Effect of molecular weight and polymer concentration on the triple temperature/pH/ionic strength-sensitive behavior of poly(2-(dimethylamino)ethyl methacrylate)

Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) samples were synthesized via aqueous atom transfer radical polymerization with DP_n of 35, 151, 390, and 546 and dispersity of 1.13, 1.17, 1.20, and 1.18, respectively. All samples were exposed to temperature and pH variations at different concentration of polymer and salt (NaCl). Results indicated that cloud point (T_cl) can be controlled by changing DP_n, polymer concentration, and ionic strength of solution. According to results, T_cl of the PDMAEMA chains shifted to lower temperatures with increasing solution pH at all molecular weight ranges due to deprotonation of tertiary amine groups in polymer structure. However, higher molecular weight polymers were more sensitive to pH variation especially in alkaline media. Also, higher polymer concentration acted as driving force to decrease cloud point of samples and formation of aggregates that was more predominant for higher molecular weights at alkaline media. T_cl of PDMAEMA chains decreased with increasing ionic strength even at low pH values for low molecular weight polymers.     

Studies of hydrodynamic properties for characterizing star-shaped poly(ethylene-co-propylene)

Linear and star-shaped polyisoprene were synthesized and hydrogenated to form the targeted poly(ethylene-co-propylene) copolymers, (EP)_lin and (EP)_star. Hydrodynamic properties of the polymers in THF at 40 °C have been studied by gel permeation chromatography, using multiple-angle laser light scattering and differential refractive index detectors.The radius of gyration R_g of (EP)_star was found proportional to the molecular weight to a power of 0.34 corroborating a globular architecture and the R_g of (EP)_lin to a power of 0.60 indicating a random coil conformation in a good solvent. The intrinsic viscosity [η] of (EP)_lin was much higher than that of (EP)_star due to the compact globular structure of star molecules. While the [η] of (EP)_lin increased with an increase in the molecular weight, the molecular weight had little effect on the [η] of (EP)_star as long as the arm length was fixed. Based on the measured R_g and [η], the coefficient q for the scaling law, the Mark-Houwink constant α, and the hydrodynamic radius R_e have been calculated. The hydrodynamic radius R_e was approximately 0.78 times of R_g for (EP)_lin and was nearly identical to R_g for (EP)_star. The value of R_e/R_g appeared to be independent of the molecular weight for both linear and star polymers and was almost equal to those of polystyrene and polyisoprene in good solvents.     

Thermal properties, miscibility and specific interactions in comparison of linear and star poly(methyl methacrylate) blend with phenolic

A series of miscible linear and star poly(methyl methacrylate) (PMMA)/phenolic blends with different compositions have been prepared. T_gs of both systems are negative derivation from the average values, implying that the self-association interaction is stronger than the inter-association interaction between linear or star PMMA with phenolic. The proton spin-lattice relaxation time in the rotating frame (T_1ρ^H) determined by high resolution solid state ¹³C NMR indicates single composition dependent T_1ρ^H from all blends, implying a good miscibility with chain dynamics on a scale of 1-2 nm. However, T_1ρ^Hs of star PMMA/phenolic blends are relatively smaller than those of linear PMMA/phenolic blends, implying that the degree of homogeneity of star PMMA/phenolic blends is higher than those of linear PMMA/phenolic blends. According to FT-IR analyses, the above results can be rationalized that the hydrogen-bonding interaction of the star PMMA/phenolic blends is greater than the corresponding linear PMMA/phenolic blends.     

