NMR study of adsorbed water on acrylic acid-grafted and methacrylic acid-grafted cellulose

The water-adsorbing properties of cellulose samples which had been graft copolymerized with hydrophilic vinyl monomers using ceric salt as an initiator were investigated by means of the width of the high-resolution NMR absorption spectrum, water retention, and moisture regain of the samples. In the change of the width at half-value of the spectrum with per cent grafting, a maximum value followed by a minimum value was observed on samples both grafted with acrylic acid and methacrylic acid. Thus, the effect of grafting on the water-adsorbing properties appeared not to be simple. Though no special change in the water retention by grafting was observed, the per cent grafting dependence on the moisture regain in high relative humidity showed a peculiar and definite relation. The per cent grafting giving maximum moisture regain was about 8% and 18% for acrylic acid and methacrylic acid, respectively, and this agreed very well with the minimum widths at half-value. The change in the glass transition temperature of the sample—water system caused by grafting is also described.     

Effect of styrene grafting on diffusion and solubility of gases in polyethylene

Diffusion and solubility coefficient data of gases for styrene-grafted high-density polyethylene obtained by γ-irradiation are reported. Diffusion coefficients were determined by the time lag method. Solubility coefficients were determined by a new, more accurate static method. Densities and volume fractions of grafted polystyrene were calculated from the observed values of extent of grafting and density of the graft copolymer films. The solubility coefficients obey simple additivity in terms of volume fraction of side-chain polystyrene and amorphous polyethylene. However, behavior of the diffusion coefficients is more complex. Inasmuch as diffusion is a kinetic process, it is influenced by morphology. The experimental results reported here, together with x-ray diffraction and DSC data, provide a basis for discussing the morphology of the graft copolymers.     

Glycidyl methacrylate–grafted linear low‐density polyethylene fabrication and application for polyester/polyethylene bonding

The grafting of glycidyl methacrylate (GMA) onto linear low‐density polyethylene (LLDPE) was investigated. The grafting was performed by free‐radical grafting in the melt state in a twin‐screw extruder using an organic peroxide as initiator. The effect of initial GMA and peroxide concentration, styrene comonomer addition, as well as initial resin viscosity, on the final content in grafted moieties, unbound homopolymer, and unreacted monomer was assessed. The effect of process parameters such as flow rate, screw rotation speed, and barrel temperature was also investigated. Chemical composition was shown to be the main parameter for controlling grafting level and grafting efficiency. Grafting levels up to 1.8% and efficiency of 90% were reported even though in most conditions, the graft efficiency was severely decreased by the homopolymerization of GMA into polyGMA chains not bound to LLDPE. Finally, the effect of grafting level and the presence of unbound GMA‐based species on the efficiency GMA‐grafted LLDPE as adhesive between polyethylene and polyester were discussed. Good adhesion to poly(ethylene terephthalate) copolymer was found for low viscosity grafted polyethylene resins. A significant improvement in adhesive strength on polyester was observed when the molecular weight of the grafted LLDPE was increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3180–3191, 2004     

Permeation of gases through modified polymer films. I. Polyethylene–styrene graft copolymers

The permeabilities of nitrogen, oxygen, and carbon dioxide through polyethylene–styrene graft copolymer films were measured by means of a gas permeability apparatus based on a modification of Barrer's high vacuum technique. Polyethylene–styrene grafts were prepared by mutual γ-ray irradiation of low-density polyethylene films in styrene–methanol solution. Densities and thicknesses of the graft copolymer films were determined. It was observed that the gas permeability constants decreased with increasing grafting to minimum values at 20–30% styrene grafting and increased again above 30% grafting. These results are explained in terms of a decrease in the free volume of the amorphous regions of the polyethylene by a “filling in” effect of the grafted polystyrene chains. Above 30% grafting, disruption of the crystallites may occur resulting in increased gas permeation. Activation energies for gas permeation through polyethylene–styrene graft copolymer films were calculated and found to decrease with increasing per cent styrene grafting. For nitrogen permeation, the activation energy decreased from 11.7 kcal/mole for unirradiated polyethylene to 9.5 kcal/mole for a 50.5% graft. Corresponding values for oxygen and carbon dioxide were 10.2–8.2 kcal/mole for a 48.7% graft and 8.4–6.5 kcal/mole for a 50.5% graft.     

