Flow rates of polymer solutions through porous disks as a function of solute. II. Thickness and structure of adsorbed polymer films

The thickness of films of poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc), and polystyrene (PS) adsorbed on Pyrex glass was studied by measuring the flow rates of polymer solutions and the corresponding pure solvents through sintered filter disks. Adsorption isotherms were in agreement with those reported by other workers and showed saturation adsorption equivalent to 2–8 condensed monolayers of monomer units. Film thicknesses were of the order of magnitude of the free coil diameters in solution and were directly proportional to the intrinsic viscosity of the polymer, except for PS in benzene where the thicknesses leveled off as molecular weight increased. It was concluded that polymers adsorb from solution in monolayers of compressed or interpenetrating coils; that below some critical molecular weight which varies with polymer and solvent, a much larger fraction of the segments lies directly in the interface; that adsorbed films may consist of a dense layer immediately adjacent to the surface and a deep layer of loops extending into the solvent; and that it is the segment—solvent interaction rather than the segment—surface interaction which dominates the conformation of the adsorbed chain.     

Viscometric study of poly(vinyl chloride)/poly(vinyl acetate) blends in various solvents

The intermolecular interactions between poly(vinyl chloride) (PVC) and poly(vinyl acetate) (PVAc) in tetrahydrofuran (THF), methyl ethyl ketone (MEK) and N,N^′-dimethylformamide (DMF) were thoroughly investigated by the viscosity measurement. It has been found that the solvent selected has a great influence upon the polymer-polymer interactions in solution. If using PVAc and THF, or PVAc and DMF to form polymer solvent, the intrinsic viscosity of PVC in polymer solvent of (PVAc+THF) or (PVAc+DMF) is less than in corresponding pure solvent of THF or DMF. On the contrary, if using PVAc and MEK to form polymer solvent, the intrinsic viscosity of PVC in polymer solvent of (PVAc+MEK) is larger than in pure solvent of MEK. The influence of solvent upon the polymer-polymer interactions also comes from the interaction parameter term Δb, developed from modified Krigbaum and Wall theory. If PVC/PVAc blends with the weight ratio of 1/1 was dissolved in THF or DMF, Δb<0. On the contrary, if PVC/PVAc blends with the same weight ratio was dissolved in MEK, Δb>0. These experimental results show that the compatibility of PVC/PVAc blends is greatly associated with the solvent from which polymer mixtures were cast. The agreement of these results with differential scanning calorimetry measurements of PVC/PVAc blends casting from different solvents is good.     

Δχ effects on the miscibility of polymer blends

The Δχ effect on the miscibility of polymer blends prepared by solution-casting has been investigated using the mixture of poly(methyl methacrylate)(PMMA) with poly(vinyl acetate) (PVAc). The PMMA/PVAc blends have been prepared by casting from eleven different solutions. The Δχ effect of the solution–cast PMMA/PVAc blends was discussed in terms of Hansen's specified solubility parameters. It was found that the miscibility of the blends could be defined mainly by the solubility parameter contributed by the hydrogen–bonding of a solvent.     

Development and characterization of reactive extruded PVC/polyacrylate blends

This paper describes a method to obtain polymer blends by the absorption of a liquid solution of monomer, initiator, and a crosslinking agent in suspension type porous poly(vinyl chloride) (PVC) particles, forming a dry blend. These PVC/monomer dry blends are reactively polymerized in a twin‐screw extruder to obtain the in situ polymerization in a melt state of various blends: PVC/poly(methyl methacrylate) (PVC/PMMA), PVC/poly(vinyl acetate) (PVC/PVAc), PVC/poly(butyl acrylate) (PVC/PBA) and PVC/poly(ethylhexyl acrylate) (PVC/PEHA). Physical PVC/PMMA blends were produced, and the properties of those blends are compared to reactive blends of similar compositions. Owing to the high polymerization temperature (180°C), the polymers formed in this reactive polymerization process have low molecular weight. These short polymer chains plasticize the PVC phase reducing the melt viscosity, glass transition and the static modulus. Reactive blends of PVC/PMMA and PVC/PVAc are more compatible than the reactive PVC/PBA and PVC/PEHA blends. Reactive PVC/PMMA and PVC/PVAc blends are transparent, form single phase morphology, have single glass transition temperature (T_g), and show mechanical properties that are not inferior than that of neat PVC. Reactive PVC/PBA and PVC/PEHA blends are incompatible and two discrete phases are observed in each blend. However, those blends exhibit single glass transition owing to low content of the dispersed phase particles, which is probably too low to be detected by dynamic mechanical thermal analysis (DMTA) as a separate T_g value. The reactive PVC/PEHA show exceptional high elongation at break (～90%) owing to energy absorption optimized at this dispersed particle size (0.2–0.8 µm). Copyright © 2005 John Wiley & Sons, Ltd.     

