Synthesis of Thermo‐Responsive Polymers With Both Tunable UCST and LCST

New water‐soluble block copolymers of 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO₂MA), oligo(ethylene glycol) methacrylate (OEGMA), and N‐(3‐(dimethylamino) propyl) methacrylamide (DMAPMA) (poly(OEGMA‐co‐MEO₂MA)‐b‐poly(DMAPMA)) were prepared via sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization. Selective quaternization of poly(DMAPMA) block gives poly(OEGMA‐co‐MEO₂MA)‐b‐poly((3‐[N‐(3‐methacrylamidopropyl)‐N,N‐dimethyl]ammoniopropane sulfonate)‐co‐N‐(3‐(dimethylamino) propyl) methacrylamide), such block copolymer exhibits double thermo‐responsive behavior in water, poly(MEO₂MA‐co‐OEGMA) block shows a lower critical solution temperature (LCST), and poly((3‐[N‐(3‐methacrylamidopropyl)‐N,N‐dimethyl]ammoniopropane sulfonate)‐co‐N‐(3‐(dimethylamino) propyl) methacrylamide) block shows a upper critical solution temperature (UCST). Both of LCST and UCST can be controlled: LCST could be tuned by the fraction of OEGMA units in poly(OEGMA‐co‐MEO₂MA), and UCST was found to be dependent on the degree of quaternization (DQ).

     

Water‐soluble,thermoresponsive, hyperbranched copolymers based on PEG‐methacrylates: Synthesis,characterization, and LCST behavior

A series of water‐soluble thermoresponsive hyperbranched copoly(oligoethylene glycol)s were synthesized by copolymerization of di(ethylene glycol) methacrylate (DEG‐MA) and oligo(ethylene glycol) methacrylate (OEG‐MA, M_w = 475 g/mol), with ethylene glycol dimethacrylate (EGD‐MA) used as the crosslinker, via reversible addition fragmentation chain transfer polymerization. Polymers were characterized by size exclusion chromatography and nuclear magnetic resonance analyses. According to the monomer composition, that is, the ratio of OEG‐MA: DEG‐MA: EGD‐MA, the lower critical solution temperature (LCST) could be tuned from 25 °C to 90 °C. The thermoresponsive properties of these hyperbranched copolymers were studied carefully and compared with their linear analogs. It was found that molecular architecture influences thermoresponsive behavior, with a decrease of around 5–10 °C in the LCST of the hyperbranched polymers compared with the LCST of linear chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2783–2792, 2010     

Synthesis and micellization of thermoresponsive galactose‐based diblock copolymers

Thermoresponsive double hydrophilic diblock copolymers poly(2‐(2′‐methoxyethoxy)ethyl methacrylate‐co‐oligo(ethylene glycol) methacrylate)‐b‐poly(6‐O‐methacryloyl‐D ‐galactopyranose) (P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP) with various compositions and molecular weights were obtained by deprotection of amphiphilic diblock copolymers P(MEO₂MA‐co‐OEGMA)‐b‐poly(6‐O‐methacryloyl‐1,2:3,4‐di‐O‐isopropylidene‐D ‐galactopyranose) (P(MEO₂MA‐co‐OEGMA)‐b‐PMAlpGP), which were prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization using P(MEO₂MA‐co‐OEGMA) as macro‐RAFT agent. Dynamic light scattering and UV–vis studies showed that the micelles self‐assembled from P(MEO₂MA‐co‐OEGMA)‐b‐PMAlpGP were thermoresponsive. A hydrophobic dye Nile Red could be encapsulated by block copolymers P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP upon micellization and released upon dissociation of the formed micelles under different temperatures. The galactose functional groups in the PMAGP block have specific interaction with HepG2 cells, and P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP has potential applications in hepatoma‐targeting drug delivery and biodetection. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Atomistic insights on the LCST behavior of PMEO2MA in water by molecular dynamics simulations

