UV-curable PU Nanocomposite Materials via a Sol-Gel processes
Wei-Hung Chen*, Yuan-Jyh Lee, Kan-Nan Chen
Department of Chemistry, TamkangUniversity, Tamsui, Taiwan 251
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Introduction
The Inorganic/Organic hybrid materials, become to promise new applications in many fields, such as optics, electronics, and biology. In order to prepare hybrid material which contain nano-size inorganic particles, an UV-curing sol-gel process was applied.
UV-curable organic/inorganic composite material was obtained from a vinyl terminated PU or epoxy resin oligomer with tetraethoxysilane (TEOS) by a sol-gel process. The morphology of composite was investigated by scanning electronic microscopy (SEM). These networked polymer properties such as physical, mechanical and thermal behavior of organic/inorganic composite material were evaluated in this report.
Experiment
Synthesis of polyurethane acrylate
Add a catalytic amount of T-12 (1% w/w) into PU pre-polymer(1000g) and keep heating to 75℃. Then the mixture was added suitable amount of HEMA and keep stirring until the reaction completed (scheme 1). The product can be defined by IR-spectra.
Synthesis of epoxy acrylate/TEOS
Add tetraethoxysilane(150g) into epoxy acrylate at 100℃,then the mixture was keep stirring for 2 hours(scheme 2). The composite compound can be defined by IR-spectra.
Result and Discussion
TGA(Thermal Gravity Analysis )
Because the polar functional group of polyurethane has strong hydrogen bonging with oxidized silica which made PU’s structure more compact, when the amount of oxidized silica increased, it will enhance the thermal stability of PU. The same situation of thermal stability enhancement did not seen in epoxy acrylate/TEOS system.(fig 1) This probably the compact structure of epoxy was destroyed due to the condensation of oxidized silica and solvent vaporized.
SEM(Scanning electron microscopic)
In PU acrylate/TEOS system, because there is no chemical bonding between these two materials, the compatibility of PU acrylate with TEOS is less than epoxy acrylate which has chemical bonding with oxidized silica, there are many oxidized silica particles can be seen upon the polymersurface(fig 2), most of the silica particle’s size is less than50nm, this can prove the hybridmaterial is an nanocomposite.
It can see there is no TEOS aggregation in the epoxy-acrylate system, and the oxidized silica particle size is less than 50nm, this can prove the hybridmaterial is a nanocomposite.
Non-Solvent System
Solvent will influence polymer’s network, and environment concern, we also try to hybrid our polymer with TEOS under non-solvent system. In the SEM picture, it can the particle size of oxidized silica is nearly 50nm, and no aggregation phenomenon was observed in both PU and epoxy matrix.(figures 3 and 4).
Gel Content Test
In non-solvent system, the UV-curing efficiency is better because solvent will restrict the transfer of free radical, made the polymer network more rigid. Although non-solvent system enhanced polymericnetworks in PU system, the influence of solvent in gel content is not very obvious. this is because without solvent, TEOS is more unstable and decrease its interaction with PU. If make this hybridized material dried, then TEOS was cross-linked via a moisture curing process, and their gel contents will rise up to 98%.
In Epoxy-acrylate/TEOS system, because there is no solvent caused structure incompact, the gel content is all above 95%.
Table 1 Gel-Content of UV-PU/TEOS
PU 5g / solvent / Non-solventTEOS / none / 4g / 8g / 4g / 8g
Gel.cont.(%) / 42 / 66 / 65 / 83 / 88
Table 2 Gel-Content of UV- Epoxy/TEOS
epoxy5g / solvent / Non-solventTEOS / none / 2g / 3.5g / 2g / 3.5g
Gel.cont.(%) / 98 / 93 / 94 / 98 / 96
Scheme 1Synthesis of polyurethane acrylate
Scheme 2 Synthesis of epoxy acrylate/TEOS
Fig 1 Epoxy acrylate hybrid different ratio of TEOS
Fig 2 SEM picture of PU/TEOS
Figure 3 SEM of non-solvent PU/TEOS
Figure 4 SEM of non-solvent PU/TEOS