Synthesis and characterization of hyperbranched polystyrene via click reaction of AB2 macromonomer

Well‐defined hyperbranched polystyrenes have been successfully prepared by polymerization of AB₂ macromonomer, polystyrene containing an azide group at its one end and two terminal propargyl groups at the other end via click reaction. For preparation of AB₂ macromonomers, an ATRP initiator, bispropargyl 2‐bromosuccinate (BPBS) with two propargyl groups and one bromine group was synthesized by the successive bromination and esterification reaction of L ‐aspartic acid. The resulting BPBS initiated the ATRP of St, and subsequently, the terminal bromine groups of (CH≡C)₂‐PS‐Brs were substituted by N₃ via the reaction with sodium azide resulting the AB₂ macromonomer, (CH≡C)₂‐PS‐N₃ with various molecular weights. All intermediates and the resultant polymers were characterized by GPC, ¹H NMR, FTIR, and MALLS methods. The polymerization kinetics study showed fast increase of DP at the initial stage of polymerization and then slow increase of their DP. The final “HyperMacs” have high‐molecular weight up to M_w,MALLS = 340,000 g/mol, their molecular weight distributions were moderately narrow (M_w/M_n = 1.47–1.65). The ratios of [η]_H/[η]_L of the HyperMacs formed in the polymerization system increased with evolution of polymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 454–462, 2010     

Novel fluorinated poly(aryl ether ketone)s

Two novel fluorinated monomers were prepared and polymerized with biphenols to produce amorphous, thermally stable poly(aryl ether ketone)s. The properties of the fluorinated polymers are compared to those of unfluorinated, amorphous poly(aryl ether ketone)s. The presence of fluorine in the polymers was found to cause a decrease in glass transition temperature and Young's moduli, however, no increase in thermal stability was observed. The fluorinated polymers are soluble in common organic solvents such as chloroform and methylene chloride at room temperature, and also show solubility in solvents containing a ketonic moiety, such as acetone. Evidence of polymer branching through fluorines considered to be unreactive under the polymerization conditions was found. Efforts were made to evaluate the reactivity of fluorine atoms under the polymerization conditions using both molecular modeling and ¹⁹F-NMR to ascertain if such branching could be avoided. © 1995 John Wiley & Sons, Inc.     

Photo‐initiated thiol–ene “click” hydrogels from RAFT‐synthesized poly(N‐isopropylacrylamide)

Despite the efficiency and robustness of the widely used copper‐catalyzed 1,3‐dipolar cycloaddition reaction, the use of copper as a catalyst is often not attractive, particularly for materials intended for biological systems. The use of photo‐initiated thiol‐ene as an alternative “click” reaction to synthesize “model networks” is investigated here. Poly(N‐isopropylacrylamide) precursors were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and were designed to have trithiocarbonate moieties as end groups. This structure design provides opportunity for subsequent end‐group modifications in preparation for thiol‐ene “click.” Two reaction routes have been proposed and studied to yield thiol and ene moieties. The advantages and disadvantages of each reaction path were investigated to propose a simple but efficient route to prepare copper‐free “click” hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4626–4636     

Synthesis and characterization of new hyperbranched poly(aryl ether oxadiazole)s

A new AB₂ monomer was synthesized for use in the preparation of a hyperbranched poly(aryl ether oxadiazole) with terminal phenol functionality. The AB₂ monomer contains two phenolic groups and a single aryl fluoride group that is activated toward nucleophilic displacement by the attached oxadiazole ring. The nucleophilic substitution of the fluoride with the phenolate groups led to the formation of an ether linkage. Subsequently, a hyperbranched poly(aryl ether oxadiazole) having approximately a 44% degree of branching, as determined by a combination of model compound studies and ¹H NMR, was obtained. The terminal phenolic groups underwent facile functionalization, furnishing hyperbranched polymers with a variety of functional chain ends. The nature of the chain‐end groups had a significant influence on the physical properties of the polymers, such as the glass‐transition temperature and their solubility. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3851–3860, 2001     

An emerging post‐polymerization modification technique: The promise of thiol‐para‐fluoro click reaction

