writer：Huagao Fang, Yaqiong Zhang, Jing Bai, Zhongkai Wang and Zhigang Wang*
keywords：长链支化，聚乳酸，伽马射线，流变学，发泡
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.

志刚等在此感谢RSC Advances期刊编辑和审稿人对于我们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-辐照制备二元链结构的长链支化聚乳酸和其流变学和发泡特性

通过γ射线辐照引发线性PLA前驱物和三官能团单体三羟甲基丙烷三丙烯酸酯（TMPTA）反应制备了一系列长链支化聚乳酸（LCB-PLAs），通过配置多角度光散射检测器的体积排阻色谱（SEC-MALLS）和流变仪研究了长链支化聚乳酸的拓扑链结构。SEC-MALLS测试结果表明，γ射线辐照制备的长链支化聚乳酸不仅有较高的重均分子量而且包含由短的线性链组分和长支化链组分组成的二元链结构，而电子束辐射制备的长链支化聚乳酸只显示出单一结构。长链支化结构的引入有助于增强聚乳酸熔体的复数粘度，剪切变稀特性和末端储能模量，使得 van Gurp-Palmen 图中，相位角出现偏离线性链的“普适”主曲线。通过热流变行为和活化能分析，长链支化聚乳酸的二元链结构被进一步确认。77 kJ/mol左右的活化能表明长链支化聚乳酸中仍然存在线性的大分子链，而在大相位角表现出较高的活化能则与LCB的存在有关。零剪切粘度与重均分子量的依赖关系（η0-Mw图）表明长链支化聚乳酸呈现树枝状的拓扑结构。文中根据γ-辐照的剂量率显著低于电子束辐照来解释了两种辐照条件所导致的不同链结构机理。长链支化聚乳酸拓扑链结构的引入有助于改善其发泡特性。

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.