Cationic polymerization of dienes VIII: Is the elimination of cross-linking by a bulky electron donor a general behavior in the presence of aluminium trichloride?

Previous works on the polymerization of 1,3-pentadiene initiated by aluminium trichloride in non polar solvent at room temperature in the presence of bulky electron donor (ED) as tri-p-tolylamine have highlighted a stabilization of the polymerizing actives centres by ED, which allowed a reduction of some side reactions and the formation of more precisely defined polypentadienes than ever by cationic polymerization in non polar medium. The aim of this research was to investigate the role of bulky EDs such as tri-p-tolylamine and similar compounds in polar medium in order to obtain if possible a complete control of the polymerization of isoprene and 1,3-pentadiene. The beneficial effect of tri-p-tolylamine was shown in the case of isoprene polymerization at room temperature, with an important reduction of the cross-linked fraction for long reaction times and strong reduction of termination reactions. At −30 °C in the presence of tri-p-tolylamine, polypentadienes more controlled than in non polar solvent could be obtained, with a nearly complete elimination of the cross-linked fraction, while keeping the microstructure approximately constant.     

Cationic polymerization of dienes VII. New electron donors in the polymerization of 1,3-pentadiene initiated by aluminum trichloride in non-polar solvent

The aim of this research was to investigate new bulky electron donors (EDs) generating hindered active species in the cationic polymerization of 1,3-pentadiene initiated by AlCl₃ in pentane, in order to avoid or strongly reduce the reaction between the active species and the double bonds of the polymer which are responsible for side reactions. At room temperature, the polymerization in the presence of new ED, such as OPh₂, N(PhBr)₃, NPh₃ and SPh₂, allowed to obtain higher conversions and lower insoluble fractions than without electron donor. The formation of a complex ED/AlCl₃ was shown for each electron donor. However, in the case of NPh₃ and SPh₂, variations of the polymer microstructure demonstrated an interaction between active species and these EDs. Similar results were obtained at lower temperature (−10 °C). The beneficial effect of the presence of electron donors such as NPh₃ and SPh₂ demonstrated the validity of the concept of sterically hindered active species, but the polymerization was still uncontrolled.     

Initiating system Me_3SiCl/AlCl_3 for cationic polymerization of 1,3-pentadiene in toluene

Cationic polymerization of 1,3-pentadiene (PD) initiated by trimethylsilyl chloride/aluminium chloride (TMSCl/AlCl3) was carried out in toluene at 30℃.The polymer yield was increased by the addition of TMSC1.However,introduction of TMSC1 gave rise to a drop of the polymer molecular weight.Kinetic results demonstrated that the polymerization initiated by TMSCl/AlCl3 was 2.8 times faster than that induced by AlCl3 alone.Various ethers and ketones were used to mediate the initiating system TMSCl/AlCl3.The polymer yield and molecular weight of the polymer were decreased in the presence of ether.Ketones and ethers had different effects on the polymerization,and the polymer yield and molecular weight were lower than those initiated by AlCl3 alone or TMSCl/AlCl3 Structural evidence revealed that the polymerization was indeed initiated by AlCl3 and HCl rcsulting from hydrolysis of TMSC1 by adventitious water.     

Cationic polymerization of 1,3-pentadiene and 2-methylpropene: Direct initiation is a general mechanism with AlCl3 in polar medium

Following previous results showing that direct initiation was operating in the cationic polymerization of 1,3-pentadiene in the presence of AlCl₃ in non-polar medium, it is shown on the same system that direct initiation also occurs in polar medium. In the case of 2-methylpropene the use of a proton trap (DtBP) allowed to show that at −30 °C, direct initiation mechanism was operating either in 64/36 or in 36/64 (v/v) CH₂Cl₂/pentane mixtures. These results show that direct initiation is a general mechanism with AlCl₃. SEC studies showed that for 2-methylpropene transfer can be minimized.     

