Hydrolysis‐improved thermosensitive polyorganophosphazenes with α‐amino‐ω‐methoxy‐poly(ethylene glycol) and amino acid esters as side groups

A series of hydrolysis‐improved thermosensitive polyorganophosphazenes with α‐amino‐ω‐methoxy‐poly(ethylene glycol) (AMPEG) and amino acid esters (AAEs) of ‘N,N‐systems’ was synthesized, and their properties were evaluated in comparison with the thermosensitive polyorganophosphazenes with methoxy‐poly(ethylene glycol) (MPEG) and AAEs of ‘O,N‐systems’, by means of ³¹P NMR spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Most of the present polymers showed a lower critical solution temperature (LCST) in the range 32.0–79.0 °C, depending on the kinds of AAE, length of AMPEG and the mol ratio of the two substituents. These polymers exhibited higher LCSTs and faster degradation rates than the MPEG‐based polymers. The aqueous solution of poly(ethyl glycinate phosphazene)‐graft‐poly(ethylene glycol) [NP(GlyEt)_0.94(AMPEG350)_1.06]_n did not show an LCST, which is presumed to be due to its high hydrophilicity, in contrast to [NP(GlyEt)_1.01(MPEG350)_0.99]_n which showing an LCST at 77.5 °C. On the other hand, the polymers with a high content of AAE or with hydrophobic amino acids such as L ‐aspartic acid and L ‐glutamic acid, have shown a similar LCST to those of the MPEG‐based polymers. The half‐lives (t_1/2) for hydrolysis of [NP(AMPEG350)_1.06(GlyEt)_0.94]_n at pH 5, 7.4 and 10 were 9, 16, and 5 days, respectively, which are almost 2.5 to 4 times faster than that of the MPEG‐based polymers. The LCST of the present N,N‐polymers has been shown to be more influenced by salts such as NaCl (‘salting‐out’ effect) and tetrapropylammonium bromide (TPAB) (‘salting‐in’ effect) compared with the ‘O,N‐system’. Such differences of the ‘N,N‐systems’ from the ‘O,N‐systems’ in thermosensitivity, hydrolysis behavior and salt effect seem to be due to the higher hydrophilicity of the amino group in AMPEG. Copyright © 2005 Society of Chemical Industry     

A study on solution properties of poly(N,N‐diethylacrylamide‐co‐acrylic acid)

Poly(N,N‐diethylacrylamide) (PDEA), poly(acrylic acid) (PAA), and a series of (N,N‐diethylacrylamide‐co‐acrylic acid) (DEA‐AA) random copolymers were synthesized by the method of radical polymerization. The measurement of turbidity showed that the phase behaviors of the brine solutions of the copolymers changed dramatically with the mole fraction of DEA (x) in these copolymers. Copolymers cop6 (x = 0.06) and cop11 (x = 0.11) in which acrylic acid content was higher presented the upper critical solution temperature (UCST) phase behaviors similar to PAA. Copolymer cop27 (x = 0.27) presented the lower critical solution temperature (LCST) behavior similar to PDEA. While copolymer cop18 (x = 0.18) in which acrylic acid content was moderate presented both UCST and LCST behaviors. The solution properties of the polymers were investigated by measurements of viscosity, fluorescence, and pH. It is reasonable to suggest that the sharp change of the phase behavior may be attributed to the interaction between acrylamide group and carboxylic group in the (DEA‐AA) copolymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dual lower critical solution temperature polymer networks based on block,laminate, and interpenetrating network structures composed of N‐alkylacrylamides and N,N‐dialkylaminoethyl methacrylates