Influence of pressure on the state of poly(N-isopropylacrylamide) and poly(N,N-diethylacrylamide) derived polymers in aqueous solution as probed by FTIR-spectroscopy

We investigated the hydration and swelling properties of poly(N-isopropylacrylamide) and poly(N-isopropylacrylamide)-poly(N,N-diethylacrylamide) derived microgels by Fourier transform infrared- (FTIR-) spectroscopy in a wide region of the temperature-pressure plane. These systems are known to show a swollen-to-collapsed-transition upon temperature elevation. Our data reveal that pressure favours the swollen, hydrated state over the collapsed state in all systems investigated. A detailed analysis of the fractions of the respective IR sensitive amide-I′-subbands allowed the calculation of ΔG^o and ΔV^o for the pressure-induced swelling process as well as evaluation of various intra- and intermolecular hydrogen bonding connectivities in the different systems. In fact, considerable differences exist between different polymer or microgel types with regards to their hydrogen bonding pattern as a function of temperature and pressure, and the microgels may even exhibit a biphasic swelling behavior. Notably, the thermodynamic parameters derived reveal to be in the same order of magnitude as measured for the pressure and cold denaturation of proteins.     

Anodic chlorination of aniline in N,N-dimethyl-formamide and N,N-dimethylacetamide

A pertinent electrochemical synthesis of 2,4,6-trichloroaniline (TCA) in anhydrous media was studied. The influence of the solvent, the chlorinating reagent, the electricity passed and the nature of the anode material, were investigated. TCA was produced in electrolytic solutions whose solvents were amides with strong nucleophilicity as N,N-dimethylformamide (DMF) and N,N-dimethylacetoamide (DMAc), and was obtained selectively by the controlled potential electrolysis of aniline in the solution containing LiCl. The definition of the experimental conditions corresponding to an optimum and selective electrolysis of TCA was described.     

N,N-dicyclohexylcarbodiimide assisted synthesis and characterization of poly(vinyl alcohol-co-vinyl levulinate)

Poly(vinyl alcohol-co-vinyl levulinate) was synthesized by N,N-dicyclohexylcarbodiimide assisted esterification of poly(vinyl alcohol) with free levulinic acid using 4-pyrrolidino pyridine as a catalyst in N,N-dimethyl acetamide/lithium chloride solvent system in order to optimize the reaction condition. The vinyl levulinate content in the copolymer was attained up to 0.95. The ¹³C NMR dyad compositional analysis indicated the block character of the copolymer was 0.92, suggesting almost random poly(vinyl alcohol-co-vinyl levulinate) was formed. Glass transition temperature dependence on vinyl levulinate content of the copolymers fitted better into Gordon-Taylor equation as compared with Fox equation and the glass transition temperature of poly(vinyl levulinate) was given as 2.3 °C by the least regression method.     

Multi-methacrylated star-shaped,photocurable poly(methyl methacrylate) macromonomers via quasiliving ATRP with suppressed curing shrinkage

Novel, star-shaped multifunctional poly(methyl methacrylate) (PMMA) macromonomers with well-defined average number of pendant methacrylate groups were synthesized by copolymerizing MMA with 2-hydroxyethyl methacrylate (HEMA) via quasiliving ATRP with a tetrafunctional initiator in methanol at 10 °C, followed by methacrylation of the hydroxyl groups of the HEMA units. The resulting tailor-made poly(methyl methacrylate-co-2-methacryloylethyl methacrylate), P(MMA-co-MEMA), multifunctional macromonomers were used as cross-linking agents in photocuring of MMA, a solvent for its own polymer, and thus chemically homogeneous PMMA networks were formed in which the tetrafunctional initiator moiety provides inherent, additional branching points in the resulting cross-linked materials. This approach, even in the presence of relatively low amounts of macromonomers of ∼35–45%, provides sol-free products and up to ∼40% less polymerization shrinkage than that by curing of MMA with a conventional low molecular weight bifunctional methacrylate. These new, unique star-shaped PMMA macromonomers are potential cross-linkers in a variety of solvent-free applications where low curing shrinkage and high conversions are critical requirements, such as in several engineering materials, coatings, dental fillings and restorations, bone cements etc.     

