Polymers high-carbon-yield

In order to control the pore texture in carbon materials, blending of two kinds of carbon precursors, the one giving a relatively high carbonization yield and the other having a very low yield, was proposed and called polymer blend method [112], This idea gave certain success to prepare macroporous carbons from poly(urethane-imide) films prepared by blending poly(amide acid) and phenol-terminated polyurethane prepolymers [113]. By coupling this polymer blend method with... 

The Influence of the Matrix Precursor. The first requirement for a suitable matrix precursor is high carbon yield, which must be achievable under simple pyrolysis conditions. Figure 14 (left-hand side) shows weight loss as a function of pyrolysis temperature for several matrix precursors practical precursors that are commercially available include coal-tar and petroleum pitches, phenolic resins, polyimides, and the para-polyphenyleneacetylene resin Hercules HA 43 (35,36) The structural formulas of some polymer binders are shown in Figure 15. 

A suitable polymer material for preparation of carbon membranes should not cause pore holes or any defects after the carbonization. Up to now, various precursor materials such as polyimide, polyacrylonitrile (PAN), poly(phthalazinone ether sulfone ketone) and poly(phenylene oxide) have been used for the fabrication of carbon molecular sieve membranes. Likewise, aromatic polyimide and its derivatives have been extensively used as precursor for carbon membranes due to their rigid structure and high carbon yields. The membrane morphology of polyimide could be well maintained during the high temperature carbonization process. A commercially available and cheap polymeric material is cellulose acetate (CA, MW 100 000, DS = 2.45) this was also used as the precursor material for preparation of carbon membranes by He et al They reported that cellulose acetate can be easily dissolved in many solvents to form the dope solution for spinning the hollow fibers, and the hollow fiber carbon membranes prepared showed good separation performances. 

The ideal requirements for a precursor are that it should be easily converted to carbon fiber, give a high carbon yield and allow to be processed economically. The attraction of PAN is that the polymer has a continuous carbon backbone and the nitrile groups are ideally placed for cyclization reaction to occur, producing a ladder polymer, believed to be the first stage towards the carbon structure of the final fiber. 

Others. Other polymers are being investigated as potential precursors for glassy carbon, such ets polyvinyiidene chloride (CH2CCl2) , polyvinyl alcohol (CH2CHOH), polyphenylene oxide and aromatic epoxy. The latter two compounds have a high carbon yield. 

Matrix Materials and Processing. In most cases, the starter matrix material is a high-carbon-yield polymer such as a phenolic (reviewed in Ch. 

The hyperbranched polymers are carbon-rich macromolecules and show excellent thermal stabilities. The thermal properties of the hb-PAs are described below as an example. Their thermal stabilities were evaluated by TGA. Figure 3 shows TGA thermograms of some hb-PAs and Table 4 lists their thermal analysis data. The hb-FAs were thermally very stable for instance, hb-P66 lost merely 5% of its weight at a temperature as high as 595 °C. All the polymers, except for hb-F(44-Vl) and hb-F(59-Vl), carbonized in > 50% yields on pyrolysis at 800 °C, with hb-P(45-V) graphitized in a yield as high as 86% (Table 4, no. 3). The thermal stabilities of the hb-PAs are similar to that of Unear pol-yarylenes such as PPP but different from those of Unear polyacetylenes such as PH and PPA. The dramatic difference in the thermal stability is mainly due to the structural difference PPP is composed of thermally stable aromatic rings (Td 550 °C) [108-112], whereas PPA and PH are comprised of labile polyene chains, which start to decompose at temperatures as low as 220 and 150 °C, respectively [113]. The excellent thermal stabilities of the hb-FAs... 

TEM and ultracentrifuge results showed (see Fig. 16) that this process results in effective encapsulation of the carbon with practically complete yield only rather small hybrid particles, but no free carbon or empty polymer particles, were found. It has to be stated that the hybrid particles with high carbon contents do not possess spherical shape, but adopt the typical fractal structure of carbon clusters, coated with a thin but homogeneous polymer film. The thickness of the monomer film depends on the amount of monomer, and the exchange of monomer between different surface layers is - as in miniemulsion polymerization - suppressed by the presence of an ultrahydrophobe. 

Polymer-supported carbonate ions have proved efficient in the conversion of (237 R1=H, R2=Me R C, CHMe R2=H) to (238) (95%)192. ct-Lactams eg. (239) are fomed in high yield from the corresponding a-brcma-amides under phase transfer catalysis using quaternary armionium salts and le-crown-e1. ... 

With the aim of finding applications in polymer electrolyte fuel cells (PEFC) Co tetramethoxyphenylporphyrin (CoTMPP) and cobalt tetraazaannulene (Co-TAA) were tested for O2 reduction in acid media (IM H2SO4) with the catalysts bound with Nafion and deposited on a glassy carbon disk and rotating-disk measurements revealed high peroxide yields, as expected for cobalt complexes. 

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