Water Resistance of Poly(imide-siloxane) Adhesives: An IGC Surface Energetics Study

Inverse Gas Chromatography was utilized to examine the interaction of water vapor with the surfaces of a polyimide homopolymer and poly(imide-siloxane) random-block copolymers of increasing siloxane content. The studies employed 45-60 meter, thin-polymer-film mega-bore capillary columns to maximize surface area. The free energies of specific surface interaction with water and the dispersive components of the solid surface free energies were determined. An increase in the polymer siloxane content from 0-wt% to 10-wt% resulted in a decrease of approximately 4 kJ/mol in the free energy of water-specific surface interaction. A further increase in siloxane content to 30-wt% was not found to increase surface water resistance significantly. Dispersive components of the solid surface free energies of the copolymers were comparable to values reported for poly(dimethylsiloxane) homopolymer.     

Water Resistance of Poly(Imide-Siloxane) Adhesives: Diffusion Coefficients by Gravimetric Sorption

Diffusion coefficients of water vapor in a polyimide homopolymer and poly(imide-siloxane) multi-block copolymers of different siloxane concentration were determined from gravimetric sorption experiments. Diffusion coefficients were of the order of magnitude of 10^-8 cm²/sec. Higher levels of siloxane incorporation caused a definite increase in the diffusion coefficient, indicating a decreased resistance to water ingression. The increase in diffusion was found to be influenced by siloxane block length and was interpreted in terms of free volume and morphology. The diffusion coefficient of the 10-weight-percent PDMS copolymer, however, was found to be the same within error as that of the polyimide. This and a previous surface study suggested that an increased surface water resistance may be achieved at low siloxane concentrations without greatly increasing the bulk diffusive properties to undesirable levels.     

反气相色谱法研究结晶聚合物的表面性质

采用反相气相色谱法测定了聚乙二醇 (PEG)不同相态结构组成下的色散成分的表面能 Yds,并探讨了 γds 与温度的关系。研究结果表明 :PEG的表面能较低 (32 .39m J- 2 40℃ ) ,在结晶态和熔融非晶态形式下 ,γds 随温度的升高而降低 ;而在 6 7～ 90℃的结晶熔融温度范围内 ,PEG的γds,随温度的升高呈现先降→后升→再下降的趋势 ,特别是当结晶熔融温度达到 6 3℃时 ,PEG的表面能发生明显的转折。     

Measurement of the Surface Free Energy of Amorphous Cellulose by Alkane Adsorption: A Critical Evaluation of Inverse Gas Chromatography (IGC)

Surface energies of amorphous cellulose “beads” were measured by IGC at different temperatures (50 to 100°C) using n-alkane probes (pentane to undecane). The equation of Schultz and Lavielle was applied which relates the specific retention volume of the gas probe to the dispersive component of the surface energy of the solid and liquid, γ^d_s and γ^d_l, respectively, and a parameter (“a”) which represents the surface area of the gas probe in contact with the solids. At 50°C, γ^d_s was determined to be 71.5 mJ/m², and its temperature dependence was 0.36 mJ m^-2 K^-1. Compared with measurements obtained by contact angle, IGC results were found to yield higher values, and especially a higher temperature dependence, d(γ^d_s)/dT. Various potential explanations for these elevated values were examined. The surface energy, as determined by the Schultz and Lavielle equation, was found to depend mostly on the parameter “a”. Two experimental conditions are known to affect the values of “a”: the solid surface and the temperature. While the surface effect of the parameter “a” was ignored in this study, the dependence of the surface energy upon temperature and probe phase was demonstrated to be significant. Several optional treatments of the parameter “a” were modeled. It was observed that both experimental imprecision, but mostly the fundamental difference between the liquid-solid vs the gas-solid system (and the associated theoretical weakness of the model used), could explain the differences between γ^d_s and d(γ^d_s)/dT measured by contact angle and IGC. It was concluded that the exaggerated temperature dependence of the IGC results is a consequence of limitations inherent in the definition of parameter “a”.     

