Acid catalyzed transesterification as a route to poly(3-hydroxybutyrate-co-epsilon-caprolactone) copolymers from their homopolymers

Copolymers of (R)-3-hydroxybutyric acid (HB) and epsilon-caprolactone (CL) with a composition ranging from 28 to 81 mol % of HB were synthesized by transesterification of the corresponding homopolymers in solution in the presence of 4-toluenesulfonic acid. The copolyesters were characterized with regard to their molecular weights, thermal properties, molar compositions, and average block length of repeating units by gel permeation chromatography (GPC), differential scanning calorimetry, (1)H NMR, and (13)C NMR, respectively. Random and microblock copolymers could be obtained depending on experimental conditions, with weight-average molecular weights of up to 20,000. The glass transition temperature decreased from 2 to -42 degrees C as the CL content was increased from 0 to 72 mol %. The melting temperature (T(m)) of the PCL phase decreased from 70 to 46 degrees C as the HB content changed from 0 to 47 mol %, while the T(m) of the PHB phase decreased from 177 degrees C to 163 degrees C as the CL content changed from 0 to 72 mol %. Matrix-assisted laser desorption ionization time-of-flight mass spectra of GPC fractionated samples allowed us to ascertain that copolymers rich in HB units have mostly hydroxyl and carboxyl end groups, while copolymers rich in CL units have mostly tosyl and carboxyl end groups.     

Synthesis of poly(epsilon-caprolactone)-b-poly(gamma-benzyl-L-glutamic acid) block copolymer using amino organic calcium catalyst

A biodegradable two block copolymer, poly(epsilon-caprolactone)-b- poly(gamma-benzyl-L-glutamic acid) (PCL-PBLG) was synthesized successfully by ring-opening polymerization of N-carboxyanhydride of gamma-benzyl-L-glutamate (BLG-NCA) with aminophenyl-terminated PCL as a macroinitiator. The aminophenethoxyl-terminated PCL was prepared via hydrogenation of a 4-nitrophenethoxyl-terminated PCL, which was novelly obtained from the polymerization of epsilon-caprolactone (CL) initiated by amino calcium 4-nitrobenzoxide. The structures of the block copolymer and its precursors from the initial step of PCL were confirmed and investigated by 1H NMR, FT-IR, GPC, and FT-ICRMS analyses and DSC measurements.     

A new pathway for poly(3-hydroxybutyrate) production in Escherichia coli and Corynebacterium glutamicum by functional expression of a new acetoacetyl-coenzyme A synthase

A biosynthetic pathway for poly(3-hydroxybutyrate) [P(3HB)] was developed in Escherichia coli and Corynebacterium glutamicum by an acetoacetyl-coenzyme A (CoA) synthase (AACS) recently isolated from terpenoid-producing Streptomyces sp. strain CL190. Expression of AACS led to significant productions of P(3HB) in E. coli (10.5 wt %) and C. glutamicum (19.7 wt %).     

L-Phe end-capped poly(L-lactide) as macroinitiator for the synthesis of poly(L-lactide)-B-poly(L-lysine) block copolymer

A poly(L-lactide)-b-poly(Nepsilon-(Z)-L-lysine) (PLLA-b-PZLys) block copolymer was synthesized through the ring-opening polymerization of Nepsilon-(Z)-lysine-N-carboxyanhydride using L-Phe-terminated PLLA as a macroinitiator. The L-Phe-terminated PLLA was prepared through a novel three-step process. First, the hydroxyl-terminated PLLA was synthesized through the ring-opening polymerization of L-lactide initiated by n-butanol under the existence of tin(II) ethylhexanoate. Subsequently, the complete capping of the hydroxyl end group of PLLA with BOC-L-Phe was achieved by using a mixed anhydride of BOC-L-Phe under the catalysis of 4-(1-pyrrolidinyl) pyridine. Finally, the free amino end group was obtained by removal of the t-butoxycarbonyl group through trifluoroacetic acid treatment under anhydrous condition. All these treatments were conducted under mild conditions, thus avoiding the breakdown of the PLLA backbone. Poly(L-lactide)-b-poly(L-lysine) block copolymer was produced after deprotection treatment of PLLA-b-PZLys. The structure of the block copolymer was confirmed by 1H NMR, IR, and GPC. Adjustment of the ratio of the NCA monomer to the macroinitiator could control the chain length of the PLys block.     

