Synthesis and characterization of amphiphilic block copolymers from poly(ethylene glycol)methyl ether and 4-methyl-?-caprolactone or 4-phenyl-?-caprolactone

MPEG-b-PMCL and MPEG-b-PBCL diblock copolymers were synthesized by ring-opening polymerization of 4-methyl-?-caprolactone (MCL) or 4-phenyl-?-caprolactone (BCL) using monomethoxy poly(ethylene glycol) (MPEG, M_n = 550 or 2000 g mol⁻¹) as the macroinitiator and SnOct₂ as the catalyst. These copolymers were characterized by differential scanning calorimetry (DSC), ¹H NMR, ¹³C NMR, and gel permeation chromatography. The thermal properties (T_g and T_m) of the diblock copolymers depend on the composition of polymers. When larger amount of MCL or BCL was incorporated into the macromolecular backbone there was an increase in T_g. Their micellar characteristics in the aqueous phase were investigated 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 0.5-2.9 mg L⁻¹, depending on the composition of polymers. The lengths of hydrophilic segment influence the shape of micelle. The mean hydrodynamic diameters of micelles from DLS were in the range of 70-140 nm. The drug entrapment efficiency and the drug-loading content of micelles depending on the composition of block polymers were described.     

Largely enhanced LED efficiency of carbazole-fluorene-silole copolymers by using TPBI hole blocking layer

A new series of soluble 3,6-carbazole-fluorene-silole copolymers (PCz-F-S) with M_w up to 52.1 kDa were synthesized by Suzuki coupling reactions. Chemical structures and optoelectronic properties of the copolymers were characterized by elemental analysis, NMR, UV absorption, cyclic voltammetry, photoluminescence (PL), and electroluminescence (EL) spectra. The main absorption peaks of solutions and films of the copolymers are at 354 nm and 347 nm, respectively, showing the combined contribution from the 3,6-carbazole and fluorene blocks. The silole absorption is at wavelength range between 400 nm and 500 nm. Compared with the solution absorption, largely decreased relative absorption of the silole to the 3,6-carbazole and fluorene blocks can be found for the films of the copolymers. The copolymers possess HOMO levels of around −5.36 eV, mainly from the contribution of 3,6-carbazole. Under excitation, the films of the copolymers show silole-dominated green emissions because of PL excitation energy transfer, with high absolute PL quantum yields up to 86%. EL devices with a configuration of ITO/PEDOT/PCz-F-S/Ba/Al only display a maximum external quantum efficiency of 0.48% whereas a device configuration of ITO/PEDOT/PCz-F-S/TPBI/Ba/Al with TPBI hole blocking layer greatly boosts the efficiency to 3.03% for a practical brightness of 236 cd/m². The improved EL efficiency suggests that more balanced charge injection and transport can be realized by inserting the TPBI hole blocking layer.     

Synthesis, characterization, and properties of chain terminated polyhedral oligomeric silsesquioxane-functionalized perfluorocyclobutyl aryl ether copolymers

A new class of perfluorocyclobutyl (PFCB) polymers covalently functionalized with polyhedral oligomeric silsesquioxane (POSS) is presented. Three discreetly functionalized POSS monomers possessing thermally reactive trifluorovinyl aryl ether (TFVE) were prepared in good yields. The POSS TFVE monomers were prepared by initial corner-capping of cyclopentyl (-C₅H₉), iso-butyl (-CH₂CH(CH₃)₂), or trifluoropropyl (-CH₂CH₂CF₃) functionalized POSS trisilanols with acetoxyethyltrichlorosilane followed by sequential acid-catalyzed deprotection and coupling with 4-(trifluorovinyloxy)benzoic acid. TFVE-functionalized POSS monomers were thermally polymerized with 4,4′-bis(4-trifluorovinyloxy)biphenyl or 2,2-bis(4-trifluorovinyloxybiphenyl)-1,1,1,3,3,3-hexafluoropropane monomers via a condensate-free, [2 + 2] step-growth polymerization. The polymerization afforded solution processable PFCB polymers with POSS macromer installed on the polymer chain ends. POSS monomers and their corresponding copolymers were characterized by ¹H, ¹³C, ¹⁹F, and ²⁹Si NMR, GPC, ATR-FTIR, and elemental combustion analysis. GPC trace analysis showed agreeable number-average molecular weight for various weight percent of cyclopentyl or iso-butyl and trifluoropropyl chain terminated POSS PFCB copolymers. DSC analysis showed the introduction of increasing POSS weight percent in the endcapped PFCB copolymers lowers the glass transition temperatures as high as 31 °C. On the other hand, the trifluoropropyl POSS endcapped PFCB polymer glass transition temperature was unaffected when copolymerized with the more fluorinated 2,2-bis(4-trifluorovinyloxybiphenyl)-1,1,1,3,3,3-hexafluoropropane monomer. TGA analysis of POSS PFCB copolymers showed step-wise decomposition of copolymers resulting from the initial degradation of the POSS cages at 297-355 °C in nitrogen and air which was confirmed by pyrolysis coupled with GC-MS. This initial weight loss was proportional to the weight percent of POSS incorporated into the polymer. The balance of decomposition was observed at 450-563 °C in nitrogen and air which is higher than the PFCB homopolymers in most cases. Polymer surface characterization was performed on spin cast transparent, flexible films. These composite films exhibited good POSS dispersion within the matrix PFCB polymer as was shown by TEM analysis.     

