1、Hydroxyl value: the amount of hydroxyl (-OH) contained in 1 gram of polymer polyol is equivalent to the number of milligrams of KOH, unit 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 polyurethane formulation, usually expressed by the letter R.
5、Chain extender: It refers to the low molecular weight alcohols and amines that can make the molecular chain extend, expand or form spatial network cross-link.
6、Hard segment: The chain segment formed by the reaction of isocyanate, chain extender and cross-linker on the main chain of polyurethane molecule, these groups have higher internal aggregation energy, larger space volume and higher rigidity.
7、Soft segment: Carbon-carbon main chain polymer polyol with better flexibility, which is a flexible segment in the main chain of polyurethane.
8、One-step method: It refers to the method of mixing oligomeric polyol, diisocyanate, chain extender and catalyst at the same time and then injecting them directly into the mold and curing and molding at a certain temperature.
9、Prepolymer method: Firstly, the oligomeric polyol is prepolymerized with diisocyanate to produce polyurethane prepolymer with terminal NCO group, and then the prepolymer is reacted with chain extender to prepare polyurethane elastomer during casting, which is called prepolymer method.
10、Semi-prepolymer method: The difference between semi-prepolymer method and prepolymer method is that part of polyester polyol or polyether polyol is added to the prepolymer in the form of mixture with chain extender and catalyst.
11, reaction injection molding: also known as reaction injection molding RIM (Reaction Injection Moulding), is measured by the molecular weight of the zwitterionic material in liquid form, instantaneous mixing while injected into the mold, and rapid reaction in the mold cavity, the material molecular weight increased rapidly to generate a new polymer containing a new structure of characteristic groups at a very fast rate of the process.
12、Foaming index：That is, the number of parts of water used in 100 parts of polyether is defined as the foaming index (IF).
13、Foaming reaction: Generally, it refers to the reaction of water and isocyanate to generate substituted urea and release CO2.
14, gel reaction: generally refers to the formation of carbamate reaction.
15, gel time: under certain conditions, the time required to form a gel of liquid material.
16、Milk time: When the I zone is about to end, the milky phenomenon appears in the liquid-phase polyurethane mixture. The time in the generation of polyurethane foam is called the cream time (cream time).
17、Chain expansion coefficient: It refers to the ratio of the amount of amino and hydroxyl groups (unit: mo1) in the chain expander component (including mixed chain expander) to the amount of NCO in the prepolymer, that is, the molarity (equivalent number) ratio of the active hydrogen group and NCO.
18、Low unsaturation polyether: mainly developed for PTMG, the price of PPG, unsaturation reduced to 0.05mol/kg, close to the performance of PTMG, using DMC catalyst, the main varieties of Bayer Acclaim series.
19、Urethane grade solvent: The solvent chosen for the production of polyurethane should consider solubility and volatility speed, but the solvent used for the production of polyurethane should focus on the heavy NC0 group in polyurethane. Can’t use the solvent such as alcohol and ether alcohol Lou that react with NCO base. The solvent also cannot contain impurities such as water and alcohol, and cannot contain alkali substances, which will make the polyurethane deteriorate.
Ester solvents are not allowed to contain water, and must not contain free acids and alcohols, which will react with the NCO group. The ester solvent used in polyurethane should be “urethane solvent” with high purity. That is, the solvent reacts with excess isocyanate, and then the amount of unreacted isocyanate is measured with dibutylamine to check whether it is suitable. The principle is that the one who consumes more isocyanate is not applicable, because it shows the total value of isocyanate consumed by water, alcohol and acid contained in the ester, and if the grams of solvent needed to consume leqNCO group are used, the value is large and stable.
Isocyanate equivalents below 2500 are not used as polyurethane solvents.
The polarity of the solvent has a great influence on the reaction of the generated resin. The greater the polarity, the slower the reaction, such as the difference between toluene and methyl ethyl ketone 24 times, the polarity of this solvent molecule is large and can form hydrogen bond with the hydroxyl group of alcohol and make the reaction slow.
Polychlorinated ester solvent is better to use aromatic hydrocarbon solvent, and their reaction speed is faster than esters and ketones, such as xylene. In the construction of polyurethane of double new points, the use of ester and ketone solvents can extend its service life. In the production of coatings, the “urethane-grade solvent” mentioned earlier in the selection sheet is beneficial to the storage of stable parts.
