The influence of industrial reaction conditions on the kinetics of the polycondensation of polyamides is discussed. For analysis reasons the overall process was subdivided into individual kinetic phases. It will be shown that the basic features of the reaction rate in the final reaction stage can be explained assuming second order kinetics combined with a superposed reaction equilibrium. The influence of non‐stoechiometry on the reaction rate is also demonstrated.
The polyoxadiazole synthesis in P 2 O 5 /CH 3 SO 3 H solution has been improved by precipitation of the reaction mixture in cold NMP. The polyoxadiazole obtained by this process did not contain uncyclized hydrazide moieties and was more stable in strongly acidic media. This process has been used to prepare some copolyoxadiazoles with dodecanedioic and isophthalic diacids or dihydrazides. The microstructure of the copolymers (alternate versus block) depends on the nature of the isophthalic derivative. With isophthalic dihydrazide, which is soluble in the reaction mixture like the dodecanedioic derivative, an alternate structure is obtained. With isophthalic diacid, which exhibits low solubility, the dodecanedioic derivate first reacts giving an aliphatic oxadiazole sequence and finally a block copolymer is obtained. The microstructure was determined by proton NMR spectroscopy allowing us also to calculate the average sequence length. UV-vis spectra of the block copolymers show a bathochromic effect compared with the spectra of the alternate copolymers. The block copolymer obtained with 75% dodecanedioic and 25% isophthalic diacid shows three transitions at −10 • C (T g 1 ), 50 • C (T m ) and 220 • C (T g 2 ). Heated at 150 • C, a moulded specimen has been stretched up to 100%, and cooled down at room temperature under stress. The temporary shape is stable at room temperature and the initial shape is restored by heating at 110 • C. The mechanical stress stored in the temporary shape was about 1.6 MPa.
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