Next Article in Journal
Synthesis and Antimicrobial Evaluation of Chroman-4-One and Homoisoflavonoid Derivatives
Previous Article in Journal
Green Approaches in High-Performance Liquid Chromatography for Sustainable Food Analysis: Advances, Challenges, and Regulatory Perspectives
Previous Article in Special Issue
Reversible Binding of Nitric Oxide in a Cu(II)-Containing Microporous Metal-Organic Framework
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Molecules
Volume 30
Issue 17
10.3390/molecules30173574
molecules-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Synthesis and Properties of Ethylene Imine-Based Porous Polymer Nanocomposites with Metal Oxide Nanoparticles

by
Naofumi Naga
1,2,*,
Julia Janas
3,
Tomoya Takenouchi
2 and
Tamaki Nakano
4,5
1
College of Engineering, Shibaura Institute of Technology, Toyosu Campus, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan
2
Graduate School of Science & Engineering, Shibaura Institute of Technology, Toyosu Campus, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan
3
MSc In Advanced Nano and Bio Materials MONABIPHOT, Wrocław University of Science and Technology, Wybrzeże Stanisława Wyspiańskiego 27, 50-370 Wrocław, Poland
4
Institute for Catalysis, Hokkaido University, N 21, W 10, Kita-ku, Sapporo 001-0021, Japan
5
Integrated Research Consortium on Chemical Sciences, Institute for Catalysis, Hokkaido University, N 21, W 10, Kita-ku, Sapporo 001-0021, Japan
*
Author to whom correspondence should be addressed.
Molecules 2025, 30(17), 3574; https://doi.org/10.3390/molecules30173574
Submission received: 30 July 2025 / Revised: 29 August 2025 / Accepted: 30 August 2025 / Published: 31 August 2025
(This article belongs to the Special Issue Functional Porous Frameworks: Synthesis, Properties, and Applications)
Browse Figures
Review Reports Versions Notes

Abstract

Ethylene imine-based porous polymer nanocomposites were prepared by ring-opening polymerization of 2,2-bishydroxymethylbutanol-tris [3-(1-aziridinyl)propionate] (3AZ), a tri-functional aziridine compound, in the presence of commercially available metal oxide nanoparticles, SiO2 or ZrO2, accompanied by polymerization-induced phase separation. The reactions with SiO2 and ZrO2 nanoparticles successfully yielded nanocomposite porous polymers as rigid materials. The nanocomposite porous polymers with SiO2 and ZrO2 nanoparticles showed characteristic surface morphologies composed of gathered particles with diameters less than 1 micrometer. These nanocomposites were effective in increasing Young’s moduli of the porous polymers due to an increase in their bulk densities. The presence of SiO2 and ZrO2 nanoparticles in the porous polymers efficiently retarded thermal decomposition.

1. Introduction

The formation of a composite is a facile and effective method to improve various properties (including tensile strength, elastic modulus, heat distortion temperature, etc.) of a wide range of materials, such as ceramics and metal- and polymer-based materials. There are examples of polymer nanocomposites where polymer matrices and nanofillers are combined [1,2,3,4,5]. As polymer matrices, both thermoplastic resins, such as polyethylene, polypropylene, polyamide, and polyvinyl alcohol, and thermosetting resins, such as epoxy resin and phenol resin, are applicable. Representative nanofiller materials include inorganic nanoparticles, such as SiO2, ZrO2, and TiO2; layered materials, such as montmorillonite, graphene, and clay; and nanocarbons, such as carbon nanotubes, carbon black, and fullerene, with sizes of about 1 to 100 nm. These fillers can effectively improve the mechanical, thermal, gas barrier, electric, and optical properties of polymer matrices that alone show limited performance. In the preparation of nanocomposites, homogenous distribution of the fillers and controlled interfacial interaction between the polymer matrices and nanofillers are important to draw practical efficiency from fillers at small quantities.
On the other hand, porosification can remarkably modify the properties of polymer matrices. In this context, various types of porous polymers have been developed to attain specific features, such as lightness, specific surface area, and gas or liquid permeability [6,7,8]. Porous polymers can be used as monolithic columns, filters, membranes, supports, and insulators. Porosity may be introduced to polymers through template polymerization, post-polymerization, and phase separation (polymerization-induced phase separation, PIPS). PIPS is one of the most practical methods to prepare porous network polymers with a variety of molecular structures. Two types of phase separation processes are possible in PIPS: nucleation growth and spinodal decomposition processes. The spinodal decomposition process is widely detected in the formation process of various porous polymers, as shown in Scheme 1. Phase separation is induced in the homogeneous reaction system, as shown in Scheme 1a, by the formation of polymer networks. At the early stage of phase separation, a co-continuous structure is formed (Scheme 1b). This structure transitions to particles by interfacial tension following the growth in their size, as shown in Scheme 1c,d. When the phase separation of the reaction preferentially occurs, the reaction yields precipitation (Scheme 1e). The morphology of the resulting porous polymer composite is determined by the fixed stage of the phase separation through network formation (polymerization).
Some porous polymers have been obtained by the ring-opening addition reaction of multi-functional epoxy and amine compounds with aliphatic and/or aromatic cyclic structures through PIPS [9,10,11,12,13,14,15,16,17]. Ring-opening reactions are considered more suited to the production of porous polymers because the reaction of the epoxy group forms an OH group, which should increase the polarity of the polymer chains being formed in the reaction and hence decrease their miscibility with non-polar organic solvents. Through such a mechanism, PIPS involving ring-opening reactions can successfully yield highly porous polymers.
In this work, we studied nanocomposite formation through PIPS. We believe that the method presented here can apply to a wide range of materials. As an example, we previously reported poly(methyl methacrylate) (PMMA) nanocomposite by a conventional radical polymerization of methyl methacrylate with polymerizable SiO2 nanoparticles in methanol. The resulting PMMA-SiO2 porous nanocomposites showed high mechanical strength, good thermal resistance, and coloration at the solvent-absorbed state due to the Christiansen effect [18]. Although this is a facile method to prepare porous polymer nanocomposite, a specific monomer containing polymerizable SiO2 nanoparticles is necessary. We found an extremely facile method to yield a porous polymer involving ring-opening polymerization of 3AZ that only requires dissolving 3AZ in water. Using this method, an ethyleneimine-based porous polymer was produced [19]. This reaction system is also applicable to preparing porous polymer composites with water-soluble cyclodextrins [20]. By contrast, composition with water-insoluble cyclodextrins is impossible due to the precipitation of the cyclodextrins during polymerization. Uniform dispersion and stability are necessary for nanocomposition using the polymerization system of 3AZ in water.
In this study, we aimed to develop a more widely applicable method using conventional and/or commercially available materials and examine the synthesis of ethyleneimine-based porous composite polymers by the ring-opening polymerization of 3AZ in commercially available metal oxide sols (aqueous colloidal metal oxides: SiO2 and ZrO2) (Scheme 2). The effects of the metal oxides on the morphology, mechanical properties, and thermal stability of the resulting porous polymer composites were systematically studied.

