WO2020028073A1

WO2020028073A1 - Functionalized polyamides and methods for the manufacture thereof

Info

Publication number: WO2020028073A1
Application number: PCT/US2019/042611
Authority: WO
Inventors: Todd Emrick; Ryan C. Hayward; Ashlin SATHYAN; Philippe Desbois
Original assignee: The University Of Massachusetts; Basf Se
Priority date: 2018-08-03
Filing date: 2019-07-19
Publication date: 2020-02-06

Abstract

A functionalized polyamide includes repeating units of formula (I), formula (II), or a combination thereof wherein x, y, and R¹ are as defined herein. Methods of making the functionalized polyamide are also described.

Description

FUNCTIONALIZED POLYAMIDES AND METHODS FOR THE MANUFACTURE

THEREOF

BACKGROUND

[0001] Aliphatic polyamides are important, high-volume engineering thermoplastics, the most common of which, polyamide-6 (PA-6) or poly(s-caprolactam), is synthesized by anionic ring-opening polymerization of e-caprolactam. See, e.g., Russo, S.; Casazza, E. Ring-Opening Polymerization of Cyclic Amides (Lactams). In Polymer Science: A

Comprehensive Reference, 10 Volume Set ; 2012; Vol. 4, pp 331-396; Hashimoto, K. Ring- Opening Polymerization of Lactams. Living Anionic Polymerization and Its Applications. Progress in Polymer Science (Oxford) 2000, 25 (10), 1411-1462 DOI: 10.1016/S0079- 6700(00)00018-6. PA-6 exhibits excellent mechanical strength and good resistance to organic solvents, abrasion, and temperature. See, e.g., Kohan, M. I.; Kohan, M. I. Nylon Plastics Handbook ; Hanser Publishers, 1995. These remarkable properties are attributable to a high degree of crystallinity, which originates from hydrogen bonding and dipole-dipole interactions between the amides of adjacent polymer chains. See, e.g., Schroeder, L. R.; Cooper, S. L. Hydrogen Bonding in Polyamides. Journal of Applied Physics 1976, 47 (10), 4310-4317 DOI: 10.1063/1.322432. These interactions contribute to backbone stiffness of the polymer and are responsible for the relatively high glass transition temperature ( T_g ) of 47 °C and melting temperature ( I_m ^' ) of 220 °C. See, e.g., Murthy, N. S. Hydrogen Bonding, Mobility, and Structural Transitions in Aliphatic Polyamides. Journal of Polymer Science Part B: Polymer Physics 2006, 44 (13), 1763-1782 DOI: 10. l002/polb.20833. However, as expected, this backbone stiffness results in significant processing challenges. See, e.g., Murthy, N. S. Hydrogen Bonding, Mobility, and Structural Transitions in Aliphatic

Polyamides. Journal of Polymer Science Part B: Polymer Physics 2006, 44 (13), 1763-1782 DOI: 10. l002/polb.20833. Facile methods to prepare polyamides with pendent substituents will afford materials with tailored thermal properties, solubility, elasticity, and adhesion, and will enhance polyamide compatibility with other polymers and with particulate fillers. See, e.g., Arvanitoyannis, L; Psomiadou, E. Composites of Anionic ( Co ) Polyamides ( Nylon 6 / Nylon 12 ) with Short Glass E-Fibers . Preparation and Properties. 1994, 57, 1-8.

[0002] While numerous papers describe successful ring-opening polymerizations of substituted lactones, few functional lactams have been prepared and there are very few published accounts of their polymerizations. See, e.g., Parrish, B.; Emrick, T. Aliphatic Polyesters with Pendant Cyclopentene Groups: Controlled Synthesis and Conversion to Polyester-Graft-PEG Copolymers. Macromolecules 2004, 37 (16), 5863-5865 DOI:

l0. l02l/ma04898ld; Parrish, B.; Breitenkamp, R. B.; Emrick, T. PEG- and Peptide-Grafted Aliphatic Polyesters by Click Chemistry PEG- and Peptide-Grafted Aliphatic Polyesters by Click Chemistry. Biomaterials 2005, 127 (17), 7404-7410 DOI: l0.l02l/ja0503 l0n; Parrish, B.; Emrick, T. Soluble Camptothecin Derivatives Prepared by Click Cycloaddition Chemistry on Functional Aliphatic Polyesters. Bioconjugate Chemistry 2007, 18 (1), 263-267 DOI: l0. l02l/bc06020ld; Gokhale, S.; Xu, Y.; Joy, A. A Library of Multifunctional Polyesters With“peptide-Like” pendant Functional Groups. Biomacromolecules 2013, 14 (8), 2489- 2493 DOI: l0. l02l/bm400697u; Parrish, B.; Quansah, J. K.; Emrick, T. Functional

Polyesters Prepared by Polymerization of a-Allyl(valerolactone) and Its Copolymerization with e-Caprolactone and d-Valerolactone. Journal of Polymer Science, Part A: Polymer Chemistry 2002, 40 (12), 1983-1990 DOI: 10. l002/pola.10277; Tarkin-Tas, E.; Mathias, L.

J. Synthesis and Ring-Opening Polymerization of 5-Azepane-2-One Ethylene Ketal: A New Route to Functional Aliphatic Polyamides. Macromolecules 2010, 43 (2), 968-974 DOI: l0. l02l/ma902233k; Sanchez-Sanchez, A.; Basterretxea, A.; Mantione, D.; Etxeberria, A.; Elizetxea, C.; de la Calle, A.; Garcia-Arrieta, S.; Sardon, FL; Mecerreyes, D. Organic-Acid Mediated Bulk Polymerization of e-Caprolactam and Its Copolymerization with e- Caprolactone. Journal of Polymer Science, Part A: Polymer Chemistry 2016, 54 (15), 2394- 2402 DOI: l0. l002/pola.28H4; Tunc, D.; Bouchekif, FL; Ameduri, B.; Jerome, C.; Desbois, P.; Lecomte, P.; Carlotti, S. Synthesis of Aliphatic Polyamide Bearing Fluorinated Groups from E-Caprolactam and Modified Cyclic Lysine. European Polymer Journal 2015, 77, 575- 584 DOI: l0. l0l6/j.eurpolymj.20l5.08.030.

[0003] In principle, functionalized aliphatic polyamides could be synthesized by ring opening polymerization of substituted lactams or by post-polymerization reactions. However, producing PA-6 from functional monomers is a synthetic challenge, since the functional groups must be compatible with high polymerization temperatures (typically about 140 °C) and metal initiators. The polymerization of substituted lactams is additionally challenging, because the substituents may interfere, either sterically or electronically, with the ring opening mechanism. In one prior example of functional polyamides, a ketone-containing polyamide was synthesized from g-ethylene ketal e-caprolactam, which proved amenable to both thermal- and photo-initiated crosslinking. See, e.g., Tarkin-Tas, E.; Mathias, L. J.

