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     

Preparation of 3‐arm star polymers (A3) via Diels–Alder click reaction

Diels–Alder click reaction was successfully applied for the preparation of 3‐arm star polymers (A₃) using furan protected maleimide end‐functionalized polymers and trianthracene functional linking agent (2) at reflux temperature of toluene for 48 h. Well‐defined furan protected maleimide end‐functionalized polymers, poly (ethylene glycol), poly(methyl methacrylate), and poly(tert‐butyl acrylate) were obtained by esterification or atom transfer radical polymerization. Obtained star polymers were characterized via NMR and GPC (refractive index and triple detector detection). Splitting of GPC traces of the resulting polymer mixture notably displayed that Diels–Alder click reaction was a versatile and a reliable route for the preparation of A₃ star polymer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 302–313, 2008     

Multiarm star block copolymers via Diels‐Alder click reaction

Two types of multiarm star block copolymers: (polystyrene)_m‐poly(divinylbenzene)‐poly(methyl methacrylate)_n, (PS)_m‐polyDVB‐(PMMA)_n and (polystyrene)_m‐poly(divinylbenzene)‐poly(tert‐butyl acrylate)_k, (PS)_m‐polyDVB‐(PtBA)_k were successfully prepared via a combination of cross‐linking and Diels–Alder click reactions based on “arm‐first” methodology. For this purpose, multiarm star polymer with anthracene functionality as reactive periphery groups was prepared by a cross‐linking reaction of divinyl benzene using α‐anthracene end functionalized polystyrene (PS‐Anth) as a macroinitiator. Thus, obtained multiarm star polymer was then reacted with furan protected maleimide‐end functionalized polymers: PMMA‐MI or PtBA‐MI at reflux temperature of toluene for 48 h resulting in the corresponding multiarm star block copolymers via Diels–Alder click reaction. The multiarm star and multiarm star block copolymers were characterized by using ¹H NMR, SEC, Viscotek triple detection SEC (TD‐SEC) and UV. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 178–187, 2009     

Polymer grafting onto polyurethane backbone via Diels–Alder reaction

The aliphatic polyurethane with pendant anthracene moieties (PU‐anthracene) was prepared from polycondensation of anthracen‐9‐yl methyl 3‐hydroxy‐2‐(hydroxymethyl)‐2‐methylpropanoate (anthracene diol), 1 with hexamethylenediisocyanate in the presence of dibutyltindilaurate in CH₂Cl₂ at room temperature for 10 days. Thereafter, the PU‐anthracene (M_n,GPC = 12,900 g/mol, M_w/M_n = 1.87, relative to PS standards) was clicked with a linear α‐furan protected‐maleimide terminated‐poly(methyl methacrylate) (PMMA‐MI) (M_n,GPC = 2500 g/mol, M_w/M_n = 1.33), or ‐poly(ethylene glycol) (PEG‐MI) (M_n,GPC = 550 g/mol, M_w/M_n = 1.09), to result in well‐defined PU‐graft copolymers, PU‐g‐PMMA (M_n,GPC = 23800 g/mol, M_w/M_n = 1.65, relative to PS standards) or PU‐g‐PEG (M_n,GPC = 11,600 g/mol, M_w/M_n = 1.45, relative to PS standards) using Diels–Alder reaction in dioxane/toluene at 105 °C. The Diels–Alder grafting efficiencies were found to be over 93–99% using UV spectroscopy. Moreover, the structural analyses and the thermal transitions of all copolymers were determined via ¹H NMR and DSC, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 521–527     

Block‐brush copolymers via ROMP and sequential double click reaction strategy

We report an efficient way, sequential double click reactions, for the preparation of brush copolymers with AB block‐brush architectures containing polyoxanorbornene (poly (ONB)) backbone and poly(ε‐caprolactone) (PCL), poly(methyl methacrylate) (PMMA) or poly(tert‐butyl acrylate) (PtBA) side chains: poly(ONB‐g‐PMMA)‐b‐poly(ONB‐g‐PCL) and poly(ONB‐g‐PtBA)‐b‐poly(ONB‐g‐PCL). The living ROMP of ONB affords the synthesis of well‐defined poly(ONB‐anthracene)₂₀‐b‐poly (ONB‐azide)₅ block copolymer with anthryl and azide pendant groups. Subsequently, well‐defined linear alkyne end‐functionalized PCL (PCL‐alkyne), maleimide end‐functionalized PMMA (PMMA‐MI) and PtBA‐MI were introduced onto the block copolymer via sequential azide‐alkyne and Diels‐Alder click reactions, thus yielding block‐brush copolymers. The molecular weight of block‐brush copolymers was measured via triple detection GPC (TD‐GPC) introducing the experimentally calculated dn/dc values to the software. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Sequential double polymer click reactions for the preparation of regular graft copolymers

