Pendant Vinyl Research Articles

Acrylate-Based PEG Hydrogels with Ultrafast Biodegradability for 3D Cell Culture.

Poly(ethylene glycol) (PEG)-based hydrogels are particularly challenging to degrade, which hinders efficient cell harvesting within the gel matrix. Here, highly branched copolymers of PEG methyl ether acrylate (PEGMA) and disulfide diacrylate (DSDA) (PEG-DS) with short primary chains and multiple pendent vinyl groups were synthesized by a "vinyl oligomer combination" approach. PEG-DS readily cross-links with thiolated gelatin (Gel-SH) to form hydrogels. Results demonstrate that shortening the primary chains of PEG-DS significantly enhances the viability of bone marrow mesenchymal stem cells (BMSCs) by up to 193.2%. Importantly, DS junctions can be easily cleaved into short primary chains using dithiothreitol (DTT), triggering ultrafast degradation of PEG-DS/Gel-SH hydrogels within 2 min under mild conditions and release of the encapsulated BMSCs. This study establishes a novel strategy to enhance the degradation of acrylate-based PEG hydrogels for three-dimensional (3D) cell culture and harvesting. These findings expand the potential applications of such hydrogels in various biomedical fields.

Photopolymerization of polyvinylethylene glycol oligomers by thiol‐ene click reaction

AbstractFunctional polyvinylethylene glycols (PVEGs) with pendent vinyl groups were synthesized by Pd/B synergistic catalysts and their structures were characterized by 1H NMR and FT‐IR. The photopolymerization of the obtained PVEGs with multifunctional thiols in the presence of a photoinitiator proceeded smoothly via thiol‐ene photo‐click reaction to give a series of crosslinked materials by the variation of the molecular weight of PVEGs and a ratio of thiols and enes. The curing behavior was studied by FT‐IR and the properties of crosslinked materials were characterized by the test of gel content, swelling ratio, and water absorption. The dynamic mechanical analysis, mechanical properties, thermogravimetry, and surface properties of the crosslinked materials were investigated and the performance of coating for the crosslinked film materials was also characterized. The crosslinked film materials can be further functionalized by post‐crosslinking modification through thiol‐ene photo‐click reaction.

Icephobic Durability of Molecular Brush-Structured PDMS Soft Coatings.

The accumulation of ice can pose numerous inconveniences and potential hazards, profoundly affecting both human productivity and daily life. To combat the challenges posed by icing, extensive research efforts have been dedicated to the development of low-ice adhesion surfaces. In this study, we harness the power of molecular dynamics simulations to delve into the intricate dynamics of polymer chains and their role in determining the modulus of the material. We present a novel strategy to prepare ultralow-modulus poly(dimethylsiloxane) (PDMS) elastomers with a molecular brush configuration as icephobic materials. The process involves grafting monohydride-terminated PDMS (H-PDMS) as side chains onto backbone chain PDMS with pendant vinyl functional groups to yield a molecular brush structure. The segments of this polymer structure effectively restrict interchain entanglement, thereby rendering a lower modulus compared to traditional linear structures at an equivalent cross-linking density. The developed soft coating exhibits a remarkably ultralow ice adhesion strength of 13.1 ± 1.1 kPa. Even after enduring 50 cycles of icing and deicing, the ice adhesion strength of this coating steadfastly stayed below 16 kPa, showing no notable increase. Importantly, the molecular brush coating applied to glass demonstrated an impressive light transmittance of 92.1% within the visible light spectrum, surpassing the transmittance of bare glass, which was measured at 91.3%. This icephobic coating with exceptional light transmittance offers a wide range of applications and holds significant potential as a practical icephobic material.

A commercially viable solution process to control long-chain branching in polyethylene.

