Virginia Tech

• CHEM 1045

• Abstract. The objectives of the experiment include, understanding basic polymer classifications, using rheology and the density of specific substances to find the weight, composition, and topology of polymers, and to modify a protein to examine a biopolymer. To accomplish these objectives, we diluted pellets and observed buoyancy, mixed chemicals and interacted with a UV light to test a biopolymer, conducted titrations, used rheology to determine molecular weight, measured the viscosity of the molecular solutions, and tested the topology of a polymer through the formation and addition of heat to it, and then the examination of the solubility of the polymer. The results showed which pellets were PP and PVC, and therefore sank in water, and which were HDPE, LDPE, and PP, and only sank with the addition of ethanol. The lowest density was the polypropylene with a calculated density of 0.87 g/cm3 . The relationship between a higher viscosity resulting in a higher concentration, was also found. The lower concentration was discovered to have a much faster time of travel (average of .92s) between two arbitrary marks than the higher concentration (average of 4.92s). I. Introduction. A Polymer is defined as a chemical compound that is made of small molecules that are arranged in a simple repeating structure to form a larger molecule. They have become incredibly important in every aspect of our human lives. We may not be aware, but we use and consume polymers every day. All the way from playing an integral role production of cars and tires, of light-weight electronic devices, and most any commercial product. The fundamental polymer parameters in this experiment consist of chemical composition, molecular weight and molecular weight distribution, morphology, topology, rheology, and surface features and polymer additives. Step-growth and chain-growth polymerization are the two main synthetic methods. Both methods require a monomer, which polymerizes into the polymer. The chemical composition of the monomer is then tested afterward to determine the final chemical composition of the polymer. The molecular weight of polymers depends on the number of chain links combined during the polymerization process. No polymer has a specific molecular weight because the range of possible molecular weights is huge and there are too many factors that determine the polymer’s size. Rheology is the branch of science that studies the flow and deformation of matter. Therefore, one can see how examining viscosity in the experiment is relatable. As the length of the polymer chains increase, as does the viscosity, or resistance to flow. This shows the correlation between the property of viscosity with molecular weight. Another way to measure viscosity is with a Brookfield viscometer. This uses a technique known as rotational viscometry, which is when something measures viscosity by calculating the torque required to rotate a spindle at constant speeds while submersed in the liquid. Topology is the shape of the molecule, which has a large influence on the material’s final composition. For example, due to branching differences, polymers such as HDPE and LDPE have the same chemical compositions to each other, but are not the same substance with the same properties. These topology differences in polymers can be classified as linear, branched, or crosslinked. These crosslinked topologies are insoluble in solvents, and can be synthesized by a two-part adhesive and biocompatible polymer system. II. Experimental. Procedures: Part 1A Add 25mL of distilled water to a 150mL beaker and then place each of the six synthetic polymer pellets into it. Using tweezers, remove the pellets that sank and place them in a small scintillation vial and cap it. Add approximately 5mL of acetone to the vial, cap it, and allow it to sit for remainder of lab. While waiting, measure out approximately 50mL of 95% ethanol in a buret and then add 15mL of it to the beaker with the floating pellets and water. Gently stir the beaker while continually adding 1mL of 95% ethanol to the beaker. Stop adding ethanol when one of the pellets begins to sink and remains sunk for 30 seconds. Record the amount of ethanol added to the beaker. Repeat this until all the pellets sink. At the end of the lab, use a glass rod to push on each of the pellets in the acetone. Note if the pellets have softened. Part 1B