Cationic ring‐opening polymerization behavior of a five‐membered cyclic thiocarbonate having a spiro‐linked adamantane moiety

This work deals with the synthesis and cationic ring‐opening polymerization behavior of a novel five‐membered cyclic thiocarbonate bearing a spiro‐linked adamantane moiety, tricyclo[3.3.1.1^3,7]decane‐2‐spiro‐4′‐(1′,3′‐dioxolane‐2′‐thione) ( TC2 ). The cationic ring‐opening polymerization of TC2 did not proceed with trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, triethyloxonium tetrafluoroborate (Et₃OBF₄), boron trifluoride etherate (BF₃OEt₂), titanium tetrachloride, or methyl iodide as the initiator, presumably because of the steric hindrance of the adamantane moiety. However, the cationic ring‐opening copolymerization of TC2 with five‐ or six‐membered cyclic thiocarbonates, that is, 1,3‐dioxolane‐2‐thione, 1,3‐dioxane‐2‐thione, 5‐methyl‐1,3‐dioxane‐2‐thione, or 5,5‐dimethyl‐1,3‐dioxane‐2‐thione, initiated by BF₃OEt₂ or Et₃OBF₄, proceeded to afford the corresponding copolymer via a selective ring‐opening direction. The increase in the feed ratio of TC2 in the copolymerization increased the unit ratio derived from TC2 in the copolymer; however, the molecular weight of the copolymer decreased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 699–707, 2003     

Cationic polymerization behavior of seven-membered cyclic sulfite

Cationic ring-opening polymerization behavior of a seven-membered cyclic sulfite ( 1 ) was examined. 1 was prepared by the reaction of 1,4-butanediol with SOCl₂ in 58% yield. The cationic polymerization of 1 was carried out at 0, 25, 60, or 100°C with trifluoromethanesulfonic acid (TfOH), methyl trifluoromethanesulfonate (TfOMe), BF₃ · OEt₂, SnCl₄, methyl p-toluenesulfonate (TsOMe), or MeI as an initiator in bulk under a nitrogen atmosphere to afford the polymer with M̄_n 1000–10,400. The order of activities of the initiators for 1 was as follows, TfOH ≅ TfOMe > SnCl₄ > BF₃ · OEt₂ > TsOMe ≅ MeI. The polymerization of 1 with TfOMe afforded a poly(sulfite) below 25°C, but afforded a polymer containing an ether unit at 60°C, which was formed by a desulfoxylation. The higher the activity of the initiator was, the more easily the desulfoxylation occurred. We expected volume expansion on polymerization because cyclic sulfites have large dipole moment values, but it turned out that 1 showed 4.34% shrinkage on polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3673–3682, 1997     

Controlled cationic ring‐opening polymerization of cyclic thiocarbonates with ester groups

This work deals with the cationic ring‐opening polymerization of the cyclic thiocarbonates 5‐benzoyloxymethyl‐5‐methyl‐1,3‐dioxane‐2‐thione ( 1 ), 5,5‐dimethyl‐1,3‐dioxane‐2‐thione ( 2 ), and 4‐benzoyloxymethyl‐1,3‐dioxane‐2‐thione ( 3 ). The polymerization was carried out with 2 mol % trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, boron trifluoride etherate, or triethyloxonium tetrafluoroborate as the initiator to afford the polythiocarbonate with a narrow molecular weight distribution accompanying isomerization of the thiocarbonate group. The molecular weight of the obtained polymer could be controlled by the feed ratio of the monomer to the initiator and increased when the second monomer was added to the polymerization mixture after the quantitative consumption of the monomer in the first stage. The block copolymerization of 2 and 3 was also achieved, and this supported the idea that the cationic ring‐opening polymerization of these monomers proceeded via a living process. The order of the polymerization rate was 3 > 2 > 1 . The cationic ring‐opening polymerization of 1 and 3 involved the neighboring group participation of ester groups according to the polymerization rate and molecular orbital calculations with the ab initio method. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 185–195, 2003     

Cationic polymerization of seven‐membered cyclic monothiocarbonate 1,3‐dioxepan‐2‐thione

The cationic ring‐opening polymerization of a seven‐membered cyclic monothiocarbonate, 1,3‐dioxepan‐2‐thione, produced a soluble polymer through the selective isomerization of thiocarbonyl to a carbonyl group {? [SC(C?O)O(CH₂)₄]_n? }. The molecular weights of the polymer could be controlled by the feed ratio of the monomer to the initiators or the conversion of the monomer during the polymerization, although some termination reactions occurred after the complete consumption of the monomer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1014–1018, 2005     

