Ring-opening polymerization of L-lactide by means of different iron compounds

L-lactide was bulk-polymerized in the presence of various commercially available iron compounds. The polymerization temperature was in the range of 140 and 230 °C, the monomer to initiator/catalyst ratio varied between 100 and 10 000, and the polymerization time between 30 minutes and 24 hours. Iron oxides, iron chlorides and sulfuric iron compounds were low efficient and are not suitable for melt polymerization of lactide. The oxidation state was noticed not to affect the efficiency. Ferrocene required long polymerization times and a high concentration of the compound before a high molar mass polymer was received. Organic iron salts were also found to be efficient initiators/catalysts, except for the hydrated iron(III)citrate. Especially iron(II)acetate caused a rapid polymerization with a high conversion and molar mass.     

Ring-opening polymerization of L-lactide with rare earth aryloxides substituted by various alkyl groups

<正>Rare earth aryloxides substituted by various alkyl groups[Ln(OAr)_3]such as methyl,isopropyl and tertbutyl,were used as single component catalysts to affect ring-opening polymerization of L-lactide(LLA).The catalytic activity, polymerization characteristics,polymerization kinetics and the mechanism were studied.It was found that the catalytic activity of rare earth aryloxides is influenced by both the structure and the number of alkyl groups on the phenyl ring.The stronger the electron-donation ability of the alkyl group,the higher the catalytic activity will be.An increase in the number of the substitute group will result in a higher catalytic activity.Lanthanum tris(2,4,6-tri-tert-butylphenolate)[La(OTTBP)_3] exhibits the highest activity among all lanthanum aryloxides.According to the ~1H-NMR data,it was proposed that the LLA polymerization proceeded via a coordination-insertion mechanism involving cleavage of acyl-oxygen bond of the lactide.     

Ring-opening precipitation polymerization of poly(D,L-lactide-co-glycolide) in supercritical carbon dioxide

The biodegradable polymer poly(D ,L -lactide-co-glycolide) was synthesized by a ring-opening precipitation polymerization in supercritical CO₂ using stannous octoate as initiator. Following polymerization, unreacted monomer was removed by supercritical fluid extraction and the polymer was recovered as a porous solid upon depressurization of the CO₂ phase. The lactide to glycolide ratio of the polymer was determined to be 70.7 : 29.3 using ¹³C NMR spectroscopy. The weight-average molecular weight of the product was measured to be 3 500, with a polydispersity of 1.4 using gel permeation chromatography.     

Ring-opening polymerization and depolymerization in respective polymers

Under certain conditions the ring-opening polymerization of cyclic monomers may be reversed to result in a ring-closing depolymerization of the respective polymers. This method of “thermodynamic recycling” was explored for a number of examples such as polytetrahydrofuran, polyalkenamers, poly-ε-caprolactone, polycarbonates, polysiloxanes and respective blockcopolymers.     

Ring-opening metathesis polymerization for the preparation of norbornene-based weak cation-exchange monolithic capillary columns

Functionalized monolithic columns were prepared via ring-opening metathesis polymerization (ROMP) within silanized fused silica capillaries with an internal diameter of 200 μm by in situ grafting. This procedure is conducted in two steps, the first of which is the formation of the basic monolithic structure by polymerization of norborn-2-ene (NBE) and 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene (DMN-H6) in a porogenic system (toluene and 2-propanol) using RuCl₂(PCy₃)₂(CHPh) as ROMP initiator. In the second step the still active initiator sites located on the surface of the structure-forming microglobules were used as receptor groups for the attachment (“grafting”) of functional groups onto the monolithic backbone by flushing the monolith with 7-oxanorborn-2-ene-5,6-carboxylic anhydride (ONDCA). Functionalization conditions were first defined that did not damage the backbone of low polymer content (20%) monoliths allowing high-throughput chromatographic separations. Variation of the functionalization conditions was then shown to provide a means of controlling the degree of functionalization and resulting ion-exchange capacity. The maximum level of in situ ONDCA grafting was obtained by a 3 h polymerization in toluene at 40 °C. The weak cation-exchange monoliths obtained provided good separation of a standard peptide mixture comprising four synthetic peptides designed specifically for the evaluation of cation-exchange columns. An equivalent separation was also achieved using the lowest capacity column studied, indicative of a high degree of robustness of the functionalization procedure. As well as demonstrably bearing ionic functional groups enabling analyte separation in the cation-exchange mode, the columns exhibited additional hydrophobic characteristics which influenced the separation process. The functionalized monoliths thus represent useful tools for mixed-mode separations.     

