Synthesis of tertiary-butyl acrylate polymers and preparation of diblock copolymers using atom transfer radical polymerization

The synthesis of tert-butyl acrylate by atom transfer radical polymerization (ATRP) is reported. This polymer was prepared using FeCl₂ · 4H₂O(PPh₃)₂ catalyst system in conjunction with methyl 2-bromopropionate as initiator, in bulk and in solution using acetone as a solvent. The addition of solvent was necessary in order to decrease the polymerization rate and to afford low polydispersity polymers. The number-average molecular weights of the resulting polymers increased in direct proportion to the monomer conversion, and the polydispersities (M_w/M_n) were as low as 1.2. In addition, the preparation of an AB diblock copolymer of poly (n-butyl methacrylate)-block-poly (tert-butyl acrylate) by ATRP is reported. The resulting polymers and copolymers were characterized by means of size exclusion chromatography and ¹H-NMR Spectroscopy.     

Facile N-tert-butoxycarbonylation of amines using La(NO3)3·6H2O as a mild and efficient catalyst under solvent-free conditions

Facile N-tert-butoxycarbonylation of amines is described by the treatment of various primary, secondary, benzylic and aryl amines with di-tert-butyl dicarbonate in the presence of catalytic amounts of La(NO₃)₃·6H₂O under solvent-free conditions at room temperature to afford N-tert-butylcarbamates in excellent yields.     

Synthesis and properties of novel aromatic polyhydrazides and poly(amide–hydrazide)s based on the bis(ether benzoic acid)s from hydroquinone and substituted hydroquinones

4,4′‐(1,4‐Phenylenedioxy)dibenzoic acid as well as the 2‐methyl‐, 2‐tert‐butyl‐, or 2‐phenyl‐substituted derivatives of this dicarboxylic acid were synthesized in two main steps from p‐fluorobenzonitrile and hydroquinone or its methyl‐, tert‐butyl‐, or phenyl‐substituted derivatives. Polyhydrazides and poly(amide–hydrazide)s were prepared from these bis(ether benzoic acid)s or their diacyl chlorides with terephthalic dihydrazide, isophthalic dihydrazide, or p‐aminobenzoyl hydrazide by means of the phosphorylation reaction or low‐temperature solution polycondensation. Most of the hydrazide polymers and copolymers are amorphous and readily soluble in various polar solvents such as N‐methyl‐2‐pyrrolidone (NMP) and dimethyl sulfoxide. They could be solution‐cast into transparent, flexible, and tough films. These polyhydrazides and poly(amide–hydrazide)s had T_gs in the range of 167–237°C and could be thermally cyclodehydrated into the corresponding poly(1,3,4‐oxadiazole)s and poly(amide–1,3,4‐oxadiazole)s approximately in the region of 250–350°C, as evidenced by the DSC thermograms. All the tert‐butyl‐substituted oxadiazole polymers and those derived from isophthalic dihydrazide were organic soluble. The thermally converted oxadiazole polymers exhibited T_gs in the range of 208–243°C and did not show significant weight loss before 450°C either in nitrogen or in air. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1169–1181, 1999     

Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for N-tert-butoxycarbonylation of amines under solvent-free conditions at room temperature

Commercially available copper(II) tetrafluoroborate hydrate was found to be a highly efficient catalyst for chemoselective N-tert-butoxycarbonylation of amines with di-tert-butyl dicarbonate under solvent-free conditions and at room temperature. Various aromatic amines were protected as their N-tert-butyl carbamates in high yields and in short times. No competitive side reactions such as isocyanate, urea, and N,N-di-t-Boc formation was observed. Chemoselective N-tert-butoxycarbonylation was achieved with substrates bearing OH and SH groups. Chiral α-amino acid esters afforded the corresponding N-t-Boc derivatives in excellent yields.     

An efficient method for the conversion of aromatic and aliphatic nitriles to the corresponding N-tert-butyl amides: a modified Ritter reaction

Aromatic and aliphatic nitriles react with tert-butyl acetate in the presence of a catalytic amount of sulfuric acid to give the corresponding N-tert-butyl amides in excellent yields.     

