Polymer modification early reviews

Starch is the major carbohydrate reserve in higher plants and has been a material of choice since the early days of human technology. Recently starch gained new importance as a raw material in the production of plastics, in particular, for the synthesis of monomers to produce polymers such as polydactic acid) and, after chemical modification (e.g. esterification) and thermomechanical processing, to produce thermoplastic starch. This chapter gives a general overview of the most recent research on the development of materials from starch, focusing on thermoplastic starch and the perspectives for future development in this field. A brief review on reactive extrusion of thermoplastic starch is also provided. 

Early structural characterization of polymers focused on solution properties and their relationship to molecular weight (Dawkins, 1986 Booth and Price, 1989 Yamakawa, 1971 Flory, 1969). Subsequently spectroscopic and chromatographic techniques were developed, and reviews are widely available (Tanaka, 1991 Campbell and White, 1989 Baldwin and Ver Strate, 1972 Hsu, 2004 Stuart, 2002 Koenig, 1999). This chapter describes various characterization techniques, including discussion of the classical methods of analysis, as well as NMR, SANS, and so on. The main modifications for the fourth edition include the addition of newer methods and results and an update of the references. 

An early discovery, which has had abundant subsequent confirmation, was that anionic surfactants are much more reactive than cationic surfactants toward simple uncharged water soluble polymers (3). Several explanations of this interesting difference in reactivity have been attempted, but none is completely satisfactory, as is evident in various review articles (3,5,9). In a similar vein it is also now accepted that nonionic surfactants are generally unreactive toward simple uncharged (and also charged) polymers. These effects are summarized in Table 2, which also includes other combinations of polymer and surfactant. For example. Table 2 shows that an anionic surfactant will react strongly with a polycation but will not react, or will react only weakly, with a polyanion, illustrating the potent effect of electrostatic forces. It must be stressed that Table 2 applies to polymers that are not hydrophobically modified as pointed out already, such modification can com-... 

A review of polymer history is beyond the scope of this paper and several such reviews are available. Most early polymer applications were modifications of poly(peptides) or poly(saccharides), although some other classes of natural polymers found utility. For example, shellac is a natural poly(ester) derived from from the excretions of the insect Lac-cifer lacca. While these materials were not recognized as polymers until... 

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