Living cationic polymerization of p-methoxystyrene by hydrogen iodide/zinc iodide at room temperature

Summary Cationic polymerization of p-methoxystyrene initiated by HI/ZnI₂ in toluene afforded living polymers not only at low temperature (–15°C) but at room temperature (+25°C) as well. The number-average molecular weight of the polymers was directly proportional to monomer conversion and in excellent agreement with the calculated value assuming that one polymer chain forms per unit hydrogen iodide. On addition of a fresh feed of monomer at the end of the first-stage polymerization, the added feed was smoothly polymerized at nearly the same rate as in the first stage; the polymer molecular weight further increased in direct proportion to monomer conversion and was close to the calculated value for living polymer. Throughout these reactions, the molecular weight distribution of the polymers stayed very narrow (¯M_w/¯M_n<1.1). This is the first example of living cationic polymerizations of styrene derivatives that proceed even at room temperature.     

Living cationic polymerization of isobutyl vinyl ether initiated by the trimethylsilyl iodide/zinc iodide system

Summary Trimethylsilyl iodide in conjunction with zinc iodide (Me₃SiI/ZnI₂) as an initiating system led to living cationic polymerization of isobutyl vinyl ether in toluene at 0 or –40°C or in methylene chloride at –40°C (ZnI₂ was dissolved in acetone). The number-average molecular weight of the polymers was directly proportional to monomer conversion and in excellent agreement with the calculated value assuming that one polymer chain forms per unit trimethylsilyl iodide. At room temperature (+25°C), however, the polymerization failed to give perfectly living polymers; the polymer molecular weight was smaller than the calculated value. On addition of a fresh feed of monomer at the end of the polymerization at –40°C, the added feed was smoothly polymerized at nearly the same rate as in the first stage, and the polymer molecular weight continued to increase in direct proportion to monomer conversion. Throughout the reaction, the molecular weight distribution of the polymers stayed very narrow (M_w/M_n< 1.1).Living cationic polymerization of vinyl ethers by electrophile/Lewis acid initiating systems, part 2. For part 1 see ref. 2     

Cationic bulk polymerization of mesogenic vinyl ethers induced by thermal decomposition of sulfonium salts

Summary Liquid crystalline vinyl ethers have been bulk polymerized cationically in the mesophase using onium salts for thermal initiation. High molecular mass polymers (M_n83 000) with a narrow molecular mass distribution (around 2) were produced at very high temperatures (120°C). Apparently the polymerization system stabilizes the propagating cation and thus reduces chain transfer reactions that are determining the molecular mass. Possible reasons for this stabilization are e.g. influence of the mesophase of the formed polymer, interfacial polymerization, and nucleophilic stabilization by nucleophiles present in the monomer or produced by the initiators.     

Synthesis of end-functionalized polymers by living cationic polymerization of isobutyl vinyl ether with EtAlCl2

Summary A series of end-functionalized polymers (4), carrying a hydroxyl, carboxyl, or primary amino terminal group Y, were obtained by living cationic polymerization of isobutyl vinyl ether. The initiating systems of choice consisted of EtAlCl₂ and the trifluoroacetate [2; X-CH₂CH₂OCH(CH₃)OOCCF₃; X = OOCCH₃, CH(COOC₂H₅)₂, N(COOC(CH₃)₃)₂] obtained from a vinyl ether with a protected functional pendant group. In the presence of 1,4-dioxane, the 2/EtAlCl₂ systems invariably induced a well-defined living polymerization of isobutyl vinyl ether in n-hexane at 0 to +40°C to give polymers, the -end group (X) of which was derived from the initiator 2. Subsequent de-protection of X of these polymers led to 4, all of which were shown to have a very narrow molecular weight distribution (¯M_W/¯M_n = 1.07–1.18), a number-average molecular weight (¯M_n = 10³-10⁴) controllable by the monomer/2 molar feed ratio, and one terminal function Y per chain.     

