Spontaneous copolymerization of 1,3-cycloheptadiene with acrylonitrile in the presence of zinc chloride

The reaction of 1,3-cycloheptadiene (1,3-CHpD) with acrylonitrile (AN) in the presence of ZnCl₂ leads spontaneously to the simultaneous formation of an alternating copolymer and a small amount of cycloadduct. The copolymer has a predominantly cis-1,4-structure. The formation of the charge—transfer complex between 1,3-CHpD and (AN)c (AN coordinated to ZnCl₂) in AN was detected by ultraviolet (UV) spectroscopy. The activation energies for the cycloaddition and for the copolymerization under the conditions used were determined to be 17.6 (in the presence of 1,1-diphenyl-2-picrylhydrazyl) and 16.3 kcal/mole, respectively. The rate of copolymerization in AN was found to depend on the 1.5th power of the concentrations of (AN)c and of 1,3-CHpD. Oxygen and UV irradiation causes an acceleration of the copolymerization only. On the basis of these results the mechanism of the spontaneous copolymerization is discussed and its relation to the cycloaddition in systems of 1,3-cyclodienes and AN in the presence of ZnCl₂ is mentioned.     

Poly(1,3-cyclohexadiene-alt-α-fluoroacrylonitrile): Synthesis and structural analysis of a new alternating copolymer

Poly(1,3-cyclohexadiene-alt-α-fluoroacrylonitrile) [poly(1,3-CHD/α-FAN)], an alternating copolymer of α-fluoroacrylonitrile and 1,3-cyclohexadiene has been prepared in bulk using varied monomer feed ratios and AIBN as initiator at 65°C. Elemental and ¹H-NMR analyses indicate that the copolymer contains an equimolar composition of α-FAN and 1,3-CHD as observed for alternating copolymers with donor-acceptor polymerizations. A 2-D ¹H-COSY NMR experiment indicates that the copolymer contains 1,4-linkages across the cyclohexene unit while more reliable ¹³C-NMR spectra suggests the copolymer to contain both 1,2- and 1,4-linkages. Poly(1,3-CHD/α-FAN) exhibits improved thermal stability relative to the alternating copolymer of 1,3-CHD and α-chloroacrylonitrile due to a higher resistance to HF elimination relative to HCl elimination.     

KF/Al2O3 mediated 1,3-dipolar cycloaddition of azomethine ylides: a novel and convenient procedure for the synthesis of highly substituted pyrrolidines

The regio- and diastereoselective synthesis of pyrrolidine derivatives through 1,3-dipolar cycloaddition of an azomethine ylide and dipolarophile mediated by KF/Al₂O₃, a versatile solid supported reagent, is reported. KF/Al₂O₃ is sufficiently basic such that it can deprotonate α-imino esters to generate azomethine ylides and it also functions as a solid supported catalyst leading to the cycloadduct rather than the Michael adduct.     

Preparation of polymers with substituted allyl end group using dimer of α-methylvinyl monomer as addition fragmentation chain transfer agent at high temperatures

The dimerization of methyl methacrylate, ethyl methacrylate, methacrylonitrile, and α-methylstyrene to 2-substituted-1-allylic compounds [CH₂?C(X)CH₂C(CH₃)₂X] (X = COOR, C₆H₅, or CN), and methyl α-ethylacrylate to a 3-substituted-2-allylic compound [CH₃CH?C(COOCH₃)CH₂C(CH₃)(C₂H₅) COOCH₃] was carried out by catalytic chain transfer using benzylbis (dimethylglyoximato) (pyridine) cobalt (III). These dimers were then used as addition-fragmentation chain transfer agents in the polymerizations of methyl methacrylate and styrene at 80⁰C or above. Cross-dimers from methacrylic ester-α-methylstyrene and methacrylonitrile-α-methylstyrene mixtures were similarly prepared. Except for those from methyl α-ethylacrylate and methacrylonitrile, all the dimers participated in the addition-fragmentation and the copolymerization to different extents. The dimer of methyl α-ethylacrylate was actually inactive during the styrene and methyl methacrylate polymerizations. The methacrylonitrile dimer was primarily incorporated in the polymer chain through copolymerization. Among the dimer and the cross-dimers from α-methylstyrene with the other monomers, those bearing the α-methylstyrene moiety in the α-substituent [CH₂?C(X)CH₂C(CH₃)₂C₆H₅, X?COOCH₃, COOC₂H₅, and CN] are noted as highly reactive chain transfer agents. © 1994 John Wiley & Sons, Inc.     

