The effect of ionic cross-links on the deformation behavior of homoblends made of poly(styrene-co-styrenesulfonic acid) and poly(styrene-co-4-vinylpyridine)

Deformation behavior of stoichiometric blends made from poly(styrene-co-styrenesulfonic acid) (SPS) and poly(styrene-co-4-vinylpyridine) (SVP) was investigated by TEM observation of strained thin films. An FTIR investigation revealed that ionic cross-links were formed between the component polymers upon blending due to intermolecular ion-ion interactions, which arose from proton transfer from sulfonic acid groups to pyridine groups. TEM observations indicate that the deformation mode of the blends changed from crazing only to crazing plus shear deformation, with the shear contribution becoming larger, as the ion content in the blends increased. Such changes in deformation mode can be understood as arising from an increase in the ‘effective’ strand density due to the formation of ionic cross-links upon blending. It was also found that the ionic cross-links via pyridinium cation/sulfonate anion ion pairs were more effective in inducing the transition of deformation mode than ionic cross-links via -SO₃⁻/Na⁺ or -SO₃⁻/Ca²⁺ ion pairs.     

Morphology and deformation behavior of polymer blends made of poly(styrene-co-styrenesulfonic acid) and poly(methyl methacrylate-co-4-vinylpyridine)

The effect of a small amount of ionic groups (interactions) on the morphology and deformation behavior of stoichiometric blends made of poly(styrene-co-styrenesulfonic acid) (SPS) and poly(methyl methacrylate-co-4-vinylpyridine) (MVP) was investigated by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). FTIR data revealed that intermolecular ion-ion interactions were formed between SPS and MVP polymers, arising from proton transfer from sulfonic acid groups to pyridine groups upon blending. TEM observations show that the morphology of the blends changes from macroscopic phase separation to microscopic phase separation, and to miscibility, with increasing ion content of the blends from 0 to 6 mol%. Correspondingly, deformation behavior of the blends changes from crazing only, to curved and branched crazing, and to crazing plus shear deformation. Such changes in deformation mode can be understood as arising from the morphological changes and the increase of ‘effective’ strand density due to the formation of ionic cross-links in the blends.     

The compatibilizing effect of poly(styrene-co-4-vinylpyridine) copolymers on the polystyrene–polyethylene-based ionomer blends

The compatibilizing effect of styrene-co-4-vinylpyridine (SVP) random copolymers on the immiscible polystyrene (PS)–polyethylene-based ionomer (Surlyn) blends was examined by means of scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and tensile test. For the binary SVP–Surlyn and ternary PS–Surlyn–SVP blends, the domain size of dispersed phase decreases dramatically with the increase in the vinyl pyridine (VP) content of the SVP copolymers. The mechanical properties are improved with increasing the VP content in copolymers. FTIR results suggest that the compatibilization in this blend system is attributed to the ion–dipole interaction between the polar VP groups of SVP copolymer and ionic groups of Surlyn. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 807–816, 1998     

The study of poly(styrene-co-p-(hexafluoro-2-hydroxylisopropyl)-α-methyl-styrene)/poly(propylene carbonate) blends by ESR spin probe and Raman

Different hydroxyl content poly(styrene-co-p-(hexafluoro-2-hydroxyisopropyl)-α-methylstyene) [PS(OH)] copolymers were synthesized and blends [noted for PP-X] with poly(propylene carbonate) [PPC] were prepared by casting from chloroform solution. The miscibility, micro heterogeneity and hydrogen bonding interaction of the component polymers were investigated by Differential Scanning Calorimetry (DSC), Electron Spin Resonance (ESR) spin probe method and Micro Raman spectroscopy. DSC results showed that the PP-2, PP-5, PP-8, PP-12 blends exhibited two distinct T_gs, indicating immiscibility, while the PP-20 and PP-27 blends were miscible with the existence of a single T_g. ESR results indicated that the probe molecule: Tempo couldn't give clear micro phase separation or miscibility information and thus was not sensitive to the investigated polymer blends system. On the contrary for all the blends spin probed with the probe molecules: Tempol and Tamine, two spectral components with different rates of motion: ‘fast’ and ‘slow’ motion were observed in different temperature range, which indicated the existence of micro heterogeneity on the molecular level; the more mobile PPC-rich micro phase and the more rigid PS(OH) rich micro phase. In addition, the scale of miscibility was progressively enhanced due to the increasing hydrogen bonding interaction between the hydroxyl in PS(OH) and the oxygen atoms in PPC. Meanwhile it was found that the degree of the probe molecule rotation detectable in the ESR spectrum was dependent on the polymer matrix rigidity and the strength of the hydrogen bonding between the probe molecule and the polymer matrix. Micro Raman substantiated the existence of the PS(OH)-rich micro phase and the PPC-rich micro phase. The hydrogen bonding strength between PS(OH) and PPC and the mixing level of the component polymers were increased gradually with the increase of hydroxyl content in the PS(OH) copolymer.     

