Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. I. γ irradiation

Mutual irradiation of polyethylene (PE) in methyl acrylate vapor easily forms a poly(methyl acrylate) (PMA) homopolymer layer on the inner graft copolymer layer consisting of both PE and PMA components as a result of the rapidly increasing surface-graft composition. This growth process of surface grafting has been found to provide some specific kinetic features different from those in other surface-grafting systems. With formation of the surface homopolymer layer, low- and highdensity PE sheets give the same grafting rate, whereas both sheets give different rates in grafting stages or conditions in which the homopolymer layer is not formed. This result indicates that most monomers, penetrating across the surface, are entrapped or consumed in the surface homopolymer layer; accordingly the rate becomes independent of the type of PE sheets that have significantly different diffusion coefficients. The thickness of the inner graft copolymer layer, which is kept constant after homopolymer-layer formation, increases with decreasing dose rate and with increasing monomer vapor pressure and temperature. This behavior can be qualitatively explained according to an equation for the initial steady-state grafting depth.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. II. High-energy electrons irradiation

Vapor-phase mutual grafting of methyl acrylate (MA) onto polyethylene (PE) at high dose rates from an electron accelerator yields the same surface graft structure as does the grafting at low dose rates from ⁶⁰Co sources; i.e., a homopolymer layer (consisting of only MA component) is easily formed on the inner graft copolymer layer (consisting of both MA and PE components) as a result of the continuously increasing surface graft composition. To produce the surface layer, 4-MeV electron irradiation with a linear electron accelerator requires only less than 3 min of irradiation time at dose rates of more than 2 Mrad/min, whereas γ irradiation with a ⁶⁰Co source requires at least 1 hr at dose rates of less than 2 × 10³ rad/min. The rate of monomer consumption (or polymerization) in the surface homopolymer layer shows no dependence of irradiation time and a positive dependence of dose rate. It has been suggested that this kinetic feature at the high dose rates shows some contribution of vapor-phase homopolymerization and subsequent deposition (onto the grafting surface) followed by recombination with the grafted side chain radicals, although secondary graft copolymerization from the grafted chain radicals is still the principal process for the growth of the surface homopolymer layer.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. III. Quantitative surface analysis by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (ESCA) has been used for quantitative surface analysis of surface grafts prepared by mutual irradiation of polyethylene (PE) in methyl acrylate (MA) vapor with γ rays and high-energy electrons. The binding-energy shift between the C_1s electrons in the ester group of poly(methyl acrylate) (PMA) and in PE is large enough (ca. 3.6 eV) to distinguish the PMA and PE components. The C_1s peak-area ratio of ester carbon to other carbons is related quantitatively to graft composition by constructing a calibration curve for a given instrument and excitation source, with a series of homogeneous grafts of known composition used as the calibration standards. Using the calibration curve and the measured peak ratio, the surface composition of the surface grafts is determined. The relations between surface compositions according to ESCA and attenuated total reflection (ATR) infrared spectroscopy and between adhesive bond strength and ESCA composition are discussed. In the electron-induced grafts, the grafted surface reaches maximum adhesive bondability with attainment of 100 mole % MA in the surface detected by ESCA; i.e., with formation of a homopolymer layer. The ESCA composition can be used as an indicator of the presence of the homopolymer layer or as a criterion for predicting adhesive bond strength.     

Graft Polymerization of a Polymer Matrix: Grafting of Tetrafluoroethylene

Graft polymerization of tetrafluoroethylene on polyethylene preirradiated by γ-rays from a cobalt-60 source at ?196°C has been investigated in the region of PE devitrification. A calorimetric technique made it possible to establish that 1.5-2% of monomer dissolves in the amorphous regions of PE at low temperatures. Efficient grafting proceeds in the temperature range directly adjoining the PE devitrification region. The graft copolymer yield amounts to ca. 1200%. The intensification of grafting is apparently caused by the following: (1) because of previous solution of TFE in the PE amorphous regions and filling of the micropores, the reaction in the initial stage is not limited by diffusion; (2) and the initiation efficiency is increased by slow passage through the PE devitrification region. The breaking strength of the graft copolymer is higher than that for the PE copolymer irradiated by the same dose.     

Effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel was investigated with the monomer amounting from less than monolayer adsorption to more than the equilibrium adsorption. The rate of graft polymerization and the molecular weight of the polymer changed with the amount of monomer adsorbed on silica gel. Maximum grafting efficiency was obtained at monolayer adsorption. The molecular weight of graft polymer was higher than that of homopolymer in both radical and cationic polymerizations, and the ratio in molecular weight of graft polymer to that of homopolymer tends to be unity with increasing amount of adsorbed monomer. These results can mainly be explained in terms of the number of initiating species (radical and cation) that change in relation to the amount of adsorbed monomer. Propagation and termination change with amount of adsorbed monomer in relation to the molecular mobility of adsorbed monomer. A very high-molecular-weight graft polymer is formed only with a small amount of adsorbed monomer in the initial stage. The grafting percent with a large amount of adsorbed monomer increased after most of the monomer has been polymerized. Secondary effect of radiation on the graft and homopolymers due to energy transfer from silica gel is suggested from the complicated phenomena in the later stage of the reaction.     

Grafting polyelectrolytes onto polyacrylamide for flocculation 1. Polymer synthesis and characterization

Low-molecular-weight high-charge-density cationic diallyldimethylammonium chloride homopolymer (polyDADMAC) was grafted onto high-molecular-weight nonionic polyacrylamide (PAM) via a free radical mechanism using a gamma radiation technique. The graft copolymer systems were characterized in terms of viscosity, composition, gel content, degree of grafting and grafting efficiency. Degree of grafting was a strong function of radiation dose, dose rate and polyelectrolyte concentration. Gels were formed at high radiation doses and high PAM levels. Crosslinking between the electrolyte polymers was limited due to electrostatic repulsion. Gelation was mainly caused by coupling of PAM chains. High grafting efficiency was achieved: the lower the poly(DADMAC) concentration, the higher the grafting efficiency observed. The grafting mechanism and the effect of ion interactions on copolymer structural properties are also elucidated and discussed. Received: 6 April 1998 Accepted in revised form: 28 August 1998     

Polymer Melt Intercalation in Clay Modified by Diblock Copolymers

Summary: The thermodynamic equilibrium in a melt of homopolymer C mixed with clay modified by a diblock copolymer AB is considered in theory. It is assumed that mixing is carried out in two stages. At first, the diblock copolymer penetrates into the interlayers formed by long clay sheets. Then, the clay with adsorbed diblock copolymer chains is added to the homopolymer melt. It is shown that the first process is thermodynamically favorable only if the interlayer width exceeds some threshold value that depends mostly on the difference in the adsorption energy of units A and B. A spontaneous mixing at the second stage is possible only if the enthalpic interactions between homopolymer and copolymer units are not very unfavorable. If so, the formation of an intercalated state is expected for a homopolymer of length comparable to the copolymer length, while for a long homopolymer the anticipated equilibrium state is exfoliation. The spatial distribution of A, B, and C units across the interlayer has been studied for different parameters of the system. The most readily adsorbing units A occupy almost all clay surface. However, the layer of block A is considerably swelled by both B and C units. The mutual distribution of units B and C may vary from almost homogeneous to having rather sharp boundary depending on the value of the Flory‐Huggins parameter χ_BC. The formation of a pure homopolymer layer at the center of the interlayer indicates about a tendency to exfoliate.

Interlayer profiles of the fractions of units A, B, and C, respectively.     

The phase behavior of comblike block copolymer A(m+1)B(m)/homopolymer A mixtures

The phase behaviors of comblike block copolymer A(m+1)B(m)/homopolymer A mixtures are studied by using the random phase approximation method and real-space self-consistent field theory. From the spinodals of macrophase separation and microphase separation, we can find that the number of graft and the length of the homopolymer A have great effects on the phase behavior of the blend. For a given composition of comblike block copolymer, increasing the number of graft does not change the macrophase separation spinodal curve but decreases the microphase separation region. The addition of a small quantity of long-chain homopolymer A increases the microphase separation of comblike block copolymer/homopolymer A mixture. However, the addition of short-chain homopolymer A will decrease the phase separation region of comblike block copolymer/homopolymer A mixture. It is also found that the microstructure formed by diblock copolymer is easier to be swelled by homopolymer than that formed by comblike block copolymer. This can be attributed to the architecture difference between the comblike block copolymer and linear block copolymer.     

