Bisalkylation Theory of Neoprene Vulcanization

Mechanism for Cross-Linking Polychloroprene With Ethylene Thiourea and Zinc Oxide

“…The evidence gathered up to this point largely substantiates the bis-alkylation mechanism of Kovacic 23 (shown in Scheme 2) including; (i) the acidic environment created when ETU is used to cross-link oligochloroprene, (ii) the new peak (at 1550 cm -1 ) in the FTIR spectrum (associated with a ν(C=C), shifted due to the ETU moiety), which does not disappear on soxhlet extraction, thus indicating the formation of this new bond during the curing process, and (iii) evidence that the cross-link bridge must be through the nitrogen atoms, as the sulfur-containing model compounds (ODT and TMTD) were unable to react with the polymer chain on their own.…”

“…29,[35][36] One of the by-products from the cross-linking mechanism proposed by Kovacic is HCl. 23 It is difficult to monitor the formation of such by-products when cross-linking in CR, but simpler to do so with low molecular weight oligomer. This is firstly because polychloroprene rubber has a relatively high molecular weight (M n ~250,000 g/mol) and reactions occurring in the polymer are thus difficult to monitor as cross-linking renders the material insoluble.…”

“…There are four isomers present within CR (shown in Figure 1), [13][14][15][16] but it is the 1,2-isomer which is central to the cross-linking process, 7,[17][18][19][20][21][22] due to its propensity to undergo allylic rearrangement. 23 There have been several cross-linking mechanisms for polychloroprene published in the literature; the two most prevalent are the bis-alkylation mechanism using ETU alone proposed by Kovacic 24 and the synergistic mechanism with ETU and ZnO initially suggested by Pariser. 25 The bis-alkylation mechanism involves ETU reacting directly to form a cross-link through the two nitrogen atoms, evolving hydrochloric acid (HCl) as a by-product.…”

Performance Level of Accelerator cum Antioxidants in Different Rubbers

“…The optimum cure time and cure rate index data indicate faster curing of natural rubber. The slow curing behavior of CR (Table 2) is due to the absence of Mg0 and/or ethylene thiourea (NA 22) which in the presence of ZnO enables faster curing [6,7].…”

Topologically Interpenetrating Polymeric Networks

“…The mixture was stirred and films were cast, dried and cured as above, thereby crosslinking the polymer via two mechanisms: the usual zinc oxide vulcanization and a bisalkylation [13] in which the crosslinking takes place at sites on the polymer chain where there are tertiary allylic chlorine atoms formed by 1, 2 polymerization of chloroprene monomer.…”