Living cationic polymerizations initiated by phosgene

Living cationic polymerization of isobutylene and styrene was performed by using phosgene as initiator and solvent, AlCl₃ as coinitiator in homogeneous phase. Polymerization of isobutylene by using phosgene and TiCl₄ also proved to be a living process, however, initiation in this case was performed by H₂O impurities, and the system was heterogeneous. In case of the COCl₂/AlCl₃ initiating system, ketonic carbonyl functionality was built-in into the polymer. The living character of the process, both in case of AlCl₃, and of TiCl₄ was demonstrated by the linear increase of ¯M_n with the cumulative amount of the monomer successively added, and by the conversion and temperature jump at every monomer additon. Observations on the permanence of the color (intensive yellow with IB and deep red with St) also support that the propagating cations are long living. An explanation of the observed phenomena is suggested on the base of Pearson's theory of hard and soft acids and bases.     

Substituted vinyl bromides as photoinitiators for cationic polymerizations

Summary The cationic polymerization of typical monomers, e.g. of oxiranes such as cyclohexene oxide and 1,4-butanedioldiglycidyl ether or of vinyl ethers such as n-butylvinyl ether, is induced by UV irradiation of monomer formulations containing a substituted vinyl bromide as light absorbing agent and an appropriate non-absorbing onium salt. Experiments performed with 1,2,2-triphenyl vinyl bromide or 1,2,2-tri(4-methoxyphenyl) vinyl bromide and N-ethoxy-2-methyl-pyridinium or triphenyl sulfonium hexafluorophosphate are described in the paper.     

异丁烯-对甲基苯乙烯正离子无规共聚反应的影响因素

以正己烷（n-Hex）为溶剂或n-Hex/一氯甲烷（CH3Cl）混合物为溶剂体系、氯化氢/氯化乙基铝/二氯二氰基苯醌为引发体系,采用正离子溶液聚合法对异丁烯（IB）与对甲基苯乙烯（p-Me St）在-90~-20℃下进行无规共聚,考察了n-Hex/CH3Cl（体积比）、二氯乙基铝（Et Al Cl2）/一氯二乙基铝（Et2Al Cl）（摩尔比）及反应温度对共聚反应转化率和共聚物相对分子质量的影响。结果表明,随着n-Hex/CH3Cl混合溶剂体系中n-Hex体积分数的增加,共聚反应转化率和共聚物的相对分子质量均下降;在Et Al Cl2/Et2Al Cl共引发体系中,随着Et2Al Cl摩尔比的增加,共聚物的相对分子质量不断增大;随着聚合反应温度的升高,共聚反应转化率和共聚物的相对分子质量均下降。     

Slow initiation by tert-butoxybenzenes in living cationic polymerization of isobutylene

Summary tert-Butoxybenzenes including the 4-substituted derivatives of anisole, toluene and p-chlorobenzene have been synthesized and studied as initiators in combination with TiCl₄ for polymerization of isobutylene (IB) in CH₂Cl₂/methylcyclohexane (MeCHx) solvent mixtures at -78°C. Living polymerizations with slow initiation were observed by the allmonomer-in (AMI) and incremental monomer addition (IMA) techniques, and polymers with narrow molecular weight distribution (MWD) (M_w/M_n>1.1) were obtained under certain conditions. Aging of the initiating system prior to charging the monomer does not improve the initiating efficiency. It has been found that the initiating efficiency can be increased by increasing the solvent polarity, however, the relative volume of CH₂Cl₂ is limited in order to avoid polymer precipitation and bimodal MWD.     

Dynamic behavior of a continuous autothermal isobutylene polymerization reactor

Industrial autothermal cationic isobutylene polymerization reactors may present very complex dynamic behavior and difficult operation. A mathemathical model was developed to describe the operation of an autothermal solution industrial reactor, and some possible sources of complex dynamical behavior were analyzed. The results obtained indicate that the most probable source of the complex behavior observed industrially is the existence of adventitious impurities in the feeed stream. The effects caused by the presence of adventitious impurities on process operation and product properties were investigated for both polymerization and oligomerization. In the first case, impurities influence the reactor productivity but do not change the polymer quality. In the oligomerization, both the polymer quality and the reactor productivity are seriously affected by the existence of impurities in the feed stream. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1403–1413, 1997     

Conductance stopped-flow study of cationic polymerizations of p-methoxystyrene and styrene

Summary Conductance stopped-flow analysis on the initial phase of cationic polymerizations of p-methoxystyrene and styrene revealed rapid changes in conductance (within 20–50 ms) that were related to the initiation process. Initiation rate constants were obtained for CF₃SO₃H, CH₃COClO₄, and BF₃O (C₂H₅)₂ initiators in 1,2-dichloroethane at 30°C. They agreed closely with those determined by stopped-flow spectroscopy, and decreased with increasing monomer concentration.     

Synthesis of hybrid liquid crystalline block copolymers by combination of cationic or promoted cationic and free-radical polymerizations

Summary The synthesis of two new classes of liquid crystalline block copolymers (1–5) by a two-step combination of cationic and free-radical polymerizations is described. An azomacroinitiator was prepared first by cationic polymerization of tetrahydrofuran or promoted cationic polymerization of cyclohexene oxide, which was then used to initiate the free-radical polymerization of an acrylate monomer containing a variously substituted biphenyl mesogenic group. The semicrystalline and liquid crystalline blocks were essentially microphase-separated and gave rise to different thermotropic mesophases.     

