Healable network polymers bearing flexible poly(lauryl methacrylate) chains via thermo‐reversible furan‐maleimide diels–alder reaction

A new ATRP initiator containing two furyl rings, namely, bis(furan‐2‐ylmethyl) 2‐bromopentanedioate was synthesized starting from commercially available l ‐glutamic acid as a precursor. Well‐defined bisfuryl‐terminated poly(lauryl methacrylate) macromonomers with molecular weight and dispersity in the range 5000–12,000 g mol^?1 and 1.30–1.37, respectively, were synthesized employing the initiator by atom transfer radical polymerization (ATRP). Independently, 1,1′,1″‐(nitrilotris(ethane‐2,1‐diyl))tris(1H‐pyrrole‐2,5‐dione) was synthesized as a tris‐maleimide counterpart for furan‐maleimide click reaction. Thermo‐reversible network polymer bearing flexible poly(lauryl methacrylate; (PLMA) chains was obtained by furan‐maleimide Diels–Alder click reaction of bisfuryl‐terminated PLMA with 1,1′,1″‐(nitrilotris(ethane‐2,1‐diyl))tris(1H‐pyrrole‐2,5‐dione). The prepared network polymer showed retro‐Diels–Alder reaction in the temperature range 110–170 °C as determined from DSC analysis. The presence of low Tg (–40 °C) PLMA chains induced chain mobility to the network structure which led to the complete scratch healing of the coating at 60 °C in five days due to furan‐maleimide adduct formation. The storage modulus of the network polymer was found to be 3.7 × 10⁴ Pa at the constant angular frequency of 5 rad/sec and strain of 0.5%. The regular reversal of storage (G ′) and loss modulus (G ″) was observed with repeated heating (40 to 110 °C) and cooling cycles (110 to 40 °C) at constant angular frequency and strain. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2700–2712     

Some applications of the diels–alder reaction in organosilicon chemistry

A review of advances in the applications of the Diels–Alder reaction in organosilicon chemistry in our laboratory is presented. Using this reaction, we have synthesized a series of organosilicon monomers and polymers with polyphenyl groups and condensed rings and established a novel vulcanization system for silicone rubber. In addition, we discuss the influences of the large aromatic groups on the properties of the polymers.     

Dendron–polymer conjugates via the diels–alder “click” reaction of novel anthracene‐based dendrons

Diblock and triblock dendron–polymer conjugates containing biodegradable polyester dendron blocks and polyethylene glycol (PEG) polymer were synthesized using the Diels–Alder “click” cycloaddition reaction. PEG polymers with furan‐protected maleimide functionality were synthesized and reacted with biodegradable polyester dendrons containing an anthracene moiety at their focal point. First through third generations of biodegradable polyester dendrons containing an anthracene unit at their focal point were synthesized using a divergent strategy. Efficient conjugation of the dendrons to polymers was demonstrated using ¹HNMR and size exclusion chromatography. This modular approach provides an easy access to the design of multivalent PEG conjugates. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3191–3201     

Various polycarbonate graft copolymers via diels–alder click reaction

In this work, we used Diels–Alder click reaction for the preparation of various types of aliphatic polycarbonates (PCs). We first prepared a novel anthracene‐functionalized cyclic carbonate monomer, anthracen‐9‐ylmethyl 5‐methyl‐2‐oxo‐1,3‐dioxane‐5‐carboxylate (2), followed by ring‐opening polymerization of this monomer to prepare PC with pendant anthracene groups (PC‐anthracene) using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU)/1‐(3,5‐bis(trifloromethyl)phenyl)‐3‐cyclohexylthiourea (TU) as the catalyst and benzyl alcohol as the initiator in CH₂Cl₂ at room temperature. Subsequently, the resulting PC‐anthracene (M_n,TDGPC = 6000 g/mol, M_w/M_n = 1.22) was grafted with a linear α‐furan protected‐maleimide terminated‐poly(methyl methacrylate) (PMMA‐MI) (M_n,GPC = 3100 g/mol, M_w/M_n = 1.31), or poly(ethylene glycol) (PEG‐MI) (M_n,GPC = 550 g/mol, M_w/M_n = 1.09), or a mixture of PMMA‐MI and PEG‐MI to yield well‐defined PC graft or hetero graft copolymers, PC‐g‐PMMA (M_n,TDGPC = 59000 g/mol, M_w/M_n = 1.22) or PC‐g‐PEG, or PC‐g‐(PMMA)‐co‐PC‐g‐(PEG) (M_n,TDGPC = 39900 g/mol, M_w/M_n = 1.16), respectively, using Diels–Alder click reaction in toluene at 110°C. The Diels–Alder grafting efficiencies were found to be over 97% using UV spectroscopy. Moreover, the structural analyses and the molecular weights of resulting graft copolymers were determined via ¹H NMR and triple detection GPC (TD‐GPC), respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A rheological and spectroscopic study on the kinetics of self‐healing in a single‐component diels–alder copolymer and its underlying chemical reaction