Structure and property studies of bioabsorbable poly(glycolide-co-lactide) fiber during processing and in vitro degradation

Structure and properties of a bioabsorbable poly(glycolide-co-lactide) (PGA-co-PLA) fiber during several processing stages and the final in vitro degradation stage were investigated by means of wide-angle X-ray diffraction, dynamic mechanical analysis and mechanical property tests. In the orientation stage, an increase in the temperature of the first encountered orientation roll resulted in a lower level of crystallinity and larger crystallites. The temperature of the second encountered pre-annealing roll (PR) imposed a smaller effect on the structure. In the hot-stretching stage after fibers were braided, the maximum crystallinity was achieved at around 126 °C. Higher hot-stretching temperatures increased the crystal size, glass transition temperature (T_g) and tensile strength, but decreased the elongation at break and the heat shrinkage near T_g. In the post-annealing stage, it was found that crystallinity, T_g and tensile strength all increased significantly while the heat shrinkage near T_g sharply decreased after annealing. This suggests that the internal stress accumulated in the orientation and hot-stretching stages can be effectively reduced by post-annealing. During in vitro degradation, crystallinity was found to increase with time while the heat shrinkage near T_g and in the supercooling region (T_g<T<T_m) was greatly reduced. These results support the process of cleavage-induced crystallization.     

Surface quantitative characterization of poly(styrene-co-4-vinyl phenol)/poly(styrene-co-4-vinyl pyridine) blends with controlled hydrogen bonding interactions

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to quantitatively correlate to the surface chemical composition determined from XPS in poly(styrene-co-4-vinyl phenol) (STVPh)/poly(styrene-co-4-vinyl pyridine) (STVPy) blends or complexes when the hydroxyl contents in STVPh copolymers were gradually increased. It was found that different mixing thermodynamics such as immiscibility, miscibility and complexation has little effect on the quantitative analysis of surface concentrations in the blends or complexes using ToF-SIMS. In the positive spectra, the normalized intensities or relative peak intensities can both be used to quantitatively analyze the surface vinyl phenol (VPh), styrene and vinyl pyridine (VPy) concentrations when peaks at m/z=119, 120 are used for VPh, peaks at m/z=103, 105, 115 for styrene and peaks at m/z=80, 93, 106 for VPy monomer units. In the negative spectra, the normalized intensities of peaks characteristic of VPh monomer units (m/z=16, 17, 93) seems to be not affected by hydrogen bonding formation and can be used in quantitative analysis.     

Miscibility and specific interactions in blends of poly(4-vinylphenol-co-methyl methacrylate)/poly(styrene-co-4-vinylpyridine)

The miscibility and phase behavior of poly(4-vinylphenol-co-methyl methacrylate) (PVPhMMA50) containing 50% of methyl methacrylate with random copolymers of poly(styrene-co-4-vinylpyridine) (PS4VPy) containing 5, 15, 30, 40, and 100% of 4-vinylpyridine, respectively, were investigated by differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). It was shown that for a composition of 4-vinylpyridine less than 30%, all blends of PVPhMMA50/PS4VPy are immiscible, characterized by the apparition of two glass transitions (T_g) over their entire composition range. However, above this composition, a single T_g has been observed in all the blends of PVPhMMA50 and PS4VPy. When the amount of vinylpyridine exceeds to 40% in PS4VPy, the obtained T_gs of PVPhMMA50/PS4VPy blends were found to be significantly higher than those observed for each individual component of the mixture indicating that these blends are able to form interpolymer complexes. FTIR analysis reveals the existence of preferential specific interactions via hydrogen bonding between the hydroxyl and pyridyl groups and intensifies when the amount of 4VPy is increased in PS4VPy copolymers. Furthermore, the quantitative FTIR study carried out for PVPhMMA50/PS4VPy blends was also performed for the vinylphenol and vinylpyridine functional groups. These results were also confirmed by SEM study. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Miscibility and esterification in the poly(styrene-co-maleic anhydride)/phenoxy blends