Electron transport in solution-grown TIPS-pentacene single crystals: Effects of gate dielectrics and polar impurities

The n-channel behavior has been occasionally reported in the organic field-effect transistors (OFETs) that usually exhibit p-channel transport only. Reconfirmation and further examination of these unusual device performances should deepen the understanding on the electron transport in organic semiconductors. 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-pentacene), a widely examined p-channel material as Au is used for source-drain electrodes, has recently been reported to exhibit electron transport when grown from non-polar solvent on divinyltetramethyldisiloxanebis (benzocyclobutene) (BCB) dielectric, spurring the study on this unusual electron transport. This paper describes FET characteristics of solution-grown TIPS-pentacene single crystals on five polymer gate dielectrics including polystyrene (PS), poly(methyl methacrylate) (PMMA), poly(4-vinyl phenol) (PVP), poly(vinyl alcohol) (PVA) and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)). In addition to the p-channel behavior, electron transport occurs in the crystals on PMMA, PS, thick PVA (40 nm) and a bilayer dielectric of PMMA on P(VDF-TrFE-CFE), while does not on PVP and thin PVA (2 nm). The two distinct FET characteristics are consistent with the previous reported trap effect of hydroxyl groups (in PVP and PVA) and reduced injection barrier by Na⁺ ions (as impurity in PVA). The highest electron mobility of 0.48 cm² V^-1 s^-1 has been achieved in the crystals on PMMA. Furthermore, the electron transport is greatly attenuated after the crystals are exposed to the vapor of a variety of polar solvents and the attenuated electron transport partially recovers if the crystals are heated, indicating the adverse effect of polar impurities on electron transport. By reconfirming the n-channel behavior in the OFETs based on TIPS-pentacene, this work has implications for the design of n-channel and ambipolar OFETs.     

A study of three-layered latex interpenetrating polymer networks used as processing modifiers and impact modifiers of thermo-plastic resins

In this paper, the latex interpenetrating polymer network poly(n-butyl acrylate) polystyrene/poly(methyl methacrylate) (PBA/PS/PMMA, or PBSM) was synthesized by microagglomeration and three-stage emulsion polymerization. The initial poly(n-butyl acrylate) latex particle was agglomerated by methacrylic acid residue containing the polymer latex and then encapsulated by PS and PMMA. The polyblend of poly(vinyl chloride) (PVC) and PBSM (PVC/PBSM) was prepared by blending PVC and PBSM. The morphology and properties of the polyblend have been studied. Experimental results have shown that the processability and impact-resistance of PVC can be enhanced considerably by means of blending 6–20 per hundred resin (phr) PBSM. The three-layered latex interpenetrating polymer network is a promising modifier for rigid PVC (RPVC) manufactures.     

STUDIES OF THE CRYSTALLIZATION BEHAVIOR IN THE CRYSTALLINE/AMORPHOUS POLYMER BLENDS: POLY(ETHYLENE OXIDE)/POLY(METHYL METHACRYLATE) AND POLY(ETHYLENE OXIDE)/POLY(VINYL ACETATE)

The crystallization process of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA)and PEO/poly(vinyl acetate) (PVAc) blends has been characterized by Fourier Transform Infrared(FTIR) spectra in conjunction with Differential Scanning Calorimeter (DSC) measurements. Thecrystallinity of PEO varies consistently with PEO content in PEO/PVAc blends and the PEO/PMMAblends containing 50 wt% or less PMMA. For the PEO/PMMA blends containing 60 wt% ormore PMMA, the crystallinity of PEO decreases more than PEO content but develops with crystal-lization time. These results can be explained in terms of difference between the crystallization tem-perature (T_c) and glass transition temperature (T_g) of the blends as a function of content of amorphouscomponent.     

