Synthesis and characterization of novel functionalized polylactides with pendent hydroxyl arms

A class of polyesters have been synthesized by the ring-opening copolymerization of dl-lactide (DLLA) and RS-benzyloxyethyl-β-malolactonate (MABE) using different monomer feeding doses. The compositions and structures of poly(dl-lactide-co-RS-benzyloxyethyl-β-malolactonate) (poly(DLLA-co-MABE)) were determined by ¹H and ¹³C NMR measurements. GPC measurement showed that the molecular weight of the copolymers decreased as the MABE content increases. After catalytic hydrogenation of the benzyl ether functions, the desired copolymers with pendent hydroxyl arms, poly(dl-lactide-co-RS-hydroxyethyl-β-malolactonate) (poly(DLLA-co-MAHE)), were recovered. Thermal properties of poly(DLLA-co-MABE) and poly(DLLA-co-MAHE) copolymers were examined by differential scanning calorimetry (DSC) measurement. Single glass transition temperature appeared in the DSC spectra, which confirmed that the copolymers were true copolymers and not blends. The hydrophilicity of poly(DLLA-co-MAHE) copolymer was tunable, which increased with the increase in MAHE content. Furthermore, the hydrolytic degradation of poly(DLLA-co-MAHE) material was investigated and the results showed that faster degradation was observed in the copolymer film containing more MAHE content.     

Injectable hydrogels of poly(?-caprolactone-co-glycolide)-poly(ethylene glycol)-poly(?-caprolactone-co-glycolide) triblock copolymer aqueous solutions

Thermogelling triblock copolymers of poly(?-caprolactone-co-glycolide)-poly(ethylene glycol)-poly(?-caprolactone-co-glycolide) [P(CL-GA)-PEG-P(CL-GA)] were successfully prepared by control of the hydrophilicity/hydrophobicity balance and chemical compositions of the copolymers. The aqueous solutions of the copolymers underwent sol-gel transition as the temperature was increased from 20 to 60 °C. The amphiphilic copolymer formed micelles in water and a gel was formed by aggregation of micelles. The structure parameters played a critical role in determining sol-gel transition behavior. Either increasing [GA]/[CL] ratio or decreasing P(CL-GA) block length could induce the increase of the lower sol-gel transition temperature. Glycolide (GA) was incorporated into the polymer chain to increase the polymer degradation rate. Sustained release of rifampicin for approximately 32 days was obtained from the gel. It is believed to have potential applications in drug delivery and tissue engineering.     

One-step synthesis of poly(2-oxazoline)-based amphiphilic block copolymers using a dual initiator for RAFT polymerization and CROP

A range of poly(2-oxazoline) (POx)-based amphiphilic block copolymers were synthesized using 4-cyano-4-(dodecylthiocarbonothioylthio)pentyl-4-methylbenzenesulfonate (CDPS) as a dual initiator for reversible addition-fragmentation chain transfer (RAFT) polymerization and cationic ring-opening polymerization (CROP) in a one-step procedure. Methyl (meth)acrylate, butyl (meth)acrylate, tert-butyl (meth)acrylate, and N-isopropylacrylamide were polymerized for the hydrophobic block, and 2-methyl-2-oxazoline and 2-ethyl-2-oxazoline were used as the hydrophilic block. RAFT polymerization and CROP proceeded independently in a controlled manner and resulted in amphiphilic block copolymers with a narrow molecular weight distribution. CDPS was found to be a useful dual initiator for the one-step synthesis of POx-based amphiphilic block copolymers via a combination of RAFT polymerization and CROP.     

Controlled release of doxorubicin from amphiphilic depsipeptide–PDO–PEG-based copolymer nanosized microspheres

