Changes in row structure of extruded polyethylene film in grafting with styrene. II. Copolymer morphology

The morphology of extruded high-density polyethylene film grafted with styrene was studied by transmission electron microscopy of thin stained sections. Near the film surface grafted polystyrene was confined to amorphous layers between lamellar crystals of polyethylene. In the film interior separate polystyrene domains were also formed and became predominant in grafting in diluted styrene. The deciding factor for the location of grafted polystyrene is the chain length because only long chains can coalesce in large separate zones. The polystyrene zones expand by cracking the stacks of lamellae along the lamellar normals. Straightening of the twisted crystalline lamellae of polyethylene occurred in grafting. “Bubbles” of styrene homopolymer were formed under conditions of high monomer concentration. The effect of staining the graft by the Kanig method² was also discussed.     

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.     

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     

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.     

Effect of swelling on radiation-induced grafting of styrene to polyethylene

The radiation-induced grafting of low-density polyethylene in contact with styrene solution was studied. The effect of the degree of swelling of the polymer on the rate of grafting was investigated by diluting the styrene with methanol and with n-octane. For styrene-methanol solution, the rate of grafting was found to increase with degree of swelling, passing through a maximum when the sorbed solvent reaches 6.2 wt-% (70 vol-% methanol in the outside solution) and decreasing therafter. The methanol fraction of the sorbed liquid is far too small to cause precipitation of the grafted chains and inhibition of their termination rate. The dilution of styrene by octane has no effect on the swelling of polyethylene, but it decreases the grafting rate over the entire concentration range. The results are explained in terms of the concentration of sorbed monomer and the viscosity of the amorphous region of the polyethylene swollen by nonpolar liquids. Supporting evidence for the mechanism is presented in the form of grafting kinetic data as a function of dose rate (2.8 × 10²?9.5 × 10⁴ rad/hr), and post-irradiation grafting measurements for polyethylene in methanol-styrene (70/30, v/v). The data indicate that at the maximum grafting rate an optimum is achieved between a high concentration of sorbed monomer and a low viscosity for the poorly swelled polymer matrix.     

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.     

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.     

Studies on Mechanism of Grafting of Polystyrene on Elastomer Backbone

The mechanism of grafting of polystyrene on a polybutadiene (PB) backbone during the preparation of impact-resistant polystyrene was studied by withdrawing samples during propolym-erization from beginning of the reaction to about 25% conversion. Good separation of the “elastomer and graft” fraction of the polymer from the free polystyrene part could be achieved by using 0.24 volume fraction of methanol in (MEK + benzene) + methanol solvent-nonsolvent. IR analysis of the grafted fraction showed that the microstructure of the elastomer remained unaltered. The unsaturation of the samples studied through the bromine number as well as by the perbenzoic acid number was also found to remain unchanged. Formation of free polystyrene started with the onset of polymerization and was faster. During prepolymerization, 80% of styrene converted constantly to form free polystyrene and 20% went into the grafted polymer. The results indicate that grafting is initiated through proton abstraction at the α-carbon of butadiene, most probably by initiator radicals. The grafted polystyrene chains possibly are shorter than free polystyrene chains.     

Radiation-induced grafting in the polyethylene–styrene system and differential thermal analysis of the grafted samples

The graft polymerization of styrene onto high-density polyethylene films was carried out by γ-irradiation in the vapor phase. Two methods were used for grafting in these experiments: a preirradiation method and a simultaneous irradiation method. The effects of these grafting methods on the reaction mechanism of grafting and on the properties of the grafted samples were investigated. The amounts of styrene homopolymer in the grafted samples is under 2% in the case of the preirradiation method and above 10% in the case of the simultaneous irradiation method. The activation energies were calculated to be 18 kcal/mole for grafting in the preirradiation method and 15 kcal/mole for weight increase of polyethylene films in styrene vapor. The difference in the dimensional expansion between in the direction of stretching and the direction prependicular to it is smaller with preirradiation grafting than with grafting by the simultaneous irradiation method. Differential thermal analysis of the grafted films shows an endothermic peak due thermal decomposition which decreases gradually from 450°C to 415°C with increase in degree of grafting from 30 to 60%. The lowering of this peak temperature appears at a lower degree of grafting when the preirradiation method is used. On the basis of these results, it is concluded that the reaction rate of radiation-induced grafting in the vapor phase depends closely upon the processes of adsorption, dissolution, and diffusion of styrene monomer in polyethylene films; in the case of simultaneous irradiation method, the reaction proceeds comparatively uniformly in the amorphous region, while in the case of the preirradiation method, the reaction proceeds mainly at the boundary of the crystalline and amorphous regions.     

