Chu-Chieh Lin

Ring-opening polymerization by lithium catalysts: an overview

This critical review summarizes recent developments in the preparation and application of lithium catalysts/initiators such as, alkyl lithium, alkoxy lithium and bimetallic lithium compounds for ring-opening polymerization (ROP). The ROP of cyclic esters, cyclic carbonates, cyclo-silazanes, cyclo-silanes, cyclo-siloxanes, cyclo-carboxylate, cyclic phosphirene and quinodimethanes are covered in this review. The present paper emphasizes the polymerization kinetics and the control exhibited by the different types of lithium initiators/catalysts. For the cases where useful properties, such as high molecular weight, narrow PDI, or stereocontrol, have been observed, a more detailed examination of the mechanistic studies of the catalysts/initiators are provided. Furthermore, this review also focuses on the synthesis of block copolymers and graft copolymers by ROP principle. The topics covered in this review regarding lithium compounds toward ROP will be of interest to inorganic, organic and organometallic chemists, material, polymer and catalytic scientists due to its unique mode of activation as compared to transition and inner transition-metals. In addition, use of these compounds in catalysis is steadily growing, because of the complementary reactivity toward ROP as compared to other metals. Finally, some aspects and opportunities which may be of interest in the future are suggested (143 references).

Efficient and controlled polymerization of lactide under mild conditions with a sodium-based catalyst

A common phenolic antioxidant provides the ligand scaffold in the first discrete sodium-based catalyst for the highly active and controlled ring-opening polymerization of lactide.

Synthesis and structural studies of heterobimetallic alkoxide complexes supported by bis(phenolate) ligands: efficient catalysts for ring-opening polymerization of L-lactide.

A series of heterobimetallic titanium(IV) complexes [LTi(O(i)Pr)(mu-O(i)Pr)(2)Li(THF)(2)], [LTi(O(i)Pr)(mu-O(i)Pr)(2)Na(THF)(2)], [LTi(mu-O(i)Pr)(2)Zn(O(i)Pr)(2)], and [LTi(mu-O(i)Pr)(2)Mg(O(i)Pr)(2)] (where L = bidentate bisphenol ligands) have been synthesized and characterized including a structural determination of [L(1)Ti(mu(2)-O(i)Pr)(2)(O(i)Pr)Li(THF)(2)] (1a). These complexes were investigated for their utility in the ring-opening polymerization (ROP) of l-lactide (LA). Polymerization activities have been shown to correlate with the electronic properties of the substituent within the bisphenol ligand. In contrast to monometallic titanium initiator 1e, all the heterobimetallic titanium initiators (Ti-Li, Ti-Na, Ti-Zn, and Ti-Mg) show enhanced catalytic activity toward ring-opening polymerization (ROP) of l-LA. In addition, the use of electron-donating methoxy or methylphenylsulfonyl functional ligands reveals the highest activity. The bisphenol bimetallic complexes give rise to controlled ring-opening polymerization, as shown by the linear relationship between the percentage conversion and the number-average molecular weight. The polymerization kinetics using 2c as an initiator were also studied, and the experimental results indicate that the reaction rate is first-order with respect to both monomer and catalyst concentration with a polymerization rate constant, k = 81.64 M(-1) min(-1).

Interpenetrating Metal–Metalloporphyrin Framework for Selective CO2 Uptake and Chemical Transformation of CO2

Herein we report a robust primitive cubic (pcu)-topology metal-metalloporphyrin framework (MMPF), MMPF-18, which was constructed from a ubiquitous secondary building unit of a tetranuclear zinc cluster, Zn4(μ4-O)(-COO)6, and a linear organic linker of 5,15-bis(4-carboxyphenyl)porphyrin (H2bcpp). The strong π-π stacking from porphyrins and the lengthy H2bcpp ligand affords a 4-fold-interpenetrating network along with reduced void spaces and confined narrow channels. Thereby, MMPF-18 presents segmented pores and high-density metalloporphyrin centers for selective CO2 uptake over CH4 and size-selective chemical transformation of CO2 with epoxides forming cyclic carbonates under ambient conditions.

