Oxidation of polyethylene surface by glow discharge and subsequent graft copolymerization of acrylic acid

Plasma-induced graft copolymerization of acrylic acid, which was incorporated into PE films, was investigated here. The influence of plasma conditions such as plasma treatment gases, power, pressure, time, monomer concentration, and graft copolymerization time on polymerization yield was determined. The samples were characterized by ESCA, IR, and water contact angle. A respective chemical shift of the C1s signal of Ar or O₂ plasmatreated and untreated PE films was revealed by ESCA, in which the presence of the grafted PAAc was also verified. An increase in polymerization yield with plasma treatment duration and power was found. That the grafted copolymerization was limited to a very thin surface region was revealed by optical microscopy on the cross section of the grafted film. © 1993 John Wiley & Sons, Inc.     

Surface changes brought about by corona discharge treatment of polyethylene film and the effect on subsequent microbial colonisation

Microbial colonisation of synthetic plastic films is normally slow, which affects the total period of biodegradation. Correlation between the modified surface condition and the ability for microorganisms to colonise low-density polyethylene (LDPE) film was studied. Corona discharge treatment was applied to obtain enriched and activated surface condition of LDPE film. It was found from water contact angle and FTIR spectrum evaluations that surface energy was significantly increased due to production of free radicals. Stabilised oxidised LDPE surface was also obtained by further exposure to the corona which gave more suitable condition for subsequent colonisation. Results were compared with UV irradiated (photo-oxidised) LDPE films. Colonisation of corona discharged and UV treated LDPE films were tested in the laboratory environment using known fungal isolates and in a natural compost environment. More active microbial colonisation was observed in all cases for corona discharged and UV treated LDPE films. Far longer UV exposure was required to have the same physicochemical and biological effect as the corona discharge treatment.     

聚乙烯表面接枝聚合改性及抗凝血性的研究

聚乙烯(PE)膜经Ar等离子体预处理,无光引发剂紫外光照接枝甲基丙烯酸缩水甘油酯(GMA),然后进行肝素化处理,以改善PE的抗凝血性能。用正交实验确定接枝反应的最优条件。通过X-射线光电子能谱(XPS)、衰减全反射红外光谱(ATR-FTIR)、扫描电子显微镜(SEM)和接触角测定PE膜接枝GMA前后表面性能和表面形貌。用复钙时间、凝血酶原时间、部分凝血活酶时间、凝血酶时间和血小板粘附实验对其抗凝血性能进行评价,结果表明,被修饰PE膜的抗凝血性能显著提高。     

Surface modification of polyethylene fiber by graft polymerization

To improve the wettability and adhesion, graft polymerization of acrylamide (AAm) and glycidyl methacrylate (GMA) was performed onto the surface of ultra-high modulus polyethylene (UHMPE) fiber pretreated with Ar plasma. Following the plasma treatment and the subsequent exposure to air to introduce peroxides onto the fiber surface, graft polymerization onto the UHMPE fiber was allowed to proceed from the polymer peroxides either in deaerated monomer solution at an elevated temperature (degassing method), or in aerated monomer solution containing riboflavin at 30°C under UV irradiation (photoinduction method). The monomer solution was prepared from water and dioxane for AAm and GMA, respectively. After rigorous removal of homopolymers, surface analysis of the grafted fibers was performed with ATR-FTIR and XPS, which revealed that PAAm and PGMA chains were grafted in the surface region of fibers. The grafting rate of PAAm by the photoinduction method was much higher than that by the degassing method when compared at the same concentration of the AAm solution. The amount of PGMA grafted was greatly affected by UV irradiation time, but depended on plasma treatment time to an insignificant extent if the treatment was carried out for longer than 30 s. Reaction of propylamine with the PGMA-grafted surface resulted in the appearance of a nitrogen peak in the XPS spectrum, suggesting the presence of epoxy groups on the surface of PGMA grafted fiber. © 1994 John Wiley & Sons, Inc.     

