Stereochemistry of copolymerization of optically active cyclohexylepoxyethane with carbon dioxide

The stereochemistry of alternating copolymerization of carbon dioxide with S-(+)-cyclohexylepoxyethane ( 1 ) using a diethylzinc/water system as catalyst was investigated. The optically active copolymer, poly[(oxycarbonyloxy)-1-cyclohexylethylene], was hydrolyzed and the epoxide was transformed into the form 1,2-bis(trimethylsilyloxy)-1-cyclohexylethane ( 2 ). From the determination of optical activity of this ether, it is concluded that the ring opening of 1 in the copolymerization takes place predominantly at the methylene-oxygen linkage.     

Stereochemistry of the copolymerization of carbon dioxide with optically active phenylepoxyethane

The stereochemistry of the copolymerization of optically active phenylepoxyethane ( 5 ) with carbon dioxide using a diethylzinc/water system as catalyst was investigated. The optically active copolymer, poly(oxycarbonyloxy-2-phenylethylene) ( 1 ), was hydrolyzed and the oxy-2-phenylethylene unit was isolated in the form of 1,2-bis(trimethylsilyloxy)-1-phenylethane ( 3 ). The determination of the optical activity of this ether led to the conclusion that the ring opening of 5 takes place predominantly at the methineoxygen linkage accompanying an inversion in the copolymerization. This fact is in sharp contrast with the stereochemistry of the copolymerization of carbon dioxide with 1,2-epoxypropane in which the ring opening takes place at the methylene-oxygen linkage.     

Stereochemistry of copolymerization of carbon dioxide with epoxycyclohexane

Copolymerization of carbon dioxide with 1.2-epoxycyclohexane (EPCH) and with 1.4-epoxycyclohexane was examined. 1.2-Epoxycyclohexane was copolymerized with carbon dioxide by the diethylzinc/water system, but 1.4-epoxycyclohexane was not polymerized by this catalyst. Determining the configuration of the EPCH unit in the EPCH/carbon dioxide copolymer by alkaline hydrolysis of the copolymer, it was found that the configuration at the carbon atom where ring opening of EPCH takes place was inverted during copolymerization.     

Ternary copolymerization of carbon dioxide with epoxybutanes

The ternary copolymerization of carbon dioxide with 1,2-epoxybutane and other epoxybutane isomers using the diethylzinc/water system as catalyst was carried out to investigate the relative reactivity between epoxides. cis-2,3-Epoxybutane was much more reactive than trans-2,3-epoxybutane in the copolymerization with carbon dioxide. The copolymer obtained from the reaction of carbon dioxide and cis-2,3-epoxybutane upon hydrolysis gave threo-2,3-butanediol, indicating the exclusive inversion of configuration in the ring-opening of the epoxide. In the formation of cyclic carbonate as a byproduct of the copolymerization, cis-2,3-epoxybutane and trans-2,3-epoxybutane exhibited a similar reactivity.     

Organozinc catalyst systems for the copolymerization of carbon dioxide with propylene oxide

A series of new catalytic systems: (C₂H₅)₂Zn/polyhydric phenols was prepared and their activity in the alternating copolymerization of carbon dioxide with propylene oxide (epoxypropane) was studied. On the basis of the results obtained, the structure of organozinc compounds formed in these systems and also in others described in the literature is proposed and discussed. It is shown that the presence of an internal coordinative bond in the catalyst molecule is responsible for its activity in copolymerization.     

Functional polycarbonate by copolymerization of carbon dioxide and epoxide: Synthesis and hydrolysis

Polycarbonates with pendant carbonate groups were synthesized by copolymerization of carbon dioxide and epoxides containing a carbonate substituent using the diethylzinc/water system as catalyst. The polycarbonates underwent acidic and basic hydrolysis to release slowly the compound attached as the pendant group via the carbonate linkage. Other hydrolysis products were glycerol and CO₂, but no oligomeric products were formed.     

