End-group Analysis Research Articles

Mechanistic studies on cationic ring-opening polymerisation of cyclodextrin derivatives using various Lewis acids

In order to investigate the potential of cyclodextrins for the preparation of block-like substituted polysaccharides, we submitted mixtures of heptakis[2,3,6-tri-O-methyl]-β-cyclodextrin (Me21-β-CD, 1) and heptakis[2,3,6-tri-O-methyl-d 3]-β-cyclodextrin ((Me-d 3)21-β-CD, 2) to cationic ring-opening polymerisation (CROP). Reactions were performed with BF3·OEt2, methyl triflate (MeOTf), and Et3OSbCl6. Products were compared with respect to their degree of polymerisation (DP) and the average block length (BL). Highest DP was observed with BF3·OEt2, while Et3OSbCl6 was the most active initiator. Average block length decreased from 14 in the early stage of product formation to about 2 due to competing chain transfer reaction. 1H NMR spectroscopy, GLC, GLC–MS, ESI-MS and MALDI-TOF-MS were applied for detailed investigations of side reactions. During incubation with BF3·OEt2, a stereroisomeric β-CD with one β-glucosidic linkage (Me21-β-CD6α1β, 3a (Me-d 3)21-β-CD6α 1β, 3b) is formed as an intermediate, while linear Me21- and (Me-d 3)21-maltoheptaose (4a/b) was detected in the early stage of the reaction promoted by MeOTf. In the case of Et3OSbCl6, both intermediates (3a/b, 4a/b) can be observed during the lag phase of polymerisation, but to a very low degree. End group analysis by GLC reveals that some alkyl exchange occurs at position 3 and 6 in the presence of Et3OSbCl6, and that polymerisation is also initiated by protons. Copolymerisation of heptakis[2,3,6-tri-O-benzyl]-β-cyclodextrin (Bn21-β-CD, 5) and Me21-β-CD (1) and subsequent debenzylation yielded a polymer of only 1,4-glcp-Me3- and 1,4-glcp-residues. Reactivity of Bn21-β-CD was significantly lower than of Me21-β-CD, resulting in higher average block length of 1,4-glcp-Me3-units.

Ring-Opening Polymerization of ε-Caprolactone Initiated with Titanium n-Propoxide or Titanium Phenoxide

Ring-opening polymerization of ε-caprolactone initiated by titanium n-propoxide Ti(O-n-Pr)4 was compared to the one initiated by titanium phenoxide or Ti(OPh)4. Polymerization was confirmed to proceed via a coordination−insertion mechanism for both initiators after end groups analysis by 1H and 13C NMR (nuclear magnetic resonance) spectroscopy. Bulk polymerization at 100 °C and with a M0/I0 (monomer/initiator ratio) equal to 300 was studied and compared with both initiators. The polymerization with Ti(OPh)4 exhibits a slower kinetic of reaction and the polymer synthesized an higher number-average molecular weight and higher polydispersity than with Ti(OPr)4. These results are consistent with evolution of the average number of active aryloxide groups per initiator ( ) during polymerization for this initiator. Indeed, determined by 1H NMR increases gradually during the polymerization to 2 for around 70% conversion and then decreases at the end of the polymerization and even over the time required for total conversion. This decrease of at the end of the conversion may be explained by important transesterification reactions with phenoxyl end groups of the polymer, which lead to the formation of larger poly(ε-caprolactone) chains. That is consistent with the increase in the number-average molecular weight of the polymer beyond the end of the conversion. The rheological study also confirms this result.

Preparation of electrorheological active ionomers from poly(2‐hydroxyethyl methacrylate)‐co‐poly(4‐vinyl pyridine)

AbstractIn this study, synthesis, characterization, partial hydrolysis, and salt formation of poly(2‐hydroxyethyl methacrylate)‐co‐poly(4‐vinyl pyridine), (poly(HEMA)‐co‐poly‐(4‐VP)) copolymers were investigated. The copolymers were synthesized by free radical polymerization using K2S2O8 as an initiator. By varying the monomer/initiator ratio, chain lengths of the copolymers were changed. The copolymers were characterized by gel permeation chromatography (GPC), viscosity measurements, 1H and 13C NMR and FTIR spectroscopies, elemental analysis, and end group analysis methods. The copolymers were partially hydrolyzed by p‐toluene sulfonic acid monohydrate (PTSA·H2O) and washed with LiOH(aq) solution to prepare electrorheological (ER) active ionomers, poly(Li‐HEMA)‐co‐poly(4‐VP). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3540–3548, 2006

