Stereoregular polymerization of β-butyrolactone by aluminoxane catalysts

A study was conducted on the application of aluminoxane catalysts to the polymerization of β-butyrolactone, including the effects of polymerization solvent, temperature, type of aluminoxane, aluminoxane preparation, aluminoxane concentration, and modifications of the aluminoxane on the yield and tacticity of the polymer obtained. Optimal conditions for the synthesis of high molecular weight, highly isotactic poly-β-butyrolactone, PBL, were determined. Quantitative yields of crude PBL could be obtained, but removal of aluminum residues from the crude PBL by treatment with acetylactone resulted in large polymer losses. The polymer lost had a low molecular weight and an atactic stereochemistry. The purified PBL was of high molecular weight and high isotacticity.     

Degradation behaviour of poly (methyl methacrylate-g-3-hydroxybutyrate) polymer films

Poly(methyl methacrylate-g-3-hydroxybutyrate) films were prepared from new graft polymers synthesised by an anionic grafting reaction of 3-butyrolactone (3-BL) on poly(methyl methacrylate) (PMMA). The resulting graft polymers form a transparent film of a one phase system, as revealed by DSC measurements. A plasticisation effect was observed for film samples containing the PBL grafted chains. This effect increased with increasing amount of PBL in the graft copolymer. The mechanical properties of the films were investigated, and thermal, hydrolytic and enzymatic degradation behaviours were evaluated. Disintegration of the films was observed during their hydrolytic degradation in phosphate buffer.     

Stereocontrol in radical polymerization

The stereospecific radical polymerization of vinyl esters, methacrylates, and alpha-substituted acrylates was studied. Fluoroalcohols, as a solvent, have remarkable effects on the stereoregularity of the radical polymerizations of vinyl acetate, vinyl pivalate, and vinyl benzoate, affording polymers rich in syndiotacticity, heterotacticity, and isotacticity, respectively. This method was successfully applied to the polymerization of methacrylates to give syndiotactic polymers. The steric repulsion between the entering monomer and the chain-end monomeric unit bound by the solvent through hydrogen bonding is important for the stereochemical control in these systems. Lewis acid catalysts, such as lanthanide trifluoromethanesulfonates and zinc salts, were also effective for the stereocontrol during the radical polymerization of methyl methacrylate, to reduce the syndiotacticity and alpha-(alkoxymethyl)acrylates to synthesize isotactic and syndiotactic polymers. Radical polymerization of the methacrylates bearing a bulky ester group, such as the triphenylmethyl methacrylate derivatives, gave highly isotactic polymers, as in the case of anionic polymerization. In addition, the control of one-handed helical conformation was attained in the radical polymerization of 1-phenyldibenzosuberyl methacrylate using chiral neomenthanethiol or cobalt(II) complexes as an additive.     

Regioselective ring-opening anionic polymerization of β-lactones

New aspects of anionic polymerization of 4-membered lactones are presented, attention being paid to regioselectivity of ß-lactones ring-opening reactions. It has been demonstrated that supramolecular complexes of alkali metal alkoxides used as initiators enable control of lactones polymerization, and due to anion activation yield polymers with specific molecular architecture. Synthesis of the analogue of natural polymer poly(3-hydroxybutyrate) via anionic polymerization of ß-butyrolactone is discussed.     

Polymerization and copolymerization of β-butyrolactone and benzyl-β-malolactonate by aluminoxane catalysts

High molecular weight poly-β-hydroxybutyrate (PHB) and poly (β-hydroxybutyrate-co-β-benzyl malate) [P (HB? BM)], were prepared by ring-opening polymerization reactions of racemic β-butyrolactone (BL) and racemic β-benzyl malolactonate (BM) using two types of oligomeric aluminoxane catalysts prepared by the reaction of water with either triethyl-aluminum (EAO) or triisobutylaluminum (IBAO). The stereoregularities, crystallinities, and molecular weights were determined for both the PHB homopolymers and the P (HB? BM) copolymers by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). All homopolymers and copolymers obtained could be separated into acetone-soluble and acetone-insoluble fractions. In every case the latter had higher degrees of crystallinity, higher molecular weights and higher degrees of stereoregularity (84–87% isotactic dyads) than the former. Hence all of the polymers obtained from both types of catalysts apparently had stereoblock isotactic structures. Copolymer compositions and monomer dyad sequence distributions were determined by NMR spectroscopy.     

