Patterned Hydrophilization of Nanoporous 1,2‐PB by Thiol‐ene Photochemistry

We present an efficient method for functionalizing the large polymer–air interface of a gyroid nanoporous polymer. The hydrophilicity of nanoporous cross‐linked 1,2‐polybutadiene is tuned by thiol‐ene photo‐grafting of mercaptosuccinic acid or sodium 2‐mercaptoethanesulfonate. The reaction is monitored by FT‐IR, UV–Vis, contact angle, and gravimetry. Overall quantum yields are calculated for the two thiol‐ene “click” reactions in nano‐confinement, neatly revealing their chain‐like nature. Top–down photolithographic patterning is demonstrated, realizing hydrophilic nanoporous “corridors” exclusively hosting water. The presented approach can be relevant for many applications where, e.g., high control and contrast in hydrophilicity, chemical functionality or refractive index are needed.

     

Polymer‐Bound Thiol Groups on Poly(2‐oxazoline)s

A new 2‐oxazoline monomer with a protected thiol group, 2‐[2‐(4‐methoxybenzylsulfanyl)ethyl]‐2‐oxazoline, MOB‐SOx , was synthesized from commercially available compounds. MOB‐SOx and 2‐ethyl‐2‐oxazoline (EtOx) were simultaneously polymerized yielding well defined copolymers with narrow molar mass distributions and target polymer chain length. The copolymerization was initiated by N‐methyl‐2‐methyl‐2‐oxazolinium triflate ( MeOxOTf ). After quantitative deprotection, poly(2‐oxazoline) with pendant thiol groups was obtained. The thiol groups were quantitatively added to the double bond of N‐phenyl‐acrylamide ( PhA ) and benzylmaleimide ( BzM ). Graft copolymers were obtained by reaction of those SH containing polymers with poly(2‐methyl‐2‐oxazoline)s bearing acrylamide ( PMeOx ₁₀ A ) and maleimide ( PMeOx ₁₀ M ) as terminal reactive groups.

     

Block Copolymer PEO‐b‐PHPMA Synthesis Using Controlled Radical Polymerization on a Chip

Summary: Block copolymers of poly(ethylene oxide‐block‐2‐hydroxypropyl methacrylate) (PEO‐b‐PHPMA) with a range of molecular masses of the PHPMA block were obtained by controlled radical polymerization on a chip (CRP chip) using a PEO macroinitiator. A series of well‐controlled polymerizations were carried out at different pumping rates or reaction times with a constant ratio of monomer to initiator. The stoichiometry of the reactants was also adjusted by varying relative flow rates to change the reactant concentrations.

A schematic of a CRP chip and SEC traces of the PEO‐b‐PHPMA produced from different pump rates with a 1:100 ratio of initiator to monomer. The dashed peaks are the macroinitiator, PEO‐Br (left), and monomer, HPMA (right).     

Direct Synthesis of Pyridyl Disulfide‐Terminated Polymers by RAFT Polymerization

A trithiocarbonate RAFT agent was modified with a pyridyl disulfide group and used in the direct synthesis of endgroup pyridyl disulfide‐functionalized homo‐ and amphiphilic block copolymers of oligo(ethyleneglycol) acrylate (PEG‐A) and butyl acrylate (BA). Both the homo‐ and copolymerizations were found to be well controlled via the RAFT mechanism. The NMR analysis indicated that both the homopolymers of PEG‐A and the amphiphilic diblock copolymers of PEG‐A and BA possessed pyridyl disulfide terminal groups. A UV‐Vis absorption test revealed that the pyridyl disulfide endgroup of the polymer could be efficiently used to couple thiol‐bearing molecules to the polymer without the need for any post‐polymerization modification. This communication presents the first efficient direct synthesis of thiol‐reactive endgroup‐functionalized well‐defined polymers via the RAFT technique.

