Preparation and polymerization mechanism of dihydroxy-capped PCL,poly(CL-b-PEG-b-CL) and poly(DTC-b-CL-b-DTC)

PCL possesses a wide range of medical applications, such as tissue engineering and controlled drug release, because of its good biodegradability and miscibility. In order to extend the use of PCL, researchers have been exploring its structural and chemica…     

Folate-targeted optical and magnetic resonance dualmodality PCL-<Emphasis Type="Italic">b</Emphasis>-PEG micelles for tumor imaging

A biodegradable tumor targeting nano-probe based on poly（ε-caprolactone）-b-poly（ethylene glycol）block copolymer（PCL-b-PEG）micelle functionalized with a magnetic resonance imaging（MRI）contrast agent diethylenetriaminepentaacetic acid-gadolinium(DTPA-Gd³⁺)on the shell and a near-infrared（NIR）dye in the core for magnetic resonance and optical dual-modality imaging was prepared.The longitudinal relaxivity（r₁）of the PCL-b-PEG-DTPA -Gd³⁺micelle was 13.4（mmol/L）^-1s^-1,three folds of that of DTPA-Gd³⁺,and higher than that of many polymeric contrast agents with similar structures.The in vivo optical imaging of a nude mouse bearing xenografted breast tumor showed that the dual-modality micelle preferentially accumulated in the tumor via the folic acid-mediated active targeting and the passive accumulation by the enhanced permeability and retention（EPR）effect.The results indicated that the dualmodality micelle is a promising nano-probe for cancer detection and diagnosis.     

The effect of PVP-<Emphasis Type="Italic">b</Emphasis>-PMAA block copolymer on morphologies control of calcium carbonate

A novel double-hydrophilic block copolymer (DHBC) poly(vinyl pyrrolidone)–block–poly(methacrylic acid) (PVP-b-PMAA) was synthesized via reversible addition–fragmentation chain transfer polymerization. The structure of the resulting copolymer was characterized by ¹H nuclear magnetic resonance, and the molecular weight of the block copolymer was determined by gel permeation chromatography. The study of morphological control of calcium carbonate (CaCO₃) has been performed in the presence of the PVP-b-PMAA block copolymer. Various morphologies of CaCO₃ particles such as rhombohedral, multilayered, and aggregated with cavities can be produced by varying the copolymer concentrations. The all-obtained CaCO₃ particles were calcite, which was confirmed by either X-ray diffraction or Fourier transform infrared spectra. Such calcium carbonate/polymer hybrids with complex morphologies may find valuable applications in biomimic mineralization.     

Ring‐opening polymerization of 1‐methyltrimethylene carbonate by rare earth initiators

Ring‐opening polymerization of 1‐methyltrimethylene carbonate (MTMC) initiated by highly active single‐component rare earth tris(2,6‐di‐tert‐butyl‐4‐methylphenolate)s [Ln(OAr)₃, Ln = La, Dy, Y] or yttrium isopropoxide [Y(OiPr)₃] is reported for the first time. PolyMTMC (M_w = 8.4 × 10⁴, molecular weight distributions = 1.5) initiated by La(OAr)₃ at [MTMC]/[initiator] = 1000 was obtained with the yield over 99% in toluene within 1 h at 30 °C. Random and block copolymers of MTMC with ε‐caprolactone (CL), 2,2‐dimethyltrimethylene carbonate (DTC) or polyethylene glycol (PEG) including poly(MTMC‐r‐CL), poly(MTMC‐b‐CL), poly(MTMC‐r‐DTC), poly(MTMC‐b‐DTC), and poly(MTMC‐b‐PEG‐b‐MTMC) were synthesized. The differential scanning calorimetry results show that thermal behaviors of the polymers sensitively depend on their compositions and chain structures. Furthermore, the measurements of ¹H‐¹H COSY and density functional theory calculation are applied to investigate the mechanism. The polymerization of MTMC takes place according to a coordination‐insertion mechanism, and the ring is opened via acyl‐oxygen bond cleavage resulting in a Ln? O active center. There exist two ring‐opening modes of MTMC in which mode b , breaking the CH₂O? CO bond, is the major pathway. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3807–3815, 2010     