Fully atomistic molecular dynamics simulations of poly(2‐[2‐methoxyethoxy]ethyl methacrylate) (PMEO₂MA) in water at temperatures below and above its lower critical solution temperature (LCST) were performed to improve the understanding of its LCST behavior. Atomic trajectories were used to calculate various structural and dynamic properties. Simulation results show that PMEO₂MA undergo a distinct coil‐to‐globule transition above LCST. Detailed analyses of the number of first hydration shell water molecules around various atomic regions are revealed that the water solubility of PMEO₂MA below LCST is mainly provided by the hydrophobic hydration around the side chain carbon atoms. This is achieved by the cage‐like water network formations which are disrupted when the temperature is increased above LCST, accompanied by significant amount of water molecule release and local water‐ordering reduction, which leads to the LCST phase transition. Furthermore, other analyses such as the number of hydrogen bonds and hydrogen bond lifetimes suggest that intermolecular hydrogen bondings between polymer and water molecules have little effect on the phase transition. Our results will contribute to a better understanding on the LCST phase transition of oligo(ethylene glycol) methyl ether methacrylate (OEGMA)‐based homopolymers at atomistic level that will be useful when designing homo‐ and co‐polymers of OEGMAs with desired properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 429–441     

Temperature‐induced phase transition of poly(N‐n‐propylacrylamide‐co‐butyl methacrylate‐co‐N,N‐diethylaminoethyl methacrylate)

Terpolymers composed of N‐n‐propylacrylamide (NPAAm), butyl methacrylate (BMA), and N,N‐diethylaminoethyl methacrylate (DEAEMA) were prepared in an attempt to investigate the temperature‐induced phase transition and its mechanism. Poly(NPAAm) showed the lower critical solution temperature (LCST) around 24°C in water. With the incorporation of DEAEMA with NPAAm, the LCST change was characterized by an initial increase. However, the LCST was shifted to the lower temperature at the later stage. This might be explained in terms of hydrophilic/hydrophobic contribution of DEAEMA to the LCST. The swelling behavior of copolymer gel in the various solvents and spin‐lattice relaxation time (T₁) study by NMR strongly suggested the hydrophilic/hydrophobic contribution of DEAEMA to the LCST depending on the local environment. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1407–1411, 1999     

Designing catechol‐end functionalized poly(DMAm‐co‐NIPAM) by RAFT with tunable LCSTs

Providing catechol‐end functionality to controlled structure lower critical solution temperature (LCST) copolymers is attractive, given the versatility of catechol chemistry for tethering to nanostructures. Controlled polymer chain lengths with catechol RAFT end groups are of interest to provide tunable LCST behavior to nanoparticles, although these polymerizations are relatively unexplored. Herein, the reactivity ratios for the RAFT copolymerization of N,N‐dimethylacrylamide (DMAm) and N‐isopropylacrylamide (NIPAM) pairs based on catechol‐end RAFT agents using an in situ NMR technique were first determined. Several catechol‐end poly(DMAm‐co‐NIPAM) samples were then prepared using the RAFT agent to provide copolymer. The reactivity ratios for the DMAm‐NIPAM pair were r_DMAm = 1.28–1.31 and r_NIPAM = 0.48–0.51. All the poly(DMAm‐co‐NIPAM) samples were found to have M_n values ≤ 26 kDa and Ð < 1.08 with LCST values ranging from 31 to 92°C, while maintaining a short range of glass transition temperature (T_g = 118–137°C). The difference in LCST values for the catechol functionalized poly(DMAm‐co‐NIPAM) based on 0.5 wt% aqueous buffered solutions at pH 5.5 and 8.5 was found to be <3.0°C. These conditions are suitable for subsequent catechol‐induced coordination and nucleophilic addition chemistry for covalent and noncovalent linkages during subsequent post‐modification. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 4062–4070     

pH and temperature responsiveness in AgNPs stabilized by a new poly(vinylidene fluoride) random graft copolymer

