Investigation of 1,3,5-tris(2-metoxypropane)benzene/BCl3 initiated living isobutylene polymerization by C13 and B11 NMR spectroscopy

Summary The living carbocationic polymerization of isobutylene initiated by 1,3,5-tris(2-methoxypropane) benzene (TriCumOMe)/BCl₃ system was investigated by C¹³ and B¹¹ NMR spectroscopy. The reaction between the TriCumOMe and BCl₃ at-30°C in CH₂Cl₂ after 15 mins reaction time resulted in 1,3,5-tris(2-chloropropane) benzene (TriCumCl) and methyl-dichloroboronite (BCl₂OMe). The same system in the presence of isobutylene yielded three-arm star, chlorine terminated telechelic polyisobutylene and BCl₂OMe. No counterions, i.e., BCl₃OMe, BCl ₄ , or neutral boron complexes, e.g., TriCumOMe, 3BCl₃ could be detected. The simultaneous measurement of static permittivity (direct monitoring method) showed different reaction rate patterns in the case of AMI method, and when the TriCumOMe+BCl₃ mixture was aged and the polymerization was started by isobutylene.     

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.     

End-functionalized polymers by living cationic polymerization

Summary End-functionalized poly(isobutyl vinyl ether) (2) with a terminal amine, carboxylic acid, or ester group was prepared by quenching the HI/I₂-initiated living polymer ends with ring-substituted anilines (H₂N-C₆H₄-X, p or m; X = NH₂, COOH, COOC₂H₅). The living polymerization of isobutyl vinyl ether and the subsequent end-capping reaction were carried out at –15°C in methylene chloride. The resulting polymers exhibited a narrow molecular weight distribution and carried one terminal function (aniline residue) per chain, according to ¹H NMR structural analysis.     

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.     

Sequence-regulated oligomers and polymers by living cationic polymerization

Summary A new trimer (3) and a tetramer (4) of vinyl ethers with controlled repeat unit sequences were prepared through the living cationic polymerization initiated with the hydrogen iodide/zinc iodide (HI/ZnI₂) system in toluene at 40°C; for example, 4 consisted of the following sequence, H−CH₂CH(OnBu)−CH₂CH[OCH₂CH₂CH(COOEt)₂]−CH₂CH(OCH₂CH₂OCOC₆H₅)−CH₂CH[OCH₂CH₂−OCOC(CH₃)=CH₂]−OCH₃, and is a new methacrylate-type macromonomer. The synthesis involved sequential and successive reactions of the corresponding four vinyl ethers (each equimolar to hydrogen iodide) with the HI/ZnI₂-generated living oligomeric growing species, starting from the quantitative addition of hydrogen iodide to n-butyl vinyl ether and subsequent activation of the resulting adduct with ZnI₂. The structure and molecular weights of these sequence-regulated vinyl ether oligomers were verified by ¹H NMR and thermospray mass spectroscopy.     

Complexation of the propagating chain-end in living cationic polymerization

Summary Kinetics of polymerization has been studied in the system isobutylene/dicumylmethylether/BCl₃ (CH₂Cl₂, –80°C) in the presence of dimethyl sulphoxide added as electron donor in a broad concentration range. The apparent propagation rate constant showed a DMSO concentration dependence typical for complex equilibria.At a given DMSO concentration, the apparent rate constant decreases with increasing initial monomer concentration showing a seemingly zero-order propagation. A possible explanation of this phenomenon is the formation of a chain-end/monomer complex. Equilibrium and propagation rate constants have been determined.     

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.     

Dynamics of continuous isobutylene cationic polymerizations

Polyisobutylene can be produced in either continuous cationic precipitation or solution polymerization reactors. It is known that the open-loop behavior of polymerization reactors may be very complex and may lead to oscillatory behavior, which is usually caused by thermal positive feedback (due to the large heats of reaction of polymerization reactions) and high viscosity effects (such as the gel effect in radical polymerization reactors and the decrease of heat transfer coefficients at high polymer concentrations). Oscillatory behavior may be observed in industrial isobutylene reactors, and it is intended to know whether these oscillations are inherent to the kinetic mechanism. Based on published experimental data, mathematical models are developed for both solution and precipitation processes. Steady-state solutions are calculated and steady-state stability is analyzed. Dynamic simulations and stability results reveal that only single stable steady-state solutions are possible for such reactors at usual operation conditions, which means that oscillatory behavior is not intrinsic to the reaction mechanism. © 1996 Wiley & Sons, Inc.     

Boric acid binding studies with diol containing polyethylenimines as determined by 11B NMR spectroscopy

Three water‐soluble polymers incorporating increasing levels of 2,3‐dihydroxy propyl attached to polyethylenimine (PEI) backbone were synthesized, characterized by NMR, and investigated for their ability to bind boric acid (BA). ¹¹B NMR spectroscopy showed that BA interacted with the polymeric 2,3‐dihydroxy propyls by forming borate monoester and borate diesters in the boron concentration range of 100–1000 ppm and at 0.0775M polymer. Borate monoester species predominated for low functionalization levels (33% of the PEI amines functionalized), whereas borate diester species dominated for the higher functionalized polymers (66–100% of the PEI amines functionalized). All three polymers showed that 100% of the BA was bound as a mixture of borate mono‐ and diesters at 100‐ppm boron. The overall best performer based on total borate ester formation was the 2/3‐PEI, with a binding K_d of 631 at 200 ppm boron. Borate ion concentration was measured from the ¹¹B NMR chemical shift of the BA/borate peak and it decreased as 1/3‐PEI > 2/3‐PEI > 3/3‐PEI. Variable temperature ¹¹B NMR showed drastic reduction of borate ester species at 65°C. Thus, PEI polymers, as the ones investigated in this work, are reasonable candidates for the selective recovery and recycle of BA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4411–4418, 2006     

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     

13C NMR spectroscopy of cationic copolymers of acrylamide

Summary Random copolymers of acrylamide and a quaternary ammonium acrylate monomer have been investigated by¹³C NMR spectroscopy in aqueous solution. Cleavage of the ester function has been shown to occur in mild alkaline media with a simultaneous intrachain reaction giving imide group formation. Sequential length distribution of the comonomers has been analyzed from triads composition and the experimental results lead to a nearly Bernouillian statistics although a more alternating distribution would be predicted from the reactivity ratios. This fact has been attribtued to the compositional heterogeneity of our copolymers which have been prepared at high degree of conversion.     

