Phosphazenes special

A number of liquid crystalline polyphosphazenes with mesogenic side groups have been prepared (48—50). Polymers with nonlinear optical activity have also been reported (51). Polyphosphazene membranes have been examined for gas, liquid, and metal ion separation, and for filtration (52—54). There is interest in phosphazene—organic copolymers, blends, and interpenetrating polymer networks (IPNs) (55—61) to take advantage of some of the special characteristics of phosphazenes such as flame retardance and low temperature flexibility. A large number of organic polymers with cydophosphazene substituents have been made (62). 

Methods are now available for the hybridization of phosphazenes with other polymer systems in order to combine the special properties of the inorganic macromolecules with those of... 

Examples of known phosphazene polymer blends are those in which phosphazenes with methylamino, trifluoroethoxy, phenoxy, or oligo-ethyleneoxy side groups form blends with poly(vinyl chloride), polystyrene, poly(methyl methacrylate), or polyethylene oxide).97 100 IPNs have been produced from [NP(OCH2CH2OCH2CH2OCH3)2] (MEEP) and poly(methyl methacrylate).101-103 In addition, a special type of IPN has been reported in which a water-soluble polyphosphazene such as MEEP forms an IPN with a silicate or titanate network generated by hydrolysis of tetraethoxysilane or tetraalkoxytitanane.104 These materials are polyphosphazene/ceramic composites, which have been described as suitable materials for the preparation of antistatic layers in the manufacture of photographic film. 

The introduction of bulky, electron-rich side groups, such as those depicted in structures 3.102-3.105 requires the use of special experimental conditions. If introduced via an aryloxide ion by the macromolecular substitutive route, these side groups impart and suffer considerable steric hindrance. Replacement of every chlorine atom along the phosphazene chain by organic side groups may be difficult. 

Actually, the PNP cation is but one special example of a group of compounds called phosphazenes. Monophosphazenes (R3P=NR ), diphosphazenes (R3P=N— PRO, and polyphosphazenes (R3P=N—(PR2=N) - PR2) are all known. Hundreds of monophosphazenes have been characterized, and a general synthetic route is... 

Phosphazene elastomers were very successful throughout the 1980s, being used mainly in military and aerospace industry. However, because of their high cost and relatively small volume market, they are not available commercially other than on special orders. 

Activity in the phosphazene area has increased over that reported in volume 21 as indicated by an increase of fifty-five in the number of citations. Three particular areas deserve special mention. These are the use of the aza-Wittig reaction in the construction of heterocyclic rings, the structural diversity and solvent selectivity in macrocycles formed by reactions of long chain diamines (or oxodiamines) with N3P3CI6 and lastly the synthesis of new heterophosphazene polymers by ring opening reactions of cyclic heterophosphazenes. 

The chemistry of phosphorus-nitrogen compounds is well covered in a series of specialized monographs (some concentrating on phosphazenes), the Royal Chemical Society s Specialist Periodical Reports (annual surveys), and numerous review articles (to be cited in the appropriate place of this chapter). 

Staudinger reaction (phosphazene synthesis and reactions with a special focus on the aza-Wittig process)and reviews of the applications of the aza-Wittig reaction to heterocyclic... 

Metaphosphimates are a special class of inorganic polyphosphazanes which were first recognised in the nineteenth century by Stokes [12]. Cyclometaphosphimates are X.W tri and higher cyclophosp-hazanes, which can be made by hydrolysis of cyclic phosphazenes. 

The poly(alky1/arylphosphazenes) are a special type of phosphazene polymer in which all substituents are attached to the backbone phosphorus by direct P-C linkages. Unlike the majority of polyphosphazenes, which are usually prepared by ring opening of fully (3 - 5) or partially (6 -8) halogenated cyclic phosphazenes followed by nucleophilic substitution of the halogens, the poly(alkyl/arylphosphazene) homopolymers and simple copolymers are made by the condensation polymerization (9, 10) of Si-N-P compounds known as N-silylphosphoranimines (eg 1 and 2). 

The synthetic flexibility of poly(organo)phosphazenes, combined, when required, with a tunable degradability, can be used to prepare speciality materials with precisely designed functions. With intelligent design and structural modifications, it is envisaged that many advanced biomedical materials of the future could be derived from polyphosphazenes. As the many reports summarised in this book confirm, progress in this direction is indeed already well underway ... 

Special interest has been focused on those aza-Wittig reactions of componnds 77 (Scheme 15.16) where both the phosphazene, moiety and the carbon-oxygen double bond (C=0) (aldehydes, ketones, esters and amides) are fonnd within one molecule. This strategy involving intramolecular aza-Wittig reactions allows a method for the preparation of five- to higher-membered heterocyclic compounds 78 under very mild reaction conditions, that are a structnral feature in the skeleton of natural products. 

Since both miscible and immiscible phosphazene blends are of considerable interest as membrances, biomaterials, or flame retardant materials, it is worthwhile to study the compatibility of these kinds of blends in more detail in order to understand more about the interaction between the polymer pair and the stability of the blends. Our goal in this study is to prepare PCPP/PS blends and investigate the compatibility and tile properties of the blends by optical clarity, DSC, SEM, FTIR, TGA and LOI. PCPP/PS is chosen in this study because (a) PCPP is known to be flame retardant (5), (b) polystyrene is a well-known versatile organic polymer and has been selected to gi t or blend with phosphazene polymers in most of the polyphosphazene-organic polymer hybrids systems (14,15), and (c) the similarity of aromatic side groups in both of the polymers. In addition, since rcPP has a special thermotropic transition temperature, T(l), and in order to further understand tiie stability of the blends, the compatibility influenced by temperature is also studied before and after T(l) transition by DSC. 

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