Optically active polymers containing side-chain trans-stilbene chromophores directly bound to the backbone: synthesis and characterization of copolymers of (-)-menthyl acrylate with trans-4-vinylstilbene

Abstract

Optically active copolymers of (-)-menthyl acrylate (MtA) with trons-4-vinylstilbene (VS) were prepared by radical initiation over a wide range of composition. Reactivity ratios, evaluated for both comonomers, indicate that VS exhibits a higher reactivity than MtA. Average sequence lengths of the co-units and their distribution in the macromolecules were also evaluated by statistical calculations. Chiroptical properties of the side-chain trons-stilbene chromophores, combined with data of composition and distribution of monomeric units as well as UV and fluorescence measurements, suggest that the copolymer macromolecules assume conformations in solution of a prevailing single chirality due to steric effects.

Synthesis and properties of photochromic cholesteric liquid crystalline polysiloxane containing chiral mesogens and azobenzene photochromic groups

“…The steric effect of bulky cholesteryl decreased quickly from P 8 , and the effect of the rigidity of azobenzene mesogen could not keep equilibrium with the decrease of the steric effect; therefore, T g decreased quickly from P 8 . The clearing point temperatures (T i s) of polymers P 1 -P 12 were lower than that of P 0 , and T i increased from P 1 to P 4 , but decreased from P 5 to P 12 , as shown in Figure 3(b). Both the steric effect of the bulky cholesteryl and the rigidity of the rigid azobenzene mesogen influenced T i of polymers; the predominating one will determine the changing of T i .…”

“…Polymers P 0 ϳP 8 exhibited a cholesteric mesophase with oily streaks and lined texture, and polymers P 9 -P 12 showed a chiral smectic mesogenic phase with layered texture. The studies of UV-induced trans-cis photoisomerization of the azo monomer and polymers P 8 and P 12 in solution indicated that the solution of the azo monomer and polymers P 8 and P 12 can undergo photoisomerization.…”

“…The monomer M1 exhibited no absorption in this wavelength region, but monomer M2 showed a strong absorption maxima at 370 -375 nm and a weak absorption at 440 -460 nm, which are due, respectively, to the -* and n-* electronic transitions of azobenzene. 12,15 Both of the absorption bands shifted to higher wavelength than that of the isolated azo, which is attributed to the conjugative effect of NAN and . Polymer P 0 showed no absorption, like monomer M1, but polymers P 1 - P 12 exhibited absorption peaks at ϳ 370 and ϳ 450 nm due to the introduction of the conjugated NAN.…”

“…11 All the polymers in toluene solution are optically active at 589 nm, which is analogous to other copolymers. 12,13 The specific rotatory powers (SRPs) of the polymers, which are negative, are listed in Table I. The SRP of polymer P 0 is lower than that of chiral monomer M1, and the SRP nearly linearly decreases from P 0 to P 12 .…”

Conformational analysis of chiral polymers in solution

“…Such a situation can be clearly regarded as a local conformational order of the chain. Chiroptical properties which seemed to be connected with local dissymmetric conformations were also observed for random copolymers of trans-4-vinylstylbene (VS) with the same optically active cononomer (-) menthylacrylate (MtA), obtained again in the presenec of free radical initiators (31). Indeed the optical rotation at the sodium D-line is negative for a con tent of MtA units larger than 30%, whereas positive values of optical activity are observed for lower contents.…”