Synthesis, degradation and in vitro controlled drug release of novel copolymers of 5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one and caprolactone

Novel biodegradable copolymers of 5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one (MMTC) and caprolactone (CL) were synthesized under different conditions by ring-opening polymerization. The structure of the resultant copolymers was characterized by IR, ¹H NMR and ¹³C NMR methods. Their molecular weight was measured by gel permeation chromatography (GPC). Incorporating the MMTC units into PCL main chain results in the great enhancement of hydrolytic degradation rate and the effective retardance of release rate of Tegafur in comparison with the PCL homopolymer. The enzymatic degradation rate increases with increasing the molar content of PCL, and the copolymers degrade faster in the presence of pseudomonas (PS) lipase than that in the absence of PS lipase. Some mechanical properties of the copolymers were tested and showed that they can be adjusted by varying the composition of the copolymers.     

Synthesis and characterization of poly(ethylene glycol)-b-poly (l-lactide)-b-poly(l-glutamic acid) triblock copolymer

A biodegradable amphiphilic triblock copolymer of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(l-glutamic acid) (PEG-b-PLLA-b-PLGA) was obtained by catalytic hydrogenation of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(γ-benzyl-l-glutamic acid) (PEG-b-PLLA-b-PBLGA) synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG-NCA) with amino-terminated MPEG-b-PLLA-NH₂ as a macroinitiator. MPEG-b-PLLA-NH₂ converted from MPEG-b-PLLA-OH first reacted with tert-Butoxycarbonyl-l-phenylalanine (Phe-^NBOC) and dicyclohexylcarbodiimide (DCC) and then deprotected the tert-butoxycarbonyl group. MPEG-b-PLLA-OH was prepared by ROP of l-lactide with monomethoxy poly(ethylene glycol) in the presence of stannous octoate. The triblock copolymer and its diblock precursors were characterized by ¹H NMR, FTIR, GPC and DSA (drop shape analysis) measurements. The lengths of each block polymers could be tailored by molecular design and the ratios of feeding monomers. The triblock polymer PEG-b-PLLA-b-PLGA containing carboxyl groups showed obviously improved hydrophilic properties and could be a good potential candidate as a drug delivery carrier.     

Synthesis and characterization of dendritic-linear-dendritic triblock copolymers based on poly(amidoamine) and polystyrene

Dendritic-linear-dendritic triblock copolymers composed of linear polystyrene (PSt) and poly(amidoamine) dendrons have been successfully synthesized. Two bromines-terminated PSt with M_n = 13,000 was prepared by atom transfer radical polymerization (ATRP) using α,α′-dibromo-p-xylene as initiator. Then the terminal bromines at both ends of PSt chains were replaced by one imine group of piperazine (PZ), and further Michael addition reaction of terminal PZ with excess 1,3,5-triacryloylhexahydro-1,3,5-triazine (TT) produced the first generation (G₁) of the triblock copolymer. Continuous growth of dendrons from G1.5 to G4 at the both ends of PSt chains was carried out by the iterative Michael addition reactions with excess PZ and following TT. The ABA triblock copolymers composed of the G₁-G₄ dendrons and the linear PSt were obtained. Structures of the triblock polymers were characterized by GPC and ¹H NMR spectra. Thermal phase transitions of the polymers were studied by DSC measurements, and all of the copolymers displayed a glass transition temperature.     

pH/temperature sensitive poly(ethylene glycol)-based biodegradable polyester block copolymer hydrogels

