Polyphosphazene block copolymers

Allcock HR, Reeves SD, Nelson JM, Crane CA, and Manners I. Polyphosphazene block copolymers via the controlled cationic, ambient temperature polymerization of phosphoranimines. Macromolecules, 1997, 30, 2213-2215. 

Polyphosphazenes block copolymers containing sulfonimide side groups, (V), were prepared by Allcock et al. (4) and used in membrane blends in fuel cells. 

Polyphosphazene block copolymers were synthesized by these chain-growth polymerization methods. The successive anionic polymerization of N-silylphosphoranimines 19d and 19a at 133 °C yielded the block copolymer with Mw/Mn of 1.4-2.3 (Scheme 80) [278,279]. However, due to the presence of two possible leaving groups in 19d, this approach yielded block copolymers where one of the block segments contained a mixture of side groups. On the other hand, the cationic polymerization of 19b with PCI5 was carried out at ambient temperature, followed by addition of a second phosphoranimine to yield a block copolymer with Mw/Mn of 1.1-1.4, where each block segment had one kind of side chain (Scheme 81) [280]. 

Soto and coworkers have developed chiral polyphosphazene block copolymers (13CEJ5644). Their synthesis starts with consecutive reactions of (trimethylsilyl)phosphorimidoyl trichloride 160 and methylphenyl-phosphorimidoyl chloride 161 monomers (Scheme 42). The polymerization was initiated by phosphazene 159 and gave the polyphosphazenes 162a—c with different ratio of block motifs. The substitution of chlorine atoms by binol was accomplished in the presence of cesium carbonate as a base and the resulting polymers 162a—c isolated in 66—77% yields. 

Matyjaszewski, K., Moore, M.K., White, M.L. (1993) Syaithesis of polyphosphazene block copolymers bearing alkoxyethoxy and trifluoroethoxy groups. Macromolecules, 26, 6741-6748. 

Well-defined polyphosphazene block copolymers with poly(ferrocenylsilane) (PFS) have also been reported, where the combination of the crystallinity of the PFS block and versatility of the polyphosphazene block crystallisation-directed living supramolecular polymerisations lead to spatially defined and controllable nanostructures [59]. Although not designed specifically for medical applications, they show a prime example of how the tunability of polyphosphazenes can be exploited for advanced macromolecular engineering. 

Figure 1.17 Helical polyphosphazene block copolymers. Reproduced with permission from S. Suarez-Suarez, G.A. Carriedo, M.P. Tarazona and A. Presa Soto, Chemistry - A European Journal, 2013,19,18, 5644. 2013, Wiley-VCH 1611...

It is also feasible to synthesize polyphosphazene block copolymers by the addition of a second phosphoranimine after complete conversion of the first. This is possible due to the existence of silyl end groups present on the polymer chain. These moieties can be spectroscopically observed by NMR. (15) Molecular weight calculations based on the integration of diese signals gives good agreement (to widiin about 20%) with the GPC data. Block copolymers have been prepared by the addition of monomer 2e after the conversion of 2a and 2b. Conversion was determined by 3lp NMR. The tabulated data for these polymers can be viewed in Table n. 

Some block copolymers of polyphosphazene and conventional polymers were also synthesized. The first example is a block copolymer of polyphos-... 

Since the procedure for the formation of macroinitiator by using 21, mentioned in the synthesis of block copolymers of polyphosphazene and PEG, enabled the synthesis of monofunctional polyphosphazenes [288], monoallyl functional polyphosphazene was prepared and underwent hy-drosilylation with dihydride-terminated poly(dimethylsiloxane) to pro-... 

Figure 1 Different types of polyphosphazenes including linear classical macromolecules (1), star structures (2), block copolymers (3), cyclolinear polymers (4), and comb or graft copolymers (5) and (6). Not shown are cyclomatrix materials in which cyclic trim eric rings are connected in three dimensions ...

In addition to the termination of living poly(dichlorophosphazene) with phos-phoranimine-terminated poly(dimethylsiloxane), another method has been presented to synthesize poly(phosphazene-siloxane) block copolymers. Hydrosilyla-tion reactions of hydride-terminated poly(dimethylsiloxane) and allyl-terminated polyphosphazenes (210a, 210b) have been shown to yield polyphos-phazene-h/ocfc-polysiloxane-h/oc/c-polyphosphazene polymers (21 la, 21 Ib). ... 

Block copolymers (228), consisting of a hydrophilic poly(ethylene glycol) and a hydrophobic polyphosphazene residue, have been investigated with respect to their micelle formation in aqueous solution Micelle formation in water has also been observed for polymers (229) with ethyl glycinato substituents. Hydrolytic degradation of these polymers has been studied in aqueous thf. ... 

There are three techniques to prepare block copolymers. In the first, a nonterminated living polyphosphazene is allowed to react with the... 

There have been other types of approaches also for the synthesis of hybrid polymers. Block copolymers containing polysiloxane segments and polyphosphazene segments have been synthesized by the reaction of hydride-terminated polysiloxane H-[Si(Me2)-0]n-SiMe2H with the telechelic polyphosphazene containing an amino end-group (Fig. 6.28) [33]. 

This S5mthetic method has been extended to the direct synthesis of poly(organophosphazenes) as well as the development of star and block copolymers. For example, triarmed star-branched polyphosphazenes (eg, 6) can be synthesized through the initiation of trifimctional phosphoranimines (22). It has also been shown that the presence of living active sites at the termini of the poljuner chains allows for addition of a second monomer and the formation of block copolymers (23), such as (7) which is formed through the initiation of a difunctional linear phosphoranimine and the subsequent introduction of two different monomers (24). These developments offer the prospect of improved routes... 

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