Synthesis and characterization of novel resorcinarene‐centered amphiphilic star‐block copolymers consisting of eight ABA triblock arms by combination of ROP,ATRP, and click chemistry

Novel amphiphilic eight‐arm star triblock copolymers, star poly(ε‐caprolactone)‐block‐poly(acrylic acid)‐block‐poly(ε‐caprolactone)s (SPCL‐PAA‐PCL) with resorcinarene as core moiety were prepared by combination of ROP, ATRP, and “click” reaction strategy. First, the hydroxyl end groups of the predefined eight‐arm SPCLs synthesized by ROP were converted to 2‐bromoesters which permitted ATRP of tert‐butyl acrylate (tBA) to form star diblock copolymers: SPCL‐PtBA. Next, the bromide end groups of SPCL‐PtBA were quantitatively converted to terminal azides by NaN₃, which were combined with presynthesized alkyne‐terminated poly(ε‐caprolactone) (A‐PCL) in the presence of Cu(I)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine in DMF to give the star triblock copolymers: SPCL‐PtBA‐PCL. ¹H NMR, FTIR, and SEC analyses confirmed the expected star triblock architecture. The hydrolysis of tert‐butyl ester groups of the poly(tert‐butyl acrylate) blocks gave the amphiphilic star triblock copolymers: SPCL‐PAA‐PCL. These amphiphilic star triblock copolymers could self‐assemble into spherical micelles in aqueous solution with the particle size ranging from 20 to 60 nm. Their micellization behaviors were characterized by dynamic light scattering and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2905–2916, 2009     

Novel synthesis of biodegradable amphiphilic linear and star block copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol)

Biodegradable, amphiphilic, diblock poly(ε‐caprolactone)‐block‐poly(ethylene glycol) (PCL‐b‐PEG), triblock poly(ε‐caprolactone)‐block‐poly(ethylene glycol)‐block‐poly(ε‐caprolactone) (PCL‐b‐PEG‐b‐PCL), and star shaped copolymers were synthesized by ring opening polymerization of ε‐caprolactone in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) or star poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature to yield monomodal polymers of controlled molecular weight. The chemical structure of the copolymers was investigated by ¹H and ¹³C NMR. The formation of block copolymers was confirmed by ¹³C NMR and DSC investigations. The effects of copolymer composition and molecular structure on the physical properties were investigated by GPC and DSC. For the same PCL chain length, the materials obtained in the case of linear copolymers are viscous whereas in the case of star copolymer solid materials are obtained with low T_g and T_m temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3975–3985, 2007     

Novel synthesis of biodegradable linear and star block copolymers based on ε‐caprolactone and lactides using potassium‐based catalyst

Biodegradable, triblock poly(lactide)‐block‐poly(ε‐caprolactone)‐block‐poly(lactide) (PLA‐b‐PCL‐b‐PLA) copolymers and 3‐star‐(PCL‐b‐PLA) block copolymers were synthesized by ring opening polymerization of lactides in the presence of poly(ε‐caprolactone) diol or 3‐star‐poly(ε‐caprolactone) triol as macroinitiator and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature to yield monomodal polymers of controlled molecular weight. The chemical structure of the copolymers was investigated by ¹H and ¹³C‐NMR. The formation of block copolymers was confirmed by NMR and DSC investigations. The effects of copolymer composition and molecular structure on the physical properties were investigated by GPC and DSC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5363–5370, 2008     

Amphiphilic star‐block copolymers based on a hyperbranched core: Synthesis and supramolecular self‐assembly

