Initiators For Ring-opening Polymerization Research Articles

Synthesis and characterization of biodegradable amphiphilic ABC Y‐shaped miktoarm terpolymer by click chemistry for drug delivery

ABSTRACTBiodegradable amphiphilic ABC Y‐shaped triblock copolymer (MPBC) containing PEG, PBLA, and PCL segments was synthesized via the combination of enzymatic ring‐opening polymerization (ROP) of epsilon‐caprolactone, ROP of BLA‐N‐carboxyanhydride and click chemistry, where PEG, PBLA, and PCL are poly(ethylene glycol), poly(benzyl‐l‐aspartate), and polycaprolactone, respectively. Propynylamine was employed as ROP initiator for the preparation of alkynyl‐terminated PBLA and methyloxy‐PEG with hydroxyl and azide groups at the chain‐end was used as enzymatic ROP initiator for synthesis of monoazido‐midfunctionalized block copolymer mPEG‐b‐PCL. The subsequent click reaction led to the formation of Y‐shaped asymmetric heteroarm terpolymer MPBC. The polymer structures were characterized by different analyses. The MPBC terpolymer self‐assembled into micelles and physically encapsulated drug doxorubicin (DOX) to form DOX‐loaded micelles, which showed good stability and slow drug release. In vitro cytotoxicity study indicated that the MPBC micelles were nontoxic and the DOX‐loaded micelles displayed obvious anticancer activity similar to free DOX against HeLa cells. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3346–3355

Ring-opening polymerization of ɛ-caprolactone with dilithium tetra-tert-butylzincate under mild conditions

We performed ring-opening polymerization (ROP) of ɛ-caprolactone with dilithium tetra-tert-butylzincate (TBZL) in toluene. TBZL is a bulky zincate complex with a range of unique reactivities such as unusually low basicity and high chemoselectivity; it is a metal catalyst of low toxicity. The initiating species for ROP of ɛ-caprolactone is, however, not the tert-butyl anion of TBZL but the hydroxyl anion derived from a trace amount of H2O in the system. Instead of a trace amount of H2O in the system, a known amount of benzyl alcohol (BnOH) was added as an ROP initiator. Poly(ɛ-caprolactone) with a BnO group at the initiating chain-end was obtained, as expected. 1H and 13C NMR spectra of a TBZL–BnOH mixture suggested the formation of a complex; the complex was the initiating species. The Mn increased linearly with increasing conversion. This means that the number of polymer chains is constant throughout the polymerization. The molecular weight distributions were relatively narrow, except with increased temperatures and/or prolonged polymerization times. This system does not need a high polymerization temperature or long polymerization time and uses a metal compound that has little effect on the environment. Poly(ɛ-caprolactone) with a narrow molecular weight distribution can therefore be obtained under mild conditions. Ring-opening polymerization (ROP) of ɛ-caprolactone with dilithium tetra-tert-butylzincate (TBZL) in toluene was performed. The initiating species for the ROP of ɛ-caprolactone is not the tert-butyl anion of TBZL but the hydroxyl anion derived from a trace amount of H2O or alcohol. Poly(ɛ-caprolactone) with a BnO group at the initiating chain-end was obtained by adding benzyl alcohol as an initiator, as expected. The molecular weight distributions were relatively narrow, except with increased temperatures and/or prolonged polymerization times. This system does not need a high polymerization temperature or long polymerization time.

New metal Aryloxide complexes as ceramic precursors and Initiators for ROP

In addition to the development of new energy-producing processes, finding new energy-saving procedures offers a promising solution to meet our energy needs in the long run. Indeed, cheap organometallic precursors for oxide materials and catalysis are key technologies for energy saving. A wide variety of metal alkoxides/aryloxides[1] has been used not only as precursors for oxide materials, but also as initiators and catalysts for ring-opening polymerization (ROP). Ceramic oxide materials are widely used for many applications, exceptionally in lithium-ion batteries (LIB) material for the last for these recent decades. Also, due to the use of cyclic esters in the tailoring synthesis of biodegradable and bioresorbable materials, interest in the development of well-defined initiators and catalysts has increased. For both cited reasons, iron-based aryloxide complexes offer many advantages, such as the large abundance of iron, their low toxicity and even their biocompatibility[1]. Aryloxide/alkoxide complexes have been also proposed like good route precursors due to their high solubility, low decomposition temperatures, cross linking ability, ease of modification and commercial availability[2].

