Influence of microstructure on dynamic mechanical behaviour of polymeric composites with complex inclusions

The dynamic mechanical properties of polymeric composites composed of crosslinked poly(n-butyl methacrylate) continuous-phase and crosslinked polystyrene dispersed phase with poly(n-butyl methacrylate) occlusion have been examined. The composite samples were prepared by mixing and swelling of the crosslinked polystyrene particles obtained by emulsifier-free emulsion polymerization, with n-butyl methacrylate and crosslinker, then photopolymerizing at the desired temperature. The composite microstructure was varied by either changing the crosslink density of polystyrene, and temperature of swelling and polymerization, or using different sizes and contents of polystyrene particles. The tan δ peak positions of composite samples are found to be dependent on morphological characteristics as well as the properties of the dispersed phase while the peak height seems to be dependent on the effective volume of dispersed phase composed of polystyrene and poly(n-butyl methacrylate) occlusions. Special attention has been paid to the comparison among composite, homonetworks, and bulk IPN samples that are expected to have the identical structure with the complex dispersed phase of the composite samples. © 1993 John Wiley & Sons, Inc.     

A comparative study of semi-2 and full interpenetrating polymer networks based on poly(n-butyl acrylate)/polystyrene

Sequential poly(n-butyl acrylate)/polystyrene (PnBA/PS) semi-2 and full IPN's of various compositions were made by UV photopolymerization. Acrylic acid anhydride and divinylbenzene were used as labile and permanent crosslinkers, respectively, for the rubbery phase and the plastic phase. After IPN formation, network I was selectively decrosslinked. After extracton of polymer I, the remaining PS network II was characterized by swelling measurements and examined by scanning electron microscopy. It was found that crosslinked PnBA affects the formation of the second network more than uncrosslinked PnBA does. A porous phase formed by an aggregate of spherical polystyrene domains was observed. The experimental domain diameter was in good agreement with previous theoretical values. The dynamic mechanical properties of full IPN's, decrosslinked IPN's, and semi-2 IPN's were also studied. A significant level of molecular mixing was found for full IPN's of midrange compositions. The major difference between the full IPN's and the decrosslinked IPN's is that the glass transitions of the respective polymers become more pronounced in the latter case, with a deeper valley between them. With the destruction of the crosslink sites, there is no longer a forced miscibility of the interlocked phases, which are, in fact, thermodynamically incompatible.     

Ionomer/ionomer thermoplastic IPNs based on poly(n-butyl acrylate) and polystyrene

Thermoplastic interpenetrating polymer networks (IPNs) were prepared by combining poly(n-butyl acrylate) with polystyrene, both polymers crosslinked independently with acrylic acid anhydride (AAA). Decrosslinking of both polymers was carried out by hydrolysis of the anhydride bonds. Neutralization of the carboxylic acid groups to form the ionomer was carried out in a Brabender Plasticorder. Two subclasses of thermoplastic IPNs were studied: (1) Chemically blended thermoplastic IPNs (CBT IPNs) were prepared by synthesizing polymer II in polymer I in a sequential synthesis; (2) mechanically blended thermoplastic IPNs (MBT IPNs) were prepared by melt blending separately synthesized polymers. Rheovibron characterization revealed that of the two combinations, the CBT IPNs were better mixed than the MBT IPNs. Investigations of phase continuity via melt viscosity and modulus suggest that the CBT IPNs have some degree of dual phase continuity. Transmission electron microscopy suggests dual phase continuity and relatively small phase domains, 2000–5000 Å for the CBT IPNs. The mechanical properties from tensile and Izod impact tests showed that the CBT IPNs were stronger than the MBT IPNs.     

Latex Interpenetrating Polymer Networks

Abstract

Latex interpenetrating polymer networks are a unique type of polymer blend, synthesized by swelling crosslinked seed latex particles of polymer I with monomer II, plus cross-linking agents, and polymerizing monomer II in situ. In a manner similar to polymer blends generally, polymer 1 and II are incompatible to greater or lesser extents, and phase separate. In IPN materials, however, the phase separation is hindered by the presence of the double networks, giving rise to especially finely divided phase domains.

