Polyethylene peroxidized

Vinyl Free radical cure systems crosslinked polyethylene, peroxide cured elastomers, polyesters. Polyethylene. Polypropylene. 

NMR Kinetic Analysis of Polyethylene-Peroxide Cross-linking Reactions... 

Another concern is the competitive interaction among polyethylene, peroxide, air and a required oxidative stabilizer additive necessary for the extrusion manufacture of crossllnked polyethylene cables. ( )... 

Figure 9. Changes In NMR Peak Height of a Polyethylene, Peroxide and Antioxidant (AA) Sample.

MCGINNISS AND NIXON Polyethylene-Peroxide Cross-Unking Reactions 251... 

Pobedimsky D.G., Kirpichnikov P.A., and Denisov E.T., About reactions of phosphorus-organic inhibitors with hydroperoxide groups and polyethylene peroxide radicals , Vysokomol. Soed., 1976, vol. A18, pp. 2650 - 2658. (Rus)... 

Polyethylene cross-linked by irradiation with high-energy electrons. Polysilicones cross-linked by reaction with benzoyl peroxide. 

Cross-linking of polyethylene can be accomphshed either chemically or by high energy radiation. Radiation cross-linking is usually accomphshed by x-rays (44) or electrons (45,46). Chemical cross-linking of polyethylene is accomphshed with dicumyl peroxide (47), d4-tert-huty peroxide (48), or other peroxides. Radiation cross-linking (49) is preferred for thin foams, and chemical cross-linking for the thicker foams. 

LDPE, also known as high pressure polyethylene, is produced at pressures ranging from 82—276 MPa (800—2725 atm). Operating at 132—332°C, it may be produced by either a tubular or a stirred autoclave reactor. Reaction is sustained by continuously injecting free-radical initiators, such as peroxides, oxygen, or a combination of both, to the reactor feed. 

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. 

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

Another use is of minor proportions of polyfunctional aHyl esters, eg, diaHyl maleate, ttiaHyl cyanurate, and ttiaHyl isocyanurate, for cross-linking or curing preformed vinyl-type polymers such as polyethylene and vinyl chlotide copolymers. These reactions ate examples of graft copolymerization in which specific added peroxides or high energy radiation achieve optimum cross-linking (see Copolymers). 

Antioxidants. The 1,2-dihydroquinolines have been used in a variety of ways as antioxidants (qv). For example, l,2-dihydro-2,2,4-trimethylquinoline along with its 6-decyl [81045-48-9] and 6-ethoxy [91-53-2] derivatives have been used as antio2onants (qv) and stabilizers (68). A polymer [26780-96-1] of l,2-dihydro-2,2,4-trimethylquinoline is used in resins, copolymers, lubricant oils, and synthetic fibers (69). These same compounds react with aldehydes and the products are useful as food antioxidants (70). A cross-linked polyethylene prepared with peroxides and other monomers in the presence of l,2-dihydro-6-ethoxyquinoline produces polymers with a chemically bonded antioxidant (71). 

High pressure (60—350 MPa) free-radical polymerization using oxygen, peroxide, or other strong oxidizers as initiators at temperatures of up to 350°C to produce low density polyethylene (LDPE), a highly branched polymer, with densities from 0.91 to 0.94 g/cm. ... 

Polymerization of olefins such as styrene is promoted by acid or base or sodium catalysts, and polyethylene is made with homogeneous peroxides. Condensation polymerization is catalyzed by acid-type catalysts such as metal oxides and sulfonic acids. Addition polymerization is used mainly for olefins, diolefins, and some carbonyl compounds. For these processes, initiators are coordination compounds such as Ziegler-type catalysts, of which halides of transition metals Ti, V, Mo, and W are important examples. 

Polyethylene glycol [25322-68-3] various, from -200 to -35,000. May be contaminated with aldehydes and peroxides. Methods are available for removing interfering species. [Ray and Purathingal Anal Biochem 146 307 7955.]... 