Novel amphiphilic star‐block copolymers, star poly(caprolactone)‐block‐poly[(2‐dimethylamino)ethyl methacrylate] and poly(caprolactone)‐block‐poly(methacrylic acid), with hyperbranched poly(2‐hydroxyethyl methacrylate) (PHEMA–OH) as a core moiety were synthesized and characterized. The star‐block copolymers were prepared by a combination of ring‐opening polymerization and atom transfer radical polymerization (ATRP). First, hyperbranched PHEMA–OH with 18 hydroxyl end groups on average was used as an initiator for the ring‐opening polymerization of ε‐caprolactone to produce PHEMA–PCL star homopolymers [PHEMA = poly(2‐hydroxyethyl methacrylate); PCL = poly(caprolactone)]. Next, the hydroxyl end groups of PHEMA–PCL were converted to 2‐bromoesters, and this gave rise to macroinitiator PHEMA–PCL–Br for ATRP. Then, 2‐dimethylaminoethyl methacrylate or tert‐butyl methacrylate was polymerized from the macroinitiators, and this afforded the star‐block copolymers PHEMA–PCL–PDMA [PDMA = poly(2‐dimethylaminoethyl methacrylate)] and PHEMA–PCL–PtBMA [PtBMA = poly(tert‐butyl methacrylate)]. Characterization by gel permeation chromatography and nuclear magnetic resonance confirmed the expected molecular structure. The hydrolysis of tert‐butyl ester groups of the poly(tert‐butyl methacrylate) blocks gave the star‐block copolymer PHEMA–PCL–PMAA [PMAA = poly(methacrylic acid)]. These amphiphilic star‐block copolymers could self‐assemble into spherical micelles, as characterized by dynamic light scattering and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6534–6544, 2005     

Preparation of pH‐sensitive star‐shaped aliphatic polyesters as precursors of polymersomes

This article reports on the synthesis of a new pH‐sensitive amphiphilic A₂B mikto‐arm star‐shaped aliphatic copolyester [with A = poly(ε‐caprolactone) and B = tertiary amine‐bearing poly(ε‐caprolactone)] with two hydrophobic arms and one hydrophilic arm when protonated at pH = 5.5. First, the ring‐opening polymerization of ε‐caprolactone (εCL) was initiated by an aliphatic diol substituted by an alkyne. The copper(I) catalyzed azide‐alkyne cycloaddition (CuAAC) was use to convert the alkyne into a hydroxyl group prone to initiate the ring‐opening copolymerization of γ‐bromo‐ε‐caprolactone (γBrεCL) and εCL. After the substitution of the bromide atoms into azide functions, the N,N‐dimethylprop‐2‐yn‐1‐amine was grafted onto the azide bearing PCL arm by CuAAC, with the purpose to make the B arm hydrophilic at low pH. The precursors of the A₂B copolymers were characterized by ¹H NMR, SEC, and MALDI‐TOF. As expected, the A₂B copolyester was soluble into water at pH = 5. The formation of polymersomes in water at pH 5 was assessed by DLS and TEM analyses. The effects of the architecture and the molecular weight of the A₂B copolymers on the formation of polymersomes were investigated. Moreover, the versatility of our approach was demonstrated by the synthesis of an AB₂ star‐shaped copolyester. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and self‐assembly of well‐defined cyclodextrin‐centered amphiphilic A14B7 multimiktoarm star copolymers based on poly(ε‐caprolactone) and poly(acrylic acid)

Novel amphiphilic A₁₄B₇ multimiktoarm star copolymers composed of 14 poly(ε‐caprolactone) (PCL) arms and 7 poly(acrylic acid) (PAA) arms with β‐cyclodextrin (β‐CD) as core moiety were synthesized by the combination of controlled ring‐opening polymerization (CROP) and atom transfer radical polymerization (ATRP). 14‐Arm star PCL homopolymers (CDSi‐SPCL) were first synthesized by the CROP of CL using per‐6‐(tert‐butyldimethylsilyl)‐β‐CD as the multifunctional initiator in the presence of Sn(Oct)₂ at 125 °C. Subsequently, the hydroxyl end groups of CDSi‐SPCL were blocked by acetyl chloride. After desilylation of the tert‐butyldimethylsilyl ether groups from the β‐CD core, 7 ATRP initiating sites were introduced by treating with 2‐bromoisobutyryl bromide, which further initiated ATRP of tert‐butyl acrylate (tBA) to prepare well‐defined A₁₄B₇ multimiktoarm star copolymers [CDS(PCL‐PtBA)]. Their molecular structures and physical properties were in detail characterized by ¹H NMR, SEC‐MALLS, and DSC. The selective hydrolysis of tert‐butyl ester groups of the PtBA block gave the amphiphilic A₁₄B₇ multimiktoarm star copolymers [CDS(PCL‐PAA)]. These amphiphilic copolymers could self‐assemble into multimorphological aggregates in aqueous solution, which were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2961–2974, 2010     

