Block and random copolymerization of ε‐caprolactone,L‐, and rac‐lactide using titanium complex derived from aminodiol ligand

A series of di‐ and triblock copolymers [poly(L ‐lactide‐b‐ε‐caprolactone), poly(D,L ‐lactide‐b‐ε‐caprolactone), poly(ε‐caprolactone‐b‐L ‐lactide), and poly(ε‐caprolactone‐b‐L ‐lactide‐b‐ε‐caprolactone)] have been synthesized successfully by sequential ring‐opening polymerization of ε‐caprolactone (ε‐CL) and lactide (LA) either by initiating PCL block growth with living PLA chain end or vice versa using titanium complexes supported by aminodiol ligands as initiators. Poly(trimethylene carbonate‐b‐ε‐caprolactone) was also prepared. A series of random copolymers with different comonomer composition were also synthesized in solution and bulk of ε‐CL and D,L ‐lactide. The chemical composition and microstructure of the copolymers suggest a random distribution with short average sequence length of both the LA and ε‐CL. Transesterification reactions played a key role in the redistribution of monomer sequence and the chain microstructures. Differential scanning calorimetry analysis of the copolymer also evidenced the random structure of the copolymer with a unique T_g. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Strontium‐based initiator system for ring‐opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr‐PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring‐opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA). The Sr‐PO initiator demonstrated an effective initiating activity for the ROP of ε‐caprolactone (ε‐CL) and L‐lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr‐PO initiator. Block copolymer PCL‐b‐PLLA was prepared by sequential polymerization of ε‐CL and LLA, which was demonstrated by ¹H NMR, ¹³C NMR, and gel permeation chromatography. The chemical structure of Sr‐PO initiator was confirmed by elemental analysis of Sr and N, ¹H NMR analysis of the end groups in ε‐CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr‐PO initiator and model monomer γ‐butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination‐insertion mechanism, and cyclic esters exclusively inserted into the Sr–O bond. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1934–1941, 2003     

Microwave‐assisted synthesis of star‐shaped poly(ε‐caprolactone)‐block‐poly(L‐lactide) copolymers and the crystalline morphologies

A monomode microwave reactor was used for the synthesis of designed star‐shaped polymers, which were based on dipentaerythritol with six crystallizable arms of poly(ε‐caprolactone)‐b‐poly(L ‐lactide) (PCL‐b‐PLLA) copolymer via a two‐step ring‐opening polymerization (ROP). The effects of irradiation conditions on the molecular weight were studied. Microwave heating accelerated the ROP of CL and LLA, compared with the conventional heating method. The resultant hexa‐armed polymers were fully characterized by means of FTIR, ¹H NMR spectrum, and GPC. The investigation of thermal properties and crystalline behaviors indicated that the crystalline behaviors of polymers were largely depended on the macromolecular architecture and the length of the block chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Deformation behavior of electrospun poly(L‐lactide‐co‐ε‐caprolactone) nonwoven membranes under uniaxial tensile loading

Biodegradable poly(L ‐lactide‐co‐ε‐caprolactone) copolymers with different L ‐lactide (LLA)/ε‐caprolactone (CL) ratios of 75/25 and 50/50 were electrospun into fine fibers. The deformation behavior of the electrospun membranes with randomly oriented structures was evaluated under uniaxial tensile loading. The electrospun membrane with a higher LLA content showed a significantly higher tensile modulus but a similar maximum stress and a lower ultimate strain in comparison with the membrane with a lower LLA content. The beaded fibers that formed in the membranes caused lower tensile properties. X‐ray diffraction and differential scanning calorimetry results suggested that the electrospun fine fibers developed highly oriented structures in CL‐unit sequences during the electrospinning process even though the concentration was only 25 wt %. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3205–3212, 2005     

Ring‐opening polymerization of cyclic esters promoted by phosphido‐diphosphine pincer group 3 complexes

