Oxygen‐Mediated Reactions in Photopolymerizable Radical Thin Films: Application to Simultaneous Photocuring Under Air and Nanoparticle Formation

Titanium propoxide, titanium isopropoxide, and titanium (triethanolaminato) isopropoxide are proposed as high‐performance additives to overcome the oxygen inhibition effects in the free radical photopolymerization of a low‐viscosity monomer thin film, under air and upon a low‐intensity UV light activation. Indeed, when added to a Type I photoinitiator such as bis(2,4,6‐trimethylbenzoyl)‐phenylphosphine oxide (BAPO), noticeably higher conversions are achieved under air (48% vs. 30%). The in situ formation of Ti‐based nanoparticles is also observed. The photochemical properties of these types of Ti‐based compounds as well as their interaction with BAPO are investigated by steady‐state photolysis and electron spin resonance. Molecular orbital calculations give an interesting insight into the possible reactions. A chemical mechanism is also proposed.

     

Online monitoring of Silicone Network Formation by Means of In‐Situ Mid‐Infrared Spectroscopy

The ReactIR™ reaction analysis system was used to monitor the crosslinking copolymerization of trimethylsilyl methacrylate with α,ω‐methacryloyl‐terminated oligo(dimethylsiloxane). Characteristic infrared bands proved useful to determine the total methacrylate concentration. After less than 12 h at 60 °C using 0.14% 2,2′‐azoisobutyronitrile (AIBN), the methacrylate conversion during the crosslinking reaction exceeded 98%. The comparison of the crosslinking reaction with a methacrylate homopolymerization showed that significant autoacceleration occurred during network formation.

Time‐dependent monomer conversion [M]/[M]₀ for TMSMA homopolymerization (run H in Table 1) and the corresponding crosslinking polymerization (run N) as revealed by the peak at 1 326 cm⁻¹.     

Blends of Immiscible Polystyrene/Polyamide 6 via Successive In‐Situ Polymerizations

Summary: A novel method has been successfully developed to prepare binary blends of PS and MCPA6. The blends are formed by the radical polymerization of styrene in CL, followed by the in‐situ anionic ring‐opening polymerization of CL in the presence of PS. The phase morphology investigated using SEM reveals that PS/MCPA6 blends with a PS content of 10 wt.‐% or lower consists of a MCPA6 matrix and a dispersed PS minor phase. Remarkably, phase inversion occurs in blends that have a PS content of 15 wt.‐% or higher, in which MCPA6 is no longer continuous but finely dispersed in the PS continuous phase. The phase inversion occurs at an extremely low PS content, and this phenomenon is unusual for traditional polymer blends prepared by melt blending. The probable reason for the particular phase morphology development is explained. The stability of the phase morphologies of the PS/MCPA6 blends after annealing at 250 °C is also investigated by SEM.

SEM micrograph of the fractured surface of a PS/MCPA6 blend with a PS content of 20 wt.‐%, in which MCPA6, as spherical particles, is dispersed in the PS continuous phase.     

A Highly Efficient Polyurethane‐Type Polymeric Photoinitiator Containing In‐chain Benzophenone and Coinitiator Amine for Photopolymerization of PU Prepolymers

Summary: A novel polyurethane‐type polymeric photoinitiator (PUIOA) was synthesized through polycondensation of a novel diamine AAPBP, TDI and MDEA. The BP and coinitiator amine structures were successfully introduced into the backbones of PUIOA. A polymeric photoinitiator without the coinitiator amine in the polymer chain (PUIO) was also synthesized for comparison. FT‐IR, ¹H NMR and GPC analyses confirmed the structures of polymeric photoinitiators. The UV‐vis spectra of PUIOA and PUIO are similar to the parent AAPBP, and both exhibit high red‐shifted maximal absorption as compared with BP. ESR spectra indicate that PUIOA can generate free radicals most efficiently. Photopolymerization of the Polyurethane prepolymer, initiated by PUIOA, PUIO/MDEA, AAPBP/MDEA and BP/MDEA, was studied by photo‐DSC. The results show that PUIOA is the most efficient photoinitiator for PU prepolymer.

Synthesis routes for polymeric photoinitiators.     

