Thermosensitive gradient copolymers by living cationic polymerization: Semibatch precision synthesis and stepwise dehydration‐induced micellization and physical gelation

Thermosensitive forced gradient copolymers with various sequence distributions were synthesized by living cationic polymerization in the presence of an added base. The synthesis was conducted using a semibatch reaction method, which is unfavorable for ionic polymerization, especially when a simple apparatus is employed. Polymerization of 2‐ethoxyethyl vinyl ether (EOVE) was initiated using a conventional syringe technique. Immediately after initiation, 2‐methoxyethyl vinyl ether (MOVE) was continuously added using a syringe pump at regulated feed rates, which allowed control of the sequence distribution. The resulting gradient copolymers of EOVE and MOVE underwent thermally induced association in water, forming micelles with a hydrophobic core derived from EOVE‐rich segments. Interestingly, the size of the micelles obtained from gradient copolymers decreased monotonously with increasing solution temperature, while the micelles of the corresponding block copolymers were unchanged in size. This self‐association behavior can be controlled by designing the gradient pattern of the instantaneous composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6151–6164, 2008     

Photoinitiated curing of mono‐ and bifunctional epoxides by combination of active chain end and activated monomer cationic polymerization methods

Photoinitiated cationic polymerization of mono‐ and bifunctional epoxy monomers, namely cyclohexeneoxide (CHO), 4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexanecarboxylate (EEC), respectively by using sulphonium salts in the presence of hydroxylbutyl vinyl ether (HBVE) was studied. The real‐time FTIR spectroscopic, gel content determination, and thermal characterization studies revealed that both hydroxyl and vinyl ether functionalities of HBVE take part in the polymerization. During the polymerization, HBVE has the ability to react via both active chain end (ACE) and activated monomer mechanisms through its hydroxyl and vinyl ether functionalities, respectively. Thus, more efficient curing was observed with the addition of HBVE into EEC‐containing formulations. It was also demonstrated that HBVE is effective in facilitating the photoinduced crosslinking of monofunctional epoxy monomer, CHO in the absence of a conventional crosslinker. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4914–4920, 2007     

Expanding vinyl ether monomer repertoire for ring-expansion cationic polymerization: Various cyclic polymers with tailored pendant groups

Herein, we clarified the ring-expansion cationic polymerization with a cyclic hemiacetal ester (HAE)-based initiator was versatile in terms of applicable vinyl ether monomers. Although there was a risk that higher reactive vinyl ethers may incur β-H elimination of the HAE-based cyclic dormant species to irreversibly give linear chains, the polymerizations were controlled to give corresponding cyclic polymers from various alkyl vinyl ethers of different reactivities. Functional vinyl ether monomers were also available, and for instance a vinyl ether monomer carrying an initiator moiety for metal-catalyzed living radical polymerization in the pendant allowed construction of ring-linear graft copolymers through the grafting-from approach. Furthermore, ring-based gel was prepared via the addition of divinyl ether at the end of the ring-expansion polymerization, where multi HAE bonds cyclic polymers or fused rings were crosslinked with each other. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3082–3089     

Synthesis of dual pH/temperature‐responsive polymers with amino groups by living cationic polymerization

For the precision synthesis of primary amino functional polymers, cationic polymerization of a phthalimide‐containing vinyl ether monomer precursor, 2‐vinyloxyethyl phthalimide (PIVE), was examined using a base‐assisting initiating system. Living polymerization of PIVE in CH₂Cl₂ in the presence of 1,4‐dioxane as an added base yielded nearly monodispersed polymers (M_w/M_n < 1.1) and higher molecular weight polymers, which have never been obtained using other initiating systems. Furthermore, block copolymers with hydrophobic or hydrophilic groups could be prepared. The deprotection of the pendant phthalimide groups gave well‐defined pH‐responsive polymers with pendant primary amino groups. Dual‐stimuli–responsive block copolymers having a pH‐responsive polyamine segment and a thermosensitive segment self‐assembled in water in response to both pH and temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1207–1213, 2010     

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     

Thermosensitive polyalcohols: Synthesis via living cationic polymerization of vinyl ethers with a silyloxy group

