Radiation grafting of methyl methacrylate monomer on natural rubber latex

A method of radiation grafting of methyl methacrylate (MMA) monomer on natural rubber (NR) latex has been studied. The irradiation dose in radiation emulsion polymerization of MMA monomer was lower compared to the irradiation dose for grafting of MMA monomer on NR latex, in order to obtain the same degree of conversion. This is due to the size of the rubber particles which are quite large and, hence, not sufficient to ensure an ideal emulsion polymerization. The irradiation dose for radiation grafting of MMA monomer on latex was around 300 krad to obtain a 75% degree of conversion. However, this irradiation dose was lower compared to the irradation dose for bulk polymerization of MMA monomer, in order to obtain the same degree of conversion. This is due to the gel effect in the viscous media. Radiation grafting of MMA monomer on NR latex does not influence the pH of the latex, but influences the viscosity significantly. The viscosity of the NR latex increased with an increase in irradiation dose, due to the increase of the total solid content in the latex. The MMA monomer converted to P-MMA in NR latex was largely grafted on the NR, or at least insoluble in a solvent for P-MMA, such as acetone or toluene. The hardness of the pure gum vulcanizate with an increase in the degree of grafting or P-MMA content, but the other physical properties, such as tensile strength, modulus, elongation at break, and thermal stability, were not greatly influenced by the degree of grafting.     

Thermoplastic ionomers based on "styrene grafted natural rubber"

Graft copolymer of natural rubber was prepared by polymerizing styrene in natural rubber latex using tertiarybutylhydroperoxide and tetraethylenepentamine through emulsion polymerization. Natural rubber thus reinforced by grafting styrene onto the hydrocarbon backbone was further converted to the ionomer by sulfonating with acetyl sulfate, followed by neutralization of the polymersulfonic acids using zinc acetate in methanol. The "zinc sulfonated styrene grafted natural rubber" designated as x.yZnS-SGNR where x.y shows number of milliequivalents of sulfonic acid/100 g of SGNR, behaves like a thermoplastic elastomer. It shows improved stress-strain properties as compared to the host polymer, styrene grafted natural rubber (SGNR). The modified samples of styrene grafted natural rubber of different sulfonic acid concentrations were prepared and evaluated using X-ray Fluorescence Spectroscopy (XRFS), Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICPAES), Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance Spectroscopy (NMR), Thermogravimetric Analysis (TGA), and by the measurement of physical properties.     

Graft copolymerization of methyl methacrylate and natural rubber

Graft copolymerization of natural rubber and MMA was carried out in the presence of Bz₂O₂ or AIBN as thermal initiator and hydrogen peroxide or benzophenone as photosensitizer. From the overall copolymerization product, the rubber–PMMA graft copolymer fraction was isolated from unreacted rubber and free PMMA fractions and composition characterization of the separated fractions was done by determination of rubber unsaturation. The efficiency of grafting under different conditions has been calculated and compared.     

Physical and mechanical properties of poly(methyl methacrylate)‐grafted natural rubber synthesized by methyl methacrylate photopolymerization initiated by N,N‐diethyldithiocarbamate functions previously created on natural rubber chains

Well‐defined poly(methyl methacrylate) (PMMA)‐grafted natural rubbers (NRs) were prepared to study the structure–property relationships. Syntheses were achieved by the photopolymerization of methyl methacrylate initiated by N,N‐diethyldithiocarbamate groups created beforehand in side positions on the NR chains. With this procedure, good control of the graft density and PMMA content could be obtained. Thermal, morphological, and mechanical properties of NR‐g‐PMMA copolymers were studied as a function of the NR/PMMA composition and graft density. NR‐g‐PMMAs containing 15–80% grafted PMMA showed characteristics of heterogeneous materials (characterized by two glass‐transition temperatures, those of PMMA and NR, in differential scanning calorimetry). Under these conditions, they developed the morphology of thermoplastic elastomers with PMMA nodules dispersed in the rubber matrix when the PMMA content was near 20%; conversely, they developed the morphology of softened thermoplastics with rubber nodules dispersed in PMMA when the PMMA content was near 80%. Graft copolymers containing about 20% PMMA remained essentially rubbery, but they were already different from pure NR. On the other hand, the thermal stability of NR wash improved after the introduction of PMMA grafts onto NR chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Process variables and their effects on grafting reactions of styrene and methyl methacrylate onto natural rubber

