Cure chemistry applications

The final physical properties of thermoset polymers depend primarily on the network structure that is developed during cure. Development of improved thermosets has been hampered by the lack of quantitative relationships between polymer variables and final physical properties. The development of a mathematical relationship between formulation and final cure properties is a formidable task requiring detailed characterization of the polymer components, an understanding of the cure chemistry and a model of the cure kinetics, determination of cure process variables (air temperature, heat transfer etc.), a relationship between cure chemistry and network structure, and the existence of a network structure parameter that correlates with physical properties. The lack of availability of easy-to-use network structure models which are applicable to the complex crosslinking systems typical of "real-world" thermosets makes it difficult to develop such correlations. 

After receiving his doctorate, he joined the Monsanto Company in St. Louis as a senior research chemist and carried out research on the characterization and material properties of exploratory polymers and composites. While he was at Monsanto, his research interests focused on molecular weight characterization, particularly by size-exclusion chromatography. Recently, his research has focused on size-exclusion chromatography, particle size distribution analysis, cure chemistry and physics, and the application of computers in the polymer laboratory. He is the author of more than 100 publications, is credited with three patents, and has edited or co-edited 10 volumes in the ACS Symposium Series and co-edited two volumes in the Advances in Chemistry series. 

The most important inference is that Chemisorption is a direct response to carboxyl group concentration indicated by the XPS photopeak component at 288.7 eV. It seems likely that weak add functionality is of minor import to applications for surface treatments, while interfacial phenomena such as practical adhesion may be sensitive to small concentrations of very high site energies. Interphase modification in epoxy resins, for example, can occur by direct reaction of epoxide groups with surface carboxyls (17), or by accelerated cure chemistry near the surface (39). Carboxyl groups on carbon surfaces may interact with basic moieties in polymers such as polycarbonate or poly(ethylene)oxide (40=42), or promote interfacial crystallinity that improves impact strength and other aspects of composite performance (43, M)-... 

Future developments will undoubtedly attempt to correct these deficiencies, so that high-temperature adhesives may become an attractive alternative to other joining methods. The introduction of addition-type polymers has gone some way toward improving and making the bonding of large areas feasible new cure chemistries could offer further improvements. The adhesive systems evaluated to date have all relied on the application of... 

Some more specific polymer chemistry applications for TG-FTIR are solvent and water retention, curing and vulcanisation reactions, isothermal ageing, product stability, identification of base polymer type and additives (plasticisers, mould lubricants, blowing agents, antioxidants, flame retardants, processing aids, etc.) and safety concerns (processing, product safety, product liability, fire hazards) [357]. A wide variety of polymers and elastomers has been studied by TG-FTIR [353,358,359]. The potential applications of an integrated TG-FTIR system were discussed by various authors [346,357]. 

Epoxy systems used in structural applications, whether as adhesives or the matrix of fibre-reinforced composites, are normally cured under some pressure and can be regarded as in closed containers. Studies on the kinetics and mechanisms of cure chemistry are often conducted without pressure in containers essentially open to the atmosphere. Extensive thermal analysis examinations at this Laboratory on a range of epoxy formulations have shown that for such fundamental quantities as the heat of reaction substantially different values can be obtained by using open or hermetic pans (Table 2). These differences are apparent with both the TDI-DMA adduct and dicyandiamide as curing agent but not with DDS. 

The use of blocked isocyanates to cure hydroxyl containing coatings is an example of a complex system having many practical applications. The chemistry of blocked isocyanates has been reviewed previously by Wicks (J.,.2). The cure reaction proceeds via consecutive first and second order reactions ... 

For many applications, it is desirable that the adhesive layer accept printable elements readily in its fully cured state. This characteristic usually requires the layer to be soft in its cured form. Adhesive thin films composed of low-modulus PDMS elastomer meet this requirement well18 and can guide transfer of elements to a target quickly (without exposure to heat or light). Surprisingly, the direction of transfer can be well defined even when the composition of the adhesive is identical to that of the stamp. Successful transfer is thus determined by several factors surface chemistry, conformability (modulus), geometrical/mechanical factors (e.g., adhesive film thickness), and others. 

---