Characterization of the viscoelastic and mechanical properties of tightly cross‐linked polythiourethane networks

Abstract

Both viscoelastic behavior and plastic deformation in compression were investigated on new polythiourethane networks based on diisocyanates and tri-or tetra-thiols. Dynamic mechanical analysis was used to characterize the mechanically-active a and b relaxations as a function of crosslink density and nature of the diisocyanate. Data molecular analysis on these novel materials led to conclusions in good agreement with earlier statements on the well-known epoxy-amine networks. Besides, consideration of the relaxational behavior, and especially in the b relaxation region, allowed one to interpret the plastic deformation properties of the systems under study and to predict their poor resistance to fracture. By the way, analysis of the energy required to yield permitted determination of a new characteristic temperature, T y , which can be compared to the thermomechanical main transition temperature, T a , and to the glass transition temperature, T g .

Characterization, structural transitions and properties of a tightly crosslinked polythiourethane network for optical applications

“…The motional processes responsible for this secondary transition were further investigated. As shown in another publication [27] and resulting from the consideration of a series of polythiourethane networks in which the type of isocyanate and thiol have been modified in order to vary the crosslink density, the β motions present a cooperative character on a rather short scale, by propagating through the thiol structure.…”

Bis(thiocarbamates): Synthesis and Substituent Effects on the Barrier to N‐CO Rotation

“…As in the case of amides and carbamates [, ], bis(thiocarbamates) are characterized by the presence of N–CO bond having a partially double bond character, which results in the presence of the two s‐cis and s‐trans conformations. In our case and as can be seen from Table , the benzyl and phenyl derivatives show the coexistence of the two conformers (i.e., two NH NMR signals), while only one signal was observed in the 1 H NMR spectra for the other derivatives at room temperature (Fig.…”

DD ArtPix

“…These may consist in a controlled variation of the resin and hardener type, of their stoichiometric amount, or in a change of the resin processing, i.e., the curing cycle parameters. Various works investigated how the mechanical behavior of epoxy resins is affected by: the stoichiometric ratio [2–5], the type of resin and hardener [3, 6–8], the employ of chains extenders [9], and the employ of blends of different diepoxy monomers [10]. It was revealed that even relatively small changes in the material composition, as for example a variation in hardener and resin relative amounts, can promote changes in the mechanical behavior at small and large strains [11], in the thermo‐mechanical behavior [3] and in thermal expansion [4].…”

“…The material response at small deformation was investigated by means of uniaxial tensile tests, whereas compression tests were employed to investigate the large (i.e., yield and postyield) deformation levels. Particular attention was reserved to the investigation of the large deformation response, in the attempt to understand the correlation between the molecular architecture of polymer glassy networks and their mechanical behavior, on the framework of the approach developed in other works [6–10, 23, 24]. Most of these papers focused their attention on epoxy‐based systems [6, 7, 9, 10, 23], in which different crosslink densities and structures were varied by changing the nature of the hardener; also other crosslinked materials were studied, such as crosslinked polythiourethane systems [8] and amorphous polystyrene–polyphenylene oxide blends, crosslinked during polymerization [24].…”

“…Particular attention was reserved to the investigation of the large deformation response, in the attempt to understand the correlation between the molecular architecture of polymer glassy networks and their mechanical behavior, on the framework of the approach developed in other works [6–10, 23, 24]. Most of these papers focused their attention on epoxy‐based systems [6, 7, 9, 10, 23], in which different crosslink densities and structures were varied by changing the nature of the hardener; also other crosslinked materials were studied, such as crosslinked polythiourethane systems [8] and amorphous polystyrene–polyphenylene oxide blends, crosslinked during polymerization [24]. Results have shown that the plastic deformation characteristics, such as the yielding, strain softening, and strain hardening behavior, can be related to material parameters like chain flexibility [9, 10], relaxation behavior (i.e., glass transition [6–8]) and the material structure (such as the crosslink density [24]).…”