The “miscibility” and esterification in poly(styrene-co-maleic anhydride) (PSTMA)/phenoxy blends were investigated by DSC and FTIR. The blends prepared by casting exhibited a single composition-dependent but broad T_g during the first scanning. The broadness of the T_g transition range is due to the presence of microphases in the blends, which acquired some stability because of the hydrogen-bonding interactions with the continuous phase. However, the blends displayed two distinct T_gs during the second scanning, which can be attributed to phenoxy-rich and PSTMA-rich phases dispersed one in another at a scale larger than the initial one. To investigate the effect of esterification, the samples subjected previously to two scannings have been additionally heat-treated several times between 30 and 220°C and annealed each time at 220°C for increasing periods of time. During the additional scannings, the two T_gs identified during the second scanning increased with increasing annealing time but remained distinct. The fact that the fraction soluble in tetrahydrofuran decreased with increasing annealing time indicates that crosslinking due to esterification has occurred in both phases. The two phases generated after the first scanning were stabilized by the esterification reaction at the interfaces. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:913–919, 1998     

Dynamic mechanical properties of annealed sulfonated poly(styrene-b-[ethylene/butylene]-b-styrene) block copolymers

Solution cast films of lightly sulfonated styrene-b-[ethylene-co-butylene]-b-styrene, (sSEBS) block copolymers were annealed for various times at 120 °C and thermal transitions are evaluated using dynamic mechanical analysis. Increased annealing time and increase in degree of sulfonation increases T_g for the PS phase while T_g for the EB phase is practically unchanged, and in some cases, there is suggestion of a relaxation due to EB-PS inter-phases. Annealing has a minor effect on the rubbery plateau storage modulus. Thus, annealing primarily alters the PS block phase. EB-PS phase separation appears to be refined with increasing SO₃H content. The region of rubber elasticity extends to higher temperatures with increased degree of sulfonation. A high temperature dynamic mechanical transition that is tentatively attributed to disruption of SO₃H—rich sub-domains within the PS block domains shifts to higher temperature with annealing.     

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.     

Reactive melt blends of nylon with poly(styrene-co-maleic anhydride)

Melt blends of nylon with poly(styrene-co-maleic anhydride) (SMA) were prepared in a twin-screw extruder. Viscoelastic properties of the melt and morphological, thermal, and mechanical properties of the blends were determined. Fourier-transform infrared (FTIR) spectroscopy measurement indicated reactions between nylon and SMA. Melting peak temperature (T_m) of nylon was not changed in blends. This, together with the FTIR results, assured that the reactions occur mainly with the free amide end groups of nylon. Melt viscosity, elasticity, and the heat-distortion temperature (HDT) of nylon was significantly increased with the addition of SMA. Tensile strength and impact strength of nylon were, respectively, in general, increased and decreased with SMA.     

Disruption of the multiplets in poly(styrene-co-methacrylate) ionomers by the addition of aliphatic diacid salts

Dynamic mechanical properties and morphology of poly(styrene-co-sodium methacrylate) ionomers containing disodium salts of aliphatic diacid were investigated. It was found that upon the addition of diacid salts to the ionomers, the position of the matrix loss tangent peak remained constant, but the cluster loss tangent peak shifted to lower temperatures; the size of the matrix loss tangent peak increased, but that of the cluster peak decreased. In addition, the ionomers containing diacid salts showed X-ray diffraction patterns at relatively wide angles but no DSC melting peak. Thus, it was postulated that the organic salts prohibit the ionic groups of the ionomer from forming multiplets, and that the ionic groups of the ionomer, not forming the multiplets, participate in the formation of ionic aggregates with the ionic groups of the diacid salts.     

Miscibility and mechanical properties of poly(styrene-co-4-vinylpyridine) and poly(butyl acrylate-co-acrylic acid) ionomer blends

The miscibility of polystyrene with poly(butyl acrylate) is very poor. Ionic interactions have been utilized recently as miscibility enhancers. In this paper, dynamic mechanical studies indicate that ion pair–ion pair interactions can be utilized to achieve miscibility in blends of polystyrene and poly(butyl acrylate). The styrenes contain 0–15mol% quaternary ammonium salt of 4-vinylpyridine, while the butyl acrylates contain 0–15mol% potassium acrylate groups. The miscibility increases with increase of ion content. When the ion content exceeds 11mol%, the polymers can be completely miscible. The mechanical properties of the ionomers and their blends were also studied. The results indicate that the tensile strength of ionomer blends is higher than that of corresponding poly(butyl acrylate-co-potassium acrylate)s (PBA-AA-K). The elongation at break of ionomer blends is higher than that of the corresponding poly(styrene-co-N-methyl-4-vinylpyridinium iodide) (PS-4VP-Q). © 1998 SCI.     