In polyolefins, long-chain branching is introduced through an energy-intensive, high-pressure radical process to form low-density polyethylene (LDPE). In the current work, we demonstrated a ladder-like polyethylene architecture through solution polymerization of ethylene and less than 1 mole % of α,ω-dienes, using a dual-chain catalyst. The ladder-branching mechanism requires catalysts with two growing polymer chains on the same metal center, thus enchaining the diene without the requirement of a steady-state concentration of pendant vinyl groups. Molecular weight distributions lacking a high-molecular weight tail, distinctive Mark-Houwink signatures, nuclear magnetic resonance characterization, and shear and extensional rheology consistent with highly branched polyethylene architectures are described. This approach represents an industrially viable solution-polymerization process capable of producing controlled long-chain branched polyethylene with rheological properties comparable to those of LDPE or its blends with linear low-density polyethylene (LLDPE).

Synthesis of polyvinylethylene glycols (PVEGs) via polyetherification of vinylethylene carbonate by synergistic catalysis.

An efficient and controllable polyetherification of vinylethylene carbonate (VEC) using diols as initiators is developed. By using a synergistic catalysis with palladium and boron reagents under mild conditions, the polymerization process enables the regioselective production of a series of polyvinylethylene glycols (PVEGs) bearing pendent vinyl groups in high yields with accurate molecular weight control and narrow molecular weight distribution. The utility of PVEGs is demonstrated by the production of functional polyurethanes and post-polymerization modification via thiol-ene photo-click chemistry.

Degradation of poly(vinyl sulfone carbonate) in aqueous media

A cyclic vinyl sulfone carbonate monomer has previously been developed and used to prepare degradable polymers through ring-opening copolymerization with cyclic ester monomers such as L-lactide. The resulting polymers have the advantage of being functionalized by reaction of the pendant vinyl sulfone moiety. However, the hydrolytic susceptibility of repeating units of the vinyl sulfone carbonate was never examined. Herein, we demonstrate that block copolymers prepared with this monomer and using methoxy poly(ethylene glycol) and 4-arm poly(ethylene glycol) as initiators are readily hydrolysable in micelle form in pH 7.4 phosphate buffer, whereas non-water soluble poly(vinyl sulfone carbonate) is resistant to hydrolysis, exhibiting little mass loss over 32 weeks. A degradation mechanism was proposed for the block copolymer micelles wherein the backbone carbonate linkage is susceptible to nucleophile attack by a hydroxyl ion due to the metal ion coordinating with the pendant thioether-vinyl sulfone group allowing access of hydroxyl ions to the carbonyl carbon of the carbonate group. The non-water soluble poly(vinyl sulfone carbonate) is only very slowly hydrolyzed due to restricted water access to the polymer backbone. Further, the block copolymers remained hydrolytically degradable following reaction of the pendant vinyl sulfone. These findings should prove useful for the broader application of this monomer in developing functionalized biodegradable polymers.

Photocatalytic Metal‐Free Radical Hydrosilylation for Polymer Functionalization†

Comprehensive SummaryPost‐modification of polymers offers a route to prepare functionalized polymers through efficient chemical reactions, and hydrosilylation is one of the most effective strategies. Silane‐functionalized polymers have found a wide range of potential applications, such as adhesives, rubbers, and drug delivery agents. For decades, the hydrosilylation for the post‐modification of polymers has typically used transition metals as catalysts. Metal‐free hydrosilylation strategies that can avoid metal residues in polymers are largely lacking in this field. Herein, we report the photocatalytic metal‐free radical hydrosilylation strategy for the post‐modification of polymers bearing pendant vinyl groups using the organic photocatalyst and hydrogen atom transfer (HAT) catalyst under blue light irradiation. We used monofunctional silanes to functionalize polymers and the bis(silane)s as crosslinkers to prepare crosslinked polymers.

