Readily Prepared and Tunable Ionic Organocatalysts for Ring-opening Polymerization of Lactones

Highly potent ionic organocatalyst is developed for room-temperature controlled ring-opening polymerization(ROP)of lactones,includingδ-valerolactone,ε-caprolactone,andδ-hexalactone.The catalysts are prepared by simply mixing tetra-n-butyl ammonium hydroxide and a(thio)urea at elevated temperature under vacuum,and used in cooperation with an alcoholic initiator.The performance of the catalyst is readily adjusted and optimized through variation of the(thio)urea precursor,catalyst composition,and reaction condition.Urea-derived catalysts are generally superior to thiourea-derived ones.Provided with proper N-substituents,the catalyst affords both high polymerization efficiency and high selectivity for monomer enchainment over macromolecular transesterification,even at high monomer conversion and/or substantially extended reaction time.In addition to acidity,structural symmetry of the urea also proves decisive for the catalytic activity,which enables a catalyst-assisted proton transfer process for the ring-opening of lactone and thus provides a novel mechanistic insight for ROP catalyzed by hydrogen-bonding type bifunctional ionic organocatalysts.

Ring-opening Polymerization of Lactones With Rare Earth Compound as Catalyst—— Polymerization of ε-caprolactone by Rare Earth Alkoxides

Recently, much attention has been paid to poly (ε-caprolactone) (PCL) since it is biodegradable with the release of nontoxic byproduct in vivo and miscible with a variety of polymers. Therefore it has already been used as materials of sustaining drug release, dental prostheses, as well as a new raw material of polyurethanes and long life plasticizer of poly(vinyl chloride).

Ring-opening Polymerization ofε-Caprolactone Using Lanthanide Tris(4-tert-butylphenolate)s as a Single-component Initiator

The ring-opening polymerization of e-caprolactone (CL) initiated by novel single lanthanide tris(4-tert-butylphenolate)s [Ln(OTBP)3] is reported. Single-component La(OTBP)3 can effectively prepare polycaprolactone (PCL) with over 90% yield and viscosity average molecular weight about 60 x 10 under quite mild conditions: molar ratio of CL to initiator is 1000, 60 C, 2 h in toluene. Mechanism study indicates that the monomer inserts into the growing chain via the break of acyl-oxygen bond of CL.

RING-OPENING POLYMERIZATION OFε-CAPROLACTONE USING LANTHANIDE TRIS(N-PHENYL-3,5-DI-T-BUTYLSALICYLALDIMINATO)S AS SINGLE COMPONENT CATALYST

Ring-opening polymerization of ε-caprolactone has been carried out by using rare earth Schiff base complexes： lanthanide tris（N-phenyl-3,5-di-t-butylsalicylaldiminato）s [Ln（OPBS）3] as single component catalyst for the first time. The influences of different rare earth elements, monomer and catalyst concentration as well as reaction time on the polymerization were investigated. Mechanism studies showed that monomer inserts into the active site with the acyl-oxygen bond scission rather than the break of alkyl-oxygen bond.

Tetrahydrosalen backboned gadolinium complex as initiator for the ring-opening polymerization of ε-caprolactone

Tetrahydrosalen ligand was employed in the synthesis of gadolinium complex. The ligand was deprotoned by LiBu, and the afforded lithium salt was reacted with anhydrous GdCl3 to produce the gadolinium complex through salt metathesis. This complex was successfully used to initiate the ring-opening polymerization of ε-caprolactone. The initiation conditions in different temperature, monomer-to-initiator ratio and time were investigated. Under the condition： [ε-caprolactone]：[catalyst] = 600, 56 ℃, toluene： 2 ml, poly（ε-caprolactone） （PCL） with Mw = 11,2782 and PDI = 1.96 was achieved.

