Polymer chain-oriented architectures offer a lightweight route to maximize mechanical performance and steer heat flow in one direction, while remaining soft and bendable. Yet their functionality is rarely described beyond a limited set of characteristics, such as tensile modulus or effective thermal conductivity. Here, we establish a tensor-level thermo-mechanical benchmark for solid-state-processed ultra-high-molecular-weight polyethylene (UHMWPE) tapes at draw ratios of 7 and 70 using contactless, all-optical techniques. Brillouin light scattering resolves direction-dependent acoustic phonon velocities in the gigahertz regime, which are converted into the full orthorhombic elastic tensor and engineering compliance matrix, yielding orientation-dependent Young’s moduli, shear moduli, and Poisson’s ratios together with the anisotropic refractive index. Complementary thermoreflectance measurements quantify thermal transport and reveal strongly anisotropic in-plane heat conduction with anisotropy ratios of about ten. The combined dataset shows that axial mechanical stiffening is not accompanied by a proportional increase in thermal-conductivity anisotropy in these hierarchical fibrillar tapes, highlighting the role of interdomain coupling and phonon scattering. More broadly, the results position chain-oriented UHMWPE as a rare insulating-material platform combining high, strongly anisotropic mechanical performance with directional heat transport, approaching the functionality otherwise associated with benchmark electrically insulating thermal conductors such as diamond, but in a lightweight, flexible form.

Semicrystalline polymers constitute crystalline and noncrystalline regions. In the crystalline region, chain segments form a well-defined unit cell. In contrast, the noncrystalline region having a lower density is strongly influenced by the crystallization conditions and considerable variation in the chain conformation/chain topology exists. Here we demonstrate, for the first time, that the mobility of the chain segments in the crystalline region of the same polymer is strongly influenced by the topological/conformational differences of the chain segments in the noncrystalline region. To undertake the study, variability in the topological constraints in the noncrystalline region is achieved by crystallization during polymerization or postpolymerization. Two sets of nascent UHMWPEs are synthesized using a conventional Ziegler-Natta (Z-N) catalytic system and a postmetallocene single-site catalytic system. The polymer obtained from the conventional Z-N catalytic system results in an entangled noncrystalline region, whereas the UHMWPE synthesized using a postmetallocene catalytic system provides a possibility to reduce the entanglement density, reducing the topological constraints. The entanglement density in the Z-N synthesized UHMWPE can be reduced by crystallization of the nascent polymer from a dilute solution. The influence of a tailored entanglement state on the chain mobility in the crystalline region is pursued by solid-state NMR; the 1H spin-lattice relaxation time in the rotating frame (T 1 rho,H) indicates that with the decreasing concentration of entanglements the chain-flip motion in the crystalline region increases. The influence of the entanglement density on the chain mobility in the crystalline region is supported by the transfer of polarization from the noncrystalline to crystalline region, arising from the fact that chain segments of the same chain reside in the crystalline as well as noncrystalline region. The ease in transfer of polarization can be expressed by the differences in the entropic barrier between the chain conformations in the noncrystalline and crystalline regions. These observations on the UHMWPE are of a generic nature, allowing us to quantify the differences in the abstract nature of the topological constraints in semicrystalline polymers.

The study explores synthesis and characterization of ultrahigh molecular weight isotactic polypropylene (UHMWiPP) using a hafnium-pyridyl amido catalytic system. The observations are that by modifying the catalyst through initial insertion of 1-decene, UHMWiPP having extremely high molecular weights, up to 13.5 x 106 g/mol, can be achieved. The effect of ligand modification on polymer properties, including molecular weight, entanglement density, and crystallization are investigated. The impact of ligand modification on UHMWiPP is assessed by DFT calculations. The calculations, aligned with the experimental observations, demonstrate that the ultrahigh molecular weight is a result of the increase in energy barrier for beta H transfer and elimination in the 1-decene modified catalyst. The controlled synthesis provides the uniqueness of the tailored entanglement state during polymerization. Surprisingly, the molar mass between entanglements (M e) increases with molar mass, reaching the unprecedented value above 22700 g/mol. Rheological analysis reveals that the nonequilibrium polymer melt with higher molecular weights exhibits the slowest equilibration process. The slow equilibration of the nonequilibrium polymer melt allows following changing chain dynamics with the entanglement's formation and its influence on crystallization kinetics. It is apparent that the higher the molecular weight, the higher is the M e and so is the crystallization rate.

