Burgess, Ryan & Wayne
Cationically-dyeable, thermally-resistant copolyester fiber comprising quaternary phosphonium organic sulfonate groups
 An improved copolyester fiber capable of being dyed with cationic dyes and having an excellent brightness, heat resistance and a satisfactory mechanical strength comprises a copolyester resin comprising a polymerization product of at least one aromatic dicarboxylic acid compound, at least one alkylene diol compound and at least one quaternary phosphonium organic sulfonate of the formula (I): ##STR1## wherein A=an aromatic or aliphatic radical, X.sup.1 =H or an ester-forming organic radical, X.sup.2 =an ester-forming organic radical, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 =an alkyl or aryl radical, n=1 or more, and having an [.eta.].sub.f of 0.5 or more, the copolyester fiber having a silk factor of 25 or more and exhibiting the number of scission of backbone chains of the copolyester molecules of 140.times.10.sup.23 or less per 10.sup.6 g of fiber when wet heat-treated in a solution of 0.4 g/l of acetic acid in distilled water at 130.degree. for 60 minutes. 
Teijin Limited
D C
D01F C08G
inventional inventional
Setsuo Hironori Togi Kimihiro Kohichi Shinji
Yamada Yamada Suzuki Ogawa Iohara Ohwaki