Length Of Flexible Segments Research Articles

Influence of flexible segment length on the phase structure and properties of poly(hexamethylene 2,5‐furandicarboxylate)‐block‐biopolytetrahydrofuran copolymers

AbstractTwo series of biobased poly(ether‐ester)s comprised of poly(hexamethylene 2,5‐furandicarboxylate) (PHF) as the rigid segments and biopolytetrahydrofuran (pTHF) with different molecular masses (1000 and 2000 g/mol) as the flexible segments were synthesized employing polycondensation in the molten state. The study mainly focuses on comparing these two series in terms of the length of the flexible segment. The content of pTHF segments in the copolymer chains varied from 25 to 75 wt.%. The molecular structure and composition, phase structure, and thermal and mechanical properties were characterized by nuclear magnetic resonance (1H NMR) and Fourier‐transformed infrared (FTIR) spectroscopies, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and positron annihilation lifetime spectroscopy (PALS). In addition, mechanical performance and thermo‐oxidative and thermal stability have been investigated. Moreover, cyclic tensile properties were studied to evaluate the elastic properties. 1H NMR and FTIR spectroscopies demonstrate that the syntheses were correctly carried out, which made it possible to obtain the desired compositions of the block copolymers with high molecular masses. The decrease in Tm1, Tc1, and XcPHF values was visible, along with the increase in the flexible segment content. Moreover, the characteristic properties measured by PALS and the values of temperatures designated from TGA (inert and oxidizing atmosphere) did not vary between copolymer series PHF‐b‐F‐pTHF1000 and PHF‐b‐F‐pTHF2000. In turn, along with an increase in flexible segment content and the length of the pTHF, the values of tensile modulus, stress at break, and hardness decrease, while the value of elongation at break increases.

Estimation of Effective Concentrations Enforced by Complex Linker Architectures from Conformational Ensembles.

Proteins and protein assemblies often tether interaction partners to strengthen interactions, to regulate activity through auto-inhibition or -activation, or to boost enzyme catalysis. Tethered reactions are regulated by the architecture of the tether, which defines an effective concentration of the interactor. Effective concentrations can be estimated theoretically for simple linkers via polymer models, but there is currently no general method for estimating effective concentrations for complex linker architectures consisting of both flexible and folded domains. We describe how effective concentrations can be estimated computationally for any protein linker architecture by defining a realistic conformational ensemble. We benchmark against prediction from a worm-like chain and values measured by competition experiments and find minor differences likely due to excluded volume effects. Systematic variation of the properties of flexible and folded segments shows that the effective concentration is mainly determined by the combination of the total length of flexible segments and the distance between the termini of the folded domains. We show that a folded domain in a disordered linker can increase the effective concentration beyond what can be achieved by a fully disordered linker by focusing the end-to-end distance at the appropriate spacing. This suggests that complex linker architecture may have advantages over simple flexible linkers and emphasizes that annotation as a linker should depend on the molecular context.

Microstructure and Mechanical/Elastic Performance of Biobased Poly (Butylene Furanoate)-Block-Poly (Ethylene Oxide) Copolymers: Effect of the Flexible Segment Length.

The aim of this paper is to extend knowledge on biobased poly(butylene furanoate)–block–poly (ethylene oxide) (PBF-b-PEO) copolymers’ performance by studying the effect of the PEO segment’s molecular weight on the microstructure and materials behavior. As crystallization ability of PEO depends on its molecular weight, the idea was to use two PEO segment lengths, expecting that the longer one would be able to crystallize affecting the phase separation in copolymers, thus affecting their mechanical performance, including elasticity. Two series of PBF-block-PEOs with the PEO segments of 1000 and 2000 g/mol and different PBF/PEO segment ratios were synthesized by polycondensation in melt, injection molded to confirm their processability, and subjected to characterization by NMR, FTIR, DSC, DMTA, WAXS, TGA, and mechanical parameters. Indeed, the PEO2000 segment not only supported the crystallization of the PBF segments in copolymers, but at contents at least 50 wt % is getting crystallizable in the low temperature range, which results in the microstructure development and affects the mechanical properties. While the improvement in the phase separation slightly reduces the copolymers’ ability to deformation, it is beneficial for the elastic recovery of the materials. The investigations were performed on the injection molded samples reflecting the macroscopic properties of the bulk materials.

Phase Separation and Elastic Properties of Poly(Trimethylene Terephthalate)-block-poly(Ethylene Oxide) Copolymers.

