Phosphazene block copolymers

Well-defined phosphazene block copolymers were prepared by the cationic polymerization of phosphoranimines [57]. Block copolymers of the type [N = PCl2]n[N = PR(R )]m were prepared using a wide variety of phos-... 

Poly(ethylene oxide)-b-poly[bis(methoxyethoxyethoxy)-phosphazene] block copolymer (about 67 mol% Ethylene oxide)... 

Scheme 7.7 Examples of phosphazene block copolymers prepared the living cationic polymerization route.

Figure 1.13 Examples of the three most common routes to hetero poly(dichloro)phosphazene block copolymers with organic or inorganic polymers...

As the synthetic approach to polydichlorophosphazene put forward by R. De Jaeger has been already described in several recent review articles [10,38,57, 172], in this paper we will illustrate only the polycondensation approach proposed by I. Manners and H. R. Allcock, together with the consequences of this reaction on the preparation of chain phosphazene copolymers (block copolymers) [220,223,224,232-234,240], and star polymers [222]. 

In the same scheme, moreover, it is evident that, besides phosphazene homopolymers, the substitution of the chlorines with two (or more) different substituents leads to the preparation of substituent phosphazene copolymers [263] containing different homosubstituted and heterosubstituted monomeric units. Moreover, the cationic polymerization of phosphoranimines [215-217] produces polymers with hving reactive ends (vide supra) from which the preparation of chain phosphazene copolymers (block copolymers) [220,223,225, 229,232-235,239, 240] formed by different polymeric backbones linked together in a unique macromolecule could be obtained. 

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). ... 

CH2 Chang, Y., Bender, J.D., Phelps, M.V.B., and Allcock, H.R., Synthesis and selfassociation behavior of biodegradable amphiphilic poly[bis(ethyl glycinat-A/ -yl)phosphazene]-poly (ethylene oxide) block copolymers. Biomacromolecules, 3, 1364, 2002. 

A critical advantage of phosphazene materials is the ability to fine tune hydrophilicity through pendant group selection. Another method demonstrated that the the same type of tuning can be performed by formation of tri-block copolymers. A synthesis of a MEEP/poly(propyleneglycol) has been reported using phosphoranimine condensation to form the phosphazene portion. ... 

S. Forster and E. Kramer, Synthesis of Pb-PEO and Pl-PEO Block Copolymers with Alkyllithium Initiators and the Phosphazene Base t-BuP4, Macromolecules 32 2783 (1999). 

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. 

Access to the living cationic polymerization technique mentioned earlier has allowed the synthesis of a range of block copolymers, either phosphazene-phosphazene blocks, phosphazene-organic polymer blocks, or phosphazene-polyorganosiloxane blocks.Both di- and triblock copolymers have been produced, and a summary of these structures is shown in Scheme 7.7. 

Phosphazene Block Organic Block IMblock Copolymers... 

Phosphazene polymers comprise a class of several hundred different macromolecules with the general formula shown in Structure 1, where R represents organic, organometallic or inorganic side groups. Two structural factors can be varied for these polymers. First, the basic skeletal architecture varies from linear polymers or block copolymers to stars, dendrimers, combs, cyclolinear or cyclomatrix structures. Second, more than 250 different side groups have been linked to the various skeletons. Most of the polymers that have been studied in detail are linear macromolecules of type 1 or block copolymers formed between 1 and classical organic polymers. 

An alternative, direct route to fluoroalkoxy phosphazene polymers and aryl derivatives which also permits access to block copolymers has been developed (eqs. 4 and 5) (17,18). 

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