Living carbocationic polymerization

Electron donors (EDs) effectively mediate living carbocationic polymerizations (LC^⊕Pzn), for example, that of isobutylene (IB). The purpose of this research was to investigate the effect of various new EDs, specifically esters and ketones on the LC^⊕Pzn of IB, and to determine the effect of these EDs on the molecular weight distribution, (MWD) of polyisobutylene (PIB) under various experimental conditions. Thus the LC^⊕Pzn of IB was effected by the dicumyl chloride (DCC)/BCl₃ initiating system in the presence of various EDs, such as dimethyl phthalate, di-t-octyl phthalate, methyl benzoate, ethyl isobutyrate, dimethyl 3,3-dimethylglutarate, dimethyl terephthalate, dimethyl 5-t-butyl-isophthalate, trimethyl 1,3,5-benzenetricarboxylate; and acetophenone and benzophenone, in CH₃Cl at-80°C, and the of the PIB was determined. It was found that the nature and the concentration of the ED strongly influence MWD. Under well-defined conditions in the presence of dimethyl phthalate or di-t-octyl phthalate, polymers with close to Poisson distribution could be obtained. For paper LX in this series see I. Majoros, J.P. Kennedy, et al. Polym. Bull. 31, 255 (1994)     

Living carbocationic polymerization

Summary The efficient synthesis of symmetrical telechelic polyisobutylenes carrying CH₂C(CH₃)₂Cl groups at either end of the molecule, , has been accomplished by rapid living polymerization using aromatic di-tert.-ether/BCl₃ initiator system in CH₃Cl at –70°. The living nature of the polymerization was demonstrated by linear M_n versus amount of PIB formed (W_PIB) plots starting at the origin. The effect of temperature and solvent composition (polar/nonpolar) on the polymer structure has been investigated. Undesirable indanyl end groups which form during polymerizations carried out at –30° and –50°C can be eliminated by decreasing the temperature to –70°C. The apparent activation energy differences have been determined in the –30 to –70°C range at different polar/nonpolar solvent compositions: E_a of decreases from 2.6 to 1.0 kcal/mole by decreasing the polarity of the medium from 100% CH₃Cl to a 60/40 v/v CH₃Cl/hexanes mixture.     

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.     

Living carbocationic polymerization

Mono- and bifunctionaltert-alcohols, i.e., cumyl alcohol (CumOH), 2,4,4-trimethyl-2-pentanol (TMPOH), 2,6-dihydroxy-2,4, 4, 6-tetramethylheptane (TMHDiOH), in conjunction with BCl₃ have been shown to be efficient initiating systems for the living polymerization of isobutylene (IB) in CH₃Cl or CH₂Cl₂ solvents in the –10° to –80°C range. The living nature of the polymerizations was demonstrated by linear M_n versus amount of polyisobutylene (PIB) formed (W_PIB) plots starting at the origin and corresponding horizontal number of PIB moles formed (N) versus W_PIB plots. Quenching with methanol producestert-chlorine terminated PIBs. Quantitative dehydrochlorination of the latter products yields exo-olefin (isopropylidene) end groups. These experiments demonstrate that living carbocationic polymerizations have in fact been conducted in these laboratories long ago (1) without having been recognized as such.     

Living carbocationic polymerization

Summary Living carbocationic polymerization of styrene (St) has been achieved by the use of the 1(p-methylphenyl)ethyl acetate (pMePhEtOAc)·BCl₃ complex in CH₃Cl solvent at –30°C using both the IMA and AMI techniques. The living nature of the polymerizations has been demonstrated by linear M_n versus W_PSt (weight of polystyrene) plots passing through the origin and horizontal N (moles of PSt) versus W_PSt plots starting at N=I_o (the number of moles of initiator used). The molecular weight distribution MWD of the PSts is broad (M_w/M_n=~5–6) due to slow initiation and/or slow exchange between dormant and active species relative to propagation. The structure of the ester initiator strongly affects the rate and outcome of living polymerization, e.g., cumyl acetate (CumOAc), cumyl propionate (CumOPr), and 2,4,6-trimethylphenylethyl acetate (TMePhEtOAc), do not lead to truly living St polymerizations. The findings with the latter esters is explained in terms of a two path process comprising a slow living polymerization and a faster conventional cationic chain reaction. With phenylethyl acetate (PhEtOAc) living polymerization is achieved, however, initiation (cation generation) is slow. Forced termination by pyridine or methanol, or heating to ambient temperature leads to-CH₂CH(C₆H₅)Cl end groups.     

