Lifetime of living polymers in cationic polymerization. II. Living polymerization of isobutyl vinyl ether initiated by the hydrogen iodide/zinc halide systems

In the living cationic polymerization of isobutyl vinyl ether (IBVE) initiated by the hydrogen iodide/zinc halide (HI/ZnX₂; X = I, Br, Cl) systems, the concentration ([P^*]) of the living propagating species was determined by quenching with sodiomalonic ester ( 1 ). The quenching reaction was shown to be clean, instantaneous, and quantitative to give poly (IBVE) with a terminal malonate group from which [P^*] was obtained by ¹H-NMR spectroscopy. In the polymerizations in toluene below +25°C, [P^*] was constant and equal to the initial concentration ([HI]₀) of hydrogen iodide, independent of the type and concentrations of ZnX₂ as well as monomer conversion. At 0 and +25°C, however, the living species started decaying immediately after the complete consumption of monomer. In contrast, such a decay process was absent at ?15°C even in the absence of monomer until about an hour (depending on the conditions) after the end of polymerization. The deactivation reaction was first order in [P^*], and the lifetime (half-life) of the living species was longer at lower temperature and at lower ZnX₂ concentration. On the basis of these [P^*] and lifetime measurements, the HI/ZnX₂ systems were also compared with the HI/I₂ counterpart.     

Role of added Lewis base and alkylaluminum halide on living cationic polymerization of vinyl ether

In the living cationic polymerization of isobutyl vinyl ether (IBVE) by the CH₃CH (OiBu) OCOCH₃ ( 1 )/EtAlCl₂ initiating system in the presence of the added base in hexane at +40°C, the stability of the initiating system 1 /EtAlCl₂, which form initiating species CH₃CH^⊕ (OiBu) derived from 1 , was investigated. In the presence of the Lewis base such as ethyl acetate or 1,4-dioxane, the active species was stable for 300 min even at +40°C in the absence of IBVE, and the living polymers were quantitatively obtained by adding IBVE. However, the active species was partly consumed by side reactions during the standing time for 60 min in the presence of a less basic additive such as ethyl benzoate, and about 50% of the active species was deactivated in the presence of methyl chloroacetate. Consequently, in the case of a less basic additive such as methyl chloroacetate (which was effective for the fast living polymerization), it can be seen that the careful selection of polymerization conditions was required. The living polymerization rate was dependent on the second order of EtAlCl₂ concentration. EtAlCl₂ induced the cleavage of 1 into CH₃CH^⊕ (OiBu) and EtAl^?Cl₂(OCOCH₃), and the reactivity of CH₃CH^⊕ (OiBu) and propagating carbocation may be controlled by EtAl^?Cl₂(OCOCH₃) with the aid of other EtAlCl₂. Et_1.5AlCl_1.5 exists as a bimetallic complex of EtAlCl₂ and Et₂AlCl, and it is expected that the polymers having a bimodal molecular weight distribution will be obtained due to two kinds of counteranions coming from EtAlCl₂ and Et₂AlCl. However, in the cationic polymerization of IBVE by 1 /Et_1.5AlCl_1.5 in the presence of ethyl acetate, the living polymer exhibiting a unimodal and very narrow molecular weight distribution was obtained. Thereby, it was suggested that the counteranions, EtAl^?Cl₂(OCOCH₃) and Et₂Al^?Cl(OCOCH₃), exchange rapidly with each other. © 1994 John Wiley & Sons, Inc.     

Controlled synthesis of glycopolymers with pendant D-glucosamine residues by living cationic polymerization

D -glucosamine-containing glycopolymers with well-controlled structure were synthesized by living cationic polymerization. To this end, D -glucosamine-containing vinyl ether (VE) of the type [CH₂()CH(OCH₂CH₂OR)] was prepared, where R denotes a 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimide-β-D -glucopyranoside, i.e., the hydroxyl and amino groups in D -glucosamine residues are protected by acetyl and phthaloyl groups, respectively. It was found that (1) the efficient living cationic polymerization of VE monomer is achieved by a combination of ethylaluminum dichloride (EtAlCl₂) with an adduct of trifluoroacetic acid (TFA) and isobutyl VE (IBVE) [CH₃CH(OiBu)OCOCF₃] (i.e., TFA/EtAlCl₂ initiating system); and (2) the polymerization in toluene at the elevated temperature (0°C) is most suitable to proceed the homogeneous polymerization over the whole conversion range. The molecular weight distribution of the resulting polymers was very narrow ($ {\bar M}_w/{\bar M}_n \sim 1.1 $). Quantitative deprotection of the resulting precursor polymers was successfully achieved with hydrazine monohydrate to afford the corresponding water-soluble polymers with pendant D -glucosamine residues. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 751–757, 1997     

