|
Copolymers are polymers that are synthesized with more than one kind of repeat unit (or monomer). It exhibits a gradual change in monomer composition from predominantly one species to predominantly the other, unlike with block copolymers, which have an abrupt change in composition, and random copolymers, which have no continuous change in composition (see Figure 1). In the gradient copolymer, as a result of the gradual compositional change along the length of the polymer chain less intrachain and interchain repulsion are observed. The development of controlled radical polymerization as a synthetic methodology in the 1990s allowed for increased study of the concepts and properties of gradient copolymers because the synthesis of this group of novel polymers was now straightforward. Due to the similar properties of gradient copolymers to that of block copolymers, they have been considered as a cost effective alternative in applications for other preexisting copolymers.〔 ==Polymer Composition== In the gradient copolymer, there is a continuous change in monomer composition along the polymer chain (see Figure 2). This change in composition can be depicted in a mathematical expression. The local composition gradient fraction is described by molar fraction of monomer 1 in the copolymer and degree of polymerization and its relationship is as follows: The above equation supposes all of the local monomer composition is continuous. To make up for this assumption, another equation of ensemble average is used: The refers ensemble average of the local chain composition, refers degree of polymerization, refers number of polymer chains in the sample and refers composition of polymer chain i at position . This second equation identifies the average composition over all present polymer chains at a given position, . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「gradient copolymers」の詳細全文を読む スポンサード リンク
|