@article{reuther_bhatt_tian_batchelor_campos_novak_2014, title={Controlled Living Polymerization of Carbodiimides Using Versatile, Air-Stable Nickel(II) Initiators: Facile Incorporation of Helical, Rod-like Materials}, volume={47}, ISSN={["1520-5835"]}, DOI={10.1021/ma5009429}, abstractNote={The new polymerization of carbodiimides using two, simple [bis(triphenylphosphino)aryl]nickel(II) bromide complexes has been discovered to occur in a controlled, living fashion. These initiators are substantially more air and moisture stable compared to their titanium(IV) counterparts making them significantly easier to synthesize, purify, and utilize. The polymerization is initiated via aryl ligand transfer to the electrophilic center carbon of the carbodiimide. Sequential insertions of the carbodiimide π-bond into the nickel–nitrogen amidinate coordination bond propagates the polymer chain in a living chain growth manner as evident by the linear relationship in the plots of percent conversion vs Mn, ln([M]o/[M]) vs time, and monomer: initiator ratio vs Mn. The transferred aryl ligand was confirmed to be appended to the terminus of the polymer chain by MALDI–TOF and 19F NMR. This added control element offers new opportunities to end functionalize rigid-rod, helical polycarbodiimides. This new technique also provides the ability to generate the active Ni(II) initiation sites on potentially any aryl bromide species for the facile incorporation of rod-like, helical polycarbodiimides into such systems as block copolymers, graft copolymer, polymer functionalized surfaces, etc. To demonstrate this, poly(4-bromostyrene) was employed as a polymer-supported aryl bromide source to generate the active [bis(triphenylphosphino)aryl]nickel(II) bromide macroinitiator. The “grafting from” reaction was then carried out upon addition of the chiral (S)-PEMC monomer forming the excess single-handed helical polycarbodiimide appended graft copolymer. The morphology of this novel polymer system was studied using TMAFM, revealing nanofibular aggregation behavior when spin coated from dilute CHCl3 solutions.}, number={14}, journal={MACROMOLECULES}, author={Reuther, James F. and Bhatt, Mahesh P. and Tian, Gonglu and Batchelor, Benjamin L. and Campos, Raymond and Novak, Bruce M.}, year={2014}, month={Jul}, pages={4587–4595} }
 @article{merten_reuther_desousa_novak_2014, title={Identification of the specific, shutter-like conformational reorientation in a chiroptical switching polycarbodiimide by VCD spectroscopy}, volume={16}, number={23}, journal={Physical Chemistry Chemical Physics}, author={Merten, C. and Reuther, J. F. and DeSousa, J. D. and Novak, B. M.}, year={2014}, pages={11456–11460} }
 @article{reuther_novak_2013, title={Evidence of Entropy-Driven Bistability through N-15 NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide}, volume={135}, ISSN={["0002-7863"]}, DOI={10.1021/ja4098803}, abstractNote={The thermo- and solvo-driven chiroptical switching process observed in specific polycarbodiimides occurs in a concerted fashion with large deviations in specific optical rotation (OR) and CD Cotton effect as a consequence of varying populations of two distinct polymer conformations. These two conformations are clearly visible in the (15)N NMR and IR spectra of the (15)N-labeled poly((15)N-(1-naphthyl)-N'-octadecylcarbodiimide) (Poly-3) and poly((15)N-(1-naphthyl)-(15)N'-octadecylcarbodiimide) (Poly-5). Using van't Hoff analysis, the enthalpies and entropies of switching (ΔHswitching; ΔSswitching) were calculated for both Poly-3 and Poly-5 using the relative integrations of both peaks in the (15)N NMR spectra at different temperatures to measure the populations of each state. The chiroptical switching (i.e., transitioning from state A to state B) was found to be an endothermic process (positive ΔHswitching) for both Poly-3 and Poly-5 in all solvents studied, meaning the conformation correlating with the downfield chemical shift (ca. 148 ppm, state B) is the higher enthalpy state. The compensating factor behind this phenomenon has been determined to be the large increase in entropy in CHCl3 as a result of the switching. Herein, we propose that the increased entropy in the system is a direct consequence of increased disorder in the solvent as the switching occurs. Specifically, the chloroform solvent molecules are very ordered around the polymer chains due to favorable solvent-polymer interactions, but as the switching occurs, these interactions become less favorable and disorder results. The same level of solvent disorder is not achieved in toluene, causing the chiroptical switching process to occur at higher temperatures.}, number={51}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Reuther, James F. and Novak, Bruce M.}, year={2013}, month={Dec}, pages={19292–19303} }
 @article{budhathoki-uprety_reuther_novak_2012, title={Determining the Regioregularity in Alkyne Polycarbodiimides and Their Orthogonal Modification of Side Chains To Yield Perfectly Alternating Functional Polymers}, volume={45}, ISSN={["1520-5835"]}, url={http://dx.doi.org/10.1021/ma301639m}, DOI={10.1021/ma301639m}, abstractNote={To understand the structure–property relationship in functional macromolecules through side chain modulation, both the accurate determination of the position of modifiable groups along the polymer chain and their subsequent modifications using high fidelity methods are crucial. In this report, the polymer microstructure of a helical alkyne polycarbodiimide has directly been probed through 15N NMR spectroscopy on isotopic labeled poly(N-(3-ethynylphenyl)-15N′-hexyl)carbodiimide and found to be a highly regioregular polymer structure. This polymer undergoes facile and quantitative CuAAC “click” chemistry, yielding perfectly alternating functional polymers. Advances have been made through the synthesis of new optically active alkyne polycarbodiimides with two independently modifiable pendant groups per repeat unit of polymers. Orthogonal postmodifications of the pendant groups were then performed to incorporate two different sets of small molecules in the repeat unit of polymers in a controlled manner and under mild reaction conditions using either sequential CuAAC “click” reactions when two dissimilar alkyne groups are present or a combination of CuAAC and thiol–ene click chemistries when pendant groups bear alkyne and vinyl moieties.}, number={20}, journal={MACROMOLECULES}, author={Budhathoki-Uprety, Januka and Reuther, James F. and Novak, Bruce M.}, year={2012}, month={Oct}, pages={8155–8165} }
 @article{reuther_desousa_novak_2012, title={Direct Probing of Regioregularity for Polycarbodiimide Systems via N-15 NMR Analysis}, volume={45}, ISSN={["1520-5835"]}, DOI={10.1021/ma301448b}, abstractNote={After more than a decade of ambiguity, polycarbodiimides have been discovered to be fully regioregular when containing two sterically inequivalent pendant groups. To directly probe the regioregularity, a series of nitrogen-15 isotopically enriched polycarbodiimides with various combinations of pendant groups was synthesized using a variety of catalysts. Subsequent 15N NMR analysis was performed on each of the labeled polymers to accurately determine the preferred regioisomer(s) and any particular bias present for monomer insertion. More sterically hindered substituents, i.e., aromatics, were found to be relegated to the imine nitrogen while the less hindered aliphatic groups were, in all cases, located on the amine nitrogen. No electronic biases were observed and the use of different titanium(IV) catalysts yielded the same regioisomer. Carbodiimides bearing sterically equivalent groups were polymerized to form regioirregular polymers with a 1:1 mixture of both regioisomers.}, number={19}, journal={MACROMOLECULES}, author={Reuther, James F. and DeSousa, Joseph D. and Novak, Bruce M.}, year={2012}, month={Oct}, pages={7719–7728} }