Living cationic polymerization of vinyl ether with a cyclic acetal group

The living cationic polymerization of 5‐ethyl‐2‐methyl‐5‐(vinyloxymethyl)‐1,3‐dioxane ( 1 ), a vinyl ether with a cyclic acetal unit, was investigated with various initiating systems in toluene or methylene chloride at 0 to ?30 °C. With initiating systems such as hydrogen chloride (HCl)/zinc chloride (ZnCl₂), isobutyl vinyl ether–acetic acid adduct [CH₃CH(OiBu)OCOCH₃]/tin tetrabromide (SnBr₄)/di‐tert‐butylpyridine (DTBP), and CH₃CH(OiBu)OCOCH₃/ethylaluminum sesquichloride (Et_1.5AlCl_1.5)/ethyl acetate (CH₃COOEt), the number‐average molecular weights (M_n's) of the obtained poly( 1 )s increased in direct proportion to the monomer conversion and produced polymers with relatively narrow molecular weight distributions [MWDs; weight‐average molecular weight/number‐average molecular weight (M_w/M_n) = 1.2–1.3]. To investigate the living nature of the polymerization with CH₃CH(OiBu)OCOCH₃/SnBr₄/DTBP, a second monomer feed was added to the almost polymerized reaction mixture. The added monomer was completely consumed, and the M_n values of the polymers showed a direct increase against the conversion of the added monomer, indicating the formation of a long‐lived propagating species. The glass transition temperature and thermal decomposition temperature of poly( 1 ) (e.g., M_n = 13,600, M_w/M_n = 1.30) were 29 and 308 °C, respectively. The cyclic acetal group in the pendants of the polymer of 1 could be converted to the corresponding two hydroxy groups in a 65% yield by an acid‐catalyzed hydrolysis reaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4855–4866, 2007     

Stimuli‐responsive reversible physical networks. I. Synthesis and physical network properties of amphiphilic block and random copolymers with long alkyl chains by living cationic polymerization

The living cationic polymerization of octadecyl vinyl ether (ODVE) was achieved with an 1‐(isobutoxy)ethyl acetate [CH₃CH(OiBu)OCOCH₃]/EtAlCl₂ initiating system in hexane in the presence of an added weak Lewis base at 30 °C. In contrast to conventional polymers, poly(octadecyl vinyl ether) underwent upper‐critical‐solution‐temperature‐type phase separation in various solvents, such as hexane, toluene, CH₂Cl₂, and tetrahydrofuran, because of the crystallization of octadecyl chains. Amphiphilic block and random copolymers with crystallizable substituents of ODVE and 2‐methoxyethyl vinyl ether (MOVE) were synthesized via living cationic polymerization under similar conditions. Aqueous solutions of the copolymers yielded physical gels upon cooling because of strong interactions between ODVE units, regardless of the copolymer structure. The product gels, however, exhibited different viscoelastic properties: A 20 wt % solution of a block copolymer (400/20 MOVE/ODVE) became a soft physical gel that behaved like a typical gel, whereas the corresponding random copolymer gave a transparent but stiff gel with a certain relaxation time. Differential scanning calorimetry analysis confirmed that the crystalline–amorphous transition of the octadecyl chains was a key step for inducing such physical gelation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1155–1165, 2005     

Sequence-regulated oligomers and polymers by living cationic polymerization. III. Synthesis and reactions of sequence-regulated oligomers with a polymerizable group

