Solution and solid‐state NMR investigation of poly(methyl methacrylate)/poly(vinyl pyrrolidone) blends

The development of polymer blends has become very important for the polymer industry because these blends have shown to be a successful and versatile alternative way to obtain a new polymer. In this study, binary blends formed by poly(methyl methacrylate) (PMMA) and poly(vinyl pyrrolidone) were prepared by solution casting and evaluated by solution and solid‐state NMR. Variations in the microstructure of PMMA were analyzed by ¹³C solution NMR. Solid‐state NMR promotes responses on physical interaction, homogeneity, and compatibility to use these blends to understand the behavior of the ternary blends. The NMR results led‐us to acquire information on the polymer blend microstructure and molecular dynamic behavior. From the NMR solution, it was possible to evaluate the microstructure of both polymer blend components; they were atactic. From the solid state, good compatibility between both polymer components was characterized. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 372–377, 2004     

NMR studies of poly(2-hydroxy ethyl methacrylate-co-2-vinyl pyridine)

Copolymers of 2-hydroxy ethyl methacrylate-2-vinyl pyridine (H/V) of different composition were synthesized by free radical bulk polymerization using azobisisobutyronitrile (AIBN) as an initiator under nitrogen atmosphere. The copolymer compositions were calculated from ¹H NMR spectra. The reactivity ratios for H/V copolymers obtained from a linear Kelen-Tudos method (KT) and nonlinear error-in-variables method (EVM) are r_H = 0.50 ± 0.10, r_V = 1.04 ± 0.08 and r_H = 0.55, r_V = 1.06 respectively. The complete spectral assignment of methine, methylene, methyl, carbonyl, and aromatic carbon regions in term of compositional and configurational sequences of H/V copolymers were done with the help of ¹³C{¹H} NMR, distortionless enhancement by polarization transfer (DEPT), two-dimensional heteronuclear single quantum coherence (HSQC) along with total correlated spectroscopy (TOCSY). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

NMR properties of poly(dimethyl siloxane) colloids as new contrast agents for NMR imaging

By connecting the field‐gradient spin‐echo theory to spin–spin relaxation, we have found that the relationship between the tube‐reptation model and spin–spin relaxation can be represented by G(t) = exp[−(t/T₂) ⁿ] in which n = 1 and 0.5 for regimes IV and III, respectively. In our experiments, the spin–spin relaxation of linear poly(dimethyl siloxane) (PDMS) agrees with G(t) = exp[−(t/T₂)] while that of crosslinked PDMS coincides with G(t) = exp[−(t/T₂)^0.5]. These results reflect that in the time interval 8–800 ms the dynamics of linear PDMS are in regime IV (governed by reptation motions) and those of the crosslinked PDMS are in regime III (dominated by wriggling motions). The line‐shapes of NMR spectra of crosslinked PDMS are consistent with the Lorentzian rather than the Gaussian model. This can be accounted for by supposing that the PDMS chains between crosslinks have liquid‐like motions even though crosslinked PDMS is a solid. The liquid‐like motions of crosslinked PDMS could be regarded as wriggling motions described by the tube‐reptation model. In addition, the experimental results of diameter distribution, viscosity, NMR image and spin–lattice relaxation are presented in this work. © 2000 Society of Chemical Industry     

两亲性超支化聚酯-酰胺的制备及其性能

引言 在同一分子中,既含有亲水性链段,又含有疏水性链段的聚合物称为两亲性聚合物,这种聚合物的凝聚态常具有多相结构,并对不同极性的化合物都具有一定的亲和力,这种独特的性质就使其既不同于低分子表面活性剂也异于一般的离子聚合物.带有亲水性支链的两亲性聚合物具有很大的应用潜能.可以用作乳液和分散体的稳定剂,颜料及塑料的表面改性剂,高分子材料的助剂及改性剂等[1-2].     

