Synthesis, characterization and degradability of the comb-type poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone)-g-poly(l-lactide)

The novel comb-type biodegradable graft copolymers based on ε-caprolactone and l-lactide were synthesized. Firstly, 2-oxepane-1,5-dione (OPD) was synthesized by the Baeyer-Villiger oxidation of 1,4-cyclohexanedione, and was subsequently copolymerized with ε-caprolactone (CL) to produce poly(2-oxepane-1,5-dione-co-ε-caprolactone) (POCL) catalyzed by stannous(II) 2-ethylhexanoate in toluene. Then, POCL was converted into poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone) (PHCL) using sodium borohydride as reductant. Finally, poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone)-g-poly(l-lactide) (PHCL-g-PLLA) were prepared successfully by bulk ring-opening polymerization of l-lactide using PHCL as a macro-initiator. All the copolymers have been characterized by ¹H and ¹³C NMR, DSC, and GPC. Compared with the random copolymer of poly(CL-co-LA), the elongation is highly increased. And the thermal analysis showed that the crystallization rate of the PCL backbone in the graft copolymers was greatly reduced compared to the PCL homopolymer. The hydrolytic degradation of the copolymer was much faster in a phosphate buffer (pH = 7.4) at 37 °C, which is confirmed by the weight loss and change of intrinsic viscosity.     

Synthesis and characterization of alkoxy derivatives with double-headed initiators for the preparation of poly(ε-caprolactone)-β-polyacrylonitrile (PCL-β-PAN) and poly(l-lactide)-β-polyacrylonitrile (PLLA-β-PAN) copolymers

The synthesis of simple single source molecular precursor based on metal alkoxides of the type,[(MMPEP)Al(μ-OBnCH₂Cl)]₂ (1),[(MMPEP-H)Li·(BnOH)]₂ (2) and[(MMPEP-H)Li·(HOB-nCH₂Cl)]₂ (3) has been reported herein. Complex 1 was prepared by the reaction of[(MMPEP)Al(CH₃)(Et₂O)] with p-(chloromethyl)benzyl alcohol. The reaction of 2,2′-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H₂) with ⁿBuLi, BnOH or p-(chloromethyl)benzyl alcohol was added to give complexes 2 and 3, respectively. Among them, only complex 1 shows excellent catalytic properties towards ring-opening polymerization (ROP) of ε-caprolactone. However, complexes 2 and 3 are active for ROP of l-lactide only. Block copolymers of poly(ε-caprolactone)-β-polyacrylonitrile and poly(l-lactide)-β-polyacrylonitrile were synthesized by using a technique known as atom transfer radical polymerization (ATRP) and the ring opening polymerization (ROP). TEM micrograph of PCL-β-PAN shows the microphase property with the help of self-assembly.     

Development of poly(ε-caprolactone-co-l-lactide) and poly(ε-caprolactone-co-δ-valerolactone) as new degradable binder used for antifouling paint

Copolyesters containing ε-caprolactone and l-lactide or ε-caprolactone and δ-valerolactone at different compositions were synthesized by using tetrabutoxytitane Ti(OBu)₄ at high temperature in bulk. A series of copolyesters were prepared by varying the compositions of both comonomers. These copolymers were characterized by using ¹H NMR, ¹³C NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and MALDI-TOF mass spectrometry. ¹³C NMR analysis gave an insight on their microstructure. Structural parameters of the copolymers were obtained by calculating the triad sequence fractions. Poly(ε-caprolactone-co-l-lactide) has a more alternate structure than poly(ε-caprolactone-co-δ-valerolactone). The potential use of these copolyesters in antifouling coatings was examined because of their solubility in aromatic solvent and their hydration and hydrolytic degradation. Paints based on these new degradable binders had a good antifouling activity in Atlantic Ocean (France).     

