Miscible blends containing a crystallizable component: poly(vinyl alcohol)/poly(ethyleneimine)

Blends of poly(vinyl alcohol) (PVAI) with poly(ethyleneimine) (PEI) were prepared by casting from a common solvent. All blends show a single, composition dependent glass transition temperature (T_g), indicating that the blends are miscible in the amorphous state and in the melt. The overall crystallization rate of PVAI in the blend decreases with increasing PEI content. The crystallinity index of PVAI in the blend does not decrease greatly with PEI content up to a composition of 70/30 PVAI/PEI, since the T_g of the crystallizable component PVAI is larger than that of the non-crystallizable component PEI. The T_g of the system PVAI/PEI decreases with increasing PEI content. The interaction parameter B of the two polymers in the melt was found to be −24 J/cm³.     

Phase behavior and interactions in blends of poly[(butylene adipate)-co-poly(butylene terephthalate)] copolyester with poly(4-vinyl phenol)

Miscibility with a linear T _g–composition relationship was proven for blend of poly(butylene adipate-co-butylene terephthalate) [P(BA-co-BT)] with poly(4-vinyl phenol) (PVPh). In comparison to the blends of PBA/PVPh and poly(butylene terephthalate) (PBT)/PVPh, the Kwei’s T _g model fitting on data for the P(BA-co-BT)/PVPh blend yields a q value between those for the PBA/PVPh and PBT/PVPh blends. The q values suggest that the interaction strength in the P(BA-co-BT)/PVPh blend is not as strong as that in the PBT/PVPh blend. Upon mixing the PVPh into the immiscible blend of PBA and PBT, the ternary PBA/PBT/PVPh blends only exhibits partial miscibility. Full-scale ternary miscibility in whole compositions is not possible owing to the significant ∆χ effect (χ _ij  – χ _ik ). The wavenumber shifts of the hydroxyl IR absorbance band indicates that the H-bonding strength is in decreasing order—PBT/PVPh > P(BA-co-BT)/PVPh > PBA/PVPh—and shows that the BA segment in the copolymer tends to defray interactions between P(BA-co-BT) and PVPh in blends.     

Miscibility and hydrolytic degradation in alkaline solution of poly(l-lactide) and poly(p-vinyl phenol) blends

Poly(l-lactide) (PLLA) was melt-blended with poly(p-vinyl phenol) (PVPh) using a two-roll mill, and the miscibility between PLLA and PVPh and degradation of the blend films were investigated. It was found that PLLA/PVPh blend has miscibility in the amorphous state because only single T_g was observed in the DSC and DMA measurements. The T_g of the PLLA/PVPh blend could be controlled in the temperature range from 55 °C to 117 °C by changing the PVPh weight fraction. In alkaline solution, degradation rate of PLLA/PVPh blends was faster than that of neat PLLA because PVPh could dissolve in alkaline solution. The surface morphology of degraded PLLA and PLLA/PVPh blend were observed by SEM. The surface morphology of degraded PLLA/PVPh blend was finer than that of PLLA. Young's modulus of PLLA/PVPh blend increased with increasing PVPh content. Yield stress of PLLA/PVPh blends whose PVPh content was less than 30 wt% kept the level of about 55 MPa and that of PLLA/PVPh blend whose PVPh content was 40 wt% is much lower than that of neat PLLA.     

Influence of compatibilization on the mechanical behavior of poly(trimethylene terephthalate)/poly(ethylene-octene) blends

Poly(trimethylene terephthalate) (PTT) based blends toughened with up to 30 wt.% of a partially maleinized poly(ethylene-octene) copolymer (mPEO) were obtained by melt mixing. The blends were composed of two pure amorphous phases and a partially crystalline PEO phase. The rubber modification clearly compatibilized the blends leading to a decrease in the dispersed phase size. The decrease was not enough to attain the brittle-tough transition, but an increase in the shear rate gave rise to an additional decrease in the dispersed phase size and in the interparticle distance (IDc) that led to very high toughness values (15-fold the notched impact strength of the matrix) at rubber contents above 25 wt.%. The critical interparticle distance of the blends was 0.17 μm. A comparison between this IDc and those of PBT/mPEO and PET/mPEO blends was explained in terms of their interfacial tensions.     

