Experiment 17 - Polymer Chemistry - Nylon-6,10 and PVA-Silicate

Chem 22 Spring 2010 Experiment 17 — Polymer Chemistry — Nylon-6,10 and PVA-Silicate _____________________________________________________________________________ Pre-lab preparation. (1) Chapter 24 in Hornback covers synthetic polymers. You'll find this interesting reading — little if any new chemistry, but lots of insight into familiar materials (plastics, rubber, etc). Bring your text — you'll need it to complete a short worksheet during lab. (2) Write the reaction between a generalized acyl chloride, R–COCl, and a generalized primary amine, R–NH2, and draw the product. (3) In Part A you will be using a di-(acyl chloride) and a di-amine. Draw the structure of the polymer you will be creating. Use the standard notation for polymers that shows one full repeating unit (not the entire polymer, of course). What does "6,10" mean? (4) Polyvinyl alcohol (Part B) cannot be made by a simple polymerization (like polystyrene, PVC, etc). Why not? How is PVA made? (5) The average molecular weight of the PVA we'll be using is 88,000. How many monomer units make up an average polymer? (6) Sketch a couple of PVA chains crosslinked by silicate. To make this easier, let's assume the silicate is hydrated to make (HO)2Si(O– Na+)2 — i.e., a tetrahedral Si with 4 Os attached — and that a couple of hydroxides and a couple of water molecules are lost in the crosslinking process. Start by determining the yield and mp of your triphenylmethanol from last week. (Is "mp" really a point or a range?). Put the finishing touches on your report and turn it in. As you do the experiments, remember to record in your notebook what you actually did and what you observed. Procedure. Part A. Nylon-6,10 by interfacial polymerization. Work in a fume hood; avoid contact with and inhalation of the acyl chloride and the amine. Transfer 25 ml of the stock solution of 1,6-hexanediamine to a small beaker. This solution contains 0.54 M diamine (and 2.5 M NaOH), so 25 ml contains 13.5 mmol of the diamine. And yes, use a beaker — this is one of those rare occasions when we'll use a beaker rather than a flask for something we care about. 1 Experiment 17 Spring 2010 Dissolve 0.45 ml (density 1.12 g/ml; 0.50g; 2.1 mmol) of sebacoyl chloride, aka decanedioyl dichloride, in 25 ml of hexanes, and carefully layer the hexane solution on top of the aqueous diamine solution. Do NOT shake, swirl, stir, jiggle, jostle, or annoy the two-phase mixture. The polymerization will occur at the interface between the layers. Make a small hook at the end of a copper wire, and carefully snag the nylon at the boundary between the liquid phases. As you pull this up, the polymerization will continue, and you will form a long strand of nylon. You can wind this around a glass stirring rod, or see how long a strand you can create. (Be careful that you don't drip on coats, backpacks, etc, and clean up all the drips when you finish — yes, this lab is the source of most of the spots on the floor) After you get tired of playing with the nylon, stir or shake the remainder of the mixture. Explain what happened. Discard the polymer and remaining solutions in the waste container. Part B. Polyvinyl alcohol - Silicate. Effect of crosslinking. This one can be done out on the benchtop, but avoid contact with the reagent solutions. In each of two small beakers, place 15 ml of polyvinyl alcohol solution (4% by weight of polymer in water; average molecular weight 88,000) — again, a beaker only because it will be easier to clean, and if it can't be cleaned, well… it's cheaper than an Erlenmeyer. To one beaker, add 3 ml of 38% aq. sodium silicate, Na2SiO3 (made from 9.1% Na2O and 29.2% SiO2 by weight), and to the other add 15 ml. Stir them both for about a minute, then lift out the gooey globs with a spatula or glass rod, squeeze out the excess liquid, and knead them with your (gloved) fingers for a minute or so. Now let's try some "processing". Split each polymer sample in half, and spread one half on an inverted watch glass to make a film. Form the other half into the shape of a tiny animal, insect, or your favorite member of congress. How easy or difficult was this? Let the samples dry for about 30 min, then rinse them with water. Is there a noticeable difference in their flexibility and stretchiness vs their toughness and ability to hold their shape? How does the extent of crosslinking affect the properties of the polymer? Explain briefly. Complete the worksheet and turn it in, along with your lab write-up, before you leave. 2