Asymmetric addition of trimethylsilylcyanide to N-benzylimines catalyzed by recyclable chiral dimeric V(V) salen complex

Chiral dimeric vanadium (V) salen complex (10 mol%) derived from 5,5-Methylene di-[(S,S)-{N-(3-tert-butyl salicylidine)-N′-(3′,5′-di-tert-butyl salicylidene)]-1,2-cyclohexanediamine] with vanadyl suphate followed by auto oxidation was used as efficient catalyst for enantioselective Strecker reaction of N-benzylimines with TMSCN at −30 °C. Excellent yield (92%) of α-aminonitrile and high chiral induction was achieved (ee up to 94%) in case of 2-methoxy substituted N-benzylimines in 10 h. The catalytic system worked well up to four cycles with retention of enantioselectivity.     

Endo- and exocyclic N-alkylation of 1- and 5-aminotetrazoles with t-BuOH-HClO4: synthesis of mono-, di-, and tri-tert-butyl substituted aminotetrazolium salts

A new method for the synthesis of 1,3,5-trisubstituted aminotetrazolium salts based on alkylation of 1- and 5-aminotetrazoles with the t-BuOH-HClO₄ system is presented. Depending on the structure of the tetrazole substrate and reaction conditions, alkylation proceeds at the endocyclic nitrogen atoms as well as at the 1- and 5-amino groups giving mono-, di-, and tri-tert-butyl substituted tetrazolium salts. An X-ray diffraction investigation of 3-tert-butyl-1,5-bis(tert-butylamino)tetrazolium perchlorate and 5-amino-1,3-di-tert-butyltetrazolium chloride was carried out.     

Nickel-catalyzed organozinc-induced unexpected 1,3-migration of tert-butyl from sulfur to carbon in N-tert-butanesulfinyl iminoacetates

The nickel-catalyzed reaction for an unexpected 1,3-migration of tert-butyl from sulfur to carbon, upon treatment of functionalized N-tert-butanesulfinyl iminoacetate in the presence of organozinc reagent, was developed. The generality has been explored by considering the flexibility in the structure of each reactive component, organozinc halide and N-tert-butanesulfinyl iminoacetate.     

Controlled radical polymerization of methacrylates of various structures in the presence of the AIBN-FeCl3-N,N-dimethylformamide catalytic system

The controlled radical polymerization of methyl methacrylate, 2-ethoxyethyl methacrylate, and tert-butyl methacrylate conducted via atom-transfer radical polymerization in the presence of the AIBN-FeCl₃· 6H₂O-N,N-dimethylformamide catalytic system is studied. For all the systems under study, the rate of reaction is first order with respect to the monomer concentration. The number-average molecular mass of the polymers linearly increases with conversion, and their polydispersity indexes are below 1.6. The rate of polymerization decreases in the following sequence: 2-ethoxyethyl methacrylate > methyl methacrylate > tert-butyl methacrylate. The presence of ω-terminal chlorine atoms in polymer macromolecules is confirmed by ¹H NMR spectroscopy and through the block copolymerization of methyl methacrylate with a poly(ethoxyethyl methacrylate)-based macroinitiator.     

Grafting copolymerization of vinyl monomers on polyimide macroinitiators by the method of atom transfer radical polymerization