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.     

UV grafting of methacrylic acid and acrylic acid on high‐density polyethylene in different solvents and the wettability of grafted high‐density polyethylene. II. Wettability

The wettability of high‐density polyethylene grafted with methacrylic acid is strongly influenced by the nature of the grafting solvent. Here, the wettability is expressed by the water contact angle and absorbency. The initial (10‐s) contact angle of polyethylene (PE) grafted in acetone/water solution decreased rapidly with the extent of grafting at low grafting levels and then remained independent of the grafting level at about 50°. When a water droplet was left on the surface for a longer time, its contact angle decreased to a very low value in the period of about 10 min. For the PE samples grafted in dichloromethane, petroleum ether, cyclohexane, and chloroform, there was only a small decrease (10°) in the contact angle of water from that observed on pure PE, even when the extent of grafting was very large. The PE films grafted in these organic solvents also took a much longer time than PE films grafted in acetone/ water solution to obtain equilibrium water absorbency. The water absorbency of PE films grafted in 30% acetone/water solution was about twice that of PE films grafted in the other solvents at the same extent of grafting. These results suggested that for the solvents other than acetone/water, the grafted layer is partially buried below the surface of PE. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 263–270, 2004     

Use of carbon suboxide to obtain block and graft copolymers. II. Grafting of carbon suboxide on polyethylene

Experiments have been carried out on grating of carbon suboxide on nonactivated polyethylene films and on films previously activated by ultraviolet irradiation and by γ-irradiation. The experiments gave a grafted copolymer. A grafted copolymer was also obtained on grafting carbon suboxide in solution on polyethylene films preactivated by means of ozonization at 70°C. Examination of the copolymer indicated its structure to be cross linked. It has been proved that below 50°C single molecules of carbon suboxide react with polyethylene. The polyethylene thus modified is then easily surfacedyed.     

Spectroscopic study of the penetration depth of grafted polystyrene onto poly(tetrafluoroethylene‐co‐perfluoropropylvinylether) substrates. 1. Effect of grafting conditions

This study concerns the radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐perfluoropropylvinylether) (PFA) substrates and the penetration depth of the graft. Grafting was obtained by the simultaneous irradiation method, and the spectroscopic analysis was made with the micro‐Raman technique. Effects of grafting conditions such as the type of solvent, dose rate, and irradiation dose on the grafting yield were investigated. Of the different solvents used, the most efficient in terms of increasing grafting yield were dichloromethane, benzene, and methanol, respectively. A mixture of methanol and dichloromethane used as a solvent for styrene achieved a higher degree of grafting and concentration of grafted polystyrene onto the surface of PFA substrates than solutions of the monomer in the separate solvents. The degree of grafting increased with increasing radiation dose up to 500 kGy, stabilizing above this dose. However, the grafting yield decreased with an increase in the dose rate. The increase in the overall grafting yield was accompanied by a proportional increase in the penetration depth of the grafts into the substrate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3191–3199, 2002     

Microphase separation of block copolymer solutions in a flow field

Films of polystyrene–polybutadiene–polystyrene (PS/PB/PS) triblock copolymer and polystyrene-poly(ethylene/propylene) (PS/PEP) diblock copolymer were cast from toluene solutions subjected to hydrodynamic flow at room temperature using a device based on a novel casting method we term ‘roll-casting.’ Polymer solutions were rolled between two corotating eccentric cylinders while at the same time the solvent was removed at a controlled rate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. A discussion of the flow field that develops during roll-casting is presented and specific attention is given to the importance of the shear and elongation rates present. For the triblock and diblock, respectively, the processed structures consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix, and unidirectional lamellae of alternating polystyrene and polyethylene/propylene. Small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) indicated the near single-crystal structure both types of films. SAXS also showed the styrene cylinders and the alternating lamellae to be packed closer together in roll-cast films than in simple quiescently cast films. A molecular orientation mechanism is proposed to describe both these results as well as the changes in packing and in macroscopic sample dimensions measured after complete solvent evaporation and after sample annealing. © 1993 John Wiley & Sons, Inc.     

Solvent effects on the synthesis of ion-exchange membranes by radiation-induced graft polymerization of methyl α,β,β-trifluoroacrylate

Methyl α,β,β-trifluoroacrylate (MTFA) was grafted onto polyethylene (PE) film and fluorine-containing films to make ion-exchange membranes. In the case of PE the grafting yield was not influenced by the presence of trifluorotrichloroethane (Freon 113) in the reaction mixture, while the presence of methanol decreased the grafting yield. The transversal distribution of graft chains in the film observed by electron-probe x-ray microanalysis showed that when the grafting was carried out in the presence of Freon the amount of graft chains in the central part of PE film was much larger than that at the film surface and that the grafts obtained in the absence of Freon were located mainly at the film surface. The electric resistance of the graft PE film obtained in the presence of Freon decreased more than that of the one obtained in the absence of Freon. The weight loss of the graft films in H₂O₂ solution was negligibly small.     

