Macromolecules最新文献

We proposed recently that the strain hardening of glassy polymers is attributed to the increase of free energy barriers for α-relaxation as a consequence of local orientation of Kuhn segments during the course of deformation. As the chains have been significantly oriented at the Kuhn segments scale, the contribution of Kuhn segments orientation to free energy barriers may become large and may then overcompensate the decrease of free energy barriers due to the increasing stress, the latter being responsible for yield and the onset of plastic flow. We show that the slow relaxation of Kuhn segments orientation explains the various memory effects observed in the strain hardening regime and generically named Bauschinger effect. It explains the fact that the stress–strain curve of a second deformation after some waiting time at some point in the strain hardening regime rejoins the reference curve, and that a yield stress is present for this second deformation. Indeed, the degrees of freedom which control the free energy barriers associated with yield relax on the time scale of the experiment, whereas Kuhn segments orientations, that is the degrees of freedom which control the free energy barriers associated with plastic flow in the strain hardening regime, relax slowly. We calculate the evolution of the relaxation time distributions, as well as that of the dominant relaxation time and of the Kuhn segments orientations, during successive deformations (traction–traction, traction-compression, compression-traction, compression–compression). These predictions could be tested experimentally.

Partially fluorinated polymers exhibit various properties owing to their fluoroalkyl groups: thus, understanding the types of fluoroalkyl groups incorporated into a polymer chain is crucial for controlling the physical properties and is of significant academic interest. Although polymer backbone structures frequently incorporate short linear fluoroalkyl groups, cyclic fluoroalkyl groups are comparatively rare. To achieve both a high glass transition temperature (T_g) and low refractive index (n), polynorbornenes with several types of cyclic fluoroalkyl side groups are synthesized by ring-opening metathesis polymerization. Most of the synthesized polymers could form thin films via spin coating from nonfluorinated organic solutions. The films were transparent to the ultraviolet and near-infrared wavelengths region. The T_g and n of partially fluorinated polynorbornenes depend on the steric bulk of the side groups. Furthermore, the effect of substituting oxygen atoms for methylene groups within the polymer backbone and side groups on T_g and n is investigated. The incorporation of cyclic fluoroalkyl side groups is promising for the molecular design of amorphous optical materials with high thermal stability.

Solid polymer electrolytes (SPEs) have garnered significant interest in the advancement of solid-state lithium batteries (SSBs) due to their excellent safety, processability, and lightweight features. Currently, there is an urgent demand for the green synthesis of high performance SPEs for applications in SSBs. In this study, we report a one-pot mechanochemical reversible complexation mediated polymerization (mechano-RCMP) approach to synthesize fluorinated polyacrylates under solventless conditions. The mechano-RCMP approach demonstrated an efficient controlled polymerization process with quantitative monomer conversion through force induced activation of the carbon–iodine bond. The chain extension experiments confirmed the high chain-end functional groups of the polymers. Further copolymerization of heptafluorobutyl acrylate (HFBA) with butyl acrylate (BA) and methoxy polyethylene glycol acrylate (mPEG) resulted in the formation of P(BA-co-HFBA-co-mPEG), which demonstrated high thermal stability and amorphous characteristics. This copolymer film exhibited a wide electrochemical window (upper cutoff voltage up to 5.4 V) and high Li⁺ conductivity (1.3 × 10^–4 S cm^–1 at 30 °C). SSBs fabricated with the P(BA-co-HFBA-co-mPEG) film showed good cycling performance, maintaining a capacity retention of 98% after 100 cycles at room temperature.

This report examines the melt self-assembly behaviors of core–shell bottlebrush polymers (csBBs), in which a single AB diblock copolymer decorates each backbone repeat unit. To access these nonlinear polymer architectures, four norbornyl end-functionalized, symmetric composition poly(ε-decalactone)-block-poly(rac-lactide) (DL) diblock copolymers (M_n = 5.9–7.6 kg/mol, Đ = 1.20–1.29, with f_L = 0.49–0.51) were first synthesized by sequential ring-opening polymerizations (ROPs). Living ring-opening metathesis polymerization (ROMP) of these DL macromonomers produces narrow dispersity csBBs (Đ = 1.02–1.18) with backbone degrees of polymerization N_bb = 6–37. For csBBs of a given DL macromonomer, small-angle X-ray scattering (SAXS) analyses reveal that the order-to-disorder transition temperatures (T_ODT’s) of their microphase-separated lamellar mesophases increase with increasing N_bb. From these data, the dependence of the critical macromonomer arm segregation strength for microphase separation (χN_arm)_ODT on N_bb is identified. Comparisons of these results with reports on related nonlinear block polymers suggest that the csBB architecture reduces the free energy penalty for chain arrangement into the self-assembled lamellar morphology, while brush grafting density directs the extent of side chain stretching, with implications for microphase-separated melt stability and the observed domain (d) spacings.

Molecular weight optimization is crucial for high-performance stretchable conjugated polymer films. However, an in-depth understanding of molecular weight distribution on solution assembly, film microstructures, and electrical/mechanical properties of conjugated polymers is lacking. Herein, a model conjugated polymer, poly(indacenodithiophene-co-benzothiadiazole) (IDTBT), with a similar weight-average molecular weight but different polydispersity indexes (PDIs) of 3.2, 2.4, and 1.6 is investigated. The low-PDI polymer, containing a high content of homogeneous long chains, facilitates sufficient interchain aggregation caused by the enhanced chain entanglement and prolonged aggregation dynamics, which creates a low-crystallinity film containing long-chain well-connected aggregates and chain entanglement networks. Consequently, the charge mobility increases from 2.1 to 3.1 cm² V^–1 s^–1 as PDI decreases from 3.2 to 1.6. During stretching, the polymer chains align more effectively along the strain direction in the low-PDI film, which creates more dynamic sliding sites and short-range aggregates to dissipate the strain energy. Thus, the low-PDI polymer film exhibits a high charge mobility of 1.0 ± 0.1 cm² V^–1 s^–1 at 100% strain and 0.9 ± 0.1 cm² V^–1 s^–1 after 100 cycles of stretching–releasing at 25% strain, which significantly outperforms the high-PDI film. This work demonstrates the significance of polydispersity optimization for developing mechanically robust polymer semiconductor films in stretchable electronics.