氟聚合物的发展简介

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2020-04-21  环球过滤分离技术网   filterelement3
This article aims at showing the usefulness of fluoropolymers (FPs), supplying an overview of their synthesis, applications, and recycling. FPs are currently prepared by conventional radical polymerization of fluoromonomers. These specialty polymers, produced in low tonnage compared to that of commodity ones, display outstanding properties, such as chemical, oxidative, and thermal resistances, low refractive index, dissipation factor, permittivity, and water absorptivity, and excellent weatherability and durability. More recent routes for their preparations are suggested, controlled or not, leading to random, alternated, block, graft, dendrimers, or multiarm copolymers, as well as their applications ranging from coatings to high performance (thermoplastic) elastomers, energy related‐materials (e.g., fuel cell membranes, components for lithium‐ion batteries, electroactive devices, and photovoltaics) to original and surfactants, optical devices, organic electronics, composites, and shape memory polymers.

1 Introduction
In the last decades, novel materials that display the suitable property for a specific application have led to an increasing interest. Among them, fluoropolymers (FPs) are relevant niche candidates endowed with outstanding properties (Table 1),[1-9] such as thermal stability, chemical inertness (to solvents, oils, water, acids, and bases), low values of the refractive index, permittivity, dissipation factor, and water absorptivity, as well as excellent weatherability, resistance to oxidation and durability. Hence, they have been involved in many High‐Tech applications (Table 1): protective coatings, fuel cell membranes, elastomers,[10-12] fabrics, specific items in automotive industries[4, 5] (350 g of FP per car (and should increase to 1‐2 kg in a few years), such as seals, gaskets, or transmission components, as well as cables and hoses, and increasing amounts of items as fuel cell membranes and electrolytes and separators of lithium ions batteries), aerospace and aeronautics (fire retardant‐coatings, elastomers for gaskets or O‐rings and cables, considered as an average of 1 km cables made of FPs per passenger in planes), microelectronics, petrochemical, chemical engineering (high performance membranes),[13] textile treatment, protective building coatings (e.g., paints resistant to UV and to graffiti or liners in oil tanks of vehicles), and optics (core and cladding of optical fibers).[14]


This contribution supplies an overview of FPs in terms of synthesis, applications, and recyclability to highlight how these relevant materials have become essential nowadays.

The fluoromonomer precursors are currently prepared from synthons obtained by fluorination, hydrofluoric acid being produced from calcium fluoride, as follows


CaF2(sol)+H2SO4(liq)     →CaSO4(sol)+2HF(gas)

(1)





Since reported in many reviews,[3, 5, 6, 9, 15] the syntheses of fluorinated monomers [as tetrafluoroethylene (TFE), vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE), 3,3,3‐trifluoropropene (TFP), hexafluoropropylene (HFP), trifluoroethylene (TrFE)] are not mentioned in this review. They are commercially available and conventional alkenes that contain one or several fluorine atoms born by ethylenic carbon atoms have also been designed on demand for specific applications. They are usually gaseous (<4 carbon atoms) and their mode of synthesis is costly.

Most FPs are synthesized by radical (co)polymerization of fluoroalkenes (except those based on hexafluoropropylene oxide (Section 2.4 and Scheme 5) and fluorinated oxetanes achieved by anionic initiations).


Actually, two main classes of FPs can be taken into account: i) FPs where the fluorinated groups are located in the polymer backbone (e.g., most homopolymers based on TFE, CTFE, VDF, and TrFE): they exhibit good thermal stability, chemical inertness, and low refractive index and dielectric constant, and ii) FPs that contain a fluorinated dangling group [poly(meth)acrylates or poly(styrene)s bearing perfluorinated side chains[1, 3, 5, 8]] that brings better surface properties.

FPs are specialty polymers which represent approximately less than 4% of all macromolecules. In 2012, their production was 223 000 tons while it is forecast to be approximately double (>405 000 t) by 2022.[16] Figure 1 sums up the production of different classes of FPs, PTFE being the most produced, while Figure 2 exhibits the FPs consumption per industry in Europe in 2015.



Global situation of the production of various FPs (2019)





Fluoropolymers consumption per industry in Europe (2015). Reproduced with permission.[17] Copyright 2016, Carl Hanser Verlag GmbH & Co.





Evolution and prediction of production of high performance FPs from ref. [16] (APAC stands for Asia Pacific accreditation cooperation).

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