1. Hydroxy value
The amount of hydroxyl group (-OH) contained in 1 gram of polymer polyol is equivalent to the number of milligrams of KOH in mgKOH/g.
2. Equivalent
The average molecular weight occupied by a functional group.
3.Isocyanate content
The content of isocyanate in the molecule
4.Isocyanate index
Indicates the degree of excess isocyanate in the polyurethane formula, usually represented by the letter R.
5.Chain extender
It refers to low molecular weight alcohols and amine compounds that can extend and expand the molecular chain or form spatial network cross-linking.
6. Hard section
The segments on the main chain of polyurethane molecules are formed by the reaction of isocyanate, chain extender and cross-linking agent. These groups have larger cohesion energy, larger space volume and greater rigidity.
7. Soft section
Carbon-carbon main chain polymer polyol has good flexibility and is a flexible segment in the polyurethane main chain.
8. One step method
It refers to a method in which oligomer polyol, diisocyanate, chain extender and catalyst are mixed at the same time and then directly injected into the mold to solidify at a certain temperature.
9. Prepolymer method
First, the oligomer polyol and diisocyanate are prepolymerized to generate a polyurethane prepolymer with terminal NCO groups. During casting, the prepolymer is reacted with a chain extender to prepare a polyurethane elastomer, which is called prepolymerization. Law of things.
10. Semi-prepolymer method
The difference between the semi-prepolymer method and the prepolymer method is that some polyester polyols or polyether polyols, chain extenders, catalysts, etc. are added to the prepolymer in the form of a mixture.
11. Reaction injection molding
Also known as Reaction Injection Molding (RIM), oligomers with small molecular weights are measured in liquid form, mixed instantly and injected into the mold. They react rapidly in the mold cavity, and the molecular weight of the material increases sharply, resulting in extremely A process that quickly generates new polymers containing new characteristic group structures.
12. Foaming index
That is, the part equivalent to the water used in 100 parts of polyether is defined as the foaming index (IF).
13. Foaming reaction
Generally refers to the reaction in which water reacts with isocyanate to form substituted urea and releases CO2.
14. Gel reaction
Generally refers to the formation reaction of carbamate.
15. Gel time
The time it takes for a liquid substance to form a gel under certain conditions.
16. Milky white time
At the end of zone I, a milky white phenomenon appears in the liquid polyurethane mixture. This time is called cream time in polyurethane foam production.
17. Chain expansion coefficient
It refers to the ratio of the amount of amino and hydroxyl groups (unit: mol) in the chain extender component (including mixed chain extender) to the amount of NCO in the prepolymer, that is, the number of moles of active hydrogen groups and NCO (number of equivalents) )ratio.
18. Low unsaturation polyether
It is mainly developed for PTMG. The price of PPG and the degree of unsaturation are reduced to 0.05mol/kg, which is close to the performance of PTMG. It uses DMC catalyst and the main variety is Bayer’s Acclaim series products.
19. Urethane grade solvent
When selecting solvents for the production of polyurethane, the solubility and evaporation speed must be considered. However, the solvent used for the production of polyurethane should focus on the heavy N0 group in the polyurethane. Solvents such as alcohols and ether alcohols that react with NCO groups cannot be used. The solvent must not contain water, alcohol and other impurities, and it must not contain alkali substances, which will cause the polyurethane to deteriorate.
Ester solvents are not allowed to contain moisture, nor are they allowed to contain free acids and alcohols, which will react with NCO groups. The ester solvent used for polyurethane should be a high purity “urethane grade solvent”. That is, the solvent is reacted with excess isocyanate, and then dibutylamine is used to measure the amount of unreacted isocyanate to test whether it is suitable for use. The principle is that it does not apply to those that consume more isocyanate, because it shows that the water, alcohol, and acid contained in the ester will consume the total value of isocyanate. If expressed in grams of solvent required to consume leqNCO groups, the one with the larger value will have better stability. .
Those with an isocyanate equivalent weight below 2500 are not used as polyurethane solvents.
The polarity of the solvent has a great influence on the reaction that produces the resin. The greater the polarity, the slower the reaction. For example, the difference between toluene and methyl ethyl ketone is 24 times. This solvent molecule is highly polar and can form hydrogen bonds with the hydroxyl group of the alcohol, making the reaction slow.
It is better to use aromatic hydrocarbon solvents as polyurethane solvents. Their reaction speed is faster than esters and ketones, such as xylene. When constructing double-button polyurethane, the use of ester and ketone solvents can extend its service life. When producing coatings, choosing the “urethane grade solvent” mentioned above is beneficial to the stability of storage.
Ester solvents have strong solubility, moderate evaporation speed, low toxicity and are often used. Cyclohexanone is also commonly used. Hydrocarbon solvents have low solid solubility and are rarely used alone. They are often used in combination with other solvents.
20.Physical foaming agent
Physical foaming agent means that foam pores are formed through changes in the physical form of a certain substance, that is, through the expansion of compressed gas, the volatilization of liquids, or the dissolution of solids.
