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H-Bonded Liquid Crystalline polymer network Materials

Chemical Research in Chinese Universities 2001年第z1期17卷 89-90页

作者： LIN Hong-Cheu Department of Materials Science and Engineering National Chiao Tung University Institute of Chemistry Academia Sinica Institute of Chemistry Academia Sinica

Side-chain copolymers, poly(mOBA-co-mStilb)s, composed of proton acceptors (stilbazoles) and proton donors (benzoic acids) connected to polyacrylate backbone with different methylene spacer lengths (m = 6 and 10) were prepared in different donor/acceptor molar ratios. The H-bonded copolymeric networks were formed once they were synthesized, and showed more homogenous phase than the physical-blended supramolecular networks consisting of donor and acceptor homopolymers, i.e.H-bonded blends of PmOBA and PmStilb. In order to compare the effects of the backbone connection of these H-bonded copolymers and blends, we also built monomer-monomer and polymer-monomer H-bonded complexes of similar structures (shown in Fig. 1). DSC, POM, and powder XRD studies reveal that the copolymers (m = 10)with mole fractions of benzoic acids between 0.33-0.83 show the smectic A (SMA) phase with layer spacing values between 42.22A-50.47A (increases with higher H-bonded crosslinking density between benzoic acids and stilbazoles), while for m = 6, liquid crystalline behavior still can be observed at 0.89 molar fraction of benzoic acids. However, on the basis of powder XRD study it is found that the d spacing values of H-bonded copolymers with m = 6 in the SmA phase increase with higher molar ratios of benzoic acids, which is agreed with the formation of microphase separation due to the hydrogen bonds of benzoic acids connected themselves from the same backbone. The isotropization temperatures of the H-bonded copolymers and blends increase as the molar ratios of benzoic acids increase, while the higher crosslinking density of the H-bonded copolymeric networks and blends can stabilize the liquid crystalline phase.

关键词： polymer network benzoic acids crosslinking density supramolecular networks microphase separation powder XRD crystalline behavior similar structures crystalline phase molar fraction hydrogen bonds

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polymer networkS BY MOLECULAR DYNAMICS SIMULATION: FORMATION, THERMAL, STRUCTURAL AND MECHANICAL PROPERTIES

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Chinese Journal of polymer Science 2013年第1期31卷 21-38页

作者： Rong-liang Wu Ting Li Erik Nies Division of polymer Chemistry and Materials Department of ChemistryThe Leuven Mathematical Modeling and Computational Science Centre (LMCC) and The Leuven Materials Research Centre (LMRC)Katholieke Universiteit Leuven

A molecular dynamics simulation method is presented and used in the study of the formation of polymer networks. We study the formation of networks representing the methylene repeating units as united atoms. The network formation is accomplished by cross-linking polymer chains with dedicated functional end groups. The simulations reveal that during the cross-linking process, initially branched molecules are formed before the gel point; approaching the gel point, larger branched entities are formed through integration of smaller branched molecules, and at the gel point a network spanning the simulation box is obtained; beyond the gel point the network continues to grow through the addition of the remaining molecules of the sol phase onto the gel （the network）; the final completion of the reaction occurs by intra-network connection of dangling ends onto unsaturated cross-linkers. The conformational properties of the strands in the undeformed network are found to be very similar with the conformational properties of the chains before cross-linking. The uniaxial deformation of the formed networks is investigated and the modulus determined from the stress-strain curves shows reciprocal scaling with the precursor chain length for networks formed from sufficiently large precursor chains （N≥ 20）.

关键词： Crosslinking polymer network network topology Molecular dynamics Mechanical properties.

