Aminated PCL‐based copolymers by chemical modification of poly(α‐iodo‐ε‐caprolactone‐co‐ε‐caprolactone)

A novel method is proposed to access to new poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) using poly(α‐iodo‐ε‐caprolactone‐co‐ε‐caprolactone) as polymeric substrate. First, ring‐opening (co)polymerizations of α‐iodo‐ε‐caprolactone (αIεCL) with ε‐caprolactone (εCL) are performed using tin 2‐ethylhexanoate (Sn(Oct)₂) as catalyst. (Co)polymers are fully characterized by ¹H NMR, ¹³C NMR, FTIR, SEC, DSC, and TGA. Then, these iodinated polyesters are used as polymeric substrates to access to poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) by two different strategies. The first one is the reaction of poly(αIεCL‐co‐εCL) with ammonia, the second one is the reduction of poly(αN₃εCL‐co‐εCL) by hydrogenolysis. This poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) (F_αNH2εCL < 0.1) opens the way to new cationic and water‐soluble PCL‐based degradable polyesters. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6104–6115, 2009     

Synthesis and Characterization of Star‐Shaped Diblock Poly(ε‐caprolactone)/Poly(ethylene oxide) Copolymers

Summary: Star‐shaped hydroxy‐terminated poly(ε‐caprolactone)s (ssPCL), with arms of different lengths, were obtained by ring‐opening polymerization (ROP) of ε‐caprolactone initiated by pentaerythritol, and were condensed with α‐methyl‐ω‐(3‐carboxypropionyloxy)‐poly(ethylene oxide)s ( = 550–5 000) to afford four‐armed PCL‐PEO star diblock copolymers (ssPCL‐PEO). The polymers were characterized by ¹H and ¹³C NMR spectroscopy and size‐exclusion chromatography (SEC). The melting behavior of ssPCLs was studied by differential scanning calorimetry (DSC). X‐ray diffraction and DSC techniques were used to investigate the crystalline phases of ssPCL‐PEOs.

The part of the synthesis of four‐armed star‐shaped diblock poly(ε‐caprolactone)‐poly(ethylene oxide) copolymers as described.     

Heterograft copolymers of poly(ε‐caprolactone) prepared by combination of ATRA “grafting onto” and ATRP “grafting from” processes

This paper aims at reporting on the synthesis of a heterograft copolymer by combining the “grafting onto” process based on atom transfer radical addition (ATRA) and the “grafting from” process by atom transfer radical polymerization (ATRP). The statistical copolymerization of ε‐caprolactone (εCL) and α‐chloro‐ε‐caprolactone (αClεCL) was initiated by 2,2‐dibutyl‐2‐stanna‐1,3‐dioxepane (DSDOP), followed by ATRA of parts of the chlorinated units of poly(αClεCL‐co‐εCL) on the terminal double bond of α‐MeO,ω‐CH₂?CH? CH₂? CO₂‐poly(ethylene oxide) (PEO). The amphiphilic poly(εCL‐g‐EO) graft copolymer collected at this stage forms micelles as supported by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The unreacted pendant chloro groups of poly(εCL‐g‐EO) were used to initiate the ATRP of styrene with formation of copolymer with two populations of randomly distributed grafts, that is PEO and polystyrene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6015–6024, 2006     

Synthesis of Novel Star Shaped Poly(ε‐caprolactone) Utilizing Fullerene as the Molecular Core

Summary: The synthesis of star shaped poly(ε‐caprolactone) (PCL) with a fullerene molecular core (s‐PCLF) was successfully achieved by the ring‐opening polymerization of ε‐caprolactone with fullerenol as the initiator. Through NMR and GPC analysis, the average number of arms of PCL on each fullerene core was estimated to be 2–3.

Fullerenol (left) and PCL star polymer (right) in THF.     

Controlled/living ring‐opening polymerization of ε‐caprolactone with salicylic acid as the organocatalyst

Ring‐opening polymerization (ROP) of ε‐caprolactone (CL) using salicylic acid (SAA) as the organocatalyst and benzyl alcohol as the initiator in bulk at 80 °C successfully proceeded to give a narrowly distributed poly(ε‐caprolactone) (PCL). In addition, 2‐hydroxyethyl methacrylate, propargyl alcohol, 6‐azido‐1‐hexanol, and methoxy poly(ethylene glycol) were also used as functional initiators. The ¹H NMR, SEC, and MALDI‐TOF MS measurements of the PCL clearly indicate the presence of the initiator residue at the chain end, implying that the SAA‐catalyzed ROP of CL was through the activated monomer mechanism. The kinetic experiments confirmed the controlled/living nature of the SAA‐catalyzed ROP of CL. Furthermore, the block copolymerization of CL and δ‐valerolactone successfully proceeded to give poly(ε‐caprolactone)‐block‐poly(δ‐valerolactone). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1185–1192     

