Formation of Structured Polygonal Nanoparticles by Phase‐Separated Comb‐Like Polymers

A simple approach using comb‐like polymers that undergo nanophase separation between the polyester backbone and the stearoyl side chains is proposed for the preparation of structured non‐spherical nanoparticles from a nanoemulsion. Depending on the degree of esterification of the OH groups of poly(glycerol adipate) differently ordered nanostructures is obtained. A perfect lamellar arrangement is obtained for polymers with a high degree of esterification and leads to spherical nanoparticles with an internal onion‐like structure. However, when the degree of esterification is only 20 mol%, polygonal nanoparticles with an internal pseudo‐hexagonal structure are obtained. The differences in the nanoparticle shapes are related to the volume fraction of the paraffinic pool.     

Synthesis of comb‐like polystyrene with poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as macroinitiator

The copolymerization of N‐phenyl maleimide and p‐chloromethyl styrene via reversible addition–fragmentation chain transfer (RAFT) process with AIBN as initiator and 2‐(ethoxycarbonyl)prop‐2‐yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2′‐bipyridine, well‐defined comb‐like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069–2075, 2006     

Crystal structure of poly(dithiotriethylene adipate)

The crystal structure of poly(dithiotriethylene adipate) has been determined through the best fitting of calculated and experimental X‐ray diffraction powder profiles. A triclinic cell was found with dimensions a = 4.942 (7) Å, b = 4.702 (2) Å, c = 20.56 (2) Å, α = 88.9 (2)°, β = 61.0 (1)°, γ = 67.8 (1)°, P‐1 space group, and one chain in the unit cell. A full extended trans conformation of the chain fitted satisfactory the experimental data, yielding to a discrepancy factor R_p = 0.073. A comparison between the crystal structures of poly(dithiotriethylene adipate) and poly (thiodiethylene adipate) is proposed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2677–2682, 2005     

Crystallization kinetics and morphology of poly(butylene succinate‐co‐adipate)

The crystallization kinetics of biodegradable poly(butylene succinate‐co‐adipate) (PBS/A) copolyester was investigated by using differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. The Avrami and Ozawa equations were used to analyze the isothermal and nonisothermal crystallization kinetics, respectively. By using wide‐angle X‐ray diffraction (WAXD), PBS/A was identified to have the same crystal structure with that of PBS. The spherulitic growth rates of PBS/A measured in isothermal conditions are very well comparable with those measured by nonisothermal procedures (cooling rates ranged from 0.5 to 15 °C/min). The kinetic data were examined with the Hoffman–Lauritzen nucleation theory. The observed spherulites of PBS/A with different shapes and textures strongly depend on the crystallization temperatures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3231–3241, 2005     

Influence of molecular weight on the phase behaviors of comb‐like polymers with long n‐alkyl side chains based on mesogen‐jacketed liquid crystalline polymers

A series of comb‐like polymers, poly{2,5‐bis[(4‐octadecyloxyphenyl)oxycarbonyl]‐styrenes{ (P‐OC18s) with different molecular weights (M_n) and low molecular weight distributions have been successfully synthesized via atom transfer radical polymerization. The phase behaviors have been investigated by a combination of techniques including differential scanning calorimetry, polarized optical microscopy, wide‐angle X‐ray diffraction, and temperature‐variable FTIR spectroscopy. One hand, phase behaviors of the alkyl tails were strongly influenced by the mesogens of polymers, leading to the poor packing of the alkyl tails and the low melting. The other hand, the liquid crystalline phase structures of polymers were found to be strongly M_n dependent. The samples with M_n ≤ 4.6 × 10⁴ formed a smectic phase in low temperature and an isotropic phase in high temperature. The samples with M_n ≥ 5.2 × 10⁴ displayed a reentrant isotropic phase, which was separating the smectic phase and columnar nematic phase. Meantime, the experiment results showed that the glass temperature and the transition temperature from smectic phase to isotropic phase both slightly increased with the increase of M_nS; however, the transition temperature from isotropic phase to columnar phase sharply decreased with the M_nS improved. The reappearance of isotropic phase is due to the competing between the driving force of the enthalpy and the driving force of the entropy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Melt‐processable poly(oxyphenylalkanoate): Synthesis,properties, and in vitro degradation of poly(4‐oxyphenylacetate)