Isotactic poly(4-methyl-1-pentene) (iP4MP1) is a unique material known for its high transparency and gas permeability. iP4MP1 possesses high thermal and chemical stabilities, making it suitable for a wide variety of applications. We investigate the influence of polymerization medium on the resulting polymorphs and mechanical properties. By employing an aryl pyridylamido hafnium catalyst in a mixture of n-heptane and toluene, ultrahigh-molecular-weight UHMW-iP4MP1 having a unimodal distribution is achieved. The use of n-heptane as the polymerization solvent, where iP4MP1 chains are poorly miscible, resulted in the formation of metastable monoclinic Form II crystals, which below melting transform into the stable tetragonal Form I. The study demonstrates that crystallization kinetics during polymerization can be tailored to synthesize single-crystal-like iP4MP1. The low-entangled single-crystal-like iP4MP1 enables uniaxial deformation below the melting temperature, facilitating chain alignment. Consistent with the stereospecific nature of iP4MP, rheological analysis suggests high molecular weight between entanglements (M e approximate to 26,000 g/mol). Mechanical properties of the synthesized polymers, including tensile strength, elongation at break, and toughness, increase with the molecular weight, highlighting the potential for achieving uniform mechanical properties required for advanced applications.

This study examines the effect of graphene oxide (GO) sheets on the thermal and rheological properties of dis-entangled ultrahigh molecular weight polyethylene (dis-UH) and their implications for two key applications: melt-blending with commercial HDPE and solid-state processed tapes, while addressing a very fundamental aspect in polymer science-the origin of melt memory. The observations are that thermal annealing of dis-UH in the melt at 160 degrees C reveals heterogeneity in its entanglement state. The dynamic heterogeneity in the non-equilibrium polymer melt is evident by the enthalpic relaxation arising with a second melting peak, whose enthalpic contribution varies with the annealing time. Rheological analysis shows that incorporating 0.75 wt% GO in dis-UH reduces the plateau modulus (G0N), while no significant changes are observed in the comparative example of a commercial HDPE. Furthermore, the addition of GO sheets causes a rise in a secondary relaxation mechanism, which increases the power exponent (G(y) similar to omega n) from-0.35 to-0.30 at intermediate frequencies, attributed to contour length fluctuations (CLF). Large amplitude oscillatory shear (LAOS) experiments indicate that GO alters the molecular dynamics of dis-UH, shifting its response from weak strain overshoot to strain thinning, suggesting a reduced entanglement density that facilitates chain alignment. The proposed mechanism suggests that the presence of GO perturbs dis-UH chains, partially restricting entanglements formation, thereby maintaining a lower entanglement state, increasing the entanglement molecular weight (Me), and reducing melt viscosity. GO incorporation significantly impacts the performance of dis-UH in both melt-processing and solid-state processing. In melt-blending with HDPE, the addition of GO to dis-UH reduces the zero-shear viscosity of the HDPE/dis-UH/GO blend by 70 % compared to HDPE/dis-UH blend, and improves dispersion by 24 %, at GO concentrations below 0.001 wt%. In solid-state processed tapes, GO increases the maximum draw ratio while the specific strength and modulus remain unchanged. Additionally, the GO-containing tapes show lower creep rates compared to their pure dis-UH samples. These findings highlight GO's potential to enhance the processability, dispersion, drawability, and creep response of dis-UH, making it a promising additive for advanced polymer applications, while providing insight on the strong influence of entanglements in the melt-memory of polymers in general.

