Diacetoxylation of conjugated dienes with thallium(III) acetate in acetic acid

The reaction of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-cyclopentadiene, and 1,3-cyclohexadiene, with thallium(III)acetate in acetic acid at 10–65° for 0.5–15 hr affords an isomeric mixture of the corresponding diacetoxyalkenes (1,2- and 1,4-addition products) in 10–92% yields. The 1,2-addition products are predominantly formed in all cases examined except the case of 1,3-cyclopentadiene. The reaction is assumed to proceed through acetoxythallation and dethallation steps, the latter step being accompanied and/or followed by an attack of acetoxyl group. An initial attack of thallium moiety is proposed to occur mainly at C-1 and C-2 carbons in the cases of linear terminal dienes and cyclic dienes, respectively.     

Preparation and polymerization of methylenecyclobutene and 1-methyl-3-methylenecyclobutene

Methylenecyclobutene (MCB) and 1-methyl-3-methylenecyclobutene (MMCB) were synthesized, characterized, and polymerized by anionic and cationic initiators. Structural analyses of the polymers were carried out by infrared and NMR spectros-copy. The cationic polymerization of MCB appeared to proceed entirely by a 1,5-propagation mechanism to form low molecular weight polymers in low yields. Anionic polymerization of this monomer, on the other hand, proceeded primarily through a 1,2-propagation path, again forming only low molecular weight polymeric products in low yield. In contrast to MCB, the methyl-substituted monomer, MMCB, polymerized readily with cationic initiators to produce unusually high molecular weight polymers in high conversions. On the basis of both infrared and NMR spectroscopic analyses, it was concluded that the polymers also contained essentially only 1,5-addition repeating units. Anionic initiators such as n-BuLi were unable to induce polymerization of this monomer, but polymerization by Ziegler-Natta catalysts proceeded readily to yield polymers virtually identical in structure and molecular weight to those obtained with cationic initiators.     

Copolymerization of isobutene and α-methylstyrene as a function of reaction conditions

The influence of reaction conditions (solvent, Lewis acid, temperature) on the cationic copolymerization of isobutene and α-methylstyrene was investigated. The crude product consists of low molecular nonprecipitable oligomers, polyisobutene, and poly(isobutene-co-α-methylstyrene). The amount of poly(α-methylstyrene) formed under the reaction conditions used was negligible. The degree of charge separation in the propagating cationic intermediate determines the selectivity of the reaction; that is, incorporation of monomer units into the polymer, ratio of different product fractions, and microstructure. Molecular weight distribution, copolymerization parameters, and sequence-length distribution functions were determined. The softening range of the copolymers depended on their isobutene content but appeared to be constant up to 15% isobutene in copolymers. The degradation temperature of the copolymers was between 340 and 390°C.     

Random copolymerization of acetylenic monomers and 1,3-dienes

Copolymerization of acetylenic monomers and 1,3-dienes was carried out by use of nickel naphthenate–diethylaluminum chloride catalyst. The molecular weight of the copolymers is rather low, and the copolymers are suitable as prepared for direct use as coating vehicles. In the system of acetylene and 1,3-dienes, the order of the copolymerization rate decreases in the following order: butadiene > isoprene > 2,3-dimethylbutadiene > chloroprene. 1,3-Dienes substituted at 1-and/or 4-position were scarcely copolymerized with acetylene. Methylacetylene and dienes tend to form cyclized copolymers. In the system of phenylacetylene and dienes, polyphenylacetylene was the main product; the copolymer was not obtained. The copolymer composition and the sequence distribution of linear copolymers were evaluated by ¹H-NMR spectra. Comparison of dyad fractions of copolymers evaluated from NMR spectra and those calculated by assuming random polymerization indicated that the copolymers of acetylene and dienes were random, and that the copolymers of methylacetylene and dienes were somewhat blocky. The coordination of monomers on the catalyst may play an important role in controlling the copolymerizability.     