Preparation of SBS/poly(styrene–methyl methacrylate) thermoplastic interpenetrating polymer network

SBS as polymer I, poly(styrene–methyl methacrylate) polymerized by atom transfer radical polymerization as polymer II, and a thermoplastic interpenetrating polymer network of SBS/poly(styrene–methyl methacrylate) were prepared by the sequential method. The effects of the polymerization temperature, the composition of the catalyst, the ratio of the monomers studied, and the kinetics at 90°C were also investigated. It was shown that when polymerization was initiated by a BPO/CuCl/bpy (BPO:CuCl:bpy = 1:1:3) system at 90°C, the mass averaged molecular weight of the poly(styrene–methyl methacrylate) increased with monomer conversion, and the polydispersities were kept very low. Fourier transform infrared spectroscopy and gel permeation chromatogram showed that poly(styrene–methyl methacrylate) with low polydispersities had been synthesized. Thus, a thermoplastic interpenetrating polymer network comprised of both narrow molecular‐weight‐distribution components was successfully prepared. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2007–2011, 2003     

Synthesis of heteroarm star-shaped (polystyrene)n–[poly(ethyl acrylate)]m via atom transfer radical polymerization

Heteroarm star-shaped polymer, (polystyrene)_n–[poly(ethyl acrylate)]_m [(PS)_n–(PEA)_m], was synthesized in three steps. In the first step, star-shaped polystyrene, (PS)_n, was synthesized by the arm-first method via atom transfer radical polymerization (ATRP) using a preformed PS macroinitiator, which was obtained by ATRP of styrene with ethyl 2-bromoisobutyrate as the initiator, in the presence of divinyl benzene (DVB). In the microgel core of (PS)_n, there were not only a number of active initiating sites for ATRP, but also some unreacted vinyl groups. Then, in the second step, the residual vinyl groups were converted to 1-bromoethylbenzene groups by hydrobromination. In the last step, heteroarm star-shaped polymer, (PS)_n–(PEA)_m, where the arm number of PEA was greater than that of PS, was prepared by ATRP of ethyl acrylate using the hydrobrominated (PS)_n as the macroinitiator from 1-bromoethylbenzene initiating sites, obtained by both the addition of linear PS macroinitiators to vinyl groups of DVB and the hydrobromination of residual vinyl groups.     

Comparison of the phase behaviour of the liquid-crystalline polymer/poly(methyl methacrylate) and poly(vinyl acetate)/poly(methyl methacrylate) blends

The phase behaviour of blends of a liquid-crystalline polymer (LCP) and poly(methyl methacrylate) (PMMA), as well as the phase state of blends of PMMA and poly(vinyl acetate) (PVA) has been investigated using light scattering and phase-contrast optical microscopy. The blends of LCP and PMMA have been obtained by coagulation from ternary solutions. The cloud point curves were determined. It was established that both pairs demix upon heating, ie have an LCST. In the region of intermediate composition, the phase separation proceeds according to a spinodal mechanism; however for LCP/PMMA blends, the decomposition proceeds according to a non-linear regime from the very onset. In the region of small amounts of LCP, the phase separation follows a mechanism of nucleation and growth. For PMMA/PVA blends, the spinodal decomposition proceeds according to a linear regime, in spite of the molecular mobility that PVA chains develop at lower temperatures. Only after prolonged heat treatment does the process transit to a non-linear regime. The data show a similarity between the phase behaviour of blends of liquid-crystalline and of flexible amorphous polymers. The distinction consists of the absence of a linear regime of decomposition for LCP-PMMA blends. © 1999 Society of Chemical Industry     

Association behavior of poly(methyl methacrylate-b-methacrylic acid-b-methyl methacrylate) in aqueous medium

ABA type triblock amphiphilic polyelectrolyte consisting of poly(methyl methacrylate-block-methacrylic acid-block-methyl methacrylate) (P(MMA-b-MAA-b-MMA)) was synthesized by atom transfer radical polymerization technique and the self-assembly behavior of the polymers in aqueous solution was studied over the course of neutralization. Combination of potentiometric and conductometric titrations along with dynamic light scattering techniques were used to investigate the size and shape of aggregates at various degrees of neutralization. The effect of hydrophobic-hydrophilic (MMA-MAA) ratio and polymer chain length on the aggregation behavior during neutralization was studied. P(MMA-b-MAA-b-MMA) with longer MMA segment self-assembles via the closed association mechanism through stronger self-entanglement of MMA chains, whereas P(MMA-b-MAA-b-MMA) with shorter MMA chain self-assembles via the open association mechanism, as confirmed by transmission electron microscopy. Conductometric titration was used to determine the counterion condensation during the course of neutralization. When the charge density of micelle approaches a critical value as neutralization progresses, counterion condensation of Na⁺ ions on the polymer chains occurs. The effect of counterion condensation on the aggregation behavior during neutralization was elucidated.     

