Benzenetricarboxamide (BTA) derivatives are versatile compounds widely employed as nucleating agents in commercial semicrystalline plastics and as supramolecular ligands in self-assembling telechelic polymer-based organogels, hydrogels, and bulk elastomers. However, their effectiveness as supramolecular modifiers is typically limited to low-molar-mass apolar polymers. Here, we report the supramolecular aggregation of a BTA-end-functionalized semicrystalline aliphatic polyester with a number-average molar mass several times its entanglement molar mass, blended with a matching low-molar-mass BTA additive. In these blends, the BTA end groups and additive co-assemble to form a new phase comprising a network of polymer-bridged nanofibrils. This network gives rise to a high-melt-strength rubbery regime that is absent from the pure telechelic polyester but extends to temperatures well above its melting point in the blends. Moreover, the nanofibrils prove to be highly efficient nucleating agents for crystallization of the polyester, significantly outperforming bulk additive precipitates. Our findings hence demonstrate that the co-assembly of polymer end groups with a low-molar-mass additive may facilitate supramolecular aggregate formation in polymer matrices where end-modification alone is insufficient, leading to materials with increased melt strength, crystallization rates, thermal dimensional stability, and valuable benefits for industrial applications.

The plastic waste crisis is among humanity's most urgent challenges. However, widespread adoption of sustainable plastics is hindered by their often inadequate processing characteristics and performance. Here, we introduce a bio-inspired strategy for the modification of a representative high molar mass, biodegradable aliphatic polyester that helps overcome these limitations and remains effective at molar masses far greater than the entanglement molar mass. We use co-assembly of oligopeptide-based polymer end groups and a low molar mass additive to create a hierarchical structure characterized by regularly spaced nanofibrils interconnected by entangled polymer segments. The modified materials show a rubbery plateau at temperatures above their melting point, associated with strongly increased melt strength, extraordinary melt extensibility, improved dimensional stability, and accelerated crystallization. These thermomechanical property changes open up otherwise inaccessible processing routes and offer considerable scope for improving solid-state properties, thereby addressing typical shortcomings of sustainable alternatives to conventional plastics.

The dynamic nature of supramolecular networks of telechelic polymers offers new avenues for the design of novel materials with enhanced melt strength and extensibility, increased energy at break, or self-healing properties. However, monitoring the kinetics of the underlying molecular-level scission-reaggregation events remains challenging, particularly in high-molar-mass polymers in the bulk state. Here, we employ solid-state 1H NMR spectroscopy relaxation dispersion experiments to investigate the aggregation-scission dynamics in poly(ε-caprolactone) modified with oligopeptide end groups that form one-dimensional hydrogen-bonded aggregates. We have successfully determined the timescale of end-group dissociation directly and independently of any relaxation of the polymer segments at different temperatures in the bulk semi-crystalline and melt state. This site-specific, non-destructive method is applicable to entangled, high-molar-mass polymers without chemical modifications or modeling, provides critical insight into the dynamics of supramolecular networks in the bulk state, and promises to be a valuable tool for the directed development of next-generation functional materials. Supramolecular networks from telechelic polymers hold promise for advanced material design, yet tracking molecular scission-reaggregation kinetics in bulk materials remains challenging. Here, the authors use solid-state 1H NMR spectroscopy to directly measure the aggregation-scission dynamics in poly(ε-caprolactone) modified with oligopeptide end groups that form one-dimensional hydrogen-bonded aggregates.

Semiaromatic polyamides are used for metal replacement in advanced engineering applications to reduce weight and improve efficiency, but their range of application is limited by their inherent lack of ductility and toughness. Here, we combined semiaromatic polyamide poly(hexamethylene terephthalamide-co-isophthalamide) (PA6TI) with up to 30 wt % amine-terminated polyethylene (PE(NH2)2) by high-temperature melt compounding, which was suggested to lead to the formation of PA-PE block copolymers at the interface between the PE(NH2)2 and the PA6TI. This resulted in PA6TI/PE(NH2)2 blends with smaller, more uniform particle sizes than in PA6TI blended with nonfunctional PE or the commercial impact modifier, maleic anhydride-functionalized styrene-ethylene-butylene-styrene (SEBS) under the same conditions. The PA6TI/PE(NH2)2 blends and the corresponding glass fiber-reinforced composites consequently showed significantly greater increases in room-temperature tensile ductility and fracture energy with respect to unmodified PA6TI, as well as maintained mechanical stability at high temperatures, and only modest decreases in stiffness and strength, even at high PE(NH2)2 contents. These improvements were attributed to the crystallinity of the PE(NH2)2 particles and to improved morphological stabilization and matrix-particle adhesion, consistent with the presence of PA-PE block copolymer at the matrix-particle interfaces.

