Quasiliving Carbocationic Polymerization. V. Quasiliving Polymerization of lndene

Quasiliving polymerization of indene, i.e., an increase of the molecular weight of polyindenes with the cumulative amount of consumed monomer, has been demonstrated using the “H₂O”/ BCl₃, 2-chloroindene/BCl, “H₂O”/TiCl₄, 2-chloroindene/TiCl₄, and cumyl chloride/TiCl₄ initiating systems in CH₂Cl₂ solvent at -50°C. However, chain transfer operates in every system investigated, and sets a limit to DP _n,max. The efficiency of the 2-chloroindene and cumyl chloride initiators is very low. The behavior of BCl₃ and TiCl₄ coinitiators on the polymerization has also been investigated.     

Quasiliving Carbocationic Poiymerization. III. Quasiliving Polymerization of lsobutylene

The polymerization of isobutylene has been investigated by the use of the steady, slow, continuous monomer addition technique in the presence of a variety of initiating systems, i.e., “H₂O”/TiCl₄, “H₂O”/AlCl₃, C₆H₅C(CH₃)₂Cl/TiCl₄, p-ClCH₂ C₆(CH₃)₄* CH₂Cl/AlCl₃ at -50°C. Quasiliving polymerizations have been obtained with the “H₂O” and C₆H₅(CH₃)₂Cl/TiC1₄ systems in 60/40 v/v n-hexane/methylene chloride solvent mixtures with very slow monomer input. After a brief “flash” polymerization, the M _n of PIB increased linearly with the cumulative amount of monomer added (consumed); however, the number of polymer molecules formed also increased, indicating the presence of chain transfer to monomer. With the “H₂O”/TiCl₄ initiating system, M _n,max was 56,000 and M _w /M _n < 2.0. By the use of the C₆H₅C(CH₃)₂CL/TiCl₄ initiating system, quasiliving polymerization has been achieved and chain transfer could virtually be eliminated.     

Quasiliving Carbocationic Polymerization. IV. Polymerization of p-tert-Butylstyrene

The mechanism of polymerization of p-tert-butylstyrene (ptBuSt) initiated by the cumyl chloride/BCl₃ initiating system in CH₂Cl₂ at -50°C has been investigated. At and below ～0.4 M ptBuSt, quasiliving polymerizations proceed, i.e., initiation is instantaneous, termination is absent or reversible, and chain transfer to monomer can be suppressed or eliminated. In the quasiliving range the M _n versus [ptBuSt]₀ plot is linear and passes through the origin, and a M _w/M _n decreases much below 2.0 with decreasing [ptBuSt]. GPC traces change from broad multimodal to narrow monomodal and the color of polymerization charges change from colorless to golden-yellow with decreasing [ptBuSt]. The effect of temperature jump subsequent to monomer addition has been examined; however, it does not explain the peculiar monomer concentration effect on the mechanism. Changes in the ionicity may be responsible for this phenomenon.     

Quasiliving Carbocationic Polymerization. I. Classification of Living Polymerizations in Carbocationic Systems

It has been shown that in addition to classical living polymerizations, several other polymerization systems exist that may exhibit partially living so-called quasiliving character. The single requirement for quasiliving polymerization is the absence of irreversible termination. The various possible living systems have been classified by taking into consideration the absence or reversibility of termination and the absence, reversibility, or irreversibility of chain transfer. In regard to chain transfer, both unimolecular and/or bimolecular processes have been considered. A comprehensive examination of all possibilities yielded, in addition to the classical terminationless-transferless living system, five quasiliving systems. Kinetic analysis led to equations defining these systems and to diagnostic techniques useful for the classification and characterization of the mechanism of living carbocationic polymerizations.     

Quasiliving Carbocationic Polymerization. XV. Forced Ideal Copolymerization of Isobutylene-lsoprene

Forced ideal carbocationic copolymerization of isobutylene and isoprene has been achieved by continuous addition of monomer mixtures of different compositions to cumyl chloride/TiCl₄ charges at -50°C. The overall rate of copolymerization could be kept equal to that of addition rate with up to 10 mol% isoprene in the mixed monomer feed. In this monomer concentration range the composition of the copolymer was identical to that of the feeds. At higher diene concentrations in the feed, chain transfer to monomer and other side reactions (intramolecular cyclization, gel formation) could not be completely avoided. The number-average molecular weight of the copolymers increased almost linearly with the amount of consumed monomers at 10 mol% isoprene concentrations in the feed (i.e., in the quasiliving range). According to ¹H-NMR and ¹³C-NMR spectroscopy, the products are random copolymers.     

