Speaker：Prof.S.Ramakrishnan
Time：May 6, 2025 (Tuesday) 10:00-11:30 AM
Location: C3-c204, GuangzhouInternational Campus,SCUT
Biography:
Ramakrishnancompleted his BSc from the University of Bombay, MSc from the Indian Instituteof Technology, Bombay and received his PhD from the University ofMassachusetts, Amherst, in 1988. After a two-year postdoctoral stint at theCorporate Research Laboratory of Exxon Research and Engineering Company atAnnandale, New Jersey, he took up a faculty position in the Department ofInorganic and Physical Chemistry at the Indian Institute of Science, Bangalore.He served as the Chairman of Chemical Sciences Division for five years andlater as Deputy Director for three years, before returning to full-timeresearch in 2018. He was awarded the prestigious S S Bhatnagar Prize forChemistry in 2005 and is currently a J C Bose Fellow. His research interestsare in the design and development of novel polymerization methods,hyperbranched polymers, conjugated polymers, polymerization in ordered media,internally functionalized porous polymers and conformational control insynthetic polymers. He served as the President of the Society of PolymerScience-India (SPSI); has served on the Editorial Boards of Macromoleculesand Polymer Chemistry, and was an Associate Editors of Chemical Communications, for almost adecade
Abstract:
Someyears 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 azigzag manner so as to collocate the alkylene segments at the center and thePEG segments on either side; it was observed that independent crystallizationof both the backbone and pendant segments helped stabilize the folded structure. Subsequently, we demonstrated that inclusion of mesogenseither within the backbone or pendant segment also lead to the formation offolded chains permitting a precise control of the distance between themesogenic layers; these studies demonstrated that periodicallygrafted polymers could be an interesting design strategy to selectively locatedesired functional units within well-defined layers in a bulk polymer.
Althoughthe zigzag folding was earlier examined primarily in the solid state, one mightexpect the formation of such folded structures in a segment-selective solvents,such a polar solvent like water, that solvates the pendant PEG segments but notthe alkylene backbone segments. In order to examine the folding of PGAPs insolution, we first prepared a periodically clickable polyester carryinga di-cinnamoyl ester unit within the hydrophobic backbone segment; this polymerwas clicked with PEG-azides of different molecular weights (750, 1000 and2000), as depicted in the above schematic. Several studies were conducted toprobe the formation of the folded conformation with increasing solventpolarity; the photodimerization process of the dicinnamoyl units within thepolymer backbone is evidently feasible only when the chain is folded in azigzag fashion, which brings the cinnamoyl units in close proximity topermit the reaction. Hence, we examined the photodimerization process as afunction of solvent polarity to gain an understandin5g of the folding process,which provided us some valuable insights into solvent induced conformationaltransition in such PGAPs. Furthermore, we showed that, when PEG2000 segmentsare installed, the cross-stitched folded chains remain in solution even aftercomplete cross-stitching, suggesting that they have transformed intosingle-chain polymer nanoparticles (SCNPs). In the talk, I shall discuss thegenesis of PGAPs, their design elements, their synthesis,Ramakrishnancompleted his BSc from the University of Bombay, MSc from the Indian Instituteof Technology, Bombay and received his PhD from the University ofMassachusetts, Amherst, in 1988. After a two-year postdoctoral stint at theCorporate Research Laboratory of Exxon Research and Engineering Company atAnnandale, New Jersey, he took up a faculty position in the Department ofInorganic and Physical Chemistry at the Indian Institute of Science, Bangalore.He served as the Chairman of Chemical Sciences Division for five years and lateras Deputy Director for three years, before returning to full-time research in2018. He was awarded the prestigious S S Bhatnagar Prize for Chemistry in 2005and is currently a J C Bose Fellow. His research interests are in the designand development of novel polymerization methods, hyperbranched polymers,conjugated polymers, polymerization in ordered media, internally functionalizedporous polymers and conformational control in synthetic polymers. He served asthe President of the Society of Polymer Science-India (SPSI); has served on theEditorial Boards of Macromolecules and Polymer Chemistry, and wasan Associate Editors of ChemicalCommunications, for almost a decade and finally theirphoto-cross-stitching process, alluding to some potential applications.