All-polyamide composites containing up to 30 vol% highly dispersed PPTA nanofibrils with diameters in the range 50-500 nm were prepared by melt-compounding polyamide 6,10 (PA610) with chopped poly(p-phenylene terephthalamide) (PPTA) fibers in the temperature range 260-300 degrees C using a twin-screw extruder. Injection moldings prepared from these composites showed not only large increases in tensile strength with respect to the unmodified PA610 matrix at temperatures well below the matrix melting point but also significant increases in melt elasticity. The melt elasticity was further enhanced by high-temperature heat treatments under quiescent conditions. It is suggested that the implied interfacial reinforcement may involve transamidation, which is known to occur extensively in polyamide melts.

Copolymerizing poly(hexamethylene terephthalamide-co-isophthalamide) (PA6TI) with 40 wt% polyamide 66 (PA66) results in only minor decreases in modulus and yield stress owing to isomorphous substitution of PA6TI units by PA66 units in the PA6TI alpha phase, so that crystallinity is maintained in the resulting PA6TI-66 terpolymer. However, the ductility also significantly increases. This is attributed to a deformation-induced transformation of the PA6TI alpha phase to a disordered form of the PA66 alpha phase, where PA6TI units constitute defects and the chains adopt extended conformations. This phase is argued to be favored in initially amorphous PA66-rich regions and hence stabilizes interlamellar micro-necks that develop during yielding. By contrast, segregation of isophthaloyl units to the amorphous regions in PA6TI hinders strain-induced crystallization, leading to failure at significantly lower strains. Brittleness may therefore be a generic problem when comonomers ar e used to facilitate processing , but one that may be overcome through proper microstructural control.

The extraordinary property profiles of many biological materials derive from their hierarchical structure and control of order and disorder at different length scales. Application of these concepts to the design of synthetic polymers may provide new routes to lightweight materials that combine high stiffness, strength, and toughness. Here, we use high-temperature reactive melt extrusion to introduce aliphatic substitutional defects into a high-performance semiaromatic copolyamide that are able to conform to the dominant crystalline phase. This allows us to generate microstructural disorder while maintaining or even increasing the macroscopic degree of crystallinity, and hence engineer a strain-induced phase transformation in the resulting polyamides that results in an increase in chain extension along the tensile axis in the crystalline regions. The yield stress and stiffness consequently remain comparable to those of the base semiaromatic polyamide, but the strain-to-failure and tensile toughness increase more than five-fold. Tailoring the concentration and distribution of microstructural defects is hence a straightforward and powerful strategy for optimizing performance in semicrystalline polyamides.

The control of local order in polymer semiconductors using non-covalent interactions may be used to engineer materials with interesting combinations of mechanical and optoelectronic properties.

Biopolymers often show deterministic chain folding templated by repeat unit sequences whose conformations are locked in by intramolecular interactions. In this work, we have used repeat units based on rigid anthracene or acridine scaffolds, which we refer to as "U-turn" repeat units, to template chain folding reminiscent of beta-serpentine folds in bulk synthetic polyamides. Unlike the rigid kinked repeat units present in certain commercial semiaromatic polyamides, the acridine-based U-turn repeat units did not impede crystallization in the polyamides, whose crystalline phase was shown to be stabilized by infinite arrays of intermolecular hydrogen bonds and pi-pi interactions between the acridine units. This led to a unique layered crystalline structure characterized by a well-defined lamellar thickness that depended on the length of the aliphatic spacers between the U-turn repeat units and regular adjacent re-entrant chain folding, which is not usually expected for semiaromatic polyamides crystallized at high supercooling. Our work hence provides the first example of the introduction of deterministic chain folding into a nonpeptidic polyamide in order to tailor its crystalline morphology and may consequently open up new perspectives for the molecular design of structural materials.

Incorporation of bithiophene segments in the polyamides results in semiconducting properties, while mechanical properties of typical engineering polyamides are maintained.

