Effects of acids on vinyl polymerization initiated by chromous acetate-alkyl halide

Effects of various acids, i.e., acetic, chloroacetic, hydrochloric, and sulfuric acids on the polymerization of styrene initiated by Cr²⁺–CHCl₃ in DMF was studied. These acids reduced the rates of polymerization by Cr²⁺–CHCl₃ initiator systems. This phenomenon could be explained by a decrease of the reducing power of Cr²⁺ for alkyl halide. On the other hand, chloroacetic acids could initiate the polymerization of styrene without CHCl₃ because these acids have active chlorine in the molecule for Cr²⁺. It was found that the polymer obtained by this initiator system had an endgroup containing chromium carboxylate, therefore this polymer was green in color and insoluble in benzene.     

Effects of ligands on the “living” radical polymerization initiated by the aged Cr2+ plus benzoyl peroxide system

The “living” radical polymerization of methyl methacrylate with the aged Cr²⁺ plus benzoyl peroxide (BPO) system in the presence of various amines as ligand has been studied in N,N′-dimethylformamide. Aliphatic amines such as ethylenediamine diminished the rate of polymerization, while dipyridyl (dipy) and o-phenanthroline (phen) accelerated the polymerization rate as follows: phen > dipy > pyridine ? none. Specifically, the rate of polymerization in the presence of phen had a maximum value at [phen]/[Cr²⁺] = 0.5. The retardation of polymerization by aliphatic amines was explained by the interaction of BPO with free and coordinated amines. The latter result may support the mechanism involving the complexed radical proposed for the living radical polymerization with the aged Cr²⁺ + BPO system. In the presence of phen the effects of aging period and aging temperature as well as polymerization temperature were studied and the nature of complexed radicals is discussed.     

The structure of copolymers of vinyl cyclohexane with styrene

Copolymerization of vinyl cyclohexane (monomer-1) with styrene was investigated in the presence of the stereospecific complex catalyst TiCl₃ + Al(iso-C₄H₉)₃. Monomer reactivity ratios were r₁ = 0·177 ± 0·051 and r₂ = 2·117 ± 0·370. The monomer unit distributions in the copolymers were estimated by comparison of the i.r.-spectra of copolymers and the isotactic homopolymers using absorption bands at 565 and 1084 cm^?1 which correspond to the vibrations of styrene blocks containing ? 5 styrene units and the band at 985 cm^?1 characterizing polystyrene crystallinity. The data indicate the tendency towards alternation in the copolymerization. Analysis of the experimental and literature data led to the conclusion that distribution of the units in copolymers of vinyl cyclohexane with α-olefins is determined by the nature of the α-olefin. The following activity series is proposed for α-olefins in their copolymerization with vinyl cyclohexane in the presence of catalytic systems based on titanium salts and organo-aluminium compounds: propylene >; 4-methylpentene-1 >; styrene >; 3-methylbutene-1 ～ vinyl cyclohexane.     

Crown Ether As The Phase-Transfer Catalyst for Free Radical Polymerization of Hydrophobic Vinyl Monomers

Various crown ethers were used as phase-transfer catalysts for free radical polymerizations of some water-insoluble vinyl monomers such as acrylonitrile, methylmethacrylate and styrene with persulfate as initiator. The catalytic abilities of these crown ethers for free radical polymerization of acrylonitrile with S₂O₈^2?ion as an initiator were in the order: 18-crown-6 > 15-crown-4 > 12-crown-4 > benzo-15-crown-5 > dibenzo-18-crown-6. Among various persulfates such as Na₂S₂O₈ K₂S₂O₈ and (NH₄)₂S₂O₈, ammonium persulfate was the optimum initiator for the polymerization of acrylonitrile catalyzed by 18-crown-6 or 15-crown-5. Among the organic solvents used, chloroform seems to be the best solvent for the catalytic polymerization of acrylonitrile. An apparent activation energy of 72.9 kJ mol^?1 was observed for the polymerization of acrylonitrile. The catalytic reaction rates of free radical polymerization for these hydrophobic vinyl monomers were in the order: acrylonitrile > methylmethacrylate > styrene > isoprene. Effects of concentrations of crown ether, initiator, and nitrogen on the polymerization of these vinyl monomers were investigated.     

