Molecular Dynamics Simulation of a Phenylene Polymer. 3. PEEK

Development of a high-performance poly(ether ether ketone) copolymer with extremely low melt viscosity

The conventional poly(ether ether ketone) (PEEK) and two other PEEK copolymers (PEEEKK-PEK and PEEEKK-PEEEK) were successfully synthesized and investigated on their thermal stabilities, mechanical properties, and rheological behaviors. Both of the PEEEKK-PEK and PEEEKK-PEEEK were composed of the same chemical components with conventional PEEK (phenyl–ether–ketone equals 3:2:1), but the sequences of their components (phenyl, ether, and ketone) were different. Differential scanning calorimetry analysis and dynamic mechanical analysis indicate that PEEEKK-PEK and PEEEKK-PEEEK have extremely close glass transition temperatures and melting points with conventional PEEK, which suggests their similar operating temperatures. They also process similarly high mechanical properties based on their stress–strain tests. However, PEEEKK-PEK, PEEEKK-PEEEK, and PEEK exhibit significant differences in their rheological behaviors; PEEEKK-PEK even shows an excessively low melt viscosity (51% of PEEK). These results reveal the effects of sequence distribution on polymer properties and thereby demonstrate the processing viscosity of PEEK could be decreased without sacrificing its operating temperature or material performances.

Phenylene ring dynamics in phenoxy and the effect of intramolecular linkages on the dynamics of some engineering thermoplastics below the glass transition temperature

We have investigated the dynamics of phenylene rings in the engineering thermoplastic bisphenol-A poly(hydroxyether) -- phenoxy -- below its glass transition temperature by means of neutron scattering techniques. A relatively wide dynamic range has been covered thanks to the combination of two different types of neutron spectrometers, time of flight and backscattering. Partially deuterated samples have been used in order to isolate the phenylene ring dynamics. The resulting neutron scattering signal of phenoxy has been described by a model that considers pi flips and oscillation motions for phenylene rings. The associated time scales are broadly distributed with mean activation energies equal to 0.41 and 0.21eV , respectively. Finally, a comparative study with the literature shows that the dielectric and mechanical gamma relaxation in phenoxy exhibit good correlation with the characteristic times of the aliphatic chain published elsewhere and with the characteristic times observed for the motion of phenylene rings by neutron scattering. These findings are discussed in a more general framework that considers, in addition, previous results on other polymers, which also contain the bisphenol-A unit.

Phenylene ring dynamics in bisphenol-A-polysulfone by neutron scattering

We have investigated the dynamics of phenylene rings in a glassy polysulfone (bisphenol-A-polysulfone) by means of quasielastic neutron scattering. Nowadays it is well known that these molecular motions are directly connected with the mechanical properties of engineering thermoplastics in general. The particular system investigated by us has the advantage that by selective deuteration of the methyl groups, the neutron scattering measured is dominated by the incoherent contribution from the protons in the phenylene rings. In this way, the dynamics of such molecular groups can be experimentally isolated. Two different types of neutron spectrometers: time of flight and backscattering, were used in order to cover a wide dynamic range, which extends from microscopic (10(-13) s) to mesoscopic (10(-9) s) times. Moreover, neutron diffraction experiments with polarization analysis were also carried out in order to characterize the structural features of the sample investigated. Fast oscillations of increasing amplitude with temperature and pi-flips are identified for phenylene rings motions. Due to the structural disorder characteristic of the amorphous state, both molecular motions display a broad distribution of relaxation times, which spreads over several orders of magnitude. Based on the results obtained, we propose a model for phenylene rings dynamics, which combines the two kinds of molecular motions identified. This model nicely describes the neutron scattering results in the whole dynamic range investigated.