报告题目：Periodically Grafted Amphiphilic Polymers – To Fold and Stitch
报 告 人：S. Ramakrishnan（印度科学研究院教授）
报告时间：2025年5月6日（星期二）上午10:00—11:30
报告地址：广州国际校区C3-c204会议室
报告邀请人：程正迪院士
邀请单位：前沿软物质学院
报告人介绍：
Ramakrishnan completed his BSc from the University of Bombay, MSc from the Indian Institute of Technology, Bombay and received his PhD from the University of Massachusetts, Amherst, in 1988. After a two-year postdoctoral stint at the Corporate Research Laboratory of Exxon Research and Engineering Company at Annandale, New Jersey, he took up a faculty position in the Department of Inorganic and Physical Chemistry at the Indian Institute of Science, Bangalore. He served as the Chairman of Chemical Sciences Division for five years and later as Deputy Director for three years, before returning to full-time research in 2018. He was awarded the prestigious S S Bhatnagar Prize for Chemistry in 2005 and is currently a J C Bose Fellow. His research interests are in the design and development of novel polymerization methods, hyperbranched polymers, conjugated polymers, polymerization in ordered media, internally functionalized porous polymers and conformational control in synthetic polymers. He served as the President of the Society of Polymer Science-India (SPSI); has served on the Editorial Boards of Macromolecules and Polymer Chemistry, and was an Associate Editors of Chemical Communications, for almost a decade
报告摘要：
Some years ago, we showed that periodically grafted amphiphilic polymers (PGAPs), carrying hydrophobic alkylene backbone segments and hydrophilic polyoxyethylene (PEG) pendant segments, located at precisely periodic intervals, fold in a zigzag manner so as to collocate the alkylene segments at the center and the PEG segments on either side; it was observed that independent crystallization of both the backbone and pendant segments helped stabilize the folded structure. Subsequently, we demonstrated that inclusion of mesogens either within the backbone or pendant segment also lead to the formation of folded chains permitting a precise control of the distance between the mesogenic layers; these studies demonstrated that periodically grafted polymers could be an interesting design strategy to selectively locate desired functional units within well-defined layers in a bulk polymer.
Although the zigzag folding was earlier examined primarily in the solid state, one might expect the formation of such folded structures in a segment-selective solvents, such a polar solvent like water, that solvates the pendant PEG segments but not the alkylene backbone segments. In order to examine the folding of PGAPs in solution, we first prepared a periodically clickable polyester carrying a di-cinnamoyl ester unit within the hydrophobic backbone segment; this polymer was clicked with PEG-azides of different molecular weights (750, 1000 and 2000), as depicted in the above schematic. Several studies were conducted to probe the formation of the folded conformation with increasing solvent polarity; the photodimerization process of the dicinnamoyl units within the polymer backbone is evidently feasible only when the chain is folded in a zigzag fashion, which brings the cinnamoyl units in close proximity to permit the reaction. Hence, we examined the photodimerization process as a function of solvent polarity to gain an understandin5g of the folding process, which provided us some valuable insights into solvent induced conformational transition in such PGAPs. Furthermore, we showed that, when PEG2000 segments are installed, the cross-stitched folded chains remain in solution even after complete cross-stitching, suggesting that they have transformed into single-chain polymer nanoparticles (SCNPs). In the talk, I shall discuss the genesis of PGAPs, their design elements, their synthesis,Ramakrishnan completed his BSc from the University of Bombay, MSc from the Indian Institute of Technology, Bombay and received his PhD from the University of Massachusetts, Amherst, in 1988. After a two-year postdoctoral stint at the Corporate Research Laboratory of Exxon Research and Engineering Company at Annandale, New Jersey, he took up a faculty position in the Department of Inorganic and Physical Chemistry at the Indian Institute of Science, Bangalore. He served as the Chairman of Chemical Sciences Division for five years and later as Deputy Director for three years, before returning to full-time research in 2018. He was awarded the prestigious S S Bhatnagar Prize for Chemistry in 2005 and is currently a J C Bose Fellow. His research interests are in the design and development of novel polymerization methods, hyperbranched polymers, conjugated polymers, polymerization in ordered media, internally functionalized porous polymers and conformational control in synthetic polymers. He served as the President of the Society of Polymer Science-India (SPSI); has served on the Editorial Boards of Macromolecules and Polymer Chemistry, and was an Associate Editors of Chemical Communications, for almost a decade and finally their photo-cross-stitching process, alluding to some potential applications.