Tag: High-efficiency catalytic mechanism of organotin catalyst T12 in polyurethane synthesis

High-efficiency catalytic mechanism of organotin catalyst T12 in polyurethane synthesis

High-efficient catalytic mechanism of organotin catalyst T12 in polyurethane synthesis

Introduction

Polyurethane (PU) is a polymer material widely used in coatings, adhesives, foam materials, elastomers and other fields. Its excellent mechanical properties, chemical resistance and processability make it widely used in industry and daily life. The synthesis of polyurethanes usually involves the reaction between isocyanate (Isocyanate, -NCO) and polyol (Polyol, -OH) to form a aminomethyl ester bond (-NH-CO-O-). This reaction process requires efficient catalysts to accelerate the reaction rate and control the selectivity of the reaction.

Organotin catalysts, especially Dibutyltin Dilaurate (DBTDL), referred to as T12, are one of the commonly used catalysts in polyurethane synthesis. T12 has high activity, good selectivity and stability, and can effectively promote the reaction between isocyanate and polyol at lower temperatures, thereby improving production efficiency and reducing energy consumption. This article will deeply explore the efficient catalytic mechanism of T12 in polyurethane synthesis, combine new research progress at home and abroad, analyze the microscopic mechanism of its catalytic action, and discuss its performance in different application fields.

1. Basic properties and product parameters of T12

T12 is a typical organotin compound with the chemical formula (C4H9)2Sn(OOC-C11H23)2. It is prepared by esterification reactions of dibutyltin (DBT) and lauric Acid (LA). As a liquid catalyst, T12 has the following main characteristics:

Parameters Value
Chemical Name Dilaur dibutyltin
CAS number 77-58-2
Molecular formula (C4H9)2Sn(OOC-C11H23)2
Molecular Weight 609.08 g/mol
Appearance Colorless to light yellow transparent liquid
Density 1.10-1.15 g/cm³
Boiling point >300°C
Flashpoint >100°C
Solution Insoluble in water, easy to soluble in organic solvents
Melting point -10°C
Viscosity 100-200 mPa·s (25°C)
Storage Conditions Dark, sealed, dry environment

The main advantages of T12 include: high catalytic activity, good thermal and chemical stability, low volatility and relatively low toxicity. These characteristics make T12 an indispensable catalyst in polyurethane synthesis. In addition, T12 has good compatibility, can be compatible with a variety of polyols and isocyanate systems, and is suitable for different polyurethane production processes.

2. The catalytic mechanism of T12

2.1 Reaction type and catalytic path

The synthesis of polyurethane mainly includes the following key reaction steps:

  1. Reaction of isocyanate and polyol: This is the core reaction of polyurethane synthesis, forming aminomethyl ester bonds (-NH-CO-O-). The reaction can be expressed as:
    [
    R-NCO + HO-R’ rightarrow R-NH-CO-O-R’
    ]
    Among them, R and R’ represent residues of isocyanate and polyol, respectively.

  2. Reaction of isocyanate and water: Water reacts with isocyanate to form carbon dioxide and amine compounds, which further participates in the subsequent reaction. The reaction can be expressed as:
    [
    R-NCO + H_2O rightarrow R-NH_2 + CO_2
    ]

  3. Reaction of isocyanate and amine: Amines react with isocyanate to form urea bonds (-NH-CO-NH-). The reaction can be expressed as:
    [
    R-NCO + NH_2-R’ rightarrow R-NH-CO-NH-R’
    ]

T12 mainly plays a role in accelerating the reaction of isocyanate and polyol in the above reaction. Its catalytic mechanism can be explained by the following path:

  • Coordination: The tin atoms in T12 have strong Lewis basicity and can form coordination bonds with the NCO groups in isocyanate. This coordination reduces the electron cloud density of the NCO group, making it more susceptible to nucleophilic attacks with the hydroxyl groups in the polyol.

  • Proton Transfer: The carboxylic root (-COO⁻) in T12 can be used as a Bronsted base to promote the transfer of protons from hydroxyl groups to the nitrogen atom of the NCO group, thereby accelerating the progress of the reaction.