Preparation and characterization of poly (ethylene glycol) grafted Ca-alginate fibers by γ-irradiation for biomedical applications

Radiation processing, being a physical process, is an environmentally friendly alternative to chemical modifications. It is economically viable, safe, and possesses several advantages over other conventional methods employed for modification and grafting. To improve the physico-mechanical properties of Ca-alginate fiber (CaAF), poly (ethylene glycol) (PEG) was grafted by applying γ-radiation of different intensities. The effect of γ-irradiation on the physico-mechanical, thermal, morphological, thermal and water aging, water, and simulated body fluid (SBF) uptake were evaluated. FT-IR results confirmed that PEG was successfully grafted onto Ca-alginate fibers by γ-irradiation. From the detailed experimental results, irradiation doses and PEG concentration were optimized for grafting processes. The results showed that 50% PEG and 2.5?kGy irradiation dose yielded the highest tensile strength. Differential scanning calorimetric (DSC) analysis showed that with increasing γ-intensity a decrease of dehydration temperature of the fibers had occurred. On the other hand, the glass transition temperature (T _g) increased with increasing irradiation dose. The tensile cracked surfaces of the grafted alginate fibers were analyzed by scanning electron microscope (SEM) in order to monitor their surface morphologies. The SEM images of the cracked surfaces demonstrated that spherical shape rods were present for irradiated fiber sample while no such rods were observed for non-irradiated fibers. The characteristic data obtained from SBF and water uptake, and water and thermal aging experiments indicated that CaAF grafted with 50% PEG by applying 2.5?kGy γ-irradiation can be potentially employed for biomedical purposes, such as surgical suture.     

Thermal decomposition of cellulose/synthetic polymer blends containing grafted products. V. Cellulose/polystyrene blends

Homogeneous grafting of styrene onto cellulose was carried out in a dimethylacetamide/lithium chloride solvent system. The grafted products were added to cellulose/polystyrene (PS) blends as compatibilizers. The thermal decomposition behavior of the blends was investigated by thermogravimetry. The thermal stability of the blends decreased with an increase in grafted product content. The crystallinity of the blends decreased with grafted product content. The microphase‐separated structures of the blends became finer with grafted product content. The glass transition temperatures for cellulose and PS in the blends were lowered with grafted product content. Differences in thermal decomposition behavior of the blends were correlated with compatibility. Thermogravimetry was effective for compatibility estimation in cellulose/PS blends containing grafted products. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Direct synthesis of polymer-grafted inorganic hybrids via reversible chain transfer catalyzed polymerization

In this work, a new simple and robust method for preparation of polymer-grafted inorganic hybrids through “grafting to” reaction is presented. Polymer chains were synthesized by reversible chain transfer catalyzed polymerization (RTCP) are capped with iodine according to the RTCP mechanism. The obtained iodine-capped polymer chains can react irreversibly with the hydroxyl groups available on the surface of inorganic materials through a nucleophilic substitution (SN) reaction. In this method, there is no need to modify the surface of inorganic materials or to functionalize polymer chains prior to the “grafting to” reaction. RTCP produced polystyrenes with different molecular weights, e.g., 4,000, 6,000, and 8,000 g/mol, and silica nanoparticles were employed as the polymer and inorganic materials, respectively. The resulting hybrids were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, and transmission electron microscopy techniques. According to the results, graft density decreased by increasing the polystyrene molecular weight. Additionally, the rheological studies of prepared polystyrene nanocomposites containing 2 wt % of the produced hybrids confirmed the better dispersion of the modified hybrids in the polystyrene matrix. The glass transition temperature (T _g) of the polystyrene nanocomposites was driven by differential scanning calorimeter technique. Analysis of nanocomposites’ T _g results revealed that increment of the grafted polymer molecular weight of hybrids increased the glass transition temperature of the prepared nanocomposites due to improvement of the dispersion level.     