Novel biodegradable amphiphilic ABA triblock copolymers, i.e. poly(3(S)-methyl-morpholine-2,5-dione-co-p-dioxanone)-block-poly(ethylene glycol)-block-poly(3(S)-methyl-morpholine-2,5-dione-co-p-dioxanone) [P(MMD-co-PDO)-b-PEG-b-P(MMD-co-PDO)], were successfully prepared by ring-opening polymerization of 3(S)-methyl-morpholine-2,5-dione (MMD) and p-dioxanone (PDO) in the presence of poly(ethylene glycol) 6000 as an initiator. These triblock copolymers were characterized by ¹H NMR, ¹³C NMR, Fourier transform infrared, gel permeation chromatography and differential scanning calorimetry measurements. P(MMD-co-PDO)-b-PEG-b-P(MMD-co-PDO) could self-assemble into stable nanosized microspheres with critical micellar concentrations of 0.41–0.66 μg/mL. The microspheres showed high hydrolytic degradation. In addition, doxorubicin (DOX) was chosen as a model drug and successfully encapsulated into the microspheres by hydrogen-bond interaction and hydrophobic effect. The transmission electron microscopy and dynamic light scattering measurements revealed that these microspheres were ellipsoidal nanoparticles with diameters ranged from 50 to 100 nm. These copolymer microspheres exhibited high loading capacity (LC), encapsulation efficiency (EE) of DOX and sustained drug release behavior in phosphate buffered solution (PBS). Moreover, the release rate of DOX from those microspheres in pH 4.0 PBS was faster than that in pH 7.4 due to pH sensitivity of the polymer–drug systems and the degradation of the matrix polymers. These amphiphilic depsipeptide multiblock copolymers would be potential promising carriers for anti-tumour drug delivery.     

Well-defined poly(2-hydroxyethyl methacrylate) and its amphiphilic block copolymers via acidolysis of anionically synthesized poly(2-vinyloxyethyl methacrylate)

Summary A novel approach to a well-defined poly(2-hydroxyethyl methacrylate) [poly(HEMA)] and to its amphiphilic block copolymers was developed. The selective living anionic polymerization of the methacryloyl group of the bifunctional monomer 2-vinyloxyethyl methacrylate (VEMA) generated a functional polymer with a controlled molecular weight and a narrow molecular weight distribution (M_w/M_n= 1.05–1.09). This polymer is very stable under normal conditions. Being soluble in the common organic solvents, its characterization could be carried out easily. The unreacted vinyl groups in the side chains of the resulting polymer were further reacted with hydrochloric acid. This acidolysis changed poly(VEMA) to a well-defined poly(HEMA). In addition, the anionic block copolymerization of VEMA with styrene or methyl methacrylate also proceeded smoothly, generating the corresponding block copolymers. After acidolysis, these copolymers were turned into amphiphilic block copolymers containing a hydrophilic poly(HEMA) block. Received: 22 June 2001/Revised version: 15 August 2001/Accepted: 15 August 2001     

Synthesis of comb-shaped copolymers by combination of reversible addition-fragmentation chain transfer polymerization and cationic ring-opening polymerization

Comb-shaped graft copolymers with poly(methyl acrylate) as a handle were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) techniques in three steps. First, copolymers of poly(styrene-co-chloromethyl styrene), poly(St-co-CMS), were prepared by RAFT copolymerization of St and CMS using 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate (EPDTB) as RAFT agent. Second, the polymerization of MA using poly(St-co-CMS)-SC(S)Ph as macromolecular chain transfer agent produced block copolymer poly(St-co-CMS)-b-PMA. Third, cationic ring-opening polymerization of THF was performed using poly(St-co-CMS)-b-PMA/AgClO₄ as initiating system to produce comb-shaped copolymers. The structures of the poly(St-co-CMS), poly(St-co-CMS)-b-PMA and final comb-shaped copolymers were characterized by ¹H NMR spectroscopy and gel permeation chromatography (GPC).     

Thermosensitive dendritic stars of tert-butyl-glycidylether and glycidol - Synthesis and encapsulation properties

Dendritic block copolymers of hydrophobic core and hydrophilic shell were prepared by a multi-step process based on anionic ring-opening polymerization. In the first step, amphiphilic stars with four or six poly(tert-butyl-glycidylether)-block-polyglycidol arms were synthesized. The hydroxyl groups of polyglycidol after ionization served as initiation centers for sequential anionic polymerization of tert-butyl-glycidylether and 1-ethoxyethyl-glycidylether. Selective removal of protective groups of glycidol hydroxyls yielded amphiphilic, dendritic copolymers with a hydrophobic core and hydrophilic shell. The hydrophobicity of the dendritic core depended on the composition of the star macroinitiator. The number of reactive hydroxyl groups in the shell was controlled by the number and length of the outer polyglycidol blocks. The structure and molar mass of the copolymers obtained were characterized by GPC-MALLS and NMR spectroscopy.The aqueous solution properties of the copolymers were studied. Some of dendritic copolymers aggregated at elevated temperature. The dependence of phase transition temperature and dimension of aggregates on the copolymer composition were followed by light scattering techniques. The spherical aggregates were visualized by AFM. The encapsulation efficiency of a hydrophobic compound (pyrene) was followed by UV-VIS spectroscopy.     

