The Importance of Branch Placement on the Dilute Solution Properties of Comb-like Macromolecules.

Branch density and length substantially impact the properties of comb-like polymers. Scientists often use the dilute solution properties of these materials to quantify their architecture. As branch spacing decreases and branch length increases at a fixed molecular mass, dilute solution properties such as the radius of gyration, intrinsic viscosity, and hydrodynamic radius typically decrease because the length of the backbone decreases. However, this decrease is only partially driven by this change in backbone length, even for relatively short branches. While many models focus on predicting the dilute solution properties of these materials with fixed branch spacing, most comb-like polymers exhibit statistical branch spacing which leads to nontrivial changes in excluded volume effects. Using molecular dynamics simulations and the ZENO code, we show how changing the distribution of branches from fixed to statistical and then to diblock affects the dilute solution properties of a coarse-grained linear low-density polyethylene (LLDPE), a canonical comb-like polymer, in 1,2,4-trichlorobenzene, a standard good solvent. This approach explicitly accounts for excluded volume interactions that were not included in prior theories. We extend our previous theoretical work to account for statistical branch spacing and test prior renormalization group estimates of diblocks in good solvent to show that it is consistent with our numerical results. Our approach provides a framework for a more quantitative understanding of chain architecture from dilute solution properties, yielding better structure-property relationships.