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.     

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.     

Carbocationic polymerization in supercritical carbon dioxide

Polymerization of isobutylene (IB) in supercritical carbon dioxide (SC·CO₂) at 32.5°C and 140 bar by the use of 2-chloro-2,4,4-trimethyl-pentane (TMPCl) initiator in conjunction with a mixture of TiCl₄/BCl₃ leads to well-defined polyisobutylenes (PIB) capped by a t-Bu head group and a t-Cl tail group (tBu-PIB-Cl^t) of M_n1800 g/mole and M_w/M_n=1.3. The TiCl₄/BCl₃ mixture may be viewed a new Friedel-Crafts Acid that effects rapid initiation, essentially chaintransferless propagation and reversible termination. The mechanism of IB polymerization of TiCl₄/BCl₃ mixtures is discussed.     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers)

Summary The possibility of undesirable intramolecular cycloalkylation exists in the polymerization of iso-butylene induced by the p-dicumyl chloride/BCl₃ inifer system. A scheme has been proposed which shows the sequence of reactions leading to indane skeletons. The structure of the indane derivatives has been characterized by ¹H NMR spectroscopy. Systematic experiments have been carried out using low isobutylene and high p-dicumyl chloride concentrations leading to polyisobutylene oligomers needed for accurate endgroup analysis. The effect of temperature, solvent composition (polar/nonpolar) , isobutylene and BCl₃ concentration on the extent of indane skeleton formation has been investigated. Indane skeleton formation can be completely suppressed by the use of relatively non-polar media, e.g., 11 mixture of CH₂Cl₂ :n-C₆H₁₄, at or below –40°C, and conditions under which symmetrical telechelic polyisobutylenes can be obtained have been defined.     

Synthesis,characterization and diels-alder extension of cyclopentadiene telechelic polyisobutylene

The use of 1-chlorodicyclopentadiene (DCp-Cl) as a minifer for the polymerization of isobutylene leading to asymmetric telechelic polymers having dicyclopentadienyl head groups and t-chloro tail groups, has been investigated. BCl₃ is ineffective, however, diethylaluminum chloride was found to be a suitable coinitiator for the polymerization. According to kinetic investigations chain transfer to monomer is absent and DCp-Cl is an efficient minifer. Polymer characterization indicated a DCp functionality close to 1.0. The t-chloro functionality was 0.27, probably due to side reactions of the t-chloro group with the strong Lewis acids formed during the polymerization.Part XXXII of the series New Telechelic Polymers and Sequential Copolymers by Polyfunctional Initiator-Transfer Agents (Inifers).The first part of this series was presented at the Kansas City Am. Chem. Soc. Meeting, September 12–17, 1982, Polym. Prepr., 23, 103 (1982) which is considered Part XXXI of the series New Telechelic Polymers and Sequential Copolymers by Polyfunctional Initiator-Transfer Agents (Inifers).     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer-agents (inifers)

Summary Linear and three-arm star telechelic polyisobutylenes PIB's with perfect end-functionalities (¯F_n = 2.0±0.1 or 3.0±0.1) have been synthesized by the use of 1,3-di(2-bromo-2-propyl)5-tert-butylbenzene (m-tBuDCB) binifer or 1,3,5-tri(2-bromo-2-propyl)benzene (TCB) trinifer/BCl₃ systems. The counter anion is most likely BCl₃Br in these polymerizations. The inifer efficiencies of these brominated inifers are lower than those of the chlorinated analogues, probably because of side reactions during the polymerization. The rate of chain transfer to inifer is similar for both the chlorinated or brominated inifer/ BCl₃ systems but that of termination is faster in the former system. Elementary analysis shows that the PIB's obtained with m-tBuDCB carry 90% bromine and 10% chlorine end groups.     

