Novel structural motifs in macromolecular chemistry are introduced by the use of the Asinger multicomponent reaction. The combination of ammonia, acetone, α‐chloroisobutyraldehyde, and either water or sodium hydrosulfide, leads to an oxazoline or thiazoline scaffold, respectively, which is subsequently modified with 10‐undecenol and 10‐undecenoyl chloride to obtain heterocycle‐functionalized α,ω‐dienes. These substrates are used as monomers in an acylic diene metathesis (ADMET) or thiol‐ene step‐growth polymerization. The thus‐obtained polymers are studied in post‐polymerization modifications, like hydrogenation and oxidation. Here, the thiazolidine‐ and oxazolidine‐containing polymers show dramatically different chemical stability due to the heterocyclic moieties.
A new polymeric material utilizing a highly efficient as well as reversible thiol‐ene click reaction is presented. For this purpose, a trithiol is reacted with a bisbenzylcyanoacetamide derivative resulting in the formation of a dynamic polymer network. The self‐healing ability of this novel material is tested by scratch healing experiments. Healing is found to take place from 60 °C onward. The underlying healing mechanism is studied in detail using temperature‐dependent Raman spectroscopy confirming the reversible opening of the thiol‐ene adducts. Additionally, the thermal and mechanical properties are investigated by differential scanning calorimetry, thermogravimetric analysis, and rheological measurements proving the network formation as well as its reversibility during the thermal treatment.
A green route is reported for functionalizing polyphosphazene via the thiol‐ene click reaction in an aqueous medium. Poly[bis(allylamino)phosphazene] is used as the precursor polymer, which is easily dissolved in water containing 5% (v/v) phosphoric acid, but barely dissolved in other acidic aqueous solutions with the same pH value. Three thiol reagents, namely, 3‐mercapto‐1,2‐propanediol, 2‐mercaptoethoxy ethanol, and l ‐cysteine, are then reacted with the precursor in the phosphoric acid aqueous solutions. 1H and 31P NMR analyses confirm that the allyl polyphosphazene can be quantitatively modified by the mercaptans without hydrolysis degradation during the synthesis and purification processes. Moreover, these polyphosphazenes exhibit higher regioselectivity than those functionalized in organic solvents. This method provides a facile route for the green synthesis of functional polyphosphazenes without organic solvents.
The functionalization of porous microgels with polyamines is presented along with their partial conversion into carbamates with CO2 for an efficient loading and release via electrostatic interactions. The resulting ammonium carbamate particles switch their charge from negative at pH 10 to positive at pH 5 and present a zwitterionic state at pH 7. Thus, they can easily be loaded with both cationic and anionic molecules. Furthermore, the ammonium carbamate functionalization allows for an efficient release at pH values between 5.0 and 7.4, whereas classical functionalization with carboxy‐ or amine‐groups requires pH values below pH 4 or above pH 9. This versatile and easy‐to‐install functionalization has a great potential for various applications, such as the loading and release of drugs or nanoparticles from hydrogels.
Thiol‐ene photopolymerizations combine the unique features of step‐growth reactions and photoinitiated polymerizations, so that they experience a growing interest for applications such as coatings or dental restoratives. Most studies have making use of a relatively flexible ester and the hydrolytically labile derivative pentaerythritoltetra(3‐mercaptopropionate) ( PETMP ) as the thiol component in common. In this study, the performance of hydrolytically stable 1,3,5‐tris(3‐mercaptopropyl)‐1,3,5‐triazine‐2,4,6‐trione ( 4a ), 1,3,5‐tris(2‐methyl‐3‐mercapto‐propyl)‐1,3,5‐triazine‐2,4,6‐trione ( 4b ), and oligomers thereof in thiol‐ene photopolymerizations is investigated. The oligomers are prepared via thiol‐Michael or thiol‐isocyanate additions by using 4a and suitable diacrylates or diisocyanates containing a rigid core structure. Compared with PETMP , the thiol derivative 4a shows better flexural strength and modulus of elasticity in thiol‐ene photopolymerizations with 1,3,5‐triallyl‐1,3,5‐triazine‐2,4,6‐trione ( TATATO ) as the‐ene derivative. This phenomenon becomes especially evident after storage in water at 37 °C for 24 h. Furthermore, the performance regarding the flexural strength, the Young's modulus of elasticity, the polymerization shrinkage stress of 4a , and the polyadducts thereof in dental filling composites is evaluated and discussed.
The synthesis of three different electron‐deficient internal alkynes for the metal‐free 1,3‐dipolar azide–alkyne cycloaddition is shown. The alkynes are polymerized with several multifunctional azides and the reaction enthalpy (ΔH) is investigated by differential scanning calorimetry (DSC). The mechanical properties of the resulting polymers are analyzed using nanoindentation. The polymerization results in hard materials with an E‐modulus of maximum 2.5 GPa, which make them interesting in particular for biomedical applications.
