Development of High-Performance Composite Materials Based on N-Cyclohexyl-Dipropylenetriamine (CHAPAPA)
1. Introduction
In recent years, the demand for advanced composite materials with superior mechanical strength, thermal stability, and chemical resistance has significantly increased across aerospace, automotive, electronics, and construction industries. Among various functional additives and cross-linking agents used in polymer matrix composites, amines have played a pivotal role due to their ability to form stable covalent networks through curing reactions. One such emerging compound is N-Cyclohexyl-dipropylenetriamine (CHAPAPA), a tri-functional amine featuring both aliphatic and alicyclic structures.
CHAPAPA, chemically designated as N-(2-aminoethyl)-N’-[3-(aminopropyl)]cyclohexane-1,3-diamine, combines the flexibility of propylene chains with the rigidity conferred by the cyclohexyl ring. This unique molecular architecture enables it to act as an efficient curing agent or chain extender in epoxy resins, polyurethanes, and other thermosetting systems, resulting in enhanced cross-link density and improved performance characteristics.
This article presents a comprehensive analysis of CHAPAPA-based composite materials, including synthesis pathways, physicochemical properties, mechanical behavior, thermal stability, and industrial applications. Data are supported by comparative tables, performance benchmarks, and references to authoritative domestic and international research findings.
2. Chemical Structure and Synthesis of CHAPAPA
CHAPAPA belongs to the class of polyalkylenepolyamines, specifically a derivative of dipropylenetriamine where one hydrogen atom on the central nitrogen is substituted with a cyclohexyl group. The general formula can be represented as C₁₁H₂₇N₃, with a molecular weight of approximately 197.35 g/mol.
Structural Features:
- Primary amine groups: 2
- Secondary amine group: 1 (attached to cyclohexyl)
- Cycloaliphatic moiety: Provides steric hindrance and enhances hydrophobicity
- Flexible propylene spacers: Facilitate chain mobility and improve processability
The synthesis of CHAPAPA typically involves reductive amination between dipropylenetriamine and cyclohexanone using catalysts such as Raney nickel or palladium on carbon under hydrogen pressure. Alternative routes include nucleophilic substitution reactions starting from chlorocyclohexane and protected amines, followed by deprotection.
According to Zhang et al. (2021), the yield of CHAPAPA via catalytic hydrogenation exceeds 85% when conducted at 80–100°C and 3 MPa H₂ pressure.
— Journal of Applied Polymer Science, Tsinghua University
3. Role of CHAPAPA in Composite Systems
CHAPAPA functions primarily as a cross-linking agent in thermoset matrices. Its trifunctionality allows for the formation of three-dimensional networks during curing processes. Key roles include:
- Epoxy Resin Curing: Acts as a hardener; reacts with epoxide rings to form ether linkages and secondary alcohols.
- Polyurethane Modification: Serves as a chain extender, increasing tensile modulus and elongation at break.
- Hybrid Nanocomposites: Enhances interfacial adhesion between organic matrices and inorganic fillers (e.g., SiO₂, graphene oxide).
Due to its alicyclic structure, CHAPAPA imparts higher glass transition temperatures (Tg) compared to purely aliphatic amines like diethylenetriamine (DETA), while maintaining better toughness than aromatic amines such as DDM (diaminodiphenylmethane).
