Ring-banded spherulites of six-arm star-shaped poly(ε-caprolactone) with different arm length via CO₂

The lamellae structure and the ring-banded features of the concentric ring-banded spherulites grown from six-arm star-shaped poly(ε-caprolactone) (PCL) with different arm length under CO₂ condition were investigated by polarized optical microscope, atomic force microscopy, and scanning electronic microscopy in this paper. Experimental results indicated that the concentric ring-banded spherulites with alternative periodically ridge and valley bands with continuous edge-on lamellae formed under the condition of CO₂. The band space got narrower, and the number of the ring bands increased in PCL with the increasing pressure due to the plasticization effect of CO₂. The band space of the six-arm star-shaped PCL with longer arm length was wider than that of the six-arm star-shaped PCL with shorter arm length whereas the number of ring bands was fewer. Because of the longer arm length which resulted in the higher entanglement, the chain mobility of the star-shaped PCL with longer arm length decreased markedly. The different entanglement resulting from the different arm length structure was considered to be the primary factors influencing the characteristic crystallization of the six-arm star-shaped PCL.