Lipase-catalyzed ring-opening polymerization of lactide

The six-membered lactide was polymerized using the ring-opening polymerization with lipase as a catalyst at a temperature between 80 and 130°C in bulk to yield the corresponding polylactide with weight-average molecular weights of up to 126000. The most preferable conditions with respect to the molecular weight of the polylactide are the bulk polymerization using lipase PS at a temperature of 100°C. The D ,L -lactide gave higher molecular weight compared to the D ,D - and L ,L -lactide.     

Novel ring-opening polymerization of lactide by lipase

Six-membered D,L-, L,L- and D,D-lactides were polymerized by lipase over a temperature range of 80 to 130 °C to yield the polylactide with a molecular weight (M_w) of greater than 270000. Among the lipases tested, lipase PS gave the greatest molecular weight of polylactide. The polymerization of D,L-lactide by lipase was better than that of L,L- and D,D-lactides. The polymerization of lactide by lipase showed the characteristic features, such as induction period for the initiation of polymerization, formation of oligomer and subsequent formation of high molecular weight polylactide, which may imply the characteristic polymerization by lipase. Immobilization of lipase on celite significantly enhanced the polymerization of lactide particularly with respect to the low concentration of the enzyme and the M_w of the resultant polymer. It was found that there is no clear relationship between enzymatic polymerizability and enzymatic degradability with respect to the enzyme origin and the stereochemistry of lactide.     

An activated equivalent of lactide toward organocatalytic ring-opening polymerization

The alpha-lactone equivalent lacOCA exhibits remarkable reactivity compared with lactide in nucleophile-catalyzed ROP. PLAs of controlled molecular weights and narrow polydispersities are typically obtained under mild conditions using DMAP and various protic initiators.     

Single-component catalyst/initiators for the organocatalytic ring-opening polymerization of lactide

The synthesis and characterization of a series of primary and secondary alcohol adducts of 1,3-dimesitylimidazolin-2-ylidene is described. These adducts are stable as solids at room temperature, but readily release alcohol and the free carbene in solution. These alcohol adducts function as excellent single-component catalyst/initiators for the ring-opening polymerization of lactide under mild conditions, providing polymers with controlled molecular weights and narrow polydispersities. Multifunctional adducts were used to prepare poly(lactide)s of more complex architectures.     

Group 4 metal initiators for the controlled stereoselective polymerization of lactide monomers

Group 4 metal initiators with a tetradentate bis(phenolato) ligand polymerized meso-lactide efficiently under ring-opening to give syndiotactic polylactide. L-Lactide was converted faster than rac-lactide and meso-lactide.     

Copolymer sequence control by ring-opening polymerization of prestructured cyclic monomers

In search for the new synthetic methods which may lead to the copolymers of controlled mer sequences, several new carbocyclic and heterocyclic monomer systems such as 1,1-disubstituted 2-vinylcyclopropanes, 1-(p-anisyl)-2-vinylcyclopropanes, substituted 3,4-dihydro-2H-pyrans, substituted 4-vinyl-2-oxetanones and α-vinyl cyclic sulfones were synthesized and their polymerization behaviors were investigated. And other promising monomer systems were also examined.     

A fast catalyst system for the ring-opening polymerization of cyclosiloxanes

Methanol, in combination with a non-ionic phosphazene base, was used to initiate the polymerization of octamethylcyclotetrasiloxane. In bulk, an instantaneous and large increase in viscosity was observed upon addition of the initiator. In toluene solution, the equilibrium state was reached in approximately 1 min. In addition to its high polymerization rate, another advantage of this system, as compared with e.g. alkali metal hydroxides, is that it is homogeneous.     

