Phase structure and compatibility studies in poly(ethylene oxide)/poly(methyl methacrylate) blends

Morphology, crystallinity, and melting behaviour of solution-cast films of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends were investigated as a function of composition, using optical and scanning electron microscopy, differential scanning calorimetry, and dilatometry. Up to a content of about 40 wt.-% of PMMA the blend films are completely filled with PEO spherulites, no separated domains of PMMA being observed. This observation suggests, in agreement with small angle X-ray scattering analysis, that for such compositions the PMMA molecules are incorporated in interlamellar regions of PEO spherulites. Blends with higher content of PMMA show islands of crystalline PEO within a matrix of PMMA; large amorphous regions coexist with not well developed PEO spherulites. Addition of PMMA strongly increases the nucleation density for PEO crystals. The solubility parameters δ of PEO and PMMA were calculated from specific volume values as a function of temperature. It was found that at temperatures higher than that of PEO melting the difference δ(PEO) - δ(PMMA) is very low suggesting that the two polymers are compatible in the melt. Compatibility of PEO and PMMA was also predicted by using a theoretical approach which allows to calculate the free energy of mixing as a function of composition and temperature.     

Melt rheology of compatible binary blends: Poly(ethylene oxide)-poly(methyl methacrylate) and poly(ethylene oxide)-poly(vinyl acetate)

A study of the rheological behaviour of poly(ethylene oxide)-poly(methyl methacrylate) and poly(ethylene oxide)-poly(vinyl acetate) compatible blends in the molten state is reported. Zero shear viscosity η₀ and the activation energy for the viscous flow ΔE* were obtained as function of both composition and molar mass of the components. Positive and negative deviations from the additivity rule were observed both in the case of log η₀ and ΔE*.     

Synthesis of ethylene oxide/methyl methacrylate diblock copolymers by group transfer polymerization of methyl methacrylate with poly(ethylene oxide) macroinitiators

Ethylene oxide/methyl methacrylate diblock copolymers were prepared by group transfer polymerization (GTP) of methyl methacrylate (MMA) with poly(ethylene oxide) macroinitiators ( 1 ). The macroinitiator containing silyl ketene acetal end-groups was synthesized by hydrosilation of poly(ethylene glycol) monomethacrylate which was previously prepared by esterification of poly(ethylene glycol) monomethyl ether (PEO OH). All synthesized macroinitiators initiated the GTP of MMA in tetrahydrofuran with tetrabutylammonium cyanide or tris(dimethylamino)sulfonium difluoride as catalysts. The polymerization proceeds rapidly at room temperature to quantitative yield. The block copolymers are contaminated with small fractions of PEO homopolymer as a result of uncomplete macroinitiator synthesis. Unreacted PEO—OH, which is present in very small amounts, reduces the concentration of active centers. Therefore, the degree of polymerization is not in good agreement with the theoretical value calculated for a living polymerization taking the monomer to macroinitiator ratio. However, after extraction of the PEO homopolymer, the block copolymers show a narrow molecular weight distribution. Induction periods in time-conversion curves obtained with 1 as initiator vanished nearly, when the reaction was started with the addition product of 1 and MMA. This is an indication, that in the system under investigation a slow initiation step between 1 and the first MMA unit precedes the propagation reaction. Tacticity measurements yield about 56% syndiotactic, 40% heterotactic and 4% isotactic triads for PMMA in the block copolymers.     

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.     

Molecular orientation relaxation in binary blends of poly(methyl methacrylate) by rheo-optical Fourier-transform infrared spectroscopy

Rheo-optical Fourier-transform infrared spectroscopy, a technique combining simultaneous mechanical measurements and infrared dichroism spectroscopy, has been employed in order to investigate the molecular chain orientation and orientation relaxation behaviour in uniaxially stretched films of binary blends of long perdeuterated and short undeuterated chains of linear poly(methyl methacrylate) (PMMA). The solution cast film samples have been stretched at constant strain rate up to 100% elongation and subsequently allowed to relax at constant strain at various temperatures above the glass transition temperature. The results reported here show that for the short-chain component a threshold value of molecular weight exists below which a drastic decrease of the long-and short-chain orientation and a change in the relaxation behaviour of the short chains are observed.     