New Segmented Copolymers by Combination of Atom Transfer Radical Polymerization and Ring Opening Polymerization

Atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP) were combined to synthesize various polymers with various structures and composition. Poly(ε-caprolactone)-b-poly(n-octadecyl methacrylate), PCL-PODMA, was prepared using both sequential and simultaneous polymerization methods. Kinetic studies on the simultaneous process were performed to adjust the rate of both polymerizations. The influence of tin(II) 2-ethylhexanoate on ATRP was investigated, which led to development of new initiation methods for ATRP, i.e., activators (re)generated by electron transfer (AGET and ARGET). Additionally, block copolymers with two crystalizable blocks, poly(ε-caprolactone)-b-poly(n-butyl acrylate)-b-poly(n-octadecyl methacrylate), PCL-PBA-PODMA, block copolymers for potential surfactant applications poly(ε-caprolactone)-b-poly(n-octadecyl methacrylate-co-dimethylaminoethyl methacrylate), PCL-P(ODMA-co-DMAEMA), and a macromolecular brush, poly(hydroxyethyl methacrylate)-graft-poly(ε-caprolactone), PHEMA-graft-PCL, were prepared using combination of ATRP and ROP.     

Controlled synthesis of AB2 amphiphilic triarm star-shaped block copolymers by ring-opening polymerization

This paper describes the synthesis of a novel amphiphilic AB₂ triarm star-shaped copolymer with A = non-toxic and biocompatible hydrophilic poly(ethylene oxide) (PEO) and B = biodegradable and hydrophobic poly(ε-caprolactone) (PCL). A series of AB₂ triarm star-shaped copolymers with different molecular-weights for the PCL block were successfully synthesized by a three-step procedure. α-Methoxy-ω-epoxy-poly(ethylene oxide) (PEO-epoxide) was first synthesized by the nucleophilic substitution of α-methoxy-ω-hydroxy-poly(ethylene oxide) (MPEO) on epichlorohydrin. In a second step, the α-methoxy-ω,ω′-dihydroxy-poly(ethylene oxide) (PEO(OH)₂) macroinitiator was prepared by the selective hydrolysis of the ω-epoxy end-group of the PEO-epoxide chain. Finally, PEO(OH)₂ was used as a macroinitiator for the ring-opening polymerization (ROP) of ε-caprolactone (εCL) catalyzed by tin octoaote (Sn(Oct)₂). PEO-epoxide, PEO(OH)₂ and the AB₂ triarm star-shaped copolymers were assessed by ¹H NMR spectroscopy, size exclusion chromatography (SEC) and MALDI-TOF. The behavior of the AB₂ triarm star-shaped copolymer in aqueous solution was studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM).     

Organic/inorganic hybrid star-shaped block copolymers of poly(l-lactide) and poly(N-isopropylacrylamide) with a polyhedral oligomeric silsesquioxane core: Synthesis and self-assembly

The star-shaped organic/inorganic hybrid poly(l-lactide) (PLLA) based on polyhedral oligomeric silsesquioxane (POSS) was prepared using octa(3-hydroxypropyl) polyhedral oligomeric silsesquioxane as initiator via ring-opening polymerization (ROP) of l-lactide (LLA). The molecular weight of POSS-containing star-shaped hybrid PLLA (POSSPLLA) can be well controlled by the feed ratio of LLA to initiator. The POSSPLLA was further functionalized into the macromolecular reversible addition-fragmentation transfer (RAFT) agent for the polymerization of N-isopropylacrylamide (NIPAM), leading to the POSS-containing star-shaped organic/inorganic hybrid amphiphilic block copolymers, poly(l-lactide)–block–poly(N-isopropylacrylamide) (POSS(PLLA–b–PNIPAM)). The self-assembly behavior of POSS(PLLA–b–PNIPAM) block copolymers in aqueous solution was investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). DLS showed the PNIPAM block in the aggregates is temperature-responsive and its phase-transition is reversible. TEM proved that the star-shaped POSS(PLLA–b–PNIPAM) amphiphilic block copolymers can self-assemble into the vesicles in aqueous solution. The vesicular wall and coronas are composed of the hydrophobic POSS core and PLLA, and hydrophilic PNIPAM blocks, respectively. Therefore, POSSPLLA and POSS(PLLA–b–PNIPAM) block copolymers, as a class of novel organic–inorganic hybrid materials with the advantageous properties, can be potentially used in biological and medical fields.     