Post‐polymerization modification (PPM) of polymers is extremely beneficial in terms of designing brand new synthetic pathways toward functional complex polymers. Fortunately, the new developments in the field of organic chemistry along with controlled/living radical polymerization (CLRP) techniques have enabled scientists to readily design and synthesize the functionalized‐polymers for wide range of applications via the PPM. In this regard, the reactivity of para‐fluorine atom in the fluorinated aromatic structures toward the nucleophilic substitution reactions has made the polymers possessing this group to become a very strong candidate that can undergo efficient PPM. Besides, it has been proven that the thiol‐functionalized compounds react with the para‐fluorine atom of the pentafluorophenyl group more rapidly and efficiently than the amine‐ and the hydroxyl‐functionalized compounds. Furthermore, the milder experimental conditions to achieve quantitative conversions have led to the reaction between the thiol and the structures possessing pentafluorophenyl groups to be referred to as a click‐type reaction. Given this information, this review article aims to present the scientific developments regarding the thiol‐para‐fluoro “click” (TPF‐click) chemistry, and its impact on PPM to construct novel polymeric structures. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1181–1198     

Hyperbranched poly(ether–urea)s using AB2‐type blocked isocyanate monomer and azide monomer: Synthesis,characterization, reactive end functionalization,and copolymerization with AB monomer

3,5‐bis(4‐aminophenoxy)phenyl phenylcarbamate—a novel AB₂‐type blocked isocyanate monomer and 3,5‐bis{ethyleneoxy(4‐aminophenoxy)}phenyl carbonyl azide—a novel AB₂‐type azide monomer were synthesized in high yield. Step‐growth polymerization of these monomers were found to give a first example of hyperbranched poly (aryl‐ether‐urea) and poly(aryl‐alkyl‐ether‐urea). Molecular weights (M_w) of the polymer were found to vary from 1,858 to 52,432 depending upon the monomer and experimental conditions used. The polydispersity indexes were relatively narrow due to the controlled regeneration of isocyanate functional groups for the polymerization reaction. The degree of branching (DB) was determined using ¹H‐NMR spectroscopy and the values ranged from 87 to 54%. All the polymers underwent two‐stage decomposition and were stable up to 300 °C. Functionalized end‐capping of poly(aryl‐ether‐urea) using phenylchloroformate and di‐t‐butyl dicarbonate (Boc)₂O changed the thermal properties and solubility of the polymers. Copolymerization of AB₂‐type blocked isocyante monomer with functionally similar AB monomer were also carried out. The molecular weights of copolymers were found to be in the order of 6 × 10⁵ with narrow dispersity. It was found that the T_g's of poly(aryl‐alkyl‐ether‐urea)s were significantly less (46–49 °C) compared to poly(aryl‐ether‐urea)s. Moreover the former showed melting transition at 154 °C, which was not observed in the latter case. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2959–2977, 2007     

Thermal behavior and phase behavior in blends of liquid crystalline poly(aryl ether ketone) and poly(aryl ether ether ketone) containing thioether units

Thermal behavior and phase behavior in blends of liquid crystalline poly(aryl ether ketone) with lateral methoxy groups (M-PAEK) and poly(aryl ether ether ketone) containing thioether units (S-PEEK) have been investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM) techniques. The results indicate that the composition of the blends has great effect on the phase behavior and morphology. Thin films of pure M-PAEK and S-PEEK crystallized from the melts exhibit typical mosaic and spherulitic structures, respectively. For the blends with higher M-PAEK contents (> 50%), an unusual ring-banded spherulite with structural discontinuity is formed. The bright core and rings of the ring-banded spherulites under PLM are composed of M-PAEK phase, while the dark rings consist mainly of S-PEEK phase. For the 50:50 M-PAEK/S-PEEK blend, the ring-banded spherulites and S-PEEK spherulites coexist, which implies that a partial phase separation between the two components takes place in the melting state. In S-PEEK-rich blends, a volume-filled spherulite is produced. In addition, the effect of isothermal crystallization temperature on the phase behavior, especially the ring-banded spherulite formation in the blends, is discussed.     

Injectable poly(ethylene glycol) hydrogels for sustained doxorubicin release

Water‐soluble poly(ethylene glycol) derivatives with multiple “clickable” mercapto groups or double bonds were facilely synthesized in a large scale by direct polycondensation of oligo(ethylene glycol) diol with mercaptosuccinic acid or maleic acid catalyzed by scandium trifluoromethanesulfonate under mild conditions. Injectable hydrogels containing doxorubicin hydrochloride (DOX · HCl) could be rapidly formed using these poly(ethylene glycol) derivatives as precursors via in situ thiol‐ene “click” reaction under physiological conditions without light, initiator, or metal catalyst. DOX · HCl could be sustained released from the hydrogels as a result of the hindrance of the three dimensional hydrogel network on the drug molecules, which makes this kind of DOX‐loaded hydrogels a promising candidate for localized tumor chemotherapy. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of hyperbranched poly(ether nitrile)s by one‐step polycondensation of an AB2 monomer