Poly(para‐dioxanone)/poly(D,L‐lactide) blends compatibilized with poly(D,L‐lactide‐co‐para‐dioxanone)

The effect of poly(D ,L ‐lactide‐co‐para‐dioxanone) (PLADO) as the compatibilizer on the properties of the blend of poly(para‐dioxanone) (PPDO) and poly(D ,L ‐lactide) (PDLLA) has been investigated. The 80/20 PPDO/PDLLA blends containing from 1% to 10% of random copolymer PLADO were prepared by solution coprecipitation. The PLADO component played a very important role in determining morphology, thermal, mechanical, and hydrophilic properties of the blends. Addition of PLADO into the blends could enhance the compatibility between dispersed PDLLA phase and PPDO matrix; the boundary between the two phases became unclear and even the smallest holes were not detected. On the other hand, the position of the T_g was composition dependent; when 5% PLADO was added into blend, the T_g distance between PPDO and PDLLA was shortened. The blends with various contents of compatibilizer had better mechanical properties compared with simple PPDO/PDLLA binary polymer blend, and such characteristics further improved as adding 5% random copolymers. The maximum observed tensile strength was 29.05 MPa for the compatibilized PPDO/PDLLA blend with 5% PLADO, whereas tensile strength of the uncompatibilized PPDO/PDLLA blend was 14.03 MPa, which was the lowest tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Investigation on the early and late stage phase-separation dynamics of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) blends through rheological and scattering functions

The phase-separation behavior of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) (PMMA/α-MSAN) blends with two different compositions was studied by time-resolved small angle light scattering (SALS) in the spinodal decomposition (SD) regime from 160 to 210 °C. The rheological function (WLF-like equation) was introduced into the processing of light scattering data. It was found that the WLF-like equation was applicable to describe the temperature dependence of apparent diffusion coefficient D_app and the relaxation time τ of normalized scattering intensity (I(t)−I(0))/(I_m−I(0)) at the early stage of SD, as well as the relaxation time τ of maximum scattering intensity I_m and characteristic scattering vector q_m with I_m at the late stage of SD for PMMA/α-MSAN blends with two different compositions. This is in consistence with the phase-separation behavior of PMMA/SAN reported in our previous paper.     

Compatibility of poly(butadiene‐co‐acrylonitrile) with poly(L‐lactide) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

Poly(L ‐lactide) (PLLA) and poly(3‐hydrobutyrate‐co‐3‐hydroxyvalerate) (PHBV) were blended with poly(butadiene‐co‐acrylonitrile) (NBR). Both PLLA/NBR and PHBV/NBR blends exhibited higher tensile properties as the content of acrylonitrile unit (AN) of NBR increased from 22 to 50 wt %. However, two separate glass transition temperatures (T_g) appeared in PLLA/NBR blends irrespective of the content of NBR, revealing that PLLA was incompatible with NBR. In contrast, a single T_g, which shifted along with the blend composition, was observed for PHBV/NBR50 blends. Moreover NBR50 suppressed the crystallization of PHBV, indicating that PHBV was compatible with NBR50. Decrease of both elongation modulus and stress at maximum load was less significant and increase of elongation at break was more pronounced in PHBV/NBR50 blends than in PLLA/NBR50 blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3508–3513, 2004     

Poly[(styrene-co-p-methylstyrene)-b-isobutylene-b-(styrene-co-p-methylstyrene)] triblock copolymers. 1. Synthesis and characterization

