Mechanism Of Ring-opening Polymerization Research Articles

Synthesis and characterization of polyacrylate modified by polysiloxane latexes and films

Abstract In this paper, a new method was designed to prepare polyacrylate modified by polysiloxane latex particles, with methyl methacrylate (MMA) and butyl acrylate (BA) as main monomers, vinyltriethoxysilane (A-151) as functional monomer and octamethylcyclotetrasiloxane (D4) as grafting agent. The chemical structure and morphology of the latexes were characterized by FTIR, TEM, and particle size analyzer. The properties of the films were tested in terms of static contact angle, water absorption and TGA. The results showed that uniform spherical structure and narrow particle size distribution could be obtained in the latexes. Furthermore, the hydrophobicity, low surface free energy and thermal stability were also noticeably increased with the content of polysiloxane. The mechanism of ring opening polymerization between D4 and A-151 was also discussed; it turned out that it was quite important to control the pH under faintly acid conditions.

Theoretical study on the mechanism and kinetics of ring-opening polymerization of cyclic esters initiated by tin(II) n-butoxide

The coordination–insertion mechanisms of ring-opening polymerizations (ROP) of γ-valerolactone (GVL), δ-valerolactone (DVL) and l-lactide (LL) initiated by tin(II) n-butoxide were investigated using hybrid density functional theory at the B3LYP level with a mixed basis set. Analysis of geometries and corresponding energies revealed six intermediate states (including two transition states) observed in all three ROP reactions, which confirmed a coordination–insertion mechanism. Calculated energy profiles demonstrated exothermicity for each ROP reaction with a rate-determining step found for the first transition state that involved the attraction of an oxygen atom of the monomer to the metal atom of the initiator. By using the resulting energy barriers and transition state theory, the thermal rate constants could be obtained with the predicted rates of GVL and LL found to be equal and faster than that of DVL. In addition, by comparisons of the ring-strain energies and the barrier heights, we found that the effect of ring strain was at most only a partial driving force for the ROP reactions.

Synthesis and characterization of crystalline graft polymer poly(ethylene oxide)-g-poly(ɛ-caprolactone)2with modulated grafting sites

The graft polymer poly(ethylene oxide)-g-poly(ɛ-caprolactone)2 (PEO-g-PCL2) with modulated grafting sites was synthesized by the combination of ring-opening polymerization (ROP) mechanism, efficient Williamson reaction, with thiol–ene addition reaction. First, the precursor of PEO-Allyl-PEO with two terminal hydroxyl groups and one middle allyl group was prepared by ROP of EO monomers. Then, the macroinitiator [PEO-(OH)2-PEO]s was synthesized by sequential Williamson reaction between terminal hydroxyl groups and thiol–ene addition reaction on pendant allyl groups. Finally, the graft polymer PEO-g-PCL2 was obtained by ROP of ɛ-CL monomers using [PEO-(OH)2-PEO]s as macroinitiator. The target graft polymer and all intermediates were well characterized by the measurements of gel permeation chromatography, 1H NMR, and thermal gravimetric analysis. The crystallization behavior was investigated by the measurements of differential scanning calorimetry, wide-angle X-ray diffraction and polarized optical microscope. The results showed that when the PCL content of side chains reached 59.2%, the crystalline structure had been dominated by PCL part and the crystalline structure formed by PEO part can be almost neglected. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2239–2247

An Overview of the Synthesis and Synthetic Mechanism of Poly (Lactic acid)

Poly(lactic acid) is the biodegradable aliphatic polyester produced in small quantity and in large quantities industrially and used very variously. Because of its good mechanical property and reconcilability with environment, it is one of the polymers most appropriate to replace non-biodegradable synthetic polymers based on crude oil. PLA can be made from lactic acid with different polymerizations such as polycondensation, ring-opening polymerization, and direct polymerizations by azeotropic dehydration or the enzymatic polymerization. The direct polymerization and the ring-opening polymerization are the most used techniques. This paper reviewed methods of making PLA such as oligomer polycondensation or ring-opening polymerization and mainly mechanism of ring-opening polymerization with 4 areas: metal catalyst, organic catalyst, cationic catalyst and stereo-controlled polymerization.