Synthesis of block copolymers of p-methoxystyrene and vinyl ethers by the hydrogen iodide/zinc iodide initiating system

Summary Amphiphilic or polar-nonpolar AB block copolymers of p-methoxystyrene (pMOS) and vinyl ethers (VE; methyl or isobutyl) were synthesized by the sequential living cationic polymerization initiated with the hydrogen iodide/zinc iodide (HI/ZnI₂) system in toluene at -15 and +25 °C. pMOS-VE block copolymers of narrow molecular weight distributions ( = 1.05−1.25; = 6000−16000) were obtained in nearly quantitative blocking efficiency, when methyl or isobutyl VE was polymerized first by HI/ZnI₂, followed by addition of pMOS to the resulting living polymer solutions; an additional amount of ZnI₂ was required to accelerate the second-phase living polymerization of the less reactive styrenic monomer. Similar block polymerizations in an opposite monomer-addition sequence (from pMOS to VE), in contrast, resulted in mixtures of the desired block polymer and homopolymer of pMOS.     

Polymerization of vinyl ethers using titanium catalysts containing tridentate triamine ligand of the type N[CH2CH(Ph)(Ts)N]2

Titanium complexes having tridentate triamine of the type N[CH₂CH(Ph)(Ts)N]₂²⁻ in combination with methylaluminoxane (MAO) was able to polymerize ethyl vinyl ether in good yields. The polymers obtained in general were having molecular weight in the order of 10⁵ with narrow molecular weight distributions. Polymerization conditions had an impact on the molecular weight and the polydispersity index (PDI). Using chlorobenzene as the solvent the polymer had an M_n of 350?000 and PDI of 1.21, where as under neat conditions the M_n was 255?000 with PDI of 1.21. The type of solvent and the temperature dictated the polymerization rate and the polymer stereo regularity. The molecular weight of the polymer is distinctly governed by the polymerization temperature. Temperature ranging between −50 and ambient (30 °C) resulted in high molecular weight polymers and vice versa at a temperature of 60-70 °C resulted in low molecular weight polymers in moderate yields. The polymers obtained below 30 °C are highly stereo-regular compared to that of the ones produced at and above ambient temperature. The polymerization of iso-butyl vinyl ether (IBVE) was faster than that of linearly substituted n-butyl vinyl ether (BVE) and less bulky ethyl vinyl ether (EVE). The order of isotacticities of the polymers obtained are polyIBVE > polyBVE > polyEVE. The use of borate cocatalyst for activation generated narrow molecular weight polymers with a linear increase in the yield and molecular weight over time suggesting the living nature of the catalyst system.     

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

Summary Three-arm star polyisobutylenes carrying tert.-chlorine end groups and a phenyl ring at the center of the star (see formula II in the Introduction) have been prepared by a continuous polymerization process. Thus into a stirred glass reactor were fed continuously a mixed feed of monomer plus trinifer (TCC) and a separate feed of BCl₃ coinitiator in methyl chloride solvent at –40°C, and the product plus unreacted ingredients were removed continuously. Stationary conditions were maintained by keeping the rates of input and output (i.e., volumes) equal and constant. After a short induction phase (2–3 residence times) telechelic polymers of essentially theoretical number average end functionalities (¯F_n=3.0+0.1), close to theoretical molecular weights (¯M_n) and molecular weight distributions were obtained. The polymerization kinetics are discussed and compared to that of an earlier semicontinuous process used for the routine synthesis of telechelic polyisobutylenes.     

