Article Cite This: Ind. Eng. Chem. Res. 2017, 56, 13743-13750
pubs.acs.org/IECR
Cross-Linked Polyamides Synthesized through a Michael Addition Reaction Coupled with Bulk Polycondensation Chenfeng Yi, Jingbo Zhao,* Zhiyuan Zhang, and Junying Zhang Key Laboratory of Carbon Fiber and Functional Polymers (Beijing University of Chemical Technology), Ministry of Education; College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China S Supporting Information *
ABSTRACT: A simple route is described to synthesize crosslinked polyamides (cPAs) with excellent mechanical properties at mild conditions through a Michael addition reaction coupled with bulk polycondensation. A Michael addition of methyl acrylate with 1,6-hexanediamine was conducted in a bulk state at a N−H/CC molar ratio of 1:1 under normal pressure at 50 °C, and a hexanediamine-tetraester was prepared. Bulk polycondensation of the hexanediaminetetraester with 1,6-hexanediamine and isophoronediamine was conducted at 170 °C for 1 h and then in tetrafluoroethylene mold under reduced pressure for another 8 h. A series of cPA films were prepared. The Michael addition and the polycondensation were monitored by Fourier transform infrared, 1H NMR, and electrospray ionization mass spectrometry spectra. The cPA films were characterized with differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and a tensile test. These cPAs exhibited Tg ranging from 37 to 61 °C, tensile strength up to 71 MPa, and strain at break of about 11%.
1. INTRODUCTION As a well-known type of commercial polymers, linear polyamides, such as nylon-6, nylon-66, nylon-1010, are widely used as fibers and engineering plastics because of their excellent mechanical strength and durability.1−5 The other type of polyamides is cross-linked polyamides (cPAs). Because of their high intermolecular force and insolubility in organic solvents, cPAs are commonly used as strong and oil-resisting coatings, adhesives, composites, and separating membranes. Nowadays, cPAs are synthesized usually in four methods: (1) In ringopening polymerization-cross-linking method, amino-terminated polyamides were first synthesized through an anionic ring-opening polymerization of ε-caprolactam, and then were cross-linked with caprolactam-capped polyisocyanate6 or terephthaloylbis(ε-caprolactam).7 (2) In the polycondensation-cross-linking method, Howland et al. synthesized a polyamide prepolymer from melt polycondensation of adipic acid with diethylenetriamine and cross-linked them with sorbitol polyglycidyl ether.8 (3) For the polyamine-polyacid halide method, cPAs were synthesized through solution polycondensation9−11 or interfacial polycondensation12 from polyamines and polyacid halides. (4) cPAs were synthesized from polyamides containing maleimide, azide, or cinnamoyl groups through a thermally reversible or UV-reversible crosslinking method.13−15 Michael ene-amine addition is a highly efficient reaction coupling C−N linkages. It is often used in the synthesis of dendrimers via several steps in organic solution. The prepared dendrimers show promising applications in coatings, drug, gene © 2017 American Chemical Society
delivery, nanotechnology, and supramolecular science due to their unique chemical and physical properties.16,17 In this paper, a simple method is described to synthesize cPAs through a Michael ene-amine addition followed with bulk polycondensation. A Michael addition reaction of methyl acrylate (MA) with 1,6-hexanediamine (HDA) was conducted in bulk state at mild conditions, and a hexanediamine-tetraester (HDATE) was synthesized. Bulk polycondensation of HDATE with HDA and isophoronediamine (IPDA) followed and was continued in film state for several hours. A series of cPA films were prepared. The Michael addition and polycondensation were monitored by Fourier transform infrared (FT-IR), 1H NMR, and electrospray ionization mass spectrometry (ESI-MS) spectra. The cPA films were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and tensile test.
