Polymerization Of CL Research Articles

Enzymatic Preparation of Novel Thermoplastic di-Block Copolyesters Containing Poly[(R)-3-hydroxybutyrate] and Poly(ϵ-Caprolactone) Blocks via Ring-Opening Polymerization

Enzymatic modification of a microbial polyester was achieved by the ring-opening polymerization of epsilon-caprolactone (CL) with low-molecular weight telechelic hydroxylated poly[( R)-3-hydroxybutyrate] (PHB-diol) as initiator and Novozym 435 (immobilized Candida antarctica Lipase B) as catalyst in anhydrous 1,4-dioxane or toluene. The ring-opening polymerization was investigated at different conditions with two different types of PHB-diols: PHB-diol(P), containing a primary OH and a secondary OH end groups, and PHB-diol(M), consisting of 91% PHB-diol(P) and 9% PHB-diol containing two secondary OH end groups. The reactions were followed by GPC analyses of the resulting polymers at different time points, and the optimal conditions were established to be 70 degrees C at a weight ratio of CL/enzyme/solvent of 8:1:24. The ring-opening polymerization of CL with PHB-diol(M) (Mn of 2380, NMR) at the molar ratio of 50:1 under the optimal conditions in 1,4-dioxane gave the corresponding poly[HB(56 wt %)-co-CL(44 wt %)] with Mn (NMR) of 3900 in 66% yield. Polymerization of CL and PHB-diol(P) ( Mn of 2010, NMR) at the same condition in toluene gave the corresponding poly[HB(28 wt %)-co-CL(72 wt %)] with Mn (NMR) of 7100 in 86% yield. Both polymers were characterized by (1)H and (13)C NMR and IR analyses as di-block copolyesters containing a PHB block with a secondary OH end group and a poly(epsilon-caprolactone) (PCL) block with a primary OH end group. NMR analyses and control experiments suggested no formation of random copolymers and no change of the PHB block during the reaction. The enzymatic ring-opening polymerization was selectively initiated by the primary OH group of PHB-diol, whereas the secondary OH group remained as an end group in the final polymers. The thermal properties of the di-block poly(HB-co-CL)s were analyzed by DSC, with excellent T g values for the elastomer domain: poly[HB(56 wt %)- co-CL(44 wt %)] with M n (NMR) of 3900 demonstrated a T g of -57 degrees C, Tm of 145, 123, and 53 degrees C; and poly[HB(28wt%)-co-CL(72wt%)] with Mn (NMR) of 7100 gave a Tg of -60 degrees C, Tm of 147 and 50 degrees C. Thus, the selective enzymatic ring-opening polymerization with PHB-diol as macro-initiator provides a new method for the preparation of PHB-based block copolymers as biomaterials with good thermoplastic properties and novel structures containing functional end groups.

Biodegradable Polycarbonate-b-polypeptide and Polyester-b-polypeptide Block Copolymers: Synthesis and Nanoparticle Formation Towards Biomaterials

The amino poly(trimethylene carbonate)-NHt-Boc (PTMC-NHt-Boc) and poly(epsilon-caprolactone)-NH -Boc (PCL-NHt-Boc) were synthesized by ring-opening polymerization (ROP) of TMC or CL and subsequently deprotected into the corresponding PTMC-NH2 and PCL-NH2. These functional homopolymers were used as macroinitiators for the ROP of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG), consequently, giving the respective diblock copolymers PTMC-b-PBLG and PCL-b-PBLG in almost quantitative yields. The (co)polymers have been characterized by NMR and SEC analyses. DSC and IR studies confirmed the block structure of the copolymers and highlighted a phase separation between the rigid peptide (alpha-helix conformation) and the more flexible polyester segments. The self-assembly and the degradation behaviors of the copolymers depended on the nature of the polyester block and on the copolymer composition. Nanoparticles obtained from PBLG block copolymers were twice smaller ( RH < 100 nm) than those formed from PTMC and PCL homopolymers. Finally, their enzymatic degradation revealed that PTMC nanoparticles degraded faster than those made of PCL.