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A spatiotemporally-nonlocal continuum field theory of polymer networks

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Science China(Physics,Mechanics & Astronomy) 2023年第5期66卷 155-172页

作者： Yiyuan Jiang Li Li Yujin Hu State Key Laboratory of Digital Manufacturing Equipment and Technology School of Mechanical Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074China

A physically-based continuum theory that captures the microstructure-dependent and temporal effects of both permanent and transient polymer networks is still lacking,despite the fact that it is greatly needed for the analysis of polymeric *** fill in this gap,this work proposes a physically-based spatiotemporally nonlocal continuum field theory.A general frame-work is established that quantitatively connects microscopic descriptions of polymer networks(chain energetics,chain-length distribution,assembly structure of the interpenetrating network,and rate of bond exchange reactions)to key components in the spatiotemporally nonlocal constitutive relations(explicit form of the nonlocal kernel function,magnitude of nonlocal characteris-tic length,two-phase weighting factors,and explicit form of the relaxation function),based on three hypotheses on the continuum viewpoint of the underlying discrete network structure:the existence of a finite bottom bound of volume to define intensive quan-tities,uniformity of energy density field inside the representative volume of a polymer network,and the condition for initiation of chain *** the general framework to a permanent 8-chain concentric network yields a concrete two-phase nonlocal elasticity constitutive relation,where the explicit form of the kernel function can be derived by simply assuming an implicit *** to a transient network with bond exchange reactions yields a spatiotemporally nonlocal constitutive *** spatiotemporally nonlocal continuum theory can be helpful for exploring transformative and subversive high-performance materials involving the specific spatial stacking and arrangement of functional units through artificial design.

关键词： spatiotemporal nonlocality polymer network transient network bond exchange reactions microstructure-dependent effect

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Non-linear Radical Additions-Coupling polymerization of Monovinyl Monomers towards polymer networks: Theory, Tunability and Heritable Architecture

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Chinese Journal of polymer Science 2022年第12期40卷 1623-1630,I0008页

作者： Li-Mei Ren Cheng-Lin Li Qi Wang MOE Key Laboratory of Macromolecular Synthesis and Functionalization Department of Polymer Science&Engineering Zhejiang UniversityHangzhou 310027China Current address:Zhejiang University-University of Edinburgh Institute Zhejiang University School of Medicineand Key Laboratory of Tissue Engineering and Regenerative Medicine of Zhejiang ProvinceZhejiang University School of MedicineHangzhou 310027China

Exploring new polymerization strategy for current available monomers is a big challenge in polymer science. Here we re-investigate radical polymerization of monovinyl monomer(MVM) initiated by uniform branched polyfunctional initiator(PFI), which is termed non-linear radical additions-coupling polymerization(NLRAs CP). In NLRAs CP, both addition and coupling reactions of radical contribute to the construction of the polymer chains, which leads to continuous growth of branch topology. Theoretical analysis of NLRAs CP predicts that the gelation is determined by the functionality of PFI(a), the extent of initiation of the PFI(q) and the termination factor of radical(φ). NLRAs CPs of styrene and methyl methacrylate promoted by Cu(0)/MeTREN or Mn_(2)(CO)_(10)/visible light were conducted. After the cleavage of incorporated PFI fragment or junctions in the network, the network was transformed to linear chains having almost the same structure as segmental chains in the precursor network. This allows the reverse deducing the network structure from its cleaved products. It has been proven that NLRAs CP includes stepwise initiation of PFI, chain-growth of segmental chains and successive endlinking of macroradicals derived from PFI. The three parameters related to the gelation process, a, q and φ, were adjusted via binary PFI, the feed ratio of [Mn_(2)(CO)_(10)]/[PFI] and addition of non-homopolymerizable comonomer respectively. The minimum values of a and q, and the minimum amount of comonomer required for gelation were determined,which can be applied to estimate φ of various macroradicals. NLRAs CP opens a general and facile strategy for synthesis of a variety of polymer networks with heritable architecture by one-pot polymerization of various MVMs.

关键词： Non-linear radical additions-coupling polymerization Monovinyl monomer Polyfunctional initiator polymer network Theory

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A tree-growing graphic model for asymmetrical phantom networks in polymeric gels undergoing dynamic mechanochemical coupling

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Science China(Technological Sciences) 2024年第2期67卷 558-567页

