Ring-opening polymerization of cyclic carbonates by alcohol–acid catalyst

Ring-opening reactions of 1,3-dioxepan-2-one ( 1 ) and 1,3-dioxan- 2 -one (2) with several alcohols were examined. The reactions proceeded without trifluoroacetic acid (TFA) in low conversions, while they proceeded smoothly with TFA to afford the ring-opened adducts and oligomers. Ring-opening polymerizations of 1 and 2 were also carried out by alcohol–acid catalysts to afford the corresponding polycarbonates (M _n = 2500−6800). The molecular weights increased with increase of the conversions of 1 and 2. The observed polymerization rates of 1 and 2 were determined as 24.4 × 10⁻⁶ and 0.8 × 10⁻⁶ s⁻¹, respectively. Mechanistic aspects were studied by NMR spectroscopy. The methylene protons α and β to the carbonate moieties shifted to lower fields in 0.06–0.11 ppm in the ¹H-NMR spectra by the addition of TFA. Downfield shifts of the carbonyl carbon signals of 1 and 2 were observed in 3.94–4.15 ppm in the ¹³C-NMR spectra. These results strongly suggest that the cyclic carbonates are activated by TFA. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2463–2471, 1998     

Anionic ring-opening polymerization behavior of a seven-membered cyclic carbonate; 1, 3-dioxepan-2-one

Anionic ring-opening polymerization of a seven-membered cyclic carbonate, 1,3-dioxepan-2-one ( 1 ), was carried out to observe that the higher the polymerization temperature and lower the initial monomer concentration were, the lower the yield and molecular weight, and wider the molecular weight distribution of the obtained polymers were. The back-biting reaction and the formation of cyclic oligomers of 1 were observed during the polymerization of 1 . The relative polymerization rate of 1 was about 35 times faster than that of six-membered carbonate, 1,3-dioxan-2-one ( 3 ). The ΔHps of 1 and 3 estimated by MO (PM3) calculations were −9.8 and −4.4 kcal/mol, respectively. 1 could easily undergo the ring-opening polymerization based on larger ring strain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1375–1380, 1997     

Synthesis of dendritic–linear block copolymers by living ring-opening polymerization of lactones and lactides using dendritic initiators

Polyether dendrons have been successfully used as macroinitiators for the living ring-opening polymerization (ROP) of lactones and lactides. A hydroxyl group located at the focal point of dendrimers of different generations was transformed into diethyl aluminum alkoxides by reaction with triethyl aluminum. The dendritic aluminum alkoxides proved to be efficient macroinitiators for the living ROP of ε-caprolactone (εCL), 1,4,8-trioxa(4,6)spiro[9]undecanone (TOSUO), D ,L - and L ,L -lactide. Formation of these block copolymers of unusual macromolecular architecture was supported by size exclusion chromatography and spectroscopy. The versatility of this synthetic approach allowed ω-functional dendrimer block-polyesters, such as macromonomer, and macromolecules with novel architectures, to be prepared. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1923–1930, 1999     

Anionic ring-opening polymerization behavior of trans-cyclohexene carbonate using metal tert-butoxides: Construction of living anionic ring-opening polymerization by lithium tert-butoxide

Anionic ring-opening polymerization (ROP) behavior of trans-cyclohexene carbonate (CHC) using metal alkoxides as initiators was investigated. As a result, lithium tert-butoxide-initiated ROP of CHC with a high-monomer concentration (10 M) at low temperature (−15 to −10°C) proceeded to afford a poly(trans-cyclohexene carbonate) (PCHC) without undesired side reactions such as mainly backbiting. The suppression of side reactions enables the control of the molecular weight (M_n = 2400–6100) of PCHC with low molar-mass dispersity values (M_w/M_n = 1.16–1.22). Furthermore, by increasing the feed ratio of the monomer to the initiator, the molecular weight increases proportionally, indicating a controllable polymerization. The results of a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis, a kinetic study, and a chain extension experiment suggested a living nature of this ROP using lithium tert-butoxide.     