Synthesis and characterization of amphiphilic diblock copolymer of polystyrene and polyvinyl alcohol using ethanolamine–benzophenone as photochemical binary initiation system

Amphiphilic diblock copolymers of polyvinyl alcohol (PVA) and polystyrene (PS), which are very difficult to prepare by common polymerization methods, have been obtained by initiation of the polymerization of styrene and vinyl acetate successively, followed by hydrolysis, using the ethanolamine–benzophenone (BP) charge-transfer complex (CTC). The effects of solvents, concentration of monomer, BP, ethanolamine, and PS prepolymer, with a reactive imino group (PS_a), on the photo-induced charge-transfer polymerization (CTP) of St and block copolymerization of VAc are discussed. The copolymer of PS-b-PVAc and the hydrolyzed product, PS-b-PVA, were characterized by FTIR, NMR, and GPC in detail. The effect of PS chain length on the crystallization of PVA was described. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 109–115, 1998     

Fabrication of polymer‐modified magnetic nanoparticle based adsorbents for the capture and release of quinolones by manipulating the metal–coordination interaction

Functional polymers with a metal–coordination interaction have been fabricated for sample pretreatment. Poly(N‐4‐vinyl‐benzyl iminodiacetic acid‐co‐methacrylic acid‐co‐styrene)‐modified magnetic nanoparticles were prepared and used as solid‐phase extraction adsorbents for the analysis of quinolones by tuning the metal–coordination interaction. In the construction of the polymer‐based adsorbents, functional monomer (N‐(4‐vinyl)‐benzyl iminodiacetic acid) and comonomers (methacrylic acid and styrene) were fabricated onto the magnetic nanoparticles by free radical polymerization. Factors affecting the performance of the adsorbents were investigated, and the results revealed that Fe³⁺ played a vital role in the formation of metal–coordination adsorbents. Compared with other compounds, the resultant adsorbents displayed good selectivity to quinolones due to the metal–coordination complex (N‐4‐vinyl‐benzyl iminodiacetic acid‐Fe³⁺‐quinolones). Interestingly, the captured quinolones could be rapidly released by manipulating the metal–coordination interaction with Cu²⁺. The linearity range for analysis of the test quinolones was 0.025–2.0 μg/mL (R² > 0.999), and the recovery varied from 80.0 to 100.7%. Further, the proposed adsorbents were combined with high‐performance liquid chromatography for the analysis of quinolones in real urine samples. The results demonstrated that the prepared adsorbents have good selectivity and sensitivity for quinolones, showing great potential for drug analysis in real samples.     

Photopolymerization with the use of titanocene dichoride as sensitizer

Titanocene dichloride sensitized photopolymerization of vinyl ethers and styrene but did not polymerize methyl methacrylate and vinyl acetate. In the case of 2-chloroethyl vinyl ether, polymerization started rapidly some time after the color of the liquid had changed from orange to green. Polymerization was also achieved by heating the monomer at 60°C after stopping the irradiation at the end of the induction period. On the basis of the reactivity of the monomers and the effect of additives, polymerization is considered to proceed cationically. In case of the polymerization of styrene, conversion increased linearly with time. The k/k_t value of 6.3 × 10^?5l./mole-sec obtained for the polymerization of styrene agrees well with the value reported for radical polymerization. The agreement of the value and ineffective inhibition of polymerization in the presence of pyridine indicates the polymerization follows a radical mechanism. Copolymerization of styrene (M₁) and 2-chloroethyl vinyl ether (M₂) proceeded radically, and the reactivity ratios were r₁ = 2.5 and r₂ = 0.6.     

Chain-transfer constant of fluoroalcohols

Chain transfer constants of some fluoroalcohols [HCF₂(CF₂)_n?1CH₂OH, n = 2, 4, 6] in the catalyzed polymerization of vinyl acetate, styrene, acrylonitrile, and methyl methacrylate at 60°C have been evaluated by a method based on degree of polymerization. Since fluoroalcohols are normally nonsolvents for polymers, a homogeneous reaction phase is maintained by carrying out the polymerization in benzene (except in case of acrylonitrile, where no solvent was used). The transfer constants vary, depending on the reactivity as well as the polarity of the radicals, in the following order: vinyl acetate > styrene > methyl methacrylate > acrylonitrile. Of the three fluoroalcohols studied, the transfer constants increase with the increasing value of n. The results have been interpreted in terms of polar structure contribution in the transition state of the transfer reactions.     

