Morphology,crystallization, and thermal behavior of isotactic polypropylene/propylene‐g‐styrene blends

Optical microscopy, differential scanning calorimetry, and small angle X‐ray scattering techniques were used to study the influence of the crystallization conditions on morphology and thermal behavior of samples of binary blends constituted of isotactic polypropylene (iPP) and a novel graft copolymer of unsaturated propylene with styrene (uPP‐g‐PS) isothermally crystallized from melt, at relatively low undercooling, in a range of crystallization temperatures of the iPP phase. It was shown that, irrespective of composition, no fall in the crystallinity index of the iPP phase was observed. Notwithstanding, spherulitic texture and thermal behavior of the iPP phase in the iPP/uPP‐g‐PS materials were strongly modified by the presence of copolymer. Surprisingly, iPP spherulites crystallized from the blends showed size and regularity higher than that exhibited by plain iPP spherulites. Moreover, the amount of amorphous material located in the interspherulitic amorphous regions decreased with increasing crystallization temperature, and for a given crystallization temperature, with increasing uPP‐g‐PS content. Also, relevant thermodynamic parameters, related to the crystallization process of the iPP phase from iPP/uPP‐g‐PS melts, were found, composition dependent. The equilibrium melting temperature and the surface free energy of folding of the iPP lamellar crystals grown in the presence of uPP‐g‐PS content up to 5% (wt/wt) were, in fact, respectively slightly lower and higher than that found for the lamellar crystals of plain iPP. By further increase of the copolymer content, both the equilibrium melting temperature and surface free energy of folding values were, on the contrary, depressed dramatically. The obtained results were accounted for by assuming that the iPP crystallization process from iPP/uPP‐g‐PS melts could occur through molecular fractionation inducing a combination of morphological and thermodynamic effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2286–2298, 2001     

Morphology,crystallization, and thermal behavior of isotactic polypropylene/polymethylmethacrylate blends: Effects of the addition of a graft copolymer of propylene with methylmethacrylate

Optical microscopy, differential scanning calorimetry, and small angle X‐ray scattering techniques were used to study the influence of crystallization conditions on the morphology and thermal behavior of samples of ternary blends constituted of isotactic polypropylene (iPP), atactic polymethylmethacrylate (aPMMA), and a novel graft copolymer of unsaturated propylene with methylmethacrylate (uPP‐g‐PMMA). The purpose was to assess the uPP‐g‐PMMA capability to act as compatibilizer for iPP/aPMMA materials. It was shown that the presence of uPP‐g‐PMMA copolymer affects the interfacial tension between the iPP and aPMMA phase in the melt state, the aPMMA particle size, and particle‐size distribution is modified. After complete crystallization of the iPP phase at relatively low undercooling, in a range of crystallization temperatures, the presence of the uPP‐g‐PMMA phase was found to modify both mode and state of dispersion of minor component and spherulitic texture and inner structure of spherulites fibrillae. The extent of the induced modifications was dependent on a combination of composition and undercooling. Also, relevant thermodynamic parameters of the iPP phase, such as the equilibrium melting temperature and the surface free energy of folding, were strongly affected by the presence of the uPP‐g‐PMMA phase, opposite effects being observed depending on the uPP‐g‐PMMA content. The observed melting temperature and surface free energy of folding values were accounted for by the growth of iPP lamellar crystals with different perfection, thickness, and surface disorder. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 143–158, 2001     

Isotactic polypropylene/polystyrene blends: Effects of the addition of a graft copolymer of propylene with styrene

