Photocrosslinking of elastomer systems. II. Ultraviolet light-induced reactions in an EPDM modified by grafting of benzoin derivatives

Photocrosslinking experiments were performed on elastomeric polymer films (EPDM) previously modified by grafting a photosensitive initiator (benzoin derivative) onto the macromolecular backbone. This modification was performed by a series of Friedel–Crafts reactions and the resulting materials were characterized by infrared (IR) spectroscopy in conjunction with model reactions. After ultraviolet (UV) irradiation the photocrosslinked samples were studied by IR spectroscopy in conjunction with the measurement of physical properties. It apperared that grafting the photosensitizer onto the elastomer considerably enhances the crosslinking reaction even with a limited quantity of grafted benzoin derivative. Moreover, the results obtained suggest that the structure of the resulting networks is strongly dependent on the crosslinking process used; that is, curing the elastomer with peroxide or UV irradiation either of a blend of elastomer and photosensitizer or of the same elastomer modified by grafting the chromophore.     

接枝改性碳酸钙及其在聚合物中的应用研究

介绍了近年来碳酸钙表面接枝改性的研究进展,讨论了自由基接枝聚合、辐照接枝聚合和力化学表面接枝聚合及偶联剂预处理与辐照并用接枝聚合改性方法。其中重点讨论了最新研究的偶联剂预处理与辐照并用接枝改性纳米碳酸钙的方法。用此方法制备的聚合物/纳米碳酸钙纳米复合材料在其他力学性能基本不变的情况下,大幅度提高了其缺口冲击强度和断裂伸长率。指出了碳酸钙表面接枝改性应向着提高接枝单体量和采用弹性体单体方面发展。     

The crosslinking mechanism in gamma irradiation of polyarylsulfone: evidence for Y-links

Measurements of molecular weights, soluble fractions and examination of NMR spectra of bisphenol-A polysulfone, after gamma irradiation in vacuum at 150°C were used to elucidate the mechanism of crosslinking. Excellent agreement was obtained between G(S) and G(X) determined from measurements above and below the gel dose when a Y-linking mechanism was assumed, whereas poor agreement was obtained when an H-link mechanism was assumed, which is the mechanism normally believed to be responsible for crosslinking. New resonances were observed in the ¹³C NMR spectra of the irradiated polymer which were consistent with the formation of Y-links involving phenylene units in the backbone chain. © 1998 John Wiley & Sons, Ltd.     

极性介质中醋酸乙烯酯的辐照引发分散聚合

用钴 60γ射线引发醋酸乙烯酯的分散聚合 ,通过选择各种极性溶剂体系 ,确立了醋酸乙烯酯在极性介质中稳定的分散聚合体系 .对异丙醇 水体系 ,聚合物分子量随剂量率的降低、稳定剂含量的增加、单体浓度的增大、反应温度的升高以及醇水比的降低而增加 .运用XPS、元素分析等表征聚合物粒子 ,及通过辐射接枝理论的分析 ,可以判断稳定剂所起的稳定作用主要是以物理吸附为主     

A new model of protein adsorption kinetics derived from simultaneous measurement of mass loading and changes in surface energy

We describe a novel technology based on changes in the resonant frequency of an acoustically actuated surface and use it to measure temporal changes in the surface energy gamma (N m(-1)) of an elastomeric polymer membrane due to the adsorption of macromolecules from aqueous solution. The resonant elastomeric surface-tension (REST) sensor permits simultaneous determination of mass loading kinetics and gamma(t) for a given adsorption process, thereby providing a multivariable data set from which to build and test models of the kinetics of adsorption at solid-liquid interfaces. The technique is used to measure gamma(t) during the adsorption of either sodium dodecyl sulfate (SDS) or hen egg-white lysozyme (HEWL) onto an acrylic polymer membrane. The adsorption of SDS is reversible and is characterized by a decrease in gamma over a time period that coincides with that required for the mass loading of the membrane. For the adsorption of HEWL labeled with Alexa Fluor 532 dye, gamma continues to change long after the surface concentration of labeled HEWL, measured by using the elastomeric polymer membrane as an optical waveguide, reaches steady state. Gradual but significant changes in gamma(t) are observed as long as the concentration of protein in the bulk solution, c(b), remains nonzero. HEWL remains adsorbed to the membrane when c(b) = 0, but changes in gamma(t) are not observed under this condition, indicating that the interaction of bound protein molecules with those free in solution contribute to the prolonged change in the surface energy. This observation has been used to define a new model for the kinetics of globular protein adsorption to a solid-liquid interface that includes a mechanism by which the molecules in the bulk can facilitate the desorption of a sorbate molecule or change the energetic states of adsorbed molecules and, thus, the overall surface energy. The model is shown to capture the unique features of protein adsorption kinetics, including the relatively fast mass loading, the much more gradual change in surface energy that does not cease until the protein is removed from the bulk, the rapid desorption of an incubation-time-dependent fraction of bound protein when the protein is removed from the bulk, and the fixing of the residual surface concentration and surface energy at constant values once the removal of reversibly bound protein and free protein is complete.     