2. EXPERIMENTAL SECTION 2.1. Materials. MA was purchased from Tianjin Reagent Plant, China. HDA was purchased from Shanghai Reagent Plant, China. IPDA was obtained from TCI. 2.2. Synthesis of HDATE. In a 250 mL 3-necked flask, 23.24 g (0.20 mol) of HDA and 68.87 g (0.80 mol) of MA were Received: Revised: Accepted: Published: 13743
August 17, 2017 October 26, 2017 October 31, 2017 October 31, 2017 DOI: 10.1021/acs.iecr.7b03416 Ind. Eng. Chem. Res. 2017, 56, 13743−13750
Article
Industrial & Engineering Chemistry Research Scheme 1. HDATE Synthesized through a Michael Addition of HDA with MA at a HDA/MA Molar Ratio of 1:4
added and mechanically stirred at 50 °C for 2.5 h. HDATE was obtained, poured out, and cooled at room temperature. 2.3. Synthesis of cPA Films. cPAs were synthesized at different HDA/IPDA molar ratios and a HDATE versus total diamine (HDATE/DA) molar ratio of 1:2 under the same reaction conditions. The cPAs were designated as cPA-x/y, in which x/y represents the HDA/IPDA molar ratio of 1:0, 9:1, 8:2, 7:3, 6:4, or 5:5. The synthesis of cPA-5/5 was as follows: In a 100 mL 3-necked flask equipped with a distilling adapter, a condenser, and a receiver, 4.61 g (0.010 mol) of HDATE, 1.16 g (0.010 mol) of HDA, and 1.70 g (0.010 mol) of IPDA were added. The mixture was mechanically stirred at 170 °C for 1 h under nitrogen atmosphere and then was poured into a tetrafluoroethylene mold. A series of 50 × 4 × 1 mm rectangle films or 75 × 5 × 2 mm dumbbell-shaped films were formed. The polycondensation was continued at 170 °C in vacuum oven for another 8 h. cPA films with different shapes were prepared. 2.4. Characterization. FT-IR spectra were acquired on a NICOLET 60SXB FTIR spectrometer. 1H NMR spectra were obtained in d6-DMSO on a Bruker 400 AVANCE by using tetramethylsilane as the internal standard. ESI-MS spectra were recorded on an Agilent Technologies 6540 UHD AccurateMass Q-TOF LC/MS spectroscope with methanol as the solvent. About 0.40 g of cPA-5/5 was refluxed in 8 mL of DMSO for 2 h. The undissolved solid was filtered, washed with methanol, dried, and weighed. About 0.16 g of undissolved solid was obtained. The low molecular weight components in filtrate were characterized by ESI-MS spectrum, while the Mn, Mw, and polydispersity index of the high molecular weight solutes in filtrate were determined via gel permeation chromatography (GPC) on an Agilent-2600 system (Agilent Technologies, Inc., United States) (PLgel 5 μm 1000 Å column, refractive index detector, 25 °C, 1 mL/min DMF eluent, polystyrene standards). DSC spectra were measured with a TA Q200 differential scanning calorimeter in N2 atmosphere via a cooling (40 °C/ min)−heating (10 °C/min) process. TGA was performed on a TGA Q50 analyzer at a heating rate of 10 °C/min from 25 to 600 °C in N2 atmosphere. Dumbbell-shaped polymer films (75 × 5 × 2 mm) were used in the tensile tests. Mechanical analysis was conducted on a Lloyd LR30K tensile testing machine at a crosshead speed of 20 mm/min. DMA was conducted with a DMTA V from −50 to 200 °C at a heating rate of 3 °C/min under nitrogen atmosphere. Rectangle films (50 × 4 × 1 mm) were used in the DMA detection. The imposed strain and frequency were 0.01% and 1 Hz, respectively.