The synthesis of polybutadiene/polystyrene and poly(ethyl methacrylate)/poly(n-butyl acrylate) latex IPN's is considered, and the dynamic mechanical properties of the resulting films or molded materials is measured as a function of temperature. Two transitions were found for incompatible materials, while one broad transition arises with semicompatible polymer pairs. While regions of true interpenetration are indicated, the effect on the mechanical properties of inverting the order of polymerization suggests the presence of a shell-core phase separation. The origin of the shell-core separation effect is considered qualitatively, the underlying cause being ascribed to the statistics of mixing of polymer I with solvent (monomer II) and non-solvent, surrounding water.     

Poly(n-butyl acrylate)/polystyrene interpenetrating polymer networks and related materials. III. Effect of grafting level and molecular weight in semi-2 IPNs

A series of poly(n-butyl acrylate)/polystyrene IPNs and semi-1 IPNs with deliberately controlled graft levels were synthesized via a urethane chemical coupling method. Also prepared were a series of semi-2 IPNs with the molecular weight of polymer II as the variable. The more highly grafted IPNs displayed poorly defined morphologies in which the domain structures were irregular and phase domain boundaries were characterized by fibrillar and interphase regions. A single glass transition peak was another feature of the more highly grafted IPNs. Polymer network II formed in the presence of linear polymer I results in morphologies dependent on the molecular weight of linear polymers. In the semi-2 IPNs, polymer I molecular weights below M_v = 20,000 caused polymer I to behave like a plasticizer or a diluent. The domain sizes of semi-2 IPNs agree with theoretical predictions developed by the present authors.     

Semiinterpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. I. Thermodynamic state and dynamic mechanical analysis

Semiinterpenetrating polymer networks (semi‐IPNs) based on polyurethane (PU) and polyvinylpyrrolidone (PVP) have been synthesized, and their thermodynamic characteristics, thermal properties, and dynamical mechanical properties have been studied to have an insight in their structure as a function of their composition. First, the free energies of mixing of the two polymers in semi‐IPNs based on crosslinked PU and PVP have been determined by the vapor sorption method. It was established that these constituent polymers are not miscible in the semi‐IPNs. The differential scanning calorimetry results evidence the T_g of polyurethane and two T_g for PVP. The dynamic mechanical behavior of the semi‐IPNs has been investigated and is in accordance with their thermal behavior. It was shown that the semi‐IPNs present three distinct relaxations. If the temperature position of PU maximum tan δ is invariable, on the contrary, the situation for the two maxima observed for PVP is more complex. Only the maximum of the highest temperature relaxation is shifted to lower temperature with changing of the semi‐IPNs composition. It was concluded that investigated semi‐IPNs are two‐phase systems with incomplete phase separation. The phase composition was calculated using viscoelastic properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 852–862, 2001     

Effects of crosslinking degree and carbon nanotubes as filler on composites based on glycidyl azide polymer and propargyl‐terminated polyether for potential solid propellant application

Triazole crosslinked polymers were prepared by reacting glycidyl azide polymer (GAP) with the propargyl ‐ terminated poly(tetramethylene oxide) (PTMP) at different molar ratios of azide versus alkyne. Based on the optimum mechanical properties of the GAP/PTMP ‐ 2.5, a series of GAP/PTMP nanocomposites reinforced by either multi ‐ walled carbon nanotubes (MWCNTs) or carboxy ‐ functionalized multiwalled carbon nanotubes (MWCNTs ‐ COOH) were prepared with different mass ratios. The glass transition temperatures (T_{g, PTMP}) assigned to PTMP of the GAP/PTMP composites almost kept at a constant range when the molar ratio of azide versus alkyne was from 1.0 to 2.5. When the loading MWCNTs was 1.0 wt %, the tensile strength and elongation at break achieved a maximum of 1.77 MPa and 36.3%, respectively. The nanocomposites with nearly similar T_{g, PTMP} indicated no phase separation in the crosslinked polymers. The results revealed that the improved properties of GAP ‐ based materials could be achieved by changing the molar ratio of azide versus alkyne and the nanofillers content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45359.     

