Synthesis,self‐assembly,fluorescence, and thermosensitive properties of star‐shaped amphiphilic copolymers with porphyrin core

Star‐shaped amphiphilic poly(ε‐caprolactone)‐block‐poly(oligo(ethylene glycol) methyl ether methacrylate) with porphyrin core (SPPCL‐b‐POEGMA) was synthesized by combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Star‐shaped PCL with porphyrin core (SPPCL) was prepared by bulk polymerization of ε‐caprolactone (CL) with tetrahydroxyethyl‐terminated porphyrin initiator and tin 2‐ethylexanote (Sn(Oct)₂) catalyst. SPPCL was converted into SPPCLBr macroinitiator with 2‐bromoisobutyryl bromide. Star‐shaped SPPCL‐b‐POEGMA was obtained via ATRP of oligo(ethylene glycol) methyl ether methacrylate (OEGMA). SPPCL‐b‐POEGMA can easily self‐assemble into micelles in aqueous solution via dialysis method. The formation of micellar aggregates were confirmed by critical micelle formation concentration, dynamic light scattering, and transmission electron microscopy. The micelles also exhibit property of temperature‐induced drug release and the lower critical solution temperature (LCST) was 60.6 °C. Furthermore, SPPCL‐b‐POEGMA micelles can reversibly swell and shrink in response to external temperature. In addition, SPPCL‐b‐POEGMA can present obvious fluorescence. Finally, the controlled drug release of copolymer micelles can be achieved by the change of temperatures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Dual‐responsive supramolecular inclusion complexes of block copolymer poly(ethylene glycol)‐block‐poly[(2‐dimethylamino)ethyl methacrylate] with α‐cyclodextrin

A new class of temperature and pH dual‐responsive and injectable supramolecular hydrogel was developed, which was formed from block copolymer poly(ethylene glycol)‐block‐poly[(2‐dimethylamino)ethyl methacrylate] (PEG‐b‐PDMAEMA) and α‐cyclodextrin (α‐CD) inclusion complexes (ICs). The PEG‐b‐PDMAEMA diblock copolymers with different ratio of ethylene glycol (EG) to (2‐dimethylamino)ethyl methacrylate (DMAEMA) (102:46 and 102:96, respectively) were prepared by atom transfer radical polymerization (ATRP). ¹H NMR measurement indicated that the ratio of EG unit to α‐CD in the resulted ICs was higher than 2:1. Thermal analysis showed that thermal stability of ICs was improved. The rheology studies showed that the hydrogels were temperature and pH sensitive. Moreover, the hydrogels were thixotropic and reversible. The self‐assembly morphologies of the ICs in different pH and ionic strength environment were studied by transmission electron microscopy. The formed biocompatible micelles have potential applications as biomedical and stimulus‐responsive material. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2143–2153, 2010     

Well‐defined succinylated chitosan‐O‐poly(oligo(ethylene glycol)methacrylate) for pH‐reversible shielding of cationic nanocarriers

A novel type of well‐defined graft copolymer, succinylated chitosan‐O‐poly(oligo(ethylene glycol)methacrylate) (SC‐POEGMA), was developed for pH‐reversible poly(ethylene glyocol) (PEG) shielding of cationic nanocarriers. Chitosan‐O‐POEGMA (CS‐POEGMA) was first synthesized via single electron transfer‐living radical polymerization of oligo(ethylene glyol) methacrylate (OEGMA) using O‐brominated chitosan (CS‐Br) as a macromolecular initiator and Cu(I)Br/1,1,4,7,10,10‐hexamethyltriethylenetetramine as a catalyst. The subsequent succinylation of the chitosan backbone gave the titled copolymers. The content of POEGMA in CS‐POEGMA could be widely modulated by varying the degree of bromination and feed ratio of OEGMA to CS‐Br, without compromising the amino density of chitosan backbone. The hierarchical assembly between SC‐POEGMA and trimethylated chitosan‐O‐poly(ε‐caprolactone) (TMC‐PCL) micelles was further studied. At pH 7.4, the stoichiometric interactions between SC and TMC segments to form polyampholyte–polyelectrolyte complexes led to the formation of PEG‐shielded micelles. The hierarchially assembled micelles could be disassembled into the pristine TMC‐PCL micelles, when the medium pH was below a certain pH (pH_φ). By varying the degree of succinylation of SC‐POEGMA, the pH_φ value could be facilely modulated from 6.5 to 3.5 to meet the needs for specific biomedical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and self‐assembling of poly(N‐isopropylacrylamide‐block‐poly(L‐lactide)‐block‐poly(N‐isopropylacrylamide) triblock copolymers prepared by combination of ring‐opening polymerization and atom transfer radical polymerization

