Synthesis of organometallic poly(dendrimer)s by macromonomer polymerization: effect of dendrimer size and structural...

Two series of first to third generation (G1-G3) oligoether dendrimers, one bearing a shorter spacer chain (C-O) and the other having a longer spacer branch (C-C-C-O) were prepared. Both series of compounds, containing two reactive C[triple bond]CH moieties on the dendrimer surface, were used as macromonomers and copolymerized with trans-[Pt(PEt(3))(2)Cl(2)] to form organometallic poly(dendrimer)s by an outer-sphere-outer-sphere connection strategy. It was found that concentration of monomer used in the polymerization, the dendrimer generation, and, most strikingly, the length of the spacer were key factors that determined the polymerization efficiency. Hence, the structurally more rigid and compact C-O linked dendrimers formed poly(dendrimer)s with a higher degree of polymerization than the structurally less rigid and more bulky C-C-C-O dendrimers. This result was due to the higher tendency to form cyclic oligomers in the latter series of compounds. In addition, the differences in the polymerization efficiency among the three generations of dendrimers could be explained by the gradual decrease of reactive functional group density on the dendrimer surface.