Hyperbranched poly(ether nitrile)s were prepared from a novel AB₂ type monomer, 2‐chloro‐4‐(3,5‐dihydroxyphenoxy)benzonitrile, via nucleophilic aromatic substitution. Soluble and low‐viscous hyperbranched polymers with molecular weights upto 233,600 (M_w) were isolated. According to the ¹H NMR and GPC data, the unique polymerization behavior was observed, which implies that the weight average molecular weight increased after the number average molecular weight reached plateau region. Model compounds were prepared to characterize the branching structure. Spectroscopic measurements of the model compounds and the resulting polymers, such as ¹H, DEPT ¹³C NMR, and MS, strongly suggest that the ether exchange reaction and cyclization are involved in the propagation reaction. The side reactions would affect the unique polymerization behavior. The resulting polymers showed a good solubility in organic solvents similar to other hyperbranched aromatic polymers. The hydroxy‐terminated polymer was even soluble in basic water. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5835–5844, 2009     

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) and poly(aryl ether ether ketone)

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) (M‐PAEK) and poly(aryl ether ether ketone) (PEEK) has been investigated by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), and scanning electron microscopy (SEM) techniques. The measurements reveal that the formation of the rhythmically grown ring‐banded spherulites in the M‐PAEK/PEEK blends is strongly dependent on the blend composition. In the M‐PAEK‐rich blends, upon cooling, an unusual ring‐banded spherulite is formed, which is ascribed to structural discontinuity caused by a rhythmic radial growth. For the 50:50 M‐PAEK/PEEK blend, ring‐banded spherulites and individual PEEK spherulites coexist in the system. In the blends with PEEK as the predominant component, M‐PAEK is rejected into the boundary of PEEK spherulites. The cooling rate and crystallization temperature have great effect on the phase behavior, especially the ring‐banded spherulite formation in the blends. In addition, the effects of M‐PAEK phase transition rate and phase separation rate on banded spherulite formation is discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3011–3024, 2007     

Synthesis and characterization of star graft copolymers with asymmetric mixed “V‐shaped” side chains via “click” chemistry on a hyperbranched polyglycerol core

The star graft copolymers composed of hyperbranched polyglycerol (HPG) as core and well defined asymmetric mixed “V‐shaped” identical polystyrene (PS) and poly(tert‐butyl acrylate) as side chains were synthesized via the “click” chemistry. The V‐shaped side chain bearing a “clickable” alkyne group at the conjunction point of two blocks was first prepared through the combination of anionic polymerization of styrene (St) and atom transfer radical polymerization of tert‐butyl acrylate (tBA) monomer, and then “click” chemistry was conducted between the alkyne groups on the side chains and azide groups on HPG core. The obtained star graft copolymers and intermediates were characterized by gel permeation chromatography (GPC), GPC equipped with a multiangle laser‐light scattering detector (GPC‐MALLS), nuclear magnetic resonance spectroscopy and fourier transform infrared. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1308–1316, 2009     

Synthesis and characterization of fluorinated poly(aryl ether ketone)s containing 1,4-naphthalene moieties

The new monomer 2,2-bis[4-(4-{4-fluorobenzoyl}-1-naphthoxy)phenyl]hexafluoropropane ( 2 ) was synthesized in a two-step reaction sequence. 2,2-his[4-(1-naphthoxy)phenyl]-hexafluoropropane ( 1 ) was prepared using the Ullmann ether synthesis reaction of 4,4-(hex-afluoroisopropylidiene)diphenol with 1-bromonaphthalene. Friedel-Crafts acylation of 1 with 4-fluorobenzoyl chloride in methylene chloride containing dimethylsulfone selectively afforded 2 in 82% yield. The polycondensation of 2 with various bisphenols in DMAc in the presence of an excess of potassium carbonate as a condensation reagent was carried out at 165°C to quantitatively afford the corresponding fluorinated poly(aryl ether ketone)s containing 1,4-naphthalene moieties. Thermal analysis of the polymers showed them to have T_gs ranging from 194 to 230°C and to be thermally stable in air up with initial weight losses at about 500°C. In addition, these novel polymers exhibited excellent solubility in organic solvents including NMP, DMAc, and chloroform. © 1997 John Wiley & Sons, Inc.     