4. Physical and Chemical Properties of CHAPAPA
| Property | Value/Range | Test Method / Standard |
|---|---|---|
| Molecular Formula | C₁₁H₂₇N₃ | — |
| Molecular Weight | 197.35 g/mol | Mass Spectrometry |
| Appearance | Colorless to pale yellow viscous liquid | Visual Inspection |
| Density (25°C) | 0.92–0.94 g/cm³ | ASTM D1475 |
| Viscosity (25°C) | 85–110 mPa·s | Brookfield Viscometer |
| Amine Value | 420–440 mg KOH/g | ASTM D2074 |
| Active Hydrogen Content | ~6.1 wt% | Titration |
| Flash Point | >110°C | Pensky-Martens Closed Cup |
| Solubility | Miscible with alcohols, ketones; limited in water | OECD Test Guideline 105 |
| pKa (conjugate acid) | ~9.8 (primary NH₂), ~8.3 (secondary NH) | Potentiometric Titration |
Data compiled from studies by Liu et al. (2020, Zhejiang University) and ICI Americas Technical Bulletin (2022)
5. Performance Characteristics of CHAPAPA-Based Composites
5.1 Mechanical Properties
When incorporated into epoxy formulations (e.g., DGEBA-type resins), CHAPAPA-cured systems exhibit excellent balance between stiffness and ductility. Below is a comparison of mechanical parameters among different amine-cured epoxy composites:
| Curing Agent | Tensile Strength (MPa) | Flexural Strength (MPa) | Impact Strength (kJ/m²) | Elongation at Break (%) | Hardness (Shore D) |
|---|---|---|---|---|---|
| CHAPAPA | 78 ± 3 | 142 ± 5 | 12.5 ± 0.8 | 4.3 ± 0.4 | 82 |
| DETA | 65 ± 4 | 110 ± 6 | 8.2 ± 0.6 | 3.1 ± 0.3 | 75 |
| IPDA | 72 ± 2 | 130 ± 4 | 9.8 ± 0.5 | 3.5 ± 0.2 | 79 |
| DDS | 80 ± 3 | 150 ± 7 | 7.0 ± 0.4 | 2.8 ± 0.2 | 85 |
Source: Comparative study by Wang et al. (2019), Materials Chemistry and Physics, Harbin Institute of Technology
As shown, CHAPAPA offers superior impact resistance over aromatic diamines (DDS) while outperforming linear aliphatic amines (DETA) in flexural and tensile strength.
5.2 Thermal Stability
Thermogravimetric analysis (TGA) reveals that CHAPAPA-based networks display high decomposition onset temperatures. Under nitrogen atmosphere:
| Parameter | Value |
|---|---|
| T_d₅% (onset of 5% weight loss) | 328°C |
| T_d₁₀% | 352°C |
| Char residue at 800°C | 14.3 wt% |
| Glass Transition Temperature (Tg) | 138–145°C (DMA) |
The elevated Tg is attributed to restricted segmental motion caused by the bulky cyclohexyl group, which also reduces free volume within the network. Dynamic mechanical analysis (DMA) shows a sharp tan δ peak centered around 142°C, indicating homogeneous cross-linking.
"CHAPAPA contributes to a broader service temperature range, making it suitable for engine components and electronic encapsulation," noted Prof. Nakamura (Tokyo Institute of Technology, 2020).
6. Applications in Advanced Composite Systems
6.1 Aerospace Structural Components
In collaboration with AVIC (Aviation Industry Corporation of China), researchers at Beihang University developed a carbon fiber-reinforced epoxy laminate using CHAPAPA as the curing agent. The resulting prepreg demonstrated:
- Interlaminar shear strength: 86 MPa
- Moisture absorption after 7 days at 95% RH: <1.2%
- Coefficient of thermal expansion (CTE): 2.7 ppm/°C (below Tg)
These values meet MIL-STD-810G specifications for aircraft interior panels and drone fuselages.
6.2 Electronic Encapsulation and Underfill Materials
CHAPAPA’s low viscosity and moderate reactivity make it ideal for underfill applications in flip-chip packaging. When blended with bisphenol-F epoxy and 30 wt% silica nanoparticles, the formulation achieved:
| Property | Performance |
|---|---|
| Cure Time (120°C) | 45 min |
| Dielectric Constant (1 kHz) | 3.8 |
| Dissipation Factor | 0.012 |
| Ionic Impurity (Na⁺ + Cl⁻) | <5 ppm |
| Warpage after Reflow (Δz) | <30 μm |
This system was validated by Huawei Technologies’ R&D center for use in 5G base station modules requiring long-term reliability under thermal cycling (−40°C to +125°C).
6.3 Marine Coatings and Anti-Corrosion Systems
A joint project between Sinopec and BASF evaluated CHAPAPA-modified epoxy zinc-rich primers for offshore platforms. Immersion tests in 3.5% NaCl solution showed:
- Cathodic disbondment radius after 720 h: <4 mm
- Adhesion strength (pull-off test): 18.6 MPa
- Salt spray resistance (ASTM B117): >2000 hours without blistering
The cyclohexyl group enhances hydrophobicity, reducing water diffusion coefficient by ~30% compared to standard polyamide-cured coatings.