In situ copolyesters containing poly(L-lactide) and poly(hydroxyalkanoate) units

In situ copolyesters containing polylactide (PLA) and polyhydroxyalkanoate (PHA) segments were obtained via ring-opening polymerization of L-lactide using PHA as a macroinitiator with stannous octoate as catalyst. Incorporation of PHA (20 wt %) into PLA affords a novel copolymer with Mn values ranging from 25 to 50 KDa and low polydispersities of 1.8-2.3. DSC analysis of the copolymer indicates well-defined crystallization and melting transitions different from the homopolymers and corresponding blend. The polymers were characterized by FT-IR, GPC, DSC, optical microscopy, NMR, and TGA. The results show successful reactivity of PHA as a macroinitiator for the ring-opening polymerization of lactide.     

Synthesis of temperature-responsive heterobifunctional block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide)

Heterobifunctional block copolymers of poly(ethylene glycol) (PEG) and poly(N-isopropylacrylamide) (PNIPAM) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of NIPAM using a macromolecular trithiocarbonate PEG-based chain transfer agent. The polymerization showed all the expected features of living radical polymerization and allowed the synthesis of copolymers with different lengths of the PNIPAM block. The synthesized block copolymers contained a carboxylic acid group from L-lysine at the focal point and a trithiocarbonate group at the terminus of the PNIPAM block. The trithiocarbonate functionality was converted into a thiol group and used for conjugation of biotin to the end of the PNIPAM block. The copolymers exhibited temperature-dependent association behavior in aqueous solution with a phase transition of approximately 32 degrees C. The described heterobifunctional block copolymers show promise for surface modifications with the potential for stimulus-controlled surface presentation of ligands attached to the terminus of the PNIPAM block.     

Synthesis and characterization of triblock copolymers of methoxy poly(ethylene glycol) and poly(propylene fumarate)

Amphiphilic block copolymers were synthesized by transesterification of hydrophilic methoxy poly(ethylene glycol) (mPEG) and hydrophobic poly(propylene fumarate) (PPF) and characterized. Four block copolymers were synthesized with a 2:1 mPEG:PPF molar ratio and mPEGs of molecular weights 570, 800, 1960, and 5190 and PPF of molecular weight 1570 as determined by NMR. The copolymers synthesized with mPEG of molecular weights 570 and 800 had 1.9 and 1.8 mPEG blocks per copolymer, respectively, as measured by NMR, representing an ABA-type block copolymer. The number of mPEG blocks of the copolymer decreased with increasing mPEG block length to as low as 1.5 mPEG blocks for copolymer synthesized with mPEG of molecular weight 5190. At a concentration range of 5-25 wt % in phosphate-buffered saline, copolymers synthesized with mPEG molecular weights of 570 and 800 possessed lower critical solution temperatures (LCST) between 40 and 45 degrees C and between 55 and 60 degrees C, respectively. Aqueous solutions of copolymer synthesized with mPEG 570 and 800 also experienced thermoreversible gelation. The sol-gel transition temperature was dependent on the sodium chloride concentration as well as the mPEG block length. The copolymer synthesized from mPEG 570 had a transition temperature between 40 and 20 degrees C with salt concentrations between 1 and 10 wt %, while the sol-gel transition temperatures of the copolymer synthesized from mPEG molecular weight 800 were higher in the range 75-30 degrees C with salt concentrations between 1 and 15 wt %. These novel thermoreversible copolymers are the first biodegradable copolymers with unsaturated double bonds along their macromolecular chain that can undergo both physical and chemical gelation and hold great promise for drug delivery and tissue engineering applications.     

Study of the synthesis, crystallization, and morphology of poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymers

Poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymers PEG-PCL were synthesized by ring-opening polymerization of epsilon-caprolactone using monomethoxy poly(ethylene glycol) as the macroinitiator and calcium ammoniate as the catalyst. Obvious mutual influence between PEG and PCL crystallization was studied by altering the relative block length. Fixing the length of the PEG block (Mn = 5000) and increasing the length of the PCL block, the crystallization temperature of the PCL block rose gradually from 1 to about 35 degrees C while that of the PEG block dropped from 36 to -6.6 degrees C. Meanwhile, the melting temperature of the PCL block went up from 30 to 60 degrees C, while that of the PEG block declined from 60 to 41 degrees C. If the PCL block was longer than the PEG block, the former would crystallize first when cooling from a molten state and led to obviously imperfect crystallization of PEG and vice versa. And they both crystallized at the same temperature, if their weight fractions were equal. We found that the PEG block could still crystallize at -6.6 degrees C even when its weight fraction is only 14%. A unique morphology of concentric spherulites was observed for PEG5000-PCL5000. According to their morphology and real-time growth rates, it is concluded that the central and outer sections in the concentric spherulites were PCL and PEG, respectively, and during the formation of the concentric spherulite, the PEG crystallized quickly from the free space of the PCL crystal at the earlier stage, followed by outgrowing from the PCL spherulites in the direction of right angles to the circle boundaries until the entire area was occupied.     

A New Pathway for Poly(3-hydroxybutyrate) Production in Escherichia coli and Corynebacterium glutamicum by Functional Expression of a New Acetoacetyl-coenzyme A Synthase

A biosynthetic pathway for poly(3-hydroxybutyrate) [P(3HB)] was developed in Escherichia coli and Corynebacterium glutamicum by an acetoacetyl-coenzyme A (CoA) synthase (AACS) recently isolated from terpenoid-producing Streptomyces sp. strain CL190. Expression of AACS led to significant productions of P(3HB) in E. coli (10.5 wt %) and C. glutamicum (19.7 wt %).     

Highly branched poly(L-lysine)

This paper describes the synthesis of several novel water-soluble highly branched polypeptides. The synthesis starts with the ring-opening polymerization of epsilon-benzyloxycarbonyl-l-lysine N-carboxyanhydride (Z-Lys NCA) or epsilon-trifluoroacetyl-l-lysine N-carboxyanhydride (TFA-Lys NCA), followed by end functionalization of the peptide chain with N(alpha),N(epsilon)-di(9-fluorenylmethoxycarbonyl)-l-lysine (N(alpha),N(epsilon)-diFmoc Lys). Deprotection of the N(alpha),N(epsilon)-diFmoc Lys end group affords two new primary amine groups that can initiate the polymerization of a second generation of branches. Repetition of this ring-opening polymerization-end functionalization sequence affords highly branched poly(epsilon-benzyloxycarbonyl-l-lysine) (poly(Z-Lys)) and poly(epsilon-trifluoroacetyl-l-lysine) (poly(TFA-Lys)) in a small number of straightforward synthetic steps. Removal of the side-chain protective groups yields water-soluble and highly branched poly(l-lysine)s, which may be of potential interest for a variety of medical applications.     

Chain transfer reaction catalyzed by various polyhydroxyalkanoate synthases with poly(ethylene glycol) as an exogenous chain transfer agent

Polyhydroxyalkanoate (PHA) synthases catalyze chain transfer (CT) reaction after polymerization reaction of PHA by transferring PHA chain from PHA synthase to a CT agent, resulting in covalent bonding of CT agent to PHA chain at the carboxyl end. Previous studies have shown that poly(ethylene glycol) (PEG) is an effective exogenous CT agent. This study aimed to compare the effects of PEG on CT reaction during poly[(R)-3-hydroxybutyrate] [P(3HB)] synthesis by using six PHA synthases in Escherichia coli JM109. The synthesized P(3HB) polymers were characterized in terms of molecular weight and end-group structure. Supplementation of PEG to the culture medium reduced P(3HB) molecular weights by up to 96% due to PEG-induced CT reaction. The P(3HB) polymers were subjected to ¹H NMR analysis to confirm the formation of a covalent bond between PEG and P(3HB) chain at the carboxyl end. This study revealed the reactivity of PHA synthases to PEG with respect to CT reaction in E. coli.     

