A Novel View on Crystallization and Melting of Semirigid Chain Polymers: The Case of Poly(trimethylene terephthalate)

Bottlebrush Pastes as a Platform for Solvent-Free, Injectable, and Shape-Persistent Materials with Tissue-Mimetic Viscoelasticity

Architecturally hindered crystallization of bottlebrush graft copolymers offers a reaction- and solvent-free pathway for creating injectable elastomers with tissue-mimetic softness. Currently, injectable materials involve solvents and chemical reactions, leading to uncontrolled swelling, leaching of unreacted moieties, and side reactions with tissue. To address this issue, bottlebrush copolymers with a poly(ethylene glycol) (PEG) amorphous block and crystallizable poly(lactic acid) (PLA) grafted chains (A-g-B) were synthesized, with grafted chains of controlled length arranged along the backbone at controlled spacing. The densely grafted PEG brush is leveraged to architecturally control both the rate and degree of crystallization of PLA grafts, offering tunability of mechanical properties as a function of architecture and time in a single-component solvent-free system covering a broad range of aggregation states comprising fluid-, paste-, and elastomer-like behaviors with modulus ranging from 1 to 50 kPa. The PLA-g-PEG pastes are particularly interesting, as they combine solvent-free injectability and time-controlled formation of shape-persistent elastomers at constant temperature. This molecular paste platform may advance reconstructive surgery, drug depots, and tissue engineering.

Preparation and Characterization of Soft-Hard Block Copolymer of 3,4-IP-b-s-1,2-PBD Using a Robust Iron-Based Catalyst System

A series of well-defined diblock copolymers, namely, 3,4-polyisoprene-block-syndiotactic-1,2-polybutadiene (3,4-PI-b-s-1,2-PBD), with a soft-hard block sequence were synthesized via an in situ sequential polymerization process using a robust iron-based catalytic system Fe(acac)3/(isocyanoimino) triptenylphosphorane (IITP)/AliBu3. This catalyst exhibits vigorous activity and temperature tolerance, achieving a polymerization activity of 5.41 × 106 g mol(Fe)-1 h-1 at 70 °C with a [IP]/[Fe] ratio of 15,000. Moreover, the quasi-living polymerization characteristics of the catalyst were verified through kinetic experiments. The first-stage polymerization of isoprene (IP) is performed at 30 °C to give a soft 3,4-PI block, and then a quantitative amount of 1,3-butadiene was added in situ to the quasi-living polymerization system to produce a second hard s-1,2-PBD. The s-1,2-PBD segments in block copolymers display a rodlike morphology contrasting with the spherulitic morphology characteristic of s-1,2-PBD homopolymers. The precise tunability of the length of the soft and hard chain segments of these novel elastic materials with the feed ratio of IP and BD, endowing them with outstanding mechanical properties and excellent dynamic mechanical properties, which are expected to be promising high-performance rubber materials.

Bottlebrush Elastomers with Crystallizable Side Chains: Monolayer-like Structure of Backbones Segregated in Intercrystalline Regions

Bottlebrush (BB) elastomers with water-soluble side chains and tissue-mimetic mechanical properties are promising for biomedical applications like tissue implants and drug depots. This work investigates the microstructure and phase transitions of BB elastomers with crystallizable polyethylene oxide (PEO) side chains by real-time synchrotron X-ray scattering. In the melt, the elastomers exhibit the characteristic BB peak corresponding to the backbone-to-backbone correlation. This peak is a distinct feature of BB systems and is observable in small- or medium-angle X-ray scattering curves. In the systems studied, the position of the BB peak ranges from 3.6 to 4.8 nm in BB elastomers. This variation is associated with the degree of polymerization of the polyethylene oxide (PEO) side chains, which ranges from 19 to 40. Upon crystallization of the side chains, the intensity of the peak decays linearly with crystallinity and eventually vanishes due to BB packing disordering within intercrystalline amorphous gaps. This behavior of the bottlebrush peak differs from an earlier study of BBs with poly(ε-caprolactone) side chains, explained by stronger backbone confinement in the case of PEO, a high-crystallinity polymer. Microstructural models based on 1D SAXS correlation function analysis suggest crystalline lamellae of PEO side chains separated by amorphous gaps of monolayer-like BB backbones.

