Copolymers Ethylene - a-olefin

Densities and crystallinities of ethylene—a-olefin copolymers mosdy depend on their composition. The classification ia Table 1 is commonly used (ASTM D1248-48). VLDPE resias are usually further subdivided iato PE plastomers of low crystallinity, 10—20%, with densities ia the range of 0.915—0.900 g/cm, and completely amorphous PE elastomers with densities as low as 0.860 g/cm. ... 

Commercial production of PE resias with densities of 0.925 and 0.935 g/cm was started ia 1968 ia the United States by Phillips Petroleum Co. Over time, these resias, particularly LLDPE, became large volume commodity products. Their combiaed worldwide productioa ia 1994 reached 13 X 10 metric t/yr, accouatiag for some 30% market share of all PE resias ia the year 2000, LLDPE productioa is expected to iacrease by 50%. A aew type of LLDPE, compositioaaHy uniform ethylene—a-olefin copolymers produced with metallocene catalysts, was first introduced by Exxon Chemical Company in 1990. The initial production volume was 13,500 t/yr but its growth has been rapid indeed, in 1995 its combiaed production by several companies exceeded 800,000 tons. 

Most Kaminsky catalysts contain only one type of active center. They produce ethylene—a-olefin copolymers with uniform compositional distributions and quite narrow MWDs which, at their limit, can be characterized by M.Jratios of about 2.0 and MFR of about 15. These features of the catalysts determine their first appHcations in the specialty resin area, to be used in the synthesis of either uniformly branched VLDPE resins or completely amorphous PE plastomers. Kaminsky catalysts have been gradually replacing Ziegler catalysts in the manufacture of certain commodity LLDPE products. They also faciUtate the copolymerization of ethylene with cycHc dienes such as cyclopentene and norhornene (33,34). These copolymers are compositionaHy uniform and can be used as LLDPE resins with special properties. Ethylene—norhornene copolymers are resistant to chemicals and heat, have high glass transitions, and very high transparency which makes them suitable for polymer optical fibers (34). 

Chromium Oxide-Based Catalysts. Chromium oxide-based catalysts were originally developed by Phillips Petroleum Company for the manufacture of HDPE resins subsequendy, they have been modified for ethylene—a-olefin copolymerisation reactions (10). These catalysts use a mixed sihca—titania support containing from 2 to 20 wt % of Ti. After the deposition of chromium species onto the support, the catalyst is first oxidised by an oxygen—air mixture and then reduced at increased temperatures with carbon monoxide. The catalyst systems used for ethylene copolymerisation consist of sohd catalysts and co-catalysts, ie, triaLkylboron or trialkyl aluminum compounds. Ethylene—a-olefin copolymers produced with these catalysts have very broad molecular weight distributions, characterised by M.Jin the 12—35 and MER in the 80—200 range. 

The ability to control the polymer from the design of the catalyst, coupled with high catalytic efficiency has led to an explosion of commercial and academic interest in these catalysts. Exxon started up a 30 million lb/5rr ethylene copol3rmer demonstration plant in 1991 using a bis-cyclopentadienyl zirconium catalyst of structure 1. The Dow Chemical Company (Dow) began operating a 125 million Ib/yr ethylene/l-octene copolymer plant in 1993 and has since expanded production capacity to 375 million Ib/yr. This paper will focus on the structure / property relationships of the catalysts used by Dow to produce single-site ethylene a-olefin copolymers. 

These are some key advantages that the metallocene catalysts have over conventional Ziegler-Natta catalysts and hence it is highly probable that inter-and intra-chain heterogeneity expected in ethylene-a-olefins copolymers can be controlled through the use of the metallocene system. 

Ethylene-alkyne metathesis, 26 955-956 Ethylene-a-olefin copolymers,... 

Figure 9. Relative scission efficiencies of short-chain branches in the 7 radiolysis of ethylene-a-olefin copolymers. Branch types are indicated.

Table IV. Yields of Isobutene and 1-Butene from Irradiation of Ethylene-a-Olefin Copolymers at 150°C...

Densities and crystallinities of ethylene-a-olefin copolymers mostly depend on their composition. The classification in Table 4 is commonly used (ASTM D1248-48). 

Also, a series of well-defined polyolefins, including perfectly branched polyethylene and ethylene/a-olefin copolymers, have been synthesised via acyclic diene metathesis polycondensation [scheme (28)] [47] these well-defined polyolefins have been designed to model the crystallisation of polyethylene and olefin copolymers. 

Monocyclopentadienyl metallocene catalysts, (VII), not requiring methylalu-moxane as a co-catalyst were prepared by Canich [6] and used to prepare ethylene/a-olefin copolymers. 

Maleic anhydride grafted ethylene-a-olefin copolymer... 

Ethylene-styrene interpolymers exhibit a novel balance of properties that are uniquely different from polyethylenes and polystyrenes. In contrast to other ethylene-a-olefin copolymers, ESI display a broad range of material response ranging from semicrystalline, through elastomeric to amorphous. The styrenic functionality and unique molecular architecture of ESI are postulated to be the basis of the versatile material attributes such as processability (shear thinning, melt strength and thermal stability), viscoelastic properties, low-temperature toughness and broad compatibility with other polymers, fillers and low molecular weight materials. 

Wang, W.Q. Kontopoulou, M. Effect of molecular structure on the rotational molding characteristics of ultra-low-density-ethylene-a-olefin copolymers. Polym. Eng. Sci. 2004, 44 (3), 496-508. 

Guillen-Castellanos, S.A. Bellehumeur, C.T. Weber, M. The effect of molecular structure on the coalescence of ethylene-a-olefin copolymers. Proceedings of the Society of Plastics Engineers Annual Technical Conference, San Francisco, CA, May 5-9, 2002 The Society of Plastics Engineers Brookfield, 2002. 

Chemically anchored, supported transition metal catalysts have been used extensively for production of high-density, linear polyethylene and ethylene-a-olefin copolymers. These supported... 

Ethylene-a-olefin copolymers, stereo-block enhanced inter-spherulitic and Lustiger, 1993... 

Nomura et al. (14) investigated the mechanical fracture behavior of PP/EPR blends containing additional ethylene-a-olefin copolymers (ECP). They found that the addition of a small content (8.2 wt%) of ECP did not change the rubber domain distributions in the matrix (corresponding TEM images are shown in Fig. 8.10). 

The ethylene-a-olefin copolymer chains that are miscible in the molten state also are excluded out from the crystalline region of iPP as described in Section 9.2. Therefore, the applied crystallization condition affects not only the characteristics of crystalline region such as spherulite texture, degree of crystallinity, and the defects in crystals but also the molecular aggregation state of iPP and the copolymers, which will play a central role in controlling the mechanical properties. 

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)... 

MAJOR APPLICATIONS POE is a new family of ethylene a-olefin copolymers produced using metallocene catalyst. The uncross-linked polymers referred to in this chapter are known to have only moderate elastomeric recovery properties (up to 96%). These copolymers are characterized by a narrow molecular weight distribution (MWD) (M /Mn = 2-2.5) and homogeneous comonomer distribution.The control of chain microstructure by the use of metallocene catalyst makes it possible to produce poly(a-olefin) copolymers with considerably lower density, which has not been possible before using the conventional Ziegler-Natta catalyst. Some of the highly branched ethylene copolymers presented in the entry on Polyethylene, metallocene linear low-density, in this handbook may be closely related. 

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