Polyphosphazene block copolymers synthesis

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. 

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-... 

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... 

Krogman et a/. ° presented the synthesis of blocked poly (phosphazene-l -carbonate)s. First, amino-terminated PTMC was synthesized via ROP. In the synthesis of block copolymers of polyphosphazenes linked to PCs the amino terminus was used to form a covalent link to poly(dichlorophosphazene). 

The synthesis of N-silyl-phosphoranimines bearing mixed alkoxyalkoxy and trifluoroethoxy substituents is reported. The polymerization kinetics and the proposed anionic mechanism are also discussed. These monomers are utilized for the preparation of polyphosphazene random copolymers by the simultaneous polymerization of two phosphoranimines. Block copolymers have also been synthesized by addition of a second phosphoranimine after conversion of the first. Evidence for copolymer formation includes and 3lp NMR, SEC, solubility and DSC data. The differences between analogous random and block copolymers are discussed. 

Other methods of polyphosphazene synthesis have also been reported [17]. The most interesting is the living cationic condensation polymerization of phosphoranimines [21,22] as it offers access to polyphosphazenes with controlled molecular weight, low polydispersity, and more complex architectures, e.g. block or graft copolymers. At the present time, only moderate molecular weights (Mw = 10 -10 ) are available via the condensation route. 

Later on, such ambient temperature synthesis approach was extended to a variety of organo-substituted phosphoranimines, to directly synthesize polyphosphazenes with controlled molecular weight and low polydispersities, so that PDCP preparation and following chlorine substitution steps were eliminated [26]. Such living cationic condensation polymerization method also allows the preparation of polyphosphazenes with complex structures such as comb, star, and dendritic architectures, as well as block and graft copolymers with organic macromolecules [18]. 

---