[E0035]
Jarosław Górczyka), Dariusz Bogdał
a) Department of Polymer
Chemistry and Technology, Cracow University of Technology, ul. Warszawska 24,
31-155 Cracow, Poland
b) Industrial Chemistry Research
Institute, ul. Rydygiera 8, 01-793 Warsaw, Poland
* e-mail: [email protected]
Received: 15 August 2001 / Uploaded 22 August 2001
1.Direct method based on polycondensation of
bisphenol A and epichlorohydrin under normal2) or higher3) pressure in the presence of NaOH as
a catalyst.
In conventional thermal
processing, energy is transferred to the material through convection, conduction
and radiation. Transfers of energy rely on diffusion of heat from the surfaces
of the material. Microwave energy is delivered directly to material through
molecular interaction with the electromagnetic field. A transfer of energy does
not rely on diffusion of heat. It is possible to achieve rapid and uniform
heating even in materials with low thermal conductivity (e.g. epoxy resin). The
significant result is the reducing of processing time.
Schematic reaction of
synthesis of high molecular weight
epoxy resins is shown in Figure 1.
Figure 1. Polyaddition of
bisphenol A to low-molecular-weight epoxy resin.
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The mixture was stirred under nitrogen at
different temperatures: 140, 160 and 170°C, in a Multi-mode Microwave Reactor
“Plazmatronika” - Figure 2 (microwave frequency - 2,45GHz, maximum of
microwave power - 300W), for time required to obtain epoxy numbers about
0,11. Normally 40% of full microwave’s power was used. Every 5 minutes a small sample of epoxy resin was taken from the mixture to determine the epoxy number. After the reaction the epoxy resin was cooled down and powdered. Plazmatronika Microwave Reactor implements novell Concentrated
Microwave Field (CMF) which provides the microwave field focused onto the
reaction vessel. |
Figure 2. A Multi-mode Microwave Reactor « Plazmatronika ».
Figure 3. GPC chromatograms
of high molecular weight epoxy resins synthesised in a microwave reactor
(160°C, 40% power).
Results of all analyses are
presented in Table
1.
GPC analysis shows that all
synthesised high molecular weight epoxy resins have comparable molecular weight
and polydispersion.
The optimal reaction
conditions for the microwave processes were found to be: 15-20 minutes,
temperature between 160-170°C, using 40% of full power. Shortening of the
reaction time for all processes provided in the microwave reactor, in comparison
to conventional heating, was observed.
It is necessary to use an atmosphere of nitrogen
to improve the colour of the synthesised epoxy resins.
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Table 1. Results of GPC
analysis of high molecular weight epoxy resins.
4) Brojer Z.: Polimery 1980, 25, 205
5) Csillag L., Antal I., Dolp H. R.: Polimery 1974, 19, 578