Ester solvents have strong solvency power, moderate evaporation speed, low toxicity and more use, cyclohexanone is also used, hydrocarbon solvents have low solvency power, less used alone, and more used with other solvents.
20, physical blowing agent: physical blowing agent is the foam pore is formed by a change in the physical form of a substance, that is, through the expansion of compressed gas, liquid volatilization or dissolution of solids.
21、Chemical blowing agent: Chemical blowing agents are those compounds that can release gases such as carbon dioxide and nitrogen after decomposition by heating, and form fine pores in the composition of the polymer.
22, physical cross-linking: In the polymer soft chain has part of the hard chain, hard chain in the softening point or melting point below the temperature with the same physical properties of chemical cross-linking of vulcanized rubber phenomenon.
23、Chemical cross-linking: refers to the process of forming a net or body-shaped structure polymer by chemical bonding between macromolecular chains under the action of light, heat, high-energy radiation, mechanical force, ultrasonic waves and cross-linking agents.
24. Foaming index: The number of parts of water equivalent to that used in 100 parts of polyether is defined as the foaming index (IF).
25. What are the commonly used isocyanates from the structural point of view?
A: Aliphatic: HDI, alicyclic: IPDI, HTDI, HMDI, aromatic: TDI, MDI, PAPI, PPDI, NDI.
26. What are the commonly used isocyanates? Write down the structural formula
A: 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?
A: TDI-100 means it is composed entirely of 2,4 structured toluene diisocyanate; TDI-80 means it is a mixture of 80% 2,4 structured toluene diisocyanate and 20% 2,6 structured.
28. What are the characteristics of each of TDI and MDI in the synthesis of polyurethane materials?
A: For 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 because, the 4-position NCO in 2,4-TDI is far away from the 2-position NCO and methyl group, and there is almost no site block, while the NCO of 2,6-TDI is affected by the site block effect of the neighboring methyl group, and the reactivity is affected.
The two NCO groups of MDI are far away from each other and there is no substituent around, so the activity of both NCOs is larger. Even if one of the NCOs participates in the reaction, the activity of the remaining NCO decreases, but the overall activity is still larger, so the reaction activity of MDI-type polyurethane prepolymer is larger than that of TDI prepolymer.
29. Which of HDI, IPDI, MDI, TDI and NDI is better in yellowing resistance?
A: HDI (belongs to non-yellowing aliphatic diisocyanate), IPDI (the polyurethane resin made has excellent optical stability and chemical resistance, and is generally used to make high-grade non-discolored polyurethane resin).
30. Purpose of MDI modification and common modification methods
A: Liquefied MDI: Purpose of modification: Liquefied pure MDI is MDI modified by liquefaction, which overcomes some defects of pure MDI (solid at room temperature, melting for use, and affecting performance by repeated heating), and also provides the basis for a wide range of modification to improve and enhance the performance of MDI-based polyurethane materials.
Methods.
①Liquefied MDI modified by carbamate (urethane ).
② Carbodiimide and uretonimine type modified liquefied MDI.
31. What are the common types of polymer polyols?
A: polyester polyol, polyether polyol
32. There are mainly several industrial production methods of polyester polyol?
A: A, vacuum melting method B, carrier gas melting method C, azeotropic distillation method
33. polyester, polyether polyol molecules on the main chain of what special structure?
A: polyester polyol: in the main chain of the molecule contains ester groups, in the end group has a hydroxyl (-OH) of large molecules of alcohol compounds. Polyether polyols: polymers or zwitterions that contain ether bonds (-O-), end groups with (-OH) or amine groups (-NH2) in the main chain structure of the molecule.
34. How many types of polyether polyols are there according to their properties?
A: Highly reactive polyether polyol, graft polyether polyol, flame retardant polyether polyol, heterocyclic modified polyether polyol, polytetrahydrofuran polyol.
35. How many kinds of common polyethers are there according to the starting agent?
A: Poly(propylene oxide diol), poly(propylene oxide triol), hard foam polyether polyol, low unsaturated polyether polyol.
36. What is the difference between terminal hydroxy polyether and terminal amine polyether?
Terminal amine-based polyethers are poly(propylene oxide) ethers in which the terminal hydroxyl group is replaced by an amine group.
