Here, as part of our experimental investigations dealing with poly(urethane-isocyanurate) networks, we investigate model irregular networks with increasing amount of dangling chains. In our study such an irregular network topology was obtained by partial substitution of a diol for a monohydroxy component during the preparation of isocyanate terminated precursors. Telechelic diisocyanates were synthesized from aromatic diisocyanate (2,4-TDI), α,ω-dihidroxypoly (oxypropylene) (PPG 2000), and diethyleneglycolmonomethylether (an aliphatic low-molecularweight monool component). The networks in undiluted state were prepared by cyclotrimerisation, in the presence of a catalyst. The network properties were estimated by multiple extraction in solvent, differential scanning calorimetry and photoelastical measurements. Independently of mechanical testing, the fraction and concentration of dangling and elastically active network chains were evaluated by the theory of branching processes (cascade theory). The influence of dangling chains on the mechanical properties was analyzed.