This work addresses the anatomy of a 2D polymer formation; that is, we identify, localize, and describe the various processes required to obtain such a macromolecule in a singlecrystal-to-single-crystal reaction. It contains aspects of lattice, local and integral strain, and the distribution of strain in the crystal and assembles the various bits and pieces to a full-scale mechanistic picture providing experimental evidence for why the polymerization avoids phase segregation and why the crystals do not shatter as a result. While lattice strain is investigated by Bragg scattering, most of the paper revolves around diffuse scattering and its analysis with the three-dimensional difference pair distribution function (3D-Delta PDF). Local and integral strain and the spatial distribution of all strains, which are fundamental issues in an endeavor to unravel the polymerization mechanism, are deciphered. These investigations use monomer crystals at three different polymerization conversions (0%, 22%, and 44%) to account for eventual mechanistic changes when oligomers start to prevail. The paper provides answers to how strain management is achieved by the crystal leading to an unprecedented level of insight into chemical reactions in crystals. First, it provides a comprehensive molecular-scale picture on how local strain is buffered during polymerization, and second, it gives an understanding of how the reactivity of the growth pairs is preserved despite the strong displacements observed in the average structure. The paper reaches out to chemists and therefore restricts crystallographic nomenclature to a minimum.

2D polymers are a relatively new class of macromolecules. Therefore, it is not astounding that so far research focused on how to provide access to this intriguing class of organic 2D materials, how to prove their existence, and how to assess their structural quality. Studies concerning the formation mechanism are comparatively scarce. We here collect and compare all the mechanistic information available for 2D polymer synthesis by photochemical means and point towards research directions to be followed in order to advance the fundamental understanding and, thus, fast development of this field. Because the two current starting situations for the photochemical synthesis of 2D polymers are layered single crystals and surface-supported monolayers, the prominent analytical tools are X-ray diffraction (XRD), local vibration spectroscopy, e. g. tip enhanced Raman spectroscopy (TERS), and scanning probe microscopy (SPM), e. g. low temperature scanning tunnelling microscopy (LT STM) in ultra-high vacuum (UHV), but also atomic force microscopy (AFM). With their advantages and shortcomings, they will therefore play an important role throughout this mini review.

The article compares two-dimensional (2D) polymers with their congeners, the abundantly available linear polymers (1D) to show that both kinds of macromolecules are in fact polymer molecules. Repeat units and end (or edge) groups fully describe both kinds of structures. Both structures are obtainable as individual entities. Growth mechanisms well known for 1D polymers have now also been either elucidated or postulated for the first few 2D polymers. 2D copolymers are accessible by reacting different monomers in different feed ratios. Molar masses and molar mass distributions are obtainable when analysing 2D polymers in monolayer sheet form. The author therefore concludes that 2D polymers are in fact polymer molecules, very much as their linear 1D counterparts and that both kinds of structures therefore belong in this very subcategory of macromolecules. Dimensionality differences come with significant property differences and may therefore justify dividing the subcategory 'polymer molecules' further into 1D, 2D and - in the near future - 3D polymer molecules. In terms of materials, 2D polymers establish a subclass of organic 2D materials with the unique characteristic of meeting the conditions for polymer molecules.

Covalent long-range ordered (crystalline) sheets called 2D polymers have recently been synthesized by irradiating single crystals of suitably packed monomers. To have such an action proceed successfully, billions of bond formation processes have to be mastered exclusively in two dimensions within 3D crystals. This raises questions as to how to elucidate the mechanism of these unusual polymerizations as well as their entire strain management. The article will show that single crystal X-ray diffraction based on both Bragg and diffuse scattering are powerful techniques to achieve such goal. The very heart of both techniques will be explained and it will be shown what can be safely concluded with their help and what not. Consequently, the reader will understand why some crystals break during polymerization, while others stay intact. This understanding will then be molded into a few guidelines that should help pave the way for future developments of 2D polymers by those interested in joining the effort with this fascinating and emerging class of 2D materials.

The year 2020 marks the 100th anniversary of the first article on polymerization, published by Hermann Staudinger. It is Staudinger who realized that polymers consist of long chains of covalently linked building blocks. Polymers have had a tremendous impact on the society ever since this initial publication. People live in a world that is almost impossible to imagine without synthetic polymers. But what does the future hold for polymer science? In this article, the editors and advisory board of Macromolecular Chemistry and Physics reflect on this question. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Organic 2D materials display valuable properties that are unique from their bulk counterparts, but creating covalent sheets with long-ranging order remains a formidable challenge. Now, reacting complementary monomers right below a surfactant monolayer on water proves to be a powerful method to create organic 2D materials with long-range order.

2D polymer sheets with six positively charged pyrylium groups at each pore edge in a stacked single crystal can be transformed into a 2D polymer with six pyridines per pore by exposure to gaseous ammonia. This reaction furnishes still a crystalline material with tunable protonation degree at regular nano-sized pores promising as separation membrane. The exfoliation is compared for both 2D polymers with the latter being superior. Its liquid phase exfoliation yields nanosheet dispersions, which can be size-selected using centrifugation cascades. Monolayer contents of ≈30 % are achieved with ≈130 nm sized sheets in mg quantities, corresponding to tens of trillions of monolayers. Quantification of nanosheet sizes, layer number and mass shows that this exfoliation is comparable to graphite. Thus, we expect that recent advances in exfoliation of graphite or inorganic crystals (e.g. scale-up, printing etc.) can be directly applied to this 2D polymer as well as to covalent organic frameworks.

