Functional monomers and polymers, 44. A modified way to form the deoxycholic acid/2,3-dimethyl-1,3-butadiene canal complex and its polymerization

Deoxycholic acid/2,3-dimethyl-1,3-butadiene canal complex was found to be prepared readily by replacing various sorts of guest molecules in the deoxycholic acid canals by 2,3-dimethyl-1,3-butadiene monomer. Post-irradiative polymerization of the monomer included in deoxycholic acid canals was studied after irradiating with γ-rays from a ⁶⁰Co source. Both the replacement and the polymerization processes were observed by differential thermal analysis (DTA), thermogravimetry (TG), and IR spectroscopy. The optimum conditions for the replacement of acetone, ethyl acetate, and acetic acid by 2,3- dimethyl-1,3-butadiene were established.     

Kinetices of polymerization of 1-octene with the catalyst system VOCl3-AlEt3 (or AlEt2Br)

Kinetic studies of the polymerization of 1-octene with the Ziegler-Natta catalyst systems VOCl₃—AlEt₃ (I) and VOCl₃—AlEt₂Br (II) are reported. The effect of the various parameters such as the Al/V ratio, catalyst and monomer concentrations, reaction time, aging time and temperature on rate of reaction and molecular weight of polymer were studied. Each of these parameters has a profound effect on the polymer yield and the rate of the reaction for both systems. The rate of polymerization increases linearly with increasing temperature, catalyst and monomer concentrations. The reaction is first order with respect to both the monomer and the catalyst concentration in the two catalyst systems studied. From the Arrhenius plot the overall activation energy of polymerization for the two systems was found to be 51,2 and 43,5 kJ/mol, respectively. The mechanism of polymerization is discussed on the basis of the dependence of the polymerization rate on the alkylaluminium concentration.     

Ni(acac)2-DAD/MAO: A new catalytic system for ethylene polymerization

The halide-free combination of Ni(acac)₂ and DAD(diazadiene, ArNCH CHNAr, where Ar = 2,6-C₆H₃(i-Pr)₂) is active for ethylene polymerization in the presence of methylaluminoxane (MAO). The performance of this new catalytic system was evaluated with respect to activity and polymer structure. The degree of branching of the obtained polyethylenes is substantially influenced by the polymerization conditions. The activation mechanism was investigated by ¹H NMR. MAO is proposed to participate in the ligand exchange process.     

Ethylene/propene copolymerization in the presence of the homogeneous catalyst system Ti(Oi-C3H7)4/Al(C2H5)2F

The behaviour of the homogeneous catalyst system Ti(Oi-C₃H₇)₄/Al(C₂H₅)₂F in ethylene/propene copolymerization was studied. The copolymer structure is discussed in view of the stereoregulation mechanism previously proposed for vanadium-based homogeneous catalyst systems.     

The initiation mechanism of polymerization by the system AlEt3/H2O

The reaction between H₂O and triethylaluminum Al(Et₃) as well as the initiation mechanism of the polymerization by the system AlEt₃/H₂O have been examined by means of tritiated water, Considerable amount of tritium from tritiated water remained in the system AlEt₃/H₂O prepared at room temperature. Heat treatment of the system causes both the extensive decrease of tritium content and loss of catalyst activity. Polymers of styrene and isobutyl vinyl ether prepared by the system AlEt₃/H₂O were found to be radioactive. These findings have been taken to assume that acid hydrogen does exist in the system AlEt₃/H₂O and is directly responsible for the initiation of cationic polymerization.     

Kinetics of polymerization of 1,3-dioxepane with the Al(C2H5)3/H2O catalyst system

The kinetics of the polymerization of 1,3-dioxepane (DH) with the catalytic system Al(C₂H₅)₃/H₂O was studied. The dependence of the polymerization rate R₀ of the monomer DH(M) may be represented by the equation: The kinetic scheme which verifies the obtained results is that which takes into consideration in the starting period of the polymerization the existence of chain transfer to the monomer. The decrease of the polymerization rate and the diminishing of the intrinsic viscosity at high conversions points to the existence of chain transfer to the polymer in this stage of the reaction. The reaction rate constants of the chain transfer to the monomer are one order of magnitude higher than those of the transfer reaction to the polymer.     