Ring-opening polymerization of ɛ-caprolactone by base catalyst for synthesis of grafted polysilsesquioxane

The polysilsesquioxane having amino and phenyl groups (APSQ) was prepared from the corresponding trimethoxysilanes by co-condensation under basic conditions. The amino group on APSQ was utilized as an initiator for graft polymerization of ɛ-caprolactone (CL). The ring-opening polymerization of CL, in the presence of a catalytic amount of the base prepared from triazabicyclodecene, proceeded effectively to afford the polysilsesquioxane having poly(CL) as the graft chains (GrPSQ). In the grafting, no formation of cross-linked product was observed. The grafted poly(CL) component in GrPSQ showed improved durability for heat as an advantage of the hybrid polymer containing polysiloxane structure.

Controlled synthesis of amphiphilic block copolymers based on polyester and poly(amino methacrylate): Comprehensive study of reaction mechanisms

The synthesis of amphiphilic and adaptative block copolymers has been envisioned following a commutative two-step strategy involving atom transfer radical polymerization (ATRP) and the Huisgen-1,3-dipolar cycloaddition techniques. The reliability of this strategy is based on the use of an azido-containing ATRP initiator, the 2-(2-azidoethoxy)ethylbromoisobutyrate (N 3E i BBr), able to be “clicked” to an alkyne-terminated derivative and to promote the ATRP polymerization from the active site. In the context of this work, an alkyne-terminated poly(ε-caprolactone) produced by ring-opening polymerization (ROP) of CL was employed as hydrophobic “clickable” segment. The N 3E i BBr initiator was obtained by nucleophilic substitution of the chloride atom from 2-(2-chloroethoxy)ethanol by an azide function and followed by the esterification of the hydroxy function by bromoisobutyryl bromide. This initiator was employed in polymerization of N, N-dimethylamino-2-ethyl methacrylate (DMAEMA) monomer by ATRP in THF at 60 °C using CuBr complexed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as catalytic complex. Low initiation efficiencies were obtained and they were ascribed to intramolecular cyclization during the polymerization as evidenced by ESI-MS and 2D NMR spectroscopy. The “Click” coupling reaction was performed in THF at r.t. and was found to be efficient when using CuBr complexed by 2,2′-bipyridine ligand. To circumvent the low initiation efficiency, the N 3E i BBr could be “clicked” in a first step to PCL precursors before initiating the polymerization of DMAEMA monomer by ATRP. In this context, various catalytic complexes in different composition ratio were employed to optimize the “click” coupling step. Moreover, this strategy was found to be suitable to produce well-defined PCL-b-PDMAEMA block copolymers, characterized by narrow polydispersity indices. Since ATRP and the Huisgen-1,3-dipolar cycloaddition both require the use of a copper(I)-based catalyst, the two first strategies were merged in a “one-pot” process in order to obtain in one step a well-defined block copolymer characterized by a narrow polydispersity index and predictable composition and block lengths.

Micelles based on amphiphilic PCL‐PEO triblock and star‐shaped diblock copolymers: Potential in drug delivery applications

In this work, the potential in drug nanodelivery of micelles made from poly(epsilon-caprolactone) (PCL) and poly (ethyleneoxide) (PEO) copolymers with triblock and star-diblock architectures was explored. Linear and 4-arm star-shaped PCL macromers with two or four --OH end groups were prepared by ring-opening polymerization of CL and condensed with alpha-methoxy-omega-carboxy-PEO. The resulting amphiphilic copolymers were characterized by (1)H NMR, size exclusion chromatography, and differential scanning calorimetry. Separate PCL and PEO crystalline phases were observed for both copolymers. Copolymers self-assembled in water giving critical association concentrations in the range 0.010-0.023 mg/mL. Micelles with a size of 32-45 nm were prepared by dialysis and characterized for hydrodynamic diameter and surface charge. Their potential as nanocarriers in drug delivery applications was evaluated too. Micelles were nontoxic to both Red blood cells and HeLa cells. Complement activation experiments indicated that micelles can escape the reticuloendothelial system once intravenously injected. Finally, a different uptake on HeLa cells was found for micelles obtained from triblock and star-shaped copolymers.