Ionic liquids: New generation stable plasticizers for poly(vinyl chloride)

Room temperature ionic liquids (ILs), based on ammonium, imidazolium and phosphonium cations, were studied as novel plasticizers for poly(vinyl chloride), PVC. All the ILs tested were able to produce flexible PVC. Upon 20 wt% plasticization, some of the ILs lowered the glass transition temperature (T_g) of PVC more than that done by several traditional plasticizers. They showed good thermodynamic compatibility as well. Several ILs showed better leaching and migration resistance than the traditional plasticizers. This was, in particular, a significant observation considering the ongoing controversy regarding the leaching and migration issues of the commonly-used phthalate plasticizers. High temperature and ultraviolet (UV) ray stability of IL-plasticized PVC samples were also studied.     

Polymer-polymer miscibility in blends of a new poly(aryl ether ketone) with poly(ether imide)

Polymer miscibility was found for a blend system comprising of a new poly(aryl ether ketone) and a poly(ether imide). Phase homogeneity was preliminarily confirmed using optical and scanning electron microscopy, indicating that the scales of phase homogeneity in the blends were beyond the resolution limits of either microscopy. A composition-dependent, single glass transition temperature (T_g) in the PAEK/PEI blends within the full range of composition was observed using differential scanning calorimetry (DSC). The thermal transition breadth also suggests that the scales of mixing are fine and uniform.     

Effect of nanoscale fully vulcanized acrylic rubber powders on crystallization of poly(butylene terephthalate): Isothermal crystallization

Poly(butylene terephthalate) (PBT) was blended with nanoscale fully vulcanized acrylic rubber (FVAR) powders in a twin extruder, and the FVAR powders were dispersed well in PBT from scanning electron microscopy (SEM) and transmission electron microscope (TEM) investigation. The isothermal crystallization kinetics of PBT/FVAR blends were investigated by differential scanning calorimeter (DSC) and simulated by Avrami model. Equilibrium melting temperature was estimated by the nonlinear Hoffman-Weeks relation. The active energy (ΔE) and nucleation parameters (K_g) increased with the addition of FVAR, suggesting that FVAR particles hindered the crystallization; however more content FVAR had a lower ΔE and K_g because FVAR powders acted as heterogeneous nuclei in the nucleation of crystallization and facilitated the crystallization of PBT. The crystallization ability followed the order: PBT > PBT/FVAR6 > PBT/FVAR3 > PBT/FVAR1 when undercooling was considered.     

Mechano-optical behavior in poly (ethylene terephthalate)/poly (ether imide) blends

Mechano-optical behavior and related structural evolution during uniaxial stretching of melt miscible poly (ethylene terephthalate) (PET)/poly (ether imide) (PEI) blends were studied near their glass transition temperature using an instrumented machine that measures true stress, true strain and spectral birefringence simultaneously. Stretching from amorphous state, two distinct stress-optical regimes were observed at temperatures between T_g and T_cc (cold crystallization). Near T_g, a typical photoelastic behavior persists until a critical temperature above which temperature independent initial stress optical behavior is observed. At those temperatures above T_g, where glassy behavior is observed, decreasing stretching rate was also found to eliminate this glassy photo elastic regime leading to the observation of a linear initial stress optical behavior that becomes temperature independent as expected from linear stress optical rule. Increasing PEI concentration in the blends suppresses crystallizability and increases temperature at which initial elastic region disappears giving way to pure liquid behavior where linear stress optical behavior is observed. This is attributed to the increase and broadening of the glass transition temperature with the addition of noncrystallizable PEI. In PET/PEI blends, the stress-optical coefficient (SOC), determined in a linear stress optical regime, was found to increase linearly with the increase in PEI concentration.     

Vitrification/devitrification phenomena during isothermal and nonisothermal crystallization of poly(aryl–ether–ether–ketone) (PEEK) and PEEK/poly(ether–imide) blends

We have established time–temperature transformation and continuous-heating transformation diagrams for poly(ether–ether–ketone) (PEEK) and PEEK/poly(ether–imide) (PEI) blends, in order to analyze the effects of relaxation control on crystallization. Similar diagrams are widely used in the field of thermosetting resins. Upon crystallization, the glass transition temperature (T_g) of PEEK and PEEK/PEI blends is found to increase significantly. In the case of PEEK, the shift of the α-relaxation is due to the progressive constraining of amorphous regions by nearby crystals. This phenomenon results in the isothermal vitrification of PEEK during its latest crystallization stages for crystallization temperatures near the initial T_g of PEEK. However, vitrification/devitrification effects are found to be of minor importance for anisothermal crystallization, above 0.1°C/min heating rate. In the case of PEEK/PEI blends, amorphous regions are progressively enriched in PEI upon PEEK crystallization. This promotes a shift of the α-relaxation of these regions to higher temperatures, with a consequent vitrification of the material when crystallized below the T_g of PEI. The data obtained for the blends in anisothermal regimes allow one to detect a region in the (temperature/heating rate) plane where crystallization proceeds in the continuously close proximity of the glass transition (dynamic vitrification). These experimental findings are in agreement with simple simulations based on a modified Avrami model coupled with the Fox equation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 919–930, 1998     