Novel pH and temperature sensitive biodegradable block copolymers composed of poly(ethylene glycol) (PEG), polyglycolide (GA), ?-caprolactone (CL) and sulfamethazine oligomers (OSMs) were synthesized by ring opening polymerization and 1,3-dicyclohexyl-carbodiimide (DCC) mediated coupling reactions. Their physicochemical properties in aqueous media were characterized by ¹H NMR spectroscopy and gel permeation spectroscopy. The sol-gel phase transition behavior of OSM-PCGA-PEG-PCGA-OSM block copolymers was investigated both in solution and injection to PBS buffer at pH 7.4 and 37 °C. Aqueous solutions of OSM-PCGA-PEG-PCGA-OSM changed from a sol to a gel phase with increasing temperature and decreasing pH. The sol-gel transition properties of these block copolymers are influenced by the hydrophobic/hydrophilic balance of the copolymers, block length, hydrophobicity, stereoregularity of the hydrophobic components within the block copolymer, and the ionization of the pH functional groups in the copolymer, which depends on the environmental pH. Degradation of the triblock and pentablock copolymers at 37 °C (pH 7.4), and at 0 °C and 5 °C both at pH 8.0, was investigated. It was demonstrated here using the in vitro test method, that the anticancer agent paclitaxel (PTX) could be loaded and released by the pH and temperature sensitive OSM-PCGA-PEG-PCGA-OSM block copolymer, such that this could be used as a suitable matrix for subcutaneous injection in drug delivery systems.     

PBT-b-PEO-b-PBT triblock copolymers: Synthesis,characterization and double-crystalline properties

We demonstrated here a facile method to synthesize novel double crystalline poly(butylene terephthalate)-block-poly(ethylene oxide)-block-poly(butylene terephthalate) (PBT-b-PEO-b-PBT) triblock copolymers by solution ring-opening polymerization (ROP) of cyclic oligo(butylene terephthalate)s (COBTs) using poly(ethylene glycol) (PEG) as macroinitiator and titanium isopropyloxide as catalyst. The structure of copolymers was well characterized by ¹H NMR and GPC. TGA results revealed that the decomposition temperature of PEO in triblock copolymers increased about 30 °C to the same as PBT copolymers, after being end-capped with PBT polymers. These triblock copolymers showed double crystalline properties from PBT and PEO blocks, observed from DSC and WAXD measurements. The melting and crystallization peak temperatures corresponding to PBT blocks increased with PBT content. The crystallization of PBT blocks showed the strong confinement effects on PEO blocks due to covalent linking of PBT blocks with PEO blocks, where the melting and crystallization temperatures and crystallinity corresponding to PEO blocks decreased significantly with increment of PBT content. The confinement effect was also observed by SAXS experiments, where the long distance order between lamella crystals decreases with increasing PBT length. For the triblock copolymer with highest PBT content (PBT₅₄-b-PEO₂₂₇-b-PBT₅₄), this effect shows a 30 °C depression on PEO crystals' melting temperature and 77% on enthalpy, respectively, compared to corresponding PEO homopolymer. The crystal morphology was observed by POM, and amorphous-like spherulites were observed during PBT crystallization.     

Stereocomplex‐induced gelation properties of polylactide/poly(ethylene glycol) diblock and triblock copolymers

The ring‐opening polymerization of L ‐ or D ‐lactide was realized in the presence of dihydroxyl or monomethoxy poly(ethylene glycol) (PEG) with a number‐average molecular weight of 2000. The resulting low‐molar‐mass poly(L ‐lactide) (PLLA)/PEG and poly(D ‐lactide) (PDLA)/PEG triblock and diblock copolymers were characterized with nuclear magnetic resonance (NMR), differential scanning calorimetry, size‐exclusion chromatography, and X‐ray diffractometric analysis. Bioresorbable hydrogels were successfully prepared from aqueous solutions containing both copolymers because of interactions and stereocomplexation between the PLLA and PDLA blocks. Gelation was evaluated with the tube inverting method and rheological measurements. A phase diagram was realized with gel–sol transitions as a function of concentration. The rheological properties of the hydrogels were investigated under various conditions through changes in the copolymer concentration, temperature, time, and frequency. It was concluded that the hydrogels constituted a dynamic and evolutive system because of the continuous formation/destruction of crosslinks and degradation. Further studies are underway to elucidate the degradation behavior and the potential of these substances as drug carriers or cell culture scaffolds. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Synthesis of biodegradable and biocompatible ABC triblock copolymers