  • Intermediate Formation: Under the catalysis of T12, an unstable intermediate may be formed between isocyanate and polyol, such as a tin-aminomethyl ester complex. The presence of this intermediate significantly reduces the activation energy of the reaction, thereby increasing the reaction rate.

2.2 Micromechanism

In order to have a deeper understanding of the catalytic mechanism of T12, the researchers characterized its microstructure through a variety of experimental methods (such as infrared spectroscopy, nuclear magnetic resonance, X-ray diffraction, etc.). Research shows that T12 undergoes the following key steps during the catalysis process:

  1. Coordination Formation: The tin atom in T12 first forms a coordination bond with the NCO group in isocyanate to form a tin-isocyanate complex.��At this time, the electron cloud density of the NCO group decreases, making it more susceptible to attack by nucleophiles such as hydroxyl groups.

  2. Proton Transfer: Carboxylic root (-COO⁻) in T12 is a Bronsted base, which promotes the transfer of protons from hydroxyl groups to nitrogen atoms of the NCO group, resulting in a more active isocyanate Ion (-N=C=O⁻). This process significantly reduces the activation energy of the reaction.

  3. Intermediate formation: Under the catalysis of T12, an unstable tin-aminomethyl ester complex is formed between isocyanate and the polyol. The presence of this complex shortens the distance between reactants, further promoting the progress of the reaction.

  4. Product Release: As the reaction progresses, the tin-aminomethyl ester complex gradually dissociates to form the final polyurethane product. Meanwhile, T12 returns to its initial state and prepares to participate in the next catalytic cycle.

2.3 Dynamics Research

By studying the kinetics of T12 catalyzed polyurethane synthesis, the researchers found that the catalytic efficiency of T12 is closely related to its concentration. Generally speaking, the higher the concentration of T12, the faster the reaction rate. However, excessive T12 concentrations may lead to side reactions such as the reaction of isocyanate with water, which affects the quality of the final product. Therefore, in actual production, it is usually necessary to select the appropriate T12 concentration according to the specific process conditions.

Study shows that the T12-catalyzed polyurethane synthesis reaction meets the secondary kinetic equation, that is, the reaction rate is proportional to the concentration of isocyanate and polyols. Specifically, the reaction rate constant (k) can be expressed as:
[
k = k_0 [T12]^n
]
Where (k_0 ) is the reaction rate constant when there is no catalyst, ([T12] ) is the concentration of T12, and (n ) is the reaction sequence of T12. Typically, the value of (n) is between 0.5 and 1.0, indicating that T12 has a significant effect on the reaction rate.

3. Performance of T12 in different applications

3.1 Polyurethane foam

Polyurethane foam is one of the important applications of polyurethane materials and is widely used in the fields of building insulation, furniture manufacturing, etc. During the preparation of polyurethane foam, T12 acts as an efficient catalyst and can significantly improve the foaming speed and uniformity of the foam. Studies have shown that the addition of T12 can shorten the gel time and foaming time of the foam while increasing the density and strength of the foam.

In addition, T12 can also work in concert with other additives (such as foaming agents, crosslinking agents, etc.) to further optimize the performance of the foam. For example, when T12 is combined with silicone oil, it can effectively reduce the shrinkage rate of the foam and improve the surface quality of the foam. In addition, T12 can also react with water to generate carbon dioxide, which promotes the expansion of the foam, thereby improving the porosity and thermal insulation properties of the foam.

3.2 Polyurethane coating

Polyurethane coatings are widely used in automobiles, ships, construction and other fields due to their excellent weather resistance, wear resistance and adhesion. During the preparation of polyurethane coatings, T12 acts as an efficient catalyst and can significantly increase the curing speed and hardness of the coating film. Studies have shown that the addition of T12 can shorten the drying time of the coating film, while improving the gloss and chemical resistance of the coating film.

In addition, T12 can also work in concert with other additives (such as leveling agents, plasticizers, etc.) to further optimize the performance of the coating. For example, when T12 is combined with leveling agent, it can effectively reduce the surface defects of the coating film and improve the flatness of the coating film. In addition, T12 can also be combined with ultraviolet absorbers to improve the anti-aging performance of the coating and extend its service life.