2. Results and Discussion

2.1. Synthesis of 3AZ–Metal Oxide Porous Composite Polymers

Ring-opening polymerization of 3AZ was carried out in the presence of SiO2 nanoparticles in water. Features of the SiO2 sols are summarized in Scheme 2, where ST-20: stabilized by sodium hydroxide, pH 10; ST-N: stabilized by ammonia, pH 10; ST-C: high-stability alkaline sol in neutral pH range, pH 9; ST-O: acidic sol (sodium ion reduced from Na type, no acid added), pH 3; and ST-AK: acidic sol (cationic surface), pH 5. Figure 1 shows the production diagrams of the reaction systems in the presence of different types of aqueous colloidal silica particles. The corresponding porous polymers were obtained under a low SiO2 nanoparticle feed. For reactions in the presence of basic SiO2 nanoparticles (ST-20, ST-N, or ST-C), high reaction temperatures were favorable to induce phase separation, yielding porous polymer composites with at most 6 wt% SiO2 nanoparticles. Low reaction temperatures and high SiO2 nanoparticle feed will decrease the phase separation rate, and the reaction system should be fixed before phase separation and yield gels. In the reactions with acidic SiO2 nanoparticles (ST-O or ST-AK), the corresponding porous polymer composites were obtained with a low SiO2 nanoparticle feed of 2 wt%. The presence of acidic SiO2 nanoparticles decreased the basicity of the reaction systems, which hindered the ring-opening polymerization of 3AZ. In the reactions with ST-AK, more than 4 wt% SiO2 nanoparticles tended to yield precipitates. One explanation for this result would be that the charge repulsion between the polymer networks and the cationic surface of the ST-AK SiO2 nanoparticles drastically decreased the miscibility between the composite and water.

