Morphologies, crystallinity and dynamic mechanical characterizations of polypropylene/polystyrene blends compatibilized with PP-g-PS copolymer: Effect of the side chain length

PP-g-PS copolymers were synthesized with the same polypropylene (PP) backbones and various side chain lengths of PS sequences via reactive comonomer p-allyltoluene (p-AT) by Ziegler–Natta copolymerization and the subsequent living anionic graft-polymerization. ¹H NMR characterized that the PP-g-PS copolymer had grafted 3.15 side chains per 1000 carbons in the PP backbones and the length of PS sequences varied in the range of 25.8–309.9 units. PP/PS blends with the PP-g-PS copolymer as compatibilizer (wt. 75/25/5) were prepared and characterized by SEM, WAXD and DMA to investigate the morphologies, crystallinity and glass transition temperatures of the PP/PS blends. All the results pointed out that the average side chain length (GL) of the graft copolymer (GL is from 25.8 to 309.9) made great effects of the PP/PS blends, such as the PS dispersed phase, the crystallinity of the PP component and the two glass transition temperatures of the blends, which showed the same trend with the increase of the GL. Overall, only with a suitable average side chain length, the PP-g-PS copolymer could achieve optimal compatibilizing efficiency of the PP/PS blends.     

Tailoring of interface of polypropylene/polystyrene/carbon nanofibre composites by polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene

Mechanical and physical properties of polypropylene (PP)/polystyrene (PS) blend, PP/PS/polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) ternary blend and their composites with carbon nanofibers (CNF) were investigated. Composites of ternary blend exhibited superior properties compared to those of binary blends. Mechanical performance of nanocomposites was intimately related to their phase morphology. PP/PS/SEBS/0.1 wt% CNF hybrid composites exhibited excellent impact strength (Four-fold increase compared to PP/PS blend) and ductility (12-fold increase in elongation at break, with respect to PP/PS blend). Moreover, these composites displayed good tensile strength and modulus (15% increase in Young's modulus, compared to PP/PS/SEBS blend) and are suitable for various end-use applications including automobile applications. Although crystallinity of PP phase is decreased by the incorporation of CNF, thermal stability of the composites remained almost unaffected. Contact angle measurements revealed that ternary composites exhibited maximum hydrophobicity.     

Correlation of Morphology Evolution with Superior Mechanical Properties in PA6/PS/PP/SEBS Blends Compatibilized by Multi-phase Compatibilizers

In this study,the maleic anhydride(MAH)and styrene(St)dual monomers grafted polypropylene(PP)and poly[styrene-b-(ethylene-co-butylene)-b-styrene](SEBS),i.e.PP-g-(MAH-co-St)and SEBS-g-(MAH-co-St)are prepared as multi-phase compatibilizers and used to compatibilize the PA6/PS/PP/SEBS(70/10/10/10)model quaternary blends.Both PS and SEBS are encapsulated by the hard shell of PP-g-(MAH-co-St)in the dispersed domains(about 2μm)of the PA6/PS/PP-g-(MAH-co-St)/SEBS(70/10/10/10)quaternary blend.In contrast,inside the dispersed domains(about 1μm)of the PA6/PS/PP/SEBS-g-(MAH-co-St)(70/10/10/10)quaternary blend,the soft SEBS-g-(MAH-co-St)encapsulates both the hard PS and PP phases and separates them.With increasing the content of the compatibilizers equally,the morphology of the PA6/PS/(PP+PP-g-(MAH-co-St))/(SEBS+SEBS-g-(MAH-co-St))(70/10/10/10)quaternary blends evolves from the soft(SEBS+SEBS-g-(MAH-co-St))encapsulating PS and partially encapsulating PP(about 1μm),then to PS exclusively encapsulated by the soft SEBS-g-(MAH-co-St)and then separated by PP-g-(MAH-co-St)inside the smaller domains(about 0.6μm).This morphology evolution has been well predicted by spreading coefficients and explained by the reaction between the matrix PA6 and the compatibilizers.The quaternary blends compatibilized by more compatibilizers exhibit stronger hierarchical interfacial adhesions and smaller dispersed domain,which results in the further improved mechanical properties.Compared to the uncompatibilized blend,the blend with both 10 wt%PP-g-(MAH-co-St)and 10 wt%SEBS-g-(MAH-co-St)has the best mechanical properties with the stress at break,strain at break and impact failure energy improved significantly by 97%,71%and 261%,respectively.There is a strong correlation between the structure and property in the blends.     