Synthesis of biocompatible and biodegradable block copolymers of polyvinyl alcohol‐block‐poly(ε‐caprolactone) using metal‐free living cationic polymerization

Applications of metal‐free living cationic polymerization of vinyl ethers using HCl · Et₂O are reported. Product of poly(vinyl ether)s possessing functional end groups such as hydroxyethyl groups with predicted molecular weights was used as a macroinitiator in activated monomer cationic polymerization of ε‐caprolactone (CL) with HCl · Et₂O as a ring‐opening polymerization. This combination method is a metal‐free polymerization using HCl · Et₂O. The formation of poly(isobutyl vinyl ether)‐b‐poly(ε‐caprolactone) (PIBVE‐b‐PCL) and poly(tert‐butyl vinyl ether)‐b‐poly(ε‐caprolactone) (PTBVE‐b‐PCL) from two vinyl ethers and CL was successful. Therefore, we synthesized novel amphiphilic, biocompatible, and biodegradable block copolymers comprised polyvinyl alcohol and PCL, namely PVA‐b‐PCL by transformation of acid hydrolysis of tert‐butoxy moiety of PTBVE in PTBVE‐b‐PCL. The synthesized copolymers showed well‐defined structure and narrow molecular weight distribution. The structure of resulting block copolymers was confirmed by ¹H NMR, size exclusion chromatography, and differential scanning calorimetry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5169–5179, 2009     

Three‐arm star block copolymers of ε‐caprolactone and acrylic acid: Synthesis and micellization behavior

A series of well‐defined three‐arm star poly(ε‐caprolactone)‐b‐poly(acrylic acid) copolymers having different block lengths were synthesized via the combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, three‐arm star poly(ε‐caprolactone) (PCL) (M_n = 2490–7830 g mol^?1; M_w/M_n = 1.19–1.24) were synthesized via ROP of ε‐caprolactone (ε‐CL) using tris(2‐hydroxyethyl)cynuric acid as three‐arm initiator and stannous octoate (Sn(Oct)₂) as a catalyst. Subsequently, the three‐arm macroinitiator transformed from such PCL in high conversion initiated ATRPs of tert‐butyl acrylate (^tBuA) to construct three‐arm star PCL‐b‐P^tBuA copolymers (M_n = 10,900–19,570 g mol^?1; M_w/M_n = 1.14–1.23). Finally, the three‐arm star PCL‐b‐PAA copolymer was obtained via the hydrolysis of the PtBuA segment in three‐arm star PCL‐b‐P^tBuA copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance (¹H NMR), and Fourier transform infrared spectroscopy. The aggregates of three‐arm star PCL‐b‐PAA copolymer were studied by the determination of critical micelles concentration and transmission electron microscope. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis,self‐assembly and drug‐loading capacity of well‐defined drug‐conjugated amphiphilic A2B2 type miktoarm star copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol)

Well‐defined drug‐conjugated amphiphilic A₂B₂ miktoarm star copolymers [(PCL)₂‐(PEG)₂‐D] were prepared by the combination of controlled ring‐opening polymerization (CROP) and “click” reaction strategy. First, bromide functionalized poly(ε‐caprolactone) (PCL‐Br) with double hydroxyl end groups was synthesized by the CROP of ε‐caprolactone using 2,2‐bis(bromomethyl)propane‐1,3‐diol as a difunctional initiator in the presence of Sn(Oct)₂ at 110 °C. Next, the bromide groups of PCL‐Br were quantitatively converted to azide form by NaN₃ to give PCL‐N₃. Subsequently, the end hydroxyl groups of PCL‐N₃ were capped with ibuprofen as a model drug at room temperature. Finally, copper(I)‐catalyzed cycloaddition reaction between ibuprofen‐conjugated PCL‐N₃ and slightly excess alkyne‐terminated poly(ethylene glycol) (A‐PEG) led to ibuprofen‐conjugated A₂B₂ miktoarm star copolymer [(PCL)₂‐(PEG)₂‐D]. The excess A‐PEG was removed by dialysis. ¹H NMR, FTIR and SEC analyzes confirmed the expected miktoarm star architecture. These amphiphilic miktoarm star copolymers could self‐assemble into multimorphological aggregates in aqueous solution, which were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). In addition, the drug‐loading capacity of these drug‐conjugated miktoarm star copolymers as well as their nondrug‐conjugated analogs were also investigated in detail. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Synthesis of branch‐ring‐branch tadpole‐shaped [linear‐poly(ε‐caprolactone)]‐b‐[cyclic‐poly(ethylene oxide)]‐b‐ [linear‐poly(ε‐caprolactone)] by combination of glaser coupling reaction with ring‐opening polymerization