Water-soluble polyelectrolyte complexes formed by poly(diallyldimethylammonium chloride) and poly(sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulphonate)-graft-poly(N,N-dimethylacrylamide) copolymers

The formation of polyelectrolyte complexes (PECs) between the cationic homopolymer poly(diallyldimethylammonium chloride) (PDADMAC) and the anionic graft copolymers poly(sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulphonate)-graft-poly(N,N-dimethylacrylamide) (P(NaA-co-NaAMPS)-g-PDMAM) was studied in aqueous solution in comparison with the PECs formed between PDADMAC and the graft copolymer backbone poly(sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulphonate). The turbidimetric study of the PECs formed revealed that associative phase separation is prevented when the anionic polyelectrolyte is grafted with the nonionic hydrophilic poly(N,N-dimethylacrylamide) side chains. The PECs are formed through a charge neutralisation process and they adopt a compact structure, as shown by conductivity and viscometry measurements respectively. The water-insoluble PEC core seems to be stabilised by a hydrophilic PDMAM corona, leading to the formation of nanoparticles with a hydrodynamic radius of some decades of nanometers as determined by quasi-elastic light scattering measurements.     

Synthesis of poly(lactide-co-glycolide) containing high glycolide contents by ring-opening polymerization as well as their structural characterizations,thermal properties,morphologies, and hydrophilicity

Random copolymers, poly(l -lactide-r-glycolide) are synthesized by one-pot ring-opening polymerization of l -lactide and glycolide in the presence of stannous octoate and 1-dodecanol. Block copolymers, poly(l -lactide-b-glycolide) are synthesized by ring-opening polymerization of l -lactide to generate poly(l -lactide) first and then further ring-opening polymerization of glycolide in the presence of poly(l -lactide) and stannous octoate. The composition ratio of l -lactide and glycolide is determined by the integration of the corresponding signals from ¹H NMR spectra, which is consistent with the feeding ratio. Very few hetero-sequences can be observed for block copolymers due to well-defined microstructures. The block copolymers are more thermally stable than that of the random copolymers. The degree of crystallinity of the bock copolymers is relatively high compared to that of the random copolymers. The image of the block copolymers determined by field-emission scanning electron microscopy (FESEM) shows partial aggregate domains containing spherical particles with an average diameter of around 200 nm, which is very different from that of the random copolymers. Block copolymers are more hydrophilic than that of the random copolymers due to the ordered structure and amphiphilic behavior of the block series.     

Development of a new azido-oxazoline monomer for the preparation of amphiphilic graft copolymers by combination of cationic ring-opening polymerization and click chemistry

A new monomer (2-(5-azidopentyl)-2-oxazoline) bearing an azido group was synthesized. The cationic ring-opening copolymerization of this monomer with 2-methyl-2-oxazoline resulted in a well-defined linear polymer backbone with pendant azido groups. Alkynyl-poly(d,l-lactide) was grafted onto the azido groups of poly(oxazoline) via a Huisgen 1,3-dipolar cycloaddition reaction to give a novel amphiphilic graft copolymer [poly(2-methyl-2-oxazoline-co-2-pentyl-2-oxazoline)-g-poly(d,l-lactide)] (P[(MeOx-co-PentOx)-g-LA]). Different graft copolymers were prepared with PLA of different lengths. Preliminary results of the self-association of this copolymer in water indicated the formation of nanoparticles, which suggests this copolymer may have applications as vehicles for drug delivery.     

Design of novel poly(methyl vinyl ether) containing AB and ABC block copolymers by the dual initiator strategy

