关键词: 反应性聚氨酯, 涂层, 有机硅, 无溶剂, 微相分离

Abstract: Polyurethane, as an emerging organic synthetic polymer material, is known as the "fifth largest plastic" and is widely used in chemical, electronics, textile, medicine, construction, automobile, and many other fields because of its excellent performance. Polyurethane is broadly categorized as solvent-based one, water-based one and solvent-free one. Traditionally produced polyurethane is mostly solvent-based one. Solvent-based polyurethane seriously jeopardizes the physical and mental health of producers because of the addition of organic solvents such as N,N dimethylformamide and acetone to the production process, and the presence of residual organic solvents in the finished product may also be harmful to the physical and mental health of consumers. And water-based polyurethane replaces organic solvents with water, solving the problem of solvent pollution. However, because of the existence of hydrophilic groups, the coating's water resistance decreases, which makes it easier to dissolve abd affects the mechanical properties. Meanwhile, the water evaporation is slow, resulting in a long drying time and heavy energy consumption. Solvent-free polyurethane (reactive polyurethanes) solves the above problems of polyurethane by virtue of the absence of solvent incorporation. Mechanical properties are an important index of coatings, and it is necessary for the article to investigate the effect of hydroxyl silicone oil on the mechanical properties of solvent-free polyurethane coatings.
     Polyurethane coatings with high strength, high-temperature thermal stability, low-temperature resistance, hydrophobicity, and softness were comprehensively designed. Diphenylmethane diisocyanate and 1,3 propylene glycol were used as hard segments, and poly(tetrahydrofuran ether diol), castor oil, and bis-hydroxy-capped polydimethylsiloxane (PDMS) were used as soft segments. The two-component method was used for prepolymerization, followed by mixing, scraping, and reaction molding. A series of solvent-free polyurethane coatings were synthesized by partially replacing castor oil with PDMS, and the effects of PDMS content on the mechanical and thermal properties, low-temperature resistance, hydrophobicity, and feel of the coatings were investigated. The effect of hydroxyl silicone oil on the mechanical properties of polyurethane was investigated in a solvent-free system. The tensile strength and elongation at break of reactive polyurethane (Si-PU) coatings modified by silicone were effectively enhanced, with a maximum increase of 51.9% in tensile strength and 99.3% in elongation at break. With the increase in PDMS mass fraction, the mixing degree of soft and hard segments of Si-PU increased, and the degree of microphase separation weakened. As the mass fraction of PDMS increased, Tmax moved toward high temperature, and the thermal stability of the coating was enhanced; the glass transition temperature (Tg) of the coating gradually decreased, and its low-temperature resistance was significantly improved; at the same time, the hydrophobicity was improved, and the handfeel became softer, thus the serviceability was improved.
    The silicone-modified polyurethane coating prepared by the above method overcomes the shortcomings of solvent-based polyurethane and water-based polyurethane, and at the same time, its breaking strength, elongation at break, high-temperature thermal stability, low-temperature resistance, hydrophobicity, and softness have been improved to a certain extent. As the national requirements for environmental protection in the chemical industry become higher and higher, further research on solvent-free polyurethane technology is expected to be more in-depth and comprehensive in the future, so that it can be more widely used in various industries.

Key words: reactive polyurethane, coating, organosilicon, solvent free, microphase separation