Vulcanisation of Other Elastomer Systems

Microstructural changes of an accelerated sulfur vulcanisation of HR with TMTD/ZnO/ sulfur has been studied by solid-state 13C NMR spectroscopy [47]. The HR containing 2% isoprene and 98% isobutylene were formulated using EV and cured at 160 °C for several cure times. The resonances at 20.3 and 24.4 ppm, which are due to trans isoprene units in the HR, decrease with cure, while the resonances at 26.9 and 25.2 ppm which arise from cis isoprene units increase with cure times. The cis trans ratio increases up to a maximum ratio of approximately 4 1 at a cure time of 60 minutes. New resonances are observed at 15, 21, 23.6 and 49 ppm. The peak at 49 ppm is assigned to the mixture of the isoprene units in czs-IIR, polysulfidic Alt and polysulfidic Ale structures. The resonance peaks at 15, 21 and 23.6 ppm are assigned to the isoprene units in mono- and polysulfidic Bit, mono- and polysulfidic Blc and polysulfidic Alt structures, respectively. No reaction occurs in the isobutylene units. No migration of the double bond saturation, internal cyclisation or sulfurisation resulting in Clt and Clc structures is observed. 

The curing of brominated poly(isobutylene-co-4-methylstyrene) by pure ZnO was studied by solid-state TT and 13C MAS NMR [48]. From NMR results, crosslinking appears to occur by aromatic ring addition of the benzylic carbocation generated from an intermediate PhCH2-Br-Zn complex. 

Solid-state 13C NMR has been used to identify elastomers in binary blends of chloroprene (CR) and NR, CR and CSM, NR and CSM, and SBR and acrylonitrile-butadiene rubber (NBR). The type of NBR can be determined by identifying the sequences of acrylonitrile and butadiene. The tertiary blend of NR/SBR/BR was also studied [49]. High-temperature 13C solid-state NMR identified ethylene-propylene diene terpolymer (EPDM) and fluoro and nitrile rubbers [50]. 

Elastomeric components and compositions in BR/SBR and NR/BR/SBR blends have been studied by 13C solid-state NMR. The MAS spectra are of sufficient quality for polymer identification of the carbon black filled vulcanisates in most cases [51]. 

Vulcanised SBR/EPDM diblends were quantitatively characterised by solid-state 13C NMR spectroscopy. The SBR/EPDM blend ratio can be determined as well as the czs-1,4, transit and vinyl-1,2 butadienes and styrene ratios in the SBR and the ethylene and propylene contents in the EPDM. No evidence for homo- and co-vulcanisation has been obtained in these systems. No evidences are found for the change in cisitrans ratio in the SBR upon the vulcanisation [52], 

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