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     

Synthesis of 4μ‐PS2PEO2, 4μ‐PS2PCL2, 4μ‐PI2PEO2, and 4μ‐PI2PCL2 star‐shaped copolymers by the combination of glaser coupling with living anionic polymerization and ring‐opening polymerization

4μ‐A₂B₂ star‐shaped copolymers contained polystyrene (PS), poly(isoprene) (PI), poly(ethylene oxide) (PEO) or poly(ε‐caprolactone) (PCL) arms were synthesized by a combination of Glaser coupling with living anionic polymerization (LAP) and ring‐opening polymerization (ROP). Firstly, the functionalized PS or PI with an alkyne group and a protected hydroxyl group at the same end were synthesized by LAP and then modified by propargyl bromide. Subsequently, the macro‐initiator PS or PI with two active hydroxyl groups at the junction point were synthesized by Glaser coupling in the presence of pyridine/CuBr/N,N,N ′,N ″,N ″‐penta‐methyl diethylenetri‐amine (PMDETA) system and followed by hydrolysis of protected hydroxyl groups. Finally, the ROP of EO and ε‐CL monomers was carried out using diphenylmethyl potassium (DPMK) and tin(II)‐bis(2‐ethylhexanoate) (Sn(Oct)₂) as catalyst for target star‐shaped copolymers, respectively. These copolymers and their intermediates were well characterized by SEC, ¹H NMR, MALDI‐TOF mass spectra and FT‐IR in details. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

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     

Titanium complexes based on aminodiol ligands for the ring‐opening polymerization of ε‐caprolactone,rac‐β‐butyrolactone,and trimethylene carbonate

Several titanium complexes based on aminodiol ligands were tested as initiators for the ring‐opening polymerization (ROP) of ε‐caprolactone under solution and bulk conditions. All complexes were found to be efficient under both conditions. For bulk polymerization at 70 °C, high activities were observed (113.3–156.2 g_poly mmol_cat^?1 h^?1) together with controlled molar mass distribution. Kinetic studies revealed controlled polymerization, and the chain propagation was first order with respect to monomer conversion. One complex was also tested for the ROP of rac‐β‐butyrolactone and the end‐group analysis suggested that ring opening occurs through acyl‐oxygen bond cleavage via coordination–insertion mechanism. The microstructure analysis of polymer by ¹³C NMR indicates atactic polymer. Another complex was also found to be efficient initiator for the ROP of trimethylene carbonate under solution and bulk conditions. Again, end‐group analysis suggests coordination–insertion mechanism. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

Organocatalyzed ring‐opening polymerization of cyclic butylene terephthalate oligomers

In this study, various organic compounds, with different activation modes, have been tested as catalysts for the ring‐opening polymerization (ROP) of cyclic butylene terephthalate oligomers (CBT) in bulk at 210 °C, using tert‐butylbenzyl alcohol (tBnOH) as initiator. Among them, 1,3,5‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) appeared to be the most efficient, achieving high monomer conversions in short reaction times (within minutes). Analysis by size‐exclusion chromatography (SEC) of the poly(butylene terephthalate) (PBT) synthesized using this catalyst also showed that the polymerization follows the expected theoretical M _n trend for molecular weights up to 50 kg·mol^?1. Chain‐end fidelity relatively to the alcohol initiator has been confirmed by MALDI‐TOF mass spectroscopy, which showed that all polymer chains possess the tert‐butylbenzyl moiety as chain‐end. Finally, to demonstrate the potential of this system for the synthesis of PBT‐based block copolymers, a monomethyl ether poly(ethylene glycol) (PEG) of 5000 g·mol^?1 has been employed as initiator for the ROP of CBT. A PEO‐b‐PBT block copolymer of 15,000 g·mol^?1 could thus been obtained, as confirmed by the shift of the SEC traces towards higher molecular weights and the same diffusion coefficient determined for ¹H NMR signals of the PEO block and the PBT block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1611–1619     

Thermoplastic elastomers based on poly(l‐Lysine)‐Poly(ε‐Caprolactone) multi‐block copolymers