Residence time dependence of molecular weight distributions in continuous polymerizations

Residence time distribution (RTD) is a spectral property of contiuous chemical reactors. Batch reactors may be viewed as having “monodisperse” residence time distributions. This article discusses molecular weight distributions (MWDs) of polymeic materials formed in continuous and in semicontinuos process and how they are affected by reaction time distributions. All synthetic high polymers, even those Prepared in batch reaction, possess a MWD which may sometimes, for a given monomer, be altered chemically by a proper choice of catalyst and diluent. An interesting concept suggested by the present work is the prospect of “tailoring” the MWD for a given monomer-catalyst-diluent system physically by selecting appropriate reactor conditions. Hence, althought this work involves analysis the results may provide a guide to synthesis.     

Investigation of the mechanism of living cationic polymerization of isobutylene by B11 NMR spectroscopy

Summary The living carbocationic polymerization of isobutylene initiated by tri-cumyl-ether (1)/BCl₃ and tricumyl-acetate(2)/BCl₃ was investigated by B¹¹ NMR spectroscopy in the presence and absence of DMSO. With BCl₃, 1 yields tri-cumyl-chloride and BCl₂OMe due to fast exchange reaction, while 2 forms complexes. If the 1/BCl₃ mixture contains DMSO, well defined complexes can be detected, i.e., DMSO.BCl₃ and BCl₂OMe.DMSO. In the system 2/BCl₃/DMSO neutral complexes with broad NMR signals are formed. In the presence of isobutylene (real polymerization mixture) the same complexes can be detected.     

Modeling of polymerization reactions. I. The cationic polymerization of isobutylene by aluminum organic compounds

This paper describes the development of a mathematical model for the polymerization of isobutylene initiated with Et₂AlCl + Cl₂. Previous experiments have shown that this polymerization is “kinetically living”. A computer analysis based on our mathematical model permits the calculation of the theoretical conversion–time curves, the molecular weight averages, and polydispersity. The good agreement between experimental and theoretical results suggests that the reaction mechanism proposed and the mathematical model derived are quite correct.     

A possible “direct initiation” of cationic polymerization of isobutylene by boron trichloride in methylene chloride

Summary Initiation of the cationic polymerization of isobutylene by BCl₃ requires a cocatalyst in most cases. However, we found conditions (=-30°C, CH₂Cl₂ as solvent, BCl₃ 0.0l m) where a direct initiation by BCl₃ (i.e. with no cocatalyst) is possible. We showed that in such conditions HCl is not a cocatalyst and that H₂O content is too low to explain the results (high vacuum and highly purified reactants and solvent).The conversion increases linearly with tine increasing concentration of BCl₃.A mechanism is proposed.     

MWD control in continuous free-radical polymerizations through forced oscillations of the transfer agent feed

This paper studies the effect of forced-feed oscillations of an intentionally added chain transfer agent on isothermal free-radical polymerizations carried out in continuous stirred-tank reactors (CSTRs). A solution polymerization is first considered. The influence on the molecular weight distribution (MWD) of rectangular waves and impulsive trains of the transfer agent feed is theoretically and experimentally investigated. The main result is that (within certain limits) the average polydispersity can be increased at will with respect to its corresponding steady-state (SS) value, without affecting the average number average chain length or the instantaneous monomer and initiator conversions. This result is extended to an emulsion copolymerization under sinusoidal oscillations of the transfer agent feed, where the “decoupling” between the average molecular polydispersity and other parameters (conversions, number average molecular weight, average number of branches per molecule, and the particle-size distribution) is also produced.     

Effect of the composition of the initiating complex acyl halides/aluminium bromide on the cationic polymerization of isobutylene

On the basis of ¹H and ¹³C spectra obtained for solutions of complexes of acyl halides with aluminium bromide RCOX·nAlBr₃ (X = Cl, Br; n = 1, 2), it is shown that these adducts can exist in solution as donor–acceptor complexes, acyl salts, or combinations of both forms. The nature of the cationic initiating species for each case is predicted. The predictions coincide well with experimental results obtained by analysis of the isobutylene polymers prepared with these initiating complexes. Initiation by the 1:2 complexes allows polymeric molecules to be synthesized with an acyl group at one end. These polymerization processes have some of the characteristics of living polymerizations. The possibility for quantitative estimation of such systems using the criteria of ‘approach to livingness’ is demonstrated. © 2000 Society of Chemical Industry     

Alkylation of phenols with isobutylene

The kinetics of absorption of isobutylene in molten phenol, p-cresol and pyrocatechol were studied in a stirred cell using concentrated sulphuric acid as a catalyst. The absorption of isobutylene in molten phenols was found to conform to pseudo-first-order mechanism. The products of various reactions were analysed by gas-liquid chromatography. The absorption of isobutylene in mono-t-butyl derivatives of phenols was studied in an agitated glass reactor. It was possible to eliminate the effect of diffusion. The values for the rate constant of the second-order reactions between isobutylene and p-t-butylphenol at 104°, isobutylene and 2-t-butyl-p-cresol at 70° and isobutylene and 4-t-butylpyrocatechol at 104° were 49, 40 and 56 ml/g mole/sec, respectively. Mass transfer influenced the rate of alkylation of phenol and p-cresol with isobutylene in a bubble column. However, no significant improvement was observed in the yield of the mono-derivative, which in some cases is the desired product.     

异丁烯的开发利用

异丁烯是一种非常重要的化工原料,若用作精细化工的原料,其身价显得更高。自世界各发达国家对清洁汽油的要求增加后,MTBE的用量得到快速增长,这就使异丁烯供需也随之趋于紧张。同时随着世界各国加快发展高附加值精细化工产品,作为精细化工原料的纯异丁烯的需求也随之增加。