Poly(vinylidene fluoride)(PVDF)‐graft‐random copolymers(PD) of diethyleneglycol methylether methacrylate(MeO₂MA) and dimethylaminoethyl methacrylate(DMAEMA) are synthesized by a combined atom transfer radical coupling and atom transfer radical polymerization technique at three different co‐monomer compositions. The molar ratio of MeO₂MA to DMAEMA in PD are measured to be 1:5.8, 1:1.3, and 1:0.5 for PD1, PD2, and PD3 graft copolymers. In PD2 the feed ratio and mole ratio are same indicating an azeotropic composition causing highest yield (89%) and highest molecular weight (9.29 × 10⁵). The grafted chains of PD are temperature and pH responsive and in basic pH they show a sudden increase in size above certain temperature for LCST‐type phase transition, however, this is not observed at pH 4 and 7. PD can generate AgNPs under UV irradiation and morphology of PD at 30 °C varies with pH from vesicle to nanosphere. The AgNPs lie on the surface of the vesicles or assemble with the PD chains forming nanosphere morphology. At different pH, PD samples exhibit plasmon peaks at different wavelengths attributed to various size, shapes and cluster formation. The UV–vis spectra of AgNPs stabilized by PD1 and PD2 samples exhibits similar LCST‐type phase transition as observed above, but that of PD3 does not show any such transition. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 960–970     

Tuning the low critical solution temperature of polymer brushes grafted on single‐walled carbon nanotubes and temperature dependent loading and release properties

A nondestructive method was developed for grafting and retrieving polymer brushes from single‐walled carbon nanotubes (SWCNT)s based on mussel‐inspired chemistry. Thermo‐responsive polymer brushes were grafted on SWCNTs by coating the tubes with polydopamine as a reactive underlayer and sequential surface‐initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate (OEGMA, M_n = 475) and 2‐(2'‐methoxyethoxy)ethyl methacrylate (MEO2MA). Copolymer brushes were retrieved from the SWCNTs using 1 M NaOH to destroy the crosslinked polydopamine coating, and after that, the pristine properties of the SWCNTs were preserved. The low critical solution temperature (LCST) and molecular weight of the copolymer were measured using a nephelometer and gel permeation chromatograph, respectively. The loading and release behavior of Rhodamine 6G on responsive polymer‐grafted SWCNTs demonstrates that the copolymer brushes confer the SWCNTs an LCST dependence. This method can accurately confirm the molecular weights and polydispersity of stimuli‐responsive polymers grafted on any other nanoparticles and predict their controlled release behavior. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1807–1814     

Miscibility of poly(styrene‐co‐butyl acrylate) with poly(ethyl methacrylate): Existence of both UCST and LCST

A miscible homopolymer–copolymer pair viz., poly(ethyl methacrylate) (PEMA)–poly(styrene‐co‐butyl acrylate) (SBA) is reported. The miscibility has been studied using differential scanning calorimetry. While 1 : 1 (w/w) blends with SBA containing 23 and 34 wt % styrene (ST) become miscible only above 225 and 185 °C respectively indicating existence of UCST, those with SBA containing 63 wt % ST is miscible at the lowest mixing temperature (i.e., T_g's) but become immiscible when heated at ca 250 °C indicating the existence of LCST. Miscibility for blends with SBA of still higher ST content could not be determined by this method because of the closeness of the T_g's of the components. The miscibility window at 230 °C refers to the two copolymer compositions of which one with the lower ST content is near the UCST, while the other with the higher ST content is near the LCST. Using these compositions and the mean field theory binary interaction parameters between the monomer residues have been calculated. The values are χ_ST‐BA = 0.087 and χ_EMA‐BA = 0.013 at 230 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 369–375, 2000     

