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Topic Review
From Tiny Seeds to Better Polymers
What if the key to better polymers lies in particles thousands of times smaller than a hair? We share how we designed tiny, uniform seeds that bring precision to emulsion polymerization.
  • 63
  • 29 Dec 2025
Topic Review
Turning Polybutadiene into Shape Memory Polymers
A semi-crystalline, shape memory polymer (SMP) is fabricated by free radical cross-linking, polymerization, and grafting in a blend of n-octadecyl acrylate and polybutadiene (PB). Poly(n-octadecyl acrylate) (PODA) is a side-chain crystalline polymer, which serves as the structure-fixing network counterbalancing the elastically deformed, cross-linked polymer network. At a constant 50/50 ratio of monomer and polymer the amount of free radical initiator, dicumyl peroxide (DCP) is varied from 1% to 5% w/w PB. From swelling measurements and calculation of the cross-link density it is determined that DCP produces greater than one cross-link per DCP molecule. It is found that lower cross-linking efficiency is favorable for higher shape fixity. This lower efficiency is found to produce a higher degree of crystallinity of the PODA in the 2–5% DCP samples, which is determined to be the main driver of higher shape fixity of the polymer. A SMP with >90% fixity and 100% recovery at uniaxial strains from 34–79% is achieved. This material should be useful for mold processing of shape memory articles. This approach provides a method to decouple the elastomeric and thermoplastic portions of a SMP to convert commodity elastomers into SMPs and tailor the shape memory response.
  • 54
  • 31 Dec 2025
Topic Review
Can Polymeric Surfactants Do More Than Lower Tension?
Polymeric surfactants are amphiphilic macromolecules that combine hydrophilic and hydrophobic segments within a single polymer chain. Their molecular architecture gives them interfacial activity while also enabling properties such as self-assembly, viscosity modification, steric stabilization, and controlled adsorption. Compared with conventional low-molecular-weight surfactants, polymeric surfactants can form more persistent interfacial layers because multiple segments of a polymer chain can interact simultaneously with an interface. Their properties depend strongly on molecular weight, polymer architecture, hydrophobic-group content and distribution, charge density, concentration, and solution conditions such as ionic strength, pH, and temperature. These features make polymeric surfactants useful in emulsification, dispersion, coatings, drug delivery, enhanced oil recovery, and other interfacial applications.
  • 48
  • 24 Aug 2026
Topic Review
Chitin Solvents
Chitin solvents are liquid media that break the dense hydrogen-bonded network of chitin and bring this otherwise intractable biopolymer into molecularly dispersed or colloidal solution. Chitin is a linear polymer of N-acetyl-D-glucosamine units joined by β-1,4-glycosidic bonds; it is the second most abundant biopolymer on Earth and the main organic constituent of crustacean shells, insect cuticles and fungal cell walls. It does not melt and is insoluble in water, dilute acids and bases, alcohols and almost all common organic solvents, so its shaping and chemical transformation generally require dissolution. Because the acetamido group at C2 is both a hydrogen-bond donor and an acceptor, chitin is markedly harder to dissolve than cellulose. Two strategies are used: derivatizing media, which convert the polymer temporarily into a soluble ester or ether that is cleaved on regeneration, and non-derivatizing media, which dissolve unmodified chitin directly—aqueous mineral acids, concentrated salt solutions and salt hydrates, alkali/urea mixtures, lithium chloride in N,N-dimethylacetamide, calcium chloride dihydrate in methanol, ionic liquids, deep eutectic solvents, and protic solvents such as hexafluoroisopropanol. Chitin solvents underpin regenerated chitin fibres, films, hydrogels, aerogels and nanofibres, and they enable homogeneous chemical modification, controlled deacetylation, molar-mass characterization and the valorization of seafood shell waste.