作者： SHI WeiLin ZHOU Jian LU HaiBao ELMARAKBI Ahmed FU Yong-Qing National Key Laboratory of Science and Technology on Advanced Composites in Special Environments Harbin Institute of TechnologyHarbin 150080China College of Mechanical and Vehicle Engineering Hunan UniversityChangsha 410082China Faculty of Engineering and Environment University of NorthumbriaNewcastle upon Tyne NEI 8STUK

network structures of various polymers have significant effects on their mechanical properties;therefore,numerous studies have investigated the constitutive relationship between symmetrical network structures and their rubber elasticity in ***,few studies have focused on asymmetrical network structures in polymers that undergo bond exchange reactions,selfassembly,or mechanochemical coupling—all of which are induced by transition probabilities of chemical bonding *** this study,an extended constraint junction and phantom network model is formulated using the tree-growing theory to establish a constitutive relationship between asymmetrical network structures and their rubber elasticity in polymers.A free-energy equation is further developed to explore working principles of configurational transitions on the dynamic rubber elasticity of symmetrical and asymmetrical network *** constitutive relationship between dynamic rubber elasticity and symmetrical and asymmetrical network structures has also been proposed for the gels undergoing mechanochemical and hydromechanical ***,the effectiveness of this newly proposed tree-growing model has been verified by comparing with the classical affine network model,finite element analysis,and the experimental results of gels reported in literature.

关键词： gel polymer network rubber elasticity asymmetric

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Recent advances of hydrogel network models for studies on mechanical behaviors

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Acta Mechanica Sinica 2021年第3期37卷 367-386,I0001页

作者： Jincheng Lei Ziqian Li Shuai Xu Zishun Liu International Center for Applied Mechanics State Key Laboratory for Strength and Vibration of Mechanical StructuresXi'an Jiaotong UniversityXi'an 710049China

Current constitutive theories face challenges when predicting the extremely large deformation and fracture of hydrogels,which calls for the demands to reveal the fundamental mechanism of the various mechanical behaviors of hydrogels from bottom *** hydrogel network model provides a better approach to bridge the gap between the micro-structure and the macroscopic mechanical *** work summarizes the theoretical and numerical researches on the hydrogel network models,aiming to provide new insights into the effect of microstructure on the swelling-deswelling process,hyperelasticity,viscoelasticity and fracture of *** network models are divided into full-atom network models,realistic network models and abstract network ***-atom network models have detailed atomic structure but small *** network models with different coarse-graining degree have large model size to explain the swelling-deswelling process,hyperelasticity and *** network models abstract polymer chains into analytical interactions,leading to the great leap of model *** shows advantages to reproduce the crack initiation and propagation in hydrogels by simulating chain *** research directions on the network modeling are *** hope this work can help integrate the merits of network modeling methods and continuum mechanics to capture the various mechanical behaviors of hydrogels.

关键词： Hydrogel polymer network Mechanical behavior Fracture

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Photoregulated supramolecular hydrogels driven by polyradical interactions

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Chinese Chemical Letters 2023年第7期34卷 340-344页

作者： Zehao Gong Qiang Yan State Key Laboratory of Molecular Engineering of polymers and Department of Macromolecular Science Fudan UniversityShanghai 200433China

Organic radical as a powerful tool has been extensively applied in synthetic chemistry. However, harnessing radical-mediated noncovalent interactions to fabricate soft materials remains elusive. Here we report a new category of supramolecular hydrogel system held by multiple radical-radical(polyradical) interactions, and its photosensitive cross-linking structure. A simple polyacrylamide with triarylamine(TAA)pendants is designed as the precursor. The TAA units in polymer can be converted into active TAA^(·+)radical cations with light and further associate each other via TAA^(·+)–TAA^(·+)stacking interactions to form stable supramolecular network. Temporal control of the light irradiation dictates the degree of radical stacks, thus regulating the mechanical performance of the resulting hydrogel materials on-demand. Moreover, the reversible collapse of this hydrogels can be promoted by adding radical scavenger or exerting reduction voltage.

关键词： Radical-radical interactions Polyradical Supramolecular hydrogel polymer network Photoresponsiveness

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Effect of polymer structures on electro-optical properties of polymer stabilized liquid crystal films

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Frontiers of Chemical Science and Engineering 2008年第3期2卷 265-268页

作者： Shoulian WANG Jie HE Yu ZENG Bin YAN Yinghan WANG College of polymer Science and Engineering State Key Laboratory of Polymer Materials and EngineeringSichuan UniversityChengdu 610065China

The polymer stabilized liquid crystal(PSLC)film is a relatively novel electro-optical material,which is generally obtained by dissolving a small amount of a bifunctional photoreactive monomer in a low molecular mass liquid *** this paper,the PSLC films were prepared with photoreactive biphenyl methacrylate monomers by photopolymerization induced phase *** effects of liquid crystal concentration,curing time,monomer structures and alignment layer on the electro-optical properties of PSLC films were *** results show that the transmittance in the OFF state(TOFF)increased with the liquid crystal concentration,but the driving voltage *** was also influenced by the curing ***,when polyimide was used as alignment layer,the films prepared from the bifunctional monomer shows a higher TOFF,while those from the single functional monomer exhibited a deformed electro-optical curve due to the unsteady polymer networks.