Ring opening polymerization initiated by methylaluminoxane/AlMe 3 complexes

The ROP of cyclic ethers, carbonates and esters in the presence of commercially available methylaluminoxane/trimethylaluminum system has been studied. MALDI-ToF end groups analysis indicates that in a majority of systems considered, the polymerization process is initiated by insertion of a monomer into the Al–O–Al bond, generating alkoxide species, which are active sites in coordination polymerization. The polymerization of six-membered carbonates proceeds selectively, forming linear polydiols with high yields at moderate temperatures. The polymerization of oxiranes and lactones is, however, accompanied by back-biting reactions leading to cyclic oligomers. The interaction of oxirane with aluminoxane electrophilic sites causes also the formation of cationic species, which initiate the polymerization of THF. The cationic species formed in those systems were trapped by triphenylphosphine and identified by 31P NMR spectra.

Structural Characterization of a Sol−Gel-Prepared Anhydrous Proton-Conducting Electrolyte

We have prepared a hybrid inorganic/organic, anhydrous proton-conducting polymer electrolyte (MePEG3SiO3)n. Structural characterization of this MePEG3 polymer through 29Si NMR spectroscopy and gel-permeation chromatography indicates that our MePEG3 polymer is composed of several different structures giving a distribution of molecular weights and silicon resonances. In this article, we show that the sol−gel-prepared MePEG3 polymer is primarily composed of incompletely condensed T8 silsesquioxane clusters. These incompletely condensed T8 clusters are seen in the 29Si NMR spectra at chemical shifts between −62 and −70 ppm. The minority composition of the MePEG3 polymer contains a small amount of completely condensed T6 silsesquioxane clusters, observed at −55.5 ppm, and T2 dimers from −48 to −50 ppm. End-group analysis shows the presence of 0.67 uncondensed Si−OH groups per silicon atom in the MePEG3 polymer, supporting the presence of incompletely condensed or ladder-type structures. The completely condense...

Intramolecularly Dinuclear Magnesium Complex Catalyzed Copolymerization of Cyclohexene Oxide with CO2 under Ambient CO2 Pressure: Kinetics and Mechanism

The intramolecularly dinuclear magnesium complexes generated in situ from the reaction of multidentate semi-azacrown ether ligands with n-Bu2Mg followed by treatment with alcohol additive were found to be efficient catalysts for the copolymerization of CO2 and cyclohexene oxide (CHO), affording the completely alternating poly(cyclohexene carbonate) (PCHC) under extremely mild conditions (1 atm pressure of CO2, temperatures ranging from 20 to 60 °C). Ligand substituent effects were observed to dramatically influence both the activity and the chemoselectivity of the catalysis, exemplifying the fine-tunability of this type of ligands. With regard to the mechanistic studies, end-group analysis of the copolymer by MALDI-TOF mass spectroscopy revealed the predominance of the butoxy-initiated CO2/CHO copolymerization process. The butoxy-containing catalytically active species in the present system was proposed to possess a dinuclear structure similar to an isolated model Mg complex which was characterized by X-r...

Ring‐Opening and polymerization of 1‐[2′‐(heptaphenylcyclotetrasiloxanyl)ethyl]‐1,3,3,5,5‐pentamethylcyclotrisiloxane

Abstract1‐[2′‐(Heptaphenylcyclotetrasiloxanyl)ethyl]‐1,3,3,5,5‐pentamethylcyclotetrasiloxane (II) was prepared from 1‐[2′‐(methyldichlorosilyl)ethyl]‐1,3,3,5,5,7,7‐heptaphenylcyclotetrasiloxane (I) and tetramethyldisiloxane‐1,3‐diol. Acid‐catalyzed ring‐opening of II in the presence of tetramethyldisiloxane gave 1,9‐dihydrido‐5‐[2′‐(heptaphenylcyclotetrasiloxanyl)ethyl]nonamethylpentasiloxane (III) and 1,9‐dihydrido‐3‐[2′‐(heptaphenylcyclotetrasiloxanyl)ethyl]nonamethylpentasiloxane (IV). Both acid‐ and base‐catalyzed ring‐opening polymerization of II gives highly viscous, transparent polymers. The structures of I–IV and polymers were determined by UV, IR, 1H, 13C, and 29Si NMR spectroscopy. In addition, molecular weights obtained by GPC and NMR end group analysis were confirmed with mass spectrometry. On the basis of 29Si NMR spectroscopy, the polymers appear to result exclusively from ring‐opening of the cyclotrisiloxane ring. No evidence for ring‐opening of the cyclotetrasiloxane ring was observed. Polymer properties were determined by DSC and TGA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 137–146, 2006

