Deformation mechanism of polystyrene toughened with sub‐micrometer monodisperse rubber particles

Core–shell polybutadiene‐graft‐polystyrene (PB‐g‐PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core‐shell rubber particles were then blended with polystyrene to prepare PS/PB‐g‐PS blends with a constant rubber content of 20 wt%. PB‐g‐PS particles with a lower PB/PS ratio (≤70/30) form a homogeneous dispersion in the polystyrene matrix, and the Izod notched impact strength of these blends is higher than that of commercial high‐impact polystyrene (HIPS). It is generally accepted that polystyrene can only be toughened effectively by 1–3 µm rubber particles through a toughening mechanism of multiple crazings. However, the experimental results show that polystyrene can actually be toughened by monodisperse sub‐micrometer rubber particles. Scanning electron micrographs of the fracture surface and stress‐whitening zone of blends with a PB/PS ratio of 70/30 in PB‐g‐PS copolymer reveal a novel toughening mechanism of modified polystyrene, which may be shear yielding of the matrix, promoted by cavitation. Subsequently, a compression‐induced activation method was explored to compare the PS/PB‐g‐PS blends with commercial HIPS, and the result show that the toughening mechanisms of the two samples are different. Copyright © 2006 Society of Chemical Industry     

Core–shell latex particles consisting of polysiloxane–poly(styrene-methyl methacrylate-acrylic acid): Preparation and pore generation

Latexes with a poly(dimethyl siloxane) core and a poly(styrene-methyl methacrylate-acrylic acid) [poly(St-MMA-AA)] shell have been prepared in two steps in order to generate particles that have a core with a very low glass transition temperature. In the first step, poly(dimethyl siloxane) particles were obtained via the ring-opening emulsion polymerization of octamethyl tetracyclosiloxane (D₄). The polymerization was carried out using either an anionic or a cationic catalyst. In the first case, sodium hydroxide was used as catalyst and sodium dodecylbenzene sulfonate as surfactant, while in the second, the alkylbenzene sulfonic acid (ABSA) was used both as catalyst and surfactant. Using a PD₄ latex as seed, a seeded emulsion polymerization of St-MMA-AA was conducted to obtain PD₄–P(St-MMA-AA) core–shell particles. Numerous recipes were attempted and the most successful were those in which the seed was prepared with a cationic catalyst (ABSA) at a relatively low temperature (75°C). The core–shell structure of the particles was identified by transmission electron microscopy, but also via wetting angle, water absorption, and T_g measurements. Finally, pores were generated in the core–shell particles via an alkali–acid treatment. Because PD₄ has a very low glass transition temperature, it cannot be easily handled. However, protected by a shell, it could be used as a constituent of composite materials with enhanced impact strength, even at very low temperatures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2235–2245, 1999     

Influence of core–shell rubber particles synthesized with different initiation systems on the impact toughness of modified polystyrene

Core–shell poly(butadiene‐graft‐styrene) (PB‐g‐PS) rubber particles were synthesized with different initiation systems by emulsion grafting polymerization. These initiation systems included the redox initiators and an oil‐soluble initiator, 1,2‐azobisisobutyronitrile (AIBN). Then the PB‐g‐PS impact modifiers were blended with polystyrene (PS) to prepare the PS/PB‐g‐PS blends. In the condition of the same tensile yield strength on both samples, the Izod test showed that the notched impact strength of PS/PB‐g‐PS(AIBN) was 237.8 J/m, almost 7 times than that of the PS/PB‐g‐PS(redox) blend, 37.2 J/m. From transmission electron microscope (TEM) photographs, using the redox initiators, some microphase PS zones existed in the core of PB rubber particles, which is called “internal‐grafting.” This grafting way was inefficient on toughening. However, using AIBN as initiator, a great scale of PS subinclusion was seen within the PB particle core, and this microstructure increased the effective volume fraction of the rubber phase with a result of improving the toughness of modified polystyrene. The dynamic mechanical analysis (DMA) on both samples showed that the glass transition temperature (T_g) of rubber phase of PS/PB‐g‐PS(AIBN) was lower than that of PS/PB‐g‐PS(redox). As a result, the PB‐g‐PS(AIBN) had better toughening efficiency on modified polystyrene than the PB‐g‐PS(redox), which accorded with the Kerner approximate equation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 738–744, 2007     

