Enantioselective Alternating Olefin-Carbon Monoxide Copolymerization: A new concept for activity and stereoselectivity

Cationic Pd-complexes modified by dicyclohexyl{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}phosphine ( 1a ) give very active catalytic systems for the regioregular isotactic specific copolymerization of propene with CO. Other alk-1-enes also give stereoregular and regioregular copolymers, even if with lower productivity. The copolymers are isolated as poly(4-alkyl-tetrahydrofuran-2,2,5,5-tetrayl-2-oxy-2-methylenes) B in the solid state and give the isomeric poly(2-alkyl-1-oxopropane-1,3-diyls) A by dissolution in (CF₃)₂CHOH. Solid polymer A (R = Et) is formed back at least partially when the dissolved material is reprecipitated from MeOH. The use of the related (ferrocenyl)diphosphine ligands 1b ? e and 2 as the catalyst modifier shows that the presence of both elements of chirality and of large substituents on the P-atoms of the ligand is necessary to achieve good stereocontrol, and that the large difference in basicity between the two P-atoms is probably the reason for the good catalytic activity.     

Isotactic and Atactic Copolymerization of Styrene and Carbon Monoxide Using Cationic Palladium-Phosphino(dihydrooxazole) Complexes. Preliminary Communication

Cationic palladium complexes 2 containing coordinated phosphino(dihydrooxazole) ligands 1 give catalytic systems which allow the production of alternating styrene-carbon monoxide copolymers. Depending on the symmetry of the ligand, the copolymers are produced either with a highly isotactic or with an essentially completely atactic microstructure. Termination of the polymeric chain is mainly due to a β-H-elimination reaction. Both linear ((E)-PhCH?CHCO? ) and branched (CH₂?C(Ph)CO? ) unsaturated end groups were identified.     

Helix‐sense‐selective copolymerization of triphenylmethyl methacrylate with chiral 2‐isopropenyl‐4‐phenyl‐2‐oxazoline

The asymmetric induction leading to a one‐handed helix was investigated in the anionic and radical copolymerization of triphenylmethyl methacrylate (TrMA) and (S)‐2‐isopropenyl‐4‐phenyl‐2‐oxazoline ((S)‐IPO), and highly isotactic copolymers with a reasonable optical activity were obtained. In the anionic copolymerization, the optical activity of the obtained copolymers depended on the polarity of solvents, and a highly optically active copolymer was produced in the copolymerization in toluene. The chiral oxazoline monomer functioned not only as a comonomer but also as a chiral ligand to endow the polymer with large negative optical rotation in the copolymerization with TrMA. The copolymers with small positive optical rotation were obtained in THF, indicating that IPO unit may work only as the chiral monomer that dictates the helical sense via copolymerization with TrMA. The isotacticity of the obtained copolymers depended on the contents of TrMA units in the copolymers, but was almost independent of the solvent for copolymerization. In the radical copolymerization, the obtained copolymers exhibited small optical activities. It seemed that the chiral monomer cannot induce one‐handed helical structure of TrMA sequences even if the sequences probably have a high isotacticity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 441–447     

Epoxide Polymerization and Copolymerization with Carbon Dioxide Using Diethylaluminum Chloride-25,27-Dimethoxy-26,28-dihydroxy-p-tert-butyl-Calix[4]arene System as a New Homogeneous Catalyst

ABSTRACT

Previously unknown substituted chelate phenolatoaluminum chloride, (25,27-dimethoxy-p-tert-butylcalix[4]arene-26,28-diolato) aluminum chloride, was derived from the reaction of diethyl-aluminum chloride and 25,27-dimethoxy-26,28-dihydroxy-p-tert-butylcalix[4]arene at reactants 1:1 mole ratio. It was applied successfully for the polymerization of propylene oxide and cyclohexene oxide, and their copolymerization with carbon dioxide, leading to respective oligomers and co-oligomers. The catalyst structure and the structure of the obtained low-molecular-weight polymers and copolymers were studied using NMR spectroscopy. Poly(propylene oxide) obtained in the presence of the studied catalyst appeared to contain isotactic diads predominantly, whereas the obtained poly(cyclohexene oxide) did not exhibit any significantly prevailing sequences of either isotactic nor syndiotactic diads. The polymerization mechanism has been proposed and discussed in view of the obtained results.     