Grafting onto Wool. XV. Graft Copolymerization of MA and MM A by Use of Mn(acac)3 as Initiator

Graft copolymerization of acceptor monomers MA and MMA onto Himachali wool fiber in an aqueous medium was studied by using Mn(acac)s as initiator. Nitric acid was found to catalyze the graft copolymerization. Percentage of grafting and percent efficiency have been determined as functions of the concentration of chelate, nitric acid, monomer, time, and temperature, Under optimum conditions, MMA produced a maximum grafting of 82.5% while MA afforded maximum grafting to the extent of 27.5%. Relative reactivities of MA and MMA toward grafting have been compared with those of EA, BA, and VAc reported earlier from this laboratory. Different vinyl monomers were found to follow the following reactivity order toward grafting onto wool fiber in the presence of Mn(acac)₃: MMA > EA > BA > MA > VAc. An attempt has been made to explain the observed reactivity pattern shown by different vinyl monomers in graft copolymerization reactions.     

Grafting onto poly(vinyl alcohol). II. Graft copolymerization of methyl acrylate and vinyl acetate and their binary mixture using γ-rays as initiator

Methyl acrylate (MA), vinyl acetate (VAc) and their binary mixture (MA + VAc) have been graft copolymerized onto poly(vinyl alcohol) using γ-rays as initiator by mutual radiation method in aqueous medium. The optimum conditions for affording maximum grafting have been evaluated. The percentage of grafting has been determined as a function of total dose, concentrations of poly(vinyl alcohol), MA, VAc, and their binary mixture. Rate of grafting (R_p) and induction period (I_p) have been determined as a function of total initial mixed monomer concentration and concentration of poly(vinyl alcohol). The graft copolymer has been characterized by thermogravimetric method. The effect of donor monomer (vinyl acetate) on percent grafting of acceptor monomer (methyl acrylate) has been explained.     

Calculation of composition heterogeneity of block and graft copolymers

The composition heterogeneity has been calculated for some block and graft copolymers. General relationships have been derived for a model of the poly(A-g-B) or poly-(A-b-B) type fulfilling the assumption of random grafting. Numerical results have been calculated for special cases of particular interest. These include a copolymer having independent molecular weight contributions from units of species A and B (a special case of which is a block copolymer) and a graft copolymer where the grafting is not accompanied by crosslinking or degradation side reactions and no homopolymer B is formed. Two other model systems represent the effects of the presence or absence of both homopolymers. For the above models, the dependence of the composition heterogeneity on the structure-determining parameters (average number of grafts in the molecule, polydispersity index of the molecular weight of the backbone and graft) is discussed. The heterogenities thus calculated are in many cases comparatively low. The composition heterogeneity of the system is in most cases increased by the presence of homopolymers.     

13C NMR Study of the grafting of 13C labeled maleic anhydride onto PE,PP and EPM

The chemical structure of polyolefins grafted with maleic anhydride (MA) has been the subject of much speculation, but thorough experimental studies are rare. MA with 99% ¹³C in the double bond was synthesized and grafted onto PE, EPM and PP in the melt and solution. 1D INADEQUATE ¹³C NMR spectroscopy was used to characterize the products. Saturated, monomeric MA graft structures are formed. Only for grafted PE short MA oligomers are demonstrated. Grafting occurs on secondary and tertiary carbons depending on the composition of the polyolefin. For PP a new, unsaturated MA graft structure on the polymer chain terminus is identified. All graft structures are rationalized using a simple grafting mechanism.     

