Properties Of A Novel Phenoxy Resin Containing Biphenyl Groups And Its Blends

Polymer blends have found many industrial applications, since this conventional strategy can often generate relatively inexpensive materials with tailormade properties from the existing commodity polymers. The ultimate performance of the resultant blend is considered to have the potential feature of combining their good properties while at the same time reducing their deficient characteristics of each blend component.However, most polymer blends are heterogeneous (immiscible). From a thermodynamic point of view, it is well-known that the entropy of mixing increase is very small in polymer blends. But miscibility can often be achieved by a favorable (negative) mixing enthalpy. In other words, the miscibility is governed by the nature of the polymer components, which can thermodynamically be interpreted as the contribution of both mixing enthalpy and mixing entropy to mixing free energy (Gmix). Further understanding of miscibility and the stability of homogeneous polymer blends is of great interest from both academic and industrial points of view. It has been crucial for the development of new materials, since only the miscible polymer blends are thermodynamically stable. Hydrogen bonding is the most important specific interaction for promoting polymer miscibility. The literature illustrates that phenoxy resin is miscible with many polymers and can be used as compatibilizaers in some blendings. Therefore, a systematic study on the phenoxy resin helps one to achieve the blends with optimized properties.Phenoxy resin is an important class of tough and ductile thermoplastic materials, which is not soluble in water and presents high hydroxyl group concentration in the structures. It is an important materials in the field of structural adhesives because of their good barrier properties, good impact resistance and a good compatibility with polar materials and fillers. Phenoxy resin has also been repeatedly verified the ability of forming miscible blends with a variety of other polymers, such as polyesters, polysulfones, polyamide, poly(butylene terephthalate) or polycarbonates. Related investigations have also shown the feasibility of promoting blends of incompatible resins, acting as compatibilizers. Its pendant hydroxyl groups can act as both proton donors and acceptors, so seem to be the origin of such miscibility and compatibility capacity, via the formation of specific interactions with other functional groups.Currently, it is bisphenol A phenoxy resin that is used broadly. But the low glass-transition temperature (Tg) limits its use in many applications. To improve the Tg and investigate the influencing factors on the properties, modifying the type of the dihydric phenols monomer might be an effective way. In this thesis, we have successfully introduced the rigid biphenyl groups into molecular chain segment to prepare high thermal performance phenoxy resin. Further we have characterized the structures and the properties of the resulted phenoxy resin in detail.(1) Synthesis and characterization of the phenoxy resin cotaining biphenyl groupsA kind of novel phenoxy resin derived from 3,3',5,5'-tetarmethyl- 4,4'- bephenyl and the epichlorohydrin was synthesized with catalyst and dispersant. FTIR and 1H-NMR spectra were performed to characterize the structure of the resin. The analyses results indicated that the structure answers our design. DMA and TGA analysis results showed, due to the molecular structure containing biphenyl groups in the resin, the conformational entropy of chain segment of the polymer depressed effectively and the Tg increased. The resin characterized also has adequate physical property and good solubility in some solvents.(2) Influence of the backone structure on the properties of phenoxy resinsIn order to determine the influence of the backone structure on the properties of phenoxy resins, the other four kinds of phenoxy resins were also investigated in the synthesis, characterization and properties. The results of FTIR and 1H-NMR were agreed with supposed structures. The DSC and TGA results indicated that the structures had an important effect on glass transition and thermal decomposition temperatures of the polymers. The thermal stability of the phenoxys increased with the content of the aromatic benzene ring or pedant group increasing. The adhesive properties of these polymers showed the similar trend. According to these results, the phenoxy resin containing biphenyl groups presented better thermal propeties, higher adhesive strength and could improve the adhesive property of the epoxy/phenoxy system a certain extent, the resin showed very good respective in adhesive usages.(3) Effect of the phenoxy resin backone structure on the properties of epoxy/ phenoxy blendsToughening epoxy resins is one important usage of phenoxy resins. Epoxy resins have been used extensively as thermosetting matrix materials in the development of high-performance light-weight composites, historically. Remarkable progresses have been made with a wide range of applications that include areas as diverse as construction, electronics, adhesives, and coatings. However, a major limitation of neat epoxy resins, particularly those for high-temperature applications, is their inherent brittleness arising from the crosslinked structure. To circumvent such shortcoming, toughening of brittle epoxy resins has been undertaken extensively by incorporating liquid rubber. The results showed that toughness could be enhanced at a rubber loading and invariably resulted in significant reduction in the tensile strength and modulus of the composites. These investigations warrant further study of combining epoxy resin with tough and ductile polymers. The mechanical properties of thermoplastic, such as phenoxy resin, modified epoxy resins show strong dependence on the morphology of phase separated domains and interfacial adhesion between these two phases. Therefore, the subject requires thorough investigation of curing behavior, emergence of biphasic domain morphology, and mechanical performance of these blends. In particular, attention is paid to the effect of the choice of phenoxy resin on the resulting