Measurement of the Surface Free Energy of Amorphous Cellulose by Alkane Adsorption: A Critical Evaluation of Inverse Gas Chromatography (IGC)

Surface energies of amorphous cellulose “beads” were measured by IGC at different temperatures (50 to 100°C) using n-alkane probes (pentane to undecane). The equation of Schultz and Lavielle was applied which relates the specific retention volume of the gas probe to the dispersive component of the surface energy of the solid and liquid, γ^d _s and γ^d _l, respectively, and a parameter (“a”) which represents the surface area of the gas probe in contact with the solids. At 50°C, γ^d _s was determined to be 71.5 mJ/m², and its temperature dependence was 0.36 mJ m^?2 K^?1. Compared with measurements obtained by contact angle, IGC results were found to yield higher values, and especially a higher temperature dependence, d(γ^d _s)/dT. Various potential explanations for these elevated values were examined. The surface energy, as determined by the Schultz and Lavielle equation, was found to depend mostly on the parameter “a”. Two experimental conditions are known to affect the values of “a”: the solid surface and the temperature. While the surface effect of the parameter “a” was ignored in this study, the dependence of the surface energy upon temperature and probe phase was demonstrated to be significant. Several optional treatments of the parameter “a” were modeled. It was observed that both experimental imprecision, but mostly the fundamental difference between the liquid-solid vs the gas-solid system (and the associated theoretical weakness of the model used), could explain the differences between γ^d _s and d(γ^d _s)/dT measured by contact angle and IGC. It was concluded that the exaggerated temperature dependence of the IGC results is a consequence of limitations inherent in the definition of parameter “a”.     

IGC study of filler–filler and filler–rubber interactions in silica‐filled compounds

A modification of the existing methods for evaluating the dispersive and specific components of surface free energy (γ_d and γ_s, respectively) was made to investigate filler–rubber and filler–filler interactions by inverse gas chromatography. Four silicas as fillers and various probes that mimic elastomers were employed in this study. It was shown that the pretreatment of silicas with helium could increase γ_d and decrease γ_s. Modification of the silica surface with silane could enhance the dispersive interaction and weaken the specific interaction. The temperature dependence of the interfacial interaction was also investigated, and it was found that lower temperatures favored filler–rubber interactions and mixing efficiency. Tests on different sizes of agglomerates demonstrated the existence of a filler–rubber and filler–filler network. It was also found that γ_d played a role in agglomeration or filler–filler interaction. Our study showed that the larger the specific surface area was, the stronger the dispersive and specific interactions were. The effectiveness of various fillers and elastomer probes was also compared. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2517–2530, 2001     

Characterization of poly(vinyl methyl ketone) using the inverse gas chromatography method

The inverse gas chromatography method was applied to the semicrystalline polymer poly(vinyl methyl ketone) (PVMK). The method was able to provide valuable information on the thermodynamic and surface properties of PVMK. Thirteen solutes with different chemical properties were used. They provided information on the type and strength of the polymer–solute interactions which were attributed to the melting behavior of PVMK. The melting temperature of PVMK was detected with precision using solutes that interacted strongly with PVMK. The interaction parameters χ₁₂ of PVMK–alkanes over the temperature range 70–180°C were obtained and were shown to be independent of temperature and number of carbons in the alkane series. The dispersive contribution of the surface energy of PVMK was measured as a function of temperature. The values ranged between 29·00 and 18·00 mJ/m². The molar heat of sorption and the molar free energy of adsorption were calculated.     

Rayleigh散射研究部分相容聚苯乙烯／顺丁橡胶合金相结构

用光散射在线采集与分析方法完成了熔融混炼过程中非相容高分子共混物的形态结构分析。选择了聚苯乙烯／顺丁橡胶合金体系；使用了小角前向光散射和小角背散射(在线)技术，用Debye-Bueche光散射理论的结构参数如相关距离ac、平均弦长l、旋转半径Rg和积分不变量Q表征了共混物中分散相尺度和均匀性，讨论了合金体系的相容性。用扫描电子显微镜测定了共混物中分散相尺寸，并与光散射的结果进行了比较。ac、l和Rg的变化规律与显微镜的结果是一致的。用积分不变量Q研究了共混物的均匀性。     

Determination of the interaction parameter χ of poly(ethylene oxide) by gas-liquid chromatography below the melting temperature

The interaction parameter χ of poly(ethylene oxide) in different solvents at temperatures below the melting point (T_m) of the polymer has been determined by means of the solubility parameters of the polymer and solvents at this temperature, chromatographically obtained from their values at higher temperatures (70°–140°C). The value of the interaction parameter so obtained is not only in good agreement with those calculated by other techniques but also independent of the temperature range employed in the chromatographic measurements. Moreover, using the equation-of-state theory formulation, we have determined values of the interaction parameter χ1 for different poly(ethylene oxide)/probe systems and from it the contact interaction energy X₁₂, in the temperature range between 70° and 140°C.     

