Precise synthesis of end‐functionalized thermosensitive poly(vinyl ether)s by living cationic polymerization

A series of poly(2‐methoxyethyl vinyl ether)s with narrow molecular weight distributions and with perfectly defined end groups of varying hydrophobicities was successfully synthesized by base‐assisting living cationic polymerization. The end group was shown to greatly affect the temperature‐induced phase separation behavior of aqueous solutions (lower critical solution temperature‐type phase separation) or organic solutions (upper critical solution temperature‐type phase separation) of the polymers. The cloud points were also influenced largely by the molecular weight and concentration of the polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Facile one‐shot synthesis of functional star‐shaped polymers by domino‐type living cationic copolymerization

This article describes the syntheses of various functional star‐shaped polymers via monomer‐selective living cationic polymerization of a vinyl ether (VE) and a divinyl compound with alkoxystyrene moieties by a one‐shot method. An aqueous solution of the resulting star‐shaped polymers with oxyethylene pendants exhibits thermally induced phase separation behavior. To achieve domino synthesis from various monomers, we investigated the optimum reactivity difference using a functional VE and a monofunctional alkoxystyrene. Moreover, the one‐shot copolymerization of a bifunctional VE and an alkoxystyrene is also conducted to yield a star‐shaped polymer via the core‐first method. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2166–2174     

Living cationic polymerization of azobenzene‐containing vinyl ether and its photoresponsive behavior

The living cationic polymerization of 4‐[2‐(vinyloxy)ethoxy]azobenzene (AzoVE) was achieved with various Lewis acids in the presence of an ester as an added base. When Et_1.5AlCl_1.5 was used as a catalyst, the living polymerization system was controllable by UV irradiation as a result of cis and trans isomerization of the azobenzene side groups. Furthermore, an initiating system consisting of SnCl₄ and EtAlCl₂ realized fast living polymerization of AzoVE. The polymerization rate of this system was 3 orders of magnitude faster than that obtained with Et_1.5AlCl_1.5. Poly(4‐[2‐(vinyloxy)ethoxy]azobenzene) was soluble in a diethyl ether/hexane mixture at 25 °C but became insoluble upon irradiation with UV light. This phase‐transition behavior was sensitive and reversible upon irradiation with UV or visible light and reflected the change in polarity occurring with cis and trans isomerization of the azobenzene side groups in the polymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5138–5146, 2005     

Stimuli‐responsive brush‐shaped conjugated polymers with pendant well‐defined poly(vinyl ether)s

For the synthesis of brush‐shaped conjugated polymers consisting of a poly(phenylene butadiynylene) backbone and well‐defined poly(vinyl ether) (polyVE) side chains, we designed polyVE‐based macromonomers bearing a diethynyl benzene group at the terminus and applied them to the grafting through synthesis. The macromonomer (DE‐PIBVE) was synthesized by living cationic polymerization of isobutyl VE (IBVE) using a functionalized initiator (TMS‐DEVE‐TFA) having a TMS protected diethynyl benzene moiety, followed by deprotection of the TMS groups. As a result, we succeeded in the synthesis of the target brush‐shaped conjugated polymers [poly(DE‐PIBVE)] by oxidative coupling reaction of the diethynyl benzene groups. We found that the solution of poly(DE‐PIBVE) with a specific side chain length exhibited solvatochromism and thermochromism depending on the polarity of the media employed. This phenomenon was attributed to self‐assembly in polar media due to the intermolecular π–π interaction between neighboring conjugated polymer backbones, where the self‐assembly behavior would be closely related to the pendant polyVE structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3318–3325     

Near-monodisperse,n-alkyl,end-functionalized poly(methyl vinyl ether)s: Synthesis by living cationic polymerization and solution characterization

Water-soluble amphiphilic diblock copolymers were synthesized by the living cationic polymerization of methyl vinyl ether (hydrophilic block) and its subsequent termination with n-alcohols of chain lengths varying from one to eight, and three n-alkyl carboxylic acids with 10, 12, and 18 carbon atoms. Additionally, water and ethylene glycol were tested as terminating agents. The extent of the functionalization was determined using ¹H NMR spectroscopy. The cloud points of 1% w/w aqueous solutions of the polymers as determined by turbidimetry decreased from 32 to 21°C as the number of carbon atoms of the terminating agent increased. Aqueous GPC revealed micellization of the stearic acid-terminated block copolymer, while the other block copolymers existed mainly as unimers. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2547–2554, 1998     

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     

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     

Selective single monomer addition in living cationic polymerization: Sequential double end‐functionalization in combination with capping agent

Amine‐functionalized and amine‐carboxylate double‐functionalized polymers ( I and II , respectively) have been synthesized by a selective single addition of a protected 2‐aminoethyl vinyl ether (BocVE) {CH₂ = CH[OCH₂CH₂N(Boc)₂]; Boc = t‐butoxycarbonyl} onto a living cationic poly(n‐butyl vinyl ether) [poly(NBVE)] initiated with the SnCl₄/n‐Bu₄NCl system: ( I ) ‐(NBVE)_n‐ CH₂CH(OCH₂CH₂NH₂)‐H; ( II ) ‐(NBVE)_n‐CH₂CH(OCH₂CH₂NH₂)‐CH₂CO₂H. The single addition was examined with a set of alkene monomers less reactive than NBVE, including BocVE, 2‐chloroethyl vinyl ether, 2‐vinyloxyethylphtalimide, and styrene (St). Upon addition of 10 molar excess of these alkenes onto the living ends, only BocVE led to the intended single adduct, and this was attributed to a chelating interaction of the two carboxylate groups in the terminal BocVE unit with the growing poly(NBVE) terminal, thus sterically hampering further propagation. A simple acid‐catalyzed Boc‐deprotection led to the amino‐functionalized version I . Alternatively, an additional quenching the BocVE‐capped living end (the precursor of I ) with sodium malonate, followed by double deprotection of the Boc and the malonate groups gave the double‐functionalized version II . The selective addition of a single monomer molecule is thus a new method for addressable or site‐specific introduction of functional groups along polymer chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3375–3381, 2010     

