Donor-Acceptor Complexes in Copolymerization. IV. Alternating Tendency in Free Radical Copolymerization. NMR Analyses of Alternating and Random Copolymers

An NMR investigation was carried out on variable composition, random and equimolar, alternating copolymers of acrylonitrile (A) with styrene (S), isoprene (I), and butadiene (B). The NMR spectra of the SA copolymers contained peaks at 3 τ (aromatic ring protons), 7.2-7.5 τ (CH protons of A), and 8.1 -8.5 τ (CH and CH₂ protons of S and CH₂ protons of A). All NM R peaks of the alternating SA copolymer were shifted to the higher field due to the shielding effect of S. The NMR spectra of the IA copolymers contained peaks at 4.72-4.91 τ (?CH protons of I), 7.27-7.4 τ (CH protons of A), 7.71-7.93 τ (CH₂ protons of I), and 8.35 τ (CH₃ protons of I and CH₂ protons of A). The peaks at 4.72 τ (?CH) and 7.72 τ (CH₂) were assigned to I in the I-A diad and the peaks at 4.91 τ (?CH) and 7.93 τ (CH₂) were assigned to I in the I-I diad. The NMR spectra of the BA copolymers contained peaks at 4.4-4.6 τ (?CH protons of B), 7.2-7.5 τ (CH protons of A), 7.71-7.97 T (CH₂ protons of B), and 8.0-8.4 τ (CH₂ protons of A). The peaks at 4.42 τ (?CH) and 7.71 τ (CH₂) were assigned to B in the B-A diad and the peaks at 4.6 τ (?CH) and 7.9 τ(CH₂) were assigned to B in the B-B diad. The alternating structure of the copolymers prepared through metal halide-activated complexes was confirmed by NMR analysis. The random copolymers prepared by free radical initiation contain a high concentration of alternating sequences, as anticipated from the values of r₁ and r₂ where r₁(S, I, and B) is 6-10 times higher than r₂ (A).     

Donor-Acceptor Complexes in Copolymerization. LIX. Alternating Diene-Dienophile Copolymers. 13. Copolymerization of Dicyclopentadiene and Maleic Anhydride

The solution and bulk copolymerization of dicyclopentadiene (DCP) and maleic anhydride (MAH) occurs over the temperature range 80–240°C, upon the addition of a free-radical catalyst which has a short half-life at the reaction temperature. An unsaturated 1/1 MAH/DCP copolymer, derived from the copolymerization of MAH with the norbornene double bond, followed by a Wagner-Meerwein rearrangement, is obtained in the presence of a large excess of DCP at 80° C, while a saturated 2/1 MAH/ DCP copolymer, derived from the cyclocopolymerization of the residual cyclopentene unsaturation, is obtained at higher temperatures or in the presence of excess MAH. The copolymers prepared under other conditions with intermediate MAH/DCP mole ratios contain both 1/1 and 2/1 repeating units. The copolymer obtained from bulk copolymerization above 170° C contains units derived from cyclopentadiene-MAH cyclocopolymerization as well as DCP-MAH copolymerization.     

Donor-Acceptor Complexes in Copolymerization. XXXVI. Alternating Diene-Dienophile Copolymers. 4. Copolymerization of Furan and 2-Methylfuran with Maleic Anhydride

Abstract

The copolymerization of furan and 2-methylfuran with maleic anhydride in the presence of a radical catalyst yields equimolar, alternating copolymers in which the furan units have a 2,5-linkage (NMR and IR). The copolymerization appears to have a floor temperature of about 40°C. The furan-maleic anhydride Diels-Alder adduct polymerizes in solution in the presence of a radical catalyst at temperatures above 60°C to yield the identical copolymer as is obtained from the monomers. The adduct undergoes a retrograde reaction above 60°C to regenerate the monomers which then copolymerize through excitation of the ground state comonomer charge transfer complex.     

Mechanism of Alternating Copolymerization of Vinyl Acetate and Maleic Anhydride

Vinyl acetate and maleic anhydride are known to give 1:1 alternating copolymerization regardless of the monomer feed composition. The existence of a charge transfer complex between the comonomers has been shown and its equilibrium constant determined.

The mechanism has been discussed, starting from a study of the copolymerization rate when varying the solvent, the temperature, and the concentration of comonomers.     