morphology, thermal and tensile properties of the blends.It has been demonstrated that the epoxy/phenoxy blends cured with DDM exhibited different miscibility as phenoxy resins with different structures. And the mechanical properties of phenoxy modified epoxy networks varied with the blend morphology. The presence of pedant groups tended to have significant effect on miscibility, possibly by molecular bulkiness. The larger the pedant group volume was, the more possibly the phase separation was found. The observed globular morphology probably contributed to property enhancement in the immiscible epoxy/phenoxy blend, in which the stretching and tearing of the phenoxy phase may be responsible for toughening of the epoxy matrix. The rigid main chain could be responsible for the changes of mechanical properties in the miscible blends. The blend with the phenoxy resin containing biphenyl groups gave the optimum results for elongation and tensile toughness with little loss of tensile modulus, tensile strength, Tg, and heat deflection temperature compared with the neat epoxy.(4) Properties of composite membranes based on sulfonated poly(ether ether ketone)s (SPEEK)/phenoxy resin for proton exchange membrane fuel cells usagesThe Proton Exchange Membrane Fuel Cell (PEMFC) has attracted considerable attention. It is a type of fuel cell, which is potentially suitable for applications in automobiles or portable applications because of its lower weight, high efficiency, simply design, simple fueling, low emissions and low operating temperatures. Each large-scale application shares a common goal of high fuel efficiency, non-polluting by-products and economical low cost proton exchange membranes. The proton exchange membrane material is a key component of the PEMFC for transferring protons from the anode to the cathode as well as providing a barrier to fuel permeability cross-over between the electrodes.Alternative membrane materials such as Nafion? membranes, sulfonated poly (aryl ether ketone)s (SPAEKs), sulfonated poly(aryl ether sulfone)s (SPAES) and sulfonated poly(imide) (SPI) etc are being widely studied. In previous work of our lab, SPAEK is developed for proton exchange membranes based on SPEEK or sulfonated poly (ether ether ketone ketone)s (SPEEKK), which obtained by directly synthesis from sulfonated monomer. The values of conductivity for the SPEEK copolymers at around degree of sulfonation 0.8 and 1.2 are 0.038 S/cm, 0.07 S/cm at 25 oC and 0.067 S/cm, 0.13 S/cm at 80 oC, respectively, indicating that they are promising candidates for PEM materials. However, although they show superior performance in fuel cells, the brittleness of the membranes at elevated temperatures and the relatively high methanol permeability in the membranes with high sulfonation have limited their usage, the methanol diffusion coefficients of the SPEEK copolymers with sulfonated degree about 1.2 are 1.47×10-6cm2/s, which also poses a critical problem in the practical use as a PEM. Many attempts have been developed to reduce the methanol permeability through the proton exchange membranes.With these objectives in mind, we research the properties of high sulfonated SPEEK composite membranes with the phenoxy resin cotaining biphenyl groups. The phenoxy resin is selected because of its good thermal properties and the possibility of forming the intermolecular hydrogen bond between the sulfonated acid groups of the SPEEK and the hydroxyl groups of phenoxy resin. Moreover, the intermolecular interaction between the aliphatic hydroxyl groups and the aromatic sulfonic groups exists in blends have been reported by Wu and Lin. The blend of sulfonic acid containing polymers with polymers containing hydroxyl groups is confirmed to be an efficient strategy to improve the mechanical and methanol crossover properties due to the special interaction between the sulfonated acid groups and hydroxyl groups, as it was found in the previous works. The interaction can lead to the compatibility of the blending polymers. This will lead to reduction of swelling, improvement of mechanical properties and a further decrease in the methanol crossover of membranes. It is well known that phenoxy resin both miscible and able to react with numerous polymers leading to compatible blends, so it is possible to add other materials in the composites to improve the membranes'general properties.In order to decrease the methanol permeability and improve the mechanical properties of the high sulfonated level SPEEK membranes, composite proton exchange membranes were prepared via blending of the SPEEK and the phenoxy resin in different weight ratios. In this paper we first introduced successfully the phenoxy resin into the SPEEK solutions, then prepared the composite membranes by solution casting. The composite membranes were characterized for PEM applications in the terms of physical and electrochemical properties. It was found that varying the compositions effectively controlled the properties of the composite membranes. The water uptake of the composite membranes decreased significantly along with the swelling ratios and IECs showed the similar trends, respectively. The water diffusion coefficients decreased with the increasing content of phenoxy resin since the water swelling behavior was restricted. Although the proton conductivities decreased for the addition of phenoxy resin, the methanol diffusion coefficients were much lower than that of pure SPEEK membranes, and the composite membranes were found to have the higher selectivity values. No matter in ambient-condition or full-hydrated state, the membranes obtained better mechanical properties and were strong and tough enough to be used as functional proton exchange membrane materials. Therefore, according to above results, a balance of proton conductivity, methanol crossover and mechanical properties could then be designed to meet the requirements for the applications and the composite membranes showed very good prospects in PEM usages.We have designed and synthesized the phenoxy resin containing biphenyl groups and investigated its properties. The results demonstrate that the phenoxy resin containing biphenyl groups seems promising for the application in blending.