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopic analysis of telechelic polythiourethanes obtained by the cationic ring‐opening polymerization of six‐membered cyclic thiourethane

A matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectroscopy analysis of polythiourethanes obtained by the cationic ring‐opening polymerization of a six‐membered cyclic thiourethane [3‐benzyltetrahydro‐1,3‐oxazine‐2‐thione (BTOT)] is described. A MALDI‐TOF mass spectrum of a polymer obtained by the polymerization of BTOT with boron trifluoride etherate (BF₃OEt₂) as the initiator in nitrobenzene at 50 °C for 24 h followed by an end‐capping reaction with diethyldithiocarbamic acid diethylammonium salt showed a series of well‐resolved signals that were assignable to polythiourethanes possessing an amino group at the initiating end and a diethyldithiocarbamate group at the terminating end. In comparison with the MALDI‐TOF mass spectra of polymers obtained by polymerization with trifluoromethanesulfonic acid or methyl trifluoromethanesulfonate, the plausible initiating species in the polymerization with BF₃OEt₂ was estimated to be a proton, which successively eliminated carbonyl sulfide to produce a secondary amine group at the initiating end. The secondary amine group in the obtained telechelic polymer was converted to a tertiary amine group by a reaction with benzyl bromide in the presence of triethylamine, and this was confirmed by MALDI‐TOF mass spectroscopy. Furthermore, a telechelic polymer with a pyrrole end group was successfully synthesized by the end‐capping reaction of the growing species in the polymerization of BTOT with sodium 1‐pyrrolecarbodithioate. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4281–4289, 2006     

Sequence‐controlled cationic ring‐opening copolymerization of spiroorthocarbonate and oxetane

Pseudo block and triblock copolymers were synthesized by the cationic ring‐opening copolymerization of 1,5,7,11‐tetraoxaspiro[5.5]undecane (SOC1) with trimethylene oxide (OX) via one‐shot and two‐shot procedures, respectively. When SOC1 and OX were copolymerized cationically with boron trifluoride etherate (BF₃OEt₂) as an initiator in CH₂Cl₂ at 25 °C, OX was consumed faster than SOC1. SOC1 was polymerized from the OX‐rich gradient copolymer produced in the initial stage of the copolymerization to afford the corresponding pseudo block copolymer, poly [(OX‐grad‐SOC1)‐b‐SOC1]. We also succeeded in the synthesis of a pseudo triblock copolymer by the addition of OX during the course of the polymerization of SOC1 before its complete consumption, which provided the corresponding pseudo triblock copolymer, poly[SOC1‐b‐(OX‐grad‐SOC1)‐b‐SOC1]. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3233–3241, 2006     

Copolymers containing a spiro orthoester moiety that undergo no shrinkage during cationic crosslinking

A spiro orthoester with an exomethylene group (exoSOE) was radically copolymerized with acrylonitrile or vinyl acetate at several feed ratios to obtain the corresponding copolymers having spiro orthoester moieties in the side chain. The obtained copolymers could be crosslinked via the double ring‐opening polymerization of the spiro orthoester moieties in their side chain by a treatment with BF₃OEt₂. The volume changes upon the crosslinking of the copolymers were evaluated by density measurements with a micromeritics gas pycnometer. The copolymers experienced less than 1% volume expansion instead of volume shrinkage during typical cationic crosslinking, regardless of the copolymer compositions. Negligible shrinkage was observed during the thermal cationic crosslinking of a film cast from a nitrobenzene solution of the copolymers containing a benzylthiophenium salt as a thermally latent cationic initiator. The constantly low volume changes during the crosslinking of the copolymers from exoSOE probably depended on the almost zero volume change during the cationic polymerizations of spiro orthoester derivatives. This indicates that exoSOE is an effective monomer for crosslinkable polymers without volume changes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3666–3673, 2006     

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

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

Cationic ring‐opening polymerization of ϵ‐thionocaprolactone: Selective formation of polythioester

Cationic ring‐opening polymerization of ϵ‐thionocaprolactone was examined. The corresponding polythioester with the number‐average molecular weight (M_n ) of 57,000 was obtained in the polymerization with 1 mol % of BF₃ · OEt₂ as an initiator in CH₂Cl₂ at 28 °C for 5 h with quantitative monomer conversion. The M_n of the polymer increased with the solvent polarity and monomer‐to‐initiator ratio. No polymerization took place below −30 °C, and the monomer conversion and M_n of the polymer increased with the temperature in the range of −15 to 28 °C. The increase of initial monomer concentration was effective to improve the monomer conversion and the M_n of the obtained polymer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4057–4061, 2000     

