Adding a nucleating agent is one of the best ways to accelerate the crystallization rate of poly(L-lactic acid) (PLLA) so as to obtain a high degree of crystallinity during the process, which will improve the heat distortion temperature of final products. In the work reported, N, N′-bis(benzoyl)sebacic acid dihydrazide (BSAD) was synthesized and used as a nucleating agent for PLLA. Isothermal and non-isothermal crystallization behaviors were investigated using differential scanning calorimetry (DSC). The addition of BSAD successfully enhances the crystallization rate of PLLA. A unique phase separation behavior of PLLA/BSAD blends is found from DSC as well as from polarized optical microscopy, which explains the difference of optimal BSAD concentration between isothermal and non-isothermal crystallization. This is the first recording of a phase separation peak in PLLA/nucleating agent blends using DSC. In thermogravimetric analysis, the enhanced thermal stability indicates that there are strong hydrogen bonds between BSAD and PLLA matrix. BSAD can dissolve in PLLA melt below its melting point through intermolecular hydrogen bonding with PLLA and self-assemble upon cooling, leading to the surface being capable of nucleating PLLA. Different phase separation temperatures can be used to control the morphology of BSAD, which finally determines the crystallite morphology of PLLA. © 2012 Society of Chemical Industry

Stimuli-sensitive synthetic polypeptides are unique biodegradable and biocompatible synthetic polymers with structures mimicking natural proteins. These polymers exhibit reversible secondary conformation transitions and/or hydrophilic–hydrophobic transitions in response to changes in environmental conditions such as pH and temperature. The stimuli-triggered conformation and/or phase transitions lead to unique self-assembly behaviors, making these materials interesting for controlled drug and gene delivery applications. Therefore, stimuli-sensitive synthetic polypeptide-based materials have been extensively investigatid in recent years. Various polypeptide-based materials, including micelles, vesicles, nanogels, and hydrogels, have been developed and tested for drug- and gene-delivery applications. In addition, the presence of reactive side groups in some polypeptides facilitates the incorporation of various functional moieties to the polypeptides. This Review focuses on recent advances in stimuli-sensitive polypeptide-based materials that have been designed and evaluated for drug and gene delivery applications. In addition, recent developments in the preparation of stimuli-sensitive functionalized polypeptides are discussed.

Medicated-fibers have been obtained through electrospinning after rifampin was dissolved in poly (lactic acid)/chloroform solution. The relationship between polymer variables [such as concentration, molecular weight (M_w), and introducing hydrophilic block] and drug release from the electrospun fibers is disclosed. The results show that polymeric concentration and M_w are crucial for producing the medicated fibers, which influence not only the morphology of the medicated-fiber but also drug release rate from fiber. At the same M_w, the drug release rate decreases with the increase of spinning concentration. At two different M_w blends, drug release behaviors change. When the low M_w content is in a dominant position, drug release rate depends largely on mixing ratio of two M_w contents; on the other hand, drug release rate is also dependent on concentration of spinning fluid. In addition, the block copolymer [poly-L-lactic acid (PLLA)-polyethylene glycol-PLLA] shows faster release rate as compared to homopolymer (PLLA). © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Thermoresponsive and pH-responsive graft copolymers, poly(L-glutamate)-g-oligo(2-(2-(2-methoxyethoxy)ethoxy)ethyl methacrylate) and poly(L-glutamic acid-co-(L-glutamate-g-oligo(2-(2-(2-methoxyethoxy)ethoxy)ethyl methacrylate))), were synthesized by ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) monomers and subsequent atom transfer radical polymerization of 2-(2-(2-methoxyethoxy)ethoxy)ethyl methacrylate. The thermoresponsiveness of graft copolymers could be tuned by the molecular weight of oligo(2-(2-(2-methoxyethoxy)ethoxy)ethyl methacrylate) (OMEO₃MA), composition of poly(L-glutamic acid) (PLGA) backbone and pH of the aqueous solution. The α-helical contents of graft copolymers could be influenced by OMEO₃MA length and pH of the aqueous solution. In addition, the graft copolymers exhibited tunable self-assembly behavior. The hydrodynamic radius (R_h) and critical micellization concentration values of micelles were relevant to the length of OMEO₃MA and the composition of biodegradable PLGA backbone. The R_h could also be adjusted by the temperature and pH values. Lastly, in vitro methyl thiazolyl tetrazolium (MTT) assay revealed that the graft copolymers were biocompatible to HeLa cells. Therefore, with good biocompatibility, well-defined secondary structure, and mono-, dual-responsiveness, these graft copolymers are promising stimuli-responsive materials for biomedical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Ultrathin mesoporous bioactive glass hollow fibers (MBGHFs) fabricated using an electrospinning technique and combined with a phase-separation-induced agent, poly(ethylene oxide) (PEO), are described. The rapid solvent evaporation during electrospinning and the PEO-induced phase separation process demonstrated play vital roles in the formation of ultrathin bioactive glass fibers with hollow cores and mesoporous walls. Immersing the MBGHFs in simulated body fluid rapidly results in the development of a layer of enamel-like apatite mesocrystals at the fiber surfaces and apatite nanocrystals inside the hollow cores. Drug loading and release experiments indicate that the drug loading capacity and drug release behavior of the MBGHFs strongly depends on the fiber length. MBGHFs with fiber length >50 µm can become excellent carriers for drug delivery. The shortening of the fiber length reduces drug loading amounts and accelerates drug release. The MBGHFs reported here with sophisticated structure, high bioactivity, and good drug delivery capability can be a promising scaffold for hard tissue repair and wound healing when organized into 3D macroporous membranes.

