Mechanism of anionic polymerization of phenylacetylene

Anionic polymerization of phenylacetylene in the presence of butyllithium has been studied. It was shown that the process of polymerization is accompanied by the appearance and growth of the ESR signal with pronounced superfine structure. The model of polymerization was suggested according to which formation of low molecular polyphenylacetylene is caused the destruction of the active centers by means of electron transfer from the active center to the conjugated chain. This type of electron transfer may also be the fundamental reaction limiting the chain length in cationic polymerization of acetylene monomers. © 1992 John Wiley & Sons, Inc.     

Unpaired-electron localization and delocalization in macromolecules with a system of conjugated C=C bonds

The radical polymerization of acetylene monomers has been studied in a wide temperature range (77–340 K) using EPR spectroscopy, calorimetry, chromatography, and gravimetry It has been found that the growing macroradical is active, and its unpaired electron is localized at a terminal fragment of the molecule. However, it lost its activity even at small chain lengths (less than ten monomer units) because of delocalization of the unpaired electron along the system of conjugated double bonds.     

Laser-induced polymerization of functional derivatives of acetylene

Photochemical and photophysical processes leading to the formation of polymers with a conjugated double bond system under He-Cd laser irradiation have been considered. Phenyl- and diphenylpropargylamines are utilized as monomers. The polymerization of these monomers is carried out only in the presence of an electron acceptor such as tetrabromomethane. The polymer formation process is directed to obtaining an intermediate compound followed by its polymerization. The polymerization of intermediate compound is carried out by cationic reaction of triple bond in the presence of electron acceptor. The polymer structure and properties have been investigated. The parameters of lightsensitive layers based on diphenylpropargylamine have been determined.     

Characteristics of the radical polymerization of acetylene monomers

The radical polymerization of acetylene monomers is studied via electron spin resonance (ESR) spectroscopy, calorimetry, chromatography, and gravimetry within a wide range of temperatures (77–340 K). A growing macroradical with an unpaired electron localized on the terminal moiety of a macromolecule is shown to lose its activity, due to the delocalization of electron over the conjugated system of double bonds after attaining the very short length of 5–10 monomer units. This explains the low conversion and molecular masses of the synthesized polymers.     

New Phenomena in Organometallic‐Mediated Radical Polymerization (OMRP) and Perspectives for Control of Less Active Monomers

The impact of reversible bond formation between a growing radical chain and a metal complex (organometallic‐mediated radical polymerization (OMRP) equilibrium) to generate an organometallic intermediate/dormant species is analyzed with emphasis on the interplay between this and other one‐electron processes involving the metal complex, which include halogen transfer in atom transfer radical polymerization (ATRP), hydrogen‐atom transfer in catalytic chain transfer (CCT), and catalytic radical termination (CRT). The challenges facing the controlled polymerization of “less active monomers” (LAMs) are outlined and, after reviewing the recent achievements of OMRP in this area, the perspectives of this technique are analyzed.     

Radical processes in the pyrolysis of acetylene

The literature on the pyrolysis of acetylene below 1000 K is reviewed and it is shown that the reaction is a radical chain polymerization initiated by H atoms. The induction period is examined and shown to arise from a rapid autocatalysis produced by the very first product, vinyl acetylene. Data from studies of acetylene polymerization induced by vinyl acetylene and styrene are examined and shown to be in good qualitative agreement with the radical chain process presented. Measured and where needed, estimated rate constants are given to produce numerical estimates of chain length, rates of polymerization, induction period, and rates of initiation. It is further shown that all the products of the polymerization are capable of efficiently initiating chains in the system. An examination of the possible kinetics of vinylidene shows that it does not play any role in acetylene chemistry.     

Radical polymerization initiated by Bergman cyclization

The diradical generated by the Bergman cyclization of 3,4-benzocyclodec-3-ene-1,5-diyne is shown to initiate the radical polymerization of several monomers. Methacrylates are polymerized to high molecular weight by the diradical initiator much more efficiently than other monomers. The relation between the rate of polymerization and the degree of polymerization indicates that the polymer primarily propagates as a monoradical. This monoradical growth is in agreement with established theory predicting that diradical initiators can produce high polymer only through chain transfer followed by monoradical growth due to the rapid intramolecular termination of short diradical chains. In agreement with this mechanism, the polymerization rate of acrylonitrile initiated by the diradical is shown to increase by more than 20-fold upon addition of a chain transfer agent. Small molecule products consistent with intramolecular termination of diradical oligomers were isolated, and the structures of these molecules suggest how the diradical self-terminates in the absence of chain transfer.     