The polymerization conditions, including solvent, catalytic system, reaction temperature, are the physical parameters that strongly influence entanglement state in the non-crystalline region of a semi-crystalline polymers. In this study, we investigate ultra-high molecular weight isotactic polypropylene (M-w similar to 3 x 10(6) g/mol) synthesized using multi-site (Ziegler-Natta) and single-site (post-metallocene) catalytic systems. The two chosen catalytic systems result in distinct nascent morphology as viewed by scanning electron microscopy. In contrast to the densely packed nascent crystals synthesized using a ZN catalytic system, platelet-like isolated single crystals of iPP are obtained when the synthesis is pursued using a post-metallocene catalytic system. The electron diffraction confirms the platelets are the single crystals of iPP, where the chains in the helical conformation pack perpendicular to the crystal thickness, and the platelet surface have the folded-chains. The ease in deformation and compaction of the platelets, below melting temperature, suggest the low entanglement state of the single crystals and provide unique opportunity in following the crystal thickening on annealing of the long chains packed within the thin platelets of several tens of nm thickness. Independent of the pursued synthesis routes, the presence of rigid amorphous fraction (RAF) in both samples is recognized. However, thermal stability of the RAF shows strong dependence on the polymerization conditions. The RAF in the nascent sample synthesized using the single-site catalytic system is found to be thermally more stable than the Z-N synthesized sample, leading to a strong shift in the glass transition temperature. With an increase in mobility of the chain segments in RAF, the lamellae thickness increases which is followed by melting and re-crystallization at higher temperatures. The thickening in the nascent crystals is a result of the localized RAF mobility that does not require cooperative motion of the long chains packed in the isolated nascent crystals.

Disentangled ultrahigh molecular weight polyethylene exhibits a time-dependent increase in rheology modulus when molten. This originates from its kinetically evolving heterogeneous microstructure consisting of disentangled and entangled regions. We report a quantitative analysis of this microstructure using X-rays and neutrons that capture the signatures of these regions. We analyze the absolute intensities to obtain the volume fraction and size distribution of the disentangled domains in the melt. Employing neutrons, we follow the changes in these parameters with time. The trends are qualitatively similar to those of the previous rheological observations. Our methodology also provides an experimental verification of the theoretical report by McLeish, T. C. B. Soft Matter 2007, 3 (1), 83-87, which predicts the presence of high density disentangled domains in a low density entangled matrix. The analysis presented here is a useful instrument for unveiling the origin of differences in the properties of polymers obtained through different processing routes.

The molecular blending achieved by the incorporation of up to 20 wt. % of UHMWPE via melt blending, facilitated by its initially low-entangled nature (dis-UH), is assessed through nonlinear transient shear and extensional rheology. The findings demonstrate that by adding dis-UH, the rheological properties of the blends are enhanced significantly. In a nonlinear shear flow, indicated by the stress ratio (sigma peak/sigma steady) in comparison to monodisperse and polydisperse solution blended polystyrene, the blends exhibit low deformability. However, increasing the dis-UH fraction leads to greater polymer network stretch, evidenced by a notable increase in maximum strain (gamma max) from 2.3 to 3.3. Additionally, the slowdown of polymer dynamics, with increasing dis-UH fraction, is reflected in the long-time stress relaxation rate after shear cessation. Under uniaxial elongational flow, increasing the dis-UH fraction up to 20 wt. % promotes strain hardening (SH) in the vicinity of melting point. The cause of SH is attributed to flow-induced crystallization (FIC), at relatively low supercoolings. Finite extensibility analysis reveals that the onset of SH is triggered at a constant strain of similar to 2.63, driven by the stretching of entanglement strands, followed by crystallization. Structural analysis using scanning electron microscopy, wide-angle x-ray diffraction, and small-angle x-ray scattering provides strong evidence of shish-kebab structure formation resulting from FIC. The quantification of long period (L-kebab), orientation degree of the (110) diffraction crystal plane S-(110), and kebab structure's orientation (S-kebab) reveals enhanced orientation by increasing both elongational strain and dis-UH content. On comparing S-kebab as a function of stress at quench normalized by the entanglement number (Z), we establish the consistency of our findings with previous studies, validating the successful molecular blending of a high fraction of intractable UHMWPE via melt blending, facilitated by its initially low-entangled nature.