2.2. Structure of 3AZ–Metal Oxide Porous Polymer Composites

The surface morphology of 3AZ-SiO2 porous polymer composites was observed by SEM. Figure 2 and Figure S1 show SEM images of some representative porous polymer composites with SiO2 nanoparticles. Most of the porous polymer composites with SiO2 showed a surface morphology composed of connected particles, whose diameters were less than 1 μm, as summarized in Table 1. The 3AZ porous polymers without SiO2 nanoparticles showed larger particle sizes: 2.9 μm (at 20 °C) or 4.8 μm (at 40 °C). The porous structures of 3AZ-SiO2 polymer composites were formed by polymerization-induced phase separation via the spinodal decomposition process, as illustrated in Scheme 1. The addition of SiO2 nanoparticles effectively transferred the co-continuous structure to the small particle structure, which was fixed before the growth of the particles. The porous colloid composite with 2.0 wt% ST-N showed a wrinkled surface, which was formed at the transition state from the co-continuous structure to the particle structure. These results indicate strong interaction between the polymer networks and SiO2 nanoparticles in the present reaction systems.
The particle size distribution was evaluated by standard deviation (SD) coefficient of validation (CV = SD/average diameter of the particles’ diameters) with histograms (Figure S2). All the porous polymer composites showed CV values ranging from 0.15 to 0.28, independent of the kind and concentration of SiO2 and reaction temperature. The results indicate that the presence of SiO2 does not affect the homogeneity of the reaction systems.
The specific surface area of the porous polymer was measured by nitrogen sorption. Although the adsorption isotherms of type V or III (IUPAC) were observed in some porous polymer composites (Figure S3), the surface area of some samples was too small (less than 5 m2/g) for quantitative evaluation.
The molecular structure of a 3AZ-SiO2 (ST-20) porous polymer composite was studied by FT-IR spectroscopy, as shown in Figure 3. Both the absorption peaks derived from the 3AZ polymer; C=O stretching at 1730 cm−1, quaternary ammonium at 1590 cm−1, and SiO2 at 1100 cm−1 were detected in the spectrum of the porous polymer composite. These results demonstrate the formation of 3AZ polymer with the existence of SiO2 nanoparticles in the porous polymer composite. The interaction between the polymer networks and SiO2 nanoparticles induced a shift and/or shape change of the peaks. Although a clear peak shift cannot be observed in the comparison between Figure 3b (3AZ porous polymer) and Figure 3c (3AZ-SiO2 porous polymer composite), the shape change at 1200–1100 cm−1 may have been caused by sialylation of the amine moieties in the polymer networks.
The distribution of SiO2 colloid in a 3AZ-SiO2 porous polymer composite was studied by SEM-EDS. Figure 4 shows the SEM-EDX images of a porous polymer composite with SiO2 nanoparticles (ST-20, 4.0 wt%, run 9). The element mapping of Si showed a clear homogeneous distribution of SiO2 colloids in the porous polymer composite, as shown in Figure 4e. The composition ratio (atomic number ratio) of the C, N, O, and Si were 60.2%, 10.9%, 26.3%, and 2.6%, respectively. These ratios were close to the calculated theoretical values (63.6%, 9.0%, 24.2%, and 3.0% for C, N, O, and Si).
SEM images of 3AZ-ZrO2 porous polymer composites are summarized in Figure 5 and Figure S4. All the porous polymer composites showed a surface morphology composed of connected particles, whose diameters were less than 1 μm, as summarized in Table 2. The average particle size tended to decrease with increasing concentration of ZrO2 nanoparticles and polymerization temperature. These factors should increase the relative rate of polymerization (network formation) to the phase separation rate and fix the morphology at the early stage of phase separation, as shown in Scheme 1c.
The particle size distribution was evaluated by SD and CV, as summarized in Table 2 (Figure S5). The CV values ranged from 0.13 to 0.23, which were lower than those of the 3AZ-SiO2 systems. Lower interaction between the polymer network and the ZrO2 nanoparticles would make it possible for the particle size distribution to be more homogeneous.
The specific surface area of some 3AZ-ZrO2 porous polymer composites was less than 5 m2/g, as observed in 3AZ-SiO2 porous polymer composites.
The molecular structure of 3AZ-ZrO2 porous polymer composites was also studied by FT-IR spectroscopy (Figure S6). In the FT-IR spectra of 3AZ-ZrO2 porous polymer composites, the absorption peaks derived from ZrO2 nanoparticles were detected at about 1160 cm−1 besides the peaks derived from the polymer networks formed by the ring-opening polymerization of 3AZ (Figure 3a). No shift changes or shape changes, which would be possible by the interaction between the polymer networks and ZrO2, were detected by the FT-IR spectroscopy.
SEM-EDX images of a porous polymer composite with ZrO2 nanoparticles (ZrO2, 4.0 wt%, run 38) also showed homogeneous distribution of the C, N, O, and Zr elements, and their composition ratios (atomic number ratio) were 54.5% (C), 10.6% (N), 32.9% (O), and 2.2% (Zr), respectively. These ratios roughly corresponded to the calculated theoretical values (63.6%, 9.0%, 24.2%, and 3.0% for C, N, O, and Si).

