Exploiting Ring-Opening AminolysisâCondensation as a

Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES

Exploiting Ring-Opening Aminolysis-Condensation as a Polymerization Pathway to Structurally Diverse Biobased Polyamides Geng Hua, and Karin Odelius Biomacromolecules, Just Accepted Manuscript • DOI: 10.1021/acs.biomac.8b00322 • Publication Date (Web): 27 Mar 2018 Downloaded from http://pubs.acs.org on March 27, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

Exploiting Ring-Opening Aminolysis-Condensation as a Polymerization Pathway to Structurally Diverse Biobased Polyamides

Geng Hua and Karin Odelius* Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, SE-100 44, Stockholm, Sweden *Corresponding author K.O. Email: [email protected]

ACS Paragon Plus Environment

Biomacromolecules 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 33

Abstract A pathway to biobased polyamides (PAs) via ring-opening aminolysis-condensation (ROAC) under benign conditions with diverse structure was designed. Ethylene brassylate (EB), a plant oil derived cyclic di-lactone, was used in combination with an array of diamines of diverse chemical structure and ring-opening of the cyclic di-lactone EB was revealed as a driving force for the reaction. The ROAC reactions were adjusted and reaction conditions of 100 °C, under atmospheric pressure using 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) as a catalyst for 24 h were optimal. The structure of the polyamides were confirmed by mass spectroscopy, FTIR and NMR and the PAs had viscosity average molecular weights (Mη) around 5-8 kDa. Glassy or semi-crystalline PAs with glass transition temperatures between 48-55 °C, melting temperatures of 120-200 °C for the semi-crystalline PAs and thermal stabilities above 400 °C were obtained and were comparable to the existing PAs with similar structures. As a proof-of-concept of their usage, one of the PAs was shown to form fibers by electrospinning and films by melt pressing. Comparing to conventional methods for PA synthesis, the ROAC route portrayed a reaction temperature at least 60-80 °C lower, could readily be carried out without a low-pressure environment and eliminated the use of solvents and toxic chemicals. Together with the plant oil derived monomer (EB), the ROAC route provided a sustainable alternative to design biobased PAs. Key

words:

Polyamide,

Biobased,

Aminolysis,

Ethylene


brassylate,

Ring-opening

Page 3 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

Introduction Polyamides (PAs) are one of the most applied commodity polymers with some 7 million tons of global consumption during 2015 and a steady annual global growth of 5% during the past decade.1 PAs have successfully been used in applications ranging from textiles for daily wear to high-performance specialty materials such as fuel lines and automotive parts.2 This is due to the strong intermolecular hydrogen bonding (H-bonding) between the amide linkages, tunable building blocks, good fiber-forming properties and chemical and heat resistance. In the pursuit of more sustainable PAs, two important and separate characteristics are considered: the use of biobased resources as building-blocks for the PAs and the development of synthesis routes with less environmental impact.3 Biobased PAs hence entail the replacement of conventional petroleum-based building blocks by e.g. plant oil derived chemicals.4–6 Commercialized biobased PAs can be exemplified by EcoPaXX® from DSM and VESTAMID® Terra from Evonik Industries, featuring PAs that are 45% - 100% biobased from castor oil derived chemicals.7,8 The synthesis of biobased PAs, which is also applicable to non-biobased PAs, is based on one of two routes: 1) the A-A B-B approach, exemplified by the melt-polycondensation of the diamine(A-A)-diacid(B-B) salt9 and 2) the A-B approach, exemplified by aminolysiscondensation of the ω-amino acid-ester.10 During the first route (A-A B-B approach), a diaminediacid salt is initially made through precipitation. The melt polycondensation of the formed salt subsequently takes place under high temperature in an autoclave yielding PAs as the desired product. In the second route (A-B approach), an ω-amino acid-ester is first prepared. A base



catalyzed intermolecular nucleophilic attack on the ester carbonyl from the free amine, noted as aminolysis, subsequently occurs upon heating and the reoccurrence of the aminolysis with the elimination of a condensate forms the PA product. Although different in mechanisms, the starting materials are either partially or completely derived from plant oil in both preparation routes to biobased PAs.11 The concept of utilizing a cyclic structure as a difunctional monomer to drive the reaction towards PA synthesis intrigued us; and ethylene brassylate (EB), a plant oil derived chemical, was an interesting candidate. EB is a 17-membered cyclic di-ester (di-lactone), which is widely used in the fragrance industry as a scent additive.12 As a macrolactone, some recent studies have shown the homo-polymerization of EB yielding the corresponding polyester through base catalyzed ring-opening polymerization (ROP)13, and enzymatic ROP in combination with diamine forms a poly(ester-amide).14 The potential of EB in making biobased PAs lays in the unique cyclic structure itself as the di-functional ring makes EB a B-B type monomer. Upon the addition of an A-A diamine, base catalyzed intermolecular aminolysis should appear with the formation of PA as the product. In addition, the slight ring strain increases the reactivity of the ester bonds15, which could facilitate the aminolysis when comparing to the linear (non-cyclic) counterpart. We aimed to synthesize biobased PAs through base catalyzed ring-opening aminolysiscondensation (ROAC) utilizing the ring-strain of EB, although low, as a driving force and design a PA synthesis methodology as a proof-of-concept. Our criteria included the following: the synthesis should be solvent-free, should utilize the mildest aminolysis-condensation reaction conditions possible, and should produce neat PAs, rather than poly(ester-amide)s, with the thermal properties and fiber- and film-forming abilities of commercial petroleum-based PAs. The


Page 4 of 33

Page 5 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

aminolysis-condensation method should also be versatile and adaptable to various diamines. The devised reaction paths will be studied, and model reactions regarding the overall ring-opening of EB and aminolysis-condensation will be investigated.