  • 48
  • 19 Oct 2026
Topic Review
Atom-Transfer Radical Polymerization
Atom-transfer radical polymerization (ATRP) is a reversible-deactivation radical polymerization in which an alkyl halide chain end and a redox-active catalyst establish a rapid equilibrium between dormant and propagating states. Activation transfers the halogen atom from the dormant polymer chain to a lower-oxidation-state metal complex, generating a carbon-centered radical and a higher-oxidation-state metal halide; deactivation reverses this step [1]. Because the equilibrium strongly favors dormant chains, the steady-state radical concentration is low, irreversible termination is suppressed, and most chains undergo comparable numbers of propagation events. The retained carbon–halogen terminus permits chain extension and block formation. Copper complexes are the most common catalysts, although other metals and photochemical or electrochemical modes can control the same activation–deactivation principle [2]. ATRP differs from RAFT and iodine-transfer polymerization because its reversible deactivation is mediated by catalyst-controlled halogen-atom transfer rather than degenerative transfer through thiocarbonylthio or iodide reagents.
  • 36
  • 19 Oct 2026
Topic Review
Iodine Transfer Polymerization
A reversible-deactivation radical polymerization in which an iodo chain end mediates degenerative transfer is iodine transfer polymerization (ITP). A propagating radical exchanges iodine with a dormant alkyl iodide (the transfer agent or a polymer–iodide), so that most chains rest as alkyl iodides and only a small fraction are active radicals at any instant. Molecular weight is set by the monomer-to-iodide ratio, and the iodine terminus remains available for block extension. ITP of ethylene and its copolymerization with vinyl acetate demonstrate that the same degenerative iodine transfer operates for unactivated and activated alkenes [1]. Chlorotrifluoroethylene-based block copolymers are likewise prepared by ITP, exploiting the stability of fluoroalkyl iodides as dormant species [2]. Reverse iodine transfer polymerization (RITP) generates the alkyl iodide in situ from molecular iodine and a conventional radical initiator, then proceeds by the same transfer equilibrium; emulsifier-free acrylate emulsions have been prepared on that basis [3]. ITP is distinct from ATRP, which requires a redox-active metal for atom transfer, and from RAFT, which uses a thiocarbonylthio rather than an iodide transfer agent.
  • 31
  • 19 Oct 2026
Topic Review
Cationic Polymerization
Chain-growth polymerization initiated and propagated by a positively charged active center is cationic polymerization. The chain carrier is a carbocation, an oxonium ion, or a related electrophilic species, and the monomers are electron-rich alkenes (vinyl ethers, N-vinylcarbazole, styrenes with donor substituents) or heterocycles that open to cationic ends. Living cationic polymerization is realized when reversible deactivation or a dormant–active equilibrium suppresses transfer and termination, allowing molecular-weight control and block-copolymer synthesis [1]. Visible-light control of vinyl-ether cationic polymerization modulates the concentration of the ionic chain end without changing the cationic nature of propagation [2]. Catalyst-controlled stereoselective cationic polymerization of vinyl ethers shows that the same electrophilic mechanism can encode tacticity when the counterion and Lewis acid are suitably paired [3]. The concept is the charge-inverted counterpart of anionic polymerization and is distinct from radical polymerization and from coordination insertion at a neutral metal alkyl. Photoinitiated and photocontrolled cationic processes remain cationic polymerizations so long as the propagating species is positively charged.
  • 28
  • 19 Oct 2026
Topic Review
Solvent Casting
Solvent Casting is a film-preparation method in which a polymer is dissolved, the solution is spread on a support, and the solvent is removed to leave a solid film [1]. A europium-substituted polyoxotungstate cast from solvent forms a film whose photophysical properties differ from those of its Langmuir-Blodgett counterpart [1]. Chitosan-filled polylactic acid films prepared by casting behave differently from melt-blended ones in mechanical and structural terms [2]. Piezoelectric poly(vinylidene fluoride)/hydroxyapatite/silver nitrate films are cast into thin biocompatible sheets [3]. Layer casting combined with freeze-drying and lamination produces porous gelatin/hydroxyapatite scaffolds with controlled porosity [4]. Compared with Pickering emulsion processing, casting gives a different balance of mechanical properties in surface-modified cellulose nanomaterial-reinforced polylactic acid composites [5].
