Miscibility and morphology of AB/C-type blends composed of block copolymer and homopolymer or random copolymer, 1. Polyisoprene-block-poly(methyl methacrylate)/modified polystyrene blends

The miscibility and morphology of AB/C-type blends composed of polyisoprene-block-poly(methyl methacrylate) [PI-b-PMMA] and a modified polystyrene with hydroxyl-containing units [PS(OH)] has been studied by transmission electron microscopy (TEM). In the blends the density of hydrogen bonding between C and B block is adjustable. The miscibility and morphology of the blends cast from toluene, which is inert to hydrogen bonding, are found to depend on the hydroxyl content in PS(OH). Immiscibility between PMMA blocks and PS(OH) alters to miscibility when the hydroxyl content in PS(OH) reaches 1,6 mol-%. Little effect of the relative molecular weight of PS(OH) to that of the PMMA block is found, which is different from that for AB/A-type blends. An apparent effect of the casting solvent on the miscibility and morphology is observed. Being a proton-acceptor solvent, tetrahydrofuran (THF) considerably decreases the miscibility, and a homogeneous microphase structure appears only when the hydroxyl content reaches 10 mol-%. This implies that the main driving force for the miscibility between PS(OH) and PMMA blocks is hydrogen bonding between hydroxyl groups of PS(OH) and carbonyl groups of PMMA.     

Miscibility behavior in blends of poly(2,6-dimethylphenylene oxide) and random or block copolymers of styrene with methyl methacrylate

The Miscibility in blends of poly(2,6-dimethylphenylene oxide)

1 Systematic IUPAC name: poly[oxy(2,6-dimethyl-1,4-phenylene)].

(PPO) with random or block copolymers of styrene and methyl methacrylate (MMA) was studied by light microscopy and glass transition temperature measurements. Blends of PPO and the random copolymers were found to be miscible up to a copolymer content of 18 wt.-% MMA. The transition from miscibility to immiscibility in these blends in independent of temperature in the range 100 to 350°C. From these data, the segmental interaction parameter between units of the homopolymer and MMA, χ_PPO/PMMA is estimated to be about 0,5. Blends of PPO and the block copolymers of styrene and MMA used behave essentially as the corresponding homopolymers in terms of miscibility.     

Miscibility in blends of random copolymers of styrene and acrylontrile with block copolymers of styrene and methyl methacrylate

Phase behavior in blends of random copolymers of styrene and acrylonitrile with block copolymers of styrene and methyl methacrylate was studied by light scattering, light microscopy and glass transition temperature measurements. The results are compared with those of respective blends containing random copolymers of styrene and methyl methacrylate. In terms of macrophase separation, the block copolymers display a more extended miscibility domain with styrene/acrylonitrile copolymers than the random copolymers. However, the extent of the miscibility domain varies as a function of temperature. Unlike the random copolymer blends, all blends containing block copolymers exhibit lower critical solution temperature behavior. Finally, it is established that the systems studied here undergo spinodal decomposition leading to macrophase separation.     

Phase separation in random copolymers from high conversion free radical copolymerization, 1

The phase separation of random copolymers during free radical copolymerization to high conversion was studied. In order to prepare in situ high impact thermoplastics during the copolymerization process, the attention was focussed on systems in which the more reactive comonomers form thermoplastics, whereas the less reactive components form elastomeric homopolymers. The studied systems (A, B) were (AN, EA), (AN, VA), (CHMA, MA) and (S, BA) (AN: acrylonitrile, EA: ethyl acrylate, VA: vinyl acetate, CHMA: cyclohexyl methacrylate, MA: methyl acrylate, S: styrene, BA: butyl acrylate). These copolymers display varying compositional heterogeneity depending on the different radical reactivity ratios and the feed composition used. Curves of instantaneous copolymer composition versus fractional conversion and the distribution functions of chemical composition were calculated for the various systems. In addition, miscibility diagrams of corresponding low conversion copolymers A_xB_1−x and A_yB_1−y, derived from the same monomer pair (A, B) but differing in composition, were recorded at high temperatures. Phase separation was detected by light microscopy and differential scanning calorimetry (DSC) using cast films. The onset of phase separation depending on the actual stage of copolymerization was recorded. The composition of the copolymers at the onset of phase separation was compared with the miscibility of low conversion copolymer blends. A satisfactory prediction of the start of phase separation during copolymerization is presented.     

