The great potential of liquid-crystalline block copolymers (LCBCs) containing photoresponsive mesogens toward novel applications in photonics and nanotechnology has been attracting increasing attention, due to the combination of the inherent property of microphase separation of block copolymers and the hierarchically-assembled structures of liquid-crystalline polymers (LCPs). The periodically ordered nanostructures in bulk film of LCBCs can be acquired by supramolecular cooperative motion, derived from the interaction between liquid-crystalline elastic deformation and microphase separation, which are able to improve physical properties of polymer film toward advanced functional applications. Moreover, various micro/nano-patterned structures have been fabricated via light manipulation of photoresponsive LCBCs with good reproducibility and mass production. Thanks to recent developments in synthesis and polymerization techniques, diverse azobenzene-containing LCBCs have been designed, resulting in the creation of a wide variety of novel functions. This review illustrates recent progresses in macroscopic regulation of hierarchical nanostructures in LCBCs towards functional materials. The existing challenges are also discussed, showing perspectives for future studies.

Photo-responsive mechanical actuator is a class of stimuli-responsive materials transferring light to mechanical energy through macroscopic transformation. To fabricate photo-responsive mechanical actuator, soft polymeric materials crosslinked with functional bridging structures are desired. Supramolecular interaction is a relatively common way to fabricate crosslinked materials due to its excellent self-assembly performance. And azobenzene and derivatives are ideal candidates of photo-responsive materials because of the unique photo-induced trans-cis isomerization. Here, a new kind of crosslinked materials based on supramolecular interaction between 4,4'-dihydroxyazobenzene and chitosan is reported. Under 355 nm irradiation, the macroscopic bending of polymeric materials occurs rapidly due to the photo-isomerization of 4,4'-dihydroxyazobenzene. Meanwhile, the photo-responsive mechanical actuator can also lift weight which is up to 200 times that of the actuator itself, and convert energy from light to mechanical work efficiently. This report suggests a new kind of photo-responsive actuator based on supramolecular interaction and may be helpful to contribute a theoretical basis to the design and synthesis of photo-responsive mechanical actuator suitable for large-scale manufacturing industrialization in future.

The infection induced by implantation of biomedical materials may result from the biofilm formation after bacteria attachment. Hence, the antibiofilm surface coating represents a novel technique to improve the antibacterial activity of biomedical materials. The traditional antibiofilm surface coatings exhibited some disadvantages and provided a limited service life. In this work, we used polyethyleneimine grafted 3-maleimidopropionic acid (PEIM) and poly(acrylic acid) grafted 2-furfurylamine (PAAF) to achieve robust and self-healable crosslinked multilayer coatings, employing Layer-by-Layer (LbL) self-assembly technique and Diels-Alder reaction. Then, thiol-terminated poly((3-acrylamidopropyl) trimethylammonium chloride) (PAMPTMA-SH) was grafted onto the crosslinked multilayer coating by thiol-ene click reaction to form a novel multilayer coating (PEIM/PAAF)₁₀-PAMPTMA. We found that this coating showed robust and self-healable activity, and significantly inhibited the bacterial growth and biofilm formation after infection with Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by in vitro and in vivo assays for 120 h. In addition, the multilayer coating did not induce significant hemolysis or affect the cell viability of red blood cells. In vivo studies also showed that (PEIM/PAAF)₁₀-PAMPTMA coating efficiently blocked the infiltration of inflammatory cells and gene expression in the mouse skin challenged with E. coli or S. aureus. Taken together, these results showed that the prepared multilayer coating exhibited strong antibiofilm activity and provided a new strategy for the application of highly efficient antibiofilm surface coating of biomedical materials.

The intramolecular cross-linking of single polymer chains can form single-chain nanoparticles (SCNPs), which have many applications. In this study, styrenic copolymers with pendent triphenylphosphine as the coordination site for platinum ions (Pt(II)) and benzocyclobutene as the latent reactive groups are synthesized. Triphenylphosphine groups in the chains can coordinate Pt(II) and aid slight single-chain folding in dilute solution. The intramolecular cross-linking caused by the ring-open reaction of benzocyclobutene completes the single-chain collapse and forms stable SCNPs in dilute solution. Pt(II) embedded in SCNPs can be further reduced to platinum atoms (Pt(0)). Pt(0) steadily and atomically dispersed in SCNPs exhibits better catalytic properties than normal polymer carried platinum particles do for the reduction of p-nitrophenol to p-aminophenol.