Intramolecular 1,3-dipolar cycloaddition of unsaturated nitrones derived from methyl α-d-glucopyranoside

The intramolecular 1,3-dipolar cycloaddition of unsaturated nitrones derived from methyl α-d-glucopyranoside with 2-furaldehyde has been studied. This cycloaddition was found to afford three 9-oxa-1-azabicyclo[4.2.1]nonane diastereomers in a 3:1:1 ratio [with the principal isomer possessing a (3S,4R,5S,6S,8S) configuration, determined by NMR spectroscopy]. The effects of different Lewis acid catalysts (MgCl₂, ZnCl₂ and BF₃·OEt₂) on yields and diastereomeric ratios have been examined in detail. The best result (90% yield) was achieved when MgCl₂ was present (in toluene, 120 °C bath temperature, 12 h). The stereoselectivity of the 1,3-dipolar cycloaddition was not significantly altered under the conditions investigated.     

Polyampholyte synthesis by cyclopolymerization

The syntheses of N-2-phenylallylacrylamide (I) and N-ethyl-2-phenallylacrylamide (II) are described. Both monomers can be polymerized with radical initiators to form cyclopolymers although complete cyclization does not occur. Lewis acids (ZnCl₂ in the case of I, Et_1.5AlCl_1.5 in the case of II) result in the formation of higher molecular weight polymers in a shorter period of time. Polymers of I and II have been hydrolyzed to polyampholytes. The copolymerization of α-methylstyrene–acrylamide in the presence of azobisisobutyronitrile (AIBN) and ZnCl₂ leads to the formation of a 1:1 copolymer, whereas styrene–acrylamide under the same conditions give a copolymer slightly dependent upon the monomer feed composition. Attempted cyclopolymerization of N-allylacrylamide (monomer I without the phenyl group) with ZnCl₂–AlBN was not successful, only crosslinked polymer being obtained. An explanation is offered for the fact that I does not form a perfect cyclopolymer, although the α-methylstyrene–acrylamide system forms a 1:1 copolymer.     

A novel Fe(II)/diaryl prolinol catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides with alkenes

A novel Fe(II)/diaryl prolinol catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides with alkenes has been developed. In the presence of FeCl₂ (10 mol %) and α,α-bis(3,5-bistrifluoromethylphenyl)prolinol L1 (10 mol %), [3+2] cycloaddition of azomethine ylides with electronic-deficient olefins underwent smoothly in CH₃CN at room temperature to generate the desired endo-adducts in moderate to good yields and enantioselectivities. This is the first example of Fe(II)/N,O-ligand (L1) catalyzed 1,3-dipolar enantioselective cycloaddition reaction of azomethine ylides.     

Alternating copolymerizations of styrene and acrylic monomers initiated with carbanions in the presence of ZnCl2

On electrochemical initiation of alternating copolymerizations of styrene–acrylonitrile (AN) and styrene–diethyl fumarate (DEF) in the presence of ZnCl₂, radical anions of AN–ZnCl₂ and DEF–ZnCl₂ complexes produced at the cathode were assumed to initiate copolymerization. In analogy with the cathode-initiated copolymerization, the radical anions of AN–ZnCl₂ and DEF–ZnCl₂, generated with the carbanions such as sodium naphthalene, disodium α-methylstyrene tetramer dianion, and butyllithium, were also found to produce alternating copolymers of styrene–AN and styrene–DEF. On the contrary, no polymers were obtained from methyl methacrylate (MMA)–styrene and methacrylonitrile (MAN)–styrene in the presence of ZnCl₂ either with carbanions or by electrochemical reduction. Styrene–MAN–ZnCl₂ yielded an alternating copolymer with carbanions upon introduction of oxygen.     

