Forward recoil spectrometry has been used to determine concentration profiles and tracer diffusion coefficients D* of undeuteriated polystyrene rings of molecular weight M, ranging from 10000 to 180000, diffusing into deuteriated linear polystyrenes (PS) of molecular weight P, ranging from 55000 to 915000. Although constraint release has been proposed as the dominant diffusion mechanism for the rings, giving D* ~M-1P"3, this scaling is only observed at low P's. For the highest P's we find D* ~M~3 2P~n, where n increases from approximately 0 at = 10000 to 1.6 at = 180000. In magnitude the data fall above the constraint release prediction and below the measured D*'s for linear PS of the same M. These results indicate two additional diffusion processes for rings: (1) the restricted reptation of that fraction of rings that is unthreaded by linear P-chain constraints, a process recently proposed theoretically by Klein; (2) constrained ring diffusion, in which that fraction of rings threaded once by P-chain constraints diffuses along these linear constraints. Predictions based on these processes are in satisfactory agreement with the experimental data.
In this work, a block copolymer (BCP) consisting of poly((butyl methacrylate‐co‐benzophenone methacrylate‐co‐methyl methacrylate)‐block‐(2‐hydroxyethyl methacrylate)) (P(BMA‐co‐BPMA‐co‐MMA)‐b‐P(HEMA)) is prepared by a two‐step atom‐transfer radical polymerization (ATRP) procedure. BCP membranes are fabricated applying the self‐assembly and nonsolvent induced phase separation (SNIPS) process from a ternary solvent mixture of tetrahydrofuran (THF), 1,4‐dioxane, and dimethylformamide (DMF). The presence of a porous top layer of the integral asymmetric membrane featuring pores of about 30 nm is confirmed via scanning electron microscopy (SEM). UV‐mediated cross‐linking protocols for the nanoporous membrane are adjusted to maintain the open and isoporous top layer. The swelling capability of the noncross‐linked and cross‐linked BCP membranes is investigated in water, water/ethanol mixture (1:1), and pure ethanol using atomic force microscopy, proving a stabilizing effect of the UV cross‐linking on the porous structures. Finally, the influence of the herein described cross‐linking protocols on water‐flux measurements for the obtained membranes is explored. As a result, an increased swelling resistance for all tested solvents is found, leading to an increased water flux compared to the pristine membrane. The herein established UV‐mediated cross‐linking protocol is expected to pave the way to a new generation of porous and stabilized membranes within the fields of separation technologies.
Front Cover: A block copolymer containing UV‐addressable benzophenone moieties within the hydrophobic block is synthesized via atom transfer radical polymerization (ATRP). The block copolymer is utilized in a self‐assembly non‐solvent induced phase separation process to obtain an integral asymmetric membrane, which can be stabilized upon UV‐ irradiation revealing enhanced solvent and pressure resistance. This work is featured in article number 2100632 by Bizan N. Balzer, Markus Gallei, and co‐workers.
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