Phosphido‐diphosphine Group 3 metal complexes 1–4 [(o‐C₆H₄PR₂)₂P‐M(CH₂SiMe₃)₂; R = Ph, 1 : M = Y, 2 : M = Sc; R = iPr, 3 : M = Y, 4 : M = Sc] are very efficient catalysts for the ring‐opening polymerization (ROP) of cyclic esters such as ε‐caprolactone (ε‐CL), L ‐lactide, and δ‐valerolactone under mild polymerization conditions. In the ROP of ε‐CL, complexes 1–4 promote quantitative conversion of high amount of monomer (up to 3000 equiv) with very high turnover frequencies (TOF) (～4 × 10⁴ mol_CL/mol_I h) showing a catalytic activity among the highest reported in the literature. The immortal and living ROP of ε‐CL and L ‐lactide is feasible by combining complexes 1–4 with 5 equiv of 2‐propanol. Polymers with controlled molecular parameters (M_n, end groups) and low polydispersities (M_w/M_n = 1.05–1.09) are formed as a result of fast alkoxide/alcohol exchange. In the ROP of δ‐valerolactone, complexes 1–4 showed the same activity observed for lactide (L ‐ and D ,L ‐lactide) producing high molecular weight polymers with narrow distribution of molar masses. Complexes 1–4 also promote the ROP of rac‐β butyrolactone affording atactic low molecular weight poly(hydroxybutyrate) bearing unsaturated end groups probably generated by elimination reactions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of various end‐functionalized polyesters by controlled/living ring‐opening polymerization of lactones using pentafluorophenylbis(triflyl)methane

The ring‐opening polymerizations (ROPs) of ε‐caprolactone (ε‐CL) and δ‐valerolactone (δ‐VL) with pentafluorophenylbis(triflyl)methane (C₆F₅CHTf₂) as the organocatalyst and alcohol initiators were carried out. For the ROP using 3‐phenyl‐1‐propanol (PPA) as the initiator in CH₂Cl₂ at room temperature with the [ε‐CL or δ‐VL]₀/[PPA]₀/[C₆F₅CHTf₂] ratio of 50/1/0.1, the polymerization homogeneously proceeded to afford poly(ε‐caprolactone) (PCL) and poly(δ‐valerolactone) (PVL) having narrow polydispersity indices. The molecular weights of the obtained polymers determined from ¹H NMR spectra showed good agreement with those estimated from the initial ratio of [ε‐CL or δ‐VL]₀/[PPA]₀ and monomer conversions. The ¹H NMR, size exclusion chromatography, and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry measurements strongly indicated that PCL and PVL possessed the 3‐phenylpropoxy group as the α‐chain‐end and the hydroxy group as the ω‐chain‐end. In addition, the controlled/living nature for the C₆F₅CHTf₂‐catalyzed ROP of lactones was confirmed by kinetic and chain‐extension experiments. The block copolymerization of PCL and PVL successfully proceeded to afford PCL‐b‐PVL and PVL‐b‐PCL. In addition, various end‐functionalized PCLs and PVLs with narrow molecular weight distributions were synthesized by the ROP of ε‐CL and δ‐VL using functional initiators, such as 6‐azido‐1‐hexanol, 2‐hydroxyethyl methacrylate, propargyl alcohol, N‐(2‐hydroxyethyl)maleimide, 4‐vinylbenzyl alcohol, 5‐hexen‐1‐ol, and 5‐norbornene‐2‐methanol. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Bis(4‐nitrophenyl) phosphate as an efficient organocatalyst for ring‐opening polymerization of β‐butyrolactone leading to end‐functionalized and diblock polyesters

The ring‐opening polymerization (ROP) of β‐butyrolactone (β‐BL) has been studied using the organocatalysts of diphenyl phosphate (DPP) and bis(4‐nitrophenyl) phosphate (BNPP). The controlled ROP of β‐BL was achieved using BNPP, whereas that of using DPP was insufficient because of its low acidity. For the BNPP‐catalyzed ROP of β‐BL, the dual activation property for β‐BL and the chain‐end models of poly(β‐butyrolactone) (PBL) were confirmed by NMR measurements. The optimized polymerization condition for the ROP of β‐BL proceeded through an O‐acyl cleavage to produce the well‐defined PBLs with molecular weights up to 10,650 g mol^?1 and relatively narrow polydispersities of 1.19–1.39. Functional initiators were utilized for producing the end‐functionalized PBLs with the ethynyl, maleimide, pentafluorophenyl, methacryloyl, and styryl groups. Additionally, the diblock copolymers consisting of the PBL segment with the polyester or polycarbonate segments were prepared by the BNPP‐catalyzed ROPs of ε‐caprolactone or trimethylene carbonate without quenching. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2032–2039     

Synthesis of block and end‐functionalized polyesters by triflimide‐catalyzed ring‐opening polymerization of ε‐caprolactone, 1,5‐dioxepan‐2‐one,and rac‐lactide

