Kinetic analysis of surface‐initiated SET‐LRP of poly(N‐isopropylacrylamide)

The single‐electron transfer living radical polymerization (SET‐LRP) of N‐isopropylacrylamide (NIPAM) from silicon wafer modified with an initiator layer composed of 2‐bromopropionyl bromide (2‐BPB) fragments is described. The amount of Cu(0) generated in situ by the disproportination of Cu(I) to Cu(0) and Cu(II) in the presence of 2,2′‐bipyridine (2,2′‐bpy) ligand and N,N‐dimethylformamide (DMF) solvent at 90 °C is dependent on the ratio of [CuBr]/[CuBr₂]. By proper selection of the [CuBr]/[CuBr₂] ratio, well‐controlled SET‐LRP polymerization of NIPAM was observed such that the thickness of the layer consisting of chains grown from the surface increased linearly with the molecular weight of chains polymerized in solution in identical. In addition, the calculation of grafting parameters, including surface coverage, σ (mg/m²); grafting density, Σ (chain/nm²); and average distance between grafting sites, D (nm), from the number‐average molecular weight, M _n (g/mol), and ellipsometric thickness, h (nm), values indicated the synthesis of densely grafted poly(NIPAM) films and allowed us to predict a “brush‐like” conformation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and characterization of stimuli‐responsive porous/hollow nanoparticles by self‐assembly of chitosan‐based graft copolymers and application in drug release

In this research, stimuli‐responsive porous/hollow nanoparticles were prepared by the self‐assembly method. First, chitosan‐graft‐poly(N‐isopropylacrylamide) (CS‐g‐PNIPAAm) copolymers were synthesized through polymerization of N‐isopropylacrylamide (NIPAAm) monomer in the presence of chitosan (CS) solution using ceric ammounium nitrate as the initiator. Then, the CS‐g‐PNIPAAm copolymers were dissolved in the acetic acid aqueous solution and heated to 40 °C to induce their self‐assembly. After CS‐g‐PNIPAAm assembled to form micelles, a cross‐linking agent was used to reinforce the structure to form nanoparticles. The molecular weight of grafted PNIPAAm on CS chains was changed to investigate its effect on the structure, morphology, thermo‐, and pH‐responsive properties of the nanoparticles. TEM images showed that a porous or hollow structure in the interior of nanoparticles was developed, depending on the medium temperature. The synthesized nanoparticles carried positive charges on the surface and exhibited stimuli‐responsive properties, and their mean diameter thus could be manipulated by changing the pH value and temperature of the environment. The nanoparticles showed a continuous release of the encapsulated doxycycline hyclate up to 10 days during an in vitro release experiment. These porous/hollow particles with environmentally sensitive properties are expected to be used in hydrophilic drug delivery system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2377–2387, 2010     

Thermosensitive and control release behavior of poly (N‐isopropylacrylamide‐co‐acrylic acid) latex particles

In this work, poly(N‐isopropylacrylamide‐co‐acrylic acid) (poly(NIPAAm‐AA)) copolymer latex particles (microgels) were synthesized by the method of soapless emulsion polymerization. Poly(NIPAAm‐AA) copolymer microgels have the property of being thermosensitive. The concentration of acrylic acid (AA) and crosslinking agent N,N′‐methylenebisacrylamide were important factors to influence the lower critical solution temperature (LCST) of poly(NIPAAm‐AA) microgels. The effects of AA and crosslinking agent on the swelling behavior of poly(NIPAAm‐AA) microgels were also studied. The poly(NIPAAm‐AA) copolymer microgels were then used as a thermosensitive drug carrier to load caffeine. The effects of concentration of AA and crosslinking agent on the control release of caffeine were investigated. How the AA content and crosslinking agent influenced the morphology and LCST of the microgels was discussed in detail. The relationship of morphology, swelling, and control release behavior of these thermosensitive microgels was established. A new scheme was proposed to interpret the control release of the microgels with different morphological structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5734–5741, 2008     

Effect of the crosslinking level on the properties of temperature‐sensitive poly(N‐isopropylacrylamide) hydrogels