Tissue-Adaptive Materials with Independently Regulated Modulus and Transition Temperature

The ability of living species to transition between rigid and flexible shapes represents one of their survival mechanisms, which has been adopted by various human technologies. Such transition is especially desired in medical devices as rigidity facilitates the implantation process, while flexibility and softness favor biocompatibility with surrounding tissue. Traditional thermoplastics cannot match soft tissue mechanics, while gels leach into the body and alter their properties over time. Here, a single-component system with an unprecedented drop of Young's modulus by up to six orders of magnitude from the GPa to kPa level at a controlled temperature within 28-43 °C is demonstrated. This approach is based on brush-like polymer networks with crystallizable side chains, e.g., poly(valerolactone), affording independent control of melting temperature and Young's modulus by concurrently altering side chain length and crosslink density. Softening down to the tissue level at the physiological temperature allows the design of tissue-adaptive implants that can be inserted as rigid devices followed by matching the surrounding tissue mechanics at body temperature. This transition also enables thermally triggered release of embedded drugs for anti-inflammatory treatment.

What Thermal Analysis Can Tell Us About Melting of Semicrystalline Polymers: Exploring the General Validity of the Technique

Thermal characterization of semicrystalline polymers can constitute a difficult task due to the metastable nature of polymer crystals. It is well documented that polymer structure can reorganize during the thermoanalytical experiment. It has become also clear that thermal analysis alone cannot discriminate the reorganization processes from multiple melting events. Therefore, instead of studying the initial sample state the measurements may simply reflect the structural evolution uncontrollably occurring during the experiment. Here an original setup combining in situ ultrafast chip calorimetry with millisecond time-resolved X-ray scattering is used to find the structural signature of the reorganization processes. The information is further used to construct the heating-rate versus crystallization-temperature reorganization (HR-CT-R) diagram. The diagram allows rationally designing thermoanalytical experiments in which one can completely exclude uncontrolled evolution of the semicrystalline structure. For a typical aromatic polyester, poly(trimethylene terephthalate), the critical heating rate above which all reorganization processes cease to exist can reach 1000 K/s and more.

An "on-off" switchable cubic phase with exceptional thermal stability and water sorption capacity

We report on the phase behaviour of a wedge-shaped mesogen, which can exist in two different states at room temperature, a stable columnar and a metastable cubic gyroid phase. The latter reveals exceptional stability and remarkable water sorption capacity accounted for by the locally-ordered peripheral alkyl chains.

High Conductivity in Molecularly p-Doped Diketopyrrolopyrrole-Based Polymer: The Impact of a High Dopant Strength and Good Structural Order

[3]-Radialene-based dopant CN6-CP studied herein, with its reduction potential of +0.8 versus Fc/Fc+ and the lowest unoccupied molecular orbital level of -5.87 eV, is the strongest molecular p-dopant reported in the open literature, so far. The efficient p-doping of the donor-acceptor dithienyl-diketopyrrolopyrrole-based copolymer having the highest unoccupied molecular orbital level of -5.49 eV is achieved. The doped films exhibit electrical conductivities up to 70 S cm(-1) .

Structural evolution analysis and cold-crystallization kinetics of spherical crystals in poly(trimethylene terephthalate) film using Raman spectroscopy

Dynamic processes and the structural evolution of cold-crystallized poly(trimethylene terephthalate) (PTT) film were investigated using Raman spectroscopy. Raman scattering of C[double bond, length as m-dash]O stretching vibration was related to the molecular chain movement and structure evolution in PTT during cold crystallization. In particular, information about each phase of crystallization, including induction, nucleation, nucleus growth, and secondary crystallization, was thoroughly revealed. The experimental results indicated that the kinetic parameters measured by the Raman method were in good agreement with those obtained by differential scanning calorimetry (DSC) and infrared spectroscopy. The blue-shifted C[double bond, length as m-dash]O stretching vibration resulting from the crystallization process is a popular phenomenon and may therefore have many potential applications in a wide range of areas.

