sowonmoon+final

Synthesis and Characterization of Nylon Sowon Moon Department of Chemistry, Drexel University Submitted December 3, 2011

**Abstract** The most widely used polymer is nylon, and nylon comes many types depending on which reactants are used when synthesis. Many types of nylon are created after the first invention of nylon 6-6 at 1935, and nylon is used for apparels, tires, parachutes and many other materials due to characterization, such as durability, high elongation, and excellent abrasion resistance. [1]

**Introduction** Since 1935 the first production of nylon, it became the most widely used polymer in the world. [1] There are many types of nylon depending on the number of carbon in the structure. It is firstly used for apparels such as stockings, socks and blouses, but soon, it is spread to military, toys, electrics and cars where even the parts we do not know. [2] The invention and spread usage of nylon, the first synthetic fiber, results to the research of other polymer, and the polymer became the third organic compound after metals and ceramics. As chemistry major, we do lab on the synthesis of nylon 6-6 in organic chemistry class, and since the nylon is related to everyday life and such an important material, the knowledge about nylon can help to improve our lives.

**Background** Invention The invention of nylon is 1935, at DuPont chemical company by Wallace Hume Carothers. After manufacturing neoprene, the research team found a synthetic rubber and Carothers made efforts toward creating synthetic rubber by condensation reaction which is combining hexamethylene diamine and adipic acid to form a new molecule by polymerizing. [3] It takes three years to produce the commercial item of nylon, nylon-bristled toothbrush. [1]

History after invention This new molecule could replace silk which was used for apparels and since the invention. Before the invention of silk-like nylon, the main import country of silk was Japan. During World War Ⅱ, the import of nylon from Japan became difficult, and from that time, nylon replaced the ingredients of parachutes, and supplies for military, and the usage and needs of nylon increased. After 1950's, the DuPont started to produce more nylon-based productions such as acrylic. [1, 2] Since the invention of nylon, the attention of polymer, a large molecule with repeated units, is increased due to the wide spread usage and benefits of nylon.

Usage The first invented nylon, nylon 6-6, is commonly called as just “nylon (also called PA66, which means polyamide 6-6” and used for carpeting, apparels, and stockings and so on. Nylon is mainly used as fiber, but also used as thermoplastic. The most important usage of nylon is stockings, which made the rapid spread of nylon and earned great financial benefits. After the inventors found out that the texture of nylon is silk-like, the DuPont invented stockings for women at 1939. Under the copyright of “as strong as steel, as fine as a spider's web” by DuPont, the nylon sold rapidly. On the first year, the nylon stockings are appeared in the movie, The Wizard of oz, and the sales volume was about 64million pairs. [4]

**Synthesis** There are two types for synthesis of nylon, polycondensation reaction and ring opening polymerization. When the entire monomer is used for polymer, we call the reaction as polycondensation reaction.



Figure 1. condensation reaction[1]

Vapor deposition polymerization - polycondensation reaction The vapor deposition polymerization is one type of condensation polymerization. In VDP process, two types of bifunctional monomers are used to react easily at the end of the chain. According to the Shao, the new alternating VDP process makes not to prepare the active sub-layer surface (surface active agent) when VDP processing. The dichloride monomer goes the substrate’s amino covered surface, so the next dichloride monomer react easily with amino group on the surface. The surface will be covered with chain ends of dichloride monomers, and the next diamine monomer goes to the layer of dichloride monomer. From the figure 2, an open triangle activated sublayers on the substrate is amino end group. (a) An adipyl chloride monomer reacts with sublayer surface’s amino group. (b) The end of adipyl chloride chain is covered with another adipyl chloride. (c) the adipyl chloride chain reacts with hexamethylene diamine. (d) the completed reaction cycle of AVDP method of condensation polymerization. (e) [5] Figure 2. Illustration of the mechanism of alternating vapour deposition polymerization of nylon 66. [5] Ring opening polymerization The ring opening polymerization is occurred when the cyclic monomer form a polymer chain. The ring is broken as the polymer produced. [6]

Nylon 6-6

Figure 3. synthesis of Nylon 6-6. [7]

The synthesis of nylon 6-6 is occurred when combining hexamethylene diamine (1,6-hexanediamine) with adipoyl chloride in sodium hydroxide solution. The intermediate layer will be formed between hexamethylene diamine and adipoyl chloride, and that layer is nylon 6-6. The terminal chloride atoms react with hydrogen atoms to form hydrochloric acid, and the nylon with repeated unit is formed.