A novel graft copolymer of unsaturated propylene with styrene (uPP-g-PS) was added to binary blends of isotactic polypropylene (iPP) and atactic polystyrene (aPS) with a view to using such a copolymer as compatibilizer for iPP/aPS materials. Differential scanning calorimetry, optical microscopy, scanning electron microscopy (SEM), wide angle X-ray scattering, and small angle X-ray scattering (SAXS) techniques have been carried out to investigate the phase morphology and structure developed in solution-cast samples of iPP/aPS/uPP-g-PS ternary blends. It was found that the uPP-g-PS addition can provide iPP/aPS-compatibilized materials and that the extent of the achieved compatibilization is composition-dependent. Blends of iPP and aPS exhibited a coarse domain morphology that is characteristic of immiscible polymer systems. By adding 2% (wt/wt) of uPP-g-PS copolymer a very broad particle-size distribution was obtained, even though the particles appeared coated by a smooth interfacial layer, as expected according to a core–shell interfacial model. With increasing uPP-g-PS content (5% wt/wt), a finer dispersion degree of particles, together with morphological evidence of interfacial adhesion, was found. With further increase of uPP-g-PS amount (10% wt/wt) the material showed such a homogeneous texture that neither domains of dispersed phase nor holes could be clearly detected by SEM. The type of interface developed in such iPP/aPS/uPP-g-PS blends was accounted for by an interfacial interpenetration model. The iPP crystalline texture, size, neatness, and regularity of iPP spherulites crystallized from iPP/aPS/uPP-g-PS blends were found to decrease when the copolymer content was slightly increased. Assuming, for the iPP spherulite fibrillae, a two-phase model constituted by alternating parallel crystalline lamellae and amorphous layers, it was shown by SAXS that the phase structure generated in iPP/aPS/uPP-g-PS blends is characterized by crystalline lamellar thickness (L_c) and interlamellar amorphous layer thickness (L_a) higher than that shown by plain iPP; the higher the copolymer content, the higher the L_c and L_a. It should be remarked that considerably larger increases have been found in L_a values. Such SAXS results have been accounted for by assuming that a cocrystallization phenomenon between propylenic sequences of the uPP-g-PS copolymer and iPP occurs and that during such a process PS chains grafted into copolymer sequences remain entrapped in iPP interlamellar amorphous layers, where they form their own separate domains. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1539–1553, 1997     

Isotactic polypropylene/polymethylmethacrylate blends: Effects of addition of propylene-graft-methylmethacrylate copolymer

A novel graft copolymer of unsaturated propylene with methyl methacrylate (uPP-g-PMMA) was added to binary blends of isotactic polypropylene (iPP) and atactic poly(methyl methacrylate) (aPMMA) with a view to using such a copolymer as a compatibilizer for iPP/aPMMA materials. Optical microscopy (OM), scanning electron microscopy, wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS) techniques showed that, contrary to expectation, the uPP-g-PMMA addition does not provide iPP/aPMMA compatibilized materials, irrespective of composition. As a matter of fact the degree of dispersion of the minor component achieved following the addition of uPP-g-PMMA copolymer remained quite comparable to that exhibited by binary blends of iPP and aPMMA with no relevant evidence of adhesion or interconnection between the phases. On the other hand the crystalline texture was deeply modified by the copolymer presence. With increasing uPP-g-PMMA content (w/w) the iPP spherulites were found to become more open and coarse and the dimensions and number per unit area of the amorphous interspherulitic contact regions were found to increase. According to such OM results the copolymer uncrystallizable sequences were assumed to be mainly located in interfibrillar and interspherulitic amorphous contact regions. SAXS analysis demonstrated that the phase structure developed in the iPP/aPMMA/uPP-g-PMMA blends is characterized by values of the long period increasing linearly with increasing copolymer content (w/w). Assuming a two phase model for the iPP spherulite fibrillae, constituted of alternating parallel crystalline lamellae and amorphous layers, the lamellar structure of the iPP phase in the ternary blends is characterized by crystalline lamellar thickness (L_c) and an interlamellar amorphous layer (L_a) higher than that shown by plain iPP and L_c and L_a values both increased with increasing uPP-g-PMMA content (w/w). Such SAXS results have been accounted for by assuming that a cocrystallization phenomenon between propylenic sequences of the uPP-g-PMMA copolymer and iPP occurs. The development of the iPP lamellar structure in the iPP/aPMMA/uPP-g-PMMA blends was thus modeled hypothesizing that during such a cocrystallization process copolymer PMMA chains with comparatively lower molecular mass remain entrapped into the iPP interlamellar amorphous layer forming their own domains. Moreover, evidence of strong correlations between the crystallization process of the uPP-g-PMMA copolymer and the iPP crystallization process was shown also by differential scanning calorimetry and WAXS experiments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2377–2393, 1997     

