Polybenzoxazine as a noble phenolic resin was modified with amine-term
inated butadiene acrylronitrile rubber (ATBN) and with carboxyl-termin
ated butadiene acrylronitrile rubber (CTBN) in order to improve its me
chanical properties. The fracture toughness, flexural modulus, and fle
xural strength of rubber-modified polybenzoxazine were measured to inv
estigate the effect of rubber modification. In fracture toughness, ATB
N is more effective than CTBN. ATBN-modified polybenzoxazine showed be
tter distribution of rubber particles in matrix phase than did CTBN-mo
dified polybenzoxazine. The cure rates in these systems were monitored
by differential scanning calorimetry to investigate the effect of cur
e rate on rubber size. The change of glass transition temperatures of
rubber-modified polybenzoxazine was measured with a dynamic mechanical
thermal analyzer to explain the Variation of mechanical properties. I
n addition, the relationship between mechanical properties and the mor
phology of rubber-modified polybenzoxazines was also undertaken. (C) 1
998 John Wiley & Sons, Inc.