PPV Polymerization through the Gilch Route: Diradical Character of Monomers

Despite various studies on the polymerization of poly(p‐phenylene vinylene) (PPV) through different precursor routes, detailed mechanistic knowledge on the individual reaction steps and intermediates is still incomplete. The present study aims to gain more insight into the radical polymerization of PPV through the Gilch route. The initial steps of the polymerization involve the formation of a p‐quinodimethane intermediate, which spontaneously self‐initiates through a dimerization process leading to the formation of diradical species; chain propagation ensues on both sides of the diradical or chain termination occurs by the formation of side products, such as [2.2]paracyclophanes. Furthermore, different p‐quinodimethane systems were assessed with respect to the size of their aromatic core as well as the presence of heteroatoms in/on the conjugated system. The nature of the aromatic core and the specific substituents alter the electronic structure of the p‐quinodimethane monomers, affecting the mechanism of polymerization. The diradical character of the monomers has been investigated with several advanced methodologies, such as spin‐projected UHF, CASSCF, CASPT2, and DMRG calculations. It was shown that larger aromatic cores led to a higher diradical character in the monomers, which in turn is proposed to cause rapid initiation.     

In Situ AFM Investigation of Electrochemically Induced Surface‐Initiated Atom‐Transfer Radical Polymerization

Electrochemically induced surface‐initiated atom‐transfer radical polymerization is traced by in situ AFM technology for the first time, which allows visualization of the polymer growth process. It affords a fundamental insight into the surface morphology and growth mechanism simultaneously. Using this technique, the polymerization kinetics of two model monomers were studied, namely the anionic 3‐sulfopropyl methacrylate potassium salt (SPMA) and the cationic 2‐(metharyloyloxy)ethyltrimethylammonium chloride (METAC). The growth of METAC is significantly improved by screening the ammonium cations by the addition of ionic liquid electrolyte in aqueous solution.     

Symmetry breaking in cationic and anionic polymethine dyes

The electron density distribution and equilibrium molecular geometry of ionic polymethine dyes containing both the simplest terminal groups and carbo and heterocyclic residues were investigated by ab initio and AM1 methods. It is shown that charge waves and wave of the carbon–carbon bond lengths in the conjugated chain are of solitonic nature. The dimensions of the charge (electron or hole) soliton and geometrical (topological) soliton are practically unsensitive to the chain lengths, while the wave shape depends on the donor/acceptor strength of the terminal groups. If the length of the chromophore exceeds the dimension of the solitons, then the soliton center in the substituted ionic conjugated systems shifted to one of the chain ends, what leads to an appearance of the asymmetrical form. The conditions of this symmetry breaking (crucial number of the vinylene groups in the chain, effective length and donor/acceptor strength of the terminal residues, total charge) was found and was established that no moving of the solitons occurs in the unsubstituted conjugated ions.     

Palladium‐Catalyzed Chain‐Growth Polycondensation of AB‐type Monomers: High Catalyst Turnover and Polymerization Rates

Chain‐growth catalyst‐transfer polycondensations of AB‐type monomers is a new and rapidly developing tool for the preparation of well‐defined π‐conjugated (semiconducting) polymers for various optoelectronic applications. Herein, we report the Pd/PtBu₃‐catalyzed Negishi chain‐growth polycondensation of AB‐type monomers, which proceeds with unprecedented TONs of above 100 000 and TOFs of up to 280 s^?1. In contrast, related AA/BB‐type step‐growth polycondensation proceeds with two orders of magnitude lower TONs and TOFs. A similar trend was observed in Suzuki‐type polycondensation. The key impact of the intramolecular (vs. intermolecular) catalyst‐transfer process on both polymerization kinetics and catalyst lifetime has been revealed.     

Photocontrolled Synthesis of n‐Type Conjugated Polymers

Current approaches to synthesize π‐conjugated polymers (CPs) are dominated by thermally driven, transition‐metal‐mediated reactions. Herein we show that electron‐deficient Grignard monomers readily polymerize under visible‐light irradiation at room temperature in the absence of a catalyst. The product distribution can be tuned by the wavelength of irradiation based on the absorption of the polymer. Conversion studies are consistent with an uncontrolled chain‐growth process; correspondingly, chain extension produces all‐conjugated n‐type block copolymers. Preliminary results demonstrate that the polymerization can be expanded to donor–acceptor alternating copolymers. We anticipate that this method can serve as a platform to access new architectures of n‐type CPs without the need for transition‐metal catalysis.     

Laser induced polymerization of acetylene derivatives

He-Cd laser induced polymerization of aryl-propargylamines such as phenyl- and diphenylpropargylamines were studied. The polymerization of these monomers was shown to be realized only in presence of acceptor of electrons. Polymer formation process is based on the formation of an intermediate compound and its following polymerization by the radical reaction of C≡C bond. Photochemical and photophysical processes leading to the formation of intermediate compound were investigated. The polymers obtained were characterized by IR-, ESR-, NMR-spectroscopy. The conjugated double bond system formation is the main characteristic of these polymers. Some polymer properties were studied.     

