One option to understand and possibly improve the properties of thermosets is to investigate well-defined polymer networks. Various novel, alpha, omega-ethylmaleate functionalized poly(propylene glycol)s were endlinked with a trifunctional thiol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol tris(3-mercaptopropionate) (EHPT). Model reactions of EHPT and diethyl maleate indicated that a substitution effect in the thiol is absent. Characterization of the model networks revealed that the molecular weight between junction points, M(c), calculated from the sol fraction (branching theory) agrees with the M(c) calculated from the tensile storage rubber modulus E’. The glass transition temperature (T-g) decreases linearly with increasing M(c). The K-1c (critical stress intensity factor) seems to be independent of the crosslink density.