Synthesis and Conformational Characteristics of Poly(phenyl isocyanate)s Bearing an Optically Active Ester Group

Abstract

Optically active phenyl isocyanates (1-9) bearing an optically active ester group were synthesized and polymerized with an achiral anionic initiator. The resulting polymers from 1 and 4-9 showed a much greater specific rotation than that of the corresponding monomer and an intense circular dichroism (CD) band caused by the main-chain absorption, indicating that these polymers have a predominantly one-handed helical conformation in solution. On the other hand, the polymers obtained from 2 and 3 showed a much smaller specific rotation and a weaker CD band than poly-1, which suggests that, as the distance between the polymer main chain and the asymmetric center on the side chain increases, the asymmetric center cannot effectively induce an excess of one helical twist sense of the polymer main chain at room temperature. However, the specific rotation and CD intensity of poly-2 greatly increased because of a predominantly one-handed helical conformation at low temperatures. The polymers obtained from 3-9 did not show such a temperature effect on conformational change. Specific rotation of the copolymers of chiral 8 and achiral 10 changed from a positive to a negative value with an increase in the content of the optically active unit. The helicity of the copolymer may depend on the composition.

Synthesis of Optically Active Poly(diphenylacetylene)s Using Polymer Reactions and an Evaluation of Their Chiral Recognition Abilities as Chiral Stationary Phases for HPLC

“…This system therefore allowed for the selective formation of right-and left-handed helical structures using a single enantiomer of 2 as the chiral unit, with the actual outcome being dependent on the mole fraction of 2. Similar helical sense inversion behaviors in the copolymers consisting of chiral and achiral units depending on the contents of the chiral units have been also reported in polyisocyanates [40], polysilanes [41], polyacetylenes [42][43][44], polyisocyanides [45] and poly(quinoxaline-2,3-diyl)s [46]. It has also been reported that these phenomena can be explained using a modified version of the Ising model proposed by Sato et al, where the helix-sense is determined by the interactions between the neighboring pendant groups, chiral-chiral units and chiral-achiral units, which can stabilize the opposite helix-sense to each other [47].…”

Optically Active Polysilylenes: State-of-the-Art Chiroptical Polymers

“…The most striking cooperativity of helical ordering in optical active artificial copolymers is the "sergeants and soldiers" principle named by Green et al, [17] whereby a minority of enantiopure chiral side groups definitively determines the overall screw-sense (P or M) of a helical main chain which has a majority of achiral side groups. Since the initial observation of this phenomenon in poly(a-olefin) copolymers comprising (S)-4-methyl-1-pentene and 4-methyl-1-hexene comonomers by Pino et al, [10] it is now well-established in stiff poly-(alkylisocyanate)s [6,17,19,21] and poly(aralkylisocyanate)s. [22] In polysilylene chemistry, Möller, Matyjaszewski and coworkers prepared two types of optically active polysilylene copolymers with high molecular weight: poly-[(bis{(S)-2-methylbutyl}silylene)-co-(dipentylsilylene)] (10) and poly[(bis{(S)-2-methylbutyl}silylene)-co-{(S)-2-methylbutylpentylsilylene}] (11). [59,61] They reported an almost linear increment of CD intensity around 320 nm in cyclohexane with an increase of the molar proportion of the symmetrical chiral Si monomer unit, indicating no significant "sergeants and soldiers" phenomenon.…”

“…Molecular mechanics calculated main chain dihedral angle dependence on the potential energy of (a) isotactic and syndiotactic (S)-3,7-dimethyloctyl{3-methylbutyl}silylene 31 repeating units with hydrogen termini(21), and (b) isotactic and syndiotactic (S)-3,7-dimethyloctyl{2-methylpropyl}silylene 31 repeating units with hydrogen termini(22).DG = G P -G M = DH -TDS = H P -H M -T (S P -S M ), (4) where DH = H P -H M , DS = S P -S M (5) at T c , DG = 0, then T c = DH / DS (6) Schematic structures of P-and M-helical poly{(S)-3,7-dimethyloctyl-3-methylbutylsilylene} below and above the P-M transition temperature. indeed demonstrated in a series of 18-based copolymers, poly[{(S)-3,7-dimethyloctyl-3-methylbutylsilylene}-co-{(S)-3,7-dimethyloctyl-2-methylpropylsilylene}] (23) and poly[{(S)-3,7-dimethyloctyl-3-methylbutylsilylene}-co-{(S)-3,7-dimethyloctyl-2-methylpropylsilylene}] (24).…”

Double screw-sense inversions of helical chiral-achiral random copolymers of fluorene derivatives in phase separating solutions

“…Helical chiral-achiral random copolymers often exhibit interesting chiroptical properties, for example, sergeants-and-soldiers behavior, [18][19][20] composition-driven helical screw-sense inversion, 21,22 and so on. Therefore, the CD induction study in phase separating solution was recently extended to a helical chiral-achiral random copolymer of fluorene derivatives, poly(2,7-[9,9-bis((S)-citronellyl)]-fluorene-random-9,9-di-n-octyl fluorene), as shown in Scheme 1, and double screw-sense inversions were found by changing the chiral monomer content x.…”