Intermediate Restorative Material

Introduction: morphology of polymers

Two different states or forms can be identified in a polymer that can display or thermo-mechanical properties that can be associated with solids, ie., In the form of a crystal or the form of a glass. That ' is not really the case that all the polymers are capable of crystallizing. In fact, a high degree of molecular symmetry and regularity of microstructures in the polymer chains are a prerequisite for crystallization to occur. Even in polymers that do crystallize in all cases, the ultimate degree of crystallinity is mainly developed in less than 100%.

Studies of fitness, arrangement and structure of molecules or molecular aggregates of a material system relates to what is known of its morphology. Morpho-logy of polymer covers the study of arrangement of macromolecules in the crystalline and amorphous regions that overlap and all combinations of physical molecular aggregates.

Once cooled from the U.S. merger, different polymers have different tendencies to crystallize at different rates depending on many factors, including physical conditions, chemical repeat units and polymer as a whole, their symmetry segmental or molecular structure and regularity or irregularity, as described above. independent groups or branches of the chain lengths of bulky molecular packing and thus hinder the crystallization. The nature of the crystalline polymers is not straightforward and should not be confused with the regular shape of crystals of low molecular weight compounds such as sodium chloride or benzoic acid. There are polymers, which are by and large, amorphous, and they tend to become very poor in ordered structures or oriented by cooling at room temperature to near or even below. natural or synthetic rubbers and glassy polymers such as polystyrene, polymers of acrylate and methacrylate belong to this class.

In a crystalline polymer, a polymer chain are given in or pass through several crystalline and amorphous areas. The crystalline regions consist of intermolecular and intramolecular alignment or tight and therefore ordered arrangement of molecules or chain segments, and a lack of results in the formation of amorphous regions.

Glass transition and melting transition

On the basis of following the evolution of a parameter of mechanical properties such as shear modulus with changes (increase) the temperature of the observation systems of polymer material, one can easily observe successively - (i) glass transition and (ii) the merger of the phenomena of transition more easily from a graphical representation, and may also have a measure of the glass transition temperature, Tg and the melting temperature, Tm

The glass transition and melting transition can be observed and verified from a curve of specific volume (PIV) based on temperature. Consider the possibilities of a magma cools from position A to a high temperature that corresponds to a relatively high value and Vsp, fig. 1. The road ABDG shows how the specific volume falls as low molecular weight compound is frozen. As the melting temperature Tm is reached at point B, a sharp discontinuity is observed PSV (BD). The slopes of AB and DG give measurements of coefficients of thermal expansion of liquid and solid, respectively. The coefficient of thermal expansion also suffers a discontinuity at t.

Fig.1: Schematic showing potential changes in the specific volume (PIV)

a polymer with temperature change.

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