Experimental Materials 1,4-Diazacyclohexane (A, 99%), 1,3-bis(aminomethyl)benzene (B, 99%), 1,3-byclohexanebis(methyl-amine)

(C,

99%),

1,10-diaminodecane

(D,

97%),

2,2’-(ethylenedioxy)-

bis(ethylamine) (E, 98%), 1,6-hexanediamine (H, 98%), 1,3-pentanediamine (P, 98%), ethylene brassylate (EB, 95%), m-cresol (99%), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD, 98%), 1,8diazabicyclo[5.4.0]undec-7-ene (DBU, 99%), trimethylamine (TEA, 99.5%), acetone (99%), acetic acid (99%), diethyl sebacate (98%), potassium trifluoroacetate (KTFA, 98%) and 1,8,9anthracenetriol (98%) were purchased from Sigma-Aldrich. Bis(aminomethyl)-norbornane (N, 98%) was purchased form TCI, Japan. 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP, 98%) was purchased from Apollo Scientific, UK. Chloroform-D (CDCl3, 99.8%) was purchased Cambridge Isotope Laboratories. All chemicals were used as received. General route for PA synthesis General procedure of PA synthesis: the desired amount of diamine C (3.32 g, 23.1 mmol) was weighed into a 100 mL round-bottom flask equipped with a magnetic stirring bar and the vessel was lowered into a preheated oil bath at 80°C. The basic catalyst TBD (0.54 g, 3.87 mmol, ~8 mol% to –NH2) was then added to the flask which was subsequently dissolved by the diamine. After 30 minutes upon mixing, ethylene brassylate (6.31 g, 22.1 mmol) was gradually added to the mixture. The reaction was left for 4 h before the temperature was elevated to 100 °C. After



the desired total reaction time 5 – 24 h, the reactions were thermally quenched. The raw product was transferred into glass containers and stored in a -20 °C freezer for future analysis. Instrumentation Nuclear magnetic resonance (NMR) The 1H-NMR (400.13 MHz) NMR spectra were recorded using an Avance 400 (Bruker, USA) spectrometer at 298 K. Fourier transform infrared spectroscopy (FTIR) spectra of all purified PA powders were recorded using a Perkin Elmer Spectrum 2000 FTIR spectrometer (Norwalk, CT) equipped with a single reflection attenuated total reflectance (ATR) accessory. The spectra were scanned at 2 cm−1 resolution in the 4000– 600 cm−1 range. Size exclusion chromatography (SEC) was used to obtain the elugram of model samples using a Verotech PL-GPC 50 Plus system equipped with two Mixed-D (300 x 7.5 mm) columns and a PL-RI detector. Chloroform was used as the mobile phase with a flow rate of 1 mL/min at 30 ˚C, and toluene was used as the internal standard for flow rate fluctuation corrections. Thermal gravimetric analysis (TGA) was performed using a TGA/DSC 1 (Mettler-Toledo, USA) with temperature from 50 - 600 °C. Differential scanning calorimetry (DSC) of the PA was measured using DSC equipment (Mettler-Toledo DSC 1 Module) with temperature from 50 - 600 °C. Matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS) was performed on a Bruker UltraFlex unit (Bruker Daltonics, Germany) equipped with an SCOUT-MTP ion source and 337nm N2 laser. Scanning electron microscopy (SEM) was used to examine the morphology of the PA-C nanofibers using a Hitachi S4800 microscope with an accelerating voltage of 1.0 kV. The samples were sputter-coated with Ag-Pd using a Cressington 208HR unit. The detailed sample preparation procedures and parameter set-ups can be found in the SI.


Page 6 of 33

Page 7 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

Viscosity measurement The viscosity average molecular weight Mη was evaluated by capillary solution viscometry. Each PA sample was dissolved in m-cresol at four different concentrations (~ 0.6, 0.7, 0.8 and 0.9 g/dL). The measurement was conducted using a LAUDA iVisc Capillary Viscometer equipped with an Ubbelhode viscometer. The measurements were conducted at 25 ± 0.1 °C in a water tank and three time intervals within a ± 0.02 s range was selected for the calculation. Electrospinning The electrospinning was performed on a lab assembled electrospinning unit. The PA was dissolved in HFIP at a concentration of 20 % (w : v) and was passed through a 0.45 µm PTFE filter right before spinning. High voltage (17.5 kV) was applied and the solution injection rate was controlled with a syringe pump at 0.35 mL/h. The fibers were collected horizontally on an aluminum foil at a distance of 15 – 25 cm.

Results and discussion Overview of aminolysis reactions used in polymer synthesis A biobased PA synthesized through ROAC is proposed here. The general biobased origin of the PA comes from the EB building block, which is a cyclic di-lactone derived from rapeseed oil and castor oil. The general aminolysis pathway and the aminolysis-condensation pathway are illustrated below (Figure 1a).



Figure 1. Compilation of amdiation through ester aminolysis. a) General reaction for ethyl ester aminolysis forming amide; b) AB type aminolysis-coondensation to form PA, where A represents the amine group and B represents the ester group; c) A-A B-B type aminolysis-condensation forming PA; d) proposed A-A EB ring-opening aminolysis-condensation route.

The aminolysis approach has been applied in organic synthesis to create amide bonds, with examples ranging from drug intermediates16,17 to polyol monomers.18 When applying aminolysis to create polymers directly, the structure of the building blocks can either be A-B type where A is an amine and B is an ester that coexist on the same molecule as an amino acid-ester (Figure 1b); or the building blocks are A-A (diamine) B-B (di-ester) type, where the aminolysis occurs between the diamine and the di-ester (Figure 1c).19 The A-B type can be exemplified by the


