Fluorinated vinyl ether homopolymers and copolymers: Living cationic polymerization and temperature‐induced solubility transitions in various organic solvents including perfluoro solvents

Partially fluorinated poly(vinyl ether)s with C₄F₉ and C₆F₁₂H groups in the side chain were synthesized via living cationic polymerization in the presence of an added base in a fluorine‐containing solvent, dichloropentafluoropropanes. For comparison, the polymerization of vinyl ether monomers with C₂F₅ and C₆F₁₃ groups and nonfluorinated monomers were also carried out. The characterization of the product polymers using size exclusion chromatography with a fluorinated solvent as an eluent indicated that all polymers had narrow molecular weight distributions (M_w/M_n ～ 1.1). Interestingly, the moderately fluorinated polymers with C₄F₉ exhibited upper critical solution temperature‐type phase separation in various organic solvents with wide‐ranging polarities, whereas highly fluorinated polymers with C₆F₁₃ are insoluble in nonfluorinated solvents. Polymers with C₄F₉ groups exhibited temperature dependent solubility transitions not only in common organic solvents (e.g., toluene, chloroform, tetrahydrofuran, and acetone) but also in perfluoro solvents [e.g., perfluoro(methylcyclohexane) and perfluorodecalin]. On the other hand, the solubility of polymers with C₆F₁₂H showed completely different from that of polymers with C₆F₁₃, despite their similar fluorine content. In addition, various types of fluorinated block copolymers were prepared in a living manner. The block copolymers with a thermosensitive fluorinated segment underwent temperature‐induced micellization and sol–gel transition in various organic solvents. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Living cationic polymerization of 2‐adamantyl vinyl ether

Living cationic polymerization of 2‐adamantyl vinyl ether (2‐vinyloxytricyclo[3.3.1.1]^3,7decane; 2‐AdVE) was achieved with the CH₃CH(OiBu)OCOCH₃/ethylaluminum sesquichloride/ethyl acetate [CH₃CH(OiBu)OCOCH₃/Et_1.5AlCl_1.5/CH₃COOEt] initiating system in toluene at 0 °C. The number‐average molecular weights (M_n's) of the obtained poly(2‐AdVE)s increased in direct proportion to monomer conversion and produced the polymers with narrow molecular weight distributions (MWDs) (M_w/M_n = ～1.1). When a second monomer feed was added to the almost polymerized reaction mixture, the added monomer was completely consumed and the M_n's of the polymers showed a direct increase against conversion of the added monomer. Block and statistical copolymerization of 2‐AdVE with n‐butyl vinyl ether (CH₂?CH? O? CH₂ CH₂CH₂CH₃; NBVE) were possible via living process based on the same initiating system to give the corresponding copolymers with narrow MWDs. Grass transition temperature (T_g) and thermal decomposition temperature (T_d) of the poly(2‐AdVE) (e.g., M_n = 22,000, M_w/M_n = 1.17) were 178 and 323 °C, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1629–1637, 2008     

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     

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 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     

Living cationic polymerization of vinyl ether with a cyclic acetal group

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

Syntheses of amphiphilic block copolymers by living cationic polymerization of vinyl ethers and their selective solvent‐induced physical gelation

Amphiphilic diblock copolymers were prepared by the living cationic polymerization of vinyl ethers in the presence of added bases, and their selective solvent‐induced physical gelation behavior was investigated. The block copolymerization of 2‐phenoxyethyl vinyl ether (PhOVE) and 2‐methoxyethyl vinyl ether (MOVE) was carried out in the presence of ethyl acetate with Et_1.5AlCl_1.5 in toluene at 0 °C. Despite the rate difference, diblock copolymers with a very narrow molecular weight distribution were obtained, quantitatively. By adding the selective solvent, water, to the acetone solution of the diblock copolymer, PhOVE₂₀₀‐b‐MOVE₄₀₀, physical gelation occurred suddenly and the system ceased to flow, maintaining transparency. Viscoelastic measurements and transmission electron microscopic observations were performed to examine the characteristic gelation behavior and structure of the obtained gels. Various gelation conditions and physical gelation by other amphiphilic block copolymers were also designed on the basis of the solubility of each block segment. Further, new forms of physical gelation, accompanied by the solubilization of immiscible organic compounds, were achieved using similar diblock copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3190–3197, 2001     