Grafting of polyamide 6 by the anionic polymerization of ɛ-caprolactam from an isocyanate bearing polystyrene backbone

The grafting of polyamide 6 (PA6) onto polystyrene (PS) can rely on the use of a copolymer of styrene (St) and 3-isopropenyl-α,α-dimethylbenzene isocyanate (TMI), PS-co-TMI, to activate the polymerization of e-caprolactam (CL) in the presence of sodium e-caprolactam (NaCL) as an anionic catalyst. This article is aimed at answering the following key questions. First, do all the isocyanate moieties of the PS-co-TMI participate in the activation of the polymerization of CL? Second, what are the composition of the resulting polymer product and the structure of the resulting graft copolymer? The results show that the isocyanate moieties had all participated in the activation of the polymerization, implying that each isocyanate moiety has led to the formation of a PA6 graft. The as-polymerized product was composed of a pure PS-g-PA6 graft copolymer, homo-PA6, and unreacted CL. Moreover, when the composition of a PS-co-TMI/CL/NaCL system was fixed, the mass ratio between the PA6 grafts and PS backbone of the pure PS-g-PA6 graft copolymer was almost a constant and was almost independent of its molar mass.

Bimetallic anilido-aldimine Al or Zn complexes for efficient ring-opening polymerization of ε-caprolactone

Four bimetallic Al or Zn complexes supported by anilido-aldimine ligands (o-C6H4(NHAr)-CH=N)2CH2CH2 (Ar = 2,6-Me2C6H3,L1H2; Ar = 2,6-iPr2C6H3, L2H2) have been synthesized and characterized. Treatment of L1H2 or L2H2 with two equiv. of AlMe3 gives bimetallic complex L1(AlMe2)2 1 or L2 (AlMe2)2 2, respectively. Reaction of L1H2 or L2H2 with two equiv. of ZnEt2 leads to bimetallic complex L1(ZnEt)2 3 or L2(ZnEt)2 4, respectively. All of the complexes 1-4 are efficient catalysts for ring-opening polymerization of epsilon-caprolactone (CL) in the presence of benzyl alcohol and catalyze the polymerization of CL in living fashion yielding polymers with a narrow polydispersity index. The activity of bimetallic Zn complexes 3 and 4 is higher than bimetallic Al complexes 1 and 2.

On polyamide 6-montmorillonite nanocomposites obtained by in-situ polymerization

AbstractNanocomposites based on polyamide 6 (PA6) and montmorillonite-type (MMT) commercial clays, either unmodified or organically modified, were prepared by in-situ polymerization of ε-caprolactam (CL). The above materials were characterized in detail by a number of experimental techniques, including transmission electron microscopy (TEM), wide angle X-ray diffraction (WAXD), infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The formation of nanostructured systems was checked not only for the commonly used ω-aminoacid-modified clay, but also for other types of organoclays. In general, a correlation was found between nanoscopic swelling of the clay in molten CL, measured by X-ray diffraction, and level of clay dispersion in PA6. Specifically, with the most swellable clays, completely exfoliated nanocomposites were obtained. However, also layered silicates modified by compatibilizers having carboxy groups, because of the active role of latter in CL polymerization, formed delaminated nanocomposites despite their low degree of swelling in CL monomer. Both molecular mass and crystallinity of the polyamide matrix were found to be strongly influenced by the presence of specific layered silicates. In particular, some characterization techniques (WAXD, FTIR) have evidenced a close relationship between the MMT used and PA6 crystal structure. Namely, PA6 γ-form is promoted by clay with compatibilizer bearing the carboxy group, which is able to induce the polymer to be tethered on the silicate layers, thus provoking conditions of restricted mobility to occur.