Novel materials that display two lower critical solution temperatures (LCSTs) were developed by forming block copolymers, laminate structures, and interpenetrating networks of crosslinked polymer systems that displayed temperature sensitivity independently. A number of LCST polymers and copolymers were investigated, including those based on N‐isopropylacrylamide, N,N‐diethylacrylamide, N,N‐diethylaminoethyl methacrylate, and N,N‐dimethylaminoethyl methacrylate. The polymer structure was found to profoundly influence the thermal sensitivity, as polymer formulation techniques led to materials with varying degrees of temperature sensitivity. Random and block copolymerization, along with interpenetrating networks and laminate systems, were studied, with only the structures having the greatest physical separation between pendent chains of different types having the ability to separate temperature transitions. Experiments were conducted to characterize the equilibrium swelling behavior and thermal transitions in the polymer systems. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2974–2981, 2003     

Simultaneous lower and upper critical solution temperature‐type co‐nonsolvency behaviour exhibited in water–dioxane mixtures by linear copolymers and hydrogels containing N‐isopropylacrylamide and N,N‐dimethylacrylamide

The co‐nonsolvency behaviour in water–dioxane mixtures of linear copolymers and hydrogels consisting of N‐isopropylacrylamide (NIPAM) and N,N‐dimethylacrylamide (DMAM) was studied as a function of solvent composition and temperature. The composition of the copolymers, P(NIPAM‐co‐DMAMx), in DMAM units, x, varies from x = 0 up to x = 100%. It is shown that the copolymers combine the lower critical solution temperature (LCST)‐type co‐nonsolvency behaviour of poly‐NIPAM with the upper critical solution temperature (UCST)‐type co‐nonsolvency behaviour of poly‐DMAM. Depending on x, both the LCST‐ and UCST‐type co‐nonsolvency behaviour may be simultaneously observed in water‐rich and dioxane‐rich solvent mixtures, respectively. Due to this complex phase separation behaviour, the variation of the reduced viscosity of the linear copolymers, as well as the swelling–deswelling behaviour of the respective hydrogels, are shown to be temperature‐ and solvent‐sensitive. Copyright © 2006 Society of Chemical Industry     

Lower critical solution temperature behavior of amphiphilic copolymers based on polyaspartamide derivatives

Novel copolymers consisting of poly(N‐isopropylaminoethyl‐co‐6‐hydroxyhexyl aspartamide) and poly (N‐isopropylaminoethyl‐co‐hexyl aspartamide) were prepared from polysuccinimide, which was the thermal polycondensation product of L ‐aspartic acid, via a ring‐opening reaction with 6‐amino‐L ‐hexanol (AH) or hexylamine (HA) and N‐isopropylethylenediamine at different ratios. The copolymers, containing 75–90 mol % of AH and 35–45 mol % of HA, produced thermoresponsive polymers through their lower critical solution temperatures (LCSTs) in aqueous solution. We could control the LCST could be controlled by modifying the hydrophobic–hydrophilic balance by changing the content of AH or HA. The pH dependencies of the LCST were opposite in these two different copolymer systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Phase behavior of temperature‐ and pH‐sensitive poly(acrylic acid‐g‐N‐isopropylacrylamide) in dilute aqueous solution

Several different composition temperature‐ and pH‐sensitive poly(acrylic acid‐g‐N‐isopropylacrylamide) (P(AA‐g‐NIPAM)) graft copolymers were synthesized by free‐radical copolymerization utilizing macromonomer technique. The phase behavior and conformation change of P(AA‐g‐NIPAM) in aqueous solutions were investigated by UV–vis transmittance measurements, fluorescence probe, and fluorescence quenching techniques. The results demonstrate that the P(AA‐g‐NIPAM) copolymers have temperature‐ and pH‐sensitivities, and these different composition graft copolymers have different lower critical solution temperature (LCST) and critical phase transition pH values. The LCST of graft copolymer decreases with increasing PNIPAM content, and the critical phase transition pH value increases with increasing Poly(N‐isopropylacrylamide) (PNIPAM) content. At room temperature (20°C), different composition of P(AA‐g‐NIPAM) graft copolymers in dilute aqueous solutions (0.001 wt %) have a loose conformation, and there is no hydrophobic microdomain formation within researching pH range (pH 3 ～ 10). In addition, for the P(AA‐g‐NIPAM) aqueous solutions, transition from coil to globular is an incomplete reversible process in heating and cooling cycles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of thermoresponsive poly(N-isopropylmethacrylamide) and poly(acrylic acid) block copolymers via post-functionalization of poly(N-methacryloxysuccinimide)