A facile approach is offered to synthesize well‐defined amphiphilic ABC triblock copolymers composed of poly(ethylene glycol) monomethyl ether (MPEO) as A block, poly(L ‐lysine) (PLLys) as B block, and poly(ε‐caprolactone) (PCL) as C block by a combination of ring‐opening polymerization (ROP) and click reactions. The propargyl‐terminated poly(Z‐L ‐lysine)‐block‐poly(ε‐caprolactone) (MPEO‐PzLLys‐PCL) diblock copolymers were synthesized via the ring‐opening polymerization of N^ε‐carbobenzoxy‐L ‐lysine N‐carboxyanhydride (Z‐L ‐Lys NCA) in DMF at room temperature using propargyl amine as an initiator and the resulting amino‐terminated poly(Z‐L ‐lysine) then used in situ as a macroinitiator for the polymerization of ε‐caprolactone in the presence of stannous octoate as a catalyst. The triblock copolymers poly(ethylene glycol) monomethyl ether –block‐poly(Z‐L ‐lysine)‐block‐poly(ε‐caprolactone) (MPEO‐PzLLys‐PCL) were synthesized via the click reaction of the propargyl‐terminated PzLLys‐PCL and azido‐terminated poly(ethylene glycol) monomethyl ether (PEO‐N₃) in the presence of CuBr and 1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) catalyst system. After the removal of Z groups of L ‐lysine units, amphiphilic and biocompatible ABC triblock copolymers MPEO‐PLLys‐PCL were obtained. The structural characteristics of these ABC triblock copolymers and corresponding precursors were characterized by NMR, IR, and GPC. These results showed the click reaction was highly effective. Therefore, a facile approach is offered to synthesize amphiphilic and biocompatible ABC triblock copolymers consisting of polyether, polypeptide and polyester. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate) triblock copolymers

Novel, monodispersed, and well‐defined ABA triblock copolymers [poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate)] were synthesized by oxyanionic polymerization with potassium tert‐butanoxide as the initiator. Gel permeation chromatography and ¹H‐NMR analysis showed that the obtained products were the desired copolymers with molecular weights close to calculated values. Because the poly(dimethylamino ethyl methacrylate) block was pH‐ and temperature‐sensitive, the aqueous solution behavior of the polymers was investigated with ¹H‐NMR and dynamic light scattering techniques at different pH values and at different temperatures. The micelle morphology was determined with transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of double‐hydrophilic poly(methylacrylic acid)–poly(ethylene glycol)–poly(methylacrylic acid) triblock copolymers and their micelle formation

The aim of the work reported was to synthesize a series of double‐hydrophilic poly(methacrylic acid)‐block‐poly(ethylene glycol)‐block‐poly(methacrylic acid) (PMAA‐b‐PEG‐b‐PMAA) triblock copolymers and to study their self‐assembly behavior. These copolymeric self‐assembly systems are expected to be potential candidates for applications as carriers of hydrophilic drugs. Bromo‐terminated difunctional PEG macroinitiators were used to synthesize well‐defined triblock copolymers of poly(tert‐butyl methacrylate)‐block‐poly(ethylene glycol)‐block‐poly(tert‐butyl methacrylate) via reversible‐deactivation radical polymerization. After the removal of the tert‐butyl group by hydrolysis, double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers were obtained. pH‐sensitive spherical micelles with a core–corona structure were fabricated by self‐assembly of the double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers at lower solution pH. Transmission electron microscopy and laser light scattering studies showed the micelles were of nanometric scale with narrow size distribution. Solution pH and micelle concentration strongly influenced the hydrodynamic radius of the spherical micelles (48–310 nm). A possible reason for the formation of the micelles is proposed. Copyright © 2010 Society of Chemical Industry     

Synthesis of monomethoxy poly(ethylene glycol) without diol poly(ethylene glycol)

Since monomethoxy poly(ethylene glycol) (mPEG) inevitably contains diol PEG and is difficult to get high molecular weight through traditional synthesis at high temperature under high pressure, a novel synthetic technique via anionic solution polymerization was reported in this study. With a new initiating system, potassium naphthalene and methanol, was introduced, the polymerization proceeded at ambient temperature and side reactions were well restrained. Furthermore, a slight excess of potassium naphthalene can effectively remove the trace of water and oxygen in the reaction system. Under this condition, mPEG was nearly quantitatively obtained without containing diol PEG. Its Mn ranged from 1 to 30 kDa and the polydispersity was kept lower than 1.07. Characterization of the mPEG obtained was carried out using GPC to determine the content of diol PEG and ¹H‐NMR and MALDI‐ToF MS spectroscopic analysis to confirm the exact structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Preparation and properties of poly(ethylene glycol)-block-poly(acrylic acid)-coated cobalt nanocrystals