Group 4 initiators for the stereoselective ROP of rac-β-butyrolactone and its copolymerization with rac-lactide

In this paper we demonstrate the utility of Group 4 metals for the well-controlled and stereoselective (syndiotactic) ring opening polymerization (ROP) of rac-β-butyrolactone (BBL) and their ability to form copolymers.     

Stereospecific polymerization of 9-fluorenyl methacrylate: Tacticity effects on the thermal and photophysical properties of the polymers

Poly(9-fluoreneyl methacrylate) was obtained through anionic polymerization with t-BuLi and t-BuMgBr and through radical polymerization with α,α′-azobisisobutyronitrile. Anionic polymerization with t-BuLi in tetrahydrofuran and radical polymerization afforded syndiotactic polymers (rr ∼ 90%), whereas anionic polymerization with Li and Mg initiators in toluene and CH₂Cl₂ led to isotactic polymers. The thermal and photophysical properties of the polymers were examined. A syndiotactic polymer tended to show higher glass transition and decomposition temperatures than an isotactic polymer. However, polymers with different tacticities were not likely to assume specific, distinctive conformations such as a helix or a π-stacked conformation in solution. An isotactic polymer showed stronger interactions in a CH₂Cl₂ solution with 2,4,7-trinitro-9-fluorenylidenemalononitrile, an electron-acceptor molecule, than a syndiotactic polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4656–4665, 2004     

A proposal on the steric course of propagation in the homogeneous cationic polymerization of vinyl and related monomers

A stereochemical scheme of propagation was proposed for polymerizations of vinyl and related monomers by Friedel-Crafts catalysts. For the cationic propagation proceeding via the simple carbonium ion pair, the following two factors were considered to be of primary importance in determining the steric course of propagation: (1) the conformation of the last two units of the propagating polymer segment and the direction of approach of the incoming monomer; (2) the tightness of the growing ion pair. Thus, the front-side (less hindered site) attack to the carbonium ion gives rise to a syndiotactic placement and the back-side attack an isotactic placement. The present model can satisfactorily explain the effects of substituents, catalysts, polymerization media, and polymerization temperature on the steric structure of polymers in cationic polymerization of vinyl ethers. Extension of the scheme to polymerization of the β-substituted vinyl ethers in nonpolar solvents predicts formation of the diisotactic structures consistent with the experimental result. The influences of the polymerization condition on the steric structure of polymer were studied for cationic polymerizations of α-methylstyrene at low temperatures. Highly syndiotactic polymers were obtained for homogeneous reactions in toluene-rich media. The isotactic unit increased by increasing the content of methylcyclohexane in the solvent mixture. The effect of catalysts, though insignificant in toluene-rich media, was clearly noted in methylcyclohexane-rich media, less active catalysts (e.g., SnCl₄) yielding higher amounts of the isotactic unit than more active catalysts (e.g., AlCl₃). These results can be readily accommodated in the present model.     

Advances in the catalyses of polymerizations

Abstract

Nearly all technical processes for the production of polymers are carried out in the presence of catalysts. In the case of addition polymerization reactions, two mechanisms are possible: Start of the reaction via an initiator (e.g., peroxides) or start via a true catalyst (e.g., Ziegler/ Natta systems). In both areas remarkable progress has been made: Cationic “living” polymerizations of oxacycloalkanes, group transfer polymerization, metal-catalyzed alternating copolymerization of ethylene with carbon monoxide, and metallocene-catalyzed polymerizations of alpha-olefins. The polymerization of alpha-olefins with metallocene catalysts not only leads to the improvement of well-known polymers like polyethylene and polypropylene, but also enables the production of new polymers like syndiotactic polypropylene, syndiotactic polystyrene, and cycloolefin copolymers on an industrial scale.     

Synthesis of stereoregular ROMP polymers using molybdenum and tungsten imido alkylidene initiators

Three of the four possible structures for polymers formed from an achiral monomer through a single ROMP polymerization step have been prepared for a small collection of monomers. Trans,syndiotactic structures have been prepared through chain end control, cis,isotactic polymers have been prepared through enantiomorphic site control, and cis,syndiotactic polymers have been prepared through stereogenic metal control. Stereogenic metal control at the metal center as a means of forming syndiotactic polymers is virtually unknown. Synthesis of ROMP polymers with a regular structure that contain alternating enantiomers from a racemic mixture of monomers is a natural consequence of stereogenic metal control. Ruthenium catalysts do not display ROMP specificities analogous to those described here, perhaps since alkylidene isomers have not been observed for Ru catalysts and the barrier to rotation of the carbene in a generic NHC dichloride Ru catalyst has been calculated to be relatively low.     