Functional bioengineering copolymers. II. Synthesis and characterization of amphiphilic poly(N-isopropyl acrylamide-co-maleic anhydride) and its macrobranched derivatives

Radical-initiated copolymerization of N-isopropyl acrylamide (NIPA) with maleic anhydride (MA) and macromolecular reactions of synthesized poly(NIPA-co-MA) with polyethyleneglycol (PEG with a methoxy chain end and molecular weight of 2000 g mol⁻¹) and polyethyleneimine (PEI with molecular weight of 2000 g mol⁻¹) have been studied as a way to obtain new reactive amphiphilic water-soluble polymers potentially useful as carriers for gene delivery. Structure, composition and thermal behaviour of synthesized copolymers and their macrobranched architectures are determined by FTIR, ¹H and ¹³C NMR spectroscopy, elemental (N content) and chemical (acid number) analysis and differential scanning calorimetry, differential thermal and thermal gravimetric methods. It is shown that synthesized copolymers with given composition have low critical solution temperature (LCST) in the range of 30.2-46.4 °C at pH values of 4.0-7.4, which suggest the possibility of their biomedical applications.     

New luminescent 1,2,4-triazole/thiophene alternating copolymers: Synthesis, characterization, and optical properties

New five-membered ring heteroaromatic copolymers composed of 1-alkyl-1H-1,2,4-triazole and thiophene or bithiophene units were prepared by palladium-catalyzed polycondensation. The copolymers were soluble in organic solvents, and showed number-average molecular weights of 6200-23,700 in the GPC analysis. NMR spectroscopy revealed that the copolymers had a regio-random molecular structure. The optical properties, as well as the electrochemical properties, of the copolymers in solutions and films were determined. The polymers exhibited blue photoluminescence (PL) with an emission peak at about 420 nm and quantum yields of 36-43% in solutions, and the PL peak shifted to 470-480 nm in films. X-ray diffraction data suggested that the polymers formed a π-stacked structure in solid state.     

Ionene segmented block copolymers containing imidazolium cations: Structure-property relationships as a function of hard segment content

Imidazolium ionene segmented block copolymers were synthesized from 1,1′-(1,4-butanediyl)bis(imidazole) and 1,12-dibromododecane hard segments and 2000 g/mol PTMO dibromide soft segments. The polymeric structures were confirmed using ¹H NMR spectroscopy, and resonances associated with methylene spacers from 1,12-dibromododecane became more apparent as the hard segment content increased. TGA revealed thermal stabilities ≥250 °C for all imidazolium ionene segmented block copolymers. These ionene segmented block copolymers containing imidazolium cations showed evidence of microphase separation when the hard segment was 6-38 wt%. The thermal transitions found by DSC and DMA analysis found that the T_g and T_m of the PTMO segments were comparable to PTMO polymers, namely approximately −80 °C and 22 °C, respectively. In the absence of PTMO soft segments the T_g increased to 27 °C The crystallinity of the PTMO segments was further evidence of microphase separation and was particularly evident at 6, 9 and 20 wt% hard segment, as indicated in X-ray scattering. The periodicity of the microphase separation was well-defined at 20 and 38 wt% hard segment and found to be approximately 10.5 and 13.0 nm, respectively, for these ionenes wherein the PTMO soft segment is 2000 g/mol. Finally, the 38 and 100 wt% hard segment ionenes exhibited scattering from correlations within the hard segment on a length scale of approximately 2-2.3 nm. These new materials present structure on a variety of length scales and thereby provide various routes to controlling mechanical and transport properties.     