The homopolyester of 4‐hydroxyphenylacetic acid (HPAA) was synthesized by one‐pot, slurry‐melt, and acidolysis melt polymerization techniques and was characterized by its inherent viscosity and IR and NMR spectra. Differential scanning calorimetry (DSC), polarizing light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD) studies of the homopolymer were carried out for its thermal and phase behavior. The results indicated that the yield and molecular weight of the polymer depended on the method of preparation; moreover, the acidolysis melt polymerization of the pure acetoxy derivative of HPAA was the best method for the preparation of high molecular weight poly(4‐oxyphenylacetate) (polyHPAA) without side reactions. DSC and PLM studies also showed that the thermal and optical properties depended largely on the polymerization conditions and inherent viscosity values. PolyHPAA did not show a clear texture typical of liquid‐crystalline polymers, whereas after cooling from the melt, structures similar to spherulitic crystals were observed. WAXD patterns showed a crystalline nature. The in vitro degradability of the polymer was also studied via the water absorption in buffer solutions of pH 7 and 10 at 30 and 60 °C; this was followed by Fourier transform infrared, inherent viscosity, DSC, thermogravimetric analysis, WAXD, and scanning electron microscopy techniques. Unlike Vectra®, which showed no degradation, polyHPAA showed an increase in hydrolytic degradation from 5.0 and 6.0% at 30 °C to 12.5 and 15.0% at 60 °C after 350 h in buffer solutions of pH 7 and 10, respectively. The results indicated a possible biomedical prosthetic application of poly(oxyphenylalkanoate)s such as polyHPAA with better crystallinity coupled with degradability as a substitute for poly(hydroxyalkanoates). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2430–2443, 2001     

Novel synthesis of biodegradable star poly(ethylene glycol)‐block‐poly(lactide) copolymers

Biodegradable star‐shaped poly(ethylene glycol)‐block‐poly(lactide) copolymers were synthesized by ring‐opening polymerization of lactide, using star poly(ethylene glycol) as an initiator and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature. Two series of three‐ and four‐armed PEG‐PLA copolymers were synthesized and characterized by gel permeation chromatography (GPC) as well as ¹H and ¹³C NMR spectroscopy. The polymerization under the used conditions is very fast, yielding copolymers of controlled molecular weight and tailored molecular architecture. The chemical structure of the copolymers investigated by ¹H and ¹³C NMR indicates the formation of block copolymers. The monomodal profile of molecular weight distribution by GPC provided further evidence of controlled and defined star‐shaped copolymers as well as the absence of cyclic oligomeric species. The effects of copolymer composition and lactide stereochemistry on the physical properties were investigated by GPC and differential scanning calorimetry. For the same PLA chain length, the materials obtained in the case of linear copolymers are more viscous, whereas in the case of star copolymer, solid materials are obtained with reduction in their T_g and T_m temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3966–3974, 2007     

RGD peptide grafted biodegradable amphiphilic triblock copolymer poly(glutamic acid)‐b‐poly(L‐lactide)‐b‐poly(glutamic acid): Synthesis and self‐assembly

A novel amphiphilic biodegradable triblock copolymer (PGL‐PLA‐PGL) with polylactide (PLA) as hydrophobic middle block and poly(glutamic acid) (PGL) as hydrophilic lateral blocks was successfully synthesized by ring‐opening polymerization (ROP) of L ‐lactide (LA) and N‐carboxy anhydride (NCA) consecutively and by subsequent catalytic hydrogenation. The results of cell experiment of PGL‐PLA‐PGL suggested that PGL could improve biocompatibility of polyester obviously. The copolymer could form micelles of spindly shape easily in aqueous solution. The pendant carboxyl groups of the triblock copolymer were further activated with N‐hydroxysuccinimide and combined with a cell‐adhesive peptide GRGDSY. Incorporation of the oligopeptide further enhanced the hydrophilicity and led to formation of spherical micelles. PGL‐PLA‐PGL showed better cell adhesion and spreading ability than pure PLA and the GRGDSY‐containing copolymer exhibited even further improvement in cell adhesion and spreading ability, indicating that the copolymer could find a promising application in drug delivery or tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3218–3230, 2007     

Micelle formation and sol–gel transition behavior of comb‐like amphiphilic poly((PLGA‐b‐PEG)MA) copolymers

