₁–η ¹: η ⁰ and μ ₁ –η¹: η¹. Compound 1 demonstrates a one-dimensional zigzag chain. There exists intermolecular hydrogen bonding interactions in compound 1 which lead to form supramolecular structure. Compound 2 is a two-dimensional (4,4) net, and further assembled twofold interpenetrating net. Furthermore, compound [Zn(dpa)(bim)] _n shows intense photoluminescence at room temperature.     

Controlled radical polymerization of styrene with an oxazolidinyl-N-oxyl stable free radical

Summary The bulk polymerization of styrene at 110 °C in the presence of 7-oxo-15-azadispiro[5.2.5.1]pentadecanyl-N-oxyl was investigated. The M _n values of poly(St) formed were increased linearly with conversion, and the M _w/M _n values were 1.48–1.54 at 90% conversion. On the basis of the results it was concluded that 1 controlled radical polymerization of St. Received: 19 October 1998/Revised version: 21 November 1998/Accepted: 26 November 1998     

Hydrothermal Synthesis of Cd(II), Mn(II) and Ni(II) Coordination Polymers Derived from Benzopenone-2,4′-carboxylate and N-door Ligands

Three new coordination polymers [Cd(L)(4,4′-bipy)_0.5]_n (1), {[Mn(L)(bpp)]·H₂O}_n (2) and [Ni(L)(2,2′-bipy)(H₂O)₂]_n(3) [H₂L = Benzopenone-2,4′-dicarboxylic acid, 4,4′-bipy = 4,4′-bipy ridine, bpp = 1,3-di(4-pyridyl) propane and 2,2′-bipy = 2,2′-bipyridine] have been synthesized and structurally characterized by elemental analysis, IR and X-ray diffraction. Single-crystal X-ray analyses revealed that the H₂L ligand acts as a bridge, exhibiting three coordination modes to link metal ion: bidentate chelating, bis-monodentate, monodentate. Compound 1 has 3-connected metal–organic framework with the (6³) topology notation; Compounds 2 and 3 are one-dimensional chain structures. The luminescent properties for compound 1 was investigated.     

N-[2-(8-heptadecenyl)-4,5-dihydro-1H-imidazole-1-ethyl]-2-bromoisobutyramide as initiator for atom transfer radical polymerization (ATRP) and surface-initiated ATRP of methyl methacrylate on iron

N-[2-(8-heptadecenyl)-4,5-dihydro-1H-imidazole-1-ethyl]-2-bromoisobutyramide (IEB) was synthesized and characterized by elemental analysis, FT-IR, and ¹H NMR. It had been successfully used as a bidentate initiator for the ATRP of methyl methacrylate with CuBr/2,2′-bipyridine as the catalyst, and N,N-dimethylformamide as the solvent at 70 °C. The kinetics was first order in monomer and the number-average molecular weight of the polymer increased linearly with the monomer conversion, indicating the ‘living’/controlled nature of the polymerization. The polymerization reached high conversions producing polymers with a low molecular weight distribution ( M _w/M _n = 1.319). The obtained poly(methylmethacrylate) (PMMA) functionalized with 2-(8-heptadecenyl)-4,5-dihydro-1H-imidazoleyl and ω-Br as the end groups were characterized by FT-IR spectroscopy. They can be used as macroinitiators for chain extension reaction. Then, PMMA coatings were grafted from iron substrates by surface-initiated ATRP from a surface-bound IEB initiator. The EIS measurements confirmed the successful grafting of the polymer coatings. Greatly improved short-term anticorrosive properties for PMMA-modified electrodes were demonstrated by substantially increased resistance of the film for a period of 24 h as compared to bare iron.     

