Here, the development of an adhesive is reported – generated via free radical polymerization – which can be degraded upon thermal impact within minutes. The degradation is based on a stimuli responsive moiety (SRM) that is incorporated into the network. The selected SRM is a hetero Diels-Alder (HDA) moiety that features three key properties. First, the adhesive can be degraded at relatively low temperatures (≈80 °C), second the degradation occurs very rapidly (less than 3 min), and third, the degradation of the network can readily be analyzed and quantified due to its self-reporting nature. The new reversible self-reporting adhesion system is characterized in detail starting from molecular studies of the retro HDA reaction. Moreover, the mechanical properties of the network, as well as the adhesion forces, are investigated in detail and compared to common methacrylate-based systems, demonstrating a significant decrease in mechanic stability at elevated temperatures. The current study thus represents a significant advance of the current state of the art for debonding on demand adhesives, making the system interesting for several fields of application including dental adhesives.

3D mesostructures with a height of up to 1 mm and micrometer feature size are fabricated employing a writing speed of 1 cm s⁻¹ via direct laser writing utilizing a novel functional photoresist based on the radical coupling reaction of thiols and alkynes. The refractive index of the resist—consisting of a tetrafunctional thiol, a tetrafunctional alkyne and a photoinitiator—is tailored to be compatible with the employed high numerical aperture (NA) objective lens, thus enabling a Dip-in configuration. Mesostructures are characterized by scanning electron microscopy, optical photography, and nondestructive 3D time-of-flight secondary ion mass spectrometry. Woodpile photonic crystals are fabricated as benchmark structures in order to investigate the axial resolution. Verification of the chemical fabrication mechanism is achieved via transmission Fourier transform infrared (FTIR) spectroscopy of fabricated cuboid structures by monitoring the decrease of corresponding thiol and alkyne absorption peaks. Postmodification reactions, namely the thiol-Michael addition and the copper-catalyzed azide alkyne cycloaddition, are conducted employing residual thiols and alkynes throughout the cuboid structures. Successful dual and orthogonal modification throughout the structure and on the surface is achieved and verified utilizing transmission FTIR spectroscopy and time-of-flight secondary ion mass spectrometry.

Polymeric materials as building blocks represent the most important membrane materials as they are relatively simple to synthesize and flexible regarding manufacturing conditions. In this contribution, the synthesis of amphiphilic diblock terpolymers and their use for the preparation of integral asymmetric membranes via nonsolvent induced phase separation (NIPS) processes is presented. The diblock terpolymers consist of a hydrophobic poly(styrene-co-isoprene) block and a hydrophilic segment of poly(N,N-dimethylaminoethyl methacrylate). The materials are synthesized either via nitroxide mediated polymerization or living anionic polymerization. The NIPS process is used for the fabrication of porous diblock terpolymer membranes where the membrane morphology can be influenced by several parameters such as the applied solvent mixture, open time, or relative humidity. The resulting anisotropic membranes are characterized by scanning electron microscopy and water flux measurements. Furthermore, the UV-induced crosslinking of the isoprene part of the membrane matrix is demonstrated.

A photochemical approach based on nitrile imine-mediated tetrazole-ene cycloaddition is introduced to functionalize gold nanorods with biomolecules. For this purpose, a bifunctional, photoreactive linker containing thioctic acid as the Au anchoring group and a tetrazole moiety for the light-induced reaction with maleimide-capped DNA was prepared. The tetrazole-based reaction on the nanoparticles’ surface results in a fluorescent pyrazoline product allowing for the spectroscopic monitoring of the reaction. This first example of nitrile imine-mediated tetrazole-ene cycloaddition (NITEC)-mediated biofunctionalization of Au nanorods paves the way for the attachment of sensitive biomolecules, such as antibodies and other proteins, under mild conditions and expands the toolbox for the tailoring of nanomaterials.

A disulfide intercalator toolbox was developed for site-specific attachment of a broad variety of functional groups to proteins or peptides under mild, physiological conditions. The peptide hormone somatostatin (SST) served as model compound for intercalation into the available disulfide functionalization schemes starting from the intercalator or the reactive SST precursor before or after bioconjugation. A tetrazole–SST derivative was obtained that undergoes photoinduced cycloaddition in mammalian cells, which was monitored by live-cell imaging.

