Polybenzobisthiazoles – Critical issues in their performance and properties - Polyimides and Other High Temperature Polymers - page 226

properties for these materials. It is known that compressive properties of these ma-
terials are not at par with other mechanical properties. Structural tailoring with
pendent groups has provided various approaches to investigate and improve com-
pressive properties of high modulus PBZT films and fibres. Polybenzobisthiazole
containing substituted p-terephenylene dicarboxylic acid ( ) [14] was utilized to

disrupt the packing order and potentially increase the compressive properties.

IV

(IV) Terphenylene unit

(V) Random copolymer containing terephthalic / terphenylene unit

Random copolymers were prepared [15] in PPA by replacing a small portion
(1-2 mol%) of the terephthalic acid with terphenylene diacid ( . Polymerisations

were carried out at 10% by weight concentrations to give copolymers. PBZT con-
taining pendent labile methyl groups were prepared [16] from 2-methyl and 2,5-
dimethylterephthalic acids by condensation with the appropriate amino mono-
mers. Benzobisthiazole random copolymers [17] were also prepared using 2-me-
thylterephthalic acid and terephthalic acid with 2,5-diamino-l, 4-benzenedithiol
dihydrochloride. Sweeny [18] developed a method for cross-linking of stiff chain
polymers such as Kevlar and PBZT. The method was based on the thermolysis of
active aryl halides contained in the polymer unit and coupling of the free radicals
formed. Intermolecular cross-linking has been considered as an effective approach
to improve the compressive strength of polymeric fibres. On this basis Mehta
et al . [19] studied the cross linking in methyl pendent PBZT fibre (

V)

VI) .