Peroxide-initiated crosslinking

Cansarz, I. and Laskawski, W. 1979. Peroxide-initiated crosslinking of maleic anhydride-modified low-molecular-weight polybutadiene. I. Mechanism and kinetics of the reaction. 

Chodak, I. and Lazdr, M. (1986) Peroxide-initiated crosslinking of polypropylene in the presence of p-benzoquinone, /. Appl. Polymer Sci., 32, 5431-5437. 

Unsaturated polyester finishes of this type do not need to be stoved to effect crosslinking, but will cure at room temperature once a suitable peroxide initiator cobalt salt activator are added. The system then has a finite pot life and needs to be applied soon after mixing. Such a system is an example of a two-pack system. That is the finish is supplied in two packages to be mixed shortly before use, with obvious limitations. However, polymerisation can also be induced by ultra violet radiation or electron beam exposure when polymerisation occurs almost instantaneously. These techniques are used widely in packaging, particularly cans, for which many other unsaturated polymers, such as unsaturated acrylic resins have been devised. 

The crosslinking efficiency of many peroxide-initiated free radicals is low. These labile radicals can be converted to more stable radicals by contact in situ with polyfunctional monomers to form a three-dimensional network. Crosslinking efficiency is thus increased by some 20%. In addition, these materials act as plasticisers during processing and in some cases also act as hardening agents. 

Crosslinking of alkyds containing conjugated double bonds results in more carbon-carbon bonds in the crosslinks than in the alkyds containing unconjugated double bonds. The crosslinking mechanism involves the formation and decomposition of cyclic peroxides, to yield radicals that initiate crosslinking by 1,4-polymerization of the polymer molecules. 

High crosslinking density was reached using BPA/DC, trimethylolpropane trimethacrylate and p-toluenesulfonic acid monohydrate [125]. A composition based on BPA/DC and 2,2-bis[4-(2-hydroxyethoxy)phenyl] propane dimethacrylate with a peroxide initiator and Fe acetylacetonate catalyst contains, moreover, a block... 

Itoh et al. [141] patented a blend of polyurethane and silicone gum with vinyl groups. The crosslinking reaction of the silicone component was achieved using a radical generator. Chorvath et al. [142] also patented a system composed of polyamide or polyester as the thermoplastic and vinyl-containing polysiloxane cured by a peroxide or non-peroxidic initiator such as 3,4-dimethyl-3,4-diphenylhexane (HTV). Moreover, they added different compatibilizers such as amino-terminated or amino-grafted polysiloxane, epoxy- or isocyanato-functionalized polysiloxane. 

Espercarb . [Witco/Aigus] Peroxide derivs. initiator, crosslinking agent for polymers. 

Perkadox [Akzo Akzo Ghent BV] Peroxide d vs. initiators, crosslinking agents. 

Trigonox . [Akzo Akzo Chem. BV] Peroxide derive. initiator, crosslinking agent... 

Peroxides initiate the crosslinking of polyolefins by a homolytic cleavage of the 0—0 bond to alkoxy radicals... 

For the decomposition of dicumyl peroxide in LDPE (2% w.) at 160 °C, the efficiency of peroxide in crosslinking was about 87% [103]. Such a hi efficiency may be ascribed to the contribution of physical entanglements to the overall number of chemical crosslinks and to the presence of unsaturated C=C bonds in a polymer. We may recall that during dimerization of low molecular alkanes initiated by rert.butyl... 

Uses Initiator, crosslinking agent, detackifier for low temp, or photocured free radical polymerizations, peroxide-cured adhesives, cast vinyl or acrylic sheet, high-solids peroxide-cured coatings, open-mold peroxide-cured composites, UV-cured coatings (esp. pigmented)... 

Uses Polymerization initiator, crosslinking agent for emulsion, bulk, sol n., and suspension polymerization, high temp, cure of polyester, and cure of acrylic syrup Trade Name Synonyms Luperox TAEC [Atofina SA http //www.atofina.com, Atofina http //www.atofinachemicals.com] Trigonox 131 f[Akzo Nobel http //www.akzonobel.com] t-Am yl peroxy neodecan oate CAS 68299-16-1 Empirical C15H30O3 Properties M.w. 258.40 Uses Initiator for vinyl polymerizations Manuf./Distrib. Akzo Nobel http //WWW. akzonobel. com Trade Name Synonyms Aztec TAPND-75-AL [Aztec Peroxides] t-Amylperoxyneoheptanoate Empirical C12H24O3 Properties M.w. 216.32 Uses Initiator for polymerizations... 

Formula (CH3)3COOCOOCH2CHC2H5(CH2)3CH3 Properties Clear liq. m.w. 246.34 sp.gr. 0.93 (20 C) f.p. < -75 C flash pt. > 93 C dec. on heating with half-life of 10 h 100 C Uses Initiator, crosslinking agent for polymerization of vinyl monomers, styrene, acrylates, and unsat. polyester resins Trade Name Synonyms Aztec TBPEH C [Aztec Peroxides] Esperox C-496 [Crompton/Olefins Styrenics] Luperox TBEC [Atofina SA http //www.atofina.com]] Trigonox 117 [Akzo Nobel http //www.akzonobel.com] t-Butyl peroxyisobutyrate CAS 109-13-7... 

Chain-Growth Polymerisation with Termination A major exponent of this class of polymerisations are free radical polymerisations in the presence of a radical initiator. A classic example is the crosslinking (co)polymerisation of unsaturated polyester resins with styrene, initiated by the decomposition of a peroxide initiator. Some important reaction steps involved in free radical polymerisations are sketched in Reaction scheme 4. 

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