RING-OPENING POLYMERIZATION OF ε-CAPROLACTONE BY LANTHANOCENE CATALYSIS*

Ring-opening polymerization of ε-caprolactone (CL) catalyzed bylanthanocenes, O(C_2H_4C_5H_3CH_3)_2YCl (Cat-YCl) and Me_2Si[(CH_3)_3SiC_5H_3]_2NdCl(Cat-NdCl) has been carried out for the first time. It has been found that both yttroceneand neodymocene are very efficient to catalyze the polymerization of CL, giving high molec-ular weight poly (ε-caprolactone) (PCL ). The effects of [cat] / [ε- CL] molar ratio, polymeriza-tion temperature and time, as well as solvents were investigated and polymerization tem-perature is found to be the most important factor affecting the polymerization. The bulkpolymerization gives higher molecular weight PCL and higher conversion than that in solu-tion polymerization. NaBPh_4 was found to promote the polymerization of ε-caprolactone,and thus to increase both the polymerization conversion and MW of poly (ε- caprolactone ).     

嵌段共聚物PDMAEMA-b-PCL的合成、修饰及其水溶液性质研究

通过甲基丙烯酸N,N-二甲氨基乙酯(dimethylamino ethyl methacrylate)和环己内酯(ε-caprolactone)之间的连续阴离子聚合, 合成了末端含有氨基的聚甲基丙烯酸N,N-二甲氨基乙酯-嵌段-聚己内酯的双亲性嵌段共聚物(PDMAEMA-b-PCL). 为了增强生物相容性, 通过末端氨基与D-葡萄糖酸内酯(D-gluconolactone)的酰胺化反应对该共聚物进行糖基修饰. 合成的共聚物的化学结构用氢核磁共振光谱(¹H NMR)和红外光谱(IR)进行表征, 聚合物的分子量分布采用凝胶色谱(GPC)测定, 该嵌段共聚物在水溶液中的自组装行为则借助于动态光散射(DLS)进行了研究.     

Bis(amido)titanium complexes having chelating diaryloxo ligands bridged by sulfur or methylene and their catalytic behaviors for ring-opening polymerization of cyclic esters

A series of bis(dialkylamido) titanium complexes coordinated by O-E-O (E=S, CH₂) chelating bis(aryloxo) ligands, Ti[E(4-Me-6-^tBuC₆H₂O)₂](NR₂)₂ (1: E=S, R=Me; 2: E=S, R=Et; 3: E=CH₂, R=Me; 4: E=CH₂, R=Et), were synthesized by the reaction of Ti(NR₂)₄ (R=Me, Et) with 2,2^′-E(4-Me-6-^tBuC₆H₂OH)₂ (E=S, CH₂). The crystal structures of complexes 2 and 4 were determined by X-ray diffraction study. Complex 2 has a trigonal bipyramidal structure with the sulfur and nitrogen atom in trans positions and complex 4 has a tetrahedral structure. The complex 2 was found to initiate the controlled polymerization of ε-caprolactone in toluene at 100 °C affording poly(ε-caprolactone) and poly(l-lactide) with relatively narrow molecular weight distributions. The complex 4 showed higher activity for the polymerization of ε-caprolactone to give a polymer with a broader molecular weight distribution in comparison with complex 2.     

Synthesis and barrier properties of poly(ε-caprolactone)-layered silicate nanocomposites

A new polymer-ceramic nanocomposite has been synthesized consisting of well-dispersed, two-dimensional layers of an organically modified mica-type silicate (MTS) within a degradable poly(ε-caprolactone) matrix. A protonated amino acid derivative of MTS was used to promote delamination/dispersion of the host layers and initiate ring-opening polymerization of ε-caprolactone monomer, resulting in poly(ε-caprolactone) chains that are ionically bound to the silicate layers. The polymer chains can be released from the silicate surface by a reverse ion-exchange reaction and were shown to be spectroscopically similar to pure poly(ε-caprolactone). Thick films of the polymer nanocomposite exhibit a significant reduction in water vapor permeability that shows a linear dependence on silicate content. The permeability of nanocomposite containing as low as 4.8% silicate by volume was reduced by nearly an order of magnitude compared to pure poly(ε-caprolactone). © 1995 John Wiley & Sons, Inc.     

