Effects of reaction conditions on laccase‐catalyzed α‐naphthol polymerization

Enzymatic oxidative polymerization of α‐naphthol was carried out batch‐wise with the laccase enzyme, produced by Trametes versicolor (ATCC 200801). The polymerization reaction was conducted in a closed, temperature controlled system containing acetone (solvent) and sodium acetate buffer for pH control. The effects of the organic solvent (acetone) composition, monomer (α‐naphthol) and enzyme concentrations, buffer pH and temperature on the polymerization rate were investigated with respect to initial reaction conditions and depletion rate of dissolved oxygen. The optimum acetone composition, pH, monomer, dissolved oxygen and enzyme concentrations were determined as 50% (v/v), 5, 3409 gm⁻³, 20.3 gm⁻³ and 0.173 U cm⁻³, respectively; these values provided the most desirable conditions for initial reaction rate. Temperature rise supported the rate increase up to 37 °C, after which the rate tended to be stable due to a drop in dissolved oxygen concentration. The product polymer, poly(α‐naphthol), with an average molecular weight of 4920 Da was soluble in common organic solvents. © 2000 Society of Chemical Industry     

Degradation and initiation polymerization mechanism of α‐methylstyrene‐containing macroinitiators

Copolymers obtained from radical copolymerization of α‐methylstyrene (AMS) and glycidyl methacrylate (GMA) behave as macroinitiators, when heated in the presence of a second monomer, giving rise to block copolymers. The relevant degradation and initiation polymerization mechanism of the macroinitiators were studied. Thermal depropagation of the macroinitiators generated monomers, identified by ¹H‐NMR, photoionization mass spectroscopy and FT‐IR. According to the results of structure analysis by GPC, ESR and NMR spectroscopy, the AMS‐GMA (head‐head) and AMS‐AMS (head‐head) bonds in the macroinitiators are easily scissored providing free radicals when the temperature is above 80°C. The radicals lead to subsequent polymerization of the second monomer, and thereby block copolymers are formed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Copolymerization of styrene with an α‐olefin via atom transfer radical polymerization

This investigation reports the preparation of styrene–α‐olefinic random copolymers, using 1‐octene as an α‐olefin, via atom transfer radical polymerization. Atom transfer radical copolymerization of styrene with 1‐octene was successfully carried out using phenylethyl bromide as initiator and CuBr as catalyst in combination with N, N, N′, N″, N″‐pentamethyldiethylenetriamine as ligand. The copolymers had controlled molecular weight, narrow dispersity and well‐defined end groups with significant 1‐octene incorporation in the polymer. Incorporation of 1‐octene in the copolymers was confirmed using ¹H NMR and matrix‐assisted laser desorption ionization time‐of‐flight mass spectroscopy. An increase in 1‐octene content in the monomer feed led to an increase in the level of incorporation of the α‐olefin in the copolymer. An increase in the concentration of 1‐octene led to a decrease in the rate of polymerization and an increase in dispersity. The glass transition temperature of the copolymer gradually decreased as the incorporation of 1‐octene increased. Copyright © 2011 Society of Chemical Industry     

Atom‐transfer radical polymerization of methyl methacrylate with α,α′‐dichloroxylene/CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine initiation system under microwave irradiation

The atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA), using α,α′‐dichloroxylene as initiator and CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst was successfully carried out under microwave irradiation (MI). The polymerization of MMA under MI showed linear first‐order rate plots, a linear increase of the number‐average molecular weight with conversion, and low polydispersities, which indicated that the ATRP of MMA was controlled. Using the same experimental conditions, the apparent rate constant (k) under MI (k = 7.6 × 10^?4 s^?1) was higher than that under conventional heating (k = 5.3 × 10^?5 s^?1). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2189–2195, 2004     

Rapid living free‐radical polymerization of methyl acrylate under 60Co γ‐ray irradiation at room temperature

Rapid living free‐radical polymerization of methyl acrylate under ⁶⁰Co γ‐ray irradiation in the presence of benzyl 1H‐imidazole‐1‐carbodithioate at room temperature is reported. The results showed that the polymerization is a fast living process, and that the molecular weight of the polymer is as high as 39 600 g mol^?1 at 68 % conversion with M_w/M_n = 1.09 within 68 min. The polymerization rate was markedly influenced by the structures of thiocarbonylthio compounds. Copyright © 2004 Society of Chemical Industry     

Synthesis of ω‐amino‐α‐phenylcarbonate alkanes and their polymerization to [n]‐polyurethanes