21.Chemical foaming agent
Chemical blowing agents are compounds that, when decomposed by heat, release gases such as carbon dioxide and nitrogen and form pores in the polymer composition.
22.Physical cross-linking
There are some hard chains in the polymer soft chains. The hard chains have the same physical properties as chemically cross-linked vulcanized rubber at temperatures below the softening point or melting point.
23.Chemical cross-linking
It refers to the process in which macromolecular chains are connected through chemical bonds under the action of light, heat, high-energy radiation, mechanical force, ultrasonic waves and cross-linking agents to form network or body-shaped polymers.
24. Foaming index
The foaming index (IF) is defined as the part of water equivalent to 100 parts of polyether.
25.What are the structural types of commonly used isocyanates?
Aliphatic: HDI; Alicyclic: IPDI, HTDI, HMDI; Aromatic: TDI, MDI, PAPI, PPDI, NDI.
26.What are the commonly used isocyanates?
Toluene diisocyanate (TDI), diphenylmethane-4,4’-diisocyanate (MDI), polyphenylmethane polyisocyanate (PAPI), liquefied MDI, hexamethylene diisocyanate (HDI).
27.What do TDI-100 and TDI-80 mean?
TDI-100 refers to a mixture composed entirely of toluene diisocyanate with a 2,4 structure; TDI-80 refers to a mixture composed of 80% of a toluene diisocyanate with a 2,4 structure and 20% of a 2,6 structure.
28.What are the characteristics of TDI and MDI in the synthesis of polyurethane materials?
Regarding the reactivity of 2,4-TDI and 2,6-TDI, the reactivity of 2,4-TDI is several times higher than that of 2,6-TDI. This is because the 4-position NCO in 2,4-TDI is far away from the 2-position. NCO is far away from the methyl group and has almost no steric hindrance. However, the NCO of 2,6-TDI is greatly hindered by the steric hindrance effect of the ortho-position methyl group, and the reactivity is affected.
The two NCO groups of MDI are far apart and have no substituents around them, so the activity of these two NCOs is relatively large. Even if one of the NCOs participates in the reaction, the activity of the remaining NCOs will decrease. Generally speaking, The activity is still relatively large, so the reactivity of MDI polyurethane prepolymer is greater than that of TDI prepolymer.
29.Which one of HDI, IPDI, MDI, TDI and NDI has the best resistance to yellowing?
HDI (a non-yellowing aliphatic diisocyanate), IPDI (the polyurethane resin produced has excellent optical stability and chemical resistance, and is generally used to manufacture high-grade non-discoloring polyurethane resin).
30.The purpose of MDI modification and commonly used modification methods
Purpose of modification: Liquefied pure MDI is MDI modified by liquefaction. It overcomes some of the shortcomings of pure MDI (solid at room temperature, needs to be melted and heated multiple times to affect performance), and also improves the performance of MDI-based polyurethane materials. Provides a basis for large-scale modifications.
method:
① Urethane modified liquefied MDI.
② Carbodiimide and uretonimine modified liquefied MDI.
31.What are the commonly used types of polymer polyols?
Polyester polyol, polyether polyol
32. What are the main industrial production methods of polyester polyols?
Vacuum melting method, carrier gas melting method, azeotropic distillation method
33. What are the special structures on the molecular backbone of polyester and polyether polyols?
Polyester polyol: a macromolecular alcohol compound containing an ester group on the main chain of the molecule and a hydroxyl group (-OH) on the end group.
Polyether polyol: a polymer or oligomer containing an ether bond (-O-) in the main chain structure of the molecule and a terminal group with (-OH) or amine group (-NH2).
34. How many types of polyether polyols are classified according to their characteristics?
Highly active polyether polyol, grafted polyether polyol, flame retardant polyether polyol, heterocyclic modified polyether polyol, polytetrahydrofuran polyol.
35. How many common polyethers are there according to the starting agent?
Polyoxypropylene glycol, polyoxypropylene triol, rigid foam polyether polyol, low unsaturation polyether polyol.
36.What is the difference between hydroxyl-terminated polyether and amine-terminated polyether?
Amino-terminated polyether is a polyoxypropylene ether in which the terminal hydroxyl group is substituted by an amine group.
37. What are the commonly used types of polyurethane catalysts? Which common varieties do they include?
Tertiary amine catalysts, commonly used varieties include: triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dimethylcyclohexylamine
Commonly used varieties of metal alkyl compounds include: organotin catalysts, which can be divided into stannous octoate, stannous oleate, and dibutyltin dilaurate.
38.What are the commonly used polyurethane chain extenders or cross-linking agents?
Polyols (1,4-butanediol), alicyclic alcohols, aromatic alcohols, diamines, alcoholamines (ethanolamine, diethanolamine)
39. Reaction mechanism of isocyanates
The reaction between isocyanate and active hydrogen compounds is caused by the nucleophilic center in the active hydrogen compound molecules attacking the carbon atoms of the NCO group. The reaction mechanism is as follows:
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40.How does the isocyanate structure affect the reactivity of the NCO group?