Expedient Synthetic Identification of a P-Stereogenic Ligand Motif for the Palladium-Catalyzed Preparation of Isotactic Polar Polypropylenes

The iso-specific statistical copolymerization of unprotected polar monomers with propylene remains a grand challenge in the field of polymer chemistry. Current research is hampered because only a single natural-product-derived dimenthylphosphine-motif is known to allow for the preparation of moderately isotactic polypropylene copolymers. To overcome this structural limitation, we developed time-efficient synthetic methods that facilitate P-donor ligand development. The strength of these methods was demonstrated with preparation of twenty-five new P-stereogenic phosphine/sulfonate- and bisphosphine-monoxide-type palladium catalysts, which could typically be developed in parallel. A lead candidate was identified for iso-specific propylene polymerization. The best-performing catalysts utilizing the P-stereogenic donor motif achieved triad isotacticities of up to mm=0.75—the highest value within those reported for group 10 metal catalysts—for the homo- and copolymerization of propylene with unprotected polar monomers at an industrially relevant temperature of 50 °C.     

Stereospecific and asymmetric polymerization of 1-phenyldibenzosuberyl methacrylate with radical and anionic initiators

Stereospecific and asymmetric (helix-sense-selective) polymerization of 1-phenyldibenzosuberyl methacrylate (PDBSMA) was performed with radical and anionic initiators. A highly isotactic polymer having triad isotacticity greater than 97% was obtained by radical polymerization with (i-PrOCOO)₂ at 40°C. The radical polymerization of PDBSMA in (+)- and (-)-menthol gave (-)-and (+)-polymers, respectively, whose optical activity is ascribed to the prevailing one-handed helical conformation of a polymer chain. The radical copolymerization of PDBSMA with a small amount of an optically active monomer, (+)-phenyl-2-pyridyl-o-tolylmethyl methacrylate, afforded an optically active copolymer with the prevailing one-handed helical structure of PDBSMA sequences. Asymmetric anionic polymerization of PDBSMA was carried out with the complex of N, N′-diphenylethylenediamine monolithium amide and a chiral ligand, (+)-1-(2-pyrrolidinylmethyl)pyrrolidine in toluene at −78°C. The obtained polymer was highly isotactic and optically active due to nearly 100% one-handed helical structure.     

Cooligomerization of carbon monoxide with cyclic olefins on supported palladium catalysts

The cooligomerization of CO with cyclic olefins, such as norbornene, 5-vinyl-2-norbornene, and dicyclopentadiene, in toluene in the presence of supported palladium catalysts containing 2,2’-bipyridine as a ligand is studied. It is shown that, during copolymerization, opening of the double bond in a ring occurs, while in the case of 5-vinyl-2-norbornene, vinyl bond C=C is not involved in the reaction. When ethylene is added to the reaction mixture, it does not participate in polymer-chain growth. The yield of the process is commensurable with the yield attained in the case of a homogeneous catalytic system, and the conversion of olefins is as high as 47%. The copolymers in the solid state occur in the form of spiroketal structures that, during dissolution, transform into ketone structures to different extents.     