2.3. Mechanical and Thermal Properties of 3AZ–Metal Oxide Porous Polymer Composites

The mechanical properties of 3AZ-SiO2 porous polymer composites were evaluated by the compression test. Figure 6 shows the stress–strain curves of the porous polymer composites obtained with 2.0 wt% SiO2 colloids in the feed. The addition of SiO2 nanoparticles made the porous polymer significantly hard. The Young’s moduli of the porous polymer composites are summarized in Table 1, with the average particle size (diameter) and the bulk density. The 3AZ-SiO2 porous polymer composites were not breakable under the compression of 50 N. The primary particles of the composition with SiO2 nanoparticles decreased in size, which increased the bulk density. The SiO2 nanoparticles affected the mechanical properties of the 3AZ-SiO2 porous composite polymers, and the 3AZ-SiO2 porous polymer composite with ST-20 showed a higher Young’s modulus than the other 3AZ-SiO2 porous polymer composites. This may be due to the stabilizing of the SiO2 nanoparticles in the reaction systems. The electrical interaction between the SiO2 nanoparticle surface (Na+ −OSi-) and the amine moieties in the polymer networks of 3AZ (R3NH+) via ion exchange (R3NH+ −OSi- + Na+) preferentially occurred in the presence of Na+ in ST-20. The high Young’s moduli of the 3AZ-ST-C porous polymer composites would have been due to the high bulk densities. An increase in the SiO2 nanoparticle feed increased the Young’s moduli of the porous polymer composites. The combinations with SiO2 nanoparticles increased the rigidity of the porous polymer composites due to the increase in the bulk density and hardness of SiO2.
The mechanical properties of the 3AZ-ZrO2 porous polymer composites were also studied by compression test. Figure 7 shows the stress–strain curves of the porous polymer composites obtained with different ZrO2 nanoparticle feeds at 60 °C. The Young’s moduli of the porous polymer composites are summarized in Table 2, with the average particle size and bulk density. The Young’s moduli drastically increased in the polymer composites with more than 4.0 wt% ZrO2 nanoparticles. Increasing the ZrO2 nanoparticle concentration slightly decreased the Young’s moduli despite the increase in bulk density. In the same way, the porous polymer composites with 2.0 wt% or 4.0 wt% ZrO2 nanoparticles prepared under the polymerization temperature of 20 °C or 60 °C showed the highest Young’s modulus. One explanation for these results is that interfacial failure between polymer networks and ZrO2 nanoparticles would be dominant in porous polymer composites with higher ZrO2 nanoparticle concentrations. The porous polymer composites prepared at lower temperatures tended to show higher Young’s moduli. However, there was no clear correlation between the bulk density and Young’s modulus. One possible explanation for this is that porous polymer composites prepared at a lower temperature (20 °C) may have higher interaction between the ZrO2 nanoparticles and the polymer network, which would induce higher physical crosslinking density.
The distribution of the Young’s modulus was evaluated by Weibull analysis [21]. The Weibull moduli of the porous polymer composites, summarized in Table 1 and Table 2, ranged from 7 to 12, indicating moderate or large variation. The results were due to the characteristics of brittle materials.
The thermal stability of the 3AZ-SiO2 (ST-20, ST-O) porous polymer composites prepared at 60 °C was evaluated by TG-DTA analysis. The TG profiles of the 3AZ-ST-20 porous polymer composites are summarized in Figure 8. The 3AZ porous polymer (without SiO2) under an Ar atmosphere showed a two-step degradation at about 260 °C and 330 °C, caused by denaturation of amine groups and cleavage of ester bonds, respectively. The porous composite polymer with 2.0 wt% SiO2 nanoparticles showed almost the same profile as that of the 3AZ porous polymer. The porous polymer composites with 4.0 wt% and 6.0 wt% SiO2 nanoparticles mitigated the first decomposition and retarded the second decomposition. These phenomena were possibly due to effects such as inhibition of heat transfer and diffusion by SiO2 (barrier effect), restriction of the polymer chains’ motion (reduction of molecular mobility), formation of physical networks, and stabilization by carbonization residues (char formation). The thermal data from the TG profiles, onset temperature of thermal degradation (Tdon), maximum degradation rate (Rdmax), and char yield at 500 °C of 3AZ-ST-20 porous polymer composites are summarized in Table 3. The increase in SiO2 concentration increased Tdon and decreased Rdmax. The char yield increased with increasing SiO2 concentration. The 3AZ-SiO2 porous polymer composite with 2.0 wt% acidic ST-O (run 24) showed similar Tdon and Rdmax values as those of the corresponding 3AZ-ST-20 porous polymer composite (run 8). The results indicate that the features of SiO2 nanoparticles do not have much impact on the thermal degradation behavior.
Figure 9 shows the TG profiles of the 3AZ-ZrO2 porous polymer composites prepared at 60 °C. The porous polymer composites showed a multi-step degradation at more than 300 °C. These profiles are different from those of the porous composite polymer with SiO2 nanoparticles (Figure 8). These may be caused by differences in the interaction of the metal oxide used. In the case of nanocomposites with 3AZ polymer and SiO2 nanoparticles, the interaction would be mainly via hydrogen bonds derived from surface OH groups on the SiO2 nanoparticles. By contrast, the interaction via coordination and/or acid–base should be possible in nanocomposites with ZrO2 nanoparticles due to Lewis acidity. A difference in thermal conductivity between SiO2 (1.3 W/mK) and ZrO2 (2.5 W/mK) may affect the thermal decomposition behavior of the porous polymer composites [22,23]. The Tdon, Rdmax, and char yield of the 3AZ-ZrO2 porous polymer composites with increasing ZrO2 concentration (Table 3) showed the same tendency as those with SiO2.

3. Materials and Methods

3.1. Materials

3AZ was kindly donated by Nippon Shokubai Co., Ltd., (Osaka, Japan) and used as received. Aqueous colloidal silicas (20 wt%, particle size 12 nm), SNOWTEX (ST-20: stabilized by sodium hydroxide, pH 10; ST-N: stabilized by ammonia, pH 10; ST-C: high-stability alkaline sol in neutral pH range, pH 9; ST-O: acidic sol (sodium ion reduced from Na type, no acid added), pH 3; and ST-AK: acidic sol (cationic surface), pH 5), were kindly donated by Nissan Chemical Corporation (Tokyo, Japan). A zirconia sol dispersed in water—NanoUse OZ-S20H: 20 wt%, particle size: 30–50 nm, weak acidity—was also kindly donated by Nissan Chemical Corporation. Methanol (MeOH) was commercially obtained from Kanto Chemical Co., Inc. (Tokyo, Japan) and used without further purification.

3.2. Synthesis of Porous Polymer Composites

The reaction of 20 wt% 3AZ in the presence of 2 wt% SiO2 nanoparticles is described as an example. Aqueous colloidal silica (0.40 g) and distilled water (2.8 g) were added to a 20 mL vial and stirred by a vortex mixer (Mixer N-40M-1, NISSIN, Tokyo, Japan) for a few minutes to make a diluted solution. Then, 3AZ (0.8 g) and the sol were added to a quadrangular prism polyethylene bottle (1.7 cm × 1.7 cm × 3.0 cm), stirred using a vortex mixer, and then stored at the desired temperature in an ESPEC SU-641 constant-temperature chamber (ESPEC CORP., Osaka, Japan) for 24 h. The obtained porous polymer composite was washed by immersion in excess of methanol for 24 h. The porous polymer composite was air-dried at room temperature for 24 h and further dried in vacuo at 40 °C for 3 h. Reactions with different metal oxides and concentrations were conducted by the same procedures.