New polyethylene macroinitiators and their subsequent grafting by atom transfer radical polymerization

A semicrystalline polyethylene (PE) macroinitiator was prepared by copolymerizing ethylene and an inititating monomer (5-norbornen-2-yl-2'-bromo-2'-methyl propanoate) (3) using [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)isobutanamidato]-Ni(eta1-CH2Ph)(PMe3) (1) and Ni(COD)2 (bis(1,5-cyclooctadiene)-nickel) (2). Although 3 decomposes Ni(COD)2, if the initiating species (1/2) are exposed to ethylene for a period of time, t1, and then 3 is introduced for another period of time, t2, the polymerization takes place in a controlled manner. Variations in temperature, pressure, and [3] afford a great deal of control over the composition and architecture of the PE macroinitiator. Subsequent grafting with methyl methacrylate (MMA) yields PE-graft-PMMA with narrow polydispersities and increasing PMMA content at longer reaction times. Because the products are semicrystalline materials with high melting points, they are anticipated to function as blend compatibilizers for linear polyethylene.     

Surface characteristics of low-density polyethylene films modified by oxyfluorination-assisted graft polymerization

In this study, a unique two-step process, i.e., an oxyfluorination-assisted graft polymerization (OAGP), was used to modify the surface properties of low-density polyethylene (LDPE) films. Based on the results of the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method, which was performed to estimate the amount of hydroperoxides generated by oxyfluorination, oxyfluorination conditions that maximize the amount of hydroperoxide groups were selected. Hydroperoxides were generated by oxyfluorination to provide active sites for the OAGP of the different monomers. Depending on the type of monomers used, two different graft polymerization behaviors were observed. Hydrophilic methacrylic acid (MA) monomers were graft polymerized onto the oxyfluorinated LDPE (OFPE) surface in a perpendicular direction, forming a spike-shaped morphology. On the other hand, hydrophobic styrene (ST) monomers were graft polymerized parallel to the OFPE surface, forming a valley-shaped morphology. By changing the type of vinyl monomers, two different surfaces could be prepared using the hydroperoxides generated by oxyfluorination. After OAGP with MA monomers, a hydrophilic surface following the Wenzel model was obtained, whereas after OAGP with ST monomers, a hydrophobic surface following the Cassie–Baxter model was obtained. Therefore, the OAGP process may be an efficient method for preparing two different surfaces by changing the monomer used.     

Laser-irradiation-induced surface graft polymerization method

A laser-induced surface graft polymerization method is reported in which surface radicals generated upon laser irradiation initiated radical polymerization. The radical concentrations generated upon excimer laser irradiation under vacuum on poly-(ethylene terephthalate) film surfaces were measured using a radical scavenger, 1,1-diphenyl-2-picrylhydrazyl. The density of surface radicals increased with laser fluence at low fluences but decreased at high fluences. Upon laser irradiation and subsequent treatment with gaseous N,N-dimethylacrylamide, surface graft polymerization occurred. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 747–750, 1997     

Synthesis and application of functional polyethylene graft copolymers by atom transfer radical polymerization

This investigation attempts to elucidate the copolymerization reaction ethylene and p-methylstyrene via the homogeneous metallocene catalyst, Et(Ind)₂ZrCl₂. With increasing of p-methylstyrene concentration, the poly[ethylene-co-(p-methylstyrene)] copolymer shows systematical decrease of melting temperature and crystallinity and increase of glass transition temperature. The benzylic protons of p-methylstyrene are ready for numerous chemical reactions, such as halogenation and oxidation, which can introduce functional groups at the p-methyl group position under mild reaction conditions. With the bromination reaction of poly[ethylene-co-(p-methylstyrene)], polyethylene graft copolymers, such as polyethylene-g-poly(methyl methacrylate) and polyethylene-g-polystyrene can be prepared via atomic transfer radical polymerization. The following selective bromination reaction of p-methylstyrene units in the copolymer and the subsequent radical graft-from polymerization were effective methods of producing polymeric side chains with well-defined structure. The products were characterized by nuclear magnetic resonance, gel-permeation chromatography, differential scanning calorimetry, and thermal gravimetric analysis. Additionally, the morphology of PE/PMMA and PE/PMMA/PE-g-PMMA blend are compared by using scanning electron microscope.     

