Model networks were prepared by the reaction of monodisperse polybutad
iene, containing 8% of double bonds in the 1,2 vinyl position, with p-
bis(dimethyl silyl) benzene at different stoichiometric imbalances. Sm
all strain modulus and measurements of the gel fraction indicate impor
tant differences with the predictions from ideal network forming react
ions and the molecular theories of rubberlike elasticity. Sol extracti
ons are higher than expected and small strain moduli are consistently
low. Other macroscopic signs of the departure from ideal behaviour are
detected. The onset of the gel point is delayed to a degree that grow
s with increasing imbalance of the reactive groups. We consider all th
e possible explanations for the observed behaviour, and suggest that t
he most likely one is the presence of intramolecular reaction. We also
propose a simple theoretical model to confirm that our assumptions ar
e consistent with the experimental results. (C) 1998 Elsevier Science
Ltd. All rights reserved.