Comparing crystallization rates between linear and cyclic poly(epsilon-caprolactones) via fast-scan chip-calorimeter measurements

State Transitions and Crystalline Structures of Single Polyethylene Rings: MD Simulations

This study investigates the structural changes of cyclic polyethylene (PE) single chains during cooling through molecular dynamics simulations. The influence of topological constraint on a ring is examined by comparing it with the results of its linear counterpart. A pseudo phase diagram of state transition for PE rings based on length and temperature is constructed, revealing a consistent chain-folding transition during cooling. The shape anisotropy of short crystallized cyclic chains exhibits oscillations with chain length, leading to a more pronounced odd-even effect in single cyclic chains compared with the linear ones. A honeycomb model is proposed to elucidate the odd-even effect of chain folding in crystalline structures of single linear and cyclic chains, and we discuss its potential to predict surface tension. Analyses of the tight folding model and the re-entry modes demonstrate that a cyclic chain possesses a shorter average crystalline stem length and a more compact folded structure than its linear counterpart. The findings highlight the impact of topological change on crystallization and the odd-even effect of chain length, providing valuable insights for understanding polymer crystallization with different topologies.

Synthesis of Linear to Cyclic Polylactide via a One-Pot Step-Wise Ring-Opening Polymerization and Back-Biting Reaction of Ring Closure Using Magnesium Complexes

The controllable synthesis of cyclic polylactide remains a challenging topic so far. In this work, a new strategy of one-pot step-wise ring-opening polymerization (ROP) followed by a back-biting reaction of ring closure was reported, in which one magnesium atrane-like complex {N,N-bis[3,5-di-cumyl-2-benzyloxy]-[2-(2-aminoethoxy)ethoxy]magnesium} was utilized to initiate the ROP of lactide using 4-dimethylaminopyridine as a co-catalyst; then, macrocyclic polylactides were liberated out via increasing temperature after complete depletion of the monomer in which a back-biting reaction was utilized as a ring-closure method. The living feature at the first ROP stage can be proved well by the controllable molecular weights ranging from 3.10 to 34.70 kDa and narrow molecular weight distributions of linear polylactides obtained after quenching the reaction. The final cyclic polylactides with molecular weights (vs polystyrene) ranging from 2.50 to 16.10 kDa can be achieved too after the back-biting reaction of ring closure. Although a shoulder peak at the gel permeation chromatography profile appears when the ratio of monomer:initiator is high up to 100:1 or 200:1, this system is suitable for the controllable syntheses of cyclic polylactides with desirable modest molecular weights.

A Cyclic Ruthenium Benzylidene Initiator Platform Enhances Reactivity for Ring-Expansion Metathesis Polymerization

Ring-expansion metathesis polymerization (REMP) has shown potential as an efficient strategy to access cyclic macromolecules. Current approaches that utilize cyclic olefin feedstocks suffer from poor functional group tolerance, low initiator stability, and slow reaction kinetics. Improvements to current initiators will address these issues in order to develop more versatile and user-friendly technologies. Herein, we report a reinvigorated tethered ruthenium-benzylidene initiator, CB6, that utilizes design features from ubiquitous Grubbs-type initiators that are regularly applied in linear polymerizations. We report the controlled synthesis of functionalized cyclic poly(norbornene)s and demonstrate that judicious ligand modifications not only greatly improve kinetics but also lead to enhanced initiator stability. Overall, CB6 is an adaptable platform for the study and application of cyclic macromolecules via REMP.

Non-Isothermal Crystallization Kinetics of Poly(Ethylene Glycol)-Poly(l-Lactide) Diblock Copolymer and Poly(Ethylene Glycol) Homopolymer via Fast-Scan Chip-Calorimeter