Thermosensitive homopolymers and copolymers with hydroxy groups were synthesized via the living cationic polymerization of Si‐containing vinyl ethers. The cationic homopolymerization and copolymerization of five vinyl ethers with silyloxy groups, each with a different spacer length, were examined with a cationogen/Et_1.5AlCl_1.5 initiating system in the presence of an added base. When an appropriate base was added, the living cationic polymerization of Si‐containing monomers became feasible, giving polymers with narrow molecular weight distributions and various block copolymers. Subsequent desilylation gave well‐defined polyalcohols, in both water‐soluble and water‐insoluble forms. One of these polyalcohols, poly(4‐hydroxybutyl vinyl ether), underwent lower‐critical‐solution‐temperature‐type thermally induced phase separation in water at a critical temperature (T_PS) of 42 °C. This phase separation was quite sensitive and reversible on heating and cooling. The phase separation also occurred sensitively with random copolymers of thermosensitive and hydrophilic or hydrophobic units, the T_PS values of which in water could be controlled by the monomer feed ratio. The thermal responsiveness of this polyalcohol unit made it possible to prepare novel thermosensitive block and random copolymers consisting solely of alcohol units. One example prepared in this study was a 20 wt % aqueous solution of a diblock copolymer consisting of thermosensitive poly(4‐hydroxybutyl vinyl ether) and water‐soluble poly(2‐hydroxyethyl vinyl ether) segments, which transformed into a physical gel above 42 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3300–3312, 2003     

Novel photocurable monomers: The synthesis of difunctional vinyl ethers with a phosphonate group and difunctional 1‐propenyl ethers with a phosphonate group and their photoinitiated cationic polymerization

Phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were prepared by the regioselective addition reaction of glycidyl vinyl ether (GVE) or 1‐propenyl glycidyl ether with diaryl phosphonates with quaternary onium salts as catalysts. The reaction of GVE with bis(4‐chlorophenyl) phenylphosphonate gave bis[1‐(4‐chlorophenoxy methyl)‐2‐(vinyloxy)ethyl]phenylphosphonate in a 68% yield. The structures of the resulting phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were confirmed by IR and ¹H NMR spectra and elemental analysis. Photoinitiated cationic polymerizations of the resulting phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were investigated with photoacid generators. The polymerization of vinyl ether groups and 1‐propenyl ether groups of the obtained monomers proceeded very smoothly with a sulfonium‐type cationic photoinitiator, bis[4‐(diphenylsulfonio)phenyl]sulfide‐bis(hexafluorophosphate), upon UV irradiation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3105–3115, 2005     

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     

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     

Living cationic polymerization of amide‐functional vinyl ethers: Specific properties of SnCl4‐based initiating system

Living cationic copolymerization of amide‐functional vinyl ethers with isobutyl vinyl ether (IBVE) was achieved using SnCl₄ in the presence of ethyl acetate at 0 °C: the number–average molecular weight of the obtained polymers increased in direct proportion to the monomer conversion with relatively low polydispersity, and the amide‐functional monomer units were introduced almost quantitatively. To optimize the reaction conditions, cationic polymerization of IBVE in the presence of amide compounds, as a model reaction, was also examined using various Lewis acids in dichloromethane. The combination of SnCl₄ and ethyl acetate induced living cationic polymerization of IBVE at 0 °C when an amide compound, whose nitrogen is adjacent to a phenyl group, was used. The versatile performance of SnCl₄ especially for achieving living cationic polymerization of various polar functional monomers was demonstrated in this study as well as in our previous studies. Thus, the specific properties of the SnCl₄ initiating system are discussed by comparing with the Et_xAlCl_3?x systems from viewpoints of hard and soft acids and bases principle and computational chemistry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6129–6141, 2008     

Interaction of epoxy and vinyl ethers during photoinitiated cationic polymerization

A kinetic study of the independent and simultaneous photoinitiated cationic polymerization of a number of epoxide and vinyl (enol) ether monomer pairs was conducted. The results show that, although no appreciable copolymerization takes place, these monomers undergo complex interactions with one another. These interactions are highly dependent on the epoxide monomer employed. In all cases, the rate of epoxide ring-opening polymerization is accelerated, whereas that of the vinyl ether is depressed. When highly reactive cycloaliphatic epoxides are subjected to photoinitiated cationic polymerization in the presence of vinyl ethers, the two polymerizations proceed in a sequential fashion, with the vinyl ether polymerization taking place after the epoxide polymerization is essentially complete. A mechanism involving an equilibration between alkoxy-carbenium and oxonium ions has been proposed to explain the results. In addition, the free-radical-induced decomposition of the diaryliodonium salt photoinitiator also takes place, leading to a decrease in the induction period. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4007–4018, 1999     

Cationic RAFT Polymerization Using ppm Concentrations of Organic Acid

A metal‐free, cationic, reversible addition–fragmentation chain‐transfer (RAFT) polymerization was proposed and realized. A series of thiocarbonylthio compounds were used in the presence of a small amount of triflic acid for isobutyl vinyl ether to give polymers with controlled molecular weight of up to 1×10⁵ and narrow molecular‐weight distributions (M_w/M_n<1.1). This “living” or controlled cationic polymerization is applicable to various electron‐rich monomers including vinyl ethers, p‐methoxystyrene, and even p‐hydroxystyrene that possesses an unprotected phenol group. A transformation from cationic to radical RAFT polymerization enables the synthesis of block copolymers between cationically and radically polymerizable monomers, such as vinyl ether and vinyl acetate or methyl acrylate.     

