Changes in row structure of extruded polyethylene film on grafting with styrene. I. Distribution of polystyrene and crystalline reorientation

Extruded films of linear polyethylene were grafted with styrene in a 1:2 styrene---methanol solution and pure styrene. The reaction was induced by simultaneous γ irradiation. Crystallinity of polyethylene was hardly affected by a polystyrene-to-polyethylene ratio as high as 13.5. From the anisotropy of film growth and small-angle x-ray diffraction it was concluded that polystyrene incorporated both into intercrystalline layers and newly formed domains alongside the stacks of lamellae. The proportion of polystyrene in interlamellar layers depends on the length of grafted chains; that is, on grafting conditions. A higher than expected proportion of occluded homopolystyrene was found in films grafted in methanol solution. The glass transition temperature of polystyrene decreased with grafting yield. Grafting in methanol solution produced changes in the x-ray orientation pattern of polyethylene. This was ascribed to untwisting and straightening crystalline lamellae in the row nucleated cylindrites.     

Mechanical properties of radiation-induced graft copolymers of styrene to polyethylene

Measurements were made of the tensile properties polyethylene-styrene grafts prepared by irradiating polyethylene films in liquid styrene. The films contained true graft and occluded styrene homopolymer. It was shown that yield strength, tensile strength, and initial modulus of elasticity increase while elongation decreases with increasing polystyrene content. The tensile strength and elongation were reduced when the grafted film was soaked in benzene more than 15 hr. The film prepared by a post-irradiation graft gave higher tensile strength and elongation than those of grafts formed by simultaneous irradiation of the film and the monomer. These results indicate that radiation-induced grafting makes the system of polyethylene and polystyrene compatible and potentially useful, provided the samples are not subjected to drastic solvent extraction procedures for the removal of homopolymer.     

Nano-matrix structure formed by graft-copolymerization of styrene onto natural rubber

Nano-matrix structure was formed by graft-copolymerization of styrene onto urea-deproteinized natural rubber (U-DPNR) latex. The grafted U-DPNR was characterized by FT-IR spectroscopy, ¹H NMR spectroscopy and transmission electron microscopy. Conversion and grafting efficiency of styrene were more than 90% under the best condition of the graft-copolymerization. In transmission electron micrograph of film specimen stained by OsO₄, it was found that natural rubber particle of about 0.5 μm in diameter was dispersed in polystyrene matrix of about 15 nm in thickness. The conversion and grafting efficiency for the grafted U-DPNR were compared with those for a control sample prepared from enzymatic deproteinized natural rubber (E-DPNR) with styrene.     

Surface modification of polymers. III. Grafting of stabilizers onto polymer films

Polypropylene, polystyrene, and polyethylene have been grafted with glycidyl acrylate and glycidyl methacrylate. After 5 min of grafting with UV irradiation, polystyrene was extensively grafted to 91% coverage of glycidyl acrylate according to ESCA, while polypropylene was grafted to only 50% coverage. With glycidyl acrylate the grafting depth is estimated to be 0.1 μm for PP and 0.23 μm for PS. Glycidyl methacrylate is grafted in a thinner layer than glycidyl acrylate. The stabilizers 2,4-dihydroxybenzophenone, phenyl 4-aminosalicylate, and 4-amino-2,2,6,6-tetramethylpiperidine were attached to LDPE surfaces containing grafted glycidyl acrylate by opening of the epoxide bond. The reaction between epoxide and stabilizer is diffusion controlled at high concentrations of stabilizer. UV spectroscopy on an LDPE film grafted and reacted with 2,4-dihydroxybenzophenone showed that 227 nmol stabilizer/cm² was bound to the surface.     