A novel amphiphilic branch‐ring‐branch tadpole‐shaped [linear‐poly(ε‐caprolactone)]‐b‐[cyclic‐poly(ethylene oxide)]‐b‐[linear‐poly(ε‐caprolactone)] [(l‐PCL)‐b‐(c‐PEO)‐b‐(l‐PCL)] was synthesized by combination of glaser coupling reaction with ring‐opening polymerization (ROP) mechanism. The self‐assembling behaviors of (l‐PCL)‐b‐(c‐PEO)‐b‐(l‐PCL) and their π‐shaped analogs of poly(ε‐caprolactone)/poly(ethylene oxide)]‐b‐poly(ethylene oxide)‐b‐[poly(ε‐caprolactone)/poly(ethylene oxide) with comparable molecular weight in water were preliminarily investigated. The results showed that the micelles formed from the former took a fiber look, however, that formed from the latter took a spherical look. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of well‐defined polystyrene and poly(ε‐caprolactone) hetero eight‐shaped copolymers

Well‐defined hetero eight‐shaped copolymers composed of polystyrene (PS) and poly(ε‐caprolactone) (PCL) with controlled molecular weight and narrow molecular weight distribution were successfully synthesized by the combination of ring‐opening polymerization, ATRP, and “click” reaction. The synthetic procedure involves three steps: (1) preparation of a tetrafunctional PS and PCL star copolymer with two PS and two PCL arms using the tetrafunctional initiator bearing two hydroxyl groups and two bromo groups; (2) synthesis of tetrafunctional star copolymer, (α‐acetylene‐PCL)₂(ω‐azido‐PS)₂, by the transition of terminal hydroxyl and bromo groups to acetylene and azido groups through the reaction with 4‐propargyloxybutanedioyl chloride and NaN₃ respectively; (3) intramolecular cyclization reaction to produce the hetero eight‐shaped copolymers using “click” chemistry under high dilution. The ¹H NMR, FTIR, and gel permeation chromatography techniques were applied to characterize the chemical structures of the resulted intermediates and the target polymers. Their thermal behavior was investigated by DSC, and their crystallization behaviors of PCL were studied by polarized optical microscopy. The decrease in chain mobility of the eight‐shaped copolymers restricts the crystallization of PCL and the crystallization rate of PCL is slower in comparison with their corresponding star precursors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6496–6508, 2008     

Core–shell‐type multiarm star polyethylenimine‐block‐poly(ε‐caprolactone): Synthesis and guest encapsulation potential

Novel multiarm star copolymers with poly(?‐caprolactone) (PCL) as the arms and hyperbranched polyethylenimine (HPEI) as the core have been successfully prepared by the tin(II) 2‐ethylhexanoate catalyzed ring‐opening polymerization of ?‐caprolactone (CL) with HPEI used directly as a macroinitiator. Not only primary but also secondary amine groups of HPEI participate in initiating the ring‐opening polymerization of CL with almost 100% initiation efficiency. The average degree of polymerization of the PCL arms can be controlled by the feed ratio of the monomers to the initiating sites. Because of the polarity difference of the PCL arms and HPEI core, the obtained multiarm star polymers display an inverted micellar structure with potential extraction and encapsulation of water‐soluble guests. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4165–4173, 2006     