The effect of composition on the dynamic and mechanical properties of natural rubber–poly(methylmethacrylate) blends

The miscibility of the components in natural rubber–poly(methylmethacrylate) blends for potential use as reinforced rubbers was evaluated using the glass transition temperatures, peak widths of the loss tangent peak at the glass transition and the complex heat capacity data obtained from dynamic mechanical thermal analysis (DMTA), and modulated differential scanning calorimetry (MDSC). In addition, the effect of the poly(methylmethacrylate) content on the dynamic mechanical and the physical properties such as tensile behavior and hysteresis loss was studied. DMTA and MDSC data clearly indicated that the blends were phase‐separated. Nevertheless, the glass transition temperature of the natural rubber component in the 30–50 wt % NR/PMMA blends has shifted to higher temperatures compared to the natural rubber treated under the same condition, indicating some limited extent of mixing of components in these blends. The physicomechanical properties including moduli at 100, 300, and 500% and tensile strength of the NR/PMMA blends were determined. Incorporation of PMMA into NR matrix improved the strength properties of the NR/PMMA blends prepared reasonably akin to interpenetrating polymer networks (IPN) polymerization method. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Grafting of poly(vinyl alcohol) on natural rubber latex particles

Poly(vinyl alcohol) (PVA) was grafted on natural rubber (NR) latex particles (NR‐g‐PVA) using potassium persulfate to generate active radicals on both NR particle surface as well as PVA molecules. ¹H‐ and ¹³C‐nuclear magnetic resonance spectroscopy suggested a possibly chemical attachment of PVA on the NR. The amount of graft‐PVA expressed in term of grafting percentage (%G) increased almost linearly with the amount of PVA adding to the NR latex. Measuring by dynamic light scattering, the particle size of NR‐g‐PVA particles was larger than the size of unmodified NR, also it increased with the molecular weight and %G of PVA. Transmission electron microscopy images of the NR‐g‐PVA latex particles revealed that the size of PVA‐grafted NR particle was enlarged by a layer of graft‐PVA surrounding the NR particle. Given by the graft‐PVA layer surrounding NR particles, the NR‐g‐PVA latex particles possessed better colloidal stability as lowering pH compared with the unmodified NR latex. Comparing with unmodified NR particles, the electrophoretic mobility of NR‐g‐PVA particles was lower due to the presence of graft‐PVA that shifted the shear plane further away from the surface of the particles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dielectric investigation on poly(methylmethacrylate) films doped with p-nitroaniline

The dielectric behaviour of solution-grown thin films of poly(methylmethacrylate) containing p-nitroaniline (p-NA) as a dopant was investigated within the temperature range 60–90°C and a 20–10⁵ Hz frequency band. It is shown that these mixtures exhibit only one relaxation process similar to that of pure PMMA. However, the addition of p-NA increases both the height and the relaxation strength of the peaks and also shifts log f_m to higher frequencies. The additive causes narrowing of the loss curves and increases the activation energy for relaxation. These results are interpreted in terms of the hydrogen bonding effects of p-NA on localized motions of carboxymethyl dipoles in PMMA. An insight into the possible origins of the β- and α-relaxations in PMMA is also presented.     

Toughening modification of PS with n‐BA/MMA/styrene core–shell structured copolymer from emulsifier‐free emulsion polymerization

Core–shell structured particles, which comprise the rubbery core and glassy layers, were prepared by emulsifier‐free emulsion polymerization of poly(n‐butyl acrylate/methyl methacrylate)/polystyrene [P(n‐BA/MMA)/PS]. The particle diameter was about 0.22 μm, and the rubbery core was uncrosslinked and lightly crosslinked, respectively. The smaller core–shell structured particle–toughened PS blends were investigated in detail. The dynamic mechanical behavior and observation by scanning electron microscopy of the modified blend system with core–shell structured particles indicated good compatibility between PS and the particles, which is the necessary qualification for an effective toughening modifier. Notched‐impact strength and related mechanical properties were measured for further evaluation of the toughening efficiency. The notched‐impact strength of the toughened PS blends with uncrosslinked particles reached almost sixfold higher than that of the untoughened PS when 15 phr of the core–shell structured particles was added. For the crosslinked particles the toughening effect for PS was not obvious. The toughening mechanism for these smaller particles also is discussed in this article. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1290–1297, 2003     

Solution and solid state nuclear magnetic resonance investigation of poly(methylmethacrylate)/ poly(ethylene oxide) blends