Living carbocationic polymerization

Summary The living synthesis of ,-di-tert.-chloropolyisobutylene ( ^t -Cl-telechelic PIB) has been accomplished by the use of the sterically hindered bifunctional initiator 1,3-di-(2-methoxy-2-propyl)-5-tert.-butylbenzene (tBu-m-DiCuOMe) in conjunction with BC1₃ coinitiator in CH₃Cl or CH₂Cl₂ diluents at –30°C and –10°C. The living nature of the polymerizations was demonstrated by linear ¯M_n versus W_PIB (g of PIB formed) plots starting at the origin and horizontal N (number of PIB moles) versus W_PIB plots. The molecular weight distributions are narrow (¯M_W/¯M_n < 2.0) and tend to decrease with increasing molecular weights. Number average end functionalities have been quantitated and found to be ¯F_n = 2.0±0.1.     

Living carbocationic polymerization

Conventional cationic polymerization can be converted into living carbocationic polymerization (LC^⊕Pzn) by the introduction of common anion into the charge. Thus the conventional polymerization of isobutylene (IB) induced by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ combination yields LC^⊕Pzn of IB upon the addition of tetrabutyl ammonium chloride (n-Bu₄NCl), most likely due to then-Bu₄NCl+TiCl₄ ?n-Bu₄N^⊕+TiCl ₅ ^⊕ equilibrium. A kinetic model has been developed and tested which corroborates these propositions. By this model we have gained for the first time quantitative insight into the quasiliving equilibrium.     

Living carbocationic polymerization

Summary Three-arm star telechelic liquid polyisobutylenes PIB carrying exactly three -CH₂C(CH₃)₂Cl end groups have been synthesized by living carbocationic polymerization using C₆H₃(C(CH₃)₂OCH₃)₃/BCl₃ complexes in CH₃Cl and CH₂Cl₂ diluents in the 0° to –30°C range. The living nature of the polymerizations was demonstrated by linear M_n versus W_PIB (g PIB) formed plots starting at the origin and horizontal N (moles of PIB) versus W_PIB plots. Initiating efficiency (I_eff) was close to 100% and M_n was determined by the [monomer]/[initiator] ratio. Polymerizations guenched by methanol yield tert.-chlorine end groups which have been quantitatively converted to isopropylidene (-CH₂C(CH₃)=CH₂) termini.     

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

Laboratory scale glass equipment was designed, assembled, and used for the continuous preparation by living cationic polymerization oftert-Cl monotelechelic polyisobutylene (PIB-Cl^t). The process involves the continuous feeding of controlled amounts of isobutylene (IB), a stream of premixed initiator (2-chloro-2, 4, 4-trimethylpentane, TMPCl) and electron donor (triethylamine, TEA) in methylene chloride/hexane, and a stream of coinitiator (TiCl₄) in hexane into a series of three stirred reactors maintained at about-42°C under a blanket of dry N₂. By controlling the residence times of the living charges in the reactors and continuously quenching the feeds in a quenching reactor, the continuous synthesis of well-defined (in terms of molecular weights, , and narrow molecular weight distribution, MWD) PIB-Cl' prepolymer was demonstrated.For paper 59 in this series see Si, J, Kennedy, JP (1993) J. Macromol. Sci., Pure Appl. Chem. A30 (12)     

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.     