Synthesis and characterization of resorcinarene‐centered amphiphilic A8B4 miktoarm star copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol) by combination of CROP and “click” chemistry

Well‐defined amphiphilic A₈B₄ miktoarm star copolymers with eight poly(ethylene glycol) chains and four poly(ε‐caprolactone) arms (R‐8PEG‐4PCL) were prepared using “click” reaction strategy and controlled ring‐opening polymerization (CROP). First, multi‐functional precursor (R‐8N₃‐4OH) with eight azides and four hydroxyls was synthesized based on the derivatization of resorcinarene. Then eight‐PEG‐arm star polymer (R‐8PEG‐4OH) was prepared through “click” reaction of R‐8N₃‐4OH with pre‐synthesized alkyne‐terminated monomethyl PEG (mPEG‐A) in the presence of CuBr/N,N,N′,N″,N″′‐ pentamethyldiethylenetriamine (PMDETA) in DMF. Finally, R‐8PEG‐4OH was used as tetrafunctional macroinitiator to prepare resorcinarene‐centered A₈B₄ miktoarm star copolymers via CROP of ε‐caprolactone utilizing Sn(Oct)₂ as catalyst at 100 °C. These miktoarm star copolymers could self‐assemble into spherical micelles in aqueous solution with resorcinarene moieties on the hydrophobic/hydrophilic interface, and the particle sizes could be controlled by the ratio of PCL to PEG. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2824–2833.     

Thermoresponsive star triblock copolymers by combination of ROP and ATRP: From micelles to hydrogels

Novel biocompatible, biodegradable, four‐arm star, triblock copolymers containing a hydrophobic poly(ε‐caprolactone) (PCL) segment, a hydrophilic poly(oligo(ethylene oxide)475 methacrylate) (POEOMA475) segment and a thermoresponsive poly(di(ethylene oxide) methyl ether methacrylate) (PMEO₂MA) segment were synthesized by a combination of controlled ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, a four‐arm PCL macroinitiator [(PCL‐Br)₄] for ATRP was synthesized by the ROP of ε‐caprolactone (CL) catalyzed by stannous octoate in the presence of pentaerythritol as the tetrafunctional initiator followed by esterification with 2‐bromoisobutyryl bromide. Then, sequential ATRP of oligo(ethylene oxide) methacrylate (OEOMA475, M_n = 475) and di(ethylene oxide) methyl ether methacrylate) (MEO₂MA) were carried out using the (PCL‐Br)₄ tetrafunctional macroinitiator, in different sequence, resulting in preparation of (PCL‐b‐POEOMA475‐b‐PMEO₂MA)₄ and (PCL‐b‐PMEO₂MA‐b‐POEOMA475)₄ star triblock copolymers. These amphiphilic copolymers can self‐assemble into spherical micelles in aqueous solution at room temperature. The thermal responses of the polymeric micelles were investigated by dynamic light scattering and ultraviolet spectrometer. The properties of the two series of copolymers are quite different and depend on the sequence distribution of each block along the arms of the star. The (PCL‐b‐POEOMA475‐b‐PMEO₂MA)₄ star copolymer, with the thermoresponsive PMEO₂MA segment on the periphery, can undergo reversible sol‐gel transitions between room temperature (22 °C) and human body temperature (37 °C). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of well‐defined cyclodextrin‐centered seven‐arm star poly(ε‐caprolactone)s and amphiphilic star poly(ε‐caprolactone‐b‐ethylene glycol)s