Preparation,Characterization and Drug Release Behavior of 5-Fluorouracil Loaded Carboxylic Poly(ε-caprolactone) Nanoparticles

In this paper, 5-Fluorouracil (5-FU) loaded carboxylic poly(ε-caprolactone) nanoparticles have been prepared by emulsification/solvent evaporation o/w method, and the drug release behaviors of 5-FU were investigated. The novel carboxylic poly (ε-caprolactone) (P(CL-OPD)-mal) was synthesized via conjugation of maleic anhydride to sodium borohydride (NaBH₄) reduced poly(ε-caprolactone-co -4- carbonyl -ε-caprolactone) (P(CL-OPD)), while P(CL-OPD) was synthesized in bulk by ring-opening polymerization of ε-caprolactone and 4-carbonyl-ε-caprolactone (OPD) with stannous octoate as a catalyst. Their structures were confirmed by ¹HNMR, FT-IR and GPC. Dynamic light scattering (DLS), transmission electron microscopy (TEM), zeta potential measurements were used for nanoparticle characterization. TEM and DLS showed the nanoparticles were with spherical shape and uniform size distribution (mean diameter 70～100 nm), respectively. Zeta potential analysis revealed that the nanoparticles had an increased negative surface with the increase of carboxyl group concentration. UV spectroscopy was adopted to study the entrapment and release behaviour. The maximum 5-FU loading efficiency was 14.39% with the entrapment efficiency be 42%. In vitro release studies were performed in PBS at 37°C. Results of the study showed that the release behavior can be well-controlled, and the balanced release was up to 96 h. P(CL-OPD)-mal nanoparticles would provide increased benefit in biomedical and pharmaceutical applications.     

Fabrication of PLCL Block Polymer with Tunable Structure and Properties for Biomedical Application

Biodegradable materials are pivotal in the biomedical field, where how to precisely control their structure and performance is critical for their translational application. In this study, poly(L-lactide-b-ε-caprolactone) block copolymers (bPLCL) with well-defined segment structure are obtained by a first synthesis of poly(ε-caprolactone) soft block, followed by ring opening polymerization of lactide to form poly(L-lactide acid)  hard block. The pre-polymerization allows for fabrication of bPLCL with the definite compositions of soft/hard segment while preserving the individual segment of their special soft or hard segment. These priorities make the bPLCL afford biodegradable polymer with better mechanical and biodegradable controllability than the random poly(L-lactide-co-ε-caprolactone) (rPLCL) synthesized via traditional one-pot polymerization. 10 mol% ε-caprolactone introduction can result in a formation of an elastic polymer with elongation at break of 286.15% ± 55.23%. Also, bPLCL preserves the unique crystalline structure of the soft and hard segments to present a more sustainable biodegradability than the rPLCL. The combinative merits make the pre-polymerization technique a promising strategy for a scalable production of PLCL materials for potential biomedical application.     

In-chain functionalized poly(ε-caprolactone): A valuable precursor towards the synthesis of 3-miktoarm star containing hyperbranched polyethylene

Well-defined 3-miktoarm star copolymer 3μ-HBPE(PCL)₂ (HBPE: hyperbranched polyethylene, PCL: poly[ε-caprolactone]) was synthesized by combining chain walking polymerization (CWP), ring-opening polymerization (ROP), and “click” chemistry. The synthetic methodology includes the following steps: (a) synthesis of in-chain ethynyl-functionalized PCL, (PCL)₂-C ≡ CH by ROP of ε-caprolactone (CL) with ethylene-functionalized solketal (3-[prop-2-yn-1-yloxy] propane-1,2-diol) as difunctional initiator and phosphazene superbase t-BuP₂ as catalyst; (b) synthesis of azido-functionalized hyperbranched PE (HBPE-N₃) by CWP of ethylene with α-diimine-Pd(II) catalyst, followed by quenching with excess 4-vinylbenzyl chloride and transformation of chloro to azide group with sodium azide; and (c) “clicking” HBPE-N₃ and (PCL)₂-C ≡ CH using copper(I)-catalyzed azide–alkyne cycloaddition. ¹H NMR spectroscopy, gel permeation chromatography, Fourier-transform infrared spectroscopy, and differential scanning calorimetry were used to determine the molecular characteristics and thermal properties of the polymers. Self-assembly behavior of 3μ-HBPE (PCL)₂ in petroleum ether, a selective solvent for HBPE, was investigated by dynamic light scattering, atomic force microscopy, and transmission electron microscopy. The in-chain alkyne-functionalized poly(ε-caprolactone) is a valuable precursor for PCL-based complex macromolecular architectures.     