The graft copolymerization of styrene and methyl methacrylate onto natural rubber latex was studied under various reaction conditions using a cumene hydroperoxide redox initiator. The monomer conversion, graft copolymer compositions, and grafting efficiency were determined. The synthesized graft copolymers were purified and then characterized by proton nuclear magnetic resonance (¹H‐NMR) analysis and differential scanning calorimetry (DSC). A 2 fractional factorial experimental design was applied to study the main effects on the grafting. The variables investigated in this work were the amount of the initiator and emulsifier, the presence or absence of a chain‐transfer agent, the styrene‐to‐methyl methacrylate ratio, the monomer‐to‐rubber ratio, and the reaction temperature. The measured response for the experimental design was the grafting efficiency. The analysis of the results from the design showed the sequence of the main effects on the observed response of the grafting of styrene and methyl methacrylate onto natural rubber, in ascending order. The amount of the chain‐transfer agent and the reaction temperature in the range of the test had significant effects and one marginally significant effect was the monomer‐to‐rubber ratio. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 63–74, 2003     

Studies on the curing behaviour and mechanical properties of styrene/methyl methacrylate grafted deproteinized natural rubber latex

The graft copolymerization of styrene/methyl methacrylate (MMA) onto deproteinized natural rubber (DPNR) latex was carried out using ammonium peroxy disulfate (N₂H₈O₈S₂) as the initiator. The presence of the grafted polystyrene (PS) and polymethyl methacrylate (PMMA) on the rubber backbone was confirmed by FTIR spectroscopy. The effects of monomer concentrations on curing characteristics and mechanical properties were studied. It was found that the cure time and scorch time were increased with increasing monomer concentration whereas the torque_max–min value was slightly decreased. It was also noted that the increase in the monomer concentration resulted in stiffer rubber with increased modulus and reduced elongation at break.     

聚乙烯亚胺-g-聚甲基丙烯酸甲酯对天然胶乳的改性研究

以聚乙烯亚胺(PEI)和甲基丙烯酸甲酯(MMA)为主要原料,采用无皂乳液聚合法制备了聚乙烯亚胺-g-聚甲基丙烯酸甲酯(PEI-g-PMMA)乳液;然后将其与天然胶乳(NRL)进行共混,并着重探讨了PEIg-PMMA对NRL膜性能的影响。研究结果表明:随着PEI-g-PMMA掺量的增加,改性NRL膜的拉伸强度呈先升后降态势;当w(PEI-g-PMMA)=15%(相对于NRL质量而言)时,改性NRL膜的拉伸强度(23.68 MPa)比纯NRL膜提高了60.22%,断裂伸长率略有提升,而耐溶剂性则明显改善。     

Compatibilizing effect of natural rubber-g-poly(methyl methacrylate) in heterogeneous natural rubber/poly(methyl methacrylate) blends

The morphology and properties of heterogeneous poly(methyl methacrylate)/natural rubber blends have been modified by the addition of a graft copolymer of natural rubber and poly(methyl methacrylate) (NR-g-PMMA). The morphology has been studied as a function of copolymer concentration. A sharp decrease in the dispersed domain size was observed by the addition of a few per cent of the copolymer followed by leveling off at higher concentrations. The compatibilizer increases the interfacial adhesion by the formation of micro-bridges with the matrix. The effects of homopolymer molecular weights, processing conditions, and mode of addition on the morphology of the dispersed phase have been investigated. The experimental results are compared with the theoretical predictions of Noolandi and Hong. Attempts have been made to explain the conformation of the graft copolymer at the interface. The changes in mechanical properties of the blends as a result of the addition of the compatibilizer were related to the morphology of the blends.     