Graft copolymers with the main polyimide chain and side chains of poly(n-butyl acrylate), poly(tert-butyl acrylate), poly(methyl methacrylate), poly(tert-butyl methacrylate), polystyrene, and polystyrene-block-poly(methyl methacrylate) were synthesized by atom transfer radical polymerization on the multicenter polyimide macroinitiators in the presence of the halide complexes of univalent copper with nitrogen-containing ligands. Polymerization of metha-crylates is most efficiently developed on the polyimide macroinitiators. The obtained graft copolymers initiate the secondary polymerization (“post-polymerization”) of methyl methacrylate. The conditions of detachment of side chains of graft polymethacrylates that do not involve the ester groups of their monomeric units were found. The molecular mass characteristics of the graft copolymers and isolated polymers, being the detached side chains of the copolymers, were determined. The detached side chains of different chemical structures have low values of the polydispersity index. The procedure developed was used for the preparation of new graft polyimides with side chains of poly-4-nitro-4′-[N-methylacryloyloxyethyl-N′-ethyl]amino-azobenzene that cause the nonlinear optical properties and with the side chains of poly(N,N-dimethylaminoethyl methacrylate) that cause the thermosensitive properties of the copolymers.     

Synthesis and structure of diamine bis(phenolate) complexes containing the Ti(OEt)–O–Ti(OEt) function

Reaction of diamine-bis(phenol) ligands containing a mixture of N-methyl and N,N′-dimethyl-N,N-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine, H₂L¹ and H₂L³, with [Ti(OCHMe₂)₄ in absolute ethanol under reflux without exclusion of air and moisture gives [(L¹)Ti (OEt–O–Ti(OEt)(L¹)] (1). [(L³)Ti(OEt)–O–Ti(OEt)(L³)] (2) forms when the remaining solution containing [(L³)Ti(OEt)₂] (3) (characterised by X-ray crystallography) is hydrolysed with H₂O. For the N-methyl and N,N′-dimethyl ligand mixture H₂L² and H₂L⁴, which contain tert-butyl groups on the ortho-positions of the aryl rings, [(L²)Ti(OEt)–O–Ti(OEt)(L²)] (4) forms much more slowly and [(L⁴)Ti(OEt)₂] (5) does not hydrolyse when H₂O is added. When the N-protonated ligand N,N-bis(2-hydroxy-3-methyl-5-tert-butylbenzyl)ethylenediamine, H₂L⁵, is used, rapid hydrolysis to two isomers of [(L⁵)Ti(OEt–O–Ti(OEt)(L⁵)] (6) occurs without addition of water. For N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine, H₂L⁶, hydrolysis to [(L⁶)Ti(OEt)–O–Ti(OEt)(L⁶)] (7) occurs slowly when H₂O is added. For pendant NMe₂ ligand N,N-dimethyl-N′,N′-bis(2-hydroxy-3-methyl-5-tert-butylbenzyl)ethylenediamine, H₂L⁷, the hydrolysis reaction readily gives [(L⁷)Ti(OEt)–O–Ti(OEt)(L⁷)] (8) for which an X-ray crystal structure was obtained. The ortho-tert-butyl ligand derivative H₂L⁸ formed a complex analysing as [(L⁸)Ti(OEt)–O–Ti(OEt)(L⁸)] (9) which could not be studied further due to insolubility. Pendant pyridine ligand N-(2-pyridylmethyl)-N,N-bis(2′-hydroxy-3′-methyl-5′-tert-butylbenzyl)amine, H₂L⁹, apparently forms isomers of [(L⁹)Ti(OEt)–O–Ti(OEt)(L⁹)] and possibly [{(L⁹)Ti(O)}₂] from [(L⁹)Ti(OEt)₂] (10). The ortho-tert-butyl ligand derivative H₂L¹⁰ formed [(L¹⁰)Ti(OEt)–O–Ti(OEt)(L¹⁰)] (11) for which an X-ray crystal structure was obtained.     

Stereoselective synthesis of piperidine derivatives [3,2-c]-fused with oxygen heterocycles

The reaction of tert-butyl 4-oxopiperidine-1-carboxylate dimethylhydrazone with BuLi and further with iodides of protected alcohols ICH₂(CH₂) _n OSiMe₂(t-Bu) (n = 1–4) led to the formation of the corresponding tert-butyl 3-{[tert-butyl(dimethyl)silyl]alkyl}-4-oxopiperidine-1-carboxylates that under the treatment with triethylsilane in the presence of anhydrous BiBr3 underwent cyclization with a high stereoselectivity into cis-isomers of N-Boc piperidine derivatives [3,2-c]-fused with oxygen heterocycles. The latter at the treatment with anhydrous HCl eliminate the Boc group affording hydrochlorides of stereochemically homogeneous N-unsubstituted fused bicyclic systems.     