Synthesis of block copolymers by the transformation of cationic polymerization into reversible atom transfer radical polymerization

Azo-containing polytetrahydrofuran (PTHF) obtained by cationic polymerization was used as a macroinitiator in the reverse atom transfer radical polymerization (RATRP) of styrene and methyl acrylate in conjunction with CuCl₂/2,2′-bipyridine as a catalyst. Diblock PTHF–polystyrene and PTHF–poly(methyl acrylate) were obtained after a two-step process. In the first step of the reaction, stable chlorine-end-capped PTHF was formed with the thermolysis of azo-linked PTHF at 65–70 °C in the presence of the catalyst. Heating the system at temperatures of 100–110 °C started the polymerization of the second monomer, which resulted in the formation of block copolymers. The decomposition behavior of the azo-linked PTHF and the structure of the block copolymers were determined by ¹H NMR and gel permeation chromatography (GPC). Kinetic studies and GPC analyses further confirmed the controlled/living nature of the RATRP initiated by the polymeric radicals. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2199–2208, 2002     

Living cationic polymerization of vinylnaphthalene derivatives

The living cationic polymerization of 6‐tert‐butoxy‐2‐vinylnaphthalene (tBOVN), a vinylnaphthalene derivative with an electron‐donating group, was achieved with a TiCl₄/SnCl₄ combined initiating system in the presence of ethyl acetate as an added base at –30 °C. The absence of side reactions at low temperature was confirmed by ¹H NMR analysis of the resulting polymer. In contrast to this controlled reaction at –30 °C, reactions performed at higher temperature, such as 0 °C, frequently involved unwanted intramolecular or intermolecular Friedel–Crafts reactions of naphthalene rings due to the high electron density of these rings. The cationic polymerization of 6‐acetoxy‐2‐vinylnaphthalene, a derivative with an acetoxy group, was also controlled under similar conditions, but chain transfer reactions were not completely suppressed during the polymerization of 2‐vinylnaphthalene. The glass transition temperature (T_g) of the obtained poly(tBOVN) was 157 °C, a value higher by 94 °C than that of the corresponding styrene derivative. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4828–4834     

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     

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.     

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     

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

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

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     

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     

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     

Living cationic polymerization of vinyl ethers with a naphthyl group: Decisive effect of the substituted position on naphthalene ring

Living cationic polymerization of a vinyl ether with a naphthyl group [2‐(2‐naphthoxy)ethyl vinyl ether, βNpOVE] was achieved using base‐assisting initiating systems with a Lewis acid. The Et_1.5AlCl_1.5/1,4‐dioxane or ethyl acetate system induced the living cationic polymerization of βNpOVE in toluene at 0 °C. The living nature of this reaction was confirmed by a monomer addition experiment, followed by ¹H NMR and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) analyses. In contrast, the polymerization of αNpOVE was not fully controlled; under similar conditions, it produced polymers with broad molecular weight distributions. The ¹H NMR and MALDI‐TOF‐MS spectra of the resultant poly(αNpOVE) revealed that the products had undesirable structures derived from Friedel–Crafts alkylation. The higher reactivity of αNpOVE in electrophilic substitution reactions, such as the Friedel–Crafts reaction, was attributable to the greater electron density of the naphthyl ring, which was calculated based on frontier orbital theory. The naphthyl groups significantly affected the properties of the resultant polymer. For example, the glass transition temperatures (T_g) of poly(NpOVE)s are higher by approximately 40 °C than that of poly(2‐phenoxyethyl vinyl ether). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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