Factors hindering thiophene

A methyl group, which displays electron-donor properties (+/, +M), facilitates the acid-catalyzed and hinders the alkali-catalyzed exchange, in deuteriated methylselenophenes. The partial rate factors (/) show that a methyl group transfers its electronic effect in selenophene79 almost as effectively as in thiophene.86... 

What are the factors most likely to be hindering the use of CPs other than P(ANi) and poly(3-alkyl thiophenes) for corrosion protection ... 

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