Biodegradable thermo‐ and pH‐responsive hydrogels for oral drug delivery

In this article, novel smart hydrogels based on biodegradable pH sensitive poly(L ‐glutamic acid‐g‐2‐hydroxylethyl methacrylate) (PGH) chains and temperature‐sensitive hydroxypropylcellulose‐g‐acrylic acid (HPC‐g‐AA) segments were designed and synthesized. The influence of pH and temperature on the equilibrium swelling ratios of the hydrogels was discussed. The optical transmittance of the hydrogels was also changed as a function of temperature, which reflecting that the HPC‐g‐AA part of the hydrogels became hydrophobic at the temperature above the lower critical solution temperature (LCST). At the same time, the LCST of the hydrogels had a visible pH‐dependent behavior. Scanning electron microscopic analysis revealed the morphology of the hydrogels before and after enzymatic degradation. The biodegradation rate of the hydrogels was directly related to the PGH content and the pH value. The in vitro release of bovine serum albumin from the hydrogels were investigated. The release profiles indicated that both the HPC‐g‐AA and PGH contents played important roles in the drug release behaviors. These results show that the smart hydrogels seem to be of great promise in pH–temperature oral drug delivery systems. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Temperature‐induced aggregation of the copolymers of N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate in aqueous solutions

A series of random copolymers of N‐isopropylacrylamide (NIPAM) and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate (AMPS) was synthesized by free‐radical copolymerization. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol %. The lower critical‐solution temperature (LCST) of copolymers in water increased strongly with an increasing content of AMPS. The influence of polymer concentration on the LCST of the copolymers was studied. For the copolymers with a higher AMPS content, the LCST decreased faster with an increasing concentration than for copolymers with a low content of AMPS. For a copolymer containing 1.1 mol % of AMPS the LCST dropped by about 3 °C when the concentration increased from 1 to 10 g/L, whereas for a copolymer containing 9.6 mol % of AMPS the LCST dropped by about 10 °C in the concentration range from 2 to 10 g/L. It was observed that the ionic strength of the aqueous polymer solution very strongly influences the LCST. This effect was most visible for the copolymer with the highest content of AMPS (9.6 mol %) for which an increase in the ionic strength from 0.2 to 2.0 resulted in a decrease in the LCST by about 27 °C (from 55 to 28 °C), whereas for the copolymer containing 1.1 mol % of AMPS the LCST decreased only by about 6 °C (from 37 to 31 °C) when the ionic strength increased from 0.005 to 0.3. The reactivity ratios for the AMPS and NIPAM monomer pairs were determined using different methods. The values of r_AMPS and r_NIPAM obtained were 11.0–11.6 and 2.1–2.4, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2784–2792, 2001     

A new thermo‐responsive block copolymer with tunable upper critical solution temperature and lower critical solution temperature in the alcohol/water mixture

The multi‐thermo‐responsive block copolymer of poly[2‐(2‐methoxyethoxy)ethyl methacrylate]‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PMEO₂MA‐b‐PVEA) displaying phase transition at both the lower critical solution temperature (LCST) and the upper critical solution temperature (UCST) in the alcohol/water mixture is synthesized by reversible addition‐fragmentation chain transfer polymerization. The poly[2‐(2‐methoxyethoxy)ethyl methacrylate] (PMEO₂MA) block exhibits the UCST phase transition in alcohol and the LCST phase transition in water, while the poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PVEA) block shows the UCST phase transition in isopropanol and the LCST phase transition in the alcohol/water mixture. Both the polymer molecular weight and the co‐solvent/nonsolvent exert great influence on the LCST or UCST of the block copolymer. By adjusting the solvent character including the water content and the temperature, the block copolymer undergoes multiphase transition at LCST or UCST, and various block copolymer morphologies including inverted micelles, core‐corona micelles, and corona‐collapsed micelles are prepared. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4399–4412     

Thermo‐ and pH‐responsive gradient and block copolymers based on 2‐(2‐methoxyethoxy)ethyl methacrylate synthesized via atom transfer radical polymerization and the formation of thermoresponsive surfaces

