Vulcanization of polychloroprene rubber. I. A revised cationic mechanism for ZnO crosslinking

Abstract

Data relating to the vulcanization of mercaptan-grade polychloroprene (CR) by ZnO and MgO (alone or in combination) are examined. Compounds were vulcanized through the isothermal heating of samples at 1408C in a laboratory press and at programmed rates in a differential scanning calorimeter. The reaction was stopped at various points during the heating process. The crosslink densities were determined via swelling. Extractable ZnCl 2 and MgCl 2 were analyzed by atomic absorption spectrometry. Three different crosslinking processes were identified. The first crosslinking process involved the activation of the highly reactive tertiary allylic 1,2-units along the polymer chain, whereas the second and third crosslinking processes were attributed to the activation toward crosslinking of 3,4-and 1,4-units, respectively. The crosslinking reactions of the 1,2-units comprised three distinct steps: isomerization (promoted by ZnO), dechlorination, and crosslinking. ZnCl 2 (which formed during compounding and upon crosslinking) promoted crosslinking, and its addition to formulations decreased but did not eliminate the induction period before crosslinking. MgO retarded the crosslinking process by limiting the formation of ZnCl 2 during mixing. The results of the CR/ZnO system are discussed, and a modified cationic mechanism for crosslinking is proposed.

MgO and ZnO as reinforcing fillers in cured polychloroprene rubber

“…(1) 14–16 where n is the number of elastically active chains per unit volume; V 1 is the molar volume of the solvent; χ is the polymer–solvent interaction parameter (the interaction parameter between CR and toluene = 0.38611,17); and υ 2 is the volume fraction of polymer in the swollen sample which can be calculated from eq. (2) 16…”

Strain‐induced crystallization behavior of polychloroprene rubber

“…Moreover, CR has peculiar vulcanization behavior, which is concluded to ionic crosslinking. 8 So the study of CR crystallization will enrich the knowledge of rubber crystallization and offer more information on the effect of crosslinking on the crystallization behavior of rubber. And its application in the improving antifatigue properties of NR by blending NR and CR will be illustrated in our following works.…”

Compatibility and nonlinear viscoelasticity of polychloroprene/polyvinyl chloride blends with nitrile butadiene rubber as a compatibilizer

“…Before blended with CR, PVC was firstly mixed with NBR in a mixing chamber (HAAKE Polylab OS, Thermo Electron Gmbh, Germany) at 120°C and 60 cpm. As HCl will be produced when the PVC is processed at high temperatures, MgO was also added into the chamber at this stage to prevent the generation of HCl. To get uniformly mixed and well dispersed CR/PVC blends, the pretreated PVC and CR gum were added into the mixing chamber again and mixed for another 6 min.…”