The miscibility and phase separation in binary blends of poly(vinyl chloride) with methyl methacrylate/acrylonitrile copolymers

The miscibility of poly(vinyl chloride) with poly(methyl methacrylate-stat-acrylonitrile) has been studied. Poly(vinyl chloride) is miscible with methyl methacrylate/acrylonitrile copolymers having acrylonitrile contents between 2,0 and 17 wt.-%. All calculated binary segmental interaction parameters were positive, suggesting immiscibility of the corresponding binary homopolymer blends.     

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.     

Stabilization of polystyrene/poly(methyl methacrylate) blends by in situ compatibilization with graft copolymers

Copolymers of styrene and ortho-vinylbenzaldehyde (o-VBA) are useful precursors to multicomponent polymer systems. Graft copolymers of poly(styrene-stat-o-VBA) can be produced by free-radical chain transfer to methyl methacrylate monomer to yield materials that display some potential as interfacial agents with binary blends of polystyrene and poly(methyl methacrylate). Significant improvements in ultimate tensile strengths and energy to rupture values have been witnessed for polystyrene/poly(methyl methacrylate) mixtures that contain various levels of the graft component. Scanning electron microscopy of representative fracture surfaces demonstrate a decrease in the particle size of the dispersed phase; it is suggested that this morphological factor contributes to the superior mechanical properties of these composites. In this regard, both the isolated and the crude graft copolymers are able to compatibilize, and thereby enhance, the material properties of polystyrene/poly(methyl methacrylate) blends.     

Synthesis and characterization of poly(ethylene oxide) and poly(perfluorohexylethyl methacrylate) containing triblock copolymers

A new series of poly(perfluorohexylethyl methacrylate)‐block‐poly(ethylene oxide)‐block‐poly(perfluorohexylethyl methacrylate), PFMA‐b‐PEO‐b‐PFMA triblock copolymers has been synthesized by atom transfer radical polymerization using bifunctional PEO macroinitiators. The molecular structure of the block copolymers was confirmed by ¹H NMR spectroscopy and SEC. X‐ray scattering studies have been carried out to investigate their bulk properties. SAXS has shown cubic arrangement of spheres (bcc), hexagonally packed cylinders (hpc) and lamellar microdomain formation in the melt of triblock copolymers investigated, depending on composition. Crystallization was, however, found to destroy the ordered melt morphology and imposes a lamellar crystalline structure. WAXS, DSC and polarized light microscopy measurements confirmed the crystallization of PEO segments in block copolymers. Long PFMA blocks were found to have significant effect on PEO crystallization.

Synthesis of triblock copolymers of EO and FMA by ATRP.     

The stereoregularity of poly(methyl methacrylate)s formed in the presence of highly syndiotactic poly(methyl methacrylate)s

Methyl methacrylate (MMA) was radically polymerized in the presence of highly syndiotactic deuterated or undeuterated poly(methyl methacrylate)s. In contrast to observations found in the literature no increase in isotacticity was observed. The stereoregularity of the polymers formed in the presence of an undeuterated PMMA as matrix was found by ¹H NMR spectroscopy to be about the same as that in polymers prepared without any matrix, except the polymers formed in the early stage of polymerization which show a little lower syndiotacticity. Determinations of triad tacticities of polymers formed in the presence of deuterated PMMA, gave values of syndiotacticity a little higher than in the case of undeuterated matrixes. The polymer formed in the graft copolymerization of MMA onto pre-irradiated syndiotactic PMMA was fractionated by GPC. The high molecular weight fraction showed a lower syndiotacticity than that of lower molecular weight.     