In this study, the effect of the level of crosslinking on the properties of poly(N‐isopropylacrylamide) (PNIPAAm) hydrogels was investigated in terms of their lower critical solution temperature (LCST), interior morphology, equilibrium swelling, and deswelling and swelling kinetics. The thermal analysis showed that PNIPAAm hydrogels, having a wide range of crosslinking levels, exhibited almost the same LCSTs, and this was different from what the conventional theory would have predicted. Scanning electron micrographs revealed that the interior network structure of the PNIPAAm matrix became more porous with an increase in the level of crosslinking. This more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to the external temperature changes during the deswelling process and the swelling process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 582–593, 2003     

Synthesis of a thermoresponsive shell‐crosslinked 3‐layer onion‐like polymer particle with a hyperbranched polyglycerol core

A novel thermoresponsive shell crosslinked three‐layer onion‐like polymer particles were prepared using hyperbranched polyglycerol (PG) as parents compound, the periphery hydroxyl groups of PG were transformed into trithiocarbonates (? SC(S)S? ) first; then, it was used as chain transfer agent to prepare star‐like block copolymer of N‐isopropyl acrylamide (NIPA) and N,N‐dimethylaminoethyl acrylate (DMA) in sequence via reversible addition fragmentation chain transfer (RAFT) process. Thus, a three‐layer polymer, PG? [SC(S)S? (DMA)? b? (NIPA)]_n, was obtained. The middle layer of poly(DMA) was then crosslinked with 1,8‐diiodoctane, and the resulting onion‐like three‐layer polymer showed a lower critical solution temperature (LCST) in water because of the outer layer of poly(NIPA). The LCST value only slightly depended on the crosslinking degree. Finally, the ? SC(S)S? were transformed into thiols by sequential treating with sodium borohydride and formic acid; thus, the core molecule was chemically detached from the crosslinked shell and a novel shell crosslinked polymer particle was obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5652–5660, 2005     

Novel thermo‐responsive self‐assembly micelles from a double brush‐shaped PNIPAM‐g‐(PA‐b‐PEG‐b‐PA)‐g‐PNIPAM block copolymer with PNIPAM polymers as side chains

A novel double brush‐shaped copolymer with amphiphilic polyacrylate‐b‐poly(ethylene glycol)‐b‐poly acrylate copolymer (PA‐b‐PEG‐b‐PA) as a backbone and thermosensitive poly(N‐isopropylacrylamide) (PNIPAM) long side chains at both ends of the PEG was synthesized via an atom transfer radical polymerization (ATRP) route, and the structure was confirmed by FTIR, ¹H NMR, and SEC. The thermosensitive self‐assembly behavior was examined via UV‐vis, TEM, DLS, and surface tension measurements, etc. The self‐assembled micelles, with low critical solution temperatures (LCST) of 34–38 ^°C, form irregular fusiform and/or spherical morphologies with single, double, and petaling cores in aqueous solution at room temperature, while above the LCST the micelles took on more regular and smooth spherical shapes with diameter ranges from 45 to 100 nm. The micelle exhibits high stabilities even in simulated physiological media, with low critical micellization concentration (CMC) up to 5.50, 4.89, and 5.05 mg L^?1 in aqueous solution, pH 1.4 and 7.4 PBS solutions, respectively. The TEM and DLS determination reveled that the copolymer micelle had broad size distribution below its LCST while it produces narrow and homogeneous size above the LCST. The cytotoxicity was investigated by MTT assays to elucidate the application potential of the as‐prepared block polymer brushes as drug controlled release vehicles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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     

Structured multistimuli‐responsive functional polymer surfaces obtained by interfacial diffusion of amphiphilic block copolymers