Polymer micelle-like aggregates of novel amphiphilic biodegradable poly(asparagine) grafted with poly(caprolactone)

Novel amphiphilic graft copolymers composed of poly(asparagine) (PAsn) as the hydrophilic backbone and poly(caprolactone) (PCL) as the hydrophobic segment were successfully synthesized by grafting PCL-HMDs to poly(succinimde). After tosylating PCL-diol with p-toluenesulfonylchloride (TsCl), tosylated poly(caprolactone) (PCL-OTs) was then reacted with hexamethylenediamine (HMD). The reaction of the amine terminated PCL with poly(succinimide) (PSI) and the following aminolysis resulted in poly(aspargine)-graft-poly(caprolactone) (PAsn-g-PCL). The degree of substitution (DS) and grafting reaction was confirmed by ¹³C NMR, FT-IR spectroscopy and elemental analysis. X-ray diffraction and DSC thermogram showed that the crystalline domain originated from PCL became apparent with an increase of DS. The amphiphilic comb-type graft polymer formed self-aggregates in aqueous solution when precipitated and dialysed against distilled water. Strong hydrophobic interaction of associated PCL grafts facilitated primary aggregate formation with DS, significantly reducing critical aggregation concentration and secondary aggregates also appeared in DLS measurements. Self-aggregates showed a bimodal size distribution originated from the self-aggregation and kinetically controlled particle aggregation, although the smaller primary aggregates was predominant. Spherical and dispersed aggregates of about 20 nm in diameter were observed by a transmission electron microscope.     

Solid state NMR analysis of poly(L‐lactide) random copolymer with poly(ε‐caprolactone) and its reactive extrusion process

A random copolymer based on poly(L ‐lactide) (PLA) with poly(ε‐caprolactone) (PCL) was prepared and characterized by mechanical testing and solid state NMR, compared with a polymer blend. For a monofilament sample consisting of PLA/PCL random copolymer, there were negative correlations between the CL content and the mechanical properties: tensile strength, tensile elastic modulus, flexural rigidity, and flexural hysteresis decreased with increasing CL content. In contrast, the mechanical properties of the polymer blend were only slightly changed by addition of the CL unit. For the random copolymer, the addition of a small amount of CL reduced relaxation times, T₁C and T_1ρH, gradually. The T₁C and T_1ρH values correlated closely with the tensile elastic modulus and the tensile strength, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

温敏性两亲嵌段共聚物相行为的耗散粒子动力学模拟

采用耗散粒子动力学模拟研究了由温敏性聚N-异丙基丙烯酰胺(PNIPAM)与聚己内酯(PCL)构成的两亲嵌段共聚物(PCL-PNIPAM-PCL)在水溶液中自组装的动力学过程及微相分离现象,考察了溶液浓度及温度对其相行为的影响。模拟发现不同体积分数的嵌段共聚物在水溶液中呈现出不同的自组装形貌,如球状胶束、柱状胶束、层状胶束等。温度对其在水溶液中的形貌及相变行为有着显著的影响。当温度较低时,PCL-PNIPAM-PCL于稀溶液中可形成稳定的以PCL为核,PNIPAM为壳的球形核壳胶束;而当温度升高到某一值时,在低温时所形成的球形核壳胶束将因温度的升高而转变为表面由PCL组成的多个不连续微区的多隔段胶束。这种温敏现象在耗散粒子动力学模拟中尚属首次被发现。另外,模拟中所得到的该体系的低临界溶解温度与实验测得的值也符合良好。对这一温敏现象作了较深入和细致的解释。本文工作表明耗散粒子动力学能用来研究温度对温敏性两亲嵌段共聚物相行为的影响并揭示其中的机制和一般规律。     

Blends of poly(ether imide) and an aromatic poly(ether amide): Phase behavior and CO2 transport properties

Blends of poly(ether imide) (PEI, Ultem 1000) and an aromatic poly(ether amide) were studied. Although homogeneous or heterogeneous blends can be obtained depending on the blend preparation method, the inherent miscibility of the mixture was finally established. The so-called enthalpy relaxation method was used to detect one or two glass transition temperatures in the blends in spite of the similarity of the pure component transitions. Fourier transform infrared analysis provided additional evidence of the specific interactions, which could be in the origin of the miscibility. A preliminary study of the influence of the homogeneity level in the transport properties of the blend films was also undertaken. Carbon dioxide at 1 bar was used as a penetrant. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2141–2149, 1998     

Relationship between pore structure and 1H‐NMR relaxation times in TiO2/poly(dimethylsiloxane) and CaCO3/poly(dimethylsiloxane) composite powders