Production of high melt strength polypropylene by gamma irradiation

High melt strength polypropylene (HMS-PP) has been recently developed and introduced in the market by the major international producers of polypropylene. Therefore, BRASKEM, the leading Brazilian PP producer, together with EMBRARAD, the leading Brazilian gamma irradiator, and the IPEN (Institute of Nuclear Energy and Research) worked to develop a national technology for the production of HMS-PP. One of the effective approaches to improve melt strength and extensibility is to add chain branches onto polypropylene backbone using gamma radiation. Branching and grafting result from the radical combinations during irradiation process. Crosslinking and main chain scission in the polymer structure are also obtained during this process. In this work, gamma irradiation technique was used to induce chemical changes in commercial polypropylene with two different monomers, Tri-allyl-isocyanurate (TAIC) and Tri-methylolpropane-trimethacrylate (TMPTMA), with concentration ranging from 1.5 to 5.0 mmol/100 g of polypropylene. These samples were irradiated with a ⁶⁰Co source at dose of 20 kGy. It used two different methods of HMS-PP processing. The crosslinking of modified polymers was studied by measuring gel content melt flow rate and rheological properties like melt strength and drawability. It was observed that the reaction method and the monomer type have influenced the properties. However, the concentration variation of monomer has no effect.     

Effect of modified graphene and microwave irradiation on the mechanical and thermal properties of poly(styrene‐co‐methyl methacrylate)/graphene nanocomposites

The effect of modified graphene (MG) and microwave irradiation on the interaction between graphene (G) and poly(styrene‐co‐methyl meth acrylate) [P(S‐co‐MMA)] polymer matrix has been studied in this article. Modification of graphene was performed using nitric acid. P(S‐co‐MMA) polymer was blended via melt blending with pristine and MG. The resultant nanocomposites were irradiated under microwave at three different time intervals (5, 10, and 20 min). Compared to pristine graphene, MG showed improved interaction with P(S‐co‐MMA) polymer (P) after melt mixing and microwave irradiation. The mechanism of improved dispersion and interaction of modified graphene with P(S‐co‐MMA) polymer matrix during melt mixing and microwave irradiation is due to the presence of oxygen functionalities on the surface of MG as confirmed from Fourier transform infrared spectroscopy. The formation of defects on modified graphene and free radicals on P(S‐co‐MMA) polymer chains after irradiation as explained by Raman spectroscopy and X‐Ray diffraction studies. The nanocomposites with 0.1 wt% G and MG have shown a 26% and 38% increase in storage modulus. After irradiation (10 min), the storage modulus further improved to 11.9% and 27.6% of nanocomposites. The glass transition temperature of nanocomposites also improved considerably after melt mixing and microwave irradiation (but only for polymer MG nanocomposite). However, at higher irradiation time (20 min), degradation of polymer nanocomposites occurred. State of creation of crosslink network after 10 min of irradiation and degradation after 20 min of irradiation of nanocomposites was confirmed from SEM studies. Copyright © 2014 John Wiley & Sons, Ltd.     

Fundamental studies of grafting reactions in free radical copolymerization. IV. Grafting of styrene,acrylate, and methacrylate monomers onto vinyl-polybutadiene using benzoyl peroxide and AIBN initiators in solution polymerization.

Vinyl-1,2 polybutadiene (vinyl-PBD) was used as the backbone polymer for the grafting of styrene, methacrylate, and acrylate monomers using both benzoyl peroxide and AIBN initiators. Radical attack on the backbone can occur through the pendant vinyl group or at the tertiary, allylic hydrogen site. Effective graft sites are formed via double bond addition of either primary (initiator) or polymer radicals. The production of tertiary allylic radicals on the backbone chain also occurs and results in moderate to dramatic reaction rate re-tardation in every monomer system. The type of initiator is only important when the polymer radicals are not very reactive, as in the case of styrene, and to a lesser extent for methacrylate monomer. Graft efficiencies are generally higher when using vinyl-PBD than when using cis-PBD. © 1995 John Wiley & Sons, Inc.     

