Synthesis of triblock copolymers from glycolysed poly(ethylene terephthalate) by living radical polymerization

Valorization of poly(ethylene terephthalate) (PET) waste has been achieved using glycolysis. The resulting diols were employed for the synthesis of triblock copolymers by atom transfer radical polymerization using copper (I) bromide and (1,1,4,7,10,10)‐hexamethyltriethylenetetramine as catalyst system. Macroinitiator was obtained after depolymerization of PET waste followed by functionalization of the obtained glycolysate with 2‐bromoisobutyrate bromide. Polymerization of styrene (S) and glycidyl methacrylate (GMA) has been achieved leading to PS‐b‐PETG‐b‐PS and (PS‐stat‐PGMA)‐b‐PETG‐b‐(PS‐stat‐PGMA) triblock copolymers. Best results were obtained at 100 °C. At this temperature, termination reaction were negligible and the measured number‐average molar mass of the product increased linearly with monomer conversion in agreement with the theoretical M_n with low polydispersity products achieved. Polymers were also characterized by ¹H NMR. This work presents a original valorization of PET waste as (PS‐stat‐PGMA)‐b‐PETG‐b‐(PS‐stat‐PGMA) copolymer could be used as heat curable coatings. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 433–443, 2008     

Synthesis of poly(chloromethylstyrene‐b‐styrene) block copolymers by controlled free‐radical polymerization

The controlled free‐radical polymerization of styrene and chloromethylstyrene monomers in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxyl (TEMPO) has been studied with the aim of synthesizing block copolymers with well‐defined structures. First, TEMPO‐capped poly(chloromethylstyrene) was prepared. Among several initiating systems [self‐initiation, dicumyl peroxide, and 2,2′‐azobis(isobutyronitrile)], the last offered the best compromise for obtaining a good control of the polymerization and a fast polymerization rate. The rate of the TEMPO‐mediated polymerization of chloromethylstyrene was independent of the initial concentration of TEMPO but unexpectedly higher than the rate of the thermal self‐initiated polymerization of chloromethylstyrene. Transfer reactions to the chloromethyl groups were thought to play an important role in the polymerization kinetics and the polydispersity index of the resulting poly(chloromethylstyrene). Second, this first block was used as a macroinitiator in the polymerization of styrene to obtain the desired poly(chloromethylstyrene‐b‐styrene) block copolymer. The kinetic modeling of the block copolymerization was in good agreement with experimental data. The block copolymers obtained in this work exhibited a low polydispersity index (weight‐average molecular weight/number‐average molecular weight < 1.5) and could be chemically modified with nucleophilic substitution reactions on the benzylic site, opening the way to a great variety of architectures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3845–3854, 2000     

Synthesis of poly(vinyl acetate)‐b‐polystyrene and poly(vinyl alcohol)‐b‐polystyrene copolymers by cobalt‐mediated radical polymerization

Well‐defined poly(vinyl acetate) macroinitiators, with the chains thus end‐capped by a cobalt complex, were synthesized by cobalt‐mediated radical polymerization and used to initiate styrene polymerization at 30 °C. Although the polymerization of the second block was not controlled, poly(vinyl acetate)‐b‐polystyrene copolymers were successfully prepared and converted into amphiphilic poly(vinyl alcohol)‐b‐polystyrene copolymers by the methanolysis of the ester functions of the poly(vinyl acetate) block. These poly(vinyl alcohol)‐b‐polystyrene copolymers self‐associated in water with the formation of nanocups, at least when the poly(vinyl alcohol) content was low enough. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 81–89, 2007     

Morphological behavior of model poly(ethylene‐alt‐propylene)‐b‐polylactide diblock copolymers

