Blue Photoluminescence from Hyperbranched Poly(amino ester)s

Blue Photoluminescence from Hyperbranched Poly(amino ester)

New Biodegradable Thermogelling Copolymers Having Very Low Gelation Concentrations

New biodegradable multiblock amphiphilic and thermosensitive poly(ether ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] (PHB), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) blocks were synthesized, and their aqueous solutions were found to undergo a reversible sol−gel transition upon temperature change at very low copolymer concentrations. The multiblock poly(ether ester urethane)s were synthesized from diols of PHB, PEG, and PPG using 1,6-hexamethylene diisocyanate as a coupling reagent. The chemical structures and molecular characteristics of the copolymers were studied by GPC, 1H NMR, 13C NMR, and FTIR. The thermal stability of the poly(PEG/PPG/PHB urethane)s was studied by thermogravimetry analysis (TGA), and the PHB contents were calculated based on the thermal degradation profile. The results were in good agreement with those obtained from the 1H NMR measurements. The poly(PEG/PPG/ PHB urethane)s presented better thermal stability than the PHB precursors. The water soluble poly(ether ester urethane)s had very low critical micellization concentration (CMC). Aqueous solutions of the new poly(ether ester urethane)s underwent a sol−gel−sol transition as the temperature increased from 4 to 80 °C, and showed a very low critical gelation concentration (CGC) ranging from 2 to 5 wt %. As a result of its multiblock architecture, a novel associated micelle packing model can be proposed for the sol−gel transition for the copolymer gels of this system. The new material is thought to be a promising candidate for injectable drug systems that can be formulated at low temperatures and forms a gel depot in situ upon subcutaneous injection

Threading α-Cyclodextrin through Poly[(<i>R,S</i>)-3-hydroxybutyrate] in Poly[(<i>R,S</i>)-3-hydroxybutyrate]−Poly(ethylene glycol)−Poly[(<i>R,S</i>)-3-hydroxybutyrate] Triblock Copolymers: Formation of Block-Selected Polypseudorotaxanes

A series of polypseudorotaxanes were synthesized from α-cyclodextrin (α-CD) and poly[(R,S)-3-hydroxybutyrate]−poly(ethylene glycol)−poly[(R,S)-3-hydroxybutyrate] (PHB−PEG−PHB) triblock copolymers with flanking PHB blocks of different lengths and the middle PEG block of Mn 3000 Da. Formation of inclusion complexes was confirmed by X-ray diffraction data, with α-CD adopting channel-type crystalline structures. The 1H NMR spectroscopy and thermogravimetric analysis results confirmed the presence of both host and guest molecules, and the compositions determined thereof from the two techniques were in good agreement. In the presence of excess α-CD, complexation stoichiometries between ethylene oxide units and α-CD for all polypseudorotaxanes were near the theoretical value of 2 despite the different lengths of PHB chains of the copolymers. Together with differential scanning calorimetry measurements where crystallization of the middle PEG block of the copolymers was completely absent while the glass transition of atactic PHB was detected, α-CD was thought to selectively cover the middle PEG block leaving telechelic PHB uncovered. The hypothesis was further substantiated by kinetic measurements; precipitation due to aggregation of the stable polypseudorotaxanes was slower with longer PHB chains. These findings demonstrated the successful threading of α-CD over the atactic PHB chain, which was previously thought to be impossible due to the mismatch in cross-sectional area. The study has highlighted the importance of block-selected molecular recognition of α-CD on PEG in the formation of stable polypseudorotaxanes of a block copolymer. The above revelations have interesting implications pertaining to design and synthesis of functional materials based on polypseudorotaxanes

Synthesis and Characterization of Polyrotaxanes Consisting of Cationic α-Cyclodextrins Threaded on Poly[(ethylene oxide)-<i>ran</i>-(propylene oxide)] as Gene Carriers