Antithetic function of alcohol in living cationic polymerization: From terminator/inhibitor to useful initiator

We employed alcohols as initiators for living cationic polymerization of vinyl ethers and p‐methoxystyrene, coupled with tolerant Lewis acid, borontrifluoride etherate (BF₃OEt₂), although they were known to be poisonous reagent to bring about chain‐breaking such as chain transfer/termination rather than such beneficial one for propagation and polymerization‐control. As well known, without assistance of additive, ill‐defined polymers with broad molecular weight distributions (MWDs) were produced. Even addition of conventional oxygen‐based bases, for example, ethyl acetate (AcOEt), 1,4‐dioxane (DO), tetrahydrofran (THF), and diethyl ether (Et₂O) was less efficient in this system to control molecular weights and MWDs (M_w/M_n > 2.0). In contrast, by addition of dimethyl sulfide (Me₂S), MWDs of the resultant polymers became much narrower (M_w/M_n < 1.23) and the number‐average molecular weight (M_n) increased in direct proportion to monomer conversion in agreement with the calculated values assuming that one alcohol molecule generates one polymer chain. Studying changed feed‐ratio of alcohol to monomer and structural analyses with NMR and MALDI‐TOF‐MS indicated that quantitative initiation from alcohol giving alkoxide counteranion. This system opens a new way to use a variety of alcohols as initiators, which would allow us to design variety of structures and functions of counteranion. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4194–4201, 2009     

Synthesis and properties of the polythiourethanes obtained by the cationic ring‐opening polymerization of cyclic thiourethanes

The cationic ring‐opening polymerization of a five‐membered thiourethane [3‐benzyl‐1,3‐oxazolidine‐2‐thione (BOT)] with boron trifluoride etherate afforded the corresponding polythiourethane with a narrow molecular weight distribution in an excellent yield. The molecular weight of the polymers could be controlled by the feed ratio of the monomer to the initiator. A kinetic study of the polymerization revealed that the polymerization rate of BOT (1.3 × 10^?2 L mol^?1 min^?1) was two times larger than that of the six‐membered thiourethane [3‐benzyltetrahydro‐1,3‐oxazolidine‐2‐thione (BTOT); 6.8 × 10^?3 L mol^?1 min^?1], and the monomer conversion obeyed the first‐order kinetic equation. These observations, along with the successful results in the two‐stage polymerization, supported the idea that this polymerization proceeded in a controlled manner. Block copolymerizations of BOT with BTOT were also carried out to afford the corresponding di‐ and triblock copolymers with narrow molecular weight distributions. The order of the 5% weight loss temperatures was as follows: poly(3‐benzyltetrahydro‐1,3‐oxazolidine‐2‐thione) [poly(BTOT)] > poly(BTOT₅₄‐b‐BOT₄₆) > poly(3‐benzyl‐1,3‐oxazolidine‐2‐thione) [poly(BOT)]. This indicated that an increase in the BTOT unit content raised the decomposition temperature. The order of the refractive indices was poly(BOT) > poly(BTOT₅₄‐b‐BOT₄₆) > poly(BTOT₅₄‐b‐BOT₄₆‐b‐BTOT₅₀) > poly(BTOT); this was in accord with the order of the sulfur content in the polymer chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4795–4803, 2006     

Cationic polymerizations of 2‐alkyloxazolines catalyzed by bismuth salts

Acidic bismuth salts, such as BiCl₃, BiBr₃, BiJ₃, and Bi‐triflate catalyzed the ring‐opening polymerization of 2‐methoxazoline (MOZ) in bulk at 100 °C, whereas less acidic salts such as Bi₂O₃ or Bi(III)acetate did not. Bi‐triflate‐catalyzed polymerizations of 2‐ethyloxazoline (EtOZ) were performed with variation of the monomer–catalyst ratio (M/C). It was found that the molecular weights were independent of the M/C ratio. The formation of cationic chain ends and the absence of cycles was proven by reactions of virgin polymerization products with N,N‐dimethyl‐4‐aminopyridine or triphenylphosphine. The resulting polymers having modified cationic chain ends were characterized by ¹H NMR spectroscopy and MALDI‐TOF mass spectrometry. The polymerization mechanism including chain‐transfer reactions is discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4777–4784, 2008     