Polyisobutylene-containing block polymers by sequential monomer addition

Novel poly(acenaphtylene-b-isobutylene-b-acenaphtylene) (PAc-PIB-PAc) triblock copolymers exhibiting thermoplastic elastomer (TPE) properties have been prepared. The synthesis involved the addition of acenaphtylene (Ac) to living polyisobutylene dications (PIB) obtained by living isobutylene (IB) polymerization induced by the dicumyl methyl ether (DiCumOMe)/TiCl₄ initiating system at-80°C. The triblocks contain very short polyacenaphtylene (PAc) blocks (M_n9,000) and consequently yield very soft, low modulus TPEs. Efforts to develop conditions for the living carbocationic polymerization (LCPzn) of Ac have failed.For Part VIII of this subseries see J. P. Kennedy, S. Midha, B. Keszler: Macromolecules (in press)     

Carbocationic polymerizations in supercritical carbon dioxide

The first carbocationic polymerization of isobutylene (IB) in supercritical carbon dioxide (SC·CO₂) has been accomplished. It was demonstrated that in CO₂ at 32.5°C and 120 bar the 2-chloro-2,4,4-trimethyl-pentane (TMPCl)/SnCl₄ and TMPCl/TiCl₄ initiating systems lead to 30% IB conversion, and gave polyisobutylenes (PIB) with M_n2000 and M_w/M_n2.0. This is the highest temperature IB was ever polymerized to reasonably high molecular weight products. Polymerizations at 32.5 °C under similar but conventional (non-living) conditions in the absence of SC·CO₂ would yield only very low molecular weight oligomers (tetramers). The structure of the PIBs obtained in SC·CO₂ is virtually identical to those obtained at much lower temperatures in conventional liquid-phase systems indicating the presence of chain transfer to monomer in both systems. In contrast to TMPCl initiated polymerizations, the 1,3-bis-(2-hydroxy-2-propyl)-5-tert-butylbenzene (HPBB) initiator in conjunction with BCl₃ and SnCl₄ yields only oligomers (M_n500) in SC·CO₂.     

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.     

Palladium-Mediated Ring-Opening Reactions of Strained Cyclotetrasilanes

Room-temperature ring-opening polymerization of the strained monomer 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane mediated by palladium complexes was attempted. Examination of the reaction products between the cyclotetrasilane and the metal complex at high concentrations indicated that insertion of one cyclotetrasilane molecule between the ligand–palladium bond was followed by reductive elimination of the tetrasilane. Among the palladium complexes examined were (³-allyl)PdCp [Cp=⁵-cyclopentadienyl], [(³-allyl) PdCl]₂, (³-allyl)PdCl(PPh₃), (³-allyl)PdCl(PPh₃)₂, (³-allyl)Pd(PPh₃)₃ and PdCl₂(PPh₃)₂. Reaction of 1,1,2,3,4-pentamethyl-2,3,4-triphenylcyclotetrasilane with (³-allyl)PdCp provides similar products.     

Direct monitoring of cationic polymerization by temperature,conductivity and permittivity measurements

Summary Direct monitoring of cationic polymerization was accomplished by simultaneous measurement of the average dielectric constant, representing the dipoles, of the conductivity, produced by unpaired ions, and of the temperature, characteristic for reaction rate. The ionogenic equilibria during the living polymerization of isobutylene by 1, 3, 5-tris(2-methoxy-2-propyl)benzen/BCl₃ in CH₂Cl₂ at-25°C were demonstrated. Temperature, resistance and capacitance were measured directly in the reaction mixture by a specially designed instrument.Both the conductivity and the average dielectric constant change characteristically during the living polymerization, indicating the presence and simultaneous change of unpaired ions and strongly polarized species.The differences between the AMI, and the aging technique were demonstrated and explained. In the latter case slow initiation was observed due to the methoxy-chlorine exchange caused by a reaction with BCl₃.The applied direct monitoring method helps to understand the role of polarized and ionic species in polymerizations and related processes.     

Living carbocationic polymerization

Summary Living carbocationic polymerization (LCPzn) of isobutylene (IB) has been achieved by the 2-chloro-2, 4, 4-trimethylpentate (TMPCl)/TiCl₄ initiating systems in the presence of KCl in conjunction with the 18-crown-6 ether in CH₂Cl₂/hexanes solvent mixture at –80°C. The rate of initiation is relatively slow and the molecular weight distribution (MWD) of the polyisobutylene (PIB) becomes narrower (M_w/M_n decreases from 1.8 to 1.2) in the course of incremental monomer addition (IMA). In the presence of the crown ether, and depending on its concentration, the charges become highly viscous rendering stirring difficult and preventing the synthesis of M_n's in excess of 15, 000 g/mole.     