A set of well‐defined poly(ethylene‐alt‐propylene)‐b‐polylactide (PEP‐PLA) diblock copolymers containing volume fractions of PLA (f_PLA) ranging between 0.08 and 0.91 were synthesized by a combination of living anionic polymerization, catalytic hydrogenation, and controlled coordination‐insertion ring‐opening polymerization. The morphological behavior of these relatively low‐molecular‐weight PEP‐PLA diblock copolymers was investigated with a combination of rheology, small‐angle X‐ray scattering, and differential scanning calorimetry. The ordered microstructures observed were lamellae (L), hexagonally packed cylinders (C), spheres (S), and gyroid (G), a bicontinous cubic morphology having Ia3 d space group symmetry. The G morphology existed in only a small region between the L‐C morphologies in close proximity to the order–disorder transition (ODT). Transformations from L to G were observed upon heating in several samples. The efficacy of the reverse G to L transition in one sample was cooling rate dependent. The PEP‐PLA Flory–Huggins interaction parameter as a function of temperature χ_PEP‐PLA(T) was estimated from T_ODT's by mean‐field theory and subsequently used in the construction of the experimental PEP‐PLA morphology diagram (χN versus f_PLA). The resultant morphology diagram was symmetric there were the well‐defined L‐C morphology boundaries. The low molecular weight of the materials imparted no significant deviation from previously documented diblock systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2364–2376, 2002     

Poly(caprolactone‐co‐lactide)/perfluoropolyether block copolymers: Synthesis,thermal, and surface characterization

Poly[(caprolactone‐co‐lactide)‐b‐perfluoropolyether‐b‐(caprolactone‐co‐lactide)] copolymers (TXCLLA) were prepared by ring‐opening polymerization of D ,L ‐dilactide (LA2) and caprolactone (CL) in the presence of α,ω‐hydroxy terminated perfluoropolyether (Fomblin Z‐DOL TX) as macroinitiator and tin(II) 2‐ethylexanoate as catalyst. ¹H NMR analysis showed that LA2 is initially incorporated into the copolymer preferentially with respect to CL. A blocky structure of the polyester segment was also indicated by the sequence distribution analysis of the monomeric units. Differential scanning calorimetry analysis showed the compatibility between poly(lactide) (PLA) and poly(caprolactone) (PCL) blocks inside the amorphous phase with glass‐transition temperature values increasing from ?60 to ?15 °C by increasing the PLA content. Copolymers with high average length of CL blocks were semicrystalline with a melting temperature ranging from +35 to +47 °C. Surface analysis showed a high surface activity of TXCLLA copolymers with values of surface tension independent from the PLA/PCL content and very close to those of pure TX. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3588–3599, 2005     

Synthesis and characterization of pH sensitive poly(glycidol)‐b‐poly(4‐vinylpyridine) block copolymers

Block copolymers of poly(glycidol)‐b‐poly(4‐vinylpyridine) were obtained by ATRP of 4‐vinylpyridine initiated by ω‐(2‐chloropropionyl) poly(glycidol) macroinitiators. By changing the monomer/macroinitiator ratio in the synthesis polymers with varied P4VP/PGl molar ratio were obtained. The obtained block copolymers showed pH sensitive solubility. It was found that the linkage of a hydrophilic poly(glycidol) block to a P4VP influenced the pK_a value of P4VP. DLS measurements showed the formation of fully collapsed aggregates exceeding pH 4.7. Above this pH values the collapsed P4VP core of the aggregates was stabilized by a surrounding hydrophilic poly(glycidol) corona. The size of the aggregates depended significantly upon the composition of the block copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1782–1794, 2009     

Synthesis of poly(di[methylamine]ethyl methacrylate)‐b‐poly(cyclohexyl methacrylate)‐b‐poly(di[methylamine]ethyl methacrylate) amphiphilic triblock copolymers by ATRP: Condensed‐phase and solution properties