Enzymatic hydrolysis of chemosynthesized atactic poly(3-hydroxybutyrate) by poly(3-hydroxyalkanoate) depolymerase from Acidovorax Sp. TP4 and Ralstonia pickettii T1

The enzymatic degradability of chemosynthesized atactic poly([R,S]-3-hydroxybutyrate) [a-P(3HB)] by two types of extracellular poly(3-hydroxyalkanoate) (PHA) depolymerases purified from Ralstonia pickettii T1 (PhaZ(ral)) and Acidovorax Sp. TP4 (PhaZ(aci)), defined respectively as PHA depolymerase types I and II according to the position of the lipase box in the catalytic domain, were studied. The enzymatic degradation of a-P(3HB) by PhaZ(aci) depolymerase was confirmed from the results of weight loss and the scanning electron micrographs. The degradation products were characterized by one- and two-dimension (1)H NMR spectroscopy. It was found that a-P(3HB) could be degraded into monomer, dimer, and trimer by PhaZ(aci) depolymerase at temperatures ranging from 4 to 20 degrees C, while a-P(3HB) could hardly be hydrolyzed by PhaZ(ral) depolymerase in the same temperature range. These results suggested that the chemosynthesized a-P(3HB) could be degraded in the pure state by natural PHA depolymerase.     

Engineering of Ralstonia eutropha for production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from fructose and solid-state properties of the copolymer

Recombinant Ralstonia eutropha capable of producing poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer [P(3HB-co-3HHx)] from fructose was engineered by introduction of genes for crotonyl-CoA reductase (CCR) from Streptomyces cinnamonensis (ccrSc) and for PHA synthase and (R)-specific enoyl-CoA hydratase from Aeromonas caviae (phaC-JAc). In this recombinant strain, C6-acyl-CoA intermediates were provided via beta-ketothiolase-mediated elongation of butyryl-CoA, which was generated from crotonyl-CoA by the function of CCR. The recombinant strain could accumulate the copolyester up to 48 wt % of dry cell weight with 1.5 mol % of 3HHx fraction from fructose, when the expression of ccrSc under the control of the PBAD promoter was induced with 0.01% L-arabinose. The absence of L-arabinose or the deletion of ccrSc from the plasmid resulted in accumulation of poly(3-hydroxybutyrate) homopolymer, indicating the critical role of CCR in the formation of the 3-hydroxyhexanoate unit. Higher CCR activity obtained by the addition of a larger amount of L-arabinose did not affect the composition but reduced the intracellular content of the copolyester. The P(3HB-co-1.5 mol % 3HHx) copolyester produced from fructose by the recombinant R. eutropha showed relatively lower melting temperatures (150 degrees C and 161 degrees C) and lower crystallinity (48 +/- 5%) compared to those (175 degrees C and 60 +/- 5%) of P(3HB) homopolymer. It has been found that the incorporation of a small amount (1.5 mol %) of 3HHx units into P(3HB) sequences leads to a remarkable change in the solid-state properties of P(3HB) crystals. The present study demonstrates the potential of the engineered pathway for the production of copolyesters having favorable characteristics from inexpensive carbon resources.     

Synthesis and characterization of glycopolymer-polypeptide triblock copolymers

Glycopolymer-polypeptide triblock copolymers of the structure, poly(l-alanine)-b-poly(2-acryloyloxyethyl-lactoside)-b-poly(l-alanine) (AGA), have been synthesized by sequential atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP). Controlled free radical polymerization of 2-O-acryloyl-oxyethoxyl-(2,3,4,6-tetra-O-acetyl-beta-d-galactopyranosyl)-(1-4)-2,3,6-tri-O-acetyl-beta-d-glucopyranoside (AEL) by ATRP with a dibromoxylene (DBX)/CuBr/bipy complex system was used to generate a central glycopolymer block. Telechelic glycopolymers with diamino end groups were obtained by end group transformation and subsequently used as macroinitiators for ROP of l-alanine N-carboxyanhydride monomers (Ala-NCA). Gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy analysis demonstrated that copolymer molecular weight and composition were controlled by both the molar ratios of the Ala-NCA monomer to macroinitiator and monomer conversion and exhibited a narrow distribution (Mw/Mn = 1.06-1.26). FT-IR spectroscopy of triblock copolymers revealed that the ratio of alpha-helix/beta-sheet increased with poly(l-alanine) block length. Of note, transmission electron microscopy (TEM) demonstrated that selected amphiphilic glycopolymer-polypeptide triblock copolymers self-assemble in aqueous solution to form nearly spherical aggregates of several hundreds nanometer in diameter. Significantly, the sequential application of ATRP and ROP techniques provides an effective method for producing triblock copolymers with a central glycopolymer block and flanking polypeptide blocks of defined architecture, controlled molecular weight, and low polydispersity.     