Enantioselective synthesis of d- and l-α-methylcysteine with hydantoinase

A scalable and cost-effective synthesis of d- and l-α-methylcysteine is described. A key step is d-selective cyclization of N-carbamoyl S-tert-butyl-d,l-α-methylcysteine catalyzed by hydantoinase. d-5-tert-Butylthiomethyl-5-methylhydantoin and N-carbamoyl S-tert-butyl-l-α-methylcysteine were obtained with excellent yield and optical purity, and these compounds were easily separated by filtration. After hydrolysis and cleavage of the tert-butyl group, d- and l-α-methylcysteine hydrochloride were obtained.     

Facile synthesis of primary amides and ketoamides via a palladium-catalysed carbonylation-deprotection reaction sequence

Various primary amides and ketoamides have been obtained in good yields in a two-step reaction sequence. The first step involves the synthesis of aryl/alkenyl N-tert-butyl amides and aryl N-tert-butyl ketoamides from the corresponding iodides via palladium-catalysed carbonylation in the presence of t-BuNH₂ as the nucleophile. Carbonylation was followed by selective cleavage of the t-Bu group using TBDMSOTf as the reagent.     

Performance of Waterborne Polyurethanes in Inhibition of Gas Hydrate Formation and Corrosion: Influence of Hydrophobic Fragments

The design of new dual-function inhibitors simultaneously preventing hydrate formation and corrosion is a relevant issue for the oil and gas industry. The structure-property relationship for a promising class of hybrid inhibitors based on waterborne polyurethanes (WPU) was studied in this work. Variation of diethanolamines differing in the size and branching of N-substituents (methyl, n-butyl, and tert-butyl), as well as the amount of these groups, allowed the structure of polymer molecules to be preset during their synthesis. To assess the hydrate and corrosion inhibition efficiency of developed reagents pressurized rocking cells, electrochemistry and weight-loss techniques were used. A distinct effect of these variables altering the hydrophobicity of obtained compounds on their target properties was revealed. Polymers with increased content of diethanolamine fragments with n- or tert-butyl as N-substituent (WPU-6 and WPU-7, respectively) worked as dual-function inhibitors, showing nearly the same efficiency as commercial ones at low concentration (0.25 wt%), with the branched one (tert-butyl; WPU-7) turning out to be more effective as a corrosion inhibitor. Commercial kinetic hydrate inhibitor Luvicap 55 W and corrosion inhibitor Armohib CI-28 were taken as reference samples. Preliminary study reveals that WPU-6 and WPU-7 polyurethanes as well as Luvicap 55 W are all poorly biodegradable compounds; BOD_t/COD_cr (ratio of Biochemical oxygen demand and Chemical oxygen demand) value is 0.234 and 0.294 for WPU-6 and WPU-7, respectively, compared to 0.251 for commercial kinetic hydrate inhibitor Luvicap 55 W. Since the obtained polyurethanes have a bifunctional effect and operate at low enough concentrations, their employment is expected to reduce both operating costs and environmental impact.     

Synthesis and characterization of new ointment-like poly(ortho esters)

Ointment-like poly(ortho esters) were synthesized for the first time from the reaction of 3,9-bis(methylene)-2,4,8,10-tetraoxaspiro[5. 5] undecane with poly(ethylene glycol)-400, N,N-bis(2-hydroxyethyl)-n-hexadecylamine and N,N-bis(2-hydroxyethyl) palmitamide, respectively. The obtained polymers were characterized by 1H NMR spectra, 13C NMR spectra, elemental analyses, light scattering, and measurements of intrinsic viscosity. The influence of catalyst on the intrinsic viscosity of polymers was investigated. The 9-[(1,3-dihydroxy-2-propoxy) methyl] guanine controlled release profiles of hydrophobic ointment-like polymers such as polymer P_II in vitro were also discussed.     