The synthesis of amphiphilic triblock copolymers, poly(di[methylamine]ethyl methacrylate)‐b‐poly(cyclohexyl methacrylate)‐b‐poly(di[methylamine]ethyl methacrylate) PDMAE‐b‐PCH‐b‐PDMAE, has been performed by atom transfer radical polymerisation. Those have been obtained in a well‐controlled manner in terms of molecular weight and polydispersity index. The triblock copolymer characterisation has been made in condensed state and in solution. The existence of microphase separation has been confirmed by differential scanning calorimetry. However, the domains of both inner and outer blocks seem not to be ordered for one another from small‐angle X‐ray scattering (SAXS) measurements using synchrotron radiation. The micelle formation in dilute methanol solutions has been confirmed for all triblock copolymers by dynamic light scattering analyses. The size of these micelles has been demonstrated to be dependent on the molecular weight. Similar observations have been made in concentrate methanol solutions by using SAXS experiments, pointed also out that an increment of the intermicelle interactions is produced as the concentration increases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 85–92, 2008     

Synthesis and characterization of well‐defined diblock and triblock copolymers of poly(N‐isopropylacrylamide) and poly(ethylene oxide)

Well‐defined diblock and triblock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) were successfully synthesized through the reversible addition–fragmentation chain transfer polymerization of N‐isopropylacrylamide (NIPAM) with PEO capped with one or two dithiobenzoyl groups as a macrotransfer agent. ¹H NMR, Fourier transform infrared, and gel permeation chromatography instruments were used to characterize the block copolymers obtained. The results showed that the diblock and triblock copolymers had well‐defined structures and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.2), and the molecular weight of the PNIPAM block in the diblock and triblock copolymers could be controlled by the initial molar ratio of NIPAM to dithiobenzoate‐terminated PEO and the NIPAM conversion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4873–4881, 2004     

Library synthesis and characterization of 3‐aminopropyl‐terminated poly(dimethylsiloxane)s and poly(ϵ‐caprolactone)‐b‐poly(dimethylsiloxane)s

Libraries of 3‐aminopropyl‐terminated poly(dimethylsiloxane) (APT–PDMS) and poly(?‐caprolactone)–poly(dimethylsiloxane)–poly(?‐caprolactone) (PCL—PDMS–PCL) triblock copolymers were synthesized. Preliminary experiments were carried out to select an appropriate catalyst and route for the poly(dimethylsiloxane) synthesis, and trial experiments were conducted to verify the successful synthesis of the intended polymer compositions. Then, a series of APT–PDMS oligomers were synthesized with an automated combinatorial high‐throughput synthesis system to cover a molecular weight range of 2500–50,000 g/mol. Trial PCL—PDMS–PCL triblock copolymers were synthesized with the automated reactor system and characterized in detail with rapid gel permeation chromatography, high‐throughput Fourier transform infrared, nuclear magnetic resonance, and differential scanning calorimetry. Finally, two library synthesis experiments were carried out in which the lengths of both the poly(dimethylsiloxane) and poly(?‐caprolactone) blocks in the PCL—PDMS–PCL triblock copolymers were varied. The results obtained from these experiments demonstrated that it was possible to synthesize libraries of well‐defined APT–PDMS oligomers and PCL—PDMS–PCL triblock copolymers with an automated high‐throughput system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4880–4894, 2006     

Synthesis of amphiphilic poly(methyl methacrylate‐ b‐ethylene oxide) copolymers from monohydroxy telechelic poly(methyl methacrylate) as macroinitiator

The synthesis of well‐defined poly(methyl methacrylate)‐block‐poly(ethylene oxide) (PMMA‐b‐PEO) dibock copolymer through anionic polymerization using monohydroxy telechelic PMMA as macroinitiator is described. Living anionic polymerization of methyl methacrylate was performed using initiators derived from the adduct of diphenylethylene and a suitable alkyllithium, either of which contains a hydroxyl group protected with tert‐butyldimethylsilyl moiety in tetrahydrofuran (THF) at ?78 °C in the presence of LiClO₄. The synthesized telechelic PMMAs had good control of molecular weight with narrow molecular weight distribution (MWD). The ¹H NMR and MALDI‐TOF MS analysis confirmed quantitative functionalization of chain‐ends. Block copolymerization of ethylene oxide was carried out using the terminal hydroxyl group of PMMA as initiator in the presence of potassium counter ion in THF at 35 °C. The PMMA‐b‐PEO diblock copolymers had moderate control of molecular weight with narrow MWD. The ¹H NMR results confirm the absence of trans‐esterification reaction of propagating PEO anions onto the ester pendants of PMMA. The micellation behavior of PMMA‐b‐PEO diblock copolymer was examined in water using ¹H NMR and dynamic light scattering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2132–2144, 2008     