In this study, graft copolymers with regular graft points containing polystyrene (PS) backbone and poly(methyl methacrylate) (PMMA), poly(tert‐butyl acrylate) (PtBA), or poly (ethylene glycol) (PEG) side chains were simply achieved by a sequential double polymer click reactions. The linear α‐alkyne‐ω‐azide PS with an anthracene pendant unit per chain was produced via atom transfer radical polymerization of styrene initiated by anthracen‐9‐ylmethyl 2‐((2‐bromo‐2‐methylpropanoyloxy)methyl)‐2‐methyl‐3‐oxo‐3‐(prop‐2‐ynyloxy) propyl succinate. Subsequently, the azide–alkyne click coupling of this PS to create the linear multiblock PS chain with pendant anthracene sites per PS block, followed by Diels–Alder click reaction with maleimide end‐functionalized PMMA, PtBA, or PEG yielded final PS‐g‐PMMA, PS‐g‐PtBA or PS‐g‐PEG copolymers with regular grafts, respectively. Well‐defined polymers were characterized by ¹H NMR, gel permeation chromatography (GPC) and triple detection GPC. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Orthogonal multifunctionalization of aliphatic polycarbonate via sequential Michael addition and radical‐thiol‐ene click reactions

Aliphatic polycarbonate (PC) copolymer is synthesized by ring opening copolymerization of acrylate‐ and allyl‐functional cyclic carbonate monomers. The post‐polymerization functionalization of the resulting copolymer is performed quantitatively using a variety of thiol compounds via sequential Michael addition and photo‐induced radical thiol‐ene click reactions within relatively short reaction time at ambient temperature. This metal‐free click chemistry methodology affords the synthesis of biocompatible PC copolymer with multifunctional groups. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1581–1587     

Quadruple click reactions for the synthesis of cysteine‐terminated linear multiblock copolymers

Synthesis of cysteine‐terminated linear polystyrene (PS)‐b‐poly(ε‐caprolactone) (PCL)‐b‐poly(methyl methacrylate) (PMMA)/or poly(tert‐butyl acrylate)(PtBA)‐b‐poly(ethylene glycol) (PEG) copolymers was carried out using sequential quadruple click reactions including thiol‐ene, copper‐catalyzed azide–alkyne cycloaddition (CuAAC), Diels–Alder, and nitroxide radical coupling (NRC) reactions. N‐acetyl‐L ‐cysteine methyl ester was first clicked with α‐allyl‐ω‐azide‐terminated PS via thiol‐ene reaction to create α‐cysteine‐ω‐azide‐terminated PS. Subsequent CuAAC reaction with PCL, followed by the introduction of the PMMA/or PtBA and PEG blocks via Diels–Alder and NRC, respectively, yielded final cysteine‐terminated multiblock copolymers. By ¹H NMR spectroscopy, the DP_ns of the blocks in the final multiblock copolymers were found to be close to those of the related polymer precursors, indicating that highly efficient click reactions occurred for polymer–polymer coupling. Successful quadruple click reactions were also confirmed by gel permeation chromatography. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

One‐pot synthesis of star‐block copolymers using double click reactions

3‐Arm star‐block copolymers, (polystyrene‐b‐poly(methyl methacrylate))₃, (PS‐b‐PMMA)₃, and (polystyrene‐b‐poly(ethylene glycol))₃, (PS‐b‐PEG)₃, are prepared using double‐click reactions: Huisgen and Diels–Alder, with a one‐pot technique. PS and PMMA blocks with α‐anthracene‐ω‐azide‐ and α‐maleimide‐end‐groups, respectively, are achieved using suitable initiators in ATRP of styrene and MMA, respectively. However, PEG obtained from a commercial source is reacted with 3‐acetyl‐N‐(2‐hydroxyethyl)‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2‐carboxamide (7) to give furan‐protected maleimide‐end‐functionalized PEG. Finally, PS/PMMA and PS/PEG blocks are linked efficiently with trialkyne functional linking agent 1,1,1‐tris[4‐(2‐propynyloxy)phenyl]‐ethane 2 in the presence of CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) at 120 °C for 48 h to give two samples of 3‐arm star‐block copolymers. The results of the peak splitting using a Gaussian deconvolution of the obtained GPC traces for (PS‐b‐PMMA)₃ and (PS‐b‐PEG)₃ displayed that the yields of target 3‐arm star‐block copolymers were found to be 88 and 82%, respectively. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7091–7100, 2008     