Michael addition was monitored via FT-IR spectra (Figure 1). At the beginning (0 h) of the addition reaction, the peak
Figure 1. FT-IR monitoring spectra of the Michael addition (HDA/ MA molar ratio, 1:4; 50 °C; bulk).
corresponding to the CC stretching vibration (1647 cm−1) of MA and that corresponding to the N−H stretching vibration (3315 cm−1) of HDA were obviously observed. When the addition was conducted for 2.5 or 4 h, the CC and N−H peaks became nearly negligible. Michael addition took place swiftly at this temperature. The Michael addition was also monitored by 1H NMR spectra (Figure 2). Figure 3 shows the conversion of the C−N formation. The conversion was calculated from the areas of peak 5 (methyl in MA) and peak 8 (methyl in the addition products) according to eq 1. At the beginning (0 h) of Michael
3. RESULTS AND DISCUSSION 3.1. Synthesis of HDATE. HDATE was synthesized through a Michael addition reaction of HDA with MA at 50 °C in bulk state under normal pressure (Scheme 1). The
Figure 2. 1H NMR monitoring spectra of the Michael addition (HDA/MA molar ratio, 1:4; 50 °C; bulk). 13744
DOI: 10.1021/acs.iecr.7b03416 Ind. Eng. Chem. Res. 2017, 56, 13743−13750
Article
Industrial & Engineering Chemistry Research
Scheme 2. Structure of the Major Components in Michael Addition (HDA/MA Molar Ratio: 1:4)
Figure 3. Conversion of the C−N formation in Michael addition at different time (HDA/MA molar ratio, 1:4; 50 °C; bulk).
addition, about 44.2% of MA was converted into addition products. This means that when HDA was mixed with MA at 50 °C, Michael addition occurred immediately. This Michael addition is rather swift. 1H NMR characterization also reveals that this Michael addition does not react completely in short time at 50 °C. After 2.5 and 4 h, merely 71.5% and 73.0% of MA was transformed into addition products. A8 conversion % = × 100 A5 + A 8 (1)
and the intensity is used to show their contents, the percentages of them might be calculated qualitatively. The reaction mixture contains about 7.7 mol % of hexanediamine-monoester, 21.8 mol % of hexanediamine-diester, 40.7 mol % of hexanediaminetriester, and 29.9 mol % of HDATE (Table S1). A similar result is also observed in the ESI-MS spectrum at 2.5 h (Figure S1), in which the m/z peak of HDATE is slightly smaller than that in Figure 4. Figure 3 also shows that this Michael addition is rather swift before 1 h. At this moment, the major components, hexanediamine-diester (a, b), hexanediamine-triester, and HDATE, were formed. After 1 h, Michael addition between hexanediamine-diester (b) or hexanediamine-triester and MA slowed. Although addition time reaches 4 h, the major components (hexanediamine-diester, hexanediamine-triester, and HDATE) changed only a little. The decrease of MA concentration and the steric hindrance of hexanediaminediester (b) or hexanediamine-triester cause the decrease of the reaction rate. Michael addition was also conducted in bulk state and in 50% toluene solution at different temperatures. In the bulk Michael
The components formed in Michael addition at 4 h were monitored by ESI-MS spectra. In Figure 4, four components were found in the reaction mixture at this moment. The structure of them is described in Scheme 2. They are hexanediamine-monoester, hexanediamine-diester, hexanediamine-triester, and hexanediamine-tetraester, i.e. HDATE. The molecular weight (M) of them is 202, 288, 374, and 460 g/mol, respectively. The m/z peaks in Figure 4 correspond to their M + 1 data except hexanediamine-monoester, of which the m/z peak corresponds to its M − 15 + 1, with a −NH− group lost. Suppose the components exhibit the same sensitivity in ESI detection (in fact some deviations remain among them),
Figure 4. ESI-MS spectrum of the major components in Michael addition at 4 h (HDA/MA molar ratio, 1:4; 50 °C; bulk). 13745
DOI: 10.1021/acs.iecr.7b03416 Ind. Eng. Chem. Res. 2017, 56, 13743−13750
Article
Industrial & Engineering Chemistry Research Scheme 3. cPAs Prepared through a Bulk Polycondensation of HDATE with HDA and IPDA
