Endcapping agent

The key to acetylene terminated polyimides is the availability of the end-capper which carries the acetylene group. Hergenrother (130) published a series of ATI resins based on 4-ethynylphthalic anhydride as endcapping agent. This approach first requires the synthesis of an amine-terminated amide acid prepolymer, by reacting 1 mole of tetracarboxylic dianhydride with 2 moles of diamine, which subsequently is endcapped with 4-ethynylphthalic anhydride. The imide oligomer is finally obtained via chemical cyclodehydration. The properties of the ATI resin prepared via this route are not too different from those prepared from 3-ethynylaniline as an endcapper. When l,3-bis(3-aminophenox)benzene was used as diamine, the prepolymer is completely soluble in DMAc or NMP at room temperature, whereas 4,4 -methylene dianiline and 4,4 -oxydianiline based ATIs were only partially soluble. The chemical structure of ATIs based on 4-ethynylphthalic anhydride endcapper is shown in Fig. 45. 

TABLE 1. Polybenzoxazole derivatives prepared using aminophenols and dicarboxylic acids with selected endcapping agents. 

Synthesis of these oligomers and the requisite endcapping agent is given below. Oligomer characterization and preliminary cure studies are also described. 

Attempts to improve the hydrolytic stability of the FEB oligomers by extending the synthetic sequence described above to fluorocarbon ether dithiomldate esters (2) derived from hexa-fluoropropylene oxide were unsuccessful. The dithiolmidate esters proved to be unreactive in the methylene chloride-Freon 113 reaction medium. A search for a solvent in which the dithiolmidate ester was sufficiently reactive and the endcapping agent was stable was unsuccessful. 

SBR is emulsion- and solution-polymerized from styrene and butadiene, plus small volumes of emulsifiers, catalysts and initiators, endcapping agents, and other chemicals. It can be sulfur-cured. SBR types are illustrated with Plioflex emulsion SBR (emulsion polymerized) and Solflex t solution SBR. Emulsion SBR is produced by hot polymerization for adhesives and by cold polymerization for tires and other molded automotive and industrial products. Solution SBR is used for tires. 

PLA end-chain modification using functional initiating systems or functional terminating agents (endcapping)... 

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