Nylon 6 Figure 4. synthesis of nylon 6. [8] When a caprolactam is heated in water about 250'c, the hydrogen atom of water attacted to the oxygen atom of caprolactam atom, and hydroxide ion is attached to carbon atom to form unstable diol as figure 5 below. a pair of electrons are donated by nitrogen atom to a hydroxyl group's hydrogen atom, the shared electron between hydrogen and oxygen forms double bond between oxygen and carbon atoms and the shared electron between carbon and nitrogen atoms goes to the nitrogen atom instead of the pair of electrons donated to hydrogen atom, and the cyclic monomer breaks into the chain. The linear amino acid reacts with caprolactam again to form polymer structure. At this time, the nitrogen in the linear amino acid react with ionized carbon atom in a caprolactam, and a shared electron between carbon and nitrogen in caprolactam goes to nitrogen atom, and a pair of electrons from nitrogen in caprolactam goes to hydrogen attached to therminal nitrogen atom, and the shared electron between those two atoms goes to nitrogen atom. The carboxylate group at the end of the molecule goes to the hydrogen atom, which locates at the middle of the linear structure, from a caprolactam, and form carbon oxygen double bond without hydrogen atom as figure 6. Finally, the acidic structure is formed, and this molecule reacts with caprolactam molecule to form a long chain of nylon 6. [9] Figure 5. unstable diol during the synthesis of nylon 6. [9]

Figure 6. forming carbon oxygen double bond. [9]

The new method – nylon 6 The most frequently used polymer, nylon 6, remains unreacted or partially reacted phases during the fast anionic polymerization, and the synthesis of new hybrid segment can improve the compatibility. when diol reacts with HDI under 80’c toluene with N2, PEG/PPG is synthesized. When this PEG or PPG reacts with HYCAR ATBN, the b-a-b type nylon(hycar ATBN-PEG or PPG-Hycar ATBN) is synthesized. The HDI and caprolactum contains acyl groups which help soft segment B to functionalize. When soft segment B reacts with caprolactum HDI adduct, the end side of soft segment, acyl group, acts as the initiator for polymerization. For 16 hours, polyether diol reacts with HDI followed by IR spectrophotometry and volumetric estimation of the NCO number. CL and HDI reaction, followed by IR spectrophotometer, is occurred. Crystallization makes HDI adduct purifies. PEU was added to HYCAR ATBN by drops, and this will use for synthesis of triblock copolymers. The mixture of above synthesized soft segment and CL and HDI adduct with CL were dried and then heated. The data archieved from above synthesis shows the new method of synthesis of nylon 6 works at higher CL concentration. [10]

Figure 7. synthesis of nylon 6 triblock copolymer [10]

**Characterization** Simply, the characterization of polymer is depending on the attractive forces between polymer chains. [11] Nylon has linear structure and amid (see figure 8 below) which are able for hydrogen bond, the physical properties are excellent as super crystallization of polymer. Some characteristics of nylon are high strength to weight ratio, excellent elastic properties, high breaking elongation and excellent dyeability. [12]

Figure 8. amide group of nylon [7]

Nylon 4 From the using of solid state 300MHz NMR with the FSLG-2 homo-nuclear dipolar decoupling method combined with high speed MAS method, the structure of nylon 4 has the crystalline and non-crystalline components. The six peaks of 1H NMR spectra of nylon 4, 8.0, 7.7, 4.7, 3.1, 2.2 and 1.7 ppm, are assigned to amide, CH2 protons. the large upfield shift is characteristic for the hydroxyl proton hydrogen bonded. CH2 assigned to two peaks on the NMR results from the 13C NMR. [13]

Nylon 4-6 It has a high melting point just like other nylons, and compared with other nylons, nylon 4-6 has excellent solvent resistance. For single crystallization of nylon 4-6, the structure is similar to nylon 6-6 or nylon 6. From figure 9 below, the hydrogen bond is formed when the temperature of melted sample decreases to the temperature of crystallization. At this time, the energy of crystal structure of nylon 4-6 is not stable. As proceeding crystallization, the crystal structure of nylon 4-6 becomes stable energetically, and forms hydrogen bond. [ 14 ] Figure 9. Proposed crystallization mechanism of nylon 4-6. [14]

Nylon 6 vs Nylon 6-6 Nylon 6 uses up to 11% less energy when manufacturing than nylon 6-6. However, nylon 6-6 is used about 54% and nylon 6 is used 46% in the manufacture. The structure of nylon 6 contains parallel chains with hydrogen bonds, and it forms a more open structure with less internal hydrogen bonding. Though nylon 6-6 is tighter with less open structures, and it makes nylon 6-6 is stronger and more resistant to heat. The melting point of nylon 6 is 220’c and nylon 6-6’s melting point is 255’c. It makes the percentage of usage of nylon 6-6 is higher than nylon 6 because of the temperature performance products. [15]

