Living cationic polymerization of vinyl ethers in the presence of a strong base: Poisonous or helpful?

A quite small dose of a poisonous species was found to induce living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene at 0 °C. In the presence of a small amount of N,N‐dimethylacetamide, living cationic polymerization of IBVE was achieved using SnCl₄, producing a low polydispersity polymer (weight–average molecular weight/number–average molecular weight (M_w/M_n) ≤ 1.1), whereas the polymerization was terminated at its higher concentration. In addition, amine derivatives (common terminators) as stronger bases allow living polymerization when a catalytic quantity was used. On the other hand, EtAlCl₂ produced polymers with comparatively broad MWDs (M_w/M_n ～ 2), although the polymerization was slightly retarded. The systems with a strong base required much less quantity of bases than weak base systems such as ethers or esters for living polymerization. The strong base system exhibited Lewis acid preference: living polymerization proceeded only with SnCl₄, TiCl₄, or ZnCl₂, whereas a range of Lewis acids are effective for achieving living polymerization in the conventional weak base system such as an ester and an ether. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6746–6753, 2008     

Living cationic polymerization of n‐butyl propenyl ether

Cationic polymerization of n‐butyl propenyl ether (BuPE; CH₃CH CHOBu, cis/trans = 64/36) was examined with the HCl–IBVE (isobutyl vinyl ether) adduct/ZnCl₂ initiating system at −15 ∼ −78 °C in nonpolar (hexane, toluene) and polar (dichloromethane) solvents, specifically focusing on the feasibility of its living polymerization. In contrast to alkyl vinyl ethers, the living nature of the growing species in the BuPE polymerization was sensitive to polymerization temperature and solvent. For example, living cationic polymerization of IBVE can be achieved even at 0 °C with HCl–IBVE/ZnCl₂, whereas for BuPE whose β‐methyl group may cause steric hindrance ideal living polymerization occurred only at −78 °C. Another interesting feature of this polymerization is that the polymerization rate in hexane is as large as in dichloromethane, much larger than in toluene. A new method in determining the ratio of the living growing ends to the deactivated ones was developed with a devised monomer‐addition experiments, in which IBVE that can be polymerized in a living fashion below 0 °C was added to the almost completely polymerized solution of BuPE. The amount of the deactivated chain ends became small in hexane even at −40 °C in contrast to other solvents. Thus hexane turned out an excellent solvent for living cationic polymerization of BuPE. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 229–236, 2000     

Rapid living cationic polymerization of vinyl ethers by a single‐molecular initiating system

Initiated by an organic molecule trifluoromethanesulfonimide (HNTf₂) without any Lewis acid or Lewis base stabilizer, cationic polymerization of isobutyl vinyl ether (IBVE) takes place rapidly and the polymerization is proved to be in a controlled/living manner. The conversion of IBVE could easily achieve 99% in seconds. The product poly(isobutyl vinyl ether) is narrowly distributed and its molecular weight increases linearly with time and fits well with the corresponding theoretical value. This single‐molecular initiating system also works well in the living cationic polymerization of ethyl vinyl ether. HNTf₂ is considered playing multiple roles which include initiator, activator, and stabilizer in the polymerization. It is quite different from the hydrogen halide‐catalyzed polymerizations of vinyl ethers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1373‐1377     