Eine photochemische Strategie nutzt λ-orthogonale Reaktionen zum Aufbau makromolekularer Architekturen und zum wellenlängenabhängigen Einbau chemischer Funktionalitäten in ein einzelnes Molekül. λ-Orthogonale pericyclische Reaktionen können unabhängig voneinander durch die spezifische photochemische Aktivierung einer chemischen Funktionalität ablaufen. Die Leistungsfähigkeit dieses neuen Konzeptes wird durch eine Eintopfreaktion belegt, bei der Maleinsäureimid mit zwei Polymeren, die unterschiedliche photoaktive Endgruppen (Photoenol und Tetrazol) tragen, selektiv reagieren. Beliebige aktivierte Doppelbindungen können durch eine gezielte Bestrahlung mit λ=310–350 nm mit einem Photoenol-funktionalisierten Polymer reagieren. Nach vollständigem Photoenolumsatz aktiviert eine Bestrahlung mit λ=270–310 nm die Reaktion des Tetrazols mit Maleimid. Die Vielseitigkeit dieses Ansatzes wird durch die λ-orthogonale Klick-Reaktionen von komplexen Maleimiden, funktionalen Enen und Polymeren an ein zentrales Polymergerüst gezeigt.

Das effiziente Abfangen photogenerierter Thioaldehyde durch funktionelle stabile Nitriloxide in einer 1,3-dipolaren Cycloaddition ist eine neue und vielseitige photochemische Strategie zur Funktionalisierung von Polymeren und zur Oberflächenmodifikation unter milden und äquimolaren Bedingungen. Die modulare Ligation in Lösung wird im Detail durch ESI-MS verfolgt. XPS wird zur Analyse der funktionalisierten Oberflächen verwendet, während ToF-SIMS die durch Anwendung einer Schattenmaske erreichte räumliche Kontrolle der Oberflächenfunktionalisierung belegt. Polymerbürsten wurden in einem räumlich begrenzten Bereich durch SI-ATRP von der Oberfläche aus wachsen gelassen, was mithilfe von ToF-SIMS, XPS sowie Ellipsometrie belegt wird.

A photochemical strategy enabling λ-orthogonal reactions is introduced to construct macromolecular architectures and to encode variable functional groups with site-selective precision into a single molecule by the choice of wavelength. λ-Orthogonal pericyclic reactions proceed independently of one another by the selection of functional groups that absorb light of specific wavelengths. The power of the new concept is shown by a one-pot reaction of equimolar quantities of maleimide with two polymers carrying different maleimide-reactive endgroups, that is, a photoactive diene (photoenol) and a nitrile imine (tetrazole). Under selective irradiation at λ=310–350 nm, any maleimide (or activated ene) end-capped compound reacts exclusively with the photoenol functional polymer. After complete conversion of the photoenol, subsequent irradiation at λ=270–310 nm activates the reaction of the tetrazole group with functional enes. The versatility of the approach is shown by λ-orthogonal click reactions of complex maleimides, functional enes, and polymers to the central polymer scaffold.

The efficient trapping of photogenerated thioaldehydes with functional shelf-stable nitrile oxides in a 1,3-dipolar cycloaddition is a novel and versatile photochemical strategy for polymer end-group functionalization and surface modification under mild and equimolar conditions. The modular ligation in solution was followed in detail by electrospray ionization mass spectrometry (ESI-MS). X-ray photoelectron spectroscopy (XPS) was employed to analyze the functionalized surfaces, whereas time-of-flight secondary-ion mass spectrometry (ToF-SIMS) confirmed the spatial control of the surface functionalization using a micropatterned shadow mask. Polymer brushes were grown from the surface in a spatially confined regime by surface-initiated atom transfer radical polymerization (SI-ATRP) as confirmed by TOF-SIMS, XPS as well as ellipsometry.

Dynamic bonding materials are of high interest in a variety of fields in material science. The reversible nature of certain reaction classes is frequently employed for introducing key material properties such as the capability to self-heal. In addition to the synthetic effort required for designing such materials, their analysis is a highly complex—yet important—endeavor. Herein, we critically review the current state of the art analytical methods and their application in the context of reversible bonding on demand soft matter material characterization for an in-depth performance assessment. The main analytical focus lies on the characterization at the molecular level.