In situ monitoring of laser-induced periodic surface structures formation on polymer films by grazing incidence small-angle X-ray scattering

The formation of laser-induced periodic surface structures (LIPSS) on model spin-coated polymer films has been followed in situ by grazing incidence small-angle X-ray scattering (GISAXS) using synchrotron radiation. The samples were irradiated at different repetition rates ranging from 1 up to 10 Hz by using the fourth harmonic of a Nd:YAG laser (266 nm) with pulses of 8 ns. Simultaneously, GISAXS patterns were acquired during laser irradiation. The variation of both the GISAXS signal with the number of pulses and the LIPSS period with laser irradiation time is revealing key kinetic aspects of the nanostructure formation process. By considering LIPSS as one-dimensional paracrystalline lattice and using a correlation found between the paracrystalline disorder parameter, g, and the number of reflections observed in the GISAXS patterns, the variation of the structural order of LIPSS can be assessed. The role of the laser repetition rate in the nanostructure formation has been clarified. For high pulse repetition rates (i.e., 10 Hz), LIPSS evolve in time to reach the expected period matching the wavelength of the irradiating laser. For lower pulse repetition rates LIPSS formation is less effective, and the period of the ripples never reaches the wavelength value. Results support and provide information on the existence of a feedback mechanism for LIPSS formation in polymer films.

Structure formation and hydrogen bonding in all-aliphatic segmented copolymers with uniform hard segments

Fully aliphatic segmented poly(ether ester amide) copolymers with uniform hard segments prepared by melt polycondensation of α,ω-hydroxyl end-functionalized polytetrahydrofuran and short glycine or β-alanine bisester-bisoxalamide units hold promise for biomedical applications. For polymers with the hard block contents varying from 10% to 27%, differential scanning calorimetry and atomic force microscopy reveal a highly phase-separated morphology, with ribbon-like nanocrystals dispersed in the soft segment matrix. To relate the polymer properties to the structure of the hard segment, the monomers were prepared and studied by optical and X-ray diffraction measurements. It was shown that the glycine and β-alanine carbonyl ester groups are tilted away from the oxalamide plane, which can affect the degradation rate via hydrolysis of the ester bond.

Structural differences between cold- and melt-crystallized poly(trimethylene terephthalate) samples

Time-resolved Fourier transform infrared spectroscopy was used to investigate the structural differences between cold- and melt-crystallized poly(trimethylene terephthalate) (PTT) samples. To elucidate the arrangement of different chain segments in the crystalline phase obtained through different crystallization processes, characteristic bands associated with the phenylene rings, the CH2 segments, and the C-O-C segments were followed during the cold and the melt crystallizations. The results show that the alignment of the phenylene rings and the C=O groups in the PTT crystals produced via cold- and melt-crystallization processes are essentially the same, while the alignment of the CH2 segments depends on the crystallization condition. It was found that the CH2 segments in the melt-crystallized sample were more stable than those in the cold-crystallized sample. This was ascribed to the different crystallization environment. Melt-crystallized PTT chains have higher mobility, and the variation of flexible segments is quicker than that of the rigid segments. However, in cold crystallization, the CH2 segments are restricted by the adjacent environment in the glass state, which weakens their capability of transforming their conformation; this leads to a cooperative change of CH2 segments, phenylene rings, and C=O groups. Therefore, the stability of CH2 segments in crystalline structure is lowered accordingly.

Grazing-incidence small-angle X-ray scattering of soft and hard nanofabricated gratings

Grazing-incidence small-angle X-ray scattering (GISAXS) has been used to structurally characterize model hard and soft gratings of nanotechnological interest. The different gratings exhibit GISAXS patterns with characteristic features that can be associated with their level of order along the direction of periodicity and the length of the lines. Highly ordered gratings, made out of silicon by electron beam lithography, and those nanofabricated on spin-coated polymer films by nanoimprint lithography, exhibit characteristic semicircle-like GISAXS patterns with intensity spots periodically distributed on a semicircle whose radius is related to the incidence angle used. These gratings can be considered as one-dimensional crystalline lattices as provided by computer simulations. Less ordered polymer gratings prepared by the laser-induced periodic surface structuring method exhibit a GISAXS pattern characterized by periodic rod-like scattering maxima whose intensity decreases with increasing horizontal scattering angle. In this case the gratings can be considered as one-dimensional paracrystals. The transition from a rod-like to a semicircle-like GISAXS pattern has been simulated and attributed to the contribution of the form factor by changing the length of the line (ripple). A critical length value for the transition is located at around a few micrometres.