Determination of the complex formation constants for some water-soluble polymers with trivalent metal ions by differential pulse polarography

The formation of metal complexes between water-soluble polymers, poly(vinyl alcohol) [PVA], poly(N-vinylpyrrolidone) [PVP], poly(acrylamide) [PAAm] and poly(ethylene oxide) [PEO] with trivalent metal ions, Fe³⁺, Cr³⁺, and V³⁺ were studied by using differential pulse polarography (DPP). The general experimental observation is the shift of totally reversible reduction peaks (M³⁺+Hg+e^–M²⁺+Hg) towards more negative potentials when the complexing water-soluble polymers are added to the solution of trivalent metal ions. The negative shift in potential permitted the determination of complex formation constants (K_f) between trivalent metal ions and water soluble polymers. The complex formation constants for Fe³⁺, Cr³⁺, and V³⁺ ions with these polymers increased in the order of V³⁺>Cr³⁺>Fe³⁺.     

Photocatalytic selective oxidation of CO with O2 in the presence of H2 over highly dispersed chromium oxide on silica under visible or solar light irradiation

A highly dispersed Cr⁶⁺-oxide species on silica (Cr/SiO₂) was found to act as an efficient photocatalyst for the selective oxidation of CO into CO₂ with O₂ in the presence of H₂ under visible (λ>420 nm) or solar light irradiation at 293 K. UV-Vis, photoluminescence and FT-IR investigations revealed that the selective reactivity of the photoexcited tetrahedral Cr⁶⁺-oxide species ([Cr⁵⁺−O⁻]^*) with CO, as well as the high reactivity of the photoreduced Cr⁶⁺-oxide species (Cr⁴⁺-oxide species) with O₂ both play significant roles in this reaction.     

Thermal Decomposition of Chloromethylated Poly(styrene)-PAN Resin and Its Complexes with Some Transition Metal Ions

The complexes formed by the chemically modified chloromethylated poly(styrene)-PAN (CMPS-PAN) as a resin chelating ion exchanger were characterized by infrared and potentiometry. The thermal degradation of pure CMPS-PAN resin and its complexes with Au³⁺, Cr³⁺, Cu²⁺, Fe³⁺, Mn²⁺ and Pt⁴⁺ in air atmosphere has been studied using thermal gravimetry (TG) and derivative thermal gravimetry (DTG). The results showed that four different steps accompany the decomposition of CMPS-PAN resin and its complexes with the metal ions. These stages were affected by the presence of the investigated metal ions. The thermal degradation of CMPS-PAN resin in the presence of the ions showed different stability of the resin in the following decreasing order: Au³⁺>Pt⁴⁺>Mn²⁺>Cu²⁺>Cr³⁺>Fe³⁺. On the basis of the applicability of a non-isothermal kinetic equation, the decomposition process was a first-order reaction. The activation energy, Ea, the entropy change, ΔS ^*, the enthalpy change, ΔH ^* and the Gibbs free energy of activation, ΔG ^* were calculated by applying the theory of the reaction rates. The effect of the different central metal ions on the calculated thermodynamic activation parameters was discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the hydrolytic polymerization of chromium (III) ion: IX. Revision of graphical method for the reaction in the presence of maleic acid by computer

The hydrolytic polymerization of Cr²⁺ in the presence of maleic acid was studied by equilibrium pH method at 60°C and constant ionic strength. Both maleic acid and Cr³⁺ are of three different concentrations: 0.006, 0.008, 0.01 mol·L^?1. The state of Cr³⁺ in aqueous solution were determined by graphical method and pqr analysis. The following species were found (CrA)^+, Cr-(OH)A and Cr₂(OH)₂A₂. The results by graphical method were revised by computer calculation with data of about fifty experimental points. Hydrolysis constants of all species were obtained with good fitting. It is obvious that the results obtained by program LEMIT are more accurate than those by graphical method. Mechanism of Cr³⁺ polymerization in the presence of maleic acid is also discussed.     

Photoinitiation. IV. The effect of lewis acid on the vinyl monomer polymerization photoinitiated by aromatic hydrocarbons

Polymerization of acrylonitrile photoinitiated by naphthalene, anthracene, phenanthrene, and pyrene is accelerated by an admixture of zinc (II) chloride, acetate, or nitrate. The effect of zinc (II) salts on the rate of pyrene-photoinitiated polymerization of acrylonitrile leads to an increase in this rate in the order Zn/OCOCH_3/2 < ZnCl₂ < Zn/NO_3/2. The maximum polymerization rate is achieved at the molar ratio [ZnCl₂]/([ZnCl₂] + [pyrene]) approximately 0.7. In contrast to the photoinitiated polymerization of acrylonitrile, the methyl methacrylate admixture of zinc (II) chloride exerts a smaller effect on the polymerization rate. In the pyrene-photoinitiated polymerization of styrene an admixture of zinc (II) chloride retards the polymerization rate. Fluorescence of aromatic hydrocarbon in the system acrylonitrile–aromatic hydrocarbon is efficiently quenched by zinc (II) chloride. Stern–Volmer constants determined for pyrene (80 dm³ mole^?1), phenanthrene (66 dm³ mole^?1), and naphthalene (49 dm³ mole^?1) are higher by about 2–3 orders of the Stern–Volmer constants for fluorescence quenching of aromatic hydrocarbons by acrylonitrile in the absence of ZnCl₂. The fluorescence of anthracene in acrylonitrile is not quenched by ZnCl₂. The acceleration effect of Zn (II) salts on the polymerization of acrylonitrile photoinitiated by aromatic hydrocarbons depends on two factors: an increase in the ratio of the rate constant of the growth and termination reactions, k_p/k_t, and an increase in the quenching constant of fluorescence of aromatic hydrocarbon, k_q, by the complex {acrylonitrile…ZnCl₂}. ZnCl₂ thus influences both the growth and initiation reactions of the polymerization process.     