Synthesis of poly(vinyl ether)‐based,ABA triblock‐type thermoplastic elastomers with functionalized soft segments and their gas permeability

The ABA‐type triblock copolymers consisting of poly(2‐adamantyl vinyl ether) [poly(2‐AdVE)] as outer hard segments and poly(6‐acetoxyhexyl vinyl ether) [poly(AcHVE)], poly(6‐hydroxyhexyl vinyl ether) [poly(HHVE)], or poly(2‐(2‐methoxyethoxy)ethyl vinyl ether) [poly(MOEOVE)] as inner soft segments were synthesized by sequential living cationic polymerization. Despite the presence of polar functional groups such as ester, hydroxyl, and oxyethylene units in their soft segments, the block copolymers formed elastomeric films. The thermal and mechanical properties and morphology of the block copolymers showed that the two polymer segments of these triblock copolymers were segregated into microphase‐separated structure. Effect of the functional groups in the soft segments on gas permeability was investigated as one of the characteristics of the new functional thermoplastic elastomers composed solely of poly(vinyl ether) backbones. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1114–1124     

Amphiphilic gradient copolymers containing fluorinated 2‐phenyl‐2‐oxazolines: Microwave‐assisted one‐pot synthesis and self‐assembly in water

Here, we present the one‐step synthesis of 2‐(m‐difluorophenyl)‐2‐oxazoline and its use as a monomer for microwave‐assisted statistical cationic ring‐opening copolymerizations (CROP). Well‐defined amphiphilic gradient copolymers, as evidenced by the polymerization kinetics, were prepared using 2‐ethyl‐2‐oxazoline as comonomer and methyl tosylate as initiator in nitromethane at 140 °C. The resulting gradient copolymers (DP = 60 and 100) were characterized by means of size exclusion chromatography and ¹H NMR spectroscopy. In the second part, we focus on a detailed study of the self‐assembly of the copolymers in aqueous solution using atomic force microscopy and dynamic light scattering. Both methods revealed the self‐assembly of the gradient copolymers into spherical micelles. To quantify the influence of the fluorine atoms and the monomer distribution on the self‐assembly, a comparative study with gradient copolymers of 2‐phenyl‐2‐oxazoline and 2‐ethyl‐2‐oxazoline was performed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5859–5868, 2008     

Near‐infrared spectroscopy investigation of water effects on the cationic photopolymerization of vinyl ether systems

Real‐time Fourier transform near‐infrared spectroscopy has been used to monitor monomer and water concentrations simultaneously during cationic vinyl ether photopolymerization. The use of near‐infrared peak area methods allows the water content to be conveniently and nondestructively determined in any monomer or polymer for which the water peak has previously been calibrated by gravimetric analysis. Although the shape of the absorption band due to absorbed water in a monomer changes with the quantity of water, the integrated intensity from about 5350 to 4900 cm^?1 can be correlated directly to the water concentration, and this region is well removed from the vinyl‐based absorption at approximately 6190 cm^?1. This approach provides a highly informative, dynamic technique for examining the influence of moisture on polymerization reactions. Significant differences have been observed in the effects of absorbed water on the cationic photopolymerization kinetics of vinyl ether monomers with or without an ? OH group. Along with the rapid consumption of water coupled to vinyl ether polymerization, acid‐catalyzed hydrolysis reactions have also been spectroscopically observed, giving rise to the formation of aldehyde groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1985–1998, 2004     

Synthesis of phosphorus‐containing vinyl ether monomers and oligomers and their photoinitiated polymerization

Divinyl ether monomers containing phosphorous residues were synthesized by the addition reaction of glycidyl vinyl ether (GVE) with various phosphonic dichlorides or dichlorophosphates with quaternary onium salts as catalysts. The reaction of GVE with phenylphosphonic dichloride gave bis[1‐(chloromethyl)‐2‐(vinyloxy)ethyl]phenylphosphonate ( 1a ) in a 77% yield. The polycondensation of 1a with terephthalic acid was also carried out with 1,8‐diazabicyclo[5.4.0]undecene‐7 (DBU) as a condensing agent to afford the corresponding phosphorus‐containing polyester. A multifunctional monomer containing both vinyl ether groups and methacrylate groups was prepared by the reaction of 1a with methacrylic acid with DBU. The photoinitiated cationic polymerization of these vinyl ether compounds proceeded rapidly with bis[4‐(diphenylsulfonio)phenyl]sulfide‐bishexafluorophosphate as the cationic photoinitiator without a solvent upon ultraviolet irradiation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2031–2042, 2004     

