Controlled ring‐expansion polymerization of thiiranes based on cyclic aromatic thiourethane initiator

Ring‐expansion polymerization (REP) of thiiranes was investigated using 3H‐benzothiazol‐2‐one (BT) as the cyclic aromatic thiourethane initiator in the presence of tetrabutylammonium chloride (TBAC) catalyst. The polymerization proceeded in a well‐controlled manner to afford cyclic polysulfides with one BT moiety per macrocycle, as confirmed by MALDI‐TOF MS spectroscopy. Differential scanning calorimetry (DSC) measurement of the obtained cyclic polysulfides revealed slight decrease in the glass‐transition temperature as the increase in the molecular weight, supporting the cyclic topology of the products. Postpolymerization of thiiranes using the BT‐initiated cyclic polysulfide as the macroinitiator afforded the ring‐expanded product while maintaining the narrow polydispersity and well‐defined cyclic structure, which enabled precise synthesis of cyclic block copolymer with different thiirane combination. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2442–2449     

Synthesis of macrocycles by the ring‐crossover reaction of a cyclic dithioester

The ring‐crossover polymerization of cyclic dithioester 1 was performed in the presence of quaternary onium salts as catalysts at 70–150 °C for 24 h in NMP. It was found that predictable cyclic polymers with the same repeating structures as 1 were obtained with M_ns in the range between 700 and 3,500, quantitatively. It was observed that intermolecular and intramolecular thioester‐exchange reactions proceeded between cyclic monomer 1 and resulting cyclic polymers under thermodynamic control to give a lower‐molecular‐weight cyclic polymer with a lower polydispersity ratio (M_n = 2,400, M_w/M_n = 1.70). © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 680–687, 2007     

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     

Recent progress on cyclic polymers: Synthesis,bioproperties, and biomedical applications

Polymer topologies exert a significant effect on its properties, and polymer nanostructures with advanced architectures, such as cyclic polymers, star‐shaped polymers, and hyperbranched polymers, are a promising class of materials with advantages over conventional linear counterparts. Cyclic polymers, due to the lack of polymer chain ends, have displayed intriguing physical and chemical properties. Such uniqueness has drawn considerable attention over the past decade. The current review focuses on the recent progress in the design and development of cyclic polymer with an emphasis on its synthesis and bio‐related properties and applications. Two primary synthetic strategies towards cyclic polymers, that is, ring‐expansion polymerization and ring‐closure reaction are summarized. The bioproperties and biomedical applications of cyclic polymers are then highlighted. In the end, the future directions of this rapidly developing research field are discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1447–1458     

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     

Synthesis of polyphosphodiesters by ring‐opening polymerization of cyclic phosphates bearing allyl phosphoester protecting groups

The allyl phosphoester group is shown to be a protecting group for the synthesis of anionic polyphosphodiesters. Our strategy relies on the synthesis of a cyclic phosphate monomer bearing a pendant allyl phosphoester group, its easy purification by fractional distillation, its organocatalyzed ring‐opening polymerization by 1,8‐diazobicyclo[5.4.0]undec‐7‐ene (DBU) and 1‐[3,5‐bis(trifluoromethyl)phenyl]‐3‐cyclohexyl‐thiourea (TU). Finally, the deprotection of the allyl phosphoester group is carried out by reaction with sodium benzenethiolate in the absence of any detectable degradation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2642–2648     

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     

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     

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     

Anionic ring‐opening polymerization of a five‐membered cyclic carbonate having a glucopyranoside structure

Anionic ring‐opening polymerizations of methyl 4,6‐O‐benzylidene‐2,3‐O‐carbonyl‐α‐D ‐glucopyranoside (MBCG) were investigated using various anionic polymerization initiators. Polymerizations of the cyclic carbonate readily proceeded by using highly active initiators such as n‐butyllithium, lithium tert‐butoxide, sodium tert‐butoxide, potassium tert‐butoxide, and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene, whereas it did not proceed by using N,N‐dimethyl‐4‐aminopyridine and pyridine as initiators. In a polymerization of MBCG (1.0 M), 99% of MBCG was converted within 30 s to give the corresponding polymer with number‐averaged molecular weight (M_n) of 16,000. However, the M_n of the polymer decreased to 7500 when the polymerization time was prolonged to 24 h. It is because a backbiting reaction might occur under the polymerization conditions. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

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     

Enantiomer‐selective polymerization of (RS)‐(phenoxymethyl)thiirane with diethylzinc/L‐amino acid

Enantiomer‐selective polymerization of (RS)‐(phenoxymethyl)thiirane (RS‐ 1 ) was carried out with ZnEt₂/L ‐α‐amino acid as an initiator system, and the effect of the initiator system on the enantiomer selectivity was examined with various amino acids. All polymerizations heterogeneously proceeded, and every initiating system was effective in producing optically active polymers. For the polymerization of RS‐ 1 with diethylzinc (ZnEt₂)/L ‐leucine (1/1), the conversion was 43.7% in 12 days, and the number‐average molecular weight of the polymer was 18,000. The enantiomer selectivity was maximum when the molar ratio of the two components in the ZnEt₂/L ‐α‐amino acid system was 1:1. When the ZnEt₂/L ‐leucine (1/1) system was used in the polymerization, the best result was obtained with an enantiomer‐selectivity value of 5.36. During the polymerization, the S enantiomer was preferentially consumed, and the isotactic‐rich polymer was enriched in the S configurational units produced. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3443–3448, 2002     

Mapping the characteristics of the radical ring‐opening polymerization of a cyclic ketene acetal towards the creation of a functionalized polyester