Anionic polymerization of optically active oxiranes. Analysis of carbon NMR spectra

The optically active epoxides (2S,3S)- and (2R,3S)-3,4-epoxy-1,2-O-isopropylidene-1,2-diols 1 and 2 were synthesized and anionically polymerized with potassium tert-butoxide as initiator. Soluble poly- 1 's with low polydispersities (M _w/M _n = 1.2 – 1.3) and medium molecular weights (M _n = 2000–5000) were obtained. Poly- 2 was insoluble in common organic solvents but soluble in hot 2,2,2-trifluoroethanol. Main-chain peaks in the ¹³C NMR spectrum of poly- 1 were fully assigned using a combination of NMR pulse techniques. End-group peak assignments were made by controlling the type of initiation and by consideration of ¹³C NMR spin-lattice relaxation times.     

Alternating copolymerization of carbon dioxide and propylene oxide in the presence of organometallic catalysts

Carbon dioxide and propylene oxide (PO) were copolymerized using diethylzinc in addition with benzenedi- and triols, aliphatic diols and triols, and aminophenols as catalyst systems. A large amount of CO₂/PO alternating copolymer, {poly(propylene carbonate), poly(oxycarbonyloxypropylene), of high molecular weight was obtained using the homogeneous (C₂H₅)₂Zn/pyrogallol (2:1 by mole) system ( 1 ). The (C₂H₅)₂Zn/o-aminophenol system ( 2 ) (also homogeneous) appeared to be much less active in the copolymerization of CO₂ with PO than the former one. From the other studied systems, that appeared to be heterogeneous, (C₂H₅)₂Zn/resorcinol (1:1 by mole) was the most active one, but less active than the system 1 . Further, the copolymerization of CO₂ and PO was studied in the presence of the (C₂H₅)₂Zn/resorcinol (1:1 by mole) system at various temperatures and in reaction media of different basicity. On the basis of the obtained results of the copolymerization of CO₂ with PO and of measurements of the quantity of ethane evolved in the reactions between the catalytic systems' components, structures of several catalysts, particularly homogeneous ones, are suggested and some aspects of the copolymerization mechanism are discussed.     

Investigations on the catalytic systems diethylzinc/Di- and trihydroxybenzenes in the copolymerization of carbon dioxide with propylene oxide

Investigations on the reactions of diethylzinc ( 1 ) with resorcinol ( 2 ) and phloroglucinol ( 8 ) were carried out for different mole ratios of the reactants. It was found that the reaction of 1 with 2 at a mole ratio of 1:1 is a two step process. In the first step 1 reacts very rapidly with half of applied 2 yielding di(ethylzinc) resorcinolate ( 6 ), which then reacts slowly with the remaining amount of 2 . It was found that zinc 3-ethylzincoxyphenolate resorcinolate ( 5 ) formed in the second step is an active catalyst of the copolymerization reaction of carbon dioxide with propylene oxide. The reaction of 1 with 8 shows a similar course.     

Polymerization of 1,2-epoxypropane and 1,2-epoxycyclohexane by diethylzinc-polyhydric phenol and/or phenol or 1-phenoxy-2-propanol as catalysts

1,2-Epoxypropane and 1,2-epoxycyclohexane were polymerized in the presence of catalysts derived from reactions of diethylzinc with a polyhydric phenol (4-tert-butylcatechol, pyrogallol) and/or phenol or 1-phenoxy-2-propanol in 1,4-dioxane solution, varying the polymerization temperature and time. The polymers formed in these polymerizations were analysed by means of ¹H NMR, ¹³C NMR and UV spectroscopy in terms of the polymer chain microstructure and chain end-groups. The poly(propylene oxide) (PPO) obtained appeared to be a high-molecular-weight polymer with prevailing isotactic diads (mole fraction in the range of 0,65–0,72). It was found to consist of a predominant amorphous (atactic) fraction and a crystalline (isotactic) fraction. An enhancement of both the crystallinity and the average molecular weight of PPO was observed with an elongation of the duration of the polymerization. Therefore, it was concluded that the catalyst enantioselectivity increases with progressing polymerization. The poly(cyclohexene oxide) (PCHO) obtained appeared to be a polymer with prevailing syndiotactic diads (mole fraction in the range of ca. 0,58–0,80) and threo-enchainement of monomeric units. This was explained in terms of inversion of the configuration at the carbon atom of the epoxide ring upon cleavage. A possible mechanism for the epoxide polymerization by the coordination catalysts studied is presented.     