Quasiliving Carbocationic Polymerization. X. Molecular Weight Averages and Polydispersity

In quasiliving polymerizations with reversible chain transfer (QL_0R systems), polymers with narrow molecular weight distribution can be obtained, It has been shown that while in true living systems (L₀₀) R = 1, and in quasiliving systems with irreversible chain transfer (QL₀₁) R = 2 is the limiting value of polydispersity, in QL_0R systems r = 4/3 is the polydispersity to which the distribution of the polymer tends with increasing polymerization time. This limit is independent of the rate of reinitiation; the course of the R vs t curves is, however, determined by the various rate constants.     

Quasiliving Carbocationic Polymerization. VIII. Quasiliving Polymerization of Methyl Vinyl Ether and Its Blocking from Quasiliving Poly(isobutyl Vinyl Ether) Dication

Quasiliving carbocationic polymerization of methyl vinyl ether (MVE) was achieved with the p-dicumyl chloride (p-DCC)/AgSbF₆ initiator system by the slow and continuous monomer-addition (quasiliving) technique. A polar solvent (CH₂Cl₂) and a low reaction temperature (-70°C) were optimum for the quasiliving MVE polymerization. Under these conditions, the number-average molecular weight (M _n) of poly(MVE) increased linearly with the cumulative weight of added monomer (W_MVE), and linear M _n versus W_MVE plots passed through the origin. M _n's were inversely proportional to the initial initiator (p-DCC) concentration. Reactions in a nonpolar solvent (toluene) at -70°C or in a polar solvent (CH₂Cl₂) at ?30°C resulted in deviations from these quasiliving characteristics. Block polymerization of MVE from quasiliving poly(isobutyl vinyl ether) dications by the quasiliving technique (p-DCC/AgSbF₆ initiator, CH₂Cl₂ solvent,(-70°C) led to novel isobutyl vinyl ether (IBVE)-MVE block polymers in high yield (>93 wt%) and at high blocking efficiency. The block polymers, most likely poly(MVE-b-IBVE-b-MVE), having M _n = 10,900–14,000 [M _n(center block) = 6,200–9,0001, were soluble in n-heptane and insoluble in water, and gave hazy homogeneous solutions when dissolved in methanol at room temperature.     

Quasiliving Carbocationic Polymerization. XIV. Synthesis of Poly(styrene-b-Isobutylene)

The synthesis of poly(styrene-b-isobutylenes) by the sequential addition of styrene and isobutylene has been accomplished. First a stream of styrene was added to a cumyl chloride/TiCl₄ in nhexane/methylene chloride charge at -50°C under quasiliving conditions. After the polystyrene block has reached a desirable sequence-length (molecular weight), gaseous isobutylene was continuously introduced to the quasiliving polystyrene carbocation until the polyisobutylene block also reached a desirable molecular weight. The M _n versus monomer input plot was uninterrupted and linear over both monomer introduction phases, indicating quasi-living conditions over the entire regime of block copolymer synthesis. The block copolymers have been characterized by selective solvent extraction and GPC, and their compositions determined by ¹H-NMR spectroscopy.     

Quasiliving Carbocationic Polymerization. IX. Forced Ideal Copolymerization of Styrene Derivatives