Living cationic polymerization of α‐methyl vinyl ethers using SnCl4

Cationic polymerization of α‐methyl vinyl ethers was examined using an IBEA‐Et_1.5AlCl_1.5/SnCl₄ initiating system in toluene in the presence of ethyl acetate at 0 ～ ?78 °C. 2‐Ethylhexyl 2‐propenyl ether (EHPE) had a higher reactivity, compared to corresponding vinyl ethers. But the resulting polymers had low molecular weights at 0 or ?50 °C. In contrast, the polymerization of EHPE at ?78 °C almost quantitatively proceeded, and the number‐average molecular weight (M_n) of the obtained polymers increased in direct proportion to the EHPE conversion with quite narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight ≤ 1.05). In monomer‐addition experiments, the M_n of the polymers shifted higher with low polydispersity as the polymerization proceeded, indicative of living polymerization. In the polymerization of methyl 2‐propenyl ether (MPE), the living‐like propagation also occurred under the reaction conditions similar to those for EHPE, but the elimination of the pendant methoxy groups was observed. The introduction of a more stable terminal group, quenched with sodium diethyl malonate, suppressed this decomposition, and the living polymerization proceeded. The glass transition temperature of the obtained poly(MPE) was 34 °C, which is much higher than that of the corresponding poly(vinyl ether). This poly(MPE) had solubility characteristics that differed from those of poly(vinyl ethers). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2202–2211, 2008     

MALDI‐TOF‐MS analysis of living cationic polymerization of vinyl ethers. III. Polymerization with SnCl4 and TiCl4 in the absence of additives

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis revealed that the precision control (or the living nature) of the cationic polymerization of vinyl ethers with SnCl₄ or TiCl₄ critically depends on the Lewis acid concentration and temperature. Specifically, at an extremely low Lewis acid concentration, for example, the polymerization with the HCl–vinyl ether adduct (an initiator) is living at ?78 °C in CH₂Cl₂ solvent, whereas side reactions occurred at a higher concentration of SnCl₄ or at a higher temperature, ?15 °C. This was more pronounced with SnCl₄ than with TiCl₄, which was due to a stronger Lewis acidity of SnCl₄ as suggested by NMR analysis of the model reactions. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1258–1267, 2001     

Precision synthesis of graft copolymers via living cationic polymerization of p‐acetoxystyrene followed by friedel–crafts‐type termination reaction

This study describes a novel precision synthesis strategy for graft copolymers using Friedel–Crafts‐type termination reaction between a cationically prepared poly(styrene derivative) and the naphthyl side groups from a poly(vinyl ether) main chain. The pendant alkoxynaphthyl groups on the poly(vinyl ether) efficiently terminated the living cationic polymerization of p‐acetoxystyrene (AcOSt) with SnCl₄ in the presence of ethyl acetate as an added base. This research provides the first example of a well‐defined graft copolymer prepared using this method. The resulting polymer contained 40 poly‐(AcOSt) branches, as calculated from the M_w determined via gel permeation chromatography–MALS analysis, which was in good agreement with the estimated number of branches obtained from ¹H NMR analysis. The acetoxy groups in the grafted poly(AcOSt) chains were easily converted into phenolic hydroxy groups under basic conditions. The as‐obtained graft copolymer with poly(p‐hydroxystyrene) side chains exhibited a pH‐sensitive phase separation in water. The synthetic method for preparing the graft copolymers was also effective in the living cationic polymerizations of other styrene derivatives. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4675–4683     

Matrix‐assisted laser desorption ionization time of flight mass spectrometry analysis of living cationic polymerization of vinyl ethers. I. Optimization of measurement conditions for poly(isobutyl vinyl ether)

Matrix‐assisted laser desorption ionization time of flight mass spectrometry (MALDI‐TOF‐MS) was utilized for the analysis of polymers obtained by the living cationic polymerization of isobutyl vinyl ether (IBVE) with the HCl‐VE adduct/SnCl₄/n‐Bu₄NCl initiating system in CH₂Cl₂ at −78 °C. Under optimized analysis conditions, well‐resolved spectra were obtained for samples with number‐average molecular weights of ≤10⁴ with the use of 1,8‐dihydroxy‐9(10H)‐anthracenone (dithranol) as a matrix and sodium trifluoroacetate as an added salt. The MS spectra showed only one series of peaks separated exactly by the mass of the IBVE. The observed mass of each peak was in good agreement with the theoretical one, which possesses one initiator fragment at the α end and one methoxy group originated from quenching with methanol at the ω end. Thus, detailed end group analysis is possible for poly(VE). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4023–4031, 2000     

Synthesis of various stimuli‐responsive gradient copolymers by living cationic polymerization and their thermally or solvent induced association behavior