Nonlinear optically active polymethacrylates with high glass transition temperatures

A number of novel nonlinear optically (NLO) active polymethacrylates were prepared from the NLO active methacrylates 2a–d with azobenzene side groups and the bulky comonomer 1-adamantyl methacrylate. The polymers exhibit unusually high glass transition temperatures between 160°C and 190°C. The copolymerization parameters of the monomer pair 1-adamantyl methacrylate (1) /Disperse red methacrylate 2b (r₁ = 1,1 ± 0,2, r₂ = 0,8 ± 0,2) show that the two monomers are incorporated almost statistically into the polymer chain. Polymers 3a–d are soluble in common organic solvents and excellent films can be obtained by spin coating. After poling in an electric field of 120 V/μm polymer 3b shows a large electrooptic (EO) coefficient (r₃₃) of 25 pm/V at 633 nm. Within two weeks, only a negligible decay of 7% of the EO coefficient was observed at room temperature. On-line monitoring of the second harmonic generation (SHG) at 100°C showed a fast initial drop (10%) of the SHG signal and subsequently a slow decay of 20% within 10 h. Afterwards, the signal remained almost constant for further 5 h at 100°C. The novel polymers can thus be considered as easy processible NLO materials with a high thermal stability of the chromophore orientation obtained by poling.     

Initiation and propagation reactions in the copolymerization of epoxide with carbon dioxide by catalysts based on diethylzinc and polyhydric phenol

Propylene oxide and cyclohexene oxide were copolymerized with carbon dioxide in the presence of catalysts such as diethylzinc with phenol or 1-phenoxy-2-propanol and/or a polyhydric phenol (polyhydroxybenzene derivatives such as 4-tert-butylcatechol, pyrogallol): The corresponding copolymers with predominant carbonate linkages and the respective cyclic alkylene carbonates as by-products were obtained in the presence of catalysts derived from diethylzinc and polyhydric phenol. Cyclic alkylene carbonates but no polymeric products were formed in the presence of catalysts derived from diethylzinc and monoprotic compound. The copolymers were analysed by means of ¹H- and ¹³C nuclear magnetic resonance (NMR) spectroscopy in terms of chain microstructure and end groups. Alkaline hydrolysis of the cyclohexene oxide/carbon dioxide copolymer was performed and the trans-structure of the obtained cyclohexane-1,2-diol was determined. Mechanisms for the initiation and propagation reactions are proposed and discussed.     

Alternating copolymerization of cyclohexene oxide and sulfur dioxide

Copolymerization of cyclohexene oxide (CHO) and sulfur dioxide (SO₂) was conducted at 80°C by using a variety of catalysts both in the presence and absence of solvent. Aromatic tertiary amines such as pyridine gave an alternating copolymer of CHO and SO₂ in the presence of solvents such as 1,2-dimethoxyethane. The alternating copolymer obtained was a white thermoplastic which could readily be thermoformed. It was soluble in acetone and chloroform but insoluble in water and hexane. From the reaction of the equimolar mixture of CHO, SO₂ and pyridine at 20°C, an 1 : 1 : 1 adduct of CHO, SO₂ and pyridine (see formula 2 ) could be isolated. This adduct was confirmed to be the active species for the present copolymerization.     

Reactivity of vinyl monomers in the copolymerization and terpolymerization with sulfur dioxide

The relative reactivities of vinyl monomers in low-temperature copolymerizations and terpolymerizations with SO₂ in the presence of tert-butyl hydroperoxide as initiator were compared. The highest copolymerization rates were found in systems containing an electron-donor monomer of low resonance stabilization, and the resulting products have an alternating structure. In reactions with monomers of high resonance stabilization and electron-acceptor properties, mainly homopropagation of the comonomer proceeds. In the terpolymerization of SO₂ with two electron-donor monomers, the relative reactivity of monomers depends mainly on their resonance stabilization. In the terpolymerization in systems SO₂/electron-donor monomer/electron-acceptor monomer the relative reactivity of acceptor monomers decreases with increasing inductive effect in the molecule.     