Synthesis and Ring-Opening Polymerization of 5-Azepane-2-One Ethylene Ketal: A New Route to Functional Aliphatic Polyamides. Macromolecules 2010, 43 (2), 968-974 DOI:

10. l02l/ma902233k. In another example, pendent functionalization of aliphatic polyamides was achieved by polymerization of cyclic lysine (a-amino-s-caprolactam) substituents, which allowed for polymer crosslinking via the pendent amines. See, e.g., Tao, Y.; Chen, X.; Jia,

F.; Wang, S.; Xiao, C.; Cui, F.; Li, Y.; Bian, Z.; Chen, X.; Wang, X. New Chemosynthetic Route to Linear e-Poly-Lysine. Chem. Sci. 2015, 6 (11), 6385-6391 DOI:

10.1039/C5SC02479J; Bouchekif, H.; Tunc, D.; Le Coz, C.; Deffieux, A.; Desbois, P.;

Carlotti, S. Controlled Synthesis of Crosslinked Polyamide 6 Using a Bis-Monomer Derived from Cyclized Lysine. Polymer (United Kingdom) 2014, 55 (23), 5991-5997 DOI:

l0. l0l6/j.polymer.20l4.09.050; Tunc, D.; Le Coz, C.; Alexandre, M.; Desbois, P.; Lecomte, P.; Carlotti, S. Reversible Cross-Linking of Aliphatic Polyamides Bearing Thermo- and Photoresponsive Cinnamoyl Moieties. Macromolecules 2014, 47 (23), 8247-8254 DOI:

10. l02l/ma502083p. Tunc, et al. synthesized aliphatic polyamides with pendent fluoroalkyl groups by ring-opening polymerization of perfluorobutyryl -substituted a-amino-s- caprolactam, producing materials that exhibited degradation temperatures up to 390 °C. See, e.g., Tunc, D.; Bouchekif, H.; Ameduri, B.; Jerome, C.; Desbois, P.; Lecomte, P.; Carlotti, S. Synthesis of Aliphatic Polyamide Bearing Fluorinated Groups from E-Caprolactam and Modified Cyclic Lysine. European Polymer Journal 2015, 77, 575-584 DOI:

l0. l0l6/j.eurpolymj.20l5.08.030. These examples are typical of functional polyamides in that they carry substituents at the g-position and are synthesized from cyclohexanedione and utilize Beckmann rearrangement chemistry. However, the incorporation of functionality directly at the a-position of e-caprolactam, followed by ring-opening polymerization of the resultant substituted lactam has not been reported.

[0004] Accordingly, there remains a continuing need for an improved method of incorporating functionality directly into polyamides.

BRIEF SUMMARY

[0005] One embodiment is a functionalized polyamide comprising repeating units of formula (I), formula (II), or a combination thereof

wherein x is an integer from 1 to 12; y is an integer from 1 to 12; and R¹ comprises a substituted or unsubstituted C1-12 alkyl group, a substituted or unsubstituted C₆-2o aryl group, a zwitterionic group, a Ci-₆ alkyl ene oxide group, a Ci-₆ hydroxyalkyl group, a peptide group, or a combination thereof.

[0006] Another embodiment is a method of making the functionalized polyamide of formula (I), the method comprising: mixing a first monomer of formula (IV)

and a second monomer of formula (V)

to provide a reaction mixture; heating the reaction mixture to a temperature effective to melt the first monomer and, when present, the second monomer, in the presence of an initiator; and adding an activator to the reaction mixture to provide the functionalized polyamide; wherein x is an integer from 1 to 12; y is an integer from 1 to 12; and z is an integer from 1 to 12.

[0007] Another embodiment is a method of making the functionalized polyamide of formula (II), the method comprising: combining an allyl-functionalized polyamide comprising repeating units of formula (I)

and a thiol-functionalized compound of formula (VI)

HS-R¹ (VI)

in the presence of a radical initiator to provide the functionalized polyamide; wherein R¹ comprises a substituted or unsubstituted C1-12 alkyl group, a substituted or unsubstituted C₆-2o aryl group, a zwitterionic group, a Ci-₆ alkyl ene oxide group, a Ci-₆ hydroxyalkyl group, a peptide group, or a combination thereof.

[0008] These and other embodiments are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following Figures represent exemplary embodiments:

[0010] FIG. 1 is a chemical scheme illustrating the synthesis of 3-(3-propenyl)-2- azepanone (top) and the synthesis of allyl-substituted aliphatic polyamides by anionic ring opening copolymerization (bottom).

[0011] FIG. 2 shows the differential scanning calorimetry (DSC) traces of polymers Pl-5. The left traces show the cooling cycle and the right traces show the second heating cycle.

[0012] FIG. 3 is a chemical scheme showing the thiol-ene reactions for the modification of allyl-functionalized polyamides.

[0013] FIG. 4 is a schematic illustration showing formation of a crosslinked thiol-ene polymer network derived from an allyl-functionalized polyamide mixed with tetrathiol and photoinitiator in trifluoroethanol and exposed to 365 nm light for 10 minutes at room temperature.

[0014] FIG. 5 shows a photograph of a crosslinked organogel network (a), rheological data of the organogel (b), and a photograph of a clear, free-standing polymer film on paper. DETAILED DESCRIPTION

[0015] The present inventors have prepared aliphatic polyamides containing pendent allyl groups, for example by anionic ring-opening copolymerization of e-caprolactam with an appropriately substituted lactam, for example 3-(3-propenyl)-2-azepanone. Copolymerization experiments revealed that up to 11 mole percent of the functionalized lactam was integrated successfully into these polyamides, which ranged in molecular weight from 27-72 kDa.

Copolymer degree of crystallinity decreased with incorporation of the functional monomer, as did melting temperatures (T_m), relative to the well-known commercial polyamide-6 (PA-6). The pendent allyl groups afforded rapid access to numerous functional aliphatic polyamides, using photo-initiated thiol-ene chemistry, and provided a pathway to cross-linked films and gels.