Amphiphilic block copolymers of high‐molecular‐weight poly(ethylene oxide) and either ε‐caprolactone or γ‐methyl‐ε‐caprolactone: Synthesis and characterization

Ethylene oxide (EO) has been block‐polymerized with both ε‐caprolactone (ε‐CL) and γ‐methyl‐ε‐caprolactone (MCL) through the combination of the anionic polymerization of EO and the ring‐opening polymerization (ROP) of ε‐CL and MCL. ω‐Hydroxyl poly(ethylene oxide) has been reacted with triethylaluminum (OH/Al = 1) and converted into a macroinitiator for ROP of ε‐CL and MCL. In toluene at room temperature, this polymerization leads to a bimodal molecular weight distribution as a result of monomer insertion in only some of the aluminum alkoxide bonds. However, in a more polar solvent (methylene chloride) added with 1 equiv of a Lewis base (pyridine), the expected diblock is formed selectively, and this indicates that aggregation of the active species in toluene is responsible for a macroinitiator efficiency of less than 1. A series of amphiphilic diblock copolymers with poly(ε‐caprolactone) (semicrystalline) and poly(γ‐methyl‐ε‐caprolactone) (amorphous) as the hydrophobic blocks have been prepared and characterized with size exclusion chromatography, ¹H NMR, IR, and wide‐angle X‐ray scattering. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1132–1142, 2004     

Gas transport properties of poly(ether‐b‐amide) segmented block copolymers

The permeation properties of H₂, N₂, and CO₂ were determined at 35 °C and pressures up to 15 atm in phase‐separated polyether‐b‐polyamide segmented block copolymers. These polymers contain poly(ethylene oxide) [PEO] or poly(tetramethylene oxide) [PTMEO] as the rubbery polyether phase and nylon‐6 [PA6] or nylon‐12 [PA12] as the hard polyamide phase. Extremely high values of polar (or quadrupolar)/nonpolar gas selectivities, coupled with high CO₂ permeability coefficients, were observed. CO₂/H₂ selectivities as high as 9.8 and CO₂/N₂ selectivities as high as 56 were obtained in polymers with CO₂ permeability coefficients of approximately 220 × 10⁻¹⁰ cm³(STP) cm/(cm² s cmHg). As the amount of polyether increases, permeability increases. Gas permeability is higher in polymers with less polar constituents, PTMEO and PA12, than in those containing the more polar PEO and PA6 units. CO₂/N₂ and CO₂/H₂ selectivities are higher in polymers with higher concentrations of polar groups. These high selectivity values derive from large solubility selectivities in favor of CO₂. Because CO₂ is larger than H₂ and has, therefore, a lower diffusion coefficient than H₂, the weak size‐sieving ability of the rubbery polyether phase, which is the locus of most of the gas permeation, also contributes to high CO₂/H₂ selectivity. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2051–2062, 2000     

Sol‐gel transition behavior of amphiphilic comb‐like poly[(PEG‐b‐PLGA)acrylate] block copolymers