PS/PE-g-MAH及PS/PE相容性评价的分子动力学模拟

采用分子动力学(MD)模拟方法对比研究了聚乙烯(PE)与聚苯乙烯(PS)共混体系和力化学反应法马来酸酐接枝聚乙烯(PE-g-MAH)与PS共混体系的相容性。通过对MD模拟得到的溶解度参数、玻璃化转变温度、径向分布函数和均方末端距的分析,对两种共混物的相容情况进行评价。研究表明,PS/PE体系的共混相容情况不好,而PS/PE-g-MAH体系相对于PS/PE体系,相容性得到明显改善。模拟结论与实验结果相一致。     

In situ preparation of Mg(OH)2/polystyrene nanocomposite via soapless emulsion polymerization

Magnesium hydroxide nanoneedles modified by oleic acid [OA–Mg(OH)₂] were synthesized via alkaline injection into magnesium chloride solution in the presence of oleic acid (OA). The magnesium hydroxide/polystyrene nanocomposite [Mg(OH)₂/PS] was then prepared by soapless emulsion polymerization technique in an aqueous suspension. The Fourier transform infrared (FT–IR) analysis shows that the polystyrene was covalently grafted onto the surfaces of the Mg(OH)₂nanoneedles [OA–Mg(OH)₂]. The dispersion of Mg(OH)₂nanoneedles in polystyrene is uniform as observed by transmission electron microscope (TEM). The grafting percentage was determined by means of elemental analysis (EA). The thermal behavior determined by the differential scanning calorimetry (DSC) indicated that Mg(OH)₂/PS had a higher glass transition temperature than PS matrix, and it can be concluded that Mg(OH)₂ could retard the degradation of PS based on the data of thermal gravimetric analysis (TGA) and differential thermoanalysis (DTA).     

Synthesis of polyethylene glycol-polystyrene core-shell structure particles in a plasma-fluidized bed reactor

Particles with core-shell structure with polystyrene (PS) core and polyethylene glycol (PEG) grafted on the surface were synthesized in a plasma-fluidized bed reactor. The virgin, plasma-treated, and grafted powders were characterized by the DPPH method, UV-vis spectrophotometer, NMR, FT-IR and SEM. The plasma-treated PS powders have well formed peroxide on the surface. By PEG grafting polymerization, PEG is well grafted and dispersed on the surface of the plasma-treated PS powders. The PEG-g-PS powder exhibits the core shell structure in the cross-sectional SEM image, and it can be claimed that well dispersed PEG grafting polymerization on PS surface can be achieved in the plasma fluidized bed reactor.     

Structure and properties of cellulose graft copolymers. I. Radiation-induced rayon–styrene graft copolymer

Rayon–styrene graft copolymers were prepared by the direct radiation method, with the use of the preswelling technique, by irradiation with γ-rays from ⁶⁰Co. The grafting was carried out in bulk styrene and in styrene–solvent mixtures, such as styrene–methanol and styrene–acetone, to study their effect on the graft copolymerization reaction and the structure of the resulting graft copolymer. The effects of carbon tetrachloride, a chain-transfer agent, was also investigated. Three different types of rayon yarn were used; Fortisan, a modifier-type high wet-modulus rayon, and a high-tenacity tire yarn, in order to study the effect of rayon microstructure on the grafting reaction. The molecular structure of the rayon–styrene graft copolymers was studied by hydrolyzing away the cellulose backbone and measuring the molecular weights of the grafted polystyrene branches. For grafting in bulk styrene, the molecular weights of the grafted polystyrene ranged from 400,000 to 1,000,000, while those of the polystyrene homopolymer formed in the outside solution were of the order of 30,000–50,000. The molecular weights of the grafted polystyrene branches tended to increase with per cent grafting in the graft copolymer. For grafting in styrene–methanol and styrene–acetone mixtures, the molecular weights of the polystyrene branches decreased with increasing solvent content. The addition of carbon tetrachloride to bulk styrene resulted in a sharp decrease in the molecular weights of the grafted branches. The grafting frequency or number of polystyrene branches per cellulose chain was calculated from the per cent grafting and the molecular weights of the polystyrene branches. The morphology of the rayon–styrene graft copolymers and some of their physical properties are discussed.     

