Homopolymer Films Research Articles

Electroactive Materials Containing Macrocyclic Pseudo‐Crown Ether Cavities Electroformed from a Solid‐State Electropolymerization Reaction

New compounds consisting of two different electropolymerizable aromatic groups (pyrrole/thiophene 1, pyrrole/dimethoxybenzene 2, and dimethoxybenzene/thiophene 3) linked together by a polyether subunit have been synthesized and their electrochemical behavior has been investigated. At relatively low anodic potential values, the oxidation of these monomers led to electroactive homopolymer films containing pendant aromatic moieties. The oxidation of the preformed polymers by applying more positive potentials promoted further anodic couplings within their structure. The efficiency of this solid‐state electropolymerization reaction was found to be strongly dependent on the film thickness. So, electroactive copolymers possessing controllable size pseudo‐crown ether cavities were thought to be obtained.

Poly(chloro- p-xylylene)/SiO 2 multilayer thin films deposited near-room temperature by thermal CVD

Multilayer thin films consisting of alternating layers of poly(chloro- p-xylylene) (PPXC) and silicon dioxide (SiO 2) were deposited at 80–85°C, taking advantage of a recently developed process to deposit SiO 2 at near-room temperature by thermal chemical vapor deposition (CVD). The method used to deposit SiO 2 is general and can be applied to near-room temperature deposition of many oxide thin films such as Al 2O 3, Y 2O 3, TiO 2, ZrO 2, Ta 2O 5, Nb 2O 5, and ZnO; but for the development of low dielectric constant materials to reduce RC-delay in ultra large scale integration (ULSI) devices, the deposition of SiO 2 with a polymeric material is more applicable. Further, the ability to deposit SiO 2 in a multilayer structure with a polymer is also advantageous to studying ultrathin polymeric films which finds applicability where polymeric materials experience confined geometry such as in composite materials, lubrication and biocompatible ultrathin films. X-ray diffraction (XRD) results showed the presence of new crystallites in the homopolymer film after post-deposition anneal at 150°C due to a decrease in the d-spacing but after a 200°C post-deposition anneal, only an increase in crystallinity occurred due the nucleation and growth of new crystallites and not the growth of existing crystallites. However, the multilayer films were more sluggish to crystallize and to form new crystallites after post-deposition anneals as compared to PPXC as a result of a thickness effect at ∼35 nm. The introduction of a polymer with SiO 2 raised the index of refraction from 1.44 to 1.59 (@630 nm) and lowered the dielectric constant from 4.0 to 3.30 (@10 kHz) with a PPXC thickness fraction of ∼0.80.

Effects of surface functional groups on film formation and tensile strength development in reactive latex systems

AbstractThe effect of surface functional groups on chain interdiffusion at the interfacial zone of reactive latexes was investigated. A series of latexes with different surface functionalities was prepared by batch or shot‐growth emulsion polymerizations. The particle surface properties were varied by changing the number density of functional groups. The rate of tensile strength development decreases with the increasing number density of surface functional groups, which indicated that inter‐particle crosslinking restricted the interdiffusion of polymer chains during film formation and annealing. The average diffusion coefficient D of polymer chains across particle interfaces was obtained from dynamic mechanical analysis and compared well with the results from the rate of tensile strength development. The magnitude of D of the reactive latex film was lower than that of the homopolymer film. The lower chain mobility of reactive latexes prevented mechanical strength development.

Polyporphyrin Thin Films from the Interfacial Polymerization of Mercaptoporphyrins

Free-standing ultrathin films of a porphyrin homopolymer have been synthesized by interfacial polymerization of a mercaptoporphyrin. Coupling of 5,10,15,20-tetrakis(α-mercapto-p-tolyl)porphyrin at the water/chloroform interface by copper acetate yields continuous, flexible films after drying with supercritical CO2. These films are amorphous and retain many characteristics of the monomeric porphyrin, such as the property that they may be metalated. Spectroscopic evidence suggests efficient cross-linking of thiols through disulfide coupling occurs in these polyporphyrins to form a network. Polymerization is accompanied by the introduction of carbonyl functionality, probably the transformation of residual thiols to thioacetate by metal-mediated reaction with excess acetate ion. As an example of the catalytic properties of these polymers, they are shown to promote photooxidation of thietane to the corresponding sulfoxide by sensitizing singlet oxygen production.

