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     

Living cationic ring‐opening polymerization of five‐membered cyclic dithiocarbonate controlled by neighboring group participation of carbamate group

A five‐membered cyclic dithiocarbonate having phenylcarbamate moiety 1 underwent cationic ring‐opening polymerization by using methyl trifluoromethanesulfonate as an initiator in nitrobenzene at 60 °C. Both of the corresponding first‐order kinetic plot and conversion‐molecular weight plot showed linearity to suggest the living fashion of the polymerization, which was then supported by two‐stage polymerization experiment. The living fashion as well as the regioselective formation of the repeating unit suggested significant contribution of the neighboring group participation of the carbamate group to form a stabilized cationic propagating end, of which structure was confirmed by performing an equimolar reaction of 1 and methyl trifluoromethanesulfonate with analyzing the resulting species by NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4459–4464, 2007     

Exploration of tertiary aminosquaramide bifunctional organocatalyst in controlled/living ring‐opening polymerization of l‐lactide

A series of tertiary aminosquaramides as bifunctional organocatalysts in the ring‐opening polymerization (ROP) of l ‐lactide (l ‐LA) were developed, allowing the activation of both the l ‐LA monomer and the alcohol group of the initiator/propagating species. Further, the impact of tertiary nitrogen substituents on catalytic activity in ROP of l ‐LA was explored. The tertiary aminosquaramide— an air‐stable and moisture‐stable catalyst—exhibited superior activity in contest with thiourea counterpart when both were equipped with a similar tertiary amine group. Kinetic and chain‐extension experiments indicated that the formed poly(l ‐LA) is featured with narrow polydispersity and high end‐group fidelity, hallmarks of a living polymerization process. The initiator efficiency was further executed at ease by preparation of an ABA triblock copolymer poly (l ‐LA)‐b‐poly (ethylene glycol)‐b‐poly (l ‐LA) in the presence of a dual‐headed PEG macroinitiator. ¹H NMR titration experiments suggested a bifunctional catalytic mechanism, wherein both the l ‐LA monomer and the propagating hydroxyl group were activated en route to polymerization. The ¹H NMR, SEC, and MALDI‐TOF MS measurements validated the quantitative incorporation of the initiator in the polymeric chains and enchainment over competitive trans‐esterification reaction. Overall, the structure‐activity relationships were surveyed to uncover aminosquaramide as a new bifunctional dual hydrogen‐bond donor catalyst for living ROP of l ‐LA. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2483–2493     

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 ring‐opening polymerization of monothiocarbonate with a norbornene group

This work deals with the cationic ring‐opening polymerization of cyclic thiocarbonates with a norbornene or norbornane moiety, that is, 5,5‐(bicyclo[2.2.1]hept‐2‐ene‐5,5‐ylidene)‐1,3‐dioxane‐2‐thione ( TC1 ) or 5,5‐(bicyclo[2.2.1]heptane‐5,5‐ylidene)‐1,3‐dioxane‐2‐thione ( TC2 ), respectively. The reaction of TC1 initiated by trifluoromethanesulfonic acid (TfOH), methyl trifluoromethanesulfonate (TfOMe), boron trifluoride etherate (BF₃OEt₂), or triethyloxonium tetrafluoroborate (Et₃OBF₄) afforded unidentified products; however, TC1 underwent cationic ring‐opening polymerization with methyl iodide as an initiator to afford polythiocarbonate because the propagating end was stabilized by the covalent‐bonding property. The polymerization of TC2 initiated by TfOH, TfOMe, BF₃OEt₂, or Et₃OBF₄ afforded polythiocarbonate with good solubility in common organic solvents and a narrow molecular weight distribution because of the absence of a double‐bond moiety. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1698–1705, 2002     

Synthesis of novel hyperbranched polymer through cationic ring‐opening multibranching polymerization of 2‐hydroxymethyloxetane

The cationic ring‐opening multibranching polymerization of 2‐hydroxymethyloxetane ( 1 ) as a novel latent AB₂‐type monomer was carried out using trifluoromethane sulfonic acid or trifluoroboron diethyl etherate by a slow‐monomer‐addition (SMA) method. The polymer yield of poly‐1 ranged from ca. 58–88%, which increase with the increasing monomer addition time on the SMA method. The absolute molecular weights (M_w,MALLS) and the polydispersities of poly‐1 were in the range of 8,000–43,500 and 1.45–4.53, respectively, which also increased with the increasing monomer addition time. The Mark‐Houwink‐Sakurada exponents α in 0.2 M NaNO₃ aq. were determined to be 0.02–0.25 for poly‐1 , indicating that poly‐1 has compact forms in the solution because of the highly branched structure. The degree of the branching value of poly‐1 , which was calculated by Frey's equation, ranged from ca. 0.50 to 0.58, which increased with the increasing monomer addition time. The steady shear flow of poly‐1 in aqueous solution exhibited a Newtonian behavior with steady shear viscosities independent of the shear rate. The results of the MALLS, NMR, and viscosity measurements indicated that poly‐1 is composed of a highly branched structure, i.e., the hyperbranched poly (2‐hydroxymethyloxetane). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Combining cationic ring‐opening polymerization and click chemistry for the design of functionalized polyurethanes