Polyurethane–polyacrylate interpenetrating polymer networks. II

Two component topologically interpenetrating polymer networks of the SIN type (simultaneous interpenetrating networks) composed of a melamine-cured polyacrylate and three different polyether-based polyurethanes were prepared. The linear polymers and prepolymers were combined in solution, together with the necessary crosslinking agents and catalysts, films were cast and subsequently chain extended and crosslinked in situ. In all cases, maxima in tensile strength significantly higher than the tensile strengths of the component networks occurred at 50% polyurethane : 50% polyacrylate. This was explained by an increase in crosslink density resulting from interpenetration. One of the interpenetrating polymer networks showed only one glass transition temperature (T_g) (measured calorimetrically) intermediate in temperature to the T_g's of the components and as sharp as the component T_g's. This is indicative of phase mixing and indicates at least partial chain entanglement (interpenetration). Some enhancement of other physical properties was also noted.     

Separation of hydrocortisone and epi-hydrocortisone by solvent extraction

Solvent extraction, instead of traditional crystallization, is suggested as a new method for separation of hydrocortisone and its optical isomer, epi-hydrocortisone. The extraction behavior of alcohols, ketones, esters, ethers and chlorinated hydrocarbons was studied experimentally. For the industrial separation process it was found that the best solvents are n-butyl acetate or chloroform. The distribution coefficients of hydrocortisone and epi-hydrocortisone in an n-butyl acetate/water system at 17°C were found to be 9·98 and 2·62, respectively, and 5·57 and 1·93, respectively, in a chloroform/water system at 17°C. When n-butyl acetate or chloroform solution of crude hydrocortisone (the mixture of hydrocortisone, epi-hydrocortisone and other steroid impurities) was scrubbed by deionized water in a nine-stage cross-current at 25°C, the organic phase hydrocortisone purity increased from 78·10% to 98·22% (wt%) for the n-butyl acetate case and from 78·10% to 98·02% (wt%) for the chloroform case. The medicinal standard for hydrocortisone was attained. The effects of alcohol concentration, temperature, salting-out and pH on extraction are also discussed. ©1997 SCI     

Polymerization of vinyl ethers using titanium catalysts containing tridentate triamine ligand of the type N[CH2CH(Ph)(Ts)N]2

Titanium complexes having tridentate triamine of the type N[CH₂CH(Ph)(Ts)N]₂²⁻ in combination with methylaluminoxane (MAO) was able to polymerize ethyl vinyl ether in good yields. The polymers obtained in general were having molecular weight in the order of 10⁵ with narrow molecular weight distributions. Polymerization conditions had an impact on the molecular weight and the polydispersity index (PDI). Using chlorobenzene as the solvent the polymer had an M_n of 350?000 and PDI of 1.21, where as under neat conditions the M_n was 255?000 with PDI of 1.21. The type of solvent and the temperature dictated the polymerization rate and the polymer stereo regularity. The molecular weight of the polymer is distinctly governed by the polymerization temperature. Temperature ranging between −50 and ambient (30 °C) resulted in high molecular weight polymers and vice versa at a temperature of 60-70 °C resulted in low molecular weight polymers in moderate yields. The polymers obtained below 30 °C are highly stereo-regular compared to that of the ones produced at and above ambient temperature. The polymerization of iso-butyl vinyl ether (IBVE) was faster than that of linearly substituted n-butyl vinyl ether (BVE) and less bulky ethyl vinyl ether (EVE). The order of isotacticities of the polymers obtained are polyIBVE > polyBVE > polyEVE. The use of borate cocatalyst for activation generated narrow molecular weight polymers with a linear increase in the yield and molecular weight over time suggesting the living nature of the catalyst system.     

(AB)n Segmented Copolyetherimides for 4D Printing

The fourth dimension in 4D printing comprises the ability of materials to recover their shape with time by utilizing 3D printing in combination with shape memory polymers. The focus of this work is on 3D printing of physically crosslinked thermoplastic polymers, which allow a reversible transformation from a temporary to an original shape by an external stimulus temperature, thus realize 4D printing. In this context, (AB)_n segmented copolyetherimides consisting of perylene and poly(ethylene glycol) (PEG) segments are synthesized and characterized regarding their thermal and rheological properties in view of 3D printing. The perylene imide segments act as reversible physical crosslinks which disassemble between 100 and 200 °C. The PEG segments exhibit a low melting temperature around 40 to 60 °C and are semi-crystalline at room temperature. The results show that this type of (AB)_n segmented copolyetherimide combines reliable 3D printing performance, which is indicated by low warp deformation and excellent interlayer bonding. With a blend of two copolymers, it is able to realize 4D printing.     

Polymeric hydrogels and supercritical fluids: The mechanism of hydrogel foaming

A novel method, the hydrogel foaming, is used in this work for the production of porous, polymer-based materials by processing with supercritical carbon dioxide (CO₂). This method is applied to crystalline hydrophilic polymers that, practically, exhibit no phase transition (melting or glass transition) below thermal decomposition temperature and, due to their crystallinity, do not absorb CO₂. Such polymers are mainly natural (semi)-crystalline polymers (e.g. chitosan, cellulose, etc.) for which the classical polymer foaming method with supercritical carbon dioxide is not applicable. The hydrogel foaming process (similar to classical polymer foaming) is applied to gelatin, chitosan, and gelatin/chitosan blend hydrogels that are physically crosslinked and may also be chemically crosslinked with glutaraldehyde vapour. After the foaming process, water is removed from the gels by mild freeze-drying leading to porous materials. Pore size control can be achieved by controlling different process parameters. Gelatin exhibits solubility in water up to high concentrations and forms thermoreversible hydrogels, rendering it a suitable choice for the investigation of the process mechanism. The mechanism of hydrogel foaming is explored on the basis of X-ray diffraction, calorimetry, rheology, sorption, Raman spectroscopy measurements and theoretical calculations with the NRHB (Non Random Hydrogen Bonding) equation-of-state model. The sorption and Raman spectroscopy measurements suggest that, besides dissolution in water (of the hydrogel), extensive CO₂ sorption by the polymer also occurs. Based on these results, a critical discussion is made and a mechanism for the hydrogel foaming is proposed.     

A novel method for preparing poly(alkyl methacrylates) and poly(methacrylic acids) of varying tacticity

In order to synthesize poly(methacrylic acid) and poly(alkyl methacrylates) over a wide range of polymer tacticity, the anionic polymerization of the following alkyl methacrylates (ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-amyl, n-hexyl, n-octyl, n-decyl, n-lauryl, and n-octadecyl) in toluene using phenylmagnesium bromide initiation was studied. It was found that the amount of isotactic polymer structure generally decreased as the size of the ester group increased. In all cases, the polymers had greater than 50% isotactic triad structure. Whether the polymerization was carried out at 0° or ?78°C had little or no effect on the tacticity of the polymer produced. It was found that the poly(alkyl methacrylates) produced could be hydrolyzed in concentrated sulfuric acid to poly(methacrylic acid). The poly(methacrylic acid) produced in the hydrolysis could be esterified with diazomethane to give poly(methyl methacrylate) or with diazoethane to give poly(ethyl methacrylate) with the same tacticity as the poly(alkyl methacrylate) from which the poly(methacrylic acid) was derived. It is possible, therefore, to produce poly(alkyl methacrylates) of a desired tacticity by polymerizing the appropriate monomer, hydrolyzing, and reesterifying the resultant poly(methacrylic acid) with a diazoalkane to give the desired poly(alkyl methacrylate).     

The effect of crosslinking on the adsorption behavior of copper (II) onto poly(2‐hydroxy‐4‐acryloyloxybenzophenone)

The adsorption behavior of Cu(II) ions onto poly(2‐hydroxy‐4‐acryloyloxybenzophenone), polymer I, and onto poly(2‐hydroxy‐4‐acryloyloxybenzophenone) crosslinked with different amounts of divinylbenzene (DVB), polymers II, III, and IV, in aqueous solutions was investigated using batch adsorption experiments as a function of contact time, pH, and temperature. The amount of metal ion uptake of the polymers was determined by using atomic absorption spectrometry (AAS) and the highest uptake was achieved at pH 7.0 and by using perchlorate as an ionic strength adjuster for polymers I, II, III, and IV. Results revealed that the adsorption capacity (q_e and Q_m) of Cu(II) ions decreases with increasing crosslinking due to the decrease of chelation sites. In addition, the rate of adsorption (k₂) of Cu(II) ions decreases with the increase of crosslinking because it becomes more difficult for Cu(II) ions to diffuse into the chelation sites. The isothermal behavior and the kinetics of adsorption of Cu(II) ions on these polymers with respect to the initial mass of the polymer and temperature were also investigated. The experimental data of the adsorption process was found to correlate well with the Langmuir isotherm model. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of cross‐linkable poly(phthalazinone ether ketone)s

A novel class of crosslinkable poly(phthalazinone ether ketone)s with relative high molecular‐weight and good solubility were successfully synthesized by the copolymerization of bisphthalazinone containing monomer, 3,3′‐diallyl‐4,4′‐dihydroxybiphenyl and 4,4′‐di‐ fluorobenzophenone. The synthesized polymers with inherent viscosities in the range of 0.42 to 0.75 dL/g can form flexible and transparent membranes by casting from their solution. The crosslinking reaction of these polymers can be carried out by thermally curing of the virgin polymers in or without the presence of crosslinking agent. The experimental results demonstrated that the crosslinking reaction also occurred to some extent during the polymerization. The crosslinked polymers exhibited equivalent glass transition temperature (T_g) at lower crosslinking density, and showed higher T_g than virgin polymers at higher crosslinking density. The crosslinked high‐temperature polymer can be used as the base material for high temperature adhesive, coating, enamel material, and composite matrices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Characteristics of zwitterionic sulfobetaine acrylamide polymer and the hydrogels prepared by free-radical polymerization and effects of physical and chemical crosslinks on the UCST

A zwitterionic sulfobetaine polymer, poly(N,N-dimethyl(acrylamidopropyl) ammonium propane sulfonate) (poly(DMAAPS)), and the hydrogels of this polymer were synthesized by free-radical polymerization in an aqueous redox system using a wide range of monomer concentrations (C_m). The resulting polymers were characterized in terms of polymer yield, intrinsic viscosity, molecular weight, gel fraction, and thermoresponsive phase-transition behavior. Parameters in the Mark–Houwink–Sakurada equation, including the molecular-weight exponent α, were determined for poly(DMAAPS) in 0.1 M NaCl aqueous solution. The physical state and transparency of the poly(DMAAPS) samples were strongly dependent on C_m and temperature. At higher values of C_m (i.e. above a critical molecular weight), poly(DMAAPS) became a gel comprising a physically crosslinked network consisting of entangled polymer chains and interchain associations of the zwitterionic groups. The poly(DMAAPS) solutions or gels exhibited a thermoresponsive phase transition with an upper critical solution temperature (UCST). The gels obtained were completely soluble in aqueous NaCl solution at ambient temperature as well as in water at temperatures above UCST. The effects of molecular weight, chemical crosslink density and copolymerization on the UCST were also elucidated.     

Development of CO2-Philic Blended Membranes Using PIM–PI and PIM–PEG/PPG

Blending is a simple method through which one can effectively tailor new polymers exhibiting the properties of their parent ones. Because the original properties of polymers are maintained after blending, various studies have used these films as gas separation membranes. In this study, a new CO₂ separation membrane is developed by physically mixing a polymer of intrinsic microporosity (PIM) with high gas permeability, polyimide (PIM-PI), as the hard segment and CO₂-philic PIM-poly(ethylene glycol)/poly(propylene glycol), or PIM-PEG/PPG, as the soft segment. Prepared by adding 5 mol.% of PIM-PEG/PPG to PIM-PI, the blended membrane PPB-5, with a tensile strength of 54 MPa and 35.5% elongation at break, shows better mechanical properties than commercial high-performance polymer membranes developed for gas separation, PEG-based blended membranes, and corresponding copolymer membranes with similar compositions developed in a previous study. In addition, it shows high CO₂ permeability (1552.6 Barrer) and CO₂/N₂ selectivity (29.3) due to the well-developed microphase separation characteristics originating from the optimal two-component composition, and the gas separation performance is close to the Robeson (2008) upper bound.     

Thermodynamics of polymer solutions and blends

To describe the thermodynamic behavior of binary and larger polymer blends, the Hoch-Arpshofen model is used to describe highly asymmetric phase diagrams, and asymmetric enthalpies of mixing, where the miscibility gap and the extremum of the enthalpy of mixing leans toward one of the components. The Gibbs energy of mixing of polymer blends is described as where z can be mole fraction, volume fraction, or weight fraction. The Hoch-Arpshofen model contains an interaction parameter W = A + B*T independent of composition and an integer number n (2, 3, 4, …), which defines the asymmetricity of the binary phase diagram and of the Gibbs energy of mixing curve. In a binary system n defines the composition where the Gibbs energy of mixing is maximum or minimum or the composition is where the temperature of a miscibility gap is maximum or minimum. In a binary system A-B the maximum effect occurs at A_n–1B. The disorder reaction in polymers is treated as a transformation temperature, and defines T₀, the temperature where the ordered and disordered material is equal.     

Glass transitions of topologically interpenetrating polymer networks

Two component topologically-interpenetrating polymer networks were made of the SIN type (simultaneous interpenetrating network) composed of two polyurethanes (a polyether-based and a polyester-based) in combination with an epoxy resin, a polyacrylate and two unsaturated polyesters. The linear polymers and/or prepolymers were combined in solution and in bulk together with the necessary crosslinking agents and catalysts. Films were cast and chains extended and crosslinked in situ. All of the IPN's exhibited one glass transition (T_g) intermediate in temperature to the T_g's of the component networks, and as sharp as the T_g's of the components. This suggests that phase separation may not occur and thus some chain entanglement (interpenetration) of the two networks is involved. The observed T_g's are always several degrees lower than the arithmetic means of the component T_g's. A theory based on interpenetration is developed to account for this.     

The application of bulk polymerized acrylic and methacrylic interpenetrating polymer networks to noise and vibration damping

Novel acrylic/methacrylic interpenetrating polymer networks (IPNs) were examined by dynamic mechanical spectroscopy for their damping capabilities. While simple homopolymers exhibit high damping properties only over a 20–30°C range, multicomponent polymer systems with controlled degree of miscibility, such as IPNs, may exhibit high damping properties over temperature ranges as broad as approximately 100°C. Two series of IPNs based on poly(n-butyl acrylate) and poly(n-butyl methacrylate) were synthesized and the dynamic mechanical properties were investigated using a Rheovibron. Graphite was incorporated into the poly(n-butyl acrylate) homopolymer and a few IPNs to measure the change in the damping properties. For important IPN compositions, tan δ values between 0.4 and 0.85 were observed over a 75°C plus temperature range. Graphite increased the damping properties of poly(n-butyl acrylate) and the IPNs, as indicated by the tan δ values.