V‐shaped graft copolymers via triple click reactions: Diels–alder,copper‐catalyzed azide–alkyne cycloaddition,and nitroxide radical coupling

We report here a simple and universal synthetic pathway covering triple click reactions, Diels–Alder, copper‐catalyzed azide–alkyne cycloaddition (CuAAC), and nitroxide radical coupling (NRC), to prepare well‐defined graft copolymers with V‐shaped side chains. The Diels–Alder click reaction between the furan protected‐maleimide‐terminated poly(ethylene glycol) (PEG) and a trifunctional core ( 1 ) carrying an anthracene, alkyne, and bromide was carried out to yield the corresponding α‐alkyne‐ and α‐bromide‐terminated PEG (PEG‐alkyne/Br) in toluene at 110 °C. Subsequently, the polystyrene or polyoxanorbornene with pendant azide functionality as a main backbone is reacted with the PEG‐alkyne/Br and 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO)‐terminated poly(ε‐caprolactone) using the CuAAC and NRC reactions in a one‐pot fashion in N,N′‐dimethylformamide at room temperature to result in the target V‐shaped graft copolymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4667–4674     

One‐pot double click reactions for the preparation of H‐shaped ABCDE‐type quintopolymer

We employed for the first time double click reactions: Cu(I) catalyzed azide‐alkyne 1,3‐dipolar cycloaddition and Diels–Alder (4 + 2) reactions for the preparation of H‐shaped polymer possessing pentablocks with different chemical nature (H‐shaped quintopolymer) using one‐pot technique. H‐shaped quintopolymer consists of poly(ethylene glycol) (PEG)‐poly(methylmethacrylate) (PMMA) and poly(ε‐caprolactone) (PCL)‐polystyrene (PS) blocks as side chains and poly (tert‐butylacrylate) (PtBA) as a main chain. For the preparation of H‐shaped quintopolymer, PEG‐b‐PMMA and PCL‐b‐PS copolymers with maleimide and alkyne functional groups at their centers, respectively, were synthesized and simply reacted in one‐pot with PtBA with α‐anthracene‐ω‐azide end functionalities in N,N‐dimethylformamide (DMF) using CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as catalyst at 120 °C for 48 h. The precursors and the target H‐shaped quintopolymer were characterized comprehensively by ¹H NMR, UV, FTIR, GPC, and triple detection GPC. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3409–3418, 2009     

3‐miktoarm star terpolymers using triple click reactions: Diels–Alder,copper‐catalyzed azide‐alkyne cycloaddition,and nitroxide radical coupling reactions

Well‐defined linear furan‐protected maleimide‐terminated poly(ethylene glycol) (PEG‐MI), tetramethylpiperidine‐1‐oxyl‐terminated poly(ε‐caprolactone) (PCL‐TEMPO), and azide‐terminated polystyrene (PS‐N₃) or ‐poly(N‐butyl oxanorbornene imide) (PONB‐N₃) were ligated to an orthogonally functionalized core ( 1 ) in a two‐step reaction mode through triple click reactions. In a first step, Diels–Alder click reaction of PEG‐MI with 1 was performed in toluene at 110 °C for 24 h to afford α‐alkyne‐α‐bromide‐terminated PEG (PEG‐alkyne/Br). As a second step, this precursor was subsequently ligated with the PCL‐TEMPO and PS‐N₃ or PONB‐N₃ in N,N‐dimethylformamide at room temperature for 12 h catalyzed by Cu(0)/Cu(I) through copper‐catalyzed azide‐alkyne cycloaddition and nitroxide radical coupling click reactions, yield resulting ABC miktoarm star polymers in a one‐pot mode. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Graft copolymers via ROMP and Diels–Alder click reaction strategy

Anthracene‐functionalized oxanorbornene monomer and oxanorbornenyl polystyrene (PS) with ω‐anthracene end‐functionalized macromonomer were first polymerized via ring‐opening metathesis polymerization using the first‐generation Grubbs' catalyst in dichloromethane at room temperature and then clicked with maleimide end‐functionalized polymers, poly(ethylene glycol) (PEG)‐MI, poly(methyl methacrylate) (PMMA)‐MI, and poly(tert‐butyl acrylate) (PtBA)‐MI in a Diels–Alder reaction in toluene at 120 °C to create corresponding graft copolymers, poly(oxanorbornene)‐g‐PEG, poly(oxanorbornene)‐g‐PMMA, and graft block copolymers, poly(oxanorbornene)‐g‐(PS‐b‐PEG), poly(oxanorbornene)‐g‐(PS‐b‐PMMA), and poly(oxanorbornene)‐g‐(PS‐b‐PtBA), respectively. Diels–Alder click reaction efficiency for graft copolymerization was monitored by UV–vis spectroscopy. The dn/dc values of graft copolymers and graft block copolymers were experimentally obtained using a triple detection gel permeation chromatography and subsequently introduced to the software so as to give molecular weights, intrinsic viscosity ([η]) and hydrodynamic radius (R_h) values. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Multiarm star block and multiarm star mixed‐block copolymers via azide‐alkyne click reaction