addition at the temperature from 30 to 70 °C, hexanediaminediester (a, b), hexanediamine-triester, and HDATE were formed as major components (Figures S2−S5 and Table S1). Hexanediamine-triester accounts for nearly 50 mol %, and the content of HDATE is obviously higher than that of hexanediamine-diester (a, b). In the solution Michael addition at 50 and 140 °C, at the same reaction time, hexanediaminediester (a, b) and hexanediamine-triester were formed as the major components with molar percentage above 38.7 mol %, while hexanediamine-monoester and HDATE were minor components with molar percentage less than 9.7 mol % (Figures S6 and S7 and Table S1). Lower MA concentration and the steric hindrance of hexanediamine-diester (b) or hexanediamine-triester hindered the formation of HDATE further, leading to less HDATE being formed. 3.2. Synthesis of cPAs. cPAs were directly synthesized through a bulk polycondensation of HDATE with HDA and IPDA (Scheme 3). The polycondensation was first conducted in a glass flask at 170 °C under normal pressure. The viscosity of the reaction mixture increased gradually. Polycondensation was continued in a tetrafluoroethylene mold. A series of cPA films with different properties were prepared (Table 1). The bulk polycondensation of HDATE with HDA and IPDA was monitored by FT-IR and 1H NMR spectra. Figure 5a shows the FT-IR spectrum of the reaction mixture after 1 h of polycondensation at a HDA/IPDA molar ratio of 5:5. Many ester groups (a strong CO stretching vibration peak at 1738 cm−1) in HDATE remained unchanged, and some amide
Figure 5. FT-IR monitoring spectra in the polycondensation of HDATE with HDA and IPDA at a HDA/IPDA molar ratio of 5:5 (a) 1 h and (b) 9 h or cPA-5/5 (170 °C).
groups were formed, with a strong CO stretching vibration peak and a N−H bending vibration peak emerging at 1649 and 1550 cm−1, respectively. After another 8 h of polycondensation in the film state, cPA-5/5 was prepared. In the FT-IR spectrum of cPA-5/5 (Figure 5b), no characteristic peaks of ester groups were found. Nearly all the ester groups were transformed into amide groups, and a cross-linked polyamide was formed. Figure 6 shows the 1H NMR spectrum of the reaction mixture after 1 h of polycondensation of HDATE with HDA and IPDA at a HDA/IPDA molar ratio of 5:5. Signals are assigned based on the literature.18,19 At this moment, signals corresponding to the CH 2 CH− hydrogens in MA disappeared, because the remaining MA in the last stage of Michael addition all reacted swiftly in 1 h at 170 °C with the N−H bonds of hexanediamine-diester, hexanediamine-triester, HDA, or IPDA. The structural units in the reaction mixture after 1 h of polycondensation are described in Figure 6. Some amide groups were formed, and some ester groups and amino groups remained unchanged. The reaction mixture in this period was a liquid and was soluble in high polar solvents such as N,N-dimethylformamide and dimethyl sulfoxide (DMSO). The ester and amino terminal groups reacted further in the following film-state polycondensation, with the cPA-5/5 prepared. In the major components of Michael addition, hexanediamine-monoester and hexanediamine-diester (a) show the
Table 1. Properties of cPA Films Synthesized at 170 °C DMA cPAx/y cPA1/0 cPA9/1 cPA8/2 cPA7/3 cPA6/4 cPA5/5
HDA/IPDA (x/y) (molar ratio)
Tg (DSC) (°C)
1:0
37
35
8.1
929.6
9:1
40
40
10.5
1191.1
8:2
42
41
8.1
915.0
7:3
61
52, 82
9.8, 7.4
1078.5, 754.3
6:4
61
56, 89
9.5, 7.2
1029.4, 719.1
5:5
61
58, 99
9.7, 4.2
1042.1, 406.6
Tα (°C)
E′(Tα + 40) (MPa)
ve (mol·m−3)
13746
DOI: 10.1021/acs.iecr.7b03416 Ind. Eng. Chem. Res. 2017, 56, 13743−13750
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Industrial & Engineering Chemistry Research
Figure 6. 1H NMR spectrum of the reaction mixture after 1 h polycondensation of HDATE with HDA and IPDA at a HDA/IPDA molar ratio of 5:5 (170 °C). Figure 7. Heating DSC scans of cPAs detected in a cooling (40 °C/ min)−heating (10 °C/min) process.