Laser-induced periodic surface structures nanofabricated on poly(trimethylene terephthalate) spin-coated films

Here we present a precise morphological description of laser-induced periodic surface structures (LIPSS) nanofabricated on spin-coated poly(trimethylene terephthalate) (PTT) films by irradiation with 266 nm, 6 ns laser pulses and by using a broad range of fluences and number of pulses. By accomplishing real and reciprocal space measurements by means of atomic force microscopy and grazing incidence wide- and small-angle X-ray scattering respectively on LIPSS samples, the range of optimum structural order has been established. For a given fluence, an increase in the number of pulses tends to improve LIPSS in PTT. However, as the pulse doses increase above a certain limit, a distortion of the structures is observed and a droplet-like morphology appears. It is proposed that this effect could be related to a plausible decrease of the molecular weight of PTT due to laser-induced chain photo-oxidation by irradiation with a high number of pulses. A concurrent decrease in viscosity enables destabilization of LIPSS by the formation of droplets in a process similar to surface-limited dewetting.

Exploring the structure of inter-platelet galleries in organically modified montmorillonite using the small-angle X-ray scattering interface distribution function approach

Small-angle X-ray scattering interface distribution function (IDF) analysis is successfully applied to evaluate the two- and three-phase inter-platelet gallery structure in synthetic montmorillonite (MMT) modified with a mixture of chemically grafted and physically adsorbed chains of a typical organic modifier, octadecyl trimethyl ammonium bromide. Two distinctly different states of adsorbed chains in the inter-platelet galleries are identified. The first one corresponds to a fully cation-exchanged structure with an inter-platelet distance of about 21 Å. In this case the organic modifier is in a liquid-like state, and the system does not exhibit any structural or thermal transitions between ambient temperature and 433 K. When the number of adsorbed chains exceeds the cation-exchange capacity of the MMT platelets the inter-platelet spacing is increased to 43 Å. In this case, the variable-temperature IDFs reveal partially crystalline order in the inter-platelet galleries, which vanishes at the melting point of the alkyl tails confined in the galleries.

1,3-Propanediol and its copolymers: research, development and industrialization

1,3-Propanediol (PDO), is now taking the transition from a traditional "specialty chemical" to a "commodity chemical". The market for PDO is growing rapidly as the technology develops. With the advancing PDO production technology, polytrimethylene terephthalate (PTT) as a new type of polyester has been applied in carpet and textile fibers, monofilaments, films, and nonwoven fabrics, and in the engineering thermoplastics area, because PTT has unique properties compared to other polymers such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Responding to the environmental and sustainability factors, one- or two-step fermentation technology for PDO production has attracted people's attention. A novel flexible process for PDO production by using aerobic fermentation from glycerol or glucose has been developed and demonstrated with a facility capacity of 4000 t/year in a pilot plant. By using engineered Escherichia coli, 135 g/L PDO was obtained with glucose as feedstock. Since the bio-process of PDO production consumes 40% less energy and reduces greenhouse gas emissions by 20% versus petroleum-based propanediol, the bio-based PTT is more environmentally friendly and sustainable compared with the fossil fuel-based polymers, which made PTT more attractive with good prospects for the future.

Theory of geometrical broadening of diffraction peaks from twisted lamellar crystals for interpretation of X-ray microbeam and selected-area electron diffraction experiments

A simple theory of angular broadening of diffraction peaks is presented for the X-ray and electron diffraction from twisted crystalline lamellae. The diffraction peak position, width and asymmetry are computed in the limit of a small natural reflection width. The peak broadening depends on the orientation of the corresponding reciprocal-space vector with respect to the helicoid axis and the normal to the lamellar basal plane. It is found that the equatorial peaks, which are close to the normal direction to the lamellar basal plane, are characterized by the highest azimuthal width. The theory also describes the azimuthal drift of the non-equatorial reflections on a flat two-dimensional detector as the incident beam scans along the main helicoid axis. The proposed approach can be useful for interpretation of microbeam diffractograms measured on banded polymer spherulites. It can be easily generalized to describe diffraction from crystals of any arbitrary shape obtained by deformation of a flat lamella, under the condition that upon the deformation all the in-plane angles and distances are preserved in the linear approximation.