Controlled Handedness of Twisted Lamellae in Banded Spherulites of Isotactic Poly(2‐vinylpyridine) as Induced by Chiral Dopants

Abstract

Herein, we suggest aunique approach to control the handedness of twisted lamellae in banded spherulites of as tereoregular polymer,i sotactic poly(2-vinylpyridine) (iP2VP). When (R)-or (S)-hexahydromandelic acid (HMA), which can associate with iP2VP,w as introduced as ac hiral dopant, mirror-image CD spectra in the complex systems showed induced circular dichroism (ICD) of the iP2VP by chiral HMA. Banded spherulites resulting from lamellar twisting due to the imbalanced stresses at the opposite folding surfaces could be formed by crystallization of the iP2VP/HMA complexes,w hichh ad ac rystalline structure similar to that of neat iP2VP.Apreferential sense of the twisted crystalline lamellae was found in the iP2VP/HMA complex, thus suggesting homochiral evolution from conformational to hierarchical chirality.Chirality at the molecular scale is vital for driving the formation of helical structures with different length scales.In polymers,as tereogenic center could be introduced in either the backbone or side chains.S uch chirality usually leads to ah elical conformation of the polymer owing to steric hindrance from intramolecular chiral interactions.B yt aking advantage of ordering through self-assembly,t hose helical chains can be collectively packed as hierarchical helical superstructures as ar esult of intermolecular chiral interactions. [1] Owing to the effect of steric hindrance,i tm ay be possible to generate helical morphologies and superstructures with exclusive handedness through chirality transfer from the molecular level. [2] Helical polymers can be classified into two types:s tatic and dynamic,d epending on the nature of the helical conformation. As tatic helical polymer possesses as table helical conformation with optical activity,w hereas adynamic helical polymer may adopt an alternating sequence of left-and right-handed helices separated by helical reversals.F or adynamic helical polymer,the formation of astable helical conformation might be possible by the complexation of chiral dopants.T his effect is known as induced circular dichroism (ICD). [3] Most dynamic helical polymers with ICD have conjugated or peptide-based backbones,and the rigidity of the main chain stabilizes the forming helical conformation. [3c] Examples of polyolefins and vinyl polymers with induced chirality are rare.R ecently,s tereoregular vinyl polymers with backbones composed of CÀCb onds were successfully used for the association of avariety of chiral guest molecules with functional side chains to give ICD signals.The ICD behaviour was found to be strongly dependent on the isotacticity of the poly(2-vinylpyridine) polymers and the acidity and bulkiness of chiral acids used as guests. [4] In thiss tudy,w eu seds tereoregulari sotactic poly(2vinylpyridine) (iP2VP)f or self-assemblyw ith ICD and crystallization as banded spherulites,and observed concentric rings or extinctionbands by polarized-light microscopy(PLM) of the resulting crystals. Thef ormationo fi P2VP banded spherulites is attributedtothe twisting of crystallinelam...

Homochiral Evolution in Self-Assembled Chiral Polymers and Block Copolymers

“…Considering the crystallizable character of stereoregular polymers, solid films of iP2VP/HMA complexes were prepared for crystallization to scrutinize the feasibility of homochiral evolution from the self-assembly of the iP2VP with ICD. 10 As shown in Figure 7A, for amorphous films, split-type Cotton effect with mirror image for iP2VP/(R)-HMA and iP2VP/(S)-HMA complexes can be found. Note that the results are similar to the ECD results from the solution state, indicating that the ICD character can be well preserved in the solid film.…”

“…Consequently, the crystallization of the iP2VP with ICD can be guided by the chiral dopants for the growth of twisted lamella with preferred handedness to give a banded spherulite with specific optical activity. 10,11 With the use of the rotation experiment of PLM for the examination of twisted lamellar handedness, the homochiral evolution from the molecular level to hierarchical superstructure can be verified.…”

Porous Crystalline Spherulite Superstructures

“…1 Spherulite superstructures refer to radially polycrystalline aggregates with an external spherical envelope, which has been widely observed in crystallization processes of polymers, metals, minerals, and inorganic crystals. [2][3][4][5][6][7][8][9] For instance, rod-like cellulose crystallites are regulated to lie along the radius or along the circumference to form spherulites. 2 Some proteins can also be self-associated into high-order spherical structures.…”

Chiroptical Sensing

“…One example of sergeant-and-soldier phenomena is the induced helicity of isotactic-rich poly(2-vinylpyridine) by means of its hydrogen-bonding with chiral hexahydromandelic acid. The mirror imaging of the CD spectra suggests the formation of rightand left-handed helical chains of the achiral polymer through complexation with the chiral guest [28]. Poly(phenylacetylene)s have also shown to present distinct chiroptical responses associated with their helicity.…”