It is well known that nuclear magnetic resonance spectroscopy (NMR) is a powerful method to characterize blends compatibility at the molecular level. In this work binary blends formed by poly(methylmethacrylate)/poly(ethylene oxide), PMMA/PEO, were investigated by different solution and solid state NMR techniques to obtain information on blends homogeneity and compatibility. It was characterized that the values of T₁^Hρ obtained by variable contact time and delayed contact time experiments, for each composition, were distinct and this fact suggests that regions with different molecular mobilities exist, as a consequence of blending interaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2955–2958, 2003     

Surface modification effects of core–shell rubber particles on the toughening of poly(butylene terephthalate)

We toughened poly(butylene terephthalate) (PBT) by loading core–shell rubber (CSR) type impact modifiers, consisting of a rubbery poly(n‐butyl acrylate) core and a rigid poly(methyl methacrylate) shell. To optimize the dispersion of CSR particles into the PBT matrix during melt compounding, the shell surface was modified with different grafting ratios of glycidyl methacrylate (GMA) reactive with PBT chain ends. In PBT blends with a 20 wt % CSR loading, the dispersed rubbery phases showed discernible shapes depending on the grafted GMA content, from predetermined spheres with 0.25 ± 0.05 μm diameters to their aggregates in the 2–3 μm diameter range. As a result, the interparticle spacing (τ) could be controlled from 0.25 to 4.0 μm in the PBT blends containing the fixed rubber loading. The Izod impact strengths of these samples increased significantly below τ = 0.4 μm. Additional thermal and morphological analyses strongly supported the hypothesis that the marked increase in toughness of the blends was related to less ordered lamellar formation of the PBT matrix under the confined geometry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study of the preparation of silicone rubber particles with core–shell structure by seeded emulsion polymerization

Silicone rubber particles with core–shell structure were prepared by polymerization of vinyl monomers in the presence of linear or cross-linked poly(dimethyl siloxane–methyl vinyl siloxane) latexes. The monomers were added in either continuous or swelled-continuous modes. Core–shell particles with poly(butyl methacrylate), or poly(methyl methacrylate), as the shell were obtained by using either addition mode. The core–shell structure was not observed for polysiloxane–polystyrene particles. The influence of monomer addition mode, the compatibilities of the monomers and their homopolymers with silicone rubber, and the reactivity ratios of the vinyl monomers with the vinyl group of linear polysiloxane particles, on the formation of the core-shell structure is discussed.     

Compatibilizing effect of diglycidyl ether of bisphenol‐A in polymer blend system: Nylon 6 combined with poly(butyl acrylate) core and poly(methyl methacrylate) shell particles

A polymeric blend system of nylon 6 and a core–shell impact modifier was studied. The modifier had a poly(butyl acrylate) core and a poly(methyl methacrylate) (PMMA) shell compatibilized with an epoxy resin, diglycidyl ether of bisphenol‐A (DGEBA). The compatibilization of DGEBA is achieved by the reaction of its glycidyl group with the amine groups of nylon 6, and hydrogen bonds may be generated between the hydroxyl groups and the carbonyl groups on PMMA. The effect of compatibilization was verified by the dramatic increase in impact strength and the finer dispersing of the core–shell particles in the nylon 6 matrix. The effects of compatibilization on other properties of the blend, such as the tensile and rheological properties, were also investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 24–29, 2000     

Hygrothermal aging and fracture behavior of styrene‐acrylonitrile/acrylate based core–shell rubber toughened poly(butylene terephthalate)

A study of hygrothermal aging in terms of the kinetics of moisture absorption by poly(butylene terephthalate) (PBT) and styrene‐acrylonitrile/acrylate based core–shell rubber (CSR) toughened PBT (PBT‐CSR) was undertaken. The diffusion of water into the PBT compounds with various CSR contents was investigated by immersion of specimens in water at temperatures between 30 and 90°C. It was observed that the equilibrium moisture content and the diffusion coefficient of the PBT both increased with increasing CSR content. The fracture behaviors of the PBT and PBT‐CSR were investigated. The focus of investigation was on the effect of an internal parameter (rubber content) and external parameters (testing temperature, deformation rates, and hygrothermal aging) on the fracture behavior of these materials. The fracture response of the various materials was evaluated by the fracture toughness and energy measured on static‐loaded compact tension specimens. The tensile and fracture behavior of PBT and PBT‐CSR was affected by both the internal and external parameters. On its own the CSR impact modifier failed to improve the toughness of PBT at either high testing speed or subambient temperature (−40°C). Based on the dynamic mechanical analysis study, the CSR is believed to behave as a rigid particulate filler in the PBT that consequently reduces the ductility of the PBT. All the materials tested showed poor retention of the tensile and fracture properties upon exposure to hygrothermal aging at 90°C, and these properties could not be restored by subsequent drying. This was attributed to severe hydrolytic degradation of the PBT that caused permanent damage to the materials. The failure modes of PBT and PBT‐CSR were assessed by fractographic studies in a scanning electron microscope. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2470–2481, 1999     