The synthesis and application of a novel reversible addition-fragmentation chain transfer (RAFT) agent carrying a photocaged thioaldehyde moiety is described (λ_max = 355 nm). RAFT polymerization of styrene, dimethylacrylamide and a glycomonomer is evidenced (3600 g mol⁻¹ ≤ M_n ≤ 15 000 g mol⁻¹; 1.07 ≤ Đ ≤ 1.20) with excellent end-group fidelity. The photogenerated thioaldehyde on the chain ends can undergo hetero Diels–Alder reactions with dienes as well as reactions with nucleophiles. The terminal photoreactive polymers are photografted to porous diene-reactive polymeric microspheres. The grafted particles are in-depth characterized via scanning electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, and high resolution FT-IR microscopy, leading to a qualitative as well as quantitative image of the core–shell objects. Grafting densities up to 0.10 molecules nm⁻² are reached. The versatility of the thioaldehyde ligation is evidenced by spatially resolved grafting of polystyrene onto nucleophilic groups present in poly (dopamine) (PDA)-coated glass slides and silicon wafers via two-photon direct laser writing (DLW) imaged by ToF-SIMS. The combination of thioaldehyde ligation, RAFT polymerization, and DLW allows for the spatially resolved grafting of a vast range of polymers onto various substrates in any desired pattern with sub-micrometer resolution.

Three-dimensional microstructures are fabricated utilizing direct laser writing combined with a non-radical step polymerization based on multiphoton-induced Diels–Alder chemistry of o-quinodimethanes and maleimides. Woodpile photonic crystals with a total of five axial periods and a rod spacing of down to 500 nm are fabricated. The structures are characterized via scanning electron microscopy and focused ion beam milling. In addition, corresponding photonic stop bands are investigated via light microscopy as well as transmission and reflection spectroscopy. The Diels–Alder based network formation during direct laser writing is verified via infrared spectroscopy. Spatially resolved surface patterning of covalently bonded functional molecules on fabricated structures is demonstrated by employing the direct laser writing setup and a bromine containing maleimide. The successful surface modification is verified via time-of-flight secondary ion mass spectrometry.

The preparation of patterned photoswitchable surfaces by employing the nitrile imine-mediated tetrazole ene cycloaddition (NITEC) photoinduced reaction in the presence of dipolarophiles based on photoresponsive azobenzene moieties is reported. The dipolarophile used is a maleimide carrying either an azobenzene unit or a first generation dendron containing two azobenzene units. X-ray photoelectron spectroscopy (XPS) is employed to analyze the functionalized silicon wafers, while time-of-flight secondary ion mass spectrometry (ToF-SIMS) evidences the spatial control of the functionalization of the surface achieved by using a micropatterned shadow mask. Water contact angle measurements and optical inspection observing the behavior of a water droplet demonstrate the photoinduced change on wettability of the structured functionalized surfaces due to the reversible trans-to-cis isomerization of the azobenzene moities.

Three-dimensional microstructures are fabricated employing the direct laser writing process and radical thiol-ene polymerization. The resin system consists of a two-photon photoinitiator and multifunctional thiols and olefins. Woodpile photonic crystals with 22 layers and a rod distance of 2 μm are fabricated. The structures are characterized via scanning electron microscopy and focused ion beam milling. The thiol-ene polymerization during fabrication is verified via infrared spectroscopy. The structures are grafted in a subsequent thiol-Michael addition reaction with different functional maleimides. The success of the grafting reaction is evaluated via laser scanning microscopy and X-ray photoelectron spectroscopy. The grafting density is calculated to be close to 200 molecules μm⁻².

The transfer reactions occurring during polymerization of 2-(phenylcarbamoyloxy)ethyl acrylate (PhCEA) were studied by a detailed product mapping with electrospray ionization mass spectrometry (ESI-MS). Unlike postulated before, PhCEA exhibits the same characteristic transfer reactions as other acrylic monomers at elevated temperatures, resulting in vinyl-terminated and saturated products. Transfer to monomer via abstraction of a hydrogen atom from the ester side chain as suggested before is not observed. When polymerized in a poly(ethylene glycol) (PEG) matrix to increase viscosity, transfer into matrix products are observed in minor amounts, demonstrating that PEG can be employed as a solvent to further increase the overall rate of polymerization without interference from side reactions.