Theoretical investigation on the mechanism and kinetics of the ring-opening polymerization of ε-caprolactone initiated by tin(II) alkoxides

A theoretical investigation of the ring-opening polymerization (ROP) mechanism of ε-caprolactone (CL) with tin(II) alkoxide, Sn(OR)₂ initiators (R = n-C₄H₉, i-C₄H₉, t-C₄H₉, n-C₆H₁₃, n-C₈H₁₇) was studied. The density functional theory at B3LYP level was used to perform the modeled reactions. A coordination-insertion mechanism was found to occur via two transition states. Starting with a coordination of CL onto tin center led to a nucleophilic addition of the carbonyl group of CL, followed by the exchange of alkoxide ligand. The CL ring opening was completed through classical acyl-oxygen bond cleavage. The reaction barrier heights of ε-caprolactone with different initiators were calculated using potential energy profiles. The reaction of ε-caprolactone with Sn(OR)₂ having R = n-C₄H₉ has the least value of barrier height compared to other reactions. The rate constants for each reaction were calculated using the transition state theory with TheRATE program. The rate constants are in good agreement with available experimental data.

Review – recent development of ring-opening polymerization of cyclic esters using aluminum complexes

With the development of the technology of ring-opening polymerization (ROP) rapidly, many novel aluminum complexes have been designed, synthesized, and applied in initiating ROP of cyclic esters and new stereoregular polymerization mechanism of lactide polymerization have been reported. In this review, the mechanism for ROP of cyclic ester, synthesis of aluminum complexes containing tetradendete ligand, tridentate ligand, bidentate ligand, and bimetallic complexes containing aluminum were reviewed. We hope to give some helpful information for designing aluminum complexes, improving activity, and stereoregularity of aluminum complexes.

Tin (IV) alkoxide initiator design for poly (d-lactide) synthesis using DFT calculations

The ring-opening polymerization (ROP) mechanism of d-lactide using tin (IV) alkoxides, (CH3(CH2)3)3SnOR, as initiators was theoretically studied. The high level adiabatic mapping B3LYP/LANL2DZ calculations were performed. This work evaluates role of the tin (IV) alkoxide initiators and gives molecular detail of the polymerization mechanism. In order to investigate the effects of the substituent (R) group of initiator on the ROP reaction rate, the R group was modeled to be linear R groups; –CH2CH3, –(CH2)3CH3, –(CH2)5CH3, –(CH2)7CH3, –(CH2)9CH3 and branch R groups; –CH2CH3, –CH2CH(CH3)2, –C(CH3)3. The calculations show that the rate limiting step of the ROP reaction mechanism is the first transition state (TS1) of the reaction which corresponds to the steric effect of the initiators. For the initiators with a linear R group, the steric effect on the potential energy barrier of the TS1 is not significant whereas the initiators with branch R groups relatively increase the potential energy barrier. However, the determined potential energies of the TS1 for most initiators studied in the work are in the same range (16.0–20.2kcal/mol). Therefore, all the initiators except (CH3(CH2)3)3SnOC(CH3)3 are suitable for the ROP of the d-lactide.

Acid catalyzed polymerization of macrolactones in bulk and aqueous miniemulsion: Ring opening vs. condensation

Aliphatic polyesters from three macrolactones (pentadecalactone, globalide and ambrettolide) were synthesized by organic acid catalyzed polymerization in bulk and in an aqueous miniemulsion. Two different mechanism of polymerization take place depending on the polymerization media. Relatively high molecular weight polyesters (Mn aprox. 10,000g/mol) were obtained in bulk following a ring opening polymerization mechanism. Interestingly, relatively fast polymerizations were observed which depended in the acid pKa (triflic acid>benzene sulphonic acids>diphenyl phosphate). On the other hand, a condensation mechanism is observed in water miniemulsion leading to oligoesters of aprox. 2000g/mol. This molecular weight limitation prevented these latexes to be suitable for most applications. Interestingly, it is demonstrated that the introduction of unsaturated macrolactones in these aqueous latexes allows subsequent cross-linking leading to cured polyester films.

Discrete Divalent Rare‐Earth Cationic ROP Catalysts: Ligand‐Dependent Redox Behavior and Discrepancies with Alkaline‐Earth Analogues in a Ligand‐Assisted Activated Monomer Mechanism