Titanium(IV) oxide/polydimethylsiloxane (PDMS) and calcium carbonate/PDMS composite powders were obtained by adsorption of the polymer from a chloroform solution onto the inorganic particles followed by a thermal treatment. The composites were characterized by ¹H‐NMR relaxation and porosimetry. The composites present shorter spin–lattice (T₁) and spin–spin (T₂) proton relaxation times than silica‐reinforced PDMS, and the activation energies for the motions that cause spin–lattice relaxation are 5.8, 4.9, and 0.72 kJ mol⁻¹ for TiO₂/PDMS, CaCO₃/PDMS, and neat PDMS, respectively, revealing the greater rigidity of the polymer chains within the composite. Spin–spin relaxation (T₂) measurements of the composites showed a major component with a shorter T₂ and a minor component with a longer T₂. The intensity ratio of these two components is very close to the ratio between the amount of polymer that remains between the particles and that penetrating the particle pores as measured by Hg intrusion porosimetry. The shorter T₂ component was thus assigned to polymer interspersed among the particles, while the longer T₂ component was assigned to polymer within the particle pores. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2660–2666, 1999     

Single molecule force spectroscopy of smart poly(ferrocenylsilane) macromolecules: Towards highly controlled redox-driven single chain motors

We investigated various stimuli-responsive poly(ferrocenylsilane) (PFS) polymers as model systems for the realization of molecular motors powered by a redox process. Covalently end-grafted PFS on gold, as well as PFS homopolymers and block copolymers in ultrathin films, were studied by AFM-based single molecule force spectroscopy (SMFS). Surface confined PFS macromolecules were chemically oxidized by addition of tetracyanoethylene or were completely and reversibly oxidized (and reduced) in situ by applying an electrochemical potential. Chemical oxidation was successful only for the block copolymers. The entropic elasticity of neutral PFS chains (Kuhn length I_K∼0.40 nm) was found to be larger than that of oxidized PFS chains (I_K∼0.65 nm) in the lower force regime. The elasticities could be reversibly controlled in situ by adjusting the applied potential in electrochemical SMFS experiments. For a single PFS macromolecule (DP=80) operating cycle, a work output and an efficiency of 3.4×10⁻¹⁹ J and ∼5%, respectively, were estimated based on the single chain experimental data.     

Probing the association behavior of poly(ethyleneglycol) based amphiphilic comb-like polymer in the presence of cationic surfactant

The interaction between an amphiphilic comb-like polymer—poly(styrene-maleic anhydride) copolymer esterified with brij-35—and a cationic surfactant, N-cetyl-N,N-diethanolyl-N-methyl ammonium bromide (CDMAB), was investigated at pH 6.2. Our earlier experiments (Polymer 42, 7801, 2001) revealed that at this pH the polymer forms intramolecular aggregates and these self-aggregates behave as polyelectrolyte due to the partial ionization of the backbone of the polymer. When surfactant is gradually added to the polymer solution in the present study, binding of the surfactant to the polymer takes place even at lowest surfactant concentration. Initially binding occurs due to electrostatic interaction, leading to compact aggregates. After complete charge neutralization of the polymer backbone, the surfactant hydrophobes are adsorbed into the microdomains formed by the polymer due to hydrophobic interactions. An exothermic enthalpy change is associated with both kinds of interactions, electrostatic as well as hydrophobic.     

Association behavior of thermo-responsive block copolymers based on poly(vinyl ethers)

Thermo-sensitive nanosized structures have been prepared in water from poly(methyl vinyl ether)-block-poly(isobutyl vinyl ether) (PMVE-b-PIBVE) block copolymers. The composition and the architecture (diblock and triblock architectures) of the PMVE-b-PIBVE copolymers have been varied. The investigated copolymers had an asymmetric composition with a major PMVE block. While the PIBVE blocks are hydrophobic, the PMVE blocks are hydrophilic at room temperature and become hydrophobic above their demixing temperature (around 36 °C) as a result of the lower critical solution temperature (LCST) behavior. At room temperature, the amphiphilic copolymers aggregate in water above a critical micelle concentration, which has been experimentally measured by hydrophobic dye solubilization. The hydrodynamic diameter of the structures formed above the cmc has been measured by dynamic light scattering (DLS) while their morphology has been studied by transmission electron microscopy (TEM). ¹H NMR measurements in D₂O at room temperature reveal that the aggregates contain PIBVE insoluble regions surrounded by solvated PMVE chains. These investigations have shown that polydisperse spherical micelles are formed for asymmetric PMVE-b-PIBVE copolymers containing at least 9 IBVE units. For copolymers containing less IBVE units, loose aggregates are formed.Finally, the thermo-responsive, reversible properties of these structures have been investigated. Above the cloud point of the copolymers, the loose aggregates precipitate while the micelles form large spherical structures.     