Stimuli‐responsive gradient copolymers, composed of various monomers, were synthesized by living cationic polymerization in the presence of base. The monomers included thermosensitive 2‐ethoxyethyl vinyl ether (EOVE) and 2‐methoxyethyl vinyl ether (MOVE), hydrophobic isobutyl vinyl ether (IBVE) and 2‐phenoxyethyl vinyl ether (PhOVE), crystalline octadecyl vinyl ether (ODVE), and hydrophilic 2‐hydroxyethyl vinyl ether (HOVE). The synthesis of gradient copolymers was conducted using a semibatch reaction method. Living cationic polymerization of the first monomer was initiated using a conventional syringe technique, followed by an immediate and continuous addition of a second monomer using a syringe pump at regulated feed rates. This simple method permitted precise control of the sequence distribution of gradient copolymers, even for a pair of monomers with very different relative monomer reactivities. The stimuli‐responsive gradient, block and random copolymers exhibited different self‐association behavior. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6444–6454, 2008     

Synthesis of end‐functionalized polymers and copolymers of cyclopentadiene with vinyl ethers by cationic polymerization

A series of cyclopentadiene (CPD)‐based polymers and copolymers were synthesized by a controlled cationic polymerization of CPD. End‐functionalized poly(CPD) was synthesized with the HCl adducts [initiator = CH₃CH(OCH₂CH₂X)Cl; X = Cl ( 2a ), acetate ( 2b ), or methacrylate] of vinyl ethers carrying pendant functional substituents X in conjunction with SnCl₄ (Lewis acid as a catalyst) and n‐Bu₄NCl (as an additive) in dichloromethane at −78 °C. The system led to the controlled cationic polymerizations of CPD to give controlled α‐end‐functionalized poly(CPD)s with almost quantitative attachment of the functional groups (F_n ∼ 1). With the 2a or 2b /SnCl₄/n‐Bu₄NCl initiating systems, diblock copolymers of 2‐chloroethyl vinyl ether (CEVE) and 2‐acetoxyethyl vinyl ether with CPD were also synthesized by the sequential polymerization of CPD and these vinyl ethers. An ABA‐type triblock copolymer of CPD (A) and CEVE (B) was also prepared with a bifunctional initiator. The copolymerization of CPD and CEVE with 2a /SnCl₄/n‐Bu₄NCl afforded random copolymers with controlled molecular weights and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight = 1.3–1.4). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 398–407, 2001     

Synthesis of biocompatible and biodegradable block copolymers of polyvinyl alcohol‐block‐poly(ε‐caprolactone) using metal‐free living cationic polymerization

Applications of metal‐free living cationic polymerization of vinyl ethers using HCl · Et₂O are reported. Product of poly(vinyl ether)s possessing functional end groups such as hydroxyethyl groups with predicted molecular weights was used as a macroinitiator in activated monomer cationic polymerization of ε‐caprolactone (CL) with HCl · Et₂O as a ring‐opening polymerization. This combination method is a metal‐free polymerization using HCl · Et₂O. The formation of poly(isobutyl vinyl ether)‐b‐poly(ε‐caprolactone) (PIBVE‐b‐PCL) and poly(tert‐butyl vinyl ether)‐b‐poly(ε‐caprolactone) (PTBVE‐b‐PCL) from two vinyl ethers and CL was successful. Therefore, we synthesized novel amphiphilic, biocompatible, and biodegradable block copolymers comprised polyvinyl alcohol and PCL, namely PVA‐b‐PCL by transformation of acid hydrolysis of tert‐butoxy moiety of PTBVE in PTBVE‐b‐PCL. The synthesized copolymers showed well‐defined structure and narrow molecular weight distribution. The structure of resulting block copolymers was confirmed by ¹H NMR, size exclusion chromatography, and differential scanning calorimetry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5169–5179, 2009     

Cationic polymerization behavior of isobutyl vinyl ether with arenesulfonates as non‐salt‐type latent thermal initiators