3.3. Analytical Procedures

FT-IR spectra of the porous polymer composites were recorded on an FTIR-8400 or an IRAffinity-1S spectrometer (SHIMADZU Corporation, Kyoto, Japan), and 30 scans were accumulated from 4000 to 500 cm−1.
Scanning electron microscopy (SEM) images or SEM/energy-dispersive X-ray spectroscopy of 3AZ–metal oxide porous polymer composites were acquired by a JEOL JSM-7610F microscope (Tokyo, Japan) with an LEI detector at an acceleration voltage of 3.0 kV or 20 kV, respectively. The nitrogen (N) content was determined by the atomic number (Z), absorption (A), fluorescence (F) (ZAF) correction method. The average size in the SEM images was evaluated by image analysis using an Image-J software package (Version 1.54). About 50 to 100 particles were counted.
The surface area of the porous polymer was measured by nitrogen sorption using an Autosorb 6AG (Quantachrome Instruments, Boynton Beach, FL, USA) and a Belsorp II mini (MicrotracBEL Corp., Osaka, Japan). The samples were dried under reduced pressure at 100 °C for 1 h immediately before the measurement.
The mechanical properties of the porous polymer composites were investigated using the compression test with a Tensilon RTE-1210 apparatus (ORIENTEC Co., Ltd., Tokyo, Japan). The test samples were cut into a 1 cm3 cube and pressed at a rate of 0.5 mm/min at room temperature. The test was conducted five times per sample, and the middle result was adopted. The samples were stored at 23 °C and a relative humidity of 50% (JIS Z 8703) for 48 h before the test.
The bulk density of the porous polymer composite, g/cm3, was calculated from the weight of the samples before the test.
Thermogravimetric (TG) analysis of the porous polymer composites was conducted with a Bruker AXS TG-DTA2020SA (Billerica, MA, USA). The sample was heated from room temperature to 500 °C at a rate of 20 °C/min under an argon atmosphere.

4. Conclusions

The ring-opening polymerizations of 3AZ in water in the presence of SiO2 and ZrO2 nanoparticles successfully yielded ethylene imine-based polymer nanocomposites. The resulting porous polymer nanocomposites showed a morphology composed of connected particles with diameters less than 1 μm, which was formed through polymerization-induced phase separation via a spinodal decomposition process. The nanocomposites with SiO2 and ZrO2 nanoparticles had drastically decreased particle sizes and increased bulk densities and Young’s moduli. In the case of the 3AZ-SiO2 porous polymer nanocomposites, the nature of the SiO2 nanoparticles used affected the porous morphology and the mechanical properties. An increase in SiO2 nanoparticle concentration increased the Young’s moduli of the resulting porous polymer nanocomposites. ZrO2 nanoparticle concentrations of 2.0 or 4.0 wt% were suitable to attain 3AZ-ZrO2 porous polymer nanocomposites with high Young’s moduli. Further increase in ZrO2 nanoparticle concentration decreased the Young’s moduli of the porous polymer nanocomposites. One explanation for the result may be an interfacial failure between the polymer networks and the ZrO2 nanoparticles. The lower polymerization temperature increased the Young’s modulus of the porous polymer nanocomposites with ZrO2 nanoparticles. The nanocomposites with SiO2 and ZrO2 nanoparticles effectively retarded thermal decomposition.
The present research can provide a facile and practical method to prepare porous polymer nanocomposites. Here, a simple dissolution of 3AZ in commercially available metal oxide sols can yield the corresponding porous polymer nanocomposites. The previously reported 3AZ porous polymers (without metal oxide) were composed of micrometer-order particles, which showed high permeability of solutions. The features of 3AZ porous polymers should be suitable for separation and purification in biochemistry by chemical interactions. The present nanocomposition decreases the particle size in porous polymers to less than 1 μm. The size is less than that of suspended particulate matter. These porous polymer composites are applicable for separators and filters for soot, smoke, etc. by utilizing thermal stability. We are also preparing some porous polymer composites with other polymer materials using similar methods. These results will be reported elsewhere in due course.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/molecules30173574/s1. Figure S1: FT-IR spectra of 3AZ-ZrO2 porous polymer nanocomposites; Figure S2: SEM images of 3AZ-ST20 porous polymer composites; Figure S3: Histograms of particle diameter of 3AZ-SiO2 porous polymer composites; Figure S4: SEM images of 3AZ-ZrO2 porous polymer composites; Figure S5: Histograms of particle diameter of 3AZ-ZrO2 porous polymer composites; Figure S6: FT-IR spectra of 3AZ-ZrO2 porous polymer nanocomposites (ZrO2 nanoparticle feed and preparation temperature).

