Fluorescence densitometry at polymer-polymer interfaces: interdiffusion in polystyrene-poly(cyclohexyl methacrylate) blends

An experimental set-up is described to determine the concentration profile of a polymer labelled with a fluorescent dye at the interface with a compatible unlabelled polymer. This method is applied to a study of interdiffusion in blends of labelled polystyrene with poly(cyclohexyl methacrylate) and compared with tracer diffusion of labelled polystyrene in the same system.     

Craze microstructure and molecular entanglements in polystyrene-poly(phenylene oxide) blends

Polystyrene and poly(phenylene oxide) are miscible over the entire range of compositions. Thin films of five blends of high molecular weight polystyrene (PS) with high molecular weight poly(phenylene oxide) (PPO), and four blends of low molecular weight PS (whose molecular weight lies below its entanglement molecular weight M_e) with the same PPO have been prepared. Following bonding of these films to copper grids, crazes were grown by uniaxial straining in air. Suitable crazes were then observed by transmission electron microscopy. From microdensitometry of the image plates it is possible to measure the extension ratio λ_craze within crazes in the nine blends. These measured values are compared with predicted values of λ_max, computed from λ_max = I_ed, where I_e is the chain contour length between entanglements and d is the root mean square end-to-end distance for a chain of molecular weight M_e. For the high molecular weight PS blends λ_max depends on the entanglement properties of both PS and PPO chains. For the low molecular weight PS blends, the PS chains cannot form part of the entanglement network and the correct value of λ_max is obtained from appropriate scaling of the pure PPO value. Comparison of λ_craze and λ_max for both types of blends shows excellent agreement, demonstrating the importance of the entanglement network in determining craze parameters and hence the toughness of a given polymer.     

A preliminary study of the dynamics of phase separation in oligomeric polystyrene-polybutadiene blends

We report here the preliminary results of a study of the kinetics of spinodal decomposition in an oligomeric blend, polystyrene with polybutadiene using small angle light scattering. The data are compared with the theoretical predictions of Cahn-Hilliard and van-Aartsen. The results corroborate the position of the critical point as determined by the pulse induced critical scattering technique.     

Kinetics of phase separation of poly(styrene‐co‐methyl methacrylate) and poly(styrene‐co‐acrylonitrile) blends

The phase behavior and kinetics of phase separation for blends of the random copolymer poly(styrene‐co‐methyl methacrylate) (SMMA) and poly(styrene‐co‐acrylonitrile) (SAN) were studied by using small‐angle laser light scattering. The partially miscible SMMA/SAN blends undergo spinodal decomposition (SD) and subsequent domain coarsening when quenched inside the unstable region. For blends of SMMA and SAN, the early stages of the phase separation process could be observed, unlike a number of other blends where the earliest stages are not visible by light scattering. The process was described in terms of the Cahn–Hilliard linear theory. Subsequently, a coarsening process was detected and the time evolution of q_m at the beginning of the late stages of phase separation followed the relationship q_m∝t^?1/3, corresponding to an evaporation–condensation mechanism. Self‐similar growth of the phase‐separated structures at different timescales was observed for the late stage. Copyright © 2004 Society of Chemical Industry     

Phase separation in polymer blends comprising copolymers: 5. Polyisoprene/poly(isoprene-g-styrene) copolymer system

As part of a programme of research into miscibility in polymer blends comprising copolymers, this paper presents the morphology of blends of polyisoprene and poly(isoprene-g-styrene) with complicated but well defined structure. The graft copolymers were prepared by polymerization of styrene initiated by metallated polyisoprene backbone and were fully characterized. All the studied blends of copolymers and polyisoprene of different molecular weights exhibit macrophase separation even when the molecular weight of the homo PI is apparently less than that of the PI segments between neighbourning junction points in the copolymers. The results provide support for the argument that the molecular architecture of a copolymer is an important factor governing its miscibility with corresponding homopolymers. Besides, it is observed that the copolymer with higher proportion of polystyrene shows apparent solubilization in polystyrene matrix of high molecular weight and solubilization varies predictably with the addition of low molecular weight polyisoprene.     

