Effect of the length of branches on hydrodynamic and conformational properties of hyperbranched polycarbosilanes

The hydrodynamic and conformational properties of hyperbranched polycarbosilanes with different lengths of branches, namely, poly(methyl(allyl)carbosilane) containing three CH2 groups between branching centers and poly(methyl(undecenyl)carbosilane) whose branches are composed of 11 CH2 groups, have been studied in dilute solutions in hexane using the methods of molecular hydrodynamics and optics. Fractions with M < 17.5 × 104 have been used in experiments. The hydrodynamic properties of the above polycarbosilanes differ significantly from those of linear polymers since hyperbranched macromolecules are compact and their shape differs only slightly from spherical. The lengthening of chains between branching centers causes a change in the hydrodynamic characteristics, and the difference between hyperbranched polymers and dendrimers becomes more pronounced. As the length of branches increases, their conformation changes from an extended trans chain to a more or less bent rod.