Comb‐like amphiphilic poly(poly((lactic acid‐co‐glycolic acid)‐block‐poly(ethylene glycol)) methacrylate (poly((PLGA‐b‐PEG)MA)) copolymers were synthesized by radical polymerization. (PLGA‐b‐PEG)MA macromonomer was prepared by ring‐opening bulk polymerization of DL ‐lactide and glycolide using purified poly(ethylene glycol) monomethacrylate (PEGMA) as an initiator. (PLGA‐b‐PEG)MA macromonomer was copolymerized with PEGMA and/or acrylic acid (AA) by radical polymerization to produce comb‐like amphiphilic block copolymers. The molecular weight and chemical structure were investigated by GPC and ¹H NMR. Poly((PLGA‐b‐PEG)MA) copolymer aqueous solutions showed gel–sol transition behavior with increasing temperature, and gel‐to‐sol transition temperature decreased as the compositions of the hydrophilic PEGMA and AA increased. The gel‐to‐sol transition temperature of the terpolymers of the poly((PLGA‐b‐PEG)MA‐co‐PEGMA‐co‐AA) also decreased when the pH was increased. The effective micelle diameter obtained from dynamic light scattering increased with increasing temperature and with increasing pH. The critical micelle concentration increased as the composition of the hydrophilic monomer component, PEGMA and AA, were increased. The spherical shape of the hyperbranched polymers in aqueous environment was observed by atomic force microscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1954–1963, 2008     

Study on the preparation and the self‐assembly of poly(propyleneimine)–poly(styrene) nanoparticles

Using 2‐chloropropionamide derivative of poly(propyleneimine) dendrimer DAB‐dendr‐(NH₂)₃₂ (DAB‐32‐Cl) as the macroinitiator, atom transfer radical polymerization of styrene was successfully carried out in DMF medium. The monodisperse poly(propyleneimine)–polystyrene (dendrimer–PSt) particles with diameters smaller than 100 nm could be prepared. The morphology, size, and size distribution of the dendrimer–PSt particles were characterized by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). The effects of reaction temperature, the ratio of St/macroinitiator, and reaction time on the size, and size distribution of the dendrimer–PSt nanoparticles were investigated. In a selective solvent (DMF/H₂O), polymers can self‐assemble into different aggregate configurations such as regular microsphere and wire‐like thread. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2658–2666, 2008     

Synthesis and self‐assembly of thermosensitive double‐hydrophilic poly(N‐vinylcaprolactam)‐b‐poly(N‐vinyl‐2‐pyrrolidone) diblock copolymers

We report on novel diblock copolymers of poly(N‐vinylcaprolactam) (PVCL) and poly(N‐vinyl‐2‐pyrrolidone) (PVPON) (PVCL‐b‐PVPON) with well‐defined block lengths synthesized by the MADIX/reversible addition‐fragmentation chain transfer (RAFT) process. We show that the lower critical solution temperatures (LCST) of the block copolymers are controllable over the length of PVCL and PVPON segments. All of the diblock copolymers dissolve molecularly in aqueous solutions when the temperature is below the LCST and form spherical micellar or vesicular morphologies when temperature is raised above the LCST. The size of the self‐assembled structures is controlled by the molar ratio of PVCL and PVPON segments. The synthesized homopolymers and diblock copolymers are demonstrated to be nontoxic at 0.1–1 mg mL^?1 concentrations when incubated with HeLa and HEK293 cancer cells for various incubation times and have potential as nanovehicles for drug delivery. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2725–2737     

Morphology and thermal properties of poly(L‐lactide)/poly(butylene succinate‐co‐butylene adipate) compounded with twice functionalized clay

Poly(L ‐lactide) (PLLA)/poly(butylene succinate‐co‐butylene adipate) (PBSA) blends were compounded with Cloisite 25A® (C25A) and C25A functionalized with epoxy groups, respectively. Epoxy groups on the surface of C25A were introduced by treating C25A with (glycidoxypropyl)trimethoxy silane (GPS) to produce so called Twice Functionalized Organoclay (TFC). Variation of morphology and properties of PLLA/PBSA/C25A composites was investigated before and after the treatment with GPS. The morphological structure of the composites was analyzed by using X‐ray diffractometry (XRD) and transmission electron microscopy (TEM). The silicate layers of PLLA/PBSA/TFC were exfoliated to a larger extent than PLLA/PBSA/C25A. Incorporation of the epoxy groups on C25A improved significantly elongation at break as well as tensile modulus and tensile strength of PLLA/PBSA/C25A. The larger amount of exfoliation of the silicate layers in PLLA/PBSA/TFC as compared with that in PLLA/PBSA/C25A was attributed to the increased interfacial interaction between the polyesters and the clay due to chemical reaction. Thermo gravimetric analysis revealed that both T_5%, which was the temperature corresponding to 5% weight loss, and activation energy of thermal decomposition of PLLA/PBSA/TFC were far superior to those of PLLA/PBSA/C25A as well as to those of PLLA/PBSA, indicating that the composites with exfoliated silicate layers were more thermally stable than those with intercalated silicate layers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 478–487, 2005     