[0016] Accordingly, one aspect of the present disclosure is a functionalized polyamide. The polyamide comprises repeating units of formula (I), formula (II), or a combination thereof

In each of formulas (I) and (II), x is an integer from 1 to 12 (i.e., x is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12) and y is an integer from 1 to 12 (i.e., x is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12). In formula (II), R¹ comprises a substituted or unsubstituted C1-12 alkyl group (e.g.,

perfluoroalkyl groups), a substituted or unsubstituted C₆-2o aryl group, a zwitterionic group (e.g., a phosphorylcholine group, a sulfobetaine group, a carboxybetaine group, and the like, or a combination thereof), a Ci_-6 alkyl ene oxide group, a Ci-₆ hydroxyalkyl group, a peptide group, or a combination thereof. As used herein, an alkylene oxide group is a group having the formula -(R^a-0)_n-R^b-, wherein R^a and R^b are independently at each occurrence a Ci_-6 alkylene group, and n is an integer from 1 to 50, for example 1 to 10, for example 1 to 4 (e.g., ethylene oxide, propylene oxide, butylene oxide, poly(ethylene oxide), and the like). The aforementioned zwitterionic group can be a zwitterion having the structure -A-B-X, wherein A is a center of permanent positive charge or a center of permanent negative charge, B is a divalent group comprising a C1-12 alkylene group, a C₆-3o arylene group, or an alkylene oxide group, and X is a center of permanent negative charge or a center of permanent positive charge, provided that the zwitterion has an overall net charge of zero (i.e., the zwitterion is net neutral). For example, in an embodiment wherein A is a center of permanent positive charge, X is a center of permanent negative charge. For example, in an embodiment wherein A is a center of permanent negative charge, X is a center of permanent positive charge. In some embodiments, a center of permanent positive charge can include a quaternary ammonium group, a phosphonium group, a sulfonium group, and the like. In some embodiments, the center of permanent positive charge is preferably an ammonium group. In some embodiments, a center of permanent negative charge can include a sulfonate group, a phosphonate group, a carboxylate group, a thiolate group, and the like. Thus, in some embodiments, each occurrence of R¹ can be a sulfobetaine zwitterion, a phosphoryl choline zwitterion, a carboxybetaine zwitterion, a phosphobetaine zwitterion, or a combination thereof. As used herein, a peptide group refers to a short chain of amino acid monomers linked by peptide (amide) bonds. Suitable amino acids can include L-amino acids or D- amino acids, and can further include a-amino acids or b-amino acids. For example, the amino acid monomers can include (but are not limited to) alanine, aspartate, asparagine, glutamate, glutamine, glycine, histidine, lysine, ornithine, proline, serine, and threonine. The shortest peptides are dipeptides, consisting of 2 amino acids joined by a single peptide bond, followed by tripeptides, tetrapeptides, etc. In some embodiments, R¹ can include one or more oligo- or polypeptides. A polypeptide is a long, continuous, and typically unbranched peptide chain. In some embodiments, suitable peptide groups can include 2 to 20 amino acids.

[0017] In some embodiments, R¹ can comprise a moiety selected so as to impart the polyamide with a particular property. For example, R¹ can be an adhesion promoting group, a UV stabilizing group, a friction control agent, a triboelectric group, a (semi)conducting group, or a combination thereof.

[0018] In some embodiments, x is preferably 2 to 10, or 2 to 8. In a specific embodiment, x is 4. In some embodiments, y is preferably 1 to 10, or 1 to 5. In a specific embodiment, y is 1. In some embodiments, the functionalized polyamide comprises repeating units of formula (I). In some embodiments, the functionalized polyamide comprises repeating units of formula (II). In some embodiments, when a combination of both repeating units of formula (I) and (II) are present, the repeating units according to formula (II) can be present in a major amount, for example, at least 50 mole percent, or at least 60 mole percent, or at least 70 mole percent, or at least 80 mole percent, or at least 90 mole percent, or at least 95 mole percent, or at least 99 mole percent, based on the total number of repeating units of formula (I) and (II).

[0019] The polyamide further comprises repeating units according to formula (III)

wherein z is an integer from 1 to 12 (i.e., z is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12). In some embodiments, z is an integer of 1 to 10, or 2 to 8. In a specific embodiment, z is 4. The repeating units according to formula (III) can be present in an amount of 1 to 99 mole percent, based on the total moles of repeating units of the polyamide. In some embodiments, the repeating units according to formula (III) can be present in an amount of 10 to 99 mole percent, or 20 to 99 mole percent, or 30 to 99 mole percent, or 40 to 99 mole percent, or 50 to 99 mole percent, or 60 to 99 mole percent, or 75 to 99 mole percent, or 85 to 99 mole percent.

[0020] In a specific embodiment, the functionalized polyamide of the present disclosure comprises 1 to 15 mole percent of repeating units according to formula (I) and 85 to 99 mole percent of repeating units according to formula (III), wherein mole percent is based on the total moles of repeating units according to formula (I) and formula (III).

[0021] In another specific embodiment, the functionalized polyamide of the present disclosure comprises 1 to 15 mole percent of repeating units according to formula (II) and 85 to 99 mole percent of repeating units according to formula (III), wherein mole percent is based on the total moles of repeating units according to formula (II) and formula (III).

[0022] The functionalized polyamide can have a number average molecular weight of 1,000 to 100,000 grams per mole, for example 5,000 to 85,000 grams per mole, or 10,000 to 75,000 grams per mole. Number average molecular weight can be determined, for example, using gel permeation chromatography relative to poly(methyl methacrylate) standards eluting with 2,2,2-trifluoroethanol (TFE). An exemplary method for molecular weight determination of the polyamides of the present disclosure is further described in the working examples below.

[0023] In a specific embodiment, the functionalized polyamide comprises 1 to 15 mole percent of repeating units according to formula (I) and 85 to 99 mole percent of repeating units according to formula (III), wherein x in formula (I) is 4, y in formula (I) is 1, z in formula (II) is 4, and the polyamide has a number average molecular weight of 10,000 to 75,000 grams per mole, as determined using gel permeation chromatography relative to poly(methyl methacrylate) standards.

[0024] In yet another specific embodiment, the functionalized polyamide comprises 1 to 15 mole percent of repeating units according to formula (II) and 85 to 99 mole percent of repeating units according to formula (III), wherein x in formula (II) is 4, y in formula (II) is 1, z in formula (II) is 4, and the polyamide has a number average molecular weight of 10,000 to 75,000 grams per mole, as determined using gel permeation chromatography relative to poly(methyl methacrylate) standards.

[0025] The functionalized polyamides of the present disclosure can be made, for example, using anionic ring opening polymerization (ROP) of the corresponding lactam monomers. These methods are further described in the working examples below. Thus, another aspect of the present disclosure is a method of making the functionalized polyamides.