Polymers exhibiting a thermoresponsive, lower critical solution temperature (LCST) phase transition have proven to be useful for many applications as “smart” or “intelligent” materials. A series of poly(N-isopropylmethacrylamide) (PNIPMAM) polymer, poly(N-isopropylmethacrylamide)-b-poly(acrylic acid) (PNIPMAM-b-PAA) diblock, and poly(acrylic acid)-b-poly(N-isopropylmethacrylamide)-b-poly(acrylic acid) (PAA-b-PNIPMAM-b-AA) triblock copolymer samples were synthesized via ATRP. A facile post-functionalization route was developed that uses an activated ester functionality to convert poly(N-methacryloxysuccinimide) (PMASI) blocks to LCST capable polyacrylamide, while poly(t-butyl acrylate) (PtBA) blocks were converted to water-soluble poly(acrylic acid) (PAA). The post-functionalization was monitored via ¹H NMR and ATR-FTIR. The aqueous solution properties were explored and the PNIPMAM polymers were shown to have a LCST phase transition varying from 35 to 60 °C. The ability to synthesize block copolymers that are thermoresponsive and water-soluble will be of great benefit for broader applications in drug delivery, bioengineering, and nanotechnology.     

pH and thermo‐responsive poly(N‐isopropylacrylamide) copolymer grafted to poly(ethylene glycol)

pH and thermo‐responsive graft copolymers are reported where thermo‐responsive poly(N‐isopropylacrylamide) [poly(NIPAAm), poly A ], poly(N‐isopropylacrylamide‐co‐2‐(diethylamino) ethyl methacrylate) [poly(NIPAAm‐co‐DEA), poly B ], and poly(N‐isopropylacrylamide‐co‐methacrylic acid) [poly(NIPAAm‐co‐MAA), poly C ] have been installed to benzaldehyde grafted polyethylene glycol (PEG) back bone following introducing a pH responsive benzoic‐imine bond. All the prepared graft copolymers for PEG‐g‐poly(NIPAAm) [ P‐N1 ], PEG‐g‐poly(NIPAAm‐co‐DEA) [ P‐N2 ], and PEG‐g‐poly(NIPAAm‐co‐MAA) [ P‐N3 ] were characterized by ¹H‐NMR to assure the successful synthesis of the expected polymers. Molecular weight of all synthesized polymers was evaluated following gel permeation chromatography. The lower critical solution temperature of graft copolymers varied significantly when grafted to benzaldehyde containing PEG and after further functionalization of copolymer based poly(NIPAAm). The contact angle experiment showed the changes in hydrophilic/hydrophobic behavior when the polymers were exposed to different pH and temperature. Particle size measurement investigation by dynamic light scattering was performed to rectify thermo and pH responsiveness of all prepared polymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Temperature‐responsive alginate‐g‐poly(N,N‐diethylacrylamide) copolymer: Synthesis,characterization, and swelling behavior