聚苯乙烯-聚甲基丙烯酸甲酯核-壳粒子的制备

由种子乳液聚合法制备了聚苯乙烯-聚甲基丙烯酸甲酯核-壳粒子。以过硫酸钾(KPS)为引发剂,辛基酚聚氧乙烯醚(OP-10)为乳化剂,合成了聚苯乙烯(PS)种子核;连续滴加甲基丙烯酸甲酯(MMA),在核表面富集MMA,制备了粒径范围在0.16~0.67μm的核-壳粒子;当单体苯乙烯与甲基丙烯酸甲酯(St/MMA)的比为30∶70(质量比)时,所得粒径在0.18μm,粒径分布为0.012。差示扫描量热(DSC)研究显示,复合粒子的玻璃化转变温度(Tg)为97.2℃,峰形单一,表现出良好的热性能。     

Influence of tacticity of poly(methyl methacrylate) on the compatibility with poly(vinyl phenol)

Isotactic, atactic, and syndiotactic poly(methyl methacrylate) (PMMA) were mixed with poly(vinyl phenol) (PVPh) separately in tetrahydrofuran to make three polymer blend systems. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to study the miscibility of these blends. Isotactic PMMA was found to be more miscible with PVPh than atactic or syndiotactic PMMA. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1773–1780, 1997     

Electrolytic admicellar polymerization of pyrrole on natural rubber/clay nanocomposites

Organic–inorganic composites consisting of natural rubber (NR), polypyrrole (PPy), and sodium montmorillonite (Na‐MMT) were synthesized via electrolytic admicellar polymerization. A constant potential of 9 volts was chosen for the synthesis. The PPy concentration was fixed at 100 mM, and the clay contents were varied from 1 to 7 parts per hundred of rubber (phr). The synthesized nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM), together with thermal stability (TGA), mechanical properties, and electrical conductivity (σ_dc) studies. The FTIR spectra indicated the characteristic peaks of both PPy and MMT clay and also evidenced a slight interaction between the PPy chain and the clay layers, verifying the success of electrolytic admicellar polymerization. XRD and TEM results pointed out the good dispersion of clay platelets in the polymer matrix, suggesting an exfoliated structure. The morphology of the nanocomposites was greatly dependent on the amount of MMT clay, especially at a 7 phr loading. The initial modulus and tensile strength of the nanocomposites containing the 7 phr loading were about four and two times higher, compared with unfilled NR/PPy, respectively. Thermal stability studies revealed a slight improvement in the decomposition temperature for the PPy component by the clay layers, whereas the opposite trend was found for the NR component. More interestingly, the electrical conductivity of the admicelled rubber increased significantly (～ 19–32 times) with increasing clay contents from 1 to 7 phr, in comparison with unfilled NR/PPy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A thermodynamic interpretation of the compatibility of chlorinated polyethylene with poly(methylmethacrylate)

The compatibility of chlorinated polyethylene with poly(methylmethacrylate) and the oligomer analogue chlorinated octadecane with oligomeric PMMA are interpreted using the equation of state theory. It is found that the interaction energy parameter X₁₂ and the interaction entropy parameter Q₁₂, obtained from the heat of mixing and the phase boundary of oligomeric mixtures, can be used to generate the phase boundary of the polymer mixture. The spinodals of different molecular weights so generated have less molecular weight dependence than might be expected, in agreement with experimental results. A negative Q₁₂ indicates that some ordering may exist in the mixture due to specific interactions.     