Reported in this paper are the preparation and properties of ?-Co nanocrystals coated by poly(ethylene glycol)-block-poly(acrylic acid) (PEG-b-PAA). These particles were prepared via the thermal decomposition of Co₂(CO)₈ at 185 °C in 1,2-dichlorobenzene, in the presence of the surfactant PEG-b-PAA and the co-surfactant trioctylphosphine oxide. At a given initial Co₂(CO)₈ concentration, the size of the particles increased with increasing Co₂(CO)₈-to-PEG-b-PAA molar ratio, and could be tuned between ∼5 and ∼20 nm. The size distribution of the particles narrowed as the Co₂(CO)₈ concentrations increased. The resultant particles were dispersible in a wide range of solvents, including chloroform, N,N-dimethylforamide, and water, which solubilized PEG. Magnetic measurements revealed that the particles possessed saturation magnetization close to that of bulk Co, suggesting high purity of the particles.     

含聚乙二醇的嵌段共聚物的合成及自组装研究进展

综述了通过活性自由基聚合如原子转移自由基聚合（ATRP）、氮氧稳定自由基聚合（NMP）、可逆加成断裂链转移聚合（RAFT）等方法合成含聚乙二醇（PEG）的嵌段共聚物的研究进展,并对含PEG类嵌段共聚物在溶液中的自组装技术和在药物载体、介孔材料以及碳纳米管中的应用进行了归纳,指出含PEG的嵌段共聚物可以自组装成多种形貌,直接影响材料的性能和应用,所以这些结构有潜在的应用价值和应用前景,并且合成新的含PEG的嵌段共聚物和开发具有新型结构、形貌可控的自组装体以及新的应用领域是今后的一个热点问题,具有重要的科学研究意义和实际应用价值。     

Nonisothermal crystallization behaviors of biodegradable double crystalline poly(butylene succinate)‐poly(ethylene glycol) multiblock copolymers

Nonisothermal crystallization behaviors of both poly(butylene succinate) (PBS) and poly(ethylene glycol) (PEG) segments within PBS‐PEG (PBSEG) multiblock copolymers were investigated by differential scanning calorimetry (DSC). The nonisothermal crystallization kinetics of both PBS and PEG segments were analyzed by Avrami, Ozawa, and Mo methods. The results showed that both of Avrami and Mo methods were successful to describe the nonisothermal crystallization kinetics of PBS and PEG segments. The results of crystallization kinetics indicated that the crystallization rate of PBS segment decreased with PBS segment content and/or L_PBS, while that of PEG segment decreased with M_n,PEG or F_PEG. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40940.     

Syntheses of well-defined poly(siloxane)-b-poly(styrene) and poly(norbornene)-b-poly(styrene) block copolymers using functional alkoxyamines

Functional alkoxyamines, 1-[4-(4-lithiobutoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl-N-oxyl)ethane (2) and 1-[4-(2-vinyloxyethoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl-N-oxyl)ethane (3) were prepared, and well-defined poly(hexamethylcyclotrisiloxane)-b-poly(styrene)[poly(D₃)-b-poly(St)] and poly(norbornene)-b-poly(St) [poly(NBE)-b-poly(St)] were prepared using the alkoxyamines. The first step was preparation of poly(D₃) and poly(NBE) macroinitiators, which were obtained by the ring-opening anionic polymerization of D₃ using 2 as an initiator and the ring-opening metathesis polymerization of NBE using 3 as a chain transfer. The radical polymerization of St by the poly(D₃) and poly(NBE) macroinitiators proceeded in the ‘living’ fashion to give well-defined poly(D₃)-b-poly(St) and poly(NBE)-b-poly(St) block copolymers.     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Synthesis and characterization of amphiphilic polyisobutylene/poly(ethylene glycol) di- and triblock copolymers

