The Impact of Isotopic Substitution on the Crystallization and Melting Behaviors of Selectively Deuterated Poly(ε-caprolactone)s*

We have previously shown that material properties of conjugated polymers can be tuned by selective deuteration,¹ which is also an important tool for various analytical techniques. Here we investigate the effects of deuteration on the crystallization and melting behaviors of poly(ε-caprolactone) (PCL). Partially and fully deuterated PCLs of matching molar masses are polymerized from novel deuterated monomers. The deuterated PCLs crystallize and melt at lower temperatures with a smaller change in enthalpy than the protonated PCL when measured by calorimetry. Considering that their crystal structure, crystallinity, and lamellar packing are minimally impacted by deuteration, we hypothesize that the observed differences are attributable to weaker intermolecular interactions of the deuterated PCLs. Interestingly, selective deuteration only on the carbons adjacent to the ester group leads to slower crystallization, which could result from the isotopic heterogeneity. Quantum mechanical MD simulations are attempted to analyze the differences in their molecular interactions.
1. Nat. Commun. 2014, 5, 3180; J. Phys. Chem. Lett. 2017, 8, 4333.