Inorganic surface nanostructuring by atmospheric pressure plasma-induced graft polymerization

Surface graft polymerization of 1-vinyl-2-pyrrolidone onto a silicon surface was accomplished by atmospheric pressure (AP) hydrogen plasma surface activation followed by graft polymerization in both N-methyl-2-pyrrolidone (NMP) and in an NMP/water solvent mixture. The formation of initiation sites was controlled by the plasma exposure period, radio frequency (rf) power, and adsorbed surface water. The surface number density of active sites was critically dependent on the presence of adsorbed surface water with a maximum observed at approximately a monolayer surface water coverage. The surface topology and morphology of the grafted polymer layer depended on the solvent mixture composition, initial monomer concentration, reaction temperature, and reaction time. Grafted polymer surfaces prepared in pure NMP resulted in a polymer feature spacing of as low as 5-10 nm (average feature diameter of about 17 nm), an rms surface roughness range of 0.18-0.72 nm, and a maximum grafted polymer layer thickness of 5.5 nm. Graft polymerization in an NMP/water solvent mixture, however, resulted in polymer feature sizes that increased up to a maximum average feature diameter of about 90 nm at [NMP] = 60% (v/v) with polymer feature spacing in the range of 10-50 nm. The surface topology of the polymer-modified silicon surfaces grafted in an NMP/water solvent mixture exhibited a bimodal feature height distribution. In constrast, graft polymerization in pure NMP resulted in a narrow feature height distribution of smaller-diameter surface features with smaller surface spacing. The results demonstrated that, with the present approach, the topology of the grafted polymer surface was tunable by adjusting the NMP/water ratio. The present surface graft polymerization method, which is carried out under AP conditions, is particularly advantageous for polymer surface structuring via radical polymerization and can, in principle, be scaled to large surfaces.     

Ozone-induced graft polymerization onto polymer surface

Ozone-induced graft polymerization was carried out to improve polymer surfaces. The polymers were exposed to ozone and the surface density of peroxides formed was determined by three methods; iodide, DPPH, and peroxidase method. The peroxide production could be readily controlled by the ozone concentration and the ozone exposure time. In addition, it was dependent on the kind of polymer. Further, it seemed probable that the ozone oxidation introduced peroxides not only on the outermost surface but also into a layer deeper from the outermost surface. Such polymeric peroxides were capable of initiating graft polymerization onto PU. All the physical and biological measurements on the grafted surface indicated that ozone-induced graft polymerization has effectively made the PU surface covered with the grafted water-soluble chains, their location being restricted to the film surface region. The interaction of the PU surface with blood components could be greatly reduced by the surface graft polymerization. © 1993 John Wiley & Sons, Inc.     

电火花引发丙烯酰胺接枝BOPP薄膜的研究

采用FT-IR,ESCA,试样与水接触角和接枝率的测定探索了电火花用于引发丙烯酰胺(AAM)在BOPP薄膜表面接枝聚合反应的方法,研究了接枝BOPP薄膜的表面结构和亲水性能。结果表明,电火花能有效地引发AAM在BOPP薄膜表面的接枝聚合反应,随着电火花处理时间和接枝反应时间的延长,AAM在BOPP薄膜表面的接枝率增大。电火花处理10min,BOPP薄膜在70℃,20%(质量分数)的AAM水溶液中反应1h,接枝率高达2.06%。接枝后BOPP薄膜与水的接触角显著下降,亲水性能得到明显改善。     

Kinetics of diffusion-free radiation graft polymerization of styrene onto polyethylene

The diffusion-free radiation graft polymerization of styrene onto polyethylene has been studied. The grafting rate shows a dependence on monomer which is far different than what has been assumed. Further, the dependence on monomer changes with increasing dose rate as does the dependence of grafting rate on radiation dose rate. Three different regions of behavior are defined: (1) a region of low dose rate where the grafting rate is 1/2-order in dose rate and 3/2-order in monomer; (2) a region of intermediate dose rate where the grafting rate is intermediate between 1/2-and zero-order in dose rate and 5/2-order in monomer; and (3) a region of high dose rate, where the grafting rate is independent of dose rate and at least 5/2-order in monomer. Various possible mechanisms responsible for these effects are discussed, including the effects of viscosity on the initiation and termination reactions, the possibility of ionic graft polymerization, and energy transfer.     