Synthesis and application as polymer electrolyte of hyperbranched polyether made by cationic ring‐opening polymerization of 3‐{2‐[2‐(2‐hydroxyethoxy)ethoxy]ethoxymethyl}‐3′‐methyl‐oxetane

A novel cyclic ether monomer 3‐{2‐[2‐(2‐hydroxyethoxy)ethoxy]ethoxy‐methyl}‐3′‐methyloxetane (HEMO) was prepared from the reaction of 3‐hydroxymethyl‐3′‐methyloxetane tosylate with triethylene glycol. The corresponding hyperbranched polyether (PHEMO) was synthesized using BF₃·Et₂O as initiator through cationic ring‐opening polymerization. The evidence from ¹H and ¹³C NMR analyses revealed that the hyperbranched structure is constructed by the competition between two chain propagation mechanisms, i.e. active chain end and activated monomer mechanism. The terminal structure of PHEMO with a cyclic fragment was definitely detected by MALDI‐TOF measurement. A DSC test implied that the resulting polyether has excellent segment motion performance potentially beneficial for the ion transport of polymer electrolytes. Moreover, a TGA assay showed that this hyperbranched polymer possesses high thermostability as compared to its liquid counterpart. The ion conductivity was measured to reach 5.6 × 10^?5 S/cm at room temperature and 6.3 × 10^?4 S/cm at 80 °C after doped with LiTFSI at a ratio of Li:O = 0.05, presenting the promise to meet the practical requirement of lithium ion batteries for polymer electrolytes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3650–3665, 2006     

Ring‐opening metathesis polymerization of amino acid‐functionalized norbornene derivatives

Amino acid‐derived novel norbornene derivatives, N,N′‐(endo‐bicyclo[2.2.1] hept‐5‐en‐2,3‐diyldicarbonyl) bis‐L ‐alanine methyl ester (NBA), N,N′‐(endo‐bicyclo[2.2.1]hept‐5‐en‐2,3‐diyldicarbonyl) bis‐L ‐leucine methyl ester (NBL), N,N′‐(endo‐bicyclo[2.2.1]hept‐5‐en‐2,3‐diyldicarbonyl) bis‐L ‐phenylalanine methyl ester (NBF) were synthesized and polymerized using the Grubbs 2nd generation ruthenium (Ru) catalyst. Although NBA, NBL, and NBF did not undergo homopolymerization, they underwent copolymerization with norbornene (NB) to give the copolymers with M_n ranging from 5200 to 38,100. The maximum incorporation ratio of the amino acid‐based unit was 9%, and the cis contents of the main chain were 54–66%. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5337–5343, 2006     

Ring‐opening grafting polymerization of cyclic monomers onto human hair

Natural human hair was successfully modified by the graft polymerization of trimethylene carbonate, β‐propiolactone, ε‐caprolactone, glycidol, ε‐caprolactam, and 5,5‐dimethyl‐1,3‐dioxane‐2‐thione. In contrast, we could not modify natural human hair by the graft polymerization of oxetane under similar conditions. The model reaction suggested that the main initiating species in these polymerizations were the amino, thiol, and hydroxyl groups in hair, which could induce ring‐opening polymerization. Among the tested monomers, β‐propiolactone was most effective for hair modification with its graft polymer, whose concentration was as high as 0.5 g/g of hair though polymerization under mild conditions. The effects of the hair pretreatment and polymerization temperature on the weight ratio of the grafted polymers were also investigated. Hair modified by grafted polymers was characterized with scanning electron microscopy and Fourier transform infrared measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 736–744, 2007     

New class of cationic ring‐opening polymerizations of 2,2‐diphenyl‐1,3‐oxathiolanes accompanying quantitative elimination of benzophenone

Cationic polymerizations of three 2‐substituted 1,3‐oxathiolanes, 2,2‐diphenyl‐1,3‐oxathiolane ( 1a ), 5‐methyl‐2,2‐diphenyl‐1,3‐oxathiolane ( 1b ), and 4‐methyl‐2,2‐diphenyl‐1,3‐oxathiolane ( 1c ), were carried out with boron trifluoride etherate (BF₃ · OEt₂) in dichloromethane at 30 °C to obtain poly(alkylene sulfide)s accompanying the elimination of benzophenone. In the cationic polymerization of 1b and 1c , the consumption of the monomers and formation of benzophenone proceeded simultaneously. The obtained poly(propylene sulfide)s from 1b and 1c contain 41% head–head units, which is in good agreement with that of the polymer from methylthiirane with BF₃ · OEt₂. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2943–2949, 2004     

