Cationic polymerization of styrene by acetyl perchlorate. II. Steric structure of the polymer and nature of the propagating species

Cationic polymerization of styrene initiated by acetyl perchlorate in CH₂Cl₂ yields a polymer having a bimodal molecular weight distribution. The high molecular weight and the low molecular weight portions of the polymer were separated by thin-layer chromatography, and the steric structure of these separated polymers was investigated by ¹³C NMR spectra. The high molecular weight polymer had a larger racemic dyad content than the low molecular weight material. From the dependence of the steric structure of the polymer on the polarity of a solvent, it was estimated that the propagating species producing the high molecular weight material was a loose ion pair or a free ion, and that producing the high molecular weight material was a loose ion pair or a free ion, and that producing the low one was a nondissociated species.     

Dual bimodal polyethylene prepared by intercalated silicate with nickel diimine complex

The ethylene polymerization was catalyzed by the intercalated montmorillonite with the nickel complex, [ArN?C(Me)? C(Me)?NAr]NiBr₂ (Ar = 2,6‐C₆H₃ (i‐Pr)₂). Polymer with low melting point and high molecular weight was produced at the early stage of polymerization followed by formation of polymer with high melting point and low molecular weight. It is proposed that the gallery of silicate lowers the propagation rate of polymerization and frequency of “chain walking” process of nickel complex anchored inside the gallery, which produces polymer with low molecular weight and low branching, whereas the nickel complex immobilized on the surface of silicate generates polymer with high molecular weight and high branching. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5506–5511, 2005     

Addition polymerization of norbornene using bis(β‐ketoamino)nickel(II)/tris(pentafluorophenyl)borane catalytic systems

Norbornene polymerizations proceeded in toluene with bis(β‐ketoamino)nickel(II) {Ni[CH₃C(O)CHC(NR)CH₃]₂ [R = phenyl ( 1 ) or naphthyl ( 2 )]} complexes as the catalyst precursors and the organo‐Lewis compound tris(pentafluorophenyl)borane [B(C₆F₅)₃] as a unique cocatalyst. The polymerization conditions, such as the cocatalyst/catalyst ratio (B/Ni), catalyst concentration, monomer/catalyst ratio (norbornene/Ni), polymerization temperature, and polymerization time, were studied in detail. Both bis(β‐ketoamino)nickel(II)/B(C₆F₅)₃ catalytic systems showed noticeably high conversions and activities. The polymerization activities were up to 3.64 × 10⁷ g of polymer/mol of Ni h for complex 1 /(B(C₆F₅)₃ and 3.80 × 10⁷ g of polymer/mol of Ni h for complex 2 /B(C₆F₅)₃, and very high conversions of 90–95% were maintained; both polymerizations provided high‐molecular‐weight polynorbornenes with molecular weight distributions (weight‐average molecular weight/number‐average molecular weight) of 2.5–3.0. The achieved polynorbornenes were confirmed to be vinyl‐addition and atactic polymers through the analysis of Fourier transform infrared, ¹H NMR, and ¹³C NMR spectra, and the thermogravimetric analysis results showed that the polynorbornenes exhibited good thermal stability (decomposition temperature > 410 °C). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4733–4743, 2007     

Polymerization of β‐pinene with Schiff‐base nickel complexes catalyst: Synthesis of relatively high molecular weight poly(β‐pinene) at high temperature with high productivity

A series of easily accessible and stable Schiff‐base nickel complexes (complex 1 – 4 ) in conjunction with methylaluminoxane (MAO) were employed for the synthesis of relatively high molecular weight β‐pinene polymers at high temperature with high productivity. The ligand structure of the complex had a substantial effect on the polymerization in terms of the productivity and the molecular weight. With complex 4 in the presence of MAO, high molecular weight polymers of β‐pinene (M_n ～ 10,900) were obtained at 40 °C with an extremely high productivity up to 1.25 × 10⁷ g polyβ‐pinene/mol of Ni. ¹H NMR analyses showed that the obtained β‐pinene polymer was structurally identical to that formed by conventional cationic Lewis acid initiators. The polymerization was presumably initiated by the nickel cation formed by the reaction of the schiff‐base nickel complex and MAO, while the propagation proceeded in a manner typical for a conventional carbocationic polymerization process. Direct evidence for the carbocationic polymerization was offered by the fact that quenching of the polymerization with methanol at a low monomer conversion resulted in incorporation of a methoxyl end group into the polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3739–3746, 2007     

Stereospecific and molecular weight‐controlled polymerization of 1,3‐butadiene with Co(acac)3‐MAO catalyst

