Pyridylphosphine ligands for iron-based atom transfer radical polymerization of methyl methacrylate and styrene

Two pyridylphosphine ligands, 2-(diphenylphosphino)pyridine (DPPP) and 2-[(diphenylphosphino)methyl]pyridine (DPPMP), were investigated as complexing ligands in the iron-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and styrene with various initiators and solvents. In studies of their ATRP behavior, the FeBr₂/DPPP catalytic system was a more efficient ATRP catalyst for the MMA polymerization than the other complexes studied in this paper. Most of these systems were well controlled with a linear increase in the number-average molecular weights (M_n) vs. conversion and relatively low molecular weight distributions (M_w/M_n = 1.15-1.3) being observed throughout the reactions, and the measured molecular weights matched the predicted values with the DPPP ligand. The polymerization rate of MMA attained a maximum at a ratio of ligand to metal of 2:1 in p-xylene at 80 °C. The polymerization was faster in polar solvents than in p-xylene. The 2-bromopropionitrile (BPN) initiated ATRP of MMA with the FeX₂/DPPP catalytic system (X = Cl, Br) was able to be controlled in p-xylene at 80 °C. The polymerization of styrene was able to be controlled using the PECl/FeCl₂/DPPP system in DMF at 110 °C.     

Molar mass determination of poly(octadecene-alt-maleic anhydride) copolymers by size exclusion chromatography and dilute solution viscometry

The number average molar mass M_n of poly(octadecene-alt-maleic anhydride) (PODMA) copolymers calculated from data obtained by size exclusion chromatography (SEC) using a polystyrene (PS) calibration was found to be inaccurate. The use of SEC combined with dilute solution viscometry enabled a method to be developed using an iterative approach, which does not require knowledge of the Mark-Houwink constants for PODMA samples. A new calibration curve was constructed as a plot of molar mass M_u for PODMA. True number-average molar masses M_n (true) calculated using the new calibration are approximately twice the apparent molar mass M_n (app) based on a PS calibration for higher molar mass samples (>10?000 g mol⁻¹).     

Amphiphilic gradient poly(styrene-co-acrylic acid) copolymer prepared via nitroxide-mediated solution polymerization. Synthesis, characterization in aqueous solution and evaluation as emulsion polymerization stabilizer

A well-defined, amphiphilic poly(styrene-co-acrylic acid) copolymer was synthesized in a single step by nitroxide-mediated controlled free-radical copolymerization of styrene and acrylic acid, without protection of the acid groups: M_n=6500 g mol⁻¹, M_w/M_n=1.5 and a composition of F_AA=0.70±0.03 in acrylic acid. In addition to the good control over molar mass and molar mass distribution, the copolymer exhibited a narrow composition distribution with a slight gradient. Such copolymer was an efficient stabilizer for the emulsion polymerizations of styrene and of mixtures of methyl methacrylate and n-butyl acrylate, until 45 wt% solids. A low amount (typically 3-4 wt% based on the monomer(s)) was needed for a good stabilization. This is approximately a decade lower than the required amount of random, amphiphilic copolymers prepared via conventional free-radical polymerization. The performances were, however, below those of analogous diblock copolymers, but the great advantage is the very easy synthetic procedure.     

Thermal polymerization of methyl (meth)acrylate via reversible addition-fragmentation chain transfer (RAFT) process

Thermal polymerization of methyl (meth)acrylate (MMA) was carried out using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) and cumyl dithionaphthalenoate (CDN) as chain transfer agents. The kinetic study showed the existence of induction period and rate retardation, especially in the CDN mediated systems. The molecular weights of the polymers increased linearly with the monomer conversion, and the molecular weight distributions (M_w/M_ns) of the polymers were relatively narrow up to high conversions. The maximum number-average molecular weights (M_ns) reached to 351?900 g/mol (M_w/M_n = 1.47) and 442?400 g/mol (M_w/M_n = 1.29) in the systems mediated by CPDN and CDN, respectively. Chain-extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA-block-polystyrene (PMMA-b-PSt) copolymer with controlled structure and narrow M_w/M_n. Thermal polymerization of methyl acrylate (MA) in the presence of CPDN, or benzyl (2-phenyl)-1-imidazolecarbodithioate (BPIC) also demonstrated “living”/controlled features with the experimented maximum molecular weight 312?500 g/mol (M_w/M_n = 1.57). The possible initiation mechanism of the thermal polymerization was discussed.     