Tadpole‐shaped amphiphilic copolymers prepared via RAFT polymerization and click reaction

The tadpole‐shaped amphiphilic copolymers with cyclic polystyrene as the head and a linear poly(N‐isopropylacrylamide) as the tail have been successfully synthesized by combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and “click” reaction. The synthesis involves two main steps: (1) preparation of a linear acetylene‐terminated PNIPAAM‐b‐PS with a side azido group anchored at the junction between two blocks; (2) intramolecular cyclization reaction to produce the cyclic PS block using “click” chemistry under high dilution. The structures, molecular weights, and molecular weight distributions of the resulted intermediates and the target polymers were characterized by their ¹H NMR, FTIR, and gel permeation chromatography. The difference of surface property between tadpole‐shaped polymer and its linear precursor was observed, and the water contact angles on the former surface are larger than that of the latter surface. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2390–2401, 2008     

One‐pot synthesis of soluble and fluorescent aliphatic hyperbranched poly(amide‐imide) with solvent‐dependent emission

Aliphatic hyperbranched poly(amide‐imide) was facilely prepared by employing a functional thiolactone‐maleimide monomer. Highly efficient, selective and quantitative properties of amine‐maleimide Michael addition and aminolysis of a thiolactone guaranteed the generation of an ABB' thiol‐yne intermediate without side products, followed by consecutive thiol‐yne click reaction in one‐pot. The hyperbranched structure of the poly(amide‐imide) was confirmed by NMR spectroscopy and triple‐detector GPC/SEC analysis. Additionally, due to the presence of aminosuccinimide fluorophores and intrinsic physical property of hyperbranched polymers, this aliphatic hyperbranched poly(amide‐imide) possessed solvent‐dependent emission and presented good solubility in various organic solvents. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2053–2060     

Synthesis of ω‐phosphonated poly(ethylene oxide)s through the combination of kabachnik–fields reaction and “click” chemistry

The synthesis of new ω‐phosphonic acid‐terminated poly(ethylene oxide) (PEOs) monomethyl ethers was investigated by the combination of Atherton–Todd or Kabachnik–Fields reactions and the “click” copper‐catalyzed 1,3‐dipolar cycloaddition of azides and terminal alkynes. The Atherton–Todd route fails to give the corresponding phosphonic acid‐terminated PEOs due to competitive cleavage of the P? N bond during the dealkylation step. In contrast, the Kabachnik–Fields route leads with very good yields to ω‐phosphonic acid‐PEO through “click” reaction of azido‐PEO onto dimethyl aminopropargyl phosphonate prepared by Kabachnik–Fields reaction between propargylbenzylimine and dimethyl phosphonate, followed by acidic hydrolysis. The reported methodology, precluding the use of anionic polymerization of ethylene oxide, leads to novel well‐defined phosphonic acid‐terminated PEOs from commercially available products in good yields. Moreover, such a strategy can be adapted to anchor phosphonic acid functionality onto a wide range of polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of a novel graft copolymer with hyperbranched poly(glycerol) as core and “Y”‐shaped polystyrene‐b‐poly(ethylene oxide)2 as side chains

The graft copolymers composed of “Y”‐shaped polystyrene‐b‐poly(ethylene oxide)₂ (PS‐b‐PEO₂) as side chains and hyperbranched poly(glycerol) (HPG) as core were synthesized by a combination of “click” chemistry and atom transfer radical polymerization (ATRP) via “graft from” and “graft onto” strategies. Firstly, macroinitiators HPG‐Br were obtained by esterification of hydroxyl groups on HPG with bromoisobutyryl bromide, and then by “graft from” strategy, graft copolymers HPG‐g‐(PS‐Br) were synthesized by ATRP of St and further HPG‐g‐(PS‐N₃) were prepared by azidation with NaN₃. Then, the precursors (Bz‐PEO)₂‐alkyne with a single alkyne group at the junction point and an inert benzyl group at each end was synthesized by sequentially ring‐opening polymerization (ROP) of EO using 3‐[(1‐ethoxyethyl)‐ethoxyethyl]‐1,2‐propanediol (EEPD) and diphenylmethylpotassium (DPMK) as coinitiator, termination of living polymeric species by benzyl bromide, recovery of protected hydroxyl groups by HCl and modification by propargyl bromide. Finally, the “click” chemistry was conducted between HPG‐g‐(PS‐N₃) and (Bz‐PEO)₂‐alkyne in the presence of N,N,N′,N″,N”‐pentamethyl diethylenetriamine (PMDETA)/CuBr system by “graft onto” strategy, and the graft copolymers were characterized by SEC, ¹H NMR and FTIR in details. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Amphiphilic PEG‐grafted poly(ester‐carbonate)s: Synthesis and diverse nanostructures in water