The ring‐opening polymerization (ROP) of cyclic esters, such as ε‐caprolactone, 1,5‐dioxepan‐2‐one, and racemic lactide using the combination of 3‐phenyl‐1‐propanol as the initiator and triflimide (HNTf₂) as the catalyst at room temperature with the [monomer]₀/[initiator]₀ ratio of 50/1 was investigated. The polymerizations homogeneously proceeded to afford poly(ε‐caprolactone) (PCL), poly(1,5‐dioxepan‐2‐one) (PDXO), and polylactide (PLA) with controlled molecular weights and narrow polydispersity indices. The molecular weight determined from an ¹H NMR analysis (PCL, M_n,NMR = 5380; PDXO, M_n,NMR = 5820; PLA, M_n,NMR = 6490) showed good agreement with the calculated values. The ¹H NMR and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry analyses strongly indicated that the obtained compounds were the desired polyesters. The kinetic measurements confirmed the controlled/living nature for the HNTf₂‐catalyzed ROP of cyclic esters. A series of functional alcohols, such as propargyl alcohol, 6‐azido‐1‐hexanol, N‐(2‐hydroxyethyl)maleimide, 5‐hexen‐1‐ol, and 2‐hydroxyethyl methacrylate, successfully produced end‐functionalized polyesters. In addition, poly(ethylene glycol)‐block‐polyester, poly(δ‐valerolactone)‐block‐poly(ε‐caprolactone), and poly(ε‐caprolactone)‐block‐polylactide were synthesized using the HNTf₂‐catalyzed ROP. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2455–2463     

Synthesis,characterization, and catalytic activity of titanium iminophenoxide complexes in relation to the ring‐opening polymerization of L‐lactide and ε‐caprolactone

This study synthesized a series of titanium iminophenoxide complexes and investigated their suitability as catalysts for the ring‐opening polymerization of L ‐lactide (L ‐LA) and ε‐caprolactone (CL). Complexes with bidentate ligands demonstrate higher catalytic activity than their tridentate counterparts since the third coordination atom needs to contend with L ‐LA and CL. Differences in the geometric framework of bidentate ligands also influence the catalytic activity. Type II ligands (N, N‐trans form of Ti complex) prevent the coordination of monomers to Ti thereby decreasing the initiation rate. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Alkaline and enzymatic degradation of L‐lactide copolymers. II. Crystallized films of poly(L‐lactide‐co‐D‐lactide) and poly(L‐lactide) with similar crystallinities

Films of poly(L ‐lactide‐co‐D ‐lactide) [P(LLA‐DLA); 95/5] and poly(L ‐lactide) [i.e., poly(L ‐lactide acid) (PLLA)] were prepared by crystallization from the melt, and a comparative study of the crystallization effects on the alkaline and proteinase K catalyzed hydrolysis of the films was carried out. The hydrolyzed films were investigated with gravimetry, differential scanning calorimetry, polarimetry, and gel permeation chromatography, and the results were compared with those reported for amorphous‐made specimens. The alkaline hydrolyzability of the P(LLA‐DLA) (95/5) and PLLA films was determined solely by the initial crystallinity (X_c) and was not affected by the content of the incorporated D ‐lactide (DLA) unit in the polymer chain; this was in marked contrast to the fact that the enzymatic hydrolyzability depended on not only the initial X_c value but also the DLA unit content. The alkaline hydrolysis rate of the P(LLA‐DLA) (95/5) and PLLA films and the enzymatic hydrolysis rate (R_EH) of the P(LLA‐DLA) (95/5) films decreased linearly as the initial X_c value increased. This meant that the hydrolyzability of the restricted amorphous regions was very similar to that of the free amorphous regions. In contrast, R_EH of the PLLA films decreased nonlinearly with the initial X_c value, and this nonlinear dependence was caused by the fact that in the PLLA films the restricted amorphous regions were much more hydrolysis‐resistant than the free amorphous regions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1064‐1075, 2005     

Ring opening polymerization and copolymerization of L‐lactide and ɛ‐caprolactone by bis‐ligated magnesium complexes

Seven magnesium complexes ( 1–7 ) were synthesized by reaction of new ( L ³ ‐H – L ⁵ ‐H ) and previously reported ketoimine pro‐ligands with dibutyl magnesium and were isolated in 59–70% yields. Complexes 1–7 were characterized fully and consisted of bis‐ligated homoleptic ketoiminates coordinated in distorted octahedral geometry around the magnesium centers. The complexes were investigated for their ability to initiate the ring opening polymerization (ROP) of l ‐lactide (L‐LA) to poly‐lactic acid (PLA) and ?‐caprolactone (?CL) to poly‐caprolactone in the presence of 4‐fluorophenol co‐catalyst. For L‐LA polymerization, complexes containing ligand electron‐donating groups ( 1–5 ) achieved >90% conversion in 2 h at 100 °C, while the presence of CF₃ groups in 6 and 7 slowed or resulted in no PLA detected. With ?CL, ROP initiated with 1–7 resulted in lower percentage conversion with similar electronic effects. Moderate molecular weight PLA polymeric material (14.3–21.3 kDa) with low polydispersity index values (1.23–1.56) was obtained, and ROP appeared to be living in nature. Copolymerization of L‐LA and ?CL yielded block copolymers only from the sequential polymerization of ?CL followed by L‐LA and not the reverse sequence of monomers or the simultaneous presence of both monomers. Polymers and copolymers were characterized with NMR, gel permeation chromatography, and differential scanning calorimetry. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 48–59     

