Dynamic covalent chemistry relates to chemical reactions carried out reversibly under conditions of equilibrium control. The reversible nature of the reactions introduces the prospects of "error checking" and "proof-reading" into synthetic processes where dynamic covalent chemistry operates. Since the formation of products occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. In kinetically controlled reactions, however, it is the free energy differences between the transition states leading to the products that determines their relative proportions. Supramolecular chemistry has had a huge impact on synthesis at two levels: one is noncovalent synthesis, or strict self-assembly, and the other is supramolecular assistance to molecular synthesis, also referred to as self-assembly followed by covalent modification. Noncovalent synthesis has given us access to finite supermolecules and infinite supramolecular arrays. Supramolecular assistance to covalent synthesis has been exploited in the construction of more-complex systems, such as interlocked molecular compounds (for example, catenanes and rotaxanes) as well as container molecules (molecular capsules). The appealing prospect of also synthesizing these types of compounds with complex molecular architectures using reversible covalent bond forming chemistry has led to the development of dynamic covalent chemistry. Historically, dynamic covalent chemistry has played a central role in the development of conformational analysis by opening up the possibility to be able to equilibrate configurational isomers, sometimes with base (for example, esters) and sometimes with acid (for example, acetals). These stereochemical "balancing acts" revealed another major advantage that dynamic covalent chemistry offers the chemist, which is not so easily accessible in the kinetically controlled regime: the ability to re-adjust the product distribution of a reaction, even once the initial products have been formed, by changing the reaction's environment (for example, concentration, temperature, presence or absence of a template). This highly transparent, yet tremendously subtle, characteristic of dynamic covalent chemistry has led to key discoveries in polymer chemistry. In this review, some recent examples where dynamic covalent chemistry has been demonstrated are shown to emphasise the basic concepts of this area of science.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3773%2820020503%2941%3A9%3C1460%3A%3AAID-ANIE11111460%3E3.0.CO%3B2-N

Dynamic covalent chemistry.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3757%2820020503%29114%3A9%3C1528%3A%3AAID-ANGE11111528%3E3.0.CO%3B2-Z

Dynamische kovalente Chemie

Sulfonated poly(arylene) ionomers containing merely electron-accepting sulfone units (−SO2−) connecting the phenyl rings have been synthesized and characterized in detail, in particular with respect to properties relevant for their application as membrane materials in polymer-electrolyte-membrane (PEM) fuel cells. The copolymers were prepared by a two-step process comprising (1) a nucleophilic aromatic polycondensation reaction of 4,4‘-difluorodiphenylsulfone and disodium 3,3‘-disulfonate-4,4‘-difluorodiphenylsulfone with 4,4‘-thiobisbenzenethiol at various molar ratios yielding sulfonated poly(phenylene sulfide sulfone)s and (2) their subsequent oxidation to sulfonated poly(phenylene sulfone)s using peroxide in acidic solution. This new class of polymers with extremely electron-deficient aromatic rings shows very high thermal, thermooxidative and hydrolytic stabilities, low solubilities, and reduced swelling in water at enhanced temperature compared to other sulfonated poly(arylene)s. The latter property...

Sulfonated Poly(phenylene sulfone) Polymers as Hydrolytically and Thermooxidatively Stable Proton Conducting Ionomers

Control of reactions and network structures of epoxy thermosets

This paper presents a preparation route which allows the formation of a poly(phenylene) ionomer containing merely sulfone units (−SO2−) connecting the phenyl rings and in which each phenyl ring is monosulfonated (100% degree of sulfonation). This corresponds to an ion exchange capacity (IEC) of 4.5 mequiv g−1 (equivalent weight of EW = 220 g equiv−1). The preparation succeeded in a two-step process comprising a polycondensation reaction of sulfonated difluorodiphenyl sulfone with sodium sulfide, yielding sulfonated poly(phenylene sulfide sulfone), and the subsequent oxidation to the corresponding sulfonated poly(phenylene sulfone). The polymer was characterized by elemental analysis, NMR, IR, GPC, viscosity measurement, TGA in air and in pure water vapor atmosphere, DSC at low and high temperatures, and ac impedance spectroscopy. Room temperature water absorption isotherms have been determined by equilibrating samples at different relative humidities. Under the chosen reaction conditions, polymers with mo...

Highly Sulfonated Poly(phenylene sulfone): Preparation and Stability Issues

Infrared spectroscopic analysis of poly(p-phenylene sulfide)

Polymerization of poly(p-phenylene sulfide) from a cyclic precursor

Infrared and Raman spectroscopy of cyclohexa(p-phenylene sulfide) and the polymer obtained therefrom

The Combination of reaction injection molding and pultrusion has resulted in a new processing technique, RIM-Pultrusion, Which has been used to produce a thermoplastic epoxy prepreg. This prepreg has been used to produce a long-fiber injection molded phenoxy/carbon fiber composite with near-Zero void content. A heat-activated curing system has been developed, which allows injecton molding of the prepreg to form a thermostet long-finer epoxy/carbon finber composite. The RIM- pultrusion conditions for producing an injection moldable prepreg are described. Capillary rheomety is used to study the epoxy resin to determine the proper molar ratio for RIM-Pultrusion. The long-fiber epoxy compostie is analyzed with dynamic mechanical analysis (DMA) and Fourier transform infrared spectroscopy (FTIR). Also., the impact strength and solvent resistance of the long-fiber composite are examined. The properties of the thermoset long-fiber epoxy xomposite are compared to those of a thermoplastic injection molded long-fiber phenoxy composite.

Dean A. Zimmerman

Papers

Infrared spectroscopic analysis of poly(p-phenylene sulfide)

Polymerization of poly(p-phenylene sulfide) from a cyclic precursor

Infrared and Raman spectroscopy of cyclohexa(p-phenylene sulfide) and the polymer obtained therefrom

The development of an epoxy resin system for the injection molding of long‐fiber epoxy composties

Polymorphism on the cyclic hexamer of p-phenylene sulfide