Thermal properties of a tough, new semicrystalline polyimide

Abstract

Thermal properties of a new semicrystalline polyimide synthesized from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and 2,2‐dimethyl‐1,3‐(4‐aminophenoxy)propane (DMDA) have been studied. Heat capacities in the solid and liquid states of BTDA‐DMDA have been measured. The heat capacity increase at the glass transition temperature (Tg = 230°C) is 145 J/°Cmol for amorphous BTDA‐DMDA. The equilibrium heat of fusion of the BTDA‐DMDA crystals has been obtained using wide‐angle X‐ray diffraction and differential scanning calorimetry measurements, and is 75.8 kj/mol. Based on the information on crystallinity and the heat capacity increase at Tg, a rigid amorphous fraction is identified in semicrystalline BTDA‐DMDA samples, which represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample, which should be associated with crystal sizes, and therefore with crystal morphology. It has also been found that this polymer has a high‐temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies of BTDA‐DMDA in nitrogen and air are determined to be 154 and 150kJ/mol, respectively.

Study of the Dual Amorphous Phases in Semicrystalline Poly(ethylene terephthalate) Using the Heat Capacity Increment at the Glass Transition

“…It can be seen that X ma decreased while X ra increased with increasing X c . This is consistent with another report, 8 but it is not a common phenomenon in semicrystalline polymers since in some other semicrystalline polymers both X ma and X ra were found to decrease with increasing X c . 7,14,15 It is interesting to find that for the T c of 403 K, when X c had reached a constant value, X ma continued to decrease while X ra continued to increase.…”

“…For all the semicrystalline samples, a perfect heat capacity step without any endothermic peak was obtained, and the T g was measured at half-devitrification. [5][6][7][8] Our experimental results showed that the ∆C p of wholly amorphous samples was ca. 0.410 J g -1 K -1 , which was consistent with another report.…”

“…The morphology of semicrystalline polymers is increasingly interesting due to its theoretical importance, , and many models have been proposed to explain the particular properties of semicrystalline polymers. − The model of “extended glass transition” proposed by Struik 3,4 describes the amorphous phase in semicrystalline polymers as a distribution of subphases with different glass transition temperatures ( T g ) and has been employed in our previous papers , to successfully explain the physical aging behaviors of semicrystalline poly(ethylene terephthalate) (PET). However, the model of “rigid amorphous phase” proposed by Wunderlich et al − divides the amorphous phase in semicrystalline polymers into a mobile amorphous subphase, which contributes to and is proportional to the heat capacity increment (Δ C p ) at the glass transition, and a rigid amorphous subphase, which does not contribute to the Δ C p .…”

“…The morphology of semicrystalline polymers is increasingly interesting due to its theoretical importance, , and many models have been proposed to explain the particular properties of semicrystalline polymers. − The model of “extended glass transition” proposed by Struik 3,4 describes the amorphous phase in semicrystalline polymers as a distribution of subphases with different glass transition temperatures ( T g ) and has been employed in our previous papers , to successfully explain the physical aging behaviors of semicrystalline poly(ethylene terephthalate) (PET). However, the model of “rigid amorphous phase” proposed by Wunderlich et al − divides the amorphous phase in semicrystalline polymers into a mobile amorphous subphase, which contributes to and is proportional to the heat capacity increment (Δ C p ) at the glass transition, and a rigid amorphous subphase, which does not contribute to the Δ C p . Besides, the concept of “rigid noncrystalline chains” proposed by Zachmann 9 separates the noncrystalline chains in semicrystalline polymers into rigid noncrystalline chains and mobile noncrystalline chains by their conformations.…”

Physical properties and β‐phase increment of AgNO3‐filled poly(vinylidene fluoride) films

“…The double melting peak at T m , observed in Fig 3 could be attributed to one of the following reasons 15–17. The first reason is that PVDF may suffer a melting, recrystallization and remelting during an upward temperature scan 18.…”