Preparation of nanoparticle colloids of methoxy poly(ethylene glycol)-<Emphasis Type="Italic">b</Emphasis>-poly(<Emphasis Type="SmallCaps">D</Emphasis>,<Emphasis Type="SmallCaps">L</Emphasis>-lactide): effects of surfactant and organic solvent

Nanoparticle colloids of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) diblock copolymer were prepared by a modified spontaneous emulsification solvent diffusion method using acetone/ethanol as the mixture organic solvents. The MPEG-b-PDLL was synthesized by ring-opening polymerization of D,L-lactide using stannous octoate and MPEG with molecular weight of 5,000 g/mol as the initiating system. The MPEG-b-PDLL obtained was an amorphous polymer with molecular weight of 73,600 g/mol. Influences of acetone/ethanol (v/v) ratios and Tween 80 surfactant concentrations on characteristics of the colloidal nanoparticles were investigated and discussed. Light-scattering analysis showed that average diameters of the surfactant-free colloidal nanoparticles were in the range of 86–124 nm. The nanoparticle sizes decreased as the ethanol ratio increased. The Tween 80 did not show the significant effect on the nanoparticle sizes. Scanning electron micrographs of dried nanoparticles that demonstrated the aggregation of most particles suggested they were the soft nanoparticles. However, the dried nanoparticle morphology can be observed from scanning electron microscopy as having a spherical shape and smooth surfaces.     

Novel synthesis of biodegradable amphiphilic linear and star block copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol)

Biodegradable, amphiphilic, diblock poly(ε‐caprolactone)‐block‐poly(ethylene glycol) (PCL‐b‐PEG), triblock poly(ε‐caprolactone)‐block‐poly(ethylene glycol)‐block‐poly(ε‐caprolactone) (PCL‐b‐PEG‐b‐PCL), and star shaped copolymers were synthesized by ring opening polymerization of ε‐caprolactone in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) or star poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature to yield monomodal polymers of controlled molecular weight. The chemical structure of the copolymers was investigated by ¹H and ¹³C NMR. The formation of block copolymers was confirmed by ¹³C NMR and DSC investigations. The effects of copolymer composition and molecular structure on the physical properties were investigated by GPC and DSC. For the same PCL chain length, the materials obtained in the case of linear copolymers are viscous whereas in the case of star copolymer solid materials are obtained with low T_g and T_m temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3975–3985, 2007     

Thermal and crystalline properties of random copolymer of CL and DTC prepared by La(OAr)3

Thermal and crystalline properties of random copolymer of ?-caprolactone (CL) and 2,2-dimethyl trimethylene carbonate (DTC) prepared by lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) (La(OAr)₃) have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and wide-angle X-ray diffraction (WAXD). Fox equation interprets the relationship between glass transition temperature (T _g) and copolymer compositions. T _g decreases from PDTC (16.7°C) to PCL (-65.1°C), reflecting the internal plasticizing effect of CL units on DTC units in the copolymers. The introduction of CL units to PDTC can effectively improve its heat resistance. Small amount of DTC (5% molar) in PCL chain improves the mechanical properties of the polymer, which had elongation of 1000, much higher than that of PCL (8.8).