Complexed copolymerization of vinyl compounds with alkylaluminum halides

The monomer reactivity in the complexed copolymerization of vinyl compounds with alkylaluminum halides has been extensively surveyed. Equimolar copolymers were obtained in various combinations of monomers which are classified into two monomer groups, A and B. The group B monomers are conjugated vinyl compounds having nitrile or carbonyl groups in the conjugated position and form complexes with alkylaluminum halides. The group A monomers are donor monomers having low values, such as olefins, haloolefins, dienes, and unsaturated esters. These A monomers belong to the same group of monomers which give alternating copolymers in conventional radical copolymerization with maleic anhydride, SO₂, and so on. In addition the complexed copolymerization has the same specific characteristics as the conventional alternating copolymerization, i.e., high reactivities of allyl-resonance monomers and inner olefins and no transfer of halogen atom to the copolymers in CCl₄. These features suggest little or no participation of the A monomer radical. The Q-e scheme is also discussed in terms of the monomer reactivity. More than two monomers selected from groups A and B give multicomponent copolymers in which alternating sequential structures hold with respect to A and B. Anomalous mutual reactivities between two B monomers in the terpolymerization were observed and indicate that the nature of radical in the complexed copolymerization may be different from that expected by the Lewis-Mayo equation. The complexed radical mechanism previously proposed is discussed in connection with the specific behavior mentioned above.     

Synthesis,characterization, and application of helical polymers

This review mainly describes the asymmetric synthesis of optically active polymers with helical conformation. Bulky methacrylates such as triphenylmethyl methacrylate and 1-phenyldibenzosuberyl methacrylate give one-handed helical and optically active polymers with almost perfectly isotactic main chain conformation by polymerization with chiral anionic initiators. The radical polymerization and copolymerization of these monomers under chiral conditions also afford optically active polymers with prevailing one-handed helicity. N, N-Disubstituted acrylamides also give optically active, helical polymers in the asymmetric anionic polymerization. Optically active polyisocyanates with a prevailing one-handed helical structure have been prepared in the copolymerization of an achiral isocyanate with a small amount of an optically active isocyanate and also in the polymerization of alkyl and aromatic isocyanates with optically active lithium alkoxide or amide compounds. The existence of a stable helical structure for polychloral has been successfully proved with the helical oligomers of chloral. One-handed helical polyisocyanides have been prepared by helix-sense-selective polymerization of bulky isocyanides and also by the cyclopolymerization of a 1, 2-diisocyanobenzene derivative with the Pd complex of a one-handed helical oligomer.     

Homo‐ and copolymerization of norbornene with styrene catalyzed by a series of copper(II) complexes in the presence of methylaluminoxane

Vinyl‐type polymerization of norbornene as well as random copolymerization of norbornene with styrene was studied using a series of copper complexes‐MAO. The precatalysts used here are copper complexes with β‐ketoamine ligands based on pyrazolone derivatives and the molecular structure of complex 4 was determined using X‐ray analysis. All of these catalyst systems are moderately active for the vinyl‐type polymerization of norbornene and random copolymerization of norbornene with styrene. The random copolymers obtained suggest that only one type of active species is present. Gel permeation chromatography (GPC) and NMR indicate that the copolymers are ‘true’ copolymers. The copolymerization reactivity ratios (r_NBE = 20.11 and r_Sty = 0.035) indicate a much higher reactivity of norbornene, which suggests a coordination polymerization mechanism. The solubility and processability of the copolymers are improved relative to polynorbornene and the thermostability of the copolymers is improved relative to polystyrene. Copyright © 2006 John Wiley & Sons, Ltd.     

Ethylene/1,3-Cyclohexadiene Copolymerization by Means of Methylaluminoxane Activated Half-Sandwich Complexes

Ethylene copolymerization with 1,3-cyclohexadiene (CHD) was investigated by using methylaluminoxane (MAO) activated single-site catalysts including bridged and non-bridged titanium half-sandwich and bimetallic cobalt(I) complexes. MAO activated CpTiCl₂[NP(^tBu)₃] (Cp = cyclopentadienyl, ^tBu = tert-butyl) gave high molecular weight CHD copolymers without encountering catalyst activity losses. According to the NMR microstructure investigation the resulting copolymers are highly regioregular.     

