Twisted Morphologies and Novel Chiral Macroporous Films from the Self‐Assembly of Optically Active Helical Polyphosphazene Block Copolymers

Abstract

A series of optically active helical polyphosphazene block copolymers of general formula R-[N=P(O2C20H12)]n-b-[N=PMePh]m (R-7 a-c) was synthesized and characterized. The polymers were prepared by sequential living cationic polycondensation of N-silylphosphoranimines using the mono-end-capped initiator [Ph3 P=N=PCl3][PCl6] (5) and exhibit a low polydispersity index (ca. 1.3). The temperature dependence of the specific optical activity ([α]D) of R-7 a,b relative to that for the homopolymers R-[N=P(O2C20H12)]n (R-8 a) and the R/S analogues (R/S-7 a,b), revealed that the binaphthoxy-phosphazene segments induce a preferential helical conformation in the [N=PMePh] blocks through a "sergeant-and-soldiers" mechanism, an effect that is unprecedented in polyphosphazenes. The self-assembly of drop-cast thin films of the chiral block copolymer R-7 b (bearing a long chiral and rigid R-[N=P(O2C20H12)] segment) evidenced a transfer of helicity mechanism, leading to the formation of twisted morphologies (twisted "pearl necklace"), not observed in the nonchiral R/S-7 b. The chiral R-7 a and the nonchiral R/S-7 a, self-assemble by a nondirected morphology reconstruction process into regular-shaped macroporous films with chiral-rich areas close to edge of the pore. This is the first nontemplate self-assembly route to chiral macroporous polymeric films with pore size larger than 50 nm. The solvent annealing (THF) of these films leads to the formation of regular spherical nanostructures (ca. 50 nm), a rare example of nanospheres exclusively formed by synthetic helical polymers.

Helical Phosphorus Derivatives

“…The authors postulated that it may be used as a chiral filter and may provide a chiral material for the resolution of racemic amines by selective adsorption/desorption resolution. (13CEJ5644). Their synthesis starts with consecutive reactions of (trimethylsilyl)phosphorimidoyl trichloride 160 and methylphenylphosphorimidoyl chloride 161 monomers (Scheme 42).…”

Branched Macromolecular Architectures for Degradable, Multifunctional Phosphorus‐Based Polymers

“…The development of a room temperature poly­merization of trichloro(trimethylsilyl)phosphoranimine (Cl 3 PNSi(CH 3 ) 3 ) has provided much needed control over the synthesis of [NPCl 2 ] n to achieve not only polymers with narrow polydispersities, but also to gain access to block polymers and more advanced structures . The most frequently used initiator for the polymerization of the monomer Cl 3 PNSi(CH 3 ) 3 to [NPCl 2 ] n is PCl 5 .…”

“…Furthermore, through the use of RPPh 2 moieties, many of which are commercially available due to their common use in catalysis, chain‐end functionalized polymers can also be prepared via this method . Chlorinated phosphine groups can be utilized for the preparation of diblock copolymers with differently substituted poly(organo)phosphazenes, with organic polymers, as well as organometallic‐inorganic block copolymers with ferrocenylsilane …”

Reversible Morphological Evolution of Responsive Giant Vesicles to Nanospheres by the Self‐Assembly of Crystalline‐b‐Coil Polyphosphazene Block Copolymers

“…Such versatile materials allowed us to synthesize block copolymers having a chosen property located in the core‐forming block and therefore assess the influence of this property on the self‐assembly processes in solution and in thin films . Thus, we prepared polyphosphazene‐based block copolymers having chiral and functional blocks– that can direct the self‐assembly to pores, helices, or nanostructures functionalized with gold nanoparticles. Motivated by the idea of combining the potential of the CDSA processes with a highly dynamic system than can be responsive to an external stimuli, in this work we studied the self‐assembly of a family of crystalline‐ b ‐coil block copolyphosphazenes of general formula [N=P(OCH 2 CF 3 ) 2 ] n ‐ b ‐[N=PMePh] m ( 4 a : n =30, m =20; 4 b : n =90, m =20; 4 c : n =200, m =85) in which highly flexible, crystalline [N=P(OCH 2 CF 3 ) 2 ] n segments (glass transition temperature T g ≈−65 °C) are linked with amorphous and flexible [N=PMePh] blocks ( T g =37 °C) .…”