A new set of block copolymers containing poly(methyl vinyl ether) (PMVE) on one hand and poly(tert-butyl acrylate), poly(acrylic acid), poly(methyl acrylate) or polystyrene on the other hand, have been prepared by the use of a novel dual initiator 2-bromo-(3,3-diethoxy-propyl)-2-methylpropanoate. The dual initiator has been applied in a sequential process to prepare well-defined block copolymers of poly(methyl vinyl ether) (PMVE) and hydrolizable poly(tert-butyl acrylate) (PtBA), poly(methyl acrylate) (PMA) or polystyrene (PS) by living cationic polymerization and atom transfer radical polymerization (ATRP), respectively. In a first step, the Br and acetal end groups of the dual initiator have been used to generate well-defined homopolymers by ATRP (resulting in polymers with remaining acetal function) and living cationic polymerization (PMVE with pendant Br end group), respectively. In a second step, those acetal functionalized polymers and PMVE-Br homopolymers have been used as macroinitiators for the preparation of PMVE-containing block copolymers. After hydrolysis of the tert-butyl groups in the PMVE-b-ptBA block copolymer, PMVE-b-poly(acrylic acid) (PMVE-b-PAA) is obtained. Chain extension of the AB diblock copolymers by ATRP gives rise to ABC triblock copolymers. The polymers have been characterized by MALDI-TOF, GPC and ¹H NMR.     

Synthesis and characterization of graft copolymers with poly(epichlorohydrin-co-ethylene oxide) as backbone by combination of ring-opening polymerization with living anionic polymerization

Series of graft copolymers with [Poly(epichlorohydrin-co-ethylene oxide)] [Poly(ECH-co-EO)] as backbone and polystyrene (PS), poly(isoprene) (PI) or their block copolymers as side chains were successfully synthesized by combination of ring-opening polymerization (ROP) with living anionic polymerization. The Poly(ECH-co-EO) with high molecular weight (M_n = 3.3 × 10⁴ g/mol) and low polydispersity index (PDI = 1.34) was firstly synthesized by ring-ROP using ethylene glycol potassium as initiator and triisobutylaluminium (i-Bu₃Al) as activator. Subsequently, by “grafting onto” strategy, the graft copolymers Poly(ECH-co-EO)-g-PI, Poly(ECH-co-EO)-g-PS and Poly(ECH-co-EO)-g-(PI-b-PS) were obtained using the coupling reaction between living PI⁻Li⁺, PS⁻Li⁺ or PS-b-PI⁻Li⁺ species capped with or without 1,1-diphenylethylene (DPE) agent and chloromethyl groups on poly(ECH-co-EO). By model experiment, the addition of DPE agent was confirmed to have an important effect on the grafting efficiency at room temperature. Finally, the target graft copolymers and intermediates were characterized by SEC, ¹H NMR, MALLS and FTIR in detail, and thermal behaviours of the graft copolymers were also investigated by DSC measurement.     

Biodegradable depsipeptide–PDO–PEG-based block copolymer micelles as nanocarriers for controlled release of doxorubicin

Nowadays, biodegradable amphiphilic block copolymers with stable performance and adjustable structure have attracted the interests of researchers in the field of drug delivery. In this work, the triblock copolymer, P(SBMD-co-PDO)-b-PEG-b-P(SBMD-co-PDO), was successfully synthesized by ring-opening polymerization of 3(S)-sec-butyl-morpholine-2,5-dione (SBMD) and p-dioxanone (PDO) with poly(ethylene glycol) (PEG) as the initiator. In phosphate buffered solution (PBS), these copolymers could self-assemble into nano-sized micelles that have a hydrophobic P(SBMD-co-PDO) core surrounded by a hydrophilic PEG shell. Because of the strong hydrogen bonding and hydrophobic interactions, doxorubicin (DOX) was loaded into the micelles with high loading capacity (LC, up to 28.4%) and encapsulation efficiency (EE, up to 62.5%). The drug-loaded micelles showed sustained-release of DOX along with the hydrolytic degradation of the micelles in PBS. Therefore, these amphiphilic triblock copolymers have potential as drug matrix for controlled release.     

Preparation of star copolymers with three arms of poly(ethylene oxide-co-glycidol)-graft-polystyrene and investigation of their aggregation in water