Author Contributions

Conceptualization, N.N. and T.N.; investigation, J.J. and T.T.; analysis, T.T., N.N., and T.N.; writing—original draft preparation, N.N.; writing—review and editing, J.J. and T.N.; supervision, N.N. and T.N.; project administration, N.N.; funding acquisition, N.N. and T.N. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partially supported by ICAT, Hokkaido University, thorough the Joint Usage/Research Center for Catalyst grant.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available in the article or in the Supplementary Material.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Shameem, M.M.; Sasikanth, S.M.; Raja, A.; Raman, R.G. A brief review on polymer nanocomposites and its applications. Mater. Today Proc. 2021, 45, 2536–2539. [Google Scholar] [CrossRef]
  2. Gobena, S.T.; Woldeyonnes, A.D. A review of synthesis methods, and characterization techniques of polymer nanocomposites for diverse applications. Discov. Mater. 2024, 4, 52. [Google Scholar] [CrossRef]
  3. Khan, I.; Khan, I.; Saeed, K.; Ali, N.; Zada, N.; Khan, A.; Ali, F.; Bilal, M.; Akhter, M.S. 7-Polymer nanocomposites: An overview. Smart Polym. Nanocompos. 2023, 167–184. [Google Scholar] [CrossRef]
  4. Jamil, H.; Faizan, M.; Adeel, M.; Jesionowski, T.; Boczkaj, G.; Balčiūnaitė, A. Recent Advances in Polymer Nanocomposites: Unveiling the Frontier of Shape Memory and Self-Healing Properties—A Comprehensive Review. Molecules 2024, 29, 1267. [Google Scholar] [CrossRef] [PubMed]
  5. Zhan, C.; Yu, G.; Lu, Y.; Wang, L.; Wujcik, E.; Wei, S. Conductive polymer nanocomposites: A critical review of modern advanced devices. J. Mater. Chem. C 2017, 5, 1569–1585. [Google Scholar] [CrossRef]
  6. Wu, D.; Xu, F.; Sun, B.; Fu, R.; He, H.; Matyjaszewski, K. Design and Preparation of Porous Polymers. Chem. Rev. 2012, 112, 3959–4015. [Google Scholar] [CrossRef]
  7. Liu, Q.; Xiong, J.; Lin, W.; Liu, J.; Wan, Y.; Guo, C.F.; Wang, Q.; Liu, Z. Porous polymers: Structure, fabrication and application. Mater. Horiz. 2025, 12, 2436–2466. [Google Scholar] [CrossRef]
  8. Ahmed, D.S.; El-Hiti, G.A.; Yousif, E.; Ali, A.A.; Hameed, A.S. Design and synthesis of porous polymeric materials and their applications in gas capture and storage: A review. J. Polym. Res. 2018, 25, 75. [Google Scholar] [CrossRef]
  9. Tsujioka, N.; Hira, N.; Aoki, S.; Tanaka, N.; Hosoya, K. A New Preparation Method for Well-Controlled 3D Skeletal Epoxy Resin-Based Polymer Monoliths. Macromolecules 2005, 38, 9901–9903. [Google Scholar] [CrossRef]
  10. Tsujioka, N.; Ishizuka, N.; Tanaka, N.; Kubo, T.; Hosoya, K. Well-Controlled 3D Skeletal Epoxy-Based Monoliths Obtained by Polymerization Induced Phase Separation. J. Polym. Sci. Part A Polym. Chem. 2008, 46, 3272–3281. [Google Scholar] [CrossRef]
  11. Hosoya, K.; Hira, N.; Yamamoto, K.; Nishimura, M.; Tanaka, N. High-Performance Polymer-Based Monolithic Capillary Column. Anal. Chem. 2006, 78, 5729–5737. [Google Scholar] [CrossRef]
  12. Kamo, Y.; Matsumoto, A. Control of Pore Sizes in Epoxy Monoliths and Applications as Sheet-Type Adhesives in Combination with Conventional Epoxy and Acrylic Adhesives. Molecules 2024, 29, 2059. [Google Scholar] [CrossRef]
  13. Sakakibara, K.; Kagata, H.; Ishizuka, H.; Sato, T.; Tsujii, Y. Fabrication of surface skinless membranes of epoxy resin-based mesoporous monoliths toward advanced separators for lithium ion batteries. J. Mater. Chem. A 2017, 5, 6866. [Google Scholar] [CrossRef]
  14. Li, J.; Du, X.; Li, H.; Zhang, C. Porous epoxy monolith prepared via chemically induced phase separation. Polymer 2009, 50, 1526–1532. [Google Scholar] [CrossRef]
  15. Wang, S.; Zhang, R. Column preconcentration of lead in aqueous solution with microporous epoxy resin-based polymer monolithic matrix. Anal. Chim. Acta 2006, 575, 166–171. [Google Scholar] [CrossRef] [PubMed]
  16. Nguyen, A.M.; Irgum, K. Epoxy-Based Monoliths. A Novel Hydrophilic Separation Material for Liquid Chromatography of Biomolecules. Chem. Mater. 2006, 18, 6308–6315. [Google Scholar] [CrossRef]
  17. Nguyen, A.M.; Phuoc, D.N.; Cam, Q.M.; Sparrman, T.; Irgum, K. Preparation and characterization of sizable microporous epoxy resin-based monolithic supports for flow-through systems. J. Sep. Sci. 2009, 32, 2608–2618. [Google Scholar] [CrossRef]
  18. Naga, N.; Takenouchi, T.; Nakano, T. Ring-Opening Polymerization of Triaziridine Compounds in Water: An Extremely Facile Method to Synthesize a Porous Polymer through Polymerization-Induced Phase Separation. ACS Macro Lett. 2022, 11, 602–607. [Google Scholar] [CrossRef]
