Oxygen barrier properties of PET copolymers containing bis(2‐hydroxyethyl)hydroquinones

A series of poly[ethylene‐co‐bis(2‐ethoxy)hydroquinone terephthalate], PET‐co‐BEHQ copolymers were prepared by polymerization of various substituted bis(2‐hydroxyethyl)hydroquinones (BEHQs), dimethyl terephthalate (DMT), and ethylene glycol (EG). In addition to copolymers containing 6–16.5 mol % BEHQ, the homopolymer of BEHQ with dimethyl terephthalate, p(BEHQ‐T), was also prepared. The thermal and barrier properties of amorphous materials were studied. As the amount of comonomer was increased, the T_g and T_m of the materials decreased relative to those of PET. Oxygen permeability also decreased with increasing comonomer content. This improvement in barrier‐to‐oxygen permeability was primarily due to a decrease in solubility of oxygen in the polymer. All of the copolymers tested displayed similar oxygen diffusion coefficients. The decrease in solubility correlates with the decrease in T_g. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 934–942, 2003     

[Poly(ethylene terephthalate) ionomer]/silicate hybrid materials via polymer–in situ sol‐gel reactions

A scheme was developed for producing poly(ethylene terephthalate (PET) ionomer)/silicate hybrid materials via polymer–in situ sol‐gel reactions for tetraethylorthosilicate (TEOS) using different solvents. Scanning electron microscopy/EDAX studies revealed that silicate structures existed deep within PET ionomer films that were melt pressed from silicate‐incorporated resin pellets. ²⁹Si solid‐state NMR spectroscopy revealed considerable Si—O—Si bond formation, but also a significant fraction of SiOH groups. ²³Na solid‐state NMR spectra suggested the presence of ionic aggregates within the unfilled PET ionomer, and that these aggregates do not suffer major structural rearrangements by silicate incorporation. For an ionomer treated with TEOS using MeCl₂, Na⁺ ions are less associated with each other than in the unfilled control, suggesting silicate intrusion between PET–SO Na⁺ ion pair associations. The ionomer treated with TEOS + tetrachloroethane had more poorly formed ionic aggregates, which illustrates the influence of solvent type on ionic aggregation. First‐scan DSC thermograms for the ionomers demonstrate an increase in crystallinity after the incorporation of silicates, but solvent‐induced crystallization also appears to be operative. Second‐scan DSC thermograms also suggest that the addition of silicate particles is not the only factor implicated in recrystallization, and that solvent type is important even in second‐scan behavior. Silicate incorporation does not profoundly affect the second scan T_g vs. solvent type, i.e., chain mobility in the amorphous regions is not severely restricted by silicate incorporation. Recrystallization and melting in these hybrids appears to be due to an interplay between a solvent‐induced crystallization that strongly depends on solvent type and interactions between PET chains and in situ‐grown, sol‐gel‐derived silicate particles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1749–1761, 2002; DOI 10.1002/app.10586     

Crosslinking studies on poly(ethylene terephthalate‐co‐1,4‐phenylene bisacrylate)

Several compositionally different poly(ethylene terephthalate‐co‐1,4‐phenylene bisacrylate) (PETPBA) copolymers were melt spun into fibers. The resulting fibers were subjected to UV irradiation to induce crosslinking. Evidence of crosslinking was obtained from FTIR, solid‐state ¹³C‐NMR, thermal analysis, and solubility. Irradiation of the fiber results in an increased glass‐transition temperature, reduced thermal shrinkage, and enhanced modulus retention at elevated temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1698–1702, 2004     

Effect of comonomers on the rate of crystallization of PET: U‐turn comonomers

The effect of incorporating phthalate, 1,8‐naphthalenedicarboxylate, and 1,8‐anthracenedicarboxylate structural units on the crystallization rate of PET are evaluated by isothermal and dynamic calorimetry. Although all of the comonomers retard crystallization, the 1,8‐naphthalene unit shows no concentration dependence between 2.5 and 10% incorporation, in contrast to the smaller phthalate and larger anthracene units. The greater rate at which the 1,8‐naphthalene copolymer crystallizes, relative to that of the other copolymers, is consistent with the notion that the U‐turn geometry induces chain folding and nucleates crystallization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1675–1682, 2001     

Structure–property evaluation of trisilanolphenyl POSS®/polysulfone composites as a guide to POSS melt blending

