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High molecular weight anlonlc block copolymer
were brought to the market place some 30 years
ago. Based on feedstocks which can be
polymerised through anionic polymerisation (e.g.
lsoprene, butadiene or styrene), such styrenic block
copolymers (SBC's) are nowadays available in a
non-hydrogenated (SIS, SBS) and in a
hydrogenated form (SEBS, SEPS). At room
temperature, these block copolymers exhibit
physical crosslinking arising from microphase
separation of the polystyrene end-bloeks which
makes them thermoplastic elastomers.
Hydrogenated SBC's show superior heat and light
stability. As they were designed for the
thermoplastic process, such SBC's exhibit high
melt viscosities and are unsusceptible to chemical
crosslinking. Early '96, a new class of hydrogenated
anionic polymers have been brought onto the
European market plaee ~ Shell under the trade
name KRATON LlQUID M Polymers. In sharp
contrast with their "predecessors", these new
polymers do not exhibit microphase separation and
are of low molecular weight. They are viscous
liquids at room temperature and as a unique feature
they bear reactive groups that allow further
chemicaI reactions: they are reactive polymers.
This paper reports on the developments achieved
so far about the use of these novel polymers in
cationic UV cured pressure sensitive adhesives1.