The Effect of Nanosized Layered Materials on the Structure-Property Relationship of Poly(aniline)s: An FTIR Kinetic Study

Aniline (ANI) was chemically polymerized in the presence of two different nanosized layered materials, zirconylphosphate (ZP) and molyptic acid (MA) under different experimental conditions with nitrogen purging at 45°C. The effect of nanosized layered materials on the rate of polymerization (R_p) and Fourier transform infra red-relative intensities (FTIR-RI) of benzenoid and quinonoid forms of poly(aniline) (PANI) were tested. The thermal stability and electrical conductivity values were boosted with the help of nanosized materials. High resolution transmission electron microscope (HRTEM) determined the size of nano material and its uniform distribution on the PANI matrix. For the sake of comparison, o-toluidine (OT) was polymerized under the same experimental conditions and its structure-property relationship in the presence of nano materials were also tested and critically compared with PANI systems.     

Chemical Functionalization of Graphene Oxide by Poly(styrene sulfonate) Using Atom Transfer Radical and Free Radical Polymerization: A Comparative Study

Poly(sodium styrenesulfonate)-functionalized graphene was prepared from graphene oxide, using atom transfer radical polymerization and free radical polymerization. In atom transfer radical polymerization route, the amine-functionalized GO was synthesized through hydroxyl group reaction of GO with 3-amino propyltriethoxysilane. Atom transfer radical polymerization initiator was grafted onto modified GO (GO-NH₂) by reaction of 2-bromo-2-methylpropionyl bromide with amine groups, then styrene sulfonate monomers were polymerized on the surface of GO sheets by in situ atom transfer radical polymerization. In free radical polymerization route, the poly(sodium 4-styrenesulfonate) chains were grafted on GO sheets in presence of Azobis-Isobutyronitrile as an initiator and styrene sulfonate monomer in water medium. The resulting modified GO was characterized using range of techniques. Thermal gravimetric analysis, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy results indicated the successful graft of polymer chains on GO sheets. Thermogravimetric analysis showed that the amount of grafted polymer was 22.5 and 31?wt% in the free radical polymerization and atom transfer radical polymerization methods, respectively. The thickness of polymer grafted on GO sheets was 2.1?nm (free radical polymerization method) and 6?nm (atom transfer radical polymerization method) that was measured by atomic force microscopy analysis. X-ray diffractometer and transmission electron microscopy indicated that after grafting of poly(sodium 4-styrenesulfonate), the modified GO sheets still retained isolated and exfoliated, and also the dispersibility was enhanced.     

Study of cryostructuration of polymer systems. XVII. Poly(vinyl alcohol) cryogels: Dynamics of the cryotropic gel formation

Freeze‐thaw treatment of concentrated (>5 g/dL) aqueous solutions of poly(vinyl alcohol) (PVA) (MW 115,000; DD ≈100%) resulted in the formation of opaque gels. The extent of such a cryostructuration process was exhibited in the rheological properties of similar PVA cryogels. The gels' strength depended on the initial polymer concentration in the solution to be frozen and on the conditions of a cryogenic influence. The key factor was the defrostation dynamics: the slower the thawing rate, the stronger the cryogel sample formed, provided other parameters of the process were identical. The observation for the kinetics of the freeze‐thaw–induced gel formation revealed the extreme character of the temperature dependence of the efficacy of PVA cryotropic gelation, the maximum point being in the vicinity of −2°C. It was shown that the effect of the strengthening of PVA cryogels prepared by means of a single‐cycle cryogenic treatment could be reached either with use of as slow as possible thawing regimes, or by the prolonged frozen storage of the samples at “high” subzero temperatures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2017–2023, 2000     

Study of cryostructuration of polymer systems. XIV. Poly(vinyl alcohol) cryogels: Apparent yield of the freeze–thaw‐induced gelation of concentrated aqueous solutions of the polymer

