2. One approach to improving the tractability of aromatic polyamides has been to

Question

2. One approach to improving the tractability of aromatic polyamides has been to synthesize polymers of structure Which, upon prolonged heating at 200 to 300°C under nitrogen, expel ethylene by the retro Diels-Alder reaction to form the anthracene system. (A. H. Frazer et al J. Polym. Sci Polym. Chem. Ed. 23, 1985, 2779 & 2791.) Explain the rationale for this approach. Suggest a potential problem that might arise in processing (other than the usual problems of availability of monomers). (Hint: Polyimide processing has a similar problem.) a. b.

Explanation / Answer

a)

Retro Diels-Alder reaction (rDA): rDA depends upon temperature. Here the diene (i.e., anthracene) and dienophile (i.e., ethylene) form the cyclic product after 4+2 cycloaddtion i.e., Diels-Alder reaction. For the given compound more heat is required for rDA due to the relative tendencies of anthracene and ethylene are less, so at the given temperature rDA happen with the compound.

b)

Problem: Formation of radical, highly toxic smoke, high volume of fire, chances of rDA, Black Specks, Blush, Brittleness, Bubbles, Burns, Cracks, Delamination / Lamination, Discoloration, Excessive Shrinkage, Flow Lines, Jetting, Mold Flash, Parts stick in mold, Short Shots, Sink Marks, Splay Marks / Silver Streaking, Surface Finish (Low Gloss), Voids, Warping, Weld Lines.

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