Three‐Dimensional Structure of Olefinic Thermoplastic Elastomer Blends Using Electron Tomography

Summary: The present communication reports the first use of electron tomography in reconstructing the three‐dimensional morphology in thermoplastic elastomer blends. The blends investigated were dynamically vulcanized blends of ethylene‐propylene‐diene (EPDM) rubber/poly(propylene)/oil and polystyrene‐block‐(ethylene‐co‐butylene)‐block‐polystyrene (SEBS)/poly(propylene)/oil. An easy identification of blend morphology could be carried out at blend compositions, where conventional transmission electron microscopic imaging gives misleading information. This technique gives a higher resolution than any other microscopic technique, and is applicable to blends with dispersed as well as co‐continuous morphologies.

Example of a tomographic model of partially co‐continuous SEBS phases in a SEBS/PP/oil thermoplastic blend. Only the contours of the SEBS phase are shown.     

Effects of Branches on the Crystallization Kinetics of Polypropylene-g- Polystyrene and Polypropylene-g-Poly（n-butyl acrylate） Graft Copolymers with Well-defined Molecular Structures

Effects of branches on the crystallization kinetics of polypropylene-g-polystyrene(PP-g-PS) and polypropylene-gpoly(n-butyl acrylate)(PP-g-PnBA) graft copolymers with well-defined molecular structures were systematically investigated by DSC.The Avrami equation was used to analyze the isothermal crystallization process,while the analysis of nonisothermal crystallization process was based on the Jeziorny-modified Avrami model and Mo model.The kinetics results of isothermal and nonisothermal crystallization verified the peculiar effects of branches on the crystallization process of PP backbones in PP-g-PS and PP-g-PnBA graft copolymers:on one hand,the interaction between branches(π-π interaction between PS branches,or dipole-dipole interaction between PnBA branches) restrained the mobility and reptation ability of the PP backbones,which hindered the crystallization process;on the other hand,the heterogeneous nucleation effect resulting from the branched structure and fluctuation-assisted nucleation mechanism(caused by microphase separation between the PS or PnBA rich phase and the PP rich phase) became more pronounced with increasing branch length,which facilitated the crystallization process.     

A novel route to the synthesis of PP-g-PMMA copolymer via ATRP reaction initiated by Si-Cl bond

The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out with conventional Ziegler-Natta catalyst supported on MgCl₂. The effects of the concentration of ADMS in the feed on the polymerization reaction and copolymer properties were investigated. The resulting copolymer PP-co-ADMS was chlorinated to PP-Si-Cl by refluxing the copolymer with SOCl₂ in benzene. The chlorinated copolymer was used to initiate ATRP of MMA with CuCl/PMDETA as catalyst to produce graft copolymer PP-g-PMMA, which was characterized with ¹H NMR, ¹³C NMR, GPC and DSC. Polymer blend of iPP/PP-g-PMMA/PMMA was prepared and the results shown that PP-g-PMMA was an effective compatilizer.     