Substituted and unsubstituted benzenesulfonic acid cyclohexyl esters (1–7) were synthesized, and their possibility as latent thermal initiators in the cationic polymerization of isobutyl vinyl ether (IBVE) was examined to develop novel non‐salt type latent cationic initiators. Thermal decomposition of cyclohexyl p‐nitrobenzenesulfonate (2) in C₆D₆ at 80°C proceeded to exclusively afford cyclohexene as well as p‐nitrobenzenesulfonic acid. Cationic polymerization of IBVE with 1 mol % of an arenesulfonate (1–6) in bulk was carried out at 40–100°C for 12 h. No polymerization took place below 50°C, while the consumption of IBVE depending on both the polymerization temperature and the structure of the arenesulfonates was observed above 60°C. The obtained polyIBVEs showed bimodal GPC curves in several cases, revealing the intervention of two independent propagation species in the polymerization. The cationic polymerization of IBVE with cyclohexyl 2,4,6‐triisopropylbenzenesulfonate (7) at 80°C confirmed the acceleration effect of bulkiness on the polymerization rate. It was concluded that the polymerization was largely dependent on both electronic and steric factors of the aryl groups of the initiators which were directly related to the stability of the sulfonate anions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 293–301, 1999     

Living cationic polymerization of an azide‐containing vinyl ether toward addressable functionalization of polymers

We first achieved the living cationic polymerization of azide‐containing monomer, 2‐azidoethyl vinyl ether (AzVE), with SnCl₄ as a catalyst (activator) in conjunction with the HCl adduct of a vinyl ether [H‐CH₂CH(OR)‐Cl; R ? CH₂CH₂Cl, CH₂CH(CH₃)₂]. Despite the potentially poisoning azide group, the produced polymers possessed controlled molecular weights and fairly narrow distributions (M_w/M_n ～ 1.2) and gave block polymers with 2‐chloroethyl vinyl ether. The pendent azide groups are easily converted into various functional groups via mild and selective reactions, such as the Staudinger reduction and copper‐catalyzed azide‐alkyne 1,3‐cycloaddition (CuAAC; a “click” reaction). These reactions led to quantitative pendent functionalization into primary amine (? NH₂), hydroxy (? OH), and carboxyl (? COOH) groups, at room temperature and without any acidic or basic treatment. Thus, poly(AzVE) is a versatile precursor for a wide variety of functional vinyl ether polymers with well‐defined structures and molecular weights. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1449–1455, 2010     

MALDI‐TOF‐MS analysis of living cationic polymerization of vinyl ethers. II. Living nature of growing end and side reactions

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis revealed that the HCl–vinyl ether adduct/SnCl₄/n‐Bu₄NCl initiating system induced living cationic polymerization of isobutyl vinyl ether in CH₂Cl₂ at ?78 °C, that is, the well‐resolved spectra demonstrated that the produced polymers consist of only one series of polymers carrying one initiator fragment at the α end and one methoxy group originated from quenching with methanol at the ω end. The polymer molecular weight as well as the terminal structure were unchanged even when the reaction mixtures were kept unquenched at ?78 °C for an interval of more than five times longer than the reaction period after complete consumption of monomer, which indicates the long lifetime of the living end even under such starved conditions. In contrast, the polymers obtained at a higher temperature, ?15 °C, showed an additional minor series of polymers formed via proton initiation, originating from adventitious water. Under the starved conditions, other side reactions occurred to generate minor series of polymers with an aldehyde ω end or a diisobutyl acetal ω end. Rather surprisingly, however, unsaturated C?C end groups were not detected, which means the absence of β‐proton elimination under these conditions. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1249–1257, 2001     

Living cationic polymerization of vinyl ethers with carboxylic acid/tin tetrahalide initiating systems. I. New initiating systems based on acetic acid and selection of Lewis acid and basic additive leading to living polymers with low polydispersity

