N,N-Dimethylcyclohexylamine: A Comprehensive Review of its Performance as a Gelling Catalyst

Introduction

N,N-Dimethylcyclohexylamine (DMCHA), a tertiary amine, is a widely utilized catalyst in the production of polyurethane (PU) foams, elastomers, and coatings. Its primary function is to accelerate the reaction between isocyanates and polyols, facilitating the gelling process and influencing the final properties of the resulting polyurethane material. This article provides a comprehensive overview of DMCHA’s properties, reaction mechanisms, performance parameters, influencing factors, and applications as a gelling catalyst. The information is structured in a manner similar to a Baidu Baike entry, emphasizing rigorous language, standardized terminology, and clear organization.

1. Chemical Identity and Properties

• Chemical Name: N,N-Dimethylcyclohexylamine
• Synonyms: Dimethylcyclohexylamine; 1-(Dimethylamino)cyclohexane; Cyclohexane, (dimethylamino)-
• CAS Registry Number: 98-94-2
• Molecular Formula: C₈H₁₇N
• Molecular Weight: 127.23 g/mol
• Structural Formula: (Insert Structural Formula Here – This is represented conceptually as this response cannot directly insert images) – A cyclohexane ring with a dimethylamino (-N(CH3)2) group attached to one of the carbons.
• Appearance: Colorless to light yellow liquid
• Odor: Amine-like odor
• Boiling Point: 160-162 °C
• Melting Point: -60 °C
• Density: 0.85 g/cm³ at 20 °C
• Refractive Index: 1.447-1.449 at 20 °C
• Viscosity: Low viscosity
• Solubility: Soluble in most organic solvents, slightly soluble in water.
• Flash Point: 45 °C (Closed Cup)
• Vapor Pressure: Low vapor pressure

Table 1: Summary of Key Physicochemical Properties of DMCHA

Property	Value	Unit
Molecular Weight	127.23	g/mol
Boiling Point	160-162	°C
Melting Point	-60	°C
Density	0.85	g/cm³ (at 20 °C)
Refractive Index	1.447-1.449	(at 20 °C)
Flash Point	45	°C (Closed Cup)

2. Reaction Mechanism as a Gelling Catalyst

DMCHA, as a tertiary amine, acts as a catalyst in the isocyanate-polyol reaction, which is the fundamental reaction in polyurethane formation. The mechanism can be summarized as follows:

1. Proton Abstraction: DMCHA, possessing a lone pair of electrons on the nitrogen atom, acts as a base, abstracting a proton from either the hydroxyl group of the polyol or from a water molecule. This proton abstraction forms a reactive alkoxide ion or a hydroxyl ion, respectively.

2. Nucleophilic Attack: The resulting alkoxide or hydroxyl ion, now a strong nucleophile, attacks the electrophilic carbon atom of the isocyanate group (-N=C=O).

3. Urethane Formation (Polyol Reaction): When the alkoxide ion attacks the isocyanate, it forms a urethane linkage (-NH-CO-O-), extending the polymer chain and contributing to the gelling process.

4. Urea Formation (Water Reaction): When the hydroxyl ion attacks the isocyanate, it forms an unstable carbamic acid intermediate. This intermediate decomposes to form an amine and carbon dioxide. The amine then reacts with another isocyanate molecule to form a urea linkage (-NH-CO-NH-), which also contributes to chain extension and the formation of hard segments in the polyurethane. The carbon dioxide generated acts as a blowing agent in foam production.

5. Catalyst Regeneration: The DMCHA molecule is regenerated in the process, allowing it to participate in further catalytic cycles.

The relative rates of the urethane and urea reactions are influenced by the catalyst type and concentration, as well as other factors such as temperature and reactant composition. DMCHA tends to favor the gelling (urethane) reaction more strongly than the blowing (urea) reaction, making it a useful catalyst for applications where a faster gel time is desired.

3. Performance Parameters and Evaluation Methods

The performance of DMCHA as a gelling catalyst is evaluated based on several key parameters:

• Cream Time: The time elapsed between the mixing of the reactants (isocyanate, polyol, catalyst, etc.) and the point at which the mixture starts to rise or cream. Shorter cream times indicate faster reaction rates.
• Gel Time: The time it takes for the mixture to transition from a liquid to a semi-solid or gelled state. Gel time is a crucial indicator of the rate of chain extension and crosslinking. Shorter gel times are generally desirable for faster processing and improved productivity.
• Tack-Free Time: The time required for the surface of the polyurethane material to become non-sticky or tack-free. This parameter is important for applications such as coatings and adhesives.
• Rise Time: The total time it takes for a polyurethane foam to reach its maximum height. This parameter is relevant for foam applications and is influenced by both the gelling and blowing reactions.
• Demold Time: The minimum time required before a molded polyurethane part can be removed from the mold without deformation.
• Tensile Strength: A measure of the material’s resistance to breaking under tension.
• Elongation at Break: The percentage increase in length of the material before it breaks under tension.
• Hardness: A measure of the material’s resistance to indentation. Typically measured using Shore A or Shore D durometers.
• Density (for foams): The mass per unit volume of the foam.
• Cell Structure (for foams): The size, shape, and uniformity of the cells in the foam. A fine and uniform cell structure generally leads to better physical properties.
• Compressive Strength (for foams): A measure of the foam’s resistance to compression.