The polymerization of butadiene (Bd) with Co(acac)₃ in combination with methylaluminoxane (MAO) was investigated. The polymerization of Bd with Co(acac)₃‐MAO catalysts proceeded to give cis‐1,4 polymers (94 – 97%) bearing high molecular weights (40 × 10⁴) with relatively narrow molecular weight distributions (M_w's/M_n's). The molecular weight of the polymers increased linearly with the polymer yield, and the line passed through an original point. The polydispersities of the polymers kept almost constant during reaction time. This indicates that the microstructure and molecular weight of the polymers can be controlled in the polymerization of Bd with the Co(acac)₃‐MAO catalyst. The effects of reaction temperature, Bd concentration, and the MAO/Co molar ratio on the cis‐1,4 microstructure and high molecular weight polymer in the polymerization of Bd with Co(acac)₃‐MAO catalyst were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2793–2798, 2001     

Poly(3-hydroxyoxetane)—an analog of poly(vinyl alcohol): Synthesis,characterization, and properties

The spontaneous polymer formed from 3-hydroxyoxetane (HO), as first reported by Wojtowicz and Polak, is linear, low molecular weight, water-soluble, atactic, poly(3-hydroxyoxetane) (PHO) of high crystallinity with ? OCH₂CH(OH)CH₂OH end units. The highly crystalline nature of this atactic polymer may be related to the crystalline nature of atactic poly(vinyl alcohol) since PHO can be considered a copolymer of vinyl alcohol and formaldehyde. Spontaneous PHO apparently is formed in a cationic polymerization by the carboxylic acids produced by the air oxidation of HO on standing at room temperature for several months. The polymerization can be duplicated by the addition of 2% hydroxyacetic acid to HO. The rate of this unusual cationic polymerization increases greatly with acid strength, e.g., trifluoromethanesulfonic acid reacts explosively with pure HO. A mechanism is proposed for this cationic polymerization. High molecular weight, water-soluble, linear atactic, and highly crystalline PHO (mp = 155°C) was made by polymerizing the trimethylsilyl ether of HO with the i-Bu₃Al–0.7 H₂O cationic catalyst followed by hydrolysis. Two ¹H-NMR methods for measuring the tacticity of PHO were developed based on finding two different types of methylene units at 400 MHz with the methine protons decoupled. Also, an ¹H-NMR method was developed for measuring branching in HO polymers. High molecular weight, linear PHO with enhanced isotacticity (80%) has been obtained in low yield as a water-insoluble fraction with T_m = 223°C. The low molecular weight PHO prepared previously by the base-catalyzed, rearrangement polymerization of glycidol is highly branched.     

High molecular weight atactic polypropene synthesized with (η5‐pentamethylcyclopentadienyl)tribenzyl titanium activated with MAO

The half‐titanocene (η⁵‐pentamethylcyclopentadienyl)tribenzyl titanium (Cp*TiBz₃) with methylaluminoxane (MAO) as the cocatalyst was employed to catalyze propene polymerization at ambient pressure. A novel atactic polypropene elastomer with a high molecular weight (M̄_w = 2 − 8 × 10⁵) was produced. The effects of the polymerization conditions on the catalytic activity and polymer molecular weight are discussed. ¹³C NMR analysis confirmed that the catalyst system Cp*TiBz₃/MAO produced atactic polypropenes, and the polymerization mechanism was in agreement with the Bernoullian process. The triad sequence distribution of the polymer was measured and found to be as follows: mm = 6.15%, mr = 40.87%, and rr = 52.98% (Bernoullian factor B = 1.03); this indicated that the insertion of propene with the catalyst system followed a chain‐end control model. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 411–415, 2000     

有机/无机复合载体负载复合催化剂用于乙烯聚合时有机载体的作用

采用溶胶-凝胶法,将苯乙烯-丙烯酸(P(S-co-AA))共聚物包覆在以硅胶/MgCl2为载体的TiCl3催化剂(M-1催化剂)上,负载(n-BuCp)2ZrCl2后制得TiCl3/(n-BuCp)2ZrCl2复合催化剂,研究聚合物载体P(S-co-AA)在复合催化剂乙烯聚合中的作用.前期实验结果表明有机载体P(S-c...     