Temperature‐responsive polymers have recently gained importance due to their applications in drug delivery. Herein, temperature‐responsive graft copolymer (Alg‐g‐PDEAAm) of alginate and N,N‐diethylacrylamide was synthesized by microwave‐assisted copolymerization using potassium persulfate/N,N,N′,N′‐tetramethylethylenediamine initiator system. The reaction conditions for the best grafting (331%) have been optimized by changing microwave irradiation time, temperature, N,N‐diethylacrylamide, and alginate concentrations. The spectroscopic characteristic, thermal properties, and surface morphology of the copolymers were investigated by FTIR, ¹H‐NMR, DSC/TGA, XRD, gel permeation chromatography, and SEM. Furthermore, low critical solution temperatures of Alg‐g‐PDEAAm copolymers were detected by UV spectroscopy. Swelling ratio of graft microspheres was carried out at 25, 32, and 37 °C, and microspheres were found exhibiting temperature‐responsive property. Cytotoxicity test indicated the Alg‐g‐PDEAAm copolymer and its microsphere were biocompatible. Therefore, based on the results the synthesized temperature‐responsive copolymer could be considered as a promising biomaterial. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46688.     

Stereoselective partitioning of organic substrates by thermoresponsive polymers in aqueous phases

Partitioning of organic substrates by thermoresponsive polymer having N‐acryloylaminoalcohol moieties in aqueous phase has been studied. Thermoresponsive polymers, such as poly(N‐isopropylacrylamide) (PNIPAAm) and poly(NIPAAm‐co‐N‐acryloyl‐(±)‐alaninol) (poly(NIPAAm‐co‐HIPAAm)), were found to concentrate several organic substrates into the hydrophobic field generated during their phase transition. The amount of the substrates recoverd from the polymer phase mainly depended on the hydrophobicity of the substrates. Aqueous solutions of PNIPAAm (lower critical solution temperature, LCST = 33°C) and poly(NIPAAm‐co‐HIPAAm) (LSCT = 41°C) containing 1‐phenylethanol showed LCSTs at 22°C and 33°C, respectively. The changes of LCSTs indicate that specific interactions such as hydrogen bonding between the side chain functionalities of the polymers and the substrates influence the phase transition behavior. Moreover, new optically active polymers having chiral aminoalcohol moieties have been synthesized by copolymerizations of NIPAAm with N‐acryloylaminoalcohols such as N‐acryloyl‐(S)‐alaninol and N‐acryloyl‐(S)‐prolinol. The (R)/(S) ratio of 1‐phenylethanol recovered from poly(NIPAAm‐co‐N‐acryloyl‐(S)‐alaninol) and poly(NIPAAm‐co‐N‐acryloyl‐(S)‐prolinol) were determined to be 75/25 and 68/32, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3458–3464, 2013     

Thermal phase transition of poly(N‐propionylethyleneimine) hydrogel

This article presents the preparation of the hydrogel of poly(N‐propionylethyleneimine) and its interpenetrating polymer network (IPN) hydrogel containing polyacrylamide by means of γ‐ray radiation and a study of the phase transition temperature of these hydrogels. As a result, the hydrogel of the crosslinked poly(N‐propionylethyleneimine) exhibited swelling below and shrinking above the phase transition temperature (about 61°C), as well as the lower critical solution temperature (LCST) of the liner polymer–water system. The experiment also showed that the LCST of the IPN hydrogel could be adjusted by the incorporation of the second component polyacrylamide. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2457–2461, 1999     

Effect of intermolecular and intramolecular forces on hydrodynamic diameters of poly(N‐isopropylacrylamide) copolymers in aqueous solutions

A novel copolymer, poly(N‐isopropylacrylamide‐co‐hydroxypropyl methacrylate‐co‐3‐trimethoxysilypropyl methacrylate) has been synthesized and the hydrodynamic diameters in various aqueous solutions under different temperatures are determined by dynamic light scattering. The results show that the hydrodynamic diameters of copolymers have no obvious change in each working solution below lower critical solution temperature (LCST); across LCST, the diameters increased suddenly at different initial temperature in various aqueous solutions; above LCST, they decreased slightly as the temperature increased in UHQ water, and increased continuously with increasing temperature or salt concentration in saline solutions, and reduced with the rising of pH value in pH buffer. These are attributed to different intermolecular and intramolecular forces leading to disparity in dimension, conformation, and LCST of copolymers. The hydrogen bonding between water molecules and copolymer chains could maintain size and conformation of copolymer single chain; the hydrogen bonding between amide linkages and hydrophobic interactions between isopropyl groups result in intramolecular collapse and intermolecular aggregation; the electrostatic repulsion weakens aggregation extent of copolymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and properties of new poly(amide imide)s containing trimellitic rings and hydantoin moieties in the main chain under microwave irradiation