Mononuclear and Dinuclear Yttrium Complexes Supported by Pyrrolide Ligands： Syntheses, Structures and Catalytic Behaviors towards the Ring-opening Polymerization of ε-Caprolactone

The syntheses, structures and catalytic activities of two yttrium complexes supported by pyrrolide ligands are reported. Treatment of Y（N（Si Me3）2）3 with one equivalent of H3bptd（H3bptd = 1,9-bis（2-pyrrolyl）-2,5,8-triazanona-1,8-diene） in THF gave a complex of composition [Y（bptd）（THF）]2（1）. Reaction of Y（N（Si Me3）2）3 with one equivalent of H3tpa（H3tpa = tris（pyrrolyl-α-methyl）amine） in THF generated [Y（tpa）（THF）3]（2） in good yield. Complexes 1and 2 have been characterized by single-crystal X-ray diffraction, elemental analyses and NMR spectroscopy. Complex 1 is dinuclear. The two metal centers are doubly bridged by two amine nitrogen atoms to form a Y–N–Y–N four-membered rhombus ring. The geometries of Y^3＋ ions in 1and 2 are well described as pentagonal bipyramid and capped octahedron, respectively. The ring-opening polymerization reactions of ε-caprolactone initiated by 1 and 2, respectively, were investigated. They both exhibited good catalytic activity for the polymerization of ε-caprolactone. All of the obtained polymers have high molecular weights and relatively narrower PDIs. The polymers generated by 2 possessed polydispersity close to 1.1. The good catalytic activities of 1 and 2 reveal their potential applications in polymer industry.

RING-OPENING POLYMERIZATION OF ε-CAPROLACTONE BY LANTHANOCENE CATALYSIS

Ring-opening polymerization of ε-caprolactone (CL) catalyzed bylanthanocenes, O(C_2H_4C_5H_3CH_3)_2YCl (Cat-YCl) and Me_2Si[(CH_3)_3SiC_5H_3]_2NdCl(Cat-NdCl) has been carried out for the first time. It has been found that both yttroceneand neodymocene are very efficient to catalyze the polymerization of CL, giving high molec-ular weight poly (ε-caprolactone) (PCL ). The effects of [cat] / [ε- CL] molar ratio, polymeriza-tion temperature and time, as well as solvents were investigated and polymerization tem-perature is found to be the most important factor affecting the polymerization. The bulkpolymerization gives higher molecular weight PCL and higher conversion than that in solu-tion polymerization. NaBPh_4 was found to promote the polymerization of ε-caprolactone,and thus to increase both the polymerization conversion and MW of poly (ε- caprolactone ).

In situ generated,tetrahydrosalen stabilized yttrium borohydride complex:Efficient initiator for the ring-opening polymerization of ε-caprolactone

In this paper, we report the preparation of a new tertrahydrosalen-stabilized yttrium complex which was employed as an initiator-precursor for the polymerization of ε-caprolactone （ε-CL） in the presence of NaBH4 to give interesting hydroxytelechelic poly（ε-caprolactone） （PCL）. The effect of [monomer]/[initiator] （[CL]/[I]）, temperature and time on the polymerization was investigated. It was found that under the condition： [CL]/[I] = 1200, 55℃, toluene： 0.5 mL, ε-CL： 0.5 mL, PCL with Mw = 32,600 and PDI = 1.47 was obtained.

TARTARIC ACID TEMPLATED SYNTHESIS OF MESOPOROUS Ti-INCORPORATED SILICA AND ITS CATALYTIC ACTIVITY FOR THE RING-OPENING POLYMERIZATION OF ε-CAPROLACTONE

Ti-incorporated mesoporous silica materials with pore diameters of 3-4 nm have been prepared via the co-hydrolysis and co-condensation reactions, that is the sol-gel reactions, of titanium (IV) tetrabutoxide and tetraethylorthosilicate in the presence of tartaric acid as template, followed by extraction with ethanol to remove the templatemolecules. The materials were characterized in detail by Fourier transform infrared spectroscopy, nitrogen adsorption-desorption test, powder X-ray diffraction, transmission electron microscopy and X-ray energy dispersive spectroscopy. Theresults indicate that the Ti-containing silica materials have large specific surface areas (ca. 1200 m^2 g^(-1)) and pore volumes(ca. 0.900 cm^3 g^(-1)). The mesoporosity arises from disordered interconnecting channels or pores. The Ti-incorporated silicasexhibit catalytic activity for the ring-opening polymerization of ε-caprolactone, otherwise, the pure mesoporous silicamaterial shows no catalytic activity under the identical conditions.

