2 -Hydroxypyridine as catalyst

Contains small amounts of the other three isomers, removed by recrystallization from methanol66 6 2-Hydroxypyridine (as catalyst) and 3 A molecular sieves were added67. 

The polymerizations were carried out in refluxing o-dichlorobenzene in the presence of 2-hydroxypyridine as catalyst. In the absence of catalyst, only low-molecular-weight polymers (IV <0.3 dL/g) could be isolated from solution. However, when 2-hydroxypyridine was used as a condensation catalyst, copolymers having IVs in excess of 0.45 dL/g could be prepared readily. The results are summarized in Table I. 

The synthesis of siloxane-polyimide elastoplastics requires an approach slightly different from that used in preparing the thermoplastic materials because of differences in reactivity between the aliphatic-anhydride-terminated siloxane oligomers and the aromatic dianhydrides. A one-pot condensation of the anhydride-terminated siloxane oligomers, BPADA, and the diamine in o-dichlorobenzene solution in the presence of 2-hydroxypyridine as catalyst leads to a siloxane-deficient polyimide. To circumvent this deficiency, a two-step synthetic scheme was used in which the anhydride-terminated siloxane oligomers were first capped with an excess of the diamine. The aromatic dianhydride was then added to the resulting amic acid oligomeric mixture and warmed to complete imidization (Scheme IV). 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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