functionality ( f) of 3. In hexanediamine-monoester, one ester group, one =N−H group, and one −NH2 group take part in the polycondensation. In hexanediamine-diester (a), two ester groups and one −NH2 group take part in polycondensation. After the self-polycondensation of hexanediamine-monoester or hexanediamine-diester (a) and the copolycondensation with HDA or IPDA, three-branched-amide (3-b-A) linkages were formed. Hexanediamine-diester (b), hexanediamine-triester, and HDATE show the f of 4 because the =N−H groups and the ester groups of them all take part in the polycondensation. Their self-polycondensation and the copolycondensation with HDA or IPDA led to the formation of four-branched-amide (4b-A) linkages. These 3-b-A and 4-b-A linkages connected each other, with hyperbranched and cross-linked polyamides formed. As hexanediamine-diester (b), hexanediamine-triester, and HDATE are the major components in Michael reaction mixture, more 4-b-A linkages might be formed in the cPAs than the 3-b-A linkages formed. The solubility of cPAs was also characterized. After cPA-5/5 was refluxed in DMSO for 2 h, about 40% undissolved solid was left. In the filtrate, the major components in the starting materials, i.e., HDA, IPDA, and the hexanediamine-monoester, hexanediamine-diester, hexanediamine-triester, and HDATE in Michael addition, were not found in the ESI-MS spectrum (Figure S8). A series of new compounds with molecular weight ranging from 100.0 to 673.5 g/mol were shown. Their structure was complex and hard to be determined. The ESI-MS spectrum merely shows the low molecular weight components in filtrate. The high molecular weight components were detected by GPC (Figure S9). They exhibit the Mn of 169 700 g/mol and Mw of 320 900 g/mol. ESI-MS, GPC, and solubility characterization indicates that cPAs are composed of some high molecular weight soluble polyamides and cross-linked polyamides. 3.3. DSC Characterization. Figure 7 shows the heating DSC scans of cPAs detected in the cooling (40 °C/min)− heating (10 °C/min) process. cPAs show a Tg ranging from 37 to 61 °C (Table 1). cPA-1/0 was synthesized from the polycondensation of HDATE with HDA. It has low Tg at 37 °C, because cPA-1/0 contains only flexible hexamethylene segments derived from HDA. From cPA-9/1 to cPA-5/5, as the amount of isophorone units increased, Tg increased because more stiff isophorone units were introduced. In the DSC curves, no melting peaks were found. These cPAs are all
amorphous polyamides. Hyperbranched characteristics and cross-linking bonds make these cPAs amorphous. 3.4. Dynamic Mechanical Analysis. DMA usually provides valuable information on the glass transition, phase separation, cross-linking density (ve), and mechanical behavior of polymers. Figure 8 shows the storage modulus (E′) and the
Figure 8. Relationship between the storage modulus or tan δ of cPAs and temperature.