Allyl chloride/AIC13/ether cationic initiating systems for polymerization of 1,3-pentadiene

Various ethers were used to mediate the polymerization of 1,3-pentadiene (PD) initiated by AlCl₃ and by allyl chloride (AllyCl)/AlCl₃. The introduction of the ethers exert considerable effects on polymer yield and molecular weight due to its interaction with the propagating carbocation. The carbocation reactivity is reduced by this interaction which is subject to the ether's nucleophilicity determined by the steric hindrance of groups adjacent to oxygen. The reduction of carbocation reactivity gives rise to a decrease of polymer yield owing to inhibition of propagation but results in an augmentation of molecular weight due to suppression of various side reactions such as terminations. By using suitably nucleophilic ethers such as diphenyl ether, the polymerization can be mediated to give an high molecular weight polymer in high yield.     

Cationic polymerization of 1,3-pentadiene : IV. Initiation by aluminum chloride in an apolar solvent: effect of various electron donors

The polymerization of 1,3-pentadiene (PD) initiated by aluminum trichloride in nonpolar solvent was carried out in the presence of various electron donors (EDs) such as ethyl acetate, (EtOAc) tert-butyl acetate, dimethyl phthalate (DMP), N,N-dimethyl formamide, N,N-dimethyl acetamide and dimethyl sulfoxide. Addition of an ED whatever its nature to the polymerization medium, in a one-to-one molar ratio relatively to the Lewis acid, resulted in a decrease of the overall yield and an increased proportion of crosslinked polymer. The molecular weight distribution of the soluble fraction was narrower than that of polymerizations carried out without ED. The microstructure of the soluble polymers can be tuned using different EDs, showing that they are interacting with the active species. For instance EtOAc increased polymer isomerization while DMP increased polymer cyclization. Thus, the nature of the chemical functions borne by the ED does not seem to be the only parameter explaining its influence on the polyPD microstructure. If crosslinking efficiency seems to be roughly correlated to the donicity scale of the EDs, termination reaction is not. It was shown that the complexation between the Lewis acid and the EDs containing a carbonyl group involved the carbonyl oxygen atom. The decrease of polymerization yield when using the EDs was assigned to this complexation between the ED and AlCl₃.     

A novel metal alkyl-free catalyst for the ring-opening polymerization of cycloolefins

A new catalytic system based on tungstic acid (H₂WO₄) and aluminum trichloride (AlCl₃) polymerizes cyclopentene and 1,5-cyclooctadiene through a ring-opening mechanism in high yields and high molecular weight.     

Synthesis of high molecular weight polyisobutylene via cationic polymerization at elevated temperatures

A novel simple but effective initiating system of H2O/AlCl3 /veratrole (VE) has been developed to synthesize high molecular weight polyisobutylene (PIB) at elevated temperatures via cationic polymerization of isobutylene (IB) in solvent mixture of hexane/methylene dichloride (n-Hex/CH2Cl2 = 2/1, V/V). VE played very important roles in decreasing cationicity of the growing chain ends, suppressing side reactions of chain transfer and termination during polymerization, leading to production of high molecular weight PIBs. PIBs with high yields, having very high weight-average molecular weight (Mw ) of 1117000 and 370000 g/mol could be synthesized with H2O/AlCl3 /VE initiating system at VE concentration of 5.4 mmol/L at 80 and 60℃ respectively. Molecular weight of PIB increased remarkably with increasing VE concentration. The reaction order with respect to VE concentration was determined to be 3.52 via FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance (ATR) immersion probe. The negative reaction order of VE was consistent with its retarding effect on IB polymerization by interacting with the propagating species. Molecular weight of PIB decreased with increasing polymerization temperature. The activation energy for polymerization degree (EDP ) could be determined to be around 23 kJ/mol when VE concentration was 5.4 mmol/L or 6.4 mmol/L.     

Cationic polymerization of 1,3-pent adiene in the presence of arenes

The cationic polymerizations of 1,3-pentadiene initiated by AlCl3 in n-hexane at 30℃ have been carried out in the presence of various arenes,i.e.,benzene,toluene,p-xylene,o-xylene,m-xylene and mesitylene.The presence of all these arenes have reduced in different degrees the formation of crossliuked products.Namely,the crosslinking reaction,a major side-reaction during the cationic polymerization of 1,3-pentadiene,has been suppressed by adding the aromatic compounds.The results showed that a chain transfer to arene took place and this transfer process hindered the generation of the crosslinked polymer.IR and 1H NMR spectra have confirmed the existence of the corresponding aryl groups in the resulting polymers.     