Preparation of core–shell latex particles by emulsion co-polymerization of styrene and butyl acrylate,and evaluation of their pigment properties in emulsion paints

A series of core–shell polymeric particles with poly(n-butyl acrylate-co-methacrylic acid-co-ethylene glycol dimethylacrylate) as core and poly(styrene-co-methyl methacrylate) as shell were prepared by seeded emulsion polymerization. The role of ethylene glycol dimethylacrylate (EGDMA) is to crosslink the core so as to avoid any probability of gel formation and to bind both the core and the shell phase together. The spherical morphology of the core–shell structure was achieved at 60:40 core to shell ratio. The core–shell morphology was confirmed by SEM and TEM analyses. GPC analysis of the particles reveals that the polymer shows a bimodal mode. The first peak has M _w = 382700 and M _n = 245200 with polydispersity index of 1.6, and the second peak has M _w = 21200 and M _n = 14800 with polydispersity index of 1.4. These core–shell latexes were applied as a pigment/binder in emulsion paint and the paint properties like gloss, rock hardness, washability, opacity, etc. were compared with the standard. The results show that these core–shell latexes can provide similar hiding power with 17% reduction of TiO₂ in the paint formulation.     

RAFT polymerization of diacrylate derivatives having different spacers in dilute conditions

Reversible addition-fragmentation chain transfer (RAFT) polymerization of four divinyl monomers, 1,4-butanediol diacrylate (BDDA) and three poly(ethylene glycol) diacrylates (PEGDAs), were investigated under dilute conditions ([M] = 0.2-0.05 mol/L). RAFT polymerization of BDDA using a dithiocarbamate-type chain transfer agent (CTA) afforded soluble polymers, whereas a cross-linked product was obtained by conventional radical polymerization. The monomer concentration, the nature of the CTA, and the CTA/initiator ratio were found to affect the polymerization behavior and structure of the resulting polymers, which is attributed to the relative propensities for intermolecular propagating/cross-linking reactions and intramolecular cyclization. RAFT polymerizations of three PEGDAs (PEG258DA, average M_n = 258; PEG575DA, average M_n = 575; PEG700DA, average M_n = 700) having different lengths of PEG spacers (n = 3, 10, 13, respectively) were also conducted under dilute conditions. Water-soluble polymers were synthesized by one-step RAFT polymerization of PEGDAs having longer spacers (n = 10 and 13), whereas RAFT polymerization of PEGDA (n = 3) afforded polymers soluble in organic solvents. The product obtained by RAFT polymerization of PEGDA (n = 10) showed a characteristic thermoresponsive property, lower critical solution temperature (LCST), in aqueous solution.     

Design of Star-Shaped Organoiron Oligomers with Azo Dye Bridges

A series of star-shaped macromolecules bearing distinct symmetrical branches with alternating organoiron complexes and azobenzene moieties were synthesized using both convergent and divergent approaches. The various azo dye and organoiron-containing branches were reacted with multifunctional cores via metal-mediated nucleophilic aromatic substitution and ester condensation reactions to afford multi-substituted three- and four-arm star-shaped oligomers. UV–vis spectral studies of complexes 15 and 22 (λ _max = 435 and 427 nm, respectively) show bathochromic shifts (λ _max = 576 and 558, respectively) at various HCl concentrations indicating their use as potential acid sensors. Cyclic voltammetric studies of the octa-iron oligomer 22 were reversibly reduced at E _1/2 = −1.53 V.     

Syntheses, Structures, and Luminescent Properties of Two Novel Coordination Polymers with Poly-Carboxylate and N-Heterocyclic Ligands

Two novel metal–organic coordination polymers {[Pb(CIPT)(1,4-BDC)]·2H₂O} _n 1 and {[Zn₂(IPDT)₂(1,4-BDC)₂(H₂O)].3H₂O} _n 2 [CIPT = 2-(3-chlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, 1,4-BDC = terephthalic acid, IPDT = 4-(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)-2,6-dimethoxyphenol] were obtained from hydrothermal reaction and characterized by elemental analysis, thermogravimetric (TG) analysis, IR and single-crystal X-ray diffraction. Both of the two coordination polymers exhibit one-dimensional (1D) infinite chain structures through non-covalent interactions, and the existence of hydrogen bonds interactions lead the 1D chain to 2D layer structures. It is noteworthy that the existence of hydrogen bonds reinforces the structural stability of the complexes 1 and 2, which can be proved by TG analysis. The photoluminescent study of coordination polymer 1 shows that it exhibits fluorescent emission band at 637 nm, which is red-shifted by 46 nm relative to the free ligand CIPT.     