Effect of the maleic anhydride content on the structural,thermal, rheological and film properties of the n-butyl methacrylate–maleic anhydride copolymers

Various copolymers of n-butyl methacrylate (nBMA)-maleic anhydride (MA) were synthesized by free radical solution polymerization using xylene as a solvent, with monomer ratio of (nBMA/MA) 80/20, 65/35 and 50/50 wt%. The nBMA/MA copolymers were analyzed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC) differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), rheology, acid value, microhardness and friction resistance. The formation of the nBMA/MA copolymers was proven by FTIR and ¹H NMR. The conversion percentage, glass transition temperature (T_g), thermal stability, hardness and the friction resistance of the nBMA/MA copolymers increased with the MA contents in the copolymers. All copolymers presented a thinning-shear rheological behavior due to the presence of entanglements. All films of the copolymers showed a good chemical resistance to HCl and NaCl solutions, but in the presence of NaOH solutions the films exhibited a blister.     

Green polymer-light-emitting-diodes based on polyfluorenes containing N-aryl-1,8-naphthalimide and 1,8-naphthoilene-arylimidazole derivatives as color tuner

A novel series of green light emitting single polymers were prepared by end-capping of N-aryl-1,8-naphthalimide and 1,8-naphthoilenearylimidazole derivatives into polyfluorene. The electroluminescence (EL) spectra of polymers (P1 ∼ P5) exhibit greenish-blue, bluish-green, pure green, and yellowish-green emission (λ_max = 465 nm, 490 nm, 500 nm, and 545 nm, respectively) from compounds (M1 ∼ M5). It was found that by the introduction of a small amount of compounds (M1 ∼ M5) (5 mol-%) into polyfluorene, the emission color can be tuned from the blue to green region. The color tuning was found to have gone through charge trapping and Förster energy transfer. The device of P4 emits pure green light with Commission Internationale de l'Eclairage (CIE) coordinates of (0.20, 0.41), and exhibits a maximum brightness of 11500 cd/m² at 12 V with a structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) [PEDOT:PSS]/PVK/emission layer/Ca/Ag. The device of P5 emits yellowish green light with Commission Internationale de l'Eclairage (CIE) coordinates of (0.36, 0.56), and exhibits a maximum brightness of 6534 cd/m² at 17 V.     

Synthesis, isothermal crystallization and micellization of mPEG-PCL diblock copolymers catalyzed by yttrium complex

Amphiphilic biodegradable mPEG-PCL diblock copolymers have been synthesized using rare earth catalyst: yttrium tris(2,6-di-tert-butyl-4-methylphenolate) [Y(DBMP)₃] in the presence of monomethoxy poly(ethylene glycol) (mPEG, M_n = 5000) as macro-initiator. The diblock architecture of the copolymers was thoroughly characterized by ¹H NMR, ¹³C NMR and SEC. The molecular weights of mPEG-PCLs can be well controlled by adjusting the feeding molar ratio of ?-CL to mPEG. Thermal and crystallization behaviors of the diblock copolymers were investigated by DSC and POM (polarized optical microscope). The crystallization property of mPEG-PCL block copolymers depends on the length of PCL blocks. As the molecular weight of PCL block increased, the crystallization ability of mPEG block was visibly restrained. Aqueous micelles were prepared by dialysis method. The critical micelle concentration of the copolymers, which was determined to be 0.9-6.9 mg/L by fluorescence technique, increased with the decreasing of PCL block length. The particle sizes determined by DLS were 30-80 nm increasing with the PCL block length. TEM images showed that these micelles were regularly spherical in shape.     

Micellization and phase transition behavior of thermosensitive poly(N-isopropylacrylamide)-poly(?-caprolactone)-poly(N-isopropylacrylamide) triblock copolymers

Thermosensitive triblock copolymers with two hydrophilic poly(N-isopropylacrylamide) blocks flanking a central hydrophobic poly(?-caprolactone) block were synthesized by atom transfer radical polymerization. Core-shell micellization of the triblock copolymers was inferred from the ¹H NMR spectra derived in two different solvent environments (CDCl₃ and D₂O). The micellar characteristics of these amphiphilic triblock copolymers were studied by pyrene fluorescence techniques, dynamic light scattering and transmission electron microscopy. The critical micelle concentrations of the triblock copolymers were in the range of 4-16 mg/L and the partition coefficients were in the range of 3.10 × 10⁴ to 2.46 × 10⁵. The mean diameters of the micelles, measured by light scattering, were between 90 and 120 nm. The temperature sensitivity of the triblock copolymers was demonstrated by the phase transition of a 250 mg/L aqueous polymer solution at the lower critical solution temperature (LCST). The enthalpy of the phase transition was determined by differential scanning calorimetry. PM3 quantum mechanical calculation method was used to understand the intermolecular interactions between the copolymer and the water molecules. A modular approach was used to simulate the phase transition observed at the LCST.     