Kinetics,Mechanism, and Rheological Properties of the Copolymers of 2-Ethylhexylacrylate and Styrene

Abstract

Copolymerization of 2-ethylhexylacrylate (2-EHA) and styrene (Sty) initiated by α,α′-azobisisobutyronitrile (AIBN) was carried out at 60, 65, and 70 ± 0.1°C in bulk in the presence of zinc chloride (ZnCl₂). R _p was a direct function of [ZnCl₂] and temperature. R _p showed an initial increase with [monomers] followed by a subsequent decrease after a maximum was reached. The accelerating effect of ZnCl₂ was predicted by a lowering of the activation energy from 42.78 to 34.38 kJ·mol^?1 and an increase in the specific rate constants ratio (k ² _p/k _t) from 4.64 to 5.83 L·mol^?1·s^?1. The product of the reactivity ratios of the two monomers was 0.018 and 0.648, favoring alternating and random copolymer structures, respectively. The copolymerization reaction mechanism was a radical complex. Rheological investigations favored Bingham and Ostwald models for the flow behaviors of alternating and random copolymers, respectively.     

The Spontaneous Copolymerization of Indene with Polar Vinyl Monomers in the Presence of Zinc Chloride

Indene (ID) was found to copolymerize spontaneously with polar vinyl monomers containing a nitrile or ester group in the presence of ZnCb and to give rise simultaneously to its cationic homopolymer in the latter comonomer. The formation of a 1:1-charge transfer complex between ID with acrylonitrile coordi-nated to ZnCl₂ ((AN)c) was confirmed by UV-spectroscopic studies and the equilibrium constant for it was estimated to be 0.121 L/mol in AN at 25°C. The overall activation energy for the copolymerization with (AN)c was obtained to be ～9.8 kcal/mol. An increasing amount of ZnCl₂ in AN resulted in increases in the copolymerization rate, viscosity, and alternating tendency of the copolymer. The addition of 1, 1-diphenyl-2-picrylhydrazyl to the System ID-(AN)c retarded the copolymerization and induced a cationic polymerization of ID. Further, terpolymers containing ～50 mol % AN were formed spontaneously in the System ID-styrene-(AN)c. Comparing these results with the corresponding ones obtained for 1,3-cyclodienes as donor monomer reported previously, a discussion is given on the reactivity of ID-(AN)c complex in the initiation and the propagation of the copolymerization. The mechanism of the attendant cationic polymerization of ID is briefly considered.     

Polymerization and polymers of silicic acid

Linear relationships among molecular weight, polymerization time, and gelation for the condensation of any monomer, including those of unknown size and functionality, are developed and applied to data on soluble silicic acids generated from tetraethyl silicate and from sodium silicate. The results suggest the formation of monomers containing ca. 12–15 ? OSi units with functionality of ca. 2.05 that condense with a rate constant of ca. 10^?4 liter/mole sec and an activation energy of 40–70 kJ/mole. One model compatible with these characteristics and the stoichiometry involved is a ladder polymer ca. 3 ? SiO units wide. Polymer isolation was achieved by replacing residual ? OH with (CH₃)₃Sio? , as well as by freezing of of aqueous solutions, which yielded fibers under special conditions. Solutions of the uncapped and capped polymers and melts of the latter had low viscosity even for fractions with M?_n ～100,000. This implies a coiled or globular nature for the polymers, which is supported by their limited propensity for film and fiber formation. Attemps to improve this situation by copolymerization, the use of other capping agents, and by the polymerization of precapped monomers were unsuccessful.     

Molecular vibrations of irregular chains. I. Analysis of infrared spectra and structures of polymethylene chains consisting of CH2, CHD,and CD2 groups

Various samples of irregularly deuterated polyethylene were prepared and their infrared spectra were studied. The results support the previously proposed view that poly-trans-CHD?CHD or -cis-CHD?CHD obtained with Al(i-Bu)₃–TiCl₄ is an irregularly deuterated chain consisting of the CH₂, CHD, and CD₂ groups. A simplified calculation of the CHD scissors and CDH rocking vibration frequencies has been made for various model chains. The assignments of the CDH rocking vibration bands in the region of 700–500 cm.^?1 have been given on this basis.     