Lanthanide Thiolate Complexes: Novel Initiators for Ring‐opening Polymerization of ε‐Caprolactone

AbstractThe ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) using lanthanide thiolate complexes [(CH3C5H4)2Sm(μ‐SPh)(THF)] 2 (1) and Sm(SPh)3(HMPA)3 (2) as initiators has been investigated for the first time. Both of 1 and 2 were found to be highly efficient initiators for the ROP of ε‐CL. The poly(ε‐caprolactone) (PCL) with molecular weight Mn up to 1.97×105 and relatively narrow molecular weight distributions (1.20< Mw/Mn<2.00) have been obtained in high yield in the temperature range of 35–65 °C. According to the polymer yield, 2 showed much higher activity than 1. However, the number‐average molecular weight of PCL obtained with 2 was much lower than with 1. The possible polymerization mechanism of the ε‐CL polymerization has been proposed based on the results of the end group analysis of the ε‐CL oligomer.

Temperature effect on ethylene polymerization with a catalyst prepared by mixing Mg(C2H5)(n-C4H9), Al(C2H5)1.5Cl1.5 and iron(II)bis (imino)pyridyl complex

Ethylene polymerization was conducted with a catalyst prepared by mixing 2,6-bis{1-[2,6-(diisopropylphenyl)imino]ethyl}pyridine iron dichloride, Mg(C2H5)(n-C4H9) and Al(C2H5)1.5Cl1.5 in the presence of common alkylaluminium as cocatalyst. Both the activity and the molecular weight of polymers produced were markedly dependent upon the polymerization temperature. The end-group analysis of polymers showed that the molecular weight of polymers produced at higher temperature was reduced by chain transfer with Al(C2H5)3 in addition to β-hydrogen elimination.

Tetramethylammonium Hydroxide (TMAH) Thermochemolysis of Lignin: Behavior of 4-O-Etherified Cinnamyl Alcohols and Aldehydes

The thermochemolytic behavior of 4-O-etherified cinnamyl alcohols and aldehydes in lignin was investigated in the presence of tetramethylammonium hydroxide (TMAH) (315 degrees C/4 s), using veratrylglycol-beta-(coniferyl alcohol) ether (1a), veratrylglycol-beta-(sinapyl alcohol) ether (1b), and veratrylglycol-beta-(coniferyl aldehyde) ether (2). The methylated products were monitored with gas chromatography-mass spectrometry. Dimers 1a and 1b provided the coniferyl and sinapyl alcohol dimethyl ethers consisting of three isomers, respectively. Coniferyl alcohol dimethyl ether isomers were also observed in the TMAH thermochemolysis pyrolysates of a bulk dehydrogenation polymer of coniferyl alcohol and a Japanese cedar (Cryptomeria japonica) wood. Coniferyl aldehyde methyl ether was not provided from TMAH thermochemolyses of coniferyl aldehyde, 2, a dehydrogenation polymer of coniferyl aldehyde, and the cedar wood. The former three provided veratryl aldehyde in a large abundance, instead of coniferyl aldehyde methyl ether. Sinapyl aldehyde provided 3,4,5-trimethoxybenzaldehyde in a large abundance and sinapyl aldehyde methyl ether in a trace abundance. The results showed that TMAH thermochemolysis is an effective tool to obtain information on cinnamyl alcohol end groups, but is not applicable to analysis of cinnamyl aldehyde end groups.

Electrorheological properties of poly(Li-2-hydroxyethyl methacrylate) suspensions

In this study, poly(2-hydroxyethly methacrylate), poly(hema), was synthesized by free radical polymerization using K 2S 2O 8 as an initiator. The polymer was characterized by FTIR, 1H NMR and elemental analysis measurements. The molecular mass of poly(hema) was determined by osmometry, viscometry and end group analysis techniques approximately as 6 × 10 3 g/mol. Poly(hema) was partially hydrolyzed and converted to a lithium salt, poly(Li-hema) before the electrorheological (ER) measurements carried out. A series of particle size of poly(Li-hema) polymeric salt were prepared and average particle diameters were determined by dynamic light scattering (DLS) as 8, 13, 19 and 25 μm. Suspensions of poly(Li-hema) polymeric salts were prepared in four insulating oils namely silicone oil (SO), mineral oil (MO), dioctylphthalete (DOP) and trioctyltrimellitate (TOTM). ER properties of poly(Li-hema)/silicone oil suspensions were studied as a function of electric field strength, particle size, dispersed phase concentration, shear rate, shear stress, temperature, frequency and promoter. For these ER suspensions, yield stresses and excess shear stresses were determined. Further dielectric properties of poly(Li-hema) ionomer were also investigated.

