Glass transition temperatures in blends of poly(N-vinyl-2-pyrrolidone) with a copolymer of bisphenol A and epichlorohydrin or with poly(vinyl butyral)

Blends of poly(vinyl butyral) (PVB) and of a copolymer of bisphenol A and epichlorohydrin (Phenoxy) with poly(N-vinyl-2-pyrrolidone) (PVP) were prepared by solution casting. The glass transition temperatures T_g for different compositions of the blends were measured by differential scanning calorimetry (DSC). The T_g behaviour of PVB/PVP blends suggests the existence of a single phase for blends containing less than 50 wt.-% PVP, and of two phases in blends containing more than 50 wt.-% PVP. Phenoxy/PVP blends showed to be miscible over the entire composition range. It was found that the Gordon-Taylor equation predicts adequately the T_g-composition dependence with a K parameter equal to 0,5 and 1,25 for PVB/PVP and Phenoxy/PVP blends, respectively.     

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.     

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}).     

Dispersion of trans-polyoctenylene in isotactic poly(propylene), 1. Morphology/mechanical properties relationships

Blends of isotactic poly(propylene) (iPP) and trans-polyoctenylene (TOR), prepared from solution, exhibit unexpected mechanical properties at specific mass fractions of TOR: While generally the elastic modulus E decreases continuously with increasing TOR content, it surpasses a maximum for mass fractions of TOR around 0,10. The reason for this behaviour is investigated. It turns out that the crystallinity as well as the crystal morphology (which is investigated by evaluating small-angle X-ray scattering by interface distribution functions) does not explain the mechanical behaviour. The order of the lamellar stacks (number of orientation-correlated crystals) proves to be well correlated with the course of the elastic modulus. This order is a consequence of the increasing dispersion of TOR at mass fractions between 0,075 and 0,20 creating interfaces and infecting subsequently the crystallization conditions in the sample.     

Effect of the catalyst-monomer ratio on the molar mass and glass transition temperature of poly(oxy-2,6-dimethoxy-1,4-phenylene)

2,6-Dimethoxyphenol was polymerized using Ag₂O-triethylamine complex as catalyst and a study made of the effect of the catalyst-monomer ratio on the yield, molar mass and polydispersity of poly(oxy-2,6-dimethoxy-1,4-phenylene). The glass transition temperatures T_g were measured with a computerized differential scanning calorimeter. The effect of the molar mass on T_g of poly(oxy-2,6-dimethoxy-1,4-phenylene) is discussed. The equation, T_g = T_{g, ∞} ? K/M, describes well the dependence of T_g on the viscosity-average molar mass M_v from 1900 to 176000 g/mol. Some poly(oxy-2,6-dimethyl-1,4-phenylene) samples were studied as reference material.     

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.     

Phase behavior and miscibility in blends of poly(sebacic anhydride)/poly(ethylene glycol)

In this research, poly(sebacic anhydride) was synthesized via melt-condensation. The polymer was then blended with poly(ethylene glycol) in various ratios by solvent casting, to obtain the desired polymer blends. A differential scanning calorimeter was employed to investigate the crystalline behavior of the blends. Blends with under 10% poly(ethylene glycol) were found to consist of two partially miscible polymers in the amorphous phase. This compatibility of the two polymers may induce the crystallization of the poly(sebacic anhydride) component from decreasing the glass transition temperature of the poly(sebacic anhydride) component in the blending system due to the presence of poly(ethylene glycol) chain segments. Furthermore, phase separation occurred and the crystallinity of poly(sebacic anhydride) diminished when at least 20% poly(ethylene glycol) was present in the blends. These results were verified by the variation in the absorptions of carbonyl groups in infrared spectra; these spectra exhibit the changes in crystallinity of poly(sebacic anhydride) in the blends.     