Rubrene‐Based Green‐Light‐Sensitive Photoinitiating Systems of Polymerization

Rubrene, a compound that exhibits green light absorption, interacts with an iodonium salt through its excited singlet state to generate cations and free radicals under a green laser line at 532 nm or a halogen lamp delivering a low light intensity of polychromatic visible light. The photochemical mechanisms are investigated by steady‐state photolysis, fluorescence, electrochemistry, and electron spin resonance spin trapping techniques. The produced cations and free radicals initiate both the cationic photopolymerization of epoxides and the free radical photopolymerization of acrylates. Moreover, the addition of N‐vinylcarbazole into the system enhances the photopolymerization efficiency. The Rubrene/amine/chlorotriazine photoinitiating system also exhibits a much higher photoinitiation ability for the free radical photopolymerization of acrylates.     

Photophysical and Photochemical Studies of Novel Thioxanthone‐Functionalized Methacrylates through LED Excitation

Five novel thioxanthone (TX)‐functionalized methacrylates as copolymerizable photoinitiators (CopPIs) for polymerization of acrylates are synthesized from reactions of tert‐butyl α‐bromomethacrylate with 2‐hydroxy thioxanthone (TX1) and 1,4‐dihydroxy thioxanthone (TX3), cleavage of their respective tert‐butyl ester groups with trifluoroacetic acid (TX2, TX4), and by reaction of the acid chloride derivative of TX2 with Irgacure 2959 (TX5). These CopPIs absorb in the near UV–visible region (390–420 nm; absorption redshift ≈10–40 nm, ε values comparable to TX). Their performances are studied under LED exposure at 385 and 405 nm using real‐time FTIR. The reactivities of TX1 and TX2 are similar to isopropyl thioxanthone, used as reference; TX3 and TX4 have lower reactivities, due to their difunctionality, which however makes them good crosslinking agents. TX5 is the first monomeric PI possessing two different type side‐chain photoinitiating groups. The migration stability of two of these CopPIs is shown in the cured polyacrylates. The photochemical mechanisms are studied by electron spin resonance, steady state photolysis, laser flash photolysis, and cyclic voltammetry.

     

Synthesis and Applications of Protein/Peptide‐Polymer Conjugates

Recent advances in synthetic methodologies have brought us closer than ever to the precision conferred by nature. For example, the control possible in reversible deactivation radical polymerization enables us to design and synthesize macromolecules with unprecedented control over not only the polymer chain ends, but also the side chain functionality. Furthermore, this functionality can be exploited to afford chemical modification of peptides and proteins, with ever‐improving site‐specificity, yielding a range of well‐defined protein/peptide‐hybrid materials. Such materials benefit from the amalgamation of the properties of proteins/peptides with those of the synthetic (macro)molecules in question. Here, the latest developments in the synthesis of functional polymers and their use for preparation of well‐defined protein/peptide‐polymer conjugates will be discussed, with particular attention focused on modulating the stability, efficacy and/or administration of therapeutic peptides.

     

Iron‐Based Metal‐Organic Frameworks (MOF) as Photocatalysts for Radical and Cationic Polymerizations under Near UV and Visible LEDs (385–405 nm)

Photoinitiating systems consisting of a highly porous iron(III)‐based metal‐organic framework (MOF), an iodonium salt, and N‐vinylcarbazole are developed to initiate the free radical promoted cationic polymerization of epoxides under air and the free radical polymerization of acrylates in laminate upon exposure to near UV (385 nm) or visible (405 nm) light‐emitting diodes. These systems present a satisfactory initiating ability. Among the five tested iron carboxylate MOFs exhibiting different compositions and topologies, the flexible microporous iron(III) terephthalate MIL53 is particularly interesting, leading to a final conversion of 58% for the ring‐opening polymerization of epoxides. This provides the possibility of designing MOF/polymer composite materials with enhanced mechanical properties through the in situ incorporation of the MOF structure during the photopolymerization process.