Page 8 of 33

Page 9 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

enzymatic aminolysis of α-amino acid ethyl esters to form peptides20 and thermal aminolysis of amine-containing carboxylic acid methyl esters, with the release of methanol as the ”condensate”.10 When using EB as the building block for PAs, the approach falls into the AA B-B scheme, where the cyclic EB is the B-B monomer, Figure 1d. The most likely reaction mechanism being nucleophilic attack of the A-A diamine on one of the two ester groups of EB occurring under the catalysis of a base, releasing the ring strain of EB, subsequently forming an ethylene glycol end. Then the amine-ethylene glycol would go through intermolecular aminolysis, releasing ethylene glycol as the “condensate”, and subsequently formed the polyamide (Figure 1d). For an aminolysis reaction, the reaction temperature, the basicity of the catalyst and the structure of the amine greatly influences the overall conversion.21 This is important for the synthesis of small molecules, but becomes even more crucial when the aminolysis is to be utilized in aminolysis-condensation polymerization. The reason is that, similarly to classic step-growth condensations, the product is still a low molecular weight oligomer even when the monomer conversion is above 90%.22 To make an applicable biobased PA, it is essential to optimize the aminolysis-condensation reaction for a desired molecular weight. Hence, a model strategy focusing on the influence of catalyst basicity and reaction temperature on the reaction needs to be conducted. When choosing a model diamine compound for the aminolysis of EB, the following criteria were considered: the diamine being an unhindered primary diamine so that it can accurately reflect the influence of the base catalysts; the diamine being a liquid at room temperature miscible with EB to establish the lowest reaction temperature range for aminolysiscondensation; the diamine at the same time having a high boiling point so that no reactant loss will occur at elevated temperatures. When considering the above guidelines, 1,3-cyclohexane



bis(methylamine) (noted as diamine C in the following text) was chosen as the model diamine (Figure 2a).

Model reactions for catalyst and reaction temperature assessment Initially, the influence of the strength of the base catalyst on the reaction was scrutinized. A great many studies have reported the mechanism of base catalyzed aminolysis of esters.23–27 A correlation between conversion and the basicity of the catalyst in aminolysis reactions was revealed, and the general trend was that a stronger base made the reaction proceed faster promoting higher yields of amide products.25,28–30 It is therefore logical to use a previously studied strong base as the catalyst. However, since EB by nature is a cyclic lactone, ROP occurs when a strong base is added as a catalyst.31 This pathway may act as a side reaction and can result in polymeric products that have ester linkages in addition to amide linkages. Some recent studies showed that lactone aminolysis readily occurs at room temperature when catalyzed by a weak base such as TEA for small molecule synthesis.32 The mild base TEA was therefore the starting point for catalysis comparisons, alongside two stronger organic bases i.e. DBU and TBD.


Page 10 of 33

Page 11 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

Figure 2. Base catalyzed aminolysis and aminolysis-condensation reactions. a) The structures of the applied base catalysts, TEA, DBU and TBD and the ROAC between ethylene brassylate and 1,3-cyclohexanebis(methylamine); b) compiled FTIR spectra for catalysis comparisons between the different bases; c) compiled FTIR spectra for temperature-dependence of aminolysiscondensation catalyzed by TBD.

Upon mixing the diamine C, EB and base catalyst (~8 mol% to –NH2 of loading for all entries) at room temperature, a solidification point of the liquid reaction mixture was reached shortly after 30 minutes for the TBD-catalyzed reaction, while no visual alteration occurred for the DBU and TEA catalyzed reactions during the complete reaction time (Figure S1). This indicated that a TBD catalyzed reaction took place, since the solidification of the reactant mixture occurred due to the formation of immiscible compounds. Crude samples were recovered after one hour and subsequently analyzed with FTIR. For the TBD catalyzed reaction, a significant decrease in the intensity of the band at 1733 cm-1 (C=O ester stretching of EB reference) was found and coupled



to the appearance of three other bands at 1548 cm-1 (N-H binding, C-N stretching), 1638 cm-1 (C=O stretching, amide) and 3295 cm-1(N-H H-bonding).33 This confirmed the abundant amide bond formation (Figure 2b) for the TBD catalyzed aminolysis. As comparison, for the DBU catalyzed reaction a band around 1620 cm-1 with very low intensity was found, representing a low conversion of the ester bonds to amide; whereas the TEA catalyzed and the uncatalyzed reactions showed no shifts in the carbonyl region. All the reactions were allowed to proceed for an additional 15 h (total reaction time 16 h), upon which the ester carbonyl adsorption band from EB (1733 cm-1) had almost disappeared for the TBD catalyzed reaction, while no differences in intensities were seen between the other catalyzed and uncatalyzed reactions (Figure S2). One of the goals was to reduce the reaction temperature as much as possible as a means to address environmental concerns, while reaching an applicable PA product. To establish the lowest possible reaction temperature for the aminolysis-condensation to achieve high conversion, the reaction was conducted at RT, 40 °C, 80 °C and 100 °C. These reactions were allowed to proceed for the same time length as before (16 h) and the crude product was examined by FTIR. The ester carbonyl stretching band from EB decreased with increasing temperature, and completely disappeared for the reaction conducted at 100 °C (Figure 2c). This confirmed that an elevated temperature further pushes the aminolysis reaction when TBD acts as catalyst and indicated that 100 °C should be enough. Model reactions to investigate the ROAC path The base-strength and temperature dependence reactions lead us to choose TBD as principle catalyst for the aminolysis-condensation at 100 °C. However, in this particular system it can be adventurous to use TBD as the catalyst for the aminolysis-condensation reaction. Since unlike


Page 12 of 33

Page 13 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

DBU or TEA, ROP of EB may occur as a prominent side reaction when adding TBD as a catalyst.13 This would directly result in either a mixture of polyester and PA or a poly(esteramide) copolymer as the final product. We hypothesized that there are two possible reaction routes can occur. The first reaction route relies on a strongly favored aminolysis reaction over the ROP of EB. Although hydroxyl groups and ethylene glycol are produced during the ROAC, this reaction would rely on the nucleophilicity of the amine groups greatly surpassing the nucleophilicity of the hydroxyl group and thereby the reaction would solely be of an aminolysiscondensation type (Figure 3a, route 1). The second possible route is that a small amount of ROP of EB occurs during the reaction (Figure 3b, route 2). The resulting esters and ester-amide products would subsequently undergo intense aminolysis by the free amines. Ester cleavage by amine catalyzed by TBD would then continue until all ester bonds are replaced by amide bonds. To elucidate the reaction route, a model aminolysis kinetic study was performed (Figure 3c).