The 1,3-bis(dicyanomethylidene)indane skeleton as a (photo) initiator in thermal ring opening polymerization at RT and radical or cationic photopolymerization

1,3-Bis(dicyanomethylidene)indane is presented as a new initiator for ring opening polymerization of epoxides at RT. This compound behaves as a strong acid (AH) with an associated basic form (A−) that does not inhibit the propagation of the cationic polymerization. Remarkably, A− is characterized by a strong visible light absorption and can also photosensitize iodonium salt decomposition. A new iodonium salt based on A− as a counter-anion is proposed. This latter compound exhibits unusual properties: (i) excellent absorption in the 300–700 nm wavelength range and (ii) a free radical initiating ability for λ > 300 nm. The chemical mechanisms are investigated by ESR, fluorescence and steady state photolysis experiments.

Trinuclear and Tetranuclear Magnesium Alkoxide Clusters as Highly Active Initiators for Ring-Opening Polymerization of l-Lactide

Trinuclear and tetranuclear magnesium alkoxide clusters supported by bulky phenolates with triangular or rhombic structures were readily synthesized in acceptable yields via the reaction of 2-N,N-dimethylaminoethanol/methoxyethanol, different phenols, and dibutylmagnesium. These complexes have been characterized using (1)H and (13)C NMR, elemental analyses, and X-ray crystallography. The experimental results indicate that these clusters are efficient and excellent initiators for the ring-opening polymerizations (ROPs) of l-lactide (LA) and afford polylactides with desired molecular weights and narrow polydispersity indexes (PDIs). Complex 2 can even catalyze the ROP of 4000 equiv of l-lactide in 1 min in a controlled model. Kinetic studies indicate that the polymerization is first-order for both the trinuclear magnesium complex 3 and LA. However, for the tetranuclear magnesium complex 5, the polymerization rate is first order for 5 and second order for LA.

Facile Synthesis of β‐Diketone Alcohols for Combined Functionality: Initiation, Catalysis, and Luminescence

Primary alcohol-functionalized β-diketones (bdks) are successfully synthesized via facile one-step Claisen condensation between aromatic monoketones and ε-caprolactone (ε-CL). To demonstrate application potentials, these bdk alcohols are used to chelate with various Lewis acids, including Tb (III), Eu (III), and B (III). It is discovered that the resulting Tb (III) and Eu (III) diketonate complexes can serve as both catalysts and initiators for ring-opening polymerization (ROP) under solvent-free conditions, using lactide monomer as an example. The polylactides (PLAs) thus obtained exhibit luminescence properties characteristic of Tb (III) and Eu (III), respectively. On the other hand, boron-chelated diketone can initiate ROP of lactide in the presence of Sn(oct)2 , and affords a PLA material with dual-emission, i.e., fluorescence and room temperature phosphorescence. The synthesis described here represents a shortcut for the preparation of bdk-based macroligands and subsequent functional materials.

One-pot synthesis of poly(triazole-graft-caprolactone) via ring-opening polymerization combined with click chemistry as a novel strategy for graft copolymers

The one-pot construction of polytriazole grafted with poly(ε-caprolactone) via the polymerization of 4-azido-1-(prop-2-yn-1-yloxy)butan-2-ol (N3hydroxypropargyl) and ε-caprolactone monomers is reported. For this purpose, a click reaction and ring-opening polymerization (ROP) were combined and carried out simultaneously. N3hydroxypropargyl served as both the ROP initiator and a monomer for the click polymerization. Thus, an in situ “grafting-through and from” strategy was established in one pot. CuBr and Sn(Oct)2 were utilized as dual catalysts, and the polymerization reactions were carried out at 120°C under a N2 atmosphere.