The first solvent-free cationic complexes of the divalent rare-earth metals, [{RO}RE(II) ](+) [A](-) (RE(II) =Yb(II) , 1; Eu(II) , 2) and [{LO}RE(II) ](+) [A](-) ([A](-) =[H2 N{B(C6 F5 )3 }2 ](-) ; RE(II) =Yb(II) , 3; Eu(II) , 4), have been prepared by using highly chelating monoanionic aminoether-fluoroalkoxide ({RO}(-) ) and aminoether-phenolate ({LO}(-) ) ligands. Complexes 1 and 2 are structurally related to their alkaline-earth analogues [{RO}AE](+) [A](-) (AE=Ca, 5; Sr, 6). Yet, the two families behave very differently during catalysis of the ring-opening polymerization (ROP) of L-lactide (L-LA) and trimethylene carbonate (TMC) performed under immortal conditions with excess BnOH as an exogenous chain-transfer agent. The ligand was found to strongly influence the behavior of the RE(II) complexes during ROP catalysis. The fluoroalkoxide RE(II) catalysts 1 and 2 are not oxidized under ROP conditions, and compare very favorably with their Ca and Sr congeners 5 and 6 in terms of activity (turnover frequency (TOF) in the range 200-400 molL-LA (molEu h(-1) )) and control over the parameters during the immortal ROP of L-LA (Mn,theor ≈Mn,SEC , Mw /Mn <1.05). The Eu(II) -phenolate 4 provided one of the most effective ROP cationic systems known to date for L-LA polymerization, exhibiting high activity (TOF up to 1 880 molL-LA ⋅(molEu h)(-1) ) and good control (Mw /Mn =1.05). By contrast, upon addition of L-LA the Yb(II) -phenolate 3 immediately oxidizes to inactive RE(III) species. Yet, the cyclic carbonate TMC was rapidly polymerized by combinations of 3 (or even 1) and BnOH, revealing excellent activities (TOF=5000-7000 molTMC ⋅(molEu h)(-1) ) and unusually high control (Mn,theor ≈Mn,SEC , Mw /Mn <1.09); under identical conditions, the calcium derivative 5 was entirely inert toward TMC. Based on experimental and kinetic data, a new ligand-assisted activated monomer ROP mechanism is suggested, in which the so-called ancillary ligand plays a crucial role in the catalytic cycle. A coherent reaction pathway computed by DFT, compatible with the experimental data, supports the proposed scenario.

Synthesis and characterization of graft copolymers poly(ethylene oxide)-g-[poly(ethylene oxide)-b-poly(ε-caprolactone)] with double crystallizable side chains

Using a “grafting from” strategy, the graft copolymer poly(ethylene oxide)-g-[poly(ethylene oxide)-b-poly(e-caprolactone)] [PEO-g-(PEO-b-PCL)] with double crystallizable side chains was synthesized by a sequential ring-opening polymerization (ROP) mechanism. First, the ethoxyethyl glycidyl ether (EEGE) monomers containing a protected hydroxyl group were copolymerized with ethylene oxide (EO) monomers to form poly(ethylene oxide-co-ethoxyethyl glycidyl ether) [poly(EO-co-EEGE)], and the pendant hydroxyl groups were recovered by cleavage of the protecting groups for give poly(ethylene oxide-co-glycidyl) [poly(EO-co-Gly)]. Then, using poly(EO-co-Gly) with the pendant hydroxyl groups as a macroinitiator, the graft copolymer poly(ethylene oxide)-g-poly(ethylene oxide) (PEO-g-PEO) was obtained by ring-opening polymerization (ROP) of the EO monomers, and the graft copolymer PEO-g-(PEO-b-PCL) was obtained by sequential ROP of e-CL monomers. The target PEO-g-(PEO-b-PCL) and intermediates were all characterized in detail by size-exclusion chromatography (SEC) and Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR). The thermal stability and crystallization behaviors were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the graft structure and compositions had important effects on the thermal stability and crystallization behaviors, and the crystallizability of graft copolymers was predominantly controlled by the outer segments.

Rare earth complexes of phenoxy-thioether ligands: synthesis and reactivity in the ring opening polymerization of cyclic esters

The potential of the phenoxy-thioether moieties as ancillary ligands in the coordination chemistry of group 3 metals was explored. The amine elimination reactions between yttrium and scandium amido precursors {M [N(SiHMe2)2]3 (THF)n} with the proligands {4,6-tBu2-OC6H2-2-CH2S(2-R-C6H4)}H [R = H (L1-H), CH3 (L2-H), Br (L3-H), CF3 (L4-H)], bearing different substituents at the ortho position of the thiophenol aryl ring, were studied. The outcome of aminolysis reactions gave different results depending on the structure of the proligand and the reaction conditions. Heteroleptic scandium and yttrium amido complexes with general formula {(L)2M [N(SiHMe2)2] (THF)n} were prevailingly obtained from phenoxy-thioether proligands L1-H and L4-H. In contrast, homoleptic yttrium complexes bearing three phenoxy-thioether ligands were favored with L2-H and L3-H. The activities of all the synthesized complexes toward the ring-opening polymerization of ε-caprolactone and L- and rac-lactide were investigated, also in combination with an alcohol as an external chain transfer agent. Polyesters with controlled molecular parameters (Mn, end groups) and low polydispersities were obtained. The monoinsertion adduct, produced by the reaction of {(L1)2ScN(SiHMe2)2} and 1 equiv. of ε-caprolactone, was isolated proving that a coordination-insertion mechanism of ring-opening polymerization was operative. In the polymerization of rac-lactide, yttrium complexes exerted a high degree of stereocontrol producing heterotactic polylactides (P(r) up to 0.91).

