Abstract
The data presented in this paper can best be summarized as follows: 1. With present equipment 13C-NMR cannot distinguish cis—trans junctures in BuLi catalyzed poly(butadiene). 2. Cis—trans content in poly(butadiene) can now be determined by 1HNMR at 300 MHz. 3. The cis—trans content in low vinyl n-BuLi catalyzed polymers is best determined in the olefinic region. 4. The cis—trans content in high vinyl is best determined in the aliphatic region, although contents above 60 per cent become difficult to determine because of overlap with the methine proton of the vinyl unit. 5. Cis—trans ratios are constant over the measurable range of vinyl content. 6. The cis—trans triad sequence distribution and hence the mole fraction of triads can be determined by 1HNMR at 300 MHz. 7. The triad sequences best fit a random distribution. 8. The 1,2 unit is inserted in a random manner, i.e., the unit enters the chain with no preference for any triad sequence.
13C-NMR of Polyisoprenes: Sequence Distribution of cis-1,4 and trans-1,4 Units