Morphology,crystallization and thermal behaviour of poly(ethylene oxide)/poly(vinyl acetate) blends

Blends of poly(ethylene oxide) (PEO) and poly(vinyl acetate) (PVAc) show a unique value of the glass transition temperature, intermediate between that of plain polymers. The addition of PVAc to PEO causes a depression in both the spherulite growth rate (G) and the overall kinetic rate constant (K_n). Such depression is larger at higher undercooling and, at a given crystallization temperature, it increases with the content of PVAc. The experimental G and K_n data were analyzed by means of latest kinetic theories in order to determine the influence of composition on the process of surface secondary nucleation. The melt behaviour of PEO/PVAc blends cannot be explained only in terms of diluent effects due to the compatibility of the components in the melt. Especially, at lower undercooling it is likely that annealing and morphological effects must also be taken into account. The morphology of thin films of blends, isothermally crystallized from melt, suggests that an amorphous mixed phase (PEO + PVAc) is formed in interlamellar regions. It was found that plain PEO crystals grow according to a regime I process of surface secondary nucleation while in the case of blends the crystals of PEO grow via regime II mechanism.     

Anionic graft copolymerization of methyl methacrylate with lithium diisopropylamide-treated poly(methacrylate)s

The anionic grafting of methyl methacrylate onto several lithium diisopropylamide (LDA)-treated polymers of methacrylates, such as 2-acetoxyethyl methacrylate ( 1 ), 2-propionyloxyethyl methacrylate ( 2 ), 2-isobutyryloxyethyl methacrylate ( 3 ), 1-methoxy-carbonylethyl methacrylate ( 4 ), and methoxycarbonylmethyl methacrylate ( 5 ), or onto the LDA-treated copolymers of the methacrylates with styrene was investigated. Graftings onto homopolymethacrylates and onto the copolymers of 1 and 2 with styrene did not occur due to the deactivation of the macromolecular lithium enolate by side reactions. Graftings onto copolymers P-3, P-4 and P-5 , from methacrylates 3, 4 and 5 with styrene, however, proceeded. The relative grafting efficiency decreases in the following order: P-3 > P-4 > P-5 . The grafting is highly influenced by the aggregation behavior of the macromolecular lithium enolates and the side reactions deactivating the lithium enolate. The aggregation behavior decreases the number of the activated points on the feed polymer, lowers the inititiation rate and the polymerization rate of the grafting, and causes a large polydispersity value (M̄_w/M̄_n) of the side-chain poly(MMA).     

Viscosities of dilute solutions of poly (methyl methacrylate) and poly (ethyl methacrylate) in organic solvents

Poly(methyl methacrylate) and poly(ethyl methacrylate) prepared by a benzoylperoxide catalysed polymerization process were fractionated. The variation of the intrinsic viscosity and HUGGINS ' constant with temperature, molecular weight and solvent was studied. From the viscosity data the thermodynamic interaction parameters χ, ψ, k etc., and the solubility parameter of the polymers were evaluated and discussed.     

Phase separation in poly(methyl methacrylate)-block-poly(2,3-dibromopropyl methacrylate) copolymers

AB block copolymers poly(methyl methacrylate)-block-poly(2,3-dibromopropyl methacrylate) were prepared by a two-stage process involving the sequential anionic polymerization of methyl methacrylate and allyl methacrylate followed by bromination of the pendant allylic groups. Transmission electron microscopy of thin sections of cast films revealed phase separation, the morphology depending upon composition of the block. In particulate form these copolymers gelled with methyl methacrylate to form doughs that could be moulded and heat cured to produce hard X-ray opaque copolymers.     

Synthesis of a stereoblock poly(methyl methacrylate)

The sequential block copolymerization of diphenylmethyl methacrylate (DMA) and trityl methacrylate (TrMA), initiated by diphenyl methyl lithium in THF at -78°C followed by hydrolysis and methylation with diazomethane, leads to the formation of an isotacticsyndiotactic stereoblock poly(methylmethacrylate) (PMMA) of narrow molecular weight and block length distribution. Complete conversion of DMA is shown to be essential, since the presence of small quantities of this monomer during the polymerization of TrMA significantly lowers the isotactic content of this block. Polymerization times of at least 12 h were found to be necessary for complete polymerization of the TrMA.     