Poly(vinyl alcohol) (PVA) cryogels, which are formed as a result of freeze–thaw treatment of concentrated solutions of the polymer, were studied in respect to the amount of gel and sol fractions in these heterogeneous macroporous gel materials depending on the conditions of the thawing step of similar cryotropic gelation. It was shown that the yield of gel fraction (the efficiency of the gelation process) was not quantitative; this was controlled by the initial PVA concentration in the solution to be frozen, and to a higher extent, by the thawing rate, when the yield increased with slowing of the defrostation process. The sol fraction could be extracted from the PVA cryogels by their rinsing with water at room temperature; the extraction of the sol was accompanied with the variations of the swelling parameters of the gels (initial slight upswelling and subsequent gradual deswelling), as well as with analogous, in their character, variations of the gel strength. It was also demonstrated that at the evaluation of the fusion enthalpies of PVA cryogels with the aid of the Eldridge–Ferry equation a consideration of the values of gel‐fraction yield gave rise to the significantly higher ΔH values than in traditional cases commonly used for the thermoreversible gels, where such an yield was not taken into account. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1822–1831, 2000     

Microwave-assisted polymer synthesis (MAPS) as a tool in biomaterials science: How new and how powerful

Lack of reproducibility, difficult and expensive scale-up and standarization of synthetic processes are the main hurdles towards the industrial production of raw synthetic and semi-synthetic polymers for (bio)pharmaceutical applications. Time- and energy-consuming synthetic pathways that usually involve the use of volatile, flammable or toxic organic solvents are apparently cost-viable and environment-friendly for the synthesis at a laboratory scale. However, they are often not viable in industrial settings especially due to the impact they have on the product cost and the deleterious effect on the environment. This has presented hurdles to the incorporation of many new biomaterials displaying novel structural features into clinics. Nevertheless, owing to unique advantages such as shorter reaction times, higher yields, limited generation of by-products and relatively easy scale-up without detrimental effects, microwave-assisted organic synthesis has become an appealing synthetic tool. Regardless of these features, the use of microwave radiation in biomaterials science has been comparatively scarce. A growing interest in the basic aspects of the synthesis of either ceramic and polymeric biomaterials has been apparent during the last decade. This article reviews the most recent and prominent applications of MW as a versatile tool to synthesize and process organic and inorganic polymeric biomaterials, and discusses the unmet goals and the perspectives for a technology that probably has the potential to make biomaterials more accessible pharmaceutical excipients and the products that involve them more affordable to patients.     

Thermoresponsive poly(oligo ethylene glycol acrylates)

Thermoresponsive polymers have been the subject of numerous publications and research topics in the last few decades mostly driven by their easily controllable temperature stimulus and high potential for in vitro and in vivo applications. P(NIPAAm) is the most studied amongst these polymers, but recently other types of polymers are increasingly being investigated for their thermoresponsive behavior. In particular, polymers bearing a short oligo ethylene glycol (OEG) side chain have been shown to combine the biocompatibility of polyethylene glycol (PEG) with a versatile and controllable LCST behavior. These polymers can be synthesized via controlled radical polymerization techniques from various monomers consisting of an OEG chain and a polymerizable group like a (meth)acrylate, styrene or acrylamide. OEG acrylates offer significant advantages over, e.g., OEG methacrylates as the lower hydrophilicity of the backbone facilitates thermoresponsive behavior with smaller, more defined side chains. Furthermore, PEG acrylates can be polymerized using all major controlled radical polymerization techniques, unlike OEG methacrylates. This review will focus on OEG acrylate based (co)polymers and will provide a comprehensive overview of their reported thermoresponsive properties. The combination and comparison of this data will not only highlight the potential of these monomers, but will also serve as a starting point for future studies.     

A review on the mechanical and electrical properties of graphite and modified graphite reinforced polymer composites

Carbon materials particularly in the form of sparkling diamonds have held mankind spellbound for centuries, and in its other forms, like coal and coke continue to serve mankind as a fuel material, like carbon black, carbon fibers, carbon nanofibers and carbon nanotubes meet requirements of reinforcing filler in several applications. All these various forms of carbon are possible because of the element's unique hybridization ability. Graphene (a single two-dimensional layer of carbon atoms bonded together in the hexagonal graphite lattice), the basic building block of graphite, is at the epicenter of present-day materials research because of its high values of Young's modulus, fracture strength, thermal conductivity, specific surface area and fascinating transport phenomena leading to its use in multifarious applications like energy storage materials, liquid crystal devices, mechanical resonators and polymer composites. In this review, we focus on graphite and describe its various modifications for use as modified fillers in polymer matrices for creating polymer-carbon nanocomposites.