Aluminum and Titanium Complexes Containing Pyrrole-imine Ligands: Syntheses, Structures, and Ring-opening Polymerization of ε-Caprolactone

Syntheses and properties of aluminum and titanium complexes incorporating the pyrrole-imine ligands,N-((1H-pyrrol-2-yl)methyl)-1-(1H-pyrrol-2-yl)methanimine(H2L^1)and 2-cyano-1H-pyrrole(HL^2),have been investigated.Addition of one equiv of H2L^1 to AlMe3 and AlEt3,respectively results in the formation of dinuclear complexes[Al2(L^1)2 Me2](1)and[Al2(L^1)2 Et2](2).Treatment of Ti(NMe2)4 with one equiv of HL^2 and two equiv of iPrOH or three equiv of BnOH results in the production of complexes[Ti(HL^3)2(OiPr)2](3)and[Ti2(HL^3)2(OBn)6](4)(H2L^3=N,N-dimethyl-1H-pyrrole-2-carboximid-amide).HL^3 anion is an intermediate which is in situ formed from the reaction of HL^2 and Ti(NMe2)4.The structures of 1~4 were characterized by single crystal X-ray diffraction.The catalytic properties of 1~4 toward ring-opening polymerization(ROP)ofε-caprolactone were studied.All of the compounds could effectively initiate the polymerization reactions with good activities.

Lanthanum heterocyclic Schiff-base complex initiated ring-opening polymerization of ε-caprolactone

Lanthanum complex supported by the heterocyclic Schiff-base ligand of N-(2-pyridyl)-3,5-di-tert-butyl-salicylaldimine was prepared and employed for the ring-opening polymerization(ROP)ofε-caprolactone(ε-CL).The polymers obtained with this initiator showed a unimodal molecular weight distribution implied that only one active species was present.Mechanism study revealed that the polymerization proceeds via acyl-oxygen bond cleavage.

Highly Branched Poly(α-Methylene-γ-Butyrolactone) from Ring-Opening Homopolymerization

New heteroleptic lanthanide complex [L1ILaN{Si(CH3)2}] (1) containing tridentate [ONO] ancillary ligand was synthesized from an acid-base ligand exchange reaction with ligands H2L1 and corresponding homoleptic lanthanide compound La[N{Si(CH3)3}2]3. Meanwhile, dimeric complexes [L1LaCl] (2) and [L1ILaCl] (3) were prepared from salt metathesis reaction between one equivalent of ligands H2LI,II, three equivalent of NaN{Si(CH3)3}2, and one equivalent of LaCl3. These compounds were characterized by nuclear magnetic resonance (300 MHz) and elemental analysis. These complexes were used as catalysts in the ring-opening homopolymerization of α-methylene-γ-butyrolactone. While compound 1 did not show any significant reactivity, compounds 2 and 3 gave significant amount of highly branched poly(α-methylene-γ-butyrolactone) as confirmed by 1H NMR spectroscopy and Malvern’s triple detector GPCMax analysis in DMSO with molecular weights of over 500,000 Dalton. The glass-transition temperatures of the branched polymer samples were determined using a Dynamic Mechanical Analyzer, DMA Q800.

RING-OPENING POLYMERIZATION OF TRIMETHYLENE CARBONATE CATALYZED BY NOVEL SINGLE COMPONENT RARE EARTH CALIXARENE COMPLEXES

In this paper,ring-opening polymerization of trimethylene carbonate(TMC)with rare earth(Nd,Y,La)ρ-tert- butylcalix[n]arene(n=4,6,and 8)complexes as catalysts has been studied.Poly(trimethylene carbonate)(PTMC)with M_v of 21,400 was produced by bulk polymerization under the conditions as follows:[TMC]_0/[Nd](molar ratio)=1000,80℃, 8 h.Mechanism study reveals that the polymerization proceeds via a coordination mechanism.

SYNTHESIS, CHARACTERIZATION AND RING-OPENING POLYMERIZATION OF CYCLIC (ARYLENE PHOSPHONATE) OLIGOMERS

A series of cyclic (arylene phosphonate) oligomers were prepared by reaction of phenylphosphonic dichloride (PPD) with various bisphenols under pseudo-high dilution conditions via interfacial polycondensation. The yield of cyclic (arylene phosphonate) oligomers is over 85% by using hexadecyltrimethylammoniun bromide as phase transfer catalyst (PTC) at 0 'C . The structures of the cyclic oligomers were confirmed by a combination of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and IR analysis. These cyclic oligomers undergo facile ring-opening polymerization in the melt by using potassium 4,4'-biphenoxide as the initiator to give linear polyphosphonate. Free-radical ring-opening polymerization of cyclic(arylene phosphonate) oligomers containing sulfur linkages was also performed in the melt using 2,2'-dithiobis(benzothiazole) (DTB) as the initiator at 270 °C and the resulting polymer had a Mw, of 8 × 103 with a molecular weight distribution of 4. Ring-opening copolymerization of these cyclic oligomers with cyclic carbonate oligomers was also achieved. The average molecular weight of the resulting copolymer is higher than the corresponding homopolymer and the thermal stability of the copolymer is better than the corresponding homopolymer.