     

Comparison of drug delivery properties of PEG-<Emphasis Type="Italic">b</Emphasis>-pdhpc micelles with different compositions

An anti-tumor drug doxorubicin was encapsulated in micelles of poly（ethylene glycol）-b-poly（2,2-dihydroxyl-methyl propylene carbonate）（PEG-b-PDHPC） diblock copolymers.The morphology of both blank micelles and drug loaded micelles was characterized by TEM.The in vitro drug release profiles of micelles were investigated.The cytotoxicity of the micelles was evaluated by incubating with Hela tumor cells and 3T3 fibroblasts.The drug loaded micelles were co-cultured with HepG2 cells to evaluate the in vitro anti-tumor efficacies.The results showed that the mean sizes of both micelles with different copolymer compositions increased after being loaded with drugs.The drug release rate of PEG₄₅-b-PDHPC₃₄ micelles was faster than that of mPEG₁₁₄-b-PDHPC₂₆,micelles.Both of the two block copolymers were non-toxic.The confocal laser scanning microscopy and flow cytometry results showed that both the drug loaded micelles could be internalized efficiently in HepG2 cells.The PEG₄₅-b-PDHPC₃₄ micelles exhibited higher anti-tumor activity comparing to mPEG₁₁₄-b-PDHPC₂₆ micelles.     

Thermal properties of amphiphilic biodegradable triblock copolymer of <Emphasis Type="SmallCaps">l</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide and ethylene glycol

Samples of poly(l,l-lactide)-block-poly(ethylene glycol)-block-poly(l,l-lactide) (PLLA-PEG-PLLA) were synthesized from l,l-lactide polymerization using stannous 2-ethylhexanoate, Sn(Oct)₂ as initiator and di-hydroxy-terminated poly(ethylene glycol) (PEG) (M _n  = 4000 g mol⁻¹) as co-initiator. The chemical linkage between the PEG segment and the PLA segments was characterized by Fourier transform infrared spectroscopy (FTIR). Thermogravimetry analysis (TG) revealed the copolymers composition and was capable to show the deleterious effect of an excess of Sn(Oct)₂ in the polymer thermal stability, while Differential Scanning Calorimetry (DSC) allowed the observation of the miscibility between the PLLA and PEG segments in the different copolymers.     

pH-responsive Micelles from a Blend of PEG-<Emphasis Type="Italic">b</Emphasis>-PLA and PLA-<Emphasis Type="Italic">b</Emphasis>-PDPA Block Copolymers: Core Protection Against Enzymatic Degradation

pH-responsive micelles with a biodegradable PLA core and a mixed PEG/PDPA shell were prepared by self-assembly of poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) and poly(2-(diisopropylamino)ethyl methacrylate)-b-poly(lactic acid) (PDPA-b-PLA). The micellization status with different pH and the enzyme degradation behavior were characterized by ¹H-NMR spectroscopy, dynamic light scattering measurement and zeta potential test. The pH turning point of PDPA block was determined to be in the range of 5.5?7.0. While the pH was above 7.0, the PDPA block collapsed onto the PLA core and could protect the PLA core from invasion of enzyme, as a result, the micelle exhibited a resistance to the enzymatic degradation.     

Isothiourea‐based lewis pairs for homopolymerization and copolymerization of 2,2‐dimethyltrimethylene carbonate with ε‐caprolactone and ω‐pentadecalactone

In this study, the homopolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and its copolymerizations with ε‐caprolactone (CL) were carried out in detail using the isothiourea‐based Lewis pairs comprised 2,3,6,7‐tetrahydro‐5H‐thiazolo(3,2‐a)pyrimidine and magnesium halides (MgX₂) with benzyl alcohol (BnOH) as the initiator. The copolymerization of DTC and CL via one‐pot addition produced randomly sequenced copolymers. On the other hand, a well‐defined linear poly(ε‐caprolactone)–block–poly(2,2‐dimethyltrimethylene carbonate) (PCL‐b‐PDTC) diblock copolymer was prepared by simple sequential ring‐opening polymerization of CL and DTC. In addition, poly(ω‐pentadecalactone)–block–PDTC diblock copolymer was successfully prepared by the same strategy. Moreover, PDTC–poly(ethylene glycol) (PEG)–PDTC triblock copolymer was synthesized in the presence of PEG 2000. The effects of different polymerization conditions on the polymerization reactions have been systematically discussed. The resulting polymers were characterized by the ¹H and ¹³C NMR spectra, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐ToF MS). The block copolyester structures were confirmed by the ¹³C NMR spectroscopy and DSC characterizations. These results indicated that the supposed mechanism was a dual catalytic mechanism. The proposed mechanism involved activation of the monomer via coordination to the MgX₂, and the initiator alcohol was deprotonated by base. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2349–2355     