Compatibility of tetramethyl polycarbonate and random poly(styrene-co-methyl methacrylate)s

Phase diagrams and concentration fluctations of blends of tetramethyl polycarbonate (TMPC)

1 Polycarbonate of 2,2′,6,6′-tetramethyl-4,4′-isopropylidenediphenol (tetramethyl derivative of bisphenol A).

and random copolymers P(S_xMMA_1?x) of styrene and methyl methacrylate were analyzed, using cast films and dry films. Phase separation was detected by light microscopy, DSC and small-angle neutron scattering. Neutron scattering was also used to measure the structure of fluctuations in one-phase as well as two-phase states. The merits and problems of the various methods are discussed. Blends TMPC/P(S_xMMA_1?x) have high-temperature miscibility gaps at x > 0,5. The copolymers interact non-ideally, in a manner that had been observed before in their blends with PS and PMMA. An equation based on the classical theory but allowing diad effects describes the interaction parameters fairly well. It was used to calculate the interaction parameter of the immiscible homopolymer blend TMPC/PMMA which was also determined from the miscibility gap of a ternary blend TMPC/PMMA/P(S_xMMA_1?x).     

Thermodynamics of random copolymer mixtures

The lattice-fluid theory of polymer solutions, previously applied to homopolymer-solvent and homopolymer-homopolymer mixtures, is now extended to random copolymer mixtures. A generalized, though simple, formalism is presented which is valid for binary copolymer mixtures, each copolymer having any number of different monomeric units (groups). Mixtures of a homopolymer with a random copolymer are treated as a special subcase. Particular emphasis is given to the phase stability of copolymer mixtures. Equations for the spinodal and the critical point are presented. The model is applied satisfactorily to various cases which attracted special attention in recent studies on the miscibility of copolymer mixtures.     

Concentration Fluctuations and Segmental Dynamics in Weakly Dynamic Asymmetric Blends in the Presence of Surface‐Functionalized Multiwall Carbon Nanotubes

Surface‐functionalized multiwall carbon nanotubes (MWCNTs) are incorporated in poly(methyl methacrylate)/styrene acrylonitrile (PMMA/SAN) blends and the pretransitional regime is monitored in situ by melt rheology and dielectric spectroscopy. As the blends exhibit weak dynamic asymmetry, the obvious transitions in the melt rheology due to thermal concentration fluctuations are weak. This is further supported by the weak temperature dependence of the correlation length (ξ ≈ 10–12 Å) in the vicinity of demixing. Hence, various rheological techniques in both the temperature and frequency domains are adopted to evaluate the demixing temperature. The spinodal decomposition temperature is manifested in an increase in the miscibility gap in the presence of MWCNTs. Furthermore, MWCNTs lead to a significant slowdown of the segmental dynamics in the blends. Thermally induced phase separation in the PMMA/SAN blends lead to selective localization of MWCNTs in the PMMA phase. This further manifests itself in a significant increase in the melt conductivity.

     

Study of the miscibility of poly(N-vinyl-2-pyrrolidone) with poly[styrene-co-(4-hydroxystyrene)]

Poly(N-vinyl-2-pyrrolidone) (PVP) was blended with poly[styrene-co-(4-hydroxytyrene)] (PSH) which was obtained from the random copolymer poly[styrene-co-(4-acetoxystyrene)] (PSA). The miscibility of PVP/PSH blends in a composition 1 : 1 by weight was evaluated by differential scanning calorimetry (DSC), non-radiative energy transfer (NET) and Fourier transform infrared (FTIR) spectroscopy. It was found that the blends become miscible when the hydroxystyrene units (HS) in PSH exceed 11 mol-%. The driving force of miscibility may be attributed to hydrogen bonding between ? OH in PSH and in PVP. The experimental results of miscibility were compared with that estimated from a “miscibility parameter” (MP) concept, and we found that the general trend of MP values is in agreement with the experimental results.     