Control of main chain structure and possibility of molecular weight control of polymer on polymerization of vinyl chloride with tert-butyllithium

The controlled polymerization of vinyl chloride (VC) with tert-butyllithium (tert-BuLi) was investigated. The polymerization of VC with tert-BuLi at −30 °C proceeded to give a high molecular weight polymer in good yield. In the polymerization of VC −30 to 0 °C under nearly bulk, the relationship between the M_n of polymers and polymer yields gave a straight line passed through the origin, but the M_w/M_n of PVC was not narrow. When CH₂Cl₂ was used as polymerization solvent, the M_n of PVC increased with the polymer yield, and the M_w/M_n of 1.25 was obtained. Structure analysis of the resulting polymers indicates that the main chain structure could be regulated in the polymerization of VC with tert-BuLi. Accordingly, a control of molecular weight of polymer and main chain structure is possible in the polymerization of VC with tert-BuLi.     

Living cationic polymerization of vinyl monomers by organoaluminium halides

Summary Living cationic polymerization of isobutyl vinyl ether was achieved by EtAlCl₂ in the presence of ethyl acetate at rather high temperatures up to +25°C in toluene. In the absence of the ester additives, neither living nor long-lived propagating species were formed under these conditions. Similarly, living propagating species of vinyl ethers with an ester unit in the pendant (2-vinyloxyethyl benzoate and methacrylate) were obtained with EtAlCl₂ alone. The obtained polymers showed a very narrow molecular weight distribution (¯M_w/¯M_n<1.2) and the ¯M_n was directly proportional to the monomer conversion.     

Elucidating the mechanism of carbocationic polymerization of α-methylstyrene

Summary The polymerization of -methylstyrene (MeSt) using the H₂O/SnCl₄ initiating system and ethyl chloride solvent has been investigated over the temperature range from –40° to –122°C in the presence and absence of the proton trap 2,6-di-tert-butylpyridine (DtBP). Arrhenius (In ¯M_n versus 1/T) plots obtained with poly (methylstyrene) (PMeSt) samples prepared in the absence of DtBP reveal the existence of two sharply defined temperature regimes (see Figure 1): at higher temperatures from –40 to –86°C, the slope of the Arrhenius plot yields H_{M n} = –4.90±0.25 kcal/mole whereas at lower temperatures, from –86° to –122°C,H_{M n} = –0.3 kcal/mole. With PMeSt samples prepared in the presence of DtBP the H_{M n} obtained for the higher temperature regime increases to –1.67 ± 0.20 kcal/mole whereas the H_{M n} reflecting the lower temperatures remains the same as that obtained in the absence of DtBP. These observations are readily explained by postulating a change in mechanism at –86°C: Evidently the ¯M_n of PMeSt is determined over the higher temperature regime by chain transfer to monomer which is frozen out at lower temperatures where termination becomes ¯M_n determinant. In the absence of DtBP chain transfer to monomer is operative which leads to the higher Arrhenius slope over the higher temperature regime; however, over the lower temperature regime where chain transfer is absent and termination is ¯M_n controlling, the Arrhenius slope remains unchanged. Evidence obtained from a Mayo plot (negligible intercept in the 1/¯M_n versus 1/[MeSt]_o plot, Figure 2) with samples prepared at –92°C, corroborate this postulate. Molecular weight dispersities (¯M_W/¯M_n) as a function of temperature have been determined in the presence and absence of DtBP (Figure 3). The proton trap affects ¯M_W/¯M_n only over the higher temperature regime which also suggests that chain transfer to monomer is frozen out at –86°C and that the polymerization becomes termination dominated at low temperatures.     

Novel initiating system based on AlCl3 etherate for quasiliving cationic polymerization of styrene

Summary Quasiliving cationic polymerization of styrene was obtained in the system 2-phenyl-2-propano-/AlCl₃·OBu₂/Bu₂O in a mixture of 1,2-dichloroethane and n-hexane (55:45 viv) at -15 °C. The molecular weights of the polymers (M_n) increased in direct proportion to the monomer conversion. However, the experimental M_ns are essentially higher than theoretical ones, indicating that slow initiation relative to propagation takes place. The molecular weight distributions were broad (M_w/M_n2.5), probably due to the slow initiation and slow exchange between reversibly terminated and propagating species.     