Ring-opening polymerization of degradable polyesters

Medium to high molecular weight random copolymers of 1,5-dioxepan-2-one (DXO) and L-lactide (L-LA) or ε-caprolactone (ε-CL) of different compositions have been investigated. Polymerization was conducted in bulk at 110°C using stannous 2-ethylhexanoate as catalyst. Poly(DXO-co-L-LA) is a hydrolysable material with a glass transition temperature (T_g) ranging from −36 up to 58°C depending on the molar composition. The material exhibited crystallinity as long as the amount of DXO did not exceed 50 weight%. Reactivity ratios were determined to r_L-LA=10 and r_DXO=0.1, giving a more blocky structure than expected in a random copolymer. The copolymer between ε-CL and DXO was shown to be a truly random copolymer by ¹³C NMR, as expected from the reactivity ratios, r_DXO=1.6 and r_ε-CL=0.6. T_g of the material was ranging from −64 up to −39°C. The ability of the poly(DXO-co-ε-CL) to crystallize was retained up to a DXO content of 40 weight%. The melting temperature and crystallinity of both copolymers decrease with increasing amount of DXO. Incorporation of semicrystalline comonomers, L-LA or ε-CL, into the amorphous poly(DXO) creates materials with adjustable properties depending on the molar composition.     

Ring-opening polymerization of unsaturated alicyclic compounds

The ring-opening polymerizations of cyclooctene, cyclododecene, 1,5-cyclooctadiene, 1,5,9-cyclododecatriene, 3-methylcyclooctene, and 3-phenylcyclooctene have been carried out by using a two-component catalyst system composed of ethylaluminum dichloride and tungsten hexachloride. NMR and infrared analyses of the respective polymers indicate structures which are consistent with a ring-cleavage mode of propagation. No evidence for double-bond shifts or transannular reactions during the polymerizations of 1,5-cyclooctadiene, 1,5,9-cyclododecatriene, 3-methylcyclooctene, and 3-phenylcyclooctene was found. The polymerizability of substituted, unsaturated, mediumsized alicyclic monomers suggests a convenient method for synthesis of certain perfectly alternating terpolymers. Since polymerizations occurred rapidly with little evolution of heat, it was concluded that entropy is a substantial contributor to the free energy of the ring-opening polymerization of medium-sized, unsaturated alicyclic monomers.     

Ring-opening polymerization of six- and seven-membered cyclic pseudoureas

The cationic ring-opening polymerization of six-membered cyclic pseudoureas, 2-(1-pyrrolidinyl)- ( 2a ) and 2-morpholino-5,6-dihydro-4H-1,3-oxazine ( 2b ), was examined, which proceeded in two different ways, depending on the nature of initiator. The polymerization of 2 with methyl p-toluenesulfonate or trifluoromethanesulfonate (MeOTf) produced poly[(N-carbamoylimino)trimethylene], while that with benzyl chloride or bromide or methyl iodide gave a polymer consisting of 1,3-diazin-2-one-1,3-diylalkylene unit (the main component) and (N-carbamoylimino)trimethylene unit. The cationic ring-opening polymerization of seven-membered cyclic pseudourea, 2-(1-pyrrolidinyl)-4,5,6,7-tetrahydro-4H-1,3-oxazepine ( 3 ) was also examined. The polymerization of 3 with MeOTf as initiator gave poly{[N-(1-pyrrolidinycarbonyl)imino]tetra-methylene}. With benzyl chloride, on the other hand, no polymerization of 3 proceeded but, instead, the quantitative isomerization of 3 to 1,1′-carbonyldipyrrolidine took place. The polymerization mechanism of 2 and 3 as well as the isomerization mechanism of 3 were discussed with comparing them to the polymerization mechanism of five-membered pseudoureas. © 1977 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 933–945, 1997     

Anionic and ionic coordinative polymerization of L-lactide

The potassium naphthalenide complex with 18-crown-6 is able to initiate anionic polymerization of L -lactide at 20°C. This type of anionic initiator does not have to be removed from the polymer as it does not affect metabolic processes. The ionic polymerization of L -lactide with an initiator based on Zn(II) acetyl acetonate, which is fairly stable, has been investigated. It has been found that this process leads to the corresponding polyesters, at high yields. © 1998 John Wiley & Sons, Ltd.     

