Natural polymers, commercial advantages

In addition, most semicrystalline polymers, particularly those produced commercially, are partially oriented i.e. their chains have an overall alignment that may impart to the bulk polymer certain advantageous properties, e.g. increased mechanical strength or dielectric polarizability. Molecular orientation, whether arising from crystallization under stress or deformation of a solidified polymer, or in naturally occurring oriented crystalline polymers such as cellulose or keratin, is always associated with an orientational morphology. 

Natural and semisynthetic polymers have some commercial advantages over many... 

The conversion of cellulose into useful products is an illustration of how degradation, fimctionalization, and molecular orientation of a polymer can be applied to commercial advantage. Cellulose is the most common naturally occurring organic polymer. Over a trillion pounds of it are converted annually into paper and other cellulose-based products. 

Neoprene elastomer was first synthesized in the 1930s and became the first synthetic elastomer to provide significant advantages over natural mbber. The monomer for neoprene is 2-chloro-l,3-butadiene and the polymer is prepared by emulsion polymerization. Being inherently a latex polymer may have been thought to provide commercial advantage over the solvent-based versions, but it was found that the tack properties and the ability of the adhesive to form a quick bond with itself... 

There are two main advantages of acrylamide—acryUc-based flocculants which have allowed them to dominate the market for polymeric flocculants in many appHcation areas. The first is that these polymers can be made on a commercial scale with molecular weights up to 10—15 million which is much higher than any natural product. The second is that their electrical charge in solution and the charge density can be varied over a wide range by copolymerizing acrylamide with a variety of functional monomers or by chemical modification. 

Among the different pressure sensitive adhesives, acrylates are unique because they are one of the few materials that can be synthesized to be inherently tacky. Indeed, polyvinylethers, some amorphous polyolefins, and some ethylene-vinyl acetate copolymers are the only other polymers that share this unique property. Because of the access to a wide range of commercial monomers, their relatively low cost, and their ease of polymerization, acrylates have become the dominant single component pressure sensitive adhesive materials used in the industry. Other PSAs, such as those based on natural rubber or synthetic block copolymers with rubbery midblock require compounding of the elastomer with low molecular weight additives such as tackifiers, oils, and/or plasticizers. The absence of these low molecular weight additives can have some desirable advantages, such as ... 

Radical polymerization is often the preferred mechanism for forming polymers and most commercial polymer materials involve radical chemistry at some stage of their production cycle. From both economic and practical viewpoints, the advantages of radical over other forms of polymerization arc many (Chapter 1). However, one of the often-cited "problems" with radical polymerization is a perceived lack of control over the process the inability to precisely control molecular weight and distribution, limited capacity to make complex architectures and the range of undefined defect structures and other forms of "structure irregularity" that may be present in polymers prepared by this mechanism. Much research has been directed at providing answers for problems of this nature. In this, and in the subsequent chapter, we detail the current status of the efforts to redress these issues. In this chapter, wc focus on how to achieve control by appropriate selection of the reaction conditions in conventional radical polymerization. 

The most important polymer on the market today is PLA, which upon degradation yields lactic acid, a natural metabolite in the human body [79]. The formation of natural metabolites should be advantageous as the body has routes to eliminate them. Other commercial degradable materials are polyparadioxane [238], the copolymer of glycolic acid and trimethylene carbonate [239], which does not give natural metabolites when degraded. Their most important charac-... 

---