Specific effect of antimony(V) containing initiators on the cationic copolymerization of 1,3-dioxolane with 5-methyl-2,3-dihydro-2-furanone

The copolymerization of 1,3-dioxolane ( 1 ) with 5-methyl-2,3-dihydro-2-furanone ( 2 ) was carried out in dichloromethane and nitrobenzene by use of triethyloxonium hexachloroantimonate, triethyloxonium hexafluoroantimonate, antimony pentachloride, antimony trichloride, and tin tetrachloride as initiators. The microstructures of the copolymers were analysed by means of ¹H-NMR, showing that monomer 2 was incorporated into the copolymer chain by the ring-opening reaction as well as by the ?normal”? vinyl addition, when triethyloxonium hexachloroantimonate, triethyloxonium hexafluoroantimonate, and antimony pentachloride were used. On the basis of NMR and IR studies on the complexation of Lewis acids with γ-lactones, it was concluded that the prominent effect of the initiators observed in the copolymerization of 1 with 2 was mainly attributable to the coordination between the initiator and the γ-lactone ring of monomer 2 .     

The synthetic non-toxic drug 2,3-dimethyl-6(2-dimethylaminoethyl)-6H-indolo-(2,3-b)quinoxaline inhibits neutrophil production of reactive oxygen species.

The effects of the non-toxic drug 2,3-dimethyl-6(2-dimethylaminoethyl)-6H-indolo-(2,3-b)quinoxaline (B220) on the generation of reactive oxygen species froin human neutrophils were investigated. The data show that B220 inhibits neutrophil release of reactive oxygen species, as well as intracellular generation of reactive oxygen species. The inhibition is not achieved through direct oxygen radical scavenger activity of B220, and the drug has no immediate effects on the activity of the assembled oxidase. Radical production and release were inhibited by all agonists tested [i.e. the protein kinase C-activating phorbol ester phobol myristate acetate; the receptor-specific agonist N-formyl-methionyl-leucyl-phenylalanine (fMLP); and serum-opsonized yeast particles] in the presence of B220. The drug also inhibits phagocytosis and fMLP-induced mobilization of granules. However, based on the fact that the effects of B220 on phagocytosis and granule mobilization are much less significant than its effect on radical production, we suggest that the signal(s) affected by B220 is (are) located mainly downstream of the point at which the signals are generated to promote oxidase activation and phagocytosis or granule secretion, respectively.     

Effect of solvents and initiators on the cationic copolymerization of 1,3-dioxolane with 5-methyl-2,3-dihydro-2-furanone

The cationic copolymerization of 1,3-dioxolane ( 1 ) with 5-methyl-2,3-dihydro-2-furanone ( 2 ) which has two functional groups, a carbon-carbon double bond and a lactone ring, was carried out with three triethyloxonium salts (Et₃O⁺Y^?, Y^?: BF, FeCl and SbCl), with the boron trifluoride ethyl ether complex, and with tin tetrachloride in nitrobenzene, dichloromethane, and toluene at 0°C. On the basis of the NMR analysis of the microstructure of the copolymer, it was revealed that the growing species of 1 attacked exclusively the carbon-carbon double bond of 2 in the cross-propagation from 1 to 2 , regardless of the solvents and initiators used, except when triethyloxonium hexachloroantimonate was used as initiator. With the latter initiator, the ring opening reaction of 2 by the attack of the growing species of 1 occurred competitively with the usual vinyl addition, although the latter mode of reaction was predominant. The ring opening reaction of 2 with this initiator is probably caused by some specific interaction of monomer 2 with the counter anion.     

Synthesis and characterization of copolymers of ethylene and 1-octadecene using the rac-Et(Ind)2ZrCl2/MAO catalyst system

The copolymerization of ethylene and 1-octadecene using a bridged metallocene was studied in order to observe the effect of the comonomer on the catalytic activity. A noticeable increase in activity is seen as the concentration of 1-octadecene in the reaction medium increases. ¹³C NMR analysis shows 6.4 mol-% incorporation of comonomer at the highest 1-octadecene concentration in the feed used here. The molecular weight of the copolymers shows a drastic decrease that may be attributed to chain termination by transfer or β-elimination of the comonomer. As to the molecular weight distribution, it remains within a narrow range, as expected with metallocene catalysts. The melting temperature and the enthalpy of melting of the copolymers show a decrease with increasing comonomer content. As usual for ethylene copolymers, the X-ray crystallinities are higher than those determined from the enthalpy of melting.     

Alternating copolymerization of butadiene and propene with the catalyst VO(ONeo)2 Cl/Al(i-C4H9)3, 1

The influence of basic reaction parameters—the ratio of catalyst components, the composition of the monomer mixture and the temperature—on the progress of the copolymerization, the molecular weight and the molecular weight distribution as well as on the composition of the copolymers obtained is reported. Conversion data for the variation of the mole ratio of comonomers show a maximum for an [Al]/[V] mole ratio of approximately 7, whereas the molecular weight of copolymers is not significantly influenced. An increase in the molecular weight of the copolymers can be obtained by an increase of butadiene content in the monomer mixture. However, there is also an increasing incorporation of butadiene into the copolymer. Raising the temperature from ?60°C to 0°C results in a significant decrease in molecular weight, whereas the composition of the copolymers is not significantly changed.     