Radiation-initiated homogeneous grafting of styrene to benzylcellulose

Graft copolymers of benzylcellulose and styrene were prepared by direct irradiation of benzylcellulose–styrene solutions with ⁶⁰Co γ-radiation. The solutions remained homogeneous during irradiation. The amount of styrene grafted to benzylcellulose increased in dilute solutions and was dose-dependent up to 4.0 MR. The graft copolymer consisted of both branched and linear structures with one in every 140–1020 benzylated anhydroglucose units carrying a grafted polystyrene chain. Grafted polystyrene was isolated from the graft copolymer by hydrolysis of the benzylcellulose substrate. The number-average molecular weight and molecular weight distribution of the grafted polystyrene were the same as those for hompolymer formed in the same solution, indicating that the substrate is fully accessible to the monomer and polymerization conditions are uniform throughout the solution during the grafting procedure. The existence of a true graft copolymer was proved by the solubility behavior, intrinsic viscosity, number-average molecular weight, and density-gradient sedimentation of the product of the grafting procedure. Column elution fractionation of the gross products of the grafting procedure failed to isolate the benzylcellulose–styrene copolymer which was eluted with ungrafted benzylcellulose.     

Kinetic approach to radiation–induced grafting in the polyethylene–styrene system

To investigate the mechanism of radiation-induced grafting in this system, the increase of monomer concentration in the polyethylene film in styrene vapor was evaluated by measuring the weight increase and formulated to be V([M_∞] ? [M]). The decay of radical concentration was also measured by ESR and the rate constant of the decay was determined. The alkyl type radical was affected only a little by styrene, while the allyl type radical was much affected by styrene. A new computer investigation method was proposed to clarify the reaction mechanism. The data obtained were substituted into differential equations and used to calculate the pattern of increase of the degree of grafting for the preirradiation method with reaction in the vapor phase. Results of these calculations suggest that only allyl type radicals induce grafting reactions and that the grafting reaction seldom occurs in the region of grafted polystyrene.     

Grafting of polymers onto and/or from silica surface during the polymerization of vinyl monomers in the presence of γ‐ray‐irradiated silica

The effects of radicals on silica surface, which were formed by γ‐ray irradiation, on the polymerization of vinyl monomers were investigated. It was found that the polymerization of styrene was remarkably retarded in the presence of γ‐ray‐irradiated silica above 60 °C, at which thermal polymerization of styrene is readily initiated. During the polymerization, a part of polystyrene formed was grafted onto the silica surface but percentage of grafting was very small. On the other hand, no retardation of the polymerization of styrene was observed in the presence of γ‐ray‐irradiated silica below 50 °C; the polymerization tends to accelerate and polystyrene was grafted onto the silica surface. Poly(vinyl acetate) and poly(methyl methacrylate) (MMA) were also grafted onto the surface during the polymerization in the presence of γ‐ray‐irradiated silica. The grafting of polymers onto the silica surface was confirmed by thermal decomposition GC‐MS. It was considered that at lower temperature, the grafting based on the propagation of polystyrene from surface radical (“grafting from” mechanism) preferentially proceeded. On the contrary, at higher temperature, the coupling reaction of propagating polymer radicals with surface radicals (“grafting onto” mechanism) proceeded to give relatively higher molecular weight polymer‐grafted silica. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2972–2979, 2006     

Solvent Effects on the Rate of Radiation-Induced Grafting of Vinyl Monomers on Polymeric Films

Earlier work indicated that in the radiation-induced grafting of vinyl monomers on polymeric films, the plasticity of the film being grafted is determined by the Hildebrand solubility parameter of the grafting solution. Film plasticity affects the termination step of the grafting reaction, and thus strongly influences the overall rate of monomer grafting on the polymeric film.

In the grafting of styrene on nylon film, a sequence of irradiation runs was made at selected volume ratios of styrene/benzene/methanol, all grafting solutions having a constant solubility parameter value of 9.5 Under these conditions, a linear plot of grafting rate vs volume percent styrene in the grafting solution was obtained. A similar sequence of runs grafting pentafluorostyrene on nylon film at constant solubility parameter also produced a linear plot of grafting rate vs volume percent PFS.

Styrene was grafted on polyethylene film in a sequence of four runs using styrene dissolved in methanol, ethanol, 1-propanol, and 1-butanol, each solution having the same solubility parameter of 10.4. A straight-line plot of grafting rate vs volume percent styrene was obtained under these conditions.     