[0026] In some embodiments, when the functionalized polyamide comprises repeating units of formula (I) and formula (III), the method of making the polyamide comprises mixing a first monomer of formula (IV)

and a second monomer of formula (V)

to provide a reaction mixture, where x, y, and z are as defined above. The method further comprises heating the reaction mixture to a temperature effective to melt the first monomer and the second monomer, in the presence of an initiator. The method further comprises adding an activator to the reaction mixture to provide the functionalized polyamide. The initiator and activator can be any that are generally known to be useful for the anionic ring opening polymerization of lactams, and can be, for example, sodium caprolactamate and hexamethylene-l,6-dicarbamoylcaprolactam, respectively. The heating of the reaction mixture can be selected depending on the melting points of the monomers used, and in some embodiments, can be, for example, 130 to 160 °C, or 130 to 150 °C, or 135 to 145 °C.

[0027] The allyl functionalized polyamides comprising repeating units of formula (I) discussed above can be particularly useful for further functionalizing the polyamides in a post-polymerization reaction. For example, the allyl group can be reacted with a thiol- containing group in a thiol-ene reaction to generate the functionalized polyamides comprising repeating units according to formula (II).

[0028] Thus, another aspect of the present disclosure is a method of making the functionalized polyamide comprising repeating units of formula (II). The method comprises providing a reaction mixture comprising a functionalized polyamide comprising repeating units of formula (I)

and a thiol-functionalized compound of formula (VI)

HS-R¹ (VI)

and a radical initiator to provide the functionalized polyamide. R¹ can be as described above The radical initiator can be, for example, a photoinitiator, and the method can further comprise exposing the reaction mixture to ETV light (e.g., about 365 nanometers).

[0029] As discussed above, the starting polymer (I) further comprises repeating units according to formula (III). Thus, the functionalized polyamide comprising repeating units according to formula (II) is understood to also comprise repeating units according to formula (III). The repeating units according to formula (III) can be present in the above-described amounts.

[0030] Crosslinked network materials (e.g., organogels and crosslinked films) can also be prepared when the allyl-functionalized polyamide is combined with a suitable multifunctional thiol-containing compound as a crosslinking moiety. This is further described in the working examples below.

[0031] Thus, the present inventors have advantageously found the functional polyamides can be prepared via a facile method, and the polyamides can desirably be further functionalized post-polymerization to include a variety of different groups depending on the desired end application.

[0032] The invention is further illustrated by the following non-limiting examples.

EXAMPLES [0033] Monomer 1, shown in Figure 1, was synthesized as described by Kunishima (see, e.g., Yamada, K.; Karuo, Y.; Tsukada, Y.; Kunishima, M. Mild Amide-Cleavage Reaction Mediated by Electrophilic Benzylation. Chemistry - A European Journal 2016 DOI: 10. l002/chem.20l603120), was isolated as a white solid in -85% yield. As shown in Figure 1, this two-step, one-pot synthesis involved the reaction of e-caprolactam with

chlorotrimethylsilane in the presence of lithium N, A-di i sopropyl a i de (LDA) in anhydrous tetrahydrofuran (THF) at -78 °C. Then, addition of allyl bromide to the caprolactam anion, followed by hydrolytic removal of the TMS group, produced the desired monomer 1, which was purified by column chromatography on silica gel. This a- substituted lactam was characterized by 'H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, noting the distinct allyl proton signals at d= 5.79 ppm ( -CH- ) and d= 4.98 ppm ( -CH2- ) in the ¹H NMR spectrum, as well as the olefin resonances at d= 136.32 ( -CH- ) ppm and d= 115.28 ppm (- CH2-) in the ¹³C NMR spectrum. Monomer 1 was easily prepared on a 10 gram scale and proved stable for months when stored under ambient conditions.

[0034] Attempts to homopolymerize monomer 1 by anionic ring-opening

polymerization were unsuccessful, despite testing a variety of conditions and initiator systems. In these experiments, after addition of initiator, the reaction mixture quickly became dark and no polymer was produced. Analysis of the reaction mixture by ¾ NMR spectroscopy showed no evidence of allyl protons, nor any indication of molecular weight increase by gel permeation chromatography (GPC). In contrast, copolymerization of monomer 1 with e-caprolactam proved successful when using 0.4 mmol sodium

caprolactamate (3) as initiator and 0.06 mmol hexamethylene-l,6 dicarbamoylcaprolactam (4) as the activator (as shown in Figure 1).

[0035] Under the copolymerization conditions tested, up to 11 mole percent incorporation of 1 into polyamide copolymers was achieved. Polymerizations were conducted neat, in glass tubes, at 140 °C under nitrogen atmosphere. Monomers 1 and 2, and initiator 3, were added to the tube as solids; then, heating the mixture to 140 °C melted the reagents and addition of activator 4 caused the mixture to solidify. The polymerization was quenched by immersing the reaction tube into liquid nitrogen, then opening the tube to ambient conditions. The solid polymer product conformed to the shape of the tube and solid product was collected after breaking the tube. For small scale polymerizations (<l g), polymer was recovered by solubilizing the mixture in trifluoroethanol. Copolymerizations were conducted on 1-5 g scales and isolated yields were typically > 85%. Reagent purity proved crucial to successful polymerization, since water and other impurities interfere with the initiating and propagating species (thus, it proved important to use flame-dried glassware and to subject the reagents to vacuum prior to use).¹ The obtained polymers were characterized by ¾ and ¹³C NMR spectroscopy.

[0036] At a reaction time of 10 minutes, monomer conversion reached 85%, as determined by ¾ NMR spectroscopy recorded on aliquots withdrawn from the reaction mixture. In the ¹H MR spectrum, the allyl protons resonated at d= 5.79 ppm ( -CH- ) and d = 4.98 ppm ( -CH2- ); in the ¹³C NMR spectrum, allyl carbon signals appeared at d= 137.2 ppm ( -CH- ) and d= 116.5 ppm ( -CH2- ). The characteristic NMR chemical shifts from monomer 2 were employed for evaluating conversion, since the allyl resonances did not shift significantly when converting from monomer to polymer; in 2, the 'H NMR signals at d = 2.30 ppm ( -CHi- ) were integrated against the same methylenes at d = 2.04 ppm (-CH2-) of the polymer. e-Caprolactam (comonomer) showed resonances for the d, b and g-methylene protons at 1.60 and 1.48 ppm at polymerization time <2 min; these shifted to 1.45 f-Oΐ2 ) and 1.36 ppm ( y-CHi -) in the polymer, with a new signal generated at 1.17 ppm {b-CHi-) as polymerization time increased.