Measurements of the Flory−Huggins Interaction Parameter for Polystyrene−Poly(4-vinylpyridine) Blends

We have measured the Flory−Huggins interaction parameter (χ) for blends of polystyrene (PS) and poly(4-vinylpyridine) (P4VP) by three different methods. First, we measured the micelle spacings in microphase-separated films of PS−P4VP diblock copolymers by secondary ion mass spectrometry and atomic force microscopy. Second, we measured the contact angle of droplets of homopolymer PS on P4VP homopolymer film. Finally we determined the interfacial width between homopolymer layers of dPS and P4VP by neutron reflectometry. From each of these experiments χ was calculated using mean field theory in the strong segregation limit. These values of χ are much larger than those of other nonionic polymer pairs. We discuss the importance of this findings.

Preparation and Electrochemical Properties of Electrically Conductive Polyetherimide-Polypyrrole Composites

In this work, electrically conductive polyetherimide(PEI)-polypyrrole(PPy) composites have been prepared and their electrochemical properties were investigated. The composites were prepared on indiumtin-oxide(ITO) coated glass electrode. The composite films showed lower conductivity but better thermal stability than PPy homopolymer film. The properties of the composite films were strongly dependent on the preparation method of the PET matrix.

Interfacially Confined Polymeric Systems Studied by Atomic Force Microscopy

ABSTRACTWithin the last few years, a surface science technique, the atomic force microscopy (AFM), has evolved to be capable of simultaneously measuring tribological (friction, wear, adhesion) and rheological (elastic moduli, viscosity, hardness) properties and topography on the nanometer scale. Particularly for thin polymeric films, the AFM can be efficiently used for studying surface mechanical properties which are of fundamental importance to help predict stress and frictional behavior of interfacially confined ultrathin films.In this paper, the following aspects will be discussed: (a) mechanical properties of ultrathin homopolymer and copolymer films, (b) dewetting dynamics of interfacially confined phase-separated homopolymers, and (c) the influence of graft-copolymers on the wetting and dewetting characteristics of homopolymers.

Using Epitaxy To Form Insoluble, Ultrathin Films of Block Copolymers

A new method of assembling functional films by epitaxy of diblock copolymers is reported. The fundamental architecture consists of a crystalline block that is used to tether the whole chain onto a substrate surface by epitaxial adsorption, and a noncrystalline block that provides functional groups. Epitaxial adsorption is realized by polymerization-induced epitaxy, where solution polymerization of monomers directly induces epitaxial growth of chains on the substrate surface. After cationic polymerization of tetrahydrofuran (THF) with the presence of graphite in a reaction mixture, a mixture of THF and 3,3-bis(chloromethyl)oxacyclobutane (BCMO) were introduced to the reaction mixture to form PTHF-block-P(THF-BCMO). Fourier transformed infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of the block copolymer on graphite even after rigorous rinsing of the substrate surface. Atomic force microscopy scanned over micrometer ranges exhibited the same island features as that of PTHF homopolymer film. But these crystalline islands are covered by ultrathin, highly viscous layers that are insoluble. Molecular resolution images by scanning tunneling microscopy showed that the features on the copolymer film are the same as that of an epitaxially adsorbed monolayer of PTHF homopolymer. No film remained on the graphite surface if the graphite was simply immersed in the copolymer solution and was rinsed similarly. These results indicate that the insoluble film of diblock copolymer was formed during polymerization, in which the crystalline PTHF block binds to the surface by epitaxial adsorption and the noncrystalline P(THF-BCMO) block is free of surface attachment.

Time-Dependent Reactive Coupling at Polymer−Polymer Interfaces

X ABSTRACT: Using recently calculated rate coefficients for reactive coupling of chains at polymer-polymer interfaces, we describe the diffusion-controlled growth of diblock copolymer at the interface between dissimilar molten homopolymer films. The growth exhibits several regimes, successively controlled by (1) the quasilocal reaction rate near the interface, (2) center-of-mass diffusion of reactive homopolymer to the interface, and (3) the diffusion barrier presented by the growing copolymer layer. Our results can be tested by time-dependent measurements of the copolymer coverage or concentration of reacted coupling groups.