A straightforward strategy for the synthesis and functionalization of polyurethanes (PUs) via the use of alkyne‐functionalized polytetrahydrofuran (PTHF) diols is described. The alkyne groups have been introduced into the PTHF chains by the cationic ring‐opening copolymerization of tetrahydrofuran and glycidyl propargyl ether. These PTHF prepolymers were combined with 1,4‐butanediol and hexamethylene diisocyanate for the synthesis of linear PUs with latent functionalization sites. The polyether segments of the PUs have then been coupled with several types of functionalized azides by the copper‐catalyzed azide‐alkyne “click” chemistry, for example with phosphonium containing azides for their antibacterial properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Anionic ring‐opening polymerization of a five‐membered cyclic urethane derived from d‐glucosamine

The anionic ring‐opening polymerization of a five‐membered cyclic urethane, 2‐amino‐4,6‐O‐benzylidene‐2‐N,3‐O‐carbonyl‐2‐deoxy‐α,d ‐glucopyranoside (MBUG), which was prepared from naturally abundant d ‐glucosamine, was examined. Potassium tert‐butoxide (t‐BuOK) was the most effective initiator among the evaluated bases and produced polyurethane with the Mn of 7800 without any elimination of CO₂. The equimolar reaction of MBUG and t‐BuOK in the presence of CH₃I produced N‐methylated MBUG and suggested that the initiation reaction involves proton abstraction from the NH group. This N‐methylated compound did not undergo the polymerization. Therefore, the mechanism of propagation in the ROP of MBUG should involve the proton abstraction and nucleophilic substitution of the resulting amide anion. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2491–2497     

Radical ring‐opening polymerization

The radical ring‐opening polymerization (RROP) behavior of the following monomers is reviewed, and the possibility for application to functional materials is described: cyclic disulfide, bicyclobutane, vinylcyclopropane, vinylcyclobutane, vinyloxirane, vinylthiirane, 4‐methylene‐1,3‐dioxolane, cyclic ketene acetal, cyclic arylsulfide, cyclic α‐oxyacrylate, benzocyclobutene, o‐xylylene dimer, exo‐methylene‐substituted spiro orthocarbonate, exo‐methylene‐substituted spiro orthoester, and vinylcyclopropanone cyclic acetal. RROP is a promising candidate for producing a wide variety of environmentally friendly functional polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 265–276, 2001     

Cationic ring‐opening polymerization of six‐membered cyclic carbonates with ester groups

This work deals with the cationic ring‐opening polymerization of the ester‐substituted cyclic carbonates 5‐methyl‐5‐benzoyloxymethyl‐1,3‐dioxan‐2‐one ( CC1 ) and 4‐benzoyloxymethyl‐1,3‐dioxan‐2‐one ( CC4 ). The polymerization was carried out with trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, boron trifluoride etherate, or methyl iodide as the initiator. The reactivity of CC1 and CC4 was higher than that of 5,5‐dimethyl‐1,3‐dioxan‐2‐one, which had no ester moiety. These results suggest that this ring‐opening polymerization was accelerated by the intramolecular ester group. CC1 showed a higher polymerizability than CC4 , affording a polymer with a higher molecular weight. Additionally, using methyl iodide as the initiator was effective for increasing the molecular weight of the obtained polycarbonate and decreasing decarboxylation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1305–1317, 2001     

Substituent effect on the cationic ring‐opening polymerization of acyloxymethyl five‐member cyclic dithiocarbonates

Five‐member cyclic dithiocarbonates were synthesized by the reactions of carbon disulfide with benzoic, p‐anisic, p‐chlorobenzoic, 1‐naphthalenecarboxylic, p‐nitrobenzoic, and p‐(tert‐butyl)benzoic glycidyl esters, and their cationic ring‐opening polymerizations were carried out with methyl trifluoromethane sulfonate and trifluoromethane sulfonic acid as initiators at room temperature to 80 °C. Polymers with number‐average molecular weights of 3400–24,900 were obtained in high yields, and their structures were estimated by NMR and IR spectroscopy. The monomers showed a clear difference in the polymerization rate according to the substituents. The rate of polymerization decreased in the order of p‐chlorobenzoic ≥ benzoic > 1‐naphthalenecarboxylic > p‐nitro‐benzoic > p‐tert‐butylbenzoic > p‐anisic. The data of the reaction kinetics, NMR studies, and molecular orbital calculations proved a plausible mechanism involving the participation of p‐substituted benzoyloxymethyl groups to stabilize the cationic propagating end. The polymers showed decomposition temperatures with 5% weight loss ranging from 200 to 260 °C. No glass‐transition temperatures for the polymers were observed below 200 °C by differential scanning calorimetry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3967–3980, 2001     

Study on the cationic ring‐opening polymerization of 1,3‐dioxepane in the presence of organic acids