The design and synthesis of a new hydrophobic monomer, that is, 4-(tert-butyl)phenyl 6-acrylamidohexanoate (TBP-AA-HO) and its ability to form supramolecular host/guest complexes with β-cyclodextrin (CD) is described. The aqueous CD-mediated reversible addition fragmentation chain transfer (RAFT) polymerization affords molecular masses up to 8600 g mol⁻¹ with polydispersities between 1.2 and 1.4. The surprisingly low molecular weights for higher monomer/chain transfer agent (CTA) ratios are investigated by comparing results obtained from free radical and RAFT radical polymerization in aqueous and organic media. The results indicate a steric hindrance caused by attached CD molecules on the growing polymer chain leading to stagnation of the polymerization process due to a restricted accessibility of the reactive chain end. This hypothesis is supported by matrix-assisted laser desorption/ionization time of flight mass spectrometry. Furthermore, the CD-mediated synthesis of amphiphilic diblock copolymers in variable aqueous media is described. Hydrophilic poly(N,N-dimethylacrylamide) macro-CTAs with different molecular weights are used to polymerize TBP-AA-HO at 50 °C. The diblock copolymers are analyzed by ¹H-nuclear magnetic resonance spectroscopy and size exclusion chromatography. The results confirm the polymer structure and reveal similar limitations of chain growth as observed for the CD-mediated homopolymerization with a limit of 7000 g mol⁻¹ for efficient chain extension. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2504–2517

The nitrile imine-mediated tetrazole-ene cycloaddition reaction (NITEC) is introduced as a powerful and versatile conjugation tool to covalently ligate macromolecules onto variable (bio)surfaces. The NITEC approach is initiated by UV irradiation and proceeds rapidly at ambient temperature yielding a highly fluorescent linkage. Initially, the formation of block copolymers by the NITEC methodology is studied to evidence its efficacy as a macromolecular conjugation tool. The grafting of polymers onto inorganic (silicon) and bioorganic (cellulose) surfaces is subsequently carried out employing the optimized reaction conditions obtained from the macromolecular ligation experiments and evidenced by surface characterization techniques, including X-ray photoelectron spectroscopy and FT-IR microscopy. In addition, the patterned immobilization of variable polymer chains onto profluorescent cellulose is achieved through a simple masking process during the irradiation.

Hetero Diels-Alder (HDA) cycloaddition – as an effective modular conjugation approach – is employed to graft thioamide endfunctional oligopeptides onto solid cyclopentadienyl (Cp) functional cellulose substrates generating cellulose-peptide hybrid materials. The highly reactive Cp moieties serve as diene functionality in the consecutive HDA reaction on the biosubstrate surface. Oligopeptides (i.e., the model peptide Gly-Gly-Arg-Phe-Pro-Trp-Trp-Gly and the antimicrobial peptide tritrpticin) are functionalized at their N-termini employing strongly electron deficient thiocarbonyl thio compounds resulting in biomacromolecules bearing a thioamide endgroup. The dienophile- functional peptides readily undergo HDA reactions at ambient temperature and under mild conditions in solution with synthetic polymers as well as on solid (bio)substrates. An in-depth investigation is provided of the influence of the temperature, the Lewis acid catalysis and the side group exchange of thioamide functional oligopeptides reacting with Cp terminated poly(methyl methacrylate) (M_n = 2100 g·mol⁻¹, PDI = 1.1) in homogenous solution as well as Cp functionalized cellulose in a heterogeneous system. To assess the success of the grafting reaction, the soluble samples were subjected to characterization methods such as size exclusion chromatography (SEC) and SEC-electrospray ionization mass spectrometry (SEC-ESI-MS). The heterogeneous “grafting-to” reactions were monitored using high resolution attenuated total reflection (ATR) Fourier transform infrared microscopy (HR-FTIRM) imaging, X-ray photoelectron spectroscopy (XPS) and elemental analysis. Evaluation via elemental analysis leads to quantitative peptide cellulose surface loading capacities.

