Etude de copolymères ABS (acrylonitrile–butadiène–styrène): Solvatation préférentielle du polybutadiène par les promoteurs

ABS resins formed by copolymerization of styrene and acrylonitrile (AN) in presence of polybutadiene, consist of a mixture of SAN graft copolymer on polybutadiene (PBut) and of ungrafted SAN copolymer (styrene-co-acrylonitrile). The kinetic study was completed by showing a preferential solvation of polybutadiene by the initiator. This solvation effect was studied as a function of the concentration ratio SAN/PBut and in relation with the type of initiator. The adsorption of initiator appeared to be maximum when its solubility parameter (σ) is close to that of polybutadiene. As a function of the polybutadiene characteristics, this selective adsorption can be given by where I₁ is the quantity of initiator in the polybutadiene medium, I is the total amount of peroxide, [PBut] is the concentration of polybutadiene, and M?_n its molecular weight. It has been shown furthermore that the preferential solvation of polybutadiene by the benzoyl peroxide can be increased by addition of SAN or acrylonitrile. The consequences of this solvation effect on the characteristics of the grafting reaction, more precisely on the molecular weight of grafted and ungrafted SAN and on the rate of polymerization, were examined.     

Impact resistant resins based on olefinic terpolymers containing a system of conjugated double bonds—V. Influence of reaction solvent on the physico-chemical properties of ungrafted SAN and some technological properties of ATS resins

Radical induced grafting of styrene (S) and acrylonitrile (AN) on to an unsaturated ethylene-propylene based terpolymer (EPTM) in mixed solvents has been investigated. Molecular weight, molecular weight distribution, conversion of ungrafted poly(styrene-co-acrylonitrile) (SAN) with 25 w% of AN and its degree of graft on to EPTM have been reported as functions of composition of the toluene/η-heptane mixture used as solvent. Mechanical properties of ATS resins are strongly dependent on the degree of graft of SAN resins and the molecular parameters of the ungrafted SAN; both are influenced by toluene content in the solvent mixture.     

PEB/MMA-AN悬浮接枝共聚反应机理

研究了乙烯-1-丁烯共聚物(PEB)弹性体与甲基丙烯酸甲酯(MMA)-丙烯腈(AN)悬浮接枝共聚反应行为及接枝共聚产物对SAN树脂增韧作用随反应时间的变化规律, 用凝胶渗透色谱法和傅里叶变换红外光谱法对接枝共聚产物进行了表征, 分析了接枝共聚反应机理, 推算了接枝链分子量. 结果表明, 体系首先发生链增长自由基向PEB转移终止形成非接枝共聚物(MAN_L)和PEB大分子自由基引发单体共聚形成接枝链(g-MAN)的反应, 接枝反应结束后体系发生明显的非接枝共聚形成非接枝共聚物(MAN_H)的反应; MAN_L的分子量低于g-MAN的分子量, 而g-MAN的分子量明显低于MAN_H的分子量; 在接枝共聚过程中发生已接枝和未接枝PEB断链并随机再接生成多嵌段共聚物的副反应; 在反应初期, 接枝链的AN单元含量接近于非接枝共聚物的AN单元含量, 在反应中后期前者远低于后者.     

An experimental study on saturation swelling of styrene–acryronitrile copolymer particles with styrene and acrylonitrile monomers

The saturation swelling behavior of styrene and acrylonitrile (SAN) copolymer particles with a styrene (St) and acrylonitrile (AN) comonomer mixture was investigated experimentally. The effects of the copolymer composition and the compositional inhomogeneity in SAN Copolymer particles on their swelling behavior were examined. The experimental results show that both the copolymer composition and the compositional inhomogeneity in SAN copolymer particles have little or no influence on the swellability of SAN copolymer particles with a St and AN comonomer mixture, as long as the weight fraction of AN monomer units in SAN copolymer particles is less than a certain value between 0.6 and 0.8. With increasing AN content in the copolymer particles beyond this value, however, the swellability of SAN copolymer particles gradually decreases. Semiempirical equations are proposed, which correlate the saturation concentration of each monomer in SAN copolymer particles as a function of the comonomer composition in the monomer droplets and the overall copolymer composition in SAN copolymer particles. © 1994 John Wiley & Sons, Inc.     