Synthesis, characterization and catalytic activity of magnesium and zinc aminophenoxide complexes: Catalysts for ring-opening polymerization of L-lactide

A series of novel magnesium and zinc aminophenoxide complexes were successfully synthesized and one zinc complex was characterized by X-ray crystallography. They were also investigated as initiators for the ring opening polymerization of L-lactide. The complexes are effective in forming polylactides with good conversions. The nature and steric bulk of the ligands coordinated to the central metal ions enormously influenced the polymer properties. Among all the complexes, the zinc aminophenoxide complexes as initiators produced polymers with good molecular weight control and relatively narrow PDIs.

Recent Developments in Metal-Catalyzed Ring-Opening Polymerization of Lactides and Glycolides: Preparation of Polylactides, Polyglycolide, and Poly(lactide-co-glycolide)

A good synergy of a catalytic system’s components, such as ancillary ligands and leaving groups at the active site of a catalyst, is of fundamental importance in the ring-opening polymerization (ROP) of lactides and lactones. This article surveys recent advances in the metal-promoted ROP of lactide and glycolide for the preparation of poly(lactide) (PLA), poly(glycolide) (PGA), and their copolymer poly(lactide-co-glycolide) (PLGA). First, there is a general discussion on mechanisms, the undesirable effects of side reactions on the rate of polymerization, and how the first generation of ROP catalysts such as SnOct2 [tin(II) 2-ethylhexanoate, also known as tin(II) octoate] work as efficient initiators. Then, the study focuses on the ROP capability of monomeric and multinuclear complexes of Li, Ca, Mg, Zn, Al, and Ti metals for the efficient preparation of PLA. Special emphasis is given to the factors controlling polymer molecular weight, molecular weight distribution, and the suppression of transesterification side reactions and epimerization of monomers. Surpassing the pure model nature of many structurally well-defined catalytic systems such as bis(phenoxide)-Li, bis(phenoxide)-Mg, trispyrazolylborate-Mg/Zn, and β-diketiiminate-Mg/Zn, the applicability and performance of N,O-donor Schiff base Mg/Zn systems in the production of PLAs are highlighted. The emerging “structure-polymerization” activity is also addressed. Special attention is given to Ca, Mg, and Zn initiators which, due to their biocompatibility, are considered the safest to be used in the preparation of PLAs for biomedical purposes. Likewise, the polymerization activity of the metal initiators is evaluated on the basis of the Lewis acidic properties of the central metal. Alternatives like trivalent lanthanide systems with ancillary ligands such as bis(amidinate), β-ketoiminate, bis(phenolate), and Schiff bases are considered. Some recently investigated coordination complexes of Cu, Ni, Ag, and Au metals used in the solvent-free melt polymerization of lactide are discussed in terms of structure–activity relationships. The substantial role of the ligand geometry on the stereocontrol of the rac-lactide polymerization is addressed to finally summarize the key components essential for obtaining PLAs of desired microstructure from rac- and meso-lactides. The development of glycolide ROP catalysts based on Sn, Zn, Sm, and Bi is addressed and their effectiveness in producing copolyesters of lactide and glycolide such as PLGA assessed.

Novel low humidity sensor made of TiO2 nanowires/poly(2-acrylamido-2-methylpropane sulfonate) composite material film combined with quartz crystal microbalance

A novel ceramic nanowires of TiO(2) and poly(2-acrylamido-2-methylpropane sulfonate) (TiO(2) NWs/PAMPS) composite material films coated on quartz crystal microbalance (QCM) was prepared as a low humidity sensor. The 50wt.% of TiO(2) NWs/PAMPS composite material films showed excellent sensitivity (2.63-DeltaHz/Deltappm(v)) at 31.5ppm(v)), linearity (R(2)=0.9959) and acceptable response time (64s at 34.6ppm(v)). The low humidity sensing mechanism was discussed in terms of surface texture and nanostructured morphology of the composite materials. Moreover, the adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding 50wt.% TiO(2) NWs into PAMPS in the increased sensitivity of low humidity sensing.