Biodegradable Polymers for Orthopedic Applications: Synthesis and Processability of Poly (l-Lactide) and Poly (Lactide-co-€-Caprolactone)

Abstract

The synthesis of poly(l-lactide) (PLLA), poly(l-lactide-co-e-caprolactone), and poly(DL-lactide-co-e-caprolactone) by ring-opening bulk polymerization was investigated. Polymerization temperature had a significant effect on the PLLA molecular weight. At 184°C a polymer with a molecular weight of only 10 × 10⁴ resulted. This was lower by a factor of 2 than that obtained at 103 and 145°C. The stannous octoate (SnOct) concentration, with a monomer/SnOct molar ratio in the range of 1,000 to 10,000, was not found to have a significant effect on the PLLA molecular weight. A heterogeneous structure in polymerized PLLA was observed. The intrinsic viscosity of poly(lactide-co-€-caprolactone), obtained at 130°C, monomer/SnOct molar ratio 5,000, and polymerization time of 30 hours, decreased with increasing €-caprolactone content within the first 9 wt% and then leveled off. Die-drawing of PLLA cylinders, for the purpose of increasing the polymer's mechanical strength, was unsuccessful due to the brittleness of the polymer. The drawability of poly(l-lactide), however, was greatly improved by copolymerization with €-caprolactone. With only 3 wt% of €-caprolactone, for example, the tensile strength of die-drawn poly(l-lactide-co-e-caprolactone) was increased by a factor of more than 3. Polymer processing temperature was also investigated. The requirement for low processing temperatures in melt manufacture of controlled release matrix devices containing thermal sensitive drugs was accomplished by three methods: through the use of low molecular weight poly(DL-lactide), adding (DL-lactic) acid oligomer to high molecular weight PDLLA, and copolymerizing DLLA with €-caprolactone. The glass transition temperatures of the modified high molecular weight PDLLA decreased significantly. Melt extrusion below 100°C could be performed.     

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

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

谷胱甘肽端基修饰聚己内酯的合成及在水溶液中的聚集行为

用开环聚合法合成了端基分别为巯基和马来酰亚胺基团的聚己内酯,利用马来酰亚胺与巯基的迈克尔加成反应和巯基之间的偶联反应,合成了两种端基为谷胱甘肽的聚己内酯(GS-PCL和GSS-PCL),利用核磁共振氢谱和凝胶渗透色谱表征了两亲性聚己内酯的结构.研究了这两种聚己内酯在水中的聚集行为,发现这两种聚已内酯都可在一定pH值下聚集形成球形胶束,胶束的形态、大小等受pH影响;同时,由GSS-PCL形成的聚集体还表现出氧化还原敏感性.     

Novel polyesteramide-based di- and triblock copolymers: From thermo-mechanical properties to hydrolytic degradation

Two types of biodegradable poly(ε-caprolactone (CLo))-co-poly(ε-caprolactam (CLa)) copolymers were prepared by catalyzed hydrolytic ring-opening polymerization. For the first type of materials, the respective cyclic comonomers were added simultaneously in the reaction medium leading to the formation of copolymers having a random distribution of co-units within the polyesteramide sequence, as evidenced by ¹H and ¹³C NMR. For the second type of copolymers, the cyclic comonomers were added sequentially in the reaction medium yielding diblock polyesteramides, again evidenced by NMR. The thermal and thermo-mechanical properties of the copolymers were investigated by DSC and DMA and correlated with the copolymer topology and composition. The copolymers were characterized by a storage modulus and α transition temperature intermediate to the modulus and T_g of the corresponding homopolymers. The chemical composition and molecular weight of the copolymers proved to have only a limited effect on the thermo-mechanical properties of the materials. The hydrolytic degradation of random copolymers was studied in a phosphate buffer at 60 °C and discussed in terms of chemical composition and molecular weight of the copolymers.     