Living carbocationic polymerization

The living continuous polymerization of isobutylene initiated by a bifunctional initiator, i.e., 2,4,4,6-tetramethyl-heptane-2,6-diacetate·BCl₃ complex, in CH₂Cl₂ and C₂H₅Cl diluent in the –12 to –20°C range is described. Experimental conditions have been found under which rather narrow molecular weight distribution ,-tert.-chloro-ended polyisobutylenes of theoretical M_n and I_eff=100% can be continuously prepared in a tubular reactor in a homogeneous system (in C₂H₅Cl at –12°C). System heterogeneity tends to increase the molecular weights, decrease the I_eff, and increase the ¯M_w/¯M_n.     

Hyperbranched polymers from divinylbenzene and 1,3-diisopropenylbenzene through anionic self-condensing vinyl polymerization

Hyperbranched polymers were synthesized using anionic self-condensing vinyl polymerization (ASCVP) by forming ‘inimer’ (initiator within a monomer) in situ from divinylbenzene (DVB) and 1,3-diisopropenylbenzene (DIPB) using anionic initiators in THF at −40 °C. The reaction of equimolar amounts of DVB and nBuLi results in the formation of hyperbranched poly(divinylbenzene) through self-condensing vinyl polymerization (SCVP). The hyperbranched polymers were invariably contaminated with small amount of gel (<15%). No gelation was observed when using DIBP with anionic initiators. The presence of monomer-polymer equilibrium in the SCVP of DIPB restricts the growth of hyperbranched poly(DIPB). The inimer synthesized from DIPB at 35 °C undergoes intermolecular self-condensation to different extent depending on the nature of anionic initiator at −40 °C. The molecular weight of the hyperbranched polymers was higher when DPHLi was used as initiator. A small amount of styrene ([styrene]/[Li⁺]=1) was used to promote the chain growth by inducing cross-over reaction with styrene, and subsequent reaction of styryl anion with isopropenyl groups of inimer/hyperbranched oligomer. The hyperbranched polymers were soluble in organic solvents and exhibited broad molecular weight distribution (2<M_w/M_n<17).     

Electron donors in carbocationic polymerization

Summary Low molecular weight (¯M_n 900–5000) narrow molecular weight distribution (MWD; ¯M_w/M_n = 1.1–1.2)tert.-chlorine telechelic polyisobutylenes (PIBs) have been synthesized by the use of thetrans-2,5-dimethyl-2,5-diacetoxy-3-hexene (DiOAcDMeH₆)/BCl₃ initiating system in the presence of the electron donor (ED) dimethyl sulfoxide (DMSO) in methyl chloride diluent at –30°C. The living character of the polymerization was demonstrated by linear M_n versus W_p (weight of polymer) plots starting at the origin with the slope of 1/[I_o] (where [I_o] = initiator concentration). DMSO reduces the overall rate of polymerization, however, it increases the initiator efficiency (I_eff) to 100%. The number averagetert.-chlorine end functionality is -F_n=1.97±0.04, by¹H NMR spectroscopy. Polymerization mechanistic details are discussed. This is the first time narrow MWDtert.-chlorine telechelic PIB has been prepared close to the reflux temperature of methyl chloride.Paper XXVII in the series on Living Carbocationic Polymerization. For paper XXVI see Kaszas et al., J. Macromol. Sci. Chem. to appear (1989)     