The width of miscibility gaps,measured by scattering

Incompatible polymers yield two-phase binary blends at almost all compositions. In equilibrium, the blends consist of two coexisting phases which have frequently very one sided compositions: Much of one component contains little of the other. The small content of the minor component, the so-called “partial miscibility”, is important for some properties. But it is difficult to measure. Conventional techniques to determine miscibility gaps which rely on transparency and turbidity fail when the gaps are too wide. More reliably, the composition of the coexisting phases can be extracted from X-ray or neutron scattering data. A series of blends of poly(methyl methacrylate) (PMMA) and random copolymers S_xMMA_l?x of styrene and MMA, of which the degree of incompatibility was varied via the copolymer composition x, was studied by small angle neutron scattering. The interactions of the polymer components were measured in homogeneous and demixed blends. The demixed blends yield at high wave vectors a scattering equal to the scattering of the two coexisting phases, superposed. The composition of the coexisting phases was extracted from the slope of the Zimm curve which responds very sensitively even when the compositions are extreme. Miscibility gaps as wide as 99.7% could be determined.     

Influence de la solvatation préférentielle dans les réactions de greffage. Polydispersité en composition des copolymères SAN dans les résines ABS

ABS resins formed by copolymerization of styrene (S) and acrylonitrile (AN) in the presence of polybutadiene, consist of a mixture of SAN graft copolymer on polybutadiene and of ungrafted SAN copolymer. After separation and analysis, the AN contents of the grafted and ungrafted SAN are compared. The change of the AN contents as a function of the conversion and the concentration of polybutadiene is studied. As a consequence of the preferential solvation of polybutadiene by styrene and the initiator, the grafted SAN has a lower AN content than the non grafted SAN. At low conversions, where preferential solvation is maximum, it is also possible to show the presence of non grafted SAN which is formed in the polybutadiene coil or polybutadiene medium (“internal free SAN”). The characteristics of this “internal free SAN” are similar to those of the grafted SAN and especially its AN content is lower than that of SAN copolymer prepared under azeotropic conditions in the absence of polybutadiene.     

The glass transition of blends of poly(2,6-dimethylphenylene oxide) and polystyrene-block-poly(2,2-dimethyltrimethylene carbonate)

The miscibility of poly(2,6-dimethylphenylene oxide) (PPO) with polystyrene-block-poly(2,2-dimethyltrimethylene carbonate) (PS-block-PDTC) was studied and compared with the corresponding PPO/PS blends. PPO/PS-block-PDTC blends show two thermal transitions in the temperature range investigated; that is the melting of the DTC block and the glass transition of the mixed PPO/PS block phase. The T_g values obtained are discussed by means of the Fox and Gordon-Taylor equation. The influence of the PDTC block leads to higher T_g values of the PPO/PS block mixture than of the corresponding homopolymer blend.     

Study on the miscibility of poly(2-hydroxyethyl methacrylate)/poly(styrene-co-acrylamide) blends by nonradiative energy transfer fluorescence spectroscopy

The miscibility of poly(2-hydroxyethyl methacrylate)/poly(styrene-co-acrylamide) (PHEMA/PSAm) blends was investigated by nonradiative energy transfer fluorescence spectroscopy using anthracene-labeled PHEMA and carbazole-labeled PSAm. The results show that the ratio of the carbazole and anthracene emission intensity, I_c/I_a, passes through a minimum at 47 to 57 mol-% of acrylamide in PSAm copolymers in the blends, indicating that a ‘miscible window’ exists. It also was found that the results are consistent with those obtained by differential scanning calorimetry. The driving force for the miscibility of PHEMA/PSAm may be explained with a mean-field theory.     