Chlorinated polyethylene nanocomposites using PCL/clay nanohybrid masterbatches

Exfoliated nanocomposites were prepared by dispersion of poly(ε-caprolactone) (PCL) grafted montmorillonite nanohybrids used as masterbatches in chlorinated polyethylene (CPE). The PCL-grafted clay nanohybrids with high inorganic content were synthesized by in situ intercalative polymerization of ε-caprolactone between silicate layers organo-modified by alkylammonium cations bearing two hydroxyl functions. The polymerization was initiated by tin alcoholate species derived from the exchange reaction of tin(II) bis(2-ethylhexanoate) with the hydroxyl groups borne by the ammonium cations that organomodified the clay. These highly filled PCL nanocomposites (25 wt% in inorganics) were dispersed as masterbatches in commercial chlorinated polyethylene by melt blending. CPE-based nanocomposites containing 3-5 wt% of inorganics have been prepared. The formation of exfoliated nanocomposites was assessed both by wide-angle X-ray diffraction and transmission electron microscopy. The thermal and thermo-mechanical properties were studied as a function of the filler content, by differential scanning calorimetry and dynamic mechanical analysis, respectively. The mechanical properties were also assessed by tensile tests. The Young’s modulus of CPE is increased by a decade when a PCL-grafted clay masterbatch is exfoliated to reach 5 wt% of clay in the resulting nanocomposite. The influence of PCL-grafting on the properties of these nanocomposites was investigated by comparison with materials obtained with ungrafted-PCL.     

Thermogelling hydrogels of poly(ε-caprolactone-co-D,L-lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-D,L-lactide) and poly(ε-caprolactone-co-L-lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-L-lactide) aqueous solutions

Thermogelling poly(ε-caprolactone-co-D,L -lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-D,L -lactide) and poly(ε-caprolactone-co-L -lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-L -lactide) triblock copolymers were synthesized through the ring-opening polymerization of ε-caprolactone and D,L -lactide or L -lactide in the presence of poly(ethylene glycol). The polymerization reaction was carried out in 1,3,5-trimethylbenzene with Sn(Oct)₂ as the catalyst at various temperatures, and the yields were about 96%. The molecular weights and polydispersities (M_w/M_n) by gel permeation chromatography were in the ranges of 5140–6750 and 1.35–1.45, respectively. The differential scanning calorimetry results showed that the melting temperatures of the poly(ε-caprolactone) components were between 30 and 40 °C. By the subtle tuning of the chemical compositions and microstructures of these triblock copolymers, the aqueous solutions underwent sol–gel transitions as the temperature increased, with the suitable lower critical solution temperature in the range of 17–28 °C at different concentrations. Transesterification in the polymerization process generated the redistribution of sequences, which remarkably affected the sol–gel transition temperature. The amphiphilic copolymers formed micelles in aqueous solutions with a diameter of 62 nm and a critical micelle concentration of about 0.032 wt % at 20 °C. Micelles aggregated as the temperature increased, leading to gel formation. The sol–gel transition was studied, with a focus on the structure–property relationship. It is expected to have potential applications in drug delivery and tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4091–4099, 2007     

Synthesis and characterization of polylactide functionalized polyacetylenes

The paper deals with the synthesis and polymerization of novel poly(l-lactide)-derived acetylene monomers and the analysis of the thermal properties of the formed graft copolymers. Poly(l-lactide) macromonomers with different acetylene end groups were prepared using stannous octanoate as a catalyst in the presence of various hydroxyacetylenes. Next, the well-characterized macromonomers were subjected to polymerization using [{RhCl(nbd)}₂]/Et₃N and [RuCl₂(CH–o–OiPrC₆H₄)(IMesH₂)] to obtain graft copolymers. Investigation of these graft copolymers by GPC and NMR spectroscopy revealed the presence of some poly(l-lactide) formed as a side product during the ring opening polymerization of l-lactide. The thermal stability of the polymeric materials has been studied as a function of the polyacetylene backbone substituents and the length of poly(l-lactide) side chains. Introducing polyacetylene into polyester increased the polymer stability. The thermal degradation behavior of the synthesized materials depends on the length of poly(l-lactide) chains and also on l-lactide homopolymer impurities in the graft copolymers.