The influence of the comonomer in the copolymerization of ethylene with α-olefins using C2H4[ind]2ZrCl2/methylaluminoxane as catalyst system

Copolymers based on ethylene with different incorporations of 1-hexene, 1-octene and 1-decene were obtained. There is not any marked variation of activity when different metallocenes were tested. The type and the concentration of the comonomer in the feed do not have a strong influence on the catalytic activity of the system, but the presence of the comonomer increases the activity compared with that in the absence of it. From ¹³C NMR it was found that below 8% of comonomer incorporated the comonomer units appear isolated between polyethylene blocks, sequences of the type ethylene-comonomer-ethylene-comonomer appear only above 8% of comonomer incorporated for all the systems studied. The reactivity of the comonomers for this particular system shows that the size of the lateral chain influences the percentage of comonomer incorporated, 1-hexene being the highest one incorporated. The crystallinity of the copolymers exerts a linear relation with the amount of comonomer incorporated, and it is independent of lateral chain lengths. The molecular weight of the copolymers obtained was found to be dependent on the comonomer concentration in the feed, showing that there is a transfer reaction with the comonomer. The polydispersity (M̄_w/M̄_n) of the copolymers is rather narrow and dependent on the concentration of the comonomer incorporated.     

Cationic copolymerization of norbornadiene with styrene by AlEtCl2/tert-butyl chloride catalyst system, 1. Effect of norbornadiene/styrene feed ratio

The cationic copolymerization of norbornadiene (NBD) and styrene (St) was carried out with the AlEtCl₂/tert-butyl chloride catalyst system in CH₂Cl₂ at ?50°C, and the effect of NBD/St feed ratio on the solubility, the glass trtansition temperature (T_g) and the molecular weight of the copolymers was investigated. A soluble copolymer was prepared at 40 mol-% (or above) of St in the feed, although the NBD homopolymer comprised an insoluble fraction which might have been formed by a crosslinking reaction between the double bonds in the NBD units of the polymer. The copolymer has a statistically random sequence distribution of the two monomeric units not only in the polymer chain but also over the whole molecular weight range (from 10³ to 10⁶). The T_g of the amorphous copolymer is controlled by the NBD/St composition in the range from 100°C through 290°C. A soluble copolymer with highest T_g (ca. 170°C) could be prepared at a NBD/St feed ratio of 60/40 mol-%.     

TiCl4/MgH2-supported Ziegler-type catalyst system, 3. New findings on the concentration of active sites in ethylene/1-hexene copolymerization

The effect of 1-hexene on the rate constant of ethylene polymerization and on the number of active centres in the copolymerization of ethylene with 1-hexene is reported. Using three TiCl₄/MgH₂? Al(C₂H₅)₃ catalysts, of different Ti contents and surface area in the polymerization reveals that the addition of small amounts of the comonomer 1-hexene results in a two- to three-fold increase in the rate of ethylene consumption when a low-Ti-content catalyst is used. In contrast, no fundamental change in the catalytic activity was observed when a high-Ti-content catalyst is employed. The determination of the concentration of active centres C* by means of the ¹⁴CO radio-labelling technique, shows that C* in ethylene/1-hexene copolymerization is more or less the same as in ethylene homopolymerization.     

The cyclopentenone (A2/J2) isoprostanes--unique, highly reactive products of arachidonate peroxidation

Cyclopentenone (A2/J2) isoprostanes (IsoPs) are a group of prostaglandin (PG)-like compounds generated in vivo from the free radical-induced peroxidation of arachidonic acid. Unlike other classes of IsoPs, cyclopentenone IsoPs contain highly reactive unsaturated carbonyl moieties on the prostane ring analogous to cyclooxygenase-derived PGA2 and PGJ2 that readily adduct relevant biomolecules such as thiols via Michael addition. The purpose of this review is to summarize our knowledge of the A2/J2-IsoPs. As a starting point, we will briefly discuss the formation and biological properties of PGA2 and PGJ2. Next, we will review studies definitively showing that cyclopentenone IsoPs are formed in large amounts in vivo. This is in marked contrast to cyclopentenone PGs, for which little evidence exists that they are endogenously produced. Subsequently, we will discuss studies related to the chemical syntheses of the 15-A2-IsoP series of cyclopentenone IsoPs. The successful synthesis of these compounds provides the recent impetus to explore the metabolism and biological properties of A-ring IsoPs, particularly as modulators of inflammation, and this work will be discussed. Finally, the formation of cyclopentenone IsoP-like compounds from other fatty acids such as linolenic acid and docosahexaenoic acid will be detailed.     