Copolymers of modified starches with polyacrylonitrile

A study was made of the ceric ammonium nitrate-initiated graft polymerization of acrylonitrile (AN) onto a number of modified starches that had been reduced in molecular weight by either acid, hypochlorite, or enzyme treatment. With highly soluble starches, much of the starting material was recovered as ungrafted carbohydrate, and the reaction product was largely dimethylformamide-soluble polymer with a high polyacrylonitrile (PAN) content. The molecular weight of grafted PAN was lower when the modified starches existed as granules in water dispersion; however, heating (60°C) an aqueous slurry of an acid-modified corn starch (with intact granules) before the reaction had relatively little effect on the composition of the copolymer. Decreasing the concentrations in water of modified starch and AN resulted in more frequent and lower molecular weight grafts of PAN. Aqueous methanol as a reaction medium for an acid-modified starch with intact granules led to more frequent grafting of lower molecular weight PAN than when water alone was used. The number of grafted chains, however, was fewer than found with unmodified wheat starch under comparable conditions. A modified starch with the granule structure completely broken down gave no detectable reaction in aqueous methanol.     

Long‐time relaxations in rubber‐modified polymer systems

Linear and nonlinear viscoelastic properties were measured in the molten state for several model ABS polymers with different rubber particle contents. Linear viscoelastic functions for ABS polymers can be separated in two parts. One is a relaxation associated with the entanglement of matrix SAN chains and the other comes from the particle‐particle interactions of rubber particles. This relaxation depends strongly on the degree of dispersion of rubber particles. The second‐plateau modulus appeared at low frequency with samples in which rubber particles agglomerate. While, the second‐plateau modulus was not observed with samples in which rubber particles are finely dispersed. Matching of AN content between grafted and matrix SAN and optimum graft density form a finely dispersed system. Large deformation relaxation measurements revealed that the damping of ABS polymers having a good dispersion of particles become stronger with an increase in rubber content. This strong damping can be explained by a layered structure. The very long relaxation was found for higher rubber content, when the neighboring grafted SAN chains contact with each other.     

Radiation synthesis of amino-functionalizated adsorbent and their application to palladium ions’ recovery

In order to prepare a new type adsorbent with an imine affinity ligand for treatment of Pd (

), polypropylene (PP) fabrics modified with amine were prepared by radiation-induced grafting of acrylonitrile (AN) onto polypropylene fabrics and subsequently amination of poly-AN graft chains. Influence of some parameters such as initial concentration and adsorption time on the absorbed amount for palladium ions was investigated. Results suggested that the chelating adsorbent possessed high-adsorption performance toward palladium ions. The grafted and aminated fabrics were characterized by FT-IR and DSC.     

SAN共聚物组成对PVC/ABS共混物相容性的影响

采用乳液聚合技术通过改变共聚单体的投料比(St/AN)合成了一系列不同AN结合量的ABS接枝共聚物粉料和SAN共聚物.将其与聚氯乙烯(PVC)和邻苯二甲酸二辛酯(DOP)熔融共混分别制得了PVC/ABS、PVC/SAN、PVC/ABS/DOP和PVC/SAN/DOP共混物,利用SEM、TEM和动态力学粘弹谱仪(DMA)对共混物的相容性和相结构进行了表征.结果发现,在PVC/ABS共混体系中,尽管改变接枝SAN共聚物的AN结合量,PVC和SAN共聚物均为不相容体系;在该共混物中引入增塑剂DOP后,虽然当SAN共聚物AN结合量小于23.4 wt%时,共混物在室温以上只存在一个tanδ峰,但形态结构研究结果表明共混物仍为不相容体系,共混物的相区尺寸明显地依赖于SAN共聚物中的AN结合量,当AN结合量为23.4 wt%时相区尺寸最小.     

Cellulose-Monomer Interaction and a Revised Mechanism for Graft Copolymerization

Graft copolymerization of electron acceptor acrylic monomers on cellulose involves cellulose-monomer complexation. Cellulose acts as a matrix promoting high localized concentrations of donor-acceptor complexes in which uncomplexed monomer, normally an electron acceptor, behaves as a donor relative to the complexed monomer which has been converted to a stronger acceptor. The cellulose-monomer complexation influences both homopolymerizability and grafting efficiency, e. g. acrylonitrile (AN) and methacrylonitrile (MAN) in the presence of a catalyst and methyl methacrylate (MMA) in the absence of a catalyst. The presence of water, cupric ion, aldehydes, and CCU influence the course of the uncatalyzed reaction. When a donor monomer is present, equimolar alternating rather than random, grafted and ungrafted copolymers are produced, e. g., styrene or butadiene with MMA, MAN, or AN, as a result of the formation of an ordered array of donor-acceptor complexes on the cellulose. The revised mechanism of polymerization involves the homopolymerization of the donor-acceptor complexes, irrespective of the nature of the initiator, and grafting results from termination of the propagating chains by coupling with radicals on the cellulose.     