Precision synthesis of microstructures in star‐shaped copolymers of ϵ‐caprolactone,L‐lactide,and 1,5‐dioxepan‐2‐one

Star‐shaped homo‐ and copolymers were synthesized in a controlled fashion using two different initiating systems. Homopolymers of ε‐caprolactone, L ‐lactide, and 1,5‐dioxepan‐2‐one were firstly polymerized using (I) a spirocyclic tin initiator and (II) stannous octoate (cocatalyst) together with pentaerythritol ethoxylate 15/4 EO/OH (coinitiator), to give polymers with identical core moieties. Our gained understanding of the versatile and controllable initiator systems kinetics, the transesterification reactions occurring, and the role which the reaction conditions play on the material outcome, made it possible to tailor the copolymer microstructure. Two strategies were used to successfully synthesize copolymers of different microstructures with the two initiator systems, i.e., a more multiblock‐ or a block‐structure. The correct choice of the monomer addition order enabled two distinct blocks to be created for the copolymers of poly(DXO‐co‐LLA) and poly(CL‐co‐LLA). In the case of poly(CL‐co‐DXO), multiblock copolymers were created using both systems whereas longer blocks were created with the spirocyclic tin initiator. © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 1249–1264, 2008     

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     

Cationic copolymerization of ε‐caprolactone and L,L‐lactide by an activated monomer mechanism

The cationic homopolymerization and copolymerization of L,L ‐lactide and ε‐caprolactone in the presence of alcohol have been studied. The rate of homopolymerization of ε‐caprolactone is slightly higher than that of L,L ‐lactide. In the copolymerization, the reverse order of reactivities has been observed, and L,L ‐lactide is preferentially incorporated into the copolymer. Both the homopolymerization and copolymerization proceed by an activated monomer mechanism, and the molecular weights and dispersities are controlled {number‐average degree of polymerization = ([M]₀ ? [M]_t)/[I]₀, where [M]₀ is the initial monomer concentration, [M]_t is the monomer concentration at time t, and [I]₀ is the initial initiator concentration; weight‐average molecular weight/number‐average molecular weight ～1.1–1.3}. An analysis of ¹³C NMR spectra of the copolymers indicates that transesterification is slow in comparison with propagation, and the microstructure of the copolymers is governed by the relative reactivity of the comonomers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7071–7081, 2006     

Synthesis of three‐armed poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L‐proline)‐block‐poly(ε‐caprolactone) copolymers

A series of novel types of three‐armed poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline)‐block‐poly(ε‐caprolactone) (PHpr‐b‐PCL) copolymers were successfully synthesized via melt block copolymerization of trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline (N‐CBz‐Hpr) and ε‐caprolactone (ε‐CL) with a trifunctional initiator trimethylolpropane (TMP) and stannous octoate (SnOct₂) as a catalyst. For the homopolycondensation of N‐CBz‐Hpr with TMP initiator and SnOct₂ catalyst, the number‐average molecular weight (M_n) of prepolymer increases from 530 to 3540 g mol^?1 with the molar ratio of monomer to initiator (3–30), and the molecular weight distribution (M_w/M_n) is between 1.25 to 1.32. These three‐armed prepolymer PHpr were subsequently block copolymerized with ε‐caprolactone (ε‐CL) in the presence of SnOct₂ as a catalyst. The M_n of the copolymer increased from 2240 to 18,840 g mol^?1 with the molar ratio (0–60) of ε‐CL to PHpr. These products were characterized by differential scanning calorimetry (DSC), ¹H NMR, and gel permeation chromatography. According to DSC, the glass‐transition temperature (T_g) of the three‐armed polymers depended on the molar ratio of monomer/initiator that were added. In vitro degradation of these copolymers was evaluated from weight‐loss measurements and the change of M_n and M_w/M_n. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1708–1717, 2005     

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     

Polyester oligodiols by cationic AM copolymerization of L,L‐lactide and ε‐caprolactone initiated by diols

