Ethylene-propylene copolymers sequence distribution

Mean-square unperturbed dimensions and dipole moments are calculated for propylene-vinyl chloride copolymers by means of RIS theory. The calculations indicate that for these chain molecules is much more sensitive to chemical sequence distribution than is 0, a conclusion in agreement with results of previous studies of ethylene-propylene copolymers and styrene-substituted styrene copolymers. In the case of propylene-vinyl chloride chains, both 0 and are most strongly dependent on chemical sequence distribution in the case of copolymers which are significantly syndiotactic in stereochemical structure. 

Mean-square unperturbed dimensions a and their temperature coefficient, d tin 0) I d T, are calculated for ethylene-propylene copolymers by means of the RIS theory. Conformational energies required in the analysis are shown to be readily obtained from previous analyses of PE and PP, without additional approximations. Results thus calculated are reported as a function of chemical composition, chemical sequence distribution, and stereochemical composition of the PP sequences. Calculations of 0 / nP- are earned out using ( ) r r2 = 0.01, 1.0, 10.0, and 100.0, (ii) p, = 0.95, 0.50, and 0.05, liii) bond length of 153 pm and bond angles of 112°for all skeletal bonds, iv) = 0 and 10°, and (v) statistical weight factors appropriate for temperatures of 248, 298, and 348 K. Matrices used are ... 

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... 

Since the discovery of olefin polymerization using the Ziegler-Natta eatalyst, polyolefin has become one of the most important polymers produeed industrially. In particular, polyethylene, polypropylene and ethylene-propylene copolymers have been widely used as commercial products. High resolution solution NMR has become the most powerful analytieal method used to investigate the microstructures of these polymers. It is well known that the tacticity and comonomer sequence distribution are important factors for determining the mechanical properties of these copolymers. Furthermore, information on polymer microstructures from the analysis of solution NMR has added to an understanding of the mechanism of polymerization. 

Ellerbe.J.S., Cox,R.C., Lane,L.H. Monomer sequence distribution in ethylene-propylene copolymers by computer analysis of infrared spectra. Anal. Chem. 40, 370-379 (1968). 

Among the most commonly utilized synthetic polymers are polyolefins, such as polyethylenes (PEs), polypropylenes (PPs), and ethylene-propylene copolymers (P(E-co-P)s). Despite their simple elemental compositions, consisting of only carbon and hydrogen, it is well known that their physical properties are quite dependent on the microstructural features, such as short- and long-chain branchings, stereoregularities, chemical inversions of monomer enchainment, sequence distributions, etc. ... 

I. Valvassori, A. Zambelli, A. Copolymers of ethylene, higher a-olefins, and monocyclomonool-efins or aUcyl derivatives thereof. U.S. Patent 3,505,301 (Montecatini Edison S.p.A.), April 7, 1970. (b) Zambelli, A. Tosi, C. Sacchi, C. Polymerization of propylene to syndiotactic polymer. VI. Monomer insertion. Macromolecules 1972, 5, 649-654. (c) LocateUi, R Immirzi, A. Zambelli, A. Palumbo, R. Maglio, G. Orientation of propylene units in polypropylene and ethylene/propylene copolymers. Makromol. Chem. 1975,176, 1121-1128. (d) Carman, C. J. Harrington, R. A. Wilkes, C. E. Monomer sequence distribution in ethylene-propylene rubber measured by C NMR. 3. Use of reaction probability mode. Macromolecules 1977, 10, 536-544. (e) Zucchini, U. Dall Occo, T. Resconi, L. Ziegler-Natta catalysis for the polyolefin industry Present status and perspectives. Indian... 

A structure of C34F23 (C14F 22)11 C14H23 is proposed, where n = 0, 1, or 2 for the dimer, trimer, or tetramer, respectively. Ethylene-propylene copolymers can contain up to four types of sequence distribution of monomeric units. These are propylene to propylene (head-to-tail and head-to-head), ethylene to propylene, and ethylene to ethylene. These four types of sequence and the average sequence lengths of both monomer units, i.e., the value of w in the structures opposite, can be measured by the Tanaka and Hatada [48] method. 

Copolymers.—Both Monomers Vinyl. Ethylene-propylene copolymers have attracted the greatest attention,befitting their industrial importance. A variety of techniques has been used to assign the rather complex C spectra observed, including the synthesis of model oligomers and model polymers e.g. by hydrogenation of isoprene ). Propylene may add by either primary or secondary insertion, and a terpolymerization model has therefore been used to quantify the sequence distribution. Alternatively, Randall has proposed an analysis in terms of —CHa— or —CH(CHs)— units, rather than monomer residues. 

