Comparison of chain-growth polymerization in solution versus on surface using reactive coarse-grained simulations
BH Deng and EF Palermo and YF Shi, POLYMER, 129, 105-116 (2017).
We developed a reactive coarse-grained model for chain-growth polymerization to study the chain length distribution of polymers grafted from a surface as compared to those grown in solution. The surface-initiated polymer chains exhibit a markedly broader distribution of chain lengths (larger dispersity) and slower chain growth kinetics as compared to the solution phase process. Two key factors that cause deviation from ideal grafting are identified: (1) the formation of chain "loops" with both termini attached to the substrate via recombination and (2) the "starvation" effect, in which the live chain ends of short polymers are sterically shielded from monomers by the presence of longer neighboring chains. Both effects are markedly amplified with increasing initiator surface density, thus limiting the density of high molecular weight chains grafted from the surface. Whereas the "loop" effect is absent in systems that are very strictly "living" (no termination), the starvation effect is likely operative in most real systems. Taken together, these results suggest a theoretical limit on the density of polymer brushes that can form on surfaces by a "grafting- from" technique, based on the kinetics of the chain- growth polymerization process. (C) 2017 Elsevier Ltd. All rights reserved.
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