Thermally resistant polymers, sulfonation

Sidfonated hydrocarbon polymers are widely used as a host matrix to prepare organic-inorganic nanocomposite for high-temperature PEM applications due to their excellent stability and high susceptibility to electrophilic sulfonation reactions for acid fimctionalization. Sulfonation of thermally resistant polymers such as polysulfones (PSF), fluoropolymers, and polyetheretherketone (PEEK) was widely studied. The sulfonation of certain polymers such as polystyrenes... 

Polyimides (PI) were introduced in 1962 as thermally non-processable Kapton . To improve processability, the main-chain flexibility was enhanced by incorporating segments with higher mobility, viz. polyamide-imide (PAl), polyether-imide (PEI), polyimide-sulfone (PISO), etc. These polymers are characterized by high T = 150-420°C and thermal resistance. They are blended with PPS to enhance its moldability, thermal stability and mechanical performance. 

Cross-linked macromolecular gels have been prepared by Eriedel-Crafts cross-linking of polystyrene with a dihaloaromatic compound, or Eriedel-Crafts cross-linking of styrene—chloroalkyl styrene copolymers. These polymers in their sulfonated form have found use as thermal stabilizers, especially for use in drilling fluids (193). Cross-linking polymers with good heat resistance were also prepared by Eriedel-Crafts reaction of diacid haUdes with haloaryl ethers (194). 

Poly(ether ether ketone) (PEEK) is an aromatic, high performance, semicrystalline polymer with extremely good thermal stability, chemical resistance, and electrical and mechanical properties. This polymer shows little solubility in organic solvents due to the crystallinity. One of the first ways to characterize PEEK was by sulfonating the polymer. By adding sulfonic acid groups to the backbone, the crystallinity decreased and solubility increased.Commercially available Victrex appears to be one of the more interesting poly(arylene ether) s used for postmodification. 

An early commercial interest in poly (olefin sulfones) was sparked by the low raw materials cost, but this interest waned when it became apparent that thermal instability is a general characteristic of this class of materials. In 1970 Brown and O Donnell reported that poly (butene-1-sulfone) is degraded by gamma radiation with a G(s) approaching 10, making it one of the most radiation-sensitive polymers known (38-39). The potential for use of this radiation sensitivity in the design of electron beam resists was quickly realized by several members of the electronics industry. Bell Laboratories, RCA, and IBM published studies demonstrating the potential of poly (alkene... 

Ionomer membranes based on perfluorocarbon polymers became available In the late 196O s. These materials have excellent chemical resistance, thermal stability, mechanical strength and strong acid strength, A number of functionalities have been studied. Including carboxylate, sulfonate and sulfonamide, but only the first two are available as commercial materials. Ferfluorlnated lonomers have been evaluated as membranes In a variety of applications, such as water electrolysis, fuel cells, air driers, Donnan dialysis In waste metal recovery, and acid catalysts, but the primary interest in these materials is for the permselective membrane In electrochemical processes such as In the production of chlorine and caustic (58). 

Poly(arylene sulfone)s and poly(arylene ketone)s are important engineering thermoplastics, and display high Tg-values, high thermal stabilities, good mechanical properties, and an exceptional resistance to both oxidation and acid-catalyzed hydrolysis. It is only during the past decade that the sulfonated aromatic polymers have been considered to be well-suited as PEM candidates for fuel cells [61-64]. 

Jn recent years, there has been a considerable amount of interest in high-molecular-weight polyarylsulfone polymers (1-3). These polymeric materials possess heat-deflection temperatures of 165°-260°C plus excellent thermal stability at the high processing temperatures required. This paper deals with the synthesis and the physical and mechanical properties of a new heat-resistant polyarylsulfone. This new polyarylsulfone thermoplastic exhibits a significant reduction in apparent (melt) viscosity with only a slight reduction in heat deflection temperature when compared with the polyarylsulfone based on bis(4-chlorophenyl)sulfone and 2,2-bis (4-hydroxyphenyl) propane. 

The mass spectroscopic analysis of the gases formed in thermal development of the UV exposed poly(l-butene sulfone)/pyridine N-oxide revealed only 1-butene and S02 as the products, which indicated depolymerization of the polymer initiated by energy transfer form the sensitizer. These photosensitized poly(olefin sulfones) are not suitable for dry etching processes, and they are not reactive ion etching resistant. Resists made of poly(olefin sulfones) and novolac resins which will be described next are CF plasma etch resistant with reasonable photosensitivities. 

In the previous section it was suggested that the parent polymer structure considerably influence the physical properties of the derived polysulfonates, imparting to them some of the mechanical and thermal properties of the precursors. This trend is particularly evident in the case of the perfluorinated hydrocarbon polymers. Polymers of this kind, such as e.g., poly(tetrafluoroethylene) (PTFE) are exceptional in their inertness to offensive environment, solvent resistance and high-temperature stability. These considerations led in the sixties to the development of unique sulfonic-acid derivatives of fluorocarbon copolymers by the DuPont Company. While several compositions were disclosed in the patent literature51, the preferred composition, which is the basis for the commercial Nafion ion-exchange membrane, is a copolymer of tetrafluoroethylene with a perfluorinated vinyl ether/sulfonyl fluoride52 ... 

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