Correlation between configuration/conformation of zirconocenes on the stereoselectivity of the propylene polymerization reaction

Summary The catalytic performance (activity and polymer properties) of metallocenes with different symmetries in combination with methylaluminoxane (MAO) in the polymerization of propylene has been investigated at different temperatures, under standardized reaction conditions. The zirconocene rac-ethylene (⁵-1-indenyl) zirconium (IV) dichloride, with C₂ symmetry, produces isotatic polypropylene and isopropylidene(⁵-cyclopentadienyl (⁵-9-fluorenyl) zirconium (IV) dichloride, with C _S symmetry, syndiotactic polypropylene. The degree of the tacticity of these polymers increases with decreasing polymerization temperature. Only atactic polypropylene was formed with the unbridged zirconocenes bis(⁵-cyclopentadienyl) zirconium (IV) dichloride and bis(⁵-indenyl zirconium (IV) dichloride at any temperature investigated (10–60°C).     

Vinyl polymerization by Ziegler catalysts

Summary Methylmethacrylate and styrene were polymerized with Co(acac)₃-AlEt₂ Br catalyst system in benzene at 40°C. Rate of polymerization is linear to monomer concentrations. Maximum percent conversion of polymer was obtained when Al/Co2 with styrene and Al/Co3 with methylmethacrylate. With increase in aging time catalytic activity decreases. Activation energy was found to be 60 KJ mol^–1. with styrene and 40 KJ mol^–1. with methylmethacrylate.The authors arc thankful to the UGC, INDIA for the financial support.     

Hydrogenolysis of alkanes and olefin polymerization on the silica-supported zirconium hydrides: A comparative DFT study

The model reactions of ethylene polymerization and hydrogenolysis of linear alkanes (propane, n-butane, and n-pentane) on the silica-supported zirconium hydrides (Si–O)₃Zr^IVH, (Si–O)₂Zr^IVH₂, and (Si–O)₂Zr^IIIH were studied using the DFT approach. Catalytic processes under study were shown to occur involving different surface hydrides. The ethylene polymerization was found to proceed at comparable rates on the zirconium monohydrides, (Si–O)₃ZrH, and dihydrides, (Si–O)₂ZrH₂. Cleavage of linear alkanes on the monohydrides (Si–O)₃ZrH is thermodynamically unfavorable; however, the dihydrides (Si–O)₂ZrH₂ can act as catalysts of the process under mild conditions. Hydrides of the trivalent zirconium, (Si–O)₂Zr^IIIH, can also contribute to the hydrogenolysis reaction. A feature of all the systems studied is low regioselectivity of the corresponding processes.     

Living carbocationic polymerization

A new family of initiating systems has been discovered that efficiently induces the truly living polymerization of isobutylene (IB). The initiating systems are complexes of organic tertiary esters e.g., cumyl acetate, 2,4,4-trimethylpentane-2-acetate, with BCl₃. Living polymerizations proceed very rapidly in a variety of solvents, i.e., CH₃Cl, CH₂Cl₂, C₂H₅Cl, and mixtures of chlorinated solvents plus n-hexane, in the range from –10° to –50°C. The living nature of the polymerizations was demonstrated by linear ¯M_n versus W_PIB (g of polymer formed) plots starting at the origin and horizontal N (number of PIB chains) versus W_PIB plots. The DP_n of the products obeys [M_o]/[I_o] where [M_o] and [I_o] are initial monomer and initiator concentrations, respectively. Conversions and initiator efficiencies are 100%. In carefully controlled experiments narrow molecular weight distribution polyisobutylenes (PIB) have been obtained, i.e., M_w/M_n=1.17 – 1.3. A mechanism is outlined that helps rationalize the findings. It is postulated that the living polymerization of IB initiated by organic tertiary ester·BCl₃ complexes most likely proceeds by a two-component group transfer polymerization process.     