The poly(ε-caprolactone) (PCL)/starch blends were prepared with a coextruder by using the starch grafted PLLA copolymer (St-g-PLLA) as compatibilizers. The thermal, mechanical, thermo-mechanical, and morphological characterizations were performed to show the better performance of these blends compared with the virgin PCL/starch blend without the compatibilizer. Interfacial adhesion between PCL matrix and starch dispersion phases dominated by the compatibilizing effects of the St-g-PLLA copolymers was significantly improved. Mechanical and other physical properties were correlated with the compatibilizing effect of the St-g-PLLA copolymer. With the addition of starch acted as rigid filler, the Young's modulus of the PCL/starch blends with or without compatibilizer all increased, and the strength and elongation were decreased compared with pure PCL. Whereas when St-g-PLLA added into the blend, starch and PCL, the properties of the blends were improved markedly. The 50/50 composite of PCL/starch compatibilized by 10% St-g-PLLA gave a tensile strength of 16.6 MPa and Young's modulus of 996 MPa, respectively, vs. 8.0 MPa and 597 MPa, respectively, for the simple 50/50 blend of PCL/starch. At the same time, the storage modulus of compatibilized blends improved to 2940 MPa. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

We present here the synthesis of two kinds of amphiphilic block copolymers, a diblock copolymer MPEG-b-PTAm and a triblock copolymer MPEG-b-PLA-b-PTAm, which can self-assemble into micelles with nitroxyl radicals-containing PTAm segment in the core. The structure of the block copolymers was characterized by ¹H NMR and GPC. Dynamic laser light scattering and transmission electron microscopy were used to study the micellar behavior of the two block copolymers in aqueous solution. The micelles carrying nitroxyl radicals in the core can generate electron paramagnetic resonance, which is stable for a period of time up to 8 min even in the presence of reducing reagent such as ascorbic acid. The enhanced stability against the reducing agent was ascribed to the inaccessibility of the nitroxyl radical core placed in the interior of the micelles. Combined with the biocompatibility, these micelles were promising to be used as the EPR probes for bioimaging in vivo. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

This work describes the design and assembly of multifunctional and cost-efficient composite fiber nonwovens as semi-occlusive wound dressings using a simple electrospinning process to incorporate a variety of functional components into an ultrathin fiber. These components include non-hydrophilic poly(L-lactide) (PLLA) as fibrous backbone, hydrophilic poly(vinyl pyrrolidone)–iodine (PVP–I), TiO₂ nanoparticles, zinc chloride as antimicrobial, odor-controlling, and antiphlogistic agents, respectively. The process of synthesis starts with a multicomponent solution of PLLA, PVP, TiO₂ nanoparticles plus zinc chloride, in which TiO₂ nanoparticles are synthesized by in situ hydrolysis of TiO₂ precursors in a PVP solution for the sake of obtaining the particle-uniformly dispersive solution. Subsequent electrospinning generates the corresponding composite fibers. A further iodine vapor treatment to the composite fibers combines iodine with PVP to produce the PVP–I complexes. Experiments indicate that the assembled composite fibers (300–400 nm) possess the ointment-releasing characteristic and the phase-separate, core-sheath structures in which PVP–I residing in fiber surface layer becomes the sheath, and PLLA distributing inside the fiber acts as the core. Based on this design, the structural advantages combining active components endow the assembled composite nonwovens with a variety of functions, especially, the existence of PVP–I, endows the nonwoven with water absorbability, antimicrobial activity, adhesive ability, and transformable characteristic from hydrophilicity to non-hydrophilicity. The multifunctional, cost-efficient, and ointment-releasing characteristics make the multicomponent composite fibrous nonwovens potentially useful in applications such as initial stage of dressing of the cankerous or contaminated wounds. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009

Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan-type) ligands [Al(OC₆H₂(R-6-R-4)CH₂)₂{CH₃N(C₆H₁₀)NCH₃}-C₂H₅] (4, 7: R=H; 5, 8: R=Cl; 6, 9: R=CH₃) are reported. Enantiomerically pure salan ligands 1–3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4, 5, and 6 as mixtures of two diastereoisomers (a and b). Each diastereoisomer a was, as determined by X-ray analysis, monomeric with a five-coordinated aluminium central core in the solid state, adopting a cis-(O,O) and cis-(Me,Me) ligand geometry. From the results of variable-temperature (VT) ¹H NMR in the temperature range of 220–335 K, ¹H–¹H NOESY at 220 K, and diffusion-ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five-coordinated aluminium central core. The geometry is intermediate between square pyramidal with a cis-(O,O), trans-(Me,Me) ligand disposition and trigonal bipyramidal with a trans-(O,O) and trans-(Me,Me) disposition. A slow exchange between these two geometries at 220 K was indicated by ¹H–¹H NOESY NMR. In the presence of propan-2-ol as an initiator, enantiomerically pure (R,R) complexes 4–6 and their racemic mixtures 7–9 were efficient catalysts in the ring-opening polymerization of lactide (LA). Polylactide materials ranging from isotactically biased (P_m up to 0.66) to medium heterotactic (P_r up to 0.73) were obtained from rac-lactide, and syndiotactically biased polylactide (P_r up to 0.70) from meso-lactide. Kinetic studies revealed that the polymerization of (S,S)-LA in the presence of 4/propan-2-ol had a much higher polymerization rate than (R,R)-LA polymerization (k_SS/k_RR=10.1).

For the films and powder of polymers containing conductive oligomer are usually obtained from solution, the choice of better solvents for the regular arrangement of oligomers is very important for the higher conductivity. Because of the poor solubility of the oligomers, it is difficult to study the arrangement directly in most common solvents, so, we synthesized a triblock copolymer, mPEG2k-aniline pentamer-mPEG2k, as the model to investigate the arrangement–solvent relationship. For the poor solubility of the AP block in common solvents, the copolymer self-assembled into spheric micelles in toluene and into lamellar crystals in water and THF. The crystallinity (X_c) and crystallization temperature (T_c) values of mPEG blocks in powders prepared from different solvents differed obviously, which may be the effect of different self-assembled structures. From the two-phase model of one-dimensional electron density correlation function of SAXS, the long period of copolymer prepared from THF was presumably equal to the long period of pure mPEG plus the chain length of AP, which demonstrates that the AP blocks arrange regularly in the noncrystalline regions. In the selected solvents, the ones with higher polarity and better solubility induced more regular arrangement of AP blocks, which may be useful for choosing solvents for preparation of higher conductivity polymers' films containing aniline oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1298–1307, 2009

A series of novel temperature- and pH-responsive graft copolymers, poly(L-glutamic acid)-g-poly(N-isopropylacrylamide), were synthesized by coupling amino-semitelechelic poly(N-isopropylacrylamide) with N-hydroxysuccinimide-activated poly(L-glutamic acid). The graft copolymers and their precursors were characterized, by ESI-FTICR Mass Spectrum, intrinsic viscosity measurements and proton nuclear magnetic resonance (¹H NMR). The phase-transition and aggregation behaviors of the graft copolymers in aqueous solutions were investigated by the turbidity measurements and dynamic laser scattering. The solution behavior of the copolymers showed dependence on both temperature and pH. The cloud point (CP) of the copolymer solution at pH 5.0–7.4 was slightly higher than that of the solution of the PNIPAM homopolymer because of the hydrophilic nature of the poly(glutamic acid) (PGA) backbone. The CP markedly decreased when the pH was lowered from 5 to 4.2, caused by the decrease in hydrophilicity of the PGA backbone. At a temperature above the lower critical solution temperature of the PNIPAM chain, the copolymers formed amphiphilic core-shell aggregates at pH 4.5–7.4 and the particle size was reduced with decreasing pH. In contrast, larger hydrophobic aggregates were formed at pH 4.2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4140–4150, 2008