New sequence-regulated macromonomers ( 3 ) with a vinyl ether terminal were prepared by the HI/ZnI₂-mediated living cationic polymerization of vinyl ethers: CH₃? CH(OR¹)? CH₂CH(OR²)? C(COOEt)₂CH₂CH₂OCH?CH₂ ( 3a : R¹ = nBu, R² = CH₂CH₂OCOPh; 3b : R¹ = iOct, R² = CH₂CH₂Cl). The synthesis consisted of three consecutive steps: (i) quantitative addition of hydrogen iodide to the first vinyl ether into an adduct [CH₃? CH(OR¹)? l]; (ii) propagation of a second vinyl ether from the adduct in the presence of zinc iodide; and (iii) quenching the resulting AB-type heterodimeric living intermediate with a carbanion [^θC(COOEt)₂CH₂CH₂OCH?CH₂] carrying a vinyl ether group. The HI/ZnI₂-initiated living cationic polymerization of 3a and 3b yielded narrowly distributed polymers $\left( {\overline {DP}} _{_n } \sim 10 \right)$ consisting of a poly(vinyl ether) backbone and sequence-regulated oligomer branches. The terminal vinyl ether function of 3 was also utilized to prepare pentamers and hexamers with controlled sequence of functional vinyl ethers by selective dimerization and chain extension reactions with HI/ZnI₂. © 1993 John Wiley & Sons, Inc.     

The propagating species in living cationic polymerization: Living nature and steric structure of polymers

This paper discusses the nature of the living growing species in cationic polymerization from the viewpoint of the steric structure of poly(isobutyl vinyl ether) [poly(IBVE)]. At −78 °C, living polymerization was induced with the HCl-IBVE adduct (1)/ZnCl₂ system in a EtNO₂/CH₂Cl₂ mixture, whereas similar systems with EtAlCl₂ led to conventional cationic polymerization. In this polar medium, both systems gave polymers with very similar and low isotacticity (meso ≈ 56%), indicating that the propagating reaction is mediated by free ions. Thus, regardless of solvent polarity, or involvement of free ions or ion pairs, living cationic polymerization requires a suitably nucleophilic counteranion. As model reactions of the growing species, 1/ZnCl₂ and 1/EtAlCl₂ were directly analyzed by ¹H NMR spectroscopy.     

Living cationic polymerization of isobutyl vinyl ether by EtAlCl2 in the presence of ether additives: Cyclic ethers,cyclic formals,and acyclic ethers with oxyethylene units

The living cationic polymerization of isobutyl vinyl ether (IBVE) was investigated in the presence of various cyclic and acyclic ethers with 1-(isobutoxy)ethyl acetate [CH₃CH(OiBu)OCOCH₃, 1 ]/EtAlCl₂ initiating system in hexane at 0°C. In particular, the effect of the basicity and steric hindrance of the ethers on the living nature and the polymerization rate was studied. The polymerization in the presence of a wide variety of cyclic ethers [tetrahydrofuran (THF), tetrahydropyran (THP), oxepane, 1,4-dioxane] and cyclic formals (1,3-dioxolane, 1,3-dioxane) gave living polymers with a very narrow molecular weight distribution (MWD) (M?_ω/M?_n ≤ 1.1). On the other hand, propylene oxide and oxetane additives resulted in no polymerization, whereas 1,3,5-trioxane gave the nonliving polymer with a broader MWD. The polymerization rates were dependent on the number of oxygen and ring sizes, which were related to the basicity and the steric hindrance. The order of the apparent polymerization rates in the presence of cyclic ether and formal additives was as follows: nonadditive ～ 1,3,5-trioxane ? 1,3-dioxane > 1,3-dioxolane ? 1,4-dioxane ? THP > oxepane ? THF ? oxetane, propylene oxide ? 0. The polymerization in the presence of the cyclic formals was much faster than that of the cyclic ethers: for example, the apparent propagation rate constant k in the presence of 1,3-dioxolane was 10³ times larger than that in the presence of THF. Another series of experiments showed that acyclic ethers with oxyethylene units were effective as additives for the living polymerization with 1 /EtAlCl₂ initiating system in hexane at 0°C. The polymers obtained in the presence of ethylene glycol diethyl ether and diethylene glycol diethyle ether had very narrow molecular weight distribution (M?_ω/M?_n ≤ 1.1), and the M?_n was directly proportional to the monomer conversion. The polymerization behavior was quite different in the polymerization rates and the MWD of the obtained polymers from that in the presence of diethyl ether. These results suggested the polydentate-type interaction or the alternate interaction of two or three ether oxygens in oxyethylene units with the propagating carbocation, to permit the living polymerization of IBVE. © 1994 John Wiley & Sons, Inc.     