Piled-lamellae structure in polyethylene film and its deformation

The fine structure of polyethylene film has been investigated by using a high-resolution scanning electron microscope equipped with a field emission source. The original film surface of a-axis-oriented blown polyethylene film and the surface of a necked region formed by drawing the film in the machine direction were observed. High magnification electron micrographs indicate that the basic unit of internal texture of this film consists of piled-lamellae units, each pile containing three to ten lamellar crystal sheets. The piled-lamellae unit acts as one body and does not separate into single lamellae during deformation. Many tie fibrils are formed between adjacent piled-lamellae units, when the film is drawn in the machine direction. Although little attention has been given to this mechanism, it is important in deformation. This fact seems to be reflected in different shapes of the stress-strain curves of films drawn the machine direction and perpendicular to it.     

Radiation-induced grafting of styrene onto ultra-high molecular weight polyethylene powder and subsequent film fabrication for application as polymer electrolyte membranes: I. Influence of grafting conditions

Ultra-high molecular weight polyethylene (UHMWPE) powder was irradiated by gamma rays using a ⁶⁰Co source. Simultaneous and pre-irradiation grafting was performed in air and in inert atmosphere at room temperature. The monomer selected for grafting was styrene, since the styrene-grafted UHMWPE could be readily post-sulfonated to afford proton exchange membranes (PEMs). The effect of absorbed radiation dose and monomer concentration in methanol on the degree of grafting (DG) is discussed. It was found that the DG increases linearly with increase in the absorbed dose, grafting time and monomer concentration, reaching a maximum at a certain level. The order of rate dependence of grafting on monomer concentration was found to be 2.32. Furthermore, the apparent activation energy, calculated by plotting the Arrhenius curve, was 11.5 kJ/mole. Lower activation energy and high rate dependence on monomer concentration shows the facilitation of grafting onto powder substrate compared with film. The particle size of UHMWPE powder was measured before and after grafting and found to increase linearly with increase in level of grafting. FTIR-ATR analysis confirmed the styrene grafting. The grafted UHMWPE powder was then fabricated into film and post-sulfonated using chlorosulfonic acid for the purposes of evaluating the products as inexpensive PEM materials for fuel cells. The relationship of DG with degree of substitution (DS) of styrene per UHMWPE repeat unit and ion exchange capacity (IEC) is also presented.     

Radiation-induced grafting of styrene vapor to polyethylene

The radiation-induced grafting of styrene vapor to low-density polyethylene film of 0.063 mm thickness was studied at 23°C at a dose rate of 1.98 × 10⁴ rad/hr. The concentration C of monomer in the film was measured as a function of pre-irradiation exposure time to monomer vapor. The concentration-dependent diffusion coefficient of styrene in polyethylene was calculated to be 4.9 × 10^?9 exp {2.0C/C₀} cm²/sec, where C₀ is the saturation concentration of styrene in the film, and a linear boundary diffusion coefficient for styrene vapor into polyethylene film was found to be 2.0 × 10^?7 cm/sec. The rate of grafting was determined as a function of the concentration of styrene absorbed in the film. The maximum graft yield was obtained with an initial styrene concentration in the film of 4 wt-%. Under conditions of low initial monomer concentration, the grafting rate increases with irradiation time. The results are compared with previously published data on grafting of polyethylene from methanol–styrene solutions. They are explained in terms of the viscosity of the amorphous region as a function of styrene content and the resistance to the diffusion of monomer at the film–vapor interface.     

Solvent‐induced reversible color changes in block copolymer films and new locking method of structural colors

The well‐defined polystyrene‐block‐poly(4‐vinylpyridine) [PS‐block‐P4VP (SV1); lamellar morphology] and polyisoprene‐block‐poly(α‐methyl styrene) [PI‐block‐PMS (IMS1); PI spherical morphology] diblock copolymers were prepared by sequential anionic polymerization techniques. The segregated chains in the P4VP lamellar layers of the SV1 film (PS lamellae: 41 nm; P4VP lamellae: 51 nm) were crosslinked with 1,4‐dibromobutane. This crosslinked film was insoluble in organic solvents such as benzene and chloroform (CHCl₃) and exhibited various structural colors under the swollen state. The IMS1 film (body‐centered cubic lattice, diameter of PI spheres: 53 nm) was soaked in the mixture of CHCl₃/hexane (1 : 10, v/v). This solvent system resulted in the swelling of PI spherical domains. The transmitted and reflected light color through the swollen film changed to a deep blue. Such color changes were reversible upon swelling in solvent and evaporation of the solvent. Subsequently, photofunctional diethyldithiocarbamate (DC) groups were introduced into the PS block of the parent block copolymer IMS1 by means of polymer reactions. The locking of the cubic lattice was performed with living radical graft copolymerization from DC groups of swollen as‐cast film in methyl methacrylate (MMA) under UV irradiation. The locking of structural colors such as blue and green was also achieved, varying the content of poly(methyl methacrylate) (PMMA) grafted chains. Copyright © 2005 John Wiley & Sons, Ltd.     

