Polyphosphazene Polymer

Abstract

Polyphosphazenes are a unique class of inorganic–organic hybrid polymers with a backbone composed of alternating phosphorus and nitrogen atoms. The ease with which the precursor prepolymer poly(dichlorophosphazene) can be modified has resulted in a versatile polymer system. The labile nature of the P−Cl bonds has allowed the substitution of chlorine atoms with groups like alkoxy‐, aryloxy, alkyl ether, fluoroalkoxy, amino acid/peptide esters, drug molecules, transition metal groups, and many more. Careful selection of the side groups offers efficient control of material properties such as bioactivity, crystallinity, solubility, and surface characteristics. Hence, these properties have led to the use of this exceptional class of polymers in a broad range of applications such as biomaterials for regenerative engineering and drug delivery, elastomers, solid membranes for gas/liquid separation, optical materials, flame retardants, and electrolytes for energy storage cells. This article gives an overview of the synthetic routes of polyphosphazene polymers and their composition–structure–properties relationships and highlights their applications in various fields.

Biomedical applications of polyphosphazenes

“…This initial step results in a highly reactive organic precursor, called poly(dichloro)phosphazene (PDCP) with labile P–Cl bonds that are later utilized to substitute in organic nucleophiles for chlorine atoms (Allcock, 2016, 2018; Ogueri, Escobar Ivirico, et al, 2019). Though ROP is the conventional synthetic route to obtain a linear and high molecular weight PDCP, other alternative technique routes such as living cationic polymerization and direct synthesis have been reported to yield PDCP intermediates with low molecular weight (Ogueri et al, 2019, 2020a). The drawbacks of ROP (such as high‐temperature requirements and uncontrollable molecular weight) can be outmanoeuvred using these alternative methods (Ogueri et al, 2020a).…”

“…Furthermore, macromolecular substitution can be used to obtain mixed‐substituent polyphosphazenes with two or more organic substituent side groups (Figure 1; Ogueri et al, 2019; Ogueri, Allcock, et al, 2019). This can be achieved by simultaneous or sequential reactions of organic nucleophilic species, where, for the later, the large groups are reacted first, followed by the small groups in a solution phase (Ogueri, Allcock, et al, 2019; Ogueri, Escobar Ivirico, et al, 2019).…”

“…Thus, polyphosphazenes provide a versatile tool that can manage this trade‐off, and they offer an optimal biologic interface between the surface of medical implants and native tissues (Z. Huang et al, 2018; Ogueri, Ogueri, Allcock, & Laurencin, 2020a; Potta, Chun, & Song, 2010). Polyphosphazene‐based polymers are a class of inorganic–organic hybrid polymers with an unusual polymer skeletal backbone composed of alternating phosphorous and nitrogen atoms (Ogueri, Allcock, & Laurencin, 2019; Strasser & Teasdale, 2020). Each phosphorous atom is linked with two substituents (e.g.…”

Injectable Hydrogels for Cancer Therapy over the Last Decade

“…On the contrary, the employment of cyclic PPZ architecture should be accurately investigated, because such derivatives are characterized by a relatively long time of degradation which can reduce the biomedical applicability [42]. Although a large number of PPZ polymers have not found commercial success [43], several research groups have developed different types of PPZ injectable hydrogels (Table 1). PPZ-based hydrogels were successfully tested for the delivery of cytotoxic drugs or sRNA to solid tumors, both in vitro and in vivo [40,44,45,46,47,48,49,50].…”

Thiophene‐based polyphosphazenes with tunable optoelectronic properties

“…Hence, the optoelectronic properties of the polymeric system are manipulated solely by the electronic and chemical structures of the side groups. 9 The optical and electrical properties of organic semiconductors can be modified efficiently by chemical or electrochemical doping via charge transfer reactions, which benefit the overall device performance. 10 It has been reported that the addition of a small amount of a suitably strong electron acceptor to p-type semiconducting polymers improves the final performance of optoelectronic devices produced from their blends.…”