Isotactic polypropylene/ethylene‐co‐propylene blends: Influence of the copolymer microstructure on rheology,morphology, and properties of injection‐molded samples

Meltrheological behavior, phase morphology, and impact properties of isotactic‐polypropylene (iPP)‐based blends containing ethylene–propylene copolymer (EPR) synthesized by means of a titanium‐based catalyst with very high stereospecific activity (EPR_Ti) were compared to those of iPP/EPR blends containing EPR copolymers synthesized by using a traditional vanadium‐based catalyst (EPR_V). The samples of EPR copolymers were synthesized ad hoc. They were characterized by comparable propylene content, average molecular masses, and molecular mass distribution in order to assess the effects of distribution of composition and sequence lengths of the structural units on the structure–properties correlations established in the melt and in the solid state while studying different iPP/EPR pairs.^1–5 Differential scanning calorimetry, (DSC), wide‐angle X‐ray spectroscopy (WAXS), small‐angle X‐ray (SAXS), and scanning electron microscopy (SEM) investigations showed that the EPR_Ti chain is characterized by the presence of long ethylenic sequences with constitutional and configurational regularity required for crystallization of the polyethylene (PE) phase occurring, whereas a microstructure typical of a random ethylene–propylene copolymer was exhibited by the EPR_V copolymer. The different intra‐ and intermolecular homogeneity shown by such EPR phases was found to affect their melt rheological behavior at the temperatures of 200 and 250°C; all the EPR_Ti dynamic–viscoelastic properties resulting were lower than that shown by the EPR_V copolymer. As far as the melt rheological behavior of the iPP/EPR_V and iPP/EPR_Ti blends was concerned, both the iPP/EPR pairs are to be classified as “negative deviation blends” with G′ and G" values higher than that shown by the plain components. The extent of the observed deviation in the viscosity values and of the increase in the amounts of stored and dissipated energy shown by such iPP/EPR pairs was found to be dependent on copolymer microstructure, being larger for the melts containing the EPR_Ti copolymer. The application of the Cross–Bueche equation also confirmed that, in absence of shear, the melt phase viscosity ratio is the main factor in determining the viscosity of iPP/EPR blends and their viscoelastic parameters. The general correlation established between EPR dispersion degree (range of particle size and number‐average particle size), as determined in injection‐molded samples, and melt phase viscosity ratio (μ) was ratified; the type of dependence of EPR size upon μ value was in qualitative agreement with the prediction of the Taylor–Tomotika theory. Contrary to expectation,^1–5 for test temperature close to iPP T_g, EPR_V particles ranging in size between 0.75 and 1.25 μm resulted and were more effective than EPR_Ti particles, ranging in size between 0.25 and 0.75 μm, in promoting multiple craze formation. Also taking into account the SAXS results, revealed that the molecular superstructure (i.e., crystalline lamellar thickness and amorphous interlayer) of the iPP matrix is unaffected by both the presence of EPR_Ti and EPR_V phase. The above finding was related to the ethylenic crystallinity degree shown by the EPR_Ti copolymer. In particular, such a degree of crystallinity was supposed to deteriorate toughening by decreasing the tie molecules density in the EPR_Ti domains, notwithstanding the beneficial effect of the ethylenic lamellar buildup. For test temperature close to room temperature, the ductile behavior exhibited by the iPP/EPR_Ti blends was accounted for by a predominant shear yielding fracture mechanism probably promoted by a high concentration of interlamellar tie molecules among iPP crystallites in agreement with DSC results. Nonisothermal crystallization experiments showed, in fact, that the crystallization peak of the iPP phase from iPP/EPR_Ti melt is shifted to higher temperatures noticeably, thus indicating a material characterized by a comparatively higher number of spherulites per unit value grown at lower apparent undercooling values. Accordingly, WAXS analysis revealed comparatively higher iPP crystal growth in the directions perpendicular to the crystallographic planes (110) and (040) of the iPP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 701–719, 1999     