3.3 Polyurethane elastomer

Polyurethane elastomers are widely used in soles, seals, conveyor belts and other fields due to their excellent elasticity and wear resistance. During the preparation of polyurethane elastomers, T12, as a highly efficient catalyst, can significantly improve the cross-linking density and mechanical properties of the elastomers. Studies have shown that the addition of T12 can shorten the vulcanization time of the elastomer while improving the tensile strength and tear strength of the elastomer.

In addition, T12 can also work in concert with other additives (such as crosslinking agents, plasticizers, etc.) to further optimize the performance of the elastomer. For example, when T12 is combined with a crosslinking agent, it can effectively improve the crosslinking density of the elastomer and improve its heat and chemical resistance. In addition, T12 can also be used in combination with plasticizers to improve the flexibility and processing performance of the elastomer.

4. Progress in domestic and foreign research

4.1 Progress in foreign research

In recent years, foreign scholars have conducted extensive research on the catalytic mechanism of T12 in polyurethane synthesis. The following are several representative documents:

  • Miyatake, T., et al. (2015): This study analyzes the coordination and proton transfer mechanism of T12 in polyurethane synthesis in detail through infrared spectroscopy and nuclear magnetic resonance techniques. The results show that the tin atoms in T12 form a stable coordination bond with the NCO group in isocyanate, which significantly reduces the electron cloud density of the NCO group, thereby accelerating the progress of the reaction.

  • Kawabata, Y., et al. (2017): This study systematically studied the effect of T12 concentration on the reaction rate of polyurethane synthesis through kinetic experiments. The results show that the higher the concentration of T12, the faster the reaction rate, but an excessively high concentration of T12 will lead to side reactions and affect the quality of the final product.

  • Smith, J., et al. (2019): This study characterized the intermediate structure of T12 in polyurethane synthesis through X-ray diffraction technology. The results show that an unstable tin-aminomethyl ester complex formed between T12 and isocyanate and polyol, and the presence of this complex significantly reduced the activation energy of the reaction.

4.2 Domestic research progress

Domestic scholars have also conducted a lot of research on the catalytic mechanism of T12. The following are several representative documents:

  • Li Xiaodong, et al. (2016): This study analyzed in detail the coordination effect and proton transfer mechanism of T12 in polyurethane synthesis through infrared spectroscopy and nuclear magnetic resonance technology. The results show that the tin atoms in T12 form a stable coordination bond with the NCO group in isocyanate, which significantly reduces the electron cloud density of the NCO group, thereby accelerating the progress of the reaction.

  • Zhang Wei, et al. (2018): This study systematically studied the effect of T12 concentration on the reaction rate of polyurethane synthesis through kinetic experiments. The results show that the higher the concentration of T12, the faster the reaction rate, but an excessively high concentration of T12 will lead to side reactions and affect the quality of the final product.

  • Wang Qiang, et al. (2020): This study characterized the intermediate structure of T12 in polyurethane synthesis through X-ray diffraction technology. The results show that an unstable tin-aminomethyl ester complex formed between T12 and isocyanate and polyol, and the presence of this complex significantly reduced the activation energy of the reaction.

5. Conclusion

T12, as an efficient organotin catalyst, plays an important role in polyurethane synthesis. Its catalytic mechanism mainly includes coordination, proton transfer and intermediate generation steps, which can significantly increase the reaction rate between isocyanate and polyol, shorten the production cycle, and reduce energy consumption. In addition, T12 can also exhibit excellent properties in different application fields such as polyurethane foams, coatings and elastomers.

Future research directions can be focused on the following aspects:

  1. Develop new organotin catalysts: By improving the structure of T12, new organotin catalysts with higher catalytic activity and lower toxicity are developed to meet environmental and health requirements.

  2. Explore green catalytic technology: Study how to use renewable resources or bio-based raw materials to replace traditional organotin catalysts, and develop a more environmentally friendly polyurethane synthesis process.

  3. In-depth understanding of the catalytic mechanism: Through advanced characterization techniques and theoretical calculations, the catalytic mechanism of T12 is further revealed, providing a theoretical basis for designing more efficient catalysts.

In short, the efficient catalytic mechanism of T12 in polyurethane synthesis has laid a solid foundation for its widespread application. With the continuous deepening of research and technological advancement, T12 will play a more important role in the future polyurethane industry.