Novel thermo‐responsive poly(N‐isopropylacrylamide)‐block‐poly(l ‐lactide)‐block‐poly(N‐isopropylacylamide) (PNIPAAm‐b‐PLLA‐b‐PNIPAAm) triblock copolymers were successfully prepared by atom transfer radical polymerization of NIPAAm with Br‐PLLA‐Br macroinitiator, using a CuCl/tris(2‐dimethylaminoethyl) amine (Me₆TREN) complex as catalyst at 25 °C in a N,N‐dimethylformamide/water mixture. The molecular weight of the copolymers ranges from 18,000 to 38,000 g mol^?1, and the dispersity from 1.10 to 1.28. Micelles are formed by self‐assembly of copolymers in aqueous medium at room temperature, as evidenced by ¹H NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The critical micelle concentration determined by fluorescence spectroscopy ranges from 0.0077 to 0.016 mg mL^?1. ¹H NMR analysis in selective solvents confirmed the core‐shell structure of micelles. The copolymers exhibit a lower critical solution temperature (LCST) between 32.1 and 32.8 °C. The micelles are spherical in shape with a mean diameter between 31.4 and 83.3 nm, as determined by TEM and DLS. When the temperature is raised above the LCST, micelle size increases at high copolymer concentrations due to aggregation. In contrast, at low copolymer concentrations, decrease of micelle size is observed due to collapse of PNIPAAm chains. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3274–3283     

Size and morphology controllable core cross‐linked self‐aggregates from poly(ethylene glycol‐b‐succinimide) copolymers

We developed a simple route to prepare stabilized micelles and nanovesicles in aqueous solutions. A hydrophobic poly(succinimide) (PSI) was conjugated with the hydrophilic poly(ethylene glycol) (PEG) as a new type of cross‐linkable unit. Spherical aggregates were formed when dissolving the amphiphilic PEG₆₈₂‐b‐PSI₁₃₀ copolymer in aqueous solutions directly, and polymer nanovesicles were prepared by a precipitation‐dialysis method using PEG₄₅₅‐b‐PSI₁₃₀ copolymer. Bifunctional primary amine was added to the micelle or nanovesicle solutions to prepare cross‐linked structures via aminolysis reaction of the succinimide units. The degree of cross‐linking was controlled by adjusting the molar ratio of the cross‐linker to the succinimide units. Increasing the degree of cross‐linking leads to the compaction of the micelle core thus reduced diameter. The cross‐linked polymer micelles or nanovesicles maintained their morphology in extremely diluted solutions because of their structural stability. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and self‐association behavior of poly[bis(2‐(2‐methoxyethoxy)ethoxy)phosphazene]‐b‐poly(propyleneglycol) triblock copolymers

Amphilic triblock copolymers with varying ratios of hydrophilic poly[bis (methoxyethoxyethoxy)phosphazene] (MEEP) and relatively hydrophobic poly(propylene glycol) (PPG) blocks were synthesized via the controlled cationic‐induced living polymerization of a phosphoranimine (Cl₃P?NSiMe₃) at ambient temperature. A PPG block can function as either a classical hydrophobic block or a less hydrophobic component by varying the nature of a phosphazene block. The aqueous phase behavior of MEEP‐PPG‐MEEP block copolymers was investigated using fluorescence techniques, TEM, and dynamic light scattering (DLS). The critical micelle concentrations (cmcs) of MEEP‐PPG‐MEEP block copolymers were determined to be in the range of 3.7–16.8 mg/L. The mean diameters of MEEP‐PPG‐MEEP polymeric micelles, measured by DLS, were between 31 and 44 nm. The equilibrium constants of pyrene in these micelles ranged from 4.7 × 10⁴ to 9.6 × 10⁴. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 692–699, 2009     