Early bird gets the network: The relative importance of reactivity ratios, Ψ parameter, and crosslinker level on gel formation in FRP

AbstractNetwork topology is manipulated in free‐radical copolymerization via proper selection of crosslinker type and its respective properties when paired with specific monomers. Our prior work has focused on the impact of the reduced reactivity parameter Ψ applied to a pendent vinyl, characteristic for each monomer/crosslinker pair, yet here we assess the relative importance of the comonomer reactivity ratios to see whether one factor can counterbalance the other. The traditional reactivity ratio determines when the crosslinker molecule is incorporated into the polymer backbone, while the reduced reactivity Ψ parameter relates to the efficiency of the resulting pendent side chain vinyl being utilized to form a crosslink node at some later point during the polymerization. Both factors are then contrasted with simply the overall loading of crosslinker. Either n‐butyl methacrylate (n‐BMA) or styrene (STY) was chosen as a primary backbone monomer to copolymerize with one of three crosslinkers: 1,4‐butanediol dimethacylate (BDDMA), 1,4‐butanediol diacrylate (BDDA), or divinylbenzene (DVB). Both kinetics and gel can be most dramatically boosted when a crosslinker is applied having a reactivity ratio favouring early insertion. This in turn leads to an earlier onset of gel formation, which ultimately results in greater final gel content. This amplification of both kinetics and gel can overcome an otherwise small Ψ due to crosslinker or main monomer choice. This reactivity ratio effect was further confirmed by Monte Carlo simulations. By whatever mechanism (higher Ψ, lower rA, or higher crosslinker level), earlier onset of gelation produces more gel overall and a tighter network topology.

Mono-material product design with bio-based, circular, and biodegradable polymers

Mono-material product design with bio-based, circular, and biodegradable polymers

Cross‐linked polystyrene and polydivinylbenzene release significant amounts of carbon monoxide and hydrogen at ambient temperature

AbstractCross‐linked polystyrene and polydivinylbenzene (PDVB) have unreacted pendant vinyl groups. They readily undergo aging or oxidation with air even at room temperature, giving rise to formation of OH and  (CO)CH3 groups within the polymers. We now report that the aging process involves the release of carbon monoxide (CO) and hydrogen (H2) in significant amounts at 40 °C and the rate increases with time and temperature. The amounts of CO and H2 released from PDVB at a given temperature can be expressed using a polynomial equation of Aa = Bt + Ct2, where Aa is the accumulated amount, t is the time in the unit of day, and B and C are the coefficients. The coefficients B and D increase with increasing temperature. This result shows that the storage rooms for the above polymers and their composites should be well ventilated to prevent inhalation of CO by the workers and H2‐induced potential hazards.

Synthesis of Hyper-cross-linked Nonpolar Polystyrene Divinylbenzene Resins by Pendent Vinyl Groups and Application to the Decolorization of Cane Molasses.

Cane molasses is a by-product of sugar industry. It is widely used in fermentation field, but pigment compounds affect its further application. In this study, nonpolar hyper-cross-linked adsorption resins (HCARs) were synthesized by pendent vinyl groups cross-linking reaction, and were applied to decolorization of molasses. The correlation between the structure and the decolorization performance of HCARs was studied, and the results showed that the Brunauer-Emmett-Teller (BET) surface area and the pore volume of the resin significantly increased to 574.4 m2·g-1 and 1.40 cm3·g-1 after the Friedel-Crafts alkylation reaction with a catalyst dosage of 2.25% at 343K for 7h. Furthermore, the decolorization rate of molasses by the HCAR was 74%, and recycle decolorization performance of the resin was stable. The adsorption kinetics results showed that the pseudo-second-order dynamic model could more realistically reflect the decolorization mechanism of molasses on HCARs, and liquid film diffusion is the main rate-limiting step. The results of fixed-bed experiments show that D-ST-DVB resin has a good decolorization effect and recycling ability. Therefore, it is a feasible strategy for the decolorization of molasses with nonpolar HCAR.

Controlled functionalization of polypropylene by VETEMPO-mediated radical chemistry

New chemistry for grafting maleic anhydride (MAn) and N-aryl maleimides to a propylene homopolymer is described. Whereas conventional peroxide-initiated maleations are accompanied by extensive degradation, formulations containing a small amount of 4-vinyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (VETEMPO) can meet graft content targets while minimizing melt viscosity losses. The first stage of a VETEMPO-mediated process involves alkyl radical trapping by nitroxyl to yield polymer-bound alkoxyamines bearing pendant vinyl ether functionality. Subsequently, copolymerization between vinyl ether and MAn builds polymer molecular weight while offsetting the degradation incurred by the standard MAn grafting mechanism. The result is a lightly branched, maleated product with a melt viscosity close to that of the starting material. This VETEMPO-based copolymerization strategy is adapted to generate thermoset PP derivatives by peroxide-initiated reactions of VETEMPO with an appropriate difunctional monomer such as N,N′-1,3-phenylene dimaleimide (PDM).

