Coarse-Grained Parameters for Simulations of Methyl-Methacrylate-Based Polymer Brushes That Reproduce Experimental Swelling Coefficients

Polymer brushes exhibit unique structural and dynamic properties compared to free polymers due to their confined and tethered nature. While coarse-grained (CG) models for free polymers are well-established in the literature, their direct application to polymer brushes is limited. This is because brushes demonstrate distinct conformational behaviors, scaling laws, and responses to environmental stimuli that may not be accurately captured by models developed for free polymers. We have systematically evaluated chemically specific CG parameters within the MARTINI v3 force field for methyl-methacrylate-based polymer brushes. We have found that the most CG parameter assignments led to an excessive coiling of the brush chains and a strong dependence of the calculated swelling coefficient S_C with the water model used (RW, SW, and TW). We traced these issues to an imbalance between polymer–polymer and polymer–water interactions. The revised parameter set accurately reproduced experimental swelling coefficients for methyl-methacrylate-based brushes with varying grafting densities, pH responsiveness, charge, and hydrophilicity, namely, poly(dimethylaminoethyl methacrylate) (pDMAEMA), poly((2-methacryloyloxy)-ethyl trimethylammonium chloride) (pMETAC), poly[2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)] ammonium hydroxide (pMEDSAH), and poly(3-sulfopropyl methacrylate) (pSPMA). Furthermore, these parameters mitigated brush chain hypercoiling and dependence on the water model, ensuring better reproducibility of experimental data and alignment with theoretical brush models.