The star graft copolymers with three arms composed of poly(ethylene oxide) (PEO) as main chain and polystyrene (PS) as side chains were prepared by sequential anionic ring-opening copolymerization of ethylene oxide and ethoxyethyl glycidyl ether (EEGE), and then atom transfer radical polymerization (ATRP) of styrene. The anionic ring-opening copolymerization of EO and EEGE was carried out using 2-ethyl-2-hydroxymethyl-1,3-propanediol as trifunctional initiator and diphenylmethyl potassium (DPMK) as deprotonating agent. The resulting three-arm star copolymer [poly(EO-co-EEGE)]₃ could be easily hydrolyzed to unmask the pendant hydroxyl groups without affecting the PEO chains. The switch from the first to the second mechanism was completed by the reaction of the multi-pendant hydroxyl groups of three-arm PEO chain with 2-bromoisobutyryl bromide. The obtained poly(ethylene oxide-co-2-bromoisobutyryloxyglycidyl ether), [poly(EO-co-BiBGE)]₃, was used as macroinitiators to initiate the polymerization of styrene in bulk at 90 °C by ATRP. The final products and intermediates were characterized by NMR, SEC and IR in detail. The amphiphilic star graft copolymers synthesized can form micelles in water. The critical micelle concentration (cmc) determined by fluorescence spectra was about 5 × 10⁻⁷ g/mL. Sphere micelles were observed by transmission electron microscopy (TEM) at low copolymer concentration (6 × 10⁻⁵ g/mL), but the micelle shape became irregular when the copolymer concentration increased to 6 × 10⁻⁴ g/mL.     

PTPFCBBMA-b-PEG-b-PTPFCBBMA amphiphilic triblock copolymer: Synthesis and self-assembly behavior

We present the synthesis and self-assembly behavior of a new semi-fluorinated amphiphilic triblock copolymer. A series of perfluorocyclobutyl aryl ether-based amphiphilic ABA triblock copolymer containing hydrophilic poly(ethylene glycol) segment as the middle block were synthesized by atom transfer radical polymerization (ATRP). ATRP of 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate was initiated by PEG-based bifunctional macroinitiators with different molecular weights to obtain the desired copolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.30) and the number of perfluorocyclobutyl linkage can be tuned by the feed ratio and the conversion of the fluorine-containing methacrylic monomer. The critical micelle concentrations of these amphiphilic ABA triblock copolymers in aqueous media were determined by fluorescence probe technique. They could aggregate to form spherical and cylindrical micelles visualized by TEM with varying the content of hydrophobic segment.     

Crystalline structures and thermal properties of poly(ethylene-co-α,ω-nonconjugated diene)s prepared by zirconocene catalysts

Crystalline structures and thermal properties of poly(ethylene-co-α,ω-nonconjugated diene)s, [diene=1,5-hexadiene (HD), 1,7-octadiene (OD), and 1,9-decadiene (DD)] have been investigated in relation to insertion mode of the dienes. In the case of poly(ethylene-co-HD), the copolymer containing high cis-1,3-cyclopentane units shows lower melting point depression with increasing the comonomer content than the copolymers containing high trans-1,3-cyclopentane units. In the case of poly(ethylene-co-OD) and poly(ethylene-co-DD), the copolymers containing pendant vinyl groups show higher ΔH_m than that of the copolymers with cyclic units or branching structures. Thermal degradation of the copolymers has been investigated under nitrogen atmosphere and the degradation of the copolymers containing the cyclic structures begins at lower temperature than the copolymers containing pendant vinyl groups.     

Study of the solution and aqueous emulsion copolymerization of vinylidene chloride with methyl acrylate in the presence a poly(ethylene oxide) macromolecular RAFT agent

The reversible addition-fragmentation chain transfer (RAFT) copolymerization of vinylidene chloride (VDC) with methyl acrylate (MeA) was studied in the presence of poly(ethylene oxide)-based macromolecular RAFT (macroRAFT) agents of the trithiocarbonate type (PEO-TTC) in solution and in aqueous emulsion. Firstly the formation of PEO-b-P(VDC-co-MeA) diblock copolymers was performed in toluene solution at 30 °C and a good control over the polymerization with high chain-end functionality was shown. A first aqueous emulsion copolymerization of VDC with MeA was performed using one of the amphiphilic PEO-b-P(VDC-co-MeA) diblock copolymers as macromolecular stabilizer. Then, in a series of experiments the PEO-TTC macroRAFT agents were directly tested as both chain transfer agents and stabilizing agents in similar conditions (aqueous batch emulsion copolymerization of VDC with MeA at 70 °C). The influence of the nature and concentration of the initiating system and the presence or not of a buffer were studied. We demonstrated that in simple conditions, nanometric latex particles composed of amphiphilic PEO-b-P(VDC-co-MeA) diblock copolymers formed by polymerization-induced self-assembly (PISA). It can thus be concluded that PEO-TTC macroRAFT agents are valuable non-ionic macromolecular stabilizers in the emulsion copolymerization of VDC and MeA and allow the formation of core–shell diblock copolymer particles in the absence of free surfactant. However, when rather high molar masses of the hydrophobic PVDC-based block were targeted, the determined molar masses deviated from the theoretical values.     