The properties of SBS-g-VP copolymer membrane prepared by UV photografting without degassing

The grafting of 4-vinylpyridine (VP) onto styrene-butadiene-styrene triblock copolymer membrane (SBS) was induced by UV-radiation without degassing to obtain the SBS-g-VP copolymer membrane. The graft copolymer membrane was characterized by electron spectroscopy for chemical analysis (ESCA) and scanning electron microscope (SEM). The tensile strengths and elongations of dry and wet SBS-g-VP copolymer membranes were measured. The contact angle of dry and wet SBS-g-VP graft copolymer membranes with different amount of grafting were determined. By using Kaelble's equation and the contact angle data, the surface energy of dry and wet SBS-g-VP graft copolymer membranes were determined. The protein absorption of fibrinogen and albumin on the SBS-g-VP membranes were evaluated. It was found that the oxygen content in the SBS-g-VP copolymer membrane increased with increasing grafting degree which resulted from the UV photografting without degassing. The tensile strength of dry SBS-g-VP membrane increased with increasing degree of grafting but the elongation decreased. The tensile strengths and elongations of wet SBS-g-VP were significantly lower than those of SBS. The surface energy of dry and wet SBS-g-VP were determined by using Kaelble's equation and the contact angle data. It was found that the surface energy of SBS-g-VP membrane increased. The surface energy of wet SBS-g-VP was higher than that of dry SBS-g-VP. The absorption of albumin and fibrinogen decreased with increasing grafting degree and then levelled off.     

Effect of dimethylaminoethyl methacrylate on the graft copolymerization of ethyl acrylate onto hydroxypropyl methylcellulose in aqueous medium

Graft copolymerization of an ethyl acrylate (EA) and dimethylaminoethyl methacrylate (DMAEMA) monomer mixture onto water-soluble hydroxypropyl methylcellulose was investigated with potassium persulfate (KPS) as the initiator in an aqueous medium. The effects of introducing DMAEMA onto the graft copolymerization and the properties of the resulting latex that was produced were studied systematically. The optimum conditions for the graft copolymerization in terms of percentage of grafting and grafting efficiency were determined. The graft copolymer was characterized by Fourier transform infrared spectra, elemental analyses, nuclear magnetic resonance, transmission electron microscopy, and dynamic light scattering methods. The results suggest that the introduction of the DMAEMA monomer clearly accelerates the initial rate of the graft copolymerization, whereas the grafting parameters decrease significantly with increasing amounts of DMAEMA. These results can be attributed to the relatively large size of the DMAEMA molecule, its redox reaction with KPS, its hydrophilicity in water, and its chain transfer effect. The equilibrium humidity adsorption behavior and acid solubility of graft the copolymer films were also studied.     

Process parameters and their effect on grafting reactions in core/shell latexes

The grafting of methyl methacrylate (MMA) onto polybutadiene (PB) latexes prepared by seeded emulsion polymerization at 50°C was investigated as a function of: (a) initiator concentration used in the secondary polymerization, (b) monomer-to-polymer ratio, (c) the specific surface area of the seed latex, and (d) the degree of conversion. The thin layer chromatography/flame ionization detection (TLC/FID) technique was used to determine the proportion of graft copolymer in the core/shell latex, It was found that grafting PMMA onto PB depended upon the concentration of initiator, decreasing as the concentration was increased. The amount of grafting increased with increasing specific surface area of the seed latex, while the molecular weight of the acetone-soluble graft copolymer decreased. The amount of graft copolymer was found to decrease concurrently with increasing monomer-to-polymer ratio and degree of conversion. These results suggest a hydrogen abstraction mechanism in the formation of graft PB–PMMA through a chain transfer process.     