  19. Oehl, G.; Naga, N.; Ziegmann, G. Facile Synthesis of Poly(methyl methacrylate) Silica Nanocomposite Monolith by In Situ Free Radical Polymerization of Methyl Methacrylate in the Presence of Functionalized Silica Nanoparticles. ACS Omega 2024, 9, 16279–16287. [Google Scholar] [CrossRef]
  20. Naga, N.; Miyazaki, Y.; Nakano, T. Porous Composite Polymers Composed of Polyethyleneimine and Cyclodextrins: Synthesis and Application as Adsorbents for an Organic Compound. Separations 2025, 12, 94. [Google Scholar] [CrossRef]
  21. Naito, K.; Nagai, C.; Kawasaki, S. Tensile Properties and Weibull Modulus of Polymeric-Fiber-Reinforced Epoxy-Impregnated Bundle Composites. J. Compos. Sci. 2024, 8, 390. [Google Scholar] [CrossRef]
  22. Cahill, D.G.; Poul, R.O. Thermal conductivity of amorphous solids above the plateau. Phys. Rev. B 1992, 46, 6131. [Google Scholar] [CrossRef] [PubMed]
  23. Levi, C.G. Emerging materials and processes for thermal barrier systems. Curr. Opin. Solid State Mater. Sci. 2004, 8, 77–91. [Google Scholar] [CrossRef]
Molecules 30 03574 sch001
Scheme 1. A model of polymerization-induced phase separation via the spinodal decomposition process, (a) homogeneous solution, (b) co-continuous structure, (c) particles, (d) grown particles, and (e) precipitation.
Scheme 1. A model of polymerization-induced phase separation via the spinodal decomposition process, (a) homogeneous solution, (b) co-continuous structure, (c) particles, (d) grown particles, and (e) precipitation.
Molecules 30 03574 sch001
Molecules 30 03574 sch002
Scheme 2. Synthesis of ethylene imine-based porous polymer nanocomposites by ring-opening polymerization of 3AZ in the presence of metal oxide nanoparticles (SiO2 and ZrO2).
Scheme 2. Synthesis of ethylene imine-based porous polymer nanocomposites by ring-opening polymerization of 3AZ in the presence of metal oxide nanoparticles (SiO2 and ZrO2).
Molecules 30 03574 sch002
Molecules 30 03574 g001
Figure 1. Production diagrams of 3AZ with SiO2 nanoparticles: (a) ST-20, (b) ST-N, (c) ST-C, (d) ST-O, and (e) ST-AK systems; 3AZ monomer concentration: 20 wt%.
Figure 1. Production diagrams of 3AZ with SiO2 nanoparticles: (a) ST-20, (b) ST-N, (c) ST-C, (d) ST-O, and (e) ST-AK systems; 3AZ monomer concentration: 20 wt%.
Molecules 30 03574 g001
Molecules 30 03574 g002
Figure 2. SEM images of 3AZ-SiO2 porous polymer composites (SiO2 colloids, SiO2 feed, and preparation temperature); 3AZ monomer concentration: 20 wt%.
Figure 2. SEM images of 3AZ-SiO2 porous polymer composites (SiO2 colloids, SiO2 feed, and preparation temperature); 3AZ monomer concentration: 20 wt%.
Molecules 30 03574 g002
Molecules 30 03574 g003
Figure 3. FT-IR spectra of (a) 3AZ monomer, (b) 3AZ porous polymer, and (c) 3AZ-ST-20 porous polymer composite (run 11).
Figure 3. FT-IR spectra of (a) 3AZ monomer, (b) 3AZ porous polymer, and (c) 3AZ-ST-20 porous polymer composite (run 11).
Molecules 30 03574 g003
Molecules 30 03574 g004
Figure 4. SEM (a) and SEM-EDX (b–e) images of 3AZ-ST-20 porous polymer composite (run 9). Element mapping: (b) C element, (c) N element, (d) O element, and (e) Si element.
Figure 4. SEM (a) and SEM-EDX (b–e) images of 3AZ-ST-20 porous polymer composite (run 9). Element mapping: (b) C element, (c) N element, (d) O element, and (e) Si element.
Molecules 30 03574 g004
Molecules 30 03574 g005
Figure 5. SEM images of 3AZ-ZrO2 (Z-S20H) porous polymer composites (ZrO2 nanoparticle feed and preparation temperature); 3AZ monomer concentration: 20 wt%.
Figure 5. SEM images of 3AZ-ZrO2 (Z-S20H) porous polymer composites (ZrO2 nanoparticle feed and preparation temperature); 3AZ monomer concentration: 20 wt%.
Molecules 30 03574 g005
Molecules 30 03574 g006
Figure 6. Stress–strain curves of 3AZ-SiO2 porous polymer nanocomposites: (a) 3AZ (run 3), (b) 3AZ-ST-20 (run 8), (c) 3AZ-ST-N (run 14), (d) 3AZ-ST-C (run 19), (e) 3AZ-ST-O (run 24), and (f) 3AZ-ST-AK (run 27); SiO2 concentration: 2.0 wt%.
Figure 6. Stress–strain curves of 3AZ-SiO2 porous polymer nanocomposites: (a) 3AZ (run 3), (b) 3AZ-ST-20 (run 8), (c) 3AZ-ST-N (run 14), (d) 3AZ-ST-C (run 19), (e) 3AZ-ST-O (run 24), and (f) 3AZ-ST-AK (run 27); SiO2 concentration: 2.0 wt%.
Molecules 30 03574 g006
Molecules 30 03574 g007
Figure 7. Stress–strain curves of 3AZ-ZrO2 porous polymer composites, ZrO2 concentration: (a) 1.0 wt% (run 36), (b) 2.0 wt% (run 37), (c) 4.0 wt% (run 38), and (d) 6.0 wt% (run 39).
Figure 7. Stress–strain curves of 3AZ-ZrO2 porous polymer composites, ZrO2 concentration: (a) 1.0 wt% (run 36), (b) 2.0 wt% (run 37), (c) 4.0 wt% (run 38), and (d) 6.0 wt% (run 39).
Molecules 30 03574 g007
Molecules 30 03574 g008