ABSTRACTColloidal silica nanoparticles (NPs) modified with eight different silane coupling agents were incorporated into an amorphous poly(tetramethylene oxide)‐based polyurethane–urea copolymer matrix at a concentration of 10 wt % (4.4 vol %) in order to investigate the effect of their surface chemistry on the structure–property behavior of the resulting nanocomposites. The rigid amorphous fraction (RAF) of the nanocomposite matrix as determined by differential scanning calorimetry and dynamic mechanical analysis was confirmed to vary significantly with the surface chemistry of the NPs and to be strongly correlated with the bulk mechanical properties in simple tension. Hence, nanocomposites with an RAF of about 30 wt % showed a 120% increase in Young's modulus, a 25% increase in tensile strength, a 15% decrease in elongation at break with respect to the neat matrix, which had no detectable RAF, whereas nanocomposites with an RAF of less than 5% showed a 60% increase in Young's modulus, a 10% increase in tensile strength and a 5% decrease in the elongation at break. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2543–2556

The impact modification of poly(methylmethacrylate) (PMMA) by the mechanical blending of a low-molecular-weight matrix with preformed particles can only be achieved by a process involving shear deformation, such as extrusion or injection molding. To maintain good optical properties, the rubbery domains in modified PMMA should be smaller than the wavelength of visible light, and/or the refractive index of the secondary phase should match that of the matrix. The most obvious distinctions between the 3L-particle-modified PMMAs and the 2L-particle-modified PMMAs lie in the nature of the particle cavitation. The crazes then propagate in the matrix perpendicular to the principal stress axis by the usual mechanism of growth at constant stress in the craze fibrils, as in unmodified PMMA. Widespread crazing has been also been reported elsewhere to occur at crack tips in notched specimens of particle-modified PMMA, where the local triaxiality and strain rates are generally much higher than in simple tension.

A major issue in composite technology is matrix micro-cracking due to low-velocity impact damage, which may severely limit service lifetimes of composite parts. In a novel approach, remarkable levels of healing of impact damage are obtained using shape memory alloy (SMA) wires to close longitudinal cracks in woven glass fibre-reinforced polymer plates with an epoxy-polycaprolactone (EP-PCL) matrix that shows dual-phase continuity. Thermal actuation of SMA wires stitched through the thickness of the stacked glass fibre plies introduces compressive loads to the cracks thanks to anchoring of the SMA loops at the fabric surfaces and debonding of the intervening threads, which prevents local deformation of the SMA, so that crack closure by about 200 mu m is achievable. Concomitant expansion of the vascular network formed by the molten PCL fills the compressed cracks, resulting in highly effective healing on cooling, as demonstrated by C-scan images. Specimens stitched with SMA wires hence show almost complete healing, i.e. damage area recovery of 85%, after low-velocity impact at up to 17 J followed by heat treatment at 150 degrees C. This represents a 55% improvement over previous results for unstitched EP-PCL composites, and hence significantly greater degrees of healing than so far reported for this range of impact energies and this type of system.

Periodontitis affects the attachment of natural teeth, and infection or inflammation associated with periodontitis may affect peri-implant tissues. Enamel matrix derivative (EMD) proteins provide stimulation for self-regeneration of the damaged tissue when applied to wide intrabony defects as part of a mixture with bone graft material. As a first step of the process enhancing cell proliferation and ligament formation, we demonstrated that EMD protein precipitation depends strongly on the physical and chemical characteristics of the bone grafts used in the mixture. To guarantee optimum protein-stimulated self-regulation, the pH of the initial EMD formulation must therefore be adjusted between 3.9 and 4.2 in order to compensate the change in pH induced by the bone graft. Moreover, the interaction between the two components resulted in precipitates of different shape and size differently covering the grafts. This outcome might potentially have clinical implications on cell attachment and periodontal ligament extension, which deserve further in vitro and in vivo tests.