Donor-Acceptor Complexes in Copolymerization. LXIII. Alternating Diene-Dienophile Copolymers. 15. Copolymerization of Cyclopentadiene and the Isomeric N-Phenyl-5-norbornene-2,3-dlcarboximides with N-Phenylmaleimide

Abstract

The copolymerization of cyclopentadiene (CPD) and N-phenyl-maleimide (NPMI) at 80–195°C, in the presence of a radical catalyst having a short half-life at the reaction temperature and less than 25% solvent, yields a 1:2 CPD-NPMI copolymer (DP 2–3) which is identical (IR, NMR) to the endo 1:1 copolymer (DP 18) obtained under the same conditions from the copolymerization of the endo CPD-NPMI Diels-Alder adduct and NPMI. The exo CPD-NPMI adduct copolymerizes with NPMI under the same conditions to yield an exo 1:1 copolymer (DP 8). Under the same conditions the homopolymerization of the endo and exo CPD-NPMI adducts is effected in the melt at temperatures up to 260°C and in solution at 120–155°C. The homopolymers (DP 3–7) prepared below 210°C retain the configuration of the adducts while the homopolymers prepared at 260°C from either isomer contain both endo and exo configurations due to isomerization. The participation of excited species is suggested by the requirement for high-speed decomposition of radical catalysts to effect homopolymerization and copolymerizations.     

Kinetic Features and Mechanism of Alternating Copolymerization of lndene with Maleic Anhydride

The radical copolymerization of indene (IN) with maleic anhydride (MA) was investigated. The charge-transfer complexes (CT complexes) between comonomers were studied by means of spectrophotometric measurements. It was found that the maximum copolymerization rate occurred at a comonomer feed ratio that did not correspond to the composition of the CT complex and the composition of copolymer. It was shown that rate maximum was displaced towards an excess of IN in the solvents with strong donicity. The Acceptor Number of solvent influences neither the initial rate nor the position of the rate maximum. Some kinetic calculations were made to assess values of the cross-propagation rate constants and to elucidate the mechanism of propagation of macromolecular chains.     

Investigations of the Mechanism of Alternating Copolymerization with Charge-Transfer Interaction of the Monomers

The applicability of the method of Giese to the measurement of the influence of monomer reactivity is examined. The reaction of alkyl mercuric salts with sodium borohydride permits the production of alkyl (cyclohexyl and butyl) radicals. Since hydrogen radicals are present in high concentration, the addition of alkenes to the reaction mixture leads to radicals from the alkenes. Further addition of alkene (polymerization) can be nearly completely excluded in this way. The composition of the reaction products is determined by gas chromatography. The addition rate of the alkenes relative to styrene allows correlation with the e value of the Q-e scheme of Alfrey and Price. The method answers the question of how far addition of the monomer complex occurs in one step or as separate addition of both monomers during copolymerization in the presence of charge-transfer (CT) complexes of the monomers. The investigations are performed by using the styrene/acrylonitrile/ZnCl₂system, and it is demonstrated that the reactivity of the complexed     

Spontaneous Alternating Copolymerization via Zwitterion Intermediates

This article describes a new concept of copolymerization which occurs spontaneously without any added catalyst. A nucleophilic monomer (M_N) combines with an electrophilic one (M_E) to generate a zwitterion ^[+]M_N—M, which is responsible for the initiation and propagation of copolymerization. Twenty-three novel copolymerizations have been explored on the basis of the new concept. M_N monomers which have been investigated are five- and six-membered cyclic imino ethers, dihydro-2(3H)-furanimine, an azetidine, a cyclic phosphinic acid ester and a Schiff base; the M_E monomers include β-propiolactone, a cyclic dicarboxylic acid anhydride, a sultone, acrylic acid, acrylamide, a β-hydroxyalkyl acrylate and ethylenesulfonamide. In most combinations, alternating 1 : 1 copolymers were produced. In addition to the above-mentioned combinations, the alternating 1 : 1 copolymerization of cyclic phosphite with α-keto acid was discovered.     

Donor-Acceptor Complexes in Copolymerization. III. Conjugated Diene-Acrylonitrile Copolymerization in the Presence of Metal Halides

The copolymerization of isoprene or butadiene with acrylonitrile in the presence of zinc chloride or ethylaluminum sesquichloride, in the presence or absence of a free radical catalyst, at 30-70°C yields an equimolar, diene-acrylonitrile alternating copolymer containing more than 90% trans-1,4 unsaturation, irrespective of monomer charge. The copolymer results from the homopolymerization of a diene-acrylonitrile…metal halide transoid charge transfer complex. When ZnCl₂ is the electron-accepting metal halide and the polymerization is carried out at temperatures of 50°C and higher or to high conversions, the equimolar copolymer is accompanied by a high acrylonitrile polymer, and in the presence of a radical catalyst, by a normal radical copolymer. In the presence of the organoaluminum halide and in the absence of a radical catalyst, the alternating copolymer is the only product, irrespective of monomer charge. However, in the presence of a radical catalyst and at high acrylonitrile monomer charges, e.g., D/AN = 10/90, the alternating copolymer is accompanied by a normal radical copolymer. The formation of equimolar, alternating copolymer at all monomer ratios and in the absence or presence of a radical catalyst indicates that the (D-AN…MX) charge transfer complex readily undergoes homopolymerization and does not copolymerize with free diene or acrylonitrile or with the AN-AN…MX complex.     

