1、 Explain the following concept Polymer: A polymer is a subtance composed of molecules characterized by the multiple repetition of one or more species of atoms or groups of atoms (constitutional repeating units) linked to each other in amounts sufficient to provide a set of properties that do not vary markedly with the addition of one or a few of the constitutional repeating units. Configuration: The term configuration refers to the ‘permanent ’ stereostructure of a polymer. The configuration is defined by the polymerization method, and a polymer preserves its configuration until it reacts chemically. Conformation：The term conformation refers to a stereostructure that can be changed by torsion about the sigma bonds and that involves much less energy than covalent-bond scission. glass transition temperature(Tg): The glass transition obeys second-order characteristics, i.e. volume and enthalpy are continuous functions through the transition. However, their temperature derivatives, the thermal expansion coefficient and the specific heat, change in a discontinuous manner at the glass temperature. Tg increases with increasing cooling rate. At higher cooling rates the time available to the system at each temperature is shorter than that at a slower cooling rate, and the curve begins to deviate from the equilibrium line at a higher temperature. A complete theoretical understanding of the glass transition phenomenon is not yet available. The current theories can be divided into three groups: free volume theories, kinetic theories and thermodynamic theories. The free volume theories state that the glass transition is characterized by an iso-free volume state, i.e. they consider that the glass temperature is the te...
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