Isotactic polystyrene (iPS) has not been commercialized because of its slow crystallization rate that limits processing efficiency. To enhance the crystallization rate of iPS, in past, the focus has been on post-polymerization processing steps, whereas crystallization during polymerization (through nascent polymer) has never been addressed. This study explores a novel approach to enhance the crystallization rate of iPS by addressing the polymerization conditions rather than the post-polymerization processing steps. We investigate various polymerization parameters that influence the crystallization kinetics of iPS. Our findings demonstrate that using heptane as a solvent, alongside low catalyst and monomer concentration at ambient temperature enhances the crystallization of growing polymer chains during polymerization. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) reveal that nascent iPS samples exhibit rapid crystallization, while 13C NMR spectroscopy confirms a fully isotactic microstructure. Gel-permeation chromatography (GPC) shows ultra-high molecular weight and narrow molecular weight distribution, and wide-angle X-ray diffraction (WAXD) complemented by DSC confirms the crystalline structure in the nascent polymer. The morphology of the resulting iPS polymers, analyzed through scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), and POM, conclusively demonstrate that the iPS synthesized in heptane exhibit lamellae-like morphology (SEM). In the plate-like crystals, (TEM) chains are packed perpendicular to the crystal thickness. Thus obtained single crystals (ED), on melt crystallization show fast-crystallizing small spherulites (POM). In contrast, using the same catalytic system, while using toluene as a solvent result in a relatively low molecular weight polymer having undefined morphology (SEM), where electron diffraction representing single crystals cannot be obtained successfully. Thus obtained nascent polymer having low crystallinity shows cold crystallization on heating. While cooling from melt, because of low nucleation and growth process, bigger spherulites are formed. These observations are complemented by small-angle X-ray scattering (SAXS), where reorganization of the nascent polymer prior to melting is observed. The rheological study in the linear viscoelastic regime indicates that the relaxation time increases with increasing molecular weight, where all synthesized polymers reach a constant plateau modulus. The zero-shear melt viscosity follows a power law dependence with an exponent of 3.4. Initial processing results show that nascent iPS can be processed in the solid state (compression-rolling-stretching) below their melting temperature. Our findings highlight the potential for optimizing iPS crystallization through tailored polymerization conditions, paving the way for future commercial applications. This study is the first to illustrate the influence of polymerization conditions on the crystallization rate of iPS.

In polyamides, hydrogen bonding and conformations of amide motifs are strongly influenced by pH, ions and their concentration, and water molecules and their structure. To fulfill the physical requirements for ultradrawing of polyamide 6, we first complete our fundamental insight into the role of water, ions, and polyamide 6 crystal structures on the concept of reversible shielding of hydrogen bonds. The reversible shielding depends on a complementary superchaotropic effect of anions and the kosmotropic effect of cations, locally affecting the structuring and interactions of water. We show that in the presence of large halogen anions, specifically polyiodides, crystallization from the random coil state or during crystallographic reorganization is suppressed by hydrophobic hydration. Among the cations, hydrated lithium and calcium cations promote the formation of polyiodides, specifically I3 -. The small size of lithium cations entails high diffusivity with water molecules, retrospectively effectively shielding the hydrogen bonding in the crystals. Upon reorganization of the conformationally distorted β phase upon heating and close to the boiling point of water, ions promote gel formation. The gel can be extruded and shaped, e.g., into monofilaments at 85 °C, and at room temperature, it can be stretched to a draw ratio of 25 to secure chain orientation. After immersion in water to remove the ions and restore the amide-amide hydrogen bonds, postdrawing and drying render high anisotropy, oriented chain crystals of high perfection, and tensile modulus and strength up to ∼19 × 103 and ∼1140 MPa, respectively. The process holds potential in achieving extended chain crystals desired for ultimate mechanical properties.

The differences in the lamellae thickening mechanisms with temperature in nascent ultrahigh molecular weight poly(ethylene-alt-CO) (UHMWPK-E) and the corresponding solution-crystallized film are investigated. The nascent UHMWPK-E, synthesized using a Pd-based single-site catalytic system, essentially consists of single-isolated crystals, where chains having a molar mass approaching 5 million g/mol fold back and forth in the lamellae thickness of 6 nm. The same nascent polymer, when crystallized from solution, is likely to form stacked crystals, resulting in a solution-crystallized film. Even though the molecular characteristics of the nascent and the solution-crystallized samples are the same, there are significant differences in the lamellae-thickening mechanisms upon heating. The nascent single crystals of UHMWPK-E, achieved through the synthesis protocol, exhibit restricted primary thickening that requires cooperative motion of the whole chain after the solid-solid phase transition (from high-density orthorhombic to low-density orthorhombic phase), followed by melting and recrystallization at the onset of melting temperature. However, the stacked crystals in the solution-crystallized film demonstrate secondary thickening, facilitated by localized mobility between the adjacent stacked crystals, followed by melt recrystallization. This difference in lamellar thickening mechanisms has been systematically investigated using transmission electron microscopy, small-angle X-ray scattering/wide-angle X-ray diffraction, solid-state NMR, and dynamic mechanical thermal analysis. These findings highlight the structural evolution pathways in UHMWPK-E under thermal conditions prior to melting and emphasize the influence of initial crystalline morphology on thickening mechanisms in the same polymer.