Intramolecular CH⋯O hydrogen bond controlling the conformation of heterocycles: synthesis, structure and catalytic reactivity of aluminum aryloxides

Abstract The reactions of R2AlX with one equivalent of 2,2′-methylene-bis-(4,6-di-tert-butylphenol) (MDBP-H2) or 2,2′-methylene-bis-(4-methyl-6-tert-butylphenol) (MMBP-H2) in oxygenated solvent afford monomeric four-coordinated compounds, XAl(MDBP)(S), 1–5 (1: R=Me, X=Br, S=Et2O; 2: R=Et, X=Cl, S=Et2O; 3: R=Me, X=Br, S=THF; 4: R=Et, X=Cl, S=THF; 5: R=X=Et, S=Et2O) or XAl(MMBP)(S), 6–8 (6: R=X=Et, S=Et2O; 7: R=X=iBu, S=Et2O; 8: R=Et, X=Cl, S=Et2O). Crystal structures of 1, 2 and 7 demonstrate that the conformation of the eight-membered heterocycles containing aluminum is controlled by an unusual intramolecular CH⋯O hydrogen bond. Et2AlCl or iBu3Al reacts with one equivalent of 2,2′-ethylidene-bis-(4,6-di-tert-butylphenol) (EDBP-H2) or MDBP-H2 in toluene giving a dimeric four coordinate compound [CLAL(μ-EDBP]2, 9 or [iBuAl(μ-MDBP)]2, 10. Some of these compounds have shown great catalytic activities toward the reaction of cyclopentadiene with methacrolein.

Structurally Diverse Copper Complexes Bearing NNO-Tridentate Schiff-Base Derivatives as Efficient Catalysts for Copolymerization of Carbon Dioxide and Cyclohexene Oxide

Structurally diverse copper acetate complexes based on NNO-tridentate Schiff-base ligands were synthesized and characterized as mono-, di-, and trinuclear complexes with respect to varied ancillary ligands. Treatment of the ligand precursors (L(1)-H = 2-(1-((2-(dimethylamino)ethyl)imino)ethyl)-4-methylphenol, L(2)-H = 4-chloro-2-(1-((2-(dimethylamino)ethyl)imino)ethyl)phenol, and L(3)-H = 2-(1-((2-(dimethylamino)ethyl)imino)ethyl)-5-methylphenol) with Cu(OAc)2·H2O (1 equiv) in refluxing ethanol afforded five-coordinate mono- or bimetallic copper complexes ([(L(1))Cu(OAc)(H2O)] (1); [(L(2))Cu(OAc)(H2O)] (2); [(L(3))2Cu2(OAc)2] (3)) in high yields. Dinuclear copper acetate analogue [(L(1))2Cu2(OAc)2] (4) resulted from treatment of L(1)-H as the ligand precursor in refluxing anhydrous MeOH with equimolar proportions of metal acetate salt under a dry nitrogen atmosphere. However, a trinuclear complex, [(L(4))2Cu3(OAc)4] (5), was obtained on utilizing 2-(1-((2-(dimethylamino)ethyl)imino)ethyl)-5-methoxyphenol (L(4)-H) as the proligand under the same synthetic route of 1-3; this complex was also synthesized in the reaction of L(4)-H and copper(II) acetate monohydrate in the ratio of 2:3, giving a quantitative yield. All complexes are active catalysts for copolymerization of cyclohexene oxide (CHO) and CO2 without cocatalysts. In particular, dinuclear Cu complex 3 performed satisfactorily to produce polycarbonates with controllable molecular weights and high carbonate linkages. These copper complexes are the first examples that are effective for both CO2/CHO copolymerization and formation of polymers in a controlled fashion.

In situ prepared polypyrrole for low humidity QCM sensor and related theoretical calculation

In situ preparation of polypyrrole (Ppy) by photo-polymerization coated on a quartz crystal microbalance (QCM) as a low humidity sensor was reported. Different concentrations of Ppy films say 0wt.% (as blank), 0.1, 1, and 10wt.% were investigated to measure humidity concentrations between 14.7 and 5412.5ppm(v). The adsorption/desorption behavior was also examined at humidity concentration 510.2ppm(v). The sensitivities of 0, 0.1 and 1wt.% Ppy films at 51.5ppm(v) were 0.143, 0.219 and 0.427, respectively. For 1wt.% Ppy, the highest sensitivity was obtained. The slope and correlation coefficients (R(2)) for 1wt.% Ppy at the ranges of 14.7-898.6ppm(v) were 0.0646 and 0.9909, respectively. A series of molecular simulations have been carried out to calculate bond energy for the water molecule interaction with Ppy, which was found to be approximately 3kcal/mol indicating the existence of hydrogen bonding during the sorption process. Based on Langmuir isotherm adsorption assumption, for 0.1 and 1wt.% Ppy films, the association constants were 2606.30 and 5792.98, respectively. This larger association constant for 1wt.% Ppy film explains higher sensitivity.