Synthesis and characterization of a biodegradable amphiphilic copolymer based on branched poly(ϵ‐caprolactone) and poly(ethylene glycol)

A novel biodegradable amphiphilic copolymer with hydrophobic poly(ε‐caprolactone) branches containing cholic acid moiety and a hydrophilic poly(ethylene glycol) chain was synthesized. The copolymer was characterized by FTIR, ¹H NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), polarizing light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD) analysis. The amphiphilic copolymer could self‐assemble into micelles in an aqueous solution. The critical micelle concentration of the amphiphilic copolymer was determined by fluorescence spectroscopy. A nanoparticle drug delivery system with a regularly spherical shape was prepared with high encapsulation efficiency. The in vitro drug release from the drug‐loaded polymeric nanoparticles was investigated. Because of the branched structure of the hydrophobic part of the copolymer and the relatively fast degradation rate of the copolymer, an improved release behavior was observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5256–5265, 2007     

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     

Poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ϵ‐caprolactone) triblock copolymers: Synthesis and self‐assembly in aqueous solutions

Nontoxic and biodegradable poly(?‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(?‐caprolactone) triblock copolymers were synthesized by the solution polymerization of ?‐caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with ¹H NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol–gel‐transition behaviors were investigated. The experimental results showed that the unimer‐to‐micelle transition did occur. In a sol–gel‐transition phase diagram obtained by the vial‐tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(?‐caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25–55 °C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 × 10^?4 g/mL, whereas necklace‐like and worm‐like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 605–613, 2007     

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     

Photoresponsive biodegradable poly(carbonate)s with pendent o‐nitrobenzyl ester

Photoresponsive amphiphilic diblock poly(carbonate)s mPEG₁₁₃‐b‐PMNC_n with pendent o‐nitrobenzyl ester group were synthesized through ring‐opening polymerization (ROP) using 1,8‐diazabi‐cyclo[5.4.0]undec‐7‐ene (DBU) as catalyst and monomethoxy poly(ethylene glycol) (mPEG) as macroinitiator. In aqueous solution, the copolymers can self‐assemble to spherical micelles with a PC core and a PEG shell. The critical micelle concentration (CMC), size, and morphology of the micelles were demonstrated by means of fluorescence spectroscopy, transmission electron microscopes (TEM), and dynamic light scattering (DLS). Under UV light irradiation, the amphiphilic copolymer micelles disassembled because of the photocleavage of o‐NB ester, and the light‐controlled release behaviors of payload Nile red were further proved. This study provides a convenient way to construct smart poly(carbonate)s nanocarriers for controlled drug release. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2770–2780     

Temperature‐induced spontaneous sol–gel transitions of poly(D,L‐lactic acid‐co‐glycolic acid)‐b‐poly(ethylene glycol)‐b‐poly(D,L‐lactic acid‐co‐glycolic acid) triblock copolymers and their end‐capped derivatives in water

The spontaneous hydrogel formation of a sort of biocompatible and biodegradable amphiphilic block copolymer in water was observed, and the underlying gelling mechanism was assumed. A series of ABA‐type triblock copolymers [poly(D,L ‐lactic acid‐co‐glycolic acid)‐b‐poly(ethylene glycol)‐b‐poly(D,L ‐lactic acid‐co‐glycolic acid)] and different derivatives end‐capped by small alkyl groups were synthesized, and the aqueous phase behaviors of these samples were studied. The virgin triblock copolymers and most of the derivatives exhibited a temperature‐dependent reversible sol–gel transition in water. Both the poly(D,L ‐lactic acid‐co‐glycolic acid) length and end group were found to significantly tune the gel windows in the phase diagrams, but with different behaviors. The critical micelle concentrations were much lower than the associated critical gel concentrations, and an intact micellar structure remained after gelation. A combination of various measurement techniques confirmed that the sol–gel transition with an increase in the temperature was induced not simply via the self‐assembly of amphiphilic polymer chains but also via the further hydrophobic aggregation of micelles resulting in a micelle network due to a large‐scale self‐assembly. The coarsening of the micelle network was further suggested to account for the transition from a transparent gel to an opaque gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1122–1133, 2007     