A series of gradient and block copolymers, based on 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO₂MA) and tert‐butyl acrylate (^tBA), were synthesized by atom transfer radical polymerization (ATRP) in a first step. The MEO₂MA monomer leads to the production of thermosensitive polymers, exhibiting lower critical solution temperature (LCST) at around room temperature, which could be adjusted by changing the proportion of ^tBA in the copolymer. In a second step, the tert‐butyl groups of ^tBA were hydrolyzed with trifluoroacetic acid to form the corresponding block and gradient copolymers of MEO₂MA and acrylic acid (AA), which exhibited both temperature and pH‐responsive behavior. These copolymers showed LCST values strongly dependent on the pH. At acid pH, a slightly decrease of LCST with an increase of AA in the copolymer was observed. However, at neutral or basic conditions, ionization of acid groups increases the hydrophilic balance considerably raising the LCST values, which even become not observable over the temperature range under study. In the last step, these carboxylic functionalized copolymers were covalently bound to biocompatible and biodegradable films of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(HB‐co‐HHx)] obtained by casting and, previously treated with ethylenediamine (ED) to render their surfaces with amino groups. Thereby, thermosensitive surfaces of modified P(HB‐co‐HHx) could be obtained. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

NMR investigation of effect of dissolved salts on the thermoresponsive behavior of oligo(ethylene glycol)‐methacrylate‐based polymers

The synthesis of thermo‐ and ionic‐responsive copolymers based on polyethylene glycol methyl ether methacrylate (OEGMA) and 2,2,2‐trifluoroethyl acrylate (TFEA) via reversible addition‐fragmentation chain transfer polymerization is described. Reactivity ratios for the copolymerization of OEGMA and TFEA are r_OEGMA = 2.46 and r_TFEA = 0.22, indicating that OEGMA is incorporated more rapidly than TFEA monomers. The copolymers are thermosensitive and exhibit volume phase transitions (lower critical solution behavior) at temperature, which depend on copolymer composition and the presence of added salts in the aqueous solutions. It was found that the copolymers exhibited LCST transitions at temperatures below 353 K only in salt solutions. ¹H NMR measurements indicated that motion of the protons located in and near the hydrophobic main chain are more sensitive to temperature than protons in the hydrophilic OEGMA side chains. The hydrophilic side chains remain largely hydrated; however, the presence of two distinct conformations of the terminal groups of the side chains was confirmed. The influence of OEGMA side chain length, copolymer composition, and salt type on aggregation behavior and dynamics was examined in detail. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2375–2385     

Amphiphilic silica/fluoropolymer nanoparticles: Synthesis,tem‐responsive and surface properties as protein‐resistance coatings

A series of amphiphilic silica/fluoropolymer nanoparticles of SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) were prepared by silica surface‐initiating atom transfer radical polymerization (SI‐ATRP) of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and poly dodecafluoroheptyl methacrylate (P12FMA). Their amphiphilic behavior, lower critical solution temperature (LCST), and surface properties as protein‐resistance coatings were characterized. The introduction of hydrophobic P(12FMA) block leads SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) to form individual spherical nanoparticles (～150 nm in water and ～170 nm in THF solution) as P(PEGMA)‐b‐P(12FMA) shell grafted on SiO₂ core (～130 nm), to gain obvious lower LCST at 36–52 °C and higher thermostability at 290–320 °C than SiO₂‐g‐P(PEGMA) (LCST = 78–90 °C, T_d = 220 °C). The water‐casted SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) films obtain much rougher surface (125.3–178.4 nm) than THF‐casted films (11.5–16.9 nm) and all SiO₂‐g‐P(PEGMA) films (26.8–31.3 nm). Therefore, the water‐casted surfaces exhibit obvious higher water adsorption amount (Δf = ?494 ～ ?426 Hz) and harder adsorbed layer (viscoelasticity of ΔD/Δf = ?0.28 ～ ?0.36 × 10^?6/Hz) than SiO₂‐g‐P(PEGMA) films, but present loser adsorbed layer than THF‐casted films (ΔD/Δf = ?0.29 ～ ?0.63 × 10^?6/Hz). While, the introduction of P(12FMA) segments does not show obviously reduce in the protein‐repelling adsorption of SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) films (△f = ?15.7 ～ ?22.3 Hz) compared with SiO₂‐g‐P(PEGMA) films (△f = ?8.3 ～ ?11.3 Hz) and no obvious influence on water adsorption of ancient stone. Therefore, SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) is suggested to be used as protein‐resistance coatings. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 381–393     