Novel chlorotitanium complexes containing chiral tridentate schiff base ligands for ring-opening polymerization of lactide

The selective synthesis of tri- and dichlorotitanium species containing chiral tridentate Schiff base ligands, derived from (1R,2S)-(-)-1-aminoindanol, was achieved by changing the solvent. Single-crystal X-ray analyses reveal that chlorotitanium complexes are monomeric and octahedral with the meridional occupation of the Schiff base. Although the chlorotitanium complexes lack typical initiating groups such as alkoxides or amides, they are effective catalysts for the controlled ring-opening polymerization of L-lactide (L-LA) as shown by the linearity of the molecular weight vs [L-LA]/[Ti] ratio plot as well as very narrow polydispersity index values.     

Complexities in the ring-opening polymerization of lactide by chiral salen aluminum initiators

The preparation of (R, R)- and (S, S)-salen Al(OR) complexes, where R = Et, CH2(i)Pr, CH2(t)Bu, and CH2CH(S)MeCl, are reported, along with their reactions with rac-lactide (salen = N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino). Rapid, reversible coordination of LA to the salen metal complex is observed, and it is shown that the relative rates of alcohol/alkoxide exchange are comparable to the NMR time scale while the rate of chain transfer involving (R, R)-salenAl(O-R-R) and (S, S)-salenAl(O-S-R) is much faster than the initial rate of ring opening of the LA monomer. For a primary [Al-OR] moiety, the ring opening of rac-LA is much faster than the ring-opening polymerization/enchainment of LA, and in the initial ring-opening event, the diastereoselectivity is dependent on the solvent, the chirality of the salen ligand, and the OR group. Irrespective of the initiator group OR or the solvent, the system moves to a pseudostatic equilibrium concentration of L- and D-LA which is dependent on the nature of the chirality of the salen ligand. Further studies show that the relative rate of trans-esterification is slower than the rate of LA enchainment and that the rate of epimerization is the slowest reaction in the system. Adventitious water leads to loss of catalytic activity and formation of the inert oxo-bridged compound [(salen)Al]2(mu-O) which has been structurally characterized.     

New mono- and difunctional monomers for polymerization

Conclusions 2-Allyl-4-phenoxyphenyl methacrylate, allyl-4-phenoxyphenyl ether, and 2-allyl-4-phenoxyphenol have been prepared for the first time by the reaction of 2-allyl-4-phenoxyphenol and methacrylyl chloride, and their properties have been described.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.1, pp. 182–183, January, 1970.     

Lithium chloride as catalyst for the ring-opening polymerization of lactide in the presence of hydroxyl-containing compounds

Lithium chloride was found to be an effective and biocompatible catalyst for the ring-opening polymerization of lactide in the presence of hydroxyl-containing compounds. Ethylene glycol (EG) and methyl α-D -glucopyranoside (MGlc) were used as multifunctional initiators. The polymerization was carried out at 128°C in bulk with 1% (w/w) of LiCl. Polylactide (PLA) of different molecular weights was obtained with varied molar ratios of monomer/initiator ([M]₀/[I]₀). The LiCl-catalyzed ring-opening polymerization was applied to the synthesis of a number of amphiphilic PLA copolymers when poly(ethylene glycol) (PEG), hydroxyethyl cellulose (HEC), and hydroxypropyl cellulose (HPC) were used as macroinitiators. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3486–3491, 1999     

Synthesis and ring-opening metathesis polymerization of eight-membered unsaturated lactams and related monomers

Novel eight-membered ring unsaturated lactams were synthesized and tested as monomers for the ruthenium-catalyzed ring-opening metathesis polymerization (ROMP). The reaction of a N-protected cyclic alkeneamine was also investigated. The Grubbs’ benzylidene complexes RuCl₂(=CHPh)(PCy₃)₂ or RuCl₂(=CHPh)(PCy₃)(IMesH₂) and selected ruthenium–arene species bearing either phosphine or stable Arduengo-type N-heterocyclic carbene ligands served as catalyst precursors. In most cases, isomerization of the starting materials took place and only 1-benzyl-1-aza-2-ketocyclooct-5-ene afforded a polymeric product. This polyamide was characterized by numerous analytical techniques.     