Interfacial activity of natural rubber-g-poly(methyl methacrylate) in incompatible natural rubber/poly(methyl methacrylate) blends

Summary Blend of natural rubber and poly(methyl methacrylate) (NR/PMMA) has been made compatible by the addition of graft copolymer of natural rubber and poly (methyl methacrylate) (NR-g-PMMA). The interfacial activity of the graft copolymer is studied as a function of concentration of the graft copolymer by following the morphology of the blend using optical and scanning electron microscopies. Domain size of the dispersed phase is decreased sharply by the addition of small amount of copolymer followed by a levelling off at higher concentration. Improvements in mechanical properties is noted with the addition of graft copolymer. Attempts have been made to correlate the morphology and properties.     

Poly(dimethylaminoethyl methacrylate) grafted natural rubber from seeded emulsion polymerization

The grafting efficiency of dimethylaminoethylmethacrylate (DMAEMA) on to natural rubber (NR) has been studied. Grafting was by ‘topology-controlled’ emulsion polymerization, whereby polymerization is initiated by a redox couple where one component (tetraethylene pentamine) is hydrophilic and the other (cumene hydroperoxide) is hydrophobic. This should promote grafting at the interface between hydrophobic natural rubber particles and the hydrophilic DMAEMA. The effects of different amounts of monomer were examined, with NMR to obtain the percent branching, transmission electron microscopy to obtain information on morphology, gel fraction measurement and dynamic mechanical analysis to obtain information on mechanical properties. Although there will be significant amounts of ungrafted polyDMAEMA present, there is good evidence for the formation of graft copolymers of NR with core-shell morphology, and significant amounts of grafting, at high concentrations of monomer.     

Glycidyl methacrylate grafted natural rubber: Synthesis,characterization, and mechanical property

Glycidyl methacrylate (GMA) was grafted onto natural rubber (NR) using emulsion polymerization method. The structures of copolymers were characterized by ¹H nuclear magnetic resonance (¹H‐NMR), solid state ¹³C‐NMR spectroscopy, and Fourier transform infrared spectrometer (FTIR). The %grafting obtained from the gravimetric method and the absorbance ratio were compared. Effects of reaction temperature, GMA content, and reaction time on %grafting, grafting efficiency, and %conversion of GMA monomer were determined. Effect of %grafting on mechanical properties of the graft copolymer was studied. Experimental result showed that the appropriate reaction time was 8 h at a reaction temperature of 30°C. Moreover, tensile strength and modulus of the graft copolymer increased with increasing %grafting. However, elongation at break of the graft copolymer decreased with increasing %grafting. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3152–3159, 2011     

Thermoplastic vulcanizates based on poly(methyl methacrylate)/epoxidized natural rubber blends: Mechanical,thermal, and morphological properties

Epoxidized natural rubbers (ENRs) with epoxide levels of 10, 20, 30, 40 and 50 mol % were prepared. The ENRs were later used to prepare thermoplastic vulcanizates (TPVs) by blending them with poly(methyl methacrylate) (PMMA) using various formulations. Dynamic vulcanization, using sulfur as a vulcanizing agent, was performed during the mixing process. The mixing torque increased as the ENR contents and epoxide molar percentage increased. This was because of an increasing chemical interaction between the polar groups of the blend components, particularly at the interface between the elastomeric and thermoplastic phases. The ultimate tensile strength of the TPVs with ENR‐20 was high because of strain‐induced crystallization. ENRs with epoxide levels >30 mol % exhibited an increase of tensile strength because of increasing levels of chemical interaction between the molecules and the different phases. The hardness of the TPVs also increased with increased epoxide levels but decreased with increased contents of ENRs. Two morphology phases with small domains of vulcanized ENR particles dispersed in the PMMA matrix were observed from scanning electron microscopy micrographs. The TPVs based on ENR‐20 and ENR‐50 showed smaller dispersed rubber domains than those of the other types of ENRs. Furthermore, the size of the vulcanized rubber domain decreased with increasing amounts of PMMA in the blends. The decomposition temperature of the TPVs also increased as both the levels of ENRs in the blends and the epoxide molar percentage increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1251–1261, 2005     