A series of poly(trimethylene terephthalate)-block-poly(ethylene oxide) (PTT-b-PEOT) copolymers with different compositions of rigid PTT and flexible PEOT segments were synthesized via condensation in the melt. The influence of the block length and the block ratio on the micro-separated phase structure and elastic properties of the synthesized multiblock copolymers was studied. The PEOT segments in these copolymers were kept constant at 1130, 2130 or 3130 g/mol, whereas the PTT content varied from 30 up to 50 wt %. The phase separation was assessed using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The crystal structure of the synthesised block copolymers and their microstructure on the manometer scale was evaluated by using WAXS and SAXS analysis. Depending on the PTT/PEOT ratio, but also on the rigid and flexible segment length in PTT-b-PEO copolymers, four different domains were observed i.e.,: a crystalline PTT phase, a crystalline PEO phase (which exists for the whole series based on three types of PEOT segments), an amorphous PTT phase (only at 50 wt % content of PTT rigid segments) and an amorphous PEO phase. Moreover, the elastic deformability and reversibility of PTT-b-PEOT block copolymers were studied during a cyclic tensile test. Determined values of permanent set resultant from maximum attained stain (100% and 200%) for copolymers were used to evaluate their elastic properties.

On performance of an oscillating plate underwater propulsion system with variable chordwise flexibility at different depths of submergence

In this work, an oscillating plate propulsor undergoing a combination of heave translation and pitch rotation is investigated experimentally. The oscillation kinematics are inspired by swimming mechanisms employed by fish and other marine animals. The primary focus was on the propulsive characteristics of such oscillating plates, which were studied by means of direct force measurements in the thrust-producing regime. Experiments were performed at constant Reynolds number and constant heave amplitude. By varying the Strouhal number, the depth of submergence and the chordwise flexibility of the plate, it was possible to investigate corresponding changes in the generated thrust and the hydromechanical efficiency. It was possible to establish a set of parameters, including the driving frequency of the system, the ratio of rigid to flexible segment length of the plate, and the range of Strouhal numbers that led to an overall increase in thrust and efficiency. The experiments, involving plates with various ratios of rigid to flexible segment lengths, showed that greater flexibility increased the propulsive efficiency and thrust compared to an identical motion of the purely rigid plate. By submerging the plate at different depths, it was observed that the proximity of the propulsor to the bottom of the channel led to an overall increase in the thrust coefficient across the oscillation frequencies considered. The flow visualization revealed the formation of large dynamic stall vortices that influenced the wake structure, and suggested that their constructive interaction with trailing edge vortices might lead to overall improvement of thrust and efficiency.

A time-of-flight secondary ion mass spectrometry study of sequential polymers with a well-defined segmental length

Two series of sequential polymers (6FBA–Cn and BA–Cn) have been synthesized by phase-transfer catalyzed polyetherification of 1,n-dibromoalkane (n=4,6,8,10,12,14and18) with 4,4′-(hexafluoroisopropylidene)diphenol (6FBA) and bisphenol A (BA). The effects of the flexible aliphatic segment length on the structure of secondary ions were investigated. The characteristic secondary positive and negative ions in the time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectra are related to the chemical structures of the sequential BA–Cn and 6FBA–Cn polymers. The emission of the characteristic secondary positive and negative ions occurs after cleavage of the C–O bonds of the polymer repeat units. In the ToF-SIMS negative spectra, a series of small peaks separated by 14amu provides the information about the flexible segment lengths of the repeat units of the BA–Cn and 6FBA–Cn polymers and can be used to directly determine the number of the –CH2– groups, n, of the flexible segment.

Surface Studies of Polymers with a Well-Defined Segmental Length by ToF-SIMS and XPS. Relationship between the Surface Chemical Composition and Segmental Length

Two series of sequential polymers were synthesized by polymerization of 1,n-dibromoalkane (n = 4, 6, 8, 10, 12, 14, and 18) with 4,4‘-(hexafluoroisopropylidene)diphenol (6FBA) and bisphenol A (BA). The flexible aliphatic segment length changes from 4 to 21 Å corresponding to 4−18 CH2 groups. The influence of the flexible aliphatic segment length on the surface composition of BA and 6FBA sequential polymers was investigated by XPS and ToF-SIMS. The O 1s/C 1s peak ratios of the BA polymers indicated that the flexible segment was enriched on the BA polymer surface when the number of the CH2 groups was larger than 14 (the length of the flexible segment ∼17 Å). The F 1s/C 1s peak ratios of the 6FBA polymers showed that the length of the flexible segment on the surface was the same as the bulk. The ratios between the intensities of the characteristic peaks of the flexible and rigid segments displayed a linear dependence on the surface flexible segment length determined by XPS.

Effect of polymer chain structure and chain distance on luminescent efficiency

Three kinds of PPV-based copolymers were synthesized and characterized. Their luminescent properties were investigated and discussed by PL spectrum, and time-dependence luminescent spectrum in film and solution state. The results show that in the range of our study, the PL intensity and lifetime of luminescent decay increase with the increasing length of flexible segments and the solution diluting, indicating the tendency of the increase of luminescent efficiency.