Polymer membranes are widely used in separation processes including desalination1, organic solvent nanofiltration2,3 and crude oil fractionation4,5. Nevertheless, direct evidence of subnanometre pores and a feasible method of manipulating their size is still challenging because of the molecular fluctuations of poorly defined voids in polymers6. Macrocycles with intrinsic cavities could potentially tackle this challenge. However, unfunctionalized macrocycles with indistinguishable reactivities tend towards disordered packing in films hundreds of nanometres thick7–9, hindering cavity interconnection and formation of through-pores. Here, we synthesized selectively functionalized macrocycles with differentiated reactivities that preferentially aligned to create well-defined pores across an ultrathin nanofilm. The ordered structure was enhanced by reducing the nanofilm thickness down to several nanometres. This orientated architecture enabled direct visualization of subnanometre macrocycle pores in the nanofilm surfaces, with the size tailored to ångström precision by varying the macrocycle identity. Aligned macrocycle membranes provided twice the methanol permeance and higher selectivity compared to disordered counterparts. Used in high-value separations, exemplified here by enriching cannabidiol oil, they achieved one order of magnitude faster ethanol transport and threefold higher enrichment than commercial state-of-the-art membranes. This approach offers a feasible strategy for creating subnanometre channels in polymer membranes, and demonstrates their potential for accurate molecular separations.

Synthetic chemists have devoted tremendous effort towards the production of precision synthetic polymers with defined sequences and specific functions. However, the creation of a general technology that enables precise control over monomer sequence, with efficient isolation of the target polymers, is highly challenging. Here, we report a robust strategy for the production of sequence-defined synthetic polymers through a combination of liquid phase synthesis and selective molecular sieving. The polymer is assembled in solution with real time monitoring to ensure couplings go to completion, on a three-armed star-shaped macromolecule to maximise efficiency during the molecular sieving process. This approach is applied to the construction of sequence-defined polyethers, with sidearms at precisely defined locations that can undergo site-selective modification after polymerisation. Using this versatile strategy, we have introduced structural and functional diversity into sequence-defined polyethers, unlocking their potential for real-life applications in nanotechnology, healthcare and information storage.Natural macromolecules, such as nucleic acids and proteins, are heteropolymers with perfectly defined chain length, monomer sequence and chirality. This precise control of the primary sequence provides structural and functional diversity sufficient to generate the molecular complexity required by all living organisms 1,2 . Polymer chemists have employed strategies such as single monomer insertion 3,4 , tandem monomer addition 5 , kinetic control 6 , segregated templating 7,8 , and sequential growth polymerisation 9,10 , to provide polymers with narrowly disperse, but not uniform, chain lengths and approximately controlled sequences. Nevertheless, these sequence-controlled approaches cannot compete with the precision of nature. To prepare truly uniform sequence-defined polymers, iterative synthesis can afford the required nature-like degree of control over the final sequence. In iterative synthesis specific monomers are added one-at-a-time to the end of a growing polymer chain, reaction debris is then separated from the chain extended polymer, and the cycle is repeated using the next monomer in the sequence 11,12 . Solid-phase iterative synthesis 13 is the premiere method for preparation of sequence-defined polymers, mainly because of the simple reaction and purification processes (i.e. filtration and washing), as well as its ease of automation 14 . However, the insoluble solid supports are often expensive, and the purity of the growing polymer is not readily monitored during synthesis 7,12 . Furthermore, the rates of solid-phase coupling reactions are limited by diffusion into the solid support, ultimately leading to a decline in coupling yields and accumulation of deletion errors 15 . Moreover, solid-phase synthesis is generally difficult to scale up, precluding many industrial applications, particularly in materials science 7,10,12 .Consequently, liquid-phase iterative synthetic methods have long been proposed to ove...

Hydrocarbon separation relies on energy-intensive distillation. Membrane technology can offer an energy-efficient alternative but requires selective differentiation of crude oil molecules with rapid liquid transport. We synthesized multiblock oligomer amines, which comprised a central amine segment with two hydrophobic oligomer blocks, and used them to fabricate hydrophobic polyamide nanofilms by interfacial polymerization from self-assembled vesicles. These polyamide nanofilms provide transport of hydrophobic liquids more than 100 times faster than that of conventional hydrophilic counterparts. In the fractionation of light crude oil, manipulation of the film thickness down to ~10 nanometers achieves permeance one order of magnitude higher than that of current state-of-the-art hydrophobic membranes while retaining comparable size- and class-based separation. This high permeance can markedly reduce plant footprint, which expands the potential for using membranes made of ultrathin nanofilms in crude oil fractionation.