(5,10,15,20-Tetraphenylporphyrinato)manganese acetate as a novel initiator for the ring-opening polymerization of 1,2-epoxypropane

(5,10,15,20-Tetraphenylporphyrinat o)manganese acetate (2) was found to bring about the ring-opening polymerization of 1,2-epoxypropane (3) (R² = CH₃) under mild conditions to give the polymer with a bimodal molecular weight distribution consisting of a sharp main peak and a small shoulder on the higher molecular weight side. The polymerization was found to proceed even in the presence of a protic compound such as an alcohol or a carboxylic acid to give the polymer with a unimodal very narrow molecular weight distribution. The number of the polymer molecules is in good agreement with the sum of those of 2 and the protic compound, demonstrating the “immortal” nature of polymerization.     

On the mechanism of the carbon dioxide/propylene oxide alternating copolymerization in the presence of organozinc catalysts

Carbon dioxide and propylene oxide were copolymerized in the presence of the catalytic systems diethylzinc/polyhydric phenols modified by pretreatment with one of the monomers. The mechanisms of initiation, propagation, termination, and chain-transfer reaction in the copolymerization are suggested and discussed.     

Regio- and stereo-selective alternating copolymerization of carbon monoxide with propene

Compounds of palladium with ten different chelated bisphosphine ligands were investigated for their catalysis of alternating copolymerization of propene with carbon monoxide. The bisphosphine structure and chelate ring size influence strongly the activity, regio- and stereo-selectivity of the catalysts. Molecular mechanics calculations on the π-olefin complex showed that the non-bonded interaction between propene and the ligands on Pd is both regio- and stereo-selective. Primary insertion is about seven times more probable than secondary insertion for the Pd complex of bis(diphenylphosphino)butane ligand. The enantioselective catalysts favor the meso enchainment of propene. Gas chromatography/mass spectrometry (GC-MS) of oligomers showed that most chains are initiated by Pd? H species with less frequent initiation by Pd? OCH₃ complexes; β-hydrogen elimination is the dominant chain termination process.     

Transesterification of poly(methyl acrylate) with optically active alcohols

Transesterifications of atactic and isotactic poly(methyl acrylate) with optically active alcohols such as (S)-2-methyl-butanol, D-borneol and L-menthol were carried out in toluene at 100°C using p-toluenesulfonic acid as catalyst to obtain optically active polymers. In addition a relationship between the conformation and the optical behaviour of the transesterified poly(methyl acrylate) was investigated. The specific rotation of the transesterified atactic poly(methyl acrylate) increased linearly with increasing introduced optically active groups at the lateral chain, in contrast to that of the isotactic poly(methyl acrylate) which increased nonlinearly with increasing introduced asymmetric groups. Since the specific rotations of the transesterified polymers depend on these tacticities the conclusion was drawn that the optical activity is caused not only by the asymmetric group in the lateral chain but also by molecular dissymmetry in the principal chain.     

Group-transfer alternating copolymerization of 2-phenyl-1,3,2-dioxaphosphorinane with trimethylsilyl 2-(acryloyloxy)ethanesulfonate

This paper describes a new class of reaction, group-transfer alternating copolymerization (GTAC), between 2-phenyl-1,3,2-dioxaphosphorinane ( 1 ) and trimethylsilyl 2-(acryloyloxy)ethanesulfonate ( 2 ). The copolymerization took place without any added catalyst and proceeded via quantitative trimethylsilyl group-transfer process to give a 1:1 alternating copolymer 3a having a ketene silyl acetal group in the main chain. Results of spectroscopy as well as alkaline hydrolysis and bromination of the copolymer confirmed the structure.