In this work, pendant groups with both furan and maleimide moieties were incorporated into a polymethacrylate copolymer with lauryl methacrylate as comonomer to yield a one‐system Diels–Alder (DA) polymer. A combined Fourier transform infrared (FTIR) spectroscopy and rheological study was performed to quantify the extent of the reversible DA reaction and the resulting changes in mechanical properties of the polymer. The kinetics of the retro‐Diels–Alder (rDA) reaction was studied at different temperatures to determine an enthalpy of activation. Control polymers with only one functional moiety, that is, the furan or maleimide, were also synthesized to study the differences in viscoelastic behavior and the absence of self‐healing. Microscratch tests were performed to obtain information about the disappearance of well‐defined intentional surface scratches under different healing conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1669–1675     

Preparation of a Porous polymer by a catalyst‐free diels‐alder reaction and its structural modification by post‐reaction

A microporous polymer is prepared by a catalyst‐free Diels–Alder reaction. A cyclopentadiene with both a diene and a dienophile functionality and a dienophilic maleimide are used for the Diels–Alder reaction. 1,3,5‐Tris(bromomethyl)‐2,4,6‐trimethylbenzene is reacted with sodium cyclopentadienide to produce the multicyclopentadiene‐functionalized monomer. A crosslinked polymer ( CDAP ) is obtained by the reaction of the cyclopentadiene monomer with N,N′‐1,4‐phenylenedimaleimide. The thermal dissociation of the cyclopentadiene dimeric unit and the subsequent Diels–Alder reaction with the maleimide group are investigated by the model reaction. We are able to restructure the crosslinked polymer network by taking advantage of the thermal reversibility of the Diels–Alder linkage. After the post thermal treatment, the BET surface area of the polymer ( CDAP‐T ) is greatly increased from 317 to 1038 m² g^?1. CDAP‐T is functionalized with pyrene by bromination with N‐bromosuccinimide and the subsequent substitution reaction with aminopyrene. The adsorption property of the pyrene‐functionalized polymer for an aromatic dye is investigated using malachite green. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3646–3653     

A Diels‐Alder/retro Diels‐Alder strategy to synthesize polymers bearing maleimide side chains

Polymers containing thiol‐reactive maleimide groups on their side chains have been synthesized by utilization of a novel methacrylate monomer containing a masked maleimide. Diels‐Alder reaction between furan and maleimide was adapted for the protection of the reactive maleimide double bond prior to polymerization. AIBN initiated free radical polymerization was utilized for synthesis of copolymers containing masked maleimide groups. No unmasking of the maleimide group was evident under the polymerization conditions. The maleimide groups in the side chain of the polymers were unmasked into their reactive form by utilization of retro Diels‐Alder reaction. This cycloreversion was monitored by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and ¹H and ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4545–4551, 2007     

Gold‐Catalyzed Cyclization of Furan‐Ynes bearing a Propargyl Carbonate Group: Intramolecular Diels–Alder Reaction with In Situ Generated Allenes

