Multifunctional coupling agents for living cationic polymerization. IV. Synthesis of end-functionalized multiarmed poly(vinyl ethers) with multifunctional silyl enol ethers

Telechelic ( 8 ) and end-functionalized four-arm star polymers ( 9 ) were synthesized through the coupling reactions of end-functionalized living poly(isobutyl vinyl ether) ( 5; DP _n ～ 10) with the bi-and tetrafunctional silyl enol ethers, H_4-nC? [CH₂OC₆H₄C(OSiMe₃) = CH₂]_n ( 3: n = 2; 4: n = 4). The precursor polymers 5 were prepared by living cationic polymerization with functionalized initiators, CH₃CH(Cl)OCH₂CH₂X(6), in conjunction with zinc chloride in methylene chloride at ?15°C. The initiators 6 were obtained by the addition of hydrogen chloride gas to vinyl ethers bearing pendant functional groups X , including acetoxy [? OC(O)CH₃], styryl (? OCH₂C₆H₄-p-CH = CH₂), and methacryloyl [? OC(O)C(CH₃) = CH₂]. The coupling reactions with 3 and 4 in methylene chloride at ?15°C for 24 h afforded the end-functionalized multiarmed polymers ( 8 and 9 ) in high yield (>91%), where those with styryl or methacryloyl groups are new multifunctional macromonomers. © 1994 John Wiley & Sons, Inc.     

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.     

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     

Living cationic polymerization of cis- and trans-ethyl propenyl ethers and synthesis of block copolymers with isobutyl vinyl ether

The cationic polymerization of cis- and trans-ethyl propenyl ethers (EPE, CH₃? CH?CH? O? C₂H₅), initiated by a mixture of hydrogen iodide and iodine (HI/I₂ initiator) at ?40°C in nonpolar media (toluene and n-hexane), led to living polymers of controlled molecular weights and a narrow molecular weight distribution (MWD) (M?_w/M?_n = 1.2–1.3). The geometrical isomerism of the monomer did not affect the living character of the polymerization. ¹³C NMR stereochemical analysis of the polymers showed that the living propagating end is sterically less crowded than nonliving counterparts generated by conventional Lewis acids (e.g., BF₃OEt₂). New block copolymers between EPE (cis or trans) and isobutyl vinyl ether were also prepared by sequential living polymerization of the two monomers.     

Multifunctional coupling agents for living cationic polymerization. I. Sodiomalonate anions for vinyl ethers

A series of multifunctional malonate anions, [Na^⊕?C(COOEt)₂CH₂]_mC₆H_6?m(I; m = 2–4), were examined as polymer coupling agents for the living cationic polymerization of vinyl ethers initiated with the hydrogen iodide/zinc iodide (HI/ZnI₂) initiating system. The bifunctional anion ( 2 ;I, m = 2), 1,4-[Na^⊕?C(COOEt)₂CH₂]₂C₆H₄, terminated living polymers of isobutyl vinyl ether (IBVE) (DP _n = 10) almost quantitatively in toluene at ?15°C to give coupled living polymers with doubled molecular weights in 96% yield; the dianion 2 was dissolved in tetrahydrofuran containing 18-crown-6 for maintaining the solution homogeneous. The yield of the coupled polymers was increased with shorter living chains or in less polar solvents. Also by coupling via 2 , ABA block copolymers were obtained from living AB block polymers of IBVE and an ester-functionalized vinyl ether (CH₂?CHOCH₂CH₂OCOCH₃). Coupling of living poly(IBVE) with the trifunctional anion ( 3 ; I, m = 3) led to tri-armed polymers in 56% yield, whereas with the tetrafunctional version ( 4 ; I, m = 4), only three out of the four anions reacted to give another tri-armed polymer in 85% yield. © 1993 John Wiley & Sons, Inc.     

Living cationic polymerization of vinyl ethers with a functional group. VII. Polymerization of vinyl ethers with a silyloxyl group and synthesis of polyalcohols and related functional polymers

Living cationic polymerizations of two silicon-containing vinyl ethers, 2-(t-butyldimethyl-silyloxyl)ethyl vinyl ether (tBuSiVE) and 2-(trimethylsilyloxyl)ethyl vinyl ether (MeSiVE), have been achieved with use of the hydrogen iodide/iodine (HI/I₂) initiating system in toluene at ?15 or ?40°C, despite the existence of the acid-sensitive silyloxyl pendants. The living nature of the polymerizations was demonstrated by linear increases in the number-average molecular weights (M?_n) of the polymers in direct proportion to monomer conversion and by their further rise upon addition of a second monomer feed to a completely polymerized reaction mixture. The polymers obtained in these experiments all exhibited very narrow molecular weight distributions (MWD) with M?_w/M?_n around or below 1.1. Desilylation of the polymers under mild conditions (with H⁺ for MeSiVE and F^? for tBuSiVE) gave poly(2-hydroxyethyl vinyl ether), a water-soluble polyalcohol with a narrow MWD. The living processes also permitted clean syntheses of amphiphilic AB block copolymers and water-soluble methacrylate-type macromonomers, all of which bear narrowly distributed segments of the polyalcohol derived from the silicon-containing vinyl ethers.     