[0037] The polyamides were purified by precipitation in ethyl acetate to remove unreacted monomer, affording a white fibrous material that was characterized by 'H and ¹³C NMR spectroscopy. The pendent allyl groups proved stable under these bulk

copolymerization conditions, and polymers containing up to 11 mole percent of monomer 1 were obtained. Integration of monomer 1 into the polyamide structure was characterized by comparing the intensity of the olefin signal at d = 5.50 ppm ( -CH- ) against the resonance at d = 2.04 ppm ( -CH2- ) for the e-caprolactam methylene units. Interestingly, copolymerization attempts that employed more than 20 mole percent of monomer 1 in the initial feed ratio were unsuccessful, yielding only ill-characterized dark brown liquids and no polymer product.

[0038] Polymers Pl-5, listed in Table 1, were prepared using identical

catalyst: activator ratios of 0.4:0.06 and polymerization times of 20 min. Table 1 indicates the extent to which monomer 1 was incorporated into the copolymers, from 1 to 11 mole percent, with molecular weights ranging from 27 to 72 kDa as estimated by gel permeation chromatography (GPC) (eluting in 2,2,2-trifluroethanol (TFE)), relative to poly(methyl methacrylate) calibration standards. The copolymers were isolated in >85% yield and exhibited polydispersity index (PDI) values in the range of 1.9-3.3. Use of sodium

caprolactamate initiator, a strong base which can induce side reactions such as transamidation and Claisen-type condensation (resulting in branching and/or crosslinking) may be

responsible for the relatively high PDI values obtained.

Table 1

“Percent monomer conversion was determined by Ή NMR spectroscopy prior to polymer purification. ' Molecular weight and PDI values were estimated by GPC, eluting in trifluroethanol (TFE). ^cMole % refers to the percentage of monomer 1 incorporated into the copolymers as determined by Ή NMR spectroscopy characterization on solutions of the purified polymer.

[0039] The reluctance of monomer 1 to homopolymerize contrasts the relatively easy polymerizability of several allyl-substituted lactones. The effect of inserting a methyl group alpha to the lactam as a small and unreactive group was tested. This monomer was prepared similarly to the route shown in Figure 1, substituting methyl iodide for allyl bromide, and the methyl-substituted lactam was isolated in -70% yield. Interestingly, even this simple methyl group prevented homopolymerization of the lactam. However, in copolymerizations with e- caprolactam, up to 16 mole percent of the methyl-substituted monomer was integrated successfully into the copolymers, a modest increase over the 11 mole percent maximum for the allyl-substituted version.

Thermal Properties of Allyl-Functionalized Polyamides

[0040] The bulk physical properties of the novel allyl -containing polyamides, including solubility, crystallization temperature ( T_c ), and melting temperature ( I_m ^' ), were evaluated to probe the impact of inserting small amounts of functionality into these polymers. PA-6 is insoluble in most organic solvents but is soluble in TFE at the level of about 0.5 mg/mL. Allyl-substituted polymers Pl-5 exhibited improved solubility in TFE. For example, P3 had a solubility of 0.75 mg/mL in TFE, which proved useful for spectroscopic characterization and molecular weight estimation. The crystallization and melting

temperatures of Pl-5 were determined by differential scanning calorimetry (DSC), as reported in Table 2. The thermal stability of the allyl-substituted polyamides was determined by therm ogravimetric analysis (TGA), which was conducted at a heating rate of 10 °C/min under nitrogen atmosphere and revealed a 5% weight loss temperature in the range of 300- 320 °C.

Table 2

T_c. crystallization temperature. T_m melting temperature; percent crystallization = ( AH_m/AH_mo) / 100 where \H_/ n = 188 J/g is the heat of fusion of polyamide-6.

[0041] DSC thermograms showed distinct melting and crystallization temperatures, allowing for estimation of T_m and T_c, which were recorded from the second heating and cooling cycles; this data is given in Figure 2. The T_m and T_c values of the functional polyamides were both lower than that of PA-6, with T_c dropping from 162 °C to 118 °C in going from PI to P5, and T_m declining from 216 °C to 188 °C over the same sample set. The allyl substituents of these polyamides appear to interrupt polymer crystallinity by weakening hydrogen bonding interactions between the neighboring amide groups. Polyamide-6 (PA-6), used in our experiments as a reference, synthesized under similar conditions as for the copolymers, had a molecular weight of 19 kDa and PDI of 1.81 (analyzed by GPC, eluting in TFE, with PMMA standards). Although this particular PA-6 sample had a lower molecular weight than the copolymers (27-72 kDa), the molecular weight range of the samples utilized nonetheless provided valuable comparisons.

Reactivity of Allyl-Substituted Polyamides

[0042] The pendent allyl groups of polyamides Pl-5 were converted efficiently into other functional moieties by photo-initiated thiol-ene reactions. This allows for the preparation of a range of novel, functional polyamides with tailored physical and chemical properties. Post-polymerization modifications were performed using P4 (10 mole percent of monomer 1 as the selected example shown in Figures 3 and 4. Using this method, the pendent allyl groups were converted easily to aliphatic alcohols (P4a) and aromatic moieties (P4b) by irradiating (335 nm) a TFE solution of the polymer with the appropriate thiol (and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as the photoinitiator), affording the desired substituted polymers in -95% yield. Polyamides P4a and P4b were purified by repeated precipitation in ethyl acetate, dried under vacuum overnight to remove excess solvent, then characterized by ¾ NMR spectroscopy.

[0043] While monitoring these thiol-ene reactions, an absence of unreacted olefin resonances in the ¾NMR spectra (d= 5.79 ppm ( -CH- ) and d= 4.98 ppm ( -CH2- )) was evident for polymers P4a and P4b. For P4a, signals from the S-methylene group ( -S-CH2- ) appeared at d= 2.48 and 2.25 ppm and a new signal for the -CH2-OH- methylene was found at d= 3.52 ppm. For P4b, aromatic signals appeared from d= 7.03 - 7.26 ppm ( -CH- ), while the resonances representing -CH2-S- and -CH2- were found at d= 3.47 and 2.53 ppm, respectively. Conjugation of hydrophilic moieties to polyamides is especially interesting for significantly altering their physical and solution properties. For example, thiol -substituted 2- methacryloyloxyethyl phosphorylcholine (MPC-SH) was synthesized and successfully conjugated to the allyl -substituted polyamides by photo-initiated thiol-ene reactions. In these reactions, P4, MPC-SH, and DMPA were dissolved in TFE and irradiated at 365 nm for 2 h at room temperature. The polymer was purified by precipitation in THF, and dialysis in water, to remove excess PC-thiol (water soluble), then lyophilized to obtain P4c as a white fluffy solid. In the ¾NMK spectrum of P4c, the allyl signals at d= 5.79 ppm ( -CH- ) and d = 4.98 ppm ( -CH2- ) were absent and the characteristic PC signals were observed, including: - N⁺-( CHs)s- at d= 3.21 ppm, -CH2-N⁺- at d= 3.21 ppm, -O-CH2- at d= 4.35 ppm, and -CH2- O- at _<5·= 4.18 ppm.