The architecture of hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE via one‐pot strategy combining living free radical polymerization with coordination polymerization

The copolymerization of styrene with ethylene was promoted by CpTiCl₃/BDGE/Zn/MAO catalyst system combining free radical polymerization with coordination polymerization via sequential monomer addition strategy in one‐pot. The effect of polymerization conditions such as temperature, time, ethylene pressure, and Al/Ti molar ratio on the polymerization performance was investigated. The hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE triblock copolymer was obtained by solvent extraction and determined by GPC, DSC, WAXD, and ¹³C‐NMR. The DSC result indicated that the aPS‐b‐random copolymer‐b‐PE had a T_g at 87°C and a T_m at 119°C which attributed to the T_g of aPS segment and the T_m of PE segment, respectively. The microstructure of the hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE was further confirmed by WAXD, ¹³C‐NMR, and ¹H‐NMR analysis; and these results demonstrated that the obtained block copolymer consisted of aPS segment, S‐E random copolymer segment, and crystalline PE segment. The connection polymerization of the hydroxy‐functionalized aPS with random copolymer‐b‐PE was revealed by GPC results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal behavior and properties of polystyrene/poly(methyl methacrylate) blends

The thermal behavior and properties of immiscible blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with and without PS‐b‐PMMA diblock copolymer at different melt blending times were investigated by use of a differential scanning calorimeter. The weight fraction of PS in the blends ranged from 0.1 to 0.9. From the measured glass transition temperature (T_g) and specific heat increment (ΔC_p) at the T_g, the PMMA appeared to dissolve more in the PS phase than did the PS in the PMMA phase. The addition of a PS‐b‐PMMA diblock copolymer in the PS/PMMA blends slightly promoted the solubility of the PMMA in the PS and increased the interfacial adhesion between PS and PMMA phases during processing. The thermogravimetric analysis (TGA) showed that the presence of the PS‐b‐PMMA diblock copolymer in the PS/PMMA blends afforded protection against thermal degradation and improved their thermal stability. Also, it was found that the PS was more stable against thermal degradation than that of the PMMA over the entire heating range. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 609–620, 2004     

Self‐assembled structures in blends of disordered and lamellar block copolymers: SAXS,SANS and TEM study

BACKGROUND: The phase behaviour of copolymers and their blends is of great interest due to the phase transitions, self‐assembly and formation of ordered structures. Phenomena associated with the microdomain morphology of parent copolymers and phase behaviour in blends of deuterated block copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), i.e. (dPS‐block‐dPMMA)₁/(dPS‐block‐PMMA)₂, were investigated using small‐angle X‐ray scattering, small‐angle neutron scattering and transmission electron microscopy as a function of molecular weight, concentration of added copolymers and temperature. RESULTS: Binary blends of the diblock copolymers having different molecular weights and different original micromorphology (one copolymer was in a disordered state and the others were of lamellar phase) were prepared by a solution‐cast process. The blends were found to be completely miscible on the molecular level at all compositions, if their molecular weight ratio was smaller than about 5. The domain spacing D of the blends can be scaled with M_n by D ～ M_n^2/3 as predicted by a previously published postulate (originally suggested and proved for blends of lamellar polystyrene‐block‐polyisoprene copolymers). CONCLUSIONS: The criterion for forming a single‐domain morphology (molecularly mixed blend) taking into account the different solubilization of copolymer blocks has been applied to explain the changes in microdomain morphology during the self‐assembling process in two copolymer blends. Evidently the criterion, suggested originally for blends of lamellar polystyrene‐block‐polyisoprene copolymers, can be employed to a much broader range of block copolymer blends. Copyright © 2008 Society of Chemical Industry     