Copolymerization of 2-methylene-4-phenyl-1,3-dioxolane with electrophilic vinyl monomers through zwitterionic mechanism

Spontaneous copolymerization of cyclic ketene acetal, 2-methylene-4-phenyl-1,3-dioxolane ( I ) with common electrophilic vinyl monomers, such as methyl α-cyanoacrylate (MCA), acrylonitrile (AN), and methyl methacrylate (MMA) were investigated to further explore zwitterion polymerization method with cyclic ketene acetals. In the reaction of I with MCA and AN, spontaneous copolymerization took place at ambient temperature. The copolymers of I with MCA gave low molecular weight polymers, but copolymers obtained with I and AN were high molecular weight polymers. In the reaction of I and MMA, high molecular weight copolymer was obtained only at temperatures above 80°C. Thus, obtained polymers were not the alternating copolymers and possessed high I content in all the cases. From the above results, macrozwitterionic mechanism was suggested as discussed.     

Radiation postpolymerization in devitrifying matrices: Different polymerization activity of acrylic and methacrylic monomers

Investigation of the effect of the α-CH₃-group on low-temperature postpolymerization in devitrifying matrices leads to the following conclusions. 1. The low-temperature postpolymerization in supercooled alcohol solutions (T_g ～ 102 K) is quite efficient with acrylic monomers. Inactivity of their methacrylic analogues under these conditions is attributed to steric screening of the unpaired electron in the growing radicals. 2. As the temperature is raised and the CH₃-group vibration intensity increases, the screening effect fades. Thus in devitrifying water-alcohol solutions of NaAA and NaMAA, at higher temperatures the postpolymerization is efficient in both cases. Data on copolymerization of NaAA and NaMAA indicate that at ～ 170 K the steric limitations due to the CH₃-group are eliminated. 3. In a glycerine matrix ($\text{T}{}_{\mathrm{g}}\text{? 195 K}$), all the acrylic and methacrylic monomers studied show efficient polymerization over virtually the same temperature range. It is concluded that the a-CH₃-group in methacrylic monomers appreciably affects their polymerization activity only at low temperatures, where steric screening of the growing polymer radical becomes important.     

Studies on the charge transfer complex and polymerization. XVI. Spontaneous copolymerization of cyclopentene and sulfur dioxide

The alternating copolymerization of cyclopentene and sulfur dioxide was studied. It takes place spontaneously at ?15°C. The rate of copolymerization in toluene was found to be proportional to [CPT]³ and [SO₂]² with the overall activation energy of 16.5 kcal/mole. Terpolymerizations with eight different third monomers were carried out to examine the character and behavior of the copolymerization system of CPT and SO₂. However, the polymerizations with styrene and methyl methacrylate as the third monomers were found to be extraordinary, in that all the three components are not incorporated into the polymer chain.     

Stereospecific synthesis of 5,6-dihydro-2H-pyran system. High-pressure cycloaddition of 1:2,3:4-di-0-isopropylidene- α-D-galactopyranose-6-ulose to 1-methoxybuta-1,3-diene

The high-pressure cycloaddition of 1:2,3:4-di-0-isopropylidene- α-D-galactopyranos-6-ulose (3) to 1-methoxybuta-1,3-diene (1) afforded diastereoisomerically pure cycloadduct 4 whose absolute configuration was determined.     

Preparation of macromonomers by copolymerization of methyl acrylate dimer involving β fragmentation

The unsaturated dimer of methyl acrylate [CH₂C(CO₂CH₃)CH₂CH₂CO₂CH₃, or MAD] was copolymerized with various monomers to prepare copolymers bearing the ω-unsaturated end group [CH₂C(CO₂CH₃)CH₂ ] arising from β fragmentation of the MAD propagating radical. Copolymerizations of MAD with cyclohexyl and n-butyl acrylate resulted in copolymers with ω-unsaturated end groups, and increasing the temperature up to 180 °C resulted in an increase in the rate of β fragmentation of MAD radicals relative to propagation. Only a small amount of unsaturated end groups was introduced by copolymerization with ethyl methacrylate (EMA), and the EMA content in the copolymer increased with temperature. These findings could be explained by the reversible addition of the poly(EMA) radical to MAD. The copolymerization with ethyl α-ethyl acrylate (EEA) did yield a copolymer containing unsaturated end groups with MAD units as part of the main chain, although the steric hindrance of the ethyl group suppressed homopropagation and crosspropagation of EEA, resulting in low polymerization rates. Therefore, the copolymerization of MAD with acrylic esters at high temperatures was noted as a convenient route for obtaining acrylate–MAD copolymers bearing unsaturated end groups at the ω end (macromonomer). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 597–607, 2004     

