STRUCTURE AND MECHANICAL-PROPERTIES OF THE COMPOSITIONS OF POLYISOCYANURATE POLYMERS WITH LOW-MOLECULAR-WEIGHT RUBBERS

The structure and properties of the compositions of polyisocyanurates modified with low molecular weight rubber networks have been investiga ted by means of dynamical mechanical analysis (DMA), electron microsco py, and stress-relaxation experiments. The network compositions consis t of two different polymeric networks. The first component (macrodiiso cyanate based on low molecular weight polybutadiene or copolymers of t etrahydrofuran and propylene oxide) has bulky cross-linked points conn ected by short flexible chains. The second component (diphenylmethaned iisocyanate) also has bulky cross-linked points of the same structure, but the linear fragments between them in this case are very small and rigid. These compositions result in the formation of the heterophase system. As a result, transparent samples were prepared, which differ f rom the mechanical properties of both the glassy and rubbery polymers. These materials have a modulus of elasticity (from 10(3) to 10 MPa) t hat is usual for the transition zone between the glassy and rubbery st ates; nevertheless, these materials show elastic (and not viscoelastic ) properties. For the materials investigated, the modulus is decreased not more than 10 times in the wide temperature interval from 200 to 5 00 K. A new state of the polymer, which differs from both the glassy a nd rubbery states, has been identified in the present case. (C) 1995 J ohn Wiley and Sons, Inc.