Synthesis of amphiphilic block copolymer by metal‐free ring‐opening oligomerization of glycidyl phenyl ether initiated with tetra‐n‐butylammonium fluoride in the presence of poly(ethylene glycol) monomethyl ether

Metal‐free ring‐opening oligomerization of glycidyl phenyl ether (GPE) initiated with tetra‐n‐butylammonium fluoride (n‐Bu₄NF) (5.0 mol %) was performed in the presence of poly(ethylene glycol) monomethyl ether (PEGM) (5.0, 10, 20 mol %) as a chain transfer agent, by which the resulting polymers having narrow molecular weight distribution (M_w/M_n < 1.2) were obtained in 80–84% yield. Solubility of the obtained polymers in water increased with the increase of amount of PEGM, owing to an increase of number of PEGM‐block‐oligo(GPE) molecules compared to that of oligo(GPE) molecules having FCH₂– group at the initiating end as well as a decrease in degree of oligomerization of oligo(GPE). The PEGM‐block‐oligo(GPE) was isolated by filtration of the polymer aqueous solution, whose number‐average molecular weights determined by NMR spectroscopic analysis were almost consistent to the theoretical values. The PEGM‐block‐oligo(GPE) formed micelles in aqueous media, whose average particle diameter was 58 and 140 nm for the copolymers having a composition of PEGM:GPE = 62:38 and 53:47, respectively. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4451–4458     

Photocrosslinked poly(vinylbenzophenone)‐core micelles via mild Friedel–Crafts benzoylation of polystyrene amphiphiles

Photocrosslinkable poly(vinylbenzophenone)‐containing polymers were synthesized via a one‐step, Friedel–Crafts benzoylation of polystyrene‐containing starting materials [including polystyrene, polystyrene‐block‐poly(tert‐butyl acrylate), polystyrene‐block‐poly(ethylene oxide), polystyrene‐block‐poly(methyl methacrylate), and polystyrene‐block‐poly(n‐butyl acrylate)] with benzoyl trifluoromethanesulfonate as a benzoylation reagent. The use of this mild reagent (which required no added Lewis acid) permitted polymers with well‐defined compositions and narrow molecular weight distributions to be synthesized. Micelles formed from one of these benzoylated polymers, [polystyrene_0.25‐co‐poly(vinylbenzophenone)_0.75]₁₁₅‐block‐poly(acrylic acid)₁₄, were then fixed by the irradiation of the micelle cores with UV light. As the irradiation time was increased, the pendent benzophenone groups crosslinked with other chains in the glassy micelle cores. Dynamic light scattering, spectrofluorimetry, and Fourier transform infrared spectroscopy were all used to verify the progress of the crosslinking reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2604–2614, 2006     

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     

Synthesis and characterization of biodegradable A–B–A triblock copolymers containing poly(ϵ‐caprolactone) A blocks and poly(trans‐4‐hydroxy‐L‐proline) B blocks

Novel, biodegradable poly(?‐caprolactone)‐block‐poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline)‐block‐poly(?‐caprolactone) triblock copolymers were synthesized by ring‐opening polymerization from dihydroxyl‐terminated macroinitiator poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline) (PHpr) and ?‐caprolactone (?‐CL) with stannous octoate as the catalyst. The molecular weights were characterized with gel permeation chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. With an increase in the contents of ?‐CL incorporated into the copolymers, a decrease in the glass‐transition temperature (T_g) was observed. The T_g values of copoly(4‐phenyl‐?‐caprolactone) and copoly(4‐methyl‐?‐caprolactone) were higher than T_g of copoly(?‐caprolactone). Their micellar characteristics in an aqueous phase were investigated with fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The block copolymers formed micelles in the aqueous phase with critical micelle concentrations in the range of 1.00–1.36 mg L^?1. With higher molecular weights and hydrophobic components in the copolymers, a higher critical micelle concentration was observed. As the feed weight ratio of antitriptyline hydrochloride (AM) to the polymer increased, the drug loading increased. The micelles exhibited a spherical shape, and the average size was less than 250 nm. The in vitro hydrolytic degradation and controlled drug release properties of the triblock copolymers were also investigated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4268–4280, 2006     