异丁烯聚合催化体系研究 Ⅰ.均聚与共聚反应

用苯甲酰氯(BC)／TiCl4引发异丁烯(IB)聚合及与苯乙烯(St)的共聚反应，得到分子量高、分布窄的聚异丁烯及其共聚物，并控制了BC的高活性。对IB均聚及其与ST共聚反应影响因素(体系浓度、残余水、第3组分三乙胺(TEA))进行优化，得到最佳条件为：[BC]=2．6mmol／L、[TEA]／[BC]=1.0(均聚)和n(TiCl4)／n(BC)=80、[TEA]／[BC=4．0(共聚)，BC／TiCl4／TEA是最佳体系，对水不敏感，可以制备分子量高及分子量分布(MWD)为1．5(均聚)和2．0(共聚)的窄分布聚合物(GPC曲线均为单峰)。     

Radiation induced copolymerization of chlorotrifluoro ethylene with butenes

The radiation induced copolymerization of chlorotrifluoro ethylene (CTFE) with various butenes was studied at temperatures between ?20°C and +40°C using ⁶⁰Co-γ rays. In the case of isobutene (IB) an almost alternating crystalline copolymer is formed in a heterogeneous reaction. At high IB-concentrations a cationic homopolymerization of this olefin occurs simultaneously to the radical copolymerization. The copolymerization rate increases with increasing temperature and degree of conversion. The highest rates are obtained for monomer mixtures with about 80 to 90 mole % CTFE. The decrease in rate for monomer mixtures with still higher CTFE concentrations is assumed to be partly due to the low IB-concentration and partly to degradative chain transfer by the isobutene. In support of this assumption molecular weights and melting points of the copolymer have been determined. Similar results were obtained for butene-1 but in this case, no cationic homopolymerization was observed and the reaction proceeded homogeneously. Cis- and trans-butene-2 only acted as polymerization inhibitors.     

Copolymerization of the cyclic monomer, 5,5-dichloro-4-hydroxy-2,4-pentadienoic acid lactone

The copolymerization of 5,5-dichloro-4-hydroxy-2,4-pentadienoic acid lactone with methyl methacrylate, methyl acrylate, vinyl acetate, and vinylidene chloride to give yellow to red copolymers is described. Infrared, nuclear magnetic resonance, and ultraviolet spectroscopy indicate that the polymerization of the lactone proceeds by a 1,4-addition mechanism, followed by hydrogen chloride elimination, to give a highly conjugated structural unit closely related to the structure of the original monomer. The intense colors of the copolymers may arise from conjugated sequences of lactone units or through further eliminations along comonomer sequences.     

经由β,β-(1,4-亚丁二硫基)-α,β-不饱和酮的芳构化反应

为研究缩醛基结构上的差异对反应性能的影响,我们对α-羰基烯酮环二硫代缩醛2的合成及其在合成上的应用做了一些讨论. 本文合成了一些新的缩醛基为七元环的标题化合物2~c~1-~c~1~0, 选择其中代表物2~c~1与烯丙基, 2-甲基烯丙基, 苄基等Grignard试剂反应, 并观察了加成产物在BF~3·Et~2O催化下的芳构化反应性能.     

Synthesis of polystyrene-based cationic copolymers and their colloidal properties in water

A series of polystyrene-based cationic copolymers was synthesized by two different methods: (1) solution copolymerization of styrene and vinylbenzyl trimethylammonium chloride (VBTMAC) in ethanol, and (2) surfactant-free emulsion copolymerization of styrene and vinylbenzyl chloride in water followed by reaction with trimethylamine. The results indicated that the different synthesis methods would result in different polymer structures and, therefore, affect the solubility and colloidal properties of the copolymers in water. For the copolymers prepared by method 2, partial crosslinking was observed. The copolymers made by this method are almost water-insoluble. In contrast, the copolymers made from direct copolymerization of styrene and VBTMAC in ethanol are water-soluble or dispersible, but the solubility and the particle size of microaggregates formed by these copolymers in water strongly depend on charge density and temperature. One of the important results from this study is that uniform colloidal particles with a very small particle size (30–50 nm) can be obtained by dispersing polystyrene-based cationic copolymers in water without adding any surfactants. Received: 29 July 1998 Accepted in revised form: 28 September 1998     