RAFT polymerization of linear ABC triblock copolymer P<Emphasis Type="Italic">t</Emphasis>BA-<Emphasis Type="Italic">b</Emphasis>-PS-<Emphasis Type="Italic">b</Emphasis>-P2VP and regulation of its hierarchical self-assembly structure in solution

Linear ABC triblock copolymer PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ was successfully synthesized by RAFT polymerization. Block copolymer micelles were prepared by the two-step hierarchical self-assembly process. Size exclusion chromatography and ¹H NMR were used to characterize the structure of samples. Morphologies and size of micelles were determined by transmission electron microscope. The results showed that the densely dispersed spherical micelles of PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ were obtained in the first step of the hierarchical self-assembly process. In the second step, core-compartmentalized micelle strings with different lengths and distribution densities were obtained when the primary self-assembled solution was dialyzed in distilled water with pH ≈ 3. When distilled water with pH ≈ 3 was added drop-wise to this solution, uniformly dispersed spherical core-compartmentalized micelles of PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ were prepared. Thus, hierarchical self-assembly structure of linear ABC triblock copolymer was obtained successfully and the preparation of uniformly dispersed spherical micelles of triblock copolymers was realized simply by changing the secondary self-assembly methods.     

Homo-and Copolymerization of ε-Caprolactone and 2,2-Dimethyltrimethylene Carbonate by Rare Earth Initiators

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Self-assembly and electrochromic property of electroactive tetraaniline-<Emphasis Type="Italic">b</Emphasis>-PEG diblock copolymer

A kind of amphiphilic rod-coil diblock copolymer consisting both of tetraaniline (TAni) and polyethylene glycol (PEG) blocks, TAni-b-PEG, was synthesized. The diblock copolymer shows excellent electrochromic properties, especially, in switching time and coloration efficiency compared with tetraaniline. TAni-b-PEG is able to self-assemble into spherical structure, which is attributed to the formation of conducting channels and increase of ion-exchange capacity of TAni-b-PEG, implying that a block copolymer with electrochromic block and high ionic conductive block simultaneously possesses improving electrochromic properties.     

Amphiphilic biodegradable poly(CL-b-PEG-b-CL) triblock copolymers prepared by novel rare earth complex: Synthesis and crystallization properties

Amphiphilic biodegradable poly(CL-b-PEG-b-CL) triblock copolymers have been successfully prepared by the ring-opening polymerization of ε-caprolactone (CL) employing yttrium tris(2,6-di-tert-butyl-4-methylphenolate) [Y(DBMP)₃] as catalyst and double-hydroxyl capped PEGs (DHPEG) as macro-initiator. The triblock architecture, molecular weight, thermal and crystallization properties of the copolymers were characterized by NMR spectra, SEC, DSC and WAXD analyses. The isothermal crystallization behavior of the copolymers was investigated by POM analysis in detail, which is greatly influenced by the length of PCL and PEG blocks. On the POM micrograph of PEG_10,000-(PCL₈₆₀₀)₂, a unique morphology of concentric spherulites was observed due to the sequent crystallization of the PCL and PEG blocks.     

Functionalizing ps microspheres by supercritical deposition of P(S-<Emphasis Type="Italic">b</Emphasis>-<Emphasis Type="Italic">t</Emphasis>BA) for diverse interfacial properties exemplified with biocidal ability

Polystyrene（PS） microspheres were functionalized with poly（styrene-b-tert-butyl acrylate）（P（S-b-tBA）） by adsorption from supercritical mixture of CO₂ and hexane.Supercritical deposition formed a shell-core structure that contained a shell of poly（tert-butyl acrylate）（PtBA） blocks and a core of the PS blocks entangling with the PS microspheres. The thickness of the PtBA layer and thereby the areal density of tert-butyl ester groups increased with the deposition pressure until plateau values attained at 20 MPa and higher.The tert-butyl ester groups were hydrolyzed to carboxyl groups for conjugation with tert-butylamine molecules via amide bonds that were further chlorinated into biocidal N-halamine moieties. The functionalization layer and its bonded N-halamine moieties were stable in flowing water and the chlorine could be regenerated upon eventual loss.This functionalization concept is applicable to polymers of any external and internal surfaces to achieve diverse surface properties by varying block copolymer and conjugated moieties.     

