The long and the short of polymer grafting†
We demonstrate that grafting a distribution of polymer chains onto an interface critically affects the shape of the distribution, with shorter chains being preferentially attached. This distortion effect is herein quantified for the first time, exploiting a quartz crystal microbalance – underpinned by single-molecule force spectroscopy – on the example of grafted poly(methyl methacrylate) (PMMA) chain distributions of different molar mass. ‘Grafting-to’ of different ratios of number average molecular weight of PMMA distributions unambiguously establishes the preferred surface grafting of shorter polymers, which can be correlated to their smaller radius of gyration. Our findings allow to establish a preferential grafting factor, k, which allows to predict the molar mass distribution of polymers on the surfaces compared to the initial distribution in solution. Our findings not only have serious consequences for functional polymer interface design, yet also for the commonly employed methods of grafting density estimation.