Cationic ring-opening polymerizations of cyclic ketene acetals initiated by acids at high temperatures

Three unsubstituted cyclic ketene acetals (CKAs), 2-methylene-1,3-dioxolane, 1a , 2-methylene-1,3-dioxane, 2a , and 2-methylene-1,3-dioxepane, 3a , undergo exclusive 1,2-addition polymerization at low temperatures, and only poly(CKAs) are obtained. At higher temperatures, ring-opening polymerization (ROP) can be dominant, and polymers with a mixture of ester units and cyclic ketal units are obtained. When the temperature is raised closer to the ceiling temperature (T_c) of the 1,2-addition propagation reaction, 1,2-addition polymerization becomes reversible and ring-opened units are introduced to the polymer. The ceiling temperature of 1,2-addition polymerization varies with the ring size of the CKAs (lowest for 3a , highest for 2a ). At temperatures below 138°C, 2-methylene-1,3-dioxane, 2a , underwent 1,2-addition polymerization. Insoluble poly(2-methylene-1,3-dioxane) 100% 1,2-addition was obtained. At above 150°C, a soluble polymer was obtained containing a mixture of ring-opened ester units and 1,2-addition cyclic ketal units. 2-Methylene-1,3-dioxolane, 1a , polymerized only by the 1,2-addition route at temperatures below 30°C. At 67–80°C, an insoluble polymer was obtained, which contained mostly 1,2-addition units but small amounts of ester units were detected. At 133°C, a soluble polymer was obtained containing a substantial fraction of ring-opened ester units together with 1,2-addition cyclic ketal units. 2-Methylene-1,3-dioxepane, 3a , underwent partial ROP even at 20°C to give a soluble polymer containing ring-opened ester units and 1,2-addition cyclic ketal units. At −20°C, 3a gave an insoluble polymer with 1,2-addition units exclusively. Several catalysts were able to initiate the ROP of 1a, 2a , and 3a , including RuCl₂(PPh₃)₃, BF₃, TiCl₄, H₂SO₄, H₂SO₄ supported on carbon, (CH₃)₂CHCOOH, and CH₃COOH. The initiation by Lewis acids or protonic acids probably occurs through an initial protonation. The propagation step of the ROP proceeds via an S_N2 mechanism. The chain transfer and termination rates become faster at high temperatures, and this may be the primary reason for the low molecular weights (M_n ≤ 10³) observed for all ring-opening polymers. The effects of temperature, monomer and initiator concentration, water content, and polymerization time on the polymer structure have been investigated during the Ru(PPh₃)₃Cl₂-initiated polymerization of 2a . High monomer concentrations ([M]/[ln]) increase the molecular weight and decreased the amount of ring-opening. Higher initiator concentrations (Ru(PPh₃)₃Cl₂) and longer reaction times increase molecular weight in high temperature reactions. Successful copolymerization of 2a with hexamethylcyclotrisiloxane was initiated by BF₃OEt₂. The copolymer obtained displayed a broad molecular weight distribution; M̄_n = 6,490, M̄_w = 15,100, M̄_z = 44,900. This polymer had about 47 mol % of ( Me₂SiO ) units, 35 mol % of ring-opened units, and 18 mol % 1,2-addition units of 2a . © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3655–3671, 1997     

Polyfunctional polyisobutenes as building blocks for amphiphilic graft polymers

Polyfunctional polyisobutenes (PIB) have been synthesized by cationic copolymerization of isobutene and chloromethylstyrene. Their potential applications with focus on their use as macroinitiators (MI) for oxazoline polymerization were discussed. The “grafting from” reaction led to tailor-made graft copolymers with various backbones and adjustable graft arm length. Graft copolymers with hydrophobic PIB backbone and poly(2-methyloxazoline) graft arms have unusual viscosity properties due to their amphiphilic character and show aggregate formation.     