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.     

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.     

Living cationic polymerization of vinyl ethers by electrophile/lewis acid initiating systems. VII. Living cationic polymerization of isobutyl vinyl ether by trimethylsilyl halide/zinc halide initiating systems in the presence of p-methoxybenzaldehyde: Effects of halide anions and zinc halides

Trimethylsilyl halides (Me₃SiY), in conjunction with zinc halides (ZnX₂) (Y and X:I, Br, Cl), were employed to investigate the living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene at ?15°C in the presence of p-methoxybenzaldehyde; with the aldehyde and IBVE monomer, Me₃SiY yields an initiating species [Me₃Si? O? CHC₆H₄(OM_e) ? CH₂CH(OiBu) ? Y] that triggers the IBVE polymerization via the activation of its carbon-halogen bond (C? Y) by ZnX₂ into C^δ+…?Y^δ?…?ZnX₂. Living polymerizations occurred with the silyl iodide and bromide irrespective of the type of ZnX₂, either when Y = X (Me₃Sil/Znl₂ and Me₃SiBr/ZnBr₂) or when Y ≠ X (Me₃Sil/ZnBr₂, Me₃SiI/ZnCl₂, and Me₃SiBr/Znl₂). With these five initiating systems, the number-average molecular weights (M?_n) of the polymers increased in proportion to monomer conversion, and the molecular weight distributions (MWDs) of the polymers were narrow (M?_w/M?_n = 1.1?1.2). The Me₃SiCl-based systems (Me₃SiCl/ZnCl₂ and Me₃SiCl/Znl₂), in (Me₃SiCl/Znl₂), in contrast, failed to give perfectly living polymerization; the M?_n indeed increased with conversion, but the MWDs of the polymers were broader (M?_w/M?_n = 1.3?1.5). Thus, the living nature of the polymerizations with Me₃SiY/Znx₂ is primarily determined by the halogen Y in Me₃SiY, which generates the terminal carbon-halogen bond (C? Y) that is activated by ZnX₂ for the propagation via a species C^δ+…?Y^δ?…?ZnX₂. For Y^?, not only the iodide but the bromide anion also is suited for living cationic polymerization. The virtual absence of the effects of X in ZnX₂ implies that the halogen exchange between ZnX₂ and Y from Me₃ SiY at the growing end (C^λ+…?Y^δ?…?ZnX₂ ?C^δ+…?X^δ?…?ZnXY) is absent or negligible.     

Synthesis of thermally-induced phase separating polymer with well-defined polymer structure by living cationic polymerization. I. Synthesis of poly(vinyl ether)s with oxyethylene units in the pendant and its phase separation behavior in aqueous solution

Living cationic polymerization of alkoxyethyl vinyl ether [CH₂?CHOCH₂CH₂OR; R: CH₃ (MOVE), C₂H₅ (EOVE)] and related vinyl ethers with oxyethylene units in the pendant was achieved by 1-(isobutoxy)ethyl acetate ( 1 )/Et_1.5AlCl_1.5 initiating system in the presence of an added base (ethyl acetate or THF) in toluene at 0°C. The polymers had a very narrow molecular weight distribution (M?_w/M?_n = 1.1–1.2) and the M?_n proportionally increased with the progress of the polymerization reaction. On the other hand, the polymerization by 1 /EtAlCl₂ initiating system in the presence of ethyl acetate, which produces living polymer of isobutyl vinyl ether, yielded the nonliving polymer. When an aqueous solution of the polymers thus obtained was heated, the phase separation phenomenon was clearly observed in each polymer at a definite critical temperature (T_ps). For example, T_ps was 70°C for poly(MOVE), and 20°C for poly(EOVE) (1 wt % aqueous solution, M?_n ～ 2 × 10⁴). The phase separation for each case was quite sensitive (ΔT_ps = 0.3–0.5°C) and reversible on heating and cooling. The T_ps or ΔT_ps was clearly dependent not only on the structure of polymer side chains (oxyethylene chain length and ω-alkyl group), but also on the molecular weight (M?_n = 5 × 10³-7 × 10⁴) and its distribution. © 1992 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.     

