Polymer synthesis.
Final report.
Submitted to: The faculty of the school of chemistry Shawnee Mission Northwest High School.
By: Charles McAnany May 2, 2007
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Abstract: Polymers are a very important aspect of our life; they provide e asy materials to work with that are resistant to many forms of attack. All plastics are polymers, as are most fabrics. An understanding of polymer chemistry will allow a person to contribute to this enormous field by designing polymers that have desirable properties. Polymers are chains of molecules made of similar repeating subunits called monomers. Monomers are molecules of low molecular weight tha t have reactive or excitable ends e nds that will form bonds with other monomers. It is the monomer that ultimately determines the properties of a polymer; even a slight variation in the properties of a monomer can greatly affect the properties of its polymer. polymer. Of particular interest, both commercially and biologically, biologically, is condensation conden sation polymerization. Condensation polymerization is the name given to reactions that form polymers by “dehydrating” the monomers. Condensation polymerization is responsible for all biological polymers, and requires far less exotic conditions than other types of polymerization reactions, such as addition reactions. This research was conducted to better understand the relation of the size of the monomer to the properties of the polymer in polyamids, p olyamids, which are better known by the trade name, nylon. Nylons are named for the length of the carbon chains that make them up. Nine different nylons were synthesized: nylon 6-6, nylon 6-8, nylon 6-10, n ylon 8-6, nylon 8-8, nylon 8-10, nylon 10-6, nylon 10-8, and nylon 10-10. The properties of these polymers were studied, and measurements were taken for density and tensile strength of the polymers.
McAnany 3 The results showed that, overall, the smaller carbon chains yield stronger polymers, and that large diamines (one of the monomers) are not effective.
McAnany 4 Introduction: Polymerization is the process of reacting small molecules called monomers in such a way that they form chains, called polymers. Polymers are very useful materials. Depending on the structure of the monomer units, the length of the polymer chains, and other o ther factors such as branching of the chains, the properties of the polymer can var y from a brittle plastic that melts in hot water, like wax, or a rubbery, malleable material that will not melt at all. The range of properties makes po lymers suitable for numerous common applications. They are often formed into filaments, as their chain-like structure gives them great structural integrity, and, hence, tensile strength. Certain polymers, notably aramids, are strong enough to stop a bullet. Kevlar, for example, is a woven aramid. Polymerization reactions are usually lumped into two categories, free radical polymerization and condensation polymerization. Free radical polymerization occurs when double bonds in a monomer break, leaving an electron that will form a covalent bond with an adjacent monomer unit. An example of free radical polymerization p olymerization is the polymerization of polytetrafluoroethylene, better known as Teflon. The monomer in this reaction is tetrafluoroethylene, F2C=CF2. During the polymerization reaction, the double bond in the molecule breaks, leaving electrons on both ends. The molecule at this stage is drawn as: . F2C-CF2., where the dots on the end represent free electrons. If the radical comes into contact with another tetrafluoroethylene monomer, the loose electrons will excite it, and its double bond will break, yielding two radicals. The electrons on the ends of these radicals merge to form a single bond, yielding, .F2C-CF2-F2C-CF2.. The ends of the molecules are still radicals, so the reaction can continue. In order for a condensation reaction to occur, the reagents must exhibit acidic or basic properties. An example of condensation polymerization is the formation of nylon 6-10. In this reaction, there are two monomers, 1,6-diaminohexane and sebacic acid. Their structural formulae are, accordingly accordingl y, H2 N(CH N(CH2)6 NH NH2 and HOOC(CH2)8COOH. A hydroxyl group from the acid and a hydrogen from the amine join together and form water, leaving what are effectively radicals of the monomers. The CO and NH join together to form an amid bond, COHN, and the two monomers are joined as H2 N(CH N(CH2)6 NHOC(CH NHOC(CH2)8COOH. The reaction can continue at the ends of the molecule. In the research done here, the sebacic acid has been replaced with sebacoyl chloride, which has ClOC as its functional group instead of HOOC. This substitution encourages the reaction, and allows it to proceed under normal conditions. Usually, Usually, when using the HOOC functional group, the reagents are heated to over 100o so that the water produced boils off and the Le Chatelier principle drives the reaction to the right, to produce more water. The goal of the project is to analyze the effects of changing the length of the monomers in polyamids. Nine polymers were synthesized, nylon 6-6, nylon 6-8, n ylon 6-10, nylon 8-6, nylon 8-8, nylon 8-10, nylon 10-6, nylon 10-8, and nylon 10-10. The polymers were examined and tested for tensile strength and an d density. density. Unfortunately, Unfortunately, some of the polymers, notably the 10-n polyamids, were uncooperative, and no data could be taken.