An efficient route for the synthesis of graft copolymers with rigid backbones via anionic ring-opening polymerization of caprolactam

Epsilon-caprolactam (CL) has been grafted onto rigid backbones to form graft copolymers via anionic ring-opening polymerization in the presence of catalyst sodium caprolactam. An allyl monomer containing N-carbamated caprolactam group was copolymerized with different rigid monomers to form the rigid backbones, which acted as the macroactivators of anionic polymerization. The time for the completion of anionic polymerization was less than 30 min. The graft copolymers were evaluated by differential scanning calorimetry and selective solvent extraction technique consisted of using methanol and chloroform as extracting solvents. The polymerization of CL in the presence of synthesized macroactivators yielded graft copolymers with high purity. The evaluation performed by thermogravimetric analysis indicated that graft copolymers had improved thermal stabilities.

Synthesis and Characterization of Random and Triblock Copolymers of ε-Caprolactone and (Benzylated)hydroxymethyl glycolide

The aim of this study was to develop new polyesters with pendant functional hydrophilic groups suitable for biomedical applications. Therefore, ε-caprolactone (CL) was copolymerized with benzyl protected hydroxymethyl glycolide (BHMG) to introduce, after deprotection, hydroxyl groups into the polyester. Random and triblock copolymers were synthesized in the melt using benzyl alcohol and tin(II) 2-ethylhexanoate as initiator and catalyst, respectively, and deprotected by hydrogenation. The synthesized polyesters before and after deprotection were characterized by NMR, GPC, and DSC measurements. Mixtures of CL and BHMG were polymerized at 110, 130, and 150 °C. A polymerization kinetics study revealed that BHMG was far more reactive than CL at the three reaction temperatures investigated. However, due to transesterification reactions, random copolymers were formed at 150 °C, whereas at 110 °C, the copolymers had a more blocky structure. Taking advantage of this knowledge, ABA triblock copolymers of poly(ε-caprolactone) (PCL, block B) and poly(benzyl protected hydroxymethyl glycolide) (PBHMG, block A) were synthesized. To this end, α,ω PCL-diols were first synthesized at 130 °C by melt polymerization of CL initiated with 1,4-butanediol, which were subsequently chain extended with BHMG at 130 °C. Four triblock copolymers with different PCL (from 2.3 to 4.8 kg/mol) and PBHMG (from 2.0 to 4.3 kg/mol) block lengths were synthesized. The random copolymers (before and after deprotection) were fully amorphous and had their Tg ranging from −29 to −16 °C. Before deprotection, the blocks of the triblock copolymers were fully miscible, while triblock copolymers showed phase separation and were semicrystalline materials after deprotection. The PCL segments crystallize with a Tm ranging from 39 to 46 °C. The latter polymers are interesting for tissue engineering applications because they enable the formation of porous dimensionally stable materials at body temperature.

Synthesis and crystallization behaviors of poly(styrene- b-isoprene- b- ε-caprolactone) triblock copolymers

The triblock copolymers, poly(styrene- b-isoprene- b- ε-caprolactone)s (PS- b-PI- b-PCL) have been synthesized successfully by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group, PS- b-PI-OH was synthesized by sequential anionic polymerization of styrene and isoprene and following end-capping reaction of EO, and then it was used as macro initiator in the ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS- b-PI on the thermal behaviors of PCL block in the triblock copolymers and the lower degree of crystalline in the triblock copolymer with higher molecular weight of PS- b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL 27, PCL 328 and PS- b-PI- b-PCL 344 are 0.71, 0.46 and 0.07 μm s −1, respectively. The atomic force microscopy (AFM) images of the PS 90- b-PI 66- b-PCL 28 show the columns morphology formed by it’s self-assembling.