     

Microwave‐Assisted Synthesis of Crosslinked Poly(vinyl alcohol) Nanocomposites Comprising Single‐Walled Carbon Nanotubes,Multi‐Walled Carbon Nanotubes,and Buckminsterfullerene

We report a facile method to accomplish the crosslinking reaction of PVA with SWNTs, MWNTs, and C‐60 using MW irradiation. Nanocomposites of PVA crosslinked with SWNT, MWNT and C‐60 were prepared expeditiously by reacting the respective carbon nanotubes with 3 wt.‐% PVA under MW irradiation, maintaining a temperature of 100 °C, representing a radical improvement over literature methods to prepare such crosslinked PVA composites. This general preparative procedure is versatile and provides a simple route to manufacture useful SWNT, MWNT and C‐60 nanocomposites.

     

Solvent Vapor‐Induced Nanowire Formation in Poly(3‐hexylthiophene) Thin Films

Summary: Nanowire lengths and length‐to‐width aspect ratios in regioregular poly(3‐hexylthiophene) (P3HT) were simply controlled through changes in the solvent vapor pressure during solidification. It is demonstrated that the nanowires grew by rod‐to‐rod association, in which the molecular long axis of the P3HT chains appeared to be well‐oriented parallel to the silicon substrate (Si/SiO_x). The formation of the nanowires took place by one dimensional self‐assembly, governed by π‐π stacking of the P3HT units.

TEM high contrast images showing P3HT nanowires fabricated by spin‐coating under a solvent vapor pressure.     

Computer Simulation of a Gold Nanoparticle Coated by Thiol‐Terminated Hydroquinonyl Oligoethers

Molecular dynamics simulations were carried out to investigate the structure of a gold‐nanoparticle including 169 Au atoms coated by 42 thiol terminated hydroquinonyl oligoether chains. Three nanoparticle systems were constructed and investigated for structural comparison. The simulation showed that in all three nanosystems thiol‐chains self‐assembled on the surface of the gold cluster to form a stable gold nanoparticle. The configurations of the thiol chains and stacking of the phenylene rings were analyzed. The thiol‐chains are bundled into groups. Each group contains no more than four chains, in which phenylene rings in the thiol‐chains are correlated in parallel and perpendicular forms. Simple quantum mechanical calculations are carried out to elucidate the correlation of the phenylene rings.

A snapshot of a TTOE‐Au nanoparticle.     

A Deeper Insight into the Postpolymerization Modification of Polypenta Fluorophenyl Methacrylates to Poly(N‐(2‐Hydroxypropyl) Methacrylamide)

This work provides a detailed insight into the synthesis of N‐(2‐hydroxypropyl)methacrylamide (HPMA) polymers employing the activated ester approach. In this approach, polypenta fluorophenyl methacrylate (PFPMA)‐activated ester polymers are synthesized by the reversible addition–fragmentation chain transfer (RAFT) polymerization and transferred into HPMA‐based systems by the use of 2‐hydroxypropylamine. To prove quantitative conversion in the absence of side reactions, special attention is devoted to investigate different reaction conditions by different analytical methods (¹H, ¹⁹F, inverse‐gated ¹³C NMR, and zeta potential measurements). Furthermore the influence of common solvent impurities, such as water, is investigated. Besides differences in polymer tacticity, the poly(N‐(2‐hydroxypropyl) methacrylamide) (PHPMA) synthesized under water‐free conditions display the same properties like the conventional synthesized control‐PHPMA. However, 3% water content in the dimethylsulfoxide are already sufficient to yield PHPMA polymers with a negative zeta potential of –15.8 mV indication the presence of carboxylic groups due to partial hydrolysis of the activated ester.

     

Hierarchically Porous Materials from Layer‐by‐Layer Photopolymerization of High Internal Phase Emulsions

A combination of high internal phase emulsion (HIPE) templating and additive manufacturing technology (AMT) is applied for creating hierarchical porosity within an acrylate and acrylate/thiol‐based polymer network. The photopolymerizable formulation is optimized to produce emulsions with a volume fraction of droplet phase greater than 80 vol%. Kinetic stability of the emulsions is sufficient enough to withstand in‐mold curing or computer‐controlled layer‐by‐layer stereolithography without phase separation. By including macroscale cellular cavities within the build file, a level of controlled porosity is created simultaneous to the formation of the porous microstructure of the polyHIPE. The hybrid HIPE–AMT technique thus provides hierarchically porous materials with mechanical properties tailored by the addition of thiol chain transfer agent.

