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Branched polymers are among the most important polymers, ranging from polyolefins to polysaccharides. Branching plays a key role in the chain dynamics. It is thus very important for application properties such as mechanical and adhesive properties and digestibility. It also plays a key role in viscous properties, and thus in the mechanism of the separation of these polymers in size-exclusion chromatography (SEC). Critically reviewing the literature, particularly on SEC of polyolefins, polyacrylates and starch, we discuss common pitfalls but also highlight some unexplored possibilities to characterize branched polymers. The presence of a few long-chain branches has been shown to lead to a poor separation in SEC, as evidenced by multiple-detection SEC or multidimensional liquid chromatography. The local dispersity can be large in that case, and the accuracy of molecular weight determination achieved by current methods is poor, although hydrodynamic volume distributions offer alternatives. In contrast, highly branched polymers do not suffer from this extensive incomplete separation in terms of molecular weight.FigureRepresentation of (a) a linear polymer chain and various branched polymer structures with (b) longchain branches (amylose-like), (c) short-chain branches (amylopectin-like), (d) both short-chain and long-chain branches (polyacrylate- or polyethylene-like).

SEC separates complex branched polymers by hydrodynamic volume, rather than by molecular weight or branching characteristics. Equations relating the response of different types of detectors are derived including band broadening, by defining a distribution function N′(M,Vh), the number of chains with molecular weight M and hydrodynamic volume Vh. While the true molecular weight distribution of complex polymers cannot be determined by SEC, irrespective of the detector used, the formalism enables multiple detection SEC data to be processed to both analyze the polymer sample and reveal mechanistic information about polymer synthesis. The formalism also shows how the true weight‐ and number‐average molecular weight, $\overline M _{\rm w}$ and $\overline M _{\rm n}$, can be obtained from correct processing of the hydrodynamic volume distributions.

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Commercial bioethanol can be readily converted into ethylene by a dehydration process using solid acids, such as Brønsted acidic H‐ZSM‐5 zeolites, and thus, it is an ideal candidate to replace petroleum and coal for the sustainable production of ethylene. Now, strong Lewis acidic extra‐framework three‐coordinate Al3+ species were introduced into H‐ZSM‐5 zeolites to improve their catalytic activity. Remarkably, Al3+ species working with Brønsted acid sites can accelerate ethanol dehydration at a much lower reaction temperature and shorten the unsteady‐state period within 1–2 h, compared to >9 h for those without Al3+ species, which can significantly enhance the ethanol dehydration efficiency and reduce the cost. The reaction mechanism, studied by solid‐state NMR, shows that strong Lewis acidic EFAl‐Al3+ species can collaborate with Brønsted acid sites and promote ethanol dehydration either directly or indirectly via an aromatics‐based cycle to produce ethylene.

Complete dissolution is needed for the separation, characterization, or homogeneous labeling of whole starch molecules. A method is presented to quantify the extent of starch dissolution in DMSO for the first time; it is validated on a commercial rice starch. It is used directly on starch dispersions containing possible undissolved or co-dissolved species. High-amylose maize starches, known to be digested slowly in vivo, only quantitatively dissolve in the presence of high concentrations of an H-bond disrupter, LiBr, although they form clear dispersions at low LiBr concentrations. Starch quantitatively dissolves from waxy rice flours; non-starch components partially co-dissolve but do not interfere with the dissolution quantification.

No abstract

Branching was detected in polyacrylates synthesised through radical polymerization via solution-state NMR, while inconsistencies have been reported for the determination of the molar mass of hydrophilic polyacrylates using aqueous-phase and organic-phase size-exclusion chromatography. In this work, poly(sodium acrylate)s, PNaAs, of various topologies were separated for the first time using free-solution capillary electrophoresis (CE). Free-solution CE does not separate the PNaAs by their molar mass, similarly to separations by liquid chromatography in the critical conditions, rather by different topologies (linear, star branched, and hyperbranched). The electrophoretic mobility of PNaAs increases as the degree of branching decreases. Separation is shown to be not only by the topology but also by the end groups as expected for a separation in the critical conditions: replacing a relatively bulky nitroxide end group with hydrogen atom yielded a higher electrophoretic mobility. This novel method, capillary electrophoresis in the critical conditions enabled, for the first time, the separation of hydrophilic polyacrylates according to their topology (branching) and their chain ends. This will allow meaningful and accurate characterization of their branched topologies as well as molar masses and progress in for advanced applications such as drug delivery or flocculation.