The effects of comb‐like amphiphilic block copolymer architectures on the physical properties such as sol‐gel transition and micellization behaviors with the change of temperature and pH were examined. Comb‐like poly((poly(ethylene glycol)‐b‐(poly(lactic acid‐co‐glycolic acid))acrylate‐co‐acrylic acid) (poly((PEG‐b‐PLGA)A‐co‐AA)) copolymers were synthesized by coupling of poly(acrylic acid) (PAA) with two different kinds of PEG‐b‐PLGA diblock copolymers to investigate the effects of the number of branches and hydrophilicity/hydrophobicity on the sol‐gel transition and micellization. The molecular weights and chemical structures were confirmed by GPC and ¹H NMR. The number of PEG‐b‐PLGA branches was gradually deviated from the feed molar ratio with increasing the molecular weight and the number of branches and due to the bulkiness of PEG‐b‐PLGA. Poly[(PEG‐b‐PLGA)A‐co‐AA] aqueous solutions showed thermosensitive sol‐gel transition behavior, and the gelation took place at lower concentration with increasing the number of branches and PLGA chain length due to the increase of hydrophobicity. The temperature, at which abrupt increase of viscosity by dynamic rheometer appeared, was also in good agreement with sol‐gel transition by tube‐titling method. The CMC, calculated from UV‐Visible spectroscopy using DPH as hydrophobic dye, also decreased with increasing the number of PEG‐b‐PLGA branches and PLGA chain length with same reason. The micelle size was increased with increasing temperature at the initial stage, however, decreased with further increase of temperature, since the micelles were, first, aggregated by hydrophobic intermolecular interaction, and then fragmented by dehydration of PEG segments with increasing temperature. PH‐sensitive PAA backbone played a key role in physical properties. With decreasing pH, sol‐to‐gel transition temperature, CMC values, and micelle size were decreased because of the increase of hydrophobicity resulting form non‐ionized acrylic acid. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1287–1297, 2010     

Synthesis and characterization of multiblock copolymers composed of poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one) outer blocks and poly(L‐lactide) inner blocks

Ethylene glycol (EG) initiated, hydroxyl‐telechelic poly(L ‐lactide) (PLLA) was employed as a macroinitiator in the presence of a stannous octoate catalyst in the ring‐opening polymerization of 5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one (MBC) with the goal of creating A–B–A‐type block copolymers having polycarbonate outer blocks and a polyester center block. Because of transesterification reactions involving the PLLA block, multiblock copolymers of the A–(B–A)_n–B–A type were actually obtained, where A is poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one), B is PLLA, and n is greater than 0. ¹H and ¹³C NMR spectroscopy of the product copolymers yielded evidence of the multiblock structure and provided the lactide sequence length. For a PLLA macroinitiator with a number‐average molecular weight of 2500 g/mol, the product block copolymer had an n value of 0.8 and an average lactide sequence length (consecutive C₆H₈O₄ units uninterrupted by either an EG or MBC unit) of 6.1. For a PLLA macroinitiator with a number‐average molecular weight of 14,400 g/mol, n was 18, and the average lactide sequence length was 5.0. Additional evidence of the block copolymer architecture was revealed through the retention of PLLA crystallinity as measured by differential scanning calorimetry and wide‐angle X‐ray diffraction. Multiblock copolymers with PLLA crystallinity could be achieved only with isolated PLLA macroinitiators; sequential addition of MBC to high‐conversion L ‐lactide polymerizations resulted in excessive randomization, presumably because of residual L ‐lactide monomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6817–6835, 2006     

Synthesis,self‐assembly,drug‐release behavior,and cytotoxicity of triblock and pentablock copolymers composed of poly(ε‐caprolactone), poly(L‐lactide), and poly(ethylene glycol)