The sintering of ceramics, metals, and polymers has been a subject of intense interest, especially when the materials can be sintered without melting in the solid state. In contrast to inorganic materials, crystallizable polymers have segments of the same chain residing in crystalline and noncrystalline regions. The topological constraints between the chain segments residing in the noncrystalline region are strongly influenced by the crystallization and/or polymerization history. Here, we address the influence of topological constraints on the deformation of crystalline domains to the extent that lattice diffusion and grain boundary diffusion in semicrystalline polymers can be achieved without melting. This allows ease in translation of the macroscopic forces to the molecular length scale in the sintered polymer, facilitating uniaxial and biaxial deformation below the melting temperature. Since solid-state processing circumvents the challenges of melt processing, entropic relaxation of the oriented chains, and thermal degradation of the polymers at high temperatures, unprecedented mechanical properties in the uniaxial and biaxial drawn intractable ultrahigh molar mass polymers have been achieved. Thus, solvent-free sustainable solutions are provided for the processing of the intractable engineering polymers needed for demanding applications. The ease of sintering allows the fabrication of grain-boundary-free products, with advantages in prostheses.

This study investigates the dispersion and compatibility of low-entangled "dis-entangled" UHMWPE (dis-UH) in a high-density polyethylene (HDPE) matrix using solvent-free melt-blending conditions and compares it with entangled UHMWPE (eUH) in the same matrix. The findings reveal that dis-UH/HDPE exhibits a significantly lower viscosity ratio than eUH/HDPE (1 and 4, respectively), indicating a lower critical capillary number (Ca-critical), thus enhanced dispersion and compatibility. Blends with varying dis-UH content up to 20 wt% show homogeneity, evidenced by DSC and SEM analysis, and demonstrate improved mechanical properties by 36 % in the maximum stress (sigma(max)) and 39 % in Young's modulus (E). Linear viscoelasticity assessments reveal that higher dis-UH content slow the dynamics and increase the apparent weight average molecular weight (M-w), consistent with previous reports for linear entangled PE. The zero-shear viscosity (eta(0)) scaling with M-w (eta(0) proportional to M (n)) is adjusted for high polydispersity, yielding a transitional point in the scaling exponent (n) from 3.6 to 3 at a reptation number of entanglement segments (M-r/M-e) of similar to 287, in line with theoretical predictions. To rationalize the success of the homogenization process, we propose a qualitative molecular picture inspired from the constraint release Rouse mechanism involved in the disorientation process of bi-disperse linear polymers. In the case of dis-UH/HDPE blends, with initially lower density of long-long entanglements within dis-UH, and the highest density of short-short entanglements within HDPE matrix, the formation of long-short entanglements between dis-UH and HDPE is facilitated, which results in successful homogenization process. In the contrary, the establishment of long-short entanglements in eUH/HDPE blends will require unwinding of the long-long entanglements, which holds a higher kinetic barrier compared to dis-UH/HDPE blends, leading to unsuccessful homogenization.