Gamma Radiation‐Induced Crosslinked PVA/Chitosan Blends for Wound Dressing

Crosslinked polyvinyl alcohol (PVA) and chitosan polymer blends have been prepared by using gamma irradiation. Chitosan was used in the blends to prevent microbiological growth, such as bacteria and fungi on the polymer. The physical properties of the blend, such as gelation, water absorption, and mechanical properties were examined to evaluate the possibility of its application for wound dressing. A mixture of PVA/chitosan, with different ratios, were exposed to gamma irradiation doses of 20, 30, 50 KGy, to evaluate the effect of irradiation dose on the physical properties of the blend. It was found that the gel fraction increases with increasing irradiation dose and PVA concentration in the blend. Swelling percent increased as the composition of chitosan increased in the blend. The PVA/chitosan blend has a water content in the range between 40% and 60% and water absorption between 60% and 100%. The water vapor transmission rate value (WVRT) of the PVA/chitosan blend varies between 50% and 70%. The examination of the microbe penetration shows that the prepared blend can be considered as a good barrier against microbes. Thus, the PVA/chitosan blend showed satisfactory properties for use as a wound dressing.     

Characterization,morphology, thermal and mechanical properties of conductive polyaniline‐functionalized EPDM elastomers obtained by casting

Conductive elastomeric blends based on ethylene–propylene–5‐ethylidene–2‐norbornene terpolymer (EPDM) and polyaniline doped with 4‐dodecylbenzenesulfonic acid [PAni(DBSA)] were cast from organic solvents. Functionalization of the elastomer was promoted by grafting with maleic anhydride. Vulcanization conditions were optimized with an oscillating disk rheometer. The conductivity, morphology, thermal stability, compatibility, and mechanical behavior of the obtained mixtures were analyzed by in situ direct current conductivity measurements, atomic force microscopy, transmission electron microscopy, wide‐angle X‐ray scattering, thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical thermal analysis, stress–strain and hysteresis tests. The vulcanization process was affected by temperature, the PAni content, and maleic anhydride. A reinforcement effect was promoted by the vulcanizing agent. The formation of links between the high‐molar‐mass phases and oligomers of PAni(DBSA) in the elastomeric matrix enhanced the thermal stability and ultimate properties of the blends. By the appropriate control of the polymer blends' composition, it was possible to produce elastomeric materials with conductivities in the range of 10^?5–10^?4 S · cm^?1 and excellent mechanical properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1767–1782, 2004     

Optical and two‐photon absorption analysis of radiation‐grafted fluoropolymer

Grafting by gamma irradiation has a significant influence on the dispersion properties of polymeric materials. Accordingly, we study the effect of grafting on the material electronic structure parameters such as the fundamental absorption edge and bandgap structure. The optical absorption of grafted polymeric films of poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA‐g‐PAAc) is determined in a very wide spectral range of 0.2–3 μm. The nonlinear two‐photon absorption coefficient is determined that showed an increase as a result to the grafting process. Moreover, a significant increase in the optical conductivity for the polymeric films is acquired after grafting. Positron annihilation spectroscopy is used to study polymer structure and volume size of nanoholes of Ps. The data revealed an increase of crosslinking with a smaller average volume size with grafting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2045–2051, 2010     

Improvement of pesticide adsorption capacity of cellulose fibre by high-energy irradiation-initiated grafting of glycidyl methacrylate

Cellulose as a renewable raw material was used for preparation of adsorbent of organic impurities in wastewater treatment. Hydrophobic surface of cellulose substrate was developed by grafting glycidyl methacrylate in simultaneous grafting using gamma irradiation initiation. Water uptake of cellulose significantly decreased while adsorption of phenol and a pesticide molecule (2,4-dichlorophenoxyacetic acid: 2,4-D) increased upon grafting. Adsorption equilibrium data fitted the Freundlich isotherm for both solutes.     