1,3‐Dioxepane was polymerized with triflic acid as an initiator in the presence of acetic acid (AA) and hexane diacid. The structure of the poly(1,3‐dioxepane) (polyDOP) obtained was characterized by ¹H NMR spectra and gel permeation chromatography. The molecular weights (MWs) were determined by vapor pressure osmometry. The results obtained in both systems were completely different from those in which low‐MW polyols were used as chain‐transfer agents. When the molar ratio of carboxylic acid to triflic acid was low, high‐MW polyDOP with a controlled MW and narrow MW distribution was obtained. The content of the ester group in the final product depended greatly on the molar ratio of AA to triflic acid. The polymerization mechanism is discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1232–1240, 2000     

Hydrogen‐bonding characteristics and unique ring‐opening polymerization behavior of Ortho‐methylol functional benzoxazine

Monofunctional benzoxazine with ortho‐methylol functionality has been synthesized and highly purified. The chemical structure of the synthesized monomer has been confirmed by ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT‐IR) and elemental analysis. One‐dimensional (1D) ¹H NMR is used with respect to varied concentration of benzoxazines to study the specific nature of hydrogen bonding in both ortho‐methylol functional benzoxazine and its para counterpart. The polymerization behavior of benzoxazine monomer has been also studied by in situ FT‐IR and differential scanning calorimetry, experimentally supporting the polymerization mechanism of ortho‐methylol functional benzoxazine we proposed before. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3635–3642     

Chemistry of 2‐oxazolines: A crossing of cationic ring‐opening polymerization and enzymatic ring‐opening polyaddition

Chemistry of 2‐oxazolines is involved in the polymer synthesis fields of cationic ring‐opening polymerization (CROP) and enzymatic ring‐opening polyaddition (EROPA), although both polymerizations look like a quite different class of reaction. The key for the polymerization to proceed is combination of the catalyst (initiator) and the design of monomers. This article describes recent developments in polymer synthesis via these two kinds of polymerizations to afford various functional polymers having completely different structures, poly(N‐acylethylenimine)s via CROP and 2‐amino‐2‐deoxy sugar unit‐containing oligo and polysaccharides via EROPA, respectively. From the viewpoint of reaction mode, an acid‐catalyzed ring‐opening polyaddition (ROPA) is considered to be a crossing where CROP and EROPA meet. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1251–1270, 2010     

Photoinduced cationic ring‐opening frontal polymerizations of oxetanes and oxiranes

The photoinitiated cationic ring‐opening polymerizations of certain epoxides and 3,3‐disubstituted oxetanes display the characteristics of frontal polymerizations. When irradiated with UV light, these monomers display a marked induction period, during which little conversion of the monomer to the polymer takes place. The local application of heat to an irradiated monomer sample results in polymerization that occurs as a front propagating rapidly throughout the entire reaction mass. For the characterization of these frontal polymerizations, the use of a new monitoring technique, employing optical pyrometry, has been instituted. This method provides a simple, rapid means of following these fast polymerizations and quantitatively determining their frontal velocities. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1630–1646, 2004     

Strontium‐based initiator system for ring‐opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr‐PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring‐opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA). The Sr‐PO initiator demonstrated an effective initiating activity for the ROP of ε‐caprolactone (ε‐CL) and L‐lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr‐PO initiator. Block copolymer PCL‐b‐PLLA was prepared by sequential polymerization of ε‐CL and LLA, which was demonstrated by ¹H NMR, ¹³C NMR, and gel permeation chromatography. The chemical structure of Sr‐PO initiator was confirmed by elemental analysis of Sr and N, ¹H NMR analysis of the end groups in ε‐CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr‐PO initiator and model monomer γ‐butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination‐insertion mechanism, and cyclic esters exclusively inserted into the Sr–O bond. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1934–1941, 2003     

Computational evaluation of radical ring‐opening polymerization

The tendencies of ring‐opening processes in radical ring‐opening polymerizations were evaluated by AM1 and PM3 semi‐empirical calculations and 6‐31G*‐level calculations based on the density functional theory (DFT) B3LYP models. Sixteen cyclic monomers bearing vinyl or exomethylene groups were categorized into ring‐opening and no‐ring‐opening monomers by the evaluation of the differences of the internal energies and the lengths of the cleaving bonds between the ground states of the initial radicals and the activated states in the ring‐opening processes. Although the semi‐empirical calculations not parameterized to radical reactions resulted in the moderate categorization of the ring‐opening monomers, the DFT calculation clearly distinguished the ring‐opening and no‐ring‐opening monomers. The ring‐opening tendencies were also evaluated with the changes in the internal energies throughout the ring‐opening processes, but this method could not group the ring‐opening and no‐ring‐opening monomers clearly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2827–2834, 2007     

Concentration effects in the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline in N,N‐dimethylacetamide

The monomer concentration for the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline in N,N‐dimethylacetamide was optimized utilizing high‐throughput experimentation methods. Detailed ¹H‐NMR spectroscopic investigations were performed to understand the mechanistic aspects of the observed concentration effects. Finally, the improved polymerization concentration was applied for the synthesis of higher molecular weight (> 10,000 Da) poly(2‐ethyl‐2‐oxazoline)s. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1487–1497, 2005