Online size exclusion chromatography–electrospray ionization–mass spectrometry (SEC/ESI–MS) is employed for quantifying the overall initiation efficiencies of photolytically generated radical fragments. In a unique experiment, we present the first quantitative and systematic study of methyl-substituted acetophenone-type photoinitiators being employed in a single cocktail to initiate the free-radical polymerization of methyl methacrylate (MMA) in bulk. The photoinitiators are constituted of a set of two known and four new molecules, which represent an increasing number of methyl substituents on their benzoyl fragment, that is, benzoin, 4-methylbenzoin, 2,4-dimethylbenzoin, 2,4,6-trimethylbenzoin, 2,3,5,6-tetramethylbenzoin, and 2,3,4,5,6-pentamethylbenzoin. The absolute quantitative evaluation of the mass spectra shows a clear difference in the initiation ability of the differently substituted benzoyl-type radical fragments: Increasing the number of methyl substituents leads to a decrease in incorporation of the radical fragments.

A novel dithioester control agent [dimethyltetrathioterephtalate (DMTTT)] is presented for the thioketone-mediated radical polymerization (TKMP) of n-butyl acrylate. The rate of polymerization is significantly decreased in the presence of DMTTT indicating formation of dormant radical species. During polymerization, molar masses increase linearly with monomer conversion with reasonably narrow initial molar mass distributions (PDI between 1.3 and 1.8), whereas the dispersity increases during the course of the polymerization due to irreversible termination of both propagating and dormant radicals. The present results thus highlight the possibility of a mixed mechanism operating in RAFT polymerization, which combines slow fragmentation (long-lived intermediates) and intermediate radical termination.

The present feature article highlights the preparation of polymeric nanoparticles and initial attempts towards mimicking the structure of natural biomacromolecules by single chain folding of well-defined linear polymers through covalent and non-covalent interactions. Initially, the discussion focuses on the synthesis and characterization of single chain self-folded structures by non-covalent interactions. The second part of the article summarizes the folding of single chain polymers by means of covalent interactions into nanoparticle systems. The current state of the art in the field of single chain folding indicates that covalent-bond-driven nanoparticle preparation is well advanced, while the first encouraging steps towards building reversible single chain folding systems by the use of mutually orthogonal hydrogen-bonding motifs have been made.

Boronic acid-functionalized microspheres are prepared for the first time via mild epoxide ring opening based on porous cross-linked polymeric microspheres (diameter ≈ 10 μm, porosity ≈ 1000 Å). Quantitative chemical analysis by XPS and EA evidences that there is a greater functionalization with boronic acid when employing a sequential synthetic method [1.7 atom% boron (XPS); 1.12 wt% nitrogen (EA)] versus a one-pot synthetic method [0.2 atom% boron (XPS); 0.60 wt% nitrogen (EA)] yielding grafting densities ranging from approximately 2.5 molecules of boronic acid per nm² to 1 molecule of boronic acid per nm², respectively. Furthermore, the boronic acid-functionalized microspheres are conjugated with a novel fluorescent glucose molecule demonstrating a homogeneous spatial distribution of boronic acid.

The evolution of material design has mirrored advancements in the understanding of materials, nature, and the requirements of target applications. Originally, materials were only intended to play a passive role, but with a deepened understanding of material properties and design has come an improved ability to harness these properties to create materials with predetermined response mechanisms. This article has three aims: i) to briefly discuss the origin of and motivation for having materials that are capable of undergoing healing either extrinsically or intrinsically; ii) to present the most recent and promising advancements in the field of self-healing materials; and iii) to discuss important material design and property specifications that should be considered in order to promote the development of optimized self-healing materials.

