Lab 5: Synthesis of a Superabsorbent Polymer Prelab Assignment-Due at the beginn

Question

Lab 5: Synthesis of a Superabsorbent Polymer Prelab Assignment-Due at the beginning of lab 1. Read this handout, Guide to Success in the Organic Chemistry Lab, and the Micropipet Instructions on Canvas before starting. 2. Print and complete the Prelab 5 Question Sheet, and turn in at the start of lab 3. Complete the following in your lab notebook IN PEN: a. Table of Contents: Find (or create) the Table of Contents at the front of the notebook: add the lab lab title, and the page for the first page of this lab report. b. Header information: Add to the top of the report's 1st page c. I. Introduction: Write this in your own words; do not copy this handout! d. II. Procedure: Write this in your own words; do not copy this handout! e. Ill. Results: Begin this section, ready to record observations. INTRODUCTION Many alkenes can be polymerized under free-radical conditions. Polymerization occurs more readily when the alkene contains a functional group that stabilizes the radical intermediate. Acrylic acid is an example of such an alkene monomer. The mechanism for the polymerization of acrylic acid involves two major steps: thermal initiation and propagation, as shown in Equations 1 and 2. A small amount of a free-radical initiator, a compound that can be induced to form radicals, is included in the reaction to get it started. In this case,VA-044 is the initiator The initiator radical adds to the C-C double bond of an alkene (acrylic acid) to form another radical. The resulting radical adds to another acrylic acid monomer to form a dimer, and so forth. The process can repeat itself many times, producing polyacrylic acid molecules containing up to millions of monomer units. The quantity of initiator used greatly affects the overall polymer product; very small amounts of initiator, enough to start only a relatively small number of polymer chains, favor high molar mass products. If large amounts of initiator were used instead, many small chains would begin, leading to large numbers of short chains. CH3 N N CH N. Equation 1 C-N N-C initiation) (VA-044) CO2H acrylic acid Equation 2 CH3 CH3 CO2H N propagation) n acrylic acid

Explanation / Answer

In the presence of divalent metal ions like Ca2+, Mg2+ etc., the absorbency of the polymer in the solvent is greatly reduced because these ions react with the polymers. For this reason, the presence of salts of divalent metal ions decreases the liquid absorption and increases the reaction time period. Only 4% of liquid is absorbed by the polymer in a divalent brine. In addition, divalent cations react with negative charges of the polymer and stabilize the matrix.As a result, prevent the polymer from creating cavities for further absorption of liquid by capillary action.

Therefore, the absorbency of the polymer will decrease towards tap water which contains divalent metal iomn

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