The Preparation of Ipns of Polystyrene-Polyethylene and Poly(Butyl Methacrylate)-Polyethylene and Their Dynamic Mechanical Behavior

IPNs based on polyethylene and vinyl polymers were prepared according to a new procedure. We studied the dynamic mechanical behavior of two series of IPNs: polystyrene (PS)-polyethylene (PE) and poly(butyl methacrylate) (PBMA)-PE at the frequency ω = 1 Hz and in the temperature region from ?50 to 200°C. Temperature dependences of the components of the dynamic modulus of elasticity G' and G" of the networks PS and PBMA have shapes typical of amorphous networks; the corresponding dependences of pure PE show, however, features typical of a semicrystalline polymer. IPNs of the system PS/PE show two-phase behavior. At T < 110°C, PE functions as a plasticizer. In the system PBMA/PE, better miscibility of components is seen, and PE exerts a reinforcing effect on the mechanical behavior over the whole temperature region. In both systems, network density increases with increasing PE content in IPNs. Better homogeneity and a slight increase in the network density of IPNs with PBMA/PE in comparison to PS/PE networks are probably caused by a greater number of grafted PBMA chains in the PE network compared to the PS network.     

Synthesis and Characterization of a Diblock Copolymer of Methyl Methacrylate and Vinyl Acetate by Successive Photo‐Induced Charge Transfer Polymerization Using Ethanolamine as the Parent Compound

Communication: A diblock copolymer consisting of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) with hydroxyl group at one end is prepared by successive charge transfer polymerization (CTP) under UV irradiation at room temperature using ethanolamine and benzophenone as a binary initiation system. The diblock copolymer PMMA‐b‐PVAc could be selectively hydrolyzed to the block copolymer of poly(methyl methacrylate) and poly(vinyl alcohol) (PVA) using sodium ethoxide as the catalyst. Both copolymers, PMMA‐b‐PVAc and PMMA‐b‐PVA, are characterized in detail by means of FTIR and ¹H NMR spectroscopy, and GPC. The effect of the solvent on CTP and the kinetics of CTP are discussed.     

Synthesis of microspheres with microphase‐separated shells

Novel structural microspheres of the Janus type, with microphase‐separated polystyrene (PS) and poly(tert‐butyl methacrylate) (PBMA) shells and crosslinked poly(2‐vinyl pyridine) (PVP) cores, were synthesized with the crosslinking of PVP spherical domains in poly(styrene‐block‐2‐vinyl pyridine‐block‐tert‐butyl methacrylate) ABC triblock terpolymer film with PS/PBMA lamellae–PVP spherical structures. For the formation of lamellae‐sphere structures, toluene, which was a selective solvent for the ABC triblock terpolymer, was used. With the crosslinking of PVP spheres in the microphase‐separated film with 1,4‐diiodobutane gas, the microphase structure of the terpolymer was fixed, and microspheres composed of microphase‐separated PS and PBMA shells and P2VP cores were obtained. The size distribution of the purified microspheres was narrow. The characteristics of the microspheres and their aggregation behaviors in selective solvents were investigated by transmission electron microscopy and light scattering methods. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2091–2097, 2000     

Phase behavior and a modified Kwei equation for ternary polymer blends containing stereoregular PMMA

Previously, poly(methyl methacrylate) (PMMA) was found to be almost immiscible with poly(vinyl acetate) (PVAc) regardless of tacticity of PMMA and casting solvent. Poly(vinyl phenol) (PVPh) was found successful previously in making immiscible atactic PMMA/PVAc miscible. In this investigation, tacticity effect of PMMA on a ternary composed of PMMA, PVAc and PVPh was studied. Isotactic PMMA ternary was shown to be miscible in all the studied compositions on the basis of single T_g observation. However, syndiotactic PMMA ternary demonstrated immiscibility at ca. 25% PVPh and miscibility was observed at higher PVPh concentrations. A modified Kwei equation based on the binary interaction parameters was proposed to describe the experimental T_g of the miscible ternary almost quantitatively.     

Direct-write multiphoton photolithography: a systematic study of the etching behaviors in various commercial polymers

The nonlinear optical processes involved in etching thin polymer films by direct-write multiphoton photolithographic methods (Higgins et al. Appl. Phys. Lett. 2006, 88, 184101) are systematically explored. Power-dependent etching data are obtained for thin films of several commercial polymers, including poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(butyl methacrylate) (PBMA), and poly[2-(3-thienyl)ethyloxy-4-butylsulfonate] (PTEBS). Femtosecond pulses of light from a Ti:sapphire laser are focused to a diffraction limited spot of approximately 570 nm 1/e2 diameter in the films to induce etching. The power dependence of etching in each polymer is used to determine the order of the nonlinear optical process involved. The results for PMMA and PBMA, both of which absorb to the blue of 240 nm, demonstrate that etching involves absorption of several (i.e., 4-6) photons by the polymer, whereas PS, which absorbs wavelengths shorter than 280 nm, is etched by a lower-order process involving fewer (i.e., 3-4) photons. PTEBS, a conducting polymer that absorbs in the visible, is etched by a two-photon process. The results are consistent with an etching mechanism that involves multiphoton-induced depolymerization of the polymer, followed by vaporization of the resulting fragments. The etching resolution is found to be highest for polymers having high glass transition temperatures, low molecular weights, and no visible absorption. Among the polymers examined, low molecular weight PMMA is concluded to be the best polymer for use with this lithographic method. Finally, soft lithography is used to transfer patterns produced in a PMMA film onto poly(dimethylsiloxane), demonstrating a simple means for fabricating submicrometer-scale structures for use in micro- and nanofluidic devices.     