Synthesis of binary-patterned brushes by combining atom transfer radical polymerization and ring-opening polymerization

Abstract This paper report the synthesis of binary-patterned brushes, combining two distinctive surface initiated-polymerizations (SIP) on the basis of different propagating species: the SI Ring Opening Polymerization (ROP) of L-Lactide (LLA) and SI atom transfer radical polymerization (ATRP) of N,N’-dimethylaminoethyl methacrylate (DMAEMA) on gold surface. First of all, a careful study of surfaceinitiated ROP of L-Lactide from hydroxyl end-group of thiol monolayer on gold surface as catalyzed by metal-free catalyst was carried out. The PLLA brushes synthesis was evaluated using two types of thiol monolayer and revealed the influence of ROP initiator chain length on the final thickness of the PLLA film. Combining the soft lithographic technique, microcontact printing, and the liquid phase deposition, the deposition onto specific micro-domains of both initiators was performed. The growth of PDMAEMA brushes and PLLA brushes was conducted by successive ATRP and ROP.

Synthesis of binary-patterned brushes by combining atom transfer radical polymerization and ring-opening polymerization

This paper report the synthesis of binary-patterned brushes, combining two distinctive surface initiated-polymerizations (SIP) on the basis of different propagating species: the SI Ring Opening Polymerization (ROP) of L-Lactide (LLA) and SI atom transfer radical polymerization (ATRP) of N,N’-dimethylaminoethyl methacrylate (DMAEMA) on gold surface. First of all, a careful study of surfaceinitiated ROP of L-Lactide from hydroxyl end-group of thiol monolayer on gold surface as catalyzed by metal-free catalyst was carried out. The PLLA brushes synthesis was evaluated using two types of thiol monolayer and revealed the influence of ROP initiator chain length on the final thickness of the PLLA film. Combining the soft lithographic technique, microcontact printing, and the liquid phase deposition, the deposition onto specific micro-domains of both initiators was performed. The growth of PDMAEMA brushes and PLLA brushes was conducted by successive ATRP and ROP.

One-pot synthesis of poly(N-vinylcaprolactam)-based biocompatible block copolymers using a dual initiator for ROP and RAFT polymerization

Thermosensitive, biocompatible poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) (PCL-b-PVCL), poly(δ-valerolactone)-b-PVCL, and poly(trimethylene carbonate)-b-PVCL block copolymers were synthesized at 30 °C using a hydroxyl-functionalized xanthate reversible addition-fragmentation chain transfer (RAFT) agent, 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate (HECP), as a dual initiator for ring-opening polymerization (ROP) and RAFT polymerization in a one-pot procedure. The hydrophobic blocks were first synthesized by the ROP of cyclic monomers using diphenyl phosphate (DPP) as a catalyst and the RAFT polymerization of the PVCL block was followed by adding N-vinylcaprolactam (VCL) and 2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile) (V-70) as an initiator to the reaction mixture. This novel one-pot process is convenient and powerful method for the synthesis of the PVCL-based biocompatible block copolymers. The lower critical solution temperature (LCST) of the PVCL-based biocompatible block copolymer can be readily tuned by controlling the hydrophobicity of the block copolymers. By copolymerizing a hydrophilic N-vinylpyrrolidone moiety to the PVCL blocks by RAFT copolymerization, the LCST of the copolymer was matched with the body temperature for its future biomedical applications.