Cation exchange membranes by pre-irradiation grafting of styrene into FEP films. I. Influence of synthesis conditions

Gamma radiation-induced grafting of styrene into FEP films was investigated by the pre-irradiation method. The degree of grafting was found to be strongly dependent on the synthesis conditions, such as radiation dose, monomer concentration, crosslinker, temperature, and film thickness. The order of dependence of the rate of grafting on pre-irradiation dose and monomer concentration was found to be 0.64 and 1.90, respectively. The activation energy for the grafting in the temperature range of 50–80°C was determined to be 27.9 kJ/mol. A negative first order dependence of grafting on film thickness was observed. The results suggest that the initial grafting takes place at the film surface and proceeds to the middle by progressive diffusion of monomer through the polystyrene grafted layers. © 1994 John Wiley & Sons, Inc.     

Surface structures of fluoropolymer,polyolefin and polyester films after modification by graft polymerization

Pristine and argon plasma pretreated polytetrafluoroethylene (PTFE), polystyrene (PS), high-density polyethylene (HDPE) and poly(ethylene terrephthalate) (PET) films have been subjected to near-UV light-induced graft polymerization with water-soluble acrylamide (AAm), the sodium salt of styrene sulfonic acid (NaSS), acrylic acid (AAc) and N,N-dimethylaminoethylmethylacrylate (DMAEMA) monomers. The structure and composition at the substrate surface with grafted polymer were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). In most cases, the density of surface grafting is enhanced by plasma pretreatment. For each polymer substrate with a substantial amount of grafting, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This stratified microstructure is consistent with the static secondary ion mass spectroscopy (SIMS) and Ar⁺ beam depth profiling results. The two latter techniques also suggest that when the grafted polymer has a bulky substituent, there is less efficient penetration of the grafted polymer below the surface.     

Structure of ultrathin polyethylene layers in multilayer films

The crystalline structures of “microlayer” and “nanolayer” polyethylene have been examined in coextruded films comprised of alternating layers of high-density polyethylene and polystyrene. Transmission electron microscopy (TEM), small-angle x-ray scattering (SAXS), and wide-angle x-ray scattering (WAXS) reveal that microlayer polyethylene, where the layer thickness is on the order of several microns, crystallizes with the normal unoriented lamellar morphology. In nanolayer films, where the film thickness of tens of nanometers is on the size scale of molecular dimensions, lamellae are oriented with the long axes perpendicular to the extrusion direction in a row-nucleated morphology similar to structures described in the literature. The lamellae are partially twisted about the long axes. The preferred twist angles of ±40° orient the lamellar surfaces normal to the layer surface. The row-nucleated morphology imparts highly anisotropic mechanical properties to the nanolayer polyethylene.     

Radiation grafting of styrene onto poly(vinylidene fluoride) films in propanol: The influence of solvent and synthesis conditions

Electron‐beam‐irradiated poly(vinylidene fluoride) films were grafted with styrene with propanol or toluene as a solvent. The influence of the synthesis conditions and, more particularly, of the solvent was investigated. In propanol, the order of dependence of the grafting rate is 0.43 on the pre‐irradiation dose and 1.2 on the monomer concentration. The activation energy of the grafting reaction in propanol is approximately 73 kJ/mol. Both the initial grafting rate and the saturation degree of grafting are considerably higher in propanol, which is unable to swell polystyrene grafts, than in toluene, which diffuses with styrene through the grafted moiety. The grafting solvent also influences the structure of the membrane: films grafted in propanol have a much reduced elongation at break and a rougher surface. It is suggested that phase‐separated polystyrene domains may be larger when grafting is carried out in a styrene–propanol solution. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1512–1519, 2000     