Effect of a triblock PCL-PDMS-PCL copolymer on the properties of immiscible poly(vinyl chloride)/poly(2-ethylhexyl acrylate) blends

Miscibility, thermal, mechanical and morphological properties of poly(vinyl chloride)/poly(2-ethylhexyl acrylate), (PVC/PEHA) blends containing 1–10 wt.-% of the triblock copolymer polycaprolactone-block-poly(dimethylsiloxane)-block-polycaprolactone (PCL-PDMS-PCL, Tegomer) were investigated by several techniques. Binary blends of PVC/PEHA are found to be immiscible according to differential scanning calorimetry and viscosity measurements. The effect of Tegomer addition on the properties of blends was examined. Ternary blends of PVC/PEHA/Tegomer exhibited a single T_g behaviour and viscosity measurements indicate some compatibility. Stress-strain results showed that Tegomer has a synergetic effect on the flexibility of the blends. FTIR analysis confirms the specific interactions between the components in ternary blends of PVC/PEHA/Tegomer. Morphological properties of the blends were examined by scanning electron microscopy.     

Compatibilité de polymères porteurs de groupements amides tertiaires avec le poly(difluoro-1,1 éthylène). Etude par enthalpimétrie différentielle

The miscibility of poly(1,1-difluoroethylene) ( 1 ) with poly(N-vinyl-2-pyrrolidone) poly(N-methyl-N-vinylacetamide) and poly(N,N-dimethylacrylamide), containing tert-amido groups, was investigated by differential scanning calorimetry. Amorphous homogeneous blends were obtained whenever the weight fractions of polymer 1 is less than 0,7. The dependence of the single glass transition temperature (T_g) versus composition may be readily analyzed either through the Gordon-Taylor equation (high values of the k parameter, suggesting strong specific interactions between the homopolymers) or by means of the Couchman relation (no adjustable parameter). The broadening of the glass transition range and the variation of the increment of specific heat at T_g for the blends are discussed.     

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.     

Stereocomplex formation in ABA triblock copolymers of poly(lactide) (A) and poly(ethylene glycol) (B)

Two series of triblock copolymers of poly(ethylene glycol) (PEG, number-average molecular weight M _n = 6000) and poly(L -lactide) (PLLA) or poly(D -lactide) (PDLA) were prepared by ring-opening polymerization of lactide initiated by PEG end groups using stannous octoate as a catalyst, either in refluxing toluene or in the melt at 175°C. The weight percentage of PLA in the polymers varied between 15 and 75 wt.-%. Blends of polymers containing blocks of opposite chirality were prepared by co-precipitation from homogeneous solutions. The melting temperatures of the crystalline PEG and PLA phases strongly depended on the composition of the polymers. The melting temperature of the PLA phase in the blends was approximately 40°C higher than that of the single block copolymers. Stereocomplex formation between blocks of enantiomeric poly(lactides) in PEG/PLA block copolymers was established for the first time. Water uptake of polymeric films prepared by solution casting was solely determined by the PEG content of the film.     

Miscibility in blends of polycarbonate and an aromatic polyester

Blends of the polycarbonate of bisphenol-A (PC) with polyacrylate (PA), an aromatic polyester formed from bisphenol A and terephthalic acid/isophthalic acid, were prepared by both melt and solution casting, and their transitional behaviour was examined by differential scanning calorimetry (DSC) and thermo-optical analysis (TOA). Each blend composition was found to have a single glass transition temperature by DSC and by TOA. This result suggests that polycaronate and polyarylate form blends containing a single amorphous phase. Ester-carbonate interchange reactions during melt-mixing were experimentally found to be unimportant. Melting point depression was used to estimate the blend interaction parameter χ₁₂.     

The phase behaviour of a poly(ether sulfone) with poly(ethylene oxide)

Blends of poly(ethylene oxide) with a poly(ether sulfone) were prepared by casting from a common solvent and were found to be miscible and show a single, composition dependent, glass transition temperature. Mixtures in both cyclohexanone and N,N-dimethylformamide phase, separated on heating and thus conditions need to be carefully chosen to obtain homogeneous blends. At higher PEO contents, PEO crystallised from the blends at lower temperatures. The melting point depression, as determined by trubidity measurements, was used to calculate an interaction parameter which was negative, as expected for miscible polymers. The blends also phase separated on heating, and the cloud point curve could be measured by turbidity measurements and confirmed by both visible and electron microscopy. The cloud point curve was very skew with a minimum at around 10 wt.-% PES content. This was not a strong function of the molecular weight and the skew nature was thus presumably due to differences in the state parameters of the pure components. The blends showed a very high mobility with sharp and reproducible could points which might make them ideal for future miscibility studies.     