Polymerization of substituted acetylenes by various rhodium catalysts: Comparison of catalyst activity and effect of additives

This research deals with comparison of the activity of various Rh catalysts in the polymerization of monosubstituted acetylenes and the effect of various amines used in conjunction with [Rh(nbd)Cl]₂ in the polymerization of phenylacetylene. A zwitterionic Rh complex, Rh⁺(nbd)[(η⁶‐C₆H₅)B^?(C₆H₅)₃] ( 3 ), was able to polymerize phenylacetylene ( 5a ), t‐butylacetylene ( 5b ), N‐propargylhexanamide ( 5c ) and n‐hexyl propiolate ( 5d ), and displayed higher activity than the other catalysts examined, that is [Rh(nbd)Cl]₂ ( 1 ), [Rh(cod)(O‐o‐cresol)]₂ ( 2 ), and Rh‐vinyl complex ( 4 ). Monomers 5a and 5c polymerized virtually quantitatively or in fair yields with all these catalysts, while monomer 5b was polymerizable only with catalyts 3 and 4 . Monomer 5d did not polymerize in high yields with these Rh complexes. The catalytic activity tended to decrease in the order of 3 > 4 > 2 > 1 . Although polymerization of 5a did not proceed at all in toluene with [Rh(nbd)Cl]₂ alone, it smoothly polymerized in the presence of various amines as cocatalysts. The polymerization rate as well as the molecular weight of polymer depended on the basicity and steric bulkiness of amines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4530–4536, 2005     

Chiral model complexes for methane monooxygenase and their asymmetric catalysis of styrene epoxidation

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Polymerization of Acrylonitrile Initiated by the Thiourea-Mn3+ Redox System

Kinetics of vinyl polymerization initiated by the redox system thiourea-Mn³⁺ were investigated in the temperature range 30–40°C in sulfuric acid, and the rates of polymerization R_p and disappearance of Mn³⁺ have been measured. The effect of certain water-miscible organic solvents and anionic surfactant on the rates of polymerization was investigated. A mechanism involving the formation of a complex between Mn³⁺ and thiourea whose decomposition yields the initiating free radical with the polymerization terminated by mutual intraction of growing radicals is suggested.     

Anionic polymerization of styrene in the presence of different anisoles

The butyllithium-initiated polymerization of styrene has been studied in toluene solution at 20°C in the presence of anisole, o-ethylanisole, and p-ethylanisole. The concentration of styrene was 0.16 mole/1.; the concentration of ether varied from 0.8 to 0.33 mole/1. The rates of initiation were followed spectrophotometrically at γ_max 330 mμ; they increased with increasing concentration of ether. The rates of propagation were measured dilatometrically. In the presence of anisole and p-ethylanisole, the rate expression is R_p = [M][PLi]^1/2(k₁ + k₂ [ether]), where k₁ is the propagation rate constant in pure hydrocarbon, k₂ that of the ether solvated chain end, and [PLi] denotes the concentration of polystyryllithium. On the contrary, o-ethylanisole did not affect the rate of propagation of styrene, possibly on account of the steric hindrance of the o-ethyl group. The apparent first-order termination rate constants were also determined spectrophotometrically at 20°C and compared to those of poly-o- and p-methoxystyryllithium. The following decreasing order of rate constant was found: poly-p-methoxystyryllithium > polystyryllithium-anisole > polystyryllithium–4-ethylanisole > polystyryllithium-2-ethylanisole > poly-o-methoxystyryllithium.     