A new monomer, N‐hexenylacrylamide, is copolymerized with N‐isopropylacrylamide by reversible addition‐fragmentation chain transfer (RAFT) polymerization using a carboxylic‐acid‐functionalized RAFT agent. Subsequently, the resulting functional copolymers are reacted with acetylated thiogalactose via a thiol‐ene reaction. After deprotection of the sugar acetyl groups, the glycopolymers show a lower critical solution temperature (LCST) behavior, as confirmed by turbidity measurements. One of these glycopolymers is subsequently immobilized onto solid supports. The obtained products are characterized by attenuated total reflection Fourier transform IR (ATR FTIR) spectroscopy, thermal gravimmetric analysis (TGA), and elemental analysis, confirming the immobilization of the glycopolymer. Additionally, the glycopolymer‐functionalized support shows interaction with the lectin RCA120.
Here, the formation of nanoparticles based on a microemulsion approach and the use of polymer surfactants are described. Therefore, two amphiphilic poly(2‐oxazoline) block copolymers P1 and P2 with alkyne groups in their hydrophobic block have been synthesized by ring‐opening, cationic polymerization. The polymers P1 and P2 are employed in a microemulsion process to stabilize the particle core by core cross‐linking of 1,6‐hexanediol diacrylate (HDDA) using either AIBN as azo‐initiator or 2‐propanethiol as a photo‐initiator for the polymerization reaction. The results show that particle size can be controlled by sonication time, the hydrophilic–hydrophobic balance of the polymer surfactant, and the ratio of polymer surfactant versus HDDA giving access to water‐soluble nanoparticles in a size range of 10–70 nm.
The synthesis of polymers with various functional groups has always been the core of polymer chemistry. Traditionally, there are two approaches to prepare such polymers: i) preparing functional monomers first and then conducting polymerization to get target functional polymers; and ii) post‐modification of a precursor polymer. Both methods unavoidably involve separation and purification of intermediate products, which is laborious and time‐consuming. A one‐pot synthesis strategy, which combines monomer preparation and controlled polymerization in just one reactor to generate well‐defined polymers efficiently, is thus proposed. Recent advances in the one‐pot synthesis of multifunctional polymers through a multicomponent system are provided in this article.
Functional nanowires with photochromic spiropyran (SP) species are prepared by reversible addition–fragmentation transfer (RAFT) dispersion polymerization of styrene using poly(4‐vinylpyridine‐co‐spiropyranyl methacrylate) as a macro‐RAFT agent, and then electrospinning technology is used to fabricate fibers from the functional nanowires. The photoisomerization of SP in the nanowires and fibers is studied, and reversible photochromism for both nanowires and fibers is observed. Since the merocyanine (ME form) of the SP emits fluorescence and the SP form is non‐fluorescent, the fluorescence of the nanowires and the fibers can be switched on and off upon alternating UV and visible‐light irradiation.
Chemo‐enzymatic methods are powerful tools for the synthesis of novel materials. By combining the flexibility of chemical synthesis and the high selectivity of enzymes, a variety of functional materials can be achieved. In the present study, a series of α,ω‐thiol telechelic oligoesters with varying amount of internal alkenes are prepared using selective lipase catalysis and are subsequently cross‐linked by thiol‐ene chemistry yielding alkene functional networks. Due to the reactivity of thiols and alkenes almost all present thiol‐ene systems consist of two components. This work demonstrates that selective lipase catalysis in combination with renewable monomers with internal alkenes is a promising system for achieving one‐component thiol‐alkene functional resins with good storage stability and a high degree of thiol end‐groups. The developed chemo‐enzymatic route yields polymer networks with tailored amount of alkene functionalities in the final thermoset, which facilitate further postmodification.
The self‐organization of colloids into defined structures offers the possibility to develop novel materials with exciting properties. However, this requires the understanding and application of the forces governing interparticle association. A novel approach for a size‐dependent anisotropic assembly between nanoparticles is achieved. Janus‐like iron oxide/polystyrene hybrid nanocolloids are prepared by heterophase polymerization and selectively coated with silica on the iron oxide face to gradually form a cavity. Hence, a shallow surface around the hydrophobic polymer face is created, enabling smaller particles of the same nature to be locked by shape complementarity and colloidal steric stabilization. Further coating with silica fixes these assemblies and allows quantitative analysis of the interaction on a nanoscale.
The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)3] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)3/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 105 g mol‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)3/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).
