Physical properties of polymer

The molecular mass M of a polymer is a function of the number of links and, in this way, we define Afn, Mw and Afz. 

Before studying the structure of polymers in solution, which is the subject of this book, we shall review a few general physical properties of polymers and solvents. This will enable us to understand why certain polymers are more adapted to a given experiment than others. 

The properties of polymers determine whether they can be used as a plastic, a fiber, an elastomer, an adhesive, or a paint. 

Important physical properties include the density, melt flow index, crystallinity, and average molecular weight. Mechanical properties of a polymer, such as modulus (the ratio of stress to strain), elasticity, and breaking strength, essentially follow from the physical properties. 

The following sections describe some important properties of polymers. 

Physical properties of common polymers and elastomers are reported in Tables 11.4 and 11.5, while physical quantities commonly used in the previous table to describe polymers characteristics are listed in Table 11.6 with the corresponding ASTM standards. On the other hand, particular mechanical properties are briefly described below. 

Shore hardness. Durometer hardness is a property that, as apphed to elastomers, measures resistance to indentation. Shore A scale is used for soft elastomers, with shore D scale for harder materials. 

Compression modulus. Compression modulus is the stress required to achieve a specific deflection, typically 50% deflection. This test measures the polymer rigidity or toughness. 

Flexural or tear strength. Tear strength measures the resistance to growth of a nick or cut when tension is applied to a test specimen. Tear strength is critical in predicting an elastomer s working fife in demanding and abusive applications. 

Tensile strength. Tensile strength describes the ultimate strength of a material when enough stress is applied to cause it to break. In combination with elongation and modulus, tensile strength can predict a material s toughness. 

PCL is a semi-crystaUine polymer with a degree of crystallinity of 50%, a low Tg (-60 °C) and a melting point of 60 °C. Injection-molded samples of PCL exhibited a modulus of 400 MPa and a yield stress of 15 MPa. Moreover, the material can be processed by injection molding, film blowing and extrusion. The rate of crystallization of PCL is slower than that of conventional polymers, while poly(ether-ester)s are more flexible due to the presence of ether linkages. Although PCL and poly(DXO) resemble each other in their chemical structure, PCL is semicrystaUine whereas poly(DXO) is an amorphous polymer with a Tg of approximately -37 °C [37]. 

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As polymer scientists continue to investigate the atomic structure and physical properties of polymers, the need for more accurate models to describe various experi-... 

The chemistry of synthetic polymers is similar to the chemistry of small molecules with the same functional groups, but the physical properties of polymers are greatly affected by size. Polymers can be classified by physical property into four groups thermoplastics, fibers, elastomers, and thermosetting resins. The properties of each group can be accounted for by the structure, the degree of crystallinity, and the amount of cross-Jinking they contain. 

J 8 Explain the role of chain length, crystallinity, network formation, cross-linking, and intermolecular forces in determining the physical properties of polymers (Section 19.12). 

Mark JE, Eisemberg A, Graessley WW, Mandelkern L, Samulski ET, Koenig JL,Wignal GD (1993) Physical properties of polymers. American Chemical Society, Washington DC... 

Brostow W (2007) In Mark JE (ed) Physical properties of polymers handbook. Springer, New York, pp 443-444... 

L. Mandelkern, The crystalline state. In J.E. Mark, et al. (Eds.), Physical Properties of Polymers, 3rd ed., Cambridge University Press, Cambridge, 2003. 

A.A. Askadskii, Physical Properties of Polymers Prediction and Control, Amsterdam, Gordon and Breach, 1996. 

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