Polysiloxanes: a paradigm or paradox since the 1960's

For poly(TMPS)

1 Poly(oxydimethylsilanediyl-1,4-phenylene-dimethylsilanediyl).

fractions and blends of fractions, it has been established experimentally that the isothermal spherulitic growth rate, G, and physical properties are strongly interrelated. Correlations also depend strongly upon molecular weight. Below the melt viscosity entanglement molecular weight M_c, G is very dependent upon molar mass whenever crystallized fractions are chain folded, brittle and lacking in tiemolecules. Above M_c, G is essentially constant, and polymers are tough and durable because of trapped entanglements, tie-molecules and the like, that are mostly located at lamellar interfaces. Growth rate measurements and other physical properties of poly(TMPS) are inconsistent with the claim that reptation is a viable process in the crystallization of this polymer. Selective chemical etching of poly(TMPS) crystal surfaces of moderate MW (≈35 × 10³ Daltons) show an increase in crystallinity from ≈75% to 95% as the surface is removed, thus testifying to a less than ordered surface morphology. Notably, in melt crystallized high MW fractions, approaching 10⁶ Daltons and beyond, the morphology is much less well organized than it is in moderate to low MW fractions. Trends in the physical properties of polyethylenes, polyisoprene and poly-(ethylene oxide) MW fractions are analogous in behavior to melt crystallized poly(TMPS) fractions over comparable molecular weights ranges, and consistent with a morphology that is dependent upon polymer chain length.     

Compositional Variation of Glass‐Transition Temperature in Miscible Polymer Blends Involving Weak and Strong Specific Interactions

The miscibilities of some styrene derivatives (polystyrene (PS), poly(p‐methylstyrene) (PPMS) and poly(p‐vinyl phenol) (PVPh)) with poly(cyclohexyl methacrylate) (PCHMA) have been compared by studying their compositional variation of glass‐transition temperatures (T_g). The mixtures of PS and PPMS with PCHMA were found to be miscible over the full composition range whereas PVPh/PCHMA blends showed two phase behaviours. Only when S was copolymerized with VPh at high styrene content (P(S₇₅‐co‐VPh₂₅)) was miscibility observed with PCHMA. All the blends studied exhibited a non‐additive composition dependence, showing both negative (PS/PCHMA and PPMS/PCHMA blends) and positive (PVPh/PMMA and P(S₇₅‐co‐VPh₂₅)/PCHMA blends) deviations from additivity. Positive deviations indicate the presence of significant specific interactions between the two polymers. The lattice‐fluid theory was combined with the Gibbs–DiMarzio approach to study the compositional variation of T_g and an extension of this last theory to hydrogen bonding was applied to mixtures with strong specific intermolecular interactions. The flex energy values and their compositional variation, as well as the hydrogen bonding contribution have been used to study the T_gs.     

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.     

Thermoplastic Vulcanizates Based on Highly Compatible Blends of Isotactic Poly(propylene) and Copolymers of Atactic Poly(propylene) and 5‐Ethylidene‐2‐norbornene

Highly compatible thermoplastic/elastomer blends were used to prepare thermoplastic vulcanizates (TPVs) with refined morphologies and improved mechanical properties. Copolymers of atactic poly(propylene) (aPP) and 5‐ethylidene‐2‐norbornene (ENB) (aPP‐co‐ENB) were prepared via metallocene catalysis. Blends of isotactic poly(propylene) (iPP) and the aPP‐co‐ENB rubbers are immiscible in the melt, but the very high compatibility leads to a refinement of the morphology in comparison to blends based on iPP and ethylene‐propylene‐ diene (EPDM) rubber. The aPP‐co‐ENB‐based blends show improved tensile properties, while the relatively high T_g of the rubber phase retards the elastic recovery at room temperature. Dilution of the TPVs with oil broadens the temperature window for applications by a signification reduction of the T_g and improves the elasticity of the TPVs. This study demonstrates that the lower limit of the rubber particle size of TPVs that is attainable via dynamic vulcanization of immiscible blends is in the order of 300–500 nm.