Polymerization of MMA catalyzed by different novel mixed ligand lanthanocene{(Cp)(Cl) LnSchiff-base (THF)},(COT) -Ln(methoxyethylindenyl)(THF) /Al (i -Bu)_3 systems

This article deals that the rare earth metal complexes along with Al(i'-Bu),can catalyze the polymerization of methyl-methacrylate (MMA) into high molecular weight poly(MMA) along with narrow molecular weight distributions (MWD).A typical example was mentioned in the case of {Cp(Cl) Sm-Schiff-base(THF)} which expresses maximum (conv.% = 55.46 and Mn=354×103) efficiency along with narrow MWD (Mw/Mn<2) at 60℃.The resulting polymer was partially syndiotactic (>60%).The effect of the catalyst,temperature,catalyst/MMA molar ratio,catalyst/Al( i-Bu)3 molar ratio on the polymerization of MMA at 60℃ were also investigated.     

Perylene as a visible light photoredox catalyst for photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of MMA

Abstract

The organic photocatalyst, perylene, was used to mediate photoinduced electron transfer (PET) reversible addition-fragmentation chain transfer polymerization (RAFT) of methyl methhacrylate (MMA) under light irradiation in N,N-dimethylformamide (DMF) at 25°C with 4-cyanopentanoic acid dithiobenzoate (CPADB) as chain transfer agent (CTA). Kinetic studies confirmed that the polymerization obeyed the first order kinetic m'odel. The production of PMMAs with a good control of molecular weights (M_n,GPC) and narrow polymer molecular weight distribution (M_w/M_n) were obtained. It is found that well-controlled PET RAFT polymerization of MMA can be manipulated even with the amount of perylene decreasing to ppm level. No polymer was obtained in the absence of light irradiation, implying that the model of PET RAFT polymerization of MMA is an ideal light “on”-“off” switchable system. Furthermore, the speed of PET RAFT polymerization of MMA was also finely tunable by the external light irradiation intensity. The resultant PMMA macro-CTA was characterized by ¹H nuclear magnetic resonance spectrum (¹H NMR) and gel permeation chromatography (GPC). The accessibility of the high end group fidelity was further demonstrated by chain extension experiments.     

Ring‐opening metathesis polymerization of cyclododecene using an electrochemically reduced tungsten‐based catalyst

The ring‐opening metathesis polymerization of cyclododecene using an electrochemically reduced tungsten‐based catalyst (WCl₆? e^?? Al? CH₂Cl₂) is described. In addition, the influence of reaction conditions on the polymerization yield was determined. The resulting polymer has been characterized by NMR, IR, gel permeation chromatography and differential scanning calorimetry. The glass transition temperature and melting point of the polydodecenamer are 19.6°C and 70.0°C respectively. Furthermore, cyclododecene has been polymerized into a low‐molecular‐weight polymer (12.0 × 10³) with a polydispersity of 2.06 in high yields (94%). IR and NMR analysis indicate that the polydodecenamer has a high trans content (60%). Copyright © 2004 John Wiley & Sons, Ltd.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). V. Kinetics of initial template polymerization

The influence of stereoregular poly(methyl methacrylate) (PMMA) as a polymer matrix on the initial rate of radical polymerization of methyl methacrylate (MMA) has been measured between ?11 and +60°C using a dilatometric technique. Under proper conditions an increase in the relative initial rate of template polymerization with respect to a blank polymerization was observed. Viscometric studies showed that the observed effect could be related to the extent of complex formation between the polymer matrix and the growing chain radical. The initial rate was dependent on tacticity and molecular weight of the matrix polymer, solvent type and polymerization temperature. The accelerating effect was most pronounced (a fivefold increase in rate) at the lowest polymerization temperature with the highest molecular weight isotactic PMMA as a matrix in a solvent like dimethylformamide (DMF), which is known to be a good medium for complex formation between isotactic and syndiotactic PMMA. The acceleration of the polymerization below 25°C appeared to be accompanied by a large decrease in the overall energy and entropy of activation. It is suggested that the observed template effects are mainly due to the stereoselection in the propagation step (lower activation entropy Δ S_p^?) and the hindrance of segmental diffusion in the termination step (higher activation energy Δ E_t^?) of complexed growing chain radicals.     

Atom Transfer Radical Polymerization of Styrene Using Multifunctional Iniferter Reagents as Initiators

Summary: Two multifunctional iniferters, 1,4-bis-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (BDCIB) and 1,3,5-tris-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (TDCIB), were successfully synthesized and used as initiators to initiate the polymerization of styrene in the presence of a CuBr/PMDETA complex. The polymerization results demonstrated that the kinetic plots in all cases were first-order to the monomer, the molecular weight of the polymers increased linearly with the monomer conversion; meanwhile, the molecular weight distribution of the polymer was kept to a very low value (M_w/M_n ≤ 1.35). Furthermore, the measured molecular weights were very close to the calculated values, which indicated the high efficiency of the initiator for the polymerization of styrene. The effect of catalyst concentration and initiator concentration was not obvious and the influence of polymerization temperature was apparent, and the polymerization rate increased with the polymerization temperature. The results of chain-extension and ¹H NMR analysis proved that the polymer obtained was capped with diethylthiocarbamoylthiy (DC) group.     