One-pot synthesis of poly(vinyl alcohol)-based biocompatible block copolymers using a dual initiator for ROP and RAFT polymerization

Biocompatible poly(ε-caprolactone)-b-poly(vinyl alcohol) (PCL-b-PVA), poly(δ-valerolactone)-b-PVA, and poly(trimethylene carbonate)-b-PVA block copolymers were synthesized at 30 °C using a hydroxyl-functionalized xanthate reversible addition-fragmentation chain transfer (RAFT) agent, 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate, as a dual initiator for ring-opening polymerization (ROP) and RAFT polymerization in a one-pot procedure. The ROP of ε-caprolactone, δ-valerolactone, and trimethylene carbonate was first performed using diphenyl phosphate as the ROP catalyst followed by the RAFT polymerization of vinyl chloroacetate after quenching the ROP with 4-dimethyamino pyridine. The resulting block copolymers were aminolyzed directly to the PVA-based biocompatible block copolymers by adding hexylamine to the reaction mixture. To the best of our knowledge, this is the most convenient method for synthesizing PVA-based biocompatible block copolymers.

Neutral and Cationic N‐Heterocyclic Carbene Zinc Adducts and the BnOH/Zn(C6F5)2 Binary Mixture – Characterization and Use in the Ring‐Opening Polymerization of β‐Butyrolactone, Lactide, and Trimethylene Carbonate

AbstractA variety of N‐heterocyclic carbene (NHC) zinc adducts of the type NHC–ZnMe2 [2a, NHC = 1,3‐dimesitylimidazol‐2‐ylidene; 2b, NHC = 1,3‐(2,6‐iPr2Ph)2‐imidazol‐2‐ylidene; 2c, NHC = 1,3‐di‐tert‐butylimidazol‐2‐ylidene] and NHC–Zn(C6F5)2 [4a, NHC = 1,3‐dimesitylimidazol‐2‐ylidene; 4b, NHC = 1,3‐(2,6‐iPr2Ph)2‐imidazol‐2‐ylidene; 4c, NHC = 1,3‐di‐tert‐butylimidazol‐2‐ylidene] were synthesized by reaction of the appropriate NHC ligand with ZnMe2 or (toluene)Zn(C6F5)2. The X‐ray molecular structures of derivatives 2b, 4b, and 4c confirmed their adduct nature, and their bonding and geometrical parameters are influenced by the nature of the Zn–X group. The ionization reaction of the dimethyl Zn species 2a and 2b with the methide abstracting reagent B(C6F5)3 in the presence of tetrahydrofuran (THF) afforded the NHC–Zn organocations (1,3‐dimesitylimidazol‐2‐ylidene)Zn(Me)(THF)2+ (3a+) and [1,3‐(2,6‐iPr2Ph)2‐imidazol‐2‐ylidene]Zn(Me)(THF)+ (3b+) as dissociated MeB(C6F5)3– salts, as deduced from NMR spectroscopic data. All of these NHC–Zn compounds and BnOH/Zn(C6F5)2 were tested as ring‐opening polymerization (ROP) initiators of β‐butyrolactone (β‐BL), rac‐lactide (rac‐LA), and trimethylene carbonate (TMC). Although cations 3a+ and 3b+ were both inactive ROP initiators, as they appear to decompose prior to any ROP activity, the NHC–Zn(C6F5)2 compounds readily mediate the ROP of β‐BL, rac‐LA, and TMC to afford the corresponding polymeric materials with a moderate level of control, as deduced from NMR, size‐exclusion chromatography (SEC), and mass spectrometric MALDI‐TOF data. In contrast, the use of the alcohol BnOH (instead of a NHC moiety) as a nucleophile for association with (toluene)Zn(C6F5)2 led to efficient, highly controlled, and immortal ROP of TMC and rac‐LA with the formation of controlled chain length and narrowly disperse materials.