Polypropylene-block-poly(methyl methacrylate) and-block-poly(N-isopropylacrylamide) block copolymers prepared by controlled radical polymerization with polypropylene macroinitiator

Polypropylene-block-poly(methyl methacrylate) (PP-b-PMMA) and Polypropylene-block-poly(N-isopropylacryramide) (PP-b-PNIPAAm) block copolymers were successfully synthesized by radical polymerizations of MMA or NIPAAm with polypropylene (PP) macroinitiators. Polypropylene macroinitiators were prepared by a series of end functionalization of pyrolysis PP via hydroalumination, oxidation and esterification reactions. The PP macroinitiators thus obtained could initiate radical polymerizations of MMA or NIPAAm by using transition metal catalyst systems, and ¹H NMR analysis and gel permeation chromatography measurement confirmed the formation of PP-b-PMMA and PP-b-PNIPAAm block copolymers. In addition, the length of the incorporated PMMA or PNIPAAm segments in these block copolymers was controllable by the feed ratio between the monomer and the PP macroinitiator, and their molecular weights were estimated to be 35700 and 68700 (PMMA) and 1760 and 13300 (PNIPAAm), respectively. Transmission electron microscopy of the polymers obtained by NIPAAm polymerization revealed specific morphological features that reflected the difference of PNIPAAm segment length. The text was submitted by the authors in English.     

Large impact in electrical properties of polypropylene by improving the filler-matrix interface effect in PP/PS blends

Inorganic nanoparticles are widely used to improve space charge behavior, DC breakdown strength and other electrical properties of polymer insulating materials, but the uniform distribution of inorganic nanofillers in matrix is difficult due to their agglomeration and bad compatibility with the polymeric matrix. In this paper, polypropylene (PP)/polystyrene (PS) blends were prepared to suppress space charge accumulation and improve DC breakdown strength. Polypropylene-g-polystyrene (PP-g-PS) graft copolymer was used as compatibilizer to improve the compatibility of PP matrix and PS filler. The evolution of microstructure of PP/PS blends were investigated by scanning electron microscope (SEM), the space charge distributions were measured by a pulsed electro-acoustic (PEA) system, and DC breakdown strength was also tested. The morphologies show that the size of PS particles reduced to 310 nm when the content of PP-g-PS graft copolymer increased to 24 wt%, and the interaction between PP matrix and PS particles enhanced. The presence of PS particles in all PP/PS blends suppressed the space charge accumulation compared to neat PP, but the DC breakdown strength in uncompatibilized blend was lower than neat PP. The increasing of content of PP-g-PS improved the DC breakdown strength with the maximum value of 408.9 kV/mm was obtained. This may attribute to excellent interface structure formed between PP matrix and PS particles.     

Synthesis of Core-Shell Particles of Polystyrene and Poly(methyl methacrylate) Using Emulsion Photopolymerization

Summary: Submicron core-shell particles of polystyrene (PS) and polystyrene-co-poly(methyl methacrylate) (PS-co-PMMA) coated with PMMA were obtained by emulsion photopolymerization. The seeds of PS or PS-co-PMMA were prepared by emulsion polymerization with or without emulsifier and a ratio of functional monomer and crosslinker (SVBS/EDGMA) in order to obtain different surfaces for the subsequent coating with PMMA. At each stage, the evolution of the average particle size were monitored by using photon correlation spectroscopy (DLS) and the final polymer particles was analyzed via transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The core-shell morphology was identified as the increase of the average particle size in the second stage by DLS technique and by the direct observation by TEM of the differentiation between PS core and PMMA shell, and by the presence of two glass transition temperatures (T_g) as a consequence of the existence of two partially miscible phases.     

Reaction-induced phase separation in a semiinterpenetrating network of reactive ternary blends

Morphology and reaction mechanisms were probed on a model reactive ternary blend system of polycarbonate (PC), poly(methyl methacrylate) (PMMA), and diglycidylether of bisphenol-A (DGEBA) epoxy by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Molecular interactions/reactions between the components in the blends after heating treatments are discussed. It was found that reactions took place among the components and that an interpenetrating network was built. The possible reaction mechanisms and the resulting structures after the heating treatments were probed. In the blends, PC and DGEBA reacted to form a network, while PMMA remained free. The semiinterpenetration, however, did not result in a network interlocked into a homogeneous state. The single T_g of the heated ternary DGEBA/PC/PMMA blends actually did not reflect a homogeneous interpenetrating network. Due to relatively small PMMA domains, the ternary blend network exhibited a single T_g. Upon etching the PMMA domains from the blend by acetone, a clearly interpenetrating network of reacted PC and epoxy was exposed and confirmed. The reactions leading to such a morphology are discussed with experimental evidence. © 1996 John Wiley & Sons, Inc.     

