There are pure epoxy systems which are cured by cationic photoinitiators
developed by 3M and GE.  Are they being used in LPISM?  I doubt it due to the
properties that they develop are not as resistant to subsequent treatment in
the PCB manufactuing.
Manufacturers like to say they have all acrylic because they may have a
predominance of that type of chemistry in their formulation.  They still need
some other type of chemical structuring, such as epoxy or urethane groups to
provide the ultimate properties.  Will any manufacturer tell you what their
formulation is?  Not outright, but they will allude to the type of chemistry
they use.  You still have to test the LPI's for yourself.

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