Figure 3. Proposed reaction routes and aminolysis-condensation kinetics. a) Proposed route for the TBD-catalyzed aminolysiscondensation reactions without the ROP of EB as a side reaction which results in a pure polyamide; b) proposed route for the TBD-catalyzed aminolysis-condensation reactions with the ROP of EB as a side reaction which results in a polyester-amide random copolymer as the product; c) aminolysis kinetics using mono-functional amine. 1st addition included 1.05 eq hexylamine, 1 eq EB and 0.08 eq TBD, Mixture 1 was the crude product after 10 minutes of addition, and the lower retention time products in the SEC elugram (900 - 1000 s) corresponded to oligo-amide-esters. 2nd addition included 0.95 eq hexylamine and 0.08 eq TBD; Product 1 was the crude product after 30 minutes upon 2nd addition. The disappearance of the oligo-amide-ester was clearly shown and the single peak in the SEC elugram corresponded to the di-hexylamine substituted product.

The model reaction was set as a two-step reaction where we would like to see: 1) if ROP occurred when combining a mono-functionalized amine base (1.05 eq) with EB (1 eq) and TBD (0.08 eq) and 2) if the potentially formed ROP product can undergo aminolysis and produce aminolysis products alone. First, TBD (0.08 eq), EB (1 eq) and hexylamine (1.05 eq) was allowed to react for 10 min at 100 °C, after which a crude reaction sample was analyzed using SEC (Mixture 1, Figure 3c). The SEC trace suggested the existence of more than one product at this stage of the reaction (Figure S3, SEC elugram). Due to the mono-functionality of hexylamine, polymers could not be formed solely through the aminolysis route. This illustrates


Page 14 of 33

Page 15 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

that ROP of EB occurred through the generated hydroxyl groups upon aminolysis and that this reaction was catalyzed by TBD (Figure S4, S5, 1H NMR). The mixture was allowed to proceed at 100°C for an additional 2 h and was then analyzed by SEC. No significant changes were observed in the SEC trace, and hence the reaction had reached end-point already after 10 min (Figure S5, SEC elugram). A second quantity of hexylamine (0.95 eq) with the corresponding amount of TBD (0.08 eq) was added to the reaction mixture, and subsequent the intensities of oligo-amide-ester peaks drastically decreased and disappeared (Figure S6, elugram compilations), and a narrowed single peak was observed by SEC (noted Product 1, Figure 3c). Through the kinetics, it is clear that even when ROP of EB occurred during the ROAC reaction, the formed mixture will transform to the amide product under the catalysis of TBD. Based on the qualitative results from FTIR and SEC, a solid confirmation of the aminolysis-condensation between EB and C was thus obtained.

Quantitative analysis of the PA-C product To ensure that the ROAC led solely to PA, rather than PA with ester linkages or a poly(esteramide), quantitative analysis was carried out utilizing MALDI-ToF MS to evaluate both the purity of the linkages within one molecular chain and achieve an indication of the molecular mass.34 As is shown in Figure 4, a single population of PA molecular ions solely constituted of amide linkages was confirmed. Based on the calculation of the found mass, three populations of PAs with different end-groups were identified. The most prevalent end-group combination was determined to be NH2-PA-NH2, which was favored over NH2-PA-COOH (noted as a) and NH2PA-OH (noted as b). This is as expected, since the two starting materials, diamine C and EB, were added in slightly off-stoichiometric amounts with 1.05 eq of diamine C over 1 eq of EB.



The detailed calculations for the NH2-PA-COOH and NH2-PA-OH combinations can be found in the SI (Figure S7, MALDI-ToF MS calculation).

Figure 4. MALDI-ToF mass spectra of purified PA-C. Full MALDI-ToF mass spectra of the PA-C sample and zoom-in area of higher molecular weight peaks. The calculation showed that the dominate peaks were the PA-C chains with amine terminal groups on both ends (NH2-PA-NH2), peak a represented the NH2-PA-COOH chains and peak b represented the NH2-PA-OH chains.

It is well known that MALDI–ToF MS has a molecular weight discrimination for disperse samples, i.e. species of relatively lower molecular weights are easier to detect than the higher molecular weight ones.35 SEC can give a relative value of the number and weight average molecular weights; however, PAs are insoluble in most common SEC solvents such as chloroform, toluene, or N,N-dimethylformamide (DMF). Therefore, solution viscometry, widely used for PA analysis, was applied to find the viscosity average molecular weight (Mη). To ensure the accuracy of the calculated Mη, four solutions of different concentrations were prepared using


Page 16 of 33

Page 17 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

m-cresol as solvent. At least three time intervals within a ± 0.02 s range were selected for the Mη calculation (for detailed calculations see Table S1). The Mark-Houwink equation ([η] = KMα) was applied in the following form (Eq. (1)).36, 37 [η] = 0.5+0.0353M0.792

(1)

Linear fits for both ηred and lnηr/c were shown for the PA-C samples and a calculated Mη ~6.4 k was obtained (Figure 5). This acquired value is slightly lower as compared to other reported PAs with similar chain structures. Several factors could contribute to this lower value including the existence of ethylene glycol in the system; a poor fit to the Mark-Houwink equation (eq. 1); the off-stoichiometric balanced addition of reactants; relatively low reaction temperature and the use of the cyclic monomer EB. The “condensate” ethylene glycol, formed during the ROAC, will remain in the system at the applied reaction temperature (100 °C) as it is lower than ethylene glycol’s boiling point. The risk of “glycolysis” as a competing reaction that would break the formed amide bond can be neglected as it should appear at a much higher temperature (≥250 °C), with excess amount of ethylene glycol and either with or without the catalysis of an acid.38,39 The Mark-Houwink equation is based on linear PA, PA-6,6, which is not the structure under evaluation here where a cyclohexane unit-containing product is measured.37 The system was also designed with a slightly off-stoichiometric balance to inhibit the molecular weight from getting overly high. A PA-C synthesized under the same conditions but with the reactants in stoichiometric balance was also analyzed, and the viscosity of the solution (Figure 5, point a) was higher than that of the off-stoichiometric products. Hence, the expected and typical feature of condensation was found, where a stoichiometric balance influences the molecular weight of the final product. The reaction temperature can also be a major factor influencing the molecular weight of the product, as ester aminolysis most often is an endothermic reaction. Thus, a reaction



