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We developed methods for synthesis of narrow molecular weight polymers with host or guest end groups. Using controlled free radical methods we prepared polymers with bis(m-phenylene)-32-crown-10 host end- and center- groups and paraquat guest end and center groups, represented by red circles and blue rectangles below.1,2 • We demonstrated by viscometry, NMR and isothermal titration microcalorimetry that these end- and center-functionalized polymers self-assemble selectively via pseudorotaxane formation, leading to chain extension, star polymers, graft copolymers and block copolymers.1,2 POLYMERS WITH MECHANICALLY LINKED ARCHITECTURES* Harry W. Gibson, Virginia Polytechnic Institute and State University , DMR 0704076 Synthesis of a 3-armed star polymer (1) Lee, M.; Schoonover, D.; Gibson, H. W. Polymer Preprints(Am. Chem. Soc., Div. Polym. Chem.) 2008, 49(1), 107-108. (2) Gibson,H. W.; Huang, F.; Ge, Z.; Wang, H.; Pederson, A. M.-P.; Lee, M.; Rouser, M.; Schoonover, D. Polymer Preprints(Am. Chem. Soc., Div. Polym. Chem.) 2008, 49(1), 1030-1031. (3) Huang, F.; Switek, K. A.; Zakharov, L. N.; Fronczek, F.; Slebodnick C.; Lam, M.; Golen, J. A.; Bryant, W. S.; Mason, P.; Ashraf-Khorassani, M.; Rheingold, A. L.; Gibson, H. W. J. Org. Chem. 2005, 70, 3231-3241. (4) Pederson, A. M.-P.; Schoonover, D. S.; Gibson, H. W. Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008, ORGN-298. Pederson, A. M.-P.; Ward, E.; Schoonover, D. S.; Slebodnick, C.; Gibson, H. W. J. Am. Chem. Soc., submitted. Synthesis of a graft copolymer
Harry W. Gibson, Virginia Tech, DMR 0704076 1 3 2 4 • To increase association constant, Ka, for pseudorotaxane formation, we designed, synthesized and characterized new cryptand hosts that are pre-organized for binding certain guests. The previously reported 32-crown-based cryptand 1 binds paraquat (3) very strongly,Ka = 5.0 x 106 M-1,3 the highest value reported for this guest. However, synthesis of 1 is slow and tedious. Thus, new 30-crown-based cryptand 2 was synthesized expeditiously in very high yield; itbinds 3 strongly, Ka = 2.0 x 105 M-1.4 Moreover, it binds diquat (4) with Ka = 1.9 x 106 M-1, the highest value ever reported for binding of this guest.4 The X-ray structure shows -stacking of the aromatic rings of 2 and 4,augmented by H-bonding between the ether oxygens and all four ethylene protons of the guest, and between the 3- and 4-protons of 4 and the pyridyl nitrogen of 2. These new systems will enable highly efficient formation of block, star and graft copolymers, the objectives of this project. Host cryptands and guests. Broader Impacts • Scholarship (since 2003) • 10 undergraduates (3 females) have actively participated in research • 51 refereed papers, 3 reviews and 8 preprints published • 2 US patents and 5 disclosures issued • 76 presentations, including 30 invited lectures (at universities, national • and international meetings) • 2 M. S. degrees awarded and 2 Ph. D. degrees awarded • 4 postdoctoral research associates (3 females) • Awards (since 2003) • Alumni Award for Research Excellence, Virginia Tech, 2004, Harry W. Gibson • Outstanding Dissertation in Science & Engineering Award, Virginia Tech, 2006, Feihe Huang • Outstanding Dissertation Advisor Award in Science & Engineering, Virginia Tech, 2006, Harry W. Gibson X-ray structure of 2•4 complex.