Photocrosslinking kinetics of polymer blends undergoing spinodal decomposition process

Photocrosslinking reaction kinetics of poly(2-chlorostyrene) performed inside the spinodal region of poly(2-chlorostyrene)/poly(vinyl methyl ether) (P2CS/PVME) blends was investigated by means of ultraviolet (UV)-visible absorption spectroscopy. The reaction was performed via photodimerization of anthracene moieties chemically labeled on the P2CS chains. The crosslinking kinetics of (P2CS/PVME) blends submitted to a temperature jump from the one-phase into the spinodal regions was observed by monitoring the irradiation time dependence of the absorbances of anthracene as well as of the blend in two regions of wavelengths. One is inside and the other is outside the absorption range of anthracene. The contribution of the sample cloudiness to the absorbance of anthracene was subtracted from the absorption data by using an empirical power law experimentally established between the incident wavelengths and the absorption of the blends. It was found that the reaction kinetics approximately follows the mean-field kinetics inside the spinodal region, resembling the behavior of the crosslinking reaction performed in the miscible region at relatively low crosslinking densities. On the other hand, the method described here fails to estimate the crosslinking densities when the phase separation proceeds rapidly, overcoming the reaction. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:885–893, 1998     

Crystallization of poly(ethylene oxide) in i-polypropylene–poly(ethylene oxide) blends

A two-stage stable system of isotactic polypropylene–poly(ethylene oxide) blend, in which poly(ethylene oxide) can be permanent either in molten or in crystallized states in the temperature range from 280 to 327 K, was described. The behavior of that blend was explained in terms of fractionated crystallization. A fine dispersion of poly(ethylene oxide) inclusions is required for efficient suppression of crystallization initiated by heterogeneous nuclei. The application of a thin film of polypropylene-poly(ethylene oxide) 9 : 1 blend obtained by quenching for multiuse erasable and rewritable carriers for visible information has been demonstrated. The same sample exhibits different dynamic mechanical properties when poly(ethylene oxide) inclusions are molten or crystallized. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2047–2057, 1997     

Probing the structure of polymer blends by vibrational spectroscopy: the case of poly(ethylene oxide) and poly(methyl methacrylate) blends

The blends of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) are prepared in the form of thin films from solution casting. The Fourier transform infrared spectra of the blends are recorded in the spectral range 400–4000 cm^?1. The spectra are analysed using various recent techniques of vibrational spectroscopy. It is concluded that upon blending PEO takes preferentially a planar zig-zag structure. Furthermore the intermolecular interactions between the molecules of PEO and PMMA in blends are very weak and their compatibility as blends is more ‘physical’ than ‘chemical’. Further, on the basis of the atomic charges transferred from model molecules it is seen that the blending is preferred with isotactic PMMA when compared to syndiotactic PMMA.     

Phase behavior and properties of poly(methyl methacrylate)/poly(vinyl acetate) blends prepared via in situ polymerization

Polymer blends composed of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) were prepared via radical-initiated polymerization of methyl methacrylate (MMA) in the presence of PVAc. Differential scanning calorimetry and dynamic mechanical analysis were employed to investigate the miscibility and phase behavior of the blends. The PMMA/PVAc blends of in situ polymerization were found to be phase separated and exhibited a two-phase structure, although some chain transferring reaction between the components occurred. The phase separation resulted from the solvent effect of MMA during the in situ polymerization, which was confirmed by the investigation of phase behavior based on solution cast blending. Solubility analysis of the polymerized blends indicated that some chain transferring reaction between the components occurred during the polymerization. An abrupt increase in gel content from 21.2 to 72.4 wt % was observed when the inclusion of PVAc increased from 30 to 40 wt %, and the gel component consisted of the component polymers as shown by infrared spectroscopy studies. The thermogravimetric analysis study indicated that the inclusion of a small amount of PVAc gives rise to a marked stabilization effect on the thermal stability. The PMMA/PVAc blends exhibited increased notched impact properties with the inclusion of 5 wt % PVAc. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 675–684, 1998     

Mapping phases of poly(vinyl alcohol) and poly(vinyl acetate) blends by FTIR microspectroscopy and optical fluorescence microscopy

Fluorescence optical microscopy (FOM) of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) blends in compositions 9/1, 1/1, and 1/9 (w/w) show that these blends present phase separation in the solid state. Each domain of the solid samples was identified by FOM as PVA-richer domains by green fluorescence of fluorescein and PVAc-richer domains by the blue fluorescence of anthracene. The dimensions, shapes, and distributions of these domains were dependent on the initial composition of the polymeric mixtures in the solution. Specific interactions between both homopolymers were studied using FTIR microspectroscopy, which allowed us to obtain spectra for both PVA-richer and PVAc-richer domains. These spectra demonstrated that partial miscibility could occur only for blends with a higher PVAc content and, in these cases, we observed interchain hydrogen-bonded carbonyl groups. Fluorescence microscopy of blends with this partial miscibility exhibited small interconnected domains produced by coalescence of droplets during the polymer phase separation process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 645–655, 1998     

