“…The 〈 r 2 〉 0 = 6〈 s 2 〉 0 relationship valid for flexible chains has been used in the above equation. The value obtained C n = 14 is in the range obtained for other polyphosphazenes, and its high value indicates a fairly extended chain. 7 Fixman extrapolations for the polymer 1 .…”
The reaction of a mixture of [NPCl2]n and Cs2CO3 first with (R)-(+)-1,1′-binaphthyl-2,2′diol (HO-C10H6-C10H6-OH) (binaphthol) and subsequently with phenol (HO-C6H5) in refluxing 1,4dioxane gave the series of the optically active random copolymers {[NP(O2C20H12)]x[NP(OC6H5)2]1-x}n (2). Absolute molecular weight distributions and radius of gyration have been determined by size exclusion chromatography, using simultaneously multiangle light scattering and differential refractive index detectors. The dependence of the dimensions of the polymers on the molecular weight through the corresponding scaling laws is studied. In addition, a stereochemical study of homopolymers [NP(O 2C20H12)]n 1 and copolymers 2 based on the CD exciton chirality method is also included. The reaction of the partially substituted polymer [NP(R-O2C20H12)0.4(Cl2)0.6]n with the stoichiometric amount of racemic binaphthol, or with a large excess of the latter, in the presence of Cs2CO3 gave the same polymer [NP(R-O2C20H12)0.4-(rac-O2C20H12)0.4]n [(-)-3] irrespective of the amount of racemic binaphthol used, showing no enantiomeric induction by the R-binaphthoxy units already present in the polymer.
“…The 〈 r 2 〉 0 = 6〈 s 2 〉 0 relationship valid for flexible chains has been used in the above equation. The value obtained C n = 14 is in the range obtained for other polyphosphazenes, and its high value indicates a fairly extended chain. 7 Fixman extrapolations for the polymer 1 .…”
The reaction of a mixture of [NPCl2]n and Cs2CO3 first with (R)-(+)-1,1′-binaphthyl-2,2′diol (HO-C10H6-C10H6-OH) (binaphthol) and subsequently with phenol (HO-C6H5) in refluxing 1,4dioxane gave the series of the optically active random copolymers {[NP(O2C20H12)]x[NP(OC6H5)2]1-x}n (2). Absolute molecular weight distributions and radius of gyration have been determined by size exclusion chromatography, using simultaneously multiangle light scattering and differential refractive index detectors. The dependence of the dimensions of the polymers on the molecular weight through the corresponding scaling laws is studied. In addition, a stereochemical study of homopolymers [NP(O 2C20H12)]n 1 and copolymers 2 based on the CD exciton chirality method is also included. The reaction of the partially substituted polymer [NP(R-O2C20H12)0.4(Cl2)0.6]n with the stoichiometric amount of racemic binaphthol, or with a large excess of the latter, in the presence of Cs2CO3 gave the same polymer [NP(R-O2C20H12)0.4-(rac-O2C20H12)0.4]n [(-)-3] irrespective of the amount of racemic binaphthol used, showing no enantiomeric induction by the R-binaphthoxy units already present in the polymer.
“…On the other hand, it have been suggested that some of the polymers obtained by macromolecular substitution from a [NPCl 2 ] n prepared by the ringopening polymerization of [N 3 P 3 Cl 6 ] exhibit anomalous behavior in solution, suggesting the formation of intermolecular aggregations and raising the question of the presence of chain imperfections, mainly as branching points [16], a fact that could affect their thermal stability [17].…”
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.
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