Structure and mechanical properties of blends of poly(ether imide) and an amorphous polyamide

Biphasic poly(ether imide)/poly(trimethyl hexamethylene terephthalamide) blends were obtained by injection moulding through the full composition range both with and without previous extrusion mixing. The extruded blends showed an improved performance, as the T_gs of the two amorphous phases changed and the changes were larger than those of directly injected blends. The T_g changes indicate the presence of the two components in the two phases of the extruded blends. The consequent low interfacial tension is proposed as the reason for the observed generally fine particle size (typically 0.3 μm). Both characteristics led to mostly ductile materials. The modulus of elasticity and the yield stress were slightly below those predicted by the rule of mixtures. As this was due to a lower orientation in the blends, both properties could improve through a change of the processing parameters. The increase in impact strength over that of pure PEI, and particularly, the sudden processability increase (35% torque decrease) upon a-PA addition, led to compatible blends that, as in the case of the 90/10 composition, could be a polymeric material alternative to unmodified PEI.     

Linear unsaturated polyester + poly(?-caprolactone) blends: Calorimetric behaviour and morphology

Blends of a linear unsaturated polyester (LUP, commercially named Al100) with poly(?-caprolactone) (PCL) of different molecular weights have been studied. The miscibility and crystallinity have been analyzed through FT-IR spectroscopy, differential scanning calorimetry (DSC) and environmental scanning electronic microscopy (ESEM). All the blends were subjected to the same heat treatment consisting of crystallizing during 45 min at constant temperature (10, 20, 30 or 40 °C). The glass transition temperature, T_g, and fusion temperature, T_fus, have been determined in the whole composition range for each blend. The T_g-composition dependence and the high degree of crystallinity detected at intermediate blend compositions denote an anomalous behaviour that could indicate the lack of homogeneity (phase separation) in the different blends studied. The ESEM measurements confirm the lack of homogeneity of the amorphous region in blends with high content of LUP. The results have been discussed as a function of the crystallization temperature and the molecular weight of PCL.     

Competition of phase dissolution and crystallization in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blend

Blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile was studied. The PCL/SAN blend having LCST (lower critical solution temperature) phase boundary above the melting point T_m of PCL offered an excellent opportunity to investigate the competition of liquid-solid phase transition (crystallization) and liquid-liquid phase transition (phase dissolution). A blend with the critical composition (80/20 PCL/SAN) underwent a temperature-jump above LCST to proceed spinodal decomposition, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below T_m at which both the crystallization and the phase dissolution could occur. By transmission electron microscopy it was found that during isothermal annealing after quenching to high temperatures close to T_m (e.g. 51 °C), the SD structure gradually disappeared, and then the crystallization started from a single-phase mixture to yield normal crystalline structure similar to that of a neat crystalline polymer. At lower temperatures (e.g. 40 °C), crystallization quickly occurred and the SD structure was preserved, implying that the crystallization prevailed over the dissolution yielding a bi-continuous structure consisting of amorphous (SAN-rich) and crystalline (PCL-rich) regions. At intermediate temperatures (e.g. 45 °C), the phase dissolution competed with the crystallization, resulting in a bi-continuous structure with longer periodic distance and a broad boundary having a gradient in composition of amorphous region between PCL crystal lamellae. Light-scattering analysis quantitatively revealed a competition of the crystallization and the phase dissolution in terms of the crystallization rate (from H_v scattering) and the apparent diffusion coefficient for dissolution (from V_v scattering).     

Poly(butylene terephthalate)/poly(ε-caprolactone) blends: Influence of PCL molecular mass on PBT melting and crystallization behavior

The isothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) (PBT) in binary blends with poly(ε-caprolactone) (PCL) was investigated as a function of PCL molecular mass by differential scanning calorimetry and optical microscopy. The components are miscible in the melt when oligomeric PCL (M_w = 1250) is blended with PBT, whereas only partial miscibility was found in mixtures with higher molecular mass (M_w = 10,000 and 50,000). The equilibrium melting point of PBT in the homopolymer and in blends with PCL was determined through a non-linear extrapolation of the T_m = f(T_c) curve. The PBT spherulitic growth rate and bulk crystallization rate were found to increase with respect to plain PBT in blends with PCL1250 and PCL10000, whereas addition of PCL50000 causes a reduction of PBT solidification rate. The crystallization induction times were determined by differential scanning calorimetry for all the mixtures through a blank subtraction procedure that allows precise estimation of the crystallization kinetics of fast crystallizing polymers. The results have been discussed on the basis of the Hoffman-Lauritzen crystallization theory and considerations on both the transport of chains towards the crystalline growth front and the energy barrier for the formation of critical nuclei in miscible and partially miscible PBT/PCL mixtures are widely debated.     