Herein, we report the preparation of structured multistimuli‐responsive surfaces able to change reversibly both their chemical composition depending on the environment and their surface behavior by varying either/both the pH or/and the temperature. For that purpose, we took advantage of the surface segregation in homopolymer/diblock copolymer blends, composed of either polystyrene‐block‐poly(N,N′‐dimethylaminoethylmethacrylate) (PS‐b‐PDMAEMA) or polystyrene‐block‐poly (N,N′‐diethylaminoethylmethacrylate) (PS‐b‐PDEAEMA) and high molecular weight polystyrene used as a matrix. The variations of the surface composition as a function of the environment of exposure (air or water vapor) was investigated were investigated by XPS and contact angle measurements. The water‐annealed surfaces contain PDMAEMA or PDEAEMA at the surface and are additionally able to respond both to pH and temperature as demonstrated by the Wilhelmy technique. Both PDMAEMA and PDEAEMA can switch from a hydrophilic state to a collapsed hydrophobic state increasing the temperature above the LCST. More interestingly, as a result of the microphase separation of the block copolymers at the interface, the surfaces of the blends exhibit structuration. Thus, either micellar structures or “donut‐like” morphologies were obtained by using THF or toluene, respectively, as solvent. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1952–1961, 2010     

Micro ATR‐FTIR study of the hydration state of poly(N‐tert‐butylacrylamide‐co‐acrylamide) copolymers during phase transition in aqueous media and in the mixture of water–methanol

Coil‐globule transition of poly(N‐tert‐butylacrylamide‐co‐acrylamide) P(NTBAM‐co‐AM) copolymers is investigated in the aqueous solution and in the mixture of water–methanol by micro ATR‐FTIR spectroscopy technique. In this study the microstructure and its changes in the hydration states of the distinct groups of these copolymers are investigated by micro ATR/FTIR technique. The results showed that by heating the solution above the LCST hydrogen bonding between C?O and water was decreased but the hydrogen bonding between polymeric chains increased, which prove the aggregation of polymer chain during phase separation. The chemical shifts of IR bands are also studied in the mixture of water–methanol. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 356–363, 2010     

Optical and two‐photon absorption analysis of radiation‐grafted fluoropolymer

Grafting by gamma irradiation has a significant influence on the dispersion properties of polymeric materials. Accordingly, we study the effect of grafting on the material electronic structure parameters such as the fundamental absorption edge and bandgap structure. The optical absorption of grafted polymeric films of poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA‐g‐PAAc) is determined in a very wide spectral range of 0.2–3 μm. The nonlinear two‐photon absorption coefficient is determined that showed an increase as a result to the grafting process. Moreover, a significant increase in the optical conductivity for the polymeric films is acquired after grafting. Positron annihilation spectroscopy is used to study polymer structure and volume size of nanoholes of Ps. The data revealed an increase of crosslinking with a smaller average volume size with grafting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2045–2051, 2010     

Thermosensitive polymer brush‐supported 4‐N,N‐dialkylaminopyridine on silica particles as catalyst for hydrolysis of an activated ester in aqueous buffers: Comparison of activity with linear polymer‐supported version and effect of LCST transition

We report on the synthesis of a thermosensitive polymer brush‐supported 4‐N,N‐dialkylaminopyridine catalyst and the comparison of its catalytic activity with the corresponding linear polymer‐supported version in the hydrolysis of p‐nitrophenyl acetate (NPA) as well as the effect of lower critical solution temperature (LCST) transition on catalytic activity. The polymer brushes were synthesized from initiator‐functionalized silica particles by surface‐initiated atom transfer radical polymerization of methoxytri(ethylene glycol) methacrylate and 2‐(N‐methyl‐N‐(4‐pyridyl)amino)ethyl methacrylate in the presence of a free initiator. Dynamic light scattering studies showed that the onset temperatures of the LCST transition of polymer brushes in pH 7.52 and 7.82 buffers were 42 and 38 °C, respectively. Under the same reaction conditions, the net initial rate of the hydrolysis of NPA catalyzed by hairy particles was 70–80% of that catalyzed by the free copolymer at the temperature below the LCST of polymer brushes. With further increasing the temperature above the LCST, the plot of logarithm of net initial rate versus inverse temperature exhibited a shift for the reactions catalyzed by hairy particles and leveled off or decreased slightly in the case of using the free copolymer as catalyst, presumably because the structures of the aggregates of hairy particles and free copolymer chains were different. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2853–2870, 2009     

Functionalized multi‐walled carbon nanotubes with poly(N‐(2‐hydroxypropyl)methacrylamide) by RAFT polymerization