Scandium alkyl and amide complexes containing a cyclen-derived (NNNN) macrocyclic ligand: synthesis, structure and ring-opening polymerization activity toward lactide monomers

Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me(3)TACD)H (= Me(3)[12]aneN(4)), reacted with [K{N(SiHMe(2))(2)}] in benzene-d(6) to give [K{(Me(3)TACD)SiMe(2)N(SiHMe(2))}] (1) under hydrogen evolution. Single-crystal X-ray diffraction of 1 shows a dinuclear structure in the solid state, featuring a bridging μ-amido and a weak β-agostic Si-H bond. 1,7-Dimethyl-1,4,7,10-tetraazacyclododecane (Me(2)TACD)H(2) (= Me(2)[12]aneN(4)) and (Me(3)TACD)H were reacted with [Sc{N(SiHMe(2))(2)}(3)(thf)] in benzene-d(6) to give [{(Me(2)TACD)SiMe(2)N(SiHMe(2))}Sc{N(SiHMe(2))(2)}] (2) and [(Me(3)TACD)Sc{N(SiHMe(2))(2)}(2)SiMe(2)] (3), respectively. Both compounds are monomeric in solution and X-ray diffraction studies showed the scandium metal centers to be six-coordinate. The scandium alkyl complex [Sc(Me(3)TACD)(CH(2)SiMe(3))(2)] (4) was obtained by reacting (Me(3)TACD)H with [Sc(CH(2)SiMe(3))(3)(thf)] in benzene-d(6). The scandium amide complexes 2 and 3 catalyzed the ring-opening polymerization (ROP) of meso-lactide to give syndiotactic polylactides.     

Stereoselective ring-opening polymerization of a racemic lactide by using achiral salen- and homosalen-aluminum complexes

Highly isotactic polylactide or poly(lactic acid) is synthesized in a ring-opening polymerization (ROP) of racemic lactide with achiral salen- and homosalen-aluminum complexes (salenH(2)=N,N'-bis(salicylidene)ethylene-1,2-diamine; homosalenH(2)=N,N'-bis(salicylidene)trimethylene-1,3-diamine). A systematic exploration of ligands demonstrates the importance of the steric influence of the Schiff base moiety on the degree of isotacticity and the backbone for high activity. The complexes prepared in situ are pure enough to apply to the polymerizations without purification. The crystal structures of the key complexes are elucidated by X-ray diffraction, which confirms that they are chiral. However, analysis of the (1)H and (13)C NMR spectra unambiguously demonstrates that their conformations are so flexible that the chiral environment of the complexes cannot be maintained in solution at 25 degrees C and that the complexes are achiral under the polymerization conditions. The flexibility of the backbone in the propagation steps is also documented. Hence, the isotacticity of the polymer occurs due to a chain-end control mechanism. The highest reactivity in the present system is obtained with the homosalen ligand with 2,2-dimethyl substituents in the backbone (ArCH==NCH(2)CMe(2)CH(2)N==CHAr), whereas tBuMe(2)Si substituents at the 3-positions of the salicylidene moieties lead to the highest selectivity (P(meso)=0.9(8); T(m)=210 degrees C). The ratio of the rate constants in the ROPs of racemic lactide and L-lactide is found to correlate with the stereoselectivity in the present system. The complex can be utilized in bulk polymerization, which is the most attractive in industry, although with some loss of stereoselectivity at high temperature, and the afforded polymer shows a higher melting temperature (P(meso)=0.9(2), T(m) up to 189 degrees C) than that of homochiral poly(L-lactide) (T(m)=162-180 degrees C). The "livingness" of the bulk polymerization at 130 degrees C is maintained even at a high conversion (97-98 %) and for an extended polymerization time (1-2 h).     