Poly(vinylidene fluoride) (PVDF) has received much attention for its electroactive properties arising from beta- and gamma-crystallographic phases. Until now, investigation deals with postpolymerization processing methods to secure beta- and gamma-polymorphs, although a deeper understanding of the promotion of beta- and gamma-phases during the polymerization of vinylidene fluoride (VDF) is scarcely reported. This study scrutinizes the polymerization conditions and demonstrates how polymerization temperatures, times, and molar masses of the "nascent PVDF powder" affect the formation of the crystalline phases (alpha, beta, and gamma). It is presented that specific molar masses produced at various polymerization temperatures strongly control PVDF polymorphs and play a pivotal role in electroactive phase formation. The molar masses ranging from 100,000 to 350,000 gmol(-1) and polymerization temperatures <= 60 degrees C result in beta- and gamma-phases, while the molar mass >= 450,000 gmol(-1) at 70 degrees C polymerization temperature promotes alpha- and beta-phases of PVDF. Additionally, PVDF chain defects also influence the electroactive phase formations; the lower the chain defects, the higher the beta-phase content in PVDF. The polymorphs of PVDF homopolymers are identified by complementary spectroscopy and diffraction techniques, whereas the morphological changes influenced by the polymerization conditions are followed by electron microscopy. The morphological variation, from facet to spherical morphology, is correlated with the polymerization conditions. Finally, the preliminary results on the processing method demonstrate that the nascent PVDF homopolymers can be processed in the solid state, below their melting temperature, without influencing the polymorph perceived during polymerization. The nascent polymer having the beta-polymorph retains its crystallographic and conformational structure prior to melting. The transformation from alpha to beta and gamma PVDF is accomplished through solid-state processing (compression-rolling-stretching) below the melting temperature of the nascent PVDF homopolymers. Compared to melt and solution processing, the solid-state processing is of advantage as it circumvents the work required against entropy to secure the oriented chains and the use of carcinogenic solvents. Moreover, environmentally friendly solid-state processing avoids the decomposition of the sample above the melting point that often causes the release of the hazardous gases in fluorinated polymers.

Different types of silica (mesoporous, spherical and nano-size particles), pre-activated with methylaluminoxane (MAO), are used to activate and support the bis[N-(3-tert-butylsalicydene)-2,3,4,5,6-pentafluoroanilinato] titanium(IV) dichloride (FI) complex with the aim to synthesize low-entangled UHMWPE having controlled particle morphology. Through the porosity analysis, nitrogen adsorption and desorption isotherms, a decreased surfaced area of the chosen silica is observed when supported by MAO. From the bonding energy study by XPS, the bonding energy difference of Si and O, between the nano-size silica and in the MAO-nano silica, suggests the formation of Al-O-Si after chemical activation with MAO. Using elementary analysis, ICP-OES and XPS characterization, the aluminum content grafted on the silica surface is found to match with the anticipated amount of MAO on the MAO-Silica/FI catalytic system, indicating a stable grafting after catalyst supporting. From the rheological studies of the polymers, coupled with DSC results using an isothermal crystallization protocol, the resultant entangled state in the semi-crystalline polymers is estimated. The observations are that the entangled state achieved during polymerization from the investigated heterogeneous catalytic systems, is the lowest in PEMAO-nano silica/FI, increases in PE-MAO-mesoporous silica/FI and is highest in PE-MAO-spherical silica/FI. Silica modification using two different silanes shows significant influence on the catalytic activity, giving lower polymer yield in MAO-modified-mesoporous silica and MAO-modified-nano silica compared to the unmodified MAO-silica. Whereas, no significant spatial effect is observed in the formation of chain entanglement, showing the increased entanglement density of the nascent polymers. By employing heterogeneous catalytic systems, reactor fouling and wall sheeting problems are resolved and the polymers show good morphology replication of the support. The UHMWPE synthesized using the nano silica as support, having the lowest entangled state and loosely packed crystals, can be uniaxially processed in the solid-state to a thin tape having thickness around 34 mu m, showing maximum tensile strength of 3.26 N/tex and tensile modulus of 170 N/tex.

Polyether ether ketone (PEEK) has replaced some parts in downhole applications in the oil and gas industry, demonstrating a huge potential to eliminate the corrosion of metallic parts, especially those that are employed in acidic atmospheres and high temperatures, such as liners, impeller, and sealing applications. However, the performance of PEEK in real downhole conditions remains unknown. In this study, we therefore investigated the evolution of the microstructural, chemical, and mechanical properties of PEEK subjected to hydrochloric acid (HCl), which is the main acid used in downhole applications, at high temperatures. PEEK films with thicknesses of 250, 125, and 50 μm, were saturated in HCl at 100 °C. Moreover, the hardness, elastic modulus, yield, and ultimate strength for the samples with a thickness of 50 μm increased owing to the formation of new crystallites and enhanced chain mobility inside the PEEK microstructure. However, the changes in the mechanical response of the thicker samples were insignificant owing to the difficulty of HCl diffusion in their subsurface layers, especially with the increased crystallinity of the surface layer upon exposure to acids.

