Ethylene/propylene copolymers configuration

RIS theory is used to predict values of the optical-configuration parameter Aa for ethylene - propylene copolymers as a function of chemical composition, chemical sequence distribution, and stereochemical structure of the propylene sequences. The calculations are based on information available for ethylene and propylene homopolymers, and on the model used to interpret the unperturbed dimensions of these copolymers. Values of Aa are generally found to decrease significantly with increase in the fraction of propene units, but to be relatively insensitive to chemical sequence distribution and stereochemical structure. Geometries and conformational energies are the same as those used for the interpretation of the unperturbed dimensions of these chains. The conformational energies used are E(q) = 0, EM 2.09, and E a>) = 0.37 kJ mol-1. 

NOESY has also been used to elucidate the chain conformation of poly(styrene-a/ -MMA).220,221 2D INADEQUATE has been applied to studies of monomer sequence distribution in ethylene-propylene copolymer.223 Additivity rules for the 13C chemical shifts of ethylene-propylene copolymer were devised for configurational sequences as well as substituent effects.226... 

Both on-column and post-column detection schemes have been developed for radionuclide detection for CE. The most common type used is an on-column configuration, which yields detection limits in the 10 M range for isotopes such as P. Isotachophoretic separations of C were among the first examples of online capillary radionuclide detection, performed by Kaniansky et al. The associated instmment uses 300-p,m ID fluorinated ethylene-propylene copolymer capillary tubing, and the separation eluent flows directly into a plastic scintillator cell between two PMTs. The scintillation events are detected coincidentally between the two PMTs, such that only if both PMTs receive an input within a short time will they register the count as signal. This kind of coincidence detection ensures that nonscintillation photons that come from outside the detection cell and only hit one PMT are not counted. This system exhibits a detection limit of 16 Bq for analytes, with a detector efficiency of 13-15%. 

Since the same will happen in Reactor 2, in the end the ratio of polypropylene to ethylene-propylene copolymer per particle exiting Reactor 2 will also vary widely, which may be undesirable in some applications. Some of the reactor configurations shown in Figure 8.35 can reduce this phenomenon, particularly the configuration adopted for the gas-phase horizontal reactor, because the residence time distribution of this reactor is the equivalent to about three to four CSTRs in series. (Remember that the residence time of an infinite series of ideal CSTRs is that of a plug-flow reactor.) A more recent solution for this problem, in fact a completely new alternative to tandem reactor technology, is the multizone reactor that will be described in more detail below (see Section 8.6.4). 

Polypropylenes (PPs) are in the polyolefin family of plastics. They are semitranslucent and milky white in color, with excellent colorability. They are produced by a stereoselective catalyst that puts order in their molecular configuration so that the basic resin has a predominantly regular, uniform structure. This means that the molecules crystallize into compact bundles, which makes them stronger than other members of the polyolefin family. PPs are an extremely versatile plastic available in many grades as well as copolymers like ethylene propylene. Neat PP has a low density of 0.90, which, combined with its good balance of moderate cost, strength, and stiffness as well as excellent fatigue, chemical resistance, and thermal and electrical properties, makes PP extremely attractive for many indoor and outdoor applications. 

Catalysts which are isospecific for the polymerization of propylene, butene-1, etc., can also be used for the preparation of copolymers of these olefins with ethylene and with each other. There is much evidence to indicate that the chiral specificity of the catalyst is retained during these reactions [72-76], Thus, the spectra of ethylene(e)-propylene(P) copolymers prepared with an isospecific catalyst system are much simpler than those prepared with a nonspecific catalyst [75]. Studies on copolymers of propylene with c-enriched ethylene prepared with an isospecific catalyst indicate that the propylene-ethylene-propylene triads have a single type of configuration, which is probably meso. This is indicated by the fact that only two resonances are observed for ethylene units in P-E-P triads. Furthermore, there is no evidence for the presence of ethylene units flanked by two tertiary carbon atoms (due to inversions of propylene units) in the copolymers. In contrast, copolymers prepared from nonspecific or syndiospecific catalysts have been shown to contain ethylene units centered in both meso- and racemic- PEP... 

There is one additional group of polymers which is derived from this chemistry, the hydrogenated polydienes. Hydrogenated polyisoprenes [41] are chemically equivalent to an alternating copolymer of ethylene and propylene when polymerized in a 1,4 configuration and would thus be expected to exhibit behaviour which is very similar to that of OCPs. Similar characteristics can be achieved with polybutadiene... 

From the chemical point of view, POs are simple materials composed of C and H. However, the configuration diversity of even the simplest polymethylene results in a spectrum of properties. The situation becomes more complex for polymers of the general formula (C H2 )dp where n>3 and the degree of polymerization, DP, is large. The next level of complexity is encountered with blends and copolymers, e.g., poly(ethylene-co-n-olefin) or poly(propylene-co-n-olefin). However, today the ultimate challenge for characterization is found in POs obtained during multi-catalyst/multi-reactor/multi-monomer polymerization processes. 

More importantly, while it is very difficult to control the nature of the site t)rpes on conventional heterogeneous Ziegler-Natta catalysts, metallocene catalysts can be designed to synthesize PP with different chain microstructures. PP chains with atactic, isotactic, isotactic-stereoblock, atactic-stereoblock and hemiisotactic configurations can be produced with metallocene catalysts (Figure 2). It is also possible to s)mthesize PP chains that have optical activity by using only one of the enantiomeric forms of the catalyst. Additionally, copolymers of propylene, ethylene and higher a-olefins made with metallocene catalysts have random (or near random) comonomer incorporation and narrow chemical composition distributions (CCD). 

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. 

Absorption at 13.3 pm which is characteristic of methylene sequences of two units is characteristic of a tail-to-tail configuration of ethylene and propylene units. This absorption is also found in polybutene-2-ethylene copolymer ... 

The measurement of the dipole moments of copolymers and its analysis in terms of both sequence distribution and local chain configurations has received attention Modern computer aided analytical procedures provide in ght into the dependence of mean square dipole moment per residue on reactivity ratios, polymer composition and rotamer probabilities. One such calculation for atactic cc ly-(p-chlorostyrene-p-methylstyrene) has shovm that at constant composition, the dipole moment is quite sensitive to the sequence distribution and thus to the reactivity ratios. This dependence would be even more marked for syndiotactic chains. For cop61y(propylene-vinyl chloride) and copoly(ethylene-vinyl chloride) d le moments are again very sequence dependent, much more so than the diaracteristk ratio. It would appear that in copolymer systems dielectric measurements can be a powerful method of investigating sequence distributions. Two copolymers, p-dilcxo-styrene with styrene and with p-methylstyrene have been examined experimentally The meamrements were made on solid amorphous samples above the ass-rubber transition temperature (Tg) and they are consistent with the predictions of the rotational isomeric state model udi known reactivity ratios and rea nable replication probabilities . However, it is the view of this author that deduc-... 

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