Living cationic polymerization of vinyl ethers with a urethane group

To study the possibility of living cationic polymerization of vinyl ethers with a urethane group, 4‐vinyloxybutyl n‐butylcarbamate ( 1 ) and 4‐vinyloxybutyl phenylcarbamate ( 2 ) were polymerized with the hydrogen chloride/zinc chloride initiating system in methylene chloride solvent at ?30 °C ([monomer]₀ = 0.30 M, [HCl]₀/[ZnCl₂]₀ = 5.0/2.0 mM). The polymerization of 1 was very slow and gave only low‐molecular‐weight polymers with a number‐average molecular weight (M_n) of about 2000 even at 100% monomer conversion. The structural analysis of the products showed occurrence of chain‐transfer reactions because of the urethane group of monomer 1 . In contrast, the polymerization of vinyl ether 2 proceeded much faster than 1 and led to high‐molecular‐weight polymers with narrow molecular weight distributions (MWDs ≤ ～1.2) in quantitative yield. The M_n's of the product polymers increased in direct proportion to monomer conversion and continued to increase linearly after sequential addition of a fresh monomer feed to the almost completely polymerized reaction mixture, whereas the MWDs of the polymers remained narrow. These results indicated the formation of living polymer from vinyl ether 2 . The difference of living nature between monomers 1 and 2 was attributable to the difference of the electron‐withdrawing power of the carbamate substituents, namely, n‐butyl for 1 versus phenyl for 2 , of the monomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2960–2972, 2004     

Thermoresponsive NIPAM block copolymers containing densely grafted poly(vinyl ether) brushes synthesized by a combination of living cationic polymerization and RAFT polymerization

Diblock copolymers consisting of a multibranched polymethacrylate segment with densely grafted poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] pendants and a poly(N‐isopropylacrylamide) segment were synthesized by a combination of living cationic polymerization and RAFT polymerization. A macromonomer having both a poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] backbone and a terminal methacryloyl group was synthesized by living cationic polymerization. The sequential RAFT copolymerizations of the macromonomer and N‐isopropylacrylamide in this order were performed in aqueous media employing 4‐cyanopentanoic acid dithiobenzoate as a chain transfer agent and 4,4′‐azobis(4‐cyanopentanoic acid) as an initiator. The obtained diblock copolymers possessed relatively narrow molecular weight distributions and controlled molecular weights. The thermoresponsive properties of these polymers were investigated. Upon heating, the aqueous solutions of the diblock copolymers exhibited two‐stage thermoresponsive properties denoted by the appearance of two cloud points, indicating that the densely grafted poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] pendants and the poly(N‐isopropylacrylamide) segments independently responded to temperature. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Polymerization of vinyl compounds in the presence of perfluoroisopropenyl ester

To report a new polymerization reaction phenomenon, this article examines the polymerization of butyl vinyl ether and N‐vinylcarbazole in the presence of 2‐benzoxypentafluoropropene [CF₂?C(CF₃)OCOC₆H₅ or BPFP]. The homopolymer of butyl vinyl ether was produced in the presence of a catalytic amount of BPFP in high yields. N‐Vinylcarbazole, which is a monomer well‐known for producing its homopolymer under cationic polymerization conditions, also yielded its homopolymer in the presence of BPFP. It was concluded that some cationic species would be yielded by the addition of BPFP. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 908–910, 2007.     

Self‐polyaddition of hydroxyalkyl vinyl ethers

With tetrahydrofuran as a solvent and pyridium p‐toluenesulfonate as a catalyst, the hydroxyalkyl vinyl ethers 2‐hydroxyethyl vinyl ether (2E), 4‐hydroxybutyl vinyl ether (4B), and 6‐hydroxyhexyl vinyl ether (6H) underwent step‐growth self‐polyaddition, generating polymers with an acetal main‐chain structure. The molecular weight of the resulting polymers increased gradually during the initial polymerization period at room temperature. However, decomposition occurred after about 22–24 h, and the presence of a large amount of catalyst accelerated the latter process. The three monomers exhibited different polymerization capabilities. In contrast to the smooth polymerization of 6H, cyclization side reactions usually took place during the polymerizations of 4B and 2E, which resulted in low polymer yields and low molecular weights because of the formation of unreactive small cyclic acetals. In the self‐polyaddition of 4B, this side reaction was greatly restricted at high concentrations of the monomer. Higher temperatures (60–70 °C) remarkably accelerated the self‐polyaddition process to produce polymers with high molecular weights. However, the polymerizations at high temperatures had to be terminated within about 2 h to avoid the severe decomposition of the polymers. Copolymers were also obtained via the copolyaddition of any two of the monomers. The easiness of the incorporation of the monomers into the copolymers was in the sequence 6H > 4B > 2E. Poly(6H), poly(4B), poly(2E), and the copolymers possessed different hydrophilicities and were stable in basic, neutral, and even weak acidic media but exhibited degradation in the presence of a strong acid. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3751–3760, 2000