The paper addresses a study on the thermoplastic elastomers (TPE) that can be synthesized using monomers retrieved from the chemically recycled semi-aromatic polyesters, such as terephthalic acid from low value stream recyclable polyethylene terephthalate (rPET). In contrast to PET, because of their physical and mechanical properties, TPEs are often used as an engineering polymer in automotive and consumer goods. The understanding of the crystallization and phase behavior of these materials is crucial to fine-tune the molecular structure and properties. We explore the interplay between the crystallization and phase separation in these materials by performing experiments on model thermoplastic elastomers consisting of polybutylene terephthalate (PBT) and polytetrahydrofuran (PTHF). A common denominator in the synthesis of PBT is terephthalic acid that can be obtained from Dimethyl Terephthalate (DMT) or recycling used PET. We show that by varying the compositions and block length of different blocks, in PBT-PTHF block copolymers, morphological variations from spherulites to dendrites can be induced, which could be captured using optical microscopy. By performing rheological and small angle X-ray scattering studies, we correlate these morphological variations at microscopic length scales, to the chain architecture at nanometer length scales. Our observations reveal that at the higher rigid PBT content, the process of phase separation strongly influences the crystallization kinetics that promotes the lamellar structure of the semi-crystalline polymer, observed at room temperature. On the other hand, in the presence of higher soft block content, the crystal growth occurs with minimal influence of the microphase separation. In broader generality, no morphological differences in the TPEs synthesized using the terephthalic acid from rPET are found. However, when the monomer from rPET is used, enhancement in crystallization rate occurs in the TPEs having similar molar mass and molecular configuration. We attribute the enhanced crystallization rate to the catalyst residues present in the terephthalic acid obtained fom rPET.

Recently we demonstrated that low entangled ultra-high molecular weight isotactic polypropylene having molecular weight up to 2.4 million g/mol can be synthesized using a Hf-pyridyl amido catalyst activated by dimethylanilinium tetrakis (pentafluorophenyl)borate. Herein, we used an aprotic borate (trityl tetrakis(pentafluorophenyl)borate) to activate a Hf-pyridyl amido catalyst leading to a fast and ease catalyst activation even at lower temperatures, thus yielding exceptionally high molecular weight (up to 7.7 million g/mol) having improved tacticity (mmmm up to 98.5 %) and peak melting temperature (up to 165 degrees C). Thus synthesized polymers show extremely slow equilibration process by rheological characterization, indicating the low entangled state. These polymers can be processed in solid-state, without melting, into uniaxial drawn tapes having high tensile strength (1.46 N/tex) and tensile modulus (33 N/tex). The superior mechanical properties enable the tapes to be used as reinforcing material for commercial polypropylene grades, opening the possibilities of making one-component easy-to-recycle composites.

Aliphatic polyketone poly(ethylene-alt-CO) (PK-E) is a remarkable material known for its exceptional thermal and mechanical properties, potential photodegradability, and overall carbon neutrality. Here, we elaborate the making of high-strength uniaxially oriented polyketone tapes through a sustainable solid-state processing route, from nascent single crystalline ultrahigh molecular weight poly(ethylene-alt-CO) (UHMWPK-E). Using a cationic palladium catalyst coordinated with a sterically protected bis(diarylphosphino)methanamine-type ligand and carefully selected polymerization conditions, we achieved the synthesis of single crystals of nascent UHMWPK-Es with molecular weights (M-w) reaching up to 5.50 x 10(6) g mol(-1). All synthesized crystalline UHMWPK-Es were characterized using NMR, ATR-FTIR, Raman spectroscopy, TGA, DSC, GPC, WAXD, SAXS, TEM, and SEM. These nascent UHMWPK-Es exhibited enhanced thermal stability and interesting surface morphologies. The highly crystalline UHMWPK-E was uniaxially drawn in the solid state at least 35 degrees C below the peak melting temperature. This resulted in an impressive tensile strength of 1.12 GPa and an initial tensile modulus of 32 GPa for a draw ratio of 10, exceeding that reported for solution spun fibers.