We present a comprehensive investigation of main-chain scission processes affecting peripherally charged and neutral members of a class of dendronized polymers (DPs) studied in our laboratory. In these thick, sterically highly congested macromolecules, scission occurs by exposure to solvents, in some cases at room temperature, in others requiring modest heating. Our investigations rely on gel permeation chromatography and atomic force microscopy and are supported by molecular dynamics simulations as well as by electron paramagnetic resonance spectroscopy. Strikingly, DP main-chain scission depends strongly on two factors: first the solvent, which must be highly polar to induce scission of the DPs, and second the dendritic generation g. In DPs of generations 1 = g = 8, scission occurs readily only for g = 5, no matter whether the polymer is charged or neutral. Much more forcing conditions are required to induce degradation in DPs of g ≠ 5. We propose solvent swelling as the cause for the main-chain scission in these individual polymer molecules, explaining in particular the strong dependence on g: g < 5 DPs resemble classical polymers and are accessible to the strongly interacting, polar solvents, whereas g > 5 DPs are essentially closed off to solvent due to their more closely colloidal character. g = 5 DPs mark the transition between these two regimes, bearing strongly sterically congested side chains which are still solvent accessible to some degree. Our results suggest that, even in the absence of structural elements which favour scission such as cross-links, solvent swelling may be a generally applicable mechanochemical trigger. This may be relevant not only for DPs, but also for other types of sterically strongly congested macromolecules.

A new, alternative route for the synthesis of a variety of a-aminoacyl amides via the four-component Ugi reaction in the presence of different types of surfactants was investigated. The best results were obtained if the reaction was carried out in the presence of either didodecyldimethylammonium bromide (DDAB) vesicles or Triton X-100 micelles. The presence of vesicles or micelles in these systems was confirmed by applying dynamic light scattering (DLS) and fluorescence measurements. Additionally, detailed studies of the dependence on the concentration of the two surfactants and on their reusability were performed. The obtained results demonstrate the beneficial effect aqueous surfactant systems may have on the course of the Ugi-multicomponent reaction.

We report about the first Raman spectroscopy study of a vesicle-assisted enzyme-catalyzed oligomerization reaction. The aniline dimer N-phenyl-1,4-phenylenediamine (= p-aminodiphenylamine, PADPA) was oxidized and oligomerized with Trametes versicolor laccase and dissolved O2 in the presence of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) vesicles (80-100 nm diameter) as templates. The conversion of PADPA into oligomeric products, poly(PADPA), was monitored during the reaction by in situ Raman spectroscopy. The results obtained are compared with UV/vis/NIR and EPR measurements. All three complementary methods indicate that at least some of the poly(PADPA) products, formed in the presence of AOT vesicles, resemble the conductive emeraldine salt form of polyaniline (PANI-ES). The Raman measurements also show that structural units different from those of "ordinary" PANI-ES are present too. Without vesicles PANI-ES-like products are not obtained. For the first time, the as-prepared stable poly(PADPA)-AOT vesicle suspension was used directly to coat electrodes (without product isolation) for investigating redox activities of poly(PADPA) by cyclic voltammetry (CV). CV showed that poly(PADPA) produced with vesicles is redox active not only at pH 1.1-as expected for PANI-ES-but also at pH 6.0, unlike PANI-ES and poly(PADPA) synthesized without vesicles. This extended pH range of the redox activity of poly(PADPA) is important for applications.

Two series of dendronized polymers (DPs) of generations g = 1–4 with different levels of dendritic substitution (low and high) and a solvatochromic probe at g = 1 level are used to study their swelling behavior in a collection of solvents largely differing in polarity as indicated by the Kamlet–Taft parameters. This is done by measuring the UV-Vis spectra of all samples in all solvents and determining the longest wavelength absorptions (λmax). The λmax values fall into a range defined by the extreme situations, when the solvatochromic probe is either fully surrounded by solvent or completely shielded against it. The former situation is achieved in a model compound and the latter situation is believed to be reached when in a poor solvent the dendritic shell around the backbone is fully collapsed. We observe that solvent penetration into the interior of the DPs decreases with increasing g and does so faster for the more highly dendritically substituted series than for the less highly substituted one. Interestingly, the swelling of the more highly substituted DP series already at the g = 4 level has decreased to approximately 20% of that at the g = 1 level which supports an earlier proposal that high g DPs can be viewed as nano-sized molecular objects. Furthermore, when comparing these two DP series with a g = 1–6 series of dendrimers investigated by Fréchet et al. it becomes evident that even the less substituted series of DPs is much less responsive to solvent changes as assessed by the solvatochromic probe than the dendrimers, suggesting the branches around the (polymeric) core in DPs to be more densely packed compared to those in dendrimers, thus, establishing a key difference between these two dendritic macromolecules.

In diesem Leitprogramm verschaffen sich die Schülerinnen und Schüler selbständig durch Experimente und Theoriearbeit einen Überblick über die vielfältigen Eigenschaften des Alkohols Ethanol.