Block, blocky gradient and random copolymers of 2-ethylhexyl acrylate and acrylic acid by atom transfer radical polymerization

The controlled synthesis of low-T_g poly(2-ethylhexyl acrylate) (P2EHA) and derived random, block and blocky gradient copolymers via atom transfer radical polymerization (ATRP) is described. After optimizing the reaction conditions for the homopolymerization of 2EHA via ATRP, the synthesis of a variety of copolymers with poly(t-butyl acrylate) (PtBuA) was investigated. First, AB-block copolymers were targeted, starting from P2EHA and PtBuA as macroinitiators. Second, random copolymers of tBuA and 2EHA with different monomer ratios were synthesized. Finally, the synthesis of “blocky” gradient copolymers via a one-pot procedure was investigated, starting with the homopolymerization of tBuA, followed by the addition of 2EHA. The hydrolysis of the PtBuA-segments to poly(acrylic acid) (PAA), which was carried out with methanesulfonic acid, resulted in block, blocky gradient and random copolymers consisting of PAA and P2EHA. Solubility testing of the copolymers in slightly basic water (pH ∼ 9) demonstrated that the gradient structure significantly enhances solubility compared to the block copolymer structures with equal composition. The polymers have been characterized by MALDI-TOF MS, GPC and ¹H NMR.     

New light-emitting hyperbranched polymers prepared from tribromoaryls and 9,9-dihexylfluorene-2,7-bis(trimethyleneborate)

Three new hyperbranched polymers (P1-P3) were prepared by copolymerization of tribromoaryl moieties (triphenylamine, carbazole and fluorene moieties) with 9,9-dihexylfluorene-2,7-bis(trimethyleneborate) from “A₂ + B₃” approach based on Suzuki polycondensation reaction. They are soluble in common organic solvents, and exhibit good thermal stable luminescence. Interestingly, unlike most of fluorene-containing polymeric materials, P3 emits strong green light due to its special structure. Double-layer devices with configurations ITO/PEDOT/Polymer (50 nm)/TPBI(50 nm)/LiF(0.5 nm)/Al(80 nm) were fabricated and emitted blue or green light, with maximum luminance in the range of 25-142 cd/m² and the current efficiency up to 0.18 cd/A.     

Synthesis, thermal stability, light emission, and fluorescent photopatterning of poly(diphenylacetylene)s carrying naphthalene pendant groups

Naphthalene (Nap)-containing poly(diphenylacetylene)s with different spacer lengths (-{C₆H₅CC[C₆H₄O(CH₂)_mO-Nap]}_n-; P1(m), m = 4, 6, 8) are synthesized. The monomers are prepared by etherifications of 1,m-dibromoalkanes with 1-naphthol and 1-(4-hydroxy)phenyl-2-phenylacetylene and are polymerized by TaCl₅-n-Bu₄Sn and WCl₆-Ph₄Sn catalysts. Whereas the tantalum-based catalyst gives insoluble products in low yields, the tungsten-based catalyst furnishes soluble polymers with high molecular weights (M_w up to 5.0 × 10⁴) in satisfactory yields (up to 62%). The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, UV, PL, and EL analyses. All the polymers are thermally stable: while the polymers lose 5% of their weights at ∼420 °C under nitrogen, no decreases in molecular weights are found after they have been annealed at 200 °C for 2 h in air. When their THF solutions are photoexcited, the polymers emit strong green lights with high efficiencies (up to 98%). No significant shifts in the photoluminescence spectra are observed when the polymers are cast into thin solid films, suggestive of little involvement of aggregative or excimeric emission. A multilayer EL device with a configuration of ITO/P1(8):PVK/BCP/Alq₃/LiF/Al is constructed, which emits a green light of 520 nm with a maximum external quantum efficiency of 0.16%. The spectral stability is outstanding: no recognizable change is observed in the EL spectrum when the device current is raised. Irradiation of a film of P1(8) through a mask photooxidizes and quenches the emission of the exposed regions, resulting in the formation of two-dimensional luminescent photopatterns.     