Morphology and grafting reactions in core/shell latexes

The particle morphology and percent grafting were investigated as a function of the crosslink density of the seed latex in two systems of core/shell latexes of polybutadiene/polymethyl methacrylate (PB/PMMA) and styrene–butadiene rubber/polymethyl methacrylate (SBR/PMMA) prepared by seeded emulsion polymerization at 50°C. The thin layer chromatography/flame ionization detection (TLC/FID) technique was used to characterize the grafting efficiency of the core/shell latexes. The percent grafting of the shell polymer was found to decrease with increasing the crosslink density of the core material. The particle morphology and precent grafting were also investigated as a function of composition and structure of the core material in four core/shell latex systems: polybutadiene/styrene–acrylonitrile copolymer (PB/SAN), (styrene-butadiene) random copolymer/styrene acrylonitrile copolymer (S:B/SAN), polystyrene : polybutadiene/styrene-acrylonitrile copolymer (PS:PB/SAN) and Kraton/styrene-acrylonitrile copolymer (Kraton/SAN), which were prepared by direct emulsification for the seed followed by emulsion polymerization at 70°C for the shell polymer. Grafting and crosslinking of the core material were found to be competitive reactions depending on the microstructure of the seed latex.     

Random grafting statistics in graft distribution analysis

Graft distribution functions have been derived from random grafting statistics. Among the functions, the weight fraction of ungrafted backbone chains, the molecular weight distribution of the ungrafted backbone chains and the GPC apparent molecular weight distribution of the graft copolymer have been found to agree with experimental values determined for a graft copolymer system in which grafting was expected to be random. The other functions, which are not directly measurable, are therefore probably also correct. In analytical work the entire set of graft distribution functions may be computed for a graft copolymer system from the following experimental data: (1) molecular weight distribution of the starting backbone chains; (2) the chemical composition of the mixture of the graft copolymer and ungrafted backbone; (3) the graft side-chain molecular weight distribution, which may be assumed to be identical to that of the ungrafted homopolymer separable from the reaction mixture.     

The analysis of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO® resin) in mixtures of PPO resin,polystyrene, and copolymers of PPO resin and polystyrene

A method of determining the quantity of ungrafted poly(2,6-dimethyl-1,4-phenylene oxide) (PPO®

1 Trademark of General Electric Company.

resin) in mixtures of such polyphenylene oxide or PPO resin, polystyrene (PS), and graft copolymers of PPO resin and PS is described. The technique is a combination of physical and chemical separations and gel permeation chromatographic (GPC) analysis. The extent of grafting on PPO resin and the quantity of ungrafted PPO resin were calculated from molecular weight data and compositional analysis.     

Study of Adhesion and Fracture of Polymer Laminates by Imaging of Interfaces

The adhesion and fracture of styrene‐acrylonitrile random copolymer and poly(methyl methacrylate) (PMMA/SAN) laminates were studied. They showed a drastic transition from brittle to ductile on varying the acrylonitrile (AN) content in SAN, with changes in the fracture mode from interfacial failure to cohesive fracture. Energy‐filtering transmission electron microscopy (EFTEM) and scanning electron microscopy (SEM) with an in‐lens detector system were employed to study the interface and adhesion of the laminates. The effect of the AN content in SAN on the PMMA/SAN interfacial structures could be revealed by imaging of the interfaces using elemental mapping and electron energy loss spectroscopy (EELS). The in‐lens detector system in the SEM enabled the differentiation of thin interfaces with poor adhesion strength, yielding smooth and flat fracture surfaces, where numerous nanosized fibrils were formed normal to the surfaces.

     

Grafting of polyacrylonitrile to granular corn starch

Acrylonitrile grafts readily to granular corn starch in aqueous slurry when initiated by hydrogen peroxide plus activator. Prime evidence for grafting lies in the ease of separating PAN from starch in high yield when the initiator is azobisisobutyronitrile rather than peroxide. Grafting efficiencies are determined by extraction with appropriate solvents: dimethylformamide for homo-PAN, and boiling water for ungrafted starch. Grafting efficiencies of PAN range from 78 to 95%, M?_n values for grafted PAN are 4,000 to 90,000, and frequency of attachment of side chains range from 300 to 1100 glucose units per chain. Increasing the monomer level, at fixed initiator concentration, tends to result in longer rather than more frequent side chains. AN behaves much as has been previously found for MMA, but the somewhat more efficient grafting at more frequent intervals and the more nearly uniform distribution of polymer in the starch granule suggest that AN penetrates the starch granule more readily than MMA.     

Irradiation‐induced grafting of acrylonitrile onto activated carbon fiber

Viscose‐based activated carbon fiber (VACF) was modified with acrylonitrile (AN) by γ‐irradiation‐induced grafting polymerization. Effects of the grafting conditions, such as concentrations of AN and divinylbenzene (DVB), pH value, and solvent on the grafting process were studied. The physicochemical properties of the fibers were characterized. The results show that AN can be effectively grafted onto the surface of VACF with the addition of DVB. The grafting yield is higher than 12% according to thermogravimetric (TG) analysis. The study shows that DVB can improve the grafting degree of AN in the form of grafting chains or agglomerate materials. After grafting modification, VACF shows a small decrease in the specific surface area. Copyright © 2009 John Wiley & Sons, Ltd.     