In this study, we grafted water‐soluble biocompatible polymer, poly(N‐(2‐hydroxypropyl)methacrylamide) (PHPMA), onto the surface of multi‐walled carbon nanotubes (MWNTs). The reversible addition‐fragmentation chain transfer (RAFT) agents, dithioesters, were successfully immobilized onto the surface of MWNTs first, PHPMA chains were then subsequently grafted onto MWNTs via RAFT polymerization by using dithioesters immobilized on MWNTs as RAFT agent. FTIR, XPS, ¹H NMR, Raman and TGA were used to characterize the resulting products and to determine the content of water‐soluble PHPMA chains in the product. The MWNTs grafted with PHPMA chains have good solubility in distilled water, PBS buffer, and methanol. TEM images of the samples provide direct evidence for the formation of a nanostructure that MWNTs coated with polymer layer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2419–2427, 2006     

Surface‐initiated atom transfer radical polymerization from porous poly(tetrafluoroethylene) membranes using the C?F groups as initiators

This work reports the surface‐initiated atom transfer radical polymerization (ATRP) from hydrogen plasma‐treated porous poly(tetrafluoroethylene) (PTFE) membranes using the C? F groups as initiators. Hydrogen plasma treatment on PTFE membrane surfaces changes their chemical environment through defluorination and hydrogenation reactions. With the hydrogen plasma treatment, the C? F groups of the modified PTFE membrane surface become effective initiators of ATRP. Surface‐initiated ATRP of poly(ethylene glycol) methacrylate (PEGMA) is carried out to graft PPEGMA chains to PTFE membrane surfaces. The chain lengths of poly(PEGMA) (PPEGMA) grafted on PTFE surfaces increase with increasing the reaction time of ATRP. Furthermore, the chain ends of PPEGMA grown on PTFE membrane surfaces then serve as macroinitiators for the ATRP of N‐isopropylacrylamide (NIPAAm) to build up the PPEGMA‐b‐PNIPAAm block copolymer chains on the PTFE membrane surfaces. The chemical structures of the modified PTFE membranes are characterized using X‐ray photoelectron spectroscopy. The modification increases the surface hydrophilicity of the PTFE membranes with reductions in their water‐contact angles from 120° to 60°. The modified PTFE membranes also show temperature‐responsive properties and protein repulsion features owing to the presence of PNIPAAM and PPEGMA chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2076–2083, 2010     

Facile synthesis of triple‐stimuli (photo/pH/thermo) responsive copolymers of 2‐diazo‐1,2‐naphthoquinone‐mediated poly(N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide)

A series of poly(N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide) P(NIPAM‐co‐NHMA) copolymers were firstly synthesized via free radical polymerization. Then, the hydrophobic, photosensitive 2‐diazo‐1,2‐naphthoquinone (DNQ) molecules were partially and randomly grafted onto P(NIPAM‐co‐NHMA) backbone through esterification to obtain a triple‐stimuli (photo/pH/thermo) responsive copolymers of P(NIPAM‐co‐NHMA‐co‐DNQMA). UV‐vis spectra showed that the lower critical solution temperature (LCST) of P(NIPAM‐co‐NHMA) ascended with increasing hydrophilic comonomer NHMA molar fraction and can be tailored by pH variation as well. The LCST of the P(NIPAM‐co‐NHMA) went down firstly after DNQ modification and subsequently shifted to higher value after UV irradiation. Meanwhile, the phase transition profile of P(NIPAM‐co‐NHMA‐co‐DNQMA) could be triggered by pH and UV light as expected. Thus, a triple‐stimuli responsive copolymer whose solution properties could be, respectively, modulated by temperature, light, and pH, has been achieved. These stimuli‐responsive properties should be very important for controlled release delivery system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2763–2773, 2009     

Synthesis of poly[N‐isopropylacrylamide‐g‐poly(ethylene glycol)] with a reactive group at the poly(ethylene glycol) end and its thermosensitive self‐assembling character