between diamine C (1.05 eq) and EB (1 eq) using TBD as catalyst was conducted at a much higher temperature (170 °C). To our surprise, the resulting product had an almost identical viscosity and hence molecular weight (Figure 5, point b) to those prepared at 100 °C. This suggested that the influence from temperature is not significant once the reaction is conducted at 100 °C and above. Since the di-ester monomer being used is the cyclic EB, our hypothesis of the ring-structure being a driving force to achieve the PA was evaluated. A linear di-ester analogue, diethyl sebacate, was used for this assessment and the aminolysis-condensation was carried out with diamine C, under the catalysis of TBD at 100 °C. The resulting product had a much lower viscosity (Figure 5, point c) than those prepared with EB and hence the molecular weight. The cyclic structure, thus, greatly promoted the reactivity of the ester functionalities, which assisted the aminolysis-condensation to reach higher conversion. From the above observations, the inherent cyclic structure of EB and the stoichiometric balanced addition of the two components are the most important factors determining the molecular weight of the final product and a higher molecular weight product was obtained when the monomers were added stoichiometrically. Thus, we have successfully established the use of ROAC to synthesis PA using EB and diamine C with TBD as the catalyst. Comparing to the study using EB as the building block for PA through N435 enzymatic catalysis14, the ROAC route was carried out at a lower temperature, with a shortened reaction time, eliminated the use of solvent during synthesis and it resulted in a neat polyamide product rather than poly(ester-amide).


Page 18 of 33

Page 19 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

Figure 5. Intrinsic viscosity plots of PA-C using m-cresol as the solvent, solution concentrations were around 0.6 g/dL, 0.73 g/dL, 0.85 g/dL and 0.93 g/dL respectively. Each point was calculated as the average values of at least three different time intervals within a 0.02 s differences. The intercept, [η], was from the linear fit that had higher r2 values and in this case was 0.372 dL/g. The red squares represent the samples prepared at 100 °C with 1.05 eq of diamine C, the straight connection line is the linear fit; the red triangle (point a) represent the sample prepared at 100 °C with 1.0 eq of diamine C; the red diamond (point b) represent the samples prepared at 170 °C with 1.05 eq of diamine C; the red circle (point c) represent the samples prepared at 100 °C with 1.05 eq of diamine C and 1 eq of diethyl sebacate.

Generality of the ROAC reaction and characterizations To ensure the generality of the ROAC for PA synthesis (Figure 6a), an array of diamines where selected and factors such as alkyl chain length (D and H), aromatic groups (B), bulky groups (N), ether linkages (E), steric hindered primary amine (P) and secondary amine (A) were all taken into consideration. From the IR spectra of the raw PA products (Figure 6b) it is determined that identical shifts are found, i.e. 1548 cm-1 (N-H binding, C-N stretching, not showing for PA-A due to the lack of hydrogen), 1638 cm-1 (C=O stretching, amide) and 3295 cm-1 (N-H H-bonding, not showing for PA-A due to the lack of hydrogen). The C=O stretching (ester) absorption band at 1728 cm-1 was very weak (PA-A, PA-B, PA-E, PA-P) to no intensities (PA-C, PA-D, PA-H, PA-N), meaning that the aminolysis reaction reached high conversion for all entries. The results from solution viscometry had good linear fits for all samples and the compiled [η] showed



similar values (Figure S8). PA-P was as an exception, for which the viscosity increased so minutely that, even at a concentration as high as ~3 g/dL (comparing to others at ~0.6 g/dL), the difference between the solution and the pure m-cresol solvent was negligible. This was caused directly by the low molecular weight of the product, which in turn was caused by the lower reactivity of the steric hindered primary amine of diamine P that only has one-hundredth of the reactivity of the unhindered primary amine.2 TGA was used to assess the thermal stability of the formed PAs. The decomposition temperatures (Td), both Td, onset (5% measured weight loss) and Td, max, fall into two separate groups with similar ranges, Figure 6c. The first group (PA-B, PA-E and PA-P) with Td, onset around 400 °C and Td, max around 420 °C; the second group (PA-A, PA-C, PA-D, PA-H and PAN) with Td, onset around 450 °C and Td, max around 470 °C. The group of PAs with reduced Tds fit well with the group of PAs with comparably higher intensities of ester carbonyl absorption in the IR spectra (Figure 6b, PA-A, PA-B, PA-E and PA-P). Since the PAs all have similar calculated Mη (Table 1), the reduced Tds most likely are caused by higher ester content as exemplified by the poly(ester-amide)s with similar structures.14 For the group with higher Tds (PA-C, PA-D, PAH and PA-N), the samples were invariably alkyl structures with either different chain length (A, D and H) or different bulkiness (A, C and N) which have very close basicity between one another. While the group with the lower Tds (PA-B, PA-E and PA-P), the diamines B, E and hindered amine of P have comparably lower basicity than the other diamines, and the decreased basicity of the diamine monomer can directly lower the conversion of the aminolysis reactions.40,41 Based on the nomenclature of A-A B-B type of PAs, the formed PA products from the ROAC of EB are denoted PA-X,13 where X refers to the structure of the diamine and 13 refers to the


Page 20 of 33

Page 21 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

carbons contributed by EB. When one or both of the building blocks of PA-X,Y reaches above 10, the corresponding PA is regarded as a long-chain PA.42 The melting temperature (Tm) of PAX,13 were compared to the long-chain PAs with similar structures (prepared through diacid and diamines), and the values were close to the reported ones ranging a Tg between 48-55 °C and a Tm of 120-200 °C.33,42 The determined Tms also match the expected structure-property relationship originating from the variations in the amines chemical structure well. PA-A that cannot form H-bonding and correspondingly has a lower Tm as compared to the other PAs, PA-N with its bulky side-group is amorphous, PA-D with a longer alkyl chain compared to PA-H has a reduced Tm and PA-E with ether linkages portrayed a lower Tm compared to PA-D and PA-H for example. The temperature difference between Tm and Td is considered as the processing window. For the PA-X,13 we reported here, the processing window is around 250 °C to 300 °C, exhibiting a good temperature range.42 The calculated molecular weight (Mη) from solution viscometry, the Tm and the Td of the purified samples are concluded in Table 1.