A series of phosphine-sulfonate ligands bearing 2-, 3- and 4-vinylphenyl on the phosphorus atom were designed, synthesized, characterized and investigated in Ni- and Pd-catalyzed ethylene polymerization. The structure of the phosphine-sulfonate Pd complex bearing 2-vinylphenyl on the phosphorus atom showed 2,1-insertion for the 2-vinyl group. The phosphine-sulfonate Ni complex bearing 2-vinylphenyl resulted in significantly increased thermal stability and polyethylene molecular weights (M_n=3.69×10⁴ g·mol⁻¹ at 80 °C) versus the counterparts bearing 3-/4-vinyl groups as well as previously reported phosphine-sulfonate Ni complexes bearing bulky biaryl substituents.

An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented. The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromethyl in polymer chains. By using this design strategy, a highly transparent polyimide film with low-k was synthesized from 3,5-diaminobenzotrifluoride (m-TFPDA) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) through a two-step method. The obtained m-TFPDA/6FDA (CPI) film (~30 μm) possesses high optical transparency (λ_cutoff=334 nm, T_450nm=85.26%, Haze=0.31) and is close to colorless (L^*=96.03, a^*=−0.34, b^*=2.12, yellow index=3.96). The intrinsic k and dielectric loss value of the film are 2.27 and 0.0013 at 10 kHz, respectively. More importantly, such low dielectric performance could remain stable up to 280 °C, and the film shows a low moisture rate (~0.51%), which helps to maintain the low-k property stability in different humid environments. Meanwhile, the film also shows good thermal stability and mechanical properties, with a glass transition temperature (T_g) of 296 °C and the 5 wt% decomposition temperature (T_d,5%) of 522 °C under N₂. The tensile strength and tensile modulus of the film are 85.1 MPa and 1.96 GPa, respectively. In addition, the film is soluble in common solvents, which allows simple solution processing and low-cost, continuous roll-to-roll processes. This design strategy is beneficial to improving the transparency, lightening yellow color, lowering the dielectric constant and meanwhile maintaining the comprehensive properties of polyimide films, which is mainly due to the introduced meta-substituted and trifluoromethyl structures effectively inhibiting the transfer of charge transfer complex (CTC) effects and increasing the free volume of film. This design strategy could also be extended to other high-performance polymer systems.

It is still a great challenge to mimic the structure and function of natural rubber by introducing polar components into synthetic polyisoprene. In order to explore the function of phosphate groups on the mechanical properties of polyisoprene rubber, a terminally functionalized compound (PIP-P) containing phosphate groups was synthesized and further vulcanized to prepare the model compound V-PIP-P. Through analyzing the test results, it was found that these phosphate groups formed polar aggregates in non-polar polyisoprene rubber matrix, serving as an additional dynamic cross-linking sites, which increases the cross-linking density and improves mechanical properties. The influence of the phosphate groups on the strain-induced crystallization (SIC) was further investigated via synchrotron wide-angle X-ray diffraction (WAXD) experiment. These phosphate group aggregates not only reduced the onset strain of SIC, but also slowed down the molecular chain mobility, which hinder the crystal lateral growth. The above results help us to gain a deeper understanding for the function of phosphate groups in the formation of “naturally occurring network” and guide the molecular design of next generation polyisoprene rubber.

Silica rods with homogeneous (hydrophilic or hydrophobic) and amphiphilic surface properties were synthesized and their efficiencies in suppressing the flow-induced droplet coalescence of immiscible polyisobutylene (PIB)/polydimethylsiloxane (PDMS) blends were evaluated via in situ visualization technique. The flow-induced coalescence behavior of blends was found to strongly depend on the surface nature and concentration of silica rods added as well as the blend ratio. While a trace amount of rods promoted coalescence, all kinds of rods demonstrated a morphology refinement effect at high rod concentrations. Good compatibilization effects were obtained at high rod concentrations, especially for hydrophilic and amphiphilic rods. Based on confocal laser scanning microscopy results, these phenomena observed were interpreted reasonably in terms of the selective distribution and aggregation of silica rods, which were suggested to be decisive for the stabilization mechanism and efficiency of these rods.