Phase separation in polymer blends comprising copolymers: 4. Polycarbonate/polystyrene ABCP system

An AB-crosslinked copolymer (ABCP) with polycarbonate as A-chain and polystyrene as B-chain was prepared and characterized. A series of blends of the ABCP and homopolystyrene fractions with different molecular weights were prepared and examined by electron microscopy. The results show that the miscibility between the homopolymer and the like chains in the copolymer is limited even if the molecular weight of the former is much less than that of the latter. Considering the relatively large miscibility in diblock copolymer/homopolymer blends and the limited miscibility in ABCP/homopolymer-A blends reported in literature, this study leads to an argument that the molecular architecture of a copolymer is an important factor governing its miscibility with homopolymer. The relatively complicated architecture of ABCPs causing more restriction to the chain conformation might be one of the main reasons for its low miscibility with homopolymers.     

High molecular weight poly( -lactide) and poly(ethylene oxide) blends: thermal characterization and physical properties

The miscibility of high molecular weight poly( -lactide) PLLA with high molecular weight poly(ethylene oxide) PEO was studied by differential scanning calorimetry. All blends containing up to 50 weight% PEO showed single glass transition temperatures. The PLLA and PEO melting temperatures were found to decrease on blending, the equilibrium melting points of PLLA in these blends decreased with increasing PEO fractions. These results suggest the miscibility of PLLA and PEO in the amorphous phase. Mechanical properties of blends with up to 20 weight% PEO were also studied. Changes in mechanical properties were small in blends with less than 10 weight% PEO. At higher PEO concentrations the materials became very flexible, an elongation at break of more than 500% was observed for a blend with 20 weight% PEO. Hydrolytic degradation up to 30 days of the blends showed only a small variation in tensile strength at PEO concentrations less than 15 weight%. As a result of the increased hydrophilicity, however, the blends swelled. Mass loss upon degradation was attributed to partial dissolution of the PEO fraction and to an increased rate of degradation of the PLLA fraction. Significant differences in degradation behaviour between PLLA/PEO blends and (PLLA/PEO/PLLA) triblock-copolymers were observed.     

Phase diagrams of blends of poly(phenylene ether), polystyrene,and diglycidyl ether of bisphenol A: Influence of the molar mass of poly(phenylene ether)

Phase diagrams of ternary blends of poly(phenylene ether) (PPE, M_n = 1.2 and 12 kg mol^?1), polystyrene (PS, M_n = 22.5 kg mol^?1), and diglycidyl ether of bisphenol A (DGEBA) were experimentally obtained in an extended range of temperatures and fitted with the Flory–Huggins model using three binary interaction parameters. A significant increase in miscibility together with the appearance of an immiscibility loop was found for PPEs with M_n values comprised in the range between 1 and 10 kg mol^?1. This enables us to obtain initial homogeneous solutions in regions of high DGEBA concentrations, a possibility that was not previously reported for this ternary blend. This opens new possibilities for the toughening of epoxies replacing a single thermoplastic with a thermoplastic blend where both components (PS and PPE) are completely miscible. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1742–1747, 2006     

Phase behavior and morphology in blends of poly(L‐lactic acid) and poly(butylene succinate)

Blends of poly(L ‐lactic acid) (PLA) and poly(butylene succinate) (PBS) were prepared with various compositions by a melt‐mixing method and the phase behavior, miscibility, and morphology were investigated using differential scanning calorimetry, wide‐angle X‐ray diffraction, small‐angle X‐ray scattering techniques, and polarized optical microscopy. The blend system exhibited a single glass transition over the entire composition range and its temperature decreased with an increasing weight fraction of the PBS component, but this depression was not significantly large. The DSC thermograms showed two distinct melting peaks over the entire composition range, indicating that these materials was classified as semicrystalline/semicrystalline blends. A depression of the equilibrium melting point of the PLA component was observed and the interaction parameter between PLA and PBS showed a negative value of ?0.15, which was derived using the Flory–Huggins equation. Small‐angle X‐ray scattering revealed that, in the blend system, the PBS component was expelled out of the interlamellar regions of PLA, which led to a significant decrease of a long‐period, amorphous layer thickness of PLA. For more than a 40% PBS content, significant crystallization‐induced phase separation was observed by polarized optical microscopy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 647–655, 2002     