Gold‐catalyzed cyclization of various furan‐ynes with a propargyl carbonate or ester moiety results in the formation of a series of polycyclic aromatic ring systems. The reactions can be rationalized through a tandem gold‐catalyzed 3,3‐rearrangement of the propargyl carboxylate moiety in furan‐yne substrates to form an allenic intermediate, which is followed by an intramolecular Diels–Alder reaction of furan and subsequent ring‐opening of the oxa‐bridged cycloadduct. It was found that the steric and electronic properties of phosphine ligands on the gold catalyst had a significant impact on the reaction outcome. In the case of 1,5‐furan‐yne, the cleavage of the oxa‐bridge in the cycloadduct with concomitant 1,2‐migration of the R¹ group occurs to furnish anthracen‐1(2H)‐ones bearing a quaternary carbon center. For 1,4‐furan‐yne, a facile aromatization of the cycloadduct takes place to give 9‐oxygenated anthracene derivatives.     

Synthesis of 1‐methoxypoly(oxyethylene)benzocyclobutene and its diels–alder reactions

A new poly(ethylene glycol) derivative, 1‐methoxypoly(oxyethylene)benzocyclobutene ( 1 ) was prepared from the reaction of 1‐benzocyclobutenyl 1‐hydroxyethyl ether with mesylate of methoxypoly(oxyethylene) in tetrahydrofuran. The degree of end‐group conversion, as determined by NMR, was 100%. The Diels–Alder reactions of 1 with maleic anhydride and N‐phenylmaleimide were carried out in refluxing toluene to obtain the corresponding adducts ( 2 and 3 , respectively) in excellent yields. NMR analyses of 2 and 3 indicated complete conversion of 1 to the corresponding products. The reaction of 2 with o‐toluidine resulted in complete conversion of the anhydride adduct to the corresponding products. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1934–1938, 2004     

Heterograft brush copolymers via romp and triple click reaction strategies involving CuAAC,diels–alder,and nitroxide radical coupling reactions

In this study, an equimolar mixture of oxanorbornenyl‐anthracene (ONB‐anthracene), oxanorbornenyl‐bromide (ONB‐Br), and oxanorbornenyl tosylate (ONB‐OTs) was polymerized via ring opening metathesis polymerization using the first generation Grubbs' catalyst in CH₂Cl₂ at room temperature to form poly(ONB‐anthracene‐co‐ONB‐Br‐co‐ONB‐OTs)₁₀ copolymer as a main backbone. Next, this main backbone was sequentially clicked with a furan protected maleimide‐terminated poly(methyl methacrylate), 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐terminated poly(ethylene glycol), and alkyne‐terminated poly(ε‐caprolactone) (PCL₂₀‐alkyne) via Diels–Alder, nitroxide radical coupling, and copper‐catalyzed azide‐alkyne cycloaddition, respectively, to yield a poly(ONB‐g‐PMMA‐co‐ONB‐g‐PEG‐co‐ONB‐g‐PCL)₁₀ heterograft brush copolymer © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Preparation of ABC miktoarm star terpolymer containing poly(ethylene glycol), polystyrene,and poly(tert‐butylacrylate) arms by combining diels–alder reaction,atom transfer radical,and stable free radical polymerization routes

The ABC type miktoarm star terpolymer was prepared utilizing “core‐in” and “core‐out” methods via combination of Diels–Alder reaction (DA), stable free radical polymerization (SFRP), and atom transfer radical polymerization (ATRP). First, in DA reaction, poly(ethylene glycol)‐maleimide (PEG‐maleimide) precursor was reacted with succinic acid anthracen‐9‐ylmethyl ester 3‐(2‐bromo‐2‐methyl‐propionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethyl‐piperidin‐1‐yloxy)‐ethoxy‐carbonyl]‐propyl ester, 8 , to give DA adduct, 9 , which has appropriate functional groups for SFRP and ATRP. Second, a previously obtained 9 was used as a macroinitiator for SFRP of styrene at 125 °C. As a third step, this PEG‐polystyrene (PEG‐PSt) precursor with a bromine functionality in the core was employed as a macroinitiator for ATRP of tert‐butylacrylate (tBA) in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 80 °C to give ABC type miktoarm star terpolymer (PEG‐PSt‐PtBA) with controlled molecular weight and low polydispersity (M_w/M_n < 1.27). The obtained polymers were characterized by gel permeation chromatography and ¹H NMR. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 499–509, 2006     