Asymmetric radiation-induced inclusion polymerization of 3-methyl-1,4-pentadiene in deoxycholic acid

The radiation-induced polymerization of 3-methyl-1,3-pentadiene (3MPD) as an inclusion complex in deoxycholic acid (DOCA) has produced in good yield the optically active polymer poly(3-methyl-1,4-pentadiene) (P3MPD) whose structure and properties were studied by FT-IR spectroscopy and thermal analysis (TGA, DTG and DTA). The data show that the polymer is essentially trans-1,4-P3MPD as expected for the polymerization in constrained media. Trans-1,4-P3MPD is optically active with [α]_D values comprised between +4.3 and +5.6. The optical rotatory dispersion curve of the P3MPD is completely different from that of DOCA as expected.     

Role of ion-pair equilibria in homogeneous Ziegler-Natta olefin polymerization catalysis

By means of a multinuclear NMR study of the complexes formed between AlCl₃ and either Cp₂TiCl₂ or Cp₂Ti(CH₂SiMe₃)Cl in methylene chloride solution, isomeric forms of the resulting 1:1 complexes have been detected. The influence of temperature, concentration, ratio of the titanocene chloride to aluminum chloride and nature of the solvent upon the ¹H, ¹³C and ²⁷Al NMR spectra has been investigated. The spectral changes caused by the foregoing factors give compelling evidence for a equilibrium in such Cp₂Ti(R)Cl · AlCl₃ complexes (R = Cl, CH₂SiMe₃) between contact ion pairs, Cp₂TiR · Cl · AlCl₃, and solvent-separated ion pairs, Cp₂TiR⁺ AlCl₄⁻. Upon experimental variations in temperature, concentration, solvent and ratio of R_nAlCl_3−n to the titanium catalyst, the polymerization activity of the catalyst system towards ethylene was markedly altered. Such changes in activity support the conclusion that the most active sites for polymerization in such systems are the solvent-separated ion pairs.     

Influence of monomer structure on chemo- and stereoselectivity of 1,3-diene polymerization

MAO/CpTiCl₃ is an active catalyst for the polymerization of various types of 1,3-dienes. Butadiene, (E) - and (Z) −1,3-pentadiene, (E) −2-methyl-1,3-pentadiene and 2,3-dimethylbutadiene yield, at room temperature, polymers with a cis-1,4 or a mixed cis/1,2 structure. 4-Methyl-1,3-pentadiene and (E,E) −2,4-hexadiene give, respectively, a 1,2 syndiotactic and a trans-1,4/1,2 polymer. MAO/CpTiCl₂·2THF and MAO/(CpTiCl₂)_n are less active than the CpTiCl₃ catalyst, but give the same type of polymers. A change of stereospecificity with temperature was observed in the polymerization of (Z)-1,3-pentadiene: a cis-1,4 isotactic polymer was obtained at +20°C, and a crystalline 1,2 syndiotactic polymer at −20°C. This effect was attributed to a different mode of coordination of the monomer, which is cis-η⁴ at +20°C and may be trans-η² at −20°C. Results obtained with catalysts from CpTi(OBu)₃ and Ti(OBu)₄ are reported for comparison. An interpretation is given of the formation of cis-1,4 isotactic poly(2-methylpentadiene) and of 1,2 syndiotactic poly(4-methylpentadiene), as well as of syndiotactic polystyrene.     

Crystalline titanium dichloride—an active catalyst in ethylene polymerization. I. Catalyst activation

Crystalline titanium dichloride, in the absence of organometallic cocatalyst, is a very poor catalyst for the polymerization of ethylene. It is transformed into a very active catalyst through mechanical activation (ball-milling). This catalyst is active in the absence not only of organometallic cocatalysts, but also metals and compounds (such as aluminium and AlCl₃) capable of forming organometallic compounds in situ (i.e., with ethylene, before polymerization starts). Ball-milling causes not only the expected increase in surface area but also disproportionation of Ti⁺⁺ to Ti⁺⁺⁺ and metallic titanium, as well as a crystal phase change to a structure not previously identified with those of TiCl₂ or TiCl₃. Catalyst activity (polymerization rate) is shown to be proportional to surface area and a direct function of Ti⁺⁺ content of the catalyst; an empirical equation relates catalyst activity to surface area and to Ti⁺⁺ lost through disproportionation. Titanium trichloride was found to be inactive in the absence of organometallic cocatalyst, even after ball-milling. The difference in structure of the catalytically active species in the conventional Ziegler (organometallic cocatalyst) and in the titanium dichloride catalyst are discussed. The mechanism of polymerization is compared with that of the supported (CrO₃ on SiO₂/Al₂O₃ and MoO₃ on Al₂O₃) catalyst systems.     

