More (most) senior CRU of a structure of a macromolecule or oligomer molecule containing two or more different types of CRUs.
Notes: - The CRU beginning with the subunit of highest (higher) seniority is chosen as the S-CRU.
- If CRUs begin with an identical subunit, the choice depends on the seniority of the remaining subunits and the number and position of substituents.
Examples: - \(\ce{-[O-CH2CH2]_{n}\bond{-}}\ \rm{not}\ \ce{-[N-CH2CH2]_{n}\bond{-}}\)
- \(\ce{-[O-COCH2]_{n}\bond{-}}\ \rm{not}\ \ce{-[O-CH2CH2]_{n}\bond{-}}\)
Source:
PAC, 2021, 93, 963. 'Structure-based nomenclature for irregular linear, star, comb, and brush polymers (IUPAC Recommendations 2020)' on page 966 (https://doi.org/10.1515/pac-2020-0103)