Multi-element determinations of N,N-dimethylformamide (DMF) coal slurries using ICP-OES

A slurry nebulisation technique was applied for elemental analysis of bituminous coals SARM 18, SARM 19 and four coals from three different seams in Witbank, South Africa, by inductively coupled plasma optical emission spectroscopy (ICP-OES). Major elements (Al, Ca, Fe, Mg, S, Si and Ti) and trace elements (Ba, Cr, Mn, Ni, Sr, V, Zn and Zr) in coal were determined. Various slurry preparations were evaluated using two dispersants (glycerol and Triton X-100) and by varying the concentration of dispersants, between 0.1% and 1.0% (v/v). The effect of initially solubilising the ground coal in N,N-dimethylformamide (DMF) was investigated by varying the volume of DMF added. The effect of wet grinding with DMF was investigated. Wet grinding with DMF was shown to drastically reduce particle sizes (50.0% < 0.28 μm and 90.0% < 6.17 μm) as compared to dry grinding (50.0% < 5.25 μm and 90.0% < 11.1 μm). The reduced particle sizes and increased transport efficiency of the coal slurries led to improved analytical recoveries of elements in the reference coal, SARM 18. The best analytical recoveries for all elements were achieved using 0.1% Triton X-100 with 10.0% DMF. Results obtained by ICP-OES after wet grinding of the coal with DMF, using 0.1% Triton X-100, also gave excellent recoveries (Al, 100%; Ca, 103%; Cr, 106%; Fe, 102%; Mg, 100%; Mn, 104%; Ni, 109%; Si, 102%; Ti, 95.0%; and V, 108%). The results obtained with 10.0% DMF and 0.1% Triton X-100 were in agreement with certified values for all selected elements according to paired t-test at the 95.0% confidence level. Selected elements (Al, Ca, Fe, Mg, Mn, Si, Ti and V) were also analysed with X-ray fluorescence for comparison with results obtained from ICP-OES. Analysis by ICP-OES of microwave digested coal was also carried out. It is suggested that the DMF slurry technique could be used for routine analysis of bituminous coals.     

Dual stimuli-responsive poly(succinyloxyethylmethacrylate-b-N-isopropylacrylamide) block copolymers as nanocarriers and respective application in doxorubicin delivery

Stimuli-responsive nanostructures were developed as anticancer drug delivery carriers. To this end, poly(2-hydroxyethylmethacrylate)-b-(N-isopropylacrylamide) (poly(HEMA-b-NIPAAm)) diblock copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization with two ratios remarked with (1) and (2). Based on gel permeation chromatography, the molecular weights of synthesized diblock copolymers were 17802 (1) and 13090 (2) g?mol^?1. The pH- and thermoresponsive poly(succinyloxyethylmethacrylate-b-N-isopropylacrylamide) (poly)SEMA-b-NIPAAm)) diblock copolymers were obtained by reacting poly(HEMA-b-NIPAAm) with excess succinic anhydride in pyridine under mild conditions. Developed micelles with poly(SEMA-b-NIPAAm) (1) and poly(SEMA-b-NIPAAm) (2) diblock copolymers around pH of 3–4 at 25°C demonstrated the critical micelles concentrations (CMCs) of 0.026 and 0.019?g?L^?1, respectively. The average sizes of poly)SEMA-b-NIPAAm) micelles using dynamic light scattering (DLS) measurements at pH 3.0, 6.0, and 9.0 were 240, 190, and 150?nm, respectively. The core-shell poly(SEMA-b-NIPAAm) micelles at pH 3 and 9 were 100–200?nm. The lower critical solution temperature (LCST) of poly)SEMA-b-NIPAAm) sample was determined to be 40°C by ultraviolet-visible (UV-vis) spectroscopy. The micelles of diblock copolymers were formed to enhance the drug solubility in aqueous solutions. Doxorubicin hydrochloride (DOX)-loading capacity was 99.1%. The release of DOX acted better at 42°C compared to 40°C. The results confirmed that pH- and temperature-dependent release of this drug carrier was particularly useful and important for the anticancer drug delivery at the tumor-like environment. Therefore, the biocompatibility of diblock copolymer was confirmed by assessing survival rate of breast cancer cell line (MCF7) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The synthesized nanoparticles would have an excellent potential as anticancer drug delivery.     