Synthesis and characterization of a series of star-branched poly(ε-caprolactone)s with the variation in arm numbers and lengths

A series of star-branched poly(ε-caprolactone)s (SPCLs) was synthesized with structural variation of the arm numbers and lengths through ring-opening polymerization under bulk condition. Arm numbers were varied to be 3, 4, and 6 by using multifunctional initiating cores such as trimethylol propane, pentaerythritol, and dipentaerythritol, respectively. The lengths of the poly(ε-caprolactone) arms were varied by controlling the molar ratio of monomer-to-initiating hydroxyl group molar ratio ([CL] 0/[–OH] 0=5, 10, 15). Molecular weights were determined by both 1H NMR end-group analysis and MALDI-TOF mass spectrometry, which gave reasonably consistent values. On the contrary, the GPC method failed to give accurate values of molecular weight of SPCLs due to the discrepancy with the linear standard. The branching architecture of SPCLs was evaluated by the branching ratio, g, which is the ratio of the mean-square radius of SPCL to that of liner counterpart, linear poly(ε-caprolactone) (LPCL), which is of the same chemistry and having the same molecular weight. The radii of gyration of SPCLs and LPCLs were determined using small-angle X-ray scattering (SAXS) from the initial slopes of Zimm plots, represented as 1/ I( q) vs q 2 with I( q) and q being the scattered intensity and scattering vector, respectively. The g values were observed to decrease with increasing arm numbers, indicating more compact molecular structure for SPCLs with higher arm numbers, while no such effect was observed for arm length variation. Thermal properties as well as the degree of crystallinity of SPCLs were found to be also dependent on structural variations. The melting points and the degradation temperatures were observed to increase with increasing arm lengths but with constant arm number. On the other hand, arm number variation with constant arm length gave no such changes to the thermal transitions of SPCLs. However, for the SPCLs with equivalent molecular weights, the degree of crystallinity was found to decrease with increasing arm numbers.

Isolation and Structure Determination of Complexed Poly(3‐hydroxyalkanoate) from Beet (Beta vulgaris L.)

Complexed poly(3-hydroxyalkanoate)s (cPHAs), one of two types of natural PHAs, occur in both prokaryotes and eukaryotes as a complex with biomacromolecules and could be involved in various physiological functions. In this study, a cPHA-component derived from a complex with calcium polyphosphate was isolated from sugar beet (Beta vulgaris L.) and determined to be a homopolymer composed of 3-hydroxybutyrate. MALDI MS provided the number-average molecular weight (Mn = 9,124 Da) and polydispersity index (PDI = 1.01), showing that beet cPHA has a slightly lower molecular mass than the known Escherichia coli cPHA. In addition, the structural analysis of both end groups showed that (i) 100 mol-% of the carboxyl end is free, while about 30 mol-% of the hydroxyl end is free and about 70 mol-% masked and (ii) the end hydroxyl group is masked by at least six identified short-chain alkanoic and alkanedioic acids. Based on such end-group characteristics, the polymerization mechanism of beet cPHA is discussed.

Thermal and mechanical behaviour of flexible poly(vinyl chloride) mixed with some saturated polyesters

Four saturated polyesters poly(hexamethylene adipate), poly(ethylene adipate), poly(hexamethylene terephthalate) and poly(ethylene terephthalate) were prepared. The resulting materials were characterized by IR and 1H NMR, end group analysis and gel permeation chromatography. The effect of blending these polyesters (5 and 10%) with poly(vinyl chloride) (PVC) in the melt was investigated in terms of changes in the thermal behaviour of PVC by studying the weight loss after 50 min at 180 °C, colour changes of the blend before and after aging for one week at 90 °C, the variation in glass transition temperature and the initial decomposition temperature. The results gave proof for the stabilizing role played by the investigated polyesters against the thermal degradation of PVC. The best results are obtained when PVC is mixed with 5% aliphatic polyesters rather than with aromatic ones. This is well illustrated not only from the increase in the initial decomposition temperature (IDT), but also from the decrease of % weight loss and from the lower extent of discolouration of PVC, which is a demand for the application of the polymer. It was also found that blending PVC with 5% of the four investigated polyesters before and after aging for one week at 90 °C gave better mechanical properties even than that of the unaged PVC blank.

