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Ethylene incorporation

Bond separation reactions and heats of formation obtained from bond separation energies suffer from two serious problems. The first is that bond types in reactants and products for some types of processes may not actually be the same or even similar . The bond separation reaction for benzene is an obvious example. Here to reactant (benzene) incorporates six equivalent aromatic carbon-carbon bonds, midway between single and double bonds, while the products (three ethanes and three ethylenes) incorporate three distinct carbon-carbon single bonds and three distinct carbon-carbon double bonds. [Pg.386]

Conventional processes for preparing COCs have some common problems. The conversion of the cycloolefin may be low and further, a high amount of ethylene incorporated results in unsatisfactory low glass transition temperatures. Catalyst compositions have been developed in order to obtain materials with high glass transition temperatures (26). Examples are shown in Table 2.3. These catalysts are used for the copolymerization of ethene and norbornene. [Pg.47]

The effect of electrons in the unsaturation in the ultimate and penultimate monomer groups on the ionicity of the catalysts has been shown by Wilke (133). His work shows that, when the catalyst contains triphenylphosphine, the added increasing nucleophilic effect of the double bonds converts the catalyst to an ethylene incorporating specie. After incorporation of the ethylene, cyclization and reduction of the metal occurs to produce cyclodecadiene and cydohexene. This effect is analogous to that shown earlier (88) of a diene system complexing with the catalyst modifying the ionicity to favor ethylene incorporation. [Pg.388]

Ethylene receptors and regulatory control. The mode of action of ethylene at the molecular level is unknown. Some attempts, however, have been made to determine the receptor sites for ethylene (54) as well as their characteristics (55). There appears to be very little incorporation of ethylene applied to tissues (only about 0.05%). The - - C ethylene incorporated into pea seedling tissues which responded physiologically to the gas was metabolized to C02 and water-soluble metabolites (55). Metabolism of the incorporated ethylene by pea seedlings and other tissues was inhibited by high levels of CO2 (7-10%) and Ag+ ions (10-500 ppm) (56). Ag+ ions prevented the incorporation of ethylene into water-soluble tissue metabolites and... [Pg.125]

The main drawback of propylene/ethylene co-polymerization with metallocenes is the frequent strong decrease of molecular mass at increasing ethylene incorporation. The available mechanistic explanation is a fast chain transfer to ethylene after a propylene insertion (Scheme 30), and has been reported for metallocenes of different symmetries C2 v-symmetric, (/ -symmetric, and fluxional bis(2-arylindenyl). This phenomenon has strongly limited the... [Pg.1073]

The incorporation efficiency of Phillips catalysts can vary widely, depending on catalyst preparation and manufacturing variables. Some catalyst comparisons are listed in Table 9. Because incorporation selectivity is first order in reactant concentration, one obtains a straight line by plotting the molar ratio of 1-hexene to ethylene incorporated in the polymer against the molar ratio of 1-hexene to ethylene concentration in the reactor. The slope of this line is the incorporation efficiency (a higher slope indicates greater efficiency). Table 9 is a list of some incorporation efficiencies obtained with 1-hexene as the comonomer under the specified conditions. In no case is the slope near unity, which would indicate equal reactivity of the two monomers. [Pg.210]

MS insertion. The values of ij x T2 are less than but near to unity in both temperatures, which suggests the nearly ideal random copolymerization reactions and very small probability to find two adjacent p-MS units in the polymer chain. In other words, the p-MS units shall be homogeneously distributed in the polymer chain. In catalyst II cases, the copolymerization reactions exhibit even higher rj (rj > 60), very strongly favorable for ethylene incorporation, and almost no possibility of p-MS consecutive insertion (r2 0). The less opened active site in Et(Ind)2ZrCl2 catalyst may sterically prohibit p-MS consecutive insertion. [Pg.171]

Table VIII. MODIFIED FISCHER TROPSCH REACTIONS Ethylene Incorporation... Table VIII. MODIFIED FISCHER TROPSCH REACTIONS Ethylene Incorporation...
Ethylene is mostly used in emulsion copolymerization with vinyl chloride and vinyl acetate to act as an efficient internal plasticizer in the polymers. Ethylene exerts about 50 atm pressure at 7 °C and requires reactors capable of withstanding 1000 atm pressure at a polymerization temperature of 50 °C. The first report of emulsion copolymerization of ethylene with vinyl chloride goes back about 50 years [16]. Some years later it was shown that the copolymer Tg could be lowered to about —20 C with about 30% ethylene incorporation [17]. [Pg.118]

Fig. 8 (a) Analysis of a PE resin of low molar mass and a PP resin of high molar mass in a GPC-IR instrument dashed lines) and a 50/50 blend of both resins, showing the total C-H concentration gray solid line) and the C-H centered at CH3 absorption solid line). The dotted solid line corresponds to the ratio of methyls to total concentration, calibrated in percentage ethylene incorporation C2%). (b) Analysis by GPC-IR of three different EP copolymers EPl, EP2, and EPS) having similar MMD but completely different ethylene incorporation along the molar mass (M)... [Pg.215]