Living cationic polymerization of vinyl ethers by electrophile/lewis acid initiating systems. XII. Phosphoric and phosphinic acids/zinc chloride initiating systems for isobutyl vinyl ether

Phosphoric and phosphinic acid derivatives (R¹R²PO₂H; R¹, R² = OPh, OPh; OnBu, OnBu; Ph, Ph; Ph, H) in conjunction with zinc chloride (ZnCl₂) led to living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene below 0°C. The number-average molecular weights (M?_n) of the polymers (M?_n > 2 × 10⁴) were directly proportional to monomer conversion and in excellent agreement with the calculated values assuming that one polymer chain forms per R¹R²PO₂H molecule. Throughout the reaction, the molecular weight distributions (MWDs) stayed narrow (M?_w/M?_n ? 1.1). A dibasic acid, PhOP (O) (OH)₂, coupled with ZnCl₂, also induced living cationic polymerization of IBVE where one molecule of the acid generated two living polymer chains. The polymerization by (PhO)₂PO₂H/ZnCl₂ and its model reactions were directly analyzed by ³¹P and ¹H-NMR spectroscopy. The analysis showed that the acid initially forms the adduct [CH₃CH(OiBu)OP(O)(OPh)₂], the phosphate linkage of which is in turn activated by ZnCl₂ so as to initiate living propagation. The finding thus indicates that (PhO)₂PO₂H indeed acts as an initiator in the living polymerization. The NMR analysis also suggested that an exchange reaction occurs between the phosphate group at the polymer terminal and the chlorine in ZnCl₂. The occurrence of living IBVE polymerization with these various R¹R²PO₂H/ZnCl₂ systems shows that phosphoric and phosphinic acids are another general class of protonic acids which are effective initiators for the living cationic polymerization assisted by Lewis acids. © 1993 John Wiley & Sons, Inc.     

Living cationic polymerization of vinyl monomers: New initiators and functional polymer synthesis

This paper focuses on two recent topics in living cationic polymerization of vinyl monomers, i.e., (a) Development of new initiating systems: RCOOH/Lewis acid for vinyl ethers; CH₃CH(C₆H₅)Cl/SnCl₄/nBu₄NCl for styrene. (b) Synthesis of shape-controlled poly(vinyl ethers): Tri-armed star polymers; Multi-armed spherical polymers. For the RCOOH-based systems, a generalized concept of living cationic polymerization was discussed on the basis of the effects of the counteranions (or R) and Lewis acids (ZnCl₂ and EtAlCl₂). The CH₃CH(C₆H₅)Cl-based system permitted a truly living cationic polymerization of styrene. The tri- and multi-armed poly(vinyl ethers) included new amphiphilic polymers of unique topology, solubility, etc., all of which were prepared by living cationic polymerization.     

Principles and design of living cationic polymerization of vinyl monomers: The nature of the growing species based on in-situ 1H NMR analysis

This paper focuses on in-situ ¹H NMR analysis of model reactions that are directed to clarify the nature of the growing species in the following three classes of living cationic polymerization based on the stabilization of the growing carbocations with nucleophilic counteranions and added salts: (a) Vinyl ethers/HCl/SnCl₄/added nBu4N+Y-; (b) Vinyl ethers/HX/ZnCl₂ (salt free); (c) Styrene/HX/SnCl₄/added nBu4N+Y- (X and Y: halogen) Through the NMR analysis, system (a) provides evidence for the generation of carbocations from adducts [CH₃CH(OR)Cl] of vinyl ethers and hydrogen chloride and also for the suppression of such ionic species by the added salts. For systems (b) and (c) the spectroscopic observation demonstrated rapid counteranion exchanges in the growing species, indicating that upon reacting with a monomer the living end assumes an ionic character.     

Quenching of metal‐catalyzed living radical polymerization with silyl enol ethers

Various silyl enol ethers were employed as quenchers for the living radical polymerization of methyl methacrylate with the R Cl/RuCl₂(PPh₃)₃/Al(Oi–Pr)₃ initiating system. The most effective quencher was a silyl enol ether with an electron‐donating phenyl group conjugated with its double bond [CH₂C(OSiMe₃)(4‐MeOPh) ( 2a )] that afforded a halogen‐free polymer with a ketone terminal at a high end functionality [F̄_n ∼ 1]. Such silyl compounds reacted with the growing radical generated from the dormant chloride terminal and the ruthenium complex to give the ketone terminal via the release of the silyl group along with the chlorine that originated from the dormant terminal. In contrast, less conjugated silyl enol ethers such as CH₂C(OSiMe₃)Me were less effective in quenching the polymerization. The reactivity of the silyl compounds to the poly(methyl methacrylate) radical can be explained by the reactivity of their double bonds, namely, the monomer reactivity ratios of their model vinyl monomers without the silyloxyl groups. The lifetime of the living polymer terminal was also estimated by the quenching reaction mediated with 2a . © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4735–4748, 2000     