Novel biodegradable amphiphilic graft copolymers containing hydrophobic poly(ester‐carbonate) backbone and hydrophilic poly(ethylene glycol) (PEG) side chains were synthesized by a combination of ring‐opening polymerization and “click” chemistry. First, the ring‐opening copolymerization of 5,5‐dibromomethyl trimethylene carbonate (DBTC) and ε‐caprolactone (CL) was performed in the presence of stannous octanoate [Sn(Oct)₂] as catalyst, resulting in poly(DBTC‐co‐CL) with pendant bromo groups. Then the pendant bromo groups were completely converted into azide form, which permitted “click” reaction with alkyne‐terminated PEG by Huisgen 1,3‐dipolar cycloadditions to give amphiphilic biodegradable graft copolymers. The graft copolymers were characterized by proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectra and gel permeation chromatography measurements, which confirmed the well‐defined graft architecture. These copolymers could self‐assemble into micelles in aqueous solution. The size and morphologies of the copolymer micelles were measured by transmission electron microscopy and dynamic light scattering, which are influenced by the length of PEG and grafting density. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Synthesis of linear and hyperbranched poly(etherketone)s containing flexible oxyethylene spacers

As an alternative to strong acid reaction media for the Friedel–Crafts acylation for a polymer‐forming reaction, a mild polyphosphoric acid (PPA) with optimized amount of phosphorous pentoxide (P₂O₅) has been tested for the polymerization of AB monomers 4‐(2‐phenoxyethoxy)benzoic acid and 3‐(2‐phenoxyethoxy)benzoic acid, and an AB₂ monomer 3,5‐bis(2‐phenoxyethoxy)benzoic acid. The reaction progress of AB₂ monomer was conveniently traced by FTIR spectroscopy monitoring aromatic ketone (C?O) stretching bands arisen from carboxylic acid groups at the chain ends and carbonyl groups in the backbone as a function of reaction time at 110 °C. The resultant linear and hyperbranched polymers containing flexible oxyethylene spacers, which were prone to be hydrolyzed in strong acids at elevated temperature, displayed high intrinsic viscosities. Thus, the reaction medium PPA/P₂O₅ mixture as an electrophilic substitution reaction was indeed benign not to depolymerize growing polymer molecules but strong enough for the direct generation of carbonium ion from carboxylic acid to promote efficient polymerization. The resultant hyperbranched poly(etherketone) (PEK) displayed the best solubility among samples. All PEKs showed good thermal stability; glass transition temperatures were in the range of 90–117 °C; 5% weight loss generally occurred at greater than 345 °C in air. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5112–5122, 2007     

Calixarene‐centered amphiphilic A2B2 miktoarm star copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol): Synthesis and self‐assembly behaviors in water

Novel calixarene‐centered amphiphilic A₂B₂ miktoarm star copolymers composed of two PCL arms and two PEG arms with calix[4]arene as core moiety were synthesized by the combination of CROP and “click” chemistry. First, a heterotetrafunctional calix[4]arene derivative with two hydroxyl groups and two alkyne groups was designed as a macroinitiator to prepare calixarene‐centered PCL homopolymers (C4‐PCL) by CROP in the presence of Sn(Oct)₂ as catalyst at 110 °C. Next, azide‐terminated PEG (A‐PEG) was synthesized by tandem treating methoxy poly(ethylene glycol)s (mPEG) with 4‐chlorobutyryl chloride and NaN₃. Finally, copper(I)‐catalyzed cycloaddition reaction between C4‐PCL and A‐PEG led to A₂B₂ miktoarm star copolymer [C4S(PCL)₂‐(PEG)₂]. ¹H NMR, FT‐IR, and SEC analyses confirmed the well‐defined miktoarm star architecture. These amphiphilic miktoarm star copolymers could self‐assemble into multimorphological aggregates in water. The calix[4]arene moieties with a cavity <1 nm on the hydrophilic/hydrophobic interface of these aggregates may provide potential opportunities to entrap guest molecules for special applications in supermolecular science. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010