Terpenes versus linear alkyl substituents: effect of the terminal groups on the oligomers derived from poly(ε-caprolactone)

Abstract

Terpenes with olefin methyl branches and bifunctional hydroxyl groups were used as initiators in the ring-opening polymerization of ε-caprolactone (CL) catalyzed by ammonium decamolybdate (NH4)6[Mo7O24], resulting in α-hydroxyl-ω-olefin poly(ε-caprolactone) (PCL) (Co–PCL–OH). The degree of polymerization was kept low (5 and 10) in all the species to increase the weight percent of the terminal group. Additionally, to compare the effects of the olefin terminal groups on PCLs, another family of PCL oligoesters with a linear alkyl terminal group α-hydroxyl-ω-alkyl PCL (Ca–PCL–OH) was synthesized under the same conditions. The olefin and alkyl terminal groups contained gradually increasing numbers of carbons (C5, C10, and C15). Both families of PCL oligoesters were characterized by different analytical techniques such as GPC, NMR, MALDI-TOF, and FT-IR spectroscopy to corroborate the chemical nature of the oligoesters and their end groups. Thermal properties were analyzed by scanning differential calorimetry (DSC), which showed significant differences between olefin and alkyl terminal groups; this affected PCL crystalline domains, as evidenced by the crystallization temperatures (Tc), melting temperatures (Tm), and crystallinities (xi) of the PCLs. In addition, computational studies using density functional theory indicated the differences in molar volume for the olefin and alkyl terminal groups.