tan δ of cPAs as functions of temperature. cPA-1/0, cPA-9/1, and cPA-8/2 are in glassy solids below 15 °C with the E′ above 1000 MPa, while cPA-7/3, cPA-6/4, and cPA-5/5 are all in glass state below 36 °C. The tan δ peak in the tan δ curves (Tα) is related to the Tg detected in DSC scans.20−23 cPA-1/0, cPA9/1, and cPA-8/2 show a Tα at 35, 40, and 41 °C, respectively, while cPA-7/3, cPA-6/4, and cPA-5/5 show two Tα values (Table 1). Their Tα values increase as the amount of stiff isophorone units increases. Meanwhile, the second Tα in cPA7/3, cPA-6/4, and cPA-5/5 becomes more obvious. The reason may be that increasing the isophorone amount leads to two cross-linking modes, i.e., a hexanediamide cross-linking mode and an isophoronediamide cross-linking mode. As cPA-1/0, cPA-9/1, and cPA-8/2 contain low isophorone amounts, they merely form a hexanediamide cross-linking mode, with only 13747
DOI: 10.1021/acs.iecr.7b03416 Ind. Eng. Chem. Res. 2017, 56, 13743−13750
Article
Industrial & Engineering Chemistry Research one Tα emerged. Because cPA-7/3, cPA-6/4, and cPA-5/5 contain higher isophorone amount, they exhibit two Tα’s, which correspond to the hexanediamide cross-linking mode and the isophoronediamide cross-linking mode. After Tα’s, E′ gradually decreased to a level at about 10 MPa and reached a rubbery plateau. ve is an important parameter of cured materials and is closely related to the mechanical performance. ve can be calculated according to eq 2.24 E′ = 3veRT
decomposition temperature (Ti) and the decomposition peaks (Tp1 and Tp2) are summarized in Table 2. In the DTGA curves, Table 2. TGA (Heating Rate, 10 °C/min under N2) and Tensile Testing Data of cPAs
(2)
where E′ is the storage modulus at Tα + 40 °C. R is the ideal gas constant. T stands for the absolute temperature at Tα + 40 °C. The ve data of cPAs are listed in Table 1. cPA-1/0, cPA-9/1, and cPA-8/2 exhibit high ve above 915 mol/m3. Their crosslinking is mainly formed from hexanediamide units because of lower or without isophoronediamide content. In cPA-7/3, cPA6/4, and cPA-5/5, hexanediamide cross-linking mode and isophoronediamide cross-linking mode remain together. The hexanediamide cross-linking mode exhibits high ve above 1029 mol/m3, while the isophoronediamide cross-linking mode shows low ve ranging from 406.6 to 754.3 mol/m3, because a higher amount of the isophoronediamide units in cPA-7/3, cPA-6/4, and cPA-5/5 brings about more steric hindrance to cross-linking. 3.5. TGA Characterization. Figure 9 shows the TGA curves (a) and the DTGA curves (b) of cPAs. The initial
cPAx/y
Ti (°C)
Tp1 (°C)
Tp2 (°C)
end mass (%)
tensile strength (MPa)
strain at break (%)
cPA1/0 cPA9/1 cPA8/2 cPA7/3 cPA6/4 cPA5/5
268
332
454
5
41
11
248
323
456
4
58
11
263
327
458
4
61
11
255
315
443
4
69
12
267
319
434
3
71
11
219
305
437
5
71
11
a tiny decomposition peak was found in the range from 100 to 200 °C because of further polycondensation between the remaining =N−H or −NH2 groups and −COOCH3 groups, with a little amount of CH3OH released. Decomposition between 200 and 370 °C is related to the scission of amide linkages, while decomposition between 370 and 500 °C corresponds to the scission of C−C linkages. cPAs are thermally stable cross-linked polyamides below their Ti (above 219 °C). 3.6. Tensile Testing. Figure 10 shows the stress−strain curves of cPAs. Their tensile strength and strain at break are
Figure 10. Stress−strain curves of cPAs.