PSSA pore-filled PVDF membranes by simultaneous electron beam irradiation: Preparation and transport characteristics of protons and methanol

Polystyrene sulfonic acid (PSSA) pore-filled poly(vinylidene fluoride) (PVDF) membranes have been prepared using simultaneous electron irradiation method. Porous PVDF films were grafted by pre-swelling in styrene solution and subsequent irradiation with an electron beam (EB) under nitrogen atmosphere and at ambient temperature. The grafted films i.e. polystyrene (PS) pore-filled PVDF were subsequently sulfonated with a diluted mixture of chlorosufonic acid. The effects of the reaction parameters on the content of PS grafted in the pores of PVDF films were investigated. The chemical and morphological properties of the membranes in comparison with their un-grafted and grafted counterparts were studied by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The transport properties of these membranes such as ionic conductivity and methanol permeability were evaluated and correlated with the content of PS grafted in the pores of the PVDF films. The PSSA pore-filled PVDF membranes with PS content in the pores of 40% and above showed superior performance characteristics compared to Nafion 117 membrane and therefore can be potential alternatives to improve the performance of direct methanol fuel cell (DMFC).     

Pre-irradiation induced grafting of styrene into crosslinked and non-crosslinked polytetrafluoroethylene films for polymer electrolyte fuel cell applications. II: Characterization of the styrene grafted films

Crosslinked and non-crosslinked polytetrafluoroethylene films (RX-PTFE and V-PTFE films, respectively) were irradiated by γ-ray and then grafted with styrene in liquid phase. Microscope FT-IR spectroscopy, TGA, solid state ¹³C CP/MAS and high resolution HS/MAS NMR spectroscopy, wide-angle X-ray diffraction (WAXD) study were used to get the structural information of the styrene grafted RX-PTFE and V-PTFE films. From microscope FT-IR spectra of the grafted RX-PTFE films, the “grafting front mechanism” was proved. TGA analysis showed that the grafted films have a small degradation step and two main degradation steps. In the ¹³C CP/MAS NMR spectra of the non-grafted films, there are no signal due to the absence of the hydrogen atom. While in the spectra of the grafted films, there are signals attributed to the polystyrene grafts. In the ¹³C HS/MAS NMR spectra of the grafted films, the relative intensity of the peaks attributed to the polystyrene grafts increased while the relative intensity of the peak attributed to PTFE matrix decreased with the increase in the DOG. From WAXD patterns, the intensity of the crystalline peak decrease with the increase in the DOG. The grafted films were sulfonated by chlorosulfonic acid and the results of highest IEC value exceeded 3.0. Those results will be reported in the near future.     

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.     

聚苯乙烯固载聚乙二醇的合成及表征

聚乙二醇在钠或浓氢氧化钠作用下接枝到氯甲基化聚苯乙烯树脂上，制成聚苯乙烯固载聚乙二醇树脂，讨论了影响接枝反应的条件．接枝反应的结果进行了电镜照片和红外光谱分析．     

N,N-二乙基丙烯酰胺与丙烯酸在聚丙烯薄膜表面光接枝制备二元接枝膜及其温度、pH值敏感特性研究

以二苯甲酮为引发剂,聚丙烯薄膜(CPP)为基材,通过紫外光接枝的方法制备了具有温度和pH值双重敏感特性的聚N,N-二乙基丙烯酰胺(PNDEA)与聚丙烯酸(PAA)二元接枝膜.在PNDEA一次接枝膜的制备过程中,引发剂与单体配比相同时,本体接枝方法的接枝速率在反应初期明显高于溶液接枝方法;采用溶液法时,增大引发剂与单体配比等可提高接枝率.用本体法所制得的PNDEA一次膜光活化接枝PAA时接枝速率较溶液法高,并且能够实现较高的PAA接枝率.用红外光谱(FTIR)、X射线光电子能谱化学分析(ESCA)对接枝层组成的表征结果证实了二元接枝层的存在.在不同温度下,PNDEA一次接枝膜的FTIR谱图中酰胺Ⅰ带特征吸收峰发生位移表明它具有温度敏感特性.用扫描电子显微镜(SEM)对PNDEA接枝层表征结果表明,用不同接枝手段所制备的接枝膜具有不同的表面形貌.通过吸水率测定研究了二元接枝膜的温度及pH值敏感特性.