     

Synthesis of MDMO‐PPV Nanoparticles Via In Situ Sulfinyl Precursor Route Polymerization in Miniemulsion

A facile route to synthesize poly[(2‐methoxy‐5‐(3′,7′,‐dimethyloctyloxy))‐1,4‐phenylene vinylene] polymer nanoparticles (NPs) using the miniemulsion technique in combination with the sulfinyl precursor route polymerization is presented. The reaction conditions involving high temperature are overcome by using ethylene glycol as a polar continuous phase. Particles can be easily transferred into the water phase without the need for additional surfactant. The characteristic UV–vis absorption and the strong fluorescence exhibited by the polymer along with the molecular weight obtained prove the success of the synthetic strategy. Such in situ synthesis of PPV in the form of NPs can be extended to other conjugated polymers, opening new doors for synthesizing luminescent NPs that have tremendous potential in biomedicine and printable electronics.

     

Double‐Hydrophilic Polymer Brushes: Synthesis and Application for Crystallization Modification of Calcium Carbonate

Summary: A water‐soluble diblock copolymer composed of poly(ethylene glycol) (PEG) and a cylindrical poly(acrylic acid) (PAA) brush is reported. It is prepared by a ‘grafting from’ approach using stepwise atom transfer radical polymerization combined with group transformation. Uniform molecular brushes, PEG₁₁₃‐b‐P(MA‐g‐PAA₂₆)₁₆₉, are thus prepared as indicated by atom force microscopy analysis. This PAA densely grafted polymer is used to induce the crystallization of calcium carbonate in aqueous solution. Different experimental conditions, fast mixing reactions and static diffusion methods, are applied to explore the effect of polymer brushes on the crystallization, which is characterized by scanning electron microscopy, X‐ray diffraction, and thermogravimetric analysis.

AFM image of the polymer brushes on mica and an SEM image of CaCO₃ particles prepared in its presence.     

Cyclodextrins in Polymer Synthesis: Free Radical Polymerization of β‐Cyclodextrin Complexes of Photosensitive Mesoionic 6‐Oxo‐1,6‐dihydropyrimidin‐3‐ium‐4‐olates in Aqueous Medium

Solid mesoionic 2‐[2‐(isopropenylcarbonyloxy)ethylthio]‐1‐methyl‐6‐oxo‐3‐phenyl‐5‐propyl‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate was complexed in water using β‐cyclodextrin (β‐CD) and randomly methylated β‐CD, which resulted in polymerizable complexes with 2:1 stoichiometry. The β‐CD complex was characterized using ¹H NMR, ROESY NMR and UV spectroscopy. Polymerization of the complex prepared from methylated β‐CD led to a photosensitive polymer, which precipitated during polymerization and was nearly free of CD. Polymerization was carried out with a water‐soluble redox initiator. In addition, a copolymer with methyl methacrylate was prepared from the complexes, which showed a different mass‐dependent distribution in the incorporation in comparison to a copolymer prepared without CD in organic solvents.

     

Facile Synthesis of a Carnosine‐Pendent Cationic Polymer via Free Radical Polymerization and Application in Gene Delivery

l ‐carnosine is a bipeptide with varieties of biomedical benefits, but rarely reported as a component in structurally defined polymers due to the unavailability of isolatable monomers. In this report, a simple method to synthesize a carnosine‐derived methacrylamide in three steps is established and a neutral polymer with a narrow molecular weight distribution (M_n 7.6 kDa, Ð 1.2) and high structural regularity is prepared via free radical polymerization, and a carnosine‐pendent cationic homopolymer is finally achieved after trifluoroacetic acid‐mediated deprotection without a concern of impurities such as metals. The antioxidative activity, cytotoxicity, DNA‐binding capability, and gene delivery performance of the cationic polymer are also studied.     

Design of Open‐Shell π‐Conjugated Microporous Polymer Film with Super‐High Conductivity

Polymers with open‐shell π‐conjugated structure and thiophene‐based building blocks are designed for electropolymerization. These systems are expected to electropolymerize and form solution‐processable conjugated microporous polymer films, which can be used for device fabrications. The designed radical structure has a low highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap, high electronic hopping rate for the hole transfer and electron transfer, and ultimately high conductivity. The eclipsed dimer has higher conductivities than that of staggered dimer. The designed monomer with substituted groups has lower conductivities due to steric effect. The open‐shell systems designed will be promising materials with various applications. Design principles for open‐shell organic materials can be established based on the trends of this paper.     

