Determination of Unknown Polymer Properties
Introduction and Background
A multi-division corporation had a small plastic piece fail in one of its specialty machines. The maintenance department has been asked to replace the part. However, the original manufacturer, Kaufmann Ltd., has gone out of business, and specifications for the part are unavailable. The purpose of this experiment, performed by Ryan Nelson, Peter Glascor, Eric Flowr was to determine the identity of the unknown polymer by comparing its properties to properties of other known polymers. Most likely, the part is one of the five following polymers: polyethylene, polypropylene, polystyrene, polycarbonate, poly(vinyl chloride). These are all extremely common, and have widespread applications in industry.
Each of these polymers exhibits properties which allow it to be of unique technological importance. Theoretical values for the properties utilized in determining the identity of the unknown sample are listed in Table 1. Density (g/cm3) Molecular Weight (g/mol) Melting Point (ºC)
Polypropylene 0.905 42.08 170
Polyethylene 0.92 28.05 130-145
Polycarbonate 1.2 158 310
Polystyrene 1.05 104 240
Polyvinyl chloride 1.4 62.5 160-172
Table 1 Properties for five known polymers (Callister 737-775)
The melting temperature of a polymer is the point at which it transforms from the solid form to a viscous liquid in which there is little molecular order (Callister 500). This temperature depends on the stiffness of the molecular chain, molecular weight, and the degree or branching (Callister, 502). Chain stiffness is controlled by the ease of rotation about the chemical bonds along the chain. Bulky or large side groups can impede rotation, thus raising the melting temperature (Callister, 502). At low molecular weights, polymers with longer chains have higher melting temperatures that those with shorter chains. This is because increased chain length leads to increased Van der Waals intermolecular forces. A polymer with a high degree
A multi-division corporation had a small plastic piece fail in one of its specialty machines. The maintenance department has been asked to replace the part. However, the original manufacturer, Kaufmann Ltd., has gone out of business, and specifications for the part are unavailable. The purpose of this experiment, performed by Ryan Nelson, Peter Glascor, Eric Flowr was to determine the identity of the unknown polymer by comparing its properties to properties of other known polymers. Most likely, the part is one of the five following polymers: polyethylene, polypropylene, polystyrene, polycarbonate, poly(vinyl chloride). These are all extremely common, and have widespread applications in industry.
Each of these polymers exhibits properties which allow it to be of unique technological importance. Theoretical values for the properties utilized in determining the identity of the unknown sample are listed in Table 1. Density (g/cm3) Molecular Weight (g/mol) Melting Point (ºC)
Polypropylene 0.905 42.08 170
Polyethylene 0.92 28.05 130-145
Polycarbonate 1.2 158 310
Polystyrene 1.05 104 240
Polyvinyl chloride 1.4 62.5 160-172
Table 1 Properties for five known polymers (Callister 737-775)
The melting temperature of a polymer is the point at which it transforms from the solid form to a viscous liquid in which there is little molecular order (Callister 500). This temperature depends on the stiffness of the molecular chain, molecular weight, and the degree or branching (Callister, 502). Chain stiffness is controlled by the ease of rotation about the chemical bonds along the chain. Bulky or large side groups can impede rotation, thus raising the melting temperature (Callister, 502). At low molecular weights, polymers with longer chains have higher melting temperatures that those with shorter chains. This is because increased chain length leads to increased Van der Waals intermolecular forces. A polymer with a high degree
References: Callister, W.D. (2003). Materials Science and Engineering: An Introduction. 6th ed. New York: John Wiley and Sons, Inc.