End groups affected crystallization behavior of unentangled poly(ε-caprolactone)s

Abstract

The dynamics of polymer chains containing various topology including entanglement loops, tie molecules and end groups plays an important role in polymer crystallization. Poly(ε-caprolactone)s (PCL) with different end groups including phenyl, naphthyl and anthracenyl were synthesized with low molecular weight to avoid entanglement. The crystallization behavior of the synthesized PCLs was investigated via DSC, POM and X-ray, and the rheology property of the PCL melts was characterized. The largest end group resulted in the smallest spherulite growth rate and the longest half-time of crystallization. However, the effect of naphthyl and phenyl on the crystallization rate is close. The rheology results show low viscosity of naphthyl modified PCL, which is due to the compatibility of naphthyl and PCL. The master curves of the spherulite growth rate and the half-time of crystallization were obtained with the same supercooling regardless the end groups, which indicates that the polymer chains containing different end groups experience the possible same conformation changes during crystallization. Simultaneous SAXS/WAXS investigations on the heating samples with different end groups after isothermal crystallization all show doubled lamellar thickness during melting, which is possibly due to the transition from folded chains to extended chains in the dynamic favored metastable structures.