Oxidative addition of 1,3-dicarbonyl compounds to dienes in the presence of Mn(III) AND Cu(II) acetates

Conclusions The selective oxidative 1,2-addition of acetylacetone and other dicarbonyl compounds to conjugated dienes was realized in an acetic acid solution containing manganese(III) and copper(II) ions. A series of 5-(1-alkenyl)-substituted 4,5-dihydrofurans were synthesized by the reaction with yields of 30–97%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2077–2084, September, 1981.     

Spontaneous copolymerizations in the reactions of electronrich dienes with electrophilic olefins

The spontaneous thermal reactions of electron-rich dienes with electrophilic olefins lead to both [4+2] cycloadducts and copolymers. The mechanism proposed for the initiation of the copolymerization involves the formation of a 2-hexene-1, 6-diradical. Structure-reactivity relationships are discussed.     

Isobutene homo- and isobutene-isoprene copolymerization initiated by protic initiators associated with a series of novel, weakly coordinating counteranions

The highly electrophilic borane B(C₆F₅)₃ reacts with a variety of carboxylic acids RCO₂H to form 1:1 and 1:2 adducts [RCO₂H][B(C₆F₅)₃] and [RCO₂H][B(C₆F₅)₃]₂. These adducts exhibit enhanced acidities, and the 1:2 adduct of n-decanoic (stearic) acid in particular is an excellent initiator for the carbocationic polymerization of isobutene and copolymerization of isobutene with isoprene in methylene chloride and methyl chloride. High conversions to high molecular weight polyisobutene and isobutene-isoprene copolymers are obtained at unusually high temperatures, consistent with the anion [n-C₁₇H₃₅CO₂ BC₆F₅)_{3 2}]⁻ being very weakly coordinating. Interestingly, the system also exhibits a surprising, as yet not understood, dependence of polymer molecular weights on the nature of R in methyl chloride.     

Synthesis and characterization of poly(ɛ-caprolactone-co-ethylene glycol) star-type amphiphilic copolymers by “click” chemistry and ring-opening polymerization

Abstract

The synthesis of poly(?-caprolactone-co-ethylene glycol) AAB star-type amphiphilic copolymers were carried out by use of a “click” chemistry reaction to block propargyl polyethylene glycol (propargyl-PEG) to terminally azide poly(?-caprolactone) (PCL-N₃). For this purpose, propargyl-PEG was synthesized by the reaction of PEGs (3000?Da, 2000?Da, 1500?Da, and 1000?Da) and propargyl chloride. Terminally chloride poly(?-caprolactone) (PCL-Cl) was carried out by means of ring-opening polymerization (ROP) of ?-caprolactone (CL) and 3-chloro-1,2-propanediol. Synthesis of PCL-N₃ was obtained by the chemical interaction of PCL-Cl and sodium azide. By reacting propargyl-PEG and PCL-N₃, the star-type amphiphilic copolymers were obtained. The characterization of products was accomplished by using multiple instruments including ¹H-NMR, FT-IR, GPC, TGA, contact angles, and elemental analysis techniques.     

Donor-Acceptor Complexes in Copolymerization. XVIII. Alternating Diene–Dienophile Copolymers. 1. Conjugated Diene–Maleic Anhydride Copolymers through Radical-Catalyzed Polymerization