Solution behavior of 4-arm poly(tert-butyl acrylate) star polymers

This paper reports the synthesis of 4-arm poly(tert-butyl acrylate) stars of different molar masses up to 10⁶ g/mol by the “core-first” method using ATRP. All obtained stars have a monomodal and narrow molar-mass distribution (<1.2).The dilute-solution properties of these star polymers were investigated in good solvents (tetrahydrofuran and acetone). Gel permeation chromatography and dynamic and static light scattering were used to measure the hydrodynamic properties including intrinsic viscosity [η], radius of gyration R_g, hydrodynamic radius R_h, second virial coefficient A₂ and diffusion coefficient D₀. These data were used to establish relationships between these parameters and the molar mass of 4-arm poly(tert-butyl acrylate) stars. The branching parameters g and g′ and the shape factor ρ were calculated for all obtained star polymers.     

Synthesis of N,N-Ac,Boc laurylthio sialoside and its application to O-sialylation

The combination of the 5-N-tert-butoxycarbonyl (Boc) group of laurylthio sialoside and cyclopentyl methyl ether (CPME) as a solvent enhanced the reactivity and α-selectivity of the sialyl donor during sialylation. Selective deprotection of the N-Boc group of sialoside, including an acid-sensitive isopropylidene function, was successfully achieved by Yb(OTf)₃-SiO₂. Transformation of N,N-Ac,Boc into an N-acetylglycolyl group of sialoglycoside was easily performed via selective N-deacylation of the mixed Ac-N-Boc carbamate, subsequent Boc group removal, and acylation.     

Synthesis and characterization of new highly soluble and thermal-stable perylene-PPV copolymers containing triphenylamine moiety

Three new copolymers containing poly(p-phenylenevinylene) (PPV) and triphenylamine (TPA) moieties carrying N-(n-butyl)-N′-ethoxy-1,6,7,12-tetra-(4-tert-butylphenoxy)-3,4,9,10-perylenetetracarboxylic bisimide (PERY) pendant groups were successfully synthesized by Wittig condensation. The molar percentage of perylene pendants in copolymers was controlled by tuning the initial feed ratio of the perylene-bisaldehyde monomer. The structures and properties of three copolymers were characterized and evaluated by FT-IR, NMR, UV, FL, and photovoltaic analyses. The copolymers were highly soluble in conventional solvents such as toluene, CHCl₃, THF, DMF, etc., and they were thermally stable (?396 °C). Three copolymers have emission spectra with characteristic features of the perylene unit, however, and their luminescence are largely quenched with the increasing amount of PERY units in copolymers. The photophysical study in solution has shown that singlet-singlet energy transfers from PPV backbone to perylene in the copolymers. The photovoltaic devices ITO/PEDOT:PSS/copolymers/Ba/Al were fabricated, and the energy conversion efficiency of the device is only about 0.0005%, further indicating that an efficient energy transfer has taken place from PPV to perylene in the copolymers.     

Nature of solvation effects and mechanism of heterolysis of <Emphasis Type="Italic">tert</Emphasis>-alkyl halides

Specificities of heterolysis of tert-alkyl halides in protic and aprotic solvents were analyzed. Values of log k ₂₅ for heterolysis of tert-butyl chloride, tert-butyl bromide, tert-butyl iodiede, 1-chloro-1-methylcyclopentane, 1-chloro-1-methylcyclohexane, 1-bromo-1-methylcyclopentane, 1-bromo-1-methylcyclohexane, 2-chloro-2-phenylpropane, 1-iodoadamantane, and 2-bromo-2-methyladamantane in 19 to 44 solvents, determined mostly by the verdazyl technique were collected. Correlation analysis of solvation effects was performed in terms of multiparameter equations based on the linear free energy relationship principle, as well as in the logk-E _T coordinates. The nature of solvation effects and mechanism of heterolysis of a covalent C-Hlg bond were discussed.