Novel thermoplastic elastomers based on multi‐block copolymers of poly(l ‐lysine) (PLL), poly(N‐ε‐carbobenzyloxyl‐l ‐lysine) (PZLL), poly(ε‐caprolactone) (PCL), and poly(ethylene glycol) (PEG) were synthesized by combination of ring‐opening polymerization (ROP) and chain extension via l ‐lysine diisocyanate (LDI). SEC and ¹H NMR were used to characterize the multi‐block copolymers, with number‐average molecular weights between 38,900 and 73,400 g/mol. Multi‐block copolymers were proved to be good thermoplastic elastomers with Young's modulus between 5 and 60 MPa and tensile strain up to 1300%. The PLL‐containing multi‐block copolymers were electrospun into non‐woven mats that exhibited high surface hydrophilicity and wettability. The polypeptide–polyester materials were biocompatible, bio‐based and environment‐friendly for promising wide applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3012–3018     

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     

Synthesis and characterization of well‐defined ABC 3‐Miktoarm star‐shaped terpolymers based on poly(styrene), poly(ethylene oxide), and poly(ϵ‐caprolactone) by combination of the “living” anionic polymerization with the ring‐opening polymerization

A series of well‐defined ABC 3‐Miktoarm star‐shaped terpolymers [Poly(styrene)‐Poly(ethylene oxide)‐Poly(ε‐caprolactone)](PS‐PEO‐PCL) with different molecular weight was synthesized by combination of the “living” anionic polymerization with the ring‐opening polymerization (ROP) using macro‐initiator strategy. Firstly, the “living” poly(styryl)lithium (PS^?Li⁺) species were capped by 1‐ethoxyethyl glycidyl ether(EEGE) quantitatively and the PS‐EEGE with an active and an ethoxyethyl‐protected hydroxyl group at the same end was obtained. Then, using PS‐EEGE and diphenylmethylpotassium (DPMK) as coinitiator, the diblock copolymers of (PS‐b‐PEO)_p with the ethoxyethyl‐protected hydroxyl group at the junction point were achieved by the ROP of EO and the subsequent termination with bromoethane. The diblock copolymers of (PS‐b‐PEO)_d with the active hydroxyl group at the junction point were recovered via the cleavage of ethoxyethyl group on (PS‐b‐PEO)_p by acidolysis and saponification successively. Finally, the copolymers (PS‐b‐PEO)_d served as the macro‐initiator for ROP of ε‐CL in the presence of tin(II)‐bis(2‐ethylhexanoate)(Sn(Oct)₂) and the star(PS‐PEO‐PCL) terpolymers were obtained. The target terpolymers and the intermediates were well characterized by ¹H‐NMR, MALDI‐TOF MS, FTIR, and SEC. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1136–1150, 2008     

Synthesis and characterization of well‐defined poly(2‐hydroxyethyl methacrylate‐co‐styrene)‐graft‐poly(ε‐caprolactone) by sequential controlled polymerization

A new graft copolymer, poly(2‐hydroxyethyl methacrylate‐co‐styrene) ‐graft‐poly(?‐caprolactone), was prepared by combination of reversible addition‐fragmentation chain transfer polymerization (RAFT) with coordination‐insertion ring‐opening polymerization (ROP). The copolymerization of styrene (St) and 2‐hydroxyethyl methacrylate (HEMA) was carried out at 60 °C in the presence of 2‐phenylprop‐2‐yl dithiobenzoate (PPDTB) using AIBN as initiator. The molecular weight of poly (2‐hydroxyethyl methacrylate‐co‐styrene) [poly(HEMA‐co‐St)] increased with the monomer conversion, and the molecular weight distribution was in the range of 1.09 ～ 1.39. The ring‐opening polymerization (ROP) of ?‐caprolactone was then initiated by the hydroxyl groups of the poly(HEMA‐co‐St) precursors in the presence of stannous octoate (Sn(Oct)₂). GPC and ¹H‐NMR data demonstrated the polymerization courses are under control, and nearly all hydroxyl groups took part in the initiation. The efficiency of grafting was very high. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5523–5529, 2004     