Electroactive Polymeric Materials for Battery Electrodes: Copolymers of Pyrrole and Pyrrole Derivatives with Oligo(ethyleneoxy) Chains at the 3-Position

The electrochemical polymerization of pyrrole derivatized at the 3-position with an oligo-(ethyleneoxy) group was investigated. Two monomers were synthesized, namely, 3-(3,6-dioxaheptyl)-pyrrole (DHPy) and 3-(3,6,9-trioxadecanyl)pyrrole (TDPy), and homopolymerized in a LiClO 4 /propylene carbonate medium. The electrical conductivity of poly[3-(3,6-dioxaheptyl)pyrrole] (PDHPy) and poly[3-(3,6,9-trioxadecanyl)pyrrole] (PTDPy), measured by the four-point probe method, was 0.08 and 15 S cm -1 , respectively. Electrochemical copolymerization of both oligo(ethyleneoxy)-substituted pyrroles with pyrrole led to good quality films which displayed considerably higher electrical conductivity than the homopolymers. The conductivity of the copolymer with DHPy was in the range from 8 to 10 S cm -1 and that with TDPy in the range from 20 to 100 S cm -1 . The cyclic voltammogram of both homopolymers and of the copolymers gave current-potential curves with larger areas (ca. 3 times) than PPy. The copolymer of TDPy and pyrrole showed that it was capable of supplying the same current for a longer period of time than polypyrrole itself. No stability problems were observed with the copolymers in contrast to the homopolymer films, and the samples charged and discharged smoothly. In scanning electron micrography, copolymers showed larger nodules than the homopolymer which entirely cover the surface of the compact layer. The results of the copolymer systems show that they have a high potential as materials for polymeric battery electrodes.

Effect of crystallization, poling and ageing conditions on the FIR, dielectric and pyroelectric properties of hot‐pressed PVDF and P(VDF/TFE)‐(0.98/0.02)

AbstractWe studied the influence of hot‐pressing temperature as well as poling and ageing conditions on the amount of polar phase of hot‐pressed PVDF and P(VDF/TFE)‐(0.98/0.02) foil. FIR transmission spectra of hot‐pressed homopolymer and copolymer films were measured in the 30‐450 cm—1 range as a function of hot‐pressing temperature Thp and poling temperature Tp. The FIR studies show that homopolymer and copolymer consist of both polar and nonpolar modifications of PVDF. The content of the polar phase tends to decrease with Thp and increase after poling. The FIR spectra of our samples exhibit a strong absorption peak near 100 cm—1 absent in the biaxially oriented Solef samples, which is believed to be due to the amorphous phase in our samples. Four thermally stimulated current (TSC) maxima are attributed to the relaxation in the amorphous region (∼40°C), to the dipolar relaxation in the nonpolar (∼60°C) and polar (∼80°C) phase, and the space charge relaxation (dependent on the poling temperature). The pyroelectric coefficient of the homopolymer and copolymer thermoelectret foil prepared by hot‐pressing is of the same order as that of the PVDF thermoelectret foil produced by Solvay and can be influenced by the hot‐pressing conditions. The dielectric response of the hot‐pressed PVDF‐type foils can be described by the Kohlrausch‐–Williams‐Watts function and is characteristic of a heterogeneous system.

Thermal Expansion of Thin Diblock Copolymer Films

AbstractThe thermal expansion of thin films of symmetric diblock copolymers of polystyrene (PS) and poly(methyl methácrylate) (PMMA) was investigated by X‐ray reflectivity. The confinement of the copolymer to the substrate, coupled with the multilayering of the copolymer where PS and PMMA layers are oriented parallel to the substrate, gives rise to unusual thermal expansion characteristics. The total thickness of the film increases as 3αL, where αL is the linear thermal expansion coefficient of the copolymer. Unlike homopolymer films, the thermal expansion of an ordered block copolymer film results in an excessive stretching of the copolymer chains at the interface between the PS and PMMA layers. This excess stretching is a result of the confinement of the junction points of the copolymer chains to the interfaces and the suppression of the lateral expansion of the copolymer. When the stretching of the chains becomes too high, relaxation occurs by transporting copolymer chains to the surface. This is evidenced by a reduction in the period of the multilayer. After the copolymer chains have relaxed, the change in the multilayer period with temperature closely follows αL.