[0044] In the ³¹P NMR spectrum of P4c, a clean phosphorous signal at d= 0 ppm supported successful incorporation of PC groups into the polyamide copolymers.

Interestingly, the pendent PC groups did not produce perfectly homogeneous polyamide solutions in DI water; instead, slightly cloudy, stably suspended materials were obtained. 'H and ³¹P NMR spectra of P4c in D₂0 showed resonances characteristic of the PC moieties, but no backbone polyamide signals, suggesting that greater than 10 mole percent of pendent hydrophilic groups will be needed to fully solubilize the structures.

[0045] UV-absorbing and perfluoroalkyl-functionalized polyamides were also accessed easily from functional polyamides Pl-5. For example, 9-fluorenylmethylthiol was conjugated successfully to allyl -substituted polyamide P4 to yield P4d, using the same reaction conditions described before and given in Figure 3. In this case, the reaction mixture was degassed with nitrogen for 20 min, then irradiated at 365 nm for 2 hours. P4d was characterized by ¾ NMR spectroscopy and absence of unreacted olefin resonances was noted. Similarly, lH,lH,2H,2H-perfluorodecanethiol was added to P4 using the thiol-ene reaction and the polymer product was characterized by ¾ NMR spectroscopy. The versatility of thiol-ene chemistry, in conjunction with these functional polyamides, will produce new materials that enhance polyamide processability and allow tracking of polyamide localization in blends.

[0046] Polyamide P4 was easily crosslinked with the pentaerythritol tetrakis(3- mercaptopropionate), the tetrathiol shown in Figure 4, using either solution or solid-state conditions and in the presence of DMPA. In solution, a 3: 1 thiol :alkene ratio in minimal TFE (just enough to solubilize the polymer) was irradiated at 365 nm at room temperature for 10 min to afford the clear, cross-linked gel, shown in Figure 5a as P4f. Rheology experiments were performed on a stress-controlled rotational rheometer (Malvern Kinexus Pro+) with a 20-mm parallel plate geometry. Oscillatory frequency sweeps were performed at 25 °C at a strain amplitude of 0.5% with frequencies ranging from 1-100 rad/s. The rheological data, as shown in Figure 5b, displayed a storage modulus G’ that exceeded the loss modulus G” by four times, with little frequency dependence in either. In an alternative experiment, the same polymer solution, drop cast on a glass Petri dish and dried under a stream of nitrogen for 5 mins, was exposed at 365 nm for 1 min to afford transparent polymer film P4g, as shown in Figure 5c. This film was peeled easily from the substrate to yield a free-standing material; as expected, both the gel and film were insoluble in TFE; these crosslinked polymers did not swell in water, but swelled rapidly in TFE.

[0047] In summary, a series of novel, allyl-substituted aliphatic polyamides was prepared by anionic ring-opening copolymerization involving an allyl-functionalized e- caprolactam monomer. With increasing mole percentages of allyl groups, the crystallinity, melting temperature (T_m), and crystallization temperature ( T_c ) of the polymers declined. The alkene moieties were easily converted into the desired chemical functionalities with high efficiency thiol-ene“click” reactions, using a variety of mono- and multifunctional thiols providing a modular method to tremendous variety of functional polyamide-6 polymers. The ability to alter the crystalline properties of these polymers by changing the mole percentage of functional groups will open new opportunities in thermoplastics and other materials classifications. Notably, even 1-11 mole percent of allyl groups significantly tailors the physical and chemical properties of the polymers. This work represents an exceptionally simply and effective approach to functional polyamide copolymers and will open new opportunities for such structures in composite materials and blends.

[0048] Experimental details follow.

[0049] Materials. Aza-2-cycloheptanone (99%), chlorotrimethylsilane (> 99%), //- butyllithium solution (2.5 M in cyclohexane), //-butyllithium solution (2 M in cyclohexane), diisopropylamine (99.95%), allyl bromide (99%), mercaptoethanol (> 99%), 4-bromobenzyl mercaptan (97%), pentaerythritol tetrakis(3-mercaptopropionate) (> 95%), 2,2-dimethoxy-2- phenyl acetophenone (99%),l,3-propanedithiol (99%) and 9-fluorenylmethylthiol (97%) were purchased from Aldrich and used without further purification. 2,2,2-trifluroethanol was purchased from Alfa Aesar and used without further purification. 2-Methacryloyloxyethyl phosphorylcholine (MPC) was purchased from Aldrich and washed with diethyl ether prior to use. Sodium caprolactam ate (Briiggolen C10) and hexamethylene-l,6- dicarbamoylcaprolactam (Briiggolen C20) were purchased from Bruggemann chemical company and used without further purification. Anhydrous THF was purified by distillation over benzophenone and sodium metal. Deuterated solvents for MR spectroscopy were purchased from Cambridge Isotope Laboratories. Chloroform, methanol, tetrahydrofuran, dichloromethane, sodium sulfate, hexane, diethyl ether and ethyl acetate were purchased from Fisher Scientific.

[0050] Instrumentation. ¾ NMR spectra were recorded on a Bruker Avance-500 spectrometer operating at 500 MHZ and chemical shifts reported in ppm were calibrated to residual solvent signals. ¹³C NMR and ¹³P NMR spectra were recorded on a Bruker Avance- 500 spectrometer operating at 126 MHZ and 202 MHZ respectively. Gel permeation chromatography was carried out at 40 °C using 0.02 M sodium trifluoroacetate in TFE as eluent at a flow rate of 1 mL min ¹ with three Agilent PL gel mixed columns (300 x 7.5 mm) with refractive index (RI) detection and calibrated against poly (methyl methacrylate) standards. Thermogravimetric analysis (TGA) was performed on a Q500 TA instrument with a heating rate of 20 °C per minute under nitrogen atmosphere heating from 0 °C to 600 °C with a flow rate of 200 mL/min. Melting temperature (T,„) and crystallization temperature (T_c) were determined by differential scanning calorimetry (DSC) on a Q200 TA instrument under nitrogen atmosphere (method: heat from -20°C to 260 °C at 10 °C/min, isothermal at 260 °C for 2 min, cool from 260 °C to -20 °C at 10 °C/min, heat from -20 °C to 260 °C at 10 °C/min). Fourier-transform infrared (FT-IR) spectra was recorded on a PerkinElmer

Spectrum 100 spectrometer with an attenuated total reflectance (ATR).