One‐Pot Synthesis of PTFEMA‐b‐PMMA‐b‐PTFEMA by Controlled Radical Polymerization with a Difunctional Initiator in Conjugation with Photoredox Catalyst of Ir(ppy)3 Under Visible Light

Visible‐light‐induced free radical polymerization of methyl methacrylate (MMA) and 1,1,1‐trifluoroethyl methacrylate (TFEMA) with a difunctional initiator, dimethyl 2,6‐dibromoheptanedioate (DMDBHD), conjugated with a photoredox catalyst, tris(2‐phenylpyridinato)iridium(III) (fac‐[Ir(ppy)₃]), is investigated. Kinetic studies demonstrate that homopolymerizations of both MMA and TFEMA are controlled radical polymerizations. The linear increase of molecular weights with monomer conversion and the narrow PDIs (1.2–1.4) reveal a good living character. In addition, PTFEMA‐b‐PMMA‐b‐PTFEMA triblock copolymer is prepared by a one‐pot process with sequential monomer addition. The of the triblock copolymers increases linearly with monomer conversion and the PDI of block copolymers is still maintained around 1.2–1.4. Experimental data confirm that the products are pure block polymers. Furthermore, the molar fraction of the TFEMA monomeric unit in the block copolymer is about 21.96%, close to the theoretical value 21.00% calculated from the monomer conversion.

     

Tailor‐Made Soluble Polymer Supports: Synthesis of a Series of ATRP Initiators Containing Labile Wang Linkers

A series of functional initiators for atom transfer radical polymerization (ATRP) was prepared. These structures contain an ATRP initiating site, a labile p‐alkoxybenzyl ester Wang linker and a functional end‐group (i.e., ? COOH, ? N₃, ? OH, ? C?CH, or ? NHFmoc). These novel initiators can be utilized for synthesizing well‐defined soluble polymer supports. For instance, the azide‐, alcohol‐, alkyne‐, and NHFmoc‐ derivatives were tested as initiators for the bulk ATRP of styrene. SEC, MALDI‐TOF‐MS, and NMR measurements indicated that well‐defined polystyrene samples with defined end‐groups have been synthesized in this process. Moreover, it was demonstrated that the labile Wang linkers could be easily cleaved with a mild trifluoroacetic acid treatment.

     

Synthesis of Cross‐Linked Comb Polysiloxane for Polymer Electrolyte Membranes

Summary: A series of comb‐like polysiloxanes was prepared as the base polymer for solvent‐free polymer electrolyte membranes. Hydrosilylation of poly(methylhydrosiloxane) (PMHS) was used to substitute hydrogen by the two types of side groups tetraethylene glycol allyl methyl ether and allyltrimethoxysilane (ATMS) with varying molar ratios between 5 and 40 mol‐% ATMS. The ATMS side groups served to cross‐link as‐prepared polymer electrolyte membranes after dissolving lithium trifluoromethylsulfonate (triflate) or lithium bis(trifluoromethylsulfonyl)imide. The ionic conductivities of these salt‐in‐polymer membranes prepared with a constant concentration of 10 wt.‐% lithium triflate showed a maximum conductivity of 4.6 × 10^?5 S · cm^?1 at 30 °C for 10 mol‐% ATMS substitution. In another series of experiments with the ATMS substitution held constant at 10 mol‐%, the salt concentration was varied yielding a maximum conductivity of 1.4 × 10^?4 S · cm^?1 at 30 °C for 12.5 wt.‐% lithium triflate.

     

Investigation of Thermoresponsive Nano‐Confined Polymer Brushes by AFM‐Based Force Spectroscopy

PNIPAM polymer brushes are synthesized in nanopores of track‐etched membranes. The internal structure of these nano‐confined brushes is studied by AFM force spectroscopy experiments as a function of the synthesis conditions. The approach force vs. distance profiles are fitted using the Alexander‐de Gennes model to determine the grafting density, and the worm‐like chain model is used to estimate the chain length from the retract profiles. The grafting density for brushes synthesized within 80 nm pores is ten times lower than that obtained in 330 nm pores. For the same polymerization time, the chain lengths are much lower if the synthesis is carried out in small pores. The elastic properties of the brushes are also directly related to the confinement conditions.     