Ring-opening polymerization of l-lactide in supercritical carbon dioxide using PDMS based stabilizers

Ring-opening suspension polymerization of l-lactide in supercritical CO₂ (scCO₂) was investigated in the presence of different stabilizer architectures based on poly(dimethyl siloxanes) (PDMS). Two amphiphilic AB type block copolymers, a graft copolymer, and an ester-capped PDMS were selected to find their efficacy as stabilizers for the synthesis of poly(l-lactide) (PLLA) in scCO₂. The stabilizer’s efficiency was analyzed in terms of the molecular weight, yield, and particle morphology of PLLA. The block copolymers, poly(dimethylsiloxane)-b-poly(acrylic acid) (PDMS-b-PAA) and poly(dimethylsiloxane)-b-poly(methacrylic acid) (PDMS-b-PMA) were found to be effective, leading to the formation of fine, discrete PLLA microparticles. On the other hand, the graft copolymer, poly(dimethylsiloxane-g-pyrrolidonecarboxylic acid) (PDMS-g-PCA) and acetylated PDMS (PDMS-OAc) failed to give an enough stabilization to the PLLA due to their short polymer-philic chains, resulting in hard agglomerates.     

Ring-opening metathesis polymerization of 9-phenyl-1,5-cyclododecadiene

Synthesis of butadiene-based sequence-controlled copolymers that are composed of commercial monomers such as styrene, butadiene, and ethylene was investigated. New substituted cyclododecadiene derivatives, 9-phenyl-1,5-cyclododecadiene was synthesized by reductive-phenylation method from 1,5-cyclododecadiene-9-one and was polymerized with tungsten-based catalyst systems to obtain a microstructure-controlled terpolymer. A sequence-controlled 2 : 1 : 1 terpolymer of butadiene, styrene and ethylene was successfully synthesized. The glass transition of the terpolymer occurred at ?33.6°C. © 1995 John Wiley & Sons, Inc.     

Ring-opening polymerization of ethylene organophosphorothioates: Stereoregular polymerization involving asymmetry at phosphorus

Stereoregular polymerization involving asymmetry at phosphorus has been obtained from ethylene methyl or phenyl phosphorothioate with R₂Mg? NH₃ catalysts, or, in some cases, with R₂Mg alone. The methyl ester gave two types of polymer: an amorphous rubber and a low-melting (75°C) crystalline polymer. The phenyl ester gave mainly a low-melting (68°C) crystalline polymer of 2.2 inherent viscosity. Proton and ³¹P NMR and infrared spectra of these polymers are in accord with the expected chain unit, ? CH₂CH₂? O? P(S)(OR)? O? . The polymerization mechanism probably involves an anionic ring-opening step with P? O cleavage. Ring opening with C? O cleavage appears to be largely excluded. This conclusion is based on the expectation that anionic ring opening with C? O cleavage should lead to a rearranged chain unit, ? CH₂CH₂? O? P(O)? (OR)? S? , because of the high nucleophilicity of sulfur as compared with oxygen. Proton and ³¹P NMR spectra give no evidence for the rearranged unit within the limit of detection (ca. 3%). However, on aging, the methyl ester polymer changes drastically to form up to 40% CH₂SP groups. Presumably, the polymer undergoes the well-known thiono-thiolo rearrangement characteristic of simple phosphorothioate esters to form ? CH₂CH₂? O? P(O)(SCH₃)? O? chain units. The phenyl ester polymer is stable under the same aging conditions.     