The synthesis of acrylonitrile-butadiene rubbers (NBRs) via trithiocarbonate-mediated reversible addition fragmentation chain transfer (RAFT) polymerization of acrylonitrile (ACN) and 1,3-butadiene (BD) in solution under azeotropic conditions (38/62) was investigated for a broad range of common solvents: N,N-dimethylacetamide (DMAc), chlorobenzene, 1,4-dioxane, tert-butanol, isobutyronitrile, toluene, trimethylacetonitrile, dimethyl carbonate, acetonitrile, methyl acetate, acetone, and tert-butyl methyl ether. The gravimetrically determined conversions for the free radical polymerizations of ACN/BD after 22 h at 100 °C were in the range of 15% for methyl acetate to 35% for DMAc. The origin of the differences in conversion is attributed to the unequal decomposition behavior of the employed azo initiator 2,2′-azobis(N-butyl-2-methylpropionamide) (1) in the solvents under investigation, as determined by ultraviolet–visible (UV–vis) spectroscopy. Relative decomposition of 1 in solution (0.1 mol L⁻¹) at 100 °C was calculated from the UV–vis spectra for selected solvents. 90% of 1 in DMAc was decomposed after 22 h, 83% in tert-butanol, 57% in 1,4-dioxane, 53% in isobutyronitrile, 45% in chlorobenzene, and 21% in toluene. The evolution of molecular weight with conversion using the initiator 1 was in accordance with the theoretically expected values, regardless of the solvent studied. Moreover, the RAFT-mediated copolymerization of ACN/BD in DMAc with azo initiators 1, 1-[(1-cyano-1-methylethyl)azo]formamide (2) and 1,1′-azobis(cyclohexanecarbonitrile) (3) was investigated. A strong deviation from the linear evolution of molecular weight due to a fast decomposition of these initiators – congruent with high primary radical delivery rates – at the selected temperature was observed when using 2 and 3. The deviation was not observed when using 1. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

We report on the controlled free radical homopolymerization of 1-ferrocenylethyl acrylate as well as of three new ferrocene bearing monomers, namely 4-ferrocenylbutyl acrylate, 2-ferrocenylamido-2-methylpropyl acrylate, and 4-ferrocenylbutyl methacrylate, by the RAFT technique. For comparison, the latter monomer was polymerized using ATRP, too. The ferrocene containing monomers were found to be less reactive than their analogues free of ferrocene. The reasons for the low polymerizability are not entirely clear. As the addition of free ferrocene to the reaction mixture did not notably affect the polymerizations, sterical hindrance by the bulky ferrocene moiety fixed on the monomers seems to be the most probable explanation. Molar masses found for 1-ferrocenylethyl acrylate did not exceed 10,000 g mol⁻¹, while for 4-ferrocenylbutyl (meth)acrylate molar masses of 15,000 g mol⁻¹ could be obtained. With PDIs as low as 1.3 in RAFT polymerization of the monomers, good control over the polymerization was achieved. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

In the present study, n-butyl acrylate macromonomer (BAMM) (M_n = 1900 g mol⁻¹; PDI = 1.96) has been synthesized via a high-temperature polymerization process. Subsequently, the olefinic termini of the BAMM have been transformed into a diol via a dihydroxylation process using KMnO₄ as an oxidizing agent. The OH-terminated macroinitiator pBA(OH)₂ has subsequently been employed for the ring-opening polymerization (ROP) of ε-caprolactone via various catalytic systems, that is, organo-(1,5,7-triazabicyclo[4.4.0]dec-5-ene), metal (tin(II) 2-ethylhexanoate), and enzymatic catalysis (Novozym® 435). The obtained pBA-b-pCL block copolymers and the initiation efficiency of the BAMM macroinitiator have been investigated via size exclusion chromatography (SEC), electrospray ionization–mass spectrometry (ESI-MS) hyphenated with SEC and liquid chromatography at the critical conditions of both poly(ε-caprolactone) (pCL) and pBA. The in vitro enzyme catalysis (eROP) approach proved to be the most efficient catalysis system due to minor transesterification side reactions during the polymerization process. However, side reactions such as transesterifications occur in each catalytic system and—while they cannot be suppressed—they can be minimized. The species generated during the eROP process include the desired block copolymer pBA-b-pCL as main species as well as pCL homopolymer and residual macroinitiator pBA(OH)₂. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

The current article contains a review of the electrospray ionization-mass spectrometry characterization of polymers prepared via thermal- and photoinitiation processes. The used analysis method permits direct access to detailed endgroup information. For a qualitative and quantitative endgroup analysis, sophisticated methods have been developed which provide a detailed image of the incorporation propensity of thermally as well as photolytically generated radicals at the polymer chain termini. Such a post-mortem analysis of polymeric materials specifically allows for the quantification of the ability of radical fragments to initiate polymerization processes. Herein, the most recent progress in the field of mass spectrometric radical reactivity mapping is outlined and open questions as well as future directions are discussed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

