Gel Formation during the Gilch Synthesis of Poly(p‐phenylene vinylenes): Evidence of an Unexpected Explanation

Gelation of the reaction mixture and insolubility of the poly(p-phenylene vinylenes) (PPVs) when isolated at this stage, but complete redissolution of the gel and excellent solubility of the resulting PPVs after further stirring for hours or days, is a phenomenon in Gilch polymerizations that has not been explained so far. It is verified that, in agreement with the literature, specific additives prevent gelation. However, it is also shown that chemical cross-linking is certainly not the reason for gel formation. Instead, it seems to be the consequence of a very high entanglement density in the pristine PPVs, which requires time for relaxation. The mentioned additives seem to support this dis-entanglement process.