Mechanism Of Ring-opening Polymerization Research Articles

Ring-Opening Polymerization of Lactones and Lactides with Sn(IV) and Al(III) Initiators

A theoretical study is presented of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and glycolide with Sn(II) and Al(III) alkoxide initiators (SnMe3MeO, SnMe2(MeO)2, and AlMe2MeO). The B3LYP density functional method has been used to perform the quantum chemical calculations. A coordination−insertion mechanism is presented with two principal reaction steps. First, the alkoxide of the initiator performs a nucleophilic attack on the carbonyl carbon, and the carbonyl bond is broken. An intermediate is formed at this point, where the former carbonyl oxygen of the monomer is coordinated to tin via an alkoxide bond, while the carbonyl carbon assumes a sp3 bonding geometry. The second step involves the acyl−oxygen cleavage of the monomer. For all three initiators it was found that the transition state involving the breaking of the carbonyl double bond (TS1) represented the highest point on the potential energy surface for DXO. For glycolide, however, the transition state of the acyl−oxygen cleavage (TS2) was the least stable structure. The reaction barriers were calculated to 17.1 kcal/mol for DXO/SnMe3MeO, 18.7 kcal/mol for glycolide/SnMe3MeO, 14.3 kcal/mol for DXO/SnMe2(MeO)2, 14.5 kcal/mol for glycolide/SnMe2(MeO)2, 13.6 kcal/mol for DXO/AlMe2MeO, and 9.3 kcal/mol for glycolide/AlMe2MeO. Both electronic and steric properties of the monomer affect the reaction barriers. It was found that the more electrophilic initiators polymerized cyclic esters faster.

Biodegradable Polymers, 9. Technologically Relevant Aspects of Kinetics and Mechanism of Ring-Opening Polymerization of L,L-Dilactide

Poly(L-lactide) is manufactured by a cascade process comprising the fermentation of glucose substrate, oligomerization of L-lactic acid, cyclization depolymerization to L,L-dilactide and ring-opening polymerization of the cyclic diester. The process development requires detailed knowledge of kinetics, thermodynamics and reaction mechanism in all process stages. This paper aims to show the influence of micro- and macrokinetic factors on the course of the ring-opening polymerization and the molecular parameters of the formed polyester. Monomer conversion and molecular weight of the polyester are determined by chemically active process parameters, like kind and concentration of catalyst and initiator, respectively, reaction temperature or presence of cocatalysts as well as by the intensity of mixing of the polymerizing melt. The highest polymerization rate is observed in presence of tin octoate, but this catalyst leads to a fast degradation of the formed polymer.

Mechanism of Ring-Opening Polymerization of 1,5-Dioxepan-2-one and l-Lactide with Stannous 2-Ethylhexanoate. A Theoretical Study

A theoretical study of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and l-lactide (LLA) with stannous(II) 2-ethylhexanoate (Sn(Oct)2) is presented. The B3LYP density functional method has been used for the quantum chemical calculations. Our results support a coordination−insertion mechanism initiated by a tin−alkoxide species formed prior to the ROP. The rate-determining step in the ROP was the nucleophilic attack of the alkoxide on the carbonyl carbon of the monomer. The activation energy for the ROP of DXO with Sn(Oct‘)2 has been determined to be 19.8 kcal/mol and for l-lactide 20.6 kcal/mol. At normal reaction temperatures, a ligand may dissociate as Oct‘H during propagation. An excess of carboxylic acid hinders the coordination of monomer to the initiating/propagating complex.

E-Caprolactone/ZnCl2 complex formation: Characterization and ring-opening polymerization mechanism

e-Caprolactone/ZnCl2 complex formation: Characterization and ring-opening polymerization mechanism

?-Caprolactone/ZnCl2 complex formation: Characterization and ring-opening polymerization mechanism

ε-Caprolactone (ε-CL) has been mixed with ZnCl2 at different mol ratios. The resulting complex was characterized through 1H and 13C NMR spectroscopy in bulk and in solutions, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and optical microscopy. Ring-opening polymerization of ε-caprolactone [M] using ZnCl2 as an initiator [I] at different monomer/initiator ratios has been successfully performed in xylene. The molecular weight of poly(ε-caprolactone) (PCL) as measured by gel permeation chromatografy (GPC) was found to depend linearly on the [M]/[I] ratio. Theoretical calculations were carried out to understand the geometry of the complex and the operating ring-opening mechanism. Both experimental and computational results and the presence of methylene–chloride end group, confirmed by NMR, are in agreement with a coordination–insertion mechanism for the ring-opening polymerization proposed in this article. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1355–1365, 2000