Isothiourea‐based lewis pairs for homopolymerization and copolymerization of 2,2‐dimethyltrimethylene carbonate with ε‐caprolactone and ω‐pentadecalactone

In this study, the homopolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and its copolymerizations with ε‐caprolactone (CL) were carried out in detail using the isothiourea‐based Lewis pairs comprised 2,3,6,7‐tetrahydro‐5H‐thiazolo(3,2‐a)pyrimidine and magnesium halides (MgX₂) with benzyl alcohol (BnOH) as the initiator. The copolymerization of DTC and CL via one‐pot addition produced randomly sequenced copolymers. On the other hand, a well‐defined linear poly(ε‐caprolactone)–block–poly(2,2‐dimethyltrimethylene carbonate) (PCL‐b‐PDTC) diblock copolymer was prepared by simple sequential ring‐opening polymerization of CL and DTC. In addition, poly(ω‐pentadecalactone)–block–PDTC diblock copolymer was successfully prepared by the same strategy. Moreover, PDTC–poly(ethylene glycol) (PEG)–PDTC triblock copolymer was synthesized in the presence of PEG 2000. The effects of different polymerization conditions on the polymerization reactions have been systematically discussed. The resulting polymers were characterized by the ¹H and ¹³C NMR spectra, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐ToF MS). The block copolyester structures were confirmed by the ¹³C NMR spectroscopy and DSC characterizations. These results indicated that the supposed mechanism was a dual catalytic mechanism. The proposed mechanism involved activation of the monomer via coordination to the MgX₂, and the initiator alcohol was deprotonated by base. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2349–2355     

Poly(ε‐caprolactone)‐Based Organogels and Hydrogels with Poly(ethylene glycol) Cross‐Linkings

Summary: The reaction of triphosgene with poly(ethylene glycol) yielded poly(ethylene glycol) dichloroformate. This difunctional cross‐linker was allowed to react with poly(ε‐caprolactone) bearing carbanionic sites obtained by activation with lithium diisopropylamide. The reaction resulted in the cross‐linking of poly(ε‐caprolactone) chains by poly(ethylene glycol) segments, giving copolymer networks that gel in both organic and aqueous media.

Schematic of the PCL‐g‐PEG copolymers synthesized here.     

Hydrolytic degradation of poly(ε‐caprolactone) with different end groups and poly(ε‐caprolactone‐co‐γ‐butyrolactone): characterization and kinetics of hydrocortisone delivery

Asymmetric telechelic α‐hydroxyl‐ω‐(carboxylic acid)‐poly(ε‐caprolactone) (HA‐PCL), α‐hydroxyl‐ω‐(benzylic ester)‐poly(ε‐caprolactone) (HBz‐PCL), and an asymmetric telechelic copolymer α‐hydroxyl‐ω‐(carboxylic acid)‐poly(ε‐caprolactone‐co‐γ‐butyrolactone) (HA‐PCB) were synthesized by ring‐opening polymerization of ε‐caprolactone (CL). CL and CL/γ‐butyrolactone mixture were used to obtain homopolymers and copolymer respectively at 150°C and 2 hr using ammonium decamolybdate (NH₄) [Mo₁₀O₃₄] (Dec) as a catalyst. Water (HA‐PCL and HA‐PCB) or benzyl alcohol (HBz‐PCL) were used as initiators. The three polylactones reached initial molecular weights between 2000 and 3000 Da measured by proton nuclear magnetic resonance (¹H‐NMR). Compression‐molded polylactone caplets were allowed to degrade in 0.5 M aqueous p‐toluenesulfonic acid at 37°C and monitored up to 60 days for weight loss behavior. Data showed that the copolymer degraded faster than the PCL homopolymers, and that there was no difference in the weight loss behavior between HA‐PCL and HBz‐PCL. Caplets of the three polylactones containing 1% (w/w) hydrocortisone were placed in two different buffer systems, pH 5.0 with citrate buffer and pH 7.4 with phosphate buffer at 37°C, and monitored up to 50 days for their release behavior. The release profiles of hydrocortisone presented two stages. The introduction of a second monomer in the polymer chain significantly increased the release rate, the degradation rate for HA‐PCB being faster than those for HBz‐PCL and HA‐PCL. At the pH studied, only slight differences on the liberation profiles were observed. SEM micrographs indicate that hydrolytic degradation occurred mainly by a surface erosion mechanism. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Characterization of Poly(ϵ‐CL)‐block‐poly(MMA‐co‐St)‐block‐poly(ϵ‐CL) by Combination of Coordination and Controlled Radical Polymerization

The triblock copolymer poly(ϵ‐caprolactone)‐block‐poly[(methyl methacrylate)‐co‐styrene]‐block‐poly(ϵ‐caprolactone) was synthesized by a combination of coordination polymerization and controlled radical mechanism. The poly(ϵ‐caprolactone) prepolymers (PCL_BP) were first obtained by coordination polymerization using benzopinacol as the initiator and aluminium triisopropoxide as the promoter at room temperature. It was determined by means of UV and NMR spectroscopy that the benzopinacolate groups are left intact in the PCL_BP prepolymers; no isomerization was found. The benzopinacolate groups incorporated into the poly(ϵ‐caprolactone) then initiate the copolymerization of styrene (St) and methyl methacrylate (MMA) via a controlled radical mechanism at 95°C. The desired block copolymers were characterized by GPC, IR, UV and NMR spectroscopy in detail.     

