A general method for introducing various side chains onto a highly branched polysilaethylene (HBPSE) backbone is described. This method starts with a commercial oligomer mixture which has a highly branched structure, consisting of [H3SiCH2], [SiH2CH2], [SiH(CH2)(2)], and [Si(CH2)(3)] subunits combined to give an overall "SiH2CH2" average formula. Several alkyl-, aryl-, and allyl-substituted HBPSEs were prepared by first converting the parent HBPSE into a highly reactive bromo-substituted derivative which was then treated with organolithium reagents (RLi, R = C4H9, C6H13, C8H17, C6H5, C6H4N(Me)(2)) or Grignard reagents (RMgBr, R = Et, allyl). The parent HBPSE and its derivatives were characterized by means of NMR and IR spectroscopy, as well as elemental analysis, DSC, GPC, and VPO. It was shown that the allyl-substituted HBPSE can be used as a synthetic platform for attaching functional side chains via the hydrosilation reaction.