Ring-opening Polymerization Of Cyclic Monomers Research Articles

Highly Active Heterogeneous Double Metal Cyanide Catalysts for Ring-Opening Polymerization of Cyclic Monomers

A series of heterogeneous Zn-Co double metal cyanide (DMC) catalysts were investigated for ring-opening polymerization (ROP) of various cyclic monomers. Notably, inexpensive and commonly used organic solvents such as acetone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, nitromethane, and 1-methylpyrrolidin-2-one were very effective complexing agents for the preparation of DMC catalysts, showing high catalytic activity for the ROP of propylene oxide, ε-caprolactone, and δ-valerolactone. The chemical structures and compositions of the resultant catalysts were determined using various techniques such as FT-IR, X-ray photoelectron spectroscopy, powder X-ray diffraction, and elemental analysis. α,ω-Hydroxyl-functionalized polyether and polyester polyols with high yields and tunable molecular weights were synthesized in the presence of various initiators to control functionality. Kinetic studies of the ROP of δ-valerolactone were also performed to confirm the reaction mechanism.

Mechanistic Investigation of ε-Thiono-Caprolactone Radical Polymerization: An Interesting Tool to Insert Weak Bonds into Poly(vinyl esters)

The incorporation of heteroatoms into the backbone of commodity polymers prepared by radical polymerization is an elegant way to confer (bio)degradability to such materials. This could be achieved via the radical ring-opening polymerization of cyclic monomers. Thionolactones were recently identified as promising comonomers for rROP but only reacting with activated monomers such as acrylate and acrylamide derivatives. Herein, we describe two thionolactone monomers, oxepane-2-thione i.e. ethiono-caprolactone (thCL) and 7-butyloxepane-2-thione, i.e e-thiono-decalactone (thDL) capable of performing radical ringopening polymerization with less activated monomers such as vinyl acetate (VAc) to produce readily degradable copolymers via the insertion of thioester containing repeating units. A thorough mechanistic investigation was performed to understand the reactivity of the two cyclic monomers. We identified the initiation as the main parameter to perform the polymerization of such thionolactone monomers. In a specific case the poly(e-thCL) homopolymer was successfully obtained. Concerning the copolymerization with vinyl acetate, a variety of polymerizations with differing feed ratios were performed, and the degradability of the copolymers via aminolysis examined by SEC. To demonstrate the usefulness of thionolactones a variety of block copolymers containing thioester linkages involving N,N-dimethylacrylamide and VAc were also prepared and degraded.

Phenoxyimine Ligands Bearing Nitrogen-Containing Second Coordination Spheres for Zinc Catalyzed Stereoselective Ring-Opening Polymerization of rac-Lactide

A series of zinc (Zn1–Zn6) and aluminum (Al6) complexes supported by phenoxyimine ligands (L1–L6) bearing nitrogen-containing second coordination spheres were synthesized and investigated for ring-opening polymerization (ROP) of rac-lactide (rac-LA). The ligands L1–L4 and L6 bearing sterically opened nitrogen donors resulted in dynamic NNO-chelates associated with facile nitrogen–metal coordination interactions. The bulky ligand L5 resulted in L2Zn-type complex Zn5 by disproportionation. The zinc complexes exhibited catalytic activities in ROP of cyclic monomers, including rac-LA, e-caprolactone (CL), δ-valerolactone (VL), and trimethylene carbonate (TMC). The zinc complex Zn6 bearing a bulky triphenylsilyl substituent at the 3-position of the phenoxy moiety exhibited good stereochemical control during the ROP of rac-LA to produce highly heterotactic PLAs at ambient temperature (Pr = 0.90) as well as low temperature (−30 °C, Pr = 0.94) with narrow molecular weight distributions (Mw/Mn < 1.2). The aluminum...

One-pot synthesis of poly(N-vinylcaprolactam)-based biocompatible block copolymers using a dual initiator for ROP and RAFT polymerization

Thermosensitive, biocompatible poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) (PCL-b-PVCL), poly(δ-valerolactone)-b-PVCL, and poly(trimethylene carbonate)-b-PVCL block copolymers were synthesized at 30 °C using a hydroxyl-functionalized xanthate reversible addition-fragmentation chain transfer (RAFT) agent, 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate (HECP), as a dual initiator for ring-opening polymerization (ROP) and RAFT polymerization in a one-pot procedure. The hydrophobic blocks were first synthesized by the ROP of cyclic monomers using diphenyl phosphate (DPP) as a catalyst and the RAFT polymerization of the PVCL block was followed by adding N-vinylcaprolactam (VCL) and 2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile) (V-70) as an initiator to the reaction mixture. This novel one-pot process is convenient and powerful method for the synthesis of the PVCL-based biocompatible block copolymers. The lower critical solution temperature (LCST) of the PVCL-based biocompatible block copolymer can be readily tuned by controlling the hydrophobicity of the block copolymers. By copolymerizing a hydrophilic N-vinylpyrrolidone moiety to the PVCL blocks by RAFT copolymerization, the LCST of the copolymer was matched with the body temperature for its future biomedical applications.

Organocatalysis: Opportunities and Challenges for Polymer Synthesis

Organocatalysis offers a number of opportunities in polymer synthesis and was among the earliest methods of catalyzing the synthesis of polyesters. In the following Perspective we attempt to highlight the opportunities and challenges in the use of organic molecules as catalysts or initiators for polymerization reactions. The ring-opening polymerization of cyclic monomers is used as a representative polymerization process to illustrate some of the features of organic catalysts and initiators and to compare them to metal-based approaches. The convergence of convenience, functional group tolerance, fast rates, and selectivities will continue to drive innovations in polymerization catalysis, and it is our perspective that organocatalysis will continue to play an important role in these developments.