Preparation and characterization of biodegradable poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers

A series of poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers were prepared with varying feed rations by using two step polymerization reactions. Poly(trimethylenecarbonate)(ε‐caprolactone) random copolymer was synthesized with stannous‐2‐ethylhexanoate and followed by adding p‐dioxanone monomer as the other block. The ring opening polymerization was carried out at high temperature and long reaction time to get high molecular weight polymers. The monofilament fibers were obtained using conventional melting spun methods. The copolymers were identified by ¹H and ¹³C NMR spectroscopy and gel permeation chromatography (GPC). The physicochemical properties, such as viscosity, molecular weight, melting point, glass transition temperature, and crystallinity, were studied. The hydrolytic degradation of copolymers was studied in a phosphate buffer solution, pH = 7.2, 37 °C, and a biological absorbable test was performed in rats. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2790–2799, 2005     

Synthesis of four‐armed poly(ε‐caprolactone)‐block‐poly(ethylene oxide) by diethylzinc catalyst

Biodegradable, amphiphilic, four‐armed poly(?‐caprolactone)‐block‐poly(ethylene oxide) (PCL‐b‐PEO) copolymers were synthesized by ring‐opening polymerization of ethylene oxide in the presence of four‐armed poly(?‐caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt₂) as a catalyst. The chemical structure of PCL‐b‐PEO copolymer was confirmed by ¹H NMR and ¹³C NMR. The hydroxyl end groups of the four‐armed PCL were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four‐armed architecture of the copolymer. Physicochemical properties of the four‐armed block copolymers differed from their starting four‐armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four‐armed block copolymer increased with PEO length and PEO content. The micelle formation of the four‐armed block copolymer was examined by a fluorescent probe technique, and the existence of the critical micelle concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. The cmc value increased with increasing PEO length. The absolute cmc values were higher than those for linear amphiphilic block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 950–959, 2004     

Synthesis,characterization, and thermal properties of a novel pentaerythritol‐initiated star‐shaped poly(p‐dioxanone)

A novel star‐shaped poly(p‐dioxanone) was synthesized by the ring‐opening polymerization of p‐dioxanone initiated by pentaerythritol with stannous octoate as a catalyst in bulk. The effect of the molar ratio of the monomer to the initiator on the polymerization was studied. The polymers were characterized with ¹H NMR and ¹³C NMR spectroscopy. The thermal properties of the polymers were investigated with differential scanning calorimetry and thermogravimetric analysis. The novel star‐shaped poly(p‐dioxanone) has a potential use in biomedical materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1245–1251, 2006     

Synthesis and self‐assembly of well‐defined cyclodextrin‐centered amphiphilic A14B7 multimiktoarm star copolymers based on poly(ε‐caprolactone) and poly(acrylic acid)

Novel amphiphilic A₁₄B₇ multimiktoarm star copolymers composed of 14 poly(ε‐caprolactone) (PCL) arms and 7 poly(acrylic acid) (PAA) arms with β‐cyclodextrin (β‐CD) as core moiety were synthesized by the combination of controlled ring‐opening polymerization (CROP) and atom transfer radical polymerization (ATRP). 14‐Arm star PCL homopolymers (CDSi‐SPCL) were first synthesized by the CROP of CL using per‐6‐(tert‐butyldimethylsilyl)‐β‐CD as the multifunctional initiator in the presence of Sn(Oct)₂ at 125 °C. Subsequently, the hydroxyl end groups of CDSi‐SPCL were blocked by acetyl chloride. After desilylation of the tert‐butyldimethylsilyl ether groups from the β‐CD core, 7 ATRP initiating sites were introduced by treating with 2‐bromoisobutyryl bromide, which further initiated ATRP of tert‐butyl acrylate (tBA) to prepare well‐defined A₁₄B₇ multimiktoarm star copolymers [CDS(PCL‐PtBA)]. Their molecular structures and physical properties were in detail characterized by ¹H NMR, SEC‐MALLS, and DSC. The selective hydrolysis of tert‐butyl ester groups of the PtBA block gave the amphiphilic A₁₄B₇ multimiktoarm star copolymers [CDS(PCL‐PAA)]. These amphiphilic copolymers could self‐assemble into multimorphological aggregates in aqueous solution, which were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2961–2974, 2010     