Living lamellar crystal initiating polymerization and brittleness mechanism investigations based on crystallization during the ring-opening of cyclic butylene terephthalate oligomers

The brittleness of polymerized cyclic butylene terephthalate (pCBT) is generally ascribed to its high crystallization degree and perfect crystal structure. Herein, a simple and effective method for improving the brittleness of pCBT is presented. Unlike other published toughening methods, this method did not decrease or destroy any of the natural advantages of cyclic butylene terephthalate oligomers (CBT) and its ring-opening polymerization (ROP). The melting behaviour and crystallization of CBT demonstrated that some CBT crystals were unable to melt completely during ROP. These un-melted crystals served as self-compatible nucleators and reduced the crystallization induction time of pCBT during ROP, they also plant many stress concentration points which result in the brittleness of pCBT, according to mechanical tests and crystallization kinetics. Finally, the “living lamellar crystal” initiating ROP and new brittleness mechanisms were proposed.

Biocatalytic Synthesis of Poly(δ-Valerolactone) Using a Thermophilic Esterase from Archaeoglobus fulgidus as Catalyst

The ring-opening polymerization of δ-valerolactone catalyzed by a thermophilic esterase from the archaeon Archaeoglobus fulgidus was successfully conducted in organic solvents. The effects of enzyme concentration, temperature, reaction time and reaction medium on monomer conversion and product molecular weight were systematically evaluated. Through the optimization of reaction conditions, poly(δ-valerolactone) was produced in 97% monomer conversion, with a number-average molecular weight of 2225 g/mol, in toluene at 70 °C for 72 h. This paper has produced a new biocatalyst for the synthesis of poly(δ-valerolactone), and also deeper insight has been gained into the mechanism of thermophilic esterase-catalyzed ring-opening polymerization.

Graft Polymerization of Anti-Fouling PEO Surfaces by Liquid-Free Initiated Chemical Vapor Deposition

Poly(ethylene oxide) (PEO), a biomedically important polymer, has been synthesized using a novel liquid-free initiated chemical vapor deposition (iCVD) via a ring-opening cationic polymerization mechanism. In addition, a grafting scheme was used to graft polymerize PEO onto amine-terminated surfaces. FTIR, NMR, and XPS showed a stoichiometric match to linear PEO homopolymer. In addition, XPS confirmed the graft polymerization of PEO to amine anchors on silicon with a high graft density. XPS and GPC were used to measure independently the grafted polymer molecular weight that also showed a narrow weight distribution. The grafted iCVD PEO surfaces were effective in minimizing nonspecific protein adsorption using a fluorescently labeled bovine serum albumin assay.

Synthesis of branch-ring-branch tadpole-shaped [linear-poly(ε-caprolactone)]-b-[cyclic-poly(ethylene oxide)]-b- [linear-poly(ε-caprolactone)] by combination of glaser coupling reaction with ring-opening polymerization

A novel amphiphilic branch-ring-branch tadpole- shaped (linear-poly(e-caprolactone))-b-(cyclic-poly(ethylene ox- ide))-b-(linear-poly(e-caprolactone)) ((l-PCL)-b-(c-PEO)-b-(l-PCL)) was synthesized by combination of glaser coupling reaction with ring-opening polymerization (ROP) mechanism. The self- assembling behaviors of (l-PCL)-b-(c-PEO)-b-(l-PCL) and their p- shaped analogs of poly(e-caprolactone)/poly (ethylene oxide))- b-poly(ethylene oxide)-b-(poly(e-caprolactone)/poly(ethylene ox- ide) with comparable molecular weight in water were prelimi- narily investigated. The results showed that the micelles formed from the former took a fiber look, however, that formed from the latter took a spherical look. V C 2012 Wiley Peri- odicals, Inc. J Polym Sci Part A: Polym Chem 50: 3095-3103, 2012

Reactivity ratios, and mechanistic insight for anionic ring-opening copolymerization of epoxides.