McAnany 5 Method: The official procedure follows: Materials: Hexane. Water. Adipoyl chloride. Suberoyl chloride. Sebacoyl chloride. 1,6, hexanediamine. 1,8 octanediamine 1,10 decanediamine Equipment: Beaker, 50 ml. (4) Buchner funnel. Filter paper to fit funnel. (20 sheets) Side-arm flask. Stopper for side arm flask. Glass stirring rod. (2) Vacuum tubing. Petri dishes. (5) Stir plate, bars. Graduated cylinder c ylinder.. (3) Volumetric flask, 25 ml or 50 ml. Wash bottle. Vials for storage of the polymers synthesized. Labels. Safety considerations: Acyl chlorides fume HCl, so only use them under a fume hood. Always safely dispose of unused solutions. Wear gloves and safety glasses. Procedure: 1. Obtain Obtain all materi materials als and equi equipme pment. nt. 2. Create Create the soluti solutions ons of the the amines amines.. 3. Hexanediamine: Hexanediamine: 3.26 ml molten molten hexanediamine hexanediamine and water water to 50 ml, ml, or 1.63 1.63 ml molten hexanediamine and water to 25 ml. 4. Octanediamin Octanediamine: e: 3.61 g and water water to 50 ml ml or 1.80 1.80 g and water water to 25 ml. 5. Decanediamine: Decanediamine: 4.31 g and water to to 50 ml or 2.15 g and water to 25 ml. ml. 6. Label bel them hem. 7. Create Create the the solut solution ionss of the the acyl acyl chlorid chlorides. es. 8. Note: the the finished finished solutions solutions are are all 50 or 25 ml. ml. Add the hexane hexane until until the solution solution reaches the desired volume. 9. Sebacoyl Sebacoyl chloride: chloride: 5.33 5.33 ml chloride chloride and hexane hexane to 50 ml or 2.66 ml ml chloride chloride and hexane to 25 ml.
McAnany 6 10. Adipoyl chloride: 3.63 ml chloride chloride and hexane to 50 ml, or 1.81 ml and hexane to 25 ml. 11. Suberoyl chloride: 4.50 ml chloride chloride to 50 ml hexane, or 2.25 ml to 25 ml hexane. 12. Label these these solutio solutions. ns. 13. Synthesize the nylons by pouring the amine solution in a beaker and then slowly adding the acyl chloride. 14. If the solution produces a strand of nylon, remove it with a stirring stirring rod. 15. If the solution fails to produce a strand, mix it with a stirring stirring rod and wait for a polymer to form as a precipitate. 16. Note the style style and rate of polymerization polymerization.. 17. After the solution has stopped producing nylon, scrape the nylon off the rod or pour the beaker containing the nylon into the Buchner funnel. 18. Activate the aspirator, and wait until the the nylon is not sopping wet. Now, Now, squirt the nylon with a wash bottle. This will remove the aque ous components of the solution. (Unreacted diamine, HCl, etc.) 19. After several rounds of squirting, turn off the aspirator and dump the filtered filtered solution into an appropriate waste container. Save the polymer that was filtered in a weigh dish. 20. Add a small amount of water to the side-arm flask, enough to fill it up ¼ of the way. way. 21. Place the filtered filtered nylon in the flask, and stopper it. 22. Activate the aspirator and allow the hexane in the nylon to boil off. This This will also help loosen up the nylon threads. 23. Pour everything in the flask flask into another beaker, beaker, and re-attach the Buchner funnel. 24. Filter the boiled nylon and wait until it’s it’s dry. dry. 25. Dispose of all garbage and place the nylon in a vial and label it. 26. Repeat this process with the other acyl chlorides and amines and make sure that everything is labeled. 27. After the polymers have been synthesized, place the vials in a dark, damp place. Analysis procedure: Purpose: to begin accumulating data on the properties of the different nylons. Materials: nylons synthesized above. Equipment: Beakers, 50 ml. Fume hood. Labels. Scale. (to .001g) Tensile testing apparatus Accurate graduated cylinders. Tweezers. Tongs. Calipers. Nice microscope. Slides, coverslips. Digital camera
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Safety: wear gloves and goggles. Procedure: Weight of the monomers: These data should be found on the side of the reagent bottles. Record them. Density of the polymer: Firstly, Firstly, make sure the polymer p olymer sample you’re using has been very thoroughly washed and boiled. Allow the polymer sample to dry overnight. Compress it into a convenient geometric shape. Measure, using calipers, the dimensions of the po lymer. lymer. Be sure to record the units, some calipers measure in inches. Calculate the volume of the polymer sample. Measure the mass of the polymer using the scale. Microscopic analysis: Firstly, Firstly, create a slide of the polymer using water as the fixative. (Adhesives may interfere with the results.) The sample used should be a piece of the strand cut from the middle. Place the sample in a microscope and adjust the focus. Now put a camera on the eyepiece, and make sure that you can see the sample in the viewfinder. Take the picture, silly. Now take a picture of the name of the polymer, for example, a label o n a bottle. Record the shape of the edges, the end of the strand, appearance of crystals, irregularities, and general shape of the polymer. Rate of polymerization: This is a simple measurement taken during the synthesis. If the polymer takes a while to form, make a note of this. Shape of polymer: Immediately after the polymer is synthesized, observe the shape of the polymer. After After washing and handling the polymer may become distorted, so this is the only time it can be done. Record the shape.