     

Polypeptide Modification of Multiwalled Carbon Nanotubes by a Graft‐From Approach

Summary: Covalent surface functionalization of carbon nanotubes with polypeptides is promising for possible medical applications. This work presents a graft‐from approach to perform the polypeptide modification of multiwalled carbon nanotubes (MWNTs). The raw MWNTs are first amine‐functionalized. The amine‐functionalized MWNTs are then used as the initiator to initiate the ring‐opening polymerization of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (BLG‐NCA), to result in the polypeptide‐grafted MWNTs. FT‐IR, XPS, and TGA data demonstrate that the functionalization is successful. The TEM images of the products show that the thickness of the polypeptide shell of the PBLG‐MWNT is about 4.5–22 nm. Using the facile route developed here, carbon nanotubes functionalized with other types of polypeptides can be easily fabricated using the corresponding NCAs.

Strategy for the polypeptide modification of multiwalled carbon nanotubes by a graft‐from approach.     

Electroactive Shape‐Memory Polyurethane Composites Incorporating Carbon Nanotubes

Summary: Electro‐active shape‐memory composites were synthesized using conducting polyurethane (PU) composites and multi‐walled carbon nanotubes (MWNTs). Surface modification of the MWNTs (by acid treatment) improved the mechanical properties of the composites. The modulus and stress at 100% elongation increased with increasing surface‐modified MWNT content, while elongation at break decreased. MWNT surface modification also resulted in a decrease in the electrical conductivity of the composites, however, as the surface modified MWNT content increased the conductivity increased (an order of 10⁻³ S · cm⁻¹ was obtained in samples with 5 wt.‐% modified‐MWNT content). Electro‐active shape recovery was observed for the surface‐modified MWNT composites with an energy conversion efficiency of 10.4%. Hence, PU‐MWNT composites may prove promising candidates for use as smart actuators.

The electro‐active shape‐recovery behavior of PU‐MWNT composites. The pictured transition occurs within 10 s when a constant voltage of 40 V is applied.     

High‐Tg Thiol‐Click Thermoset Networks via the Thiol‐Maleimide Michael Addition

Thiol‐click reactions lead to polymeric materials with a wide range of interesting mechanical, electrical, and optical properties. However, this reaction mechanism typically results in bulk materials with a low glass transition temperature (T_g) due to rotational flexibility around the thioether linkages found in networks such as thiol‐ene, thiol‐epoxy, and thiol‐acrylate systems. This report explores the thiol‐maleimide reaction utilized for the first time as a solvent‐free reaction system to synthesize high‐T_g thermosetting networks. Through thermomechanical characterization via dynamic mechanical analysis, the homogeneity and T_gs of thiol‐maleimide networks are compared to similarly structured thiol‐ene and thiol‐epoxy networks. While preliminary data show more heterogeneous networks for thiol‐maleimide systems, bulk materials exhibit T_gs 80 °C higher than other thiol‐click systems explored herein. Finally, hollow tubes are synthesized using each thiol‐click reaction mechanism and employed in low‐ and high‐temperature environments, demonstrating the ability to withstand a compressive radial 100 N deformation at 100 °C wherein other thiol‐click systems fail mechanically.

     

Exploring Network Formation of Tough and Biocompatible Thiol‐yne Based Photopolymers

This work deals with the in‐depth investigation of thiol‐yne based network formation and its effect on thermomechanical properties and impact strength. The results show that the bifunctional alkyne monomer di(but‐1‐yne‐4‐yl)carbonate ( DBC ) provides significantly lower cytotoxicity than the comparable acrylate, 1,4‐butanediol diacrylate ( BDA ). Real‐time near infrared photorheology measurements reveal that gel formation is shifted to higher conversions for DBC /thiol resins leading to lower shrinkage stress and higher overall monomer conversion than BDA . Glass transition temperature (T_g), shrinkage stress, as well as network density determined by double quantum solid state NMR, increase proportionally with the thiol functionality. Most importantly, highly cross‐linked DBC /dipentaerythritol hexa(3‐mercaptopropionate) networks (T_g ≈ 61 °C) provide a 5.3 times higher impact strength than BDA , which is explained by the unique network homogeneity of thiol‐yne photopolymers.