Esterification of ethylene-vinyl alcohol copolymers in homogeneous phase using N,N′-dimethylpropyleneurea as solvent

Ethylene-vinyl alcohol copolymers (EVAL) were esterified with 3,5-dinitrobenzoyl chloride using the cycled urea N,N′-dimethylpropyleneurea (1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone) (DMPU) as the solvent. Ethylene-vinyl alcohol-vinyl-3,5-dinitrobenzoate terpolymers (EVALVDNB) and ethylene-vinyl-3,5-dinitrobenzoate copolymers (EVDNB) were obtained. Both EVAL copolymers (6-73 mol% VAL) and esterified polymers, EVDNB, and EVALVDNB dissolve in DMPU. The substitution may become total under the experimental conditions. The degree of transformation was determined by ¹H NMR. EVDNB copolymers were characterised by IR spectroscopy and ¹H and ¹³C NMR. Thermal properties were studied by DSC. The glass transition temperature of the EVDNB copolymers having a low VDNB content (up to 14 mol%) is roughly constant, whereas above 50 mol% increases. Melting temperature decreases as the VDNB content is increased, owing to the fact that the VDNB groups are excluded from the polyethylene crystal lattice.     

Synthesis and characterization of polyimides and co-polyimides having pendant benzoic acid moiety

A novel diamine monomer, 2,4-diamino-4′-carboxy diphenyl ether had been synthesized. Several polyimides were prepared by reacting this diamine with commercially available dianhydrides, such as benzophenone tetracarboxylic acid dianhydride (BTDA), 4,4′-bis{hexafluoroisopropylidene bis (phthalic anhydride)}(6-FDA), oxydiphthalic anhydride (ODPA) and 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA). Furthermore, copolymers from the resulting diamine and oxydianiline (ODA) with 6 FDA were also synthesized. The inherent viscosities of the polymers were 0.42-0.67 dl g⁻¹. The polymers have good solubility in polar aprotic solvents, high thermal stability up to 410 °C in nitrogen and high glass transition temperatures (T_g) ranging from 260-330 °C. These polymers formed tough flexible films by solution casting.     

Electrosyntheses and characterizations of novel electrochromic and fluorescent copolymers based on 2,2′-bithiophene and pyrene

Poly (2,2′-bithiophene-co-pyrene), a novel copolymer, is successfully achieved by electrochemical oxidation of the monomer mixtures of 2,2′-bithiophene (BT) and pyrene in acetonitrile (ACN) containing sodium perchlorate (NaClO₄). FT-IR and ¹H NMR characterizations support that the obtained copolymers contain both pyrene and BT units. A series of experiments are carried out to investigate the properties of the copolymers obtained from 0.2 M NaClO₄/ACN with different monomer feed ratios. The electrochemical properties of the obtained copolymers are studied by cyclic voltammetry (CV). Compared with polypyrene, the copolymers perform reversible redox process. Elemental analyses results indicate that the ratio of BT/pyrene units in copolymers increases as the feed ratio of BT/pyrene increases. The obtained copolymers also present properties of tunable electrochromism, good thermal stability and smooth morphology. The UV-vis absorption peaks of the copolymers exhibit obvious red-shift. Fluorescence spectra studies reveal that the copolymer is a good green-light emitter.     

Synthesis and characterization of biodegradable and biocompatible amphiphilic block copolymers bearing pendant amino acid residues

Polylactide (PLA)-based biodegradable and biocompatible amphiphilic block copolymers bearing pendant amino acid residues were synthesized through a relatively easy and efficient way. The composition and structure of these copolymers were characterized by gel permeation chromatography (GPC) and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. The self-assembly behavior of the copolymers was investigated by fluorescence (FL), dynamic light scattering (DLS), and transmission electron microscope (TEM). It was shown that aggregates less than 100 nm in average size were formed by these copolymers, which changed from micelles to vesicles with the variation of the block length. In addition, the in vitro cytotoxicity of these copolymers was determined and compared with that of PEO-b-PLA in the presence of Bel-7402 cells. The result suggested that the block copolymers PAGE/cys-b-PLA exhibited better biocompatibility. Therefore, these PLA-based copolymers are expected to find promising applications in drug delivery or tissue engineering.     

