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Polychloroprene cross-linking

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. [Pg.223]

In some cases, diene polymers (for instance polychloroprene rubbers) can add to the growing polymer chain by 1,2 addition (also called vinyl addition). This creates labile hydrogen or reactive halogen on tertiary carbon atoms. A few percent of this type of structure in the rubber will assist cross-linking reactions. [Pg.580]

During emulsion polymerization, a high conversion of monomer to polymer produces cross-linked rubber which is insoluble. To obtain a high conversion in the polymerization reaction and a processable polymer, suitable polymer modification should be made. The use of sulphur moieties allows this goal to be reached [2]. Sulphur-modified polychloroprenes contain di- and polysulphide sequences in the polymer chains. After the polymerization reaches the desired degree, reaction is stopped by adding thiuram disulphide ... [Pg.590]

Metal oxides. Magnesium oxide is used to cure polychloroprene by converting its few active allylic chloride from 1,2 addition into ether cross-links. There is a synergistic effect when magnesium oxide is used in combination with t-butyl phenolic resins in solvent-borne polychloroprene adhesives. When solvent is removed, the phenolic group in the resin reacts with the magnesium oxide to cross-link [49]. [Pg.639]

The most common use of curing agents is with carboxylic latices. Isocyanates and melamines can be used but zinc oxide is the most common curing agent. Zinc oxide cross-links carboxylated latices and improves bond strength by ionomer formation [78]. Carboxylated polychloroprene reacts slowly with zinc oxide in dispersed form, causing a gradual increase in adhesive gel content. This can lead to restricted adhesive shelf life. Resin acid sites compete with the polymer acid sites for Zn(II). The more resin acid sites, the more stable the adhesive. [Pg.669]

Polychloroprene and Hypalon are usually cross-linked with metal oxides which combine with reactive side groups in the polymer chain. [Pg.939]

In more recent years, lining compounds have been developed that vulcanise at ambient temperatures. Most polymers can be used for such compounds, although most materials are based on natural rubber, acrylonitrile-butadiene rubber and polychloroprene. These compounds contain accelerators which usually give rise to a material which has a delay in the onset of vulcanisation with a subsequent rapid rise in cross-link formation to give full vulcanisation in 6 to 8 weeks. Such materials, unless to be used within a few days of manufacture, are refrigerated to arrest the sel f-vulcanisation. [Pg.940]

Better cross-linking with the latter also improves post Tg viscoelastic responses of the rubber vulcanizates. Similar effect has also been observed with polychloroprene as investigated by Sahoo and Bhowmick [41]. Figure 4.8 represents the comparative tensile stress-strain behavior of polychloroprene rubber (CR) vulcanizates, highlighting superiority of the nanosized ZnO over conventional rubber grade ZnO [41]. [Pg.94]

The rate of 7-radiation-induced cross-linking in the crystalline and amorphous regions of a crystallizable polychloroprene has been measured by Makhlis et al. [75] who have found a considerably lower cross-link density and less degradation in the crystalline portion of the rubber. The cross-links have been posmlated to be mainly intramolecular in crystalline regions and intermolecular in the amorphous phases. [Pg.863]

Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. [Pg.864]

The cross-linking efficiency of the more branched polychloroprene latex (mercaptan modified) has been found to be higher than the less branched sulfur-modified one. The latex dispersion is found to display higher rate of cross-linking than the coagulated and subsequently dried mbber films [386] due to higher concentration of radical in the former. [Pg.891]

In the case of crystaUizable polychloroprene, the cross-link density has been found to be lower in the crystalline region as compared to the amorphous portion of the mbber due to the lower radical mobility in the former. The cross-links are found to be intramolecular in the crystalline zone [387]. [Pg.891]

Chemicals like polyorthoaminophenol, diphenylamine in small amounts have been found to decrease the yield of cross-linking [388]. The tensile strength of the carbon black-filled polychloroprene compounds has been found to be comparable to the conventional thermally cured one. The physical properties [389] have been observed to improve on adding cross-linking promoters like A,A -hexamethylene-bis-methacrylamide into the polymer matrix. [Pg.891]

These steps are typical for most of the synthetic elastomers. The use of sulfur for vulcanization is common for the production of most elastomers. Magnesium and zinc oxides are often used for the cross-linking of polychloroprene (CR). Saturated materials such as EPM and fluoroelastomers are cross-linked using typical organic cross-linking agents such as peroxides. [Pg.556]

Metal Oxides. Halogen-containing elastomers such as polychloroprene and chlorosulfonated polyethylene are cross-linked by their reaction with metal oxides, typically zinc oxide. The metal oxide reacts with halogen groups in the polymer to produce an active intermediate which then reacts further to produce carbon—carbon cross-links. Zinc chloride is liberated as a by-product and it serves as an autocatalyst for this reaction. Magnesium oxide is typically used with ZnCl to control the cure rate and minimize premature cross-linking (scorch). [Pg.236]

Irradiation of polychloroprene latexes of two different structures, one containing some sulfur and having a lower degree of branching, and another highly branched polymer made by mercaptane modification, showed a more rapid cross-linking of... [Pg.107]

The oxidation of polychloroprene is more complex, largely as a result of the scission and cross-linking of the polymer. The general features of... [Pg.242]

The vulcanization of polychloroprene (Neoprene) is carried out in different ways. Conventional sulfur vulcanization is not practiced to a large extent, since best physical properties of neoprene rubber are achieved by vulcanization with metal oxides (without diamine), either alone or in combination with sulfur (sometimes together with an accelerator). Halogenated butyl rubber is cross-linked in a similar manner. The mechanism for cross-linking with metal oxide alone is not established. [Pg.74]

The influence of additives on thermal degradation may be exemplified by the FTIR-EGA study of the effect of zinc oxide on the pyrolysis of polychloroprene (15). This effect (fig 5) has been recognised for some time (16-18) and has generally been attributed to the catalytic action of zinc chloride formed during cross-linking of the polychloroprene (19). We have examined the effect of ZnO, ZnS, ZnCl2 and ZnS04 on the pyrolysis of polychloroprene and found that only zinc oxide results in the effects seen in fig 5. [Pg.106]

When the polymerization reaches 90% conversion, the reaction mixture is cooled to 20°C and tetraethylthiuram disulfide is added. This is done to prevent the pendant unsaturation in the polychloroprene backbones from cross-linking or forming branches. An unmodified polymer is difficult to process even at a 70% conversion. To overcome this, a sulfur-tetraethylthiuram modification is carried out. [Pg.359]

Most Rubber-based adhesives may be cured by a sulphur-based vulcanizing system (see Rubber-based adhesives compounding), however, as mentioned in Polychloroprene rubber adhesives applications and properties, CR adhesives are cross-linked by various reactions involving the labile chlorine atoms in the repeat unit. This is reflected in the additives used, as discussed below. ... [Pg.332]


See other pages where Polychloroprene cross-linking is mentioned: [Pg.891]    [Pg.439]    [Pg.891]    [Pg.439]    [Pg.223]    [Pg.543]    [Pg.545]    [Pg.635]    [Pg.395]    [Pg.223]    [Pg.1349]    [Pg.180]    [Pg.41]    [Pg.545]    [Pg.492]    [Pg.185]    [Pg.227]    [Pg.243]    [Pg.142]    [Pg.151]    [Pg.635]    [Pg.435]   
See also in sourсe #XX -- [ Pg.139 ]




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