Unsaturated polyesters are synthesized via ring‐opening copolymerization of α‐methylene‐δ‐valerolactone and δ‐valerolactone. These polyesters 4a–c are mixed with ethyl methacrylate (EMA), 2‐hydroxyethyl methacrylate (HEMA), and α‐methylene‐δ‐valerolactone (α‐MVL), respectively. Then, crosslinking is carried out by free radical polymerization initiated by an azo‐initiator. A second glass transition is found with incorporation of HEMA and α‐MVL. These findings indicate the formation of phase‐separated polyester blocks crosslinked with the poly(meth)‐acrylic‐segments, respectively poly(α‐methylene‐δ‐valerolactone) segments.
Four‐arm poly(l ‐2‐hydroxybutanoic acid) [P(L‐2HB)]/poly(d ‐lactic acid) (PDLA) blends are phase‐separated to form P(L‐2HB)‐rich and PDLA‐rich domains. Hetero‐stereocomplex (HTSC) crystallization should occur at the interface of two types of domains. The crystallization temperature ranges, wherein HTSC crystallites, P(L‐2HB), and PDLA homocrystallites are crystallizable in the star‐shaped 4‐arm P(L‐2HB)/PDLA blends, are much narrower than those reported for linear 1‐arm P(L‐2HB)/PDLA blends, indicating that the star‐shaped architecture disturbs the isothermal crystallization of the blends. Exclusive HTSC crystallization is not observed for the star‐shaped 4‐arm blends during isothermal crystallization in marked contrast with the result reported for the linear 1‐arm blends.
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.
Recently, graphene and its derivative nanosheets have been considered as potential candidates for gas barrier membranes. Here, the effect on the water‐vapor barrier properties of incorporating graphene nanoplatelets into a UV‐curable perfluoropolyether methacrylic oligomer is investigated. By combining the hydrophobicity of the highly fluorinated polymer with the tortuous path induced by the graphene sheets, the barrier properties of the crosslinked films are further enhanced, acting both on the thermodynamic (low solubility) and kinetic (longer diffusion path) contribution of the water‐vapor diffusion through the polymeric films. Good performance in increasing water‐vapor barrier properties at a very low filler loading is obtained: the permeability is halved in the presence of only 0.3 wt% graphene.
Narrowly distributed (N‐isopropylacrylamide) (NIPAM) polymers are prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. After successful cleavage of the trithiocarbonate end groups (thiol generation), they can be grafted to styrene‐butadiene rubber (SBR) by a radical thiol‐ene reaction leading to various grafted SBR‐copolymers. During the grafting reaction, no crosslinking or branching of the SBR can be observed. Measurements of the contact angle of water show that the lower critical solution temperature (LCST) properties of the PNIPAM fraction affect the SBR. Films of the graft‐copolymer exhibit a distinct hydrophilicity below the LCST, while they show hydrophobic behavior above the LCST. Rheological measurements reveal a physical crosslinking of the functionalized SBR due to nanophase separation of the PNIPAM chains (hard phase) in the unpolar SBR. Compared with blends of SBR and PNIPAM, the PNIPAM‐grafted SBR possesses a much finer distribution of the PNIPAM domains (10–30 nm) within the matrix. In addition, two novel difunctional chain‐transfer agents are used, leading to difunctional PNIPAM, enabling a covalent crosslinking of SBR.
Polystyrenes (PS) end‐functionalized with perfluorotridecyl (PFTD), perfluorodecyl (PFD), and perfluoroheptyl (PFH) groups are synthesized using the corresponding perfluoroalkyl initiators by atom transfer radical polymerization. Polymer thin films deposited on silicon wafers are studied by dynamic nanoindentation (NI). NI measurements of the 15k PFTD‐PS sample showed increases of about 80 and 300% in the storage and loss moduli, respectively, compared to the 15k PS homopolymer. Measurements made on different regions of the PFTD‐functionalized PS show a fivefold greater standard deviation compared to the 15k PS homopolymer. The effects for the PFD and PFH groups are smaller in all respects consistent with expectations.
Poly(2‐(3‐butenyl)‐2‐oxazoline)s (PBOX) with glucose‐S‐butyl (Glc) and perfluoroalkyl‐S‐butyl (F) side chains (three samples: Glc/F = 100/0, 0/100, and 88/12) are synthesized by ring‐opening polymerization of 2‐butenyl‐2‐oxazoline and thiol‐ene click photochemistry, and their thermal properties are analyzed by direct‐pyrolysis mass spectrometry. Significant changes in the thermal stability and thermal‐degradation products are observed depending on the structure of the side chain. The thermal degradation of PBOX‐Glc and PBOX‐F homopolymers starts with loss of side chains at relatively low temperatures and successive cleavage along the side and main chains follows. The stability of the glucose units of the PBOX‐Glc/F copolymer is significantly increased by the presence of perfluoroalkyl groups, attributable to OH···F hydrogen bonding interactions during pyrolysis.
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