Reactivity ratios were evaluated for anionic ring-opening copolymerizations of ethylene oxide (EO) with either allyl glycidyl ether (AGE) or ethylene glycol vinyl glycidyl ether (EGVGE) using a benzyl alkoxide initiator. The chemical shift for the benzylic protons of the initiator, as measured by (1)H NMR spectroscopy, were observed to be sensitive to the sequence of the first two monomers added to the initiator during polymer growth. Using a simple kinetic model for initiation and the first propagation step, reactivity ratios for the copolymerization of AGE and EGVGE with EO could be determined by analysis of the (1)H NMR spectroscopy for the resulting copolymer. For the copolymerization between EO and AGE, the reactivity ratios were determined to be r(AGE) = 1.31 ± 0.26 and r(EO) = 0.54 ± 0.03, while for EO and EGVGE, the reactivity ratios were r(EGVGE) = 3.50 ± 0.90 and r(EO) = 0.32 ± 0.10. These ratios were consistent with the compositional drift observed in the copolymerization between EO and EGVGE, with EGVGE being consumed early in the copolymerization. These experimental results, combined with density functional calculations, allowed a mechanism for oxyanionic ring-opening polymerization that begins with coordination of the Lewis-basic epoxide to the cation to be proposed. The calculated transition-state energies agree qualitatively with the observed relative rates for polymerization.

Effect of Heat Treatment on the Structure and Properties of MC Nylon 6

Monomer casting nylon 6 (MC nylon 6) was fabricated by means of a cast moulding technique via the mechanism of anionic ring-opening polymerization, and the effect of heat treatment on the structure and properties of MC nylon 6 were studied. It was found that the heat treatment both in water and oil can improve the crystallinity of MC nylon 6; however, during the process of water heat treatment, the absorbed water in the sample may act as plasticizer, resulting in the remarkable difference in the physical and mechanical properties before and after heat treatment.

Synthesis and copolymerization of fully bio-based benzoxazines from guaiacol, furfurylamine and stearylamine

Two fully bio-based benzoxazine monomers, 3-furfuryl-8-methoxy-3,4-dihydro-2H-1,3-benzoxazine (Bzf) and 3-octadecyl-8-methoxy-3,4-dihydro-2H-1,3-benzoxazine (Bzs), have been successfully synthesized via a solventless method. Their structures have been confirmed by FTIR spectroscopy, NMR spectroscopy, and elemental analysis. Copolymerization of the monomers has been investigated by differential scanning calorimetry (DSC) measurements. The results reveal that they undergo homogeneous copolymerization when the Bzf–Bzs molar ratio exceeds 1 : 2. The furan moiety of Bzf was found to have beneficial effects on the copolymerization, including an accelerating effect on the curing process, improvement of the cross-linking density, and enhancement of the thermal properties of the copolymerized resins. Based on the mechanism of ring-opening polymerization of benzoxazines, these effects may be attributed to the electrophilic aromatic substitution of the furan ring structure. These findings have significant implications for the design of new fully bio-based polybenzoxazines with desirable properties.

Poly(cyclic imino ether)s Beyond 2‐Substituted‐2‐oxazolines

2-Oxazolines (2-OZO) are 5-membered cyclic imino ethers whose cationic ring-opening polymerization (CROP) mechanism and resulting polymer properties are extensively studied. However, also 6- and 7-membered cyclic imino ethers can be polymerized via CROP. Together with the much less studied 4- and 5-substituted main-chain chiral poly(2-oxazoline)s (P-2-OZO), these compounds are interesting monomers to enhance the versatility of (co)poly(cyclic imino ether)s. To emphasize the potential of such alternative cyclic imino ether monomers, we provide an overview on the polymerizations of 2-oxazine (2-OZI) and chiral 4- and 5-substituted 2-OZO as well as of selected properties of the resulting polymers. In addition, the hydrolysis of these polymers into the corresponding poly(alkylene imine)s will be addressed.

Preparation and Properties of Polydicyclopentadiene/MMt Nanocomposites Using Supported Tungsten Catalyst

Polydicyclopentadiene (PDCPD) is a kind of engineering plastic which possesses excellent mechanical performance. It can be made by dicyclopentadiene (DCPD) through Ring-opening metathesis polymerization. In this paper, a supported catalyst of WCl6-phenol on montmorillionite (MMt) was prepared, formed a high efficienct, low-cost and more stable in air, tagether with Et2AlCl as activator, to polymerize the DCPD monomer through ring-opening metathesis polymerization mechanism, and obtained a Polydicyclopentadiene/MMt Nanocomposites. The Molding of PDCPD was finally made by Gusmer-decker’s RIMcell Lt Machine, and the products were characterized by X-ray diffraction, TEM, TGA, SEM, DMA. Mechanical properties were also measured. The result showed that the supported catalyst had good catalytic activity in polymerizing DCPD. MMt was exfoliated in the matrix after the in-situ polymerization, according to the XRD and TEM, which brought about improved properties of PDCPD with small amount MMt dispersed in the matrix.