Polymer modification research

Introduction Polymer Modification—Some Problems and Possibilities—Areas in Need of Research... 

The book, divided into four sections, begins with a brief chapter describing some present problems in need of research and future trends related to polymer modification. The volume is not exhaustive but chapters were selected to illustrate specific aspects of more general areas of polymer modification. 

The chemistry reported in this volume was selected to give the uninitiated an appreciation of the scope of propellant research. The areas of thermochemistry, combustion research, polymer modification, materials research, etc., have intentionally been excluded since other forums have existed for them. 

The continuing developments in the preparation of dendrimers and hyper-branched polymers ° have moved this field into consideration by the polymer colloids community. As dendrimers and hyperbranched polymers get ever larger, their dimensions become sufficient to consider their solutions as molecular polymer colloids. Inevitably, therefore, research into such polymers will feature in new directions for polymer colloids research, both as polymer colloids in their own right and as additives for modification of the properties of existing polymer colloids. Such research will be most effective if carried out through collaborations of organic and polymer chemists with colloid scientists. 

Problems of chemistry and physico-chemistry of PCS attracted attention not only of researchers working in the field of theoretical chemistry and physics but also researchers, working in the field of polymer modification [290]. 

WILLIAM M. DOANE received his PhD in Biochemistry from Purdue University in 1962. Since that time he has conducted and led research in isolation, characterization, and modification of natural polymers, principally starch. Currently he is Research Leader of Derivatives and Polymer Exploration Research at USDA s Northern Regional Research Center. 

Z. Su, J.M. Bijen, J.A. Larbi Influence of polymer modification on the hydration of portland cement. Cement Concrete Research 21/1991, pp. 535-544. 

After over fifteen years of intense research PHCs have passed from a short list of raw materials to a lai e number of variously functionalized polymers. Modification of the monomeric structures has allowed processability by conventional polymer techniques and the specificity for applications such as fine tuning of color for displays or enzyme recognition. Conductive properties have been greatly improved so that conductivities as high as 5000 S cm have been obtained [434] while for the optoelectronic characteristics the... 

This overview briefly surveys the use of enzymatic and wholecell approaches in polymers. Three types of reactions are covered polymer syntheses, polymer modifications, and polymer hydrolyses. Thus far, most of the enz3une-related R D activities involve hydrolases, oxidoreductases, and transferases, with occasional use of lyases and isomerases. Whole-cell methods continue to be valuable in both academic and industrial labs. All these research areas display continued vitality and creativity, as evidenced by the large number of publications. Advances in biotechnology have provided new and improved enzymes and additional tools. Also included in diis overview is the related topic of biomaterials. 

Because of good thermal and hydrolytic stability, excellent mechanical and chemical stability, low cost, and commercial availability of sulfonated aromatic hydrocarbon polymers, recent research has focused on the synthesis and development of sulfonated aromatic hydrocarbon polymers specifically for high-temperature PEMFCs. Typical examples include sulfonated poly(ether ether ketone) (SPEEK) or poly(ether ketone ketone) (SPEKK) [1,2], sulfonated poly(ether sulfone) (SPSE) [3], alkyl sulfonated polybenzimidazole (PBI), sulfonated naphthalenic polyinrides (sNPl) [4-6], sulfonated polyCphenylene sulfide) [7,8]. Both post- and pre-sulfona-tion methods have been used in the past. Other than the post-sulfonation modification of aromatic polymers, recently, efforts have been dedicated to direct polycondensation from sulfonic acid containing monomers to synthesize sulfonated polymers [9]. The latter approach, namely pre-sulfonation, is widely applied because of the ease of controlling sulfonation degree and deactivated sites in the arylene backbones, which further avoid side reactions such as decomposition and hydrolysis of polymers resulted from the post-sulfonation method. 

The researches carried out so far har pror that incorporation of inorganic nanopai ticles into polymers can efifectirrely improw the latter s properties. It opens a new road for polymer modification that is superior to the addition of microparticles. Because of the specific surface feature of the nanoparticles, a variety of possibilities is offered developing novel manufacturing techniques,... 

Finally, it is appropriate to say a few words on the choice of solvent for the chemical modification of polymers under phase transfer catalysis. As was mentioned earlier, numerous reactions which do not proceed in non-polar solvents such as toluene or dichloromethane in the absence of a phase transfer catalyst do proceed satisfactorily In DMF. Thus, many research groups, including ours, have used DMF extensively in polymer modifications with or without added catalyst, with increases in reaction rates and conversions being observed in the former case. As DMF is often a solvent for both the polymer and, in many instances, at least some of the reagent, it is debatable whether or not the term "phase transfer catalysis" applies (Ref. 50). More important perhaps is the fact that considerable amounts of dimethylamine can be produced through decomposition of DMF when the solvent is treated with concentrated aqueous base in the presence of a phase transfer catalyst. Obviously this may lead to undesirable side-reactions with incorporation of dimethylamine moieties into the modified polymers (Ref. 50). 

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