Crystallization,morphology, structure and miscibility of poly(ethylene oxide) based blends

Results of an investigation on the morphology, structure, isothermal crystallization, thermal behaviour and miscibility of poly(ethylene oxide) (PEO) based binary blends are reported. In particular poly(vinyl acetate)(PVAc), poly(methyl methacrylate) (PMMA) at different tacticity and poly(ethyl methacrylate) (PEMA) were added to PEO. It was found that with the only exception of isotactic poly(methyl methacrylate) (IPMMA), the addition of the above cited components causes a depression in both the spherulite growth rate and the overall kinetic rate constant. The experimental G and Kn were analyzed by means of the latest kinetic theory in order to determine the influence of composition on the process of surface secondary nucleation. The optical microscopy of thin films of the sample revealed that the blends crystallized with volume filling crystals at least up to 50/50 blend composition. The small angle X-ray scattering curves were analyzed using a recently developed methodology. The structural properties of the blends were attributed to the presence of the non crystallizable material in the interlamellar or interfibrillar regions of PEO. From the glass transition temperature it has been deduced that an homogeneous amorphous phase is present for all the blends except for the PEO/IPMMA amorphous system. For the system PEO/atactic poly(methyl methacrylate) (APMMA) the miscibility was also predicted by theoretical approaches.     

Proton spin-lattice relaxation study of polymer solutions

Proton spin-lattice relaxation times of solvent molecules were measured on ternary mixtures of a polymer and two solvents by the adiabatic rapid-passage method. The selective adsorption of a good solvent was verified by this experimental technique for the systems benzene—cyclohexane—polystyrene(PS), benzene—carbon tetrachloride—poly(methyl methacrylate)(PMMA), and chloroform—carbon tetrachloride—PMMA. The number of molecules of adsorbed benzene per monomeric unit of PS was estimated to be about four, which is almost identical with that determined previously by thermodynamic measurements. The number of molecules of benzene and chloroform adsorbed on PMMA were also determined to be about five and four, respectively. It was found that the interaction between chloroform and PMMA has the greatest effect on the molecular motion of the solvent, whereas the benzene—PS interaction is weak.     

Interactions and prediction of phase diagrams in ternary blends comprising poly(vinyl acetate), poly(vinyl p‐phenol), and poly(methyl methacrylate)

This study investigated and discovered a new miscible ternary blend system comprising three amorphous polymers: poly(vinyl acetate) (PVAc), poly(vinyl p‐phenol) (PVPh), and poly(methyl methacrylate) (PMMA) using thermal analysis and optical and scanning electron microscopies. The ternary compositions are largely miscible except for a small region of borderline ternary miscibility near the side, where the binary blends of PVAc/PMMA are originally of a borderline miscibility with broad T_g. In addition to the discovering miscibility in a new ternary blend, another objective of this study was to investigate whether the introduction of a third polymer component (PVPh) with hydrogen bonding capacity might disrupt or enhance the metastable miscibility between PVAc and PMMA. The PVPh component does not seem to exert any “bridging effect” to bring the mixture of PVAc and PMMA to a better state of miscibility; neither does the Δχ effect seem to disrupt the borderline miscible PVAc/PMMA blend into a phase‐separated system by introducing PVPh. Apparently, the ternary is able to remain in as a miscible state as the binary systems owing to the fact that PVPh is capable of maintaining roughly equal H‐bonding interactions with either PVAc or PMMA in the ternary mixtures to maintain balanced interactions among the ternary mixtures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1147–1160, 2006     

Investigation of polymer miscibility by spectroscopic methods. III. Labeling of poly(vinyl chloride), poly(methyl methacrylate) and poly(styrene-co-acrylonitrile) with fluorescent chromophores for nonradiative energy transfer studies

