Adhesive molecular design

From a practical point of view, it is advantageous that critical gel properties depend on molecular parameters. It allows us to prepare materials near the gel point with a wide range of properties for applications such as adhesives, absorbents, vibration dampers, sealants, membranes, and others. By proper molecular design, it will be possible to tailor network structures, relaxation character, and the stiffness of gels to one s requirements. 

The chemistry of a structural adhesive is designed to do at least two important things. First, the adhesive must at some time pass through a fluid state in order to wet the adherends. Second, the adhesive in its final state in the bond line must be a solid, high-molecular-weight polymer that is able to carry and transfer mechanical forces. In almost all cases, the polymer matrix of a structural adhesive will be crosslinked. The chemistry must... 

In the area of molecularly designed hot-melt adhesives, the most widely used resins are the polyamides (qv), formed upon reaction of a diamine and a dimer acid. Dimer acids (qv) are obtained from the Diels-Alder reaction of unsaturated fatty acids. Linoleic acid is an example. Judicious selection of diamine and diacid leads to a wide range of adhesive properties. Typical shear characteristics are in die range of thousands of kilopascals and are dependent upon temperature. Although hot-melt adhesives normally become quite brittle below the glass-transition temperature, these materials can often attain physical properties that approach those of a structural adhesive. These properties severely degrade as the material becomes liquid above the melt temperature. 

Since the mid-1980s significant progress has been made with respect to the precision of polymer synthesis ranging from free-radical polymerization to advanced olefin polymerization and biotechnology. Novel structural and functional polymers are now at hand and offer new opportunities for improving adhesive formulations. Modern polymers can be tailored to offer problem solutions and properties on demand. This includes molecular design in conjunction with con-... 

A distinct set of hot-melt adhesives are designed through synthetic rather than formulation means. Thus, polyesters and polyamides are synthesized with appropriate monomers to provide the desired performance. The polyester chemistry used to make these hot-melt adhesives is the same as that used to make polyester film and fiber but the molecular weight is usually lower and the mixtures of diols and diesters are chosen to control crystallinity and flexibility. One class of monomers used to make polyamide amide hot melts is based on dimer acids that are made from natural products. 

Recently, several researchers (8,10-12) have reported that compatibilized LCP blends exhibit much enhanced mechanical properties, and they have attributed it to the improved interface adhesion between LCP and matrix phases. In this study, an isotropic polymer was incorporated to the binary LCP blends as a third component to solve the problems caused by interface instabilities and poor deformation of LCP domains. The third component was selected from the commercially available block copolymers on the experimental basis, or prepared by synthesizing block copolymers by molecular design. 

Biomimetic adhesives are synthetic adhesives designed to closely mimic the molecular structure and mechanisms of adhesion found in nature. Bioinspired adhesives are synthetic adhesives whose design is inspired in biological concepts, mechanisms, functions, and design features. The aim is not to emulate any particular biological architecture or system, but to use such knowledge as a source of guiding principles and ideas. 

Molecularly designed hot melt adhesives are based primarily on polyesters and polyamides. Both typ>es of polymers start with a diadd, hut polyamides use a diamine as the comonomer while polyesters use a diol. The choice of these monomers is made depending upon the following criteria ... 

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