Poly[N‐isopropylacrylamide‐g‐poly(ethylene glycol)]s with a reactive group at the poly(ethylene glycol) (PEG) end were synthesized by the radical copolymerization of N‐isopropylacrylamide with a PEG macromonomer having an acetal group at one end and a methacryloyl group at the other chain end. The temperature dependence of the aqueous solutions of the obtained graft copolymers was estimated by light scattering measurements. The intensity of the light scattering from aqueous polymer solutions increased with increasing temperature. In particular, at temperatures above 40°C, the intensity abruptly increased, indicating a phase separation of the graft copolymer due to the lower critical solution temperature (LCST) of the poly(N‐isopropylacrylamide) segment. No turbidity was observed even above the LCST, and this suggested a nanoscale self‐assembling structure of the graft copolymer. The dynamic light scattering measurements confirmed that the size of the aggregate was in the range of several tens of nanometers. The acetal group at the end of the PEG graft chain was easily converted to the aldehyde group by an acid treatment, which was analyzed by ¹H NMR. Such a temperature‐induced nanosphere possessing reactive PEG tethered chains on the surface is promising for new nanobased biomedical materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1457–1469, 2006     

Characteristic properties of film prepared from poly(L‐lactide)‐grafted dextran of a relatively high sugar unit content as a degradable biomaterial

To develop novel biomedical soft materials with degradability, amphiphilic poly(L ‐lactide)‐grafted dextrans (Dex‐g‐PLLAs) of relatively high sugar unit contents were synthesized with the trimethylsilyl protection method. The characteristic properties of solution‐cast films prepared from the obtained Dex‐g‐PLLAs were investigated. The water absorption and degradation rate of the Dex‐g‐PLLA films increased with increasing sugar unit content. The morphology of the bulk phase and top surface of the Dex‐g‐PLLA films was evaluated with transmission electron microscopy and atomic force microscopy, respectively. The bulk phase of the Dex‐g‐PLLA films with a sugar unit content of 16–25 wt % was found by transmission electron microscopy to form a lamellar type of phase‐separated structure composed of approximately 80–100‐nm‐wide nanodomains because of their amphiphilic and branched structures. The hydrophobic top surface for a Dex‐g‐PLLA film with a sugar unit content of 25 wt % covered with PLLA segments was confirmed by atomic force microscopy phase images to be easily converted to a wettable top surface covered with hydrophilic dextran aggregates showing an 8–10‐nm‐wide honeycomb pattern by means of annealing in water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6402–6409, 2006     

A simple FTIR spectroscopic method for the determination of the lower critical solution temperature of N‐isopropylacrylamide copolymers and related hydrogels

Linear and crosslinked polymers based on N‐isopropylacrylamide (NIPAAm) exhibit unusual thermal properties. Aqueous solutions of poly(N‐isopropylacrylamide) (PNIPAAm) phase‐separate upon heating above a lower critical solution temperature (LCST), whereas related hydrogels undergo a swelling–shrinking transition at an LCST. A linear copolymer made of NIPAAm/acryloxysuccinimide (98/2 mol/mol) and two hydrogels with different hydrophilicities were prepared. Fourier transform infrared (FTIR) spectroscopy was employed to determine the transition temperature and provide insights into the molecular details of the transition via probing of characteristic bands as a function of temperature. The FTIR spectroscopy method described here allowed the determination of the transition temperature for both the linear and crosslinked polymers. The transition temperatures for PNIPAAm and the gel resulting from the crosslinking with polylysine or N,N′‐methylenebisacrylamide (MBA) were in the same range, 30–35 °C. For the gels, the transition temperature increased with the hydrophilicity of the polymer matrix. The spectral changes observed at the LCST were similar for the free chains and the hydrogels, implying a similar molecular reorganization during the transition. The C H stretching region suggests that the N‐isopropyl groups and the backbone both underwent conformational changes and became more ordered upon heating above the LCST. An analysis of the amide I band suggests that the amide groups of the linear polymer were mainly involved in hydrogen bonding with water molecules below the LCST, the chain being flexible and disordered in a water solution. During the transition, around 20% of these intermolecular hydrogen bonds between the polymer and water were broken and replaced by intramolecular hydrogen bonds. Similar changes were also observed at the LCST of a gel crosslinked with MBA. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 907–915, 2000     

Mechanical property and biodegradability of solution‐cast films prepared from amphiphilic polylactide‐grafted dextran

