Introduction to Polyurethane Basics

1. Hydroxyl Value: The amount of hydroxyl groups (-OH) per gram of polyol equivalent to the milligrams of KOH, denoted as mgKOH/g.

2. Equivalent Weight: The average molecular weight occupied by one functional group.

3. Isocyanate Content: The content of isocyanate groups in the molecule.

4. Isocyanate Index: Indicates the excess of isocyanate in the polyurethane formulation, typically represented by the letter "R".

5. Chain Extender: Low molecular weight alcohols or amines that extend or form a spatial network in the molecular chain.

6. Hard Segment: Segments formed on the main chain of polyurethane molecules through the reaction of isocyanate, chain extenders, and crosslinking agents, characterized by higher cohesion, larger spatial volume, and greater rigidity.

7. Soft Segment: Polyether polyols with good flexibility, forming flexible segments in the main chain of polyurethane.

8. One-Step Method: A method of directly injecting a mixture of oligomeric polyols, diisocyanates, chain extenders, and catalysts into a mold for curing at a certain temperature.

9. Prepolymer Method: Prepolymerizing oligomeric polyols with diisocyanates to form urethane prepolymers, which are then reacted with chain extenders during pouring to prepare polyurethane elastomers.

10. Semiprepolymer Method: Differs from the prepolymer method by adding a mixture of some polyester or polyether polyols with chain extenders and catalysts to the prepolymer.

11. Reaction Injection Molding (RIM): A process where low molecular weight polymers are metered in liquid form, instantly mixed, injected into molds, and rapidly react in the mold cavity to form a completely new polymer with new characteristic groups.

12. Foam Index: The number of parts of water equivalent to 100 parts of polyether used in foam formation, defined as the foam index (IF).

13. Foam Reaction: Generally refers to the reaction where water reacts with isocyanate to form substituted urea and release CO2.

14. Gelation Reaction: Typically refers to the formation reaction of urethane.

15. Gel Time: The time required for a liquid substance to form a gel under certain conditions.

16. Cream Time: The appearance of a milky white phenomenon in the liquid polyurethane mixture just before the end of Zone I. In the production of polyurethane foam, this time is called the cream time.

17. Chain Extender Coefficient: The ratio of the amount of amino and hydroxyl groups in the chain extender component (including mixed chain extenders) to the amount of NCO in the prepolymer, i.e., the ratio of the molar number of active hydrogen groups to NCO.

18. Low Unsaturated Polyether: Developed mainly for PTMG, reducing unsaturation to 0.05 mol/kg, similar to PTMG's performance, using DMC catalyst, mainly Bayer's Acclaim series products.

19. Urethane-Grade Solvent: Solvents used in polyurethane production should consider their dissolving power and volatility, with particular attention to the heavy NCO base in polyurethane. Solvents that react with NCO bases, such as alcohols and ether alcohols, should not be used. Solvents should also be free from impurities such as water and alcohols, and should not contain alkaline substances, which may degrade polyurethane.

20. Physical Blowing Agent: A substance that forms foam pores through physical changes, such as expansion of compressed gas, evaporation of liquid, or dissolution of solid.

21. Chemical Blowing Agent: Compounds that release gases such as carbon dioxide and nitrogen upon heating, forming pores in the polymer composition.

22. Physical Crosslinking: Some hard chains exist in the polymer soft chain, which exhibit physical properties similar to chemically crosslinked vulcanized rubber below the softening or melting point.

23. Chemical Crosslinking: The process of forming a network or three-dimensional structure of polymer chains by linking large molecules through chemical bonds under the action of light, heat, high-energy radiation, mechanical force, ultrasound, or crosslinking agents.

24. Foam Index: The number of parts of water equivalent to 100 parts of polyether used in foam formation, defined as the foam index (IF).