Cationic equilibrium ring-opening polymerization of bicyclic monomers and its application to chemical recycling

Spiro orthoesters give poly(cyclic orthoester)s by single ring-opening polymerization in the presence of acid catalysts, and this process undergoes the equilibrium polymerization. We have applied the function of equilibrium polymerization to chemical recycling of polymeric materials. Crosslinked poly(cyclic orthoester)s, prepared by radical additions of poly(cyclic orthoester)s possessing exomethylene groups and dithiols, efficiently decrosslinked to bifunctional spiro orthoesters in the presence of CF₃CO₂H in CH₂Cl₂. The dithiol-linked bifunctional spiro orthoester monomers, prepared by the radical additions of spiro orthoester possessing exomethylene group and dithiols, afforded the corresponding crosslinked polymers in the presence of CF₃CO₂H as a catalyst in bulk. The decrosslinking of the obtained crosslinked polymer proceeded quantitatively to obtain the corresponding bifunctional monomer at room temperature in CH₂Cl₂. Further, an acid-catalyzed reversible crosslinking-decrosslinking of a polymer having a spiro orthoester group in the side chain was carried out. The copolymer obtained by the radical copolymerization of 2-methylene-1,4,6-trioxaspiro[4.6]undecane with acrylonitrile was treated with CF₃CO₂H at −10 °C in CH₂Cl₂ to afford the crosslinked polymer quantitatively. The crosslinked polymer was then treated with CF₃CO₂H at room temperature at a low concentration in CH₂Cl₂ to recover the original polymer.     

Zinc and magnesium complexes incorporated by bis(amine) benzotriazole phenoxide ligand: synthesis, characterization, photoluminescent properties and catalysis for ring-opening polymerization of lactide

A new bis(amine) benzotriazole phenoxide ligand, (C8NN)BTP-H (1) was prepared from the Mannich condensation of 2-(2H-benzotriazol-2-yl)-4-(2,4,4-trimethylpentan-2-yl)phenol with the mixtures of excess paraformaldehyde and N,N,N-trimethylethylenediamine under reflux conditions. Zinc and magnesium complexes bearing the N,N,O-tridentate (C8NN)BTP ligand were synthesized and fully characterized. The reaction of (C8NN)BTP-H with ZnEt(2) (1.2 molar equiv.) in toluene gives the monomeric tetra-coordinated zinc complex [((C8NN)BTP)ZnEt] (2). The homoleptic and monomeric complexes [((C8NN)BTP)(2)M] (M = Zn (3) and M = Mg (4)) result from treatment of ZnEt(2) or Mg(n)Bu(2) with (C8NN)BTP-H (two equiv.), in which the metal center is hexa-coordinated by two tridentate (C8NN)BTP ligands. Luminescent properties and catalysis for lactide (LA) polymerizations of complexes 2-4 are studied. Complexes 2-4 produce bright green fluorescence with emission maxima ranging from 510 to 520 nm in the solid state. Experimental results indicate that complex 2 catalyzes the ring-opening polymerization of LA in the presence of 9-anthracenemethanol (9-AnOH) with efficient catalytic activities in a controlled fashion, yielding poly(rac-lactide) with a slight isotactic predominance (P(m) = 0.59).     

New results of the free radical ring-opening polymerization

The reaction of 5-ring ketene-O, N-acetals with peroxides was investigated. It was shown that benzoyl peroxide adds to monomers 5a and 5b by ring opening, giving the corresponding linear diester amides 6a and 6b , respectively. The ketene-O,N-acetal 5c adds benzoyl peroxide, without ring opening, by addition to the exomethylene group, giving the cyclic-O,N-acetal diester 6c . With phthaloyl peroxide cyclic esteramides 7 and oligomeric products are formed. The chemical structures of the addition products were confirmed by NMR spectra and elemental analysis. © 1994 John Wiley & Sons, Inc.     

Macrocycles in dual role: ancillary ligands in metal complexes and organocatalysts for the ring-opening polymerization of lactide

Journal of Inclusion Phenomena and Macrocyclic Chemistry - In the twenty-first century, one of the central focus of polymer research in academia and industries is directed towards the design of...