New thermo-responsive polymer materials based on poly(2-ethyl-2-oxazoline) segments

First, the solution behavior of poly(2-ethyl-2-oxazoline) (PEtOx) in water has been investigated. The dependence of the cloud points on the molecular weight and concentration indicates a typical Flory-Huggins (Type I) demixing behavior with a lower critical solution temperature (LCST). Secondly, the synthesis and properties of temperature-responsive hydrogels and segmented polymer networks, based on PEtOx bis-macromonomers, are reported. PEtOx hydrogels have been prepared by UV-induced radical polymerization of the corresponding α,ω-bis-acrylates. The networks exhibited a continuous shrinkage with increasing temperature. Series of segmented networks with LCST-behavior have been obtained by free radical copolymerization of PEtOx bis-macromonomer with the comonomers 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl acrylate (HPA) or methyl methacrylate (MMA). The LCST-behavior of the materials is controlled by varying the philicity of the comonomer and the fraction of PEtOx in the networks. PHEMA-PEtOx and PHPA-PEtOx hydrogels exhibited a large and reversible swelling-deswelling process, whereas the volume changes in PMMA-PEtOx swollen networks were small and occurred in a broad temperature interval.     

Synthesis and properties of amphiphilic poly(ethylene oxide)-grafted cardo poly(aryl ether sulfone) copolymers

A series of comb-type amphiphilic copolymers (PES-g-PEO) with a stiff poly(aryl ether sulfone) backbone and flexible PEO side chains was synthesized via a “grafting onto” technique. By controlling the monomer feed ratios, high molecular weight copolymers with a range of PEO side chain content were prepared and used to form tough and flexible membranes. The PES-g-PEO membranes displayed high thermal stability (T_d > 230 °C) and good mechanical properties. The water contact angles of the PES-g-PEO membranes ranged from 60.5° to 66.7°, 20° lower than those of poly(aryl ether sulfone) membranes (82-86°), indicating that the PEO side chains improved the hydrophilicity of the membranes. Wide-angle X-ray diffraction results indicated that the PES-g-PEO membranes possessed an amorphous structure, that is, crystallization of the PEO side chains did not occur. The Li-ion conductivity reached 2.26 × 10⁻⁴ S/cm at room temperature, much higher than that of the pure PEO-based system (10⁻⁶ S/cm), due to the presence of the amorphous PEO side chains between the PES backbones, which provided an effective Li-ion transport pathway.     

Electrochemical behavior of an interpenetrating polymer network hydrogel composed of poly(propylene glycol) and poly(acrylic acid)

An interpenetrating polymer network (IPN) hydrogel based on poly(propylene glycol) and poly(acrylic acid) was prepared by UV irradiation. The swelling behavior of the IPN hydrogel was studied by the immersion of the gel in aqueous NaCl solutions of various concentrations. The swelling ratio decreased with an increase in the NaCl concentration. The electrically sensitive behavior of the IPN hydrogel in electric fields was also investigated. The IPN hydrogel also showed a stepwise bending behavior that depended on the electric stimulus. The bending angle and bending speed of the IPN hydrogel were greatest in 0.6 wt % aqueous NaCl and increased with an increase in the applied voltage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2301–2305, 2003     

Thermal and NMR characterization on trans-esterification-induced phase changes in blends of poly(ethylene-2,6-naphthalate) with poly(pentylene terephthalate)

By using thermal and NMR analyses with supporting evidence from X-ray and scanning electron and optical microscopy, this study has attempted to clarify confusing issues of physical miscibility vs. chemical trans-reaction in blends of aryl polyesters upon heating. The study demonstrated that the blends of poly(pentylene terephthalate) (PPT) with poly(ethylene naphthalate) (PEN) were initially immiscible; however, with heating/annealing at high temperatures (300 °C) for long enough times, the original two phases merged into one single phase composed of two polyesters and some minor fractions of copolyesters. Upon extended heating, however, two original polyesters disappeared, and a random copolyester, coded as EN-co-PT, of various sequence lengths was produced as a result of extensive trans-reactions between PEN and PPT. The trans-reacted products from heated PEN/PPT (50/50) blend were characterized using ¹H NMR. The sequence structures of the produced co-polyesters and intermediate products were determined by a triad analysis, which showed that the mean sequence lengths became shorter and the randomness increased with time of heating. X-ray analysis confirmed that the PEN/PPT (50/50) blend completely lost its crystallizability only when heated at 300 °C for time of 60 min or longer, indicating formation of fully random copolyesters.     

