Silicone resin, process for producing the same, and curable resin composition comprising the same

#This invention relates to a silicone resin, a process for producing the said silicone resin, and a curable resin composition comprising the said silicone resin and, more particularly, this invention relates to a novel silicone resin that is crosslinked by silanols in spite of the co-presence of radically reactive groups, a process for producing the said silicone resin, and a curable resin composition comprising the said silicone resin.

#Cured silicone resins show excellent heat resistance, weather resistance, oil resistance, low-temperature resistance, and electric insulation and, at the same time, low modulus of elasticity and low stress. In consequence, cured silicone resins are used in a wide variety of applications including protection of electronic parts installed in vehicles and electrical appliances. In recent years, there is a demand especially for cured silicone resins which are flexible and tough.

#In order to obtain cured silicone resins, curable reactive functional groups are generally introduced to silicone resins. In particular, in order to obtain cured products which are flexible and tough, silicone resins are synthesized by utilizing such means as introduction of long silicone chains and optimization of the number of functional groups or produced in the form of polymer blends by mixing resins.

#FIG. 1 shows a GPC chart of silicone resin A obtained in Example 1.

#FIG. 2 shows a GPC chart of silicone resin B obtained in Example 2.

#FIG. 3 shows a GPC chart of silicone resin C obtained in Example 3.

#This invention will be explained in detail below with reference to the examples and comparative examples, but will not be limited thereto.

#In a reaction vessel equipped with a stirrer and a thermometer were placed 27 ml of toluene, 0.95 g of N,N-diethylhydroxylamine, and 22.01 g of an organohydrogenpolysiloxane represented by the following structural formula (i) (wherein R is a methyl group, s=7, and m=73). To the reaction vessel was added dropwise a toluene solution of 3.49 g of a polysiloxane containing hydroxyl groups at both ends represented by the following structural formula (ii) (wherein R is a methyl group and n=35) over 5 minutes with stirring at room temperature. Upon completion of the dropwise addition of the polysiloxane containing hydroxyl groups at both ends, the reaction solution was heated at 50° C. and stirred for 5 minutes, then 9.00 g of 2-hydroxyethyl methacrylate was added dropwise, and the reaction solution was stirred for 6.5 hours. The reaction solution was washed with an aqueous citric acid solution and water until the solution became neutral and was then dehydrated by anhydrous magnesium sulfate. The anhydrous magnesium sulfate was filtered off and the filtrate was concentrated to yield 27 g (90% recovery) of a silicone resin containing radically reactive groups. The silicone resin thus obtained will be referred to as silicone resin A.

#Silicone resin A obtained above was a colorless viscous liquid soluble in a variety of organic solvents. The disappearance of the peak assignable to the SiH group was confirmed by 1H-NMR analysis. The numbers of repeating structural units (s, m, n) of the organohydrogenpolysiloxane and the polysiloxane containing hydroxyl groups used in the reaction, the molar ratio of N,N-diethylhydroxylamine to the SiH group of the organohydrogenpolysiloxane, and the rate of introduction of the methacryl group to the silicone resin obtained are shown in Table 1. The rate of introduction of the methacryl group was calculated from the ratio of the peaks assignable to the silicone resin and the raw materials in 1H-NMR analysis. Furthermore, a GPC chart of the silicone resin obtained is shown in FIG. 1. As is apparent from FIG. 1, a resin with an Mw of 38,000 is obtained here.