Novel star-like hyperbranched polymers with amphiphilic arms were synthesized via three steps. Hyperbranched poly(amido amine)s containing secondary amine and hydroxyl groups were successfully synthesized via Michael addition polymerization of triacrylamide (TT) and 3-amino-1,2-propanediol (APD) with feed molar ratio of 1:2. ¹H, ¹³C, and HSQC NMR techniques were used to clarify polymerization mechanism and the structures of the resultant hyperbranched polymers. Methoxyl poly(ethylene oxide) acrylate (A-MPEO) and carboxylic acid-terminated poly(ε-caprolactone) (PCL) were sequentially reacted with secondary amine and hydroxyl group, and the core–shell structures with poly(1TT-2APD) as core and two distinguishing polymer chains, PEO and PCL, as shell were constructed. The star-like hyperbranched polymers have different sizes in dimethyl sulfonate, chloroform, and deionized water, which were characterized by DLS and ¹H NMR. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1388–1401, 2008

A novel water-soluble electroactive polymer, aniline pentamer crosslinked chitosan (Pentamer-c-Chi), was prepared by condensation polymerization of the terminal carboxyl groups in aniline pentamer with the amino side groups in chitosan in aqueous solution. The carboxyl groups were activated by N-hydroxysuccinimide (NHS) and N,N′-dicyclohexylcarbodiimide (DCC). The electrochemical behavior of anilinepentamer in this kind of crosslinked polymer was studied in acidic aqueous solution by means of cyclic voltammetry (CV), UV–vis, and electron spin resonance (ESR) spectroscopy. There were three reversible redox peaks in the CV of Pentamer-c-Chi. A new emeraldine oxidization state in the form of radical cations was proposed, which was associated with the new absorption band at 370 nm in the UV–vis spectra. The ESR of the aqueous solution of Pentamer-c-Chi showed a single Lorentzian shaped signal, which suggested the existence of radical cations. The new redox state was pH dependent and appeared only at pH < 3. The stability of radical cations could be attributed to the hydrogen bonds between radical cations, water, and chitosan. Morphological structure of the Pentamer-c-Chi can be adjusted by varying the content of aniline pentamer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1124–1135, 2008

Enolic Schiff base zinc (II) complex 1 was synthesized. XRD revealed 1 was a novel crown-like macrocycle structure consisted of hexanuclear units of (LZnEt)₆ via the coordination chelation between the Zn atom and adjacent amine nitrogen atom. Further reaction of 1 with one equivalent 2-propanol at RT produced Zn-alkoxide 2 by in situ alcoholysis. Complex 2 was used as an initiator to polymerize rac-lactide in a controlled manner to give heterotactic enriched polylactide. Factors that influenced the polymerization such as the polymerization time and the temperature as well as the monomer concentration were discussed in detail in this paper. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 643–649, 2008

A series of enolic Schiff base aluminum(III) complexes LAlR (where L=NNOO-tetradentate enolic Schiff base ligand) containing ligands that differ in their steric and electronic properties were synthesized. Their single crystals showed that these complexes are five-coordinated around the aluminum center. Their coordination geometries are between square pyramidal and trigonal bipyramidal. Their catalytic properties in the solution polymerization of racemic lactide (rac-LA) were examined. The modifications in the auxiliary ligand exhibited a dramatic influence on the catalytic performance. Lengthening the backbone from C₂ alkylene to C₃ alkylene resulted in remarkable enhancement of both the stereoselectivity and the polymerization rate because of the increasing flexibility of the diimine backbone. Electron-withdrawing substituents in the diketone also highly improved the activity and the stereoselectivity. Among these complexes, 4 b had the highest activity and the stereoselectivity owing to the C₃ alkylene backbone and the two gem-methyl groups on the middle carbon atom. The value of the polymerization rate constant (k_p) catalyzed by 4 b in 70 °C was 1.90 L mol⁻¹ min⁻¹, the activation energy of the polymerization (35.4 kJ mol⁻¹) was calculated according to the Arrhenius equation. Other factors that influenced the polymerization, such as the polymerization time, the temperature, and the monomer concentration, are also discussed in detail.