Summary Di- and triblock copolymers of polyisobutylene PIB and poly(ethylene glycol) PEG have been prepared and characterized. The syntheses involved the capping with tolylene 2,4-diisocyanate TDI various molecular weight -phenyl--(p-phenol) polyisobutylenes C₆H₅-PIB-C₆H₄OH and ,-di-(p-phenol)polyisobutylenes HOC₆H₄-PIB-C₆H₄OH, or commercially available mono- and di-hydroxyl-terminated PEGs. In this manner a series of PIB-b-PEG diblock copolymers, and PEG-b-PIB-b-PEG and PIB-b-PEG-b-PIB triblock copolymers have been obtained. The complete removal of the prepolymers from these amphiphilic sequential copolymers by conventional solvent extraction techniques could not be achieved because of the very high emulsifying action of the latters. In contrast, satisfactory separation was obtained by column chromatography using mixed (polar/nonpolar) eluents. The blocking efficiencies and composition of the block copolymers have been determined.Part XL V of the Series on New Telechelic Polymers and Sequential Copolymers by Polyfunctional Initiator-Transfer Agents (Inifers).     

Synthesis and bulk properties of poly(tetrahydrofuran)-poly(2-methyl-2-oxazoline) ABA triblock copolymers

A series of linear triblock-copolymers of the ABA type in which the central B-block is poly(tetrahydrofuran) (polyTHF) and the A-segments are poly(2-methyl-2-oxazoline) (polyMeOX) were synthesized by a one-pot sequential monomer addition copolymerization, utilizing the living nature of the cationic ring-opening polymerization of both monomers. Films of the copolymers, casted from chloroform solutions, exhibit excellent mechanical properties in comparison with the homopolymers with comparable molecular weights, which was ascribed to the phase separation occurring between the two copolymer segments. Materials, in which the polyTHF B-segment have a molecular weight 13 000 g/mol or higher and each polyMeOX A-block a molecular weight 1500 g/mol, kept elastomeric properties up to 130 °C notwithstanding the fact that this temperature is considerably higher than the melting point of polyTHF and the glass transition temperature of polyMeOX. It was found that these triblock-copolymer materials show a shape memory effect. These observations are attributed to the high degree of phase separation between the two blocks and the strong polar interactions between the polyMeOX segments. Received: 20 March 1997/Revised: 5 September 1997/Accepted: 8 September 1997     

Synthesis and characterization of new biodegradable comb‐dendritic triblock copolymers

A series of well‐defined dumbbell‐shaped triblock copolymers consisting of linear poly(ethylene glycol) (PEG) and comb‐like poly(ε‐caprolactone) (PCL) with varied PCL arm lengths have been synthesized via the sequential preparation of different generation terminal dendronized PEG and ring‐opening polymerization of ε‐caprolactone. The copolymers were characterized using Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopy and gel permeation chromatography. Differential scanning calorimetry was performed to measure the glass transition temperature, melting point and degree of crystallinity and the PEG segment and PCL segment crystallization temperatures. The crystallization of the copolymers was also studied using X‐ray diffraction. The dumbbell‐shaped copolymers were further used to construct microspheres using a double emulsion method. Scanning electron microscopy and dynamic light scattering results showed the size of the microspheres was about 2 to 4 µm and the size distribution was quite narrow. Copyright © 2012 Society of Chemical Industry     

Synthesis and self-association in aqueous media of poly(ethylene oxide)/poly(ethyl glycidyl carbamate) amphiphilic block copolymers

New temperature sensitive AB, ABA, and BAB amphiphilic block copolymers consisting of hydrophilic poly(ethylene oxide) and hydrophobic poly(ethyl glycidyl carbamate) blocks were synthesized by anionic polymerization followed by chemical modification reactions. The self-association of the block copolymers in aqueous media was studied by UV-vis spectroscopy and dynamic and static light scattering. The obtained block copolymers spontaneously form micelles in aqueous media. The critical micellization concentration varied from 0.5 to 4 g/L depending on the copolymer architecture and composition. The influence of the temperature upon the self-association of the block copolymers was investigated. The increase of temperature did not affect the value of the critical micellization concentration, but led to the formation of better defined micelles with narrow size distribution.