Photoinduced graft polymerization of 2-methacryloyloxyethyl phosphorylcholine on polyethylene membrane surface for obtaining blood cell adhesion resistance

Phospholipid polymer, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)], was grafted with polyethylene (PE) membrane using photoinduced polymerization technique to make the membrane resistant to cell adhesion. The water contact angle on the PE membrane grafted with poly(MPC) decreased with an increase in the photopolymerization time. This decrease corresponded to the increase in the amount of poly(MPC) grafted on the PE surface. The same graft polymerization procedure was applied using other hydrophilic monomers, such as acrylamide (AAm), N-vinylpyrrolidone (VPy) and methacryloyl poly(ethylene glycol) (MPEG). These monomers were also polymerized to form grafted chains on the PE membrane, and the grafting was confirmed with X-ray photoelectron spectroscopy. Analysis of amount and distribution of plasma proteins at the plasma-contacting surface of the original and the modified PE membranes were analyzed using immunogold assay. The grafting of poly(MPC) and poly(VPy) on PE membrane reduced the plasma protein adsorption significantly compared with that on the original PE membrane. However, the PE membranes grafted with poly(AAm) or poly(MPEG) did not show any effects on protein adsorption. Platelet adhesion on the original and modified PE membranes from platelet-rich plasma was also examined. A large number of platelets adhered and activated on the original PE membrane. Grafting with poly(AAm) did not suppress platelet adhesion, but grafting with poly(MPC) or poly(VPy) on the PE membrane was effective in preventing platelet adhesion. It is concluded that the introduction of the phosphorylcholine group on the surface could decrease the cell adhesion to substrate polymer.     

Synthesis of functional polyethylene graft copolymers by nitroxide‐mediated living radical polymerization

This paper describes a new method to prepare graft copolymers, such as polyethylene‐g‐polystyrene (PE‐g‐PS), with a relatively well‐controlled reaction mechanism. The chemistry involves a transformation process from the metallocene copolymerization of ethylene and m,p‐methylstyrene (m,p‐MS) to nitroxide‐mediated “living” free radical polymerization (LRFP) of styrene. The metallocene catalysis produces ethylene‐co‐m,p‐methylstyrene (EMS) random copolymers. Next, 1‐hydroxyl‐2,2,6,6‐tetramethylpiperidine (HO‐TEMPO) was synthesized by the reduction of TEMPO with sodium ascorbate. The macroinitiator (EMS‐TEMPO) was synthesized with the bromination reaction of EMS, and the following nucleofilic reaction with this functional nitroxyl compound. The resulting macroinitiator (EMS‐TEMPO) for LRFP was then heated in the presence of styrene to form graft copolymer. DSC, ¹H‐NMR, FTIR spectroscopy were employed to investigate the structure of the polymers. The results of Molau test showed that PE‐g‐PS could be a potential good compatilizer. Copyright © 2008 John Wiley & Sons, Ltd.     

Pre-irradiation induced emulsion graft polymerization of acrylonitrile onto polyethylene nonwoven fabric

Acrylonitrile has been widely used in the modification of polymers by graft polymerization. In the present work, pre-irradiation induced emulsion graft polymerization method is used to introduce acrylonitrile onto PE nonwoven fabric instead of the traditional reaction in organic solvents system. The degree of grafting (DG) is measured by gravimetric method and the kinetics of the graft polymerization is studied. The existence of the graft chains is proven by Fourier transform infrared spectroscopy (FT-IR) analysis. Thermal stability of the grafted polymer is measured by Thermogravimetric analysis (TGA).     

Surface graft polymerization of glycidyl methacrylate onto polyethylene and the adhesion with epoxy resin

Surface graft polymerization of glycidyl methacrylate (GMA) was carried out onto a high- density polyethylene (PE) sheet pretreated with corona to introduce peroxides onto the PE surface. Graft polymerization of GMA was effected by UV irradiation of the coronatreated PE in the presence of monomer solution without the use of any photosensitizer. The graft layer was found by staining the PE cross section to localize in the surface region of PE. The physical change in the PE surface was characterized by scanning electron microscopy, while the chemical changes due to the GMA graft polymerization were assessed by the dynamic contact angle, FT-IR, and x-ray photoelectron spectroscopy (XPS) measurement. The peroxide formation by corona exposure was confirmed by the XPS measurement after derivatization with SO₂. The epoxy groups introduced onto the PE surface by the GMA graft polymerization were reactive with water (in the presence of HCI) and amines. The adhesion between the GMA-grafted PE and an epoxy resin was studied by means of a shear strength test method. The GMA-grafted PE exhibited strong interfacial adhesion with the epoxy resin, compared to the original and corona-treated PE. The adhesion strength of the GMA-grafted PE was nearly two times higher than that of the corona-treated PE. This strongly suggests that the enhanced adhesion between the surface-grafted PE and the epoxy resin is ascribed to covalent bonding of the epoxy groups on the GMA-grafted surface to the amines in the epoxy resin. © 1995 John Wiley & Sons, Inc.     