Compatibilizing effect of functionalized polystyrene blends: a study of morphology,thermal, and mechanical properties

Polystyrene (PS), being an amorphous polymer is immiscible with other polymers. To engender miscible blends, PS has been functionalized with an active amino‐functional group on the molecular chains of PS to yield amino‐substituted polystyrene (APS), which serves as a reactive compatibilizer. The compatibilization effect of amino functionalized polystyrene on the rubber toughening was explored and results were compared in terms of morphology, thermal, and mechanical properties of PS/SEBS‐g‐MA versus APS/SEBS‐g‐MA blends. In addition, the effect of rubber content on the blend morphology and mechanical properties were investigated. An appreciable change in the thermal stability of APS blends in comparison with PS blend has been probed. A marked correlation has been observed between phase morphology and thermal stability. Use of APS produced the compatibilized blends which render improved blend morphology, enhanced thermal and mechanical properties. Optimal thermal, morphological and mechanical profiles were depicted by 20‐wt% APS blend. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of graft polymer on the formation of micron-sized,monodisperse, "onion-like" alternately multilayered poly(methyl methacrylate)/polystyrene composite particles by reconstruction of morphology with the solvent-absorbing/releasing method

Some factors contributing to the formation of an alternately multilayered structure of micron-sized, monodisperse poly(methyl methacrylate) (PMMA)/polystyrene (PS) (1/1, w/w) composite particles by reconstruction of the morphology with the solvent-absorbing/releasing method (SARM) were discussed. The original composite particles, which were produced by seeded dispersion polymerization (SDP) of styrene, had a core–shell structure. When PS/PMMA (1/1, w/w) composite particles produced by SDP of methyl methacrylate were treated by the SARM with toluene, the reconstructed morphology of the composite particles was not the multilayered structure but a hemisphere (or core–shell). The PS/PMMA composite particle contained less than 10 wt% PMMA- g-PS. On the other hand, the PMMA/PS composite particles contained about 40 wt% graft polymer. The graft polymer would exist at the interfaces of the alternate multilayers and decrease their interfacial energy. This was the main reason why the alternately multilayered structure was constructed by the SARM, though the total interfacial area between PMMA and PS layers in the multilayered particle is much larger than that of the hemisphere (or core–shell).     

In-situ polymer blends via chain transfer living polymerization (CTLP)

In-situ polymer blends of polystyrene (PS)/poly(methyl methacrylate) (PMMA) with controlled and variable different compositions and molecular weights were found to be successfully synthesized by “chain transfer living polymerization (CTLP)” methodology by a combination of size-exclusion chromatographic analysis, differential scanning calorimetry (DSC), UV/Vis and H NMR spectroscopy, and optical microscopic analysis. The PMMAs prepared in tetrahydrofuran (THF) in the presence of polystyrene exhibit highly syndiotactic stereoregularity (over 70 mol-%) and a glass transition temperature over 120°C. A dispersed morphology was found even for blends with over 31 vol.-% of the weight fraction of one component due to the discrepancy in the molecular weights of two components in the PS/PMMA blends. A ternary polymer blend system having PS/PMMA/PS -block- PMMA can be generated by control of the concentration of fluorene as the chain transfer agent in the CTLP.     