Aliphatic [n]‐polyurethanes have recently been synthesized from ω‐isocyanato‐α‐alkanols or, more traditionally, by cationic ring‐opening polymerization of cyclourethanes or by the Bu₂Sn(OMe)₂‐promoted polycondensation of ω‐hydroxy‐α‐O‐phenylurethane alkanes. For the latter procedures, the conditions employed do not seem to be suitable for highly functionalized monomers. In contrast, the polymerization of ω‐amino‐α‐phenylcarbonate alkanes is expected to occur under milder conditions. ω‐Amino‐α‐phenylcarbonate alkanes have been synthesized from 6‐aminohexanol (1) and 3‐aminopropanol (6). The procedure involves the N‐Boc protection of the amino group, followed by activation of the alcohol. Removal of the N‐Boc affords the corresponding ω‐amino‐1‐O‐phenyloxycarbonyloxyalkane hydrochlorides. Other oligomeric comonomers between 1 and 6 have been prepared. The polymerization of these precursors takes place in the absence of metal catalysts to afford the corresponding linear and regioregular [n]‐polyurethanes. The procedure described is useful for the preparation of stable ω‐amino‐α‐phenylcarbonate alkane derivatives, which possess varied chain lengths between the terminal functions. These monomers yield [n]‐polyurethanes having various structures starting from just two aminoalkanols. The polyurethanes were obtained in high yields, with reasonable molecular weight and polydispersity values, and they were characterized spectroscopically and thermally. These studies reveal constitutionally uniform structures that are free of carbonate or urea linkages. Copyright © 2010 Society of Chemical Industry     

Direct Decarboxylative Alkynylation of α,α‐Difluoroarylacetic Acids under Transition Metal‐Free Conditions

An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K₂S₂O₈)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.

     

Maghnite‐H+, a solid catalyst for the cationic polymerization of α‐methylstyrene

The polymerization of α‐methylstyrene (AMS) catalyzed by Maghnite‐H⁺ (Mag‐H) was investigated. Mag‐H is a montmorillonite sheet silicate clay, exchanged with protons. It was found that the cationic polymerization of AMS is initiated by Mag‐H at ambient temperature in bulk and in solution. The effect of the amount of Mag‐H, the temperature, and the solvent was studied. The polymerization rate increased with increase in the temperature and the proportion of catalyst, and it was larger in nonpolar solvents. These results indicated the cationic nature of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from Mag‐H. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cationic copolymers of α,β‐poly‐(N‐2‐hydroxyethyl)‐DL‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy): synthesis and characterization

In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry     

Highly Enantioselective Phase‐Transfer Catalytic α‐Alkylation of α‐tert‐Butoxycarbonyllactams: Construction of β‐Quaternary Chiral Pyrrolidine and Piperidine Systems

A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers.     

Lipase‐catalyzed dynamic hydrolytic resolution of (R,S)‐2,2,2‐trifluoroethyl α‐chlorophenyl acetate in water‐saturated isooctane

The hydrolytic resolution of (R,S)‐2,2,2‐trifluoroethyl α‐chlorophenylacetate in water‐saturated isooctane containing Lipase MY(I) at 35 °C is selected as the best reaction condition for producing (R)‐α‐chlorophenyl acetic acid. The kinetic constants, and hence an enantiomeric ratio of 33.6, are estimated and employed for the modeling of time‐course conversions of both substrates by considering product inhibition and enzyme deactivation effects. A successful dynamic kinetic resolution is also achieved, giving the desired (R)‐α‐chlorophenylacetic acid of 93.0% yield and ee_P = 89.5% when 80 mmol dm^?3 trioctylamine acting as the racemization catalyst and enzyme activator is initially added. Copyright © 2006 Society of Chemical Industry     

Photo‐Induced atom transfer radical polymerization with nanosized α‐Fe2O3 as photoinitiator

Photo‐induced atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was achieved in poly(ethylene glycol)‐400 with nanosized α‐Fe₂O₃ as photoinitiator. Well‐defined poly(methyl methacrylate) (PMMA) was synthesized in conjunction with ethyl 2‐bromoisobutyrate (EBiB) as ATRP initiator and FeCl₃·6H₂O/Triphenylphosphine (PPh₃) as complex catalyst. The photo‐induced polymerization of MMA proceeded in a controlled/living fashion. The polymerization followed first‐order kinetics. The obtained PMMA had moderately controlled number‐average molecular weights in accordance with the theoretical number‐average molecular weights, as well as narrow molecular weight distributions (M_w/M_n). In addition, the polymerization could be well controlled by periodic light‐on–off processes. The resulting PMMA was characterized by ¹H nuclear magnetic resonance and gel permeation chromatography. The brominated PMMA was used further as macroinitiator in the chain‐extension with MMA to verify the living nature of photo‐induced ATRP of MMA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42389.     