Synthesis and evaluation of a star amphiphilic block copolymer from poly(epsilon-caprolactone) and poly(ethylene glycol) as a potential drug delivery carrier

A star polymer composed of amphiphilic block copolymer arms has been synthesized and characterized. The core of the star polymer is polyamidoamine (PAMAM) dendrimer, the inner block in the arm is lipophilic poly(epsilon-caprolactone) (PCL), and the outer block in the arm is hydrophilic poly(ethylene glycol) (PEG). The star-PCL polymer was synthesized first by ring-opening polymerization of epsilon-caprolactone with a PAMAM-OH dendrimer as initiator. The PEG polymer was then attached to the PCL terminus by an ester-forming reaction. Characterization with SEC, (1)H NMR, FTIR, TGA, and DSC confirmed the star structure of the polymers. The micelle formation of the star copolymer (star-PCL-PEG) was studied by fluorescence spectroscopy. Hydrophobic dyes and drugs can be encapsulated in the micelles. A loading capacity of up to 22% (w/w) was achieved with etoposide, a hydrophobic anticancer drug. A cytotoxicity assay demonstrated that the star-PCL-PEG copolymer is nontoxic in cell culture. This type of block copolymer can be used as a drug delivery carrier.     

Monohydroxylated poly(3-hydroxyoctanoate) oligomers and its functionalized derivatives used as macroinitiators in the synthesis of degradable diblock copolyesters

The presence of a hydroxyl group at the end of poly(3-hydroxyoctanoate) oligomers, noted PHO oligomers, is required to prepare diblock copolymers with improved properties by ring-opening polymerization of cyclic monomer as epsilon-caprolactone. Several chemical methods such as basic hydrolysis, acid-catalyzed reaction with APTS, and methanolysis were used to prepare well-defined low molar masses PHO oligomers. The methanolysis reaction was allowed to proceed for 10-60 min to produce PHO oligomers with Mn values ranging from 20,000 to 800 g mol-1 with low polydispersity index. Detailed analysis of the MALDI-TOF mass spectra of the obtained oligomers has revealed the presence of linear structures bearing methyl ester on one side and hydroxyl end group on the other side. The same procedure was applied to poly(3-hydroxyoctanoate-co-3-hydroxyundecenoate), PHOU, a poly(3-hydroxyalkanoate) containing unsaturated units in its side chains. These oligomers were further used to initiate the polymerization of epsilon-caprolactone by varying the PHO (or PHOU) and PCL lengths. By copolymerization with epsilon-caprolactone, the properties of PHO or PHOU have been improved. The crystallinity of the obtained copolymers was modified by controlling the length of the two different blocks. The unsaturations in the side chains of the PHOU block were oxidized in acid carboxylic functions to obtain a novel artificial biopolyester. Moreover, degradation was followed to study the influence of carboxylic groups on the hydrolysis of the copolymers.     

Stereoselective polymerization of rac-lactide using a monoethylaluminum Schiff base complex

A monoethylaluminum Schiff base complex (2) with formula LAlEt (L = N,N'-(2,2-dimethylpropylene)bis(3,5-di-tert-butylsalicylideneimine) was synthesized and employed for the stereoselective ring-opening polymerization of rac-lactide (rac-LA). The complex 2 was characterized by nuclear magnetic resonance, crystal structure, and elemental analysis. It contains a five-coordinate aluminum atom with distorted trigonal bipyramidal geometry in the solid state. In the presence of 2-propanol, 2 showed high stereoselectivity for the polymerization of rac-LA. The polymerization yielded crystalline poly(rac-LA) with a high melting temperature (193-201 degrees C). NMR, differential scanning calorimetry, and wide-angle X-ray diffraction indicated that the poly(rac-LA) was highly isotactic, and a stereocomplex was formed between poly-l- and poly-d-lactide block sequences. By the analysis of electrospray-ionization mass spectrometry and (1)H NMR, the polymer was demonstrated to be endcapped in both terminals with an isopropyl ester and a hydroxy group, respectively. The polymerization was of first order in rac-LA concentration. The relationship between the rac-LA conversion and molecular weights of the polymer was linear so that the polymerization could be well controlled.     