Sequential reordering in condensation copolymers, 2. Melting- and crystallization-induced sequential reordering in miscible poly(butylene terephthalate)/polyarylate blends

A 50/50 (weight ratio (38/62 mole ratio referred to repeating units)) blend of poly(butylene terephthalate) (PBT) and polyarylate (PAr), was studied by means of thermal, solubility, X-ray and nuclear magnetic resonance techniques after annealing procedures that enable transesterification. Prolonged thermal treatment at 290°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples at the relatively low temperature of 140°C results in the reappearance of melting endotherms in the differential scanning calorimetry curves. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions. In that way a PBT/PAr blend was shown to be another polymer system, along with poly(ethylene terephthalate) (PET)/polycarbonate (PC) and PET/PAr blends, in which the entire cycle is realized, from two homopolymers via a block- and random copolymer to a block copolymer. The unusually low temperature at which the crystallization-induced sequential reordering to block polymers takes place is explained by the miscibility of PBT and PAr which enables transreactions to take place in the bulk.     

Blend encapsulation by random copolymers: C/B/A-ran-B and C/D/A-ran-B systems

Random copolymers with the same monomeric units as blended homopolymers A and B have a strong tendency to encapsulate the minor phase in A/B/A-ran-B ternary systems. In this study we investigate encapsulation when one or both monomeric units in the random copolymer are chemically distinct from, but completely or partially miscible with, the other blend components, i.e., a C/D/A-ran-B blend. As model polymers, a styrene/methyl methacrylate random copolymer (70% styrene by weight) (SMMA), and polystyrene (PS), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and poly(phenylene oxide) (PPO) homopolymers are chosen; PPO is completely miscible with PS and PC is partially miscible with PMMA. Three blend systems were prepared by melt mixing: PS/PC/SMMA, PPO/PMMA/SMMA, and PPO/PC/SMMA. Transmission electron microscopy demonstrated that for all cases SMMA moves to the interface between the matrix and dispersed phases during melt mixing, and forms an encapsulating layer. However, the resulting average size of a dispersed phase droplet is not significantly decreased by the addition of SMMA. Moreover, this size increased significantly upon further annealing, except for the blend with a PPO matrix which has a very high melt viscosity, demonstrating that encapsulation by SMMA does not provide stability against static coalescence.     

Effect of composition on the entanglement density in random copolymers

The plateau moduli of poly(styrene-ran-acrylonitrile) and poly[styrene-ran-(methyl methacrylate)] copolymers are investigated. Plots of the plateau moduli versus composition of the copolymers show a large negative deviation from linearity in both cases. Molecular weights between entanglements are determined from the plateau moduli. The experimental data are discussed in terms of models recently proposed for miscible blends. The physical picture emerges of a random copolymer as a “forced miscible blend”.     

Compatibilizing effect of polystyrene-block-poly(4-vinylpyridine) for poly(2,6-dimethyl-1,4-phenylene oxide)/chlorinated polyethylene blends

The compatibilizing effect and mechanism of compatibilization of the diblock copolymer polystyrene-block-poly(4-vinylpyridine) P(S-b-4VPy) on immiscible blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)/chlorinated polyethylene (CPE) were studied by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC), mechanical properties and FTIR measurements. The block copolymer was synthesized by sequential anionic polymerization and melt-blended with PPO and CPE. The results show that the P(S-b-4VPy) added acts as an effective compatibilizer, located at the interface between the PPO and the CPE phase, reducing the interfacial tension, and improving the interfacial adhesion. The tensile strength and modulus of all blends increase with P(S-b-4VPy) content, whereas the elongation at break increases for PPO-rich blends, but decreases for CPE-rich blends. The polystyrene block of the diblock copolymer is compatible with PPO, and the poly(4-vinylpyridine) block and CPE are partially miscible.     

Compatibility of poly(ethylene oxide) and poly(methyl methacrylate) chains in solutions of their blends,diblock and triblock copolymers

Solvent activity data were obtained from vapour pressure measurements at 50°C, 70°C, 100°C and reduced to χ-functions in systems consisting of benzene or toluene on the one hand and blends or block copolymers of poly(ethylene oxide) and poly(methyl methacrylate) on the other. The χ_BC-values are negative for all polymer subsystems, but miscibility on a segmental scale is somewhat different for block copolymers and blends. χ_BC depends on the concentration of solvent and is mainly influenced by the Δχ-effect in solution and correlated with the syndiotacticity of the PMMA chains. There is only a small influence of temperature and blend composition or block ratio.     