稀土硫化物：e–己内酯开环聚合新催化剂

The ring-opening polymerization （ROP） of ε-caprolactone （ε-CL） using lanthanide thiolate complexes [（CH3CsH4）2Sm（μ-SPh）（THF）]2 （1） and Sm（SPh）3（HMPA）3 （2） as initiators has been investigated for the first time. Both of 1 and 2 were found to be highly efficient initiators for the ROP of ε-CL. The poly（ε-caprolactone） （PCL） with molecular weight Mn up to 1.97 ×10^5 and relatively narrow molecular weight distributions （1.20〈MW/Mn〈 2.00） have been obtained in high yield in the temperature range of 35-65℃. According to the polymer yield, 2 showed much higher activity than 1. However, the number-average molecular weight of PCL obtained with 2 was much lower than with 1. The possible polymerization mechanism of the ε-CL polymerization has been proposed based on the results of the end group analysis of the ε-CL oligomer.     

Crystallization of Poly(ε‐caprolactone) under Nanoparticle Confinement

Solid‐state ¹³C‐NMR spectroscopy has been used to characterize the conformation of the hydrophobic poly(ε‐caprolactone) core of a nanoparticle having a cross‐linked hydrophilic poly(acrylic acid)/polyacrylamide shell. The amphiphilic nanoparticles were synthesized from the diblock copolymer, poly(ε‐caprolactone)₁₂₁‐b‐poly(acrylic acid)₁₆₅ by self‐assembly into polymer micelles, followed by cross‐linking via condensation reactions between the carboxylic acid groups of the hydrophilic shell and the amine groups of 2,2′‐(ethylenedioxy)bis(ethylamine). NMR Experiments performed at −30° on nanoparticles rapidly quenched from 60° show that the core is largely noncrystalline and locally disordered. Heating to 25° results in some crystallization, although far less than that observed for bulk poly(ε‐caprolactone) homopolymer. Storage at −30° results in further crystallization and conversion of most rubbery, mobile regions into more rigid, locally ordered amorphous domains. The absence of dipolar coupling between natural‐abundance ¹³C in the poly(ε‐caprolactone) core of the nanoparticle, and ¹⁵N labels dispersed throughout the cross‐linked shell show that the interface between core and shell is sharp. The dipolar coupling measurements were accomplished by ¹³C{¹⁵N} rotational‐echo double resonance.     

Preparation of novel poly(ethylene oxide‐co‐glycidol)‐graft‐poly(ε‐caprolactone) copolymers and inclusion complexation of the grafted chains with α‐cyclodextrin

A well‐defined comblike copolymer of poly(ethylene oxide‐co‐glycidol) [(poly(EO‐co‐Gly)] as the main chain and poly(ε‐caprolactone) (PCL) as the side chain was successfully prepared by the combination of anionic polymerization and ring‐opening polymerization. The glycidol was protected by ethyl vinyl ether to form 2,3‐epoxypropyl‐1‐ethoxyethyl ether (EPEE) first, and then ethylene oxide was copolymerized with EPEE by an anionic mechanism. The EPEE segments of the copolymer were deprotected by formic acid, and the glycidol segments of the copolymers were recovered after saponification. Poly(EO‐co‐Gly) with multihydroxyls was used further to initiate the ring‐opening polymerization of ε‐caprolactone in the presence of stannous octoate. When the grafted copolymer was mixed with α‐cyclodextrin, crystalline inclusion complexes (ICs) were formed, and the intermediate and final products, poly(ethylene oxide‐co‐glycidol)‐graft‐poly(ε‐caprolactone) and ICs, were characterized with gel permeation chromatography, NMR, differential scanning calorimetry, X‐ray diffraction, and thermogravimetric analysis in detail. The obtained ICs had a channel‐type crystalline structure, and the ratio of ε‐caprolactone units to α‐cyclodextrin for the ICs was higher than 1:1. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3684–3691, 2006     

Synthesis and Characterization of Amphiphilic Poly(caprolactone) Star Block Copolymers

Summary: Novel, star‐shaped, amphiphilic block copolymers composed of fully degradable poly(caprolactone) were synthesized by sequential addition polymerization. In the first step, four‐arm macroinitiators were produced by ring‐opening polymerization of caprolactone by initiation with pentaerythritol. Then, block copolymers were synthesized by sequential addition of 4‐(2‐benzyloxyethyl)‐ε‐caprolactone to the four‐arm macroinitiators. Star‐shaped, amphiphilic block copolymers containing poly(caprolactone)‐block‐poly[4‐(2‐hydroxyethyl)caprolactone] segments were obtained by catalytic debenzylation.