The present study investigates the degradation behavior of various high-molecular-weight acrylic polymers (50,000 < M_n/g mol⁻¹ < 100,000), namely poly(methyl methacrylate) (PMMA), poly(n-butyl methacrylate) (PBMA), poly(n-butyl acrylate) (PBA), and poly(lauryl methacrylate) (PLMA), under extreme environmental conditions. These polymers were synthesized via various polymerization techniques to create different end-groups. The polymers chosen are readily applicable in the formulation of surface coatings and were degraded under conditions which replicate the harsh Australian climate, where surface coatings may reach temperatures of up to 95 °C and are exposed to broad-spectrum UV radiation of up to 1 kW m⁻². The degradation behavior of the polymeric materials on their surface was followed via ATR-IR spectroscopy, high resolution FTIR microscopy, and X-ray photoelectron spectroscopy. The extent of the observed thermal and photo-oxidation is directly related to the length of the ester side group, with the degradation susceptibility decreasing in the order of PLMA > PBMA/PBA > PMMA, with PMMA still stable even after 5 months exposure to the harshest condition used (UV light at 95 °C). The general degradation mechanism involves the loss of the ester side groups to form methacrylic acid followed by cross-linking. The effect of the variable end groups was found to be minimal. The results from this study are in good agreement with previous studies of low-molecular-weight model polymers under identical conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

In a recent article (W. Meiser, M. Buback, Assessing the RAFT Equilibrium Constant via Model Systems: An EPR Study, Macromol. Rapid Commun.2011, 18, 1490-1494), it is claimed that evidence is found that unequivocally proves that quantum mechanical calculations assessing the equilibrium constant and fragmentation rate coefficients in dithiobenzoate-mediated reversible addition fragmentation transfer (RAFT) systems are beset with a considerable uncertainty. In the present work, we show that these claims made by Meiser and Buback are beset with a model dependency, as a critical key parameter in their data analysis – the addition rate coefficient of the radicals attacking the C=S double bond in the dithiobenzoate – induces a model insensitivity into the data analysis. Contrary to the claims made by Meiser and Buback, their experimental results can be brought into agreement with the quantum chemical calculations if a lower addition rate coefficient of cyanoisopropyl radicals (CIP) to the CIP dithiobenzoate (CPDB) is assumed. To resolve the model dependency, the addition rate coefficient of CIP radicals to CPDB needs to be determined as a matter of priority.

This study investigates the degradation behavior of poly(n-butyl methacrylate) (p(nBMA)), poly(tert-butyl methacrylate) (p(tBMA)), and poly(hexafluoro butyl methacrylate) (p(HFBMA)) on a molecular level under extreme environmental conditions. The polymers chosen are readily applicable in the formulation of surface coatings and were degraded under conditions which replicated the harsh Australian climate, in which surface coatings may reach temperatures of up to 95 °C and are exposed to broad-spectrum UV radiation of up to 1 kW m⁻². The degradation profiles were mapped with high-resolution electrospray ionization mass spectrometry (ESI-MS) with a LCQ quadrupole ion trap mass analyzer, with the peak assignments confirmed to within 3 ppm using ESI-MS with a LTQ-Orbitrap mass detector. It was found that in all the butyl ester polymers analyzed herein—regardless of their tertiary side-chain structure—the loss of the butyl ester group and subsequent formation of acid side groups are a component of the overall degradation pathway of poly(butyl methacrylate)s under these harsh conditions. However, it is also demonstrated that the magnitude of this pathway is intimately linked to the side-chain structure with the propensity for degradation decreasing in the order p(tBMA) > p(nBMA) > p(HFBMA). The degradation mechanisms identified in this study, in combination with the previous end-group degradation studies of poly(methyl methacrylate) and poly(n-butyl acrylate), have allowed a much deeper understanding of the molecular degradation behavior of poly(acrylate)s and poly(methacrylate)s in an extreme natural environment. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Well-defined heterotelechelic poly(styrene) carrying thymine/diaminopyridine (DAP) (M_n,SEC = 9300, PDI = 1.04) and Hamilton wedge (HW)/cyanuric acid (CA) (M_n,SEC = 8200, PDI = 1.04) bonding motifs are prepared via a combination of controlled/living radical polymerization and copper catalyzed azide/alkyne “click” chemistry and are subsequently self-assembled as single chains to emulate—on a simple level—the self-folding behavior of natural biomacromolecules. Hydrogen nuclear magnetic resonance (¹H NMR) in deuterated dichloromethane and dynamic light scattering analyses provides evidence for the hydrogen bonding interactions between the α-thymine and ω-DAP as well as α-CA and ω-HW chain ends of the heterotelechelic polymers leading to circular entropy driven single chain self-assembly. This study demonstrates that the choice of NMR solvent is important for obtaining well-resolved NMR spectra of the self-assembled structures. In addition, steric effects on the HW can affect the efficiency of the self-assembly process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