The non-isothermal crystallization kinetics of double-crystallizable poly(ethylene glycol)-poly(l-lactide) diblock copolymer (PEG-PLLA) and poly(ethylene glycol) homopolymer (PEG) were studied using the fast cooling rate provided by a Fast-Scan Chip-Calorimeter (FSC). The experimental data were analyzed by the Ozawa method and the Kissinger equation. Additionally, the total crystallization rate was represented by crystallization half time t1/2. The Ozawa method is a perfect success because secondary crystallization is inhibited by using fast cooling rate. The first crystallized PLLA block provides nucleation sites for the crystallization of PEG block and thus promotes the crystallization of the PEG block, which can be regarded as heterogeneous nucleation to a certain extent, while the method of the PEG block and PLLA block crystallized together corresponds to a one-dimensional growth, which reflects that there is a certain separation between the crystallization regions of the PLLA block and PEG block. Although crystallization of the PLLA block provides heterogeneous nucleation conditions for PEG block to a certain extent, it does not shorten the time of the whole crystallization process because of the complexity of the whole crystallization process including nucleation and growth.

Ultrasensitive label-free detection for lung cancer CYFRA 21-1 DNA based on ring-opening polymerization

Cytokeratin fragment antigen 21-1 (CYFRA 21-1) DNA is perceived as sensitive tumor marker for the diagnosis of non-small cell lung cancer and other tumor. Herein, linear chain poly(ε-caprolactone) (PCL) synthesized by ring-opening polymerization is applied to ultrasensitive label-free electrochemical impedance detection system for CYFRA 21-1 DNA. First, thiolated peptide nucleic acid (PNA) is self-assembled into the Au electrode surface through the formation of Au-S bonds, allowing the PNA to act as biomolecular probe and form PNA/DNA heteroduplex with the target DNA via specific hybridization. Then, PCL is conjugated to the immobilized DNA on the electrode via "carboxylate-Zr⁴⁺-phosphate" bridges. Finally, the electrochemical response of modified PNA/DNA/Zr⁴⁺/PCL electrode is determined by electrochemical impedance method to quantify of CYFRA 21-1 DNA. Under optimal conditions, this method exhibits highly sensitivity with a broad linear range (0.1 fM - 1 nM) (R² = 0.995) and the limit of detection (LOD) is as low as 10.73 aM, which is equivalent to just 64 molecules in a 10 μL sample. What's more, the high selectivity, good anti-interference, label-free operation, and real-time monitoring in complex samples of the proposed strategy demonstrate its broad application for the early diagnosis and clinical monitoring.

Cyclic topology effects on the morphology of biocompatible and environment-friendly poly(ε-caprolactone) under nanoscale film confinement

Quantitative grazing incidence X-ray scattering analysis combined with X-ray reflectivity using synchrotron radiation sources was explored for the first time cyclic topology effects on the nanoscale film morphology of poly(ε-caprolactone).

Thermal Conductivity of Protein-Based Materials: A Review

Fibrous proteins such as silks have been used as textile and biomedical materials for decades due to their natural abundance, high flexibility, biocompatibility, and excellent mechanical properties. In addition, they also can avoid many problems related to traditional materials such as toxic chemical residues or brittleness. With the fast development of cutting-edge flexible materials and bioelectronics processing technologies, the market for biocompatible materials with extremely high or low thermal conductivity is growing rapidly. The thermal conductivity of protein films, which is usually on the order of 0.1 W/m·K, can be rather tunable as the value for stretched protein fibers can be substantially larger, outperforming that of many synthetic polymer materials. These findings indicate that the thermal conductivity and the heat transfer direction of protein-based materials can be finely controlled by manipulating their nano-scale structures. This review will focus on the structure of different fibrous proteins, such as silks, collagen and keratin, summarizing factors that can influence the thermal conductivity of protein-based materials and the different experimental methods used to measure their heat transfer properties.

An accelerated united-atom molecular dynamics simulation on the fast crystallization of ring polyethylene melts

To investigate crystallinities based on trans-structures, we determined the differences in the crystallization properties of ring and linear polymers by performing united-atom-model molecular dynamics (MD) simulations of homogeneous polyethylene melts of equal length, N, which refers to the number of monomers per chain. Modified parameters based on the DREIDING force field for the CH₂ units were used in order to accelerate the crystallization process. To detect polymer crystallization, we introduced some local-order parameters that relate to trans-segments in addition to common crystallinities using neighboring bond orders. Through quenching MD simulations at 5 K/ns, we roughly determined temperature thresholds, T_th, at which crystallization is observed although it was hard to determine the precise T_th as observed in the laboratory time frame with the present computing resources. When N was relatively small (100 and 200), T_th was determined to be 320 and 350 K for the linear- and ring-polyethylene melts, respectively, while T_th was found to be 330 and 350 K, respectively, when N was 1000. Having confirmed that the crystallization of a ring-polyethylene melt occurs faster than that of the analogous linear melt, we conclude that the trans-segment-based crystallinities are effective for the analysis of local crystal behavior.