Concerted processes in supercritical fluids

The possibility of obtaining concerted mechanisms of chemical activation in supercritical fluids (SCFs) with the formation of a multicenter general transition state that includes a group of reagent atoms in which the subsequent breaking of chemical bonds and the formation of new chemical bonds start and proceed simultaneously is discussed. Two processes are considered that can occur only in SCF media: the reduction of anthracene in an isopropyl alcohol SCF and the impregnation of the photochromic compound spiroanthrooxazine (SAO) in a polycarbonate matrix in SC CO₂ accompanied by an irreversible conformational rearrangement of the SAO structure. Concepts of the possible dependence of the concerted mechanism of the considered processes on the intertwining or entanglement of electron subsystems in forming multicenter transition states are developed. The decisive role of the electromagnetic component of a physical vacuum in obtaining a high degree of correlation in systems of entangled electrons is discussed.     

Ring-opening polymerization of DD-lactide catalyzed by Novozyme 435

In contrast to LLA, DLA is converted in toluene solution under mild reaction conditions (50-70 degrees C) using Novozyme 435 (immobilized CALB) to form the corresponding polymer. The influence of several parameters, such as enzyme concentration, temperature and monomer concentration, on the polymerization rate and the monomer conversion was studied. In contrast to the Novozyme 435 catalyzed polymerization of epsilon-caprolactone, enzyme deactivation occurs. It is attributed to the deprivation of water from the enzyme. This work points out that by careful selection of the reaction conditions, it is possible to obtain poly(D-lactide) in reasonable molecular weights and in high yields using Novozyme 435 catalysis.     

Extraction of atrazine and its metabolites using supercritical fluids and enhanced-fluidity liquids

Supercritical fluid and enhanced-fluidity liquid extractions are performed on spiked sediment samples containing atrazine (ATRA) and five of its metabolites including desisopropyldesethylatrazine, desethylhydroxyatrazine (DEHA), desisopropylatrazine, desethylatrazine, and hydroxyatrazine (HA). The hydroxylated metabolites are of particular interest because of their increased water solubility and the fact that their high polarity makes them difficult to analyze. Soxhlet extractions using methanol are conducted for the purpose of comparison. Results of the extractions show that the hydroxy-containing metabolites of ATRA are not effectively extracted with supercritical CO2 alone. The solvating or desorbing power of carbon dioxide appears too low to extract HA and DEHA. The extraction recoveries of the hydroxylated metabolites increase when enhanced-fluidity liquid mixtures of methanol/CO2 are used, and these rates increase with the methanol concentration. Enhanced-fluidity ternary liquid mixtures of H2O/methanol/CO2 yield the best recoveries for these compounds. ATRA recoveries are equally effective when using supercritical CO2 or enhanced-fluidity mixtures. The other nonhydroxy-containing metabolites require the increased solvent strength of either large percentages of methanol in CO2 or ternary mixtures of H2O, methanol, and CO2 for high recoveries. Recoveries with enhanced-fluidity liquid ternary mixtures are better than the recoveries from Soxhlet for all the compounds in the study.     

Degradation of polycaprolactone in supercritical fluids

The degradation of polycaprolactone (PCL) was studied in subcritical and supercritical toluene from 250 to 375 °C at 50 bar. The degradation was also investigated in various solvents like ethylbenzene, o-xylene and benzene at 325 °C and 50 bar. The effect of pressure on degradation was also evaluated at 325 °C at various pressures (35, 50 and 80 bar). The variation of molecular weight with time was analyzed using gel permeation chromatography and modeled using continuous distribution kinetics to evaluate the degradation rate coefficients. PCL degrades by random chain scission in subcritical conditions (250-300 °C) and by chain end scission (325-375 °C) in supercritical conditions in toluene. The degradation of PCL in other solvents at 325 °C was by chain end scission under both subcritical and supercritical conditions indicating that the mode of scission depends on the temperature and not on the supercriticality of the solvent. The thermogravimetric analysis of PCL was investigated at various heating rates (2-24 °C/min) and the activation energy was determined using Friedman, Ozawa and Kissinger methods. It was shown that PCL degrades by random scission at lower temperatures and by chain end scission at higher temperatures again indicating that the mode of scission is dependent on the temperature.