Cationic copolymerization of L,L ‐lactide (LA) and ε‐caprolactone (CL) initiated by low molecular weight diols in the presence of acid catalyst gives corresponding copolyesters terminated at both ends with hydroxyl groups in practically quantitative yield. Copolymerization proceeds by Activated Monomer mechanism. LA is consumed preferentially and at the later stages of copolymerization the reaction mixture is enriched with CL. In spite of that, random distribution of both units is observed and end‐groups are mainly ? LA‐OH groups and not ? CL‐OH groups. This is explained by the fact that to reach high conversion of both comonomers the relatively long reaction times are required and at those conditions transesterification reaction becomes significant. Thus the microstructure of copolymers and the nature of the end‐groups is governed by transesterification rather then by the kinetics of comonomers incorporation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3090–3097, 2007     

Brønsted acid‐catalyzed polymerization of ε‐caprolactone in water: A mild and straightforward route to poly(ε‐caprolactone)‐graft‐water‐soluble polysaccharides

The polymerization of ε‐caprolactone (ε‐CL) has been assessed in water using various Brønsted acids as catalysts. The reaction was found to be quantitative at 100 °C, leading to number–average molecular weights up to 5000 g mol^?1. The Brønsted acid‐catalyzed polymerization of ε‐CL in water was further conducted in the presence of water‐soluble polysaccharides thereby affording graft copolymers. The approach enables an easy, mild access to dextran hydroxyesters. For low degree of substitution, the latter self‐assembles in water to form nanoparticles. Poly(ε‐CL)‐graft‐methylcellulose copolymers can also be obtained via a similar approach. It is noteworthy that the methodology reported herein is a one‐step route to poly(ε‐CL)‐graft‐water‐soluble polysaccharides, operating in mild conditions, that is, at low temperatures, using readily available metal‐free catalysts and water as a solvent. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2139–2145     

An efficient avenue to poly(styrene)‐block‐poly(ε‐caprolactone) polymers via switching from RAFT to hydroxyl functionality: Synthesis and characterization

The recently introduced procedure of quantitatively switching thiocarbonyl thio capped (RAFT) polymers into hydroxyl terminated species was employed to generate narrow polydispersity (PDI ≈ 1.2) sulfur‐free poly(styrene)‐block‐poly(ε‐caprolactone) polymers (26,000 ≤ M_n/g·mol^?1 < 45,000). The ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) was conducted under organocatalysis employing 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD). The obtained block copolymers were thoroughly analyzed via size exclusion chromatography (SEC), NMR, as well as liquid adsorption chromatography under critical conditions coupled to SEC (LACCC‐SEC) to evidence the block copolymer structure and the efficiency of the synthetic process. The current contribution demonstrates that the RAFT process can serve as a methodology for the generation of sulfur‐free block copolymers via an efficient end group switch. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Carbohydrate‐based amphiphilic diblock copolymers: Synthesis,characterization, and aqueous properties

Amphiphilic poly(ε‐caprolactone)‐b‐poly[(methacrylate‐graft‐poly(ethylene oxide))‐co‐6‐O‐methacryloyl‐D ‐galactopyranose] (PCL‐b‐P(MAPEO‐co‐GaMa)) with various compositions and molecular weights were synthesized via a controlled four‐step strategy. The first step involves the synthesis of functionalized poly(ε‐caprolactone) macroinitiator by ring‐opening polymerization (ROP) of ε‐caprolactone (CL) as initiated by aluminum triisopropoxide (Al(OⁱPr)₃). After selective bromination of the hydroxyl end‐group of the resulting α‐isopropoxy, ω‐hydroxy poly(ε‐caprolactone) by using 2‐bromoisobutyryl bromide, the controlled radical copolymerization of α‐methoxy, ω‐methacrylate poly(ethylene oxide) (MAPEO) with 6‐O‐methacryloyl‐1,2;3,4‐di‐O‐isopropylidene‐D ‐galactopyranose (DIGaMa) was performed by atom transfer radical polymerization (ATRP) in THF at 60 °C using CuBr ligated with 1,1,4,7,10,10 hexamethyltriethylenetetramine (HMTETA) as catalytic complex. In the final step, isopropylidene protective functions were selectively removed using an aqueous formic acid solution leading to the expected amphiphilic graft 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 as well as the related critical micellization concentration (CMC) in aqueous media were determined by dynamic light scattering (DLS) and fluorescence spectroscopy, respectively. In parallel, the morphology of the solid deposits of micellar aggregates was examined with atomic force microscopy (AFM). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3662–3672, 2008