Effect of in situ synthesized macroactivator on morphology of PA6/PS blends via successive polymerization

In situ polymerization and in situ compatibilization was adopted for preparation of ternary PA6/PS‐g‐PA6/PS blends by means of successive polymerization of styrene, with TMI and ε‐caprolactam, via free radical copolymerization and anionic ring‐opening polymerization, respectively. Copolymer poly(St‐g‐TMI), the chain of which bears isocyanate (? NCO), acts as a macroactivator to initiate PA6 chain growth from the PS chain and graft copolymer of PS‐g‐PA6 and pure PA6 form, simultaneously. The effect of the macroactivator poly(St‐g‐TMI) on the phase morphology was investigated in detail, using scanning electron microscopy. In case of blends with higher content of PS‐g‐PA6 copolymer, copolymer nanoparticles coexisting with the PS formed the matrix, in which PA6 microspheres were dispersed evenly as minor phase. The content of the compositions (homopolystyrene, homopolyamide 6, and PS‐g‐PA6) of the blends were determined by selective solvent extraction technique. The mechanical properties of PA6/PS‐g‐PA6/PS blends were better than that of PA6/PS blends. Especially for the blends T10 with lower PS‐g‐PA6 copolymer content, both the flexural strength and flexural modulus showed significantly improving because of the improved interfacial adhesion between PS and PA6. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of SBS on phase morphology of iPP/aPS blends

The supermolecular structure of binary isotactic polypropylene/poly(styrene‐b‐butadiene‐h‐styrene) (iPP/SBS) and isotactic polypropylene/atactic polystyrene (iPP/aPS) compression molded blends and that of ternary iPP/aPS/SBS blends were studied by optical microscopy, scanning and transmission electron microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry. Nucleation, crystal growth, solidification and blend phase morphology are affected by the addition of amorphous components (SBS and aPS). As a compatiblizer in immiscible iPP/aPS blends, SBS formed interfacial layer between dispersed honeycomb‐like aPS/SBS particles and the iPP matrix, thus influencing the crystallization process in iPP. The amount of SBS and aPS, and compatibilizing efficiency of SBS, determine the size of dispersed aPS, SBS, and aPS/SBS particles and, consequently, the final blend phase morphologies: well‐developed spherulitic morphology, cross‐hatched structure with blocks of sandwich lamellae and co‐continuous morphology. The analysis of the relationship between the size of spherulites and dispersed particles gave the criterion relation, which showed that, in the case of a well‐developed spherulitization, the spherulites should be about fourteen times larger than the incorporated dispersed particles; i.e. to be large enough to engulf dispersed inclusions without considerable disturbing of the spherulitic structure.     

The effect of propylene–ethylene copolymers with different comonomer content on melting and crystallization behavior of polypropylene

The effect of propylene–ethylene copolymers (PEc) with different ethylene‐unit contents on melting and crystallization behaviors of isotactic‐polypropylene (iPP) were investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The results show that the addition of PEc decreases significantly crystallization temperature (T_c) of iPP, but slightly affects melting temperature (T_m). With increasing the ethylene‐unit content of the propylene–ethylene copolymers, the decrease in crystallization temperature of iPP is smaller. The PLM results show that the spherulite growth rate decreases with increasing crystallization temperature for iPP and iPP/PEc blends. The higher the ethylene‐unit content of the copolymers is, the lower the spherulite growth rate (G) of iPP/PEc blends is. The influence of the PEc on nucleation rate constant (K_g) and fold surface energy (σ_e) of iPP was examined by nucleation theory of Hoffman and Lauritzen. The results show that both K_g and σ_e of iPP/PE20(80/20) and iPP/PE23(80/20) blends are higher than those of iPP, demonstrating that the overall crystallization rate of iPP/PEc blends decreased as compared to that of iPP, resulting from the decrease of the nucleation rate and the spherulite growth rate of iPP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Compatibilizing effects of poly(styrene-graft-ethylene oxide) in blends of polystyrene and butyl acrylate polymers