Radical ring‐opening polymerization of cyclic ketene acetals is a means to achieve novel types of aliphatic polyesters. 2‐methylene‐1,3‐dioxe‐5‐pene is a seven‐membered cyclic ketene acetal containing an unsaturation in the 5‐position in the ring structure. The double bond functionality enables further reactions subsequent to polymerization. The monomer 2‐methylene‐1,3‐dioxe‐5‐pene was synthesized and polymerized in bulk by free radical polymerization at different temperatures, to determine the structure of the products and propose a reaction mechanism. The reaction mechanism is dependent on the reaction temperature. At higher temperatures, ring‐opening takes place to a great extent followed by a new cyclization process to form the stable five‐membered cyclic ester 3‐vinyl‐1,4‐butyrolactone as the main reaction product. Thereby, propagation is suppressed and only small amounts of other oligomeric products are formed. At lower temperatures, the cyclic ester formation is reduced and oligomeric products containing both ring‐opened and ring‐retained repeating units are produced at higher yield. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4587–4601, 2009     

Ring‐opening polymerization of the cyclic dimer of poly(trimethylene terephthalate)

Poly(trimethylene terephthalate) (PTT) was prepared by the ring‐opening polymerization of its cyclic dimer. Antimony(III) oxide, titanium(IV) butoxide, dibutyltin oxide, and titanium(IV) isopropoxide were used as catalysts. Among the catalysts, titanium(IV) butoxide was the most effective for the same reaction conditions. A weight‐average molecular weight of 63,500 g/mol was obtained from ring‐opening poly merization at 265 °C for 2 h in the presence of 0.5 mol % titanium(IV) butoxide. The PTTs obtained from the polymerization catalyzed with increasing amounts of antimony(III) oxide showed increasing weight‐average molecular weights and reaction conversions. When 1 mol % antimony(III) oxide was used, the weight‐average molecular weight was 32,000 g/mol and the conversion was 82% after 1 h of polymerization at 265 °C. In the case of the polymer catalyzed by titanium(IV) butoxide under the same conditions, the weight‐average molecular weight and conversion were 40,000 g/mol and 77% when 0.25 mol % was used, whereas 0.5 mol % catalyst produced a weight‐average molecular weight of 27,000 g/mol and a conversion of 95%. To get an acceptable molecular weight and relatively high reaction conversion, a catalyst concentration of at least 0.5 mol % was found to be necessary, in contrast to conventional condensation polymerizations, which require only about one‐tenth of this amount of the catalyst. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6801–6809, 2006     

Cyclic polylactides via simultaneous ring‐opening polymerization and polycondensation catalyzed by dibutyltin mercaptides

l ‐Lactide is polymerized in bulk at 160 °C either with dibutyltin bis(benzylmercaptide) (SnSBzl), dibutyltin bis(benzothiazole 2‐mercaptide) (SnMBT), or with dibutyltin bis(pentafluorothiophenolate) (SnSPF) as catalysts. SnSBzl yields linear polylactides having benzylthio‐ester end groups in addition to cyclic polylactides, whereas SnMBT and SnSPF mainly or exclusively yield cyclic polylactides. This finding, together with model reactions, indicates that the SnS catalysts promote a combined ring‐opening polymerization and polycondensation process including end‐to‐end cyclization. SnMBT caused slight racemization (3%–5%), when used at 160 °C. With SnSPF optically pure cyclic poly(l ‐lactide)s with high‐molecular weights can be prepared at 160 °C. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3767–3775     

Synthesis and characterization of block copolymers by metal‐ and solvent‐free ring‐opening polymerization of cyclic carbonates initiated from PEG‐based surfactants

Ring‐opening polymerizations of trimethylene carbonate (TC) and 2,2‐dimethyltrimethylene carbonate (DTC) are initiated from hydroxyl‐terminated polyethylene glycol (PEG) and PEG‐based surfactants (Triton X‐100 or Triton X‐405) in the absence of any catalysts. The metal‐ and solvent‐free polymerizations proceed under melt at 150 °C, affording Triton X‐100‐block‐poly(TC) with M_n of 1400–5200 and Triton X‐100‐block‐poly(DTC) with M_n of 1800–7100 in excellent yields. The molecular weights and the comonomer composition of the resulting copolymers are controlled by the feed ratios of the monomers to the initiators, confirmed by gel permeation chromatography and ¹H NMR spectroscopy. The solubilities of the block copolymers composed of hydrophilic PEG segment and hydrophobic poly(TC) or poly(DTC) segment depend on both the compositions and the components. For example, Triton X‐100‐block‐poly (TC) (TC/EG = 9.5/9.5) and Triton X‐405‐block‐poly(TC) (TC/EG = 28/40, 46/40) milky suspend in water, while Triton X‐405‐block‐poly(TC) (TC/EG = 9.7/40) dissolves in water. A dynamic light scattering study reveals that the particle distribution of a copolymer, Triton X‐405‐block‐poly(TC) (TC/EG = 9.7/40) in water, has a monodisperse unimodal pattern ranging from 92 to 368 nm. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1985–1996, 2006     

Radical ring‐opening polymerization of five‐membered cyclic vinyl sulfone using p‐toluenesulfonyl halides

Radical ring‐opening polymerizations of a five‐membered cyclic vinyl sulfone monomer, 2‐vinylthiolane‐1,1‐dioxide (VTDO), was carried out by using p‐toluenesulfonyl iodide (TosI) and bromide (TosBr) as radical initiators, and the corresponding ring‐opened polymer (PVTDO) was obtained. Both TosI and TosBr were found to work as the radical initiators for the polymerization of VTDO in bulk. The use of TosI gave PVTDOs with a broad, multimodal distribution of molecular weight in low yields. When 10 mol % of TosBr was employed, the isolated yield of PVTDO reached 49%, and the obtained PVTDO had a relatively narrow, monomodal molecular weight distribution of 1.8 with an M_n of 4100. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

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