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     

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     

Fluorine‐containing vinyl ether polymers: Living cationic polymerization in fluorinated solvents as new media and unique solubility characteristics in organic solvents

Living cationic polymerization of fluorine‐containing vinyl ethers [CH₂?CH? O? C₂H₄? O? C₃H₆? C_nF_2n+1: 5FVE (n = 2), 13FVE (n = 6)] was investigated in various solvents with a CH₃CH(OiBu)OCOCH₃/Et_1.5AlCl_1.5 initiating system in the presence of an added base. 5FVE was polymerized quantitatively in toluene at 0 °C, and the obtained polymers had predetermined molecular weights with narrow molecular weight distributions (M_w/M_n < 1.1). On the other hand, for the polymerization of 13FVE, the product polymers precipitated due to their extremely poor solubility in nonfluorinated organic solvents. Therefore, fluorinated solvents such as hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers, or α,α,α‐trifluorotoluene, as‐yet uninvestigated for cationic polymerization, were employed. In these solvents, living polymerization was achieved even with 13FVE, yielding well‐defined polymers (M_w/M_n < 1.1, by size exclusion chromatography using a fluorinated solvent as an eluent). The solvents were also shown to be good for living polymerization of isobutyl vinyl ether. The obtained fluorine‐containing polymers underwent temperature‐responsive solubility transitions in organic solvents. Poly(5FVE) showed sensitive upper critical solution temperature (UCST)‐type phase separation behavior in toluene. Copolymers of 13FVE and isobutyl vinyl ether showed UCST‐type phase separation in common organic solvents with different polarities depending on their composition, while a homopolymer of 13FVE was insoluble in all nonfluorinated organic solvents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of ABA‐triblock and star‐diblock copolymers with poly(2‐adamantyl vinyl ether) and poly(n‐butyl vinyl ether) segments: New thermoplastic elastomers composed solely of poly(vinyl ether) backbones

ABA‐type triblock copolymers and AB‐type star diblock copolymers with poly(2‐adamantyl vinyl ether) [poly(2‐AdVE)] hard outer segments and poly(n‐butyl vinyl ether) [poly(NBVE)] soft inner segments were synthesized by sequential living cationic copolymerization. Although both the two polymer segments were composed solely of poly(vinyl ether) backbones and hydrocarbon side chains, they were segregated into microphase‐separated structure, so that the block copolymers formed thermoplastic elastomers. Both the ABA‐type triblock copolymers and the AB‐type star diblock copolymers exhibited rubber elasticity over wide temperature range. For example, the ABA‐type triblock copolymers showed rubber elasticity from about ?53 °C to about 165 °C and the AB‐type star diblock copolymer did from about ?47 °C to 183 °C with a similar composition of poly(2‐AdVE) and poly(NBVE) segments in the dynamic mechanical analysis. The AB‐type star diblock copolymers exhibited higher tensile strength and elongation at break than the ABA‐type triblock copolymers. The thermal decomposition temperatures of both the block copolymers were as high as 321–331 °C, indicating their high thermal stability. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Star-shaped polymers by living cationic polymerization. VIII. Size and shape of star poly(vinyl ether)s determined by dynamic light scattering and computer simulation

The sizes and shapes of star-shaped poly(vinyl ether)s, prepared by living cationic polymerization, were studied by dynamic light scattering and molecular mechanics-based computer simulation. The hydrodynamic radii (R_h) of star poly(isobutyl vinyl ether)s (4a; M?_w = 2.2 × 10⁴ ? 1.7 × 10⁵) determined by dynamic light scattering were in the range from 30 to 90 Å in tetrahydrofuran or ethyl acetate. Consistent with the expected multiarmed architecture of 4a, the radius for a given number (f) of arms per molecule increased with the degree of polymerization [DP(arm)] of the arms, and for a fixed DP(arm), the radius increased with f. The relationship between arm number f and the “shrinking” factor h [R_h(star)/R_h(linear)] was consistent with multibranched structures for the star polymers. These results are supported by those for the molecular weight itself; the apparent weight-average molecular weights by size-exclusion chromatography are less than the corresponding absolute values by static light scattering. The dependence of h on f suggests some degree of asymmetry in the star shape. Similar results were also obtained by the computer simulation of potential energy-minimized conformations of the arms, which implied almost spherical but slightly asymmetric shapes. The computer simulation also demonstrated that the star polymer (4b) with pendant hydroxyl groups in the arms is smaller in size than the corresponding alkyl (isobutyl) (4a) with the identical arm number and arm degree of polymerization. © 1995 John Wiley & Sons, Inc.     

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