A few physical properties of grafted polyethylene and nylon films

Methyl methacrylate, vinyl acetate, or N-vinylpyrrolidone was graft-copolymerized onto low-density polyethylene or nylon 6 film by simultaneous irradiation method. Higher extent of grafting was attained by liquid-phase grafting than by vapor-phase grafting. The relative change in the degree of crystallinity of backbone polymer caused by grafting was measured with differential scanning calorimetry. In polyethylene-g-vinylpyrrolidone, the degree of crystallinity decreased markedly with the extent of grafting. However, in other grafted films, especially in grafted nylon, the crystallinity decrease was limited, or substantially no decrease was observed in a few systems. Water vapor permeability of the grafted films changed uniformly with increasing extent of grafting, and particularly polyethylene- and nylon-g-vinylpyrrolidone films showed excellent permeability, and some were able to be used as dialyzer. The difference in grafting method, liquid-phase grafting or vapor-phase grafting, produced no difference in those properties. The grafting was found to bring about a change in the molecular orientation of the original film.     

Process of grafting styrene onto LLDPE by swelling and suspension copolymerization

A technology of swelling and suspension copolymerization was conducted to graft styrene onto linear low‐density polyethylene (LLDPE). The graft mechanism of styrene with LLDPE had been described by ¹H NMR and IR. The mean particle diameter and size distribution of the products with different proportions of LLDPE to styrene monomer were calculated. The morphology and thermal behavior of copolymers were characterized by scanning electron microscopy and differential scanning calorimetry. The glass transition temperature of copolymers increased with the addition of LLDPE, which proved the existence of the polyethylene‐g‐polystyrene copolymer. The grafting efficiency and granulation rate of suspension copolymerization were investigated. It was found that the grafting efficiency increased and the granulation rate decreased with the addition of LLDPE. POLYM. ENG. SCI., 50:1713–1720, 2010. © 2010 Society of Plastics Engineers     

Dynamic viscoelastic behavior of styrene-grafted nylon 6 fiber

Styrene-grafted nylon 6 fibers which had been prepared by the UV irradiation method were investigated by dynamic viscoelasticity and dilatometry. It was found that nylon 6 is relaxed and polystyrene is simultaneously plasticized by nylon 6 during grafting. These phenomena are interpreted as follows. The grafting process causes nylon 6 to have a lower glass transition temperature and increases grafting frequency of polystyrene to nylon 6 by increasing the chemical junctions between the two components, so that they necessarily become more compatible.     

Enhanced mechanical properties of acrylate based shape memory polymer using grafted hydroxyapatite

In the present study, the effect of grafted and ungrafted hydroxyapatite (HAp) filler on the mechanical properties of acrylate based shape memory polymer (SMP) composite is reported. HAp is grafted with polyethylene glycol methacrylate (PEGMA) monomer to avoid agglomeration and the same is embedded as reinforcement in tBA – PEGDMA matrix (70 wt% tBA: tert-butyl acrylate +30 wt% PEGDMA: polyethylene glycol dimethacrylate). The grafting process improved the interfacial interactions of the particles, dispersed in the polymer system and subsequently enhanced the mechanical properties of the shape memory polymer composites. The morphology of HAp particles is investigated by field emission scanning electron microscopy. The mechanical properties of SMP composites are evaluated at room temperature and above glass transition temperature (Tg) with grafted and ungrafted HAp particles. The addition of grafted HAp significantly improved the tensile strength (40%) and shape recovery rate (25%) of the SMP composite when compared to the SMP composite containing ungrafted HAp. SMP composite containing grafted HAp exhibited higher cell viability compared to the neat SMP and the SMP composite containing ungrafted HAp.     