Cycloarsanes (AsCF3)n (n = 4, 5) – Precursors for the Highly Reactive Diarsene F3CAs=AsCF3

Tetrakis(trifluoromethyl) cyclotetraarsane (F₃CAs)₄ ( 2 ) was used to repeat the UV initiated [4+2]‐cycloaddition reaction of the diarsene F₃CAs=AsCF₃ ( 1 ) with cyclohexa‐1,3‐diene (CHD) and to isolate single crystals of the cycloadduct 4 for a X‐ray diffraction analysis. 4 crystallizes in the space group and contains the diarsene group in its E‐configuration. 2 was also applied for [2+2]‐cycloaddition reactions of 1 with tBuC≡P and MeC≡CNⁱPr₂, but in contrast to positive results with (F₃CP)₄ the products were too labile for isolation. However, 2 was successfully used at room temperature as precursor for coordinating 1 as π‐donor ligand to the Pd(PPh₃)₂ complex fragment yielding η²‐bis(trifluoromethyl)diarsene‐bis(triphenylphosphane)‐palladium(0) 5 , which was characterized by X‐ray diffraction of single crystals and by spectroscopic investigations (NMR, IR, MS). Attempts to prove the existence of the diarsene 1 , generated by different methods, by spectroscopic studies very probably failed due to its extreme reactivity, not allowing the necessary concentrations for detection. Quantum chemical calculations of the stability of 1 with respect to dimerization, the stability of the [2+2]‐cycloadduct with 1‐di(isopropyl)aminopropyne and the energy difference between 4 and the 2,3‐dimethyl‐1,3‐butadiene cycloadduct of 1 were performed to understand the considerable differences between 1 and the related diphosphene F₃CP=PCF₃.     

Mechanism of alternating copolymerization of 4-hydroxy-4′-vinylbiphenyl with α-chloromaleic anhydride

The copolymerization of 4-hydroxy-4′-vinylbiphenyl (HVB) with α-chloromaleic anhydride (CMAn) was investigated in THF, 1,4-dioxane, and acetonitrile. The formation of the 1:1 charge transfer complex between HVB and CMAn was confirmed spectroscopically, and the corresponding equilibrium constant (K_eq) was determined as follows: K_eq = 0.19, 0.11, and 0.058 mol/L in THF, 1,4-dioxane, and CH₃CN, respectively. The copolymer composition is affected by the solvent, i.e., the content of HVB in the copolymer obtained in THF or 1,4-dioxane is lower than 50 mol % whereas the copolymer obtained in CH₃CN has excess of HVB units. The maximum rate of copolymerization was observed at a 1:1 initial comonomer mole ratio, irrespective of the solvent polarity. Plots of R_p/[HVB] vs. [HVB] gave a straight line with a slope and an intercept for the copolymerization in THF whereas a straight line in CH₃CN has no slope. On the basis of these results and ¹³C-NMR spectra of the copolymers, the mechanism of the predominant formation of alternating copolymers is discussed.     

Radical polymerization in the presence of complexing agents. III. Effect of low concentrations of ZnCl2 on the radical polymerization of methyl methacrylate

The formation of complexes between ZnCl₂ and methyl methacrylate (MMA) or between ZnCl₂ and AIBN was tested at two different polymerization temperatures, taking into account the Haeringer and Riess treatment. For any concentration of ZnCl₂ between 0.01 and 0.1 mole/liter the formation of ZnCl₂?MMA complexes is favored, whereas AIBN?ZnCl₂ complexes are hardly showed. The effect of zinc chloride on the stereostructure of poly(methyl methacrylate) was also investigated at both temperatures.