New Insights Into Polyurethane Modified Epoxy Resins

Epoxy resin has many advantages, such as high mechanical strength, strong cohesive force, low shrinkage, good stability and excellent processability. It is widely used in coatings, adhesives, electrical products, civil engineering, Xia he materials and other fields.

However, because of its fragility, lack of toughness and impact resistance, it has become a difficult problem affecting its market expansion.

At present, one of the main modification methods of epoxy resin is polyurethane modified epoxy resin. Recently, domestic researchers have designed a series of schemes, and used infrared spectroscopy to characterize the structure of polymers. Studying the types of reaction and reaction mechanism that may occur in the process of epoxy resin modification by polyurethane prepolymer, has important guiding significance for the application research of polyurethane modified epoxy resin.

Polyurethane modified epoxy resin, under suitable conditions, enables the 2 to form an interpenetrating network structure, so as to improve the toughness of epoxy resin without reducing its strength and heat resistance.

However, due to the diversity of raw materials and the functional groups contained in various materials, the curing mechanism of polyurethane modified epoxy resin system is complicated.

The general literature is generally based on the functional groups of various materials, pointing out possible reactions in the system, or simply analyzing the starting materials and final products, without further studying the reaction process.

Using infrared spectroscopy to study the structural characterization of polymers has made a new way in this regard.

The raw materials used in the research include toluene diisocyanate (TDl), polyether 210, 1, 4- butanediol, two lauric acid two butyltin, l, 2- epoxycyclohexane -4, 5- two formic acid two glycidyl ester (TDE-85), methyl four hydrogen ortho benzyl two, anhydride (MeTHPA), 2, 4, 6- three (three methylamine methyl) phenol (DMP-30), etc.

The isocyanate terminated PU prepolymer and IPN product were prepared in the experiment.

The performance test was carried out by AVATAR360 infrared analyzer (Nicolet, USA). The raw materials TDE - 85, polyether diols GM210 and PU prepolymer and samples were analyzed by infrared spectrum. Solid samples were detected by potassium bromide tabletting method, liquid samples were directly tested or diluted by carbon tetrachloride.

The results show that: first, the accelerator DMP-30 attacks the anhydride to form carboxylate anion; secondly, the carboxylate anion and epoxy group react to form oxygen anion; finally, the oxygen anion reacts with another anhydride to regenerate carboxylate anion; the carboxylate anion then reacts with the epoxy group to produce ring opening polymerization so that the curing reaction is carried out step by step.

In this project, the polyurethane modified epoxy resin system was prepared, and the interaction between the polyurethane prepolymer, chain extender, epoxy resin and curing agent was studied by IR spectrum analysis.

The results showed that the curing reaction between epoxy resin and its curing agent formed during the formation of IPN structure between polyurethane and epoxy resin. The chain extender 1, 4- butanediol extended the PU prepolymer, and there were two chemical reactions between TDE-85 and PU prepolymer at the same time.

This can effectively improve the compatibility and stability between the 2 polymers, which can improve the performance of epoxy resin and achieve the purpose of modification.

TDE-85 and chain extender 1, 4- butanediol did not react. The hydroxyl vibration peak in the IR spectrum was due to the presence of chain extender 1, 4- butanediol, which led to the introduction of hydroxyl absorption peak, the reaction of polyether and TDI of polyurethane system, the formation of -NCC end group prepolymer, then reacting with the chain extender diol to form a polyurethane network system. The epoxy group in epoxy system was cured with anhydride to form an epoxy network system. There were two chemical reactions between TDE-85 and PU prepolymer in epoxy system, which could effectively improve the compatibility and stability of 2 polymers, and improve the toughness and heat resistance of epoxy resin without decreasing its strength. In the curing process of polyurethane modified epoxy resin,