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Tensile strength: If possible, send the polymers, clearly labeled, to a laboratory capable of analyzing the tensile strength. If no lab exists, use the following apparatus ap paratus to test the tensile strength.
Bar clamp
Spring.
Strand.
Meter stick
Set up the experiment as in the diagram, with the strand dangling from the spring. Simply wrap the strand around the end of the spring, and it should stick there. Measure the length of the spring using u sing the meter stick, record it. Slowly and carefully wrap the other end of o f the strand, (the one that’s dangling) around your finger, do not pinch it. Gently pull down on the strand and keep your eye on the length of the spring. Keep a mental count of the spring’s length, as it will return to its initial length when the strand snaps. When the strand snaps, record the final length of the spring, and use the equation: F tobreak K ( H f H O =
−
Where K is the spring constant, which should be previously determined, H(f) is the final length of the spring, and H(o) is the initial length of the spring. When choosing a spring, try to keep k eep the spring constant low. 10-20N/M is ideal. Malleability: This is a very qualitative test, simply attempt to squish the polymer. Record any observations.
McAnany 9 Opacity: Look at the polymer. If you can see through it, record this. If not, record that.
McAnany 10 Results: Data for nylon 6-6: Weight of acyl chloride 183.03 Weight of amine 116.2 (density test) mass of blob .022 Volume of blob Density of blob .359 g/cm3 Notes from microscopic analysis. (Attach picture to back of report with a label.) The nylon formed a sheet, which was pulled out as a pleated strand.. Shown are the entire strand and a piece of the pulled sheet that was cut from the strand. Rate of polymerization Instantaneous Shape of polymer
Strand, thick.
Force required to break strand
.054 N
Malleability
Silky, bends easily.
Opacity
Rather opaque.
Data for nylon 6-8: Weight of acyl chloride 211.09 Weight of amine 116.2 (density test) mass of blob .005 Volume of blob Density of blob .291 g/cm3 Notes from microscopic analysis. (Attach picture to back of report with a label.) The polymer formed more strands, unlike the 6-6, which formed sheets. The strands bent at points, and not in a continuous arc. Rate of polymerization
Instantaneous
Shape of polymer
Strand
Force required to break strand
.071 N
Malleability Opacity
Less malleable than 6-6, still very malleable. Translucent.
Data for nylon 6-10: Weight of acyl chloride Weight of amine
239.14 116.2
McAnany 11 (density test) mass of blob .203 Volume of blob Density of blob .396 g/cm3 Notes from microscopic analysis. (Attach picture to back of report with a label.)
The strand was notably thinner, and did not fray like the 6-8. It also bent more smoothly, smoothly, and was covered with very small bubbles. Rate of polymerization Instantaneous. Shape of polymer
Strand
Force required to break strand
.054 N
Malleability
Between 6-6 and 6-8.
Opacity
Clear when thin.
Data for nylon 8-6: Weight of acyl chloride 183.03 Weight of amine 144.26 (density test) mass of blob Volume of blob Density of blob Notes from microscopic analysis. (Attach picture to back of report with a label.) The polymer stuck to the weighing dish, and was unrecoverable. No microscopic analysis was possible.
Rate of polymerization
Fast.
Shape of polymer
Sheet, not strand.
Force required to break strand
No strand.
Malleability
Same as 6-8.
Opacity
Opaque.