Functionalization and patterning of reactive polymer brushes based on surface reversible addition and fragmentation chain transfer polymerization

We present the synthesis of reactive polymer brushes prepared by surface reversible addition–fragmentation chain transfer polymerization of pentafluorophenyl acrylate. The reactive ester moieties can be used to functionalize the polymer brush film with virtually any functionality by simple post‐polymerization modification with amines. Dithiobenzoic acid benzyl‐(4‐ethyltrimethoxylsilyl) ester was used as the surface chain transfer agent (S‐CTA) and the anchoring group onto the silicon substrates. Reactive polymer brushes with adjustable molecular weight, high grafting density, and conformal coverage through the grafting‐from approach were obtained. Subsequently, the reactive polymer brushes were converted with amino‐spiropyrans resulting in reversible light‐responsive polymer brush films. The wetting behavior could be altered by irradiation with ultraviolet (UV) or visible light. Furthermore, a patterned surface of polymer brushes was obtained using a lithography technique. UV irradiation of the S‐CTA‐modified substrates leads to a selective degradation of S‐CTA in the exposed areas and gives patterned activated polymer brushes after a subsequent RAFT polymerization step. Conversion of the patterned polymer brushes with 5‐((2‐aminoethyl)amino)naphthalene‐1‐sulfonic acid resulted in patterned fluorescent polymer brush films. The utilization of reactive polymer brushes offers an easy approach in the fabrication of highly functional brushes, even for functionalities whose introduction is limited by other strategies. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Influence of gamma irradiation on high density polyethylene/ethylene‐vinyl acetate/clay nanocomposites

The study of high density polyethylene (HDPE)/ethylene‐vinyl acetate (EVA)/and organically‐modified montmorillonite (OMT) nanocomposites prepared by melt intercalation followed by exposure to gamma‐rays have been carried out. The morphology and properties of the nanocomposites were studied using X‐ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and cone calorimetry. The purpose of the study focuses on the influence of gamma irradiation on the morphology, thermal stability and flammability properties of the nanocomposites. XRD studies and TEM images verified that the ordered intercalated nanomorphology of the nanocomposites was not disturbed by gamma irradiation. TGA data showed that the nano‐dispersion of clay throughout the polymer inhibited the irradiation degradation of HDPE/EVA blend, which led to the nanocomposites exhibiting superior irradiation‐resistant properties than that of the pure blend. Cone calorimetry results indicated that the improvement in heat release rate (HRR) for irradiated HDPE/EVA blend was suppressed efficiently when clay was present. Increasing clay loading from 2 to 10% was beneficial by improving the flammability properties of the nanocomposites, but promoted a rapid increase in the sub‐peak HRR at high irradiation dose level. Copyright © 2004 John Wiley & Sons, Ltd.     

Fracture toughness of gamma irradiated polycarbonate sheet using the essential work of fracture

Polycarbonate (PC), a ductile polymer, has been found by both linear elastic fracture mechanics and impact tests to present a ductile-brittle transition, which depends on notched specimen thickness, test speed and gamma irradiation. Owing to large amounts of plastic deformation, fracture toughness measurements by these test methods are not precise. In the present communication, a better method, the Essential Work of Fracture (EWF), to assess the fracture characteristics in plane state of stress was for the first time used to evaluate the fracture toughness of PC sheets subjected to gamma irradiation dose. Three-points bend tests of sharp pre-cracked specimens with different ligament lengths were 340 kGy gamma irradiated. EWF results showed that the total fracture work increased linearly with length for both non-irradiated and gamma irradiated conditions. A significant decrease in EWF fracture toughness was associated with brittleness promoted by gamma irradiation. This brittleness was also confirmed by macro and microscopy (SEM) evidence.     

Radiation‐assisted controlled grafting and reaction parameter optimization of an industrially important polyolefin elastomer (POE)

Controlled (low degree) grafting of a polar group to a non‐polar polymer or reverse is an important means to change the polarity of the base polymer, maintaining the properties of the polymer. In the present study, a polar monomer, methacrylic acid (MAA), was grafted onto three different types of “Engages” (a special type of polyolefin elastomer) in aqueous medium by gamma radiation. Grafting parameters (total dose, MAA concentration, and Mohr's salt concentration) were optimized for the desired amount of low‐degree grafting (less than 15 wt%). The grafting yields were measured gravimetrically. Pure and grafted Engages were characterized by Fourier transformed infrared spectroscopy, contact angle measurement, and scanning electron microscope. Fourier transformed infrared spectroscopy spectra confirmed the successful grafting of MAA onto the Engages. For all three, the best yields were found at 3‐kGy gamma radiation dose, 25‐vol% MAA, and 20‐mM Mohr's salt concentration. The grafting efficiencies follow a descending trend like Engage 8150 > Engage 7447 > Engage 8003. From contact angle measurement, it was seen that the hydrophilicities of all Engage surfaces were increased after grafting. Scanning electron microscope illustrated the best distribution of grafted MAA molecules to be on Engage 8150 surface followed by Engage 7447 and Engage 8003, respectively. The tensile testing results suggested that the mechanical properties of the base polymers remained almost unchanged after grafting. Thus, without detrimenting any basic properties, polyolefin elastomers can be grafted to achieve desired yield by an environmental‐friendly method, gamma radiation grafting, in aqueous media. Copyright © 2016 John Wiley & Sons, Ltd.     

