Intrinsic viscosity, polyimide

Comparison of Chain Dimensions. Knowledge of the intrinsic viscosities and molecular weights of a series of PMDA/DAPE polyamic acids allows estimation of the unperturbed chain dimensions. Comparison may then be made with the cured polyimide, with results obtained by other workers, and with calculated values. The expressions in the literature using values for [n] obtained in good solvents generally involve extrapolation of [t)]/M toM = 0, where excluded volume effects are presumed to be minimal (12-14). Although this method is not strictly valid, it is useful for comparison purposes when direct measurement of the dimensions is impractical. The data in Table I for the polyamic acid in distilled NMP and in the poorer mixed solvent NMP/dioxane yield (see Figure... 

We have been able to measure both the weight average molecular weight and the intrinsic viscosity for equilibrated polyamic acid precursors in NMP, and for stable solutions of the cured polyimide in concentrated sulfuric acid. These measurements were not complicated by either polyelectrolyte effects in the amide solvent or degradation in the acid, as have been reported by other workers for these systems. The results show that molecular weight achieved in the condensation to the polyamic acid is retained in the final polyimide, at least for moderate molecular weights. The condensation reaction appears to follow the expected kinetics and leads to a most probable distribution at equilibrium. 

Figure . Intrinsic viscosity effect on the UNB values for 6FDA-PFMB polyimides...

The use of d catalyst is not necessary In the copolymerization of polyimides arxf amtnopropyl terminated polydimethylsiloxanes. Intrinsic viscosities after 2 hours reaction time are comparable for copolymerization either with or without a catalyst. Solution cast films from the reaction flask were tough, flexible and transparent. Figure 2 shows a representative NMR of a polyimide-siloxane copolymer. 

The intrinsic viscosities of the graft copolymers were in the range of 1.3 1.9 dl/g, compared to O.S- l.l dl/g for their polyimide precursors. The block copolymers exhibited intrinsic viscosities of 2.2 4.6 dl/g, compared to 1.0-1.4 dl/g for the end-capped polyimides. The increase in the viscosity of the graft and block copolymers was the lowest when the most rigid polyimides were used. 

Intrinsic viscosities of polyamic acid solutions were measured in DMF at 30 . Infared spectra of polyamic acid and polyimide were recorded on a Perkin-Elmer Model 137 Spectrophotometer. X-ray diffractograms were obtained using a Debye-Scherrer powder diffractometer with Ni-filtered copper K radiation(l.54) at 33CV. 

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