Cationic polymers have been receiving growing attention as gene delivery carriers. Herein, a series of novel cationic supramolecular polyrotaxanes with multiple cationic α-cyclodextrin (α-CD) rings threaded and blocked on a poly[(ethylene oxide)-ran-(propylene oxide)] (P(EO-r-PO)) random copolymer chain were synthesized and investigated for gene delivery. In the cationic polyrotaxanes, approximately 12 cationic α-CD rings were threaded on the P(EO-r-PO) copolymer with a molecular weight of 2370 Da and an EO/PO molar ratio of 4:1, while the cationic α-CD rings were grafted with linear or branched oligoethylenimine (OEI) of various chain lengths and molecular weights up to 600 Da. The OEI-grafted α-CD rings were only located selectively on EO segments of the P(EO-r-PO) chain, while PO segments were free of complexation. This increased the mobility of the cationic α-CD rings and the flexibility of the polyrotaxanes, which enhanced the interaction of the cationic α-CD rings with DNA and/or the cellular membrane. All cationic polyrotaxanes synthesized in this work could efficiently condense plasmid DNA to form nanoparticles that were suitable for delivery of the gene. Cytotoxicity studies showed that the cationic polyrotaxanes with all linear OEI chains of molecular weights up to 423 Da exhibited much less cytotoxicity than high-molecular-weight branched polyethylenimine (PEI) (25 kDa) in both HEK293 and COS7 cell lines. The cationic polyrotaxanes displayed high gene transfection efficiencies in a variety of cell lines including HEK293, COS7, BHK-21, SKOV-3, and MES-SA. Particularly, the gene delivery capability of the cationic polyrotaxanes in HEK293 cells was much higher than that of high-molecular-weight branched PEI (25 k)

2A₂ + BB‘B‘ ‘ Approach to Hyperbranched Poly(amino ester)s

Hyperbranched poly(amino ester)s were synthesized via a novel 2A2 + BB‘B‘ ‘ approach, represented by the Michael addition polymerization of a trifunctional amine, 1-(2-aminoethyl)piperazine (AEPZ) (BB‘B‘ ‘-type monomer), with a double molar diacrylate, 1,4-butanediol diacrylate (BDA) (A2-type monomer). The formation of B‘ ‘A2-type intermediate via its precursor, B‘B‘ ‘A-type intermediate, was verified by in situ monitoring the polymerizations using NMR and MS (ESI). High molecular weight hyperbranched poly(BDA2-AEPZ1) with vinyl terminal group was obtained from the B‘ ‘A2-type intermediate when the polymerization was performed in DMSO at 70 °C for ca. 101.0 h. Then the terminal vinyl group was tuned to primary, secondary, and tertiary amine, as verified by NMR. The radius of gyration (Rg) and hydrodynamic radius (Rh) of hyperbranched poly(BDA2-AEPZ1)-MPZ were measured using small-angle X-ray scattering (SAXS) and laser dynamic light scattering (LDLS), respectively, and the ratio of Rg/Rh of ca. 1.0 confirmed the hyperbranched structure. Molecular weights, glass transition temperatures (Tg), and thermal stability (Td) of hyperbranched poly(amino ester)s were characterized using GPC, DSC, and TGA, respectively

Synthesis, Characterization, and Morphology Studies of Biodegradable Amphiphilic Poly[(<i>R</i>)-3-hydroxybutyrate]-<i>a</i><i>lt</i>-Poly(ethylene glycol) Multiblock Copolymers

Novel biodegradable amphiphilic alternating block copolymers based on poly[(R)-3-hydroxybutyrate] (PHB) as biodegradable and hydrophobic block and poly(ethylene glycol) (PEG) as hydrophilic block (PHB-alt-PEG) were successfully synthesized through coupling reaction. Their chemical structures have been characterized by using gel permeation chromatography, 1H nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) analysis revealed that both PHB and PEG blocks in PHB-alt-PEG block copolymers can crystallize to form separate crystalline phase except in those with a short PEG block (Mn 600) only PHB crystalline phase has been observed. However, due to the mutual interference from each other, the melting transition of both PHB and PEG crystalline phases shifted to lower temperature with lower crystallinity in comparison with corresponding pure PHB and PEG. The crystallization behavior of PHB block and PEG block has also been studied by X-ray diffraction, and the results were in good agreement with those deduced from DSC study. The surface morphologies of PHB-alt-PEG block copolymer thin films spin-coated on mica have been visualized by atomic force microscopy with tapping mode, indicating formation of laterally regular lamellar surface patterns. Static water contact angle measurement revealed that surface hydrophilicity of these spin-coated thin films increases with increasing PEG block content