Coordination polymerization LLDPE

The presence of long chain branches in low density polyethylene (LDPE) accounts for the difference in properties e.g. higher melt strength, greater toughness for the same average molecular weight) between LDPE and linear low density polyethylene (LLDPE, made by coordination polymerization). 

Coordination copolymerization of ethylene with small amounts of an a-olefin such as 1-butene, 1-hexene, or 1-octene results in the equivalent of the branched, low-density polyethylene produced by radical polymerization. The polyethylene, referred to as linear low-density polyethylene (LLDPE), has controlled amounts of ethyl, n-butyl, and n-hexyl branches, respectively. Copolymerization with propene, 4-methyl-1-pentene, and cycloalk-enes is also practiced. There was little effort to commercialize linear low-density polyethylene (LLDPE) until 1978, when gas-phase technology made the economics of the process very competitive with the high-pressure radical polymerization process [James, 1986]. The expansion of this technology was rapid. The utility of the LLDPE process Emits the need to build new high-pressure plants. New capacity for LDPE has usually involved new plants for the low-pressure gas-phase process, which allows the production of HDPE and LLDPE as well as polypropene. The production of LLDPE in the United States in 2001 was about 8 billion pounds, the same as the production of LDPE. Overall, HDPE and LLDPE, produced by coordination polymerization, comprise two-thirds of all polyethylenes. 

Ethylene Polymers. Depending on the polymerization conditions, three major types of polyethylene are manufactured low-density polyethylene (LDPE) by free-radical polymerization, linear low-density polyethylene (LLDPE) by copolymerization of ethylene with terminal olefins, and high-density polyethylene (HDPE) by coordination polymerization. The processes yield polymers with different characteristics (molecular weight, molecular weight distribution, melt index, strength, crystallinity, density, processability). 

The three major classes of polyethylene are described by the acronyms HOPE. LDPE. and LLDPE. High-density polyethylene (HOPE) is a linear, semicrystalline ethylene homopolymer Tm 135 °C) prepared by Ziegler—Natta and chromium-based coordination polymerization technology. Linear low-density polyethylene (LLDPE) is a random copolymer of ethylene and a-olefins (e.g.. 1-butene. 1-hexene, or... 

Two different types of (PS-b-PBDh) diblock can be presently synthesized. The first one by classical anionic initiation (s-buty1-lithium) and "living" propagation of the (PS-b-PBD) copolymer (8), followed by the hydrogenation procedure described here as discussed above, the resulting product will be close to a (PS-b-LLDPE) copolymer. The second one came from the discovery (9) of a "living" polymerization of butadiene into a pure (99 %) 1,4 polymer by a bis n allylnickel-tri-fluoroacetate) coordination catalyst, followed by styrene polymerization unfortunately, the length of the polystyrene block is limited (to a M.W. of ca. 20,000) by transfer reactions. 

Continuous stirred-tank reactors (CSTRs) are used for large productions of a reduced number of polymer grades. Coordination catalysts are used in the production of LLDPE by solution polymerization (Dowlex, DSM Compact process [29]), of HDPE in slurry (Mitsui CX-process [30]) and of polypropylene in stirred bed gas phase reactors (BP process [22], Novolen process [31]). LDPE and ethylene-vinyl acetate copolymers (EVA) are produced by free-radical polymerization in bulk in a continuous autoclave reactor [30]. A substantial fraction of the SBR used for tires is produced by coagulating the SBR latex produced by emulsion polymerization in a battery of about 10 CSTRs in series [32]. The CSTRs are characterized by a broad residence time distribution, which affects to product properties. For example, latexes with narrow particle size distribution cannot be produced in CSTRs. 

The coordination catalyst was fed to the reactor containing hydrocarbon solvent and appropriate monomers. Polymerization was carried out at T = 105-310 °C. The catalyst was deactivated and either left in the obtained LLDPE (p = 0.915-0.965 g mL ) or the solution was passed through a hed of activated alumina or bauxite to remove at least a part of the deactivated catalyst residues... 

A solution polymerization for high-MW LLDPE uses a coordination catalyst at T = 105-320 °C. The catalyst was heat treated at 180-250 °C, then cooled to a T < 150 °C. Additional VOX3 was added and catalyst activated with an A1 compound. The catalyst had greater activity than the one without additional VOX3 or with that added at T >... 

LLDPE was polymerized in solution with a coordination catalyst at T = 180-320 °C and P = 4-20 MPa. The new modification relates to a method for activating Z-N coordination catalysts using an alkoxy aluminum alkyl compound prepared by mixing an alcohol and alkyl aluminum. The activator retains its activity and is easy to prepare simplifying the polymerization process. Small amount of H2 may be used for MW control (see Elston CA Patent 703704 of 1965 to DuPont of Canada Ltd.)... 

Ethene polymerization by coordination chemistry also allowed the defined incorporation of 1-alkenes into the polymer chain, leading to production of LLDPE. The term LLDPE was coined together with the first large-volume production process by Union Carbide in 1978. 

The preparation of ethylene copolymers (or terpolymers) such as linear low-density polyethylenes (LLDPE), ethylene/propylene elastomers (EP), ethylene/ propylene/diene terpolymers (EPDM) is also based on these catalytic systems. Stereoregular polyisoprene and polybutadiene elastomers are also obtained by this method of polymerization the formation of 1,4-m-polydienes requires the prior double coordination of the monomer onto the growing active center ... 

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