MMA/DVB emulsion surface graft polymerization initiated by UV light

Methyl methacrylate/1,2-divinylbenzene (MMA/DVB) in an opaque emulsion were successfully grafted onto the surface of polymeric substrate under the irradiation of UV light with benzophenone (BP) as a photoinitiator that was previously coated on the substrate surface. Monomer conversion, grafting efficiency, and grafting yields were determined by the gravimetric method. ATR-IR, AFM, and TEM were used to characterize the surface composition, to observe the topography of the grafted substrates, and to view inter-film colloid particles formed by cross-linking. The results reveal that, with the opaque MMA/DVB emulsion system and CPP film as substrate, the monomer conversion is in the range of 15-55%, the grafting efficiency is about 80%, the grafting yield reaches 5%, and the thickness of the graft layer can be controlled in the range 0.09-1.5 microm. Images of AFM show that the graft layer is piled up by nanoparticles (about 30-50 nm in diameter), which are linked together and tied to the substrate surface with covalent bonds. A possible model of surface graft polymerization including surface initiating, nucleation, and shish kebab growing is put forward to interpreting the above results.     

Modification of surface properties of high and low density polyethylene by Ar plasma discharge

Structural changes induced by Ar plasma discharge in low and high density polyethylene (LDPE and HDPE) were studied by different techniques. AFM and SEM methods were used to determine surface morphology, the changes in chemical structure were followed using FTIR and UV-vis spectroscopy. The content and the depth profile of incorporated oxygen was determined by RBS method. The degree of polymer ablation was determined gravimetrically. Standard goniometry was used to determine contact angle and to follow aging of plasma modified polymer. As a result of plasma treatment a lamellar structure or spherulites appear on the surface of HDPE and LDPE, respectively. Pronounced increase of the surface roughness is observed on HDPE contrary to LDPE. Plasma treatment for 400 s leads to the ablation of the surface layer of about 0.6 and 1 μm thick for LDPE and HDPE, respectively. Plasma treatment results in oxidation of the polymer surface layer which is more pronounced in HDPE. Concentration maximum of incorporated oxygen lies 25 nm beneath the sample surface in both polymer types. After exposure to plasma discharge carbonyl, carboxyl and amide groups were detected in the polymer surface layer together with CC bonds either in aromatic or in aliphatic structures. Immediately after the plasma treatment strong decline of the contact angle is observed, the decline being larger in HDPE. Later, in aged specimens the contact angle increases rapidly. The increase, which may be due to rearrangement of degraded structures, is stronger in the specimens exposed to plasma for longer times.     

Encapsulation of silica nanoparticles by redox-initiated graft polymerization from the surface of silica nanoparticles

This study describes a facile and versatile method for preparing polymer-encapsulated silica particles by ‘grafting from’ polymerization initiated by a redox system comprising ceric ion (Ce⁴⁺) as an oxidant and an organic reductant immobilized on the surface of silica nanoparticles. The silica nanoparticles were firstly modified by 3-aminopropyltriethoxysilane, then reacted with poly(ethylene glycol) acrylate through the Michael addition reaction, so that hydroxyl-terminated poly(ethylene glycol) (PEG) were covalently attached onto the nanoparticle surface and worked as the reductant. Poly(methyl methacrylate) (PMMA), a common hydrophobic polymer, and poly(N-isopropylacrylamide) (PNIPAAm), a thermosensitive polymer, were successfully grafted onto the surface of silica nanoparticles by ‘grafting from’ polymerization initiated by the redox reaction of Ce⁴⁺ with PEG on the silica surface in acid aqueous solutions. The polymer-encapsulated silica nanoparticles (referred to as silica@PMMA and silica@PNIPAAm, respectively) were characterized by infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. On the contrary, graft polymerization did not occur on bare silica nanoparticles. In addition, during polymerization, sediments were observed for PMMA and for PNIPAAm at a polymerization temperature above its low critical solution temperature (LCST). But the silica@PNIPAAm particles obtained at a polymerization temperature below the LCST can suspend stably in water throughout the polymerization process.