Synthesis of Branched Polymers by Means of Living Anionic Polymerization, 9. Radical Coupling Reaction of 1,1‐Diphenylethylene‐Functionalized Polymers with Potassium Naphthalenide and Its Application to Syntheses of In‐Chain‐Functionalized Polymers and Star‐Branched Polymers

Radical coupling reactions of both 1,1‐diphenylethylene (DPE)‐chain‐end‐ and DPE‐in‐chain‐functionalized polymers with potassium naphthalenide have been studied under the conditions mainly in THF at –78°C. Chain‐end‐functionalized polymers having M̄_n values of less than 10 kg/mol were very efficiently coupled in more than 90% yield to afford the polymeric dianion that were dimeric coupled products with two 1,1‐diphenylalkyl anions in the middle of the chains. However, the dimer yield decreased with increasing the molecular weight. The dimer was obtained in 59% yield with use of the chain‐end‐functionalized polymer having M̄_n of 33.9 kg/mol. Well‐defined in‐chain‐functionalized polymers with two benzyl bromide and DPE moieties each have been successfully synthesized by the reaction of the polymeric dianion thus obtained with 1‐(4‐bromobutyl)‐4‐(tert‐butyldimethylsilyloxymethyl)benzene and 1‐[4‐(4‐bromobutyl)phenyl]‐1‐phenylethylene, respectively. The radical coupling reaction of in‐chain‐functionalized polymers with DPE (M̄_n ca. 20 kg/mol) with potassium naphthalenide also proceeded efficiently to afford the coupled products that were A₂A′₂ and A₂B₂ four‐arm star‐branched polymers with well‐defined structures (M̄_n ca. 40 kg/mol).     

Fabrication of Ternary Hybrid Colloids via In‐Situ Polymerization at the Interface of Oil/Water Emulsion

This article describes a simple method to fabricate ternary hybrid colloids by using snowman‐like PEO‐SiO₂/PS colloids as nucleuses at the interface of oil/water emulsion. The ternary hybrid colloids are composed of three parts with asymmetric compositions and constructions, SiO₂ hemisphere with PEO groups, disc‐like or ring‐like cross‐linked poly(4‐vinylbenzyl chloride), and PS hollow sphere. In a certain condition, snowman‐like PEO‐SiO₂/PS colloids, deionized water, divinylbenzene, 4‐vinylbenzyl chloride, and n‐alkane are mixed to form homogenous and stable oil/water emulsion. The snowman‐like PEO‐SiO₂/PS colloids are vertically situated at the interface of oil/water emulsion for their amphiphilicity. At the interface of oil/water emulsion, divinylbenzene and 4‐vinylbenzyl chloride are initiated to polymerize and generate cross‐linked poly(4‐vinylbenzyl chloride) surrounding snowman‐like PEO‐SiO₂/PS colloids and thus PEO‐SiO₂/PVBC/PS colloids are fabricated. This method provides a versatile and modular tool to fabricate ternary hybrid colloids at the interface of oil/water emulsion.     

Synthesis of a Liquid Bisoxazolin‐5‐one by Radical Reaction of Bismercaptan onto 2‐Ethenyloxazolin‐ 5‐one

The synthesis of a liquid chain‐coupling agent obtained by the radical diaddition of bis(mercaptoethyl) ether on 2‐ethenyl‐4,4‐dimethyloxazolin‐5‐one is described. Different methods of synthesis have been studied and their products were characterized by IR, ¹H NMR spectroscopy, and by SEC. The classic thermal radical initiation leads to bisazlactone compounds, but a side reaction of azlactone ring opening occurs, which prevents this product from being employed as a chain‐extender. The low thermal initiation and the UV initiation lead to interesting products, but they are not suitable for being employed as chain‐coupling agent because of their functionality (less or more a difunctional compound). The most interesting method consists in synthesizing by low thermal initiation in a first step, and then in transforming residual 2‐ethenyl‐4,4‐dimethyloxazolin‐5‐one by UV initiation in a second step. The compound is composed by more than 95 per cent of difunctional azlactone compound and a few polyazlactone functional compound. The final compound is a stable liquid at room temperature under nitrogen atmosphere.