In-depth understanding of interfacial crystallization via Flash DSC and enhanced energy storage density in ferroelectric P(VDF-CTFE)/Au NRs nanocomposites for capacitor application

High-capacity or high-power-density capacitors are being actively investigated for portable electronics, electric vehicles, and electric power systems. We describe the filler system in dielectric nanocomposites with a small loading of Au nanorods [NRs] to elucidate the mechanism of interfacial crystallization behavior including the crystallization kinetics, and crystalline morphology and structure, and to investigate the intrinsic causes for concurrent great improvements in the dielectric constant and energy density in the nanocomposite system. Remarkly, at high crystallization temperature, the addition of Au NRs, which are used as heterogeneous nucleators, can reduce the nucleation barrier, resulting in accelerating the crystallization rate. However, the crystallization rate slows down at low temperatures because the addition of Au NRs limited the mobility of poly(vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] chains, and thus enhanced the diffusion barrier. Furthermore, the addition of NRs has a huge impact on the crystalline morphology and structure which changes from large paraelectric α-phase spherulites with TGTG' conformations into minor ferroelectric γ-phase spherulites with T3GT3G' conformations, and also produces more exogenous interfaces between the lamellar crystals and amorphous regions, resulting in a higher dielectric constant and higher electric energy density in P(VDF-CTFE)/Au NRs nanocomposites. Our approach provides a facile and straightforward way to design or understand PVDF-based polymers for their practical applications in high-energy-density capacitors.

Precise Synthesis, Properties, and Structures of Cyclic Poly(ε-caprolactone)s

Cyclic PCL (c-PCL) has drawn great attention from academia and industry because of its unique, unusual structure and property characteristics due to the absence of end groups in addition to the biocompatibility and biodegradability of its linear analogue. As a result of much research effort, several synthetic methods have been developed to produce c-PCLs so far. Their chain, morphology and property characteristics were investigated even though carried out on a very limited basis. This feature article reviews the research progress made in the synthesis, morphology, and properties of c-PCL; all results and their pros and cons are discussed in terms of purity and molecular weight distribution in addition to the cyclic topology effect. In addition, we attempted to synthesize a series of c-PCL products of high purity by using intramolecular azido-alkynyl click cyclization chemistry and subsequent precise and controlled separation and purification; and their thermal degradation and phase transitions were investigated in terms of the cyclic topology effect.

Influence of chain topology on polymer crystallization: poly(ethylene oxide) (PEO) rings vs. linear chains

The absence of entanglements, the more compact structure and the faster diffusion in melts of cyclic poly(ethylene oxide) (PEO) chains have consequences on their crystallization behavior at the lamellar and spherulitic length scales. Rings with molecular weight below the entanglement molecular weight (M < M_e), attain the equilibrium configuration composed from twice-folded chains with a lamellar periodicity that is half of the corresponding linear chains. Rings with M > M_e undergo distinct step-like conformational changes to a crystalline lamellar with the equilibrium configuration. Rings melt from this configuration in the absence of crystal thickening in sharp contrast to linear chains. In general, rings more easily attain their extended equilibrium configuration due to strained segments and the absence of entanglements. In addition, rings have a higher equilibrium melting temperature. At the level of the spherulitic superstructure, growth rates are much faster for rings reflecting the faster diffusion and more compact structure. With respect to the segmental dynamics in their semi-crystalline state, ring PEOs with a steepness index of ∼34 form some of the "strongest" glasses.

The influence of small amounts of linear polycaprolactone chains on the crystallization of cyclic analogue molecules

C-PCL/L-PCL blends show a synergistic decrease in their isothermal crystallization rates as compared to the expectation of a simple mixing law due to the threading effect of the linear on the cyclic chains.