Targeted synthesis of homo-and copolymers of propylene in liquid propylene initiated by highly efficient homogenous metallocene catalysts

Studies devoted to the homo-and copolymerization of propylene with ethylene and higher olefins (1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene) in liquid propylene under the action of homogeneous metallocene catalysts of various types are surveyed in brief. The main kinetic features of the processes and the properties of the polymers are discussed. The optimal conditions for the highly efficient syntheses of isotactic, syndiotactic, hemiisotactic, and stereoblock PPs are described. It is shown that the combined cocatalyst—polymethylaluminoxane coupled with (i-Bu)₃Al—shows promise for the processes under consideration. Depending on the type of catalyst used, the copolymerization of propylene with ethylene yields copolymers with a block, random, or close to alternating distribution of comonomer units in a polymer chain. The copolymerization of propylene with higher olefins in the monomer bulk initiated by highly active sterically hindered isospecific catalytic systems shows an ideal character, and the reactivity ratios are r ₁ ≈ r ₂ ≈ 1; that is, the composition of the copolymer is equal to the composition of the monomer mixture at all comonomer ratios. It is demonstrated that the synthesis of homo-and copolymers of propylene in the monomer bulk in the presence of modern homogeneous catalysts is promising for highly efficient production of both traditional and new polymer materials with a unique combination of mechanical and thermal properties.     

From atactic to isotactic CO/p-methylstyrene copolymer by proper modification of Pd(II) catalysts bearing achiral alpha-diimines

Cationic Pd(II) complexes modified with achiral C(2v)-symmetric alpha-diimine ligands allow preparation of atactic or isotactic stereoblock CO/p-methylstyrene copolymers; both catalyst activity and polyketone microstructure depend on the choice of alpha-diimine substituents and counterion.     

Fluorocyclopropanes. IV. Copolymers of perfluorocyclopropene

Perfluorocyclopropene undergoes free-radical copolymerization with ethylene, isobutylene, cis- and trans-2-butene, vinyl acetate, methyl vinyl ether, vinyl chloride, styrene, acrylonitrile, tetrafluoroethylene, vinyl fluoride, and vinylidene fluoride. The copolymerization proceeds most readily with electron-rich olefins such as methyl vinyl ether (to yield a 1:1 copolymer), but conditions were found to give copolymers with electron-deficient olefins such as tetrafluoroethylene and vinylidene fluoride. Copolymers with methyl vinyl ether, tetrafluoroethylene, vinyl fluoride, and vinylidene fluoride were examined in detail. Evidence is presented that the perfluorocycloproply ring is incorporated intact into the copolymer and can be subsequently isomerized to a perfluoropropenyl unit by heating at 200–300°C.     

Isospecific homo- and copolymerization of styrene with ethylene in the presence of VCl3, AlCl3 as catalyst

The homopolymerization of styrene and its copolymerization with ethylene in the presence of a vanadium-based supported catalyst, {VCI₃, 1 AICI₃}, associated to triethylaluminium is examined. As indicated by means of ¹³C nuclear magnetic resoance and differential scanning calorimetry analysis, the homopolystyrenes obtained present a highly isotactic microstructure and are semicrystalline (melting temperature 220°C). In the case of styrene/ethylene random copolymerization, the formation of both, polyethylene blocks and isotactic polystyrene sequences was identified by analysis of the crude polymer. Solubility characteristics and structural characteristics from nuclear magnetic resonance spectra of these products support the formation of copolymers with ethylene and isotactic styrene blocks rather than that of two distinct homopolymers.     

Synthesis and Mechanical Properties of Polypropylene-based Polymer Hybrids via Controlled Radical Polymerization

Isotactic polypropylene-based graft copolymers linking poly(methyl methacrylate), poly(n-butyl acrylate) and polystyrene were successfully synthesized by a controlled radical polymerization with isotactic polypropylene (iPP) macroinitiator. The hydroxylated iPP, prepared by propylene/10-undecen-1-ol copolymerization with a metallocene/methyl-aluminoxane/triisobutylaluminum catalyst system, was treated with 2-bromoisobutyryl bromide to produce a Br-group containing iPP (PP-g-Br). The resulting PP-g-Br could initiate controlled radical polymerization of methyl methacrylate, n-butyl acrylate and styrene by using a copper catalyst system, leading to a variety of iPP-based graft copolymers with a different content of the corresponding polar segment. These graft copolymers demonstrated unique mechanical properties dependent upon the kind and content of the grafted polar segment.     