  • 28
  • 06 Nov 2026
Biography
Martin Kröger
Research areas: Computational Physics and Biophysics, Algorithms, Applied Mathematics, Statistical Physics, Theoretical Physics, Physical Chemistry, Epidemology, Gradient Elasticity, Polymers, Networks, Ferrofluids.  Relevant references see ‪‬google scholar.  Member of the Editorial Boards of Polymers, Frontiers in Physics, Covid, preprints.org, Open Physics.  Born March 21, 1965 in Rh
  • 27
  • 11 Jun 2026
Topic Review
Biobased Polymers
Biobased polymers are polymers whose carbon skeleton derives, wholly or partly, from a renewable feedstock rather than from petroleum. The feedstock can be a sugar, a vegetable oil, a terpene, or a lignin fragment, and the monomer is obtained by fermentation or by chemical conversion [1]. Being biobased says nothing about biodegradability, because a bio-derived polyethylene is chemically identical to the fossil one and does not degrade faster [2]. The properties of the resulting polymer follow from the repeat unit, so a rigid ring in the backbone raises the glass transition while a long aliphatic chain lowers it [3]. The cost of the monomer, not the polymerisation, is what keeps several biobased grades out of the market [4]. The end-of-life route has to be specified at the design stage, because a biobased but non-degradable polymer still needs a waste stream that can handle it [5].
  • 25
  • 23 Oct 2026
Topic Review
Free Radical Suspension Polymerization
Free-radical suspension polymerization is a heterogeneous process in which droplets of a monomer-rich phase are dispersed in a continuous liquid phase, usually water, and polymerize by a free-radical chain mechanism. A monomer-soluble initiator generates radicals inside the droplets, so each stabilized droplet behaves approximately as a small bulk-polymerization reactor [1]. Protective colloids or particulate stabilizers limit droplet coalescence, while agitation and interfacial stabilization determine the droplet and final bead size distributions. Within each droplet, initiation, propagation, chain transfer, and bimolecular termination follow the usual free-radical mechanism. The product is generally obtained as polymer beads after separation from the continuous phase. Suspension polymerization differs from emulsion polymerization because initiation and principal growth occur in monomer droplets rather than in surfactant micelles or nucleated latex particles; recent reviews of aqueous dispersed radical polymerization maintain this distinction [2].
  • 23
  • 19 Oct 2026
Topic Review
Polyamide Synthesis
Polyamide synthesis constructs macromolecules in which amide groups, –C(=O)–NH–, are recurring main-chain linkages. Two principal routes define the class: step-growth polycondensation of diamines with dicarboxylic acids or activated derivatives, and ring-opening polymerization of lactams [1][2]. AA/BB monomer pairs require near-equimolar functional groups and high conversion to reach high molar mass, whereas AB amino acids contain both functions in one monomer. Lactam polymerization is a chain process initiated by water, acids, bases, or activated lactam species; anionic ring-opening is especially important for nylon formation [2]. Aliphatic nylons and aromatic aramids both satisfy the definition because the amide linkage belongs to the backbone, although their monomer structures and polymerization conditions differ. Polyamide synthesis is distinguished from peptide synthesis by its synthetic-polymer context and from polyester, polyurethane, and polyimide synthesis by the identity of the repeat linkage. Polymers bearing only pendant amides are not polyamides under this constitutional definition.