Synthesis of poly(vinyl acetate)‐graft‐polystyrene by a combination of cobalt‐mediated radical polymerization and atom transfer radical polymerization

Vinyl acetate and vinyl chloroacetate were copolymerized in the presence of a bis(trifluoro‐2,4‐pentanedionato)cobalt(II) complex and 2,2′‐azobis(4‐methoxy‐2,4‐dimethylvaleronitrile) at 30 °C, forming a cobalt‐capped poly(vinyl acetate‐co‐vinyl chloroacetate). The addition of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy after a certain degree of copolymerization was reached afforded 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐terminated poly(vinyl acetate‐co‐vinyl chloroacetate) (PVOAc–MI; number‐average molecular weight = 31,000, weight‐average molecular weight/number‐average molecular weight = 1.24). A ¹H NMR study of the resulting PVOAc–MI revealed quantitative terminal 2,2,6,6‐tetramethyl‐1‐piperidinyloxy functionality and the presence of 5.5 mol % vinyl chloroacetate in the copolymer. The atom transfer radical polymerization (ATRP) of styrene (St) was studied with ethyl chloroacetate as a model initiator and five different Cu‐based catalysts. Catalysts with bis(2‐pyridylmethyl)octadecylamine (BPMODA) or tris(2‐pyridylmethyl)amine (TPMA) ligands provided the highest initiation efficiency and best control over the polymerization of St. The grafting‐from ATRP of St from PVOAc–MI catalyzed by copper complexes with BPMODA or TPMA ligands provided poly(vinyl acetate)‐graft‐polystyrene copolymers with relatively high polydispersity (>1.5) because of intermolecular coupling between growing polystyrene (PSt) grafts. After the hydrolysis of the graft copolymers, the cleaved PSt side chains had a monomodal molecular weight distribution with some tailing toward the lower number‐average molecular weight region because of termination. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 447–459, 2007     

Effect of alkyl substituents on initiator activity in cationic polymerization of styrene with p-methoxybenzyldialkylsulfonium salts as initiators

The effect of alkyl substituents on cationic polymerization of styrene with p-methoxybenzyldialkysulfonium salts was studied. p-Methoxybenzyl tetramethylene ( 1 ), dimethyl ( 2 ), diethyl ( 3 ), dibuty ( 4 ), and diisopropylsulfonium salts ( 5 ) were synthesized by the reaction of p-methoxybenzyl bromide with the corresponding sulfides, followed by exchange of the counter anion Br^? with SbF^?₆. These sulfonium salts served as potent cationic thermal initiators of which activity was estimated by the bulk and solution polymerizations of styrene. The bulk polymerizations with 1–4 (0.1 mol %) for 30 min gradually proceeded at 30–50°C, but the exothermic polymerization occurred vigorously at 40–60°C. The Polymerization with 5 took place exothermically even at room temperature. Temperature-conversion curves of the polymerizations for 30 and 5 min revealed that the activity of the sulfonium salts was in the following order: 5 > 4 > 3 > 2 ≈ 1 . This order was explained by the order of the bulkiness of the alkyl substituents on the sulfur atom. Number-average molecular weight (M?_n) of polystyrene obtained by the polymerization undergoing no exothermic process was in a range of 6600–16000, which depended on the structure of the alkyl substituents: the more bulky the substituent was, the higher M?_n was.     

Synthesis of isotactic polystyrene with a rare-earth catalyst

Polymerization of styrene with the neodymium phosphonate Nd(P₅₀₇)/H₂O/Al(i-Bu)₃ catalytic system has been examined. The polymer obtained was separated into a soluble and an insoluble fraction by 2-butanone extraction. ¹³C-NMR spectra indicate that the insoluble fraction is isotactic polystyrene and the soluble one is syndiotactic-rich atactic polystyrene. The polymerization features are described and discussed. The optimum conditions for the polymerization are as follows: [Nd] = (3.5–5.0) × 10⁻² mol/L; [styrene] = 5 mol/L; [Al]/[Nd] = 6–8 mol/mol; [H₂O]/[Al] = 0.05–0.08 mol/mol; polymerization temperature around 70°C. The percent yield of isotactic polystyrene (IY) is markedly affected by catalyst aging temperature. With increase of the aging temperature from 40 to 70°C, IY increases from 9% to 48%. Using AlEt₃ and Al(i-Bu)₂H instead of Al(i-Bu)₃ decreases the yield of isotactic polystyrene. Different neodymium compounds give the following activity order: Nd(P₅₀₇)₃ > Nd(P₂₀₄)₃ > Nd(OPrⁱ)₃ > NdCl₃ + C₂H₅OH > Nd(naph)₃. With Nd(naph)₃ as catalyst, only atactic polystyrene is obtained. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1773–1778, 1998