     

Effect of the core-shell latex polymer content on the compatibility,morphology and mechanical properties of PC/PBA-cs-PMMA blends

The toughening effect of the content of a core-shell poly(butyl acrylate)/poly(methyl methacrylate) latex polymer (PBA-cs-PMMA) on the mechanical properties, morphology and compatibility of its blends with polycarbonate(PC), i.e., PC/PBA-cs-PMMA, was studied. The mechanical properties of the blends are strongly affected by varying the content of PBA-cs-PMMA in the blend. When the PBA-cs-PMMA content is only 5 wt.-%, the impact strength of PC/PBA-cs-PMMA is almost 19 times as high as that of pure PC, indicating that PBA-cs-PMMA is a very good impact modifier for PC. With increasing interphacial layer thickness and decreasing interphacial tension, the interphacial activity becomes more and more effective and, at the same time, miscibility increases too.     

New chitin-based polymer hybrids, 3. Miscibility of chitin-graft-poly(2-ethyl-2-oxazoline) with poly(vinyl alcohol)

The miscibility of blends of poly(vinyl alcohol) (PVA) with chitin-graft-poly(2-ethyl-2-oxazoline) ( 1 ) and poly(2-ethyl-2-oxazoline) homopolymer (PEtOZO) was investigated. Calorimetric results showed a single glass transition temperature (T_g) in the entire range of compositions for both blend systems, which indicated that PVA is miscible with both the graft copolymer 1 and PEtOZO. The T_g of PVA is also shifted to lower temperature upon blending with the graft copolymer 1 . IR analysis revealed the existence of specific interactions via hydrogen bonding between the hydroxyl groups in PVA and the carbonyl groups in the poly(2-ethyl-2-oxazoline) side chain of graft copolymer 1 . The results show that the interaction of graft copolymer 1 with PVA is increased by introduction of longer poly(2-ethyl-2-oxazoline) side chains. Thermal decomposition (TG) measurements supported the compatibility of PVA with graft copolymer 1 and with PEtOZO, and showed that the thermal stability of PVA is improved upon blending with 1 or PEtOZO.     

Evolution of the Morphology and Characterization of Compatibilized PBT/EVA Blends Prepared by Reactive Extrusion

Summary: In this work, the possibility of preparing compatibilized blends of poly(butylene terephthalate) (PBT) and an ethylene vinyl acetate (EVA) copolymer by reactive extrusion in the presence of an ethylene acrylic acid copolymer (EAA) and a bisoxazoline compound (PBO) as compatibilization promoters has been studied. In addition, the evolution of the morphology of the blends under different annealing conditions in the presence and absence of the compatibilizing promoters has been studied. Binary blends of PBT and EVA showed behavior typical of incompatible blends with a gross morphology and bad mechanical performance. The situation was however different for ternary PBT/EVA/EAA and especially for quaternary PBT/EVA/EAA/PBO blends. In the latter case, the morphology was finer, the adhesion improved and the mechanical properties were enhanced, with values almost doubled with respect to those of uncompatibilized blends. These results can be explained by the formation of in situ EAA‐g‐(PBO)PBT copolymers which act as compatibilizers for the blends. While the binary and, to some extent, the ternary blend display coalescence under annealing with rapid coarsening of the morphology, the quaternary compatibilized blends showed the best morphological stability as the particle dimensions remained practically unchanged. This phenomenon was interpreted considering the role of kinetic hindrance played by the compatibilizer formed in situ.

SEM micrograph of PBT/EVA/EAA/PBO blend at 5 000×.