Synthesis and characterization of amphiphilic functional polyesters by ring-opening polymerization and click reaction

During this work we have prepared novel amphiphilic graft-block (PαN₃CL-g-alkyne)-b-PCL functional polyesters, comprising poly(α-azido-ε-caprolactone-graft-alkyne) (PαN₃CL-g-alkyne) as the hydrophilic segment and poly(ε-caprolactone) (PCL) as the hydrophobic segment, by ring-opening polymerization of ε-caprolactone (ε-CL) with hydroxyl-terminated macroinitiator PαClCL, substituting pendent chloride with sodium azide. The copolymers were subsequently used for grafting of 2-propynyl-terminal alkyne moieties by the Cu(I)-catalyzed Huisgen’s 1,3-dipolar cycloaddition, thus producing a “click” reaction. ¹H NMR, FT-IR, GPC, and differential scanning calorimetry (DSC) examined the characteristics of the copolymers. Grafting of PMEs or PMPEGs onto the PαN₃CL-b-PCL caused these amphiphilic copolymers to self-assemble into micelles in the aqueous phase. Fluorescence, dynamic light scattering (DLS) and transmission electron microscopy (TEM) then examined these micelles. The critical micelle concentration (CMC) ranged from 8.2 mg L⁻¹ to 39.8 mg L⁻¹ at 25 °C and the average micelle size ranged from 140 to 230 nm. The hydrophilicity and length of the hydrophilic segment influenced micelle stability. The current study describes the drug entrapment efficiency and drug loading content of the micelles, dependent on the composition of graft-block polymers. The results from in vitro cell viability assays indicated that (PαN₃CL-g-alkyne)-b-PCL shows low cytotoxicity.     

Synthesis and self-assembly of comb-like amphiphilic Doxifluridine-poly(?-caprolactone)-graft-poly(γ-glutamic acid) copolymer

Advances in amphiphilic copolymers can potentially be exploited in drug or gene delivery. This study develops novel comb-like amphiphilic copolymers that comprise poly(γ-glutamic acid) (γ-PGA) as a hydrophilic backbone and Doxifluridine-poly-(?-caprolactone) (5′-deoxy-5-fluorouridine-poly(?-caprolactone), 5′DFUR-PCL) as a hydrophobic side chain. A novel 5′DFUR-PCL polymer was synthesized with antitumor agent Doxifluridine (5′DFUR) as the initiator via the ring-opening polymerization of ?-caprolactone (?-CL) using tin(II) 2-ethylhexanoate (Sn(Oct)₂) as the catalyst. The 5′DFUR-PCL polymer was then grafted on γ-PGA to yield a 5′DFUR-PCL-γ-PGA comb-like copolymer with the help of 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide (EDC). The characteristics of these copolymers were examined by ¹H NMR, FT-IR, GPC, contact angle measurement and thermal properties. Grafting 5′DFUR-PCL would significantly increase the contact angle and decrease the melting temperature (T_m) of the copolymers. The micelles self-assembled from these amphiphilic copolymers were formed in an aqueous phase and were examined via fluorescence approaches, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The average sizes of the micelles were in the range from 130 to 230 nm and their zeta potentials were negative and less than −16.7 mV. The critical micelle concentration (CMC) was from 1.49 mg/L to 4.63 mg/L at 25 °C. TEM images demonstrated that the micelles were spherical and clearly had a core-shell structure.     

Toward an understanding of thermoresponsive transition behavior of hydrophobically modified N-isopropylacrylamide copolymer solution

Poly(N-isopropylacrylamide-co-vinyl laurate)(PNIPAAm-co-VL) copolymers were prepared at various feed ratios via conventional radical random copolymerization. The formation, composition ratios and molecular weight of copolymers were examined. The thermoresponsive behaviors of PNIPAAm and PNIPAAm-co-VL solutions at low and high concentrations were intensively investigated by turbidity measurement, Micro-DSC, temperature-variable state fluorescence, ¹H NMR and dynamic light scattering (DLS). Several important results were obtained that (1) incorporation of PVL results in much lower and broader LCST regions of the copolymer solutions, and facilitates the formation of hydrophobic microdomains far below LCST, causing a pronounced aggregation in solutions (2) temperature-variable ¹H NMR spectra shows that during the phase transition, the ‘penetration’ of PNIPAAm into the hydrophobic core is a process accompanied with a transition of isopropyl from hydration to dehydration as well as a self-aggregation of hydrophobic chains at different temperature stages (3) according to the ¹H NMR spectra of polymer solutions obtained at varied temperatures, the microdomains from hydrophobic VL moieties have a different accessibility for isopropyl groups and the entire chains during phase transition (4) temperature-variable DLS demonstrates that the temperature-induced transition behavior of copolymers is supposedly divided into three stages: pre-LCST aggregation (<20 °C), coil-globule transition at LCST (20-25 °C) and post-LCST aggregation (>25 °C).