Fundamental studies of grafting reactions in free radical copolymerization. III. Grafting of styrene,acrylate, and methacrylate monomers onto cis-polybutadiene using benzoyl peroxide initiator in solution polymerization

Benzoyl peroxide (BPO), due to its higher radical reactivity as compared to AIBN, is known to promote grafting onto cis-polybutadiene. Switching from AIBN to BPO initiator made a dramatic difference in the extent of grafting for styrene and methacrylate monomers, but only a modest difference for acrylate monomer. For styrene and methacrylate monomers, graft site formation is due to BPO initiator radical attack onto the backbone via allylic hydrogen abstraction. Significant levels of grafting are achieved and depend upon the relative concentrations of monomer and backbone polymer but not upon the level of initiator. For acrylic monomer, graft site formation was found to be due to polymer radical attack at the double bond in the backbone. Abstraction of allylic hydrogen also occurs but results in retardation of the overall reaction rate. Graft level was dependent upon initiator and back-bone polymer concentrations but not upon monomer concentration. The effective role of the initiator is only to produce polymer radicals; the BPO has no direct role in the formation of effective graft sites. © 1995 John Wiley & Sons, Inc.     

SEC with UV and ELSD detection for analysis of gamma-irradiated PS-radiation-grafted P(VDF/HFP) films

Summary Thin poly(vinylidene fluoride/hexafluoropropylene) (P(VDF/HFP)) films ahve been irradiated with gammarays to induce the initiation of styrene grafting by the indirect method. To obtain a better understanding of the radiation-grafting process we have used size exclusion chromatography (SEC) to study the effect of irradiation of this polymer and the evolution of the molecular weights of the polystyrene (PS) grafted chains as a function of the grafting time. Pristine, irradiated and PS radiation-grafted samples have been compared. We present evidence that the gamma irradiation induces both scission and crosslinking of the P(VDF/HFP) chains. We show that the average molecular weights of the PS grafted chains increase with grafting time and that the asymmetry of the chromatographic peak increases also. These grafted chains have molecular weights much higher than those of pristine P(VDF/HFP) and they cannot be confused with PS homopolymer chains, which have higher molecular weights as both, pristine and radiation-grafted P (VDF/HFP). Reversed-phase high-performance liquid chromatography (RPHPLC) has shown the absence of additives in pristine P(VDF/HFP) and has provided evidence of the presence of oligomers.     

Synthesis of ion-exchange membranes by radiation-induced multiple grafting of methyl α,β,β-trifluoroacrylate

Methyl α,β,β-trifluoroacrylate (MTFA) was grafted onto polymer films with the multiple grafting technique initiated by α-rays: the yields were similar to those of the single-step grafting procedure with any irradiation dose. Grafted polymer obtained in the single-step experiments were distributed mainly near the film surface, whereas graft polymer from the multiple grafting experiments were distributed uniformly in the film at graft yields greater than 20%. The electric resistance of the hydrolyzed multiple graft polymer film in a 2N NaOH solution was much lower than that of one-step graft film at the same graft yield.     

Applicability of photochemically generated pendant benzoyl peroxides in both “grafting from” and “grafting to” techniques

Methyl methacrylate and styrene copolymers containing pendant benzil groups, such as 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-methyl metacrylate (BzMA/MMA), 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-styrene (BzMA/S), and 1-phenyl-2-(4-propenoylphenyl)-1,2-ethanedione-co-styrene (PCOCO/S), were prepared and used as precursors for photochemically generated pendant benzoyl peroxides. Decomposition of the pendant benzoyl peroxides was subsequently used in grafting processes. Either irradiation or a combination of irradiation with subsequent thermal treatment was adopted for grafting a thin layer of BzMA/MMA copolymer onto the surface of LDPE films. The grafting resulted in a significant decrease in contact angle of the film surface. The same activation strategy was successfully adopted to initiate the polymerisation of acrylic or methacrylic acids from the surface of styrene copolymer films containing the initiator precursor in the polymer side chains (BzMA/S and PCOCO/S). The successful surface grafting was proved by contact angles measurement as well as by infrared spectroscopic analysis.