Fabrication of nanoscale latex arrays based on hydroxylated poly(butyl methacrylate-<Emphasis Type="Italic">b</Emphasis>-glycidyl methacrylate)

We succeeded in fabricating nanoscale arrays of polymers based on hydroxylated poly(butyl methacrylate-b-glycidyl methacrylate) which was prepared via a novel atom-transfer radical polymerization technique. Nanosized latex particles of the copolymer were obtained in the tetrahydrofuran/toluene solvent system. By evaporation of the latex solution on a substrate, the ordered self-organization monolayer was formed. Rather regular, two-dimensional arrays of nanopaticles with diameters down to approximately 12 nm were observed by means of transmission electron microscopy. The regular nature of the arrays can be controlled well by depositing the monolayer at a lower temperature.     

Synthesis and characterization of aba-type block copolymer of poly(ϵ-caproplactone) with poly(ethylene glycol), by mean of activation end groups

Poly(?-caprolactone)-b-poly(ethylene glycol)-b-poly(?-caprolactone) (PCL-b-PEG-b-PCL) triblock copolymer were synthesized by mean anionic activation of the hydroxyl end groups of poly(ethylene glycol) in presence of diphenylmethylsodium. Copolymers were characterized by SEC, FT-IR and ¹H-NMR spectroscopy, TGA and DSC. Size exclusion chromatographic analysis of obtained copolymers indicated incorporation of CL monomer into PEG without formation of PCL homopolymer. Characterization by FT-IR and ¹H NMR spectroscopy of the resulting polymeric products, with respect to their structure, end-groups and composition, showed that they are best described as ester-ether-ester triblock copolymers, whose compositions can be adjusted changing the feeding molar ratio of PEG to CL. The thermal stability of triblock copolymers was less that PEG precursor, but higher that PCL homopolymer. Analysis by mean DSC showed that all copolymers were semi-crystalline and their thermal behavior depending on their composition.     

Magnolol entrapped ultra-fine fibrous mats electrospun from poly(ethylene glycol)-<Emphasis Type="Italic">b</Emphasis>-poly(L-lactide) and <Emphasis Type="Italic">in vitro</Emphasis> release

Ultra-fine fibrous mats with magnolol entrapped have been prepared by electrospinning biodegradable copolymer poly(ethylene glycol) blocked poly(L-lactide). Drug entrapment was perfect which was confirmed by scanning electron microscopy and differential scanning calorimetry. According to in vitro drug release investigation by high performance liquid chromatography, it was found that fibers with 10%, 20% and 30% drug entrapped respect to polymer (mass ratio) presented dramatically different drug release behavior and degradation behavior under the effect of proteinase K. The reason may be that fibers with 10% drug entrapped was more easily affected by enzyme while, to some degree, magnolol in fibers with 20% and 30% entrapped prevented polymer from being degraded by enzyme.     

Morphology of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) assemblies in diluted aqueous solution and gel studied by atomic force microscopy

Morphologies of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) triblock copolymer self‐assemblies in the diluted solution and in gel were studied by atomic force microscopy (AFM). The copolymer self‐assembled into wormlike aggregates, of uniform diameter, in water. The wormlike aggregates arranged in order to form separate clusters in the diluted copolymer solution; at a higher copolymer concentration, the clusters became bigger and bigger, and packed together to form gel. Copyright © 2008 John Wiley & Sons, Ltd.