Basic Concept Q&A on Polyurethane(Part Two)

1. Purpose and Common Modification Methods of MDI Modification:

   Answer: Liquid MDI: Purpose of Modification: Liquid MDI is MDI modified to overcome some drawbacks of pure MDI (solid at room temperature, requires melting for use, performance affected by multiple heating cycles), providing a basis for extensive modification to enhance and improve the properties of MDI-based polyurethane materials.

   Methods:

   1) Urethane-modified liquid MDI.

   2) Carbodiimide and uretonimine-type modified liquid MDI.

2. What are the common types of polymeric polyols?

   Answer: Polyester polyols, polyether polyols.

3. What are the main industrial production methods of polyester polyols?

   Answer: A. Vacuum Melting Method B. Blowing Agent Melting Method C. Azeotropic Distillation Method.

4. What are the special structures on the main chain of polyester and polyether polyols?

   Answer: Polyester polyols: Large-molecule alcohols containing ester groups in the main chain and hydroxyl groups (-OH) at the terminals. Polyether polyols: Polymers or copolymers with ether bonds (-O-) in the main chain structure and hydroxyl (-OH) or amine (-NH2) groups at the terminals.

5. How many categories of polyether polyols are there based on their characteristics?

   Answer: High-activity polyether polyols, graft polyether polyols, flame-retardant polyether polyols, heterocyclic-modified polyether polyols, polytetrahydrofuran polyols.

6. How many types of common polyethers are there based on initiators?

   Answer: Polypropylene glycol, polyethylene glycol, rigid foam polyether polyols, low unsaturation polyether polyols.

7. What is the difference between hydroxyl-terminated polyether and amine-terminated polyether?

   Answer: Amine-terminated polyether is polypropylene oxide with hydroxyl groups replaced by amine groups.

8. What are the common types of polyurethane catalysts? Which specific varieties are included in each?

   Answer: Tertiary amine catalysts, including: triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dimethylcyclohexylamine. Metal alkyl compounds, including: organotin catalysts, which can be divided into tin octoate, tin oleate, dibutyltin dilaurate.

9. What are the common polyurethane chain extenders or crosslinkers?

   Answer: Polyols (1,4-butanediol), cyclic fatty alcohol, aromatic alcohol, diamine, alcohol amine (ethanolamine, diethanolamine).

10. Reaction Mechanism of Isocyanate:

   Answer: The reaction between isocyanates and compounds containing active hydrogen occurs because the nucleophilic center in the molecule of the compound containing active hydrogen attacks the carbon atom of the NCO group. The reaction mechanism is as follows: