Study on structure-property relationship of polyimide blends

Summary Three pairs of polyimide/polyimide blends (50/50 wt%) with different molecular structures were prepared by two ways, i.e. mixing of the polyamic acid precursors with subsequent imidization, and direct solution mixing of the polyimides. The blends were studied with DMA technique. The results obtained show that all the blends prepared with these two different ways are miscible, as there existed only one glass transition temperature (Tg) for all the blends. It is suggested that the miscibility of these polyimide/polyimide blends is a result of the strong inter-molecular charge-transfer interaction between the chains of their components.     

Miscible blends of poly(4‐vinyl phenol)/poly (trimethylene terephthalate)

A new miscible blend of all compositions comprising poly(4‐vinyl phenol) (PVPh) and poly(trimethylene terephthalate) (PTT) was discovered and reported. The blends exhibit a single composition‐dependent glass transition and homogeneous phase morphology, with no lower critical solution temperature (LCST) behavior upon heating to high temperatures. Interactions and spherulite growth kinetics in the blends were also investigated. The Flory–Huggins interaction parameter (χ₁₂) and interaction energy density (B) obtained from analysis of melting point depression are negative (χ₁₂ = ?0.74 and B = ?32.49 J cm^?3), proving that the PVPh/PTT blends are miscible over a wide temperature range from ambient up to high temperatures in the melt state. FTIR studies showed evidence of hydrogen‐bonding interactions between the two polymers. The miscibility of PVPh with PTT also resulted in a reduction in spherulite growth rate of PTT in the miscible blend. The Lauritzen–Hoffman model was used to analyze the spherulite growth kinetics, which showed a lower fold‐surface free energy (σ_e) of the blends than that of the neat PTT. The decrease in the fold‐surface free energy has been attributed to disruption of the PTT lamellae exerted by PVPh in an intimately interacted miscible state. Copyright © 2004 Society of Chemical Industry     

Linear and networked blends and copolymers of polyimide

Preparation and characterization of blends and copolymers of a fluorinated polyimide with network constituents is reported. 4,4′‐Hexafluoroisopropylidene diphthalic anhydride and 4,4′‐diaminodiphenyl ether (6FDA–DDE) polyimide were used as the linear hosts and mellitic acid hexamethyl ester ‐ 4,4′‐diaminodiphenyl ether (MAHE–DDE) was employed as the network constituent for the blend and copolymer. Cast films of the polyimides were characterized by FTIR, XPS, DMA, and TGA. The multifunctional nature of MAHE facilitated crosslinking among the constituents. Both blends and copolymers showed significant improvement in the storage modulus and glass transition temperature relative to that observed for the 6FDA homopolymer. The occurrence of a single glass transition temperature for the blends suggests that they were at least partially miscible. Presence of low molecular weight species in the copolyimides, combined with steric hindrance to crosslinking, may have resulted in the existence of an optimum in the amount of the network components for improving the mechanical properties. Inclusion of network components is presented as a facile method for improving the desirable properties of polyimide. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3000–3008, 2006     

Miscibility,crystallization, and morphology studies of thermosetting polyimide PMR-15/PEK-C blends

Miscibility, crystallization, and mechanical properties of blends of thermosetting polyimide PMR-15 and phenolphthalein poly(ether ketone) (PEK-C) were examined. With the exception of the 90/10 blend, which has two glass transition peaks, all the blends with PMR-15 less than 90 wt % are miscible in the amorphous state according to DMA results. Addition of PEK-C hindered significantly the crystallization of PMR-15, indicating that there must exist some kind of interaction between molecular chains of PMR-15 and those of PEK-C. The semi-IPN system of PMR-15/PEK-C blends exhibits good toughness. Two distinct microphases, interweaving at the phase boundaries, were found in the PMR-15/PEK-C 60/40 blend. The toughness effect of the blends is discussed in terms of the interface adhesion between the two distinct phases and the domain sizes of the phases. The relation between miscibility and toughness of the blends was investigated. © 1996 John Wiley & Sons, Inc.     

Dielectric investigation of the molecular dynamics in blends: polymers with similar molecular architecture (TMPC/PC blend)

Broad band dielectric spectroscopy was used in the investigation of the molecular dynamics and compatibility of tetramethyl polycarbonate/polycarbonate (TMPC/PC) blends. Frequency scan measurements in the range 10^?2?10^?5 Hz were carried out in the temperature range 50–220°C for several blends with different compositions, namely, 0, 12.5, 25, 50, 75, 87.5 and 100 wt% of TMPC. The results obtained show that these two polymers are ideally compatible over the entire composition range. The blends reveal only one common glass process. The dielectric relaxation strength and the common glass transition temperature, T_g, were found to vary linearly with composition. Moreover, it was found, surprisingly, that blending has no effect on the distribution of relaxation times of the common glass process of the blends. Furthermore, neither the kinetics (relaxation frequency at a certain temperature) nor the distribution of relaxation times of the local process were influenced by blending. It is concluded that the polymeric chains of the different components are not miscible on a segmental level although the blend exhibits only one glass transition temperature.     

Miscibility and mechanical properties of poly(ether imide)/poly(ether ether ketone)/liquid crystalline polymer ternary blends

This paper is concerned with a novel ternary blend composed of poly(ether imide) (PEI), poly(ether ether ketone) (PEEK) and a liquid crystalline polymer (LCP; HX4000, Du Pont). Different compositions were prepared by extrusion and injection moulding. Dynamic mechanical thermal analysis and the observation of the fracture surfaces, before and after annealing, allowed determination of the cold crystallization temperatures and miscibility behaviour of these systems. PEEK/PEI blends are known from previous studies to be miscible at all compositions. In this case it was observed that the PEEK/HX4000 blend was miscible up to 50 wt% HX4000 but partially miscible above this value. The PEI/HX4000 blends were found to be partially miscible in the whole concentration range. As a result, some ternary blend compositions exhibited only one phase, while others exhibited two phases. The measurement of the tensile properties showed that ternary blends with high modulus can be obtained at high LCP loadings, while compositions with high ultimate tensile strength can be obtained with high loadings of PEI or PEEK.     

Solvent effect on the curing of polyimide resins

The effect of the solvent 1-methyl-2-pyrrolidinone (NMP) on the curing of polyimide resins synthesized from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) has been investigated. Three polyimide precursors, i.e., the polyamic acid (PAA), with controlled amount of NMP were prepared. The study was aimed first to independently investigate the decomplexation process, which involved the evolution of hydrogen-bonded NMP from PAA, without interference from imidization. This was accomplished by TGA at varying heating rates using different solvent content in PAA. The observed one-stage decomplexation process suggested that the complex formation of NMP and PAA was not the same as the model compound studied by others. An average value of 150 kJ/mol for the activation energy of the decomplexation process was obtained. The study then sought to identify the effect of the decomplexation on the imidization kinetics by employing DSC at several drying temperatures and also varying heating rates. This allowed one to control the extent of plasticization that occurred to facilitate the imidization process. Our DSC data showed that over-drying PAA resulted in prolonged imidization due mainly to the lack of plasticization by decomplexed NMP. The estimated enthalpy of imidization and that of decomplexation were 114 KJ/mol and 53 kJ/mol NMP, respectively. Finally, the imidization kinetics was independently investigated using FTIR, without the interference from decomplexation process. The results indicated that there were four stages during the entire imidization process. Up to a temperature of 150°C, less than 20% of amide groups had reacted to give imide groups and the reaction was slow. Most of the imidization took place between 150 and 180°C with conversion as high as 90%. The imidization process was completed after the temperature was further raised to 250°C. Above 250°C, the reverse reaction became more significant (due probably to configurational and packing preference) and resulted in a lowering of final conversion back to 80%. © 1992 John Wiley & Sons, Inc.     

Modification of recycled high‐density polyethylene by low‐density and linear‐low‐density polyethylenes

The present study investigated mixed polyolefin compositions with the major component being a post‐consumer, milk bottle grade high‐density polyethylene (HDPE) for use in large‐scale injection moldings. Both rheological and mechanical properties of the developed blends are benchmarked against those shown by a currently used HDPE injection molding grade, in order to find a potential composition for its replacement. Possibility of such replacement via modification of recycled high‐density polyethylene (reHDPE) by low‐density polyethylene (LDPE) and linear‐low‐density polyethylene (LLDPE) is discussed. Overall, mechanical and rheological data showed that LDPE is a better modifier for reHDPE than LLDPE. Mechanical properties of reHDPE/LLDPE blends were lower than additive, thus demonstrating the lack of compatibility between the blend components in the solid state. Mechanical properties of reHDPE/LDPE blends were either equal to or higher than calculated from linear additivity. Capillary rheological measurements showed that values of apparent viscosity for LLDPE blends were very similar to those of the more viscous parent in the blend, whereas apparent viscosities of reHDPE/LDPE blends depended neither on concentration nor on type (viscosity) of LDPE. Further rheological and thermal studies on reHDPE/LDPE blends indicated that the blend constituents were partially miscible in the melt and cocrystallized in the solid state.     

Miscibility and crystallization behaviors of biodegradable poly(butylene succinate‐co‐butylene terephthalate)/phenoxy blends

Miscibility and crystallization behaviors of biodegradable poly(butylene succinate‐co‐butylene terephthalate) (PBST)/poly(hydroxyl ether biphenyl A) (phenoxy) blends were investigated with various techniques in this work. PBST and phenoxy are completely miscible as evidenced by the single composition‐dependent glass transition temperature over the entire blend compositions. Nonisothermal melt crystallization peak temperature is higher in neat PBST than in the blends at a given cooling rate. Isothermal melt crystallization kinetics of neat and blended PBST was studied and analyzed by the Avrami equation. The overall crystallization rate of PBST decreases with increasing crystallization temperature and the phenoxy content in the PBST/phenoxy blends; however, the crystallization mechanism of PBST does not change. Moreover, blending with phenoxy does not modify the crystal structure but reduces the crystallinity degree of PBST in the PBST/phenoxy blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Toughening effect of PNBR on ASA/SAN binary blends

In this work, (acrylonitrile‐styrene‐acrylic terpolymer)/(styrene‐acrylonitrile copolymer)/(powder nitrile butadiene rubber) ternary blends with different compositions were prepared by melt blending. Differential scanning calorimetry, dynamic mechanical analysis, and Fourier‐transform infrared spectra were used to analyze the glass transition behavior and interactions among components of the blends, while scanning electron microscopy was used to observe the microstructure. Furthermore, mechanical properties, heat resistance, and melt flow rate of the blends were tested. The results showed that addition of powder nitrile butadiene rubber can enhance toughness of the blends on a large scale, and the blend system seems to be miscible according scanning electron microscopy images. J. VINYL ADDIT. TECHNOL., 20:268–274, 2014. © 2014 Society of Plastics Engineers     

Adhesion behavior of blends of polybutadiene and tackifiers

The adhesion behavior of blends of polybutadiene (PB) and tackifiers was investigated. The peel strength was found to be significantly dependent on blend composition, and a maximum strength behavior was observed for all blend systems. The tack mechanisms were proposed to explain the observed adhesion behavior. The position of the glass transition temperature is related to where the highest tack appears for the miscible blend; for the partially miscible blend the dispersed phase plays an important role in determining the maximum adhesion, and the critical size of the dispersed phase and the Tg of the tackifier phase together determine what concentration of tackifier gives the maximum tack. For the immiscible blends, the maximum adhesion is controlled by both the surface glass transition temperature and the critical diameter of the domains of the tackifier phase.     

Miscible blends of poly(tetrahydrofurfuryl methacrylate) with two hydroxyl-containing polymers

Summary Poly(tetrahydrofurfuryl methacrylate) (PTHFMA) was found to be miscible with poly(hydroxy ether of bisphenol A) (phenoxy) as shown by the existence of a single glass transition temperature in each blend. PTHFMA/phenoxy blends containing 50% or less of PTHFMA showed reversible lower critical solution temperatures. PTHFMA was judged to be miscible with poly(styrene-co-allyl alcohol) based on the optical clarity of the blends.     

Miscibility and hydrogen bonding in blends of poly(vinyl acetate) with phenolic resin

The miscibility of phenolic resin and poly(vinyl acetate) (PVAc) blends was investigated by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FT-IR) and solid state ¹³C nuclear magnetic resonance (NMR). This blend displays single glass transition temperature (T_g) over entire compositions indicating that this blend system is miscible in the amorphous phase due to the formation of hydrogen bonding between hydroxyl groups of phenolic resin and carbonyl groups of PVAc. Quantitative measurements on fraction of hydrogen-bonded carbonyl group using both ¹³C solid-state NMR and FT-IR analyses result in good agreement between these two spectroscopic techniques. According to the proton spin-lattice relaxation time in the rotating frame (T_1ρ^H), the phenolic/PVAc blend is intimately mixed on a scale less than 2-3 nm. Furthermore, the inter-association equilibrium constant and its related enthalpy of phenolic/PVAc blends were determined as a function of temperatures by infrared spectra based on the Painter-Coleman association model.     

Simulation of polyimide fibers with trilobal cross section produced by dry‐spinning technology

As one type of high performance fibers, polyimide fibers can be prepared from polyamic acid (PAA) solution by dry‐spinning technology. The transformation from the precursor of polyamic acid to polyimides via thermal cyclization reaction in the dry‐spinning process is a main distinguishing feature, which is very different from other fibers produced by dry‐spinning such as cellulose acetate fiber and polyurethane fiber. In this report, the dry‐spinning formation of polyimide fibers with trilobal cross section from PAA solution in N,N‐dimethylacetamide is simulated via a one‐dimensional model based on a viscoelastic constitutive equation, combined with profile degree equation of cross section and imidization kinetics equation. The glass transition temperature, imidization degree and profile degree of the filament along the spinline are predicted by the model, as well as relative parameters such as solvent mass fraction and temperature. As a simulated result, solidification of polyimide fibers take place about 150 cm from the spinneret which is farther than for cellulose acetate fiber (70 cm). Moreover, the final profile degree of fiber is affected by many spinning parameters, such as spinning temperature, surface tension, spinning solution concentration, major, and minor axis length of the spinneret hole. POLYM. ENG. SCI., 55:2148–2155, 2015. © 2015 Society of Plastics Engineers     

Biaxially oriented films prepared from poly(vinyl chloride)/poly(methyl methacrylate co imide) blends

A study was conducted of blends of poly(vinyl chloride) (PVC) with a poly(methyl methacrylate co imide). The latter polymer was found to be miscible in PVC and to raise the glass transition temperature of the blend. Blends of all compositions could be oriented, but the processing temperature increased in proportion with T_g. For a given blend composition, orientation increased with increasing stretch ratio and strain rate and with decreasing stretch temperature. Increasing copolyimide content and increasing orientation generally lead to improved mechanical properties, though the blends containing high levels of copolyimide exhibited low ductilities.     

Miscibility and crystallization behavior of biodegradable poly(ε‐caprolactone)/tannic acid blends

Miscibility, isothermal melt crystallization kinetics, spherulitic morphology and growth rates, and crystal structure of completely biodegradable poly(ε‐caprolactone) (PCL)/tannic acid (TA) blends were studied by differential scanning calorimetry, polarized optical microscopy, and wide angle X‐ray diffraction in detail in this work. PCL and TA are miscible as evidenced by the single composition dependent glass transition temperature over the whole compositions range and the depression of equilibrium melting point of PCL in the PCL/TA blends. Isothermal melt crystallization kinetics of neat PCL and an 80/20 PCL/TA blend was investigated and analyzed by the Avrami equation. The overall crystallization rates of PCL decrease with increasing crystallization temperature for both neat PCL and the PCL/TA blend; moreover, the overall crystallization rate of PCL is slower in the PCL/TA blend than in neat PCL at a given crystallization temperature. However, the crystallization mechanism of PCL does not change despite crystallization temperature and the addition of TA. The spherulitic growth rates of PCL also decrease with increasing crystallization temperature for both neat PCL and the PCL/TA blend; moreover, blending with TA reduces the spherulitic growth rate of PCL in the PCL/TA blend. It is also found that the crystal structure of PCL is not modified in the PCL/TA blend. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Blends of poly(2,6-dimethyl-1,4-phenylene oxide)/ poly(styrene-co-methacrylic acid)/ poly(ethyl methacrylate-co-4-vinylpyridine)

Summary The miscibility of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with poly(styrene-co-acrylic acid) (SAA) or poly(styrene-co-methacrylic acid) (SMA) containing respectively up to 22 mol % of acrylic or methacrylic acid was studied by Differential Scanning Calorimetry and viscosimetry. All PPO/SAA or PPO/SMA blends containing 60% or less by weight of PPO were miscible and showed only one glass transition temperature (Tg). Above 60% of PPO, two Tg's were however observed for the blends in which the acid content in the SAA or SMA reaches 20% or 12% by mole respectively; the higher Tg is slightly lower than the one of pure PPO, while the lower one corresponds to a miscible blend of lower content of PPO.A DSC study showed that depending on the blend ratio, two or three glass transition temperatures were observed when a copolymer of ethyl methacrylate containing 8 mol % of 4-vinylpyridine (EM4VP-8) was added to miscible PPO/SMA-12 blends. The PPO dissolution in the SMA-12 copolymer was affected by the specific interactions that occurred between this latter copolymer and the EM4VP-8.     

Synthesis and processing of PMR-15/LaRC-TPI semi-IPN systems

To improve the fracture toughness of PMR-15 polyimide and to alleviate its high susceptibility to microcracking induced by thermal cycling, a thermoplastic polyimide, LARC-TPI, was incorporated to form a sequential semi-interpenetrating polymer network (semi-2 IPN). The imidization kinetics of LARC-TPI in the semi-IPNs were studied using a thermal gravimetric analyzer. Both the solvent and the glass transition temperature of the semi-IPN were found to have significant effects on the imidization kinetics. The kinetics could be modeled by a two-step reaction: the first step being a second-order reaction followed by a second step, which is a first-order diffusion-controlled reaction. Differential scanning calorimetry was chosen to investigate the curing of PMR-15 and PMR-15/LARC-TPI semi-IPNs. The curing process was well correlated by a first-order reaction kinetics, which suggested that the reverse Diels-Alder reaction of the Norbornene end group was the rate controlling step. The glass transition temperatures of these semi-IPNs were again found to play important an important role in dictating the curing kinetics. A higher proportion of LARC-TPI or a higher glass transition temperature of the semi-IPN prepolymer tended to result in a slower curing reaction. The optimum molding cycle of PMR-15 and PMR-15/LARC-TPI semi-IPNs were then determined from the obtained kinetics. © 1995 John Wiley & Sons, Inc.     

Phase study of nylon 6/poly (acrylic acid) blends cast from solutions in aqueous formic acid

Blends of nylon 6 (Ny6) with poly(acrylic acid) (PAA) were prepared in film form from solutions in a mixture of formic acid and water by evaporating the solvent. The miscibility and phase constitution of the binary blends obtained over a wide composition range (5/95–95/5) were examined by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical measurements. A Ny6 homopolymer film and Ny6/PAA blends with PAA concentrations ≥ 50 wt% exhibited a WAXD profile stemmed from the coexistence of two different crystalline modifications of Ny6, i.e. the α and γ forms. Above 50 wt% PAA content, the solution-cast blends showed no definite crystallinity. It was found by DSC thermal analysis that the polymer pair is substantially miscible in the non-crystalline state, since a single glass transition temperature (T_g) was situated between the T_gs of the two homopolymers at every composition; however, the T_g versus composition plots did not follow a monotonic function but yielded a peak maximum at a PAA concentration of c. 25 wt%. In order to interpret this phenomenon, attention was given to the following point revealed by dynamic mechanical measurements: at the compositions of Ny6/PAA = 100/0–50/50, a phase of low regularity such as a nematic structure is formed in the cast films.     

Novel blends of alternating propene-carbon monoxide copolymers and styrenic copolymers

Summary Alternating propene-carbon monoxide copolymers (P-CO) were melt-blended with polystyrene, poly(styrene-co-acrylonitrile) (SAN), and with poly(styrene-co-maleic anhydride) (SMA). P-CO forms homogeneously miscible blends with SAN containing 25 wt% AN at the investigated blend compositions. The transparent blends have single, intermediate glass transition temperatures that fit the Fox equation. The elastic properties of P-CO at room temperature disappear upon blending with SAN because the T _g is driven above RT. Polystyrene and SMA are not miscible with P-CO and form heterogeneous blends with two glass transitions. This demonstrates that both the polarity of the styrenic copolymer and the nature of the comonomer govern its phase behavior. Received: 14 January 1999/Revised version: 19 April 1999/Accepted: 19 April 1999