Douglass S. Kalika

Glass transition characteristics of poly(aryl ether ketone ketone) and its copolymers

Abstract The glass transition characteristics of poly(aryl ether ketone ketone) (PEKK) have been investigated as a function of backbone structure and crystallization history; PEKK 100 0 homopolymer and PEKK 70 30 and 60 40 copolymers were examined, where the numbers represent the terephthalic/isophthalic (T/I) ratio. For the all- para -connected homopolymer, the presence of crystallinity had a significant influence on the calorimetric glass transition properties of the amorphous phase: T g was offset by as much as 20°C in the crystallized samples as compared to the wholly amorphous material, and a sizeable ( W RAP ∼ 0.30) rigid-amorphous-phase fraction was observed. In the copolymers, crystallinity had only a very minor effect on T g . The rigid-amorphous-phase fraction in the copolymer samples was smaller as compared to the homopolymer, and was negligible ( W RAP → 0) for samples prepared under less-restrictive crystallization conditions. Dielectric studies indicated progressive mobilization of the rigid-amorphous-phase fraction above T g for the copolymer samples, with full mobilization of the non-crystalline fraction observed for those samples crystallized at the highest temperatures. These results show that the introduction of 1,3-connected isophthalate moieties in the PEKK copolymers has a disrupting influence on the persistence of crystalline constraint into the amorphous phase. Similar observations have been reported for poly(phenylene sulfide) copolymers and thermoplastic polyimides that incorporate meta -phenylene linkages in the chain backbone.

Microporous membranes based on poly(ether ether ketone) via thermally-induced phase separation

Abstract The fabrication of poly(ether ether ketone) based membranes via thermally-induced phase separation has been investigated. Microporous membranes were generated from solid-liquid phase separation of miscible polymer-polymer mixtures comprised of PEEK and polyetherimide, with subsequent extraction of the PEI diluent; the introduction of a high polymer diluent provides a number of advantages in terms of melt processing and ultimate membrane properties. The nature of the solid-liquid phase separation and corresponding PEI segregation was investigated as a function of crystallization temperature and diluent molecular weight using dynamic mechanical thermal analysis. DMTA studies revealed segregation of PEL to both interlamellar and interfibrillar/interspherulitic regions. PEI extraction with liquid dichloromethane was found to be site specific, with diluent removal solely from the interfibrillar and interspherulitic regions; the retention of interlamellar PEI in the final article was reflected in a significant increase in the thermal resistance characteristics of the material. Scanning electron microscopy revealed a microporous morphology comprised of a spherulitic superstructure with two distinct pore size scales corresponding to PEI extraction from between fibrillar bundles and in interspherulitic regions, respectively. The relative morphological distribution could be shifted with variations in initial blend composition.

Dynamic mechanical relaxation properties of poly(ether ether ketone)

The influence of crystalline morphology on the dynamic mechanical relaxation properties of poly(ether ether ketone) (PEEK) has been investigated for the glass-rubber (α) and sub-glass (β) relaxations; a series of both cold-crystallized and melt-crystallized specimens were examined. The presence of crystallinity had a marked influence on the glass-rubber relaxation characteristics of PEEK owing to the relative constraint imposed on the amorphous-phase motions by the crystallites. Above Tg, a progressive relaxation of rigid amorphous-phase material was evident, as well as a small incremental decrease in modulus reflecting the onset of the low-temperature melting component. The sub-glass mechanical relaxation was bimodal, comprising a lower-temperature β1 component, which originated in the bulk of the amorphous material, and a higher-temperature β2 component, which originated in organized regions of the amorphous phase (i.e. at the crystal-amorphous interphase). Both the dynamic mechanical and corresponding dielectric results displayed morphological sensitivity in the β relaxation region, with the mechanical results encompassing motions of a more complex (i.e. cooperative) nature.

Investigation of semicrystalline morphology in poly(ether ether ketone)/poly(ether imide) blends by dielectric relaxation spectroscopy

Abstract The semicrystalline morphology of a series of poly(ether ether ketone) [PEEK]/poly(ether imide) [PEI] blends has been investigated as a function of blend composition and crystallization condition by dielectric relaxation spectroscopy. Dielectric scans of the crystallized blends revealed two glass-rubber relaxations for all specimens corresponding to the coexistence of a mixed amorphous interlamellar phase, and a pure PEI phase residing in interfibrillar/interspherulitic regions; no (pure PEEK) crystal-amorphous interphase was observed. Variations in the composition of the mixed interlamellar phase with crystallization temperature were consistent with kinetic control of the evolving morphology: lower crystallization temperatures led to an increase in the amount of PEI trapped between crystal lamellae. Comparison of the relaxation characteristics of the interfibrillar/interspherulitic phase with those of pure PEI indicated a much broader spectrum of local relaxation environments for PEI in the blends, consistent with PEI segregation across a wide range of size scales.

Crystallization, melting, and relaxation of modified poly(phenylene sulfide). I. Calorimetric studies

Abstract The crystallization, melting, and glass-rubber relaxation characteristics of a series of random poly(phenylene sulfide) (PPS) copolymers based on sodium hydrosulfide (NaSH) and 1,4- and 1,3-dichlorobenzene monomers have been investigated; sample compositions included the PPS homopolymer, and copolymers incorporating 5%, 8%, and 10% meta-phenylene linkages. The introduction of increasing levels of meta-phenylene units led to a modest decrease in amorphous glass transition temperature (from 86°C [0%] to 74°C [10%]) and a strong decrease in equilibrium melting temperature as determined by Hoffman-Weeks extrapolation(from 331°C[0%] to 273°C [10%]). Wide-angle x-ray scattering (WAXS) studies indicated that the meta units were excluded as defects from the bulk crystal structure, with no variation in unit cell parameters. Measurements of glass transition temperature for the crystallized polymers revealed a significant positive offset in Tg with the presence of crystallinity owing to the constraints impo...