FI catalysts: new olefin polymerization catalysts for the creation of value-added polymers

This contribution reports the discovery and application of phenoxy-imine-based catalysts for olefin polymerization. Ligand-oriented catalyst design research has led to the discovery of remarkably active ethylene polymerization catalysts (FI Catalysts), which are based on electronically flexible phenoxy-imine chelate ligands combined with early transition metals. Upon activation with appropriate cocatalysts, FI Catalysts can exhibit unique polymerization catalysis (e.g., precise control of product molecular weights, highly isospecific and syndiospecific propylene polymerization, regio-irregular polymerization of higher alpha-olefins, highly controlled living polymerization of both ethylene and propylene at elevated temperatures, and precise control over polymer morphology) and thus provide extraordinary opportunities for the syntheses of value-added polymers with distinctive architectural characteristics. Many of the polymers that are available via the use of FI Catalysts were previously inaccessible through other means of polymerization. For example, FI Catalysts can form vinyl-terminated low molecular weight polyethylenes, ultra-high molecular weight amorphous ethylene-propylene copolymers and atactic polypropylenes, highly isotactic and syndiotactic polypropylenes with exceptionally high peak melting temperatures, well-defined and controlled multimodal polyethylenes, and high molecular weight regio-irregular poly(higher alpha-olefin)s. In addition, FI Catalysts combined with MgCl(2)-based compounds can produce polymers that exhibit desirable morphological features (e.g., very high bulk density polyethylenes and highly controlled particle-size polyethylenes) that are difficult to obtain with conventionally supported catalysts. In addition, FI Catalysts are capable of creating a large variety of living-polymerization-based polymers, including terminally functionalized polymers and block copolymers from ethylene, propylene, and higher alpha-olefins. Furthermore, some of the FI Catalysts can furnish living-polymerization-based polymers catalytically by combination with appropriate chain transfer agents. Therefore, the development of FI Catalysts has enabled some crucial advances in the fields of polymerization catalysis and polymer syntheses.     

Polymeres cryptants: Application a la polymerisation du methacrylate de methyle

The purpose of the present work, relative to anionic polymerization, is to describe the use of cryptands fixed on polymers in order to prepare alkali salts of radical anions complexed in tetrahydrofuran. All these new species initiate the polymerization of methyl methacrylate. The presence of complexed ion pairs increases the syndiotactic structure. The polymerization seems to obey Bernoullian statistics.     

采用阴离子、基团转移及自由基聚合方法合成旋光性聚甲基丙烯酸薄荷酯

近年来, 旋光性高分子的广泛应用及其特有的功能已引起了广泛关注, 尤其在手性记忆功能材料[1～3]、液晶及手性催化等方面[4～6]皆表现出良好的应用前景. 用旋光性单体合成旋光性聚合物是最常用的方法之一. 早在20世纪70年代, 就有关于聚甲基丙烯酸薄荷酯(PMnMA)的研究[7], 但有关配体参与的阴离子聚合, 基团转移聚合(GTP)及其立构规整性的研究还未见报道.     

Polymerization of asymmetric polyfunctional monomers. III. Ionic polymerization of acrylic and methacrylic esters of 2-allylphenol

The polymerization of acrylic and methacrylic esters of 2-allyphenol with different anionic, cationic and coordination catalysts was studied. The polymerization occurs exclusively or predominantly through (meth)acrylic C?C double bonds in all the studied cases. With anionic catalysts the allylic groups are not polymerizable and the polymers have linear structure. Polymerization with catalysts based on dialkylaluminum chloride (alone or associated with some metal salts) yields soluble or partially crosslinked polymers, depending on the reaction conditions. The crosslinking is due to the participation of allylic groups in the polymerization reactions. Copolymers of acrylic and methacrylic esters of 2-allylphenol with styrene, acrylonitrile, methyl methacrylate, N-vinylcarbazole and 1,3-pentadiene were synthesized by copolymerization in the presence of anionic catalysts and of systems based on dialkylaluminum chloride.     

Synthesis and characterization of poly-β-hydroxybutyrate. II. Synthesis of D-poly-β-hydroxybutyrate and the mechanism of ring-opening polymerization of β-butyrolactone

Synthesis of the naturally occurring polyester, D -poly-β-hydroxybutyrate (PHB) was accomplished by using an optically active monomer. Polymerization of D -(+)-β-butyrolactone (β-BL) of 73% optical purity with a catalyst system of Et₃Al–H₂O produced a polymer with a similar optical activity and essentially identical to the natural polymer as isolated from bacterial cells. This paper describes the synthesis and characterization of this optically active polyester along with a suggested mechanism to account for the observed stereospecific polymerization of β-BL with this catalyst system.     