交替共聚中的自由单体－络合理论

自由基交替共聚理论是共聚合研究中的重要理论问题。本文从交替共聚各种理论中整理出自由单体－络合理论，并从机理、共聚组成和动力学等几方面进行分析和综述，认为该理论能比较全面、真实地反映交替共聚的机理。     

Synthesis of Copolymers by Living Carbanionic Alternating Copolymerization

The synthesis and characterization of copolymers from styrene and 1,3‐pentadiene (two isomers) are reported. Styrene/1,3‐pentadiene (1:1) copolymerization with carbanion initiator yield living, well‐defined, alternating (r₁ = 0.037, r₂ = 0.056), and highly stereoregular copolymers with 90%–100% trans‐1,4 units, designed M_ns and low Ð_Ms (1.07–1.17). The first‐order kinetic resolution and NMR spectra demonstrate that the copolymers obtained possess strictly alternating structure containing both 1,4‐ and 4,1‐enchaiments. Also a series of copolymers with varying degrees of alternation are synthesized from para‐alkyl substituted styrene derivatives and 1,3‐pentadiene. The degree of alternation is strongly dependent on the polarity of solvent, reaction temperature, type of trans‐cis isomer of 1,3‐pentadiene and para‐substituted group in styrene. The macro zwitterion forms (SPC) through the distribution of electronic charges from the donor (1,3‐pentadiene) to the acceptor (styrenes) are proposed to interpret the carbanion alternating copolymerization mechanism. Owing to the versatility of the carbanion‐initiating reaction, the present alternating strategy based on 1,3‐pentadiene (especially cis isomer) can serve as a powerful tool for precise control of polymer chain microstructure, architecture, and functionalities in one‐pot polymerization.

     

General Method for Evaluation of Alternating Tendency in Copolymerization

A new method for deriving expressions for the mole fractions of alternating n-ads and the average lengths of the alternating sequences of n-component copolymers (n > 2) was developed based on the apparatus of finite Markov chains. These characteristics are considered as indexes of alternating tendency forn-component copolymerization. A specific property of n-component copolymerization (n > 3) compared with binary copolymerization is the fact that alternating n-ads might be constructed by two, three, or more types of monomeric units. In order to express this specific property of three and multi-component copolymers the term, alternating order, is introduced. The method developed in the paper permits the alternating indexes to be determined differentially in dependence of alternating order. Expressions for the average lengths and the compositions of all possible alternating sequences starting with a given monomer unit and ending with unit found only at that position, are derived as well. The alternating indexes for binary radical copolymerization of styrene and methyl methacrylate and for ternary radical copolymerization of styrene, methyl methacrylate, and acrylonitrile were determined.     

芳香醛亚胺与一氧化碳的交替共聚反应

以苯乙酰基四羰基钴作为催化剂,研究了对芳香醛亚胺与一氧化碳(CO)的交替共聚反应.采用6种芳香醛亚胺单体,分别与CO进行交替共聚反应,得到了6种新的多肽类聚合物.利用核磁共振谱、红外光谱、凝胶渗透色谱(GPC)及MALDI-TOF质谱等对聚合物的结构进行了表征.探讨了芳香醛亚胺苯环上取代基的位阻效应和电子效应对聚合反应的影响.结果表明,聚合物链终止端存在3种不同类型的端基,分别具有慕尼黑酮类结构、咪唑啉类结构以及酰胺类结构,对这些端基的形成机理进行了讨论.     

Donor-Acceptor Complexes in Copolymerization. XXXVII. Alternating Diene-Dienophile Copolymers. 5. Formation of Conjugated Diene-Maleic Anhydride Copolymers through Retrograde Dissociation of Furan-Maleic Anhydride Diels-Alder Adduct

Abstract

The equimolar, alternating copolymer of isoprene, as well as other conjugated dienes, and maleic anhydride is formed by the radical catalyzed reaction of the conjugated diene with maleic anhydride in the presence of furan as well as with the furan-maleic anhydride Diels-Alder adduct. The retrograde dissociation of the cyclic adduct above 60°C regenerates furan and maleic anhydride which in the presence of isoprene forms the isoprene-maleic anhydride ground state complex. The latter yields the corresponding cyclic adduct in the absence of a radical catalyst and undergoes excitation and homopolymerization in the presence of a catalyst.     