Alternating copolymer of butadiene and propylene. III

Alternating copolymerizations of butadiene with propylene and other olefins were investigated by using VO(acac)₂–Et₃Al–Et₂AlCl system as catalyst. Butadiene–propylene copolymer with high degree of alternation was prepared with a monomer feed ratio (propylene/butadiene) of 4. Alternating copolymers of butadiene and other terminal olefins such as butene-1, pentene-1, dodecene-1, and octadiene-1,7 were also obtained. However, the butadiene–butene-2 copolymerization did not yield an alternating copolymer but a trans-1,4-polybutadiene.     

Ligand‐Dependent Diastereoselectivity in the Palladium‐Catalyzed Copolymerization of Styrene with Carbon Monoxide

[(LL′)Pd(H₂O)](OTf)₂ complexes, in which LL′ is a chelate ligand containing the chiral 4‐benzyl‐4,5‐dihydrooxazole moiety and either pyridin‐2‐yl or 2‐(diphenylphosphino)phenyl substituents, catalyze the copolymerization of styrene with carbon monoxide with an isotactic or prevailingly syndiotactic microstructure, respectively. The chiroptical properties of the copolymers and model studies for carbon monoxide and olefin insertion on related Pd complexes suggest that the reason for the different stereochemistry of the copolymers is a site‐selective coordination of the olefin in the intermediates containing the PN ligand; a lower regioselectivity in the coordination and a different coordination site lead to the different diastereoselectivity for the copolymer formation by the complex containing the NN′‐ligand.     

The Control of the Stereochemistry in the Palladium‐Catalyzed Alternating Styrene/Carbon Monoxide Copolymerization: Effect of the Chirality of the Ligand and of the Ligand‐to‐Palladium Ratio,Preliminary Communication

Diaquapalladium(2+) trifluoromethanesulfonates modified with (4R,4′S)‐ or (4S,4′S)‐2,2′‐bis(4‐benzyl‐4,5‐dihydrooxazole) (C_s‐ and C₂‐ligands) produce isotactic poly(1‐oxo‐2‐phenylpropane‐1,3‐diyl) through copolymerization of styrene with carbon monoxide. However, the same meso‐catalyst in the presence of the free ligand leads to prevailingly syndiotactic growth of the copolymer, whereas the optically active catalyst, when used in the presence of the free enantiomeric ligand, gives an atactic copolymer.     

Fluorinated and ring‐substituted bisbenzimidazole copper complexes for ethylene/acrylate copolymerization

Bisbenzimidazole copper dichloride complexes (CuBBIMs), when activated with methylaluminoxane, catalyze the random copolymerization of ethylene with acrylates to produce highly linear functional copolymers. To probe the sensitivity of the copolymerization to the catalyst structure, a series of CuBBIM catalysts with various steric, electronic, and geometric ligand characteristics was prepared, including CuBBIMs having benzimidazole ring substituents and ligand backbones of various lengths. Four different acrylates were also evaluated as comonomers (t‐butyl acrylate, methyl acrylate, t‐butyl methacrylate, and methyl methacrylate). Although no obvious ligand‐based influences on copolymerization were identified, the structure of the acrylate comonomer was found to exert significant effects. Copolymers prepared with t‐butyl methacrylate comonomer exhibited the highest ethylene contents (31–63%), whereas those prepared with methyl acrylate contained only minor amounts of ethylene (<15%). Copolymerizations carried out at lowered acrylate feed levels generally had increased ethylene contents but showed smaller yields, lowered molecular weights, and increased branching. Unusual ketoester structures were also observed in the methyl acrylate and methyl methacrylate containing copolymers, suggesting that the acrylate ester group size may be an important controlling factor for copolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1817–1840, 2006