The invention concerns a thermosetting elastomer composition based on modified
polycyanurate with improved thermal resistance obtainable by a polymerization method
in the presence of a catalyst (D) of a mixture comprising at least: (A) a cyanate,
(B) a block copolymer consisting of: a) at least a central block (B1) non-miscible
with the cyanate and sufficiently long to provide the composition with elastomeric
character; and b) at least two terminal blocks (B2) located on each side of the
central block and comprising groups reactive with the cyanate, each of the blocks
(B2) being sufficiently long to be miscible with the cyanate; and (C) a mineral
filler reactive with the cyanate, in proportions such that the ratio r is not less
than 5, but remains less than a threshold value to avoid phase inversion, said
method comprising steps which consist in: I) mixing (A), (B), (C) and (D) until
a homogeneous mixture is obtained at a temperature higher than the melting point
of (A) and of (B) but lower than about 130 C.; II) polymerizing the mixture
at a temperature ranging between about 130 and about 170 C.; III) post-curing
the polymerized mixture at a temperature not lower than about 200 C. to complete
the reaction; the values of dsrupt and of derupt of the resulting composition being
not more than +-;30%. The invention also concerns the method for preparing said
composition and its use.