Thermal decomposition of 3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane in solution and its use in methyl methacrylate polymerization

The kinetics of the thermal decomposition reaction of diethylketone triperoxide (3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane, DEKTP) in ethylbenzene solution were studied in the temperature range of 120.0–150.0 °C and at an initial concentration range of 0.01–0.10 M. This peroxide was used as a new initiator in methyl methacrylate (MMA) polymerization process at high temperatures (110.0–140.0 °C) in ethylbenzene solution. The effects of initiator concentration and reaction temperature on the polymerization rate were investigated in detail. Thus, activation parameters of the solution polymerization process (ΔE _d* = 83.3 kJ mol⁻¹ and ΔE _p* − ΔE _t*/2 = 54.0 kJ mol⁻¹) will be obtained. DEKTP can effectively act as initiator in MMA polymerization and its performance is similar to that presented by a multifunctional initiator resulting in high-molecular weight polymethylmethacrylate with a high reaction rate.     

Syntheses, Structures, and Luminescent Properties of Two Novel Coordination Polymers with Mixed Ligands

Two novel metal–organic coordination polymers {[Pb₂(MIP)₂(BDC)₂]·H₂O} _n 1 and [Cd(MIP)(NDC)] _n 2 [MIP = 2-(3-methoxyphenyl)-1H-imidazo [4,5-f] [1, 10] phenanthroline, BDC = terephthalic acid, NDC = naphthalene-1,4-dicarboxylic acid] were obtained from hydrothermal reaction and characterized by elemental analysis, thermogravimetric (TG) analysis, infrared spectrum (IR) and single-crystal X-ray diffraction. The coordination polymers crystallize in triclinic, space group P-1 with a = 1.0335(2), b = 1.4224(3), c = 1.8156(4) nm, β = 106.088(3)° for complex 1 and the complex 2 crystallizes in monoclinic, space group P2(1)/n with a = 1.2562(8), b = 1.4800(9), c = 1.3723(8) nm, β = 97.257(1)°, respectively. The metal ions Pb(II) are located in [:PbN2O4] pentagonal bipyramidal geometry in complex 1. The metal ions Cd(II) in complex 2 act as distorted octahedral geometry, being surrounded by four carboxylate oxygen atoms from three NDC ligands and two donor nitrogen atoms from one MIP molecule. Moreover, there are hydrogen bonds in the two complexes, and it is noteworthy that the existence of hydrogen bonds and π–π interactions reinforce the structural stability of the title complexes, which have been proved by TG analysis. The luminescent properties for the ligand MIP, NDC and complex 2 are also discussed in detail.     

Hydrothermal Synthesis, Characterization of Mn(II) and Cd(II) Coordination Polymers Assembled from Semi-Rigid Oxo-Bridged Carboxylate and N-Donor Ligands

Two new metal–organic coordination polymers containing Mn(II) and Cd(II) with oxo-bridged and N-donor ligands, [Mn(oba)(2,2′-bipy)] _n (1) and {[Cd(oba)(bib)]·H₂O} _n (2) [2,3′-H₂oba = 2-(3-carboxyphenoxy)benzoic acid, 2,2′-bipy = 2,2′-bipyridine, and bib = 4,4′-bis(2-methylimidazole-1-ylmethyl)biphenyl], have been prepared and characterized by elemental analysis, Fourier infrared spectroscopy, and X-ray diffraction. Complex 1 has a 3D supramolecular network constructed from 1D zigzag chain via π–π stacking interactions. Complex 2 features 1D ladder-like chain which consists of 1D helical arrays and bib pillars. Moreover, photoluminescence properties of the bib ligand and the Cd(II) complex were investigated.