Effect of polystyrene‐b‐poly(ethylene oxide) on self‐assembly of polystyrene‐b‐poly(N‐isopropylacrylamide) in aqueous solution

Mixed micelles of polystyrene‐b‐poly(N‐isopropylacrylamide) (PS‐b‐PNIPAM) and two polystyrene‐b‐poly(ethylene oxide) diblock copolymers (PS‐b‐PEO) with different chain lengths of polystyrene in aqueous solution were prepared by adding the tetrahydrofuran solutions dropwise into an excess of water. The formation and stabilization of the resultant mixed micelles were characterized by using a combination of static and dynamic light scattering. Increasing the initial concentration of PS‐b‐PEO in THF led to a decrease in the size and the weight average molar mass (〈M_w〉) of the mixed micelles when the initial concentration of PS‐b‐ PNIPAM was kept as 1 × 10^?3 g/mL. The PS‐b‐PEO with shorter PS block has a more pronounced effect on the change of the size and 〈M_w〉 than that with longer PS block. The number of PS‐b‐PNIPAM in each mixed micelle decreased with the addition of PS‐b‐PEO. The average hydrodynamic radius 〈R_h〉 and average radius of gyration 〈R_g〉 of pure PS‐b‐PNIPAM and mixed micelles gradually decreased with the increase in the temperature. Both the pure micelles and mixed micelles were stable in the temperature range of 18 °C–39 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1168–1174, 2010     

Calixarene‐centered amphiphilic A2B2 miktoarm star copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol): Synthesis and self‐assembly behaviors in water

Novel calixarene‐centered amphiphilic A₂B₂ miktoarm star copolymers composed of two PCL arms and two PEG arms with calix[4]arene as core moiety were synthesized by the combination of CROP and “click” chemistry. First, a heterotetrafunctional calix[4]arene derivative with two hydroxyl groups and two alkyne groups was designed as a macroinitiator to prepare calixarene‐centered PCL homopolymers (C4‐PCL) by CROP in the presence of Sn(Oct)₂ as catalyst at 110 °C. Next, azide‐terminated PEG (A‐PEG) was synthesized by tandem treating methoxy poly(ethylene glycol)s (mPEG) with 4‐chlorobutyryl chloride and NaN₃. Finally, copper(I)‐catalyzed cycloaddition reaction between C4‐PCL and A‐PEG led to A₂B₂ miktoarm star copolymer [C4S(PCL)₂‐(PEG)₂]. ¹H NMR, FT‐IR, and SEC analyses confirmed the well‐defined miktoarm star architecture. These amphiphilic miktoarm star copolymers could self‐assemble into multimorphological aggregates in water. The calix[4]arene moieties with a cavity <1 nm on the hydrophilic/hydrophobic interface of these aggregates may provide potential opportunities to entrap guest molecules for special applications in supermolecular science. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and properties of amphiphilic and biodegradable poly(ε‐caprolactone‐co‐glycidol) copolymers

We have synthesized poly(ε‐caprolactone‐co‐tert‐butyl glycidyl ether) (CL‐co‐BGE) statistical copolymers using 1‐tert‐butyl‐4,4,4‐tris(dimethylamino)‐2,2‐bis [tris(dimethylamino)phophoranylidenamino]‐2Λ5,4Λ5‐catenadi(phosphazene) (t‐BuP₄) as the catalyst. The hydrolysis of the resulting polymers yields amphiphilic poly(ε‐caprolactone‐co‐glycidol) (CL‐co‐GD) copolymers. By use of the quartz crystal microbalance with dissipation (QCM‐D), we have investigated the enzymatic degradation of the copolymers. It is shown that the degradation rate increases with the content of hydrophilic (GD) units. (3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide) (MTT) assay experiments demonstrate that the CL‐co‐GD copolymers have low cytotoxicity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 846–853