Page 22 of 33

Figure 6. Generality of the ROAC reaction and characterization of the corresponding products. a) Selected diamines and their naming. The capital letters in red italic in the full name corresponded to the diamines in the main text; b) FTIR compilation of the purified product; c) TGA compilation of the purified products.

Table 1. Summary of physical properties of the purified PA products. -3 e

Tg/°Ca

Tm/°Cb

Td,onset/°Cc

Td, max/°Cd

PA-Ag

45.6

124.2

456.6

476.8

5.3

294.45

36

PA-B

54.0

161.2

396.1

410.6

6.6

344.51

38

PA-C

52.3

178.6

450.0

470.3

6.4

348.51

36

PA-D

50.1

181.2

445.4

466.5

6.1

380.63

32

PA-E

48.8

164.2

399.1

426.8

6.5

356.52

36

PA-H

52.6

196.1

441.6

464.3

6.5

324.52

40

PA-N

48.8

-

445.2

465.5

8.4

362.57

46

a

Mη*10

collected from the first heating scan collected form the second heating scan c Td onset at 5 wt% mass loss d Td maximum e determined by solution viscometry, using m-cresol as solvent and calculated against eq. (1) f rounded up/down to the closest integer g PA-A was polymerized at 120°C and all others were polymerized at 100°C for 24 h. b


f

Mrep

Page 23 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

Fiber and film formation from PA-C A direct method to evaluate the ROAC of PA was to assess if they could be processed into fibers or films. The main concern was associated with the comparably low molecular weight. Commonly, polymers with low molecular weight have poor to no film and fiber formation properties due to the lack of chain entanglement.43,44 As a fiber-forming polymer, PA nanofibers has shown great potential as a substrate for a variety of applications ranging from sensors for detection 45,46, bundles with enhanced conductivity47 to filtration membranes.48,49 Electrospinning was used to form PA-C fibers from HFIP solutions and the fibers were collected horizontally for ten minutes on the aluminum foil. From the SEM images below (Figure 7a-c), well-defined nanofibers (⌀ ~150 nm) with smooth surface were obtained, and no beads or large droplets were seen on any of the fibers. The crude PA-C samples were also granulated and melt-pressed into thin films that came with good flexibility (Figure 7d).



Figure 7. SEM images of the formed fibers and a photo of the melt-pressed films. a-c) SEM images of the collected fibers from electrospinning. PA-C (prepared with stoichiometric balanced addition of the monomers) was dissolved at a concentration of 20 % (w:v) in HFIP (1,1,1,3,3,3-Hexafluoro-2-propanol) and was spun under 17.5 kV at a pumping rate of 0.35 mL/h. The fibers were collected horizontally for 10 min on aluminum foils. The diameter of the fibers was analyzed using Image J software and an average value around 150 nm was presented; d) crude PA-C was granulated into powder in a grinding crucible and the meltpressed at 200 °C for 3 minutes. The photo showed the integrity and flexibility of the formed thin film.

Conclusion In summary, the synthetic methodology, i.e. ring-opening aminolysis-condensation, we developed in this study has for the first time been successfully applied to make biobased and pure PA from ethylene brassylate utilizing TBD as catalyst at as low temperature as 100 °C. Unlike the conventional salt-condensation method to make PA, the aminolysis-condensation method eliminates the use of solvent throughout the entire route. Pure PA with diamine terminal chain-ends was obtained as the major product with a measured Mη above 6k. The cyclic structure of the EB increases the reactivity of the ester groups, which makes the aminolysis-condensation reach higher conversion comparing to the linear di-ester analogue. The resulting products can be


Page 24 of 33

Page 25 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

easily formed into both nanofibers and thin films. The selected diamines with a variety structures shows the generality of the aminolysis-condensation method. The Tm and Td are in the same range as the structurally similar long-chain PAs. With the increasing interest and demand for biobased PAs, we envision a great opportunity for this methodology to thrive along the development and explorations of new renewable materials.

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Photographs and IR of raw samples for catalysis comparisons, SEC elugrams, 1H-NMR and their compilations of the corresponding raw material and aminolysis intermediates, MALDI-ToF calculation of molecular ion peaks, sample calculation of intrinsic viscosity and compilation of intrinsic viscosities for different PA samples.

Author Information Corresponding Author * E-mail: [email protected]. Tel.: +46-8-790 80 76 (K.O.) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes



The authors declare no competing financial interest.

Acknowledgement This work was financially supported by the Swedish Research Council, VR (grant ID: 621201356 25).

References (1)

Scheibitz, M.; Kanebo, R.; Spies, P. Polyamide 6 and 66 (PA6 and PA66) Demand for Polyamides Is Determined by Asia and the Automotive Industry. Kunststoffe Int. 2016, No. 10, 40–44.

(2)

Marchildon, K. Polyamides - Still Strong After Seventy Years. Macromol. React. Eng. 2011, 5, 22–54.

(3)

Lancaster, M. Green Chemistry: An Introductory Text, 2nd Editio.; The Royal Society of Chemistry: Cambridge, 2010.

(4)

Wang, Z.; Wei, T.; Xue, X.; He, M.; Xue, J.; Song, M.; Wu, S.; Kang, H.; Zhang, L.; Jia, Q. Synthesis of Fully Bio-Based Polyamides with Tunable Properties by Employing Itaconic Acid. Polymer (Guildf). 2014, 55, 4846–4856.

(5)

Jiang, Y.; Loos, K. Enzymatic Synthesis of Biobased Polyesters and Polyamides. Polymers (Basel). 2016, 8, 243.

(6)

van Velthoven, J. L. J.; Gootjes, L.; Noordover, B. A. J.; Meuldijk, J. Bio-Based, Amorphous Polyamides with Tunable Thermal Properties. Eur. Polym. J. 2015, 66, 57–66.


Page 26 of 33

Page 27 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

(7)

EcoPaXX® - DSM http://www.dsm.com/products/ecopaxx/en_US/home.html (accessed Mar 26, 2018).