Nylon 6-6 : surface characteristic By using inverse gas chromatography and contact angle, the characterization of surface could be defined. Because of the structure of combination of high thermal and mechanical properties, nylon 6-6 is a semi crystalline thermoplastic polymer. The Lewis acid and Lewis base concept are used to describe the surface properties of nylon. When the temperature increases, the solid material’s surface free energy decreases generally. From the experimental data of journal, the surface free energy of nylon 6-6 increases from around 35mJ/m^2 to 47 mJ/m^2 along the increase of temperature from 343.2K to 373.2K. By using the equation from figure 10 below, we can calculate the Lewis acid-base number, the Ka number is 2.03 and the Kb number is 7.17. This means that the surface properties of nylon 6-6 is Lewis basic, and the Lewis acidic is very small. So combining nylon 6-6 with acidic material could result in formation a good interface. [16] Figure 10. Equation for Lewis acid and Lewis base number calculation. [16]

Nylon 13-13 Nylon 13-13 is made from Brassylic acid. It has higher melting point and better bonding for adhesives and paint. Among nylon 11, nylon12 and nylon 13-13, the nylon 13-13 has slightly lower density, and lowest dielectric constant and water affinity. The melt viscosity of nylon 13-13 is less sensitive to molecular weight effects thatn is that of nylon 6-6. The molecular weights of nylon 13-13 preparations were conveniently estimated by measuring inherent viscosities in m-cresol or hexafluoroisopropyl alcohol. The crystal structures found in the nylon 13-13 are complex, and they are chemically, termally or mechanically treated interconvertible. The solid state deformability of nylon 13-13 requires lower force than for lower members in the nylon family. [17]

**Nylon/nylon grafted compound usage on research**

Enzymatic synthesis in organic solvents The amino acid substitution affects to the synthetic activity to the hydrolytic activity. At high concentration of water, the hydrolytic and synthetic activities are both improved. To generate nylon 6, a condensation reaction between amino group and carboxyl group is catalyzed by nylon-oligomer hydrolase. The stable binding of the first Ahx at the N-terminal reagion, interaction of the second-Ahs at the C-terminal reason, and motion of Tyr 170 generated a closed form in the catalytic center of Ald hydrolase make the nylon 6’s enzymatic synthesis efficient. [18]

Glycolysis of nylon 6-6 Nylon 6-6 N,N-Hexamethylenebis(hexamide) (HMHA) and ethylene glycol go under glycolysis in a closed system with the ratio of 1:5, and nylon 6-6 goes under glycolysis with ethylene glycol with the ratio of 1:2. The FT-IR spectra of HMHA shows the absorbance of ester and amide bands around 3500 - 3000 cm^ (-1), but the 1' amine band is too low to distinguish. The ester band of 1734 cm^ (-1) is formed under glycolysis of HMHA. The glycolysis of nylon 6-6 is similar to HMHA's glycolysis. glycolysis of nylon 6-6 produces ester and primary amine just like HMHA. From the FT-IR spectra of glycolysed nylon 6-6, the ester band of 1733cm^ (-1) and 1632 cm^ (-1) are shown due to disruption of the bond between carbon and nitrogen. The formation of ester by the hydroxyl group of EG is the result of glycolysis of HMHA, and it is equilibrium in a closed system. The beta-hydroxyethylester, beta-hydroxyethyl hexanoate, and delta valerolactone are main products of glycolysis of nylon 6-6 with EG. [19]

Electron beam IR and sieving of nylon 6-6 Through electon beam irradiation, nylon 6-6 can be crosslinked, and it causes the change of polymer properties. As different irradiation doses, the nylon 6-6 membrane surface and penetration characteristics changed such as flux and solute rejection. [20]

frictional properties and abrasive wear resistance of nylon/graphite composite by oil impregnation By incorporating graphite or carbon black with polymer, the build up of electrical charge in the sliding of polymer can be solved. Integration of graphite into nylon increases the coefficient of resistance form that of neat nylon, and it can be solved by incorporation oil or wax into the nylon. The resistivity of nylon decreased by impregnation with graphite, but not with oil. The impact strength of nylon decreased by containing graphite could be compensated by the impregnation of two percent oil. Impregnation of graphite makes the coefficient of friction of nylon increase, but impregnation of oil makes it low, and addition of graphite decreases the abrasive wear rate. [21]

**Conclusion** Simply, the usage of nylon in research is not sole used, grafted with other molecules. The synthesis of nylon is divided into two types, ring opening polymerization and condensation polymerization. The number after nylon is depending on the number of carbons and the different types of nylons shows different characteristics. However, the common characterization of nylon is the high melting point, high strength to weight ratio, excellent elastic properties, high breaking elongation and excellent dye ability. [12]

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