Data for nylon 8-8: Weight of acyl chloride Weight of amine
211.09 144.26
McAnany 12 (density test) mass of blob .08 Volume of blob Density of blob .327 g/cm3 Notes from microscopic analysis. (Attach picture to back of report with a label.) This sample had no interesting characteristics microscopically.
Rate of polymerization
Fast
Shape of polymer
Strand
Force required to break strand
.0599 N
Malleability
Breaks then bends.
Opacity
Very opaque.
Data for nylon 8-10: Weight of acyl chloride 239.14 Weight of amine 144.26 (density test) mass of blob .23 Volume of blob Density of blob .4432 g/cm3 Notes from microscopic analysis. (Attach picture to back of report with a label.) Like the 8-8, the 8-10 had no interesting characteristics.
Rate of polymerization
Fast.
Shape of polymer
Strand.
Force required to break strand
.0599 N
Malleability
Fragile, breaks, then bends.
Opacity
Extremely opaque.
Data for nylon 10-6: Weight of acyl chloride Weight of amine (density test) mass of blob Volume of blob Density of blob
183.03 172.32
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Rate of polymerization
Notes from microscopic analysis. (Attach picture to back of report with a label.) This polymer produced very little product, and virtually none of it was in the form of a strand. Interestingly, Interestingly, the tiny strand that was produced (in the picture) was very v ery malleable. It was also very opaque. Slow, does not go very far.
Shape of polymer
Dust, occasional strand.
Force required to break strand
0N
Malleability
Like 6-6.
Opacity
No light transmission.
Data for nylon 10-8: Weight of acyl chloride Weight of amine (density test) mass of blob Volume of blob Density of blob Notes from microscopic to back of report with a
Rate of polymerization Shape of polymer
211.09 172.32
analysis. (Attach picture
label.) The polymer formed as a dust, although there was a significant amount produced. Pictured here is a very ve ry small piece of the polymer that formed as a sheet. Additionally, Additionally, black specks were found in the polymer, their origin is unknown. Faster than 10-6. Dust.
Force required to break strand Malleability Opacity
No transmission, retsin.
Data for nylon 10-10: Weight of acyl chloride 239.14 Weight of amine 172.32 (density test) mass of blob .07 Volume of blob Density of blob .328 g/cm3 Notes from microscopic analysis. (Attach picture to back of report with a label.) The polymer formed a slab, which was too opaque for a proper microscopic analysis.
McAnany 14 Rate of polymerization
Force required to break strand
Slower than 6 and 8-n faster than other 10ns. Sheet, breaks when attempt is made for strand. 0N
Malleability
Shatters when touched.
Opacity
Opaque.
Shape of polymer
McAnany 15 Analysis:
Tensile strength
y = -0.0005x + 0.2241
0.1 0.08
h t g n e r t s e l i s n e T 0.06 0.04 0.02 0 0
100
200
300
400
500
Polymer weight This graph clearly shows the relation of polymer weight to tensile strength. As the monomers that made up the polymers got heavier, the polymers got weaker. Most likely, likely, the heavier monomers are too large to be held together by a single covalent bond, and therefore tend to fall apart.
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Density
y = 0.0003x + 0.2434 0.5 0.4 y t i s n e D 0.3 0.2 0.1 0 0
100
200
300
400
500
Polymer weight While the small coefficient of correlation would appear to invalidate the initial predictions, upon analysis, it makes sense that the density of the polymers would remain constant. Take, for example, the densities of the following molecules. (Ignore the density of the substance, the molecular formula is of interest here.)
Dodecane. Hexane While these molecules have different sizes and masses, their “structural” density is identical. That is, their densities are (12 carbons)/(12 bonds long) and (6 carbons)/(6 bonds long). If this idea is extrapolated to very long molecules, such as polymers, the trend would continue.
Supposing this is a polymer, polymer, the density den sity is still (n carbons)/(n bonds long). Theoretically Th eoretically,, the smaller monomers would yield heavier polymers, because the NHOC bond would be heavier than CH2CH2. In all likelihood, the differences in density were due to experimental error. A method to compress the polymer into a solid block should be explored for future research.
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Fragility
8 7 6 y r a r t i b r a ( y t i g a r F 5 i l u ) s t i n 4 3 2 1 0 0
y = 0.0386x - 10.277
100
200
300
400
500
Polymer weight Please note, when reading this graph, the higher fragility values represent brittle polymers. These data agree with those collected during the tensile testing, although there are more data points. The data are entirely qualitative, although a qualitative test was not necessary, necessary, as the main goal of this research was to determine patterns, not exac t values.