The synthesis of multiarm star block (and mixed‐block) copolymers are efficiently prepared by using Cu(I) catalyzed azide‐alkyne click reaction and the arm‐first approach. α‐Silyl protected alkyne polystyrene (α‐silyl‐alkyne‐PS) was prepared by ATRP of styrene (St) and used as macroinitiator in a crosslinking reaction with divinyl benzene to successfully give multiarm star homopolymer with alkyne periphery. Linear azide end‐functionalized poly(ethylene glycol) (PEG‐N₃) and poly (tert‐butyl acrylate) (PtBA‐N₃) were simply clicked with the multiarm star polymer described earlier to form star block or mixed‐block copolymers in N,N‐dimethyl formamide at room temperature for 24 h. Obtained multiarm star block and mixed‐block copolymers were identified by using ¹H NMR, GPC, triple detection‐GPC, atomic force microscopy, and dynamic light scattering measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 99–108, 2010     

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     

In situ preparation of hetero-polymers/clay nanocomposites by CUAAC click chemistry

A series of polymer/clay nanocomposites containing mechanistically two different polymers, poly(ethylene glycol) (PEG) and poly(epsilon caprolactone) (PCL), were prepared by simultaneous copper(I)-catalyzed alkyne-azide cycloaddition click reactions. Both clickable polymers, PEG-Alkyne and PCL-Alkyne, were simultaneously clicked on to azide-functional montmorillonite (MMT-N₃) nanoclay to get corresponding PEG-PCL/MMT nanocomposites. The chemical structures of the resulting nanocomposites were verified by following azide and silicone-oxygen bands using FT-IR and characteristic bands of PEG and PCL segments using ¹H-NMR spectroscopy. The combined XRD and TEM analysis confirmed that all PEG-PCL/MMT nanocomposites had partially exfoliated/intercalated morphologies. In addition, the increase of MMT-N₃ loading not only improved the onset and maximum degradation temperatures of the nanocomposites but also their char yields. Furthermore, the incorporation of MMT-N₃ in the polymer matrix did not significantly influence the crystallization behavior of both PEG and PCL segments.     

Heteroarm H‐shaped terpolymers through click reaction

Heteroarm H‐shaped terpolymers, (polystyrene)(poly(methyl methacrylate))‐ poly(tert‐butyl acrylate)‐(polystyrene)(poly(methyl methacrylate)), (PS)(PMMA)‐PtBA‐(PMMA)(PS), and, (PS)(PMMA)‐poly(ethylene glycol)(PEG)‐(PMMA)(PS), through click reaction strategy between PS‐PMMA copolymer (as side chains) with an alkyne functional group at the junction point and diazide end‐functionalized PtBA or PEG (as a main chain). PS‐PMMA with alkyne functional group was prepared by sequential living radical polymerizations such as the nitroxide mediated (NMP) and the metal mediated‐living radical polymerization (ATRP) routes. The obtained H‐shaped polymers were characterized by using ¹H‐NMR, GPC, DSC, and AFM measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1055–1065, 2007     

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     

ABCD 4‐miktoarm star quarterpolymers using click [3 + 2] reaction strategy

Two samples of ABCD 4‐miktoarm star quarterpolymer with A = polystyrene (PS), B = poly(ε‐caprolactone) (PCL), C = poly(methyl methacrylate) (PMMA) or poly(tert‐butyl acrylate) (PtBA), and D = poly(ethylene glycol) (PEG) were prepared using click reaction strategy (Cu(I)‐catalyzed Huisgen [3 + 2] reaction). Thus, first, predefined block copolymers of different polymerization routes, PS‐b‐PCL with azide and PMMA‐b‐PEG and PtBA‐b‐PEG copolymers with alkyne functionality, were synthesized and then these blocks were combined together in the presence of Cu(I)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as a catalyst in DMF at room temperature to give the target 4‐miktoarm star quarterpolymers. The obtained miktoarm star quarter polymers were characterized by GPC, NMR, and DSC measurements. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1218–1228, 2008