Forced ideal carbocationic copolymerization of α-methylstyrene (αMeSt) with p-tert-butylstyrene (ptBuSt) and (αMeSt) with styrene (St) has been achieved by continuous monomer feed addition to a cumyl chloride/BCl₃ charge at -50°C by keeping the feeding rate of the monomer mixtures equal to the overall rate of copolymerization, The composition of the copolymers was identical to the composition of the monomer feeds over the entire concentration range. A quantitative expression has been derived to show that under forced ideal copolymerization conditions the composition of the copolymer can be controlled by the composition of the feed. Further, conditions have been found for forced ideal quasiliving copolymerizations, i.e., the number-average molecular weight of the copolymers increased almost linearly with the cumulative weight of consumed monomers by the use of suitably slow, continuous feed addition in the presence of relatively nonpolar solvent mixtures (60/40 v/v n-hexane + methylene chloride). In polar solvent (methylene chloride) the molecular weight increase was less pronounced due to chain transfer to monomer involving indane-skeleton formation; however, with charges containing large amounts of ptBuSt the molecular weight increase was surprisingly strong. Interestingly, ptBuSt does not homopolymerize in 60/40 v/v n-hexane/methylene chloride but it readily copolymerizes with αMeSt. This observation was explained by examining the relative rates of terminations of the cationic species involved. Conditions have been found for the pronounced quasiliving polymerization of St. In forced ideal quasiliving copolymerizations neither the molecular weights of αMeSt/ptBuSt or αMeSt/St copolymers nor the initiating efficiencies of the initiating systems used show a depression. The microstructure of representative αMeSt/ptBuSt copolymers obtained under forced ideal quasiliving conditions has been analyzed by ¹³C-NMR spectroscopy. According to these studies, true copolymers have formed and resonance peaks for various triads have been deduced.     

Quasiliving Carbocationic Polymerization. XII. Forced Ideal Copolymerization of lsobutylene with Styrene

Forced ideal carbocationic copolymerization of isobutylene/styrene systems has been achieved by continuous addition of mixed monomer feeds to 2-chloro-2,4,4-trimethylpentane/TiCl₄ in n-hexane/methylene chloride charge by keeping the input rate equal to the overall rate of copolymerization. The composition of the copolymers was identical to that of the feeds over the entire monomer concentration range. The number-average molecular weight of the copolymers increased almost linearly with the amount of consumed monomers at higher isobutylene concentrations in the feed. The molecular weight increase was less pronounced at higher styrene concentration because more methylene chloride had to be used in the solvent system to keep the copolymer in solution. The micro-structure of the copolymers is uniform as determined by gel permeation chromatography (UV plus RI) and ¹³C-NMR spectroscopy According to these studies, true copolymers have formed. The probability of triads in the copolymer has been determined.     

Quasiliving Carbocationic Polymerization. XI. An Interpretation of Solvent Effects by Donor and Acceptor Numbers

Counteranion/solvent interactions (counteranion solvation) profoundly influence each and every elementary step of carbocationic polymerizations and are just as important as the commonly emphasized cation/solvent interactions (cation solvation). Counteranion solvation and carbocation solvation have been characterized by Gutmann' s acceptor number AN and donor number DN, respectively. Analysis of earlier data leads to the conclusion that the effect of monomer concentration on the rate, molecular weight, and molecular weight distribution obtained in cationic olefin polymerizations in “polar” solvents are in fact due to subtle changes in solvent concentration. Indeed, olefin monomers behave as “nonpolar” solvents and by changing the monomer concentration the character of the medium may profoundly change. It is further concluded that quasiliving polymerizations cannot be achieved in batch operations because the conditions that prevail in the initial charge, although possibly suitable for quasiliving polymerizations, must continuously change with the diminishing monomer concentration, i.e., by continuously changing the solvent character of the system. In contrast, in continuous systems initial conditions in the charge suitable for the attainment of living or quasiliving conditions can be maintained even for long periods of time by continuously replenishing the consumed monomer. By the use of these concepts, heretofore unexplained observations made in the course of quasiliving polymerization studies have been accounted for and, beyond this, new insight into solvation phenomena in cationic polymerizations is generated.     

Quasiliving Carbocationic Polymerization. XVII. Synthesis Of Poly (Styrene-β-Isobutylene-β-Styrene)

Poly(styrene-b-isobutylene-b-styrene) has been synthesized by sequential carbocationic polymerization under quasiliving conditions at -90°C. The quasiliving synthesis was effected by first continuously and slowly condensing gaseous isobutylene (IB) to a bifunctional initiating system (p-dicumyl chloride/TiCl₄) dissolved in a hexane-methylene chloride (60:40 v/v) mixture. After the quasiliving polyisobutylene (PIB) sequence had reached a desired molecular weight, styrene (St) was continuously and slowly added to produce the polystyrene (PSt) sequence. The products consisted of the target triblock. However, due to initiation by impurities and possibly to chain transfer to both IB and St, it also contained diblocks and small amounts of homopolymers. While the latter could be removed by selective fractionation, the triblocks and diblocks could not be separated. The mechanism of quasiliving polymerization leading to PIB/PSt blocks is discussed.     