Synthesis of novel polymer containing selenium by radical addition polymerization of 1,4-benzenediselenol to 1,4-divinylbenzene

A novel addition polymerization of 1,4-benzenediselenol (BDSe) to 1,4-divinylbenzene (DVB) was carried out with various azo radical initiators [dimethyl 2,2′-azobisisobutyrate (DAIB), 1,1′-azobis(1-acetoxy-1-phenylethane) (AAPE), and AIBN] in toluene at 65 and 75°C under a nitrogen atmosphere. The polymerization proceded without an induction period, and pale-yellowish powder polymers were obtained in 89% yields for 75 h (DAIB), 89% yields for 24 h (AAPE), and 60% yields for 8 h (AIBN). The molecular weight (M_w) of the insoluble polymers in toluene was about 4000 (IBN) to 14,000 (DAIB or AAPE) by GPC. The polymer had an alternating structure of BDSe to DVB units by ¹H-NMR, IR analyses, and selenium contents, but the polymer contained the diselenide linkage by Raman spectroscopy. By AIBN initiator, the yield of the polymers did not increase over 60% and higher molecular weight polymer was hardly obtained. According to the model addition reaction of benzeneselenol to styrene by AIBN, it was found that AIBN was consumed by the side reaction between dimethyl-N-(2-cyano-2-propyl)ketenimine derivedAppl 11 from AIBN and benzeneselenol to give the adduct C, MH⁺ 295 by DCI MS. On the other hand, DAIB and AAPE initiators, which do not form a ketenimine intermediate, gave the polymers of higher molecular weight in a higher yield. The polymer film exhibited high refractive index (n²⁵_D = 1.81) and a reversible phase transition between a transparency and an opaque by thermal mode. © 1994 John Wiley & Sons, Inc.     

Synthesis of highly branched polyethylene using para‐phenyl‐substituted α‐diimine nickel catalysts

A series of para‐phenyl‐substituted α‐diimine nickel complexes, [(2,6‐R₂‐4‐PhC₆H₂N═C(Me))₂]NiBr₂ (R = ⁱPr ( 1 ); R = Et ( 2 ); R = Me ( 3 ); R = H ( 4 )), were synthesized and characterized. These complexes with systematically varied ligand sterics were used as precatalysts for ethylene polymerization in combination with methylaluminoxane. The results indicated the possibility of catalytic activity, molecular weight and polymer microstructure control through catalyst structures and polymerization temperature. Interestingly, it is possible to tune the catalytic activities ((0.30–2.56) × 10⁶ g (mol Ni·h)^?1), polymer molecular weights (M_n = (2.1–28.6) × 10⁴ g mol^?1) and branching densities (71–143/1000 C) over a very wide range. The polyethylene branching densities decreased with increasing bulkiness of ligand and decreasing polymerization temperature. Specifically, methyl‐substituted complex 3 showed high activities and produced highly branched amorphous polyethylene (up to 143 branches per 1000 C).     

Synthesis and Characterization of Poly(allyl methacrylate) Obtained by Free Radical Initiator

Allyl methacrylate was polymerized in CCl₄ solution by α,α′‐azoisobutyronitrile at 50, 60, and 70°C. The kinetic curves were auto‐accelarated types at 60 and 70°C, but almost linear at 50°C. Arrhenius activation energy was 77.5 kJ/mol. The polymer was insoluble in common organic solvents. It was characterized by FT‐IR, NMR, DSC, TGA and XPS methods. About 98–99% of allyl side groups were remained as pendant even after completion of the polymerization. The spectroscopic and thermal results showed that polymerization is not a cyclopolymerization type, but may have end group cyclization. The high molecular weight is the main cause of a polymer being insoluble even in the early stage of the polymerization. Molecular weight of 1.1×10⁶ for a soluble polymer fraction was measured by light scattering method. The Tg of polymer was 94°C, and after curing at 150–200°C, increased to 211°C. The thermal pyrolysis of polymer at about 350°C gave an anhydride by linkage type degradation, and side group cyclization. The XPS analysis showed the presence of radical fragments of AIBN (initiator) and CCl₄ (solvent) associated with oligomers.     