Preparation of degradable aliphatic polyester elastomers with tunable strength and elasticity via photo‐crosslinking

AbstractDegradable polyester elastomers are highly desirable for biomedical applications. Here, highly transparent and degradable aliphatic polyester elastomers were prepared using the ring‐opening copolymerization (ROCP) of commercial monomers, followed by a photo‐crosslinking process. A series of the semi‐crystalline copolyester (PMBL‐co‐PBL‐co‐PCL) precursors with different molecular weights and pendent vinyl contents were synthesized by one‐pot ROCP of α‐methylene‐γ‐butyrolactone (MBL), ε‐caprolactone (ε‐CL) and γ‐butyrolactone (γ‐BL). Then, UV irradiation was applied to photo‐crosslink the precursors to obtain several elastomers. The obtained aliphatic polyester elastomers (CPEs) displayed excellent mechanical properties with high tensile strength (11.3 MPa), high elongation at break (1300%) and high elastic recovery (about 99% after 10 hysteresis cycles). In addition, the elastomer showed much better stability than uncrosslinked (co)polyesters, but maintained degradability in the basic aqueous solution, with ~30% of the mass loss in 1 M NaOH solution after 30 days. Through efficient ROCP, we demonstrated a strategy to prepare degradable CPEs bearing high strength, good elasticity, excellent resilience and degradation capability, which can serve as sustainable elastomers for various applications.

Butyl rubber as a macro-cross-linker in the preparation of a shape-memory and self-healing polymer

Recently, a simple strategy was developed for preparing interconnected interpenetrating polymer networks (IPNs) based on butyl rubber (IIR) and poly(n-octadecyl acrylate) (PC18A). Solvent-free UV polymerization of n-octadecyl acrylate (C18A) monomer in the melt of IIR at ambient temperature resulted in IPNs with self-healing and shape-memory functions. Here, we demonstrate that the use of IIR grafted with acrylic acid, methacrylic acid, and 10-undecenoic acid instead of unmodified IIR provides a significant improvement in the mechanical properties of IPNs. Differential scanning calorimetry, small-angle x-ray scattering, and wide-angle x-ray scattering analysis reveal side-by-side packing of C18 side chains of PC18A to form lamellar crystals with a melting temperature Tm between 46 and 52 °C. Transmission electron microscopy analysis indicates the existence of quasispherical nanoparticles composed of crystalline domains, which are dispersed in a continuous interpenetrating rubber-PC18A matrix. This microstructure provides them a complete self-recovery behavior induced by heating and an efficient shape-memory function. IPNs exhibit around tenfold higher chemical cross-link density as compared to those prepared from the native IIR, reflecting the effect of pendant vinyl groups on the extent of covalent interconnections between the IIR and PC18A components. The type of the grafted monomers significantly affects the mechanical performance of IPNs, which can be explained with the individual contributions of chemical and physical cross-links to the total cross-link density. The amount of the grafted rubbers in IPN could be further increased up to 80 wt. % by the incorporation of toluene into the reaction system, resulting in IPNs with a wide range of tunable thermal and mechanical properties.

