The orientation of block copolymer (BCP) features in thin films can be obtained by spin-coating a BCP solution on a substrate surface functionalized by a polymer brush layer of the appropriate random copolymer (RCP). Although this approach is well established, little work reporting the amount and distribution of residual solvent in the polymer film after the spin-coating process is available. Moreover, no information can be found on the effect of trapped solvent on the interface between the BCP film and RCP brush. In this work, systems consisting of poly(styrene)-b-poly(methyl methacrylate) thin films deposited on poly(styrene-r-methyl methacrylate) brush layers are investigated by combining neutron reflectivity (NR) experiments with simulation techniques. An increase in the amount of trapped solvent is observed by NR as the BCP film thickness increases accompanied by a significant decrease of the interpenetration length between the BCP and RCP, thus suggesting that the interpenetration between grafted chains and block copolymer chains is hampered by the solvent. Hybrid particle-field molecular dynamics simulations of the analyzed system confirm the experimental observations and demonstrate a clear correlation between the interpenetration length and the amount of trapped solvent.
Partly deuterated hydroxy-terminated poly(styrene d8-r-methyl methacrylate) statistical copolymers with different molecular weights were grafted to a silicon substrate. Then, fully hydrogenated hydroxy-terminated poly(styrene-r-methyl methacrylate) statistical copolymers were spun over the pregrafted substrate and let to react at 250 °C following the time evolution of the brush thickness and composition. Over time, the grafting density of the deuterated polymers decreases, whereas the grafting density of the hydrogenated polymers increases thus indicating the simultaneous occurrence of grafting and degrafting reactions. Moreover, keeping constant the grafting time, the total grafting density decreases as the molecular weight of the hydrogenated polymers increases, until a limiting value is reached when the molecular weight of the incoming polymer is equal to the one of the preformed brush. The overall picture of the experimental data, further supported by hybrid-particle field coarse-grained simulations, suggests that the reactivity of the system is related to the degree of stretching of the brush layer induced by the entering of additional polymer chains. This new vision of the grafting to mechanism implies that the self-limiting nature of this process derives from a mechanochemical control of the reaction rather than from diffusion/penetration effects.
A substantial partition by molecular weight takes place during the grafting to reactions.
Phosphorus δ-layers in SiO 2 have been prepared by means of poly(methyl methacrylate) (PMMA), terminated with a phosphoruscontaining moiety acting as an anchoring group. In particular, grafting of two P-terminated PMMA samples with M n = 7.5 kg/mol (D̵ = 1.14) and M n = 17.8 kg/mol (D̵ = 1.23) onto 10 nm thick SiO 2 films deposited on Si substrates has been investigated, focusing on the thickness evolution of the brush layer as a function of the processing parameters, that is, annealing temperature and time. Upon removal of the polymer chains and subsequent encapsulation into a SiO 2 matrix, the concentration of phosphorus atoms into the P δ-layers has been monitored by time-of-flight secondary ion mass spectrometry. The effective P dose in the P δ-layer is mainly dictated by the molecular weight of the P-terminated PMMA, and the doping process results are highly reproducible, provided that tight control over the experimental protocol is granted. However, although the grafting density is expected to progressively increase as a function of annealing time with a linear correlation between grafting density and thickness, the measured P dose in the δ-layers is observed to follow the opposite trend. This effect has been accounted for by considering a distortion of the molecular weight distribution of the grafted species with respect to the initial molecular weight distribution of the polymer. The overall picture reveals important information about the mechanism and dynamics governing the "grafting to" process of P-terminated PMMA polymers onto nondeglazed Si substrates.
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