Biocompatible and biodegradable ABC and ABCBA triblock and pentablock copolymers composed of poly(ε‐caprolactone) (PCL), poly(L ‐lactide) (PLA), and poly(ethylene glycol) (PEO) with controlled molecular weights and low polydispersities were synthesized by a click conjugation between alkyne‐terminated PCL‐b‐PLA and azide‐terminated PEO. Their molecular structures, physicochemical and self‐assembly properties were thoroughly characterized by means of FT‐IR, ¹H‐NMR, gel permeation chromatography, differential scanning calorimetry, wide‐angle X‐ray diffraction, dynamic light scattering, and transmission electron microscopy. These copolymers formed microphase‐separated crystalline materials in solid state, where the crystallization of PCL block was greatly restricted by both PEO and PLA blocks. These copolymers self‐assembled into starlike and flowerlike micelles with a spherical morphology, and the micelles were stable over 27 days in aqueous solution at 37 °C. The doxorubicin (DOX) drug‐loaded nanoparticles showed a bigger size with a similar spherical morphology compared to blank nanoparticles, demonstrating a biphasic drug‐release profile in buffer solution and at 37 °C. Moreover, the DOX‐loaded nanoparticles fabricated from the pentablock copolymer sustained a longer drug‐release period (25 days) at pH 7.4 than those of the triblock copolymer. The blank nanoparticles showed good cell viability, whereas the DOX‐loaded nanoparticles killed fewer cells than free DOX, suggesting a controlled drug‐release effect. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Morphological transitions in aggregates of thermosensitive poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) block copolymers prepared via RAFT polymerization

Double hydrophilic poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) (PEO‐b‐PNIPAM) block copolymers were synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization, using a PEO‐based chain transfer agent (PEO‐CTA). The molecular structures of the copolymers were designed to be asymmetric with a short PEO block and long PNIPAM blocks. Temperature‐induced aggregation behavior of the block copolymers in dilute aqueous solutions was systematically investigated by a combination of static and dynamic light scattering. The effects of copolymer composition, concentration (C_p), and heating rate on the size, aggregation number, and morphology of the aggregates formed at temperatures above the LCST were studied. In slow heating processes, the aggregates formed by the copolymer having the longest PNIPAM block, were found to have the same morphology (spherical “crew‐cut” micelles) within the full range of C_p. Nevertheless, for the copolymer having the shortest PNIPAM block, the morphology of the aggregates showed a great dependence on C_p. Elongation of the aggregates from spherical to ellipsoidal or even cylindrical was observed. Moreover, vesicles were observed at the highest C_p investigated. Fast heating leads to different characteristics of the aggregates, including lower sizes and aggregation numbers, higher densities, and different morphologies. Thermodynamic and kinetic mechanisms were proposed to interpret these observations, including the competition between PNIPAM intrachain collapse and interchain aggregation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4099–4110, 2009     

Synthesis and characterization of poly(L‐lactide‐co‐ε‐caprolactone) (B)‐poly(L‐lactide) (A) ABA block copolymers

ABA triblock copolymers of L ‐lactide (LL) and ε‐caprolactone (CL), designated as PLL‐P(LL‐co‐CL)‐PLL, were synthesized via a two‐step ring‐opening polymerization in bulk using diethylene glycol and stannous octoate as the initiating system. In the first‐step reaction, an approximately 50:50 mol% P(LL‐co‐CL) random copolymer (prepolymer) was prepared as the middle (B) block. This was then chain extended in the second‐step reaction by terminal block polymerization with more L ‐lactide. The percentage yields of the triblock copolymers were in excess of 95%. The prepolymers and triblock copolymers were characterized using a combination of dilute‐solution viscometry, gel permeation chromatography (GPC), ¹H‐ and ¹³C‐NMR, and differential scanning calorimetry (DSC). It was found that the molecular weight of the prepolymer was controlled primarily by the diethylene glycol concentration. All of the triblock copolymers had molecular weights higher than their respective prepolymers. ¹³C‐NMR analysis confirmed that the prepolymers contained at least some random character and that the triblock copolymers consisted of additional terminal PLL end (A) blocks. From their DSC curves, the triblock copolymers were seen to be semi‐crystalline in morphology. Their glass transition, solid‐state crystallization, and melting temperature ranges, together with their heats of melting, all increased as the PLL end (A) block length increased. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and characterization of a series of biodegradable and biocompatible PEG‐supported poly(lactic‐ran‐glycolic acid) amphiphilic barbell‐like copolymers

