Isotactic propylene , copolymers

Similarly, the random introduction by copolymerization of stericaHy incompatible repeating unit B into chains of crystalline A reduces the crystalline melting point and degree of crystallinity. If is reduced to T, crystals cannot form. Isotactic polypropylene and linear polyethylene homopolymers are each highly crystalline plastics. However, a random 65% ethylene—35% propylene copolymer of the two, poly(ethylene- (9-prop5lene) is a completely amorphous ethylene—propylene mbber (EPR). On the other hand, block copolymers of the two, poly(ethylene- -prop5iene) of the same overall composition, are highly crystalline. X-ray studies of these materials reveal both the polyethylene lattice and the isotactic polypropylene lattice, as the different blocks crystallize in thek own lattices. 

ISO 9113 1986 Plastics - Polypropylene (PP) and propylene-copolymer thermoplastics -Determination of isotactic index... 

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 Ziegler-Natta catalysts have acquired practical importance particularly as heterogeneous systems, mostly owing to the commercial production of linear high- and low-density polyethylenes and isotactic polypropylene. Elastomers based on ethylene-propylene copolymers (with the use of vanadium-based catalysts) as well as 1,4-cz s-and 1,4-tran.y-poly(l, 3-butadiene) and polyisoprene are also produced. These catalysts are extremely versatile and can be used in many other polymerisations of various hydrocarbon monomers, leading very often to polymers of different stereoregularity. In 1963, both Ziegler and Natta were awarded the Nobel Prize in chemistry. 

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]. 

Isotactic poly(4-methyl-l -pentene) Ethylene/isotactic propylene block (compact) copolymers (polyallomers)... 

Hydroperoxides are much more efficient than ketones for initiating photooxidation of ethylene-propylene copolymers [19]. This fact was confirmed by the results from photolysis of low-molecular model compounds and isotactic polypropylene [20]. 

Toughened polypropylene may be prepared by block copolymerization in which ethylene monomer is added during the final stages of the polymerization of propylene (4). Thus, some polypropylene chains would contain an end block of rubbery ethylene-propylene copolymer. Alternatively, a blend of an elastomeric copolymer of ethylene and propylene (EPR or EPDM) with isotactic polypropylene (PP) can produce an impact-resistant polymer (5). 

Present-day Ziegler-Natta catalysts are supremely suitable for the production of linear polyethylene and of highly isotactic polypropylene. They are also used to produce the softer ethylene-propylene copolymers, used for packaging and related purposes. Due to the presence of distinct catalyst sites in typical Ziegler-Natta catalysts, these copolymers suffer from non-uniformity however, and copolymers which contain increased amounts of higher ot-olefins, desirable for certain applications, cannot easily be made with these catalysts. 

In isospecific polymerization the stereocontrol does not depend on the chirality of the last monomeric unit. It was found that some ethylene units in ethylene-propylene copolymers (TiCla as a catalyst) are surrounded by isotactic blocks of the same stereoregularity ... 

Blends between Isotactic Polypropylene and Ethylene Propylene Copolymers... 

The miscibility of olefin copolymers such as ethylene-a-olefin copolymers was found to be controlled by the structural composition and the primary strucmre of the copolymers. Using these copolymers, binary blends with various compatibilities were prepared and the effects of compatibihty on mechanical properties in the binary blends were investigated. The tensile properties in binary blends of iPP with rubbery olefin copolymers are considerably influenced by the miscibility between iPP and the copolymers. The miscibility of iPP with other polyolefins is described in detail based on the dynamic mechanical properties, morphology observation, and solidification process. It is found that EBR, EHR, and EOR having more than 50 mol% of a-olefin are miscible with iPP in the molten state. In the solid state, the miscible copolymers are dissolved in the amorphous region of iPP, although the copolymers are excluded from crystalhne lattice of iPP. The isotactic propylene sequence in the EP copolymers with a propylene-unit content of more than 84 mol% participates in the crystallization process of iPP, resulting that a part of the EP copolymers is included in the crystalline lattice of iPP. 

High density polyethylene (HOPE) Linear low density polyethylene (LLDPE) Isotactic polypropylene (iPP) Syndiotactic polypropylene (sPP) tram-1,4-Polyisoprene Syndiotactic polystyrene (sPS) Cyclooleflns Ethylene-propylene copolymers Styrene-ethylene copolymers cw -1,4-polybutadiene rrarw -1,4-Poly isoprene Random ethylene-a-olefin copolymers Ethylene-propylene rubber (EPR) Ethylene-propylene-diene copolymers (EPDM)... 

M /g.mor = 240000,4.9 wt% ethene, 90% isotactic, 58.1 wt% crystallinity, impact propylene copolymer, Mitsubishi Chemical, Kurashiki, Japan... 

Copolymers of isotactic propylene (iPP) with a-oleflns also exhibit diffraction peaks due to iPP crystallites. As one would predict, increasing the a-olefln content decreases the percent crystallinity. When the copolymer is blended with iPP homopolymer, the copolymer will cocrystallize with the homopolymer, a phenomenon that is rare in polymers. Cocrystallization is believed to substantially contribute to the improved mechanical properties found in the blend (Starkweather, 1980). Large spherulites are not generally found in these blends as opposed to the homopolymer, and the crystal form is monoclinic rather than smectic (Kresge, 1984). 

ICP = blends of isotactic propylene homopolymer with ethylene-propylene rubber. These materials are commonly called "impact copolymers," "heterophasic copolymers," or, incorrectly, "block copolymers." These are typically prepared during the polymerization process using a series of reactors. L = low rubber (less than about 15% rubber by weight typically witli an ethylene content of less than about 10%). H = high rubber content blends (greater than about 15% rubber by weight typically with an ethylene content of at least 7%). 

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