listed in Table 2. cPAs all show excellent mechanical properties because they have high Tg and ve (Table 1). cPA-1/0 was prepared merely from HDATE and HDA. It exhibits a tensile strength of 41 MPa and a strain at break of 11%, because only flexible hexanediamide linkages were formed in the crosslinking step. From cPA-9/1 to cPA-5/5, as more isophoronediamide units were introduced, tensile strength increased obviously. Isophorone units influence the tensile strength evidently. The reason is that bulky isophoronediamide units are stiff structural units. Introducing isophoronediamide units increases the stiffness of cPAs (with the Tg increased) and improves the intermolecular interaction between different polyamide sequences. Thus, cPAs with higher Tg show higher tensile strength. Meanwhile, introducing bulky isophoronedia-
Figure 9. TGA (a) and DTGA (b) curves of cPAs (heating rate, 10 °C·min−1; atmosphere, N2). 13748
DOI: 10.1021/acs.iecr.7b03416 Ind. Eng. Chem. Res. 2017, 56, 13743−13750
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Industrial & Engineering Chemistry Research ORCID
mide units also lowers the ve, particularly for cPA-7/3, cPA-6/4, and cPA-5/5. Decreasing ve also improves the tensile strength to some extent. Lower ve benefits the formation of longer polyamide sequences, which lead to better flexibility, easier rearrangement, and higher intermolecular interaction between polyamide sequences. Thus, better tensile strength was observed. However, the strain at break of cPAs was little influenced. The reason is that cross-linking through hexanediamide linkages is still the major cross-linking mode in cPAs from cPA-9/1 to cPA-5/5, although introducing isophoronediamide units lowers ve and brings about isophoronediamide cross-linking mode to some extent. The major cross-linking structure was formed through hexanediamide linkages. Thus, the strain at break of cPAs is almost the same. cPA films were also prepared at lower temperatures of 130 and 150 °C. The obtained cPA-1/0-130, cPA-5/5-130, cPA-1/ 0-150, and cPA-5/5-150 show obviously lower Tg and tensile strength (Figures S10−S12 and Table S2) than the respective cPA-1/0 and cPA-5/5 synthesized at 170 °C (Table 1). Lower temperature causes lower extent of cross-linking, leading to the decrease of Tg and tensile strength.
Jingbo Zhao: 0000-0001-7374-4519 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors acknowledge the financial support from the National Natural Science Foundation of China (Grant 21244006).
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4. CONCLUSION A reaction mixture containing mainly hexanediamine-diester, hexanediamine-triester, and hexanediamine-tetraester was obtained through a Michael addition of methyl acrylate with 1,6-hexanediamine at a N−H/CC molar ratio of 1:1 in bulk state at 50 °C. Bulk polycondensation of this mixture with 1,6hexanediamine and isophoronediamine was conducted at 170 °C followed by the film state. A series of cross-linked polyamide, cPA, films were prepared. The cPAs exhibit Tg from 37 to 61 °C, initial decomposition temperature at over 219 °C, tensile strength up to 71 MPa, and strain at break of about 11%. Introducing bulky isophoronediamide units increases the stiffness or Tg and lowers the cross-linking density. This effect benefits the increase of tensile strength. An efficient and simple route was established to synthesize crosslinked polyamides at mild conditions through a Michael addition reaction coupled with bulk polycondensation. Crosslinked polyamides with excellent mechanical properties were successfully prepared.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b03416. ESI-MS spectrum of the major components in the Michael addition at 2.5 h (Figure S1); ESI-MS spectra of the major components in the Michael addition at 4 h (Figures S2−S7); contents of the major components in the Michael addition at different conditions (Table S1); ESI-MS spectrum (Figure S8) and GPC curve (Figure S9) of the components in the filtrate of cPA-5-5 refluxed in DMSO for 2 h; heating DSC scans of cPA-x/y-Ts (Figure S10); stress−strain curves of cPA-130s and cPA150s (Figures S11 and S12); properties of cPA films synthesized at 130 and 150 °C (Table S2) (PDF)
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DOI: 10.1021/acs.iecr.7b03416 Ind. Eng. Chem. Res. 2017, 56, 13743−13750
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DOI: 10.1021/acs.iecr.7b03416 Ind. Eng. Chem. Res. 2017, 56, 13743−13750