[0051] Synthesis of 3-(3-propenyl)-2-azepanone (monomer 1). Monomer 1 was synthesized per the previous literature with some modifications e-caprolactam (1 g, 8.86 mmol) was added to a flame dried round bottom flask charged with stir bar and THF (52 mL). To the clear reaction mixture «-BuLi (3.54 mL, 9.38 mmol, 2.5 M in cyclohexanes) was added dropwise at -78 °C. After 15 min, chlorotrimethylsilane (1.17 mL, 9.26 mmol) was added dropwise to the reaction mixture at -78 °C followed by warming up the reaction to 0 °C for 15 min. The reaction mixture was cooled back to -78 °C and the clear reaction mixture was transferred carefully to a solution of freshly prepared LDA (20.3 mmol) at -78 °C. After 30 min, allyl bromide (1.87 mL, 22.1 mmol) was added at -78 °C dropwise, followed by warming to room temperature and stirring under nitrogen for 5 h. The reaction mixture was quenched by the addition of saturated ammonium chloride solution followed by separation with ethyl acetate. The organic phase was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure. The crude was purified by column chromatography with 3:2 (hexane: ethyl acetate) as eluent in silica to remove the yellow liquid impurity and the product was collected by flashing the column with 1 : 1 (hexane: ethyl acetate) as a white powder with -85% yield. ¾ NMR (500 MHz, CDCh, d, ppm): d 5.79(m, 1H), 4.98 (m, 2H), 3.22 (m, 2H), 2.54 (m, 1H), 2.41-2.02 (m, 2H), 1.92- 1.32 (m, 10H); ¹³C NMR (CDCh, 126 MHz): d 179.6, 137.2, 116.5, 43.4, 42.4, 35.9, 29.8, 29.6, 29.2.

[0052] General Procedure for Anionic Ring Opening Copolymerization. All the reagents were subjected to vacuum overnight and the reaction tubes used in the

polymerizations were flame dried. The polymerization was carried out in a flame dried glass tube charged with stir bar.

[0053] Synthesis of P4: Monomer 1 (370 mg, 2.4 mmol), e-caprolactam (1.7 g, 15.5 mmol) and the initiator C10 (319 mg, 0.4 mmol) was added to the reaction flask and the system was purged with nitrogen for 30 min (Figure 2b). The polymerization tube was heated to 140 °C by placing it into the oil bath. After the complete melting of the mixture, activator C20 (138 mg, 0.06 mmol) was added to the reaction mixture and the polymerization was carried out for 30 min under nitrogen atmosphere. To determine reaction kinetics, multiple polymerizations were carried out in polymerization tubes at different time intervals, followed by monomer conversion analysis by 'H NMR and molecular weight characterization by GPC. To terminate the polymerization, the tube was cooled to room temperature. For purification, the polymer was solubilized in hot TFE followed by precipitation in a non-solvent, ethyl acetate. Precipitation was carried out multiple times to remove excess monomers and other impurities and the precipitated polymer was dried under high vacuum to isolate polyamides with pendent allyl group (Pl-5) as a white fibrous solid. P4: ¾ NMR (500 MHz, TFE-d₃, d, ppm): d 5.50 (1.02H), 4.81 (2.00H), 2.97 (19.96H), 2.10-1.97 (20.81H), 1.41-1.21 (40.47H), 1.11 (20.89H); ¹³C NMR (CDCh, 126 MHz, d, ppm): d 179.6, 137.2, 116.5, 43.4, 42.4, 35.9, 29.8, 29.6, 29.2.

[0054] General Procedure for Thiol-Ene Click Photoreaction. Allyl-functionalized polyamide P4 was dissolved in minimum amount of TFE in a 20 mL glass scintillation vial charged with a stir bar. Respective thiols (3 equivalents with respect to alkene) and DMPA (0.3 equivalents) were added to the reaction vial as solids. The mixture was solubilized and degassed with nitrogen for 10-20 min. The reaction mixture was exposed to 365 nm (~3.5 mWcm²) light in a UV crosslinker chamber (model: CL- 1000L, UVP, Upland, CA) for 2 h at room temperature while stirring. P4a, P4b, P4d and P4e were purified by precipitation in ethyl acetate to afford off- white solid products with a typical yield of < 95%. Phosphoryl choline substituted polyamide P4c was purified by precipitation in THF, followed by dialysis against water and lyophilizing to obtain a white fluffy product with a yield of 85-90%.

[0055] P4f, the organogel, was obtained by solubilizing 50 mg of P4, (SH: alkene 3: 1) in the presence of DMPA in TFE, degassing with nitrogen for 10 min, and exposing to 365 nm UV light for 10 min.

[0056] P4g, the polymeric film, was obtained by drop casting the polymeric mixture (P4c) before UV exposure on a glass substrate and evaporating the solvent under the stream of nitrogen and exposing to 365 nm for 10 min.

[0057] The invention includes at least the following embodiments.

[0058] Embodiment 1 : A functionalized polyamide comprising repeating units of formula (I), formula (II), or a combination thereof

[0059] Embodiment 2: The functionalized polyamide of embodiment 1, comprising repeating units of formula (I).

[0060] Embodiment 3: The functionalized polyamide of embodiment 1, comprising repeating units of formula (II).

[0061] Embodiment 4: The functionalized polyamide of any one of embodiments 1 to 3, wherein x is 4.

[0062] Embodiment 5: The functionalized polyamide of any one of embodiments 1 to 4, wherein y is 1.

[0063] Embodiment 6: The functionalized polyamide of any one of embodiments 1 to 5, wherein the functionalized polyamide is a copolymer further comprising repeating units of formula (III)

wherein z is an integer from 1 to 12.

[0064] Embodiment 7: The functionalized polyamide of embodiment 6, wherein z is 4.

[0065] Embodiment 8: The functionalized polyamide of embodiment 6 or 7, wherein the copolymer comprises 1 to 99 mole percent of repeating units according to formula (III).

[0066] Embodiment 9: The functionalized polyamide of any one of embodiments 6 to 8, wherein the copolymer comprises 1 to 15 mole percent of repeating units according to formula (I); and 85 to 99 mole percent of repeating units according to formula (III).