Hydroxyl-bearing poly(α-hydroxy acid)-type aliphatic degradable polyesters prepared by ring opening (co)polymerization of dilactones based on glycolic, gluconic and l-lactic acids

The synthesis of HO-protected poly(glycolic acid-co-gluconic acid) and poly(l-lactic acid-co-glycolic acid-co-gluconic acid) by copolymerisation of l-lactide and 3-(1,2-3,4-tetraoxobutyl-diisopropylidene)-1,4-dioxane-2,5-dione (DIPAGYL) is reported. The resulting polymers were characterized by size exclusion chromatography, FT Infrared, nuclear magnetic resonance, differential scanning calorimetry and X-ray diffractometry. The composition of reaction media and the reactivity ratios of the two cyclic monomers were determined at low conversion and indicated random distributions of lactyl and gluconoglycolyl constitutive units. X-ray diffraction data showed semi-crystalline morphology, as observed for poly (lactide) stereocopolymers containing more than 90% of l-enantiomer. Deprotection of the isopropylidene-protected side chain OH was possible under acidic conditions and yielded copolymers with various degrees of hydroxylation. Deprotection of the 5-6 OH groups was fast and complete whereas that of 3-4 ones was partial and occurred at the expenses of partial degradation of the aliphatic polyester chains. T_g increased with the number of hydroxyl functions, a feature attributed to the formation of hydrogen bonds. Comparison is made with features reported previously for analogs derived from dl-lactide.     

Aggregation of biodegradable amphiphilic poly(succinimide-co-N-propyl aspartamide) and poly(N-dodecyl aspartamide-co-N-propyl aspartamide) in aqueous medium and its preliminary drug-released properties

Two series of biodegradable amphiphilic copolymers, poly(succinimide-co-N-propyl aspartamide) (PSI-PA) and poly(N-dodecyl aspartamide-co-N-propyl aspartamide) (PDDA-PA) were synthesized by partial and total aminolysis of polysuccinimide (PSI), respectively. PSI-PA copolymers could self-aggregate in water directly under ultrasonication at room temperature. Differing from PSI-PA copolymers, the aggregates of PDDA-PA need to add PDDA-PA DMF solution into an excessive amount of water. The aggregative properties of PSI-PA and PDDA-PA copolymers have been investigated by dynamic light scattering (DLS) and surface tension measurements. Hydrophilicity of these two copolymers was attributed to the N-propyl aspartamide segments. Due to the stiff structure, succinimide segments preferred to form irregular hydrophobic microdomains, and some aggregates of PSI-PA are bimodal size distribution in water medium, while the more flexible PDDA-PA copolymer chains preferred to form monodispersed spherical aggregates. Elevated temperature could reduce the aggregate size of both PSI-PA and PDDA-PA copolymers due to the breaking of the hydrogen bonding and the releasing of the bonded water molecules. PSI-PA copolymers were surface active, while the surface tension of PDDA-PA copolymers was independent on concentration. The drug-loaded aggregates of PSI-PA also have been prepared and the preliminary release properties have been studied in vitro.     

Synthesis and properties of ABA-type triblock copolymers of poly(glycolide-co-caprolactone) (A) and poly(ethylene glycol) (B)

Poly(glycolide-co-caprolactone) (A)-poly(ethylene glycol) (B) ABA-type triblock copolymers (PGCE) were synthesized by bulk ring opening polymerization, using the hydroxyl endgroups of poly(ethylene glycol) (PEG) as initiator and stannous octoate as catalyst. The resulting copolymers were characterized by various analytical techniques. Gel permeation chromatographic analysis indicated that the polymerization product was free of residual monomers, PEG and oligomers. ¹H NMR and differential scanning calorimeter results demonstrated that the copolymers had a structure of poly(glycolide-co-caprolactone) (PGC) chains chemically attached to PEG segments. All the PGCE copolymers showed improved hydrophilicity in comparison with the corresponding PGC copolymers with the same molar ratio of glycolidyl and caproyl units. The microspheres of PGCE copolymer exhibited rough surfaces quite different from the smooth surface of PGC microspheres. This phenomenon was attentively ascribed to the highly swollen ability of PGCE copolymers and the freeze-drying process in the microspheres fabrication.