Per‐2,3‐acetyl‐β‐cyclodextrin with seven primary hydroxyl groups was synthesized by selective modification and used as multifunctional initiator for the ring‐opening polymerization of ε‐caprolactone (CL). Well‐defined β‐cyclodextrin‐centered seven‐arm star poly(ε‐caprolactone)s (CDSPCLs) with narrow molecular weight distributions (≤1.15) have been successfully prepared in the presence of Sn(Oct)₂ at 120 °C. The molecular weight of CDSPCLs was characterized by end group ¹H NMR analyses and size‐exclusion chromatography (SEC), which could be well controlled by the molar ratio of the monomer to the initiator. Furthermore, amphiphilic seven‐arm star poly(ε‐caprolactone‐b‐ethylene glycol)s (CDSPCL‐b‐PEGs) were synthesized by the coupling reaction of CDSPCLs with carboxyl‐terminated mPEGs. ¹H NMR and SEC analyses confirmed the expected star block structures. Differential scanning calorimetry analyses suggested that the melting temperature (T_m), the crystallization temperature (T_c), and the crystallinity degree (X_c) of CDSPCLs all increased with the increasing of the molecular weight, and were lower than that of the linear poly(ε‐caprolactone). As for CDSPCL‐b‐PEGs, the T_c and T_m of the PCL blocks were significantly influenced by the PEG segments in the copolymers. Moreover, these amphiphilic star block copolymers could self‐assemble into spherical micelles with the particle size ranging from 10 to 40 nm. Their micellization behaviors were characterized by dynamic light scattering and transmission electron microscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6455–6465, 2008     

Synthesis of amphiphilic A3B mikto‐arm copolymers from a sugar core: Combination of hydrophobic PCL and hydrophilic glycopolymers for biocompatible nanovector preparation

Amphiphilic A₃B mikto‐arm copolymers have been synthesized using a t‐butyl‐diphenyl silyl‐based methylglucoside derivative. The latter has been first used as initiator for the polymerization of ε‐caprolactone leading to three‐arm star‐shaped structures followed by several postpolymerization steps to obtain star‐shaped poly(ε‐caprolactone) macroinitiator. Atom transfer radical polymerization (ATRP) of diisopropylidene galactose methacrylate in THF at 60 °C using CuBr ligated with 1,1,4,7,10,10‐hexamethyltriethylenetetramine (HMTETA) as catalytic complex allowed the formation of A₃B mikto‐arm copolymers with different compositions and molecular weights. Selective deprotection of sugar protecting groups finally generated amphiphilic mikto‐arm copolymers. The molecular characterization of those copolymers was performed by ¹H NMR spectroscopy and gel permeation chromatography (GPC) analysis. The self‐assembly of the copolymers into micellar aggregates and the related critical micellization concentration (CMC) in aqueous media were determined by dynamic light scattering (DLS) and UV‐visible spectroscopy, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3271–3280, 2010     

Amphiphilic block copolymers of high‐molecular‐weight poly(ethylene oxide) and either ε‐caprolactone or γ‐methyl‐ε‐caprolactone: Synthesis and characterization

Ethylene oxide (EO) has been block‐polymerized with both ε‐caprolactone (ε‐CL) and γ‐methyl‐ε‐caprolactone (MCL) through the combination of the anionic polymerization of EO and the ring‐opening polymerization (ROP) of ε‐CL and MCL. ω‐Hydroxyl poly(ethylene oxide) has been reacted with triethylaluminum (OH/Al = 1) and converted into a macroinitiator for ROP of ε‐CL and MCL. In toluene at room temperature, this polymerization leads to a bimodal molecular weight distribution as a result of monomer insertion in only some of the aluminum alkoxide bonds. However, in a more polar solvent (methylene chloride) added with 1 equiv of a Lewis base (pyridine), the expected diblock is formed selectively, and this indicates that aggregation of the active species in toluene is responsible for a macroinitiator efficiency of less than 1. A series of amphiphilic diblock copolymers with poly(ε‐caprolactone) (semicrystalline) and poly(γ‐methyl‐ε‐caprolactone) (amorphous) as the hydrophobic blocks have been prepared and characterized with size exclusion chromatography, ¹H NMR, IR, and wide‐angle X‐ray scattering. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1132–1142, 2004     

A convenient synthesis of α,α′‐ homo‐ and α,α′‐hetero‐bifunctionalized poly(ε‐caprolactone)s by ring opening polymerization: The potentially valuable precursors for miktoarm star copolymers

