Vulcanization of chlorobutyl rubber. I. The identification of crosslink precursors in compounds containing ZnO/ZnCl2

✍ Scribed by K. G. Hendrikse; W. J. Mcgill; J. Reedijk; P. J. Nieuwenhuizen

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 201 KB
• Volume: 78
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/1097-4628(20001220)78:13<2290::aid-app60>3.0.co;2-p

✦ Synopsis

Chlorinated poly(isoprene-coisobutylene) (CIIR or chloro-butyl) was characterized by Nuclear Magnetic Resonance. Compounds with ZnO, ZnCl 2 , and ZnO/ ZnCl 2 were vulcanized in a DSC at a programmed heating rate and isothermally at 150°C in a press. Crosslink densities were determined by swelling and extracted ZnCl 2 analyzed by atomic absorption. ZnCl 2 formation precedes crosslinking, and at equilibrium only 50% of the chlorine in the rubber is extractable as ZnCl 2 . ZnCl 2 promotes crosslinking, and its addition to formulations decreases but does not eliminate the induction period prior to crosslinking. Dehydrohalogenation, which is catalyzed by ZnCl 2 in an autocatalytic process, is accompanied by the formation of conjugated diene butyl on the polymer chain. It is demonstrated that both species, not only ZnCl 2 , are necessary precursors to crosslink formation. Moist ZnCl 2 catalyzes dehydrohalogenation but not crosslinking, while ZnO does not promote either reaction. CIIR can be crosslinked to polybutadiene and to polyisoprene, no induction period applying when ZnCl 2 is present in the formulation, and high crosslink densities develop in blends precipitated from solution. Severe reversion occurs in formulations where there is insufficient ZnO to trap all of the HCl evolved.