Table 2: Common Evaluation Methods for DMCHA Catalyst Performance

Parameter	Evaluation Method
Cream Time	Visual observation, stopwatch
Gel Time	Visual observation (stirring rod test), automatic gel timer
Tack-Free Time	Touch test, visual observation
Rise Time	Visual observation, measuring height of rising foam
Demold Time	Trial and error, observing for deformation upon demolding
Tensile Strength	ASTM D412, ISO 37
Elongation	ASTM D412, ISO 37
Hardness	ASTM D2240 (Shore A or D), ISO 868
Density (Foam)	ASTM D1622, ISO 845
Cell Structure	Microscopic analysis (optical or scanning electron microscopy)
Compressive Strength (Foam)	ASTM D1621, ISO 844

The choice of evaluation methods depends on the specific application and the properties of interest.

4. Factors Influencing Catalyst Performance

Several factors can influence the performance of DMCHA as a gelling catalyst:

• Concentration: The concentration of DMCHA directly affects the reaction rate. Higher concentrations generally lead to faster gel times, but excessive amounts can cause undesirable side reactions or affect the final properties of the polyurethane. An optimal concentration range should be determined experimentally for each specific formulation.
• Temperature: Reaction rates are generally temperature-dependent. Higher temperatures typically accelerate the reaction, leading to shorter cream and gel times. However, excessively high temperatures can also lead to premature gelling or degradation of the reactants.
• Moisture Content: Moisture can react with isocyanates to form urea linkages and carbon dioxide, affecting the gelling and blowing balance. High moisture content can lead to uncontrolled foaming or reduced mechanical properties.
• Type of Polyol: The type of polyol used (e.g., polyether polyol, polyester polyol) influences the reactivity and compatibility of the system. Polyols with higher hydroxyl numbers generally react faster with isocyanates.
• Type of Isocyanate: Different isocyanates (e.g., TDI, MDI, HDI) exhibit different reactivities. Aromatic isocyanates (TDI, MDI) are generally more reactive than aliphatic isocyanates (HDI, IPDI).
• Additives: Other additives, such as surfactants, blowing agents, and stabilizers, can also affect the catalyst’s performance by influencing the miscibility of the reactants, the foam cell structure, or the stability of the polyurethane material.
• Presence of Co-catalysts: DMCHA is often used in conjunction with other catalysts, such as metal catalysts (e.g., tin catalysts), to achieve a specific balance of gelling and blowing. The combination of catalysts can provide synergistic effects, allowing for greater control over the reaction profile.
• Steric Hindrance: The steric hindrance around the nitrogen atom in DMCHA can affect its ability to abstract protons. While DMCHA is less sterically hindered than some other tertiary amine catalysts, it still exhibits some degree of steric hindrance, which can influence its selectivity for different reactions.
• pH of the System: While not a primary concern in typical polyurethane formulations, extreme pH values can affect the catalyst’s activity.

Table 3: Impact of Factors on DMCHA Catalyst Performance

Factor	Impact on Gel Time	Impact on Cream Time	Impact on Foam Rise Time (if applicable)
DMCHA Concentration	Decreases	Decreases	Decreases
Temperature	Decreases	Decreases	Decreases
Moisture Content	Can vary (usually decreases slightly for gelling)	Can vary (usually decreases slightly)	Increases (due to CO2 formation)
Polyol Type	Varies (depends on reactivity)	Varies (depends on reactivity)	Varies
Isocyanate Type	Varies (depends on reactivity)	Varies (depends on reactivity)	Varies
Co-catalysts	Varies (synergistic or antagonistic)	Varies (synergistic or antagonistic)	Varies

5. Applications of DMCHA in Polyurethane Production

DMCHA is widely used in the production of various polyurethane materials, including:

• Flexible Polyurethane Foams: Used in furniture, bedding, automotive seating, and packaging. DMCHA helps to achieve the desired gel time and cell structure in these foams.
• Rigid Polyurethane Foams: Used in insulation for buildings, appliances, and transportation. DMCHA contributes to the rapid gelling required for efficient production of rigid foams.
• Semi-Rigid Polyurethane Foams: Used in automotive parts, shoe soles, and other applications where a balance of flexibility and rigidity is needed.
• Polyurethane Elastomers: Used in seals, gaskets, tires, and other applications requiring high elasticity and durability. DMCHA helps to control the reaction rate and achieve the desired mechanical properties.
• Polyurethane Coatings and Adhesives: Used in a wide range of applications, including automotive coatings, wood finishes, and industrial adhesives. DMCHA accelerates the curing process and improves the adhesion of the coating or adhesive.
• Spray Polyurethane Foam (SPF): Used for insulation and roofing applications. DMCHA is crucial for achieving the fast reaction and rapid curing required for SPF application.
• Reaction Injection Molding (RIM): Used for manufacturing large, complex polyurethane parts. DMCHA helps to control the reaction rate and ensure proper mold filling.

