Confined crystallization of poly(DL-lactide) -b-poly (ethylene oxide) block copolymers: Molecular architecture influence
Recently, considerable attention has been paid to confined polymer crystallization. Both physical and chemical methods have been used to design various models of confined environments for polymers to further investigate the mechanism of crystallization. In our previous papers 1～3, it was demonstrated that chain end restriction on the crystalline block is the main cause for confined crystallization in block copolymers but not spatial confinement. In this study, by designing different molecular architectures4, such as linear and star-shaped crystalline-amorphous block copolymers, which varies the chain end restriction on the crystalline block, we investigate the molecular architecture influences on the confined crystallization of linear poly(DL-iactide) -b-poly(ethylene oxide) (LPDLLA-b-PEO) and four-armed star-shaped poly(DL-lactide)-b-poly(ethylene oxide) (S4PDLLA-b-PEO), with poly(ethylene oxide) (PEO) homopolymer as a comparison. Firstly, the crystallization behaviors of the samples from the melt were determined by differential scanning calorimetry (DSC). The free PEO homopolymer crystallizes easily at 37.8℃, but a greater driving force isneeded for LPDLLA-b-PEO which has a crystallization temperature of 22.6 ℃, for PEO block is tethered by the amorphous block in LPDLLA-b-PEO. However, the most fiercely tethered PEO block in S4PDLLA-b-PEO does not crystallize during the cooling process at all. The difference of the crystailizability of the samples leads to obviously various spherulitic morphologies as determined by polarized optical microscope (POM): The free PEO homopolymer presents general spherulites,while ring-banded spherulites are found in both the LPDLLA-b-PEO and S4PDLLA-b-PEO samples, with different interband widths. It implies the effect of the chain end restriction could induce the formation of ring-banded spherulites.
confined crystallization chain end restriction four-armed star-shaped poly(DL-lactide)-b-poly(ethylene oxide) linear poly(D, L-lactide)-b-poly(ethylene oxide)
Feng-Bo Zhang Xu-Ming Xie Wei-Zhong Yuan Jin-Ying Yuan
Advanced Materials Laboratory,Department of Chemical Engineering,Tsinghua University,Beijing,100084, Department of Chemistry,Tsinghua University,Beijing,100084,China
国际会议
5th East-Asian Polymer Conference(第5届东亚高分子学术研讨会)
上海
英文
222-223
2008-06-03（万方平台首次上网日期，不代表论文的发表时间）