Crystallisation of star polyesters with poly (ε-caprolactone) arms approaching the problem of early stages in polymer crystallisation

Detta är en avhandling från KTH Royal Institute of Technology

Sammanfattning: The knowledge regarding early stages in polymer crystallisation remains inconclusive due to experimental limitations. The reason is that the initially formed polymer crystals rearrange rapidly at the crystallisation temperature. Faster experimental techniques or simulation would be suitable alternatives to approach the problem. Another possibility would be to use constrained polymer structures, in which crystal rearrangement would be slower. Star polymers with crystallisable arms may be structures sufficiently constrained to be captured in their early crystallisation stages.This study reports the crystallisation behaviour of linear poly(c-caprolactone) (PCL) and star polymers based on dendritic cores with grafted PCL arms. Wide angle X-ray scattering proved that the crystal structures of the different polymers were the same. The samples were also studied by differential scanning calorimetry, finding that the star PCL’s had lower crystallinity, lower rate of crystal rearrangement and higher equilibrium melting point than the linear analogues. Polarized optical microscopy showed that the star polymers crystallized slower and had greater tendency to form spherulites and higher fold surface free energy than linear PCL. The single crystal morphology was more irregular in the star polymers as observed by transmission electron microscopy.These findings confirm the constraining effect of the dendritic cores in the crystallisation of the PCL arms, which retard molecular rearrangement during crystallisation and turn the studied star polymers into excellent candidates to investigate the early stages in polymer crystallisation.