关键词： polymer network liquid crystal network morphology electric-optical properties

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Unique Ligand Exchange Dynamics of Metal-Organic Polyhedra for Vitrimer-like Gas Separation Membranes

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CCS Chemistry 2022年第11期4卷 3563-3572页

作者： Mingxin Zhang Haitao Yu Qin Zou Zi-Ang Li Yuyan Lai Linkun Cai Panchao Yin State Key Laboratory of Luminescent Materials and Devices South China Advanced Institute for Soft Matter Science and TechnologySouth China University of TechnologyGuangzhou 510640

Metal-organic polyhedra(MOPs)possess a microporous framework and impose hierarchical constraints on their surface ligands,leading to the long-ignored,logarithmic ligand exchange ***,polymer networks with MOP as nanoscale cross-linkers(MOP-CNs)can integrate unique ligand exchange dynamics and microporosity,affording vitrimer-like gas separation membranes with promising mechanical performance and(re)*** the ligands on the MOP surfaces are confined and correlated via a 3D coordination framework and their neighboring spaces,giving rise to a high energy barrier for ligand ***,MOP-CNs demonstrate high mechanical strengths at room temperature due to their negligible ligand *** thermo-activated ligand exchange process with integrated network topology enables facile(re)processing and high solvo-resistance at high *** facilitates Arrhenius type temperature dependence of flowability and stress relaxation,giving rise to the simultaneous achievement of promising mechanical strengths and(re)***,the cage topologies of MOPs endow the materials with a bonus microporous feature and spur their applications as gas separation membranes.

关键词： metal-organic polyhedra supramolecular chemistry polymer network soft matter dynamics coordination chemistry polymer recycling gas separation membrane

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Cell thickness dependence of electrically tunable infrared reflectors based on polymer stabilized cholesteric liquid crystals

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Science China Materials 2018年第5期61卷 745-751页

作者： Xiaowen Hu Laurens T. de Haan Hitesh Khandelwal Albertus P.H.J. Schenning Li Nian Guofu Zhou SCNU-TUE Joint Laboratory of Device Integrated Responsive Materials （DIRM） National Center for International Research on Green Optoelectronics South China Normal University No 378 West Waihuan Road Guangzhou Higher Education Mega Center Guangzhou 510006 China Laboratory of Functional Organic Materials ＆ Devices Department of Chemical Engineering and Chemistry Eindhoven University of Technology P. O. Box 513 5600 MB Eindhoven The Netherlands Institute of Electronic Paper Displays and Guangdong Provincial Key Laboratory of Optical Information Materials and Technology South China Academy of Advanced Optoelectronics South China Normal University Guangzhou 510006 China Shenzhen Guohua Optoelectronics Tech. Co. Ltd. Shenzhen 518110 China

We reported here the fabrication of the elec- trically tunable infrared （IR） reflectors based on the polymer stabilized cholesteric liquid crystal （PSCLC） with negative dielectric anisotropy. A systematic study of the influence of cell gap on the electrically tunable reflection bandwidth was performed. When a direct current （DC） electric field was ap- plied, the reflection bandwidth red shifted in the cells with small cell gap, whereas the bandwidth broadening was ob- served in the cells with large cell gap. It is therefore reasonable to deduct that the reflection is dictated by the pitch gradient steepness which strongly relies on the cell thickness. The re- sults reveal that for making PSCLC based IR reflector windows with electrically induced bandwidth broadening, a minimal cell gap thickness is required. The resulted IR reflectors pos- sess a short native switching time and long-term operation stability, and are potentially applicable as smart energy saving windows in buildings and automobiles.

关键词： cholesteric cell gap polymer network electric reg-ulating infrared reflector

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