Living cationic isomerization polymerization of β-pinene. III. Synthesis of end-functionalized polymers and graft copolymers

α-End-functionalized polymers and macromonomers of β-pinene were synthesized by living cationic isomerization polymerization in CH₂Cl₂ at −40°C initiated with the HCl adducts [ 1; CH₃CH(OCH₂CH₂X)Cl; X = chloride ( 1a ), acetate ( 1b ), and methacrylate ( 1c )] of vinyl ethers carrying pendant substituents X that serve as terminal functionalities. In conjunction with TiCl₃(OiPr) and nBu₄NCl, these functionalized initiators led to living β-pinene polymerization where the carbon–chlorine bond of 1 was activated by TiCl₃(OiPr). Similarly, end-functionalized poly(p-methylstyrene)-block-poly(β-pinene) were also obtained. ¹H-NMR analysis showed that the polymers possess controlled molecular weights (DP _n = [M]₀/[ 1 ]₀) and number-average end functionalities close to unity. The end-functionalized methacrylate-capped macromonomers form 1c were radically copolymerized with methyl methacrylate (MMA) to give graft copolymers carrying poly(β-pinene) or poly(p-methylstyrene)-block-poly(β-pinene) as graft chains attached to a PMMA backbone. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1423–1430, 1997     

Determination of concentration of propagating species in cationic polymerization of tetrahydrofuran

A spectroscopic method is described for the determination of the concentration of propagating species, [P^*], in the polymerization of tetrahydrofuran catalyzed by a mixture of AlEt₃?H₂O (1:0.5) and epichlorohydrin. A phenyl ether group was introduced at the polymer chain end by the quantitative reaction of the propagating species with excess sodium phenoxide. From the amount of phenyl ether groups in the polymer and of the remaining sodium phenoxide, [P^*] was determined by means of ultraviolet spectroscopy. The [P^*] value so determined was found to be in good agreement with that calculated from the amount and molecular weight of polymer based on a stepwise addition mechanism without chain transfer or termination. The present method of [P^*] determination was employed to examine the course of polymerization. It has now been found that [P^*] increases progressively during an induction period and remains unchanged in the subsequent period of polymerization.     

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl³ complexes under conventional laboratory conditions in various solvents from −10 to −50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. obeys [IB]/[CH₃COOR^t · BCl₃]. Molecular weight distributions (MWD) are very narrow in homogeneous systems whereas somewhat broader values are obtained when the polymer precipitates out of solution . The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at −10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester · BCl₃ complexes most likely proceeds by a two-component group transfer polymerization.     

End-Functionalized polymers by living cationic polymerization. IV. Poly(vinyl ethers) with acidic or basic terminal groups by functional initiator method

Carboxylic acid or primary amine-terminated poly(isobutyl vinyl ethers) were synthesized by living cationic polymerizations with functionalized initiators (CH₃CHIO? CH₂CH₂ ? X; X: that are the adducts of the corresponding vinyl ethers (CH₂ ? CH ? OCH₂CH₂? X) with hydrogen iodide. In the presence of iodine, these initiators induced living cationic polymerization of isobutyl vinyl ether to give polymers with the α-end group of X originating from the initiators. The polymer molecular weights were regulated by the monomer to initiator feed ratio and the molecular weight distributions were very narrow (M _w/M _n ≤ 1.15). Subsequent deprotection of the terminal group X led to polymers with a terminal carboxylic acid or primary amine. ¹H- and ¹³C-NMR analyses showed that the end functionalities of these polymers were all close to unity.     