Equilibrium polymerization behavior in the cationic single ring‐opening polymerization of bicyclo orthoesters

The synthesis and cationic polymerization of the following bicyclo orthoesters were examined: 4‐ethyl‐2,6,7‐trioxabicyclo[2.2.2]octane, 1,4‐diethyl‐2,6,7‐trioxabicyclo[2.2.2]octane, 4‐ethyl‐1‐phenyl‐2,6,7‐trioxabicyclo[2.2.2]octane, 4‐ethyl‐1‐(4‐methoxyphenyl)‐2,6,7‐trioxabicyclo[2.2.2]octane, and 4‐ethyl‐1‐(4‐nitrophenyl)‐2,6,7‐ trioxabicyclo[2.2.2]octane. All the monomers underwent equilibrium polymerization, which was confirmed by the relationships between the polymerization temperature and monomer conversion. The obtained polymers afforded the original monomers via an acid‐catalyst treatment with a low reagent concentration in CH₂Cl₂ at 20 °C. The equilibrium monomer concentration was constant, regardless of the initial reagent concentration, in both polymerization and depolymerization. The bicyclo orthoesters with a bulky and electron‐withdrawing substituent showed a larger equilibrium monomer concentration. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3159–3167, 2001     

Cationic cyclopolymerization of divinyl ethers with norbornane‐, norbornene‐, or adamantane‐containing substituents: Synthesis of cyclopoly(divinyl ether)s with bulky rigid side chains leading to high glass transition temperature

Cationic cyclopolymerizations of 2,2‐bis(vinyloxymethyl)bicyclo[2.2.1]heptane ( 1 ), 5,5‐bis(vinyloxymethyl)‐2‐bicyclo[2.2.1]heptene ( 2 ), and 2,2‐bis(vinyloxymethyl)tricyclo[3.3.1.1]^{3, 7}decane ( 3 ), divinyl ethers with a norbornane, norbornene, or adamantane unit, respectively, were investigated with the HCl/ZnCl₂ initiating system in toluene and methylene chloride at ?30 °C. All the reactions proceeded quantitatively to give gel‐free, soluble polymers in organic solvents. The number‐average molecular weight (M_n) of the polymers increased in direct proportion to monomer conversion and further increased on addition of a fresh monomer feed to the almost completely polymerized reaction mixture. The contents of the unreacted vinyl groups in the produced soluble polymers were less than ～10 mol %, and therefore, the degree of cyclization of the polymers was determined to be over ～90%. These facts show that cyclopolymerization of 1 , 2 , and 3 exclusively occurred and the poly(vinyl ether)s with the cyclized repeating units and polycyclic pendants were obtained with their molecular weights being regulated. BF₃OEt₂ initiator also caused cyclopolymerization of 1 , 2 , and 3 to give the corresponding high‐molecular‐weight cyclopolymers quantitatively. Glass transition temperatures (T_g's) of poly( 1 ) and poly( 2 ) were 165–180 °C, and T_g's of poly( 3 ) were 211–231 °C; these values are very high as vinyl ether polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2445–2454     

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     

Formation of linear and cyclic polyoxetanes in the cationic ring‐opening polymerization of 3‐allyloxymethyl‐3‐ethyloxetane and subsequent postpolymerization modification of poly(3‐allyloxymethyl‐3‐ethyloxetane)

The synthesis of 3‐allyloxymethyl‐3‐ethyloxetane (AllylEHO) and its polymerization with BF₃ × Et₂O is described in this study. Size exclusion chromatography (SEC) and membrane osmometry are used for the determination of molecular weights of the obtained products, ranging from M_n,SEC = 41,500‐131,500 g/mol. ¹H NMR spectroscopy, SEC, as well as MALDI‐TOF MS reveal the formation of cyclic tetramer beside low, but detectable concentrations of larger cyclic oligomers as by‐products during the polymerization process. These results help to understand mechanistically why attempts for a controlled homopolymerization of AllylEHO fail and why a controlled homopolymerization of oxetanes has not been described so far in the literature. Additionally, the high versatility of allyl‐functional polyoxetane for postpolymerization modification is proven by thiol–ene reactions with 3‐mercaptopropionic acid and N‐acetyl‐L ‐cysteine methyl ester. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013