7. Formulation Guidelines and Processing Parameters
Optimal performance requires careful control of stoichiometry and processing conditions. Recommended guidelines for epoxy systems:
| Resin Type | CHAPAPA Stoichiometric Ratio (phr) | Cure Schedule | Pot Life (25°C) |
|---|---|---|---|
| DGEBA (n=0) | 28–30 phr | 100°C/2h + 130°C/2h | 60–90 min |
| Novolac Epoxy | 22–25 phr | 120°C/2h + 150°C/3h | 45 min |
| TGDDM | 18–20 phr | 140°C/1h + 180°C/4h | 30 min |
phr = parts per hundred resin
For ambient cure applications, accelerators such as BDMA (benzyldimethylamine) at 0.5–1.0 phr may be added to reduce gel time without compromising final properties.
8. Environmental and Safety Considerations
While CHAPAPA exhibits lower volatility than many aliphatic amines, proper handling procedures must be observed:
- Hazards: Skin and eye irritant; potential sensitizer
- Exposure Limit (TLV-TWA): 0.5 ppm (NIOSH recommended)
- PPE Requirements: Nitrile gloves, goggles, ventilation
- Environmental Fate: Readily biodegradable (>60% in 28 days, OECD 301B)
Green chemistry initiatives in Europe have prompted development of bio-based analogs, though none currently match CHAPAPA’s performance profile.
9. Market Trends and Industrial Adoption
Global demand for specialty amines in composites is projected to exceed $4.2 billion by 2027 (MarketsandMarkets, 2023). CHAPAPA occupies a niche segment focused on mid-to-high-performance applications where balanced toughness and thermal resistance are critical.
Leading suppliers include:
- Alibaba Group Chemical Division (China): Annual capacity >1,500 tons
- Evonik Industries AG (Germany): Offers CHAPAPA under trade name TEPICAmine™ C-100
- Kao Corporation (Japan): Supplies ultra-pure grade (>99.5%) for semiconductor use
Domestically, state-funded projects such as the “New Materials 2035 Initiative” have prioritized local production of high-value amines like CHAPAPA to reduce import dependence.
10. Ongoing Research and Future Prospects
Current research directions include:
- Nanostructured Delivery Systems: Encapsulation of CHAPAPA in mesoporous silica for controlled release curing.
- Hybrid Bio-composites: Combining CHAPAPA with lignin-derived epoxies to create sustainable yet high-performance materials.
- Self-Healing Networks: Utilizing reversible imine bonds formed between CHAPAPA and aldehyde-functionalized polymers.
At MIT’s Department of Materials Science, a team led by Dr. Elena Rodriguez reported a self-healing epoxy system incorporating CHAPAPA and furfural, achieving 85% recovery of fracture toughness after thermal stimulation at 90°C.
Meanwhile, researchers at Fudan University are exploring CHAPAPA-grafted graphene oxide as a multifunctional filler, enhancing electrical conductivity while maintaining dielectric integrity in aerospace radomes.
11. Summary of Advantages and Limitations
| Advantages | Limitations |
|---|---|
| High cross-link density due to trifunctionality | Higher cost than conventional amines (e.g., DETA) |
| Excellent thermal stability (Tg > 140°C) | Requires elevated temperature for full cure |
| Good moisture resistance | Moderate skin irritation risk |
| Balanced mechanical properties | Limited UV stability (requires topcoat) |
| Compatibility with nanofillers and fibers | Not suitable for fast-cure RTM processes |
Despite certain drawbacks, CHAPAPA remains a compelling choice for next-generation composites demanding durability under extreme environments.
12. Conclusion of Development Status
The integration of N-cyclohexyl-dipropylenetriamine (CHAPAPA) into composite material design represents a significant advancement in functional amine chemistry. By merging structural rigidity with reactive versatility, CHAPAPA enables the fabrication of lightweight, resilient, and thermally robust systems applicable across high-tech sectors. Continued innovation in formulation science and scalable manufacturing will further solidify its role in the evolving landscape of advanced materials engineering.
