Ethylene/propylene copolymers insertion

On the basis of 13C NMR analysis on ethylene-propylene copolymers obtained with the soluble VCiy A1(C2H5)2C1 catalyst, Zambelli et al. 90,91> have shown that the syndiotactic propagation of propylene occurs by secondary insertion, i.e. in the 1 unit sequence blocks, whereas the primary insertion in the 0 unit blocks results in either atactic or isotactic propagation. 

The same conclusion as in the case of propylene homopolymerisation has been drawn considering IR [396] and NMR [389,395] spectra of ethylene/propylene copolymers obtained with vanadium-based syndiospecific catalysts. The type of propylene insertion depends on the kind of last inserted monomer unit secondary insertion [scheme (40)] occurs more frequently when the last monomeric unit of the growing chain is propylene, while primary propylene insertion [scheme (39)] is more frequent when the last monomeric unit of the growing chain is ethylene [2]. The above explains the microstructure of ethylene/propylene copolymers obtained with vanadium-based Ziegler-Natta catalysts. These copolymers contain both m and r diads when the sequence of propylene units is interrupted by isolated ethylene units i.e. a propylene insertion after an ethylene insertion is substantially non-stereospecific [327,390,397], The existence of a steric interaction between the incoming monomer molecule and the last added monomer unit is also confirmed by the fact that the propagation rate for the secondary insertion of propylene in syndiospecific polymerisation is lower than for primary insertion in non-stereospecific polymerisation [398],... 

Random ethylene/propylene copolymers are amorphous and represent an interesting class of synthetic elastomers. The introduction of double bonds, useful for sulphur vulcanisation in the copolymer, can be achieved by copolymerisation of ethylene and propylene with non-conjugated dienes containing only one double bond capable of insertion for instance, 1,4-hexadiene, dicy-clopentadiene and 5-ethylidene-2-norbornene (endocyclic double bond)... 

It is interesting that some heterogeneous superhigh-activity Ziegler-Natta catalysts such as MgC /TiCU/LB—AlEt3 also yield random ethylene/propylene copolymers. These copolymers, however, exhibit a blocky nature and highly isotactic propylene sequences (with no 2,1-inserted propylene units) that contribute to undesired crystallinity [68,456]. 

The same technique can be used to dye a material that is otherwise difficult to dye. An ethylene-propylene copolymer rubber was reacted first with maleic anhydride, then with an aromatic amine dye in an extruder to produce a dyed rubber.81 Dye sites can also be inserted into polyolefins by grafting them with dimethylaminoethyl methacrylate, using azo or peroxide catalysts in an extruder.82 jV-Vinylimidazole has been grafted to polyethylene in an extruder with the help of dicumylperoxide.83 The product was mixed with an acrylic acid-modified polypropylene and used to compatibilize polyethylene and polypropylene. This could be helpful in the recycling of mixed polyolefins from municipal solid waste. Recycling of cross-linked (thermoset) polymers is more of a problem because they cannot be remelted in an extruder. However, they can be if... 

PROPYLENE INSERTION ON CRYSTALLIZATION BEHAVIOR AND ELASTICITY OF ETHYLENE/PROPYLENE COPOLYMERS... 

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... 

Guerra, G Galimberti, M. Piemontesi, F. Ruiz de Ballesteros, O. Influence of regio- and stereoregularity of propylene insertion on crystalhzation behavior and elasticity of ethylene-propylene copolymers. 7. Am. Chem. Soc. 2002,124, 1566-1567. 

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. 

A second functionalization approach was based on the insertion of carbenes into the C-H bond (Scheme 3). The reaction of different polyolefins, such as high density polyethylene (HDPE), atactic polypropylene (aPP), isotactic polypropylene (iPP), ethylene-propylene copolymers (EP) and polyisobutene (iPBu) with diazoesters at 210T in bulk has been shown to give a product containing the carboxylate functionality attached to the polymer backbone. The presence of the functional groups in the polymer was inferred by IR spectroscopy (carbonyl stretching band at 1740 cm "1 and in case of chloroethyldiazoacetate... 

Certain studies are concerned with crystallinity and melting-point measurements in ethylene-propylene copolymers 129,136—141) and in model copolymers 107,110). Here the main conclusion is that the insertion of even a small number of propylene units in polyethylene chains leads to a sharp reduction of the polyethylene crys ini from 70-80% for pure polymer down to 25-30% for 25%Cp, copolymers, and to practically amorphous products for 35%Cj copolymers 136, 137). It was found (141) that, for copolymers characterize by different rj T2 values, the dependence of polyethylene crystallinity on copolymer composition correlates well with the calculated dependence of the... 

The polymerization is highly regiospecific only head-to-tail einchained monomer units are detected in highly isotactic polymers and only odd methylene sequences are detected in ethylene/propylene copolymers (10-12). The insertion of all propylene units into the reactive metal-carbon bond is primary (or antimarkownikow)... 

Natta and co-workers [5] determined the degree of alternation of ethylene and propylene units in ethylene-propylene copolymers from the infrared spectrum, using peaks at 13.35, 13.70 and 13.83 pm, the one at 13.70 pm being attributed to a sequence of three methylene groups between branch points, presumably due to the insertion of one ethylene between two similarly oriented propylene molecules ... 

The Himont spheripol loop reactor process is initiated by injecting specially prepared supported catalyst and cocatalyst into liquid propylene circulated in a relatively simply high L/D ratio loop reactor, followed by monomer removal (Figure 4.2). The homopolymers so produced can he circulated through ethylene and ethylene/propylene gas phase reactors for insertion of copolymer fractions before final... 

In the case of polypropylene copolymers, typically ethylene propylene (EP) copolymers, the insertion of ethylene into the growing PP chain will result (for the same reasons as discussed above) in dismption of the methyl sequence and thus reduce the crystallizability, as shown in Fig. 4a. In terms of crystallinity, the addition of ethylene in EP copolymers result in a u-shape curve, as shown in Fig. 4b where both homopolymers have a higher crystallinity than the intermediate EP copolymers. 

The crystallinity and physical properties of EP copolymers mainly depend on comonomer content (composition) and comonomer distribution (constitution). However, for industrially relevant ethylene-rich copolymers, the regio- and stereoregularity of propylene insertion also plays a fundamental role in controlling both crystallinity and elastic properties. Highly stereo- and regioregular propylene units are at the origin of elasticity in the uncured state. These microstructural features are further dependent upon both the catalytic system employed and the polymerization conditions. 

Random insertion of ethylene as comonomer and, in some cases, butene as termonomer, enhances clarity and depresses the polymer melting point and stiffness. Propylene—butene copolymers are also available (47). Consequendy, these polymers are used in apphcations where clarity is essential and as a sealant layer in polypropylene films. The impact resistance of these polymers is sligbdy superior to propylene homopolymers, especially at refrigeration temperatures, but still vastiy inferior to that of heterophasic copolymers. Properties of these polymers are shown in Table 4. 

Under the same conditions, syndiospecihc (Cs-symmetric) metallocenes are more effective in inserting a-olefins into an ethylene copolymer than isospecific (C2-symmetric) metallocenes or unbridged metallocenes. In particular, hafnocenes are more efficient than zirconocenes. An interesting effect is observed for the polymerization with ethylene(bisindenyl)zirconium dichloride and some other metallocenes. The catalytic activity for the homopolymerization of ethylene is very high, and it increases when copolymerization with propylene occurs (114) (Fig. 12). Munoz-Escalona et al. (125) observed similar effects in the copolymerization of ethylene with 1-hexene. 

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