Cyclopolymerization of Disiloxane-Tethered Divinyl Monomers To Synthesize Chirality-Responsive Helical Polymers

Abstract

Synthetic polymers mimicking the stimuli-responsive coiled-coil structures of naturally occurring macromolecules such as motor proteins remain challenging. Here we report that chirality switchable quasi-double helical polymers can be synthesized by the free radical cyclopolymerization of the tetramethyl­disiloxane-tethered divinyl monomers. Two cyclopolymers (pbSt and pbMA) are obtained in this work, which in solid state are helical polymers investigated by both ECD and VCD. According to VCD analysis, the C–H deformation modes including C–H bending (mode I) and C–H rocking (mode II) in the main-chain helix show strong signals in VCD spectra and the plots of the division of VCD by IR, which have different responses to solvation histories or thermal treatment compared with other vibrational signals arising from side rings (especially signals from tetramethyl­disiloxane groups). After thermal treatment, all the side-ring VCD signals of both pbSt and pbMA are inverted, while the VCD signals from mode II of the main chain are unchanged. In cast films from chloroform solutions, pbSt shows only and inverted VCD signals arising from mode I and mode II of the main-chain helix, but not any VCD signals from side rings. Ab initio quantum calculation reveals that the change in the orientation of side-ring distortion against the main chain may account for the inversion of side-ring VCD signals. The responses of the experimental VCD spectra of the cyclopolymers can thus be rationalized based on the quantum calculation results. The main-chain helices of the cyclopolymers remained unchanged, while the side rings changed their distortion orientation during thermal treatment. In cast films from chloroform solutions, the polymer main-chain helix was inverted, hence inverted main-chain VCD; while the side rings might be randomly distorted, causing loss of VCD from side rings. Overall, the main-chain helices and side-ring pseudohelices can be switched independently. This work presents the first example that a single macromolecule can display such (quasi-)­double-helical conformation. Besides the theoretical value, this kind of chirality switchable quasi-double-helical polymer may find application in asymmetric catalyst, smart molecular devices, etc.

Controlled Polymerization of Multivinyl Monomers: Formation of Cyclized/Knotted Single‐Chain Polymer Architectures

“…[51,52] Alternatively, one can perform selective polymerization by varying the reactivity of two different vinyl groups, where only one vinyl group undergoes polyaddition while another remains as a pendent. [51,52] Alternatively, one can perform selective polymerization by varying the reactivity of two different vinyl groups, where only one vinyl group undergoes polyaddition while another remains as a pendent.…”

“…Besides using conventional monomers, cyclopolymerization can also be achieved by making specialized monomers in which the two vinyl groups are strained in such a way that is favorable for intramolecular ring-closing reactions. [51,52] Alternatively, one can perform selective polymerization by varying the reactivity of two different vinyl groups, where only one vinyl group undergoes polyaddition while another remains as a pendent. Wooley and co-workers demonstrated the facile and successful selective RAFT polymerization of 4-(3'-buten-1'-oxy)-2,3,5,6-tetrafluorostyrene, which bears styrenyl and alkene groups, to obtain polymers with pendant alkene functionalities.…”

Complex polymer architectures through free-radical polymerization of multivinyl monomers

“…In a recent study, the Thorpe-Ingold or gem-dimethyl effect has been applied by Li and co-workers to promote the cyclization of dimethacrylate and bisstyrenic groups ( Figure 5, 10 and 14) with RAFT cyclopolymerization producing a quasidouble-helical cyclopolymer with switchable chirality. 105 Hydrogen bonding can also be exploited to tether and orient vinyl groups, either by using a template molecule such as a catechol ( Figure 5, 17) 106 to tether two vinyl monomers, or connecting two vinyl monomers with complementary hydrogen bonding moieties ( Figure 5, 16). 107 While these pseudo-DVMs can assist in controlling the tacticity of the final products, the ability to control the polymer topology is limited.…”

Facile Synthesis of Helical Rod–Coil Block Polymers by the Combination of ATRP and Pd(II)‐Initiated Isocyanides Polymerizations

“…Recently, helical structure has been widely investigated aiming at exploring the miraculous architectures and functions . Inspired by nature materials, the goal to build artificial macromolecular structure with stable helix is still a prominent challenge to scientists intending for further development and applications . In recent researches, some stereotyped macromolecules containing helical conformation in solid state were reported, yet the helicity was not stable and the ordered structure would transform to random coil in solution .…”

“…[4,5] Inspired by nature materials, the goal to build artificial macromolecular structure with stable helix is still a prominent challenge to scientists intending for further development and applications. [6][7][8][9][10][11] In recent researches, of the mild reaction condition and the adaptability of various vinyl monomers. [41,42] Taking advantage of the tolerance to most solvents, the approved living method was widely applied to produce polymers with desired M n s and narrow M w /M n s. The initiator of ATRP possessed flexible structures with faithful properties, so that the modified and functionalized initiators provide infinite possibility in creating novel polymers with complicated structures.…”