Thermal,mechanical, and morphological characterization studies of poly(2,6‐dimethyl‐1,4‐phenylene oxide) blends with polystyrene and brominated polystyrene

The miscibility of the binary and ternary blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide), brominated polystyrene, and polystyrene was investigated using a differential scanning calorimeter. The morphology of these blends was characterized by scanning electron microscopy. These studies revealed a close relation between the blend structure and its mechanical properties. The compatibilizing effect of poly(2,6‐dimethyl‐1,4‐phenylene oxide) on the miscibility of the polystyrene/brominated polystyrene blends was examined. It was found that poly(2,6‐dimethyl‐1,4‐phenylene oxide), which was miscible with polystyrene and partially miscible with brominated polystyrene, compatibilizes these two immiscible polymers if its contention exceeds 33 wt %. Upon the addition of poly(2,6‐dimethyl‐1,4‐phenylene oxide) to the immiscible blends of polystyrene/brominated polystyrene, we observed a change in the morphology of the mixtures. An improvement in the mechanical properties was noticed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 225–231, 2000     

Crystallization and phase separation in blends of high stereoregular poly(lactide) with poly(ethylene glycol)

The effect of cooling rate on crystallization and subsequent aging of high stereoregular poly(lactide) (PLA) blended with poly(ethylene glycol) (PEG) was studied by thermal analysis and by direct observation of the solid state structure with atomic force microscopy (AFM). Blending with PEG accelerated crystallization of PLA. When a PLA/PEG 70/30 (wt/wt) blend was slowly cooled from the melt, PLA crystallized first as large spherulites followed by crystallization of PEG. The extent of PLA crystallization depended on the cooling rate, however, for a given blend composition the PEG crystallinity was proportional to PLA crystallinity. The partially crystallized blend obtained with a cooling rate of 30 °C min⁻¹ consisted of large spherulites dispersed in a homogeneous matrix. The blend was not stable at ambient temperature. With time, epitaxial crystallization of PEG on the edges of the spherulites depleted the surrounding region of PEG, which created a vitrified region surrounding the spherulites. Further from the spherulites, the homogeneous amorphous phase underwent phase separation with formation of a more rigid PLA-rich phase and a less-rigid PEG-rich phase. Decreasing the amount of PEG in the blend decreased the crystallization rate of PLA and increased the nucleation density. The amount of PLA crystallinity did not depend on blend composition, however, PEG crystallinity decreased to the extent that PEG did not crystallize in a PLA/PEG 90/10 (wt/wt) blend.     

Biodegradable polymer blends of poly(lactic acid) and poly(ethylene glycol)

Poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were melt-blended and extruded into films in the PLA/PEG ratios of 100/0, 90/10, 70/30, 50/50, and 30/70. It was concluded from the differential scanning calorimetry and dynamic mechanical analysis results that PLA/PEG blends range from miscible to partially miscible, depending on the concentration. Below 50% PEG content the PEG plasticized the PLA, yielding higher elongations and lower modulus values. Above 50% PEG content the blend morphology was driven by the increasing crystallinity of PEG, resulting in an increase in modulus and a corresponding decrease in elongation at break. The tensile strength was found to decrease in a linear fashion with increasing PEG content. Results obtained from enzymatic degradation show that the weight loss for all of the blends was significantly greater than that for the pure PLA. When the PEG content was 30% or lower, weight loss was found to be primarily due to enzymatic degradation of the PLA. Above 30% PEG content, the weight loss was found to be mainly due to the dissolution of PEG. During hydrolytic degradation, for PLA/PEG blends up to 30% PEG, weight loss occurs as a combination of degradation of PLA and dissolution of PEG. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1495–1505, 1997     

Poly(ethylene oxide)–polyelectrolyte blends: viscometric and thermal analysis behaviour

The miscibility of binary poly(ethylene oxide) (PEO) and sodium poly(4‐styrene sulphonate) (PSS) or [3,6]‐ionene (ION) systems, was analysed in aqueous solutions and in the solid state by viscometry and thermal analysis, respectively. Both techniques indicate partial miscibility of PEO–PSS and immiscibility of PEO–ION blends. In water solution, the partial miscibility of the PEO–PSS system is probably due to the counterion Na⁺ which can partially provide the driving force association in a similar manner to that observed for PEO–surfactant systems. In blend films, the PEO–polyelectrolyte interaction is also analysed in terms of the effect on the PEO crystallization observed through optical microscopy, and the results indicate compatibility between the components in the PEO–PSS system. © 2000 Society of Chemical Industry