Surface modification of polymers. I. Vapour phase photografting with acrylic acid

Surfaces of low density polyethylene, high density polyethylene, and polystyrene have been modified by grafting with acrylic acid. Benzophenone and acrylic acid in the vapor phase were UV-irradiated in the presence of a polymer substrate. Grafting with acrylic acid took place in a thin layer on the surface, thus increasing the wettability of the polymer. After 5 min of irradiation, the contact angle against water had decreased to 20° for polystyrene and 50° for the polyethylene samples. ESCA measurements on samples irradiated for 5 min showed a 90% poly(acrylic acid) coverage of the surface for polystyrene, 63% for low density polyethylene, and 56% for high density polyethylene. Acetone or ethanol were used as carriers of monomer and initiator. Acetone was able to initiate grafting and was found to promote and direct grafting to the surface. The stability of the acrylic acid grafted surfaces was studied by contact angle measurements and ESCA. At room temperature, the grafted layer is confined to the surface, but when the material was heated in air the surface was reshaped into a hydrophobic one. The process was reversible. In aqueous surroundings at elevated temperatures the hydrophilic character of the surface was restored.     

Effect of nitrobenzene in the styrene–cellulose acetate graft polymerization system

The effect of nitrobenzene, a polymerization retarder, upon the direct γ-ray-induced graft polymerization of styrene onto pyridine-swollen cellulose acetate film was studied. When the films were not highly swollen, small nitrobenzene additions caused an increase in the amount of grafted polystyrene and grafted cellulose acetate. However, when the substrate was highly swollen, nitrobenzene additions reduced the amount of grafted polystyrene without pronounced changes in the amount of grafted cellulose acetate. The number-average molecular weights of the grafted side chains were always two to three times those of the homopolystyrene formed in the bulk monomer solution, which is indicative of hindered chain termination within the substrate film under all reaction conditions. Nitrobenzene additions prevented polystyrene crosslinking reactions, probably because the termination reactions in the presence of nitrobenzene occur by disproportionation rather than by coupling of chain ends. Viscometric results indicated that the polystyrene side chains were branched.     

Mechanism of graft copolymerization of styrene onto deproteinized natural rubber

High conversion and high grafting efficiency attained by graft copolymerization of styrene onto deproteinized natural rubber (DPNR) was investigated with respect to the molecular weight of grafted polystyrene. The graft copolymerization was performed with tert-butyl hydroperoxide/tetraethylenepentamine as an initiator after deproteinization of natural rubber with urea. Grafted polystyrene was isolated from the resulting graft copolymer by ozonolysis reaction. After the ozonolysis of the graft copolymer of DPNR and polystyrene (DPNR-g-PS), the molecular weight of grafted polystyrene was determined by size exclusion chromatography. Effects of initiator and monomer concentrations were investigated with respect to the molecular weight of the grafted polystyrene, which was found to depend on not only the number of active site generated on the rubber particle but also the feed of styrene. Deactivation and chain transfer of the active sites were attributed to effective amount of styrene used for the graft copolymerization.     

ESR studies of the radiation-induced multiple graft polymerization

The radiation-induced multiple-graft polymerization was studied by an ESR method. When methyl methacrylate vapor was introduced onto preirradiated polyethylene already grafted with styrene, the second step of grafting of methyl methacrylate occurred mainly in the polyethylene portion. The kinetic treatment proved that the termination rate constant k_t of methyl methacrylate decreased with the amount of styrene grafted in advance. On the other hand, when styrene vapor was introduced onto polyethylene grafted with methyl methacrylate, only radicals of poly(methyl methacrylate) decreased. In this case, the second step of grafting of styrene occurred in the poly-(methyl methacrylate) portion which covered the whole surface of the polyethylene powder. When monomer vapors were alternately introduced onto preirradiated polyethylene powder, the second step of grafting occurred at the growing chain end of the first monomer.