Determination of interactions between aryl polyesters and poly(ether imide) via glass transition temperatures of separated phases in immiscible blends

Phase behavior in domains of immiscible blends of poly(pentamethylene terephthalate)/poly(ether imide) (PPT/PEI) and poly(hexamethylene terephthalate)/poly(ether imide) (PHT/PEI) were investigated using differential scanning calorimetry (DSC). The measured glass transition temperature (T _g) reveals that aryl polyesters dissolve more in the PEI-rich phase than the PEI does in the aryl polyester-rich phase, for both PPT/PEI and PHT/PEI systems. Additionally, optical microscopy supports the conclusion that PPT (or PHT) dissolves more in the PEI-rich phase than PEI does in the PPT-rich (or PHT-rich) phase in the aryl polyester/PEI blends. Furthermore, the Flory–Huggins interaction parameters (χ₁₂) for the PPT/PEI and the PHT/PEI blends were calculated to be 0.12 and 0.17, respectively. For the blend systems comprising of PEI and homologous aryl polyesters, the value of χ₁₂ exhibits a trend of variation with respect to structure of aryl polyesters. For the PPT/PEI and PHT/PEI blends, investigated in this study, value of the polymer–polymer interaction parameter (χ₁₂) between the aryl polyester and the PEI was found to be positive, which increases with the number of methylene moieties in the repeating unit of the aryl polyester, ultimately resulting in phase separation observed.     

Thermal and crystallization characteristics of poly(trimethylene terephthalate)/poly(ethylene naphthalate) blends

Poly(trimethylene terephthalate) (PTT)/poly(ethylene naphthalate) (PEN) blends were miscible in the amorphous state in all of the blend compositions studied, as evidenced by a single, composition-dependent glass transition temperature (T_g) observed for each blend composition. The variation in the T_g value with the blend composition was well predicted by the Gordon-Taylor equation, with the fitting parameter being 0.57. The cold-crystallization peak temperature decreased with increasing PTT content, while the melt-crystallization peak temperature decreased with increasing amount of the minor component. The subsequent melting behavior after both cold- and melt-crystallization exhibited melting point depression, in which the observed melting temperatures decreased with increasing amount of the minor component. During melt-crystallization, both components in the blends crystallized concurrently just to form their own crystals. The blend with 60% w/w of PTT exhibited the lowest total apparent degree of crystallinity.     

Effect of PEO‐PPO‐PEO copolymer on the mechanical and thermal properties and morphological behavior of biodegradable poly (L‐lactic acid) (PLLA) and poly (butylene succinate‐co‐L‐lactate) (PBSL) blends

A blend of two biodegradable and semi‐crystalline polymers, poly (L‐lactic acid) (PLLA; 70 wt%) and poly (butylene succinate‐co‐L‐lactate) (PBSL; 30 wt%), was prepared in the presence of various polyethylene oxide‐polypropylene oxide‐polyethylene oxide (PEO‐PPO‐PEO) triblock copolymer contents (0.5, 1, 2 wt%). Mechanical, thermal properties, and Fourier transform infrared (FTIR) analysis of the blends were investigated. It was found that the addition of copolymer to PLLA/PBSL improved the fracture toughness of the blends as shown by mode I fracture energies. It was supported by morphological analysis where the brittle deformation behavior of PLLA changed to ductile deformation with the presence of elongated fibril structure in the blend with copolymer system. The glass transition temperature (T_g), melting temperature (T_m) of PLLA, and PBSL shift‐closed together indicated that some compatibility exists in the blends. In short, PEO‐PPO‐PEO could be used as compatibilizer to improve the toughness and compatibility of the PLLA/PBSL blends. Copyright © 2010 John Wiley & Sons, Ltd.     