Grafting of vinyl monomers onto natural rubber,II. Graft copolymerization of methyl methacrylate onto natural rubber using tetravalent ceric ions

The use of tetravalent ceric ions to initiate graft-copolymerization of methyl methacrylate onto natural rubber (NR) has been investigated. The rate of grafting has been determined by varying the concentration of monomer and cerium(IV), the temperature and the solvents. The graft yield increases with increasing monomer concentration up to 1.877 M, with further increase of the monomer, the graft yield decreases. The percentage of grafting increases with increasing cerium(IV) concentration up to 0.035 M, thereafter it decreases. With increasing temperature the graft yield increases. The effect of CuSO₄ on the rate of grafting has also been investigated. A plausible mechanism has been suggested and the kinetic rate expressions have been derived.     

The grafting of methyl methacrylate onto cotton by tri-n-butylborane

Methyl Methacrylate was grafted onto cotton by tri-n-butylborane in the presence of water. No graft was obtained in organic solvents, i.e., in the absence of water. The percentage of grafting increased with increases in reaction time, cotton amount, and initiator concentration. Pretreatment of cotton with pyridine also enhanced the percentage of grafting. Glycidyl methacrylate and ethyl acrylate were grafted onto cotton by tri-n-butylborane, while no grafting occurred when vinyl acetate and 4-vinyl pyridine were used. Usual radical initiators, such as azobisisobutyronitrile and benzoyl peroxide/dimethyl-p-toluidine, were not effective under the same conditions.     

Mechanical properties and failure mode of thermoplastic elastomers from natural rubber/poly(methyl methacrylate)/natural rubber-g-poly(methyl methacrylate) blends

The mechanical properties and fracture behavior of natural rubber/poly-(methyl methacrylate) blends were investigated as a function of composition, graft copolymer concentration, and mixing conditions. The mechanical properties and failure behavior vary with the blend ratio, graft copolymer concentration, and mixing conditions. Various two-phase models were used to fit the experimental mechanical properties. Mechanical properties such as stress–strain behavior, tensile strength, tensile modulus, tear strength, and Izod impact strength were evaluated as a function of compatibilizer concentration. The domain size of the dispersed phase decreases with graft copolymer concentration followed by a leveling off at higher concentration. The mechanical properties attain a maximum value at the leveling point, which is an indication of interfacial saturation and the attainment of maximum interfacial adhesion between the homopolymers. Tensile and tear fracture surfaces were examined by scanning electron microscopy. The detachment of the dispersed domains from the matrix is an indication of no adhesion between the two phases in the case of uncompatibilized blends. Microfibrils between the matrix and the dispersed phase indicate a sign of interfacial adhesion between the phases in the case of compatibilized blends. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:1245–1255, 1997     

Ionic elastomer blends of zinc salts of maleated natural rubber and carboxylated nitrile rubber: Effect of grafted maleic anhydride

Zinc neutralized maleated natural rubbers (Zn‐MNR) were prepared by solution grafting and neutralization with zinc acetate in one‐step. It was later used for blending with carboxylated nitrile rubber (XNBR) in the composition of 50/50 parts by weight. The effect of grafted anhydride content (1.2, 1.6, 2.0, and 2.5% wt of NR) on the tensile properties of ionic rubber blends (Zn‐MNR/XNBR) was investigated. The tensile strength of the ionic blends was found to be greater than those of pure rubbers. The modulus, tensile, and tear strength of the blends dramatically increased with increasing levels of grafted anhydride. The ionic rubber blends also possessed superior physical properties compared to those of the corresponding nonionic rubber blends (MNR/XNBR). Dynamic mechanical thermal analysis and scanning electron microscopic studies were performed to verify the process of mixing. Fourier transform infrared spectroscopic studies were carried out to characterize the nature of specific intermolecular interactions between Zn‐MNR and XNBR chain segments. The results indicated that the ion‐ion (Zn⁺ ‐COO^?) interactions between Zn‐MNR and XNBR are formed at the interface, which provides the mean of compatibilization in the ionic rubber blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007