Bond alternation in infinite polyene: Peierls distortion reduced by electron correlation

The formation of the bond-alternating structure in polyene is investigated both within the one-particle (Hartree-Fock) picture and including electron correlation effects by perturbation theory. An off-diagonal charge-density wave of the equi-distant structure is identified at the Hartree-Fock level as precursor of the bond-alternate state which is found by subsequent lattice optimization. The valence-shell correlation energy is calculated by using second-order Møller-Plesset perturbation theory. It is found to be finite also in the metallic one-dimensional chain and a comparison with results obtained for the acetylene unit shows that this method recovers ~-70–75% of the total valence-shell correlation. Correlation effects are shown to reduce the Peierls distortion and the corresponding energy barrier but the bond alternation persists also if the results are extrapolated to the case of full correlation.     

非共轭单体的活性自由基聚合进展

活性自由基聚合经过十多年的发展,已成为一种有效的高分子设计手段.代表性的活性自由基聚合技术包括氮氧调控自由基聚合(NMP),原子转移自由基聚合(ATRP)和可逆加成-断裂链转移(RAFT)聚合或通过黄原酸酯交换法设计大分子(MADIX).这些技术已成功应用到多数共轭单体上,但对非共轭单体的聚合控制还不太成功.本文总结了几类适合非共轭单体的活性自由基(共)聚合方法,主要有RAFT/MADIX体系,某些ATRP体系,碘退化转移体系及近年新出现的有机碲调控自由基聚合(TERP)和有机锑调控自由基聚合(SBRP)体系,其中,TERP和SBRP的独特性值得关注.     

Spontaneous polymerization of acrylamide in glycerol

The spontaneous polymerization of acrylamide in glycerol in the range of 250–350°C has been first observed and investigated. It has been shown that the polymerization proceeds during dissolution of acrylamide in glycerol and leads to formation of gel globules in which the growth of polymer chains takes place. The reaction occurs without termination of kinetic chains in the living polymerization mode. The effective chain transfer at a low concentration of active centers ensures a high yield of the polymer.     

在稀土体系催化下的丁二烯聚合动力学

本文应用键谷勤聚合动力学公式进行动力学研究。求出了活性中心数目,有关的动力学常数和聚合速度方程(R_p=k_p[C~*][M])并着重研究了聚合物活性链性质。 在链引发阶段,发现20℃和50℃聚合,属于迅速引发类型,在0℃时则是缓慢引发类型。聚合过程中,存在明显的链转移反应。Al(i-C_4H_9)_3是主要的链转移剂。在50℃聚合时,有活性中心失活现象发生,并表明其为双基终止。     

Time-resolved molecular beam mass spectrometry of the initial stage of particle formation in an Ar/He/C2H2 plasma

The temporal evolution of the neutral plasma chemistry products in a capacitively coupled plasma from argon/helium/acetylene is followed via molecular beam mass spectrometry with a time resolution of 100 ms. Several chemistry pathways are resolved. (i) The formation of C2nH2 (n = 2-5) molecules proceeds via the following sequence: the production of highly reactive C2H radicals in electron impact dissociation of C2H2 is followed by C2H induced chain polymerization of C2nH2 (n = 1-4). (ii) CnH4 (n = 4, 5, 6) compounds are detected already at an early stage of the discharge excluding polymerization reactions with C2H radical being responsible for their formation. Instead, vinylidene reactions with acetylene or mutual neutralization reactions of ionic species are proposed as sources of their formation. (iii) Surface reactions are identified as the source of C8H6. The measured hydrocarbon molecules represents possible precursors for negative ion formation via dissociative electron attachment reactions and can hence play a crucial role in particle nucleation. On the basis of the comparison of our data with available experimental and modeling results for acetylene plasmas in the literature, we propose C2nH2 (n > 1) molecules as important precursors for negative ion formation.     

二过碘酸合银(II)氧化还原引发丙烯酸甲酯在尼龙1010上接枝共聚合反应的研究

二过碘酸合银（ＩＩ）氧化还原引发丙烯酸甲酯在尼龙１０１０上接枝共聚合反应的研究刘盈海刘卫宏赵敏孟劲功（河北大学化学系保定０７１００２）关键词二过碘酸合银（ＩＩ）钾，尼龙１０１０，氧化还原引发，丙烯酸甲酯，接枝共聚目前Ｃｅ（ＩＶ）被认为是一种十分...