Radiation-induced grafting polymerization of MMA onto polybutadiene rubber latex

The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core–shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core–shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration.     

Grafting vinyl monomers to starch by ceric ion. I. Acrylonitrile and acrylamide

Studies were carried out on the grafting of acrylonitrile (AN) and acrylamide (AA) to starch by ceric ion. The variables affecting the grafting of AN and AA were investigated with granular wheat starch dispersed in aqueous N,N-dimethylformamide and ceric ammonium nitrate as catalyst. Results showed that the concentrations of monomer and catalyst are the major factors influencing the grafting of AN; thus the monomer content of the grafts can be regulated by these variables. The grafting of AA is also influenced by these variables, but to a much less degree. Increasing concentrations of monomer promote homopolymerization and increasing concentration of catalyst inhibit grafting. The extent of grafting of this monomer can best be controlled by reaction time. Under the most favorable conditions, maximum grafting efficiency (ratio of amount of grafted monomer to total amount of monomer converted to polymer) was 87% for AN and 43.8% for AA. Although the monomer content of the AN grafts was higher than that of AA grafts prepared under identical conditions, the number of branches in the grafts was almost the same; only the length of the branches was different. The AN-starch grafts have branches of higher molecular weight.     

Reduction of the Thrombogenicity of Polyethylene Membranes by Radiation Grafting

A new anti-thrombosis dialytic membrane with a hydrophilic-hydrophobic microphase structure was prepared by pre-irradiation grafting of -hydroxyethyl methacrylate (HEMA) and styrene (St) onto polyethylene (PE) membranes. The effects of reaction conditions on the degree of grafting were determined, and the properties of the grafted films were investigated. Compared with PE grafted with hydrophilic monomer, the antithrombogenicity and permeability of the PE-g-(HEMA-co-St) were 30 and 15 times higher than that of the ungrafted films, respectively, if the volume ratio (HEMA:St) is about 1:1.     

Physicomechanical properties of grafted polymers obtained by radiation-induced polymerization by radical and ionic mechanisms

The radiation-induced grafting of acrylonitrile, 4-vinylpyridine, and styrene was carried out by both radical and ionic mechanisms. Grafted polymers with equal percentages of graft were obtained by the radical and ionic propagation of the grafted chains. The molecular weight of homopolymers has been determined. The thermomechanical properties of the graft polymers were investigated. The yield temperatures for the graft polymers obtained by ionic propagation of the grafted chains is higher than that of graft polymers obtained by a radical mechanism. This is attributed to the higher molecular weight of the grafted chains obtained by the radiation-induced grafting by the ionic mechanism. The radiation-induced grafting of polyacrylonitrile increases significantly the thermal stability of polyethylene. The differential thermal analysis shows no marked differences in properties of the polymers.     

构建巯基-Ce(Ⅳ)盐氧化还原引发体系实现丙烯腈在硅胶微粒表面的高效接枝聚合

使用偶联剂γ-巯丙基三甲氧基硅烷(MPMS,KH-590),对微米级硅胶微粒进行了表面化学改性,将巯基引入硅胶微粒表面(SiO2-MPMS),构成巯基-Ce(Ⅳ)盐氧化-还原引发体系,探索研究了丙烯腈在硅胶微粒表面的引发接枝聚合,制得了高接枝度(30 g/100g)的接枝微粒SiO2-MPMS-g-PAN.采用红外光谱(FTIR)、扫描电镜(SEM)及热重分析(TGA)等方法对接枝微粒SiO2-MPMS-g-PAN进行了表征.在此基础上,重点研究了主要因素对巯基-Ce(Ⅳ)盐体系引发AN接枝聚合的影响.研究结果表明,类似于羟基-Ce(Ⅳ)盐体系,巯基-Ce(Ⅳ)盐体系也可以有效地引发乙烯基单体在固体微粒表面接枝聚合.与在固体微粒表面引入可聚合双键的"grafting through"接枝聚合法相比,铈盐引发的接枝聚合,由于活性位点居于载体表面,故具有高的接枝度,是一种高效率的表面引发接枝法.为制得高接枝度的接枝微粒SiO2-MPMS-g-PAN,本研究体系适宜的酸浓度为0.25 mol/L;Ce(Ⅳ)盐浓度为5.0×10-3 mol/L;接枝聚合宜在50℃下进行.