@article{tian_lu_novak_2004, title={Helix-sense selective polymerization of carbodiimides: Building permanently optically active polymers from achiral monomers}, volume={126}, ISSN={["1520-5126"]}, DOI={10.1021/ja049548m}, abstractNote={The helix-sense selective polymerization of achiral monomers by homochiral catalysts was investigated. Polymerization of chiral carbodiimides (N-(R)-2,6-(dimethylheptyl)-N'-phenylcarbodiimide) by achiral catalysts yields polymers that undergo mutorotation at elevated temperatures, thus illustrating that these chains are formed under kinetic rather than thermodynamic control. Building on this observation, the polymerization of achiral carbodiimides by (S-BINOL)Ti(OiPr)2, I, was studied. Monomers (N-hexyl-N'-(X)carbodiimide, where X = isopropyl (3), hexyl (4) or phenyl (5)), N-methyl-N'-(2-methyl-6-isopropylphenyl)carbodiimide, 6, and N-dodecyl-N'-(1-naphthyl)carbodiimide, 7, were all polymerized with I in good yields (86-95%), and all showed varying degrees of asymmetric induction. Poly-3, -4, and -5 racemized upon heating at elevated temperatures, but poly-6 and poly-7, bearing nonsymmetric phenyl groups, yielded optically active polymers that could not be racemized even at elevated temperatures. Thin films of poly-7 were found to be highly opalescent.}, number={13}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Tian, GL and Lu, YJ and Novak, BM}, year={2004}, month={Apr}, pages={4082–4083} }
 @article{tang_lu_tian_capracotta_novak_2004, title={Stable helical polyguanidines: Poly{N-(1-anthryl)-N '-[(R)- and/or (S)-3,7-dimethyloctyl]guanidines}}, volume={126}, ISSN={["1520-5126"]}, DOI={10.1021/ja049937g}, abstractNote={Using chiral catalysts of (R)- and/or (S)-BINOL-Ti, the asymmetrical polymerization of achiral monomer, N-(1-anthryl)-N'-n-octadecylcarbodiimide, yielded soluble nonregioregular polyguanidines of Poly-R1 and Poly-S1. A racemization process occurred when the toluene solution of Poly-R1 was annealed at elevated temperatures (70-80 degrees C). Kinetic studies reveal this to be a slow process with an activation energy of ca. 36 kcal/mol. On the other hand, using titanium(IV) trifluoroethoxide catalyst, the polymerization of N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]carbodiimides afforded highly regioregular polyguanidines of Poly-R2 and Poly-S2. These polymers adopt stable helices in various solvents and elevated temperatures, whose kinetically controlled conformations and thermodynamically controlled conformations are essentially the same.}, number={12}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Tang, HZ and Lu, YJ and Tian, GL and Capracotta, MD and Novak, BM}, year={2004}, month={Mar}, pages={3722–3723} }