Polyolefins such as polyethylene and polypropylene contain only C—C and C—H bonds and may be considered as high molecular weight paraffins. Like the simpler paraffins they are somewhat inert and their major chemical reaction is substitution, e.g. halogenation. In addition the branched polyethylenes and the higher polyolefins contain tertiary carbon atoms which are reactive sites for oxidation. Because of this it is necessary to add antioxidants to stabilise the polymers against oxidation Some polyolefins may be cross-linked by peroxides. 

Polymers containing oxazoline groups are obtained either by grafting the 2-oxazoline onto a suitable existing polymer such as polyethylene or polyphenylene oxide or alternatively by copolymerising a monomer such as styrene or methyl methacrylate with a small quantity (<1%) of a 2-oxazoline. The grafting reaction may be carried out very rapidly (3-5 min) in an extruder at temperatures of about 200°C in the presence of a peroxide such as di-t-butyl peroxide Figure 7.13). 

Vulcanised (cross-linked) polyethylene is being used for cable application where service temperatures up to 90°C are encountered. Typical cross-linking agents for this purpose are peroxides such as dicumyl peroxide. The use of such agents is significantly cheaper than irradiation processes for the cross-linking of the polymer. An alternative process involves the use of vinyl silanes (see Section 10.9). 

Calendering processes, of great importance in the production of sheet materials from PVC compounds, are little used with polyethylene because of the difficulty in obtaining a smooth sheet. Commercial products have, however, been made by calendering low-density polymer containing a small amount of a peroxide such as benzoyl peroxide to give a stiff but crinkly sheet (Crinothene) which was suitable for lampshades and other decorative applications. 

The third process for cross-linking is the Sioplas process developed by Dow. The first stage of this involves the grafting of an easily hydrolysable trialkoxyvinylsilane onto the polyethylene chain, the site activation having been achieved with the aid of a small amount of peroxide. The compound is then extruded onto the wire, which is collected on a drum. The drum is then exposed to hot water, or, more commonly, low-pressure steam. The water hydrolyses the alkoxy groups, which then condense to form a siloxane cross-link. ... 

Another common initiator system is based on chlorosulfonated polyethylene (trade-name HYPALON ). Adhesives based on this technology were referred to as RF (short for Reactive Fluid) or DH (DuPont HYPALON ) in the early literature. Chlorosulfonated polyethylene reacts with an amine (and optionally a peroxide) to form free radicals [55]. 

Po[yamine disulphides do not inhibit peroxide vulcanization of polyethylene, are stable in air up to 300-350°C, exhibit good compatibility and show no sweating out from the polyethylene mass. Table 8 gives the comparison between the efficiency of polyamine disulphides as thermostabilizers of cured polyethylene. 

ACPA azobis(4-cyanopentanoic acid) AIBN azobis isobutyronitrile) BPO benzoyl peroxide DVB divinyl benzene, EGA 2-ethylcyano-acrylate HPC hydroxypropyl cellulose MMA methyl methacrylate PAAc polyacrylic acid PEI polyethyleneimine, PEO/PPO polyethylene oxide/polypyropylene oxide copolymer PVME polyvinylmethylether PVP polyvinylpyrrolidone K-30 DMSO dimethylsulfoxide PGA polyglutaraldehyde CMS chloromethylstyrene PMMA-g-OSA polymethylmethacrylate grafted oligostearic acid. 

MMA onto cellulose was carried out by Hecker de Carvalho and Alfred using ammonium and potassium persulfates as radical initiators [30]. Radical initiators such as H2O2, BPO dicumylperoxide, TBHP, etc. have also been used successfully for grafting vinyl monomers onto hydrocarbon backbones, such as polypropylene and polyethylene. The general mechanism seems to be that when the polymer is exposed to vinyl monomers in the presence of peroxide under conditions that permit decomposition of the peroxide to free radicals, the monomer becomes attached to the backbone of the polymer and pendant chains of vinyl monomers are grown on the active sites. The basic mechanism involves abstraction of a hydrogen from the polymer to form a free radical to which monomer adds ... 

---