Trimellitic anhydride was reacted with 4,4′‐diaminodiphenyl ether in a mixture of acetic acid and pyridine (3 : 2) at room temperature and was refluxed at 90–100°C, and N,N′‐(4,4′‐diphenylether) bistrimellitimide (3) was obtained in a quantitative yield. 3 was converted into N,N′‐(4,4′‐diphenylether) bistrimellitimide diacid chloride (4) by a reaction with thionyl chloride. Then, six new poly(amide imide)s were synthesized under microwave irradiation with a domestic microwave oven through the polycondensation reactions of 4 with six different derivatives of 5,5‐disubstituted hydantoin in the presence of a small amount of a polar organic medium such as o‐cresol. The polycondensation proceeded rapidly and was completed within 7–10 min, producing a series of new poly(amide imide)s in high yields with inherent viscosities of 0.27–0.66 dL/g. The resulting poly(amide imide)s were characterized by elemental analysis, viscosity measurements, differential scanning calorimetry, thermogravimetric analysis, derivative thermogravimetry, solubility testing, and Fourier transform infrared spectroscopy. All the polymers were soluble at room temperature in polar solvents such as N,N‐dimethylacetamide, N,N‐dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, and N‐methyl‐2‐pyrrolidone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3447–3453, 2004     

Synthesis and characterization of temperature‐sensitive block copolymers from poly(N‐isopropylacrylamide) and 4‐methyl‐ε‐caprolactone or 4‐phenyl‐ε‐caprolactone

This study synthesizes thermally sensitive block copolymers poly(N‐isopropylacrylamide)‐b‐poly(4‐methyl‐ε‐caprolactone) (PNIPA‐b‐PMCL) and poly(N‐isopropylacrylamide)‐b‐poly(4‐phenyl‐ε‐caprolactone) (PNIPA‐b‐PBCL) by ring‐opening polymerization of 4‐methyl‐ε‐caprolactone (MCL) or 4‐phenyl‐ε‐caprolactone (BCL) initiated from hydroxy‐terminated poly(N‐isopropylacrylamide) (PNIPA) as the macroinitiator in the presence of SnOct₂ as the catalyst. This research prepares a PNIPA bearing a single terminal hydroxyl group by telomerization using 2‐hydroxyethanethiol (ME) as a chain‐transfer agent. These copolymers are characterized by differential scanning calorimetry (DSC), ¹H‐NMR, FTIR, and gel permeation chromatography (GPC). The thermal properties (T_g) of diblock copolymers depend on polymer compositions. Incorporating larger amount of MCL or BCL into the macromolecular backbone decreases T_g. Their solutions show transparent below a lower critical solution temperature (LCST) and opaque above the LCST. LCST values for the PNIPA‐b‐PMCL aqueous solution were observed to shift to lower temperature than that for PNIPA homopolymers. This work investigates their micellar characteristics in the aqueous phase by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 0.29–2.74 mg L^?1, depending on polymer compositions, which dramatically affect micelle shape. Drug entrapment efficiency and drug loading content of micelles depend on block polymer compositions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and tunable thermoresponsive solution morphologies of 2,2‐bis‐methylolpropionic acid dendron–azobenzene–poly(N‐isopropyl acrylamide) copolymers