     

One‐Pot Difunctionalization of Poly(ω‐pentadecalactone) with Thiol‐Thiol or Thiol‐Acrylate Groups,Catalyzed by Candida antarctica Lipase B

Summary: An enzymatic one‐pot procedure has been developed for the synthesis of difunctional polyesters containing terminal thiols and acrylates. Candida antarctica lipase B was used as a catalyst for the ring‐opening polymerization of ω‐pentadecalactone. The polymerization was initiated with 6‐mercaptohexanol, then terminated with γ‐thiobutyrolactone or vinyl acrylate to create two types of difunctional polyesters with a very high content of thiol‐thiol or thiol‐acrylate end‐groups.

Difunctionalization of poly‐PDL.     

A Green Approach for the Synthesis and Thiol‐ene Modification of Alkene Functio1489lized Poly(2‐oxazoline)s

The bulk polymerization of 2‐(dec‐9‐enyl)‐2‐oxazoline ( DecEnOx ), a fatty acid‐based monomer for the cationic ring‐opening polymerization, is reported. Furthermore, under optimal conditions, namely microwave heating at 100 °C, the bulk copolymerization with 2‐ethyl‐2‐oxazoline yielded well‐defined copolymers. Due to its pendant alkene groups DecEnOx ‐based polymers possess the potential to be modified in efficient thiol‐ene reactions. The functionalization with thiols, e.g., dodecanethiol and 2,3,4,6‐tetra‐O‐acetyl‐1‐thio‐β‐D ‐glycopyranose in “green” solvents is demonstrated.

     

pH‐Disintegrable Polyelectrolyte Multilayer‐Coated Mesoporous Silica Nanoparticles Exhibiting Triggered Co‐Release of Cisplatin and Model Drug Molecules

We report on the fabrication of pH‐disintegrable polyelectrolyte multilayer‐coated mesoporous silica nanoparticles (MSN) capable of triggered co‐release of cisplatin and model drug molecules. The outer polyelectrolyte multilayer was assembled from permanently cationic polyelectrolyte, poly(allyl amine hydrochloride) (PAH), and negatively charged polyelectrolyte, P(DMA‐co‐TPAMA), consisting of N,N‐dimethylacrylamide (DMA) and 3,4,5,6‐tetrahydrophthalic anhydride‐functionalized N‐(3‐aminopropyl)methacrylamide (TPAMA) monomer units, which exhibits pH‐induced charge conversion characteristics. Thus, the subtle alteration of solution pH from 7.4 to ≈5–6 can lead to the disintegration of outer polyelectrolyte multilayers, accompanied with the co‐release of cisplatin and RhB.

     

Fatty Acid Derived Monomers and Related Polymers Via Thiol‐ene (Click) Additions

Thiol‐ene additions of methyl 10‐undecenoate, a castor oil derived renewable platform chemical, were studied with the goal of preparing a set of renewable monomers. Good to excellent yields were obtained for these solvent and initiator free thiol‐ene additions. The resulting monomers were then polymerized using TBD as a catalyst, to linear as well as hyperbranched polyesters that also contain thio‐ether linkages. All thus prepared polymers were fully characterized (NMR, GPC, DSC, and TGA) and the results of these investigations will be discussed within this contribution. The thermal analysis of these polymers revealed melting points in the range from 50 to 71 °C. Moreover, no significant weight loss was observed below 300 °C.

     

A Strategy for Synthesis of Ion‐Bonded Supramolecular Star Polymers by Reversible Addition‐Fragmentation Chain Transfer (RAFT) Polymerization

We have developed a novel strategy for the preparation of ion‐bonded supramolecular star polymers by RAFT polymerization. An ion‐bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert‐butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by ¹H NMR and GPC. The results show that the polymerization possesses the character of living free‐radical polymerization and the ion‐bonded supramolecular star polymers PSt, PtBA, and PSt‐b‐PtBA, with six well‐defined arms, were successfully synthesized.