Cancer‐associated pH‐responsive tetracopolymeric micelles composed of poly(ethylene glycol)‐b‐poly(L‐histidine)‐b‐poly(L‐lactic acid)‐b‐poly(ethylene glycol)

To create a novel vector for specifically delivering anticancer therapy to solid tumors, we used diafiltration to synthesize pH‐sensitive polymeric micelles. The micelles, formed from a tetrablock copolymer [poly(ethylene glycol)‐b‐poly(L ‐histidine)‐b‐poly(L ‐lactic acid)‐b‐poly(ethylene glycol)] consisted of a hydrophobic poly(L ‐histidine) (polyHis) and poly(L ‐lactic acid) (PLA) core and a hydrophilic poly(ethylene glycol) (PEG) shell, in which we encapsulated the model anticancer drug doxorubicin (DOX). The robust micelles exhibited a critical micellar concentration (CMC) of 2.1–3.5 µg/ml and an average size of 65–80 nm pH 7.4. Importantly, they showed a pH‐dependent micellar destabilization, due to the concurrent ionization of the polyHis and the rigidity of the PLA in the micellar core. In particular, the molecular weight of PLA block affected the ionization of the micellar core. Depending on the molecular weight of the PLA block, the micelles triggering released DOX at pH 6.8 (i.e. cancer acidic pH) or pH 6.4 (i.e. endosomal pH), making this system a useful tool for specifically treating solid cancers or delivering cytoplasmic cargo in vivo. Copyright © 2008 John Wiley & Sons, Ltd.     

Poly(L‐glutamic acid) grafted with oligo(2‐(2‐(2‐methoxyethoxy)ethoxy)ethyl methacrylate): Thermal phase transition,secondary structure,and self‐assembly

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     

Pendant groups fine‐tuning thermal gelation of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) aqueous solution

Novel poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) bearing pendant hydrophobic γ‐(carbamic acid benzyl ester) groups (PECB) and hydrophiphilic amino groups (PECN) were synthesized based on the functionalized comonomer γ‐(carbamic acid benzyl ester)‐ε‐caprolactone (CABCL). The thermal gelation behavior of the amphiphilic copolymer aqueous solutions was examined. The phase transition behavior could be finely tuned via the pendant groups, and an abnormal phenomenon occurred that the sol–gel transition temperature shifted to a higher temperature for PECB whereas a lower temperature for PECN. The micelles percolation was adopted to clarify the hydrogel mechanism, and the effect of the pendant groups on the micellization was further investigated in detail. The results demonstrated that the introduction of γ‐(carbamic acid benzyl ester) pendant groups significantly decreased the crystallinity of the copolymer micelles whereas amino pendant groups made the micelles easy to aggregate. Thus, the thermal gelation of PEG/PCL aqueous solution could be finely tuned by the pendant groups, and the pendant groups modified PEG/PCL hydrogels are expected to have great potential biomedical application. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2571–2581     

Synthesis,characterization, and properties of tunable thermosensitive amphiphilic dendrimer‐star copolymers with Y‐shaped arms

Novel and well‐defined amphiphilic dendrimer‐star copolymer poly(ε‐caprolactone)‐block‐(poly(2‐(2‐methoxyethoxy)ethylmethacrylate‐co‐oligo(ethylene glycol) methacrylate))₂ with Y‐shaped arms were synthesized by the combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The investigation of thermal properties and the analysis of crystalline morphology indicate that the high‐branched structure of dendrimer‐star copolymers with Y‐shaped arms and the presence of amorphous P(MEO₂MA‐co‐OEGMA) segments together led to the complete destruction of crystallinity of the PCL segments in the dendrimer‐star copolymer. In addition, the hydrophilicity–hydrophobicity transition of the dendrimer‐star copolymer film can be achieved by altering the external temperatures. The amphiphilic copolymers can self‐assemble into spherical nanomicelles in water. Because the lower critical solution temperature of the copolymers can be adjusted by varying the ratio of MEO₂MA and OEGMA, the tunable thermosensitive properties can be observed by transmittance, dynamic laser light scattering, and transmission electron microscopy (TEM). The release rate of model drug chlorambucil from the micelles can be effectively controlled by changing the external temperatures, which indicates that these unique high‐branched amphiphilic copolymers have the potential applications in biomedical field. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011