119. Bimodal architecture and rheological and foaming properties for gamma-irradiated long-chain branched polylactides
writer：Huagao Fang, Yaqiong Zhang, Jing Bai, Zhongkai Wang and Zhigang Wang*
keywords：長鏈支化，聚乳酸，伽馬射線，流變學，發泡
source：期刊
specific source：RSC Advances, 2013, 3(23), 8783-8795.
Issue time：2013年
Bimodal architecture and rheological and foaming properties for gamma-irradiated long-chain branched polylactides
Huagao Fang, Yaqiong Zhang, Jing Bai, Zhongkai Wang and Zhigang Wang*
RSC Advances, 2013, 3 (23), 8783-8795.
志剛等在此感謝RSC Advances期刊編輯和審稿人對于我們研究工作的理解和支持！
Zhigang Wang et al. appreciate the nice consideration on our work from the journal editor and the reviewers. We are grateful to their understanding and their supporting.
γ-輻照制備二元鏈結構的長鏈支化聚乳酸和其流變學和發泡特性
通過γ射線輻照引發線性PLA前驅物和三官能團單體三羥甲基丙烷三丙烯酸酯（TMPTA）反應制備了一系列長鏈支化聚乳酸（LCB-PLAs），通過配置多角度光散射檢測器的體積排阻色譜（SEC-MALLS）和流變儀研究了長鏈支化聚乳酸的拓撲鏈結構。SEC-MALLS測試結果表明，γ射線輻照制備的長鏈支化聚乳酸不僅有較高的重均分子量而且包含由短的線性鏈組分和長支化鏈組分組成的二元鏈結構，而電子束輻射制備的長鏈支化聚乳酸只顯示出單一結構。長鏈支化結構的引入有助于增強聚乳酸熔體的復數粘度，剪切變稀特性和末端儲能模量，使得 van Gurp-Palmen 圖中，相位角出現偏離線性鏈的“普適”主曲線。通過熱流變行為和活化能分析，長鏈支化聚乳酸的二元鏈結構被進一步確認。77 kJ/mol左右的活化能表明長鏈支化聚乳酸中仍然存在線性的大分子鏈，而在大相位角表現出較高的活化能則與LCB的存在有關。零剪切粘度與重均分子量的依賴關系（η0-Mw圖）表明長鏈支化聚乳酸呈現樹枝狀的拓撲結構。文中根據γ-輻照的劑量率顯著低于電子束輻照來解釋了兩種輻照條件所導致的不同鏈結構機理。長鏈支化聚乳酸拓撲鏈結構的引入有助于改善其發泡特性。
Abstract: A series of long-chain branched polylactides (LCB-PLAs) were prepared from a linear PLA precursor by applying gamma radiation with addition of the trifunctional monomer, trimethylolpropane triacrylate (TMPTA) and their topological structures were investigated by size-exclusion chromatography coupled with a multiangle light scattering detector (SEC-MALLS) and rheology. SEC-MALLS measurements show that LCB-PLAs exhibit not only the increased weight-average molecular mass but also a bimodal architecture with a short linear chain fraction and a LCB fraction, as compared with LCB-PLA samples
generated by electron-beam radiation, which only show the monomodal macromolecular structure. The introduction of LCB structure contributes to the enhancement of complex viscosity, shear-thinning and storage modulus, and the deviations of phase angle, d from the ‘‘universal’’ curve of linear PLA in d(|G*|) plots (van Gurp–Palmen plot). By the analysis of the thermorheological behaviors and determination of activation energies, the bimodal architecture is confirmed. Activation energies around 77 kJ mol21 lead to an expectation that some linear macromolecules are still present in LCB-PLAs, while the higher activation energies at large phase angles are associated with the existence of the LCB ones. A conclusion with respect to the tree-like topography for LCB-PLAs is drawn from the molecular mass dependences of zero-shear viscosity (g0–Mw plot). An explanation to these findings is provided under the consideration of the radiation dose rate for the gamma radiation. The remarkable modification of PLA topological chain structure contributes to the improvement of the foaming properties of LCB-PLAs.