Polychloroprene polymers

Polychloroprene polymers also vary in the degree of branching in the polymer. Polychloroprenes with little or no branching are called sol polymers, whereas those with considerable branching are referred to as gel polymers. Sol polymers are soluble in aromatic solvents. All of the solvent-grade polychloroprene polymers (except Neoprene AG) are sol polymers. The gel content in the polychloroprene affects the cohesive strength, resilience, elongation, open tack time, resistance to permanent set, and oil swell. 

Heat, See also High temperature entries Hot entries Temperature entries Therm- entries effect on rubber aging, 27 785 in ethylene oxidation, 70 650 exponents of dimensions, 8 585t external resistance to, 25 312-316 in industrial hygiene, 74 221 wood reaction to, 26 348-351 Heat aging, of polychloroprene polymers, 79 844-845... 

Polychloroprene latex adhesives, 1 533-534 Polychloroprene latexes, 19 854-861 applications for, 19 857, 859-861 compounding, 19 857-859 global product line of, 19 855 stabilization of, 19 855-857 Polychloroprene polymers branching parameters of, 19 839 commercial, 19 851-852 crystallization of, 19 843-844 cure site for, 19 837... 

The allylic chloride moiety is the cure site for polychloroprene pol5uners (Fig. 2). The reaction of the labile allylic chlorides with bifimctional nucleophiles, metal oxides, or thioureas covalently joins interpolymer chains into a polymer network. The pol5uner cross-link density is proportional to the concentration of allylic chlorides on the polymer backbone. Thus mechanical goods with high modulus are made from polymers of high allylic chloride concentration. On the other hand, high levels of allylic chlorides decrease the thermal stability of polychloroprene polymers per mechanism described for thermal degradation of imsaturated diene polymer (56,57)... 

Hydrogen chloride evolution with polymer degradation did not occur readily at 120°C in a nitrogen atmosphere (96). At much higher temperatures (eg 275°C), the polychloroprene polymer was carbonized with HCl liberated by a non-free-radical mechanism (134). Polymer polymerized at low temperatures showed better thermal stability (93). 

Polychloroprene latexes are aqueous dispersions of synthetic polychloroprene polymers with surfactants. The surfactants of choice are markedly different than the protein-based surfactants contained in natural rubber latex that is reportedly at the root of human hypoallergenic reactions associated with the use of natin-al rubber latex. 

As shown above, the bulk of a commercial polychloroprene polymer chain consists of trans-1,4- segments. The presence of the chlorine atom attached to one of the double bond carbons results in both the double bond and the chlorine having a low reactivity. Because of the low double bond reactivity such polychloroprenes are not reactive to sulphur and cannot be vulcanized by conventional diene polymer methods. 

Fig.1. The effect of radiation dose on the mechanical properties of a polychloroprene polymer. E denotes elongation at break, H represents Shore D hardness, and R represents the tensile strength [18]...

Polychloroprene (Neoprene) (Steinfink, 1977 Dick, 1987 Prane, 1990) -Polychloroprene polymers were developed in 1932 but not widely used because of high price until natural rubber became unavailable during World War II. Neoprene is manufactured by the polymerization of 2 chloro-1,3-butadiene. Dming polymerization the chloroprene molecule is added to die polymer chain in four different isomeric forms. 

The bi-products of polymer degradation can also have a damaging effect on the durability of adhesive and sealant bonds necessitating the addition of specific stabilizers. For example polychloroprene polymers can decompose by dehydrochlorination, liberating hydrochloric acid, which can attack the adhesive or sealant and the substrates. The addition of metal oxides, such as zinc oxide or magnesium oxide, which act as add acceptors helps to overcome this problem. 

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