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 amphiphilic A2B star‐shaped copolymers of polystyrene‐b‐[poly(ethylene oxide)]2 via atom transfer nitroxide radical coupling

The amphiphilic A₂B star‐shaped copolymers of polystyrene‐b‐[poly(ethylene oxide)]₂ (PS‐b‐PEO₂) were synthesized via the combination of atom transfer nitroxide radical coupling (ATNRC) with ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP) mechanisms. First, a novel V‐shaped 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐PEO₂ (TEMPO‐PEO₂) with a TEMPO group at middle chain was obtained by ROP of ethylene oxdie monomers using 4‐(2,3‐dihydroxypropoxy)‐TEMPO and diphenylmethyl potassium as coinitiator. Then, the linear PS with a bromine end group (PS‐Br) was obtained by ATRP of styrene monomers using ethyl 2‐bromoisobutyrate as initiator. Finally, the copolymers of PS‐b‐PEO₂ were obtained by ATNRC between the TEMPO and bromide groups on TEMPO‐PEO₂ and PS‐Br, respectively. The structures of target copolymers and their precursors were all well‐defined by gel permeation chromatographic and nuclear magnetic resonance (¹H NMR). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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 and characterization of crystalline graft polymer poly(ethylene oxide)‐g‐poly(ɛ‐caprolactone)2 with modulated grafting sites

The graft polymer poly(ethylene oxide)‐g‐poly(?‐caprolactone)₂ (PEO‐g‐PCL₂) with modulated grafting sites was synthesized by the combination of ring‐opening polymerization (ROP) mechanism, efficient Williamson reaction, with thiol–ene addition reaction. First, the precursor of PEO‐Allyl‐PEO with two terminal hydroxyl groups and one middle allyl group was prepared by ROP of EO monomers. Then, the macroinitiator [PEO‐(OH)₂‐PEO]_s was synthesized by sequential Williamson reaction between terminal hydroxyl groups and thiol–ene addition reaction on pendant allyl groups. Finally, the graft polymer PEO‐g‐PCL₂ was obtained by ROP of ?‐CL monomers using [PEO‐(OH)₂‐PEO]_s as macroinitiator. The target graft polymer and all intermediates were well characterized by the measurements of gel permeation chromatography, ¹H NMR, and thermal gravimetric analysis. The crystallization behavior was investigated by the measurements of differential scanning calorimetry, wide‐angle X‐ray diffraction and polarized optical microscope. The results showed that when the PCL content of side chains reached 59.2%, the crystalline structure had been dominated by PCL part and the crystalline structure formed by PEO part can be almost neglected. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2239–2247     

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     

One‐step synthesis of block‐graft copolymers via simultaneous reversible‐addition fragmentation chain transfer and ring‐opening polymerization using a novel macroinitiator

One‐step synthesis of block‐graft copolymers by reversible addition‐fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) by using a novel initiator was reported. Block‐graft copolymers were synthesized in one‐step by simultaneous RAFT polymerization of n‐butylmethacrylate (nBMA) and ROP of ε‐caprolacton (CL) in the presence of a novel macroinitiator (RAFT‐ROP agent). For this purpose, first epichlorohydrin (EPCH) was polymerized by using H₂SO₄ via cationic ring‐opening mechanism. And then a novel RAFT‐ROP agent was synthesized by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin (poly‐EPCH). By using the RAFT‐ROP agent, poly[CL‐b‐EPCH‐b‐CL‐(g‐nBMA)] block‐graft copolymers were synthesized. The principal parameters such as monomer concentration, initiator concentration, and polymerization time that affect the one‐step polymerization reaction were evaluated. The block lengths of the block‐graft copolymers were calculated by using ¹H‐nuclear magnetic resonance (¹H NMR) spectrum. The block length could be adjusted by varying the monomer and initiator concentrations. The characterization of the products was achieved using ¹H NMR, Fourier‐transform infrared spectroscopy, gel‐permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, elemental analysis, and fractional precipitation (γ) techniques. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2651–2659     

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     

One‐step synthesis of poly(N‐vinylpyrrolidone)‐b‐poly(l‐lactide) block copolymers using a dual initiator for RAFT polymerization and ROP

