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The sealant system formed by some pure-end NC0-based polyurethane prepolymers can not withstand long-term water soaking and blistering. Some people have studied the modification of polyurethanes with silicones and achieved success. In this modification system, part or all of the terminal NCO-based PU prepolymer is reacted with an alkoxysilane (generally a coupling agent) containing active hydrogen, and an alkoxysilane [-Si(0R)3 is produced. ,] The terminal base prepolymer. This type of prepolymer cross-linking shortens quickly, and it is said that it also improves the adhesion to the substrate, is resistant to water soaking, and has good weather resistance.
Hale.WF et al. reported in 1971 that the Carbon Corporation laboratory developed a silane-terminated prepolymer with free NCO free from the reaction of a functional silane with a terminal NCO prepolymer. This silicone-modified PU is yellow transparent. Viscous liquid, density 1.0lg/m3, solids content 95%. The extrusion performance of a sealant formulated from the prepolymer through a 3.175 mm (1/8 in) orifice is: 8 to 10 g/min when the extrusion force is 0.21 MPa, and 15 to 20 g/min when the pressure is 0.41 MPa. 0.62MPa, 25-30g/min non-stick time is about 1h, complete curing requires 48h. After curing for 7 days, the hardness (Shore A) was 40-50, the tensile strength was 3.45-4.14 MPa, the elongation was 150%-2%, and the flexibility was still at -40°C. No foaming during curing, good adhesion, retention of adhesion after 7 days of immersion, and good weather resistance.
Silane compounds capable of reacting with NCO groups are silanes containing amine groups, hydroxyl groups, and mercapto groups.
Some people think that the terminal NCO group of the prepolymer can be partially blocked with silane, and the amount of NCO reacted is between 5% and 10%, preferably about 10%. If <5%, there is no significant effect on the performance. Improved; 100% silane end groups reduce the cohesive strength of the sealant.
An example of preparing a one-component PU sealant from a partially silylated PU prepolymer is as follows.
Example 1: An NCO-based polyurethane prepolymer was prepared by reacting PPG, 2,4-TDI and PPT in the presence of stannous octoate with an NCO content of 1.78%. This prepolymer, 112.1 g, was reacted with 0.7 g of N,N-bis[(trimethoxysilyl)propyl]amine and about 5% of the NCO was capped. The sealant formulation is:
The above prepolymer 100 parts of zinc oxide 16. 6
Talc 33.4 hydrogenated castor oil 3.5
Titanium Dioxide 16.6
The sealant still has excellent adhesion after dry and immersed in water (20°C, 7 days).
Example 2: Formulation of per-silane-terminated PU prepolymer:
Polyoxypropylene glycol (NiaxPPG-2025) 2001g Aminopropyltrimethoxysilane 68.3g
Toylene diisocyanate (Hylene TM) 204g
One-component sealant formulation (parts by mass):
Carbon black (moisture <0.05%) 35 3-(2-aminoethylamine) 0.5
Thixeseal (10x) 0.5 Propyltrimethoxysilane Dibutyltin dilaurate 0.08
The above prepolymer 100 antioxidant 0.65
The sealant crosslinker has a fast speed and good adhesion performance.
Acrylic prepolymers
Synthesizing NCO prepolymers from hydroxyl-containing acrylic oligomers, polyethers, and diisocyanates to form a sealant, due to the introduction of photo-oxidizing acrylates, improves the weatherability of PU sealants. Japan has products for sale, with an annual output of several thousand tons.
Acrylate polyol oligomers are generally composed of acrylates, hydroxyethyl (meth)acrylate, and other unsaturated monomers in the presence of an initiator, a chain transfer agent (such as mercaptoethanol) that can react with NCO groups. be made of.
The formulation (parts by mass) of an acrylate polyol is:
Butyl acrylate 100 2-mercaptopropanol 2
Hydroxyethyl Acrylate 3 Azobisisobutyronitrile 0.2
The above compound was polymerized at 70°C to give a polyol having an average hydroxyl group functionality of 3.01 and an average molecular weight of 5,000.
Acrylates and polyethers can be radically polymerized together. For example, an acrylate oligomer is first synthesized and used as a starter, and then propylene oxide ring-opening polymerization is performed to obtain an acrylate-polyoxypropylene block copolymer polyol.
Example: The composition of an acryl urethane sealant is as follows.
The polyacrylate polyol preparation recipe (parts by mass) is:
(1) Butyl Acrylate 100
Acrylonitrile 10
2-Hydroxyethyl acrylate 4
2-mercaptoethanol 2.6
AIBN Small amount (2) Butyl acrylate 100
Acrylonitrile 10
2-Hydroxyethyl acrylate 2
2-mercaptoethanol 1.3
AIBN's small amount of two-component sealant formulation (parts by mass) is as follows:
NCO component:
The above polyacrylate oligomer polyol 100
2,4-TDI 11
DBDTL 0.001
The NCO-based urethane acrylate prepolymer was made by reacting at 65 °C for 5 h.
Curing component (OH component):
The above polyacrylate polyol (2) 113.3 CaCO3 130
TiO2 30 Surfactant 2
DBDTL 0.2
From the NCO component 111 parts plus 400 parts of the curing component, mixed uniformly, the gel after curing 50% modulus 78.4kPa, tensile strength 804kPa, elongation of 700%.
6. Other modified polyurethane
The introduction of epoxy groups in polyurethanes improves adhesion and heat resistance. For example, a sealant formulation is:
Polyurethane-epoxy resin prepolymer 100 parts calcium carbonate 25 parts acetylene carbon black 6 parts
The above prepolymer was prepared by the following method: polyoxyethylene glycol (Mw 2000) 2400 points and TDI 1416 parts reacted at about 80°C until the viscosity reached 2.3-2.7 Pa·s, and niobium added polyoxypropylene triol (Mw 4000) 782.4 parts and 0.7 parts of stannous octoate were prepared to obtain a prepolymer with a free NCO content of 2%, and 53.1 parts of the prepolymer were reacted with 0.817 parts of a liquid bisphenol A epoxy resin at 50° C. for 15 minutes to obtain an NCO-containing and epoxy resin. Group of PU prepolymers.
Synthesizing the terminal NCO-based polyurethane prepolymer from polyether polyol and excess diisocyanate, and then adding stoichiometric 2-mercaptoethanol reaction, can obtain PU prepolymer without NCO group and end group as SH. Based on PbO2, ZnO as a curing agent to obtain sealant. Since the cured product contains disulfide bonds (S-S-one), it has certain excellent properties of polysulfide rubber, such as can improve the chemical resistance.
Polyurethane sealant formulation example (2)
4. Alkoxysilane-based polyurethane prepolymers