Poly(ether tert‐amine): A novel family of multiresponsive polymer

A novel multiresponsive poly(ether tert‐amine) (PEA) was synthesized by nucleophilic addition/ring‐opening reaction of commercial poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), and di‐epoxy and di‐amine monomer. The process of synthesis was very simple and green in ethanol as reactive media. These PEAs exhibit sharp response to temperature, pH, and ionic strength, with adjustable and sharp phase transitions in the range of 27–100 °C. The lower critical solution temperature (LCST) of PEA's aqueous solution presents a linear relationship to the PEO content (y = 35.7 + x), indicating well‐tunable LCST. The concentration of PEA has no obvious effect on LCST. Therefore, PEA will be potential in applications of drug delivery, separation, and biotechnology. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1292–1297, 2009     

Synthesis,self‐assembly,and thermosensitivity of amphiphilic POEGMA‐PDMS‐POEGMA triblock copolymers

In this article, the synthesis and self‐assembly of a novel well‐defined biocompatible amphiphilic POEGMA‐PDMS‐POEGMA triblock copolymer were studied. The copolymer was synthesized by atom transfer radical polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) using α,ω‐dibromo polydimethylsiloxane macroinitiator (Br‐PDMS‐Br). Br‐PDMS‐Br was synthesized through the esterification of α,ω‐hydroxypropyl polydimethylsiloxane and 2‐bromoisobutyryl bromide. The structures of the copolymers were confirmed by proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The copolymers showed reversible aggregation in response to temperature cycles with a lower critical solution temperature (LCST) between 61 and 66 °C, as determined by ultraviolet‐visible spectrophotometry and dynamic light scattering. The LCST values increased in proportion to the length of the hydrophilic block and were lower than that of the POEGMA homopolymer. The self‐assembly behavior of the copolymers in aqueous solution was investigated by fluorescence spectroscopy and transmission electron microscopy. The critical micelle concentration value (1.08–0.26 10^?6 mol L^?1) decreased as the length of the POEGMA chain increased. The POEGMA‐PDMS‐POEGMA copolymers can easily self‐assemble into spherical micelles in aqueous solution. Such biocompatible block copolymers may be attractive candidates as ‘‘smart'' thermo‐responsive drug delivery systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2684‐2691     

Hydrophilic CO2‐based biodegradable polycarbonates: Synthesis and rapid thermo‐responsive behavior

Common CO₂‐based biodegradable polycarbonates like poly(propylene carbonate) or poly(cyclohexene carbonate) are generally hydrophobic, leading to slow biodegradation rate and poor cell adhesion, which limit their applications in the biomedical field. Here hydrophilic polycarbonates were prepared by one‐pot terpolymerization of CO₂, propylene oxide (PO), and 2‐((2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)methyl)oxirane (ME₃MO) using binary Salen Co(III)‐Cl/PPNCl catalyst system. The resultant terpolymers showed one glass transition temperature (T_g), which decreased with the increase of ME₃MO units in the terpolymers (F_ME3MO). Water contact angles of the resultant terpolymers with F_ME3MO of 4.2?23.6% were 68?25°, while that of poly(propylene carbonate) was 90°, indicating that the terpolymers became hydrophlilic. Furthermore, the terpolymers with F_ME3MO more than 25.8% exhibited reversible and rapid thermo‐responsive property in water, and the lower critical solution temperature (LCST) was highly sensitive to F_ME3MO. In particular, aqueous solution of the terpolymer with F_ME3MO of 72.6% showed a LCST around 35.2 °C, close to body temperature, which was promising for biomedical applications, especially for in vivo applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2834–2840.     

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