TiCl4/MgH2-supported Ziegler-type catalyst system, 4. The influence of 14CO contact time and mole ratio Al(C2H5)3/Ti on concentration of active sites in ethylene homo- and copolymerization

The effect of varying ¹⁴CO contact time upon the concentration of active centres C* in ethylene homopolymerization using the TiCl₄/MgH₂ · Al(C₂H₅)₃ catalytic system shows that the polymer radioactivity, and hence C*, increase sharply in the first sixty minutes of ¹⁴CO contact with the polymerization centres. For contact times longer than one hour, the polymer radioactivity continues to increase, but very slowly. Studies on the effect of the mole ratio Al(C₂H₅)₃/Ti on ethylene homopolymerization show that both the catalytic activity and C* increase sharply when increasing the mole ratio Al(C₂H₅)₃/Ti in the range from 5 to 20. When increasing the mole ratio Al(C₂H₅)₃/Ti above 50, C* tends to decrease very slightly. In ethylene/1-hexene copolymerization a similar effect of the mole ratio Al(C₂H₅)₃/Ti on the polymerization is observed. However, even though the catalytic activity in copolymerization is observed to be higher than in homopolymerization, at the same mole ratio Al(C₂H₅)₃/Ti, yet C* in both cases is found to be more or less the same.     

Copolymerization of ethylene and propene with a TiCl4/MgCl2-Al(C2H5)3 catalyst system using a stopped-flow method

Copolymerization of ethylene with a small amount of propene was conducted with a TiCl₄/MgCl₂-Al(C₂H₅)₃ catalyst system using a stopped-flow method. With an increase in the polymerization time from 0,035 to 0,145 s, the copolymer yield increases linearly but the number-average molecular weight of the copolymer showed a tendency of saturation. The rate constants of the propagation reaction as well as the concentrations of active sites were estimated using these data. On the other hand, the ¹H NMR spectra of copolymer did not display the resonances due to C?C double bonds which should be formed by chain transfer with monomer and/or by β-hydrogen elimination. It was also found that the crystallinity of the copolymer decreases to a great extent upon incorporation of even a very small quantity of propylene units. From these results, it was concluded that the apparent rate of copolymerization is not controlled by monomer diffusion through the polymer films. Rather the transfer reaction with Al(C₂H₅)₃ might predominantly take place during the copolymerization.     

Synthesis of functional unsaturated polyesters using rare earth coordination catalysts, 3. Mechanistic aspects of maleic anhydride-epichlorohydrin copolymerization with Nd[(RO)2 PO2]3/Al[CH2CH(CH3)2]3 as a catalyst

Ring-opening alternating copolymerization of maleic anhydride and epichlorohydrin was carried out at 70°C with rare earth coordination catalysts composed of Nd[(RO)₂ PO₂]₃ (R = CH₃(CH₂)₃CH(C₂H₅)CH₂? )and trialkylaluminium. Anlaysis of end-groups showed that the copolymer chain contains one ? OH and one ? CH?CH? CO? CH₂CH(CH₃)₂ end-group. IR, UV-Vis, ¹H NMR and GPC results imply that a catalyst-maleic anhyride complex is formed in the initiation step that the ring-opening copolymerization proceeds via coordinate insertion mechanism accompanied with chain-transfer.     

Preliminary results on ethylene/propene copolymerization in the presence of Cp2Ti(CH3)2/Al(CH3)3/H2O

Ethylene/propene copolymerizations were carried out in the presence of the catalyst system Cp₂Ti(CH₃)₂/Al(CH₃)₃/H₂O (Cp = cyclopentadienyl group), and the reactivity ratios r₁, r₂ were determined through the Fineman and Ross equation and via ¹³C NMR. A nearly alternating copolymer structure was pointed out. The yields as well as the molecular weights of the copolymers strongly decrease with increasing propene mole fraction in the copolymers.     

Synthesis of linear poly(4-vinylbenzaldehyde) by means of anionic living polymerization of 1,3-dimethyl-2-(4-vinylphenyl)imidazolidine and subsequent hydrolysis

Poly(4-vinylbenzaldehyde)s ( 4 ) of known chain lengths and of narrow molecular weight distributions (M?_w/M?_n ≈ 1,1) were synthesized by means of anionic living polymerization of 1,3-dimethyl-2-(4-vinylphenyl)imidazolidine ( 1 ) with oligo[α-methylstyryl]potassium ( 2 ) and subsequent acid hydrolysis to remove the imidazolidine protective group. The living polymer of 1 can initiate further polymerization of α-methylstyrene, resulting in the preparation of a triblock copolymer of the type poly[α-methylstyrene-b-(4-vinylbenzaldehyde)-b-α-methylstyrene] in quantitative yield after hydrolysis.