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.     

Reactivity and mechanism in the cationic polymerization of isobutyl vinyl ether

The cationic polymerization of isobutyl vinyl ether initiated by triphenyl methyl and tropylium hexachloroantimonates, and by triphenyl methyl tetrafluoroborate, has been studied in detail. Initiation was rapid and complete, termination was shown to be insignificant, polymerization half lives were of the order of 5–10 s and reaction rates were measured by an adiabatic calorimetric technique. Catalyst concentrations employed were sufficiently low that essentially complete dissociation into free ions is indicated by ion-pair dissociation constants, and this permits estimation of the rate coefficient for propagation by free cations (k_p). At 0°C in methylene dichloride k_p ∼ 5 × 10³ M⁻¹ s⁻¹, in substantial agreement with values obtained by radiation induced polymeirzation of bulk monomer. Molecular weights of the poly(isobutyl vinyl ether) samples fell in the range 2000–5000 on account of monomer transfer processes. Detailed mechanisms for initiation, propagation, transfer and termination reactions are considered.     

On the mechanism of photoinitiated cationic polymerization in the presence of polyols

The photoinitiated polymerization of cyclohexene oxide by using triphenyl sulfonium hexafluoroarsenate in the presence of poly(ε-caprolactone) polyols was studied. The polymerization was suggested to proceed via the activated monomer (AM) mechanism. The polymerization rate tended to decrease with increasing concentration of polyol. The enhanced curing rate observed in the presence of polyols was attributed to the multifunctional nature of the components, i. e., monomers and polyols.     

Bulk polymerization of isobutylene initiated by PVC/SnCl4 systems

Summary It has been surprisingly discovered that an initiator system based on PVC/SUCl₄ produces bulk polymerization of isobutylene even under conditions, when a mixture of isobutylene and SnCl₄, in the absence of a polar medium, does not polymerize. The PVC polymers used were the powders of the commercial suspension PVC Neralit S-652, lower-molecular-weight PVC prepared by extraction of Neralit S-652 with acetone (PVC-AE) and the copolymer of vinyl chloride with 2-chloropropene (VC/2CP). The kinetics of polymerizations were studied dilatometrically at –78°C. It was found that the bulk polymerization of isobutylene proceeds at the boundary between the solid (PVC) and liquid (isobutylene) phase over an unusually long period of time which, depending on the type of PVC used, can last more than 7 days. It followed from the determination of the initial polymerization rate that the activity of the studied types of PVC decreases in the order PVC-AE > VC/2CP PVC.     

Reactivity and mechanism in the cationic polymerization of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate

The cationic polymerization of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate in dichloromethane solution has been studied in some detail. Reactions proved to be highly exothermic, and rates of monomer consumption were measured using an adiabatic calorimetric technique. Termination was deduced to be insignificant during kinetic lifetimes, and $\text{M}\text{?}{}_{\mathrm{n}}$ values in the range 10000–50000 showed chain breaking to occur by transfer mechanisms. Appropriate analysis of conversion/time curves allowed computation of enthalpies of polymerization and rate coefficients for propagation, k_p (obs), under various conditions. Data for k_p (obs) were found to vary with the initial concentrations of initiator and monomer employed, and these dependences are discussed in terms of current theories regarding ion pair/free ion equilibria in nonaqueous solvents. In particular values of 3.6 × 10³ M^?1s^?1 and 4.8 × 10³ M^?1s^?1 at 0° and +10°C respectively for the rate constant for propagation by free poly (p-methoxystyryl) cation have been deduced, and a tentative value of 450 M^?1s^?1 at 0°C has been estimated for the rate constant for propagation by the corresponding hexachloroantimonate ion pairs. These data and the related activation parameters are compared with independent results in the literature. Polymerizations carried out in the presence of excess common ion salt, dimethyl benzyl phenyl ammonium hexachloroantimonate, showed rate depressions far in excess of those predicted by a simple mass law effect, arising possibly as a result of a more dramatic ionic association than simple ion pairing.     

Photoinduced living cationic polymerization of tetrahydrofuran(IV): Syringe method

The living nature of cationic poly(tetrahydrofuran), which is generated by the addition of the photolytic products of diphenyliodonium hexafluorophosphate (initiator) via syringe, was investigated in connection with the direct polymerization method in which polymerization of tetrahydrofuran is carried out in the presence of the initiator. Although the living nature of the polymerization (i.e., the linear relationship between the percentage of conversion and the molecular weight of the resulting polymer) is observed in the syringe method because of the absence of chain transfer or termination, unexceptionally, a lower rate of polymerization and higher molecular weights of the resulting polymers were observed in the syringe method when compared with those of the corresponding direct polymerization method. This leads us to the conclusion that the living nature is ascribed to the stabilization of the propagating cationic species due to ion pair formation with the less‐nucleophilic complex metal halide anion (PF), and the decreased rate of polymerization and higher molecular weight in the syringe method is attributed to the partial loss of the activity of the cationic species because of the nucleophilic attack of basic impurities, such as water, introduced to the system in the syringe manipulation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2082–2087, 2002