The compatibilizing effect of poly(styrene-graft-ethylene oxide) in polystyrene (PS) blends with poly(n-butyl acrylate) (PBA) and poly(n-butyl acrylate-co-acrylic acid) (PBAAA) was investigated. No significant effects of the graft copolymer on the domain size were found in the PBA blends. By functionalizing PBA with acrylic acid, the average size of the polyacrylate domains was reduced considerably by the graft copolymer. Thermal and dynamic mechanical analysis of the PS/PBAAA blends revealed that the PBAAA glass transition temperature (T_g) decreased with increasing graft copolymer content. The effect of the graft copolymer in the PS/PBAAA blends can be explained by interactions across the interface due to the formation of hydrogen bonds between the poly(ethylene oxide) (PEO) side chains in the graft copolymer and the acrylic acid segments in the PBAAA phase. Hydrogen bonding was confirmed by IR analysis of binary blends of PEO and PBAAA. Partial miscibility in the PEO/PBAAA blends was indicated by a PEO melting point depression and by a T_g reduction of the PBAAA phase. The thermal properties of the PEO/PBA blends indicated only very limited miscibility. © 1996 John Wiley & Sons, Inc.     

Glass transition behavior of polypropylene/polystyrene/styrene-ethylene-propylene block copolymer blends

Summary The glass transition behavior of ternary blends of polypropylene (PP), polystyrene (PS) and styrene-ethylene-propylene-styrene block copolymer (SEPS) was investigated. The blends were prepared by an internal mixer, and their dynamic mechanical properties and morphology were measured. The blends showed phase inversion at around 75wt% PS composition. The glass transition temperature (T_g) of the PP phase shifted to lower temperature as the PS contents were increased in PP/PS binary blends, probably due to the mismatch of thermal expansion coefficients between two components. As the SEPS copolymer contents were increased, the T_g's of the PP phase in the blends increased. In particular, the large increase in T_g of the PP phase was observed in the PP/PS (25/75) blends where the phase inversion takes place. Received: 2 February 1998/Revised version: 24 March 1998/Accepted: 13 April 1998     

Polymer blends of poly(ethylene‐2,6‐naphthalate) with polystyrene compatibilized by styrene‐glycidyl methacrylate copolymers. I. Rheology,morphology, and mechanical properties

The compatibilization of blends of poly(ethylene‐2,6‐naphthalate) (PEN) with polystyrene (PS), through the styrene‐glycidyl methacrylate copolymers (SG) containing various glycidyl methacrylate (GMA) contents, was investigated in this study. SG copolymers are able to react with PEN terminal groups during melt blending, resulting in the formation of desirable SG‐g‐PEN copolymers in the blend. These in situ formed copolymers tend to reside along the interface preferentially as the result of interfacial reaction and thus function as effective compatibilizers in PEN/PS blends. The compatibilized blends exhibit higher viscosity, finer phase domain, and improved mechanical properties. It is found that the degree of grafting of the in situ formed SG‐g‐PEN copolymer has to be considered as well. In blends compatibilized with the SG copolymer containing higher GMA content, heavily grafted copolymers would be produced. The length of the styrene segment in these heavily grafted copolymers would be too short to penetrate deep enough into the PS phase to form effective entanglements, resulting in the lower compatibilization efficiency in PEN/PS blends. Consequently, the in situ formation of SG‐g‐PEN copolymers with an optimal degree of grafting is the key to achieving the best performance for the eventually produced PEN/PS blends through SG copolymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 967–975, 2003     