Plasma polymerization of phenylsilane

Comparative studies on plasma polymerizations of phenylsilane (PhSiH₃) and toluene (PhCH₃) have been carried out to prepare plasma polymers containing aromatic groups. The IR and ESCA spectra show that PhSiH₃ and PhCH₃ are subjected to ring-opening reactions in a discharge state to form polymers involving alkyl chains as well as aromatic groups. The ring-opening reactions are more feeble in the PhSiH₃ system than in the PhCH₃ system, which may be due to stabilization of phenyl–Si bonds in PhSiH₃ by contribution of p_π?d_π bonding. Aromatic groups incorporated into the plasma polymers from PhSiH₃ are mono-substituted.     

Cationic polymerization of 1,3-pentadiene in the presence of vanadium oxychloride

The cationic polymerization of 1,3-pentadiene in the presence of vanadium oxytrichloride is studied. 1,3-Pentadiene is shown to polymerize at a high rate to high monomer conversions in the absence of proton-donor compounds in the catalytic system. The initial rate of 1,3-pentadiene polymerization is proportional to the concentration of VOCl₃ in the system and demonstrates an extremal dependence on the initial concentration of 1,3-pentadiene. The polymerization process is distinguished by an induction period whose duration increases with a decrease in the reaction temperature. Regardless of polymerization conditions, with an increase in the monomer conversion, the molecular-mass distribution of the polymer widens owing to formation of a high-molecular-mass fraction, which, depending on reaction conditions, can be consumed in formation of the gel fraction. It is shown that the degree of unsaturation and the microstructure of poly(1,3-pentadiene) are almost independent of the polymerization conditions.     

Synthesis of highly reactive polyisobutylene by selective polymerization with o‐cresol/AlCl3 initiating system

Highly reactive polyisobutylenes (HRPIBs) with very large proportion (up to 95 mol%) of exo‐double bond end groups and number average molecular weight (M_n) of 5400–8500 Dalton (Da) could be successfully synthesized by the selective cationic polymerization of isobutylene (IB) from the mixed C₄ fraction feed using o‐cresol/AlCl₃ as initiating system at ?20°C. A possible mechanism was proposed for the cationic polymerization process. The presence of large weakly coordinating counteranion in propagating species could lead to decreasing the possibility of the side transfer reactions via carbenium ion arrangements. This o‐cresol/AlCl₃ initiating system exhibited extremely high selectivity toward IB polymerization in the mixed C₄ fraction feed and a good property for rapid β‐proton abstraction from ? C H ₃ in the growing polyisobutylenes (PIBs) chain ends. High extent of α‐double bond end groups in HRPIBs prepared in the mixed C₄ fraction feed could be comparable to that in those commercially produced by cationic polymerization of IB in inert solvent (e.g. hexane). To our knowledge, this is the first example to achieve HRPIBs via completely selective polymerization of IB from C₄ mixed feed with AlCl₃‐based initiating system, providing a potentially practical process for its simplicity and low costs. Copyright © 2011 John Wiley & Sons, Ltd.     

Stereoregular polymerization of methyl vinyl ether with fluoro aluminum initiators

The reactions of HF, BF₃, or certain organic fluorine compounds with AlCl₃, (C₂H₅)₃Al, or ethylaluminum chlorides in chlorinated hydrocarbons give rise to gels which exhibit pronounced stereoregular polymerization initiating ability toward methyl vinyl ether. The active sites are believed to involve species of the type RAlF₄. Polymeric products having a wide range of stereoregularities are obtained. Several polymerization variables were examined. The reaction systems exhibit a variety of appearances and interesting rheological sequences. These are the consequences of differential solubility behaviors of the various stereoregular fractions. The most highly stereoregular fractions may be fabricated as fibers, films, or molded objects. Fractions of intermediate stereoregularity exhibit interesting emulsion-forming properties. Stereoregularity is shown to afford a novel control over degree of water absorption in films.     