Diamido-Ether Actinide Complexes as Initiators for Lactide Ring-Opening Polymerization

The synthesis and characterization of a series of new diamido-ether actinide(IV) alkoxide complexes are reported. Addition of 2 equiv of LiOiPr to [tBuNON]ThCl5Li3·DME ([tBuNON]2– = [(tBuNSiMe2)2O]2–) in toluene gives [tBuNON]Th(OiPr)3Li·DME (1-DME). Recrystallization of 1-DME from diethyl ether gives [tBuNON]Th(OiPr)3Li·Et2O (1-Et2O). The addition of 2 equiv of LiOiPr to {[tBuNON]UCl2}2 gives {[tBuNON]U(OiPr)2}2 (2). If KOtBu is used instead, the product is {[tBuNON]U(OtBu)}2 (3). The reaction of 2 equiv of KOtBu with [iPr2PhNCOCN]ThCl2·DME ([iPr2PhNCOCN]2– = [(2,6-iPr2PhNCH2CH2)2O]2–) gives [iPr2PhNCOCN]Th(OtBu)2 (4), while addition of 1 equiv of KOtBu to [iPr2PhNCOCN]UCl3Li·THF results in [iPr2PhNCOCN]U(OtBu)Cl (5). Complexes 1–5 as well as the previously reported diamido actinide dialkyl complexes [tBuNON]An(CH2SiMe3)2 (An = Th (6), U (7)) and [iPr2PhNCOCN]An(CH2SiMe3)2 (An = Th (8), U (9)) were evaluated as initiators for the ring-opening polymerization (ROP) of l-lactide (l-LA) and racemic lactide (...

Mesoporous Polystyrenes via Lamellar Block Copolymer Assembly

Block copolymers (BCPs) are well-known to self-assemble into a variety of nanostructures, such as spherical, cylindrical, gyroid-like, and lamellar morphologies, depending on the volume fraction of the block and/or the chain architecture. Organic mesoporous materials applicable to separations, sensors, etc., could be one of the interesting fields using block copolymers. To prepare organic mesoporous materials, block copolymers should consist of chemically inert and labile blocks. A polystyrene-block-polylactide (PS-b-PLA) system is a representative example. The PS block is mechanically and chemically robust, while the PLA block is easily hydrolyzed under basic conditions. In a given morphology, PLA domain structures determine the resulting pore morphology. Among possible pore architectures, one-dimensional cylindrical pores have been intensively studied, perhaps because the morphology exists over a wide range of volume fraction, and also because it consists of confined pores. Recently, a three-dimensionally connected mesoporous structure from a gyroid morphology was also reported. On the other hand, due to its wide volume fraction range near 0.5, a lamellar morphology can be obtained as readily as a cylindrical morphology. Nevertheless, a lamellar morphology has rarely been utilized for preparing organic mesoporous materials. With this in mind, it would be interesting to prepare lamellar mesoporous materials using a lamellar BCP. In this paper, we report a mesoporous material, consisting of PS layers, by a chemical etching of sacrificial PLA layers in a lamellar structure. To obtain the porous material, we first synthesized a block copolymer (PS-b-PLA) using a click reaction of individually prepared PS and PLA blocks. The PS was prepared by the anionic polymerization of styrene. The PS end was functionalized with a hydroxyl group, which was converted into an alkynyl group for the next click coupling (Scheme S1(b)). From the H NMR data, the number average molecular weight (Mn) of the obtained PS was determined to be 14,400 g/mol. The other PLA block was synthesized by a ring opening polymerization (ROP) of D,L-lactide using triethyl aluminum as the catalyst (Scheme S1(c)). For the click coupling with the PS block, the ROP initiator contained an azide end. From the H NMR analysis, the Mn was estimated to be 10,500 g/mol, and the GPC data showed the polydispersity (Mw/Mn) to be 1.06. The click coupling was carried out using Cu(I)Br/PMDETA as the catalyst (Scheme 1). The obtained block copolymer showed a triazolyl hydrogen at 7.39 ppm in the H NMR spectrum (Figure S1), and the polydispersity was 1.04, indicative of its narrow molecular weight distribution (Figure S2). The volume fraction ( f ) of the PS block was calculated to be 0.60. The differential scanning calorimetry (DSC) data of the block copolymer displayed two glass transitions at 51.4 C

