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 M n , ln ([M] o /[M]) vs time, and monomer: initiator ratio vs M n . The transferred aryl ligand was confirmed to be appended to the terminus of the polymer chain by MALDI−TOF and 19 F 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 CHCl 3 solutions.

Using the living nickel(II)-mediated polymerization of carbodiimides, the chiral (R)-or (S)-N-1-phenethyl-N′-methylcarbodiimide (PMC) monomers were polymerized with a new TIPS protected alkyne functional nickel initiator forming PPMC with an excess single-handed screw sense and the alkyne moiety covalently attached to the terminus of the polymer, as confirmed by 1 H NMR and MALDI-TOF MS. After deprotection, the alkyne end groups of rigid-rod PPMC-2 were coupled with azide-terminated, random-coil PS and PEG homopolymers forming a novel class of helical-b-coil block copolymers. In the thin-film, all synthesized diblock copolymers formed interesting nanofibular morphologies when subject to specific conditions. The triblock RCP-4, however, adopted unique macroporous morphology as identified by AFM and SEM with average pore diameters of ca. 832 ± 194 nm. The origin of this was found to be associated with the ordering of large, hollow vesicle aggregates upon solvent evaporation followed by the melting of these aggregates filling in the hollow interior forming the submicron pores observed. Furthermore, the size of these aggregates can be easily modulated in a linear fashion from 272 to 1648 nm simply by increasing the concentration of RCP-4 in THF. Finally, the three PPMC−PEG copolymers synthesized were found to adopt lyotropic cholesteric mesophases in concentrated toluene solutions (ca. 30 wt %). ■ INTRODUCTIONThe tunable self-assembly and microphase separation of conventional coil−coil block copolymer (CCP) have been studied and modeled extensively. 1,2 The ability to covalently bind polymers of varying composition and structure allows for the combination of polymer properties often with synergistic effects and expanded function. The self-assembly of these macromolecules is governed by a variety of noncovalent forces such as hydrophobic/hydrophilic interactions, electrostatic interactions, hydrogen bonding, and microphase separation. To date, directed block copolymer self-assembly remains as one of the most powerful, versatile methods of tailoring nanometer-size features.The synthesis of rigid rod-b-random coil block copolymers, however, has only recently attracted significant attention due to their unique capabilities to form stable supramolecular structures with a wide array of unique self-assembly behaviors observed in solution and the solid state. 3−6 The anisotropic nature of rigidrod blocks characteristically results in lyotropic/thermotropic liquid crystallinity with nematic or highly ordered smectic mesophases adopted in solution and/or in the melt. 7,8 Therefore, the assembly behaviors of rod−coil block copolymers (RCP) in solution and the solid state vastly differ from those of CCPs arising from a combination of microphase immiscibility of the two blocks and the self-organization behaviors of the rigid-rod block.

Molecular switches offer wide applicability through conformational changes which can be triggered by external stimuli. Azobenzenes are excellent candidates to contribute toward a rational design of molecular switches because they exist as either cis or trans isomers as a result of the dynamic photoisomerization process. In this study, we leverage the azobenzene stimuli response by attaching it as a pendant group on polycarbodiimides synthesized using screw sense polymerization. The exposure of the polymer sample in solution to UV light induces the transformation of the azobenzene pendant groups to the cis isomer with re-emergence of the trans conformer under visible light or heat. Corroborating experimental and computational data reveal that these events induce spring-like expansion–contraction motions throughout the helical backbone. Our finding suggests the use of polycarbodiimide-derived photoswitches as dynamic materials in biological applications and materials science.

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Here the microscopic mechanism that leads to the surprising formation of a nanopattern upon methanol reacting with a H-terminated Si (111) surface [Michalak et al., Nat. Mater. 2010, 9, 266−271] is reinvestigated from both theory and experiment. First-principles calculations determine the fully OCH 3