Electronegativity of the R group: If the R group is an electron-withdrawing group, the electron cloud density of the C atoms in the -NCO group will be even lower, and it will be more susceptible to attack by nucleophiles, that is, it will be easier to carry out nucleophilic reactions with alcohols, amines and other compounds. . If R is an electron-donating group, it will be transferred through the electron cloud, which will increase the electron cloud density of the C atoms in the -NCO group, making it less susceptible to attack by nucleophiles and reducing its ability to react with compounds containing active hydrogen.
Induction effect: Since aromatic diisocyanate contains two NCO groups, when the first -NCO gene participates in the reaction, due to the conjugation effect of the aromatic ring, the -NCO group that did not participate in the reaction will act as an electron-withdrawing group. The effect increases the reactivity of the first NCO group. This effect is the induction effect.
Steric hindrance effect: In aromatic diisocyanate molecules, if two -NCO groups are on an aromatic ring at the same time, then one NCO group will often have a significant impact on the reactivity of the other NCO group. However, when two NCO groups are on different aromatic rings in the same molecule, or they are separated by a hydrocarbon chain or aromatic ring, the interaction between them is not large, and as the length of the chain hydrocarbon increases or the aromatic ring increases, decreases as the number of rings increases.
41. Types of active hydrogen compounds and NCO reactivity
Aliphatic NH2>Aromatic NH2>Primary OH>Water>Secondary OH>Phenolic OH>Carboxyl>Substituted urea>amide>urethane. (If the electron cloud density of the nucleophilic center is larger, its electronegativity is stronger, its reaction activity with isocyanate is higher, and the reaction speed is faster; otherwise, the activity is low.)
42. Effect of hydroxyl compounds on their reactivity with isocyanates
The reactivity of active hydrogen compounds (ROH or RNH2) is related to the nature of R. When R is an electron-withdrawing group (low electronegativity), it is difficult to transfer hydrogen atoms, and the reaction between active hydrogen compounds and NCO is more difficult; if R is Electron-donating substituents can improve the reactivity of active hydrogen compounds and NCO.
43. What are the uses of the reaction between isocyanate and water?
It is one of the basic reactions for preparing polyurethane foam. The reaction between them first generates unstable carbamic acid, and then decomposes into CO2 and amine. If there is an excess of isocyanate, the generated amine will react with isocyanate to form urea.
44. When preparing polyurethane elastomer, the water content of polymer polyol should be strictly controlled.
It is required that there should be no bubbles in elastomers, coatings, and fibers, so the moisture content in the raw materials must be strictly controlled, usually less than 0.05%.
45. Differences in the catalytic effects of amine and tin catalysts on isocyanate reactions
Tertiary amine catalysts have high catalytic efficiency for the reaction between isocyanate and water, while tin catalysts have high catalytic efficiency for the reaction between isocyanate and hydroxyl groups.
46. Why can polyurethane resin be regarded as a block polymer? What are the characteristics of the segment structure?
Because the chain segment of polyurethane resin is composed of hard segments and soft segments, the hard segment refers to the segment formed by the reaction of isocyanate, chain extender, and cross-linking agent on the main chain of the polyurethane molecule. These groups have larger cohesion energy. , larger space volume and greater rigidity. The soft segment refers to the carbon-carbon main chain polymer polyol, which has good flexibility and is a flexible segment in the polyurethane main chain.
47.What are the factors that affect the performance of polyurethane materials?
Cohesive energy of the group, hydrogen bonding, crystallinity, degree of cross-linking, molecular weight, hard segment, soft segment
48. What raw materials do the soft segments and hard segments on the main chain of polyurethane material molecules come from?
The soft segment is composed of oligomer polyols (polyester, polyether glycol, etc.), and the hard segment is composed of polyisocyanate or a small molecule chain extender.
49. How do soft segments and hard segments affect the performance of polyurethane materials?
Soft segment: (1) Molecular weight of the soft segment: Assuming that the molecular weight of the polyurethane is the same, if the soft segment is polyester, the strength of the polyurethane increases with the increase in the molecular weight of the polyester diol; if the soft segment is polyether, the strength of the polyurethane The strength decreases as the molecular weight of the polyether glycol increases, but the elongation increases. (2) Crystallinity of soft segments: It contributes greatly to the crystallinity of linear polyurethane segments. Generally speaking, crystallinity is beneficial to improving the performance of polyurethane products, but sometimes crystallization reduces the low-temperature flexibility of the material, and crystalline polymers are often opaque.
Hard segments: Hard segments usually affect the softening, melting temperature and high-temperature properties of polymers. Polyurethane prepared from aromatic isocyanate has a rigid aromatic ring in the hard segment, which increases the cohesive strength of the hard segment. The material strength is generally greater than that of aliphatic isocyanate polyurethane, but its resistance to ultraviolet degradation is poor and it is prone to yellowing. Aliphatic polyurethane does not yellow.
50.Polyurethane foam classification
Hard foam and soft foam; high-density and low-density foam; polyester and polyether foam; TDI and MDI foam; polyurethane foam and polyisocyanurate foam; block foam and molded foam.