The synthesis of poly(isobutylene) (PIB)-based triblock copolymers having copolymer end blocks containing styrene and p-methylstyrene (pMSt) repeat units was investigated in an attempt to minimize chain-coupling reactions that occur at the 4-position on styrene repeat units during end block polymerization. Model end block copolymerizations using varying feed ratios of styrene and pMSt were conducted, and it was determined by ¹H NMR analysis that the addition of pMSt to the living chain end was favored slightly at low conversion. However, DSC revealed a single T_g that increased with increasing pMSt content verifying the absence of blockiness in the microstructure. Poly[(styrene-co-pMSt)-b-isobutylene-b-(styrene-co-pMSt)] triblock copolymers were synthesized using varying feed ratios of styrene and pMSt. The rate of end block propagation increased with increasing pMSt in the feed, and the end block copolymerizations initiated by PIB displayed longer reaction times and more curvature in their first order plots than did the model end block copolymerizations initiated by TMPCl. This effect was attributed to lower ionization equilibrium constant and higher degree of termination caused by the more non-polar local reaction medium provided by the PIB center blocks in block copolymerization. GPC analysis of the final BCPs revealed a decrease in a high molecular weight peak representing the chain-coupled product as the concentration of pMSt in the feed was increased.     

Miscibility of copolycarbonate blends with poly(styrene-co-acrylonitrile) copolymer and their interaction energies

The phase behavior of dimethyl polycarbonate-tetramethyl polycarbonate (DMPC-TMPC) blends with poly(styrene-co-acrylonitrile) copolymers (SAN) and the interaction energies of binary pairs involved in blend has been explored. DMPC-TMPC copolycarbonates containing 60 wt% TMPC or more were formed miscible blends with SAN containing limited amounts of AN. The miscibility of copolycarbonate with SAN decreases as the DMPC content increases. The miscible blends showed the LCST-type phase behavior or did not phase separate until thermal degradation. The binary interaction energies involved in the miscible blends were calculated from the phase boundaries using the lattice-fluid theory combined with binary interaction model. The phenyl ring substitution with methyl groups did not lead to interactions that are favorable for miscibility with polyacrylonitrile (PAN). The interaction energies of the polycarbonates blends with SAN copolymers as a function of AN content were obtained. It was revealed that the incline of the number of methyl groups on the phenyl rings of bisphenol-A unit acts favorably for the miscibility with SAN copolymer when SAN contains less than about 30 wt% AN and shifts the most favorable interaction to the low AN content.     

Uniaxial orientation and tensile properties of poly(ethylene terephthalate)/poly(ethylene-2,6-naphthalate) blends

Amorphous films of poly(ethylene terephthalate)/poly(ethylene-2,6-naphthalate) (PET/PEN) blends with different blend ratios were uniaxially drawn by solid-state coextrusion and the structure development during solid state deformation was studied. As-prepared blends showed two T_gs. The lower T_g was ∼72 °C, independent of the blend ratio. In contrast, the higher T_g increased with increasing PEN content. Thus, the coextrusion was carried out around the higher T_g of the sample. At a given draw ratio of 5, which was close to the achievable maximum draw ratio, the tensile strength of the drawn samples from the initially amorphous state increased gradually with increasing PEN content. On the other hand, the tensile modulus was found to decrease initially, reaching a minimum at 40-60 wt% PEN, and then increased as the PEN content increased. The results indicate that we can get the drawn films with a moderate tensile modulus and a high tensile strength. The drawn samples from the blends containing 40-60 wt% of PEN showed a maximum elongation at break, and a maximum thermal shrinkage around 100 °C. Also, the degree of stress-induced crystallinity showed a broad minimum around the blend ratio of 50% of PEN. These morphological characteristics explained well the effects of blend ratio on the tensile modulus and strength of drawn PET/PEN blend films.     

Effect of dehydrochlorination of PVC on miscibility and phase separation of binary and ternary blends of poly(vinyl chloride), poly(ethylene-co-vinyl acetate) and poly(styrene-co-acrylonitrile)

The enhancement of miscibility at the lower critical solution temperature (LCST) of the blends poly(vinyl chloride)/poly(ethylene-co-vinyl acetate) (PVC/EVA), poly(vinyl chloride)/poly(styrene-co-acrylonitrile) (PVC/SAN) and poly(vinyl chloride)/poly(ethylene-co-vinyl acetate)/poly(styrene-co-acrylonitrile) (PVC/EVA/SAN) was observed at the micron level. Such miscibility is attributed to the dehydrochlorination and formation of hydrogen bonds between blend components. However, macrolevel immiscibility of these blends heated to the LCST was observed. Such microdomain compatibility of these blends gives a synergistic character. Brittle-type failure observed for LCST samples testifies to the synergism in treated blends. ©1997 SCI