Effect of additives on the composition dependent glass transition variation in PS/PP blends

The effect of additives on glass transition behavior in melt processed blends of polystyrene (PS) and polypropylene (PP) was studied. Blends of additive‐free polystyrene and additive‐free polypropylene revealed the known effect of the PS T_g increase in blend compositions where PP surrounds PS. Glass transition behavior in these blends was compared to blends prepared from additive‐free PP and commercial grade PS, which contained lubricant additives. The thermal transitions of PS and PP were measured using modulated DSC. Although the behavior of low PS concentration blends was similar in both systems, the characteristics of the high PS blends differed substantially. These differences and the contrast in the PP T_g behaviors were attributed to the migration of additives from the PS phase across the immiscible interface into the PP phase. Similar T_g variations were observed in blends of commercial grade PS and commercial grade PP. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of confinement on glass dynamics and free volume in immiscible polystyrene/high‐density polyethylene blends

The effect of confinement on glass dynamics combined with the corresponding free volume changes of amorphous polystyrene (PS) in blends with semi‐crystalline high‐density polyethylene (HDPE) have been investigated using thermal analyses and positron annihilation lifetime spectroscopy (PALS). Two different glass transition temperatures (T_g) were observed in a PS/HDPE blend due to the dissimilarity in the chemical structure, consistent with an immiscible blend. However, T_g of PS in the incompatible PS/HDPE blend showed an upward trend with increasing PS content resulting from the confinement effect, while T_g of the semi‐crystalline HDPE component became lower than that of neat HDPE. Moreover, the elevation of T_g of PS was enhanced with a decrease of free volume radius by comparing annealed and unannealed PS/HDPE blends. Positron results showed that the free volume radius clearly decreased with annealing for all compositions, although the free volume hole size agreed well with linear additivity, indicating that there was only a weak interaction between the two components. Combining PALS with thermal analysis results, the confinement effect on the glass dynamics and free volume of PS phase in PS/HDPE blends could be attributed to the shrinkage of HDPE during crystallization when HDPE acted as the continuous phase. © 2015 Society of Chemical Industry     

Synthesis of PS‐g‐POSS hybrid graft copolymer by click coupling via ”graft onto” strategy

Polystyrene (PS)‐incorporated polyhedral oligomeric silsesquioxanes (POSS) organic–inorganic hybrid graft copolymer could be achieved by click coupling reaction between alkyne groups in POSS and azido groups in PS via “graft onto” strategy. Alkyne‐functionalized POSS was synthesized via thiol‐ene facile click reaction and subsequent amidation reaction with very high yield. Azido‐multifunctionalized PS could be synthesized by chloromethylation and subsequent azido reaction. The chemical structures of PS‐(CH₂Cl)_m, PS‐(CH₂N₃)_m, and PS‐g‐POSS were determined by Fourier transform infrared and ¹H NMR characterization. PS‐g‐POSS presented a better hydrophobic property with contact angle of 113° than that of PS (85°). And PS‐g‐POSS with ≤5% of grafting degree had lower glass transition temperature (T_g) than that of PS and then it increased up to 112°C with grafting degree. An obvious aggregation of POSS phase with 10–80 nm in size was formed in PS‐g‐POSS matrix. In addition, 5 wt % of PS‐g‐POSS was added to general purpose polystyrene (GPPS) to remarkably improve its tensile strength from 45 to 57 MPa. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Microstructural characteristics of glass bead‐ and wollastonite‐filled isotactic‐polypropylene composites modified with thermoplastic elastomers