Multiphase blends from poly(L-lactide) and poly(methyl mathacrylate)

Melt processing of poly(L-lactide) (PLLA) and poly(methyl methacrylate) (PMMA) was conducted over a targeted range of compositions with PLLAs of 118 and 316 kDa in molecular mass to identify morphologies and the phase relationships in these blends. These blends are of interest for use in biomaterials and the morphologies are critical for tissue-engineering studies where biodegradability, pore connectivity and surface texture control tissue viability and adhesion. Simple extrusion of the two polymers produced multiphase blends with an average domain size near 25 microm. Scanning electron microscopy and dynamic mechanical analysis demonstrated that these blends are immiscible, at least in a metastable sense, and regions of co-continuous structures were identified. Such co-continuous, which occurred generally in accordance with rheology prediction models, exhibit a fine interconnected structure that appears effective for fabricating certain biomaterials. A broad and unexpected transition appears in these blends, as measured by modulated differential scanning calorimetry between 70 and 100 degrees C, which may be the glass transition temperature of an alloy phase. The magnitude of this transition is greatest in the fine-structured co-continuous composition region of blends, suggesting the presence of a complex or other derivative of the two primary phases.     

Multiphase blends from poly(L-lactide) and poly(methyl mathacrylate)

Melt processing of poly(L-lactide) (PLLA) and poly(methyl methacrylate) (PMMA) was conducted over a targeted range of compositions with PLLAs of 118 and 316 kDa in molecular mass to identify morphologies and the phase relationships in these blends. These blends are of interest for use in biomaterials and the morphologies are critical for tissue-engineering studies where biodegradability, pore connectivity and surface texture control tissue viability and adhesion. Simple extrusion of the two polymers produced multiphase blends with an average domain size near 25 μm. Scanning electron microscopy and dynamic mechanical analysis demonstrated that these blends are immiscible, at least in a metastable sense, and regions of co-continuous structures were identified. Such co-continuous, which occurred generally in accordance with rheology prediction models, exhibit a fine interconnected structure that appears effective for fabricating certain biomaterials. A broad and unexpected transition appears in these blends, as measured by modulated differential scanning calorimetry between 70 and 100°C, which may be the glass transition temperature of an alloy phase. The magnitude of this transition is greatest in the fine-structured co-continuous composition region of blends, suggesting the presence of a complex or other derivative of the two primary phases.     

The glass transition temperatures of homogeneous blends of polystyrene,poly(methyl methacrylate), and copolymers of styrene and methyl methacrylate

The glass transition temperatures T_g of homogeneous binary blends of the homo- and the statistical copolymers of the system poly(styrene-co-methyl methacrylate) were studied. Some of the blends, which are in the equilibrium phase separated, were forced into homogeneity. T_g (?) of the homopolymer blends (PS/PMMA)? follows the Fox equation, while T_g (x) of the pure copolymers P(S_xMMA_{1 ? x}) exhibits a minimum. This minimum can be effectively removed by blending the copolymers with small fractions (? ≈ 0,2) of one of the two homopolymers or a differently composed copolymer P(S_yMMA_{1 ? y}).     

Crystallization behaviour of poly(ethylene terephthalate) and poly(tetramethylene terephthalate) blends

The isothermal and non-isothermal crystallization behaviour of blends of poly(ethylene terephthalate) (PET) and poly(tetramethylene terephthalate) (PBT) is investigated at low percentage of the second component. The melting behaviour of the isothermally crystallized sample shows that the crystallization behaviour in the blend is governed by the mobility of PBT. Below 200°C the crystallization process is hindered, whereas above 200°C the PET crystals are larger in case of added PBT. The non-isothermal crystallization behaviour shows that the crystallization process is hindered when the PBT content in the blend is less or higher than 6 wt.-%.