Characteristics of poly(ether ether ketone) microporous membranes prepared via thermally induced phase separation (TIPS)

The morphology and bulk properties of microporous membranes based on poly (ether ether ketone) (PEEK) have been investigated as a function of initial casting composition and thermal and mechanical processing history. Membranes were prepared via solid—liquid phase separation of miscible blends of PEEK and polyetherimide (PEI), with subsequent extraction of the PEI diluent. Scanning electron microscopy studies revealed a microporous morphology with two distinct pore size scales corresponding to diluent extraction from interfibrillar and interspherulitic regions, respectively. The membrane structure was sensitive to both initial blend composition and crystallization temperature, with the resulting pore size distribution reflecting the kinetics of phase separation. For membranes prepared with lower initial diluent content or at lower crystallization temperatures, mercury intrusion porosimetry indicated a relatively narrow distribution of fine interfibrillar pores, with an average pore size of approximately 0.04 microns. Membranes prepared at higher diluent content or at higher crystallization temperatures displayed a broad pore distribution, with a sizeable population of coarse, interspherulitic pores (0.1 to 1 μm in size). Uniaxial drawing led to a fibrillated network structure with markedly higher water flux characteristics compared to the as-cast membranes.

Relationship between morphology and glass transition temperature in solvent‐crystallized poly(aryl ether ketones)

The relationship between semicrystalline morphology and glass transition temperature has been investigated for solvent-crystallized poly(ether ether ketone) (PEEK) and poly(ether ketone ketone) (PEKK). Solvent-crystallized specimens of both PEEK and PEKK displayed a sizeable positive offset in Tg compared to quenched amorphous specimens as well as thermally crystallized specimens of comparable bulk crystallinity; the offset in Tg for the crystallized samples reflected the degree of constraint imposed on the amorphous segments by the crystallites. Small-angle X-ray scattering studies revealed markedly smaller crystal long periods (d) for the solvent-crystallized specimens compared to samples prepared by direct cold crystallization. The strong inverse correlation observed between Tg and interlamellar amorphous thickness (lA) based on a simple two-phase model was in excellent agreement with data reported previously for PEEK, and indicated the existence of a unique relationship between glass transition temperature and morphology in these poly(aryl ether ketones) over a wider range of sample preparation history and lamellar structure than was previously reported.

The semicrystalline morphology of aliphatic–aromatic polyamide blends

Abstract The morphology of a series of melt-miscible blends based on the combination of (crystalline) polyamide (PA) 4,6 and (amorphous) PA 6I has been investigated as a function of blend composition and thermal history. Wide-angle X-ray scattering (WAXS) was used to determine the unit cell structure and crystallinity index in PA 4,6 and the blends: the introduction of PA 6I resulted in no change in unit cell parameters and a monotonic decrease in bulk crystallinity. Dynamic mechanical studies revealed the coexistence of two amorphous phases in the crystallized blends: a mixed phase held between the crystal lamellae (interlamellar) and a PA 6I-rich phase excluded to interfibrillar and interspherulitic regions. There was no evidence of a separate crystal–amorphous interphase layer comprised of pure PA 4,6. Transamidation reactions over longer melt times led to the apparent homogenization of the two amorphous populations owing to the formation of increasingly random copolymers.

Dielectric Spectroscopy of Crystalline Polymers and Blends

Publisher Summary This chapter reviews the dielectric relaxation characteristics of semi-crystalline polymers and blends. The chapter also describes the molecular mechanisms associated with each motional transition. It explores the relationship between dielectric relaxation response and crystalline morphology, which is influenced by polymer backbone structure and thermal and mechanical process history. Dielectric relaxation in single-component systems is also addressed. Representative examples of high crystallinity, medium crystallinity, and low crystallinity polymers are illustrated, with an emphasis on the low crystallinity semiflexible thermoplastics. Dielectric spectroscopy serves as a versatile and sensitive thermal analysis technique to probe these transitions and their relationship to polymer backbone structure and morphology. The chapter illustrates the application of dielectric methods and the strategies necessary to establish the origin and underlying mechanisms of the various relaxations encountered in semi-crystalline thermoplastics and blends. It states that improvements in electronic components and measurement techniques will continue to increase both the power and accessibility of dielectric methods. These improvements, in combination with advances in the theoretical description and simulation of polymer chain motion, will provide further insight into the chain dynamics of solid polymers and blends. This insight will help drive the development of new polymeric materials for a range of applications, as well as the refinement and control of processing for more conventional thermoplastic formulations.

Crystallization, melting, and relaxation of modified poly(phenylene sulfide). II. Dynamic relaxation characteristics

Abstract The relaxation characteristics of a series of random PPS copolymers based on sodium hydrosulfide (NaSH) and 1,4- and 1,3-dichlorobenzene monomers have been investigated via dielectric and dynamic mechanical methods. Comparison of dielectric and dynamic mechanical glass-rubber (α) relaxation temperatures measured for the crystallized copolymers with their amorphous analogues indicated that the presence of meta-phenylene defects led to a progressive reduction in the degree of constraint imposed by the crystallites on the relaxing amorphous chains. Estimation of the mobile amorphous phase fraction in the crystallized samples based on dielectric relaxation intensity revealed complete mobilization of the rigid amorphous phase above Tg for those copolymers containing 8% and 10% meta-phenylene units. Examination of the subglass (β) relaxation in the amorphous samples showed that the introduction of meta segments in the polymer chain backbone produced a positive offset in relaxation temperatures and a co...