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     

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     

Selective vinyl cationic polymerization of monomers with two cationically polymerizable groups. II. p-vinylphenyl glycidyl ether: An epoxy-functionalized styrene

p-Vinylphenyl glycidyl ether (VPGE), a styrene derivative with an epoxy pendant, was polymerized by various cationic initiators, and its selective vinyl polymerization was investigated at low temperatures below ?15°C. BF₃OEt₂ (a metal halide) and CF₃SO₃H (a strong protonic acid) polymerized both vinyl and epoxy groups of VPGE, and produced cross-linked insoluble polymers. The HI/I₂ initiating system and iodine, in contrast, polymerized its vinyl group in polar solvents (CH₂Cl₂ and nitroethane) highly selectively in the temperature range of ?15 to ?40°C to give soluble polymers with a polystyrene backbone and epoxy pendants; however, under these conditions, 10–15% of the epoxy groups of the polymers were consumed during the polymerization by the reaction with the growing species. The polymerization by HI/I₂ in CH₂CI₂ involved a long-lived propagating species, as indicated by a progressive increase in the molecular weight (M?_n) of the polymers with monomer conversion and their fairly narrow molecular weight distributions (M?_w/M?_n ～ 1.6). The differences between the polymerizations of VPGE and p-isopropenylphenyl glycidyl ether, an α-methylstyrene-type counterpart of VPGE, were also discussed with an emphasis on the effects of the α-methyl group in the latter monomer.     

Lifetime of living polymers in cationic polymerization. III. Living polymerization of isobutyl vinyl ether initiated by a cationogen/etalcl2 system in the presence of 1,4-dioxane as an added base

The concentration ([P^*]) and lifetime (half-life) of the propagating species were measured in the living cationic polymerization of isobutyl vinyl either initiated by the 1-(isobutoxy) ethyl acetate [CH₃COOCH (OiBu) CH₃]/ethylaluminum dichloride (EtAlCl₂) system in the presence of excess 1,4-dioxane in n-hexane at 0 to +70°C; the acetate serves as a cationogen that forms an initiating vinyl ether-type carbocation. The measurements were based on the end-capping reaction with sodiomalonic ester [Na^⊕?CH (COOEt)₂], which was shown to react rapidly and quantitatively with the living growing end. From the terminal malonate group of the quenched polymers, [P^*] was determined by ¹H-NMR spectroscopy. In contrast to its constancy during the polymerization, [P^*] progressively decreased with time after the complete consumption of monomer. The postpolymerization decay was first order in [P^*], and the lifetime (half-life) of the living end was determined from the decay rate constant. The lifetime increased on lowering polymerization temperature, decreasing EtAlCl₂ concentration, and increasing dioxane concentration. In particular, the “base-stabilized” living ends, generated by the CH₃COOCH (OiBu) CH₃/EtAlCl₂/dioxane system, turned out extremely stable at 0°C (half-life > 5 days in the absence of monomer).     

Selective vinyl cationic polymerization of monomers with two cationically polymerizable groups. IV. New initiating systems for selective and living polymerization of p-isopropenylphenyl glycidyl ether

A variety of cationic initiators were employed for p-isopropenylphenyl glycidyl ether (IPGE), an α-methylstyrene derivative with an epoxy pendant, and optimum initiators and reaction conditions were evaluated in terms of its selective vinyl polymerization and living polymerization. Despite the coexistence of two cationically polymerizable groups in IPGE, binary initiating systems (HI, CF₃COOH, or CH₃CH(OiBu)-OCOCH₃, each coupled with ZnI₂) and sulfonic acids (CF₃SO₃H and CH₃SO₃H) selectively polymerized the vinyl group of IPGE in CH₂Cl₂ at ?78°C to produce soluble polymers with epoxy pendant groups in high yield. Metal halides (BF₃OEt₂ and AlEtCl₂) polymerized both the vinyl and epoxy groups of IPGE to give crosslinked insoluble polymers. In contrast, under these conditions, the HI/ZnI₂ system also led to a long-lived polymer, the molecular weight of which increased upon addition of a fresh feed of monomer to a completely polymerized reaction mixture, whereas the use of other initiators resulted in nonliving polymers. At higher temperatures (?40 and ?15°C), soluble poly(IPGE) was also obtained with HI/ZnI₂, but the polymer yield decreased with raising temperature, because of the occurrence of termination reaction.     

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     

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.     

Controlled synthesis of amphiphilic block copolymers with pendant glucose residues by living cationic polymerization

Amphiphilic block copolymers of vinyl ethers (VEs) of the type —[CH₂CH(OCH₂CH₂OR)]_m—[CH₂CH(OiBu)]_n—were synthesized by living cationic polymerization, where R is a D-glucose residue, and m and n are the degrees of polymerization (m = 20–50; n = 11–89). To obtain them, sequential living block copolymerization of isobutyl vinyl ether (IBVE) and the vinyl ether carrying 1,2:5,6-diisopropylidene-D -glucose residue was conducted by using the HCl adduct of IBVE, CH₃CH(OiBu)Cl, as initiator in conjunction with zinc iodide. These precursor block copolymers had a narrow molecular weight distribution (M̄_w/M̄_n ∼ 1.1) and a controlled composition. Treatment of them with a trifluoroacetic acid/water mixture led to the target amphiphiles. The solubility of the amphiphilic block copolymers in various solvents depended strongly on composition or the m/n ratio. Their solvent-cast thin films were observed, under a transmission electron microscope, to exhibit various microphase-separated surface morphologies such as spheres, cylinders, and lamellae, depending on composition. © 1997 John Wiley & Sons, Inc.