A novel route to α,ω-telechelic poly(ɛ-caprolactone) diols, precursors of biodegradable polyurethanes, using catalysis by decamolybdate anion

A new convenient route for the synthesis of poly(ɛ-caprolactone) (PCL) with α,ω-telechelic diols' end-groups is presented. Synthesis of α,ω-telechelic PCL diols (HOPCLOH) was achieved by ring-opening polymerization (ROP) of ɛ-caprolactone (CL) catalyzed with ammonium decamolybdate (NH 4) 8[Mo 10O 34] and using diethylene glycol (DEG) as initiator. Obtained HOPCLOH was characterized by 1H and 13C NMR, FT-IR, GPC and MALDI-TOF. Comparative studies demonstrate that ammonium decamolybdate (NH 4) 8[Mo 10O 34] is better catalyst than Sn-octanoate (SnOct 2) toward CL polymerization in presence of DEG, under the conditions tested. A biodegradable poly(ester-urethane-urea) derivative was efficiently prepared from synthesized HOPCLOH. Obtained polymer shows minor differences with respect to the properties recorded for a poly(ester-urethane-urea) obtained from commercial HOPCLOH.

Blends of Immiscible Polystyrene/Polyamide 6 via Successive In‐Situ Polymerizations

AbstractSummary: A novel method has been successfully developed to prepare binary blends of PS and MCPA6. The blends are formed by the radical polymerization of styrene in CL, followed by the in‐situ anionic ring‐opening polymerization of CL in the presence of PS. The phase morphology investigated using SEM reveals that PS/MCPA6 blends with a PS content of 10 wt.‐% or lower consists of a MCPA6 matrix and a dispersed PS minor phase. Remarkably, phase inversion occurs in blends that have a PS content of 15 wt.‐% or higher, in which MCPA6 is no longer continuous but finely dispersed in the PS continuous phase. The phase inversion occurs at an extremely low PS content, and this phenomenon is unusual for traditional polymer blends prepared by melt blending. The probable reason for the particular phase morphology development is explained. The stability of the phase morphologies of the PS/MCPA6 blends after annealing at 250 °C is also investigated by SEM.SEM micrograph of the fractured surface of a PS/MCPA6 blend with a PS content of 20 wt.‐%, in which MCPA6, as spherical particles, is dispersed in the PS continuous phase.magnified imageSEM micrograph of the fractured surface of a PS/MCPA6 blend with a PS content of 20 wt.‐%, in which MCPA6, as spherical particles, is dispersed in the PS continuous phase.

Modification of Hydroxyapatite Nanosurfaces for Enhanced Colloidal Stability and Improved Interfacial Adhesion in Nanocomposites

This work describes a rational approach of hydroxyapatite (HAp) nanosurface modification for graft polymerization of e-caprolactone (CL). The ring-opening polymerization of CL on HAp surfaces was carried out using three types of HAp with different surface hydroxyl functionality: unmodified HAp (surface OH), HAp modified with l-lactic acid (secondary OH), and HAp modified with ethylene glycol (primary OH). The grafting efficiency and the amount of grafted poly(e-caprolactone) (PCL) were dependent on the nature and steric environment of the hydroxyl groups on the HAp surfaces. Transmission electron microscopy measurements and time-dependent phase monitoring indicated that surface-modified HAp could be more uniformly dispersed in methylene chloride than unmodified HAp, and its colloidal stability increased dramatically as the amount of grafted PCL increased. The nanocomposites of PCL and PCL-grafted HAp showed enhanced tensile strength and toughness, compared with that of unmodified HAp and PCL. Increased i...