Nonisothermally fusion bonded butt joints were prepared by overmolding thermoplastic elastomers (TPEs) onto isotactic polypropylene (iPP) inserts in order to investigate the effect of processing conditions on the bond strength and interfacial microstructure. The mold temperature (Tm) was the most important factor for bond strength, as determined from interfacial mechanical tests. Extensive melting and recrystallization took place at the surface of the iPP insert at high Tm, promoted by migration of plasticizer from the TPE, whereas the original structure of the iPP remained intact at low Tm. Bond strengths of at least 50% of the cohesive strength of the TPE were nevertheless obtained at low Tm, suggesting intimate contact between the TPE melt and the iPP surface to be sufficient to provide useful adhesive bond strengths in these materials. The influence of pressure was less marked than the Tm, high pressures not being necessary to achieve intimate contact for the bonding times of about 5 s used here. However, the combination of a low bonding pressure with a high Tm typically led to poor quality bonds in thick specimens owing to uncompensated shrinkage during solidification, and voiding at the interface and in the melt zone of the iPP insert. POLYM. ENG. SCI., 58:E82–E92, 2018. © 2017 Society of Plastics Engineers

ABSTRACTHigh‐performance thermoplastic composites based on semiaromatic polyamides are prime candidates for metal replacement in lightweight structural applications. However, the low ductility and toughness of semiaromatic polyamides remain major obstacles to their wider industrial application. In this study, we showed that novel random copolymers were formed by the unexpectedly efficient transamidation during the melt compounding of semicrystalline semiaromatic and aliphatic polyamides. Thus, homogeneous materials with a single glass transition and a high degree of crystalline order were obtained from blends of the semiaromatic poly(hexamethylene terephthalamide‐co‐isophthalamide) (PA6TI) with poly(hexamethylene adipamide) (PA66) or poly(hexamethylene sebacoamide) (PA610). By contrast, phase segregation and a less efficient transamidation was observed for cocompounded PA6TI and polylaurolactam (PA12). We attributed this to differences in the hydrogen‐bonding patterns of the two polyamides. This study opened the way for the preparation of novel high‐performance thermoplastic polyamides and composites through simple melt compounding. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44349.

An overview is given in this article of the most widely used matrix materials for fiber-reinforced plastics and their relative merits. The processing routes commonly used to produce composite parts are then discussed, with reference to cost forecasting, life cycle engineering, and developing technologies. Finally, the important question of process–structure–property relationships in thermoset- and thermoplastic-based fiber-reinforced plastics is addressed.

Objective To evaluate the cost-effectiveness of implantable cardioverter defibrillators (ICDs), cardiac resynchronisation therapy pacemakers (CRT-Ps) and combination therapy (CRT-D) in patients with heart failure with reduced ejection fraction based on a range of clinical characteristics. Methods Individual patient data from 13 randomised trials were used to inform a decision analytical model. A series of regression equations were used to predict baseline all-cause mortality, hospitalisation rates and health-related quality of life and device-related treatment effects. Clinical variables used in these equations were age, QRS duration, New York Heart Association (NYHA) class, ischaemic aetiology and left bundle branch block (LBBB). A UK National Health Service perspective and a lifetime time horizon were used. Benefits were expressed as quality-adjusted life-years (QALYs). Results were reported for 24 subgroups based on LBBB status, QRS duration and NYHA class. Results At a threshold of £30 000 per QALY gained, CRT-D was cost-effective in 10 of the 24 subgroups including all LBBB morphology patients with NYHA I/II/III. ICD is cost-effective for all non-NYHA IV patients with QRS duration <120 ms and for NYHA I/II non-LBBB morphology patients with QRS duration between 120 ms and 149 ms. CRT-P was also cost-effective in all NYHA III/IV patients with QRS duration >120 ms. Device therapy is cost-effective in most patient groups with LBBB at a threshold of £20 000 per QALY gained. Results were robust to altering key model parameters. Conclusions At a threshold of £30 000 per QALY gained, CRT-D is cost-effective in a far wider group than previously recommended in the UK. In some subgroups ICD and CRT-P remain the cost-effective choice.

Amelogenin refers to a class of intrinsically disordered proteins that are the major constituents of enamel matrix derivative (EMD), an extract of porcine fetal teeth used in regenerative periodontal therapy. Modifications in molecular conformation induced by external stresses, such as changes in temperature or pH, are known to reduce the effectiveness of EMD. However, detailed descriptions of the conformational behavior of native amelogenin are lacking in the open literature. In the present work, a molecular model for the secondary and tertiary structure of the full-length major porcine amelogenin P173 was constructed from its primary sequence by replica exchange molecular dynamics (REMD) simulations. The REMD results for isolated amelogenin molecules at different temperatures were shown to be consistent with the available spectroscopic data. They therefore represent an important first step toward the simulation of the intra- and intermolecular interactions that mediate self-organization in amelogenin and its behavior in the presence of other EMD components under conditions representative of its therapeutic application.