Living carbocationic polymerization

Summary The effect of polymer precipitation that occurs during polymerization on the number average molecular weight ¯M_n has been investigated in conjunction with the recently described trans-2,5-diacetoxy-2,5-dimethyl-3-hexene (DiAcODMH₆)/BCl₃/isobutylene(IB)/CH₃Cl/- 35° system using both the IMA and AMI techniques. All the experimental data could be described by a common rectilinear l/¯M_n versus l/W_p (W_p = weight of polymer) plot exhibiting an intercept l/¯M_n,max. A simple equation has been derived that explains quantitatively the results and suggests that product molecular weights obtained in heterogeneous polymerizations are determined by polymer precipitation which in turn leads to chain transfer. An Arrhenius analysis of ¯M_n,max values obtained at various temperatures corroborates this proposition and suggests polymer precipitation to control ¯M_n. That precipitation conditions determine ¯M_n seem also to hold true for conventional AlCl₃-induced IB polymerizations.Papers XXI of this series will appear in Polymer Preprints, R. Faust and J.P. Kennedy, 29(2), 1988     

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.     

Living cationic polymerization of vinyl ethers with a functional group

Summary Vinyl ethers having oxyethylene units [CH₂=CHO-(CH₂CH₂O)-_nC₂H₅, n=1–4] were cleanly polymerized by the HI/I₂ initiator in a nonpolar solvent (toluene) at low temperatures (–15 and –40°C) to yield living-like polymers with a very narrow molecular weight distribution (Mw/Mn 1.2); the oxyethylene units in the monomers hardly disturbed the polymerization. The number-average molecular weight of the polymers increased proportionally to monomer conversion and the monomer-to-HI feed ratio. The polymerization rates of the (poly)ether-containing vinyl ethers were much greater than those of alkyl vinyl ethers under similar conditions, and it is presumed that the pendant ether oxygens intramolecularly activate the growing end. The polymers were soluble in methanol (with n1) and in water (with n2), depending on the number of oxyethylene units in the pendant.     

Quantitative aspects of chain extension of telechelics

Summary Quantitative aspects of chain extension of telechelics have been studied. Molecular weight independent characteristic terms were defined and simple expressions were derived for number average extension, , and number average degree of extension, , as a function of number average functionality (¯F_n) of telechelic prepolymers. Analysis of these expressions indicate that _n and ¯DE_n are enormously sensitive to insignificant changes in ¯F_n close to ideal ¯F_n = 2.0. Molecular weight of the extended polymer (¯M_r) has also been calculated considering ¯F_n, number average molecular weight of the prepolymer (¯M_n), and molecular weight of the extender (M_e).     

Micellar polymerization of surfactants

Summary Micelle-forming sodium 6-acrylamidocaproate (Na 6-AAC) and sodium 11-(N-methyl acrylamido)undecanoate (Na 11-MAAU) were synthesized and polymerized in aqueous solutions. The polymerization was very rapid and it followed first-order kinetics with respect to the monomer and one-half order to K₂S₂O₈. The activation energy for the polymerization of Na 11-MAAU (62.3 kJ/mol) was much lower than that for Na 6-AAC (98.1 kJ/mol). The ¯M_w. for the former was around one million and it was only one-third of that for the latter. Their MWD (¯M_w/¯M_n - 1.5) are relatively narrow. The relationships between intrinsic viscosity []_o and ¯M_w for these polysurfactants have also been established.     

A new iodine-free initiating system for the living polymerization of isobutyl vinyl ether

Summary A new iodine-free initiating system, MeCH(Oi-Bu)Cl/n-Bu₄NTiCl₅, was found to induce the living carbocationic polymerization (LCPzn) of isobutyl vinyl ether (IBuVE) at-20 °C in CH₂Cl₂. Using this system, poly(isobutyl vinyl ether) (PIBuVE) with the theoretical molecular weights (up toca. 45,000) calculated from the initiator/monomer input and narrow molecular weight distribution (M_w/M_n < 1.1) can be readily obtained. The polymerization is first order in the monomer. The coinitiating function ofn-Bu₄NTiCl₅ may be due to a salt effect or to its Lewis acid character. An attempt for the synthesis of the polyisobutylene (PIB)-PIBuVE block copolymer has failed most likely becausen-Bu₄NTiCl₅ is unable to activate the C(CH₃)₂-Cl bond of the PIB termini.