Fragility
8 7 6 e n i m a y b y t i l w i g a r F t h g i5 e 4 3 2 1 0 0
y = 0.0594x - 5.1241
50
100
150
200
Amine weight When plotted by amine weight, the fragilities show the same patterns.
250
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Tensile strength by amine weight y = -0.001x + 0.1834
0.1 0.08 0.06 h t g n e r t s e l i s n e T 0.04 0.02 0 0 -0.02
50
100
150
200
250
Amine weight When plotted by amine weight, the tensile strength showed a nearly linear correlation. This is an exciting fact, as is means that the experiments yielded fairly accurate data.
Density
y = -3E-05x + 0.3621 0.5 0.4 y t i s n e D 0.3 0.2 0.1 0 0
50
100
150
200
250
Amine weight The density graphed by amine weight showed the correlation that was predicted in the analysis of the density by polymer weight, namely that there is no correlation.
McAnany 19 Conclusion: The results indicate that polymers of higher molecular weight are less suitable for most applications. They are generally more fragile than the short-chain pol ymers, and the very high chain-length polymers refused to form strands. From a purely practical standpoint, the monomers of higher molecular weight were very expensive, and it is likely that in the rare occasion where these properties would be desirable, a more inexpensive polymer would be used. The polymers of high weight also were reluctant to polymerize, even when the carboxylic acids were replaced with acyl ac yl chlorides. It is possible that these monomers would not polymerize at all if the acyl chloride were not present. Unfortunately, the polymerizations involving carboxylic acids often take place under exotic reaction conditions that cannot be easily ea sily duplicated in a research situation. Another possibility is that the 1,10 diaminodecane was not soluble enough in water to form an acceptable polymer, and therefore the reaction was the problem. The most useful polymer pol ymer synthesized was the nylon 6-6. It polymerized readily, and was extremely strong. Additionally, Additionally, it was made mad e with adipoyl chloride, which is less expensive than other acyl ac yl chlorides. Should this research continue, it would be ad visable to attempt to synthesize nylon 6-6 using bulk polymerization methods, or a carboxylic acid in place of an acyl chloride. Several problems were encountered during the research, perhaps the most notable was that the 1,10 diaminodecane was not soluble in cold water. The other diamine solutions were made as .25 M solutions, but the diaminodecane was not soluble enough. The solution that was used was to mix the diaminodecane with water in a flask, and then to place the flask in a hot water bath. The diaminodecane was soluble at elevated temperatures, and after all the diaminodecane had dissolved, the flask was allowed to cool. After the diaminodecane had precipitated, it was assumed that the solution would be saturated with the monomer. Using a hot solution was not an option, as the acyl chloride was dissolved in hexane which might have boiled and ignited. The unknown concentration of the solution may have influenced the results. Initially, Initially, the testing that was planned included a melting point test. However, the ovens available did not melt the polymers, and so the test was abandoned. Should an oven capable of melting the polymers be found, this test is strongly encouraged, as it does not depend on the conditions of the polymerization. Another set of data that were abandoned were the enthalpies of the reactions. This turned out to be impossible to measure, as the heat was not ev enly distributed, and the product was removed from the reaction vessel. If bulk polymerization had been attempted, determining the enthalpy of the reaction would have been feasible.
McAnany 20 Future studies: While the results from this research have yielded various insights into polymer chemistry, there are many exciting discoveries that can still be made. Some of the polymers synthesized did not form strands, which certainly would have affected properties such as tensile strength. A more reliable route of polymerization, such as bulk polymerization, may yield more similar reactions, which would allow higher certainty in the data. da ta. Additionally, Additionally, bulk polymerization p olymerization would allow measurements of enthalpy, enthalpy, which might allow insight into the mechanics mec hanics of the reaction. A method of compressing the polymers synthesized would be very useful. Most of the commercially available polymers are drastically altered from their initial state, either by compression or heating. Nylons are thermoset polymers, so melting them to form them would be impractical. Most likely, high pressure would force the strands to form a brick, which would allow more accurate testing. In terms of the monomers, increasing the molecular weight would likely have a limited benefit. Experimentation with smaller monomers may yield polymers which are much stronger, and easier to manufacture. Additionally, Additionally, adding unusual functional groups may create useful polymers. An aspect of research which was not pursued was synthesizing aramids. Aramids are condensation polymers that involve benzene rings. In addition to having a very different shape, benzene rings can have more than two functional groups, as in 1,3,5 triaminobenzene. Such highly branched polymers p olymers may have very interesting properties.
McAnany 21 This document and all content con tent therein are copyright 2007 Charles McAnany. All All rights reserved.