Segmented polymer networks based on poly(N-isopropyl acrylamide) and poly(tetrahydrofuran) as polymer membranes with thermo-responsive permeability

Segmented polymer networks (SPNs) containing a polymer with a lower critical solution temperature were prepared by free radical copolymerization of poly(tetrahydrofuran) (PTHF) bis-macromonomers with N-isopropyl acrylamide (NIPAA). The PTHF bis-macromonomers, which were prepared by living cationic polymerization of tetrahydrofuran, were provided with acrylate or acrylamide end-groups by end-capping the living polymer chains with acrylic acid and 3-acrylaminopropanoic acid, respectively. Differential Scanning Calorimetry (DSC) experiments showed clearly that, for the same fractions of both network components, the phase morphology of the SPNs was highly influenced and adjustable by the nature of the end-groups of the bis-macromonomer as a result of their copolymerization behavior with NIPAA. For the same type of multi-component networks, the morphology changed from a heterogeneous up to a rather homogeneous nature by application of bis-macromonomers with, respectively, acrylate or acrylamide end-groups during their preparation. Swelling and DSC experiments on the swollen SPNs revealed, respectively, that the swelling properties and the cloud point temperature (T_cp) could be controlled by the network composition. The thermo-responsive water permeability and the possible application of the SPNs as pervaporation membranes for the separation of a water/isopropanol mixture were investigated as a function of temperature and network composition. The permeability and selectivity of the membranes decrease when the T_cp is reached. The permeability increases while the selectivity decreases with decreasing crosslink density or higher overall hydrophilicity of the SPNs.     

Molecular weight studies of the γ‐irradiation degradation of poly(methyl methacrylate) doped with poly(p‐sulfanilamide)

The protection of some poly(methyl methacrylate) (PMMA) samples against γ rays was investigated in the absence and presence of poly(p‐sulfanilamide). Pure PMMA (without additives) and PMMA–poly(p‐sulfanilamide) blend samples were irradiated with γ rays for different exposure doses (5, 15, 25, 35, 50, 75, and 100 kGy). The viscosity‐average molecular weights were determined and thin‐layer chromatography measurements were carried out after each irradiation dose. The maximum protection against γ rays was found when 1% poly(p‐sulfanilamide) was used. The radiation chemical yield for main scission (G_s) was calculated and had lower values in the case of 1% poly(p‐sulfanilamide). The energy absorption per scission was maximum for 1% poly(p‐sulfanilamide), and this confirmed the obtained G_s data. From thin‐layer chromatography studies, it was observed that both the retention factor (R_f) values and polydispersity of the PMMA samples increased with an increasing exposure dose. The effect of γ irradiation on PMMA films doped with 1% poly(p‐sulfanilamide) was investigated with UV spectroscopy after the extraction of the additives. A change in the intensity of the absorption bands with an increasing irradiation dose was recorded. It is suggested that PMMA films doped with this type of polymer can be used as dosimeters. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Highly conductive new aniline copolymers: poly(aniline‐co‐aminoacetophenone)s

Copolymers of aniline and o‐/m‐aminoacetophenone of different compositions were synthesized by oxidative chemical copolymerization. Two different methods were employed, emulsion and inverse emulsion, with different oxidants, ammonium persulphate and benzoyl peroxide, to study the effect of synthesis conditions on the yield, solubility and conductivity of the copolymers. The copolymer compositions were determined using proton NMR spectroscopy. The reactivity ratios determined by the Finemann–Ross method indicate lower reactivity for m‐aminoacetophenone relative to aniline in the emulsion method, while the reverse holds true in the inverse emulsion method. Copolymers formed by the former pathway are random type as determined by the Finemann–Ross method. The copolymers have crystalline/amorphous morphologies and good conductivity. They exhibit enhanced solubility compared with polyaniline. Copyright © 2005 Society of Chemical Industry     

Rheological studies of the poly(styrene-co-acrylonitrile) and poly(vinyl chloride-co-vinyl acetate) blends

The rheological studies of the poly(vinyl chloride-co-vinyl acetate) and poly(styrene-co-vinyl acetate) and poly(styrene-co-acrylonitrile) blends were performed by a Brabender Rheotron at three different temperatures and also at different shear rates. Flow curves of the blends at different temperatures were drawn. The flow behavior index and, also, zero-shear viscosity of the blends at different temperatures were determined. From the flow curves, it has been found that as shear stress increases, melt viscosity decreases at all temperatures, indicating that pseudoplastic behavior and experimental values lies above the line of the log-additivity value and below the line of the additivity rule of mixture. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2577–2583, 1998