  • 21
  • 19 Oct 2026
Topic Review
Cotton Fabric
Cotton fabric is a woven or knitted textile built from twisted cellulose fibres, and it remains the most widely used apparel substrate. Its properties come from the fibre structure: the lumen and the convolutions give moisture uptake and a soft hand, while the crystalline cellulose provides strength [1]. The natural waxes and pectins on the raw fibre must be removed by scouring and bleaching before dyeing, and the finishing sequence determines the final whiteness and absorbency [2]. Functional finishing adds flame retardancy, antimicrobial behaviour, or water repellency, usually at the cost of tensile strength because the treatment also attacks the cellulose chain [3]. Grafting monomers onto the fibre surface is an alternative that leaves the bulk structure largely intact [4]. Durability of the finish to repeated laundering, rather than the initial performance, is the property that most often fails [5].
  • 21
  • 20 Oct 2026
Topic Review
Emulsion Styrene Butadiene Rubber
Can emulsion SBR evolve to meet the demands of next generation rubber applications? Explore how molecular architecture, polymer filler interactions, and sustainable feedstocks could unlock new possibilities for this established material.
  • 20
  • 30 Oct 2026
Topic Review
Cellulose-Lignin Interactions
Cellulose-lignin interactions denote the physical and chemical associations between cellulose microfibrils and the polyphenolic lignin polymer within the plant cell wall matrix, predominantly in secondary cell walls where both biopolymers are abundantly co-deposited [1]. These interactions encompass two principal categories: covalent linkages and non-covalent associations. Covalent bonds between lignin and cellulose occur through lignin–carbohydrate complexes (LCCs), wherein lignin units form direct chemical bonds with cellulose or, more commonly, with intervening hemicellulose molecules that bridge the two polymers [1]. The covalent linkages include benzyl ether and benzyl ester bonds formed during lignin polymerization, in which reactive lignin intermediates couple with carbohydrate hydroxyl groups [2]. Non-covalent interactions comprise hydrogen bonding between lignin phenolic and aliphatic hydroxyl groups and cellulose surface hydroxyls, hydrophobic associations driven by the aromatic nature of lignin and the relatively hydrophobic cellulose (100) crystal face, van der Waals forces, and physical entanglement of lignin chains within the polysaccharide network [3]. The heterogeneity of lignin—arising from its non-enzymatic, free-radical polymerization of monolignols—confers considerable variability in the nature and strength of cellulose-lignin contacts, with binding affinity modulated by lignin methoxylation patterns, oligomeric size, and aromatic ring orientation [3]. Unlike lignin–hemicellulose interactions, which are extensively characterized as discrete LCC fractions, direct cellulose-lignin contacts were historically presumed to be predominantly physical; however, contemporary molecular evidence confirms that covalent cellulose-lignin linkages also contribute to the structural integrity of the cell wall matrix [2]. The most prevalent covalent linkage is the benzyl ether bond, formed between the benzylic carbon of a lignin unit and a hydroxyl group on the carbohydrate chain. Benzyl ester linkages also occur, typically involving the carboxyl groups of glucuronic acid residues in hemicelluloses. These covalent bonds provide a robust chemical tether that anchors the lignin polymer to the cellulose-hemicellulose network, preventing the dissociation of the matrix components under physiological conditions. [1].
  • 19
  • 22 Sep 2026
Topic Review
Addition Polymerization
Addition polymerization is a polymer-forming process in which monomer molecules combine without the stoichiometric elimination of a small molecule. In its principal chain-growth form, an active radical, ionic, or coordination site adds successively to unsaturated monomers, transferring the active center to the newly incorporated repeat unit. The category also includes addition to heteroatom-containing multiple bonds, as demonstrated by polymerization across a phosphaalkene P=C bond [1]. Conjugate-addition polymerizations are mechanistically distinct polyaddition processes in which multifunctional nucleophiles and activated alkenes form successive bonds without a condensate [2]. N-heterocyclic-carbene-catalyzed conjugate-addition polymerization illustrates a chain process with identifiable initiation, propagation, and termination steps [3]. The absence of an eliminated byproduct distinguishes addition polymerization from condensation polymerization, whereas the manner in which molecular mass develops distinguishes chain-growth addition from step-growth polyaddition.