SYNTHESIS OF POLY(5,5-DIMETHYL-1,3-DIOXAN-2-ONE)BY LIPASE-CATALYZED RING-OPENING POLYMERIZATION

Porcine pancreas lipase (PPL) and PPL immobilized on narrow distributed micron-sized glass beads wereemployed successfully for the ring-opening polymerization of 5, 5-dimethyl-1, 3-dioxan-2-one (DTC) for the first time.Different polymerization conditions such as enzyme concentration and reaction temperature were studied. Immobilized PPLexhibits higher activity than native PPL. Along wth the increasing enzyme concentration, the molecular weigh of resultingPDTC decreases. PPL immobilized on narrow distributed micron-sized glass beads has outstanding recyclability. For thethird recycle time, immobilized PPL exhibits the highest catalytic activity and with high activity even after the fifth recyletime for the synthesis of PDTC. The ~1H-NMR spectra indicate that decarboxylation does not occur during the ring-openingpolymerization.

Calcium chloride doped zinc-cobalt metal-cyanide complex:Unexpected highly activity towards ring-opening polymerization of propylene oxide

Highly active calcium chloride（CaCl2） doped Zn-Co^Ⅲdouble metal-cyanide（Ca-DMC） catalysts were firstly reported.Ca-DMCs presented a very higher polymer yield（54 kg polymer/g catalyst） at relative low temperature（80-115℃） toward ringopening polymerization（ROP） of propylene oxide（PO） than did DMC catalysts without modification.

A Series of Rare Earth Phenolates Substituted by Alkyl Groups for D,L-Lactide Ring-Opening Polymerization

Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides＇ structure and catalytic activity in the ring-opening polymerization of D,L-lactide has also been investigated.The catalytic activity of all rare earth aryloxides,characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated.The results showed that both phenolates＇ catalytic activities and polymerization characteristics changed regularly,keeping in good concordance with variations in substitutents＇ number on phenol and structure of aryloxide ligands.The stronger ability of electron-donation of alkyl groups,the higher catalytic activity.Moreover,the more numbers of substituted alkyl on phenyl ring,the higher catalytic activity.The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.

RING-OPENING POLYMERIZATION OF TRIMETHYLENE CARBONATE BY CALIX[8]ARENE-NEODYMIUM

Ring-opening polymerization of trimethylene carbonate (TMC) with a rare earth calixarene compound as catalyst has been studied for the first time. The effect of TMC/Nd (molar ratio) and polymerization conditions were investigated in detail. It was found that calix[8]arene-neodymium is a highly effective catalyst for the bulk polymerization of TMC and gives high molecular weight (M-v = 60,000) polymer. The optimum conditions of TMC polymerization were found to be as follows:TMC/Nd (molar ratio) = 2,000, 80 degrees C, 16 h. The polymers were characterized by NMR, GPC and DSC. Studying the mechanism by NMR showed that the polymerization of TMC catalyzed by calix[8]arene-neodymium proceeds via a cationic mechanism.

SYNTHESIS OF NOVEL BI-FUNCTIONAL COPOLYMER BEARING STERICALLY HINDERED PHENOL AND HINDERED AMINE GROUPS VIA RING-OPENING METATHESIS POLYMERIZATION

Norbornene derivatives exo,endo-2-[2-(3,5-di-tert-butyl-4-hydroxyphenoxy)-acetoxy]methyl-5-norbornene(M1) and 3,3,5,5-tetramethyl-4-piperidinyl 5-norbornene-exo,endo-2-carboxylate(M2)were synthesized and polymerized by RuCl_2(=CHPh)(PCy_3)_2 to prepare a novel kind of bi-functional polymer bearing sterically hindered phenol(SHP)and hindered amine(HLAS)groups via ring-opening metathesis polymerization(ROMP).The resulting copolymers were characterized by gel permeation chromatography(GPC),~1H-NMR and differen...