Living carbocationic polymerization of p-halostyrenes

The total synthesis of diblock copolymers comprising poly(p-chlorostyrene) (PpClSt) and polytetrahydrofuran (PTHF) segments have been accomplished. The syntheses involved the living polymerization of p-chlorostyrene (pClSt) by the 2-chloro-2,4,4-trimethylpentane/TiCl₄ initiating system followed by the blocking of tetrahydrofuran (THF) from thesec-benzylic chlorine end-group of PpClSt in the presence of AgPF₆ in THF at room temperature and quenching with methanol: A series of PpCISt-b-PTHF diblocks have been prepared. Themolecular weight of the PTHF segments increased with reactiontime. The blocking efficiency (B_eff) calculated by¹H NMRspectroscopy was nearly 100%.Paper XXXV in the series of Living carbocationic polymerization     

Livig carbocationic polymerization

Summary Diblock copolymers of isobytylene (IB) — methyl vinyl ether (MeVE) have been prepared by sequential monomer addition by employing 2-chloro-2, 4, 4-trimethylpentane (TMPCl)/TiCl₄ initiating system in the presence of nBu₄NCl or dimethyl-acetamide (DMA) in CH₂Cl₂/hexanes at –80°C. In line with our earlier observations (1), living carbocationic polymerizations (LCPZn) were obtained in the presence of nBu₄NCl (i.e., the molecular weight of the poly(vinyl methyl ether) segment increased upon TiCl₄ addition), however, extensive chain transfer occurred in the presence of DMA. According to column chromatography analysis, the product prepared in the presence of nBu₄NCl is essentially pure PIB-b-PMeVE diblock (96w%) contaminated with a very small amount (4w%) of PIB. In contrast, the product obtained with DMA contains only 21w% PIB-b-PMeVe together with 72w% PIB and 5w% PMeVe homopolymers. This large difference in blocking efficiencies suggests that the structures of the growing species are different in the presence of the common anion salt,nBu₄NCl, and the electron donor, DMA.For paper LIII in this series see Polym. Bull., vol. 29/1     

Macromers by carbocationic polymerization

Summary The validity of the copolymer composition equation for the copolymerization of macromers with small monomers for the preparation of graft copolymers has been examined. The reactivity ratios of high molecular weight macromers r₁ cannot be determined experimentally with sufficient accuracy whereas those of small monomers r₂ may be calculated by r₂=ln(1-p₂)/ ln(1-p₁), where p₁ and p₂ are the respective conversions of the macromer and small monomer. A single experimental datum obtained even at high conversions may be used. The error of the method can be readily calculated.     

Macromers by carbocationic polymerization

Summary This communication describes the synthesis of two novel CH₂=CH-O-headed polyisobutylene (PIB)-based macromers: and The syntheses were worked out by the help of model experiments and subsequently implemented on polymers. The structures were established by detailed¹H and¹³C NMR spectroscopies.See J. P. Kennedy, S. Midha, A. Gadkari: J. Macromol. Sci. Chem., in press, for paper X in this series     

Macromers by carbocationic polymerization

Polymer Bulletin - Copolymerization of α-(p-vinylphenyl) polyisobutylene(p-polyisobutenylstyrene, PIB-St) with styrene (St) in emulsion has been investigated. Copolymerization occurs only when...     

Macromers by carbocationic polymerization

Summary The reactivity ratio of -(p-vinylphenyl) polyisobutylene (p-polyisobutenylstyrene, PIB-St) macromers in copolymerization with methyl methacrylate (MMA) and styrene (St) has been examined at various conversions in various solvents and with three macromer chain lengths. Examination of copolymerization reactivity ratios in PIB-St/MMA and PIB-St/St systems indicate that the reactivity of PIB-St with respect to MMA and St comonomers in various solvents is the same as that of styrene. Larger than expected small-comonomer reactivity ratios (r₂) obtained at high conversions and high macromer molecular weights have been attributed to the onset of microphase separation during copolymerization.