Room temperature copolymerization to improve the thermal and dielectric properties of polyxylylene thin films by chemical vapor deposition

Polyxylylene thin films grown by chemical vapor deposition (CVD) have long been utilized for uniform, pinhole-free conformal coatings. Homopolymer films are highly crystalline and have a glass transition temperature around room temperature. We show room temperature copolymerization with previously untested comonomers during the CVD process. Samples were studied with wavelength dispersive analysis, FTIR, scanning variable angle ellipsometry, and x-ray diffraction. Copolymerizing chloro-p-xylylene with perfluoro-octyl methacrylate results in dielectric constants at optical frequencies as low as 2.19, compared to 2.68 for the homopolymer. Copolymerizing p-xylylene with 4-vinylbiphenyl resulted in films whose onset of weight loss in TGA measurements was 450 °C, compared to 270 °C for the homopolymer.

New polyurethane compositions able to bond high amounts of both albumin and heparin

In order to prepare polymers provided with better haemocompatibility with respect both to the coagulative cascade and to platelet aggregation and activation, we have synthesized new polyurethanes containing in the chain extender [di-(2-hydroxyethyl) hexa-decylamine (DHHA)] both a long chain alkyl group (able to bond albumin) and a tertiary ammonium group able, after suitable quaternization reaction, to bind ionically significant amounts of heparin. The amounts of heparin and albumin bonded to the polymer films were determined spectrophotometrically. A biological in vitro evaluation of the heparinized and albuminized films was also carried out, with respect to the blood coagulation factors (by APTT measurements) and to platelet adhesion. For the sake of comparison, polyurethanes containing as chain extenders two different monomers (containing, respectively, the long alkyl and the quaternary ammonium group), and polymer blends consisting of these copolymers, were also prepared and evaluated as above. It was seen that the type of the adsorption sequence for albumin and heparin, respectively, onto films of the various homopolymers, copolymers and blends, plays an important role in their biological properties.

Wetting behavior of homopolymer films on chemically similar block copolymer surfaces.

The wetting properties of thin polystyrene (PS) homopolymer films (polymerization index ${N}_{H}$) were studied on the surfaces of polyvinylpyridine-polystyrene (PVP-PS) block copolymer films (polymerization indices ${N}_{\mathrm{PS}}$ and ${N}_{\mathrm{PVP}}$) oriented into lamellae with the PS block present at the vacuum interface. Autodewetting was observed on the diblock copolymer surface when $\frac{{N}_{H}}{{N}_{\mathrm{PS}}}\ensuremath{\ge}5$, with a contact angle independent of ${N}_{H}$, but decreasing with N. The dewetting nucleated at the base of islands on the ordered PVP-PS surfaces. The dewetting processes were explained using mean field theories and Monte Carlo simulations.

Synthesis and Electrical Properties of Crosslinked Poly(1,2,4,5-Phenylenedivinylene) and Copolymers

Crosslinked conjugated conducting polymer, poly(1,2,4,5-penylene divinylene)(PPDV) and its copolymers were prepared by the water-soluble precursor method. The spectral characteristics of these materials have been investigated by using W-visible and FT-IR spectroscopy. PPDV homopolymer film could not be stretched due to its crosslinked structure, so this homopolymer could slightly be doped with strong oxidant, FeCl 3 , to produce a very low conductivity value of 3 x 10 -6 Scm -1 . However, copolymers containing PDV units and DMPV units showed considerably high conductivities ranging from 3 x 10 -2 to 68 Scm -l , when doped with FeCl 3, depending upon the copolymer composition.

