Regio- and stereoselective construction of stimuli-responsive macromolecules by a sequential coupling-hydroamination polymerization route

Abstract

Herein we reported a new facile one-pot multicomponent sequential polymerization approach for the construction of conjugated nitrogen-substituted polymers. Catalyzed by Pd(PPh3)2Cl2/CuI at room temperature, the couplinghydroamination polymerizations of 1,2-bis(4-ethynylphenyl)-1,2-diphenylethene, terephthaloyl chloride and secondary aliphatic amines proceeded smoothly in a regioregular and stereoselective manner, furnishing poly(arylene enaminone)s (PAEs) with high molecular weights (Mw up to 34 600) in satisfactory yields (up to 91%). Model compound was eleborately designed and synthesized to verify the chemical structures of the corresponding polymeric products. All the PAEs exhibited good solubility in common organic solvents and were thermally stable with degradation temperatures of up to 313 o C under nitrogen. They possessed good film-forming ability and their thin solid films showed high refractive indices (RI = 1.9318-1.6320) in a wide wavelength region of 400-1000 nm, whose value could be further modulated by UV irradiation. Although the model compound and the PAEs possessed a typical aggregation-induced emission luminogen of tetraphenylethene, they were weakly emissive either in solutioins or at the aggregated state, due to the photoinduced electron transfer (PET) effect. Their strong emission in the aggregated state could be readily recovered by blockage of the PET effect through protonation of the amino groups. Thus, this work demonstrated a powerful polymerization tool to access conjugated polymeric materials with pH-responsive properties.

Elastomeric polyamide biomaterials with stereochemically tuneable mechanical properties and shape memory

“…Recently, the nucleophilic Michael addition reaction between nucleophiles and activated alkynes (amino-yne, phenol-yne and thiol-yne) has attracted considerable attention as an efficient path to stepgrowth polyesters 57,58 . There has been some progress in controlling the stereochemistry of the resultant alkene in the backbone [59][60][61][62][63][64][65] , but many "yne-type" polymers are not synthesised in a stereocontrolled manner, despite the well-established impact of double-bond stereochemistry on bulk material properties (e.g., glass transition and stiffness) 60 . Initially, we screened reaction conditions that were used for the analogous stereocontrolled reaction between thiols and propiolate esters 63 .…”

Stereochemical enhancement of polymer properties

“…256 Several other studies have utilised the stereo-controlled thiol-yne polymerisation to synthesise new structures; however, the effect of stereochemistry on the properties of the polymers has to date not been investigated. [261][262][263][264] Similarly, other nucleophilic addition reactions (such as phenol-yne 263 or amino-yne) [265][266][267][268][269] have yielded stereo-controlled unsaturated polymers, but structure-property relationships were also not investigated, most likely on account of the initial difficulty to control the cis/trans ratio of the resultant polymers in these reactions. In many cases certain limitations, such as widely variable molecular weights between isomeric polymers and/or different overall material compositions, precluded direct material comparisons.…”

Multicomponent Polymerization for π‐Conjugated Polymers

“…Encouraged by the successful preparation of the sulfur‐substituted π‐cross‐conjugated polymers, Lam and Tang extended this method by replacing thiols with primary/secondary amines, and developed a one‐pot Sonogashira/hydroamination tandem polymerization to access nitrogen‐substituted π‐cross‐conjugated polymers ( 3‐P6 s) with high regio‐ and stereo‐selectivity. [ 30,31 ] Remarkably, while primary amines afforded 100% ( Z )‐selectivity for the newly formed vinylenes, [ 30 ] secondary amines exhibited ( E )‐selectivity. [ 31 ] This is because, as depicted in Figure 6, the primary amine adducts can benefit from the intramolecular hydrogen bonding between the NH and the CO groups in the product, whereas the products derived from secondary amines cannot.…”

“…[ 30,31 ] Remarkably, while primary amines afforded 100% ( Z )‐selectivity for the newly formed vinylenes, [ 30 ] secondary amines exhibited ( E )‐selectivity. [ 31 ] This is because, as depicted in Figure 6, the primary amine adducts can benefit from the intramolecular hydrogen bonding between the NH and the CO groups in the product, whereas the products derived from secondary amines cannot. This switch in stereochemistry affected photophysical properties of the resulting polymers, as well.…”