Use of a chromium tricarbonyl complex in a diels–alder reaction: Improved preparation of angularly trifluoromethyl-substituted tetrahydrophenanthrone

The tricarbonyl complex prepared from 1-trifluoromethyldihydronaphthalene and Cr(CO)₃(NH₃)₃ undergoes Diels–Alder cycloaddition under high-pressure conditions (15 kbar) to give after decomplexation by natural light and deprotection, the tetrahydrophenanthrone product in 65% yield. This new methodology allows the activation of unreactive styrenes in Diels–Alder cycloaddition.     

Linear tetrablock quaterpolymers via triple click reactions,azide‐alkyne,diels–alder,and nitroxide radical coupling in a one‐pot fashion

Azide‐alkyne and Diels–Alder click reactions together with a click‐like nitroxide radical coupling reaction were used in a one‐pot fashion to generate tetrablock quaterpolymer. The various living polymerization generated linear polymers with orthogonal end‐functionalities, maleimide‐terminated poly(ethylene glycol) (PEG‐MI), anthracene‐ and azide‐terminated polystyrene, alkyne‐ and bromide‐terminated poly(tert‐butyl acrylate) or alkyne‐poly(n‐butyl acrylate), and tetramethylpiperidine‐1‐oxyl (TEMPO)‐terminated poly(ε‐caprolactone) (PCL‐TEMPO) were clicked together in a one‐pot fashion to generate PEG‐b‐PS‐b‐PtBA‐b‐PCL or PEG‐b‐PS‐b‐PnBA‐b‐PCL quaterpolymer using Cu(0), CuBr, and N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst in dimethyl formamide at 80 °C for 36 h. Linear precursors and target quaterpolymers were analyzed via ¹H NMR and gel permeation chromatography. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of tadpole polymers via triple click reactions: Copper‐catalyzed azide–alkyne cycloaddition,diels–alder,and nitroxide radical coupling reactions

We designed a trifunctional initiator ( 3 ) containing anthracene, bromide, and OH functionalities and subsequently used as an initiator in atom transfer radical Polymerization (ATRP) of styrene to yield linear polystyrene (PS) with α‐anthracene, OH, and ω‐bromide terminal groups, of which bromide is later transformed into azide to result in the linear anthracene‐, OH‐, and azide‐terminated PS (l‐α‐anthracene‐OH‐ω‐azide‐PS). The copper‐catalyzed azide–alkyne cycloaddition reaction between l‐α‐anthracene‐OH‐ω‐azide‐PS and α‐furan‐protected‐maleimide‐ω‐alkyne linkage, 4 afforded the linear anthracene‐, OH‐, and maleimide‐terminated PS. The cyclization via intramolecular Diels–Alder click reaction of this linear PS and the subsequent conversion of the hydroxyl into bromide resulted in the cyclic PS with one bromide located on the ring, (c‐PS)‐Br. Finally, the c‐PS‐Br was clicked with either well‐defined tetramethylpiperidine‐1‐oxyl‐terminated poly(ethylene glycol) (PEG) or poly(ε‐caprolactone) (PCL) yielding the tadpole polymer, (c‐PS)‐b‐PEG or (c‐PS)‐b‐PCL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Maleimide‐based thiol reactive multiarm star polymers via Diels‐Alder/retro Diels‐Alder strategy

Multiarm star polymers containing thiol‐reactive maleimide groups at their core have been synthesized by utilization of atom transfer radical polymerization (ATRP) of various methacrylates using a masked maleimide containing multiarm initiator. One end of the initiator contains multiple halogen groups that produce the star architecture upon polymerization and the other end contains a masked maleimide functional group. Unmasking of the maleimide group after the polymerization provides the thiol reactive maleimide core that is widely used in bioconjugation. Functionalization of the core maleimide group with a thiol containing tripeptide was used to demonstrate facile reactivity of the core of these multiarm polymers under reagent‐free conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2546–2556, 2010     