活性聚合、表观活性聚合和准活性聚合

活性聚合是连锁聚合反应体系中链转移和终止反应速率为零时的特殊反应类型,表现活性聚合和准活性聚合则是链转移或终止反应未被完全消除而又具有活性聚合特征的两类聚合反应,是非活性聚合向活性聚合过渡和逼近时的两种聚合反应类型。本文对活性聚合、表观活性聚合和准活性聚合的基本概念及它们之间的区别作了简单的介绍。     

Living Carbocationic Polymerization. LVII. Kinetic Treatment of Living Carbocationic Polymerization Mediated by the Common Ion Effect

Abstract

The effect of anion concentration on the apparent rate constant of polymerization k^A _p of isobutylene (IB) induced by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ initiating system using the CH₂Cl₂/nC₆H₁₄ (60/40 v/v) solvent system at ?40 and ?80°C was studied by the use of nBu₄NCl. Computer simulation has shown that k^A _p decreases several orders of magnitude upon the addition of even a very small amount of common anion TiCl^?- ₅ to the charge. The rate of change is reduced in the concentration range of experimental interest. It was concluded that the decrease of k^A _p with increasing TiCl ^?- ₅ concentration is mainly due to the decreasing contribution of propagation by free ions. The contribution (%) of propagation by free ions to the apparent rate of propagation was calculated.     

Living Carbocationic Polymerization. XXIII. Analysis of Slow Initiation in Living Isobutylene Polymerization

The aim of this research was to develop a quantitative treatment of the consequences of relatively slow initiation on M _n and N (the number of molecules formed, W_p/M _n , where W_p =weight of polymer formed) in living carbocationic polymerizations, particularly for the case of the incremental monomer addition (IMA) technique. This has been achieved by analysis of the effect of initiator efficiency (I_eff (%) = 100N/[I ₀], where [I ₀] = initiator input) on M _n versus W_p , and N versus W_p plots. Three types of systems have been discerned: 1) I_eff equal to 100%; 2) I_eff constant but less than 100%; and 3) I_eff less than 100% but increasing with increasing number of monomer increments j by the IMA technique. Thus conditions can be found under which slowly initiating systems yield close to “ideal” product, i.e., one with M _n = [M₀ ]/[I₀ ] and narrow molecular weight distribution (M _w /M _n ≈ 1.1). The corresponding equations and plots can be used to diagnose the mechanism. Subsequently, this quantitative analysis was used to describe a novel living system, trans‐2,5‐diacetoxy‐2,5‐dimethyl‐3‐hexene (DiOAcDMH₆)/BCI₃/isobutylene/CH₃CI. This system produces linear t‐chlorine‐telechelic polyisobutylenes under homogeneous conditions. Surprisingly, cationation seems to be rate determining. This conclusion is illustrated by chemical equations.     

Living Carbocationic Polymerization. XLIX. Two-Stage Living Polymerization of Isobutylene to Di-tert-chlorine Telechelic Polyisobutylene