Poly(vinyl chloride) (PVC) is generally recognized as miscible with s.poly(methyl methacrylate) (s.PMMA), poly(?-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) copolymer (SAN) containing 27 wt % AN. Nonradiative energy transfer (NRET) is a very sensitive technique in the investigation of the polymer miscibility. To compare by NRET the actual degree of miscibility of the PVC/s.PMMA, PVC/PCL, and PVC/SAN polymer pairs, each polymer is to be labeled with a fluorescent chromophore to an extent of 1 or 2 mol %. This paper reports efficient pathways to attach anthracene (acceptor) or naphthalene (donor) onto preformed PVC, s.PMMA, and SAN samples. All the attempts for grafting carbazole (donor) moieties have failed, as well as any labeling of PCL whatever the nature of the chromophore.     

Investigation into new materials for optical devices: the miscibility and solvent effects of azobenzene derivative blends

With the increasing demand for novel devices with optical applications the search for new materials to data store and process becomes a priority. By introducing blends, tailor made properties and low cost give added advantage. Miscibility is an essential requirement for a new material, this research thus involves miscibility studies of poly(4‐(N‐(2‐methacryloyloxyethyl)‐N‐ethylamino)‐4′‐nitroazobenzene)₉₀‐co‐(methyl methacrylate)₁₀, (azobenzene derivative) with polymethyl‐methacrylate (PMMA), polyvinylacetate (PVAc) and polyvinylchloride (PVC) prepared in tetrahydrofuran (THF), and/or dimethylformamide (DMF) and/or dichloromethane (CH₂Cl₂). The glass transitions, solvent and varying molecular weight effect were investigated, since these all primarily influence the miscibility. THF was found to encourage miscibility at specific compositions of PVAc and PVC blends. However, with CH₂Cl₂ and DMF immiscibility is encouraged. The Fox–Flory equation was applied to the blends analyzing the PVC blends in DMF as deviations from ideality. Different molecular weights of PMMA were identified as immiscible regardless of solvent. PMMA's lower solubility in THF and CH₂Cl₂ compared to the azobenzene derivative, displayed the existence of PMMA islands. In all blends the favorable and unfavorable interactions between polymer–solvent–polymer systems are considered. Furthermore, the miscibility effect on increasing the MMA content of the azobenzene derivative was also investigated. Copyright © 2002 John Wiley & Sons, Ltd.     

VISCOMETRIC STUDY OF POLY(METHYL METHACRYLATE) AND POLYSTYRENE BLENDS IN DIFFERENT SOLVENTS

The intermolecular interaction between poly(methyl methacrylate) (PMMA) and polystyrene (PS) intetrahydrofuran (THF) and N,N'-dimethyl formamide (DMF) solvents was studied at 28℃ using a dilute solution viscometrymethod. Solvent is believed to play a key role in characterizing the viscosity behavior of the polymer solution. The intrinsicviscosity and viscosity interaction parameter were experimentally measured for the binary (solvent/polymer) and for theternary systems in two solvents. The compatibility of the polymer mixture was discussed in terms of the sign of △b_m. Theresults show that the compatibility of PMMA/PS blend in DMF is larger than that in THF.     

A comparison of electrospray-ionization and matrix-assisted laser desorption/ionization mass spectrometry with nuclear magnetic resonance spectroscopy for the characterization of synthetic copolymers

Electrospray ionization (ESI-MS) and matrix assisted laser desorption-ionization (MALDI-MS) were used to determine the composition (monomer ratios) and structure (end group analysis) relative to 1H NMR spectroscopy and theoretical predictions for three different copolymers: poly(butyl acrylate/vinyl acetate) (PBA/PVAc), poly(methyl methacrylate/vinyl acetate) (PMMA/PVAc) and poly(butyl acrylate/methyl methacrylate) (PBA/PMMA). We found that the ESI results were in excellent agreement with 1H NMR spectroscopy for PBA/PVAc and PBA/PMMA copolymers whereas there was more divergence in the case of PMMA/PVAc. In the case of PBA/PMMA copolymers similar distributions of products were observe by ESI-MS and MALDI-MS with the two major products classes differing by their end-groups. One class has hydrogen and dodecylthio end groups while in the other the dodecylthio has been replaced by alpha-cyanoisopropyl from the initiator. The relative abundance of these distributions as a function of copolymer conversion for a series of reaction conditions was investigated by both ESI and MALDI. MALDI results consistently underestimated (relative to ESI) the butylacrylate monomer ratio in PBA/PMMA and the abundance of co-polymer oligomers terminated by a dodecylthio group from the chain transfer agent.