Kinetics and mechanism of acetylene polymerization

The kinetics of acetylene polymerization initiated by Ti(OBu)₄/4AlEt₃ catalyst was studied by radioquenching with C^*O to count the number of active sites [C] and by CH₃OT^* to determine the total metal polymer bonds [MPB] and M?_n of the polymer. The amount of quenching agent and time of reaction required and the kinetic isotope effect for CH₃OT^* were determined. The effects of Al/Ti ratio, catalyst aging, catalyst concentration, temperature, and monomer pressure on the polymerization were investigated. Detailed kinetic data on the variation of rate of polymerization, R_p, [C] [MPB], and M?_n with time were obtained at 298 and 195°K. The results required the assumption that the catalytic species C, is initially active and within less than 30 min all are converted by bimolecular kinetics to a far less active species. Analysis of the data yielded rate constants of propagation and termination and their energies of activation. Estimates of chain transfer efficiency were obtained. The mechanisms for the propagation, termination, and transfer processes were discussed. By drawing on our earlier EPR results we propose probable structures for the catalytically active species.     

Model simulation of cationic polymerization by an iterative technique

Using a simple, instructive model of living polymerizations, we develop an economic technique for solving a complete set of kinetic equations for active polymers P_n^* with chain length n. The method consists of two steps: (i) solution of the global kinetic equations for the global species P^* which comprises all individual polymers P_n^* together with monomer M and other non-polymeric species, followed by (ii) iterative solution of the original kinetic equations, successively for the individual polymers P₁^*, P₂^*, P₃^*, …, P_n^*. The method is applied successfully to a rather complex, realistic model of cationic polymerizations. In general, our iterative scheme serves to reduce numerical storage requirements, in comparison with traditional direct integrations for all individual kinetic equations. Therefore it may allow simulations of very demanding polymerizations, including very high degrees of polymerization, which cannot be evaluated by traditional techniques.     

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl₃ complexes under conventional laboratory conditions in various solvents from ?10 to ?50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear M _n versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. DP _n obeys [IB]/[CH₃COOR^t · BCl₃]. Molecular weight distributions (MWD) are very narrow in homogeneous systems (M _w/M _n = 1.2–1.3) whereas somewhat broader values are obtained when the polymer precipitates out of solution (M _w/M _n = 1.4–3.0). The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at ?10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester. BCl₃ complexes most likely proceeds by a two-component group transfer polymerization.     

Star-shaped polymers by living cationic polymerization. VII. Amphiphilic graft polymers of vinyl ethers with hydroxyl groups: Synthesis and host–guest interaction

Amphiphilic graft polymers of vinyl ethers (VEs) ( 6 ) where each branch consists of a hydrophilic polyalcohol and a hydrophobic poly(alkyl vinyl ether) segment were prepared on the basis of living cationic polymerization, and their properties and functions were compared with the corresponding amphiphilic star-shaped polymers. In toluene at ?15°C, the HI/ZnI₂-initiated living block polymer 2 of an ester-containing VE (CH₂? CHOCH₂CH₂OCOCH₃) and isobutyl VE (IBVE) was terminated with the diethyl 2-(vinyloxy)ethylmalonate anion [ 3 ; ^ΦC(COOEt)₂CH₂CH₂OCH ? CH₂] ( 2/3 = 1/2 mole ratio) to give a macromonomer ( 4 ), H[CH₂CH(OCH₂CH₂OCOCH₃)] _m-[CH₂CH(OiBu)]_n? C(COOEt)₂CH₂CH₂OCH ? CH₂ (m = 5, n = 15; M?_n = 2600, M?_w/M?_n = 1.13, 1.10 vinyl groups/chain). Subsequently, 4 was homopolymerized with HI/ZnI₂ in toluene at ?15°C. In 3 h, 85% of 4 was consumed and a graft polymer ( 5 ) was obtained [M?_w = 15000, DP_n (for 4 ) = 6]. The apparent M?_w (10,900) of 5 by size-exclusion chromatography (SEC) is smaller than that by light scattering as well as that (18,300) by SEC of the corresponding linear polymer with the almost same molecular weight, indicating the formation of a multi-branched structure. Hydrolysis of the pendant esters in 5 gave the amphiphilic graft polymer 6 where each branch consists of a hydrophilic polyalcohol and a hydrophobic poly(IBVE) segment. The graft polymer 6 was found to interact specifically with small organic molecules (guests) with polar functional groups, and 6 differed in solubility and host-guest interaction from the corresponding star-shaped polymer. © 1993 John Wiley & Sons, Inc.