Polylactide (PLA)‐grafted dextran was synthesized with a trimethylsilyl protection method to produce novel biodegradable, biomedical materials. PLA‐grafted dextrans with various lengths and numbers of graft chains were synthesized. The properties of solution‐cast films prepared from PLA‐grafted dextrans were investigated with thermal and dynamic mechanical analyses. The graft‐copolymer films exhibited lower glass‐transition temperatures, melting temperatures (T_m's), and crystallinities as well as higher viscosity properties as compared with poly‐L ‐lactide film. The T_m and crystallinity and mechanical properties at 37 °C could be adjusted by controlling the molecular structure such as the lengths and numbers of graft chains. Furthermore, the biodegradability of PLA‐grafted dextran films was investigated through the weight change of film and the molecular weight change of polymer during the in vitro degradation test. PLA‐grafted dextrans exhibited different degradation behavior from poly‐L ‐lactide with the introduction of a polysaccharide segment and branched structure as well as the change of end‐functional group. The degradation rate of PLA‐grafted dextran and the cast film prepared from PLA‐grafted dextran could be adjusted by controlling the sugar content or the length of graft chains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2462–2468, 2003     

Water‐soluble triply‐responsive homopolymers of N,N‐dimethylaminoethyl methacrylate with a terminal azobenzene moiety

Novel water‐soluble triply‐responsive homopolymers of N,N‐dimethylaminoethyl methacrylate (DMAEMA) containing an azobenzene moiety as the terminal group were synthesized by atom transfer radical polymerization (ATRP) technique. The ATRP process of DMAEMA was initiated by an azobenzene derivative substituted with a 2‐bromoisobutyryl group (Azo‐Br) in the presence of CuCl/Me₆TREN in 1,4‐dioxane as a catalyst system. The molecular weights and their polydispersities of the resulting homopolymers (Azo‐PDMAEMA) were characterized by gel permeation chromatography (GPC). The homopolymers are soluble in aqueous solution and exhibit a lower critical solution temperature (LCST) that alternated reversibly in response to Ph and photoisomerization of the terminal azobenzene moiety. It was found that the LCST increased as pH decreased in the range of testing. Under UV light irradiation, the trans‐to‐cis photoisomerization of the azobenzene moiety resulted in a higher LCST, whereas it recovered under visible light irradiation. This kind of polymers should be particularly interesting for a variety of potential applications in some promising areas, such as drug controlled‐releasing carriers and intelligent materials because of the multistimuli responsive property. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2564–2570, 2010     

Synthesis of thermo‐responsive 4‐arm star‐shaped porphyrin‐centered poly(N,N‐diethylacrylamide) via reversible addition‐fragmentation chain transfer radical polymerization

Tetrafunctional porphyrins‐containing trithiocarbonate groups were synthesized by an ordinary esterification method. This tetrafunctional porphyrin (TPP‐CTA) could be used as a chain transfer agent in a controlled reversible addition‐fragmentation chain transfer (RAFT) radical polymerization to prepare well‐defined 4‐arm star‐shaped polymers. N,N‐Diethylacrylamide was polymerized using TPP‐CTA in 1,4‐dioxane. Poly(N,N‐diethylacrylamide) (PDEA) is known to be a thermo‐responsive polymer, and exhibits a lower critical solution temperature (LCST) in water. The star‐shaped PDEA polymer (TPP‐PDEA) was therefore also thermo‐responsive, as expected. The LCST of this polymer depended on its concentration in water, as confirmed by turbidity, dynamic light scattering (DLS), static light scattering (SLS), and ¹H NMR measurements. The porphyrin cores were compartmentalized in PDEA shells in aqueous media. Below the LCST, the fluorescence intensity of TPP‐PDEA was about six times larger than that of a water‐soluble low molecular weight porphyrin compound (TSPP), whose fluorescence intensity was independent of temperature. Above the LCST, the fluorescence intensity of TPP‐PDEA decreased, while the intensity was about three times higher than that of TSPP. These observations suggested that interpolymer aggregation occurred due to the hydrophobic interactions of the dehydrated PDEA arm chains above the LCST, with self‐quenching of the porphyrin moieties arising from these interactions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009