polymer end group analysis (FSU)

polymer end group analysis (FSU) - POLYMER END-GROUP...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
POLYMER END-GROUP ANALYSIS: THE DETERMINATION OF AVERAGE MOLECULAR WEIGHT Background reading: This exercise uses a strong acid titration by a strong base with a visual indicator. See; Harris, 7 th ed., Chap. 11. Skoog, West, Holler and Crouch, 7 th ed., Chap. 14. Introduction Polymers Polymers are a special form of macromolecules They are compounds of high molecular weight formed by combining a large number of small molecules. The small molecules, called monomers, may all be of one type, as in the compound used in this experiment, or may be of different types. Polymers are very important in biological systems. For example, proteins are composed of intricate sequences of amino acids, and polysaccharides contain repeating units of simple sugar molecules. Our everyday lives are also greatly influenced by polymers that are not obtained from natural sources. Synthetic polymers are known to us as various fibers (e.g., Dacron), plastics (e.g., polyvinyl chloride), abbreviated PVC, and polystyrene), and elastomers. See Fig. 1. Like PVC and polystyrene, the compound involved in this experiment is synthesized from only one kind of monomer molecule, ethylene glycol. The monomers are joined by elimination of a molecule of water to form a series of ether linkages. (n+2) HO-CH 2 -CH 2 -OH ! HO-CH 2 -CH 2 -[O-CH 2 -CH 2 ] n -O-CH 2 -CH 2 -OH + n H 2 O The polymer is called either poly(ethylene glycol) (PEG for short), poly(ethylene oxide), or, more properly, poly(oxyethylene). PEG is commonly found in the list of ingredients in hair preparations and cosmetics. It is a good lubricant and also has the desirable property of being soluble in water. Therefore, PEG is heavily used as a base for therapeutic ointments, and it is used industrially as a lubricant in the formation of textile fibers and metal products. Molecular Weight The physical properties of polymers depend heavily on their molecular weights, which vary according to the number of repeating monomer units (the n’s in the structures in Fig. 1) per polymer molecule. For example, the PEG molecules to be studied in this experiment have molecular weights less than 1000 and are viscous liquids. As the molecular weight increases, the compound is more grease-like, and, if the MW is greater than about 6000, PEG is a white solid. The use of the term “molecular weight” is somewhat misleading, because it implies that a sample of a polymer has a uniform formula weight (i.e., that n is the same for all the polymer molecules in a sample). For many biopolymers, most notably proteins, the sequence of the monomers is dictated by the specific biological role of the compound, and the structure and molecular weight is the same for all molecules of that type.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

polymer end group analysis (FSU) - POLYMER END-GROUP...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online