Structurally well-defined group 4 metal complexes as initiators for the ring-opening polymerization of lactide monomers

Polylactide (PLA) is an attractive polymeric material due to its origin from annually renewable resources and its biodegradability. The ring-opening polymerization (ROP) of lactide initiated by Lewis acidic and oxophilic metal-based catalysts constitutes the method of choice to access PLA in a controlled and stereoselective manner. The design and synthesis of ligand-supported metal complexes to act as effective ROP initiators of lactide monomers have been the subject of numerous investigations over the past decades. In view of their oxophilic nature, well-defined group 4 metal complexes supported by polydentate supporting ligands have appeared as active initiators for lactide ROP. This perspective summarizes various classes of structurally well-defined group 4 metal initiators developed for lactide ROP. It also provides observed trends regarding their catalytic performance. Whenever appropriate and possible, catalyst structure-ROP performance (i.e. activity, control and stereoselectivity) relationships are rationalized.

Synthesis and structural determination of zinc complexes based on an anilido-aldimine ligand containing an O-donor pendant arm: zinc alkoxide derivative as an efficient initiator for ring-opening polymerization of cyclic esters

Zinc complexes bearing the anilido-aldiminate AA(OMe) ligand (AA(OMe)-H = (E)-2,6-diisopropyl-N-(2-(((2-methoxyethyl)imino)methyl)phenyl)aniline) were synthesized in a stepwise method and were structurally characterized. The reaction of AA(OMe)-H (1) with one equivalent of diethyl zinc (ZnEt2) furnishes a three-coordinated and mononuclear zinc complex [(AA(OMe))ZnEt] (2). Further reaction of 2 with a stoichiometric amount of benzyl alcohol (BnOH) affords a four-coordinated and dinuclear zinc benzylalkoxide complex [(AA(OMe))Zn(μ-OBn)]2 (3). In the presence of two equivalents of AA(OMe)-H with ZnEt2, a homoleptic and four-coordinated zinc complex [(AA(OMe))2Zn] (4) is formed. The geometry around the zinc centres of 3 and 4 are both distorted tetrahedrals, while 2 adopts a different coordination mode with a slightly distorted trigonal planar geometry. The variable-temperature (1)H NMR studies of 3 illustrate that 3 exhibits a dinuclear structure in solution at low temperature as well as in the solid state. While raising the temperature, it drifts towards dissociation to form a mononuclear zinc benzylalkoxide species, which coexists in solution. The ring-opening polymerizations of ε-caprolactone (ε-CL) and β-butyrolactone (β-BL) catalyzed by complexes 3 and 4 are investigated. The ε-CL and β-BL polymerizations initiated by zinc alkoxide 3 were demonstrated to have living characteristics and to proceed in a controlled manner with narrow polydispersity indices (PDIs < 1.12). An efficient catalytic performance for the β-BL polymerization with a high monomer-to-initiator ratio (1200/1) initiated by 3 has also been reported.

Synthesis and structures of tridentate ketoiminate zinc complexes bearing trifluoromethyl substituents that act as l-lactide ring opening polymerization initiators