Amphiphilic temperature‐ and photoresponsive linear–dendritic block copolymers comprising second‐generation acetonide‐2,2‐bis‐methylolpropionic acid‐based polyester dendron and linear poly(N‐isopropyl acrylamide) (PNIPAM) linked by an azobenzene unit were synthesized using atom transfer radical polymerization (ATRP) followed by click chemistry. Linear PNIPAM precursor was prepared from an azide‐functionalized azobenzene containing ATRP initiator. Two polymers obtained by varying the chain length of the PNIPAM block showed different morphologies and lower critical solution temperature (LCST) values in aqueous solution. Complete change in morphology of the two polymers into large spherical aggregates and nanotubes, respectively, was observed upon heating the micellar solution above LCST. The azobenzene unit was found to undergo trans–cis photoisomerization in the assemblies and caused a change in the microenvironment of an encapsulated hydrophobic dye without any release. Acetonide groups on the dendron were deprotected to afford hydroxylated polymer that showed well‐defined morphologies above the LCST and after heating–cooling cycle while significant dye encapsulation was seen only above the LCST. © 2017 Society of Chemical Industry     

Thermoresponsive and biocompatible poly(vinyl alcohol)‐graft‐poly(N,N‐diethylacrylamide) copolymer: Microwave‐assisted synthesis,characterization, and swelling behavior

Novel thermoresponsive poly(vinyl alcohol)‐graft‐poly(N,N‐diethylacrylamide) (PVA‐g‐PDEAAm) copolymers were prepared by microwave‐assisted graft copolymerization using a potassium persulfate/N,N,N′,N′‐tetramethylethylenediamine (KPS/TEMED) initiator system. The structures of PVA‐g‐PDEAAm copolymers were characterized by ¹H‐NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry/thermogravimetric analysis, gel permeation chromatography, X‐ray diffraction, and scanning electron microscopy. The effects of various process parameters on grafting were systematically studied: microwave power, KPS, monomer and PVA concentrations, and ultraviolet irradiation. Under optimal conditions, the maximum grafting percent and graft efficiency were 101% and 93%, respectively. Furthermore, a lower critical temperature of copolymers was measured in the range 29–31 °C by ultraviolet spectroscopy. The swelling behavior of graft membranes was carried out at various temperatures, and the results showed that the swelling behavior of membranes was dependent on the temperature. In vitro cell culture studies using L929 fibroblast cells confirmed cell compatibility with the PVA‐g‐PDEAAm copolymer and its membrane, making them an attractive candidate for drug delivery systems. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45969.     

Self‐assembly and drug delivery behaviors of thermo‐sensitive poly(t‐butyl acrylate)‐b‐poly(N‐isopropylacrylamide) micelles

Self‐assembly of thermo‐sensitive poly (t‐butyl acrylate)‐b‐poly(N‐isopropylacrylamide) (PtBA‐ b‐PNIPAM) micelles in aqueous medium and its applications in controlled release of hydrophobic drugs were described. PtBA‐b‐PNIPAM was synthesized by atom transfer radical polymerization and aggregated into thermo‐sensitive core‐shell micelles with regular spheres in water, which was confirmed by ¹H‐NMR, fluorescence spectroscopy, transmission electron microscopic (TEM), and UV–vis spectroscopic techniques. The critical micelle concentration of micelles decreased with the increase of the hydrophobic components. The anti‐inflammation drug naproxen (NAP) was loaded as the model drug into polymeric micelles, which showed a dramatic thermo‐sensitive fast/slow switching behavior around the lower critical solution temperature (LCST). When the temperature was enhanced above LCST, release of NAP from core‐shell micelles was accelerated ascribed to the temperature‐induced deformation of micelles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Photoluminescence and excimer emission of functional groups in light‐emitting polymers