Temperature rising elution fractionation of a random ethene/styrene copolymer

A random ethene/styrene copolymer containing 13.8 mol-% styrene was prepared with the Ziegler-Natta catalyst system Me₂Si(Me₄Cp)(N-t-butyl)TiCl₂/methylaluminoxane and characterized by means of preparative temperature rising elution fractionation (TREF) combined with size exclusion chromatography, NMR, differential scanning calorimetry and wide-angle X-ray scattering analyses of the copolymer fractions. Efforts are made to describe the distribution of the styrene content of the copolymers using the Stockmayer-Tacx distribution function. Both, comonomer distribution and molar mass distribution strongly support the presence of a single type of catalytically active center.     

Sequential reordering in condensation copolymers, 1. Melting- and crystallization-induced sequential reordering in immiscible blends of poly(ethylene terephthalate) with polycarbonate or polyarylate

Unlike previous attempts, the entire cycle of melting- and crystallization-induced reordering is realized in binary polymer blends in the following order: two homopolymers → block copolymer → random copolymer → block copolymer. Blends of poly(ethylene terephthalate)

1 Systematic IUPAC name: poly(oxyethyleneoxyterephthaloyl).

(PET) and bisphenol-A/polycarbonate (PC) as well as PET/polyarylate (PAr) blends, are annealed directly in a differential scanning calorimeter at 280°C for various times. Scanning the samples in the heating mode reveals the complete disappearance of crystallization or melting in the blends where the ratio of PET/PC repeating units is less than 5.7/1.0. Such an amorphization is attributed to the formation of random copolymers. This statement is confirmed by NMR measurements, by the observation of one glass transition temperature T_g in the range between the initial two T_gs, and by solubility tests. Once randomized, annealing the samples at 235°C and 245°C, i. e., below melting of PET, results in a T_g shift toward the T_g of PET as well as in reappearance of melting. This effect is accompanied by an eight-fold crystallinity increase in the equimolar blend, as compared to the randomized sample. The regenerated crystallization ability is explained by restoration of the blocks. According to previous findings, it is concluded that the considerable enthropy increase is the main driving force of randomization. The rival trend to the formation of a block copolymer by sequential reordering is driven by the crystallization of PET blocks formed. The conclusion that the observed changes in the crystallization ability and T_g-values are based on sequential reordering is supported by experiments with samples containing increased amounts of transesterification catalyst leading to a much faster appearance of these changes. No randomization is observed with the blend composition ratio of repeating units PET/PC > 5.7/1.0. When the annealing is performed for 300 min at 165°C, where no significant exchange reactions are expected to occur, no restoration of the crystallization ability is observed.     

Miscibility of poly(vinyl chloride) with ethylene/N,N-dimethylacrylamide copolymers.

The incorporation of N,N-dimethylacrylamide (DMA) as a comonomer in polyethylene yields a material possessing dramatically improved mechanical compatibility with poly(vinyl chloride) (PVC). At increased levels of DMA (25–30 wt.-%) miscibility with PVC is achieved. This behavior is believed to be due to the specific interaction of the tertiary hydrogen of poly(vinyl chloride) (weak “acid” or proton donor) with the disubstituted amide in the ethylene copolymer (weak “base” or proton acceptor). Dynamic mechanical characterization of the ethylene/DMA copolymer (EDMA)/PVC blends reveals separate glass transitions temperatures at DMA levels below 20 wt.-%; they merge into a single T_g when the DMA content reaches a value above 25 wt.-% in the ethylene copolymer. The secondary loss transition for PVC (?40°C) is lowered in temperature and greatly suppressed in magnitude. This is further evidence of molecular miscibility. Mechanical property data obtained on the EDMA/PVC blends are consistent with the foregoing considerations.