What drives the price gap between polymer-grade and industrial-grade isobutene in China?

What drives the price gap between polymer-grade and industrial-grade isobutene in China?
Isobutene pricing in China is fundamentally tiered by purity, with each grade serving a distinct value chain. Industrial-grade (50-85%) feeds MTBE, tert-butanol and tert-butylamine, competing largely on feedstock cost from refinery C4 streams. Chemical-grade (≥95%) goes into MMA, pivalic acid and isoprene, while polymer-grade (≥99%) is the critical monomer for butyl rubber and polyisobutylene. The purity spread is not linear—polymer-grade commands a significant premium because impurities poison cationic polymerization catalysts and destabilize molecular weight distribution. Downstream demand is shifting upward: butyl rubber accounts for roughly 60% of isobutene consumption, and growth in new-energy vehicle tires and medical stoppers is pulling more volume into the high-purity segment. Meanwhile, MTBE demand is structurally declining as gasoline additive policies tighten, which is squeezing the low-end market and reinforcing the premium for ≥99% material.