Effect of Inhibitors on Atom Transfer Radical Polymerization of MMA

AbstractEffect of a series of inhibitors as additives on atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with FeCl2/PPh3 as catalyst system was studied, including 2,4,6‐trinitrophenol (TNP), 4‐methoxyphenol (4‐MP), hydroquinone (HQ) and nitrobenzene (NB). It was found that TNP was the only efficient additive for ATRP among these inhibitors. In the presence of small amounts of TNP, the polymerization proceeded rapidly after induction period to yield the polymers with controlled molecular weights and narrow molecular weight distributions (MWD). The initiating efficiency of the modified catalyst system with TNP was increased. The mechanism was proposed and confirmed by the end group analysis of the polymer.

Synthesis and comparative biodegradability studies of three poly(alkylene succinate)s

Poly(alkylene succinates) were synthesized from succinic acid and aliphatic diols with 2 to 4 methylene groups by melt polycondensation. DSC, 1H NMR, WAXD and molecular weight measurements were used to characterise the polymers. Biodegradability studies of polyesters with the same average molecular weight, included enzymatic hydrolysis for several days using Rhizopus delemar lipase at pH 7.2 and 30 °C. DSC traces of biodegraded polyesters revealed that hydrolysis affected mainly the amorphous material. For all polyesters an increase in glass transition, melting point and heat of fusion was recorded. In the first days of enzymatic hydrolysis, fast rates of mass loss were observed accompanied by a rapid reduction of intrinsic viscosity and molecular weight, thus indicating a mixed endo- and exo-type hydrolysis mechanism. Afterwards, it turned to an exo-type mechanism, taking place in the crystalline phase, since after 15–25 days of enzymatic hydrolysis molecular weight was stabilized, while mass loss kept on decreasing though in a slower rate. End-group analysis revealed that carboxyl and hydroxyl groups increased due to ester bonds' scission. The biodegradation rates of the polymers decreased following the order PPSu > PESu ≥ PBSu and it was attributed to the lower crystallinity of PPSu compared to other polyesters, rather than to differences in chemical structure. Finally, a simple theoretical kinetic model was developed and Michaelis–Menten parameters were estimated.

Quinone Transfer Radical Polymerization of Styrene Catalyzed by Metal Complexes in the Presence of Various o-Quinones

Several o-quinones have been tested as control agents for the quinone transfer radical polymerization (QTRP) of styrene in the presence of cobalt(II) acetylacetonate. In contrast to the commercially available 3,5-di-tert-butyl-o-benzoquinone (3,5-DtBBQ) and tetrachloro-1,2-benzoquinone (tetrachloro-1,2-BQ), 3,6-dimethoxy-9,10-phenanthrenequinone (3,6-DMPhQ) imparts a better control to the radical polymerization of styrene compared to 9,10-phenanthrenequinone (PhQ) used as a reference. Indeed, whenever 3,6-DMPhQ is added with a catalytic amount of metal complexes (Co(acac)2 or Al(acac)3), the evolution of the molar mass with the monomer conversion is linear, and low polydispersity (Mw/Mn ∼ 1.1−1.2) is observed until very high monomer conversion (∼90%). Finally, the methoxy protons of 3,6-DMPhQ have been detected by 1H NMR analysis of the polystyrene end groups, which is important mechanistic information.

New Bis(allyl)(diketiminato) and Tris(allyl) Lanthanide Complexes and Their Reactivity in the Polymerization of Polar Monomers

The reaction of LnCl3(THF)n (Ln = La, n = 4; Ln = Y, Sm, Nd, n = 3) with 3 equiv of allylMgCl in THF/1,4-dioxane followed by crystallization in 1,4-dioxane/toluene proceeds in very high yields to give the tris(?3-allyl) complexes [La(?3-C3H5)3(?1-dioxane)]2(µ-dioxane) and [Ln(?3-C3H5)3(µ-dioxane)]8 (Ln = Y, 1 ; Sm, 2 ; Nd). Improved one-pot syntheses for the tris(?3-allyl) lanthanum and neodymium compounds are reported. The crystal structures of 1 and 2 show that the compounds consist of distorted square-pyramidal lanthanide centers in linear polymer chains. The reaction of [La(?3-C3H5)3(?1-dioxane)]2(µ-dioxane) and [Ln(?3-C3H5)3(µ-dioxane)]8 with the diketimine ligand 2-(2,6-diisopropylphenyl)amino-4-(2,6-diisopropylphenyl)imino-2-pentene (BDI-H) in THF at 60 °C generates cleanly the s-diketiminato complexes Ln(?3-C3H5)2{?2-HC(MeCNAr)2} (Ar = 2,6-C6H3iPr2; Ln = La, 3 ; Y, 4 ; Sm, 5 ; Nd, 6 ) with propene elimination. The crystal structure of 5 shows a distorted tetrahedral SmN2(allyl)2 core, with the samarium atom positioned 1.438(4) A out of the C3N2 ligand plane. All complexes are highly effective single-component catalysts for the ring-opening polymerization of e-caprolactone and rac-lactide. Polymer end group analysis shows that the polymerization process is initiated by allyl transfer to monomer.