Abstract

A two-stage process was developed for the living polymerization of isobutylene (IB) employing di-tert-alcohol initiators in conjunction with BCl₃ coinitiator in the first or initiation stage, followed by TiCl₄ coinitiator in the second or propagation stage; the process was shown to yield high molecular weight (up to M ⁿ 20,000), narrow molecular weight distribution (MWD) M ^w/M ⁿ = 1.1–1.2) di-tert-chlorine telechelic polyisobutylenes (^tCl-PIB-Cl^t). The initiation stage involves the homogeneous solution living polymerization of IB induced by the di-tert-alcohol/BCl₃ combination in the presence of an electron donor such as N,N-dimethylacetamide in CH₃Cl solvent at ?80°C and proceeds up to M ⁿ < 5000; this is followed by the propagation stage in which TiCl₄ and the bulk of IB plus a sufficient amount of n-C₆H₁₄ are added to the charge to bring the solvent composition to CH₃Cl/n-C₆H₁₄ 60/40 v/v and the living polymerization is continued until high M ⁿ product is obtained. This two-stage process was developed because 1) it employs very inexpensive chemicals; 2) di-tert-alcohol/BCl₃ combinations initiate living IB polymerization in CH₃Cl but the product after reaching M ⁿ ≤ 5000 precipitates out of the CH₃Cl solution, and di-tert-alcohol/BCl₄ combinations do not initiate IB polymerization; and 3) di-tert-alcohol/BCl₃ systems do not initiate (or only very slowly) the living polymerization of IB in CH₃Cl/n-C₆H₁₄ mixtures, whereas similar TiCl₄-based systems do. The polymerization remains living during both stages although the propagating species and solvent polarity are profoundly altered. The livingness of the system has been analyzed by kinetic experiments and the structure of the ^tCl-PIB-Cl^t product by routine spectroscopic means.     

Living Carbocationic Polymerization. V. Linear Telechelic Polyisobutylenes by Bifunctional Initiators

The synthesis of α,ω-di-t-chloropolyisobutylene has been accomplished by living polymerization using aliphatic and aromatic tert-diacetate initiators in conjunction with BCl₃ coinitiator in various solvents in the ?20 to ?70°C range. The living nature of the polymerizations was demonstrated with the instantaneous initiators 2,4,4,6-tetramethyl-heptane-2,6-diacetate and 1,4-di(2-propyl-2-acetate)benzene by linear [Mbar]_n versus amount of PIB formed (W _PIB) plots starting at the origin. The formation of undesirable indanyl structures that arise with the aromatic initiator can be suppressed by decreasing the temperature and the polarity of the polymerization medium (i.e., by using CH₃Cl/n-C₆H₁₄ mixtures). Living polymerization of isobutylene can also be obtained with noninstantaneous initiators, e.g., 2,5-dimethylhexane-2,5-diacetate, 2,5-dimethylhexyne-2,5-diacetate. However, with these systems the initiator efficiency is less than 100%.     

Living Carbocationic Polymerization. LIX. The Synthesis of Novel Asymmetric Telechelic Polyisobutylenes

Abstract

The synthesis of novel asymmetric telechelic polyisobutylenes (PIB) carrying a CH₃OCO— headgroup and a —CH₂C(CH₃)₂C1 tailgroup by the use of novel initiators mediating the living carbocationic polymerization (LC⁺Pzn) of isobutylene (IB) is described. Subsequently, the parent headgroup has been quantitatively converted into a HOCO— group, and the parent tailgroup into a —pC₆H₄OH group. Scheme 1 summarizes the synthesis routes to the initiators, as well as the polymerizations and functionalizations leading to various asymmetric telechelic PIBs. The CH₃OCO— headgroup of the initiator most likely functions as an internal electron donor during the LC⁺Pzn of IB.     

Polyisobutylene Based Supramolecular Networks via Living Carbocationic Polymerization

Functionalized, styrene based monomers were investigated for copolymerization with isobutylene (IB) via living carbocationic polymerization. The achieved incorporation of polar moieties into the polymer backbone yielded supramolecular networks, which were analyzed and characterized via rheological measurements.     

Novel Epoxide Initiators for the Carbocationic Polymerization of Isobutylene

Summary: We recently reported the synthesis of polyisobutylene (PIB) via direct initiation by epoxycyclohexyl isobutyl polyhedral oligomeric silsesquioxane (POSS®) (Figure 1 ) in conjunction with titanium tetrachloride (TiCl₄). This system successfully initiated the living carbocationic polymerization of isobutylene (IB) in hexane/methyl chloride (Hx/MeCl -60/40, v/v) at T = −80 °C, yielding an asymmetric telechelic PIB with one POSS® cage head group and one tert-Cl end group. 1 This paper will discuss IB polymerizations initiated by 1,2-epoxycyclohexane and bis[3,4-(epoxycyclohexyl)ethyl]-tetramethyl-disiloxane, in conjunction with TiCl₄.