Use of block copolymer-stabilized cadmium sulfide quantum dots as novel tracers for laser scanning confocal fluorescence imaging of blend morphology in polystyrene/poly(methyl methacrylate) films

This paper describes the first use of polymer-coated quantum dots (QDs) as fluorescent tracers for LSCFM imaging of phase morphology in polymer blends. Cadmium sulfide (CdS) QDs stabilized at the surface with a PS-b-PAA block copolymer are shown to be well dispersed via their polystyrene (PS) brush layer in the PS phase of solvent-cast 40/60 (w/w) PS/PMMA blends. The QDs are excluded from the PMMA phase, providing excellent fluorescence contrast for LSCFM imaging of the phase-separated blends. The presence of PS-b-PAA-stabilized QDs does not appear to affect the blend morphology, since the observed morphologies are the same when the percentage of QDs within the PS phase is varied from 10 to 50 wt %. These QD fluorescent tracers are used to characterize several aspects of blend morphology in solvent-cast 40/60 PS/PMMA blends containing PS homopolymer with either 100 (low molecular weight) or 1250 (high molecular weight) repeat units. In the PS(1250)/PMMA blends, a percolating distribution of PMMA droplets (2-25 mum) in a PS matrix is observed in the bulk, and a distinct inversion in the continuous phase is found near the glass substrate. In the PS(100)/PMMA blends, a "phase-in-phase" morphology is found, consisting of large PS domains (20-100 mum) dispersed in a PMMA continuous phase and small PMMA domains (1-2 mum) scattered throughout the larger PS droplets. The observed change in blend structure is attributed to a lower interfacial tension for the lower molecular weight PS.     

Morphological stability,interfacial tension,and dual-phase continuity in polystyrene-polyethylene blends

The morphological stability of polystyrene high-density polyethylene (PS/PE) blend is investigated in the region of dual-phase continuity. The effect of the addition of a triblock SEBS copolymer to the blends on the stability of these morphologies, is examined. The results show that the morphology of the unmodified blends changes from co-continuous to droplet matrix for PS-rich blends whereas the morphology of a 50/50 blend maintains continuity but coarsened significantly upon annealing at 200°C. In the presence of the copolymer, these morphologies are much more stable. Selective solvent extraction of polystyrene in di-ethyl ether reveals that the level of PS continuity in the 50/50 blend is higher for the unmodified system than for the modified one. Upon annealing, the level of PS continuity significantly increases for the unmodified 50/50 PS/PE blend. The effect of the copolymer content in the blend on the interfacial tension between the two components is also investigated using the breaking thread method. The interfacial tension is found to be reduced from 5.6 to 1.1 mN/m by the addition of 20 parts of the copolymer to the blend. © 1997 John Wiley & Sons, Inc.     

Study on anti-UV aging mechanism of PP-<Emphasis Type="Italic">g</Emphasis>-AN in the PP/PP-<Emphasis Type="Italic">g</Emphasis>-AN blend

In order to verify the anti-UV aging mechanism about polypropylene-grafting-acrylonitrile (PP-g-AN) to polypropylene (PP), the structural analysis of the PP/PP-g-AN blend before and after aging was carried out via the X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectrometry (FTIR) and UV-visible Absorbance Spectrum (UV–Vis). Inference on PP-g-AN anti-aging process was proposed and confirmed.     

Influence of Reactive Compatibilization on the Morphology of Polypropylene/Polystyrene Blends

To study the efficiency of different mechanisms for reactive compatibilization of polypropylene/polystyrene blends (PP/PS blends), main chain or terminal-functionalized PP and terminal-functionalized PS have been synthesized by different methods. While the in-situ block and graft copolymer formation results in finer phase morphologies compared to the corresponding non-reactive blends, the morphology development in the ternary blend system PP/PS + HBP (hyperbranched polymer) is a very complex process. HBP with carboxylic acid end groups reacts preferably with the reactive sites of the oxazoline functionalized PS (PS-Ox) and locates mainly within the dispersed PS-Ox phase. A bimodal size distribution of the PS-Ox particles within the oxazoline modified PP (PP-Ox) matrix phase is observed with big PS-Ox particles (containing the HBP as dispersed phase) and small PS-Ox particles similar in size to the unimodal distributed particles in the non-reactive PP-Ox/PS-Ox blends. Factors influencing the morphology are discussed.     

