Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: smokescreen318 on February 20, 2018, 10:32:05 PM
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For an experiment in school, I wanted to do an experiment synthesizing Nylon-10,6 using the instructions given in this webpage:
http://www.rsc.org/learn-chemistry/resource/res00000755/making-nylon-the-nylon-rope-trick?cmpid=CMP00000834 (http://www.rsc.org/learn-chemistry/resource/res00000755/making-nylon-the-nylon-rope-trick?cmpid=CMP00000834)
However, the experiment did not go as planned. The nylon started to synthesize, but it did not hold together strongly enough to pull it out as a string and just broke apart when the tweezers touched the nylon.
The only difference between the expt. directed and the procedure done in the lab were that since it was a trial, we did it with half the given quantities i.e 1.1g 1,6-hexamethylene diamine in 25cm3 of water and 0.75g of sebacoyl dichloride in 25cm3 of cyclohexane.
I posted this in the High School Chemistry sub-forum and no one replied so I think the Organic Chemistry sub-forum should be the next best option.
Any idea as to why the experiment did not work and suggested ways to improve this procedure so as to ensure the nylon holds together are appreciated.
Thanks! :)
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Not a strong polymer means incomplete polymerization or else, the formed (elastomer) polymer has not the adequately high molecular weight, in order to be elastic enough.
This may be due to various factors, e.g. deteriorated (partially hydrolyzed) sebacoyl dichloride, not using anhydrous cyclohexane (cyclohexane may contain water up to 1% per weight and you work in high dilution), using non-deionized water (solubility of 1,6-hexamethylene diamine is different), fast addition of the aqueous phase, solvents temperature, surrounding temperature, etc. Even the cross-sectional interface area plays an important role in this trial, as interfering in the regulation of the exothermic reaction temperature (Beakers from various suppliers are not all exactly the same).
Hint: You can use molecular sieves to dehydrate 4 Å, in order to dehydrate cyclohexane but you cannot use molecular sieves for dehydration of sebacoyl dichloride, because they react with it.
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smoke,
I think you should try doing this experiment in more concentrated solution. Perhaps increase concentration by 2x. Drying the cyclohexane with sieves is a decent idea too, but you may not have any activated 4A sieves. How fresh is your sebacoyl chloride?
When I've done this experiment I would dip a glass rod in and slowly curl it up and the polymer will form as you are draw the interface up onto the rod.
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Polymerisation is not a typical reaction in organic synthesis.
I had a problem to determine how long the polymer chain was. It's difficult to monitor the progress of the reaction.
Eventually,the reaction was monitored with exothermic peak using differential scanning calorimetry and viscosity of the mixture. This was very unconventional to me.
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For a well known polymer, using viscosity to measure the reaction is not unusual. The most typical method is GPC/SEC to measure molecular weight.
This interfacial condensation polymerization is unusual because high conversion occurs at the interface. Usually a condensation polymerization must reach greater than 99.9% conversion to produce useful polymer.
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However, the experiment did not go as planned. The nylon started to synthesize, but it did not hold together strongly enough to pull it out as a string and just broke apart when the tweezers touched the nylon.
It may simply be a case of your technique. When I'd heard of this demonstration before (and I didn't know the specific reactants, so than you for giving us that,) the "skin" of polymer from the lower layer is lifted and wrapped around a wooden rod, loosely supported a fixed distance from the reaction vessel, and slowly rotated, to gradually pull the growing skein out of the vessel, through the upper solution, and through the air to dry it, before winding on the rod. Likewise, it seems to me the volume of the upper layer, and its depth in the vessel, determines contact time, which may be crucial for material strength.
Anyway, you're not going to make your own clothes this way. So you can certainly use the demonstration, as is, for the kids.