Figure 8. TG curves of 3AZ-SiO2 (ST-20) porous polymer composites with different SiO2 concentrations: (a) 0 wt% (run 3), (b) 2.0 wt% (run 8), (c) 4.0 wt% (run 9), and (d) 6.0 wt% (run 10).
Figure 8. TG curves of 3AZ-SiO2 (ST-20) porous polymer composites with different SiO2 concentrations: (a) 0 wt% (run 3), (b) 2.0 wt% (run 8), (c) 4.0 wt% (run 9), and (d) 6.0 wt% (run 10).
Molecules 30 03574 g008
Molecules 30 03574 g009
Figure 9. TG curves of 3AZ-ZrO2 porous polymer composites with different ZrO2 nanoparticle concentrations: (a) 2.0 wt% (run 37), (b) 4.0 wt% (run 38), and (c) 6.0 wt% (run 39).
Figure 9. TG curves of 3AZ-ZrO2 porous polymer composites with different ZrO2 nanoparticle concentrations: (a) 2.0 wt% (run 37), (b) 4.0 wt% (run 38), and (c) 6.0 wt% (run 39).
Molecules 30 03574 g009
Table 1. Polymerization conditions, structure, and Young’s moduli of 3AZ-SiO2 porous polymer nanocomposites.
Table 1. Polymerization conditions, structure, and Young’s moduli of 3AZ-SiO2 porous polymer nanocomposites.
RunSiO2SiO2 Concentration (wt%)Temp.
(°C)		Average Diameter (nm)SD a
(nm)		CV bBulk
Density
(g/cm3)		Young’s
Modulus (kPa)		Wibull Constant
1non0204070 0.272434.19.4
2non0404820 0.295381.111.7
3non0604710 0.279316.78.8
4ST-202.02026844.50.170.61145797.4
5ST-202.04024066.50.280.49910927.1
6ST-204.040555112.50.200.66076117.3
7ST-206.04037272.80.200.75314,56510.6
8ST-202.06026758.90.220.46451108.0
9ST-204.060473123.80.260.64262517.3
10ST-206.060535123.40.200.81298387.7
11ST-N2.020--- 0.61649059.3
12ST-N2.040443112.00.250.46012967.1
13ST-N4.040416103.00.250.795423010.2
14ST-N2.06041297.60.240.48521047.4
15ST-N4.06019836.70.190.82435618.6
16ST-C2.02034651.90.150.69754007.6
17ST-C2.04031172.10.230.52714729.3
18ST-C4.04019839.50.200.81289527.6
19ST-C2.060506140.90.280.465147711.5
20ST-C4.06022151.20.230.75155727.4
21ST-C6.06021544.40.210.90515,0429.6
22ST-O2.02041583.70.200.77337449.0
23ST-O2.040463118.10.260.499984.28.6
24ST-O2.06036854.60.150.482734.38.6
25ST-AK2.02024156.40.230.82255489.9
26ST-AK2.040808179.00.220.382146810.1
27ST-AK2.0601004247.20.250.47818759.1
a Standard deviation of the particles’ diameters, b coefficient of validation: SD/average diameter.
Table 2. Polymerization conditions, structure, and Young’s moduli of the 3AZ-ZrO2 porous polymer nanocomposites.
Table 2. Polymerization conditions, structure, and Young’s moduli of the 3AZ-ZrO2 porous polymer nanocomposites.
RunZrO2 Concentration (wt%)Temp.
(°C)		Average
Particle Size (nm)		SD a (nm)CV bBulk Density (g/cm3)Young’s Modulus (kPa)Wibull Constant
281.020750107.30.140.26827869.5
292.02044868.50.150.42613,90411.3
304.02026342.20.160.45733868.6
316.02017134.90.200.57019667.7
321.040687117.50.170.42421279.0
332.04039753.40.130.46517008.4
344.04029958.30.200.46931599.8
356.04017029.30.170.51629249.1
361.06061999.10.160.426143510.2
372.06042980.00.190.50217089.7
384.06023841.20.170.52929178.5
396.06016737.90.230.549865.79.7
a Standard deviation of the particles’ diameters, b coefficient of validation: SD/average diameter.
Table 3. Thermal properties of 3AZ-SiO2 and ZrO2 porous polymer nanocomposites.
Table 3. Thermal properties of 3AZ-SiO2 and ZrO2 porous polymer nanocomposites.
RunMetal
Oxide		Metal Oxide Concentration (wt%)Tdon a
(°C)		Rdmax b
(wt%/K)		Char c
(wt%)
3non0234.71.2126.4
8ST-202.0236.01.0727.0
9ST-204.0240.30.8634.2
10ST-206.0240.70.6140.1
24ST-O2.0242.51.0229.2
37ZrO22.0224.62.6826.5
38ZrO24.0233.41.1830.5
39ZrO26.0233.60.7440.0
a Onset temperature of thermal degradation (intersection of tangents), b maximum degradation rate, c char yield at 500 °C.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Naga, N.; Janas, J.; Takenouchi, T.; Nakano, T. Synthesis and Properties of Ethylene Imine-Based Porous Polymer Nanocomposites with Metal Oxide Nanoparticles. Molecules 2025, 30, 3574. https://doi.org/10.3390/molecules30173574

AMA Style

Naga N, Janas J, Takenouchi T, Nakano T. Synthesis and Properties of Ethylene Imine-Based Porous Polymer Nanocomposites with Metal Oxide Nanoparticles. Molecules. 2025; 30(17):3574. https://doi.org/10.3390/molecules30173574

Chicago/Turabian Style

Naga, Naofumi, Julia Janas, Tomoya Takenouchi, and Tamaki Nakano. 2025. "Synthesis and Properties of Ethylene Imine-Based Porous Polymer Nanocomposites with Metal Oxide Nanoparticles" Molecules 30, no. 17: 3574. https://doi.org/10.3390/molecules30173574

APA Style

Naga, N., Janas, J., Takenouchi, T., & Nakano, T. (2025). Synthesis and Properties of Ethylene Imine-Based Porous Polymer Nanocomposites with Metal Oxide Nanoparticles. Molecules, 30(17), 3574. https://doi.org/10.3390/molecules30173574

Article Metrics

Back to TopTop