Semicrystalline polymers can crystallize in the unique crystalline polymorph and show different phase behaviors under the high-pressure CO₂ treatment. Understanding such unique crystallization and phase transition behavior is of fundamental importance for the CO₂-assisited processing of semicrystalline polymers. Herein, we investigated the polymorphic crystalline structure, phase transition, and structure-property relationships of poly(L-lactic acid) (PLLA) treated by CO₂ at different pressures (1−13 MPa) and crystallization temperatures (T_c’s, 10−110 °C). PLLA crystallized in the PLLA/CO₂ complex crystals under 7−13 MPa CO₂ at T_c≤50 °C but the common α crystals under the high-pressure CO₂ at T_c≥70 °C. Solid-state nuclear magnetic resonance analysis indicated that the PLLA/CO₂ complex crystals possessed weaker interactions between the PLLA chains than the common α crystals. The PLLA/CO₂ complex crystals were metastable and transformed into the thermally stable α crystals via the solid-to-solid route during heating or annealing at the temperature above 50 °C. The complex crystals of PLLA produced at low T_c was more ductile than the α crystals due to the lower crystallinity and the plasticizing effect of CO₂.

Spherulites are the most common crystalline morphology and thus the visual expression of crystal structures for polymers. The diversified patterns have provided intuitive morphology probes for various crystallization behaviors, while the correlations between them are still needed to be enriched. In this work, the complicated spherulitic morphology of poly(propylene fumarate) (PPF), which is sensitive to crystallization temperature, is investigated. PPF melt, respectively, crystallizes into rough spherulites, regularly banded spherulites, and spherulites containing both two kinds of morphology at low, high, and mediate temperatures. By systematically assaying, it is clear that the growth axis along the radial direction changes from a-axis to b-axis as the crystallization temperature increases, which leads to the formation of unique crystallization-temperature-dependent spherulites. Based on detailed characterization of Fourier transform infrared spectroscopy, the packing state of the specific hydrogen bonds of “C＝C―H···O＝C―C＝C” in PPF crystal lattices is determined, and furthermore, the mechanism for temperature-dependent selection of growth axes for PPF spherulites in melt is reasonably speculated.

The stability of ultrathin polymer films plays a crucial role in their technological applications. Here, we systematically investigated the influence of interfacial adsorption in physical aging and the stability of thin polymer films in the solvent-induced process. We further identify the stability mechanism from the theory of thin film stability. Our results show that the aging temperature and film thickness can strongly influence the stability of thin PS films in acetone vapor. Physical aging can greatly improve the stability of thin polymer films when the aging temperature T_aging1>T_g. A thinner PS film more quickly reaches a stable state via physical aging. At short aging time, the formation of the adsorbed layer can reduce the polar interaction; however, it slightly influences the stability of thin polymer films in the solvent-induced process. At later aging stage, the conformational rearrangement of the polymer chains induced by the interfacial effect at the aging temperature T_aging1 plays an important role in stabilizing the thin polymer films. However, at T_aging2<T_g, the process of physical aging slightly influences the stability of the thin polymer films. The formation of the adsorbed layer at T_aging2 can reduce the short-range polar interaction of the thin film system and cannot suppress the instability of thin polymer films in the solvent-induced process. These results provide further insight into the stable mechanism of thin polymer films in the solvent-induced process.

Chain architecture effect on static and dynamic properties of unentangled polymers is explored by molecular dynamics simulation and Rouse mode analysis based on graph theory. For open chains, although they generally obey ideal scaling in chain dimensions, local structure exhibits nonideal behavior due to the incomplete excluded volume (EV) screening, the reduced mean square internal distance (MSID) can be well described by Wittmer’ theory for linear chains and the resulting chain swelling is architecture dependent, i.e., the more branches a bit stronger swelling. For rings, unlike open chains they are compact in term of global sizes. Due to EV effect and nonconcatenated constraints their local structure exhibits a quite different non-Gaussian behavior from open chains, i.e., reduced MSID curves do not collapse to a single master curve and fail to converge to a chain-length-independent constant, which makes the direct application of Wittmer’s theory to rings quite questionable. Deviation from ideality is further evidenced by limited applicability of Rouse prediction to mode amplitude and relaxation time at high modes as well as the non-constant and mode-dependent scaled Rouse mode amplitudes, while the latter is architecture-dependent and even molecular weight dependent for rings. The chain relaxation time is architecture-dependent, but the same scaling dependence on chain dimensions does hold for all studied architectures. Despite mode orthogonality at static state, the role of cross-correlation in orientation relaxation increases with time and the time-dependent coupling parameter rises faster for rings than open chains even at short time scales it is lower for rings.