The preparation of ABA-type block copolymers via tandem enhanced spin capturing polymerization (ESCP) and nitroxide-mediated polymerization (NMP) processes is explored in-depth. Midchain alkoxyamine functional polystyrenes (M_n = 6200, 12,500 and 19,900 g mol⁻¹) were chain extended with styrene as well as tert-butyl acrylate at elevated temperature NMP conditions (T = 110 °C) generating a tandem ESCP-NMP sequence. Although the chain extensions and thus the block copolymer formation processes function well (yielding in the case of the chain extension with styrene number average molecular weights of up to 20,800 g mol⁻¹ (PDI = 1.22) when the 6200 g mol⁻¹ precursor is used and up to 67,500 g mol⁻¹ (PDI = 1.36) when the 19,900 g mol⁻¹ precursor is used and 21,600 g mol⁻¹ (PDI = 1.17) as well as 37,100 g mol⁻¹ (PDI = 1.21) for the tert-butyl acrylate chain extensions for the 6200 and 12,500 g mol⁻¹ precursors, respectively), it is also evident that the efficiency of the block copolymer formation process decreases with an increasing chain length of the ESCP precursor macromolecules (i.e., for the 19,900 g mol⁻¹ ESCP precursor no efficient chain extension with tert-butyl acrylate can be observed). For the polystyrene-block-tert-butyl acrylate-block-polystyrene polymers, the molecular weights were determined via triple detection SEC using light scattering and small-angle X-ray scattering. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

The surface modification of divinylbenzene (DVB)-based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero-Diels–Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this “grafting-to” method. Two variants of the RAFT-HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number-averaged molecular weight, M_n = 4200 g mol⁻¹; polydispersity index, PDI = 1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2 × 10²⁰ chains per gram of microspheres. In the second approach, the functionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (M_n = 6000 g mol⁻¹, PDI = 1.25; M_n = 26 000 g mol⁻¹, PDI = 1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T = 60 °C) yet in the absence of a catalyst. In this case the surface grafting density is close to 7 chains nm⁻² for M_n = 6000 g mol⁻¹ and 4 chains nm⁻² for M_n = 26 000 g mol⁻¹, or 2.82 × 10¹⁹ and 1.38 × 10¹⁹ chains g⁻¹, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry.

Comb polymers were synthesized by the “grafting-onto” method via a combination of Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization and the hetero-Diels-Alder (HDA) cycloaddition. The HDA reactive monomer trans, trans-hexa-2,4-dienylacrylate (ttHA) was copolymerized with styrene via the RAFT process. Crosslinking was minimized by decreasing the monomer concentration—whilst keeping monomer to polymer conversions low—resulting in reactive backbones with on average one reactive pendant diene groups for 10 styrene units. The HDA cycloaddition was performed between the diene functions of the copolymer and a poly(n-butyl acrylate) (PnBA) prepared via RAFT polymerization with pyridin-2-yldithioformate, which can act as a dienophile. The coupling reactions were performed within 24 h at 50 °C and the grafting yield varies from 75% to 100%, depending on the number average molecular weight of the PnBA (3500 g mol⁻¹ < M_n < 13,000 g mol⁻¹) grafted chain and the reaction stoichiometry. The molecular weights of the grafted block copolymers range from 19,000 g mol⁻¹ to 58,000 g mol⁻¹ with polydispersities close to 1.25. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1773–1781, 2010