37. What are the common types of polyurethane catalysts? What are the common varieties of each?
A: Tertiary amine catalysts, commonly used varieties include: triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dimethylcyclohexylamine
Metal alkyl compounds, commonly used varieties include: organotin catalysts, which can be divided into stannous octanoate, stannous oleate, dibutyltin dilaurate.
38. What are the commonly used polyurethane chain extenders or cross-linking agents?
A: Polyols (1,4-butanediol), alicyclic alcohols, aromatic alcohols, diamines, alcohols and amines (ethanolamine, diethanolamine)
39. Reaction mechanism of isocyanate
A: The reaction between isocyanate and active hydrogen compounds is caused by the attack of the nucleophilic center of the active hydrogen compound molecule on the carbon atom of the NCO group. The reaction mechanism is as follows.
40. How does the structure of isocyanate affect the reactivity of the NCO group?
A. Electronegativity of R group: If R group is electron-absorbing group, the electron cloud density of C atom in -NCO group is more reduced and more easily attacked by nucleophilic reagents, i.e. more easily nucleophilic reaction with alcohols, amines and other compounds. If R is an electron donor group, through electron cloud transfer, it will increase the electron cloud density of C atoms in the -NCO group, making it less susceptible to attack by nucleophilic reagents, and its ability to react with compounds containing active hydrogen decreases. b. Induced effect: Since aromatic diisocyanates contain two NCO groups, when the first -NCO gene participates in the reaction, due to the conjugation effect of the aromatic ring, the non-participating -C. Spatial site blocking effect: In aromatic diisocyanate molecules, if two -NCO groups are in an aromatic ring at the same time, then one of the NCO groups on the other NCO group reaction activity is often more significant. But when the two NCO groups are in the same molecule on different aromatic rings, or they are separated by hydrocarbon chains or aromatic rings, so that the interaction between them is not significant, and with the increase in the length of the chain hydrocarbon or the number of aromatic rings to reduce.
41. Reactivity of active hydrogen compound species with NCO
A: Aliphatic NH2 > aromatic NH2 > primary drunken OH > water > secondary OH > phenolic OH > carboxylate > substituted urea > amide > carbamate. (If the electron cloud density of the nucleophilic center is greater, the stronger its electronegativity, the higher its reaction activity with isocyanate, and the faster the reaction speed; vice versa, the activity is low.)
42. Effect of hydroxyl compounds on their reactivity with isocyanates
A: The reactivity of active hydrogen compounds (ROH or RNH2) is related to the nature of R. When R is an electron-absorbing group (low electronegativity), it is difficult to transfer out the hydrogen atom, and the reaction of active hydrogen compounds with NCO is more difficult; if R is an electron-donating substituent, it can improve the reactivity of active hydrogen compounds with NCO.
43. What is the use of the reaction of isocyanate with water?
A: It is one of the basic reactions for the preparation of polyurethane foam. The reaction between them first produces unstable carbamic acid and then decomposes into CO2 and amine. If there is an excess of isocyanate, the resulting amine will react with isocyanate to form urea.
44. In the preparation of polyurethane elastomer, the water content of polymer polyol should be strictly controlled
A: For elastomers, coatings, fibers require that there should be no air bubbles, so the water content in raw materials must be strictly controlled, usually requiring less than 0.05%.
45. The difference of catalytic effect of amine and tin catalysts on isocyanate reaction
A: The catalytic efficiency of tertiary amine catalyst for the reaction between isocyanate and water is large, while the catalytic efficiency of tin catalyst for the reaction between isocyanate and hydroxyl group is large.
46. Why can polyurethane resin be regarded as a block polymer and what are the characteristics of the chain structure?
A: Because the chain segment of polyurethane resin is composed of hard and soft segments. Hard segment refers to the chain segment formed by the reaction of isocyanate, chain extender and cross-linker on the main chain of polyurethane molecule, and these groups have higher internal aggregation energy, larger space volume and higher rigidity. And the soft segment refers to the carbon-carbon main chain polymer polyol, which is more flexible and is a flexible segment in the main chain of polyurethane.
47. What are the factors affecting the performance of polyurethane materials?
A: cohesion energy of groups, hydrogen bonding, crystallinity, cross-linking, molecular weight, hard segment, soft segment.
48. Which raw materials are the soft and hard segments in the main chain of polyurethane material?
A: The soft segment is composed of oligomeric polyol (polyester, polyether glycol, etc.), and the hard segment is composed of polyisocyanate or its chain extender with small molecules.