A series of multihydroxyl (2, 4, and 8) terminated poly(ethylene glycol)s and their biodegradable, biocompatible, and branched barbell‐like (PLGA)_n‐b‐PEG‐b‐(PLGA)_n (n = 1, 2, 4) copolymers have been synthesized. The lengths of the PLGA arms were varied by controlling the molar ratio of monomers to hydroxyl groups of PEG ([LA+GA]₀/[? OH]₀ = 23, 45, 90). Chemical structures of synthesized barbell‐like copolymers were confirmed by both ¹H and ¹³C‐NMR spectroscopies. Molecular weights were determined by ¹H‐NMR end‐group analysis and gel permeation chromatography. The result of hydrolytic degradation indicated that the rate of degradation increased with the increase of arm numbers or with the decrease of arm lengths. The thermal properties were evaluated by using differential scanning calorimetry and a thermogravimetric analysis. The results indicated that the thermal properties of barbell‐like copolymers depended on the structural variations. The morphology of (PLGA)_n‐PEG‐(PLGA)_n copolymers self‐assembly films were investigated by atomic force microscope, the results indicated that the microphase separation existed in (PLGA)_n‐PEG‐(PLGA)_n copolymers. Because of the favorable biodegradability and biocompatibility of the PLGA and PEG, these results may therefore create new possibilities for these novel structural amphiphilic barbell‐like copolymers as potential biomaterials. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3802–3812, 2008     

Synthesis of well‐defined amphiphilic polymethylene‐b‐poly(ε‐caprolactone)‐b‐poly(acrylic acid) triblock copolymer via a combination of polyhomologation,ring‐opening polymerization,and atom transfer radical polymerization

Well‐defined amphiphilic polymethylene‐b‐poly(ε‐caprolactone)‐b‐poly(acrylic acid) (PM‐b‐PCL‐b‐PAA) triblock copolymers were synthesized via a combination of polyhomologation, ring‐opening polymerization (ROP), and atom transfer radical polymerization (ATRP). First, hydroxyl‐terminated polymethylenes (PM‐OH; M_n = 1100 g mol^?1; M_w/M_n = 1.09) were produced by polyhomologation followed by oxidation. Then, the PM‐b‐PCL (M_n = 10,000 g mol^?1; M_w/M_n = 1.27) diblock copolymers were synthesized via ROP of ε‐caprolactone using PM‐OH as macroinitiator and stannous octanoate (Sn(Oct)₂) as a catalyst. Subsequently, the macroinitiator transformed from PM‐b‐PCL in high conversion initiated ATRPs of tert‐butyl acrylate (^tBA) to construct PM‐b‐PCL‐b‐P^tBA triblock copolymers (M_n = 11,000–14,000 g mol^?1; M_w/M_n = 1.24–1.26). Finally, the PM‐b‐PCL‐b‐PAA triblock copolymers were obtained via the hydrolysis of the P^tBA segment in PM‐b‐PCL‐b‐P^tBA triblock copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Porous films of such triblock copolymers were fabricated by static breath‐figure method and observed by scanning electron microscope. The aggregates of PM‐b‐PCL‐b‐PAA triblock copolymer were studied by transmission electron microscope. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ϵ‐caprolactone) triblock copolymers: Synthesis and self‐assembly in aqueous solutions

Nontoxic and biodegradable poly(?‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(?‐caprolactone) triblock copolymers were synthesized by the solution polymerization of ?‐caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with ¹H NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol–gel‐transition behaviors were investigated. The experimental results showed that the unimer‐to‐micelle transition did occur. In a sol–gel‐transition phase diagram obtained by the vial‐tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(?‐caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25–55 °C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 × 10^?4 g/mL, whereas necklace‐like and worm‐like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 605–613, 2007