Preparation of antibacterial poly(methyl methacrylate) by solution blending with water-insoluble antibacterial agent poly[(tert-buty1amino) ethyl methacrylate]

A simple and effective way was developed to prepare antibacterial poly(methyl methacrylate) (PMMA) materials from commercial PMMA and synthesized poly[2-(tert-butylamino) ethyl methacrylate] (PTBAEMA) by solution blending and solvent evaporation methods. The chemical structure of as-synthesized PTBAEMA was characterized by FTIR and ¹H-NMR, and the molecular weight (M_w) and polydispersity index was determined by Gel Permeation Chromatograph. The two components, that is, PMMA and PTBAEMA, were partially miscible and of regular domain size and shape as revealed by SEM observation. Antibacterial assay revealed PMMA/PTBAEMA blends inherited the good antibacterial activity of PTBAEMA against both Staphylococcus aureus and Escherichia coli, no matter whether the bacteria were waterborne or airborne. Besides, the antibacterial performance of PMMA/PTBAEMA blends depended on the M_w and dosage of PTBAEMA, and type of bacteria strain. Furthermore, it was proved that PMMA/PTBAEMA blends killed bacteria on direct contact without releasing active component, which sufficiently met the demand of developing environment-friendly antibacterial materials. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The limits of linear viscoelasticity in poly(methyl methacrylate) and poly(ethyl methacrylate)

The limit of linear viscoelasticity is determined for poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) in uniaxial tension creep over the temperature range of 20° to T_g ?10°C. The time span covered is from 10 to 1000 sec. The linear limit is defined as the point at which the creep compliance deviates by more than 1% from its mean value in the linear viscoelastic range. For both materials, the stress limit of linear viscoelasticity falls to a minimum or plateau level at a temperature below T_g. It is suggested that the β-mechanism plays an important role in the existence of this minimum.     

Effect of molecular architecture on the self-diffusion of polymers in aqueous systems: A comparison of linear, star, and dendritic poly(ethylene glycol)s

Star polymers with a hydrophobic cholane core and four poly(ethylene glycol) (PEG) arms, CA(EG_n)₄, have been synthesized by anionic polymerization. Pulsed-gradient spin-echo NMR spectroscopy was used to study the diffusion behavior of the star polymers, ranging from 1000 to 10,000 g/mol, in aqueous solutions and gels of poly(vinyl alcohol) (PVA) at 23 °C. The star polymers have a lower self-diffusion coefficient than linear PEGs at equivalent hydrodynamic radius. In water alone, the star polymers and their linear homologues have a similar diffusion behavior in the dilute regime, as demonstrated by the similar concentration dependence of the self-diffusion coefficients. In the semidilute regime, the star polymers tend to aggregate due to their amphiphilic properties, resulting in lower self-diffusion coefficients than those of linear PEGs. ¹H NMR T₁ measurements at 10-70 °C revealed that the PEG arms of the star polymers are more mobile than the core, suggesting the star polymers in solution have a conformation similar to that of poly(propylene imine) dendrimers.     