Biobased poly(2,5‐furandimethylene succinate‐co‐butylene succinate) crosslinked by reversible Diels–Alder reaction

We synthesized biobased poly(2,5‐furandimethylene succinate‐co‐butylene succinate) [P(FS‐co‐BS)] copolymers by polycondensation of 2,5‐bis(hydroxymethyl)furan, 1,4‐butanediol, and succinic acid. These copolymers could be crosslinked to form network polymers by means of a reversible Diels–Alder reaction with bis‐maleimide. The thermal properties, mechanical properties, and healing abilities of the P(FS‐co‐BS)s and the network polymers were investigated. The mechanical properties of the network polymers depended on the comonomer composition of the P(FS‐co‐BS)s and the maleimide/furan ratio in the network polymers. Some of the copolymers exhibited healing ability at room temperature, and their healing efficiency was enhanced by solvent or heat. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 216–222     

Dendronized polymers via Diels–Alder “click” reaction

A modular approach toward the synthesis of polymers containing dendron groups as side chains is developed using the Diels–Alder “click” reaction. For this purpose, a styrene‐based polymer appended with anthracene groups as reactive side chains was synthesized. First through third‐generation polyester dendrons containing furan‐protected maleimide groups at their focal point were synthesized. Facile, reagent‐free, thermal Diels–Alder cycloaddition between the anthracene‐containing polymer and latent‐reactive dendrons leads to quantitative functionalization of the polymer chains to afford dendronized polymers. The efficiency of this functionalization step was monitored using ¹H and ¹³C NMR spectroscopy and FTIR and UV–vis spectrometry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 410–416, 2010     

A Near‐Infrared Photothermal Effect‐Responsive Drug Delivery System Based on Indocyanine Green and Doxorubicin‐Loaded Polymeric Micelles Mediated by Reversible Diels–Alder Reaction

Near‐infrared light (NIR) possesses great advantages for light‐responsive controllable drug release, such as deep tissue penetration and low damage to healthy tissues. Herein, a NIR‐responsive drug delivery system is developed based on a NIR dye, indocyanine green (ICG), and anticancer drug, doxorubicin (DOX)‐loaded thermoresponsive block copolymer micelles, in which the drug release can be controlled via NIR irradiation. First, block copolymers, poly(oligo(ethylene glycol) methacrylate)‐block‐poly(furfuryl methacrylate) (POEGMA‐b‐PFMA), are synthesized by sequential reversible addition‐fragmentation chain‐transfer (RAFT) polymerization, followed by modification with N‐octyl maleimide through Diels–Alder (DA) reaction to produce POEGMA‐b‐POMFMA. The self‐assembly of POEGMA‐b‐POMFMA by nano­precipitation in aqueous solution affords the polymeric micelles which are used to simultaneously encapsulate ICG and DOX. Upon irradiation by NIR light (805 nm), the loaded DOX is released rapidly from the micelles due to partial retro DA reaction and local temperature increase‐induced faster drug diffusion by the photothermal effect. Cytotoxicity evaluation and intracellular distribution observation demonstrate significant synergistic effects of NIR‐triggered drug release, photothermal, and chemotherapy toward cancer cells under NIR irradiation.

     

Synthesis and characterization of organic–inorganic hybrid block copolymers containing a fully condensed ladder‐like polyphenylsilsesquioxane

A series of inorganic–organic hybrid block copolymers were synthesized via atom transfer radical polymerization using a fully condensed, ladder‐like structured polyphenylsilsesquioxane end‐functionalized macroinitiator. The inorganic portion, ladder‐like polyphenylsilsesquioxane, was synthesized in a one‐batch, base‐catalyzed system, whereas organic hard and soft monomers, styrene, and n‐butyl acrylate, were polymerized and copolymerized on the ends of the linear, inorganic backbone. Synthesized hybrid diblock, triblock, and random copolymers were characterized by ¹H NMR, ²⁹Si NMR, gel permeation chromatography, static light scattering, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. Hybrid block copolymers were well‐defined with low polydispersity (<1.4) and exhibited enhanced thermal properties in the form of increased glass transition and degradation onset temperatures over their organic analogues.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012