Co γ-irradiation-initiated RAFT polymerization of VAc at room temperature

In this work, the reversible addition-fragmentation chain transfer (RAFT) polymerization of vinyl acetate (VAc) was successfully performed at room temperature using ⁶⁰Co γ-irradiation as the initiation source. Under the dose rate of 10 Gy/min irradiation, the polymerization proceeded smoothly and converted approximately 90% of the monomer within 7 h. The molecular weight distribution (M_w/M_n) remained narrow (M_w/M_n < 1.35) up to 90% conversion. Compared to AIBN-initiated RAFT polymerization at 60 °C, ⁶⁰Co γ-irradiation-initiated RAFT polymerization is a technique that can better control the molecular weight, especially at high conversion. The ¹H NMR spectra and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry confirmed that most of the chain ends of poly(VAc) (PVAc) from γ-irradiated RAFT polymerization were living and can be reactivated for chain-extension reactions. The microstructures of PVAc from ⁶⁰Co γ-irradiated RAFT polymerization (almost head-to-tail addition) and AIBN-initiated RAFT polymerization (5% tail-to-tail addition) were different, as revealed by the ¹³C NMR spectra. For the first time, ⁶⁰Co γ-irradiation was used as an initiation source for RAFT polymerization of VAc at room temperature.     

Atom transfer radical polymerization of methyl methacrylate with low concentration of initiating system under microwave irradiation

Homogeneous atom transfer radical polymerization of methyl methacrylate (MMA) under microwave irradiation (MI) with low concentration of initiating system [ethyl 2-bromobutyrate (EBB)/CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA)] was successfully carried out in N,N-dimethylformamide (DMF) at 69 °C. Plots of ln ([M]₀/[M]) vs. time and molecular weight evolution vs. conversion showed a linear dependence. A 27.3% conversion for a polymer with number-average molecular weight (M_n) of 57,280 and a polydispersity index (PDI) of 1.19, was obtained under MI (360 W) with the ratio of [MMA]₀/[EBB]₀/[CuCl]₀/[PMDETA]₀=2400/1/2/2 in only 150 min; but 963 min was needed under conventional heating (CH) process to reach a 26.0 % conversion (M_n=63,990 and PDI=1.14) under identical polymerization conditions, indicating a significant enhancement of the polymerization rate under MI.     

Effects of PVA content on the synthesis of LaFeO3 via sol-gel route

LaFeO₃ were synthesized via a sol-gel route based on polyvinyl alcohol (PVA). Differential scanning calorimetry (DSC), Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM) techniques were used to characterize precursors and derived oxide powders. The effect of the ratios of positively charged valences to hydroxyl groups of PVA (Mⁿ⁺/-OH) on the formation of LaFeO₃ was investigated. XRD analysis showed that single-phase and well-crystallized LaFeO₃ was obtained from the Mⁿ⁺/-OH = 4:1 molar ratio precursor at 700 °C. For the precursor with Mⁿ⁺/-OH = 2:1, nanocrystalline LaFeO₃ with average particle size of ∼50 nm was formed directly in the charring procedure. With increase of PVA content to Mⁿ⁺/-OH = 1:1, phase pure LaFeO₃ was obtained at 500 °C.     

Soluble neodymium chloride 2-ethylhexanol complex as a highly active catalyst for controlled isoprene polymerization

Soluble NdCl₃·3EHOH (2-ethyl hexanol) in hexane combined with AlEt₃ is highly active for isoprene polymerization in hexane. The NdCl₃·3EHOH/AlEt₃ has higher activity than the typical binary catalyst NdCl₃·3ⁱPrOH (isopropanol)/AlEt₃ and ternary catalyst NdV₃ (neodymium versatate)/AlEt₂Cl/Al(i-Bu)₂H. The molecular weight of polyisoprenes can be controlled by variation of [Nd], [Al]/[Nd] ratio and polymerization temperature and time. The NdCl₃·3EHOH/AlEt₃ catalyst polymerized isoprene to afford products featuring high cis-1,4 stereospecificity (ca. 96%), high molecular weight (ca. 10⁵) and relatively narrow molecular weight distributions (M_w/M_n = 2.0-2.8) simultaneously. More importantly, some living polymerization characteristics were demonstrated: (a) absence of chain termination; (b) linear correlation between M_n and polymer yield; (c) increment of molecular weight in the ‘seeding’ polymerization. Though some deviation from the typical living polymerization such as molecular weight distribution is not narrow enough and the line of M_n and polymer yield does not extrapolate to zero, controlled polymerization with the current catalyst can still be concluded.     