A series of polysulfone/phenyl trisilanol POSS nanocomposites were produced by melt blending by twin screw batch mixing. These materials were then injection molded, and their thermal, mechanical, and morphological properties were tested. The tensile properties of polysulfone were moderately compromised by the addition of phenyl TPOSS, because of the formation of large (∼ 1 μm) voided POSS aggregates. These domains however did cause the improvement of the impact resistance of the composites as described by the mechanism of crack pinning and bowing. Flexural properties remained essentially unchanged, which is attributed to the formation of an aggregate free-skin layer, which formed in the injection molded parts. Thermal behavior of the composites also remained largely unchanged due to the lack of POSS-polymer interactions on the molecular/chain segment scale. Initially, it was hypothesized that a high degree of POSS-polymer interactions would be present in these composited based on examination of their chemical structures. This however, was not the case as phase separation was clearly present. This work highlights the need for a better understanding of the prediction of POSS-polymer interaction. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effects of physical and chemical interactions in the formation of cellulose aerogels

Aerogels are low density materials which are produced from wet gels, and find a variety of potential uses. The relative importance of shape/geometry and self-association of the starting materials for the production of aerogels is studied herein. Aerogels were produced from microcrystalline cellulose (MCC) and its functionalized analog, carboxymethyl cellulose (CMC). With increasing functionalization, CMC gains the potential for self-association, differentiating itself from MCC. The present study explores the preparation of aerogels from MCC and CMC, comparing performance with and without significant self-association potential, and more broadly evaluating the production of low density structural materials from renewable cellulose. It was observed that the self-association present in CMC substantially increases aerogel mechanical properties when compared those of non-interactive MCC. Aspect ratio is proposed to also be an import parameter in the structure–property relationship for these materials.     

Chemico-physical characterization of hybrid composites based on hydroxyethyl methacrylate and nanosilica

Novel hydrogels are often designed to mimic the transport and mechanical properties of natural soft tissue such as ligaments, tendons, intervertebral discs, or to be exploited as scaffold for tissue engineering. Recently, novel hydrogels based on 2-hydroxylethyl methacrylate and fumed silica nanoparticles (5–25% w/w) were synthesized by our group and demonstrated to improve cell adhesion and proliferation. The chemico-physical properties and mechanical behaviour of these new polymers have been studied and are presented in this article. The swelling equilibria in water and water solutions were evaluated in relation to ionic strength and pH. The sorption kinetic estimated through gravimetric analysis showed a diffusive transport behaviour of the hybrid composite materials as of early stages of the process. The elastic modulus was evaluated by Dynamic-Mechanical Analyses and proved to increase with the filler content reaching values compatible with the mechanical characteristics of natural material. This result supports the possibility of future applications of the novel hybrid composite in several fields, in dentistry as dental filling or in systems for the controlled released of drugs.     

Memory effects in supramolecular networks of diacids and polyfunctional pyridine derivatives

Highly crosslinked networks were produced through a series of diacids and tetrakis pyridyls. These materials displayed complex crystallization behaviors over multiple heat/cool cycles. The shifting of crystallization behaviors with time in the melt phase seems to indicate that the materials move toward thermodynamically ideal structures. This behavior is suggestive of a type of memory in which the networks remember the morphological structure previous to the melt and improve upon that structure in the next cooling cycle. The network/memory phenomena observed in small molecule diacid/tetrapyridyl systems also appeared to exist when poly(ethylene terephthalate) (PET) polymer was used as the source of carboxylic acid functionalities. The same time‐ dependent behaviors, suggestive of sequential steps toward thermodynamically optimum states, were observed when the PET/tetrapyridyl systems were thermally cycled. It was also observed that complexation of tetrapyridyl with PET brought about a significant change in oxygen gas barrier properties; these changes were opposite to those obtained when covalent crosslinks were introduced into PET. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3097–3106, 2004     

Foam‐like polymer/clay aerogels which incorporate air bubbles

The structure/property relationships of polymer/clay aerogels interfused with uniformly distributed air bubbles were examined. Through the incorporation of a polyelectrolyte in a montmorillonite(MMT) clay solution, the viscosity was systematically changed by the addition of ions with different charges. The bubbles were achieved via high speed mixing and were stabilized through the use of the surfactant sodium dodecyl sulfate (SDS). As the charge of the ion increased from +1 (Na⁺ ions) to +2 (Ca²⁺ ions) to finally +3 (Al³⁺ ions), the modulus of the resultant aerogels increased. The foamed polymer/clay aerogels showed a reduction in thermal conductivity while retaining similar mechanical properties to unfoamed polymer/clay aerogels. The most promising composition was one which contained 5% MMT clay/5% poly(vinyl alcohol)/0.5% xanthum gum/0.5% SDS/0.2% Al₂(SO₄)₃·6(H₂O) possessing a density of 0.083 g/cm³, an average modulus of 3.0 MPa, and a thermal conductivity of 41 W/m·K. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39546.