Reversible Transformation between Amorphous and Crystalline States of Unsaturated Polyesters by Cis–Trans Isomerization

Abstract

An aliphatic polyester has been prepared from ethylene oxide and maleic anhydride that undergoes reversible transformation between amorphous (T g = 18 8 8C) and crystalline (T m = 124 8 8C) states through cis-trans isomerization of the C=Cb onds in the polymer backbone without any change in either the molecular weight or dispersity of the polymer.A similar transformation was also observed in chiral unsaturated polyesters formed from enantiopure terminal epoxides,such as epichlorohydrin, phenyl glycidyl ether,and (2,3-epoxypropyl)benzene. These unsaturated polyesters with 100 %E -configuration in the crystalline state were prepared by quantitative isomerization of their Z-configuration analogues in the presence of ac atalytic amount of diethylamine,w hile in the presence of benzophenone,i rradiation with 365 nm UV light resulted in the transformation of about 30 %t rans-alkene to cis-maleate form, thereby affording amorphous polyesters.

Reversible Actuation via Photoisomerization-Induced Melting of a Semicrystalline Poly(Azobenzene)

“…On subsequent thermal cycles, the initial thermogram of trans -p­(A6) is recovered (Figure C, blue), confirming thermal isomerization of cis -p­(A6). Furthermore, the glass transition temperature ( T g ) changes from ≈34 °C in trans -p­(A6) to ≈−33 °C in cis -p­(A6), similar to previous observations for side-chain azopolymers. ,− Additionally, the T g broadens upon crystallization (Figure D), likely due to restricted molecular relaxation near the crystalline regions. , These thermograms suggest that cis -p­(A6) is amorphous and crystallizes upon thermal relaxation to trans -p­(A6) providing evidence that crystallinity is modulated via trans–cis photoisomerization, similar to how changes in stereochemistry modulate crystallinity in some thermoplastics − though rarely controlled using light . These effects are corroborated by wide-angle (WAXS) and medium-angle X-ray scattering (MAXS; Figure E,F).…”

“…55,56 These thermograms suggest that cis-p(A6) is amorphous and crystallizes upon thermal relaxation to trans-p(A6) providing evidence that crystallinity is modulated via trans−cis photoisomerization, similar to how changes in stereochemistry modulate crystallinity in some thermoplastics 57−59 though rarely controlled using light. 60 These effects are corroborated by wide-angle (WAXS) and medium-angle X-ray scattering (MAXS; Figure 1E,F). Prior to photoisomerization, transp(A6) shows scattering peaks at q = 17.4, 12.9, and 1.6 nm −1 ; the highest-q peaks are presumably associated with interchain spacings between neighboring polymer chains while the peak at q = 1.6 nm −1 (corresponding to a d-spacing of 3.9 nm) likely reflects the periodicity along the chain axis.…”

Photoinduced Reversible Semicrystalline‐to‐Amorphous State Transitions of Stereoregular Azopolyesters

“…Moreover, via irradiation with 365 nm UV light in the presence of benzophenone over a prolonged period of up to 5 h, about 30 % of the trans ‐alkene units could be transformed into the cis ‐maleate form. Interestingly, in some cases, a reversible transformation between amorphous (30 % cis ‐configuration units randomly distributed in the polymer backbone) and crystalline (100 % trans ‐alkene form) states was achieved by the cis‐trans isomerization process [21] …”

“…Interestingly, in some cases, a reversible transformation between amorphous (30 % cis-configuration units randomly distributed in the polymer backbone) and crystalline (100 % trans-alkene form) states was achieved by the cis-trans isomerization process. [21] Herein, we report the synthesis of stereoregular semicrystalline azopolyesters through enantioselective resolution copolymerization of racemic azobenzene-containing epoxides and cyclic anhydrides, mediated by enantiopure binuclear aluminum complexes. The resultant isotactic polyesters undergo reversible transitions, transforming between semicrystalline and amorphous states via trans-cis isomerization stimulated by light absorption.…”

Twisted Surfaces in Porous Single Crystals to Deliver Enhanced Catalytic Activity and Stability

“…[6][7][8][9][10] The facets and atomic termination layers are very complex on the surfaces of polycrystalline and amorphous materials. [11][12][13][14][15] The complicated interactions between adsorbed species and active surfaces would distract main reactions, which therefore degrades the conversion, selectivity, and even stability in many catalytic reactions.…”