β Scribed by Irvin S. Klaus; William S. Knowles
No coin nor oath required. For personal study only.
Volume changes during curing of an unfilled epoxy resin using a series of anhydrides It was shown that a significant reduction in shrinkage could be were measured. achieved by proper choice of structure.
Shrinkage occurs generally in polymerizations as a logical consequence of forming large molecules from small ones. It amounts to 34% in vinyl polymerization' and is as low as 1% when rings are converted to chains.2 It is fairly low (5-6y0) in typical unfilled epoxy r ~s i n s , ~ but in no case does it appear to be absent. At present there are three general ways to combat this contraction problem. The f i r ~t ~, ~ is to use an inert filler to dilute the effect. The second is to use materials that are liquid a t high molecular weights so there will be less change in molecular size going from liquid to solid. Use of Thiokol-epoxy blends affords an example of this type.4
The third comprises adding a gas-forming agent4 like isocyanate and a little water to form a slightly foamed polymer. All pay some penalty for the lowered shrinkage.
This work was undertaken to determine whether the structure of a crosslinking agent in a typical unfilled epoxy resin could be altered to minimize shrinkage. It is obvious that a low-shrinkage crosslinking reaction must not split off volatile by-products and therefore should be of the type: A + B -. C
Volumsanderungen wiihrend der Hartung ungefullter Epoxyharze mit einer Reihe von Durch Wahl einer geeigneten Struktnr konnte eine Anhydriden wurden gemessen. wesent,liche Herabsetzung der Rchrumpfung erreicht werden.
π SIMILAR VOLUMES
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