In the case of polypropylene homo and copolymer resins, besides the CCD, which is related to the ethylene incorporation, there is an additional feature, the tacticity, which very often is meastmed combined with the CCD. In all cases, low tacticity or the incorporation of comonomers result in reduced crystallinity therefore, it is understandable that most popular techniques for the measurement of the CCD are based on the crystallizability of the polymer. [Pg.218]

The TREF-GPC analysis can be performed with an additional composition sensor (CH3 sensor), as discussed in previous sections. This is especially important for ethylene propylene copolymers or blends since crystallizability is influenced in the case of PP by both tacticity and ethylene incorporation, as discussed for Fig. 4. The composition sensor provides a means to assign the crystallization temperature to one or the other polymer. The analysis of a high impact PP containing a significant amount of PE homopolymer is shown in Fig. 40. A small peak eluted before the iPP is clearly associated with PE by having a significantly lower methyl content than the overall concentration response. The PE peak is eluted on the tail of the iPP where other EP species are also eluted (as discussed with Fig. 19) and the molar mass of the PE peak could be differentiated from the polypropylene part. [Pg.244]

A comparison of the emulsion and miniemulsion processes used to copolymerize ethylene with vinyl acetate [78] showed that, for batch processes, the extent of ethylene incorporation into the copolymer was greater for miniemulsions... [Pg.458]

Catalysts such as 56 also lead to alternating isotactic ethylene—propylene copol5uners through a similar mechanism (198), since conditions can he arranged such that ethylene incorporates predominantly on the more hindered catalyst side. Other Monomers. [Pg.4596]

Lomonte and Tirpak [1 ] have developed a method for the determination of the percentage of ethylene incorporated in ethylene-propylene block copolymers. Standardisation is done from mixtures of the homopolymers. Both standards and samples are scanned at 180 °C in a spring-loaded demountable cell. The standardisation is confirmed by the analysis of copolymers of known ethylene content prepared with " C-labelled ethylene. By comparison of the infrared results from the analyses performed at 180 °C and also at room temperature, the presence of the ethylene homopolymer can be detected. These workers derived an equation for the quantitative estimation of the percentage of ethylene present as copolymer blocks. [Pg.72]

A series of ethylene-propylene block copolymers prepared with " C-labelled ethylene was analysed for percentage of ethylene incorporation by radiochemical methods. These samples when scanned at 180 °C gave results that agreed with the radiochemical assay quite well. However, when the cooled samples were scanned, the results from the cold calibration were low in comparison with the known ethylene content. These data are shown in Table 3.1. [Pg.72]

A pair of samples were prepared in which the active sites on the growing propylene polymer were eliminated by hydrogen before addition of ethylene. Practically identical values for percentage of ethylene incorporation were calculated for both the hot and cold scans. These data are shown in Table 3.2. [Pg.73]

IR absorbance at 13.66 pm is sufficiently sensitive to the ethylene incorporation to determine the wt% ethylene within 0.1-0.2% at the 95% confidence level. From C-NMR data, it can be concluded that the propylene units occur in predominantly isotactic, heat-to-tail sequences, and that the ethylene units are incorporated as isolated units only. Thus, this structural prerequisite is needed for application of this method because it has not been tested on copolymers containing propylene configurational irregularities or ethylene sequences two units and longer. [Pg.121]

A series of ethylene-propylene block copolymers prepared with C-labelled ethylene was analysed for percentage of ethylene incorporation by radiochemical methods. [Pg.239]

The infrared absorbance at 732cm is sufficiently sensitive to the ethylene incorporation to determine the wt% ethylene to within 0.1 - 0.2 % at the 95% confidence level. [Pg.409]

As indicated in Table 6, the glass transition temperature (7 ) has notable effects on properties of adhesive emulsions. Varying the amount of ethylene incorporated into a copolymer has a direct relationship to the T the more ethylene, the lower the Tg. The glass transition temperature affects such properties as flexibility, water resistance, PVC adhesion, paper adhesion, and setting speed. The three emulsions in Table 6 are all protected with polyvinyl alcohol. The major difference among them is the ethylene content as illustrated by the Tg, It should be noted that water resistance and ease-of-cleanup are inversely related. [Pg.391]

In case of ionic surfactants, MCM-41 type of PMOs containing traws-l,2-bis(4-pyridyl)ethylene incorporated in the silica walls synthesized by TEOS and trans-l,2-bis[N-(trimethoxysilylpropyl)pyridiumyl]ethylene (t-BES) as silicon sources and CTABr surfactant are worth mentioning [64]. PMOs with a carbapalladacycle complex, TEOS, and CTAB have been also prepared by Corma et al. [65]. [Pg.96]


See other pages where Ethylene incorporation is mentioned: [Pg.205]    [Pg.21]    [Pg.1073]    [Pg.96]    [Pg.87]    [Pg.214]    [Pg.459]    [Pg.17]    [Pg.7666]    [Pg.195]    [Pg.128]    [Pg.829]   
See also in sourсe #XX -- [ Pg.173 ]

See also in sourсe #XX -- [ Pg.257 ]




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