Some mixed cyclopentadienyl–indenyl zirconium complexes with PhCH2 or PhCH2CH2 substituents in ethylene polymerization

(RCp)(R′Ind)ZrCl₂ complexes 1 – 6 (Cp = cyclopentadienyl; Ind = indenyl; 1 , R = PhCH₂ and R′ = H; 2 , R = PhCH₂ and R′ = PhCH₂; 3 , R = PhCH₂CH₂ and R′ = H; 4 , R = PhCH₂CH₂ and R′ = PhCH₂; 5 , R = o‐Me? PhCH₂CH₂ and R′ = H; 6 , R = o‐Me? PhCH₂ and R′ = H) were synthesized and characterized with ¹H NMR, elemental analysis, mass spectrometry, and infrared spectroscopy. Their catalytic behaviors were compared with those of (Et₃SiCp)(PhCH₂CH₂Cp)ZrCl₂, (PhCH₂Cp)₂ZrCl₂, (PhCH₂‐ CH₂Cp)₂ZrCl₂, (o‐Me? PhCH₂CH₂Cp)₂ZrCl₂, and (Ind)₂ZrCl₂ in ethylene polymerization in the presence of methylaluminoxane. Complex 5 showed high activity up to 2.43 × 10⁶ g of polyethylene (PE)/mol of Zr h, and complex 4 produced PE with bimodal molecular weight distributions. The methyl group at the 2‐position of phenyl in complex 5 increased the activity greatly. The relationships between the polymerization results and the structures were analyzed with NMR spectral data. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1261–1269, 2005     

Donor–acceptor interactions in cationic polymerization. VII. Relationship between the degree of dissociation of complex and the molecular weight of polyisobutylene formed in the presence of some complexes of aluminum trichloride with electron donors

The concentration dependence of the specific conductivity of the complexes of aluminum trichloride with dibutyl ether, anisole, phenol, and diphenyl ether at equimolar ratios of the two compounds has been measured. Conductivity measurements have been carried out in ethyl chloride at ?78.5°C. Except for dibutyl ether, all the complexes studied are associated over the whole concentration range and their degree of dissociation and molar conductivity are independent of the concentration. In the case of the BuOBu·AlCl₃ complex these quantities begin to be independent of the concentration only at concentrations higher than 20 mmoles/l. The degree of polymerization or the molecular weight of polyisobutylene formed by the polymerization in the presence of given complexes is inversely proportional to the concentration of the anions present. This is especially evident from the fact that the relation between x and 1/M? is also linear in the case of the BuOBu·AlCl₃ complex, whose degree of dissociation and therefore molar conductivity varies distinctly with the concentration of the complex. The comparison of the chain-breaking efficiency of the anions derived from phenol and diphenyl ether with those derived from phenetole and anisole shows that the mixed aryl alkyl ethers split after reacting with aluminum trichloride under these conditions, so that the phenyl group becomes a part of the cation and the alkyl group a part of the anion. On the basis of the different behaviors of the ions and the dipoles, the differences in the dependence of the degree of polymerization on the dielectric constant of the medium in the cationic polymerization have been explained.     

Monomer-isomerization polymerization. XXII.. Isomerization and polymerization of propenylbenzene with various ziegler–natta catalysts

The isomerization and polymerization of propenylbenzene (PB) with various Ziegler–Natta catalyst systems have been investigated. With the TiCl₃–(C₂H₅)₃Al (Al/Ti > 2.0) catalyst at 80°C, PB polymerized to give a polymer exclusively consisting of allylbenzene (AB) unit. During the polymerization, AB, which polymerized readily with the catalyst, was produced through isomerization of PB, indicating that PB underwent monomer-isomerization polymerization. PB also polymerized with isomerization to AB in the presence of TiCl₃?(C₂H₅)₂AlCl?NiCl₂ catalyst system, and a copolymer with PB and AB units was obtained. With TiCl₃?C₂H₅AlCl₂ catalyst, poly(PB) was formed via ordinary vinylene polymerization without isomerization. From these facts, it was concluded that the structure of the polymers produced from PB widely changed, depending on the catalyst systems used, which determine the rate of isomerization to AB and the polymerization reactivity of the PB and AB isomers formed.