The ratio of crystallinity and thermodynamical interactions of polycaprolactone with some aliphatic esters and aromatic solvents by inverse gas chromatography

Summary The retention diagrams of benzene, toluene, ethyl benzene, chloro benzene, n-propyl benzene, isopropyl benzene, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate and isoamyl acetate on the polycaprolactone were plotted at temperatures between 70 and 140^oC by inverse gas chromatography technique. Percent crystallinity of polycaprolactone were obtained at temperatures below melting point from the retention diagrams of benzene, toluene and ethyl benzene. It was concluded that the data obtained by inverse gas chromatography were comparable those of obtained by differential scanning calorimetry. Specific retention volume, V_g^o, Flory-Huggins polymer-solvent interaction parameters, ₁₂, the weight fraction activity coefficients of the solvents at infinite dilution, ₁, effective exchange energy parameters, X_eff were determined. Later, the partial molar heat of sorption, H_1,sorp and the partial molar heat of mixing, H₁ were obtained from the slope of the logarithm of specific retention volume, Ln V_g^o versus 1/T plot and from the slope of the logarithm of the weight fraction activity coefficients, ₁versus 1/T plot, respectively.     

Effect of PVC on low-polar isobutylene polymerization in the presence of BCl3

Summary The isobutylene polymerizations in the presence of BCl₃ were carried out in dichloromethane ([M]=7 mol/l) at-20°C in the presence and absence of PVC. The products of polymerizations in the absence of PVC are oligoisobutylenes with a narrow molecular weight distribution ; their structure was analyzed by ¹H-NMR spectroscopy. In addition to the signals assigned to known unsaturated terminal structures [ 4.62 and 4.82-CH₂C(CH₃)=CH₂, 5.12-CH=C(CH₃)₂], a new intense signal was found at 5.09 ppm and assigned to the structure-CH=C(CH₃)CH₂CH₃. A mixture of isobutylene homopolymers and PVC grafted with isobutylene (approx. 9.5% wt. isobutylene grafted) is formed in the presence of PVC.     

Novel and Ideal Zirconium-Based Dense Membrane Reactors for Partial Oxidation of Methane to Syngas

A novel and ideal dense catalytic membrane reactor for the reaction of partial oxidation of methane to syngas (POM) was constructed from the stable mixed conducting perovskite material of BaCo_0.4Fe_0.4Zr_0.2O_3– and the catalyst of LiLaNiO/-Al₂O₃. The POM reaction was performed successfully. Not only was a short induction period of 2 h obtained, but also a high catalytic performance of 96–98% CH₄ conversion, 98–99% CO selectivity and an oxygen permeation flux of 5.4–5.8 mlcm^–2min^–1 (1.9–2.0 molm^–2S^–1Pa^–1) at 850°C were achieved. Moreover, the reaction has been steadily carried out for more than 2200 h, and no interaction between the membrane material and the catalyst took place.     

Neutral Pd(II) and Ni(II) Acetylide Catalysts for the Polymerization of Methyl Methacrylate

Homogenous polymerization of methyl methacrylate using Pd(II)- and Ni(II)-based acetylide complexes as initiators has been investigated. M(PR'₃)₂(CCR)₂ (M=Pd, Ni; R'=PPh₃, Pn-Bu₃; R=Ph, CH₂OH, CH₂OOCCH₃, CH₂OOCPh, CH₂OOCPhOH-o) were found to be a novel type of effective initiators for the polymerization of methyl methacrylate. Among them, Pd(C CPh)₂(PPh₃)₂ (PPP) shows the highest activity in the MMA polymerization and the PMMA obtained is a syndiotactic polymer with high number-average molecular weight (M _n) of 14.1 × 10⁴. Some features and kinetic behavior of MMA polymerization initiated by PPP were studied in detail. The polymerization reaction is first-order with respect to both [PPP] and [MMA]. Radical polymerization mechanism is proposed.