I’m seeing a copolyester where 2 mol% urethane-bearing comonomer cuts oxygen permeability about 30% but pushes Tg by +8 °C; has anyone cleanly decoupled barrier from transition temperature with supramolecular fillers or sparse ionic crosslinks rather than traditional plasticizers? DMA/TGA yesterday showed a narrower tan δ and Izod down about 20% at 23 °C, so I’m hunting architectures or additive windows that keep toughness while keeping O2 down for food-packaging grades…
I’d try a UPy “sticker” additive: blend about 0.5–1 wt% UPy-endcapped oligomer to form reversible H-bond clusters that tighten O2 pathways without a big Tg bump — think “Velcro, not bolts.” If you can, a light biaxial orient/anneal just above Tg often amplifies the barrier without a Tg penalty, and it kept Izod acceptable in our PET films.
@juliaf67’s idea plus catechol–Fe3+ clusters (about 0.3 wt%): tighten O2 without +Tg, minimizing further Izod loss at 23 °C.