Living/controlled olefin polymerization initiated by nickel diimine complexes: The effect of ligand ortho substituent bulkiness

Polymerization of hex-1-ene and propene initiated by several methylalumoxane-activated diimine complexes was critically investigated. Effect of bulkiness of ortho aryl diimine substituents on extent of transfer reactions was examined. All of the complexes allowed us to prepare poly(hex-1-ene) with a very narrow molar mass distribution, molar mass being controlled by stoichiometry in a broad range of reaction conditions. Poly(hex-1-ene)s with molar mass between 15 and 220 kg mol^?1 and dispersity (M_w/M_n) between 1.01 and 1.20 were prepared by varying the catalyst, temperature and monomer concentration. Livingness of hex-1-ene polymerization was demonstrated for the first time for nickel complex bearing ethyl ortho aryl substituents by reinitiation of chain growth upon addition of a new portion of monomer. Complexes with ortho methyl substituents did not allow complete reinitiation of chain growth and despite its good control over molar mass cannot be classified as a living polymerization catalyst. Chain branching can effectively be controlled by the choice of the ligand structure due to the chain-walking mechanism. Transfer reactions were more pronounced in propene polymerization. Polypropylene with narrow molar mass distribution could not be prepared using complexes with methyl substituents.     

Synthesis, characterization and ring-opening polymerization of a novel six-membered cyclic carbonate bearing pendent allyl ether group

A novel six-membered cyclic carbonate with pendent allyl ether group, 5-allyloxy-1,3-dioxan-2-one (ATMC), was synthesized from glycerol, and the corresponding polycarbonate, poly(5-allyloxy-1,3-dioxan-2-one) (PATMC) was further synthesized by ring-opening polymerization in bulk at 120 °C. Two kinds of catalyst, tin(II) 2-ethylhexanoate (Sn(Oct)₂) and immobilized porcine pancreas lipase on silica particles (IPPL), were employed to perform the polymerization. The structures of the novel monomer and the resulting functional polymers were confirmed by FTIR, ¹H NMR, ¹³C NMR, GPC and DSC. The molecular weight (M_n) of PATMC decreased rapidly with the increase of IPPL or Sn(Oct)₂ concentration. The highest molecular weight (M_n = 48,700 g/mol) of PATMC with the polydispersity of 1.31 was obtained at 0.1 wt% concentration of IPPL for 48 h. Postpolymerization oxidation reactions to epoxidize the unsaturated bonds of the PATMC were also achieved. The epoxide-containing polymers could afford facilities for further modification.     

Synthesis of star polymer by means of the living polymerization of [(o-trifluoromethyl)phenyl]acetylene using a MoOCl4-based catalyst and the linking method

A star polymer was synthesized by addition of 1,4-diethynyl-2,5-dimethylbenzene as linking agent (30 °C, 24 h) after living polymerization of [(o-trifluoromethyl)phenyl]acetylene (o-CF₃PA) with MoOCl₄-n-Bu₄Sn-EtOH catalyst (in anisole, 30 °C, 20 min; [Mo]=10 mM, [P^∗]/[Mo]=40%, [o-CF₃PA]₀=200 mM). The M_n values of the living and star polymers were 8.1×10³ and 5.3×10⁴, respectively, according to gel permeation chromatography, while these values determined by multi-angle laser light scattering (MALLS) were 7.8×10³ and 2.5×10⁵. The M_w/M_n and arm number of the star polymer were 1.04 and 29, respectively, according to MALLS. The molecular weight and arm number of star polymer increased with increasing linking agent concentration and polymerization temperature.     

Polymerization of 1,3-butadiene with VO(P204)2 and VO(P507)2 activated by alkylaluminum

The oxovanadium phosphonates (VO(P₂₀₄)₂ and VO(P₅₀₇)₂) activated by various alkylaluminums (AlR₃, R = Et, i-Bu, n-Oct; HAlR₂, R = Et, i-Bu) were examined in butadiene (Bd) polymerization. Both VO(P₂₀₄)₂ and VO(P₅₀₇)₂ showed higher activity than those of classical vanadium-based catalysts (e.g. VOCl₃, V(acac)₃). Among the examined catalysts, the VO(P₂₀₄)₂/Al(Oct)₃ system (I) revealed the highest catalytic activity, giving the poly(Bd) bearing M_n of 3.76 × 10⁴ g/mol, and M_w/M_n ratio of 2.9, when the [Al]/[V] molar ratio was 4.0 at 40 °C. The polymerization rate for I is of the first order with respect to the concentration of monomer. High thermal stability of I was found, since a fairly good catalytic activity was achieved even at 70 °C (polymer yield > 33%); the M_n value and M_w/M_n ratio were independent of polymerization temperature in the range of 40-70 °C. By IR and DSC, the poly(Bd)s obtained had high 1,2-unit content (>65%) with atactic configuration. The 1,2-unit content of the polymers obtained by I was nearly unchanged, regardless of variation of reaction conditions, i.e. [Al]/[V], ageing time, and reaction temperature, indicating the high stability of stereospecificity of the active sites.     