Alternating Ethene/Propene Copolymerization with a Metallocene Catalyst

A small variation in the substituent R′ on the metallocene catalyst employed in the copolymerization of ethene and propene leads to a highly alternating (81–83%) structure ( 1 ) rather than a statistical copolymer. Such copolymers were until recently only accessible by hydrogenation of polyisoprene or 1,4-poly(pentadiene).     

Elucidation of the Alternating Copolymerization Mechanism of Epoxides or Aziridines with Cyclic Anhydrides in the Presence of Halide Salts

Organic halide salts in combination with metal or organic compound are the most common and essential catalysts in ring-opening copolymerizations (ROCOP). However, the role of organic halide salts was neglected. Here, we have uncovered the complex behavior of organic halides in ROCOP of epoxides or aziridine with cyclic anhydride. Coordination of the chain-ends to cations, electron-withdrawing effect, leaving ability of halide atoms, chain-end basicity/nucleophilicity, and terminal steric hindrance cause three types of side reactions: single-site transesterification, substitution, and elimination. Understanding the complex functions of organic halide salts in ROCOP led us to develop highly active and selective aminocyclopropenium chlorides as catalysts/initiators. Adjustable H-bonding interactions of aminocyclopropenium with propagating anions and epoxides create chain-end coordination process that generate highly reactive carboxylate and highly selective alkoxide chain-ends.     

Co-syndiospecific Alternating Copolymerization of Functionalized Propylenes and Styrene by Rare-Earth Catalysts

The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of functional polymers, but studies toward this goal have met with only limited success to date. Now, the co-syndiospecific alternating copolymerization of methoxyphenyl- and N,N-dimethylaminophenyl-functionalized propylenes with styrene by half-sandwich rare-earth catalysts is reported. This reaction efficiently afforded the corresponding functionalized propylene-alt-styrene copolymers with a perfect alternating sequence and excellent co-syndiotacticity (rrrr >99 %), thus constituting the first example of co-stereospecific alternating copolymerization of polar and non-polar olefins.     

Alternating Copolymerization of Styrene and N-(4-Bromophenyl)Maleimide

Abstract

Free radical copolymerization of styrene (St) and N(4-bro-mophenyl)maleimide (4BPMI) in dioxane solution gave an alternating copolymer in all proportions of feed comonomer compositions. The monomer reactivity ratios were found to be r ₁, = 0.0218 ± 0.0064 (St) and r ₂, = 0.0232 ± 0.0112 (4BPMI), and the activation energy of the copolymerization reaction for the equimolar ratios of comonomer was E _a, = 51.1 kJ/mol. The molecular weights of the copolymers obtained are relatively high, the T _g's showed similar values (490 K), and the thermal stability is higher than that of polystyrene. The initial rate of copolymerization depends on the total concentration of the comonomers and the maximum occurred at higher 4BPMI mol fractions; however, the overall conversion is highest at equimolar comonomer composition. It has been shown that a charge-transfer complex participates in the process of copolymerization. The initial reaction rate was measured as a function of the monomer molar ratios, and the participation of the charge-transfer complex monomer and the free monomers was quantitatively estimated.     

Heterocycle/Heteroallene Ring-Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

Heteroatom-containing polymers have strong potential as sustainable replacements for petrochemicals, show controllable monomer–polymer equilibria and properties spanning plastics, elastomers, fibres, resins, foams, coatings, adhesives, and self-assembled nanostructures. Their current and future applications span packaging, house-hold goods, clothing, automotive components, electronics, optical materials, sensors, and medical products. An interesting route to these polymers is the catalysed ring-opening copolymerisation (ROCOP) of heterocycles and heteroallenes. It is a living polymerization, occurs with high atom economy, and creates precise, new polymer structures inaccessible by traditional methods. In the last decade there has been a renaissance in research and increasing examples of commercial products made using ROCOP. It is better known in the production of polycarbonates and polyesters, but is also a powerful route to make N-, S-, and other heteroatom-containing polymers, including polyamides, polycarbamates, and polythioesters. This Review presents an overview of the different catalysts, monomer combinations, and polymer classes that can be accessed by heterocycle/heteroallene ROCOP.