The preparation,characterization, and application of cellulose–MMA graft copolymers. I. The aqueous-based preparation of cellulose–MMA graft copolymers

Cellulose-MMA graft copolymers have been produced using aqueous-based, Ce(IV)-initiated and periodate-initiated systems and also photochemical initiation. The reaction variables studied include the effect on grafting of varying the MMA monomer concentration, the initiator type and concentration, and also the reaction time. Of the three initiator types examined, the Ce (IV)-initiated and the photochemically-initiated systems are comparable in their effects on graft copolymer formation. Concurrent homopolymer formation was in the region of 50% by weight. Periodate-initiation leads to less efficient grafting of MMA onto cellulose, although homopolymer formation is also lower (typically <20% by weight). The characterization of the copolymeric products through their properties as solids and, as their carbanilated derivatives, through their solution properties has been undertaken. Values of the activation onergy of decomposition (E_A) of the cellulose-MMA graft copolymers decrease with increasing MMA content, ranging between 227 and 155kJ mol^?1. There is also a dependence on initiator type and grafting reaction conditions used (E_A (cellulose wood pulp) = 239 kJ mol^?1; E_A (PMMA) = 115 kJ mol^?1). Quantitative zeta-potential (ζ) determinations for cellulose-MMA graft copolymer samples produce negative surface charge density (σ) values. At a comparable MMA grafting level of 70–80%, values are of the order: photochemical (?730 esu/cm²) > periodate (?470 esu/cm²) > Ce (IV)-initiation (?351 esu/cm²). Characterization of carbanilate solutions (by rheological examination) and of dry, carbanilate films (by study of surface wetting behavior) highlighted differences in the physical conformation of copolymers prepared by the different initiation routes. The highly degradative effect on cellulose of a periodate initiator, in comparison with the Ce (IV)-initiation system, is reflected in significantly reduced molar mass values (typically, M_n 65,000 as opposed to 130,000 for Ce (IV)-initiated graft copolymer carbanilates).     

均聚物链吸附在胶束表面上的非平衡态耗散粒子动力学

利用平衡态耗散粒子动力学（Dissipative Particle Dynamics, DPD）方法,研究了嵌段共聚物自组装形成胶束以及均聚物链在其表面的吸附。进一步采用非平衡态耗散粒子动力学（Non-Equilibrium Dissipative Particle Dynamics, NEDPD）方法,通过加入剪切,研究了均聚物的脱落和胶束的分裂过程。模拟结果揭示了脱落时间随剪切速率的变化规律。     

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.     

Control of surface properties using fluorinated polymer brushes produced by surface-initiated controlled radical polymerization

Surface-grafted styrene-based homopolymer and diblock copolymer brushes bearing semifluorinated alkyl side groups were synthesized by nitroxide-mediated controlled radical polymerization on planar silicon oxide surfaces. The polymer brushes were characterized by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and time-dependent water contact angle measurements. Angle-resolved XPS studies and water contact angle measurements showed that, in the case of the diblock copolymer brushes, the second block to be added was always exposed at the polymer-air interface regardless of its surface energy. Values of z*/Rg were estimated based on the radius of gyration, Rg, of the grafted homopolymer or block copolymer chains for the grafted brushes and thickness of the brush, z*. The fact that z*/Rg > 1 suggests that all these brushes are stretched. These results support the idea that after grafting the first block onto the surface the nitroxide-end capped polymer chains were able to polymerize the second block in a "living" fashion and the stretched brush so formed was dense enough that the outermost block in all cases completely covers the surface. NEXAFS analysis showed a relationship between the surface orientation of the fluorinated side chains and brush thickness with thicker brushes having more oriented side chains. Time-dependent water contact angle measurements revealed that the orientation of the side chains of the brush improved the surface stability toward reconstruction upon prolonged exposure to water.     

淀粉与丙烯酸甲酯的接枝共聚物作为生物降解塑料的研究

如何解决废弃塑料制品的再资源化和使用无污染的降解塑料是当今人类急待解决的热点课题．淀粉与丙烯酸甲酯（MA）进行接技共聚以制备塑料发泡产品的研究已有报道［‘－‘1，一般认为塑料中淀粉含量在40％以上的产品，很容易在土壤中被微生物降解掉［‘］．这些研究都是在水溶液体系中进行的，本文的目的在于开发高淀粉含量的接校共聚物，为此对比了在3种不同体系（MA－CH3OHA12O三元均相溶液体系，水溶液体系和乳液体系）中得到的接校共聚物的力学性能、形态观察与组成情况，发现单纯追求高接技效率与接枝链MA的高分子量并不一定能得到…