Synthesis of graft copolymers onto styrenic polymer backbone via “grafting from” raft process

A new synthetic methodology is developed for preparing graft copolymers via RAFT polymerization method by the “R group approach” onto styrenic polymers. In this approach, latent sites of the styrenic polymer was brominated first and then converted into macro‐RAFT agents with pyrazole and thio dodecyl as the Z groups. This was used to synthesize graft copolymer such as polystyrene‐graft‐polymethyl methacrylate (PS‐g‐PMMA), polystyrene‐graft‐poly(isobornyl acrylate), polystyrene‐graft‐poly[2‐(acetoacetoxy)ethyl methacrylate] (PS‐g‐PAEMA), and poly(para‐methoxystyrene)‐graft‐polystyrene (P(p‐MS)‐g‐PS). The polymers are characterized by gel permeation chromatography, ¹H NMR, IR, and atomic force microscopy (AFM). The morphology of PS‐g‐PMMA in THF was investigated using AFM and island‐like features were noticed. The AFM studies of the PS‐g‐PAEMA graft copolymers revealed the formation of globules and ribbon‐like morphological features. The PS‐g‐PAEMA graft copolymers form complex with Fe(III) in dimethylformamide and the AFM studies suggest the formation of globular superstructures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The Formation of Ordered Nanoholes in Binary,Chemically Similar,Symmetric Diblock Copolymer Blend Films

Summary: Binary symmetric diblock copolymer blends, that is, low‐molecular‐weight poly(styrene‐block‐methyl methacrylate) (PS‐b‐PMMA) and high‐molecular‐weight poly(styrene‐block‐methacrylate) (PS‐b‐PMA), self‐assemble on silicon substrates to form structures with highly ordered nanoholes in thin films. As a result of the chemically similar structure of the PMA and the PMMA block, the PMMA chain penetrates through the large PMA block that absorbs preferentially on the polar silicon substrate. This results in the formation of nanoholes in the PS continuous matrix.

An atomic force microscopy image of the thin film obtained from the blend of low‐molecular‐weight PS‐b‐PMMA and high‐molecular‐weight PS‐b‐PMA. The regular array of nanoholes in the films surface is clearly visible.     

Synthesis and characterization of polypropylene-graft-poly(l-lactide) copolymers by CuAAC click chemistry

The syntheses of polypropylene-graft-poly(l -lactide) copolymers (PP-g-PLAs) via copper (I)-catalyzed azide-alkyne cycloaddition “click” reaction (CuAAC) using azide side-chain functionalized polypropylene (PP-N₃) and alkyne end-functionalized poly(l -lactide) (PLA-Alkyne) were reported. The CuAAC was then applied to azide and different feeding ratios of alkyne functional polymers to give PP-g-PLAs that were characterized by FTIR, ¹H-NMR, GPC, DSC, and WCA measurements. The CuAAC click reaction was achieved by two different feeding ratio (PP-N₃:PLA-Alkyne = 1:5 and 1:10) and thermal, biodegradable, and surface properties of obtained graft copolymers were investigated. The molar ratio of PLA were calculated as 72.7 (PP-g-PLA-1) and 78.4% (PP-g-PLA-2) by ¹H-NMR spectroscopy. The water contact angle (WCA) values of PP-g-PLA-1 (81^o ± 1.3) and PP-g-PLA-2 (75^o ± 1.6) copolymers were compared with commercial chlorinated polypropylene (PP-Cl) (90^o ± 1.0), suggesting a more hydrophilic nature of desired graft copolymers produced. Conversely, the enzymatic biodegradation studies revealed that the weight losses of graft copolymers were determined as 13.6 and 22.1%, which is about 4% for commercial PP-Cl sample. Thus, it was clear that this simple and facile method was effective in promoting biodegradation of commercial polypropylene and attractive particularly for worldwide environmental remediation goals. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2595–2601