Four‐arm amphiphilic polycaprolactone star block copolymer.     

Towards the Nature of Active Sites in Polymerization of Cyclic Esters Initiated by Aluminium Alkoxides: First Structurally Authenticated Aluminium‐ε‐Caprolactone Complex

Summary: The isolation and structural characterization of a methylaluminium(bisphenoxide)‐ε‐caprolactone complex is reported. While the three‐coordinate methylaluminium complex was found not to catalyze the polymerization of ε‐caprolactone, its oxygenation led to the formation of an aluminium methoxide compound, which appeared to be a very good initiator. The relative propensity of the Al X bonds for monomer insertion in the initial step of polymerization is also discussed.

Structure of the methylaluminium(bisphenoxide)‐ε‐caprolactone complex reported here.     

Ring‐Opening Polymerization of ε‐Caprolactone by Poly(ethylene glycol) by an Activated Monomer Mechanism

Summary: The polymerization of ε‐caprolactone (CL) in the presence of HCl · Et₂O by an activated monomer mechanism was performed to synthesize diblock or triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PCL block copolymers by a metal‐free method.

The non‐metal catalyzed living ring‐opening polymerisation of ε‐caprolactone by PEG.     

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     

Pendant groups fine‐tuning thermal gelation of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) aqueous solution

Novel poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) bearing pendant hydrophobic γ‐(carbamic acid benzyl ester) groups (PECB) and hydrophiphilic amino groups (PECN) were synthesized based on the functionalized comonomer γ‐(carbamic acid benzyl ester)‐ε‐caprolactone (CABCL). The thermal gelation behavior of the amphiphilic copolymer aqueous solutions was examined. The phase transition behavior could be finely tuned via the pendant groups, and an abnormal phenomenon occurred that the sol–gel transition temperature shifted to a higher temperature for PECB whereas a lower temperature for PECN. The micelles percolation was adopted to clarify the hydrogel mechanism, and the effect of the pendant groups on the micellization was further investigated in detail. The results demonstrated that the introduction of γ‐(carbamic acid benzyl ester) pendant groups significantly decreased the crystallinity of the copolymer micelles whereas amino pendant groups made the micelles easy to aggregate. Thus, the thermal gelation of PEG/PCL aqueous solution could be finely tuned by the pendant groups, and the pendant groups modified PEG/PCL hydrogels are expected to have great potential biomedical application. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2571–2581     

“Coordination‐insertion” ring‐opening polymerization of 1,4‐dioxan‐2‐one and controlled synthesis of diblock copolymers with ε‐caprolactone

This communication deals with the coordination‐insertion ring‐opening polymerization of 1,4‐dioxan‐2‐one (DX) as initiated by aluminium triisopropoxide (Al(OⁱPr)₃) either in bulk or in solution. First, polymerization of DX has been carried out in bulk at 100°C and compared to the ring‐opening polymerization promoted by tin(II)octoate. Block copolymers of ε‐caprolactone (CL) and DX have been then selectively obtained by first initiating CL polymerization with Al(OⁱPr)₃ in toluene and then adding DX to the living PCL macroinitiator solution at room temperature. In spite of the inherent poor solubility of poly(1,4‐dioxan‐2‐one) in most organic solvents, DX polymerization has proven to proceed through a “living” mechanism. Interestingly enough, the semi‐crystalline P[CL‐b‐DX] block copolymers displayed two well separated melting endotherms at ca. 55 and 102°C for PCL and PDX sequences, respectively.     

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     

The Synthesis of Magnetic Core‐Shell Nanoparticles by Surface‐Initiated Ring‐Opening Polymerization of ε‐Caprolactone

Summary: The synthesis of core‐shell particles with a poly(ε‐caprolactone) (PCL) shell and magnetite (Fe₃O₄) contents of between 10 wt.‐% and 41 wt.‐% proceeds by surface‐initiated ring‐opening polymerization of ε‐caprolactone to give surface‐immobilized oligomers with between 1 400 g · mol⁻¹ and 11 500 g · mol⁻¹. The particles are dispersable in good solvents for the PCL shell. Magnetization experiments on the resulting superparamagnetic ferrofluids give a core‐size distribution with an average diameter, d_v, of about 9.7 nm.

TEM image of Fe₃O₄/PCL core‐shell particles cast from CHCl₃ dispersion.