Table 4: Applications of DMCHA in Various Polyurethane Products

Polyurethane Product	Function of DMCHA	Benefits
Flexible Foam	Gelling catalyst	Controls gel time, influences cell structure, improves foam properties
Rigid Foam	Gelling catalyst	Accelerates reaction, enables efficient production, contributes to insulation properties
Elastomers	Gelling catalyst	Controls reaction rate, achieves desired mechanical properties (tensile strength, elongation, hardness)
Coatings/Adhesives	Curing catalyst	Accelerates curing process, improves adhesion, enhances durability
Spray Foam	Gelling catalyst	Enables fast reaction and rapid curing, ensures proper adhesion to substrate
RIM Parts	Reaction rate control	Ensures proper mold filling, improves part quality, reduces cycle time

6. Safety and Handling

DMCHA is a flammable and corrosive liquid. It is important to handle it with care and follow appropriate safety precautions:

• Personal Protective Equipment (PPE): Wear appropriate PPE, including gloves, safety glasses, and a respirator, when handling DMCHA.
• Ventilation: Use adequate ventilation to prevent inhalation of vapors.
• Storage: Store DMCHA in a tightly closed container in a cool, dry, and well-ventilated area.
• Fire Hazards: Keep DMCHA away from heat, sparks, and open flames.
• First Aid: In case of skin or eye contact, flush with plenty of water for at least 15 minutes and seek medical attention. If inhaled, move to fresh air and seek medical attention.

7. Alternatives to DMCHA

While DMCHA is a widely used catalyst, there are several alternatives available, depending on the specific application and desired properties:

• Other Tertiary Amines: Examples include triethylenediamine (TEDA), dimethylbenzylamine (DMBA), and bis(2-dimethylaminoethyl) ether. These amines offer different reactivities and selectivity for the gelling and blowing reactions.
• Metal Catalysts: Examples include tin catalysts (e.g., dibutyltin dilaurate – DBTDL) and bismuth catalysts. Metal catalysts are often used in combination with amine catalysts to achieve a specific balance of properties.
• Delayed-Action Catalysts: These catalysts are designed to provide a delayed onset of catalytic activity, allowing for better control over the reaction process.
• Environmentally Friendly Catalysts: Research is ongoing to develop more environmentally friendly catalysts for polyurethane production, with a focus on reducing VOC emissions and improving the sustainability of the materials.

Table 5: Comparison of DMCHA with Alternative Catalysts

Catalyst Type	Advantages	Disadvantages
DMCHA	Good gelling catalyst, relatively low cost, widely available	Amine odor, potential VOC emissions, may require co-catalysts
TEDA	Strong blowing catalyst, can improve foam cell structure	Strong amine odor, may require co-catalysts
DMBA	Good balance of gelling and blowing, lower odor than some other amines	May be more expensive than DMCHA, potential VOC emissions
DBTDL (Tin Catalyst)	Strong gelling catalyst, can improve mechanical properties	Toxicity concerns, potential for hydrolysis
Bismuth Catalyst	Less toxic than tin catalysts, good gelling activity	May be more expensive than DMCHA or tin catalysts, may require higher loading levels

The selection of the appropriate catalyst depends on a variety of factors, including the desired reaction rate, the target properties of the polyurethane material, and environmental considerations.

8. Conclusion

N,N-Dimethylcyclohexylamine (DMCHA) remains a valuable and widely used gelling catalyst in the production of polyurethane materials. Its ability to accelerate the isocyanate-polyol reaction, along with its relatively low cost and availability, makes it a popular choice for a wide range of applications. However, it’s crucial to understand the factors influencing its performance, handle it safely, and consider potential alternatives to meet specific requirements and address environmental concerns. Further research and development efforts are focused on improving the sustainability and performance of polyurethane catalysts, ensuring the continued advancement of this important class of materials.

Literature Sources (Example References – Actual citations would need to be found and inserted):

1. Oertel, G. (Ed.). Polyurethane Handbook. Hanser Gardner Publications. (This is a general reference for polyurethane chemistry)
2. Randall, D., & Lee, S. The Polyurethanes Book. John Wiley & Sons. (Another general reference)
3. Saunders, J. H., & Frisch, K. C. Polyurethanes: Chemistry and Technology. Interscience Publishers. (Classic text on polyurethane chemistry)
4. Specific journal articles on polyurethane catalysis (e.g., Journal of Applied Polymer Science, Polymer, European Polymer Journal) – Search for articles focusing on amine catalysts and their performance in polyurethane systems. These articles would need to be located and cited specifically.
5. Technical Data Sheets from DMCHA Manufacturers (e.g., Huntsman, Evonik, etc.) – These provide specific information on product properties and handling.
6. Patents related to polyurethane catalysts and formulations.

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