Ring-Opening Polymerization of Cyclic Monomers by Complexes Derived from Biocompatible Metals. Production of Poly(lactide), Poly(trimethylene carbonate), and Their Copolymers

Tridentate Schiff base calcium derivatives have been prepared and shown to be very effective catalysts for ring-opening polymerization of both lactides and trimethylene carbonate to produce high molecular weight polymers with narrow polydispersity. Optimization of the calcium catalyst was achieved changing the imine backbone, initiator, and substituent on the phenolate ring of the calcium complex. Turnover frequencies were obtained up to 1124 h−1 for a melt polymerization of l-lactide carried out at 110 °C. Solution studies in CDCl3 demonstrated the polymerization reaction is first order in [monomer] and [catalyst], with k = 19.9 M−1 h−1 for lactide polymerization and k = 500.0 M−1 h−1 for trimethylene carbonate polymerization at ambient temperature. The activation parameters for the ring-opening polymerization of l-lactide using catalyst 1a were determined to be ΔH⧧ = 73.5 ± 3.8 kJ/mol and ΔS⧧ = −42.5 ± 12.6 J/(mol K), and catalyst 1a was shown to produce heterotactic polylactide from rac-lactide with a Pr value of 0.73. It was also found that the ring-opening polymerization of trimethylene carbonate is a lower energy process than that of lactide polymerization as revealed by its activation parameters, which were determined to be ΔH⧧ = 37.9 ± 3.1 kJ/mol and ΔS⧧ = −135.1 ± 11.4 J/(mol K). Furthermore, this class of catalysts afforded from biocompatible metals is very effective at producing diblock copolymer from trimethylene carbonate and lactides. Kinetic studies of the copolymerization of trimethylene carbonate and l-lactide are presented as a function of the feed ratio of the two cyclic monomers.

Well defined polymer structures by ionic ring‐opening polymerization of cyclic monomers comprising the respective structure

AbstractRing‐opening polymerization of cyclic monomers is the method of choice when tailor‐made polymers and copolymers with heteroatoms in the main chain are to be prepared. Triblock copolymers comprising a poly(ethylene oxide) block [poly(EO)] and two poly(2,2‐dimethyltrimethylene carbonate) blocks [poly(DTC)] were prepared using a telechelic poly(EO) as initiator for the DTC polymerization. These block copolymers dissolve suitable salts leading to solid polymeric electrolytes. The thermal properties and the ionic conductivity of these materials are presented. Block copolymers comprising a poly(tetrahydrofuran) block [poly(THF)] and a poly(trimethylene urethane) block [poly(TU)] were obtained by sequential cationic polymerization of THF and TU with methyl trifluoromethane‐sulfonate as initiator. Mechanistic and kinetic aspects of the TU polymerization are discussed. To achieve the synthesis of block copolymers with a poly(L‐lactide) block [poly(LLA)] and a poly(α‐amino acid) block [poly(AA)] amino‐terminated poly(LLA) was prepared which served as initiator for the polymerization of α‐amino acid N‐carboxyanhydrides.

Macromolecular engineering of polylactones and polylactides. 14. A carbon-13 and aluminum-27 NMR study of the effect of .gamma.-butyrolactone on the structure of aluminum isopropoxide in toluene

Solutions of Al isopropoxide in toluene have been investigated by {sup 13}C and {sup 27}Al NMR spectroscopy. Since Al(O{sup i}Pr){sub 3} is currently used as an initiator for the living polymerization of {epsilon}-caprolactone, special attention has been paid to the effect of the monomer on the coordinative structure of Al(O{sup i}Pr{sub 3}) in toluene. {gamma}-Butyrolactone (BL) has been chosen as a nonpolymerizable model, representative of {epsilon}-caprolactone. The NMR spectra have been recorded at various concentrations of {gamma}-butyrolactone and temperatures. As a rule, Al(O{sup i}Pr){sub 3} is coordinatively aggregated in toluene in such a way that tetrameric and trimeric species are in equilibrium. Upon the addition of BL, this equilibrium is shifted toward the formation of an octahedric [Al(O{sup i}Pr){sub 3} {center_dot} 3BL] mixed tetramer coexisting with [Al(O{sup i}Pr){sub 3}]{sub 4} tetramers, the external tetrahedric Al atoms of which are coordinated with extra BL molecules. In the presence of a large excess of BL, only the mixed tetramer persists, which suggests that the single [Al(O{sup i}Pr){sub 3} {center_dot} 3M] species would be the actual initiator for the ring-opening polymerization of cyclic monomers M, such as {epsilon}-caprolactone, lactides, glycolide, and cyclic anhydrides.

Tutorial: Thermodynamics of ring-opening polymerization; Am. Chem. Soc. 199th national meeting, Boston, april 22-27, 1990, 6th international symposium on ring-opening and cyclo-polymerization

The ring-opening polymerization of cyclic monomers shows the characteristic features of any addition polymerization or any physical aggregation process, in particular a ceiling temperature above which the formation of the aggregate (long-chain polymer), under given conditions of monomer concentration, solvent and pressure, would involve a positive change of free energy and is therefore impossible. Conversely for a given temperature, pressure and solvent, there is an equilibrium monomer concentration below which long-chain polymer cannot be formed. Cyclic monomers must therefore have a negative free energy of polymerization, under given conditions, if they are to be capable of undergoing a significant extent of ring-opening polymerization. The effect of monomer structure, including ring size, on thermodynamic polymerizability is discussed, as well as the possibility of copolymerizing monomers which cannot themselves give homopolymers. Examples are given for various possible mechanisms of polymerization.