Moisture-cured Molecular structures

The amorphous polyesters are becoming increasingly important for one-component 100% solid moisture-curing adhesives. These materials are usually viscous, amorphous liquids. Poly(2-methylpropane adipate), an example of an amorphous polyester, is a liquid even at a molecular weight of 2000. The amorphous polyesters are usually asymmetrical in structure. In the poly(2-methylpropane adipate) example, the pendant methyl group would be expected to interfere with chain packing, thereby preventing crystallization [27]. 

Modified cyclo-olefin thermoset (MCOT) resins are liquids that cure when heated at 150 °C for a minimum of 30 minutes to form the general polymer structure shown in Figure 3.14. The monomers cure by an addition polymerization and, as such, no water or other by-products are evolved. The molecular structures are essentially nonpolar which impart very low moisture absorption properties. For two formulations developed by Johnson-Matthey, water absorptions of 0.05% were recorded when exposed to 85 °C/85% RH conditions for 168 hours. Only 0.1% water absorption was measured even after pressure cooker testing at 150 °C, 85% RH, for 168 hours. These low moisture absorption values make MCOT adhesives and molding... 

Despite similarities in size and structure between precipitated silicas and carbon blacks, fundamental differences in surface activity exist. The silica surface is highly polar and hydrophilic and contains adsorbed water. The surface hydroxyl groups are acidic and tend to retard cure rate. The adsorbed moisture volatilizes at compoimding temperatures. The tendency of silica surfaces to react with the zinc oxide acceleration activator was discussed previously. High molecular weight polyethylene glycols are the most common additives used with precipitated silicas to reduce their reactivity toward zinc oxide and organic accelerators, and to reduce their polarity. 

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