Antifouling and chlorine-resistant cyclodextrin loose nanofiltration membrane for high-efficiency fractionation of dyes and salts

Antifouling loose nanofiltration membranes are prepared for effective fractionation of dyes and salts by the construction of a porous cyclodextrin polymer layer on membrane substrate. Octopus-shaped cyclodextrin macromonomers with pendant vinyl groups can be facilely prepared via a union of controlled radical polymerization and esterification reaction, which are then used to fabricate membrane. The surface-initiated photopolymerization of β-cyclodextrin-centered macromonomers could yield a porous polymer layer on the surface of the PVDF substrate. The porous structure could be well-tuned by adjusting the concentration of macromonomers or regulating the polymerization time. The optimal loose nanofiltration membranes have demonstrated high-efficiency separation ability for different dyes and low rejection ability for salts (<10%), owing to the selective layer of porous cyclodextrin polymer. Meanwhile, it maintains a high Congo red (CR) retention (∼99%) in a long-term filtration test. Furthermore, the cyclodextrin polymer layer also endows the membranes with predominant chlorine-resistance performance even after 15 days of immersion in sodium hypochlorite solution. The flux recovery ratio value of optimal membrane towards bovine serum albumin is 97.6% even after 5 antifouling cycles, and the antifouling ability is more than 10 times higher than that of the pristine PVDF membrane depending on the degree of membrane fouling by CR. The proposed strategy could provide helpful guidance in preparing antifouling loose nanofiltration membranes.

Enzymatic synthesis, post-polymerization modification and cross-linking of functionalized poly(β-thioether ester) with pendant vinyl group

Vinyl-functionalized poly(β-thioether ester) (PVTE) was synthesized by enzyme-catalyzed polymerization using immobilized lipase B from Candida antarctica (CALB) for the first time. Four different functionalized monomers were prepared and three polymerization strategies including polycondensation (PC), ring-opening polymerization (ROP), and ring-opening and condensation copolymerization (ROCCP) were investigated. The influences of reaction conditions such as polymerization temperature, time, and monomer ratio on the molecular weight of functionalized poly(β-thioether ester)s were also studied. Both the homopolymer and copolymers were characterized by NMR, SEC, TGA and DSC. Moreover, these poly(β-thioether ester)s containing pendant double bonds toward postfunctionalization were demonstrated by photoinitiated thiol-ene click chemistry and Michael addition reaction, providing a way to cross-linked polyester gels.

Tunable and recyclable polyesters from CO2 and butadiene.

Carbon dioxide is inexpensive and abundant, and its prevalence as waste makes it attractive as a sustainable chemical feedstock. Although there are examples of copolymerizations of CO2 with high-energy monomers, the direct copolymerization of CO2 with olefins has not been reported. Here an alternative route to functionalizable, recyclable polyesters derived from CO2, butadiene and hydrogen via an intermediary lactone, 3-ethyl-6-vinyltetrahydro-2H-pyran-2-one, is described. Catalytic ring-opening polymerization of the lactone by 1,5,7-triazabicyclo[4.4.0]dec-5-ene yields polyesters with molar masses up to 13.6 kg mol-1 and pendent vinyl side chains that can undergo post-polymerization functionalization. The polymer has a low ceiling temperature of 138 °C, allowing for facile chemical recycling, and is inherently biodegradable under aerobic aqueous conditions (OECD-301B protocol). These results show that a well-defined polyester can be derived from CO2, olefins and hydrogen, expanding access to new polymer feedstocks that were once considered unfeasible.

Reactions of Alkyl‐Substituted Rhenacyclobutadiene Complexes with Electron‐Rich Alkynes

AbstractThe reactivity of low‐valent alkyl‐substituted metallacyclobutadienes towards electron‐rich alkynes was studied. Treatment of the alkyl‐substituted rhenacyclobutadiene complexes Re{−C(R)=C(CO2Et)C(OEt)=}(CO)4 (R=Me, Et) with HC≡COEt produced a mixture of the cyclopentadienyl complexes Re{η5‐C5H(R)(CO2Et)(OEt)2}(CO)3 and the new rhenacyclobutadienes Re{−C(OEt)=C[C(R)=CH(CO2Et)]C(OEt)=}(CO)4 bearing a pendant vinyl substituent C(R)=CH(CO2Et) at the β‐carbon. The reactions proceed through initial nucleophilic attack of the terminal carbon of HC≡COEt on the ReC(R) carbon of the starting rhenacyclobutadienes. The rhenacyclobutadiene complex Re{−C(Me)=C(CO2Et)C(OEt)=}(CO)4 reacted with aminoalkynes RC≡CNEt2 (R=Ph, Me) to produce the unusual coupling products Re{−C(OEt)=C(CO2Et)C[CH=C(NEt2)CH2R]=}(CO)4, metallacyclobutadiene complexes bearing the vinyl substituent CH=C(NEt2)CH2R at an α‐carbon. The mechanisms of the reactions are discussed.

