The units composing polymers derive, actually or conceptually, from molecules of low relative molecular mass. During the polymerization process, some chemical groups may be lost from each monomer. O-, which corresponds to the combination of the two monomers with the loss of two water molecules. Many commercially important polymers are synthesized by chemical modification of naturally polymer blends handbook pdf polymers.
The process of polymer degassing is necessary to suit polymer for extrusion and pelletizing, increasing safety, environmental, and product quality aspects. Nitrogen is generally used for this purpose, resulting in a vent gas primarily composed of monomers and nitrogen. Polymer properties are broadly divided into several classes based on the scale at which the property is defined as well as upon its physical basis. The most basic property of a polymer is the identity of its constituent monomers. These basic structural properties play a major role in determining bulk physical properties of the polymer, which describe how the polymer behaves as a continuous macroscopic material. Chemical properties, at the nano-scale, describe how the chains interact through various physical forces. At the macro-scale, they describe how the bulk polymer interacts with other chemicals and solvents.
Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Structure has a strong influence on the other properties of a polymer. For example, two samples of natural rubber may exhibit different durability, even though their molecules comprise the same monomers. An important microstructural feature of a polymer is its architecture and shape, which relates to the way branch points lead to a deviation from a simple linear chain.
A polymer’s architecture affects many of its physical properties including, but not limited to, solution viscosity, melt viscosity, solubility in various solvents, glass transition temperature and the size of individual polymer coils in solution. For example, as chain length is increased, melting and boiling temperatures increase quickly. Since synthetic polymerization techniques typically yield a polymer product including a range of molecular weights, the weight is often expressed statistically to describe the distribution of chain lengths present in the same. A final measurement is contour length, which can be understood as the length of the chain backbone in its fully extended state. Monomers within a copolymer may be organized along the backbone in a variety of ways. The branches are added on to a preformed main chain macromolecule.
Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space. Few synthetic polymers are entirely crystalline. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. Thus for many polymers, reduced crystallinity may also be associated with increased transparency. The bulk properties of a polymer are those most often of end-use interest.
These are the properties that dictate how the polymer actually behaves on a macroscopic scale. This is very important in applications that rely upon a polymer’s physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature. DMA measures this complex modulus by oscillating the load and measuring the resulting strain as a function of time.