Amphiphilic, biocompatible poly(N‐vinylpyrrolidone)‐b‐poly(l ‐lactide) (PVP‐b‐PLLA) block polymers were synthesized at 60 °C using a hydroxyl‐functionalized N,N‐diphenyldithiocarbamate reversible addition–fragmentation chain transfer (RAFT) agent, 2‐hydroxyethyl 2‐(N,N‐diphenylcarbamothioylthio)propanoate (HDPCP), as a dual initiator for RAFT polymerization and ring‐opening polymerization (ROP) in a one‐step procedure. 4‐Dimethylamino pyridine was used as the ROP catalyst for l ‐lactide. The two polymerization reactions proceeded in a controlled manner, but their polymerization rates were affected by the other polymerization process. This one‐step procedure is believed to be the most convenient method for synthesizing PVP‐b‐PLLA block copolymers. HDPCP can also be used for the one‐step synthesis of poly(N‐vinylcarbazole)‐b‐PLLA block copolymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1607–1613     

Organic‐acid mediated bulk polymerization of ε‐caprolactam and its copolymerization with ε‐caprolactone

Polyamides (PA) constitute one of the most important classes of polymeric materials and have gained strong position in different areas, such as textiles, fibers, and construction materials. Whereas most PA are synthesized by step‐growth polycondensation, PA 6 is synthesized by ring opening polymerization (ROP) of ε‐caprolactam (ε‐CLa). The most popular ROP methods involve the use of alkaline metal catalyst difficult to handle at large scale. In this article, we propose the use of organic acids for the ROP of ε‐CLa in bulk at 180 °C (below the polymer's melting point). Among evaluated organic acids, sulfonic acids were found to be the most effective for the polymerization of ε‐CLa , being the Brønsted acid ionic liquid: 1‐(4‐sulfobutyl)?3‐methylimidazolium hydrogen sulfate the most suitable due to its higher thermal stability. End‐group analysis by ¹H nuclear magnetic resonance and model reactions provided mechanistic insights and suggested that the catalytic activity of sulfonic acids was a function of not only the acid strength, but of the nucleophilic character of conjugate base as well. Finally, the ability of sulfonic acid to promote the copolymerization of ε‐CLa and ε‐caprolactone is demonstrated. As a result, poly(ε‐caprolactam‐co‐ε‐caprolactone) copolymers with considerably randomness are obtained. This benign route allows the synthesis of poly(ester amide)s with different thermal and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2394–2402     

Exploration of tertiary aminosquaramide bifunctional organocatalyst in controlled/living ring‐opening polymerization of l‐lactide

A series of tertiary aminosquaramides as bifunctional organocatalysts in the ring‐opening polymerization (ROP) of l ‐lactide (l ‐LA) were developed, allowing the activation of both the l ‐LA monomer and the alcohol group of the initiator/propagating species. Further, the impact of tertiary nitrogen substituents on catalytic activity in ROP of l ‐LA was explored. The tertiary aminosquaramide— an air‐stable and moisture‐stable catalyst—exhibited superior activity in contest with thiourea counterpart when both were equipped with a similar tertiary amine group. Kinetic and chain‐extension experiments indicated that the formed poly(l ‐LA) is featured with narrow polydispersity and high end‐group fidelity, hallmarks of a living polymerization process. The initiator efficiency was further executed at ease by preparation of an ABA triblock copolymer poly (l ‐LA)‐b‐poly (ethylene glycol)‐b‐poly (l ‐LA) in the presence of a dual‐headed PEG macroinitiator. ¹H NMR titration experiments suggested a bifunctional catalytic mechanism, wherein both the l ‐LA monomer and the propagating hydroxyl group were activated en route to polymerization. The ¹H NMR, SEC, and MALDI‐TOF MS measurements validated the quantitative incorporation of the initiator in the polymeric chains and enchainment over competitive trans‐esterification reaction. Overall, the structure‐activity relationships were surveyed to uncover aminosquaramide as a new bifunctional dual hydrogen‐bond donor catalyst for living ROP of l ‐LA. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2483–2493