Low Dielectric Constant, High Temperature Stable Copolymer Thin Films by Room Temperature Chemical Vapor Deposition

ABSTRACTPolyxylylene thin films grown by the chemical vapor deposition (CVD) process have long been utilized to achieve uniform, pinhole-free conformal coatings. They have recently been cited as possible low dielectric constant films for intermetal layers in high-speed ICs. Homopolymer films are highly crystalline and have a glass transition temperature around room temperature. We have demonstrated that room temperature copolymerization with previously untested comonomers can be achieved during the CVD process. Copolymerizing chloro-p-xylylene with perfluorooctyl methacrylate results in the dielectric constant at optical frequencies being lowered from 2.68 to 2.19. Copolymerizing p-xylylene with vinylbiphenyl resulted in films which increase the temperature at which oxidative scission occurs from 320 to 450C. Copolymerizing p-xylylene with 9-vinylanthracene resulted in a brittle, yellow film.

Synthesis and electrical and optical properties of poly‐(2‐methoxy‐1,4‐phenylenevinylene) and copolymers

AbstractPoly(2‐methoxy‐1,4‐phenylenevinylene) (PMVP) and copolymers containing both unsubstituted (1,4‐phenylenevinylene, PV) and 2‐methoxy‐1,4‐phenylenevinylene (MPV) units were prepared in thin films from their water‐soluble sulfonium salt precursor polymers. Drawn films (L/L0 = 6) of the PMPV homopolymer could be doped with I2 vapor and FeCl3 to give conductivities of 3,2 and 4,0 ċ cm−1, respectively. The conductivity of FeCl3‐doped copolymer films ranged from 100 to ca. 102 ċ cm−1 depending on the composition. The third‐order nonlinear susceptibility, χ(3), for the PMPV film was investigated by degenerate four‐wave mixing technique using 400 femtosecond pulses at 602 nm. A relatively large χ(3) value (7,9 ċ 10−10 esu) with a subpicosecond response was observed.

Characterisation of shrinkage in oriented PET films and containers by thermomechanical analysis (TMA)

AbstractIn this paper, we report from an extensive series of tests in which the thermal shrinkage behaviour of poly(ethylene terephthalate) (PET) homopolymer and copolymer films and containers has been studied by thermomechanical analysis (TMA). Several independent variables have been investigated, and the accuracy of dynamic TMA scans of temperature‐dependent shrinkage has been verified by parallel measurements made isothermally. Typical shrinkage levels of biaxially oriented films, of draw ratios between 2.7 and 4.1, are of the order of 5% at 100°C. The magnitude of shrinkage increases with draw ratio, and any evidence to suggest that PET copolymer is marginally more prone to shrinkage is thought to arise from differences in strain‐induced crystallinity induced by elongational deformations during processing. Correlations between measurements made on films and commercial containers are good enough to suggest that the simulation technique used is sufficiently valid for further experimentation on processing behaviour.

Phase study of nylon 6/poly (acrylic acid) blends cast from solutions in aqueous formic acid

AbstractBlends of nylon 6 (Ny6) with poly(acrylic acid) (PAA) were prepared in film form from solutions in a mixture of formic acid and water by evaporating the solvent. The miscibility and phase constitution of the binary blends obtained over a wide composition range (5/95–95/5) were examined by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical measurements. A Ny6 homopolymer film and Ny6/PAA blends with PAA concentrations ≥ 50 wt% exhibited a WAXD profile stemmed from the coexistence of two different crystalline modifications of Ny6, i.e. the α and γ forms. Above 50 wt% PAA content, the solution‐cast blends showed no definite crystallinity. It was found by DSC thermal analysis that the polymer pair is substantially miscible in the non‐crystalline state, since a single glass transition temperature (Tg) was situated between the Tgs of the two homopolymers at every composition; however, the Tg versus composition plots did not follow a monotonic function but yielded a peak maximum at a PAA concentration of c. 25 wt%. In order to interpret this phenomenon, attention was given to the following point revealed by dynamic mechanical measurements: at the compositions of Ny6/PAA = 100/0–50/50, a phase of low regularity such as a nematic structure is formed in the cast films.