In polyisocyanates composed only of randomly distributed (R) and (S) units, the chiral optical properties of the polymer are far out of proportion to the enantiomeric excess of the monomers. This highly disproportionate relationship, which arises from a majority-rule effect among these enantiomeric units on the helical sense of the backbone, is now found to be unaffected, within certain limits, by the overwhelming presence of achiral units randomly distributed along the chain. This experimental result can be explained quantitatively by an analysis based on the one-dimensional random-field Ising model, which shows that dilution of the chiral units with achiral units increases the helical domain size in a manner that compensates for the dilution. In qualitative terms, since the random-field domain size is limited by the “objection” of the minority units to the helical sense dictated by the majority units, dilution of this “objection” acts to increase the domain size. As long as this domain size is not limited by the chain length or by thermal fluctuations, the achiral dilution will not reduce the optical activity of the polymer.

Mechanism of the transformation of a stiff polymer lyotropic nematic liquid crystal to the cholesteric state by dopant-mediated chiral information transfer Green, M.M.

Optical rotation (OR) of random copolymers of chiral 2,6-dimethylheptyl isocyanate (NIC) and achiral hexyl isocyanate (HIC) was measured as a function of mole fraction x of the chiral monomer, temperature, and molecular weight, with hexane, 1-chlorobutane, and dichloromethane as the solvents. The data as a function of molecular weight were analyzed by the statistical mechanical theory of copolymers developed (Gu, H.; et al. Polym. J. 1997, 29, 77−84), in which a polyisocyanate chain is modeled by an alternating sequence of left-handed and right-handed helices occasionally interrupted by helical reversals. The theory involves two parameters, the left-handed−right-handed free energy bias, 2ΔG h, and the helical reversal free energy, ΔG r. With appropriate values for these parameters, the experimental OR values were well described by the theory. When compared with poly((R)-i-deuterio-n-hexyl isocyanate (i = 1, 2), the values of ΔG r were nearly the same but those of |2ΔG h| were much larger:  71 ± 14 cal/mol for the terpene derived chiral unit vs 1∼2 cal/mol for the deuterated chiral monomer units. These free energy values are reasonable considering the chemical structures of the respective chiral monomer units.

Human experience informs us of the two extreme consequences of crowding: random behavior of the individuals, in which each takes a singular path; and cooperative behavior, in which the individuals in the crowd act in a predictable uniform manner, such as in a military organization These extremes find parallels in the crowded situations encountered at the molecular level, exemplified for the former by glassy states, such as often encountered in polymeric materials,1 or for the latter, in the uniform archetypal arrangements of crystals or liquid crystals. Here we review the cooperative characteristics of uniform arrangements that take a chiral form and explore how these characteristics lead to left‐ and right‐handedness. These studies lead us to understand the basis of amplification of chirality in regular arrays, in which small influences have large consequences, and how chiral cooperativity acts in the resolution of conflict between influences favoring left‐ and right‐handedness.2

Side chain functionalized polyisocyanates with ether, ester, and ketone groups, i.e. poly-(3-(benzyloxy)-n-propyl isocyanate) (PIET), poly(3-(benzyloxycarbonyl)-n-propyl isocyanate) (PIES), and poly(3-oxobutyl isocyanate) (PIK), were synthesized to enhance the possibility of forming miscible blends with hydrogen-bonding donor random coil polymers. While such blends do not form with poly(n-hexyl isocyanate) (PHIC) and a 9l/9 copolymer of styrene and vinylphenol (PHS-91, several criteria are consistent with miscible blend formation with the functionalized polyisocyanates above. Infrared spectrometry demonstrates hydrogen bonding between the phenol hydroxyl groups and the polar side chain functions. The glass transitions of the blends are intermediate between those of PHS-9 and the polyisocyanate in certain composition ranges in which optical microscopy shows no evidence of birefringence or cloudiness. Optical activity properties and light-scattering measurements show that PIES and PIET are stiff helical macromolecules, as is well-known for PHIC. PIES was hydrogenolyzed to yield the unprotected polymer with carboxylic acid pendant groups. This polyelectrolyte was soluble in water with a pH 7 buffer and at higher pHs but with a depolymerization whose rate increased at higher pH.

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The molecular and supramolecular structure of poly(n-hexyl isocyanate) in n-octane has been studied in the sol state and in the gel state by neutron and light scattering. In the sol state the chains appear stiff with dimensional characteristics consistent with the literature on this polymer. The gel consists of a network phase and free chains. The network phase appears to be an array of cross-section polydispersed fibers which can be described with a cross-section radius distribution function of the type w(r) ∼ r -1 with two cut-off radii r max = 6.7 ± 0.4 nm and r min = 1.3 ± 0.1 nm. These results are compared to the morphology revealed by electron microscopy. The sol state was also studied by dynamic light scattering as a function of concentration, time, and temperature. This revealed the presence of slow and fast modes which could be correlated respectively with the aggregates leading to gelation and to the individual polymer chains. The sol optical activity properties of the pregels revealed a reduction in the population of kinked helical reversals along the backbone consistent with the close parallel packing in the fibers as suggested both by electron microscopy and neutron scattering.