Cationic polymerization of isobutyl vinyl ether (IBVE) with acetic acid (CH₃COOH)/tin tetrahalide (SnX₄: X = Cl, Br, I) initiating systems in toluene solvent at 0°C was investigated, and the reaction conditions for living polymerization of IBVE with the new initiating systems were established. Among these tin tetrahalides, SnBr₄ was found to be the most suitable Lewis acid to obtain living poly(IBVE) with a narrow molecular weight distribution (MWD). The polymerization with the CH₃COOH/SnBr₄ system, however, was accompanied with the formation of a small amount of another polymer fraction of very broad MWD, probably due to the occurrence of an uncontrolled initiation by SnBr₄ coupled with protonic impurity. Addition of 1,4-dioxane (1–1.25 vol %) or 2,6-di-tert-butylpyridine (0.1–0.6mM) to the polymerization mixture completely eliminated the uncontrolled polymer to give only the living polymer with very narrow MWD (M _w/M _n ≤ 1.1; M _w, weight-average molecular weight; M _n, number-average molecular weight). The M _n of the polymers increased in direct proportion to monomer conversion, continued to increase upon sequential addition of a fresh monomer feed, and was in good agreement with the calculated values assuming that one CH₃COOH molecule formed one polymer chain. Along with these results, kinetic study and direct ¹H-NMR observation of the living polymerization indicated that CH₃COOH and SnBr₄ act as so-called “initiator” and “activator”, respectively, and the living polymerization proceeds via an activation of the acetate dormant species. The basic additives such as 1,4-dioxane and 2,6-di-tert-butylpyridine would serve mainly as a “suppressor” of the uncontrolled initiation by SnBr₄. The polymers produced after quenching the living polymerization with methanol possessed the acetate dormant terminal and they induced living polymerization of IBVE in conjunction with SnBr₄ in the presence of 1,4-dioxane. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3173–3185, 1998     

Precise synthesis of pH‐responsive copolymers with naphthoic acid side groups via living cationic polymerization

pH‐Responsive homopolymers and copolymers with naphthoic acid side groups were synthesized via base‐assisting living cationic polymerization. To this end, the feasibility of the living cationic polymerization of ethyl 6‐[2‐(vinyloxy)ethoxy]‐2‐naphthoate (EVEN) was first examined using a base‐assisting initiating system. Et_1.5AlCl_1.5 as a Lewis acid catalyst induced the living cationic polymerization of EVEN in the presence of ethyl acetate or 1,4‐dioxane in CH₂Cl₂ at 0 °C. In contrast, the use of naphthoxyethyl vinyl ether (NpOVE), which is a nonsubstituted counterpart, resulted in a poorly controlled polymerization under these conditions. The presence of the carboxy ester was most likely critical in preventing side reactions. A subsequent alkaline hydrolysis of the side‐chain esters quantitatively yielded a carboxy‐containing polymer. Aqueous solutions of this polymer underwent pH‐driven phase separation at pH 7.0. Well‐defined random and block copolymers were also prepared with various functional segments, and their stimuli‐responsive behaviors were investigated in terms of solution transmittance and aggregate size. Block copolymers containing two different pH‐responsive segments formed micelle‐like structures between the two phase‐separated pH values, and dual stimuli‐responsive copolymers containing a pH‐responsive polyacid segment and a thermosensitive segment self‐assembled in the water in response to both the pH and temperature. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5239–5247     

Controlled Cationic Polymerization of 1‐Methoxy‐1,3‐Butadiene: Long‐Lived Species‐Mediated Reaction and Control over Microstructure with Weak Lewis Bases

Controlled cationic polymerization of trans‐1‐methoxy‐1,3‐butadiene was achieved through the design of appropriate initiating systems, yielding soluble polymers with controllable molecular weights. The combined use of SnCl₄ or GaCl₃ as a Lewis acid catalyst and a weak Lewis base in conjunction with HCl as a protonogen resulted in efficient and controlled polymerization. The M_n values of the product polymers increased linearly along the theoretical line, which indicates that intermolecular crosslinking reactions negligibly occurred. In addition, the polymer microstructure was critically dependent on the weak Lewis base employed. In particular, the use of tetrahydrofuran as an additive resulted in the highest 4,1/4,3‐structure ratio (96/4). Weak Lewis bases also affected the polymerization rates but exhibited unique trends that differed from their effects on the cationic polymerization of alkyl vinyl ethers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 288–296     