[0067] Embodiment 10: The functionalized polyamide of any one of embodiments 6 to 8, wherein the copolymer comprises 1 to 15 mole percent of repeating units according to formula (II); and 85 to 99 mole percent of repeating units according to formula (III).

[0068] Embodiment 11 : The functionalized polyamide of any one of embodiments 1 to 10, wherein the functionalized polyamide has a number average molecular weight of 1,000 to 100,000 grams per mole, as determined using gel permeation chromatography relative to poly(m ethyl methacrylate) standards eluting in 2,2,2-trifluoroethanol. [0069] Embodiment 12: The functionalized polyamide of embodiment 1, comprising 1 to 15 mole percent of repeating units according to formula (I), formula (II), or a combination thereof; and 85 to 99 mole percent of repeating units according to formula (III); wherein x in formula (I) is 4; y in formula (I) is 1; z in formula (II) is 4; and the polyamide has a number average molecular weight of 10,000 to 75,000 grams per mole, as determined using gel permeation chromatography relative to poly(methyl methacrylate) standards.

[0070] Embodiment 13: A method of making the functionalized polyamide of embodiment 2, the method comprising: mixing a first monomer of formula (IV)

and a second monomer of formula (V)

to provide a reaction mixture; heating the reaction mixture to a temperature effective to melt the first monomer and, when present, the second monomer, in the presence of an initiator; and adding an activator to the reaction mixture to provide the functionalized polyamide; wherein x, y, and z are as defined in embodiments 1 and 6.

[0071] Embodiment 14: The method of embodiment 13, wherein the initiator comprises sodium caprolactamate.

[0072] Embodiment 15: The method of embodiment 13 or 14, wherein the activator comprises hexamethylene-l,6 dicarbamoylcaprolactam.

[0073] Embodiment 16: The method of any one of embodiments 13 to 15, wherein the reaction mixture is heated to a temperature of 130 to 160 °C.

[0074] Embodiment 17: A method of making the functionalized polyamide of embodiment 3, the method comprising: combining an allyl-functionalized polyamide comprising repeating units of formula (I)

and a thiol-functionalized compound of formula (VI)

HS-R¹ (VI)

in the presence of a radical initiator to provide the functionalized polyamide; wherein R¹ comprises a substituted or unsubstituted C_1-12 alkyl group, a substituted or unsubstituted C_6-2o aryl group, a zwitterionic group, a Ci-₆ alkyl ene oxide group, a Ci-₆ hydroxyalkyl group, a peptide group, or a combination thereof.

[0075] Embodiment 18: The method of embodiment 17, wherein the radical initiator is a photoinitiator, and the method further comprises exposing the reaction mixture to UV light.

[0076] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention.

The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

[0077] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0078] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. Each range disclosed herein constitutes a disclosure of any point or sub-range lying within the disclosed range.

[0079] The use of the terms“a” and“an” and“the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Further, it should further be noted that the terms“first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifier“about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity).

Claims

1. A functionalized polyamide comprising repeating units of formula (I), formula (II), or a combination thereof

wherein

x is an integer from 1 to 12;

y is an integer from 1 to 12; and

R¹ comprises a substituted or unsubstituted C1-12 alkyl group, a substituted or unsubstituted C₆-2o aryl group, a zwitterionic group, a Ci-₆ alkylene oxide group, a Ci-₆ hydroxyalkyl group, a peptide group, or a combination thereof.

2. The functionalized polyamide of claim 1, comprising repeating units of formula (I).

3. The functionalized polyamide of claim 1, comprising repeating units of formula (II).

4. The functionalized polyamide of claim 1, wherein x is 4.

5. The functionalized polyamide of claim 1, wherein y is 1.

6. The functionalized polyamide of claim 1, wherein the functionalized polyamide is a copolymer further comprising repeating units of formula (III)

wherein z is an integer from 1 to 12.

7. The functionalized polyamide of claim 6, wherein z is 4.

8. The functionalized polyamide of claim 6, wherein the copolymer comprises 1 to 99 mole percent of repeating units according to formula (III).

9. The functionalized polyamide of claim 6, wherein the copolymer comprises

1 to 15 mole percent of repeating units according to formula (I); and

85 to 99 mole percent of repeating units according to formula (III).

10 The functionalized polyamide of claim 6, wherein the copolymer comprises

1 to 15 mole percent of repeating units according to formula (II); and

85 to 99 mole percent of repeating units according to formula (III).

11. The functionalized polyamide of claim 1, wherein the functionalized polyamide has a number average molecular weight of 1,000 to 100,000 grams per mole, as determined using gel permeation chromatography relative to poly(methyl methacrylate) standards eluting in 2,2,2-trifluoroethanol.

12. The functionalized polyamide of claim 1, comprising

1 to 15 mole percent of repeating units according to formula (I), formula (II), or a combination thereof; and

85 to 99 mole percent of repeating units according to formula (III);

wherein

x in formula (I) is 4;

y in formula (I) is 1;

z in formula (II) is 4; and

the polyamide has a number average molecular weight of 10,000 to 75,000 grams per mole, as determined using gel permeation chromatography relative to poly(methyl methacrylate) standards.

13. A method of making the functionalized polyamide of claim 2, the method comprising: mixing a first monomer of formula (IV)

and a second monomer of formula (V)

to provide a reaction mixture;

heating the reaction mixture to a temperature effective to melt the first monomer and, when present, the second monomer, in the presence of an initiator; and

adding an activator to the reaction mixture to provide the functionalized polyamide; wherein x, y, and z are as defined in claims 1 and 6.

14. The method of claim 13, wherein the initiator comprises sodium caprolactamate.

15. The method of claim 13, wherein the activator comprises hexamethylene-l,6 di carb amoyl caprol actam .

16. The method of claim 13, wherein the reaction mixture is heated to a temperature of 130 to 160 °C.

17. A method of making the functionalized polyamide of claim 3, the method comprising: combining an allyl-functionalized polyamide comprising repeating units of formula

(I)

and a thiol-functionalized compound of formula (VI)

HS-R¹ (VI)

in the presence of a radical initiator to provide the functionalized polyamide;

wherein R¹ comprises a substituted or unsubstituted C1 - 12 alkyl group, a substituted or unsubstituted C₆-2o aryl group, a zwitterionic group, a Ci-₆ alkylene oxide group, a Ci-₆ hydroxyalkyl group, a peptide group, or a combination thereof

18. The method of claim 17, wherein the radical initiator is a photoinitiator, and the method further comprises exposing the reaction mixture to UV light.