Ethylene-propylene copolymers can contain up to four types of sequence distribution of monomeric units. These are propylene-propylene (head-to-tail and head-to-head), ethylene-propylene and ethylene to ethylene ... 

The factors determining the stereospecificity in the polymerization of a-olefins have not been singled out with certainty. We tackled this problem from three different points of view, i.e. analysis of the sequence distribution in ethylene-propylene copolymers, microstructural analysis of partially stereoregular propylene polymers, microstructural analysis of ethylene-propylene copolymers. 

The sequence distribution is random in ethylene-propylene copolymers prepared in the presence of isospecific or not stereospecific catalysts, whereas it tends to the alternance of different units in copolymers prepared in the presence of syndiospecific catalysts [5]. 

In conclusion, the isospedfic steric control should be due to the chirality of M, whereas the syndiospecific steric control should be due to the chirality of the last unit of the growing chain end. This conclusion also agrees with the statistics of sequence distribution observed in ethylene-propylene copolymers (74). 

Fig. 2. Distribution of propylene units in ethylene-propylene copolym s in the isotactic sequences of different lengths (72). Catalytic sykem TiCls—Al(C2Hs)3. = data for the 973 cm band, O = dataforthe 8an band. The calculations are carried out with Eqs. (8) and (12) for n = 4 [rj = 1.7 and 0.8 (55)] and frar...

Fig. 7a and b. Distribution of moncnner units in propylene-styraie copolyrtwrs 47). a) Distribution of styrene units. Experimental points are for the 565 cm band CalculaticHis are for n = 2, r, = 1 and 5. b) Comparisrm between the and Ag Ali ratios (the parameters of the distributicm of propylene units in long isotactic sequences, see Table 1) for prylene-styrene copolymers ( ) and ethylene-propylene copolymers (O)... 

Fig. 8a and b. Distribution of propylene units in propylene-vinyl cyclohexane copolymers (46). a) Data for the 973cm band, a-specially normalized values of - 973Mi38o s e (II). Calculations are for n = 4, ri r2 = 3.9. b) Comparison between the Agge/Ag 3 ratios (the parameters of the distribution of prt ylene units in long isotactic sequences) in propylene-vinyl cyclohexane copolymns a (O) and in ethylene-propylene copolymers ( )... 

The infrared absorption of ethylene copolymers in the 14.28-11.76 pm region can provide information about their sequence distributions. Studies on model hydrocarbons by workers various [1-4] have shown that the absorption of methylene groups in this region is dependent on the size of methylene sequences in the compounds. Methylene absorptions observed in this region, and their relation to structures occurring in ethylene copolymers, are shown in Table 7.1. The absorptions at 13.81 and 13.68 pm of several ethylene-propylene copolymers have been assigned [5] to... 

This avoids problems associated with propylene inversion and comonomer sequence assignment. He gives methylene sequence distributions from one to six and larger consecutive methylene carbons for a range of ethylene-propylene copolymers, and uses this to distinguish copolymers which have either random, blocked or alternating comonomer sequences. 

Figure 22 Sequence length distributions for ethylene-propene copolymers (Karssenberg et al. [130]). Top normalized ethylene sequence length distribution bottom normalized propylene sequence length distribution. Reproduced from Karssenberg et al. [130]. Copyright 2006, John Wiley Sons, Inc. Reprinted with permission of Wiley-Liss, Inc., a subsidiary of John Wiley Sons, Inc.

The same model has been used lt6) to explain the copolymerization of ethylene and propylene with TiCl+/EB/MgCl2—AlEt3, with various amounts of EB added to the cocatalyst. The triad sequence distribution calculated for the copolymer obtained without EB was in disagreement with reactivity ratios, while the values obtained with high concentrations of EB did agree. Thus, the two active species mentioned, having two and one vacancies respectively, would be characterized by... 

When propylene (P) is copolymerized with ethylene (E), the copolymerization parameters and are excellent measures for the olefin sequence distribution as shown below for different copolymer sequences ... 

The most important properties of the matrix polymer are its chemical composition and melt viscosity. Copolymers have lower stiffness and higher impact strength than the homopolymer, which are transferred also to the composites. Products with Mgher modulus are usually prepared from homopolymers, while those subjected to dynamic loads during application are made from copolymers. Also the sequence distribution of the ethylene and propylene units is of importance, as... 

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