Polymers from 1,2-Disubstituted Ethylenic Monomers. IX. Radical High Polymerization of Methyl-tert-butyl Fumarate

Methyl-tert-butyl fumarate (MtBF) was found to homopolymerize in bulk in the presence of 2,2′-azobisisobutyronitrile (AIBN) at 50–80°C to give a high molecular weight polymer. From IR, ¹H-NMR and ¹³C-NMR spectra, this polymer was assumed to consist of alternating methoxycarbonylmethylene and tert-butoxycarbonylmethylene units, indicating that it was produced from MtBF through an ordinary vinylene polymerization mechanism. Consideration of a molecular model suggested that this polymer had a less flexible rodlike structure with the diameter of about 13.5 Å. The thermal properties of this polymer were also evaluated. Moreover, the bulk polymerization of MtBF initiated by AIBN was investigated kinetically at 60°C. The overall activation energy for this polymerization was determined to be 83.5 kJ/mol. The reaction orders with respect to the monomer and initiator concentrations were obtained as 2.0 and 0.33, respectively.     

Poly(lactic acid) Synthesis in Solution Polymerization

The step-growth polymerization of L-lactic acid in solution was studied in this work. In order to attain a polymer with high molecular weight, the water formed during the polymerization must be continuously removed. The use of organic solvents with high boiling point, drying agents and reduced pressure led to poly(lactic acid) (PLA) with high molecular weight, directly from the monomer. Tin (II) chloride dihydrate, SnCl₂.2H₂O, was the best of the catalysts tested as it allowed achieving PLA with a molecular weight close to 80 000 g.mol⁻¹. However, the stereoregurarity control is a severe problem in PLA synthesis by step-growth due to transesterification reactions, which lead to an inversion of the conformation and a decrease of the optical purity of the polymer. Specific rotation measurements were used in this work and showed to be a powerful technique to evaluate the racemization extent. The thermal stability of the PLA samples was evaluated by DSC which exhibits a thermal behaviour similar to the commercial Polylactide.     

Synthesis and kinetic analysis of DPE controlled radical polymerization of MMA

The 1,1‐diphenylethene (DPE) controlled radical polymerization of methyl methacrylate was performed at 80 °C by using AIBN as an initiator and DPE as a control agent. It was found that the molecular weight of polymer remained constant with monomer conversion throughout the polymerization regardless of the amounts of DPE and initiator in formulation. To understand the result of constant molecular weight of living polymers in DPE controlled radical polymerization, a living kinetic model was established in this research to evaluate all the rate constants involved in the DPE mechanism. The rate constant k₂, corresponding to the reactivation reaction of the DPE capped dormant chains, was found to be very small at 80 °C (1 × 10^?5 s^?1), that accounted for the result of constant molecular weight of polymers throughout the polymerization, analogous to a traditional free radical polymerization system that polymer chains were terminated by chain transfer. The polydispersity index (PDI) of living polymers was well controlled <1.5. The low PDI of obtained living polymers was due to the fact that the rate of growing chains capped by DPE was comparable with the rate of propagation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Atom transfer radical polymerization of methyl methacrylate using copper-based homogeneous and heterogeneous catalysts

This study aimed at polymerization of methyl methacrylate with novel catalysts in the atom transfer radical polymerization (ATRP) condition at 90 °C. This was accomplished using CuBr/N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (CuBr–AEAPTMS) as a homogeneous catalyst and one time with CuBr@AEAPTMS/SBA-15 as a heterogeneous catalyst. Catalysts were characterized using TGA, FT-IR, and UV–Vis spectroscopy. The structural analysis of the polymer was carried out by ¹³C NMR spectroscopy and GPC. Three characteristic parts of polymer produced by ATRP method including the initiator, monomer units, and end group was shown in ¹³C NMR spectra. In addition, the presence of C–Br unit showed that the polymerization process is alive. The ¹H NMR analysis was used for kinetic investigation of methyl methacrylate polymerization with homogeneous and heterogeneous catalysts that showed high monomer conversion (98 and 90% after 35 min, respectively) and good control of molecular weight with a dispersity (Р= 1.5–1.7). In addition, the plot of ln ([monomer]₀/[monomer] _t ) versus time gave linear relationships indicating a constant concentration of the propagating species throughout the polymerization. Finally, the results of the polymerization using heterogeneous catalyst compared with homogeneous catalyst revealed that it was according to ATRP method.