Synthesis and characterization of polyrotaxanes comprising α‐cyclodextrins and poly(ε‐caprolactone) end‐capped with poly(butyl methacrylate)s

Biodegradable polyrotaxane‐based triblock copolymers were synthesized via the bulk atom transfer radical polymerization (ATRP) of n‐butyl methacrylate (BMA) initiated with polypseudo‐rotaxanes (PPRs) built from a distal 2‐bromoisobutyryl end‐capped poly(ε‐caprolactone) (Br‐PCL‐Br) with α‐cyclodextrins (α‐CDs) in the presence of Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine at 45 ºC. The structure was characterized in detail by means of ¹H NMR, gel permeation chromatography, wide‐angle X‐ray diffraction, DSC and TGA. When the feed molar ratio of BMA to Br‐PCL‐Br was changed from 128 to 300, the degree of polymerization of PBMA blocks attached to two ends of the PPRs was in the range 382 ? 803. Although about a tenth of the added α‐CDs were still threaded onto the PCL chain after the ATRP process, the movable α‐CDs made a marked contribution to the mechanical strength enhancement, blood anticoagulation activity and protein adsorption repellency of the resulting copolymers. Meanwhile, they could also protect the copolymers from the attack of H₂O and Lipase AK Amano molecules, exhibiting a lower mass loss as evidenced in hydrolytic and enzymatic degradation experiments. © 2013 Society of Chemical Industry     

Ruthenium(II)‐Catalyzed Protocol for Preparation of Diverse α,β‐ and β,β‐Dihaloenones from Diazodicarbonyls

Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.

     

Organocatalytic Enantioselective Aziridination of α‐Substituted α,β‐Unsaturated Aldehydes: Asymmetric Synthesis of Terminal Aziridines

The first example of a highly enantioselective organocatalytic aziridination of α‐substituted α,β‐unsaturated aldehydes is presented. The reaction is catalyzed by simple chiral amines and gives access to highly functional terminal azirdines containing an α‐tertiary amine stereocenter in high yields and enantiomeric ratios (95.5:4.5–98:2).     

Catalytic Hydrogenation of α‐Iminophosphonates as a Method for the Synthesis of Racemic and Optically Active α‐Aminophosphonates

It was shown that the catalytic hydrogenation of α‐iminophosphonates by molecular hydrogen can serve as a convenient method for the synthesis of racemic and optically active α‐aminophosphonates. Up to 94% ee was achieved in the rhodium‐catalyzed enantioselective hydrogenation using chiral ligand (R)‐BINAP.     

Highly Enantioselective Michael Addition of Cyclic 1,3‐Dicarbonyl Compounds to β,γ‐Unsaturated α‐Keto Esters

A highly enantioselective Michael addition of cyclic 1,3‐dicarbonyl compounds to β,γ‐unsaturated α‐keto esters catalyzed by amino acid‐derived thiourea‐tertiary‐amine catalysts is presented. Using 5 mol% of a novel tyrosine‐derived thiourea catalyst, a series of chiral coumarin derivatives were obtained in excellent yields (up to 99%) and with up to 96% ee under very mild conditions within a short reaction time.     

The preparation of α‐bis and α,ω‐tetrakis aromatic oxazolyl‐ and carboxyl‐functionalized polymers using 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene in atom transfer radical polymerization reactions

The preparation of new compounds, 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethanol and a new symmetrically disubstituted 1,1‐diphenylethylene derivative, 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene, is described. 1,1‐Bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene was utilized as a dioxazolyl initiator precursor for the polymerization of styrene by atom transfer radical polymerization (ATRP) methods to produce α‐bis(oxazolyl) polystyrene. The kinetic study of the polymerization process indicated that the free radical polymerization reaction for the preparation of α‐bis(oxazolyl) polystyrene follows first‐order rate kinetics with respect to monomer consumption. α,ω‐Tetrakis(oxazolyl) polystyrene was prepared by a new, in situ, controlled/living, post‐ATRP chain‐end‐functionalization reaction which involves the direct addition of 1,1‐bis[4‐(2‐(4,4‐dimethyl‐1,3‐oxazolyl))phenyl]ethylene to the ω‐terminus of the α‐bis(oxazolyl) polystyrene derivative, without the isolation and purification of the polymeric precursor. α‐Bis(carboxyl) and α,ω‐tetrakis(carboxyl) polystyrene derivatives were obtained by the quantitative chemical transformation of the oxazoline groups of the respective aromatic oxazolyl chain‐end‐functionalized polystyrene derivatives to the aromatic carboxyl groups. The organic precursor compounds, the dioxazolyl‐functionalized 1,1‐diphenylethylene derivative and the functionalized polymers were characterized using ¹H NMR and ¹³C NMR spectrometry and Fourier transform infrared spectroscopy, size‐exclusion and thin‐layer chromatography and non‐aqueous titration measurements. © 2014 Society of Chemical Industry     

Efficient Synthesis of β,γ‐Alkynyl α‐Amino Acid Derivatives by Ag(I)‐Catalyzed Alkynylation of α‐Imino Esters

The first catalytic synthesis of β,γ‐alkynyl α‐amino acid derivatives was achieved by direct addition of terminal alkynes to α‐imino esters in the presence of an Ag(I) salt under mild reaction conditions.