Synthesis and Properties of Novel Poly(Hexyl-Substituted Lactides) for Pharmaceutical Applications

Monohexyl-substituted lactide (mHLA) was synthesized by reaction of 2-hydroxyoctanoic acid with 2-bromopropionyl bromide, and polymerized with tin(II) 2-ethylhexanoate (Sn(Oct)2) or 4-dimethylaminopyridine (DMAP) in the presence of benzyl alcohol by ring-opening polymerization (ROP). Poly(monohexyl-substituted lactide) (PmHLA) of predictable molecular weights and narrow polydispersities were obtained in convenient bulk conditions at 100 °C within short polymerization times. The polymerizations were well controlled, showing a 'living' character for targeted degrees of polymerization up to DP = 60 as evidenced by molecular weight versus conversion studies and 1H NMR end group analysis. The hexyl groups have a strong impact on the glass transition temperature (Tg), which is low for PmHLA compared to standard poly(D,L-lactide) (PLA). Tg and zero shear viscosities at 25 °C can be controlled by the polymer molecular weight, ranging from ?22 °C for Mn = 2800 g/mol to ?10 °C for Mn = 9100 g/mol and 140 to 4850 Pa.s, respectively. These data are in correspondence with the Fox and Flory equations. The degradation mechanism of the PmHLA polymer in phosphate buffer pH 7.4 at 37 °C was shown to be similar to that of the standard PLA ('bulk erosion' type), with a slightly higher degradation rate, leading to the non-toxic degradation products lactic acid and 2-hydroxyoctanoic acid. PmHLA has the great potential as an alternative to conventional PLA/PLGA for drug delivery systems. By the hexyl-substitution the biodegradable PLA-ester backbone is conserved but the hydrophobicity is increased in comparison to standard PLA, while a viscous polymer is obtained. This leads to advantageous injectable solvent-free drug delivery systems, in which drugs can easily be incorporated by simple mixing.

Copolymerization of Cyclohexene Oxide with CO2 by Using Intramolecular Dinuclear Zinc Catalysts

The intramolecular dinuclear zinc complexes generated in situ from the reaction of multidentate semi-azacrown ether ligands with Et(2)Zn, followed by treatment with an alcohol additive, were found to promote the copolymerization of CO(2) and cyclohexene oxide (CHO) with completely alternating polycarbonate selectivity and high efficiency. With this type of novel initiator, the copolymerization could be accomplished under mild conditions at 1 atm pressure of CO(2), which represents a significant advantage over most catalytic systems developed for this reaction so far. The copolymerization reaction was demonstrated to be a living process as a result of the narrow polydispersities and the linear increase in the molecular weight with conversion of CHO. In addition, the solid-state structure of the dinuclear zinc complex was characterized by X-ray crystal structural analysis and can be considered as a model of the active catalyst. On the basis of the various efforts made to understand the mechanisms of the catalytic reaction, including MALDI-TOF mass analysis of the copolymers' end-groups, the effect of alcohol additives on the catalysis and CO(2) pressure on the conversion of CHO, as well as the kinetic data gained from in situ IR spectroscopy, a plausible catalytic cycle for the present reaction system is outlined. The copolymerization is initiated by the insertion of CO(2) into the Zn--OEt bond to afford a carbonate-ester-bridged complex. The dinuclear zinc structure of the catalyst remains intact throughout the copolymerization. The bridged zinc centers may have a synergistic effect on the copolymerization reaction; one zinc center could activate the epoxide through its coordination and the second zinc atom may be responsible for carbonate propagation by nucleophilic attack by the carbonate ester on the back side of the cis-epoxide ring to afford the carbonate. The mechanistic implication of this is particularly important for future research into the design of efficient and practical catalysts for the copolymerization of epoxides with CO(2.).