posted on 2016-06-13, 00:00authored byAndrew J. Guenthner, Christopher M. Sahagun, Kevin
R. Lamison, Josiah T. Reams, Timothy S. Haddad, Joseph M. Mabry
The
impact of silica functionalization in determining the performance
of polycyanurate networks polymerized from 1,1-bis(4-cyanatophenyl)ethane,
known commercially as Primaset LECy, reinforced with modified fumed
silica, was elucidated through systematic comparison of the properties
of nanocomposite networks in which the silica surface treatment was
altered. Three types of surfaces were investigated: moderately acidic
(unmodified silanol), neutral (alkylsilane modified), and slightly
basic (3-aminopropylsilane modified). In terms of cyanate ester cure,
the acidic surface proved to be moderately catalytic, the neutral
surface mildly catalytic due to slight residual silanol content, and
the basic amino-functional surface mildly inhibitory. In terms of
network performance, the amino-functional surface led to significant
degradation of the network at elevated temperatures, while the silanol-functional
surface outperformed the alkyl-functional surface in terms of protection
against hydrolytic degradation. In agreement with expectations, the
addition of 2–5 wt% of relatively well-dispersed silica nanoparticles
had negligible impact on the fracture toughness of the cyanurate networks.
Overall, these results demonstrate that the functionalization of nanoparticle
additives for polycyanurate networks is an important determinant of
performance and must be taken into consideration in the development
of polycyanurate nanocomposites, even at levels that are too low to
strongly affect mechanical properties.