Abstract
Free-radical crosslinking polymerization behavior of triallyl isocyanurate (TAIC) was specific as compared with those of common multiallyl monomers. This is due to the steric effect on the transition state formation in the reaction at the sterically crowded, terminal reaction site of growing polymer radical caused by the sequential, bulky TAIC units, i.e., the reduced monomer chain transfer, the non-terminal units effect on the cyclopolymerization of TAIC, and the sequence length dependence of steric effect on the reactivity of growing polymer radical. Non-filled TAIC cured resin was too brittle for practical use. The brittleness of crosslinked resins has been conceived to be due to the inhomogeneity of their network structures consisting of colloidal particles; however, the complete loss of flexibility of poly (TAIC) chain does not satisfy the prerequisite of the locally-enhanced occurrence of intramolecular crosslinking reaction inducing microgelation to form a colloidal particle. Therefore, the correlation between brittleness and network structure of TAIC resins was further discussed, especially focusing on the characterization of resulting TAIC network polymer precursors (NPPs). Thus, an alternative explanation for the brittleness of TAIC resins is provided : the insufficient growth of the network structure of TAIC resin because of steric hindrance on the crosslinking reaction between sterically crowded growing polymer radical and pendant allyl groups belonging to the rigid primary polymer chains at the surface of coreshell type dendritic NPP. This was extended to the mechanical formation of finely divided particles originated in an extreme brittleness of TAIC resin, and, furthermore, we proposed that a network polymer should be considered as “a crosslinked system material” consisting of NPP modules as metastable intermediates of crosslinked polymers in place of “an indefinitely large sized, giant molecule”.