Synthesis and radical ring-opening polymerization behavior of vinylcyclopropane bearing six-membered cyclic acetal moiety

Synthesis and radical ring-opening polymerization of vinylcyclopropane bearing six-membered cyclic acetal moiety, 1-vinyl-4,8-dioxaspiro[2.5]octane (1), were carried out. 1 was prepared by the reaction of 1,1-dichloro-2-vinylcyclopropane and 1,3-propanediol in DMF in the presence of a base. Radical polymerization of 1 was carried out in the presence of an appropriate initiator (3 mol % vs. 1) at 60 and 120°C in degassed sealed ampoules for 20 h. A colorless transparent viscous polymer was obtained by the isolation with preparative HPLC. The structure of poly(1) was determined to consist of two 1,5-ring-opened units and a unit bearing no olefinic moiety. The difference of the activation energies for the ring-opening reaction of the cyclopropane ring calculated by the molecular orbital method could explain the selectivity in the direction of the cleavage of the cyclopropane ring. Acid hydrolysis of poly(1) afforded the corresponding polyketone in quantitative conversion. © 1996 John Wiley & Sons, Inc.     

Syntheses and radical ring-opening polymerization behavior of vinylcyclopropanone cyclic acetals having exomethylene and phenyl groups

Syntheses and radical ring-opening polymerizations of vinylcyclopropanone derivertives having cyclic six-membered acetal, exomethylene, and phenyl groups; 1-vinyl-6-methylene-4,8-dioxaspiro[2.5&]octane ( 2b ), 1-vinyl-5,7-dimethyl-6-methylene-4,8-dioxaspiro[2.5]octane ( 2c ), 1-vinyl-5-phenyl-4,8-dioxaspiro[2.5]octane ( 2d ), and 1-vinyl-5,7-diphenyl-4,8-dioxaspiro[2.5]octane ( 2e ), were carried out. The monomers were prepared by reactions of 1,1-dichloro-2-vinylcyclopropane and the corresponding diols in DMF in the presence of sodium hydride. Radical polymerizations of 2b – 2e were carried out at 60, 80, and 120°C in the presence of an appropriate initiator (3 mol % vs. monomer) in degassed sealed ampoules for 20 h. Although colorless transparent polymers (M̄_n 2300–13,500) were isolated by preparative HPLC for the most monomers, a crosslinked polymer was obtained in the case of 2b . The structures of the polymers were determined to consist of single and double ring-opening units. The content of the double ring-opened unit was 25–75% by comparison of IR spectra to a model compound. It is suggested that the double ring-opened propagating chain end is stabilized by the substituents on the cyclic acetal rings. The two-center energies of the cyclopropane ring and activation energy of ring-opening calculated by molecular orbital methods may explain the selectivity in the cleavage of the cyclopropane ring, and the degree of double ring-opening. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2501–2512, 1997     

Synthesis of functional polycarbonates by lipase-catalyzed ring-opening polymerization

Poly(5-benzyloxy-trimethylene carbonate) (PBTMC), a new functional polycarbonate was synthesized by enzymatic ring-opening polymerization in bulk at 150°C using Porcine pancreas lipase (PPL) or Candida rugosa lipase (CL) as catalyst. Influences of different polymerization conditions such as the source of enzyme, enzyme concentration and polymerization time on the molecular weight and yield were studied. The results showed that PPL exhibited higher activity than CL. Both higher molecular weight(Mn, 18953) and yield(98%) could be obtained by the use of PPL as catalyst. ¹H NMR spectrum showed no decarboxylation occurrence during the ring-opening polymerization.     

Ring-opening polymerization of six- and seven-membered cyclic pseudoureas

The cationic ring-opening polymerization of six-membered cyclic pseudoureas, 2-(1-pyrrolidinyl)- ( 2a ) and 2-morpholino-5,6-dihydro-4H-1,3-oxazine ( 2b ), was examined, which proceeded in two different ways, depending on the nature of initiator. The polymerization of 2 with methyl p-toluenesulfonate or trifluoromethanesulfonate (MeOTf) produced poly[(N-carbamoylimino)trimethylene], while that with benzyl chloride or bromide or methyl iodide gave a polymer consisting of 1,3-diazin-2-one-1,3-diylalkylene unit (the main component) and (N-carbamoylimino)trimethylene unit. The cationic ring-opening polymerization of seven-membered cyclic pseudourea, 2-(1-pyrrolidinyl)-4,5,6,7-tetrahydro-4H-1,3-oxazepine ( 3 ) was also examined. The polymerization of 3 with MeOTf as initiator gave poly{[N-(1-pyrrolidinycarbonyl)imino]tetra-methylene}. With benzyl chloride, on the other hand, no polymerization of 3 proceeded but, instead, the quantitative isomerization of 3 to 1,1′-carbonyldipyrrolidine took place. The polymerization mechanism of 2 and 3 as well as the isomerization mechanism of 3 were discussed with comparing them to the polymerization mechanism of five-membered pseudoureas. © 1977 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 933–945, 1997     