  • 19
  • 19 Oct 2026
Topic Review
Solution Polymerization
Solution polymerization is a polymerization process whose initial reaction mixture contains monomer dissolved in a molecular solvent together with an initiator or catalyst as required. In the strict homogeneous case, both monomer and growing polymer remain soluble under the reaction conditions, so propagation occurs throughout a single liquid phase [1]. The solvent dilutes the reacting species, moderates viscosity, and transfers heat, but it can also alter catalyst speciation, propagation kinetics, and molar mass through chain transfer; solvent-derived chain transfer is a defining kinetic consideration in radical solution polymerization [2]. If the forming polymer becomes insoluble and precipitates, the process is classified as precipitation polymerization rather than homogeneous solution polymerization. The method is also distinct from suspension and emulsion polymerization, where monomer-rich droplets or particles are dispersed in a continuous phase. Removal or retention of solvent after conversion does not define the polymerization; classification depends on the physical state and composition of the reaction medium during chain growth.
  • 19
  • 19 Oct 2026
Topic Review
Glycidyl Methacrylate
Glycidyl Methacrylate is a methacrylate monomer carrying a pendant epoxide ring, which makes it a handle for both radical polymerisation and post-polymerisation epoxy chemistry [1]. Grafted from cellulose by RAFT-mediated polymerisation, it installs epoxy groups on the polysaccharide backbone [1]. Grafting poly(glycidyl methacrylate) onto alumina particles and crosslinking the chains raises the thermal conductivity of the resulting epoxy composite [2]. Combining atom transfer radical polymerisation with anionic ring-opening polymerisation converts the epoxide into a polyether block, giving poly(glycidyl methacrylate)-g-dimethylsiloxane [3]. Melt grafting onto polypropylene is moderated by tea polyphenols, which limit radical side reactions [4]. Statistical, gradient and block copolymers with alkyl methacrylates have been prepared by nitroxide-mediated polymerisation, fixing the epoxide content per chain [5].
  • 18
  • 06 Nov 2026
Topic Review
Anionic Polymerization
Nucleophilic initiation of a chain-growth process in which the propagating species is an anion defines anionic polymerization. Typical initiators are organolithium reagents, alkali metal aromatic radical anions, or alkoxides; the monomer is an electron-deficient alkene, a strained heterocycle, or a related unsaturated electrophile. In the living limit, termination and transfer are absent, so the number-average molecular weight is set by the monomer-to-initiator ratio and the chain end remains available for further monomer addition or end-capping [1]. Ring-opening anionic polymerization of β-lactam sugar monomers produces poly-amido-saccharides, showing that the same ionic mechanism applies to cyclic amides [2]. Living anionic polymerization of phosphaalkenes likewise affords homopolymers and block copolymers with controlled chain length from a P=C monomer [3]. Architectural complexity—stars, combs, and cyclic polymers—arises from multifunctional initiation or from coupling of living carbanionic ends [1]. The concept is distinct from cationic polymerization (positively charged active centers) and from radical polymerization (neutral odd-electron chain ends).
  • 18
  • 19 Oct 2026
Topic Review
Polyurethane Foam
Polyurethane foam is a cellular polymer formed by the reaction of a polyol with an isocyanate in which a blowing agent, whether produced by the reaction itself or added separately, expands the reacting mixture into a gas-filled structure. The properties follow from the cell size and from whether the cells are open or closed: closed-cell rigid foam carries load and insulates, while open-cell flexible foam recovers from compression. Both burn readily, and a large part of the literature concerns flame retardancy; a phosphorus-nitrogen intumescent system in rigid foam forms a char that shields the underlying polymer [1], and modifying the intumescent formulation changes how effective that char is [2]. Understanding how the intumescent layer works during a fire is what allows the formulation to be chosen rationally [3]. Building the flame-retardant moiety into the polymer backbone rather than adding it as a filler avoids the loss of mechanical properties that a high filler loading causes [4]. Surface coatings offer a way to keep the bulk formulation unchanged [5].
  • 17
  • 19 Oct 2026
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