The copolymerization of isoprene, butadiene, and other conjugated dienes with maleic anhydride was readily initiated in polar solvents by conventional free radical catalysts, including peroxides, hydroperoxides, and azobisisobutyronitrile, at high concentrations or at temperatures at which the catalyst had a half-life of 1 hr or less and the total reaction time was 0.5-1 hr. Decreasing the reaction temperature or the rate of catalyst addition resulted in increased yields of Diels-Alder adduct and decreased yields of copolymer. The molecular weight decreased as the temperature increased. Dioxane and tetrahydrofuran peroxides, obtained by the passage of oxygen or UV irradiation in air, also initiated the copolymerization. The soluble diene-maleic anhydride copolymers were equimolar and alternating, had [n] 0.1-6 (cyclohexanone) and contained 75-95% 1,4 structure according to ozonolysis, titration with IC1 and NMR. The IR spectrum of the butadiene–maleic anhydride copolymer indicated 75-95% cis-1,4, 5-20% trans-1,4 and 0-5% 1,2-vinyl unsaturation. The proposed mechanism of polymerization involves a donor-acceptor (diene-dienophile) interaction generating a ground-state charge transfer complex which is readily converted to the cyclic adduct. Under the influence of radicals the ground-state complex is transformed into an excited complex which undergoes polymerization. High concentrations of radicals are necessary to generate polymerizable excited complexes in competition with adduct formation.     

Expanding the C2-symmetric bicyclo[2.2.1]hepta-2,5-diene ligand family: concise synthesis and catalytic activity in rhodium-catalyzed asymmetric addition

New C2-symmetric bicyclo[2.2.1]hepta-2,5-dienes bearing methyl and phenyl substituents at the 2 and 5 positions were prepared enantiomerically pure through a two-step sequence starting from the readily available bicyclo[2.2.1]hepta-2,5-dione. Due to the instability or volatility of these dienes, their isolation was achieved through the formation of the corresponding stable [RhCl(diene)]2 complexes. These chiral rhodium complexes displayed high activity and enantioselectivity (up to 99% ee) in the rhodium-catalyzed 1,4-addition and 1,2-addition of phenylboronic acid to cyclic enones and N-sulfonylimines, respectively.     

Halosulfenylation of Conjugated Dienes with Arylsulfenamides in the Presence of Phosphorus Oxyhalides

Electrophilic sulfenylation of cyclic and open-chain conjugated dienes effected by a system arylsulfenamide-phosphorus oxyhalide was investigated. The initially formed adducts of 1,2-halosulfenylation in the course of the reaction and also at storage and chromatograqphic purification on silica gel undergo quantitative isomerization into a mixture of stereoisomeric products of 1,4-addition. The effect of halogen nature and the character of substituents in the benzene ring of arenesulfenamide on the addition rate of sulfenamides activated by phosphorus oxyhalides to open-chain and cyclic conjugated dienes and isomerization rate of the arising 1,2-adducts was examined.     

Spontaneous copolymerizations in the reactions of electron-rich dienes with electrophilic olefins

The spontaneous thermal reactions of electron-rich dienes with electrophilic olefins lead to both [4+2] cycloadducts and copolymers. The mechanism proposed for the initiation of the copolymerization involves the formation of a 2-hexene-1,6-diradical. Structure-reactivity relationships are discussed.     

Electrophilic Reactivities of 1,2‐Diaza‐1,3‐dienes

The kinetics of the reactions of 1,2‐diaza‐1,3‐dienes 1 with acceptor‐substituted carbanions 2 have been studied at 20 °C. The reactions follow a second‐order rate law, and can be described by the linear free energy relationship log k(20 °C)=s(N+E) [Eq. (1)]. With Equation (1) and the known nucleophile‐specific parameters N and s for the carbanions, the electrophilicity parameters E of the 1,2‐diaza‐1,3‐dienes 1 were determined. With E parameters in the range of ?13.3 to ?15.4, the electrophilic reactivities of 1 a–d are comparable to those of benzylidenemalononitriles, 2‐benzylideneindan‐1,3‐diones, and benzylidenebarbituric acids. The experimental second‐order rate constants for the reactions of 1 a – d with amines 3 and triarylphosphines 4 agreed with those calculated from E, N, and s, indicating the applicability of the linear free energy relationship [Eq. (1)] for predicting potential nucleophilic reaction partners of 1,2‐diaza‐1,3‐dienes 1 . Enamines 5 react up to 10² to 10³ times faster with compounds 1 than predicted by Equation (1), indicating a change of mechanism, which becomes obvious in the reactions of 1 with enol ethers.