Ethylene-propylene copolymers cross-linking

Discuss copolymers of ethylene with propylene. How are they prepared What catalysts are used in the preparations How are ethylene-propylene rubbers cross-linked ... 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

Combination techniques such as microscopy—ftir and pyrolysis—ir have helped solve some particularly difficult separations and complex identifications. Microscopy—ftir has been used to determine the composition of copolymer fibers (22) polyacrylonitrile, methyl acrylate, and a dye-receptive organic sulfonate trimer have been identified in acryHc fiber. Both normal and grazing angle modes can be used to identify components (23). Pyrolysis—ir has been used to study polymer decomposition (24) and to determine the degree of cross-linking of sulfonated divinylbenzene—styrene copolymer (25) and ethylene or propylene levels and ratios in ethylene—propylene copolymers (26). 

The use of TAG as a curing agent continues to grow for polyolefins and olefin copolymer plastics and mbbers. Examples include polyethylene (109), chlorosulfonated polyethylene (110), polypropylene (111), ethylene—vinyl acetate (112), ethylene—propylene copolymer (113), acrylonitrile copolymers (114), and methylstyrene polymers (115). In ethylene—propylene copolymer mbber compositions. TAG has been used for injection molding of fenders (116). Unsaturated elastomers, such as EPDM, cross link with TAG by hydrogen abstraction and addition to double bonds in the presence of peroxyketal catalysts (117) (see Elastol rs, synthetic). 

FIGURE 1.12 Master curve of tear energy Gc versus rate R of tear propagation at Tg for three cross-linked elastomers polybutadiene (BR, Tg — —96°C) ethylene-propylene copolymer (EPR, Tg — —60°C) a high-styrene-styrene-butadiene rubber copolymer (HS-SBR, Tg — —30°C). (From Gent, A.N. and Lai, S.-M., J. Polymer Sci., Part B Polymer Phys., 32, 1543, 1994. With permission.)... 

Cross-linking with peroxides has been known since 1915 when Ostromyslenski [46] disclosed that NR could be transformed into a cross-linked state with dibenzoyl peroxide. However, little interest in peroxide cross-linking evolved until the development of fully saturated ethylene-propylene copolymers in the early 1970s. 

Cross-Linking of Ethylene-Propylene Copolymer Rubber with Dicumyl Peroxide-Maleic Anhydride... 

Since the excellent work of Moore and Watson (6, who cross-linked natural rubber with t-butylperoxide, most workers have assumed that physical cross-links contribute to the equilibrium elastic properties of cross-linked elastomers. This idea seems to be fully confirmed in work by Graessley and co-workers who used the Langley method on radiation cross-linked polybutadiene (.7) and ethylene-propylene copolymer (8) to study trapped entanglements. Two-network results on 1,2-polybutadiene (9.10) also indicate that the equilibrium elastic contribution from chain entangling at high degrees of cross-linking is quantitatively equal to the pseudoequilibrium rubber plateau modulus (1 1.) of the uncross-linked polymer. 

The promotion of cross-linking of polypropylene and ethylene-propylene copolymers has been confirmed. However, other bases, such as amines, were not found to be effective, and in some cases they acted as retarders of radiahon cross-linking. ... 

PVC, another widely used polymer for wire and cable insulation, crosslinks under irradiation in an inert atmosphere. When irradiated in air, scission predominates.To make cross-linking dominant, multifunctional monomers, such as trifunctional acrylates and methacrylates, must be added. Fluoropolymers, such as copol5miers of ethylene and tetrafluoroethylene (ETFE), or polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack, and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance. Ethylene propylene rubber (EPR) has also been used for wire and cable insulation. When blended with thermoplastic polyefins, such as low density polyethylene (LDPE), its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation. ... 

Ethylene propylene rubber (EPR) has been also used for wire and cable insulation. When blended with thermoplastic polyefins such as LDPE its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation.34... 

Copolymer of adipic acid and ethylene and propylene glycols, cross-linked by naphthalene 1,4-diisocyanate and 1,4-butanediol. m Polypropylene ether) cross-linked by toluene diisocyanate and trimethylol propane. n Data by Te Nijenhuis (1974, 1979). 

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... 

While the first vulcanization involved heating the elastomer with sulfur, it has since been recognized that neither heat nor sulfur is imperative for the vulcanization process. Vulcanization or cure can be effected by nonsulfur-containing compounds, including peroxides, nitro compounds, quinones, or azo compounds. Polyethylene, ethylene-propylene copolymers, and polysiloxanes are cross-linked by compounding them... 

Sim, C. X., van der Mee, A. ]., Goossens, J. G. R, and van Duin, M. 2006. Thermoreversible cross-linking of maleated ethylene/ propylene copolymers using hydrogen-bonding and ionic interactions. Macromolecules 39 3441-3449. 

Copolymer of adipic acid and ethylene and propylene glycols, cross-linked by naphthalene 1,4-diisocyanate and 1,4-butanediol. 

The modified fillers were used in two matrices with different polarity the ethylene-propylene copolymer EPM and hydrogenated acrylonitrile-butadiene rubber HNBR. Elastomers were crosslinked with dicumyl peroxide DCP. The influence of the variously modified fillers on the cross-linking density of the vulcanizates, rheometric and mechanical properties of filled systems were investigated. The ageing studies (thermal, atmospheric and under UV radiations) were conducted. 

A styrene copolymer cross-linked with DVB was lightly sulfonated and the product incorporated into poly(vinylidenefluoride) and ethylene-propylene-diene with addition of antimonic acid (HSb). The resultant composites were sulfonated using chlorosulfonic acid and the procedure afforded membranes showing good physical properties (Chapter 8, Section 6). 

Some atmospheric plasma treatments allow in-line surface modification of almost any wire insulation material. Examples include polyamides, polyesters, and the fluoropolymers most difficult to treat. A treated surface can then accept inkjet printing for marking purposes. Table 5.13 shows a comparison of the marking durability on ethylene tetrafluoro-ethylene copolymer (ETFE) and fluorinated ethylene propylene copolymer (FEP) for untreated (U), flame treated (FI), and plasma treated (PI) conditions. Some wires have been cross-linked by irradiation (IR) to enhance cut-through resistance of the insulation. Wire suppliers have been identified in each case and all ink was UV curable. 

In consequence ethylene-propylene rubbers were introduced with a small amount (3-8%) of a third, diene, monomer which provided a cross-link site for accelerated sulphur vulcanisation. Such ethylene-propylene-diene monomer ternary copolymers are designated as EPDM rubbers. 

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