Experimental and Theoretical Study of the Living Polymerization of N-Silylphosphoranimines. Synthesis of New Block Copolyphosphazenes

Abstract

The sequential living polymerization of N-silylphosphoranimines for the synthesis of polyphosphazene-b-polyphosphazene diblock copolymers (PP-b-PP) has been studied both experimentally and theoretically. For the experiments, BrMe 2 PN−SiMe 3 , [Cl 3 PNPCl 3 ][X] (X = PCl 6 − , Cl − ), Cl 3 PN−SiMe 3 , ClMe 2 PN−SiMe 3 , and [Me 3 PNPMe 2 Cl] + were used as representative model reagents. Density functional theory (DFT) calculations in the gas phase adjusted for solvent effects on ClMe 2 PN− SiMe 3 , [Cl 3 PNPCl 3 ] + , Cl 3 PN−SiMe 3 , and ClMe 2 PN−SiMe 3 confirmed the experimental observations. The results have shown the necessity of starting with monoend-capped initiators to avoid the formation of triblock chains. It was also demonstrated that the nature of the nucleophilic N-silylphosphoranimines and the electrophilic cationic end groups of the living polyphosphazenes strongly affects the polymerization reaction, imposing limits to its synthetic potential. Thus, good electron donor N-silylphosphoranimines, i.e. XR 2 PN−SiMe 3 , react better with electron-deficient cationic end groups such as N−PCl 3 + , probably by molecular orbital (MO) control. The results led to the designed synthesis of well-defined PP-b-PP block copolymers with narrow molecular weight distributions of formula [N P(Ph)(Me)] n -b-[NP(OCH 2 CF 3 ) 2 ] m and [NP(Ph)(Me)] n -b-[NP(O 2 C 12 H 8 )] m , which are excellent candidates for micellation studies.

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

“…Synthesis and characterization of chiral ( R ‐7 a–c) and achiral ( R / S ‐7 a,b) block copolyphosphazenes : The block copolymers R ‐[NP(O 2 C 20 H 12 )] n ‐ b ‐[NPMePh] m , [O 2 C 20 H 12  R ‐2,2′‐dioxy‐1,1′‐binaphthyl, n =50, m =35 ( R ‐ 7 a ); n =200, m =50 ( R ‐ 7 b ); n =30, m =150 ( R ‐ 7 c )] and the analogous optically inactive derivatives R / S ‐[NP(O 2 C 20 H 12 )] n ‐ b ‐[NPMePh] m [( n =50, m =35 ( R / S ‐ 7 a ); n =200, m =50 ( R / S ‐ 7 b )] were synthesized by a three‐step strategy previously described by us17 (Scheme and ) from the mono‐end‐capped initiator [Ph 3 PNPCl 3 ][PCl 6 ] ( 5 ) (Scheme a). The completeness of the macromolecular chlorine substitution in the [NPCl 2 ] n ‐ b ‐[NPMePh] m ( 6 a – c ) precursors with the R ‐ or R / S ‐(C 20 H 14 O 2 ) was experimentally confirmed by the total disappearance of the 31 P NMR signal at δ =−17 ppm ([NPCl 2 ] n ) and the appearance of a new broad signal centered at δ =−3 ppm ([NP(O 2 C 20 H 12 )] n ) with the same relative integration.…”

“…N ‐(trimethylsylil)phosphoranimines Cl 3 PN‐SiMe 3 ( 1 )32 and Cl(PhMe)PN‐SiMe 3 ( 3 )17 and the initiator [Ph 3 PNPCl 3 ][PCl 6 ] ( 5 )17 were prepared according to literature procedures.…”

“…This polymerization also provides a direct route to block copolymers through sequential monomer addition 16. We have recently shown17 that authentic polyphosphazene‐ b ‐polyphosphazene polymers (PP‐ b ‐PP) may be obtained by using mono‐end‐capped initiators of the type [Ph 3 PNPCl 3 ][A] (A=Cl, PCl 6 ) that avoid the bidirectional chain growth of the N ‐(trimethylsilyl)phosphoranimine monomers (XRR′PN‐SiMe 3 ; X=Cl; R=R′=Cl; R=Me, R′=Ph; Scheme ). This methodology allows the synthesis of well‐defined block copolyphosphazenes with controlled molecular weights and narrow polydispersity indexes (PDI), which are suitable for self‐assembly studies.…”

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

“…Block copolymers 4 a – c were synthesized by following a previously reported methodology . FTIR spectra were recorded with a PerkinElmer Paragon 1000 spectrometer.…”

Gold‐Decorated Chiral Macroporous Films by the Self‐Assembly of Functionalised Block Copolymers

“…MeLi (1.6 M in diethyl ether), NaH (60 % in mineral oil), LiN(SiMe 3 ) 2 , CF 3 CH 2 OH, NaBH 4 , 4‐hydroxypyridine (C 5 H 5 NO) (all from Aldrich), ( R )‐(+)‐1,1′‐binaphthyl‐2,2′‐diol ( R ‐(C 20 H 14 O 2 ); from Merck), and HAuCl 4 (from Johnson Matthey) were used without further purification. The N ‐(trimethylsilyl)phosphoranimines Cl 3 PNSiMe 3 24d ( 1 ), Cl(PhMe)PNSiMe 3 24c ( 2 ) , and the initiator [Ph 3 PNPCl 3 ][Cl]24c,e ( 3 ), were prepared according to the literature procedures.…”