Microstructural characteristics of isotactic‐polypropylene/glass bead (iPP/GB) and iPP/wollastonite (iPP/W) composites modified with thermoplastic elastomers, poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) copolymer (SEBS) and corresponding block copolymer grafted with maleic anhydride (SEBS‐g‐MA), were investigated. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analyses (DMA) showed that the iPP/SEBS and iPP/SEBS‐g‐MA blends were partially compatible two‐phase systems. Well‐dispersed spherical GB and acicular W particles without evidence of interfacial adhesion were observed in the iPP/GB and iPP/W binary composites respectively. Contrary to the blends, melt flow rates of the iPP/GB and PP/W composites decreased more with SEBS‐g‐MA than with SEBS because of enhanced interfacial adhesion with SEBS‐g‐MA elastomer. The SEM analyses showed that the ternary composites containing SEBS exhibited separate dispersion of the rigid filler and elastomer particles (i.e., separate microstructure). However, SEBS‐g‐MA elastomer not only encapsulated the spherical GB and acicular W particles completely with strong interfacial adhesion (i.e., core‐shell microstructure) but also dispersed separately throughout iPP matrix. In accordance with the SEM observations, the DSC and DMA revealed quantitatively that the rigid filler and SEBS particles in iPP matrix acted individually, whereas the rigid filler particles in the ternary composites containing SEBS‐g‐MA acted like elastomer particles because of the thick elastomer interlayer around the filler particles. The Fourier transform infrared analyses revealed an esterification reaction inducing the strong interfacial adhesion between the SEBS‐g‐MA phase and the filler particles. POLYM. COMPOS., 31:1265–1284, 2010. © 2009 Society of Plastics Engineers     

Compatibility study in poly(tetramethyleneadipate‐co‐terephthalate)/polystyrene bioblends

Bioblends of the biodegradable copolyester poly(tetramethyleneadipate‐co‐terephthalate) (EBU) and polystyrene (PS) were prepared in different weight compositions on a twin‐screw extruder at 160–200°C. The various bioblend compositions were then investigated using thermogravimetric analysis (TGA), modulated differential scanning calorimetry (MDSC), and Fourier transform infrared photoacoustic spectroscopy (FTIR‐PAS). TGA studies showed that 25/75 and 50/50 EBU/PS blends had higher thermal stability than the more thermally stable blend component, PS. The MDSC studies showed a single T_g and single T_m for the blends, that were concentration independent. The FTIR‐PAS studies indicated a small shift (4–8 cm^?1) in the carbonyl absorption peaks of EBU to lower wavenumbers in 50/50 EBU/PS blend relative to that of neat EBU. It is concluded that, while the MDSC results were inconclusive, the TGA and FTIR‐PAS results support the existence of some degree of intermolecular interaction between EBU and PS components and, hence, partial compatibility in EBU/PS blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polyamide 6 toughened by maleated polystyrene‐based copolymers: Mechanical properties,morphology, and rheology

Poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polyamide 6 (PPO/PA6 30/70) blends were impact modified by addition of three kinds of maleated polystyrene‐based copolymers, i.e., maleated styrene‐ethylene‐butylene‐styrene copolymer (SEBS‐g‐MA), maleated methyl methacrylate‐butadiene‐styrene copolymer (MBS‐g‐MA), and maleated acrylonitrile‐butadiene‐styrene copolymer (ABS‐g‐MA). The mechanical properties, morphology and rheological behavior of the impact modified PPO/PA6 blends were investigated. The selective location of the maleated copolymers in one phase or at interface accounted for the different toughening effects of the maleated copolymer, which is closely related to their molecular structure and composition. SEBS‐g‐MA was uniformly dispersed in PPO phase and greatly toughened PPO/PA6 blends even at low temperature. MBS‐g‐MA particles were mainly dispersed in the PA6 phase and around the PPO phase, resulting in a significant enhancement of the notched Izod impact strength of PPO/PA6 blends from 45 J/m to 281 J/m at the MBS‐g‐MA content of 20 phr. In comparison, the ABS‐g‐MA was mainly dispersed in PA6 phase without much influencing the original mechanical properties of the PPO/PA6 blend. The different molecule structure and selective location of the maleated copolymers in the blends were reflected by the change of rheological behavior as well. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010