Pore structure and glass transition temperature of nanoporous poly(ether imide)

The effect of nanopores on the glass transition temperature (T_g) of poly(ether imide) was studied with differential scanning calorimetry. Nanoporous poly(ether imide) samples were obtained through the phase separation of immiscible blends of poly(ether imide) and polycaprolactone diol and by the removal of the dispersed minor phase domains with a selective solvent. Microscopy and statistical methods were used to characterize the pore structure and obtain the pore structure parameters. The pore size was found to depend on the processing time and the initial blend composition, mainly because of phase-coarsening kinetics. A decrease in T_g was observed in the nanoporous poly(ether imide) in comparison with the bulk samples. The change in T_g was strongly influenced by the pore structure and was explained by the percolation theory. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3546–3552, 2006     

Single-step synthesis of proton conducting poly(vinylidene fluoride) (PVDF) graft copolymer electrolytes

The single-step synthesis of proton conducting poly(vinylidene fluoride) (PVDF) graft copolymer electrolytes is demonstrated. The graft copolymers of PVDF backbone with poly(sulfopropyl methacrylate) (PVDF-g-PSPMA) and poly(styrene sulfonic acid) (PVDF-g-PSSA) were synthesized using PVDF as a macroinitiator for atom transfer radical polymerization (ATRP). ¹H NMR and FT-IR spectroscopy show that the “grafting from” method using ATRP was successful and the maximum grafting degrees were 35 and 25 wt% for PVDF-g-PSPMA and PVDF-g-PSSA, respectively. The IEC values were 0.63 and 0.45 meq/g, the water uptakes were 46.8 and 33.4 wt% and the proton conductivities were 0.015 and 0.007 S/cm at room temperature, for PVDF-g-PSPMA and PVDF-g-PSSA, respectively. Both membranes exhibited excellent thermal stability up to around 350 °C, verified by thermal gravimetric analysis (TGA).     

Glass transition study of blends of poly(N-methyldodecano-12-lactam) with poly(styrene-co-acrylic acid)

The blends of poly(N-methyldodecano-12-lactam) (MPA) with poly(styrene-co-acrylic acid) (PSAA) prepared from dioxane solutions were studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The experimental DSC data of glass transition temperature T_g as a function of composition of amorphous phase were fitted for the as-prepared and re-scanned samples using theoretical approaches. The as-prepared blends show monotonic single-T_g dependence. The values of the Gordon-Taylor coefficient not far from unity suggest miscibility of the blend system in amorphous phase in the whole concentration range. As documented by FTIR, this miscibility is associated with hydrogen bonds between COOH groups of the acrylic acid units in PSAA molecules acting as the H-bond donor and CO groups of MPA acting as the H-bond acceptor. The T_g-dependencies obtained form the second runs have a profound sigmoid character. The Schneider treatment induced an idea of partial limited miscibility in the MPA/PSAA blends caused by prevalence of homogeneous contacts. The difference in T_g between the first and second run can partly be attributed to higher crystallinities in the former.     

Transition metal compatibilization of poly(vinylamine) and poly(ethylene imine)

Poly(vinylamine), PVA, complexes with cobalt chloride hexahydrate exhibit a 45 °C enhancement in the glass‐transition temperature per mol % of the d‐block metal cation. Poly(ethylene imine), PEI, complexes with CoCl₂(H₂O)₆ exhibit a 20 °C enhancement in T_g per mol % Co²⁺. Since the basicities of primary and secondary amines are comparable (i.e., pK_b,PVA ≈ 3.34 vs. pK_b,PEI ≈ 3.27) and the rates at which each polymeric ligand displaces waters of hydration in the coordination sphere of Co²⁺ are similar, transition metal compatibilization is operative in blends of both polymers with CoCl₂(H₂O)₆. These two polymers are immiscible in the absence of the inorganic component. Infrared spectroscopy suggests that nitrogen lone pairs in PVA and PEI coordinate to Co²⁺. The stress–strain response of a 75/25 blend of PVA and PEI with 2 mol % Co²⁺ reveals a decrease in elastic modulus from 4.4 × 10⁹ N/m² to 5.7 × 10⁷ N/m², a decrease in fracture stress from 3.7 × 10⁷ N/m² to 2.0 × 10⁶ N/m², and an increase in ultimate strain from 1.3 to 12% relative to the 75/25 immiscible polymer–polymer blend. A plausible explanation for this effect is based on the fact that cobalt chloride hexahydrate compatibilizes both polymers by forming a coordination bridge between nitrogen lone pairs in dissimilar chains. Hence, poly(ethylene imine), which is very weak with a T_g near −40 °C, is integrated into a homogeneous structure with poly(vinylamine) and the mechanical properties of the individual polymers are averaged in the compatibilized ternary complex. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 552–561, 2000