Soluble tin(II) macroinitiator adducts for the controlled ring‐opening polymerization of lactones and cyclic carbonates

Polyesters and poly(ester carbonates) were synthesized via ring‐opening polymerization with new tin(II) macroinitiator adducts containing oligomeric L ‐lactide (LLA), rac‐lactide (rac‐LA), and ?‐caprolactone (CL). The novel initiating species were synthesized by the reaction of LLA, rac‐LA, or CL with Sn(OEt)₂ (monomer concentration/initiator concentration ≤20) and then were dissolved in methylene chloride or toluene and stored in a stoppered flask for the subsequent ring‐opening polymerization of cyclic esters and carbonates. The soluble tin alkoxide macroinitiators yielded predictable and quantitative initiation of polymerization for up to 1 month of storage time at room temperature. The resulting polymers displayed low polydispersity (≤1.5), and a high monomer conversion (>95%) was obtained within relatively short polymerization times (≤2 h). Adjusting the monomer/macroinitiator ratio effectively controlled the molecular weights of the polymers. NMR was used to characterize the initiating species and polymer microstructure, and size exclusion chromatography was used to determine the molecular weight properties of the polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3434–3442, 2002     

Lipase-catalyzed ring-opening polymerization of molecularly pure cyclic oligomers for use in synthesis and chemical recycling of aliphatic polyesters

The lipase-catalyzed ROP of molecularly pure cyclic oligomers with a definite degree of oligomerization is analyzed with respect to the molecular weights of the resulting polymers and certain kinetic parameters of the enzymatic reaction. Cyclic BA dimers, trimers, and tetramers polymerize faster than the equivalent monomer; however, the latter produces PBA of significantly higher molecular weight. The reason is that the ring opening of the cyclic monomer is slow, leading to a lower initiator concentration than that produced by the cyclic BA dimer and trimer. Similarly, the cyclic BS dimer produces PBS of higher molecular weight than that obtained from the cyclic BS trimer.     

Single-electron and two-electron transfer in the anionic polymerization of vinyl monomers and the ring-opening polymerization of lactones*

Single-electron-transfer (SET) and two-electron-transfer reactions and their mechanisms were examined in the anionic polymerization of vinyl monomers and in the ring-opening polymerization of lactones. SET resulted in the formation of radical anions or enolates at the initiation step of styrene or lactone polymerization with naphthalene sodium as a catalyst. However, alkali-metal supramolecular complexes such as M⁺crown–M⁻ (M = Na or K) were able to transfer two electrons to both these monomers to form carbanions as reactive intermediates. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2158–2165, 2002     

Organocatalysts for the controlled "immortal" ring-opening polymerization of six-membered-ring cyclic carbonates: a metal-free, green process

Six-membered cyclic carbonates, namely trimethylene carbonate (TMC), 3,3-dimethoxytrimethylene carbonate (DMTMC) and 3-benzyloxytrimethylene carbonate (BTMC), undergo controlled "immortal" ring-opening polymerization (iROP) under mild conditions (bulk, 60-150 °C), by using organocatalysts, including an amine [4-N,N-dimethylaminopyridine (DMAP)], a guanidine [1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD)], or a phosphazene [2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP)], in the presence of an alcohol [benzyl alcohol (BnOH), 1,3-propanediol (PPD), glycerol (GLY)] that acts as both a co-initiator and a chain-transfer agent. Remarkably, such organocatalysts remain highly active in the iROP of technical-grade, unpurified TMC. Under optimized conditions, as much as 100,000 equivalents of TMC were fully converted by as little as 10 ppm of BEMP with the simultaneous growth of as many as 200 polymer chains, allowing the preparation of high molar mass poly(trimethylene carbonate)s (up to 45,800 g mol(-1)). These catalyst systems enable among the highest activities (TOF=55,800 h(-1)) and productivities (TON=95,000) ever reported for the ROP of TMC.     

Kinetics and mechanism studies on scandium calix[6]arene complex initiating ring-opening polymerization of 2,2-dimethyltrimethylene carbonate

Scandium p-tert-butylcalix[6]arene complex has been synthesized from scandium isopropoxide and p-tert-butylcalix[6]arene and used as a single component initiator for the first time. The polymerization of 2,2-dimethyltrimethylene carbonate (DTC) using this complex can proceed under mild conditions. Poly (2,2-dimethyltrimethylene carbonate) (PolyDTC) with weight-average molecular weight of 33700 and molecular weight distribution of 1.21 can be prepared. Kinetics study indicates that the polymeri- zation rate is first order with respect to both monomer and initiator concentrations, and the apparent activation energy of the polymerization is 22.7 kJ/mol. 1H NMR spectrum of the polymer reveals that the monomer ring opens via acyl-oxygen bond cleavage leading to an active center of Sc-O.     