The influence of the internal structure of core–shell particles on poly(vinyl chloride)/(methyl methacrylate–butadiene–styrene) blends

Methyl methacrylate–butadiene–styrene (MBS) core–shell particles were prepared by grafting styrene and methyl methacrylate onto polybutadiene seeds via emulsion polymerization. All the MBS particles were designed with the same chemical composition, similar grafting degree but different internal structures. The difference in internal structure was realized by controlling the ratio of ‘external grafting’ and ‘internal grafting’ of styrene. The work focused on the influence of the internal structure of MBS core–shell particles on the properties of poly(vinyl chloride)/MBS blends. From transmission electron microscopy, three different internal structures were observed: rare sub‐inclusions, a large number of small sub‐inclusions and large sub‐inclusions. The results of dynamic mechanical analysis illustrated that the different internal structures greatly affected the glass transition temperature T_g of the rubber phase and the storage modulus of the core–shell particles. The notched Izod impact test results showed that the MBS with large sub‐inclusions had the lowest brittle–ductile transition temperature, while the transparency test revealed that the presence of sub‐inclusions in the rubbery phase reduced the transparency of the blend. Copyright © 2012 Society of Chemical Industry     

Effect of acrylic core–shell rubber particles on the particulate flow and toughening of PVC

Different types of acrylic core–shell rubber particles with a poly(butyl acrylate) (PBA) core and a grafted poly(methyl methacrylate) (PMMA) shell were synthesized. The average size of acrylic core–shell latex particles ranged from 100 to 170 nm in diameter, having the core gel content in the range of 35–80%. The melt blending behavior of the poly(vinyl chloride) (PVC) and the acrylic core–shell rubber materials having different average particle sizes and gel contents was investigated in a batch mixing process. Although the torque curves showed that the particulate flow of the PVC in the blends was dominant, some differences were observed when the size and gel content of the particles varied. This behavior can be attributed to differences in the plasticizing effect and dispersion state of various types of core–shell rubber particles, which can vary the gelatin process of the PVC in the mixing tool. On the other hand, the highest toughening efficiency was obtained using core–shell rubber particles with the smallest particle size (i.e., 100 nm). The results showed that increasing the gel content of the core–shell impact modifiers with the same particle size improved the particle dispersion state in the PVC matrix. The toughening efficiency decreased for the blends containing 100 and 170 nm rubber particles as the gel content increased. Nevertheless, unexpected behavior was observed for the blends containing 140 nm rubber particles. It was found that a high level of toughness could be achieved if the acrylic core–shell rubber particles as small as 100 nm had a lower gel content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Investigation on thermoplastic co‐poly(ether‐ester) elastomer toughened poly(methylmethacrylate) blends

Blends of poly(methyl methacrylate) (PMMA) and copoly(ether‐ester) (COPE) elastomer have been prepared in different compositions namely, 95/5, 90/10, 85/15, and 80/20 wt % (PMMA/COPE), by melt mixing technique using twin screw extruder. The influence of COPE content on the mechanical properties especially impact strength, thermal behavior, and chemical resistance of PMMA have been investigated. The impact strength of the PMMA/COPE blends for all the compositions were found to be improved remarkably as compared to the virgin PMMA without affecting the other mechanical properties significantly. Various composite models, such as series model, parallel model, Halpin‐Tsai equation, and Kerner's model have been used to fit the experimental mechanical properties. The effect of chemical and thermal ageing on the performance of the PMMA/COPE blends was also studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Radiation‐initiated graft polymerization of methylmethacrylate onto poly(tetrafluoroethylene): Characterization by 1H‐NMR

A broad‐line ¹H‐NMR study was carried out to examine the local structure of poly(methylmethacrylate) (PMMA) grafted onto Poly(tetrafluoroethylene) (PTFE). The NMR spectra were observed for three different samples with 1.0, 5.4, and 7.0 wt % PMMA over the temperature range from 150 to 380 K. With the help of selectively deuterated PMMA (PMMA‐d₅ and PMMA‐d₈)‐grafted samples, the NMR spectra were analyzed in terms of two components—a Gaussian (G) component, and a Lorentzian (L) component. Based on the second moments (〈ΔH²〉) analysis, the L and G components were attributed to the ¹H–¹H dipolar interactions within one CH₃ group and the interactions of CH₃ groups that are closely located in aggregated PMMA chains. Combining the results with the temperature dependence of 〈ΔH²〉 and the angular resolved XPS, the location and rotational motion of PMMA grafted onto PTFE are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1386–1394, 1999