Near‐UV and blue‐light‐emitting polymers were synthesized with luminescent functional groups in the side chains or in the polymer main chain. The unsubstituted fluorophores, 2,5‐diphenylfuran, 2‐phenylbenzoxazole, and triphenylamine, do not form excimers in solution; however, in the case of polymers, excimer emission was negligible only with 2‐phenylbenzoxazole derivatives. The monomers as well as the polymers, poly(2‐(4‐vinylphenyl)‐benzoxazole), poly{N‐(4‐benzoxazol‐2‐yl‐phenyl)‐N′‐[2‐(methacryloyloxy)ethyl]urea}, and the polyurea of 2‐(4‐aminophenyl)‐5‐aminobenzoxazole with 1,5‐diisocyanato‐2‐methylpentane, were strong blue emitters; photoluminescence shifted to longer wavelengths than that of 2‐phenylbenzoxazole. Light‐emitting polymers containing 2,5‐diphenylfuran derivatives, including poly[2‐(4‐vinylphenyl)‐5‐phenylfuran], poly[2‐(4‐vinylphenyl)‐5‐(4‐tert‐butylphenyl)furan], and poly(N‐[2‐(methacryloyloxy)ethyl]‐N′‐{4‐[5‐(4‐tert‐butylphenyl)‐2‐furyl]phenyl}urea), particularly in solid films, exhibited a strong blue excimer emission. The emission characteristics of polymers with triphenylamine side chains were influenced by the mode of attachment of the luminescent group. A longer spacer group between the lumophore and the polymer main chain successfully minimized excimer emission in poly{N‐[2‐(methacryloyloxy)ethyl]‐N′‐[4‐(N,N‐diphenylamino)phenyl]urea}, showing near UV/violet photoluminescence. Polymers with a shorter connecting group, such as poly[4‐(N,N‐diphenylamino)benzyl acrylate], displayed blue excimer emission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1634–1645, 2003     

Controlled‐Release LCST‐Type Nonwoven Depots via Squeezing‐Out Thermal Response

A novel thermoresponsive fibrous matrix as controlled release depots upon heating is described. The matrix is composed of electrospun fibers of a lower critical solution temperature (LCST)‐type poly(methacrylamide‐co‐N‐tert‐butylacrylamide‐co‐4‐acryloylbenzophenone) P(MAAm‐NtbAAm‐ABP) copolymer. Spherical particles, simulating depots of drugs, are embedded with liquid‐filled inter‐fiber spaces (pores). On heating above 25 °C up to 45 °C, the nanofibers undergo a contraction of about 40%. This solid deformation is attributed to the LCST transition. Fibrous matrix contraction drives expulsion of depots and water solution stored in the pores of the matrix, as evidenced by in situ observations. The liquid flow in the deformable porous medium demonstrates liquid drainage from the matrix as a function of temperature. Experimental results reveal that 70% of the particles are expelled from the matrix upon heating to 45 °C from room temperature. The presented particles encapsulation and release model system using LCST‐type fibrous matrix can be used as a transdermal patch.     

Synthesis and characterization of temperature‐responsive poly(vinyl alcohol)‐based copolymers

A poly(vinyl alcohol) (PVA)/sodium acrylate (AANa) copolymer was synthesized to improve the water solubility of PVA at the ambient temperature. Furthermore, a series of temperature‐responsive acetalyzed poly(vinyl alcohol) (APVA)‐co‐AANa samples of various chain lengths, degrees of acetalysis (DAs), and comonomer contents were prepared via an acid‐catalysis process. Fourier transform infrared and ¹H‐NMR techniques were used to analyze the compositions of the copolymers. The measurement of the turbidity change for APVA‐co‐AANa aqueous solutions at different temperatures revealed that the lower critical solution temperature (LCST) of the copolymers could be tailored through the control of the molecular weight of the starting PVA‐co‐AANa, DA, and comonomer ratios. Lower LCSTs were observed for APVA‐co‐AANa with a longer chain length, a higher DA, and fewer acrylic acid segments. In addition, the LCSTs of the APVA‐co‐AANa aqueous solutions appeared to be salt‐sensitive. The LCSTs decreased as the concentration of NaCl increased. Moreover, atomic force microscopy images of APVA‐co‐AANa around the LCST also proved the temperature sensitivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008