Synthesis and solid state structures of macromolecular cylindrical brushes with varying side chain length

Cylindrical brushes with a macromolecular backbone and well-defined side chains of different length (4≤P_n^sc≤38) were synthesized by polymerization of macromonomers. The effect of side chain length on the intermolecular order has been investigated by means of X-ray scattering on the melt-extruded samples. The increase of the side chain molar mass results in an increase of the intermolecular distance d according to d∼(M_n^sc)^0.476. The contour length of the cylindrical brush polymers per main chain monomer unit, l_m, was determined to slightly vary with side chain molar mass M_n^sc according to l_m∼(M_n^sc)^0.059. The resulting values are much less than the maximum extension, which is found to be almost independent of side chain molar mass. Also, supermolecular structure formation of a random copolymer brush prepared by radical copolymerization of methacryloyl end functionalized polyvinylpyridine and polymethylmethacrylate macromonomers has been observed and is interpreted as a consequence of intramolecular phase separation.     

Living polymerization of 1,3-butadiene by a Ziegler-Natta type catalyst composed of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite

Living characteristics of facilely prepared Ziegler-Natta type catalyst system consisting of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite have been found in the polymerization of 1,3-butadiene in hexane at 40 °C. The characteristics have been well demonstrated by: a first-order kinetics with respect to monomer conversion, a narrow molecular weight distribution (M_w/M_n = 1.48-1.52) of polybutadiene in the entire range of polymerization conversion and a good linearity between M_n and the yield of polymer. Feasible post-polymerization of 1,3-butadiene and block co-polymerization of 1,3-butadiene and isoprene further support the living natures of the catalyst bestowed with. The current catalyst system is highly active (yield > 80%, 35 min), providing polybutadiene with 1,2, cis-1,4 and trans-1,4 units about 44.0%, 51.0% and 5.0%, respectively.     

Trimethylsilyl‐substituted triazole‐based ligand for copper‐mediated single‐electron transfer living radical polymerization of methyl methacrylate

The tripodal ‘click’ compound tris(4‐trimethylsilylmethyl‐1,2,3‐triazolylmethyl)amine (TTTA) was prepared and investigated as a ligand for copper‐catalysed single‐electron transfer living radical polymerization of methyl methacrylate (MMA). Bulk polymerizations catalysed by Cu⁰/CuBr₂/TTTA with a molar ratio of [MMA]₀/[ethyl‐2‐bromoisobutyrate]₀/[CuBr₂]₀/[TTTA]₀ = 200:2:1:1 and a 1.0 × 1.0 cm² Cu⁰ sheet were fast and well controlled (76% conversion with M_w/M_n = 1.19 after 3.5 h). Greater amounts of added air generally gave slower polymerizations although M_w/M_n remained low (<1.3) even when the polymerization was carried out under aerobic conditions. Decreasing initial concentrations of the Cu⁰/CuBr₂/TTTA catalyst system or polymerization temperatures also resulted in slower polymerizations and yielded polymers with broader dispersity. Kinetic studies in the temperature range 40–90 °C revealed an apparent activation energy of 22.6 kJ mol^?1. © 2014 Society of Chemical Industry     

Activators regenerated by electron transfer in ATRP of methyl methacrylate with alcohol as reducing agent in the presence of a base