Behaviour of poly(N-vinylcaprolactam) macromolecules in the presence of organic compounds in aqueous solution

Dynamic light scattering measurements have been performed for aqueous solutions of thermosensitive linear poly(N-vinylcaprolactam) (PVCa) macromolecules in the presence of NaCl and different water soluble amphiphilic organic compounds: pyrogallol (neutral amphiphilic compound), cetylpyridinium chloride (cationic surfactant) and sodium dodecylsulfate (anionic surfactant). A decrease in the macromolecular hydrodynamic diameter is observed upon addition of ionic surfactants (SDS, CPC) at low surfactant concentrations. This trend changes to an increase in the macromolecular hydrodynamic diameter at high surfactant concentration at temperatures below the temperature of polymer aggregation. This effect is in contrast with the behaviour of the systems of PVCa–non-ionic organic compounds (pyrogallol) and NaCl where we always observed the weak monotonic decrease of the hydrodynamic diameter with the increase in the concentration of organic compound, NaCl.

The behaviour of ternary systems PVCa macromolecules–ionic surfactant–pyrogallol and PVCa macromolecules–ionic surfactant–NaCl was studied. The addition of pyrogallol leads to the suppression of the intermacromolecular aggregation induced by temperature increase that is still observed at low surfactant concentrations and to the decrease of macromolecular hydrodynamic diameter. Also, the addition of NaCl to the PVCa/ionic surfactant systems results in the increase of the macromolecular hydrodynamic diameter. It is speculated that these results are due to the suppression of the cross-linking role of surfactant aggregates upon the addition of NaCl and pyrogallol.     

Synthesis and characterization of amphiphilic graft copolymers with hydrophilic poly(acrylic acid) backbone and hydrophobic poly(methyl methacrylate) side chains

A series of well-defined amphiphilic graft copolymers containing hydrophilic poly(acrylic acid) backbones and hydrophobic poly(methyl methacrylate) side chains were synthesized by successive atom transfer radical polymerization followed by the selective hydrolysis of poly(methoxymethyl acrylate) backbone. Grafting-from strategy was employed for the synthesis of graft copolymers with narrow molecular weight distributions. Hydrophobic side chains were connected with the backbone through stable C-C bonds instead of ester connections. The backbone can be easily hydrolyzed to poly(acrylic acid) with HCl without affecting the hydrophobic side chains. The amphiphilic graft copolymers can form stable micelles in water. The critical micelle concentration was determined by fluorescence spectroscopy. The micellar morphologies were found to be vesicles by transmission electron microscopy and changed to spheres with the addition of NaCl.     

Synthesis and self-assembly of poly(benzyl ether)-b-poly(methyl methacrylate) dendritic-linear polymers

Here, the dendritic chloric poly(benzyl ether) (G₁-Cl, G₂-Cl and G₃-Cl) as the macroinitiator for the controlled atom transfer radical polymerization (ATRP) of methyl methylacrylate was investigated. Polymers obtained were characterizated by GPC, ¹H NMR, FT-IR, TGA and DSC. These dendritic-linear block polymers that consist of linear and dendritic segments have very good solubility in common organic solvents at room temperature. In a selective solvent (THF/H₂O), polymers can self-assembled into the micelles that have a spherical morphology in shape due to the lowest of the surface energies.     

线形和星形聚L-丙交酯大分子单体的合成

以辛酸亚锡为催化剂,分别以聚乙二醇、甲基丙烯酸羟乙酯、三羟甲基丙烷、季戊四醇、甘露醇和山梨醇等和L-丙交酯反应,得到末端为羟基的线形和星形聚L-丙交酯。通过和甲基丙烯酰氯反应,在上述线形和星形聚L-丙交酯成功引入双键,得到了相应的反应性大分子单体,其双键的存在经红外谱图和高锰酸钾试验得到证实。通过在过氧化二苯甲酰引发下的热交联,研究了上述大分子单体的反应性,发现端基数对交联产物的性质有一定影响。溶解试验、凝胶含量测定和热重分析表明,端基数目较多的大分子单体的交联产物有较高的凝胶含量,交联密度较大,热性能较好。