A series of NNO ketoimines bearing trifluoromethyl substituents were synthesized from the Schiff base condensation of 1,3-diketones (1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione, 4,4,4-trifluoro-1-phenyl-1,3-butanedione, and 1,1,1-trifluoro-2,4-pentanedione, 1,1,1,5,5,5-hexafluoroacetylacetone) and 8-aminoquinoline or 8-amino-2-methylquinoline and isolated in 40-70% yield. The ketoimines were combined with zinc bis-(trimethylsilyl)amide to prepare a zinc amide complex in 41% yield or were combined with zinc bis-(trimethylsilyl)amide and 2,6-di-tert-butylphenol to prepare zinc phenoxide complexes in 81-94% yield. The ketoimines and zinc complexes were characterized with (1)H, (13)C, and (19)F NMR, absorbance spectroscopy, mass spectrometry, elemental analysis and X-ray crystallography. The mononuclear solid state structures of the zinc amide and phenoxide complexes showed tridentate coordination of the zinc center by the ketoiminate and monodentate coordination by the amide or phenoxide. The zinc complexes were assessed for their ability to catalyze the ring opening polymerization (ROP) of L-lactide into poly-lactic acid (PLA) with some complexes reaching 100% conversion in 3 h. As the monomer to catalyst ratio increased, the molecular weight of the isolated polymeric material increased in a nearly linear fashion while retaining a narrow molecular weight distribution. Homonuclear decoupled (1)H NMR spectra of the isolated polymeric material showed the retention of stereochemistry in the isotactic poly-L-lactic acid. Kinetic studies, where the substituents on the ketoiminate and quinolyl moiety were varied, showed that lower electron density on the Zn metal center yielded lower ROP catalytic activity than their electron rich counterparts. The complexes are proposed to use the coordination-insertion mechanism for living polymerization of L-lactide.

One‐step synthesis of block copolymers using a hydroxyl‐functionalized trithiocarbonate RAFT agent as a dual initiator for RAFT polymerization and ROP

AbstractA range of well‐defined block copolymers were synthesized using 4‐cyano‐4‐(dodecylsulfanylthiocarbonyl)sulfanylpentanol (CDP) as a dual initiator for reversible addition‐fragmentation chain transfer (RAFT) polymerization and ring‐opening polymerization (ROP) in a one‐step process. Styrene, (meth)acrylate, and acrylamide monomers were polymerized in a controlled manner for one block composed of vinyl monomers, and δ‐valerolactone (VL), ε‐caprolactone (CL), trimethylene carbonate (TMC), and L‐lactide (LA) were used for the other block composed of cyclic monomers. Diphenyl phosphate was used as a catalyst for the ROP of VL, CL, and TMC, and 4‐dimethyamino pyridine for the ROP of LA. These catalysts did not interfere with RAFT polymerization and the synthesis of various block copolymers proceeded in a controlled manner. CDP was found to be a very useful dual initiator for a one‐step synthesis of various block copolymers by a combination of RAFT polymerization and ROP. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

New Design of Thiol‐Responsive Degradable Polylactide‐Based Block Copolymer Micelles

A new design to synthesize thiol-responsive degradable polylactide (PLA)-based micelles having a disulfide linkage in the middle of triblock copolymers is reported. They were synthesized by a new method that centers on the use of a disulfide-labeled diol as an initiator for ring-opening polymerization, followed by controlled radical polymerization. These well-controlled copolymers with monomodal and narrow molecular weight distribution (M(w) /M(n) < 1.15) self-assembled to form aqueous micellar aggregates with disulfide-containing PLA cores, which is not toxic to cells. Central disulfide linkages were cleaved in response to thiols; such thiol-triggered degradation enhanced the release of encapsulated anticancer drugs.

Development of creatine and arginine-6-oligomer for the ring-opening polymerization of cyclic esters

Natural creatine and arginine-6-oligomer have been effectively engaged as ring-opening polymerization initiators of poly(L-lactide) (PLLA) and poly(ɛ-caprolactone) (PCL) in bulk. The nonlinear structure and thermal properties of the resulted polymers were further elucidated by 1H, 13C nuclear magnetic resonance, and a modulated differencial scanning calorimetry (MDSC). Thermal analysis indicated that the synthesized polymers had lower melting points, glass-transition temperatures, fusion enthalpy, and crystallization temperature than those of linear PCL or PLLA due to the presence of the arginine-6-oligomer in the macromolecule and crystalline imperfections caused by the branched structure. This study provides an efficient and metal-free method for the synthesis of branched biodegradable polymers with incorporated compounds, which exhibit therapeutic properties, adequate for the drug carrier applications. Open image in new window