Synthesis of brush‐shaped polymers consisting of a poly(phenylacetylene) backbone and pendant poly(vinyl ether)s via selective reaction of 2‐Vinyloxyethyl 4‐Ethynylbenzoate

We have newly designed an original bifunctional monomer (PAVE) containing both a phenylacetylene (PA) group and a vinyl ether (VE) group, which is expected to be a key material for the synthesis of brush‐shaped polymers consisting of a poly(phenylacetylene) (polyPA) main chain and polyVE side chains. Actually, we have demonstrated the selective chemical transformation of the VE moiety of PAVE to an initiator site for the living cationic polymerization of isobutyl vinyl ether (IBVE), and then succeeded in the controlled synthesis of a novel PA‐end‐capped polyIBVE macromonomer. Moreover, using this macromonomer, the first synthesis of a brush‐shaped polyPA bearing polyVE side chains was achieved via Rh complex‐mediated homopolymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2800–2805     

Stereoregulation in cationic polymerization. III. High isospecificity with the bulky phosphoric acid [(RO)2PO2H]/SnCl4 initiating systems: Design of counteranions via initiators

In the cationic polymerization of isobutyl vinyl ether (IBVE) with binary initiating systems consisting of a protonic acid as an initiator and a Lewis acid as an activator/catalyst, phosphoric acid derivatives [(RO)₂POOH] coupled with SnCl₄ gave highly isotactic poly(IBVE)s, whereas those with a bulky substituent (R), [C₄H₉CH(C₂H₅)CH₂O]₂POOH ( 7 ) and (n‐C₁₀H₂₁)₂POOH ( 8 ), led to the highest isotacticity [meso dyad (m) = 86%]. In contrast, isospecificity was lower with IBVE–HCl and CF₃COOH under the same conditions. From the effects of the polymerization temperature (−78 to 0 °C), it was concluded that the high isospecificity with 7 and 8 was due to an enthalpic factor. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1067–1074, 2001     

Cyclometalated 2‐phenylpyridine complex [RuII(o‐C6H4‐py)(MeCN)4]PF6 as a tunable catalyst for living radical polymerization

The cyclometalated complex [Ru^II(o‐C₆H₄‐py)(MeCN)₄]PF₆ ( 1 ) with a σ‐Ru? C bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n‐butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2‐bromoisobutyrate, methyl 2‐bromopropionate, and 1‐phenylethyl bromide. The polymerization requires the presence of Al(OiPr)₃ and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)₃ and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl₂ as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion‐dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst ( 1 ), when the added amount of ( 1 ) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the ( 1 )‐catalyzed polymerization are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193–4204, 2008     

Living cationic polymerization of dihydrofuran and its derivatives

Cationic polymerization of 2,3‐dihydrofuran (DHF) and its derivatives was examined using base‐stabilized initiating systems with various Lewis acids. Living cationic polymerization of DHF was achieved using Et_1.5AlCl_1.5 in toluene in the presence of THF at 0 °C, whereas it has been reported that only less controlled reactions occurred at 0 °C. Monomer‐addition experiments of DHF and the block copolymerization with isobutyl vinyl ether demonstrated the livingness of the DHF polymerization: the number–average molecular weight of the polymers shifted higher with low polydispersity as the polymerization proceeded after the monomer addition. Furthermore, this base‐stabilized cationic polymerization system allowed living polymerization of ethyl 1‐propenyl ether and 4,5‐dihydro‐2‐methylfuran at ?30 and ?78 °C, respectively. In the polymerization of 2,3‐benzofuran, the long‐lived growing species were produced at ?78 °C. The obtained polymers have higher glass transition temperatures compared to poly(acyclic alkyl vinyl ether)s. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4495–4504, 2008