Zinc-Mediated Allylation-Lactonization One-Pot Reaction to Methylene Butyrolactones: Renewable Monomers for Sustainable Acrylic Polymers with Closed-Loop Recyclability.

Despite biomass-derived methylene butyrolactone monomers having great potential in substituting the petroleum-based methacrylates for synthesizing the sustainable acrylic polymers, the possible industrial production of these cyclic monomers is unfortunately not practical due to moderate overall yields and harsh reaction conditions or a time-consuming multistep process. Here we report a convenient and effective synthetic approach to a series of biomass-derived methylene butyrolactone monomers via a zinc-mediated allylation-lactonization one-pot reaction of biorenewable aldehydes with ethyl 2-(bromomethyl)acrylate. Under simple room-temperature sonication conditions, near-quantitative conversions (>90%) can be accomplished within 5-30 min, providing pure products with high isolated yields of 70-80%. Their efficient polymerizations with a high degree of control and complete chemoselectivity were enabled by the judiciously chosen Lewis pair catalyst based on methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) [MeAl(BHT)2] Lewis acid and 3-diisopropyl-4,5-dimethylimidazol-2-ylidene (I i Pr) Lewis base, affording new poly(methylene butyrolactone)s with high thermal stability and thermal properties tuned in a wide range as well as pendant vinyl groups for postfunctionalization. Through the development of an effective depolymerization setup (370-390 °C, ca. 100 mTorr, 1 h, a muffle furnace), thermal depolymerizations of these polymers have been achieved with monomer recovery up to 99.8%, thus successfully constructing sustainable acrylic polymers with closed-loop recyclability.

Silicon-Doped Graphene Oxide Quantum Dots as Efficient Nanoconjugates for Multifunctional Nanocomposites.

Graphene oxide quantum dots (GOQDs) hold great promise as a new class of high-performance carbonaceous nanomaterials due to their numerous functional properties, such as tunable photoluminescence (PL), excellent thermal and chemical stability, and superior biocompatibility. In this study, we developed a facile, one-pot, and effective strategy to engineer the interface of GOQDs through covalent doping with silicon. The successful covalent attachment of the silane dopant with pendant vinyl groups to the edges of the GOQDs was confirmed by an in-depth investigation of the structural and morphological characteristics. The Si-GOQD nanoconjugates had an average dimension of ∼8 nm, with a graphite-structured core and amorphous carbon on their shell. We further used the infrared nanoimaging based on scattering-type scanning near-field optical microscopy to unveil the spectral near-field response of GOQD samples and to measure the nanoscale IR response of its network; we then demonstrated their distinct domains with strongly enhanced near fields. The doping of Si atoms into the sp2-hybridized graphitic framework of GOQDs also led to tailored PL emissions. We then sought to explore the potential applications of Si-GOQDs on the surface of plastic films where poly(dimethylsiloxane) (PDMS) served as a bridge to tightly anchor the Si-GOQDs to the surface. The bi-layered coated films which were built with co-assembly of Si-GOQDs and PDMS contributed to suppressing the transmission of water molecules due to the generation of compact and less accessible passing sites, achieving a nearly twofold reduction in water permeability compared to the single-layered coated films. The nanoindentation and PeakForce quantitative nanomechanical mapping showed that Si-GOQD-coated substrates were softer and more deformable than those coated only with PDMS. The co-assembly of PDMS and Si-GOQDs yielded films that were less stiff than those made from PDMS alone. Our findings provided conceptual insights into the importance of nanoscale surface engineering of GOQDs in conferring excellent dispersibility and enhancing the performance of nanocomposite films.