(8)

VESTAMID® Terra - VESTAMID®—A history of the evolution of high-performance polyamides http://www.vestamid.com/product/vestamid/en/products-services/vestamidterra/Pages/default.aspx (accessed Mar 26, 2018).

(9)

Samanta, S.; He, J.; Selvakumar, S.; Lattimer, J.; Ulven, C.; Sibi, M.; Bahr, J.; Chisholm, B. J. Polyamides Based on the Renewable Monomer, 1,13-Tridecane Diamine II: Synthesis and Characterization of Nylon 13,6. Polymer (Guildf). 2013, 54, 1141–1149.

(10)

Kolb, N.; Winkler, M.; Syldatk, C.; Meier, M. A. R. Long-Chain Polyesters and Polyamides from Biochemically Derived Fatty Acids. Eur. Polym. J. 2014, 51, 159–166.

(11) Ogunniyi, D. S. Castor Oil: A Vital Industrial Raw Material. Bioresour. Technol. 2006, 97, 1086–1091. (12)

Sell, C. Ingredients for the Modern Perfumery Industry. In The Chemistry of Fragrances; Royal Society of Chemistry: Cambridge, 2006; Vol. 6, pp 52–131.

(13)

Pascual, A.; Sardon, H.; Veloso, A.; Ruipérez, F.; Mecerreyes, D. Organocatalyzed Synthesis of Aliphatic Polyesters from Ethylene Brassylate: A Cheap and Renewable Macrolactone. ACS Macro Lett. 2014, 3, 849–853.

(14)

Ragupathy, L.; Ziener, U.; Dyllick-Brenzinger, R.; von Vacano, B.; Landfester, K. Enzyme-Catalyzed Polymerizations at Higher Temperatures: Synthetic Methods to Produce Polyamides and New Poly(amide-Co-Ester)s. J. Mol. Catal. B Enzym. 2012, 76, 94–105.



(15) Baker, M. B.; Ferreira, R. B.; Tasseroul, J.; Lampkins, A. J.; Al Abbas, A.; Abboud, K. A.; Castellano, R. K. Selective and Sequential Aminolysis of Benzotrifuranone: Synergism of Electronic Effects and Ring Strain Gradient. J. Org. Chem. 2016, 81, 9279–9288. (16)

Ye, W.; Xu, J.; Tan, C.-T.; Tan, C.-H. 1,5,7-Triazabicyclo[4.4.0]dec-5-Ene (TBD) Catalyzed Michael Reactions. Tetrahedron Lett. 2005, 46, 6875–6878.

(17)

Price, K. E.; Larrivée-Aboussafy, C.; Lillie, B. M.; McLaughlin, R. W.; Mustakis, J.; Hettenbach, K. W.; Hawkins, J. M.; Vaidyanathan, R. Mild and Efficient DBU-Catalyzed Amidation of Cyanoacetates. Org. Lett. 2009, 11, 2003–2006.

(18)

Narain, R.; Armes, S. P. Synthesis of Low Polydispersity, Controlled-Structure Sugar Methacrylate Polymers under Mild Conditions without Protecting Group chemistry. Chem. Commun. 2002, 23, 2776–2777.

(19)

Wróblewska, A. A.; Lingier, S.; Noordijk, J.; Du Prez, F. E.; De Wildeman, S. M. A.; Bernaerts, K. V. Polyamides Based on a Partially Bio-Based Spirodiamine. Eur. Polym. J. 2017, 96, 221–231.

(20)

Fagerland, J.; Finne-Wistrand, A.; Numata, K. Short One-Pot Chemo-Enzymatic Synthesis of L -Lysine and L -Alanine Diblock Co-Oligopeptides. Biomacromolecules 2014, 15, 735–743.

(21)

Blain, M.; Jean-Gérard, L.; Auvergne, R.; Benazet, D.; Caillol, S.; Andrioletti, B. Rational Investigations in the Ring Opening of Cyclic Carbonates by Amines. Green Chem. 2014, 16, 4286–4291.

(22)

Odian, G. Principles of Polymerization; John Wiley & Sons, Inc.: Hoboken, NJ, USA,


Page 28 of 33

Page 29 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

2004; Vol. 58. (23)

Desmet, G. B.; D’hooge, D. R.; Sabbe, M. K.; Marin, G. B.; Du Prez, F. E.; Espeel, P.; Reyniers, M.-F. Computational Study and Kinetic Analysis of the Aminolysis of Thiolactones. J. Org. Chem. 2015, 80, 8520–8529.

(24)

Adalsteinsson, H.; Bruice, T. C. What Is the Mechanism of Catalysis of Ester Aminolysis by Weak Amine Bases? Comparison of Experimental Studies and Theoretical Investigation of the Aminolysis of Substituted Phenyl Esters of Quinoline-6- and -8Carboxylic Acids. J. Am. Chem. Soc. 1998, 120, 3440–3447.

(25)

Sabot, C.; Kumar, K. A.; Meunier, S.; Mioskowski, C. A Convenient Aminolysis of Esters Catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-Ene (TBD) under Solvent-Free Conditions. Tetrahedron Lett. 2007, 48, 3863–3866.

(26)

Guo, W.; Gómez, J. E.; Martínez-Rodríguez, L.; Bandeira, N. A. G.; Bo, C.; Kleij, A. W. Metal-Free Synthesis of N -Aryl Amides Using Organocatalytic Ring-Opening Aminolysis of Lactones. ChemSusChem 2017, 10, 1969–1975.

(27)

Ilieva, S.; Galabov, B.; Musaev, D. G.; Morokuma, K.; Schaefer, H. F. Computational Study of the Aminolysis of Esters. The Reaction of Methylformate with Ammonia. J. Org. Chem. 2003, 68, 1496–1502.

(28)

Ballini, R.; Fiorini, D.; Maggi, R.; Righi, P.; Sartori, G.; Sartorio, R. TBD-Catalysed Solventless Synthesis of Symmetrically N,N′-Substituted Ureas from Primary Amines and Diethyl Carbonate. Green Chem. 2003, 5, 396–398.

