Transformation of Semicrystalline Polymer Mechanics by Cyclic Polymers

Cyclic polymers have garnered significant interest due to the lack of chain ends and the unique topological constraints of non-concatenation. Experiments in this joint experimental and computational work focus on comparative analysis of semicrystalline linear and cyclic polycyclooctene (PCOE). Uniaxial tensile tests show that crosslinked cyclic PCOE exhibits lower tensile strength than crosslinked linear PCOE at the same crosslinking density, while it may be stretched to a larger strain before failure. DMA shows that the cyclic PCOE possesses a lower glass transition temperature and a lower rubbery plateau modulus. WAXS results show that the crystallinity in crosslinked cyclic PCOE is lower than in its linear counterpart, but the crystallinity is less than 25% and converges to an intermediate value of 15% upon deformation to a tensile strain of 100%. Molecular dynamics simulations using a crystallizable coarse-grained polyethylene model reproduce the lower stress level and larger stretchability of crosslinked semicrystalline cyclic polymers at low crystallinity. The simulations further demonstrate the more compact conformations of non-concatenated cyclic polymers result in fewer entanglements per network strand and thus transform the semicrystalline polymer mechanics.