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     

Radical polymerization behavior of a vinyl monomer bearing five‐membered cyclic carbonate structure and reactions of the obtained polymers with amines

Radical polymerization behavior of a vinyl substituted cyclic carbonate, 4‐phenyl‐5‐vinyl‐1,3‐dioxoran‐2‐one ( 1 ), is described. Radical polymerization of 1 proceeded through selective vinyl polymerization to produce polymers bearing carbonate groups in the side chain, in contrast to that of an oxirane analogue of 1 , 1‐phenyl‐2‐vinyl oxirane that proceeds via the selective ring‐opening fashion. Although the homopolymerization of 1 produce polymers in relatively lower yield, copolymerizations effectively provided cyclic carbonate‐containing copolymers. Nucleophilic addition of primary amines to the resulting homopolymers and copolymers produced the corresponding multifunctional polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 584–592, 2005     

Controlled polymerization of acrylic acid under 60Co irradiation in the presence of dibenzyl trithiocarbonate

The polymerization of acrylic acid (AA) was performed under ⁶⁰Co irradiation in the presence of dibenzyl trithiocarbonate at room temperature, and well‐defined poly(acrylic acid) (PAA) with a low polydispersity index was successfully prepared. The gel permeation chromatographic and ¹H NMR data showed that this polymerization displays living free‐radical polymerization characteristics: a narrow molecular weight distribution (M_w/M_n = 1.07–1.22), controlled molecular weight, and constant chain‐radical concentration during the polymerization. Using PAA? S? C(?S)? S? PAA as an initiator, the extension reaction of PAA with fresh AA was carried out under ⁶⁰Co irradiation, and the results indicated that this extension polymerization displayed controlled polymerization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3934–3939, 2001     

Controlled radical polymerization of styrene in the presence of cyclic 1,2‐disulfides

The thermal polymerization of styrene (St) in the presence of cyclic 1,2‐disulfides at 120 °C was investigated. In the polymerization of St in the presence of 1,2‐dithiane (DT), that is, six‐member cyclic 1,2‐disulfide, the polymer yields and molecular weights increased with the reaction time. The linear relation between the polymer yields and molecular weights was observed, and the line passed through an original point. The molecular weight distributions of the polymers remained almost constant but were not narrow. For this polymerization with a living nature, we proposed the following mechanism: the propagating St radical reacted with thiyl radicals derived from DT, leading to the formation of dormant species, and the formed C S bond of the dormant was dissociated again to give the propagating polystyryl radical and thiyl radical. Similar results were obtained in the thermal polymerization of St at 120 °C in the presence of 1,2‐dithiacycloheptane, that is, seven‐member cyclic 1,2‐disulfide. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 145–151, 2001     

Polymers of carbonic acid. XIV. High molecular weight poly(trimethylene carbonate) by ring-opening polymerization with butyltin chlorides as initiators

Numerous BuSnCl, Bu₂SnCl, and Bu₃SnCl-initiated polymerizations of cyclo(tri-methylene carbonate) (TMC) were conducted in bulk. In addition to the initiator, reaction time, temperature, and monomer/initiator (M/I) ratio were varied. Yields above 90% were obtained with all three initiators, but their reactivities decrease in the order BuSnCl₃ > Bu₂SnCl₂ > Bu₃SnCl. The maximum molecular weights decrease in the same order. With BuSnCl₃ M_ws up to 250,000 were obtained. These molecular weights were determined by GPC on the basis of the universal calibration method. In this connection Mark-Houwink equations for two solvents, tetrahydrofuran (THF) and CH₂Cl₂ were determined and compared with literature data. Furthermore, mechanistic aspects were studied. ¹H- and ¹³C- NMR spectra revealed that BuSnCl₃ forms complexes with the CO-group of TMC, whereas Bu₂SnCl₃ do not cause NMR spectroscopic effects. Kinetic studies in chloroform and nitrobenzene and a comparison with Bu₃SnOMe suggest that at least BuSnCl₃ initiates a cationic mechanism. However, in contrast to SnCl₄ (or SnBr₄), BuSnCl₃ does not cause decarboxylation. Regardless of the initiator ¹H-NMR spectroscopy revealed CH₂OH and CH₂CI endgroups in all cases. © 1995 John Wiley & Sons, Inc.