(29)

Blain, M.; Jean-Gérard, L.; Auvergne, R.; Benazet, D.; Caillol, S.; Andrioletti, B. Rational



Investigations in the Ring Opening of Cyclic Carbonates by Amines. Green Chem. 2014, 16, 4286–4291. (30)

Liu, W.; Xu, D. D.; Repič, O.; Blacklock, T. J. A Mild Method for Ring-Opening Aminolysis of Lactones. Tetrahedron Lett. 2001, 42, 2439–2441.

(31)

Pascual, A.; Sardón, H.; Ruipérez, F.; Gracia, R.; Sudam, P.; Veloso, A.; Mecerreyes, D. Experimental and Computational Studies of Ring-Opening Polymerization of Ethylene Brassylate Macrolactone and Copolymerization with ε-Caprolactone and TBD-Guanidine Organic Catalyst. J. Polym. Sci. Part A Polym. Chem. 2015, 53, 552–561.

(32)

Hua, G.; Odelius, K. From Food Additive to High-Performance Heavy Metal Adsorbent: A Versatile and Well-Tuned Design. ACS Sustain. Chem. Eng. 2016, 4, 4831–4841.

(33)

Cui, X.; Yan, D.; Xiao, D. Synthesis and Characterization of Novel Polyamides Based on Tridecanedioic Acid: Nylons 3 13, 5 13, 6 13, 7 13, 9 13, 10 13, 11 13. e-Polymers 2004, 4, 784.

(34)

Jiang, Y.; Maniar, D.; Woortman, A. J. J.; Alberda van Ekenstein, G. O. R.; Loos, K. Enzymatic Polymerization of Furan-2,5-Dicarboxylic Acid-Based Furanic-Aliphatic Polyamides as Sustainable Alternatives to Polyphthalamides. Biomacromolecules 2015, 16, 3674–3685.

(35)

Rashidzadeh, H.; Guo, B. Use of MALDI-TOF To Measure Molecular Weight Distributions of Polydisperse Poly(methyl Methacrylate). Anal. Chem. 1998, 70, 131–135.

(36)

von Elias, H.-G.; Schumacher, R. Über Das Lösungsverhalten von Nylon 6,6. Die Makromol. Chemie 1964, 76, 23–53.


Page 30 of 33

Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

(37)

Polymer Handbook, Third edit.; Brandrup, J., Immergut, E. H., Eds.; Wiley-Interscience: Chichester, 1989.

(38)

Huczkowski, P.; Kapko, J.; Olesiak, R. Degradation of Nylon-6 in Ethylene Glycol. Polymer (Guildf). 1978, 19, 77–80.

(39)

Kim, K. J.; Dhevi, D. M.; Lee, J. S.; Cho, Y. D.; Choe, E. K. Mechanism of Glycolysis of Nylon 6,6 and Its Model Compound by Ethylene Glycol. Polym. Degrad. Stab. 2006, 91, 1545–1555.

(40)

Fukushima, K.; Lecuyer, J. M.; Wei, D. S.; Horn, H. W.; Jones, G. O.; Al-Megren, H. A.; Alabdulrahman, A. M.; Alsewailem, F. D.; McNeil, M. A.; Rice, J. E.; et al. Advanced Chemical Recycling of Poly(ethylene Terephthalate) through Organocatalytic Aminolysis. Polym. Chem. 2013, 4, 1610–1616.

(41)

Hall, H. K. Correlation of the Base Strengths of Amines 1. J. Am. Chem. Soc. 1957, 79, 5441–5444.

(42)

Stempfle, F.; Ortmann, P.; Mecking, S. Long-Chain Aliphatic Polymers To Bridge the Gap between Semicrystalline Polyolefins and Traditional Polycondensates. Chem. Rev. 2016, 116, 4597–4641.

(43)

Aharoni, S. M. On Entanglements of Flexible and Rodlike Polymers. Macromolecules 1983, 16, 1722–1728.

(44)

Ojha, S. S.; Afshari, M.; Kotek, R.; Gorga, R. E. Morphology of Electrospun Nylon-6 Nanofibers as a Function of Molecular Weight and Processing Parameters. J. Appl. Polym. Sci. 2008, 108, 308–319.



(45)

Soares, J. C.; Iwaki, L. E. O.; Soares, A. C.; Rodrigues, V. C.; Melendez, M. E.; Fregnani, J. H. T. G.; Reis, R. M.; Carvalho, A. L.; Corrêa, D. S.; Oliveira, O. N. Immunosensor for Pancreatic Cancer Based on Electrospun Nanofibers Coated with Carbon Nanotubes or Gold Nanoparticles. ACS Omega 2017, 2, 6975–6983.

(46)

Scagion, V. P.; Mercante, L. A.; Sakamoto, K. Y.; Oliveira, J. E.; Fonseca, F. J.; Mattoso, L. H. C.; Ferreira, M. D.; Correa, D. S. An Electronic Tongue Based on Conducting Electrospun Nanofibers for Detecting Tetracycline in Milk Samples. RSC Adv. 2016, 6, 103740–103746.

(47)

Guan, X.; Zheng, G.; Dai, K.; Liu, C.; Yan, X.; Shen, C.; Guo, Z. Carbon NanotubesAdsorbed Electrospun PA66 Nanofiber Bundles with Improved Conductivity and Robust Flexibility. ACS Appl. Mater. Interfaces 2016, 8, 14150–14159.

(48)

Zhang, S.; Liu, H.; Yu, J.; Luo, W.; Ding, B. Microwave Structured Polyamide-6 Nanofiber/net Membrane with Embedded Poly(m-Phenylene Isophthalamide) Staple Fibers for Effective Ultrafine Particle Filtration. J. Mater. Chem. A 2016, 4, 6149–6157.

(49)

Zhang, S.; Liu, H.; Zuo, F.; Yin, X.; Yu, J.; Ding, B. A Controlled Design of Ripple-Like Polyamide-6 Nanofiber/Nets Membrane for High-Efficiency Air Filter. Small 2017, 13, 1603151.


Page 32 of 33

Page 33 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

TOC


Exploiting Ring-Opening AminolysisâCondensation as a

Recommend Documents

Exploiting Ring-Opening AminolysisâCondensation as a