Preparation and characterization of chitosan‐graft‐poly (ϵ‐caprolactone) with an organic catalyst

AbstractChitosan‐graft‐poly(ϵ‐caprolactone) was prepared via the ring‐opening graft polymerization of ϵ‐caprolactone (CL) through chitosan with 4‐dimethylaminopyridine as a catalyst and water as a swelling agent. The graft content of PCL within the graft copolymer was adjusted by the feed ratio of CL to chitosan, and the highest grafting concentration of PCL was up to about 400%. Fourier transform infrared, 1H NMR, and two‐dimensional heteronuclear single quantum coherence analyses indicated that the amino group (NH2CH‐2) of chitosan initiated the graft polymerization of CL through the backbone of chitosan, and the hydroxyl group (HOCH2–6) of chitosan did not participate in initiating the graft polymerization. The percentage of amino groups initiating the graft polymerization decreased with an increasing molar ratio of CL to chitosan in the feed, and this was attributed to the fact that the graft polymerization system increasingly became heterogeneous with an increasing feed ratio of CL to chitosan. The physical properties of the graft copolymers were characterized by thermogravimetric analysis and wide‐angle X‐ray diffraction, respectively. These suggested that the introduction of PCL grafts through the chitosan backbone would to some extent destroy the crystalline structure of chitosan, and the PCL grafts existed in an amorphous structure. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5353–5361, 2006

Preparation of diblock copolymers consisting of methoxy poly(ethylene glycol) and poly(ε‐caprolactone)/poly(L‐lactide) and their degradation property

AbstractMethoxy poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (MPEG‐PCL) or MPEG‐b‐poly(L‐lactide) (MPEG‐PLLA) diblock copolymers were prepared by the polymerization of CL or LA, using MPEG as an initiator in the presence of stannous octoate. MPEG‐b‐poly(ε‐caprolactone‐ran‐L‐lactide) (MPEG‐PCLA) diblock copolymers with different chemical composition of PCL and PLLA were also prepared by adjusting the amount of CL and LA from MPEG in the presence of stannous octoate. In degradation study, the degradation of the MPEG‐PCLA diblock copolymers mainly depends on the PCL and PLLA segments present in their structure. MPEG‐PCLA, with intermediate ratio of PCL and PLLA segment, completely degraded after 14 weeks. Meanwhile, partially degraded MPEG‐PCLA segments and parent MPEG segments were observed at higher PCL or PLLA segment contents. Introduction of PLLA into the PCL segments caused a lowering of the crystallinity of the diblock copolymers, thus, inducing a faster incoming of water into the copolymers. We confirmed that the diblock copolymers, with lower degree of crystallinity, have degraded more rapidly. POLYM. ENG. SCI., 46: 1242–1249, 2006. © 2006 Society of Plastics Engineers

Polymer layered silicate/carbon nanotube nanocomposites: The catalyzed polymerization approach

AbstractA two‐step route to polymer/layered silicate nanocomposites characterized by a large extent of nanoplatelet delamination is presented. It consists first in the preparation of poly(ε‐caprolactone) (PCL)‐grafted clay masterbatches (containing ∼30 wt% clay) by in situ intercalative polymerization of ε‐caprolactone (CL) in bulk. The CL polymerization is promoted at the surface of organomodified clays bearing targeted amounts of alcohol functionalities used as initiating species. The influence of alcohol concentration on clay platelets coverage by PCL has been studied by atomic force microscopy. In a second step, these masterbatches are readily dispersed in commercial matrices (PCL, PVC, chlorinated polyethylene) via rather conventional melt blending. The morphology of the resulting nanocomposites has been characterized as well as their thermal and mechanical properties. Interestingly enough, this “masterbatch” process can be extrapolated to another type of nanocomposites, i.e., polyolefin carbon nanotube nanocomposites. Accordingly, homogeneous surface coating of multi‐walled carbon nanotubes (MWNTs) is first achieved by in situ polymerization of ethylene as catalyzed directly from the nanotube previously surface‐treated by a highly active metallocene‐based complex. This polyolefin coating allows for the destructuration of the native nanotube bundles leading upon further melt blending with, e.g., ethylene‐co‐vinyl acetate copolymers (EVA), to high performance nanocomposites with finely dispersed MWNTs. POLYM. ENG. SCI. 46:1022–1030, 2006. © 2006 Society of Plastics Engineers