Thermogelling aqueous solutions of alternating multiblock copolymers of poly(L-lactic acid) and poly(ethylene glycol)

We are reporting alternating multiblock copolymers of poly(L-lactic acid)/poly(ethylene glycol) aqueous solution (> 15 wt %) undergoing sol-gel-sol transition as the temperature increases from 20 to 60 degrees C. Micelles of the multiblock copolymers (in water) are about 20 nm in radius at low temperature. They are aggregated to a larger size as the temperature increases, which should play a critical role in the sol-to-gel transition. The transition temperature and gel window were affected by the molecular weight and composition of the multiblock copolymer. In particular, the aqueous solution of an alternating multiblock copolymer (Mn approximately 6700 daltons) prepared from poly(ethylene glycol) (Mn approximately 600 daltons) and poly(L-lactic acid) (Mn approximately 1300 daltons) showed a maximum modulus at body temperature (37 degrees C). The in situ gel forming ability of the polymer aqueous solution in vivo as well as in vitro indicates that it can be a promising injectable biomaterial.     

Hyperproduction of poly(4-hydroxybutyrate) from glucose by recombinant Escherichia coli

ABSTRACT: BACKGROUND: Poly(4-hydroxybutyrate) [poly(4HB)] is a strong thermoplastic biomaterial with remarkable mechanical properties, biocompatibility and biodegradability. However, it is generally synthesized when 4-hydroxybutyrate (4HB) structurally related substrates such as gamma-butyrolactone, 4-hydroxybutyrate or 1,4-butanediol (1,4-BD) are provided as precursor which are much more expensive than glucose. At present, high production cost is a big obstacle for large scale production of poly(4HB). RESULTS: Recombinant Escherichia coli strain was constructed to achieve hyperproduction of poly(4-hydroxybutyrate) [poly(4HB)] using glucose as a sole carbon source. An engineering pathway was established in E. coli containing genes encoding succinate degradation of Clostridium kluyveri and PHB synthase of Ralstonia eutropha. Native succinate semialdehyde dehydrogenase genes sad and gabD in E. coli were both inactivated to enhance the carbon flux to poly(4HB) biosynthesis. Four PHA binding proteins (PhaP or phasins) including PhaP1, PhaP2, PhaP3 and PhaP4 from R. eutropha were heterologously expressed in the recombinant E. coli, respectively, leading to different levels of improvement in poly(4HB) production. Among them PhaP1 exhibited the highest capability for enhanced polymer synthesis. The recombinant E. coli produced 5.5 g L-1 cell dry weight containing 35.4% poly(4HB) using glucose as a sole carbon source in a 48 h shake flask growth. In a 6-L fermentor study, 11.5 g L-1 cell dry weight containing 68.2% poly(4HB) was obtained after 52 h of cultivation. This was the highest poly(4HB) yield using glucose as a sole carbon source reported so far. Poly(4HB) was structurally confirmed by gas chromatographic (GC) as well as 1H and 13C NMR studies. CONCLUSIONS: Significant level of poly(4HB) biosynthesis from glucose can be achieved in sad and gabD genes deficient strain of E. coli JM109 harboring an engineering pathway encoding succinate degradation genes and PHB synthase gene, together with expression of four PHA binding proteins PhaP or phasins, respectively. Over 68% poly(4HB) was produced in a fed-batch fermentation process, demonstrating the feasibility for enhanced poly(4HB) production using the recombinant strain for future cost effective commercial development.     

A facile synthesis of azido-terminated heterobifunctional poly(ethylene glycol)s for "click" conjugation

New azido-terminated heterobifunctional poly(ethylene glycol) (PEG) derivatives having primary amine and carboxyl end groups, (Azide-PEG-NH 2 and Azide-PEG-COOH, respectively) were synthesized with high efficiency. An alpha-allyl-omega-hydroxyl PEG was prepared as the first step to Azide-PEG-X (X = NH 2 and COOH) through the ring-opening polymerization of ethylene oxide (EO) with allyl alcohol as an initiator, followed by two-step modification of the hydroxyl end to an azido group. To introduce primary amino or carboxyl functional groups, amination and carboxylation reactions of the allyl terminal ends was then conducted by a radical addition of thiol compounds. Molecular functionalities of both ends of the PEG derivatives thus prepared were characterized by (1)H, (13)C NMR, and MALDI-TOF MS spectra, validating that the reaction proceeded quantitatively. The terminal azido functionality is available to conjugate various ligands with an alkyne group through the 1,3-dipolar cycloaddition reaction condition ("click chemistry").