Two new ring opening polymerization (ROP) initiators, namely, (3‐allyl‐2‐(allyloxy)phenyl)methanol and (3‐allyl‐2‐(prop‐2‐yn‐1‐yloxy)phenyl)methanol each containing two reactive functionalities viz. allyl, allyloxy and allyl, propargyloxy, respectively, were synthesized from 3‐allylsalicyaldehyde as a starting material. Well defined α‐allyl, α′‐allyloxy and α‐allyl, α′‐propargyloxy bifunctionalized poly(ε‐caprolactone)s with molecular weights in the range 4200–9500 and 3600–10,900 g/mol and molecular weight distributions in the range 1.16–1.18 and 1.15–1.16, respectively, were synthesized by ROP of ε‐caprolactone employing these initiators. The presence of α‐allyl, α′‐allyloxy and α‐allyl, α′‐propargyloxy functionalities on poly(ε‐caprolactone)s was confirmed by FT‐IR, ¹H, ¹³C NMR spectroscopy, and MALDI‐TOF analysis. The kinetic study of ROP of ε‐caprolactone with both the initiators revealed the pseudo first order kinetics with respect to ε‐caprolactone consumption and controlled behavior of polymerization reactions. The usefulness of α‐allyl, α′‐allyloxy functionalities on poly(ε‐caprolactone) was demonstrated by performing the thiol‐ene reaction with poly(ethylene glycol) thiol to obtain (mPEG)₂‐PCL miktoarm star copolymer. α‐Allyl, α′‐propargyloxy functionalities on poly(ε‐caprolactone) were utilized in orthogonal reactions i.e copper catalyzed alkyne‐azide click (CuAAC) with azido functionalized poly(N‐isopropylacrylamide) followed by thiol‐ene reaction with poly(ethylene glycol) thiol to synthesize PCL‐PNIPAAm‐mPEG miktoarm star terpolymer. The preliminary characterization of A₂B and ABC miktoarm star copolymers was carried out by ¹H NMR spectroscopy and gel permeation chromatography (GPC). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 844–860     

Synthesis of amphiphilic biodegradable glycocopolymers based on poly(ε‐caprolactone) by ring‐opening polymerization and click chemistry

Amphiphilic, biodegradable block glycopolymers based on poly(ε‐caprolactone) (PCL) with various pendent saccharides were synthesized by combination of ring‐opening polymerization (ROP) and “click” chemistry. PCL macroinitiators obtained by ROP of ε‐caprolactone were used to initiate the ROP of 2‐bromo‐ε‐caprolactone (BrCL) to get diblock copolymers, PCL‐b‐PBrCL. Reaction of the block copolymers with sodium azide converted the bromine groups in the PBrCL block to azide groups. In the final step, click chemistry of alkynyl saccharides with the pendent azide groups of PCL‐b‐PBrCL led to the formation of the amphiphilic block glycopolymers. These copolymers were characterized by ¹H NMR spectroscopy and gel permeation chromatography. The self‐assembly behavior of the amphiphilic block copolymers was investigated using transmission electron microscopy and atomic force microscope, spherical aggregates with saccharide groups on the surface were observed, and the aggregates could bind reversibly with Concanavalin A. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3583–3594, 2009     

Synthesis and crystallization of star‐shaped photocleavable poly(ε‐caprolactone)s

Here, we report on the synthesis and different crystallization behavior of linear‐ and star‐ PCL's containing a photocleavable linker (5‐hydroxy‐2‐nitro benzaldehyde), modulated by photochemical switching. Basis is the attachment of a photocleavable moiety close to the star‐core of a three‐arm star poly(caprolactone), so that the crystallization behavior can be controlled via a photochemical stimulus. The polymerization of ε‐caprolactone using a trivalent photocleavable initiator and stannous octanoate catalyst resulted in the synthesis of different molecular weights of star‐shaped photocleavable polymers. Various techniques like ¹H NMR and ESI‐TOF‐MS confirmed the successful synthesis of the star‐shaped polymers. Complete photocleavage is ensured via GPC, HPLC, and ESI‐TOF‐MS. DSC studies clearly indicated the enhancement in crystallinity after photocleavage of the star‐shaped poly(ε‐caprolactone)s. Hence, for the first time phototriggered crystallization behavior of PCL polymers is reported, where the confinement exerted by the star architecture is removed by photoirradiation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 642–649