Structural Analysis of Ultrasoft PDMS- g-PDMS Shell-Only Particles

We have used anionic polymerization to synthesize polymers of linear and bottlebrush architecture each with a polydimethylsiloxane backbone. The blending of polymer architectures has the effect of changing material properties, e.g., the viscoelasticity, which are connected to the chain conformation. Thus, we explore the conformation of bottlebrush polymers in a linear host melt both as a function of the concentration and for various molecular weights of the linear host matrices. Our bottlebrush polymers are seen as shell-only particles with a negligible core size. We find a substantial influence of the molecular weight of the linear matrices on the structure of the bottlebrushes and their interactions. In samples with a low molecular weight matrix that have the same degree of polymerization as the side chains, the bottlebrush behavior is consistent with an effective theta solvent condition for all concentrations. With increasing molecular weight of the host matrix, this condition is only reached at the highest concentration of the bottlebrush polymers. The increase of the molecular weight of the host matrix leads to a shrinkage of the bottlebrushes and subsequently to a formation of clusters at higher volume fractions. None of the scattering patterns show a pronounced correlation peak; however, decreased forward scattering associated with a structure factor effect is observed.