Progress in the syndiotactic polymerization of styrene with metallocene/mao catalysts

Metallocene/MAO catalysts are useful for the production of syndiotactic polystyrene - a new class of high performance polymers. The melting point of the obtained syndiotactic polystyrene depends on the metallocene used and can reach up to 275 °C. In the past, the most active catalysts in polymerization have been half-sandwich titanocenes such as CpTiCl₃ and Cp*TiCl₃. If the chlorinated compounds are changed into the fluorinated compounds as CpTiF₃ and Cp*TiF₃, the activity increases by a factor of 5 to 100. The fluorinated titanocenes are more stable at higher temperatures and need a lower MAO excess in order to obtain optimal activities. Polymers obtained with the unsubstituted CpTiF₃ show melting points which are 17 °C lower than those synthesized by pentamethylcyclopentadienyltitaniumtrifluoride. Especially Cp*TiF₃ shows a much higher activity and, compared with the chlorinated compound, gives polymers with a higher molecular weight. Substituted cyclopentadienyltitanocenes have even higher activities. Ethene/styrene copolymers can be obtained by catalysis with zirconocene compounds.     

Preparation and polymerization of methylenecyclobutene and 1-methyl-3-methylenecyclobutene

Methylenecyclobutene (MCB) and 1-methyl-3-methylenecyclobutene (MMCB) were synthesized, characterized, and polymerized by anionic and cationic initiators. Structural analyses of the polymers were carried out by infrared and NMR spectros-copy. The cationic polymerization of MCB appeared to proceed entirely by a 1,5-propagation mechanism to form low molecular weight polymers in low yields. Anionic polymerization of this monomer, on the other hand, proceeded primarily through a 1,2-propagation path, again forming only low molecular weight polymeric products in low yield. In contrast to MCB, the methyl-substituted monomer, MMCB, polymerized readily with cationic initiators to produce unusually high molecular weight polymers in high conversions. On the basis of both infrared and NMR spectroscopic analyses, it was concluded that the polymers also contained essentially only 1,5-addition repeating units. Anionic initiators such as n-BuLi were unable to induce polymerization of this monomer, but polymerization by Ziegler-Natta catalysts proceeded readily to yield polymers virtually identical in structure and molecular weight to those obtained with cationic initiators.     

Polymerization of vinyl ethers with transition‐metal catalysts: An examination of the stereoregularity of the formed polymers

The polymerization of isobutyl vinyl ether (IBVE) and tert‐butyl vinyl ether (TBVE) was carried out with metallocene and nonmetallocene catalysts, and the stereoregularity of the formed polymers was examined with ¹³C NMR spectroscopy. IBVE afforded polymers with 63–68% dyad isotacticity by polymerization with mixtures of metallocene catalysts and methyl aluminoxane as a cocatalyst in toluene as a solvent. However, TBVE yielded polymers with 47–52% dyad isotacticity (21–28% triad isotacticity) under the same conditions, the isotacticity being lower than that of poly(isobutyl vinyl ether) (PIBVE). Nonmetallocene catalysts, including Ti, Zr, and Hf complexes with two phenoxy imine chelate ligands, provided PIBVE and poly(tert‐butyl vinyl ether) with 63–68 and 45–51% dyad isotacticity, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3938–3943, 2002     

Studies on tacticity of polyacrylonitrile. I. High-resolution nuclear magnetic resonance spectra of polyacrylonitrile

The nuclear magnetic resonance spectra of polyacrylonitriles prepared under various polymerization conditions were measured in NaCNS–D₂O solution. The methylenic proton resonance could be separated into two triplets: one is due to the protons of the syndiotactic methylene groups and the other is due to the isotactic ones. The tacticity of polyacrylonitrile could be determined by the ratio of the integrated intensities of the two triplets. Polyacrylonitriles prepared with radical catalysts are approximately 75% syndiotactic, and polyacrylonitriles prepared by the anionic polymerization at low temperature, γ-irradiation in the solid state, Mg molecular beam, and γ-irradiation on the urea canal complex are more isotactic but have no remarkable stereoregularity.     

Highly syndiospecific polymerization of styrene catalyzed by allyl lanthanide complexes

Allylic complexes of lanthanides bearing a fluorenyl-based ligand are active single-component catalysts for the polymerization of styrene, giving highly syndiotactic polymers (rrrr > 99%) with low to high molecular weight (Mn = 8000-135 000) and narrow polydispersities (Mw/Mn = 1.25-2.1).