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

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

Synthesis and Micellization Properties of Novel Symmetrical Poly(ε‐caprolactone‐b‐[R,S] β‐malic acid‐b‐ε‐caprolactone) Triblock Copolymers

AbstractSummary: A four‐step strategy to synthesize well‐defined amphiphilic poly(ε‐caprolactone‐b‐[R,S] β‐malic acid‐b‐ε‐caprolactone) triblock copolymers [P(CL‐b‐MLA‐b‐CL)], which combines the anionic polymerization of [R,S] benzyl β‐malolactonate (MLABz), and the coordination‐insertion ring‐opening polymerization (ROP) of ε‐caprolactone (CL), followed by the selective removal of benzyloxy protective groups of the central poly(malolactonate) block is described. The first step involves MLABz initiated by potassium 11‐hydroxydodecanoate in the presence of 18‐crown‐6 ether. This step was carried out at 0 °C with an initial monomer concentration of 0.2 mol · L−1 in order to limit the occurrence of undesirable transfer and termination reactions by proton abstraction. After selective reduction of the carboxylic acid end‐group of the resulting α‐hydroxy, ω‐carboxylic poly([R,S] benzyl β‐malolactonate) leading to an α,ω‐dihydroxy PMLABz, the polymerization of CL was initiated by each hydroxyl end‐groups previously activated by AlEt3. Finally, after catalytic hydrogenation of the benzyl ester functions, the P(CL‐b‐MLA‐b‐CL) triblock copolymer was recovered and the amphiphilic character evidenced by UV spectroscopy. As demonstrated, the CMC of these new P(CL‐b‐MLA‐b‐CL) triblock copolymer is higher by one order of magnitude than that of a P(MLA‐b‐CL) diblock copolymer of similar composition.Concentration dependence of pyrene I338/I335 intensitiy ratio for P(MLA‐b‐CL) diblock and P(CL‐b‐MLA‐b‐CL) triblock copolymers in water.magnified imageConcentration dependence of pyrene I338/I335 intensitiy ratio for P(MLA‐b‐CL) diblock and P(CL‐b‐MLA‐b‐CL) triblock copolymers in water.

Monoaryloxo ytterbium(III) chlorides supported by β‐diketiminato ligands as novel initiators for the living ring‐opening polymerization of ε‐caprolactone

AbstractRing‐opening polymerization of ε‐caprolactone (ε‐CL) was carried out using β‐diketiminato‐supported monoaryloxo ytterbium chlorides L1Yb(OAr)Cl(THF) (1) [L1 = N,N′‐bis(2,6‐dimethylphenyl)‐2,4‐pentanediiminato, OAr = 2,6‐di‐tert‐butylphenoxo‐], and L2Yb(OAr′)Cl(THF) (2) [L2 = N,N′‐bis(2,6‐diisopropylphenyl)‐2,4‐pentanediiminato, OAr′ = 2,6‐di‐tert‐butyl‐4‐methylphenoxo‐], respectively, as single‐component initiator. The influence of reaction conditions, such as polymerization temperature, polymerization time, initiator, and initiator concentration, on the monomer conversion, molecular weight, and molecular weight distribution of the resulting polymers was investigated. Complex 1 was well characterized and its crystal structure was determined. Some features and kinetic behaviors of the CL polymerization initiated by these two complexes were studied. The polymerization rate is first order with respect to monomer. The Mn of the polymer increases linearly with the increase of the polymer yield, while polydispersity remained narrow and unchanged throughout the polymerization in a broad range of temperatures from 0 to 50 °C. The results indicated that the present system has a “living character”. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1147–1152, 2006