Block and star block copolymers by mechanism transformation. I. Synthesis of PTHF-PSt-PTHF by the transformation of ATRP into CROP

Polystyrene (PSt) with end-terminal bromine (Br-PSt-Br) was synthesized by the atom transfer radical polymerization of styrene with the difunctional initiator 1,2-bis(2′-bromobutyryloxy)ethane in combination with CuBr and bipyridine. The Br-PSt-Br reacted with silver perchlorate at −78 °C, and the resulting macromolecular initiator was used to initiate the polymerization of tetrahydrofuran. Triblock poly(tetrahydrofuran)-polystyrene-poly(tetrahydrofuran) (PTHF-PSt-PTHF) diol was obtained after propagation at −15 °C. The conversion of the polymerization was measured by gas chromatography. The structures of the triblock copolymer PTHF-PSt-PTHF diol were characterized by 1H NMR and gel permeation chromatography. The mechanism of cationic ring-opening polymerization is discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 337–344, 2000

Concerning the Mechanism of Ring-Opening Polymerization by Coordinate Catalysts: The 2D Homonuclear J-Resolved Spectrum of Poly(cyclohexene oxide)

The use of 2D homonuclear J-resolved 1H NMR spectroscopy in the examination of the methine region of poly(cyclohexene oxide) formed by polymerization of cyclohexene oxide employing the Union Carbide calcium−amide−alkoxide catalyst reveals that the majority of the ring opening occurs by backside attack.

On the copolymerization of epichlorohydrin and glycidol

The boron trifluoride-catalyzed cationic copolymerization of epichlorohydrin and glycidol is examined in some detail, with reference to the effect of various reaction variables such as temperature, water content, and stirring rate on the polymerization process and the copolymer product. The reaction temperature does not have a strong effect on the molecular weight of the copolymer, but the water content of the reaction mixture is inversely related to the molecular weight. The stirring rate strongly affects the exotherm associated with the initial stages of the reaction: improved stirring diminishes the exotherm. Based on the relative rates of monomer consumption and other observations, a reaction mechanism is proposed for the formation of the copolymer, in which glycidol polymerizes via what is known as the activated monomer (AM) mechanism rather than by the standard cationic ring-opening polymerization mechanism. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1897–1904, 1997

Stereochemistry of ring-opening reactions of epoxide with aluminum and zinc porphyrins. Relation to the mechanism of ring-opening polymerization

It is shown that the ring-opening reactions of 2,3-epoxybutanes with aluminum 5,10,15,20-tetraphenylporphine and zinc 5,40,15,20-tetraphenyl-21-methylporphine in th presence of protic compounds such as 1-propanethiol and methanol both proceed with inversion of the configuration at the carbon atom of the epoxide ring where cleaved

The mechanism of stereoselective ring-opening metathesis polymerization of norbornene and several derivatives

The properties of several noble metal halide catalysts for ring-opening metathesis polymerization of norbornene, endo-dicyclopentadiene and norbomadiene have been investigated as a function of prior or in situ treatment by the latter pair of diolefins, which may also be monomers as stated. Microstructures of the various polymers and sometimes copolymers were examined in detail using 13C NMR, 1H NMR and IR spectroscopic techniques. In the case of Ru and Os chlorides, there is a dramatic swing from high- trans to high- cis polymer in all cases where chelating diolefin is present, whereas IrCl 3 is unaffected in this respect. High- cis polymers of norbornene, made using RhCl 3 and endo-dicyclopentadiene-modified RuCl 3, show a strong tendency for the small number of trans units that are present to occur in triplets and larger blocks, an unusual blockiness feature previously noted only when the OsCl 3 catalyst was used. The usual tendency for high- cis-poly(norbornene) made using numerous Mo, W and Re based catalysts is to have the trans units in pairs. In all cases, therefore, there is a virtual absence of ctc triads, in contradiction to expectation for random high- cis polymers. This general feature is discussed in terms of a new mechanism based on two or more kinetically distinct metallacarbenes and various conformational forms of metallacyclobutanes undergoing disrotatory [2 + 2] cycloreversion reactions.