Poly(methyl methacrylate) (PMMA) was synthesized via activators regenerated by electron transfer (ARGET) in atom transfer radical polymerization (ATRP) (ARGET ATRP) of methyl methacrylate in N,N-dimethylformamide and using ethyl 2-bromoisobutyrate as initiator, CuCl₂ as catalyst, N,N,N′,N′-tetramethylethylene-diamine as ligand and ethanol as a reducing agent. The polymerization temperature was kept at 70 °C. A well-defined PMMA with predetermined molecular weight and narrow molecular weight distribution was obtained. A linear relationship between ln([M]₀/[M]) and polymerization time was found to show the living and controllable radical polymerization. The molecular weights of the obtained polymers increased linearly with monomer conversion and the data are in good agreement with the theoretical values with narrow molecular weight distribution (M _w/M _n). That is to say, alcohols were found to be a kind of highly efficient agents in the presence of Na₂CO₃ in this system. The effects of temperature, different types of alcohols and the amount of n-propanol on the polymerization were investigated. With increasing temperature (changed from 70 to 90 °C) and the amount of n-propanol (changed from 500:1:1:2:1:2 to 500:1:1:2:10:2), the conversion increased from 15.6 to 34.7 % and from 8.6 to 26.8 %, respectively. However, the value of M _w/M _n became broader when the molar ratio of [MMA]₀/[EBiB]₀/[CuCl₂]₀/[TMEDA]₀/[n-propanol]₀/[Na₂CO₃]₀ was 500:1:1:2:1:2, indicating that the amount of n-propanol played an important role in ARGET ATRP of MMA. The activation energy was calculated to be 51.96 kJ/mol. The different types of alcohol were demonstrated to be an efficient reducing agent in this system except for tert-butyl alcohol. The “living” feature of the obtained polymer was further verified by a chain extension experiment. The obtained polymer was characterized by ¹H NMR and GPC.     

Synthesis and properties of polymer brush consisting of poly(phenylacetylene) main chain and poly(dimethylsiloxane) side chains

A novel polymer brush consisting of poly(phenylacetylene) (PPA) main chain and poly(dimethylsiloxane) (PDMS) side chains was synthesized by the polymerization of phenylacetylene-terminated PDMS macromonomer (M-PDMS). The macromonomer was prepared by the esterfication of monohydroxy-ended PDMS (PDMS-OH, degree of polymerization (DP) = 42) with p-ethynylbenzoic acid. The polymerization of M-PDMS using [(nbd)RhCl]₂/Et₃N catalyst led to polymer brush, poly(M-PDMS), with M_n up to 349?000 (DP of main chain 104). Poly(M-PDMS) with narrow molecular weight distribution (M_n = 39?900, M_w/M_n = 1.11) was obtained with a vinyl-Rh catalyst, [Rh{C(Ph)CPh₂}(nbd){P(4-FC₆H₄)₃}]/(4-FC₆H₄)₃P. Poly(M-PDMS)s were brown to orange viscous liquids and soluble in organic solvents such as toluene and CHCl₃. The UV-vis absorptions of poly(M-PDMS) were observed in the range of 350-525 nm, which are attributable to the PPA main chain.     

Effects of molecular weight on liquid-crystalline behavior of a mesogen-jacketed liquid crystal polymer synthesized by atom transfer radical polymerization

The synthesis of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) with different molecular weight and low polydispersity was achieved by atom transfer radical polymerization in methoxybenzene solution using 1-bromoethylbenzene as an initiator and CuBr/sparteine complex as a catalyst. The concentration of the living centers throughout the polymerization was found to be constant. The liquid-crystalline behavior of the polymers with M_n ranging from 3800 to 17,400 g/mol was studied using DSC and POM. Only the polymers with M_n beyond 10,200 g/mol formed a liquid-crystalline phase, which was quite stable with a high clearing point (higher than the decomposition temperature of the polymer).     

Synthesis and applications of triblock and multiblock copolymers using telechelic oligopropylene

Isotactic polypropylene (iPP)-polystyrene (PS) and iPP-poly(methyl methacrylate) (PMMA) multiblock copolymers were synthesized by atom transfer radical coupling (ATRC) of PS-iPP-PS and PMMA-iPP-PMMA triblock copolymers obtained by atom transfer radical polymerization (ATRP) of styrene (St) and methyl methacrylate (MMA), respectively, using α,ω-dibromoisobutyrateoligopropylene (iPP-Br) as a bifunctional macroinitiator. The iPP-Br was prepared by hydroxylation and subsequent esterification of telechelic oligopropylene having terminal vinylidene double bonds at both ends obtained by controlled thermal degradation of iPP. ATRP of St and (meth) acrylic monomers using iPP-Br formed the corresponding triblock copolymers. It was confirmed that the PMMA-iPP-PMMA triblock copolymer was effective as the compatibilizer for the iPP/PMMA blend. An iPP-PS multiblock copolymer (M_n: 25?000 g/mol and M_w/M_n: 4.1) was prepared by ATRC of PS-iPP-PS triblock copolymer (M_n: 8900 g/mol and M_w/M_n: 1.3). ATRC with St of PMMA-iPP-PMMA triblock copolymer (M_n: 13?000 g/mol and M_w/M_n: 1.4) provided an iPP-PMMA multiblock copolymer containing St chains (M_n: 39?000 g/mol and M_w/M_n: 2.8).