Graft polymerization of acrylic acid onto polyethylene film by preirradiation method. I. Effects of preirradiation dose,monomer concentration,reaction temperature,and film thickness

Low-and high-density polyethylenes were irradiated by electron beams with dose of 2–50 Mrad and then immersed in aqueous solution of acrylic acid (monomer concentration from 30 to 100 wt %) for 10 min?5 h at a temperature of 25–40°C. The degree of grafting increases with time and levels off. High density polyethylene shows lower grafting rate and higher final % grafting in compared with low-density polyethylene. Both grafting rate and final % grafting increase with total dose of preirradiation, but show some saturation at high doses. The highest grafting rate was observed at 60 wt % of monomer concentration where the grafted polyethylene swells to the largest extent in the monomer mixture. Apparent activation energies for the grafting are 19.6 and 27.3 kcal/mol for low- and high-density polyethylenes, respectively, reflecting the proces of monomer diffusion in the film. Grafting rate decreases with increasing film thickness. Graft polymerization starts on the surface of the film and proceeds to the inner part with monomer diffusion through the grafted layer.     

紫外光辐射接枝及胺化法制备温敏性聚乙烯薄膜

实验探索在水性体系中经紫外光辐射,引发丙烯酸(AAC)在聚乙烯(PE)薄膜表面接枝,并经过胺化反应,在已改性的丙烯酸-聚乙烯(AAC-g-PE)薄膜上继续引入功能团,使改性后的PE薄膜具有温度敏感性。考察了引发剂用量、紫外光照射时间对接枝率的影响,并对不同胺化剂合成产物的温敏效应进行比较,从而达到实验目的。通过红外光谱和尺寸变化率证明丙烯酸接枝在PE表面,胺化反应后,生成聚N-异丙基丙烯酰胺聚合聚乙烯(PNIAAm-g-PE)薄膜和聚N-正丙基丙烯酰胺聚乙烯(NNPA-g-PE)薄膜具有温敏性。     

聚苯乙烯接枝聚乙二醇6000的制备及表征

以1,4-二氯甲氧基丁烷为氯甲基化试剂,通用级聚苯乙烯(PS)为原料,制备了氯甲基化聚苯乙烯(CMPS);将CMPS与聚乙二醇(PEG)6000采用碱催化法制备了PS接枝PEG6000聚合物(PEG6000-g-PS)。对CMPS,PEG6000-g-PS进行傅里叶变换红外光谱分析、X射线光电子能谱分析,对PS,PEG,PEG6000-g-PS进行差示扫描量热法分析、热重分析。结果表明:成功制备了PEG6000-g-PS,且接枝率为12.3%;PEG6000-g-PS的熔融温度为63.03℃,相变焓为15.313 J/g,起始分解温度为314℃,热稳定性良好。     

Distribution of acrylic acid grafted chains introduced into polyethylene film by simultaneous radiation grafting with water and ethanol as solvents

The graft copolymerization of acrylic acid onto low‐density polyethylene films by simultaneous γ‐ray irradiation was carried out. The effect of water and ethanol as grafting solvents on the distribution of grafted poly (acrylic acid) in the low‐density polyethylene films was studied with optical microscopy observations of dyed and sliced samples and attenuated total reflection/Fourier infrared spectroscopy analysis. When no vigorous homopolymerization occurred, both polyethylene and poly(acrylic acid) existed in the grafted layer, and the thickness of the grafted layer and the poly(acrylic acid) concentration in the grafted layer increased with an increasing degree of grafting, regardless of the grafting conditions, the former increasing faster than the latter. In comparison with water as the solvent, in the absence of the inhibitor, homopolymerization could be suppressed to a certain degree in the ethanol solvent system, whereas in the presence of the inhibitor, obvious homopolymerization occurred at a lower monomer concentration, and both the degree of grafting and the thickness of the grafted layer were lower. Such differences could be explained by the chain transfer and the relatively low solubility of poly(acrylic acid) in ethanol. In addition, an experimental scheme using optical microscopy to observe the dyed and sliced polymers was optimized. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1570–1577, 2007     

Structural changes in the grafted copolymer polyethylene-styrene

The general method for phase analysis was used on X-ray diffractograms of copolymers produced by the direct and the indirect method of grafting styrene to polyethylene. It was established that both copolymer systems show small deviations from a two-phase structure. Up to a polyethylene to polystyrene ratio of 1:1 the grafting process did not cause any substantial change in crystalline structure. Crystallites were not destroyed in either system. The main structural changes resulting from grafting appeared in disordered regions of polyethylene. The diffraction curves determined for individual structural states are discussed and used as a basis to construct structural models.