Preparation and reactions of tantalum alkylidene complexes containing bulky phenoxide or thiolate ligands. Controlling ring-opening metathesis polymerization activity and mechanism through choice of anionic ligand

Addition of LiDIPP = O-2,6-C{sub 6}H{sub 3}-i-Pr{sub 2} to Ta(CH-t-Bu)(THF){sub 2}Cl{sub 3} yields Ta(CH-t-Bu)(DIPP){sub 3}(THF) (1) in high yield. Ta(CH-t-Bu)(DMP){sub 3}(THF) (3; DMP = O-2,6-C{sub 6}H{sub 3}Me{sub 2}) and Ta(CH-t-Bu)(TIPT){sub 3}(THF) (5; TIPT = S-,2,4,6-C{sub 6}H{sub 2}i-Pr{sub 3}) can be prepared by analogous methods. 1 reacts rapidly with 1 equiv of styrene to give the tantalacyclobutane complex Ta(CH(Ph)CH(t-Bu)CH{sub 2})(DIPP){sub 3}. The crystal and molecular structure of the complex are reported. An analogous reaction between 1 and vinyltrimethylsilane gives Ta(CHSiMe{sub 3})(DIPP){sub 3}(THF) or Ta(CH(SiMe{sub 3})CH(SiMe{sub 3})CH{sub 2})(DIPP){sub 3} depending upon reaction conditions; the two are in ready equilibrium. 1 reacts smoothly with ethylene to give Ta(CH{sub 2}CH{sub 2}CH{sub 2})(DIPP){sub 3} in high yield, but treatment of 1 with olefins such as propylene or 1-butene did not lead to any characterizable species. Addition of excess cis-2-pentene to 1 results in rapid metathesis (100 equiv to equilibrium in < 15 min), but activity is short-lived. In contrast to reactions between 1 and olefins, Ta(CH-t-Bu)(TIPT){sub 3}(THF) does not react with ordinary olefins and will not metathesize them. Tantalacyclobutane complexes containing the DIPP ligand react with the carbonyl functionality to give a mixture of insertion chemistry (oxytantalacyclohexane complexes) and Wittig-like reactivity, depending upon the carbonylmore » compound, the tantalacycle, and the temperature. 1 reacts with norbornene to give an isolable tantalacyclobutane complex, Ta(CH(C{sub 5}H{sub 8})CHCH(t-Bu))(DIPP){sub 3}, whose crystal structure is reported. 25 references, 9 figures, 7 tables.« less

Kinetics and mechanism of the boron trichloride-catalyzed thermal ring-opening polymerization of hexachlorocyclotriphosphazene in 1,2,4-trichlorobenzene solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics and mechanism of the boron trichloride-catalyzed thermal ring-opening polymerization of hexachlorocyclotriphosphazene in 1,2,4-trichlorobenzene solutionMichael S. Sennett, Gary L. Hagnauer, Robert E. Singler, and Geoffrey DaviesCite this: Macromolecules 1986, 19, 4, 959–964Publication Date (Print):April 1, 1986Publication History Published online1 May 2002Published inissue 1 April 1986https://doi.org/10.1021/ma00158a003RIGHTS & PERMISSIONSArticle Views327Altmetric-Citations31LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (706 KB) Get e-Alerts Get e-Alerts

Mechanism of ring-opening polymerization of cyclic olefins. Formation of active centres in decomposition of transition metal complexes and their role in catalysis

Specific peculiarities of the metallacarbenes involved as chain carriers in olefin metathesis and ring-opening polymerization of cycloalkenes are discussed. Reaction of many main group metal alkyls with transition metal chlorides have been extensively investigated and pathways to the formation of metallacarbene intermediates deduced from the composition and nature of the reaction products.

Mechanism of ring-opening polymerization of cycloalkenes initiated by metathesis catalysts

(+)—exo—5—methylbicyclo[2.2.l—hept—2—ene has been prepared and polymerized by ring—opening using a variety of metathesis catalysts. ReCl5 gives an all—cis polymer which is fully syndiotactic, as revealed

On the mechanism of ring-opening polymerization of cyclo-olefins

From experimental data, a conclusion is drawn on chain character of cyclo-olefin ring-opening polymerization. It was suggested that the active centres of this process are carbene complexes of transition metals (W, Mo, Re). The confirmation of this view comes from studies on the initiation of ring-opening polymerization by complexes of tungsten chlorides with phenylcarbene. The latter is formed in the coordination sphere of tungsten by decomposition of phenyl diazomethane.

Radical Isomerization Polymerization of 1,1-Dicyclopropylethylene

Abstract The polymerization of 1,1-dicyclopropylethylene with radical (ABIN) and cationic (A1EtCl2) initiators has been investigated. The structure of the polymers was elucidated by IR and NMR spectroscopy. These studies indicated that the major repeat unit of the polymer obtained by radical initiator is suggesting a ring-opening isomerization polymerization mechanism, whereas that produced with cationic initiator is the unrearranged unit.