Search

Your search keyword '"Li, Zi‐Chen"' showing total 496 results
Start Over Author "Li, Zi‐Chen"
496 results on '"Li, Zi‐Chen"'

101. Modular synthesis of photodegradable polymers with different sensitive wavelengths as UV/NIR responsive nanocarriers.

Author

Li, Lei, Wu, Yuhuan, Du, Fu‐Sheng, and Li, Zi‐Chen

Subjects
POLYMERS, WAVELENGTHS, NANOCARRIERS, ADIPIC acid, POLYMERIZATION
Abstract

We report the modular and facile synthesis of three novel polymers able to photodegrade by UV and visible light via the Passerini multicomponent polymerizations of 1,6‐hexanedioic acid and 1,6‐diisocyanohexane with 5‐methoxy‐2‐nitrobenzaldehyde (M2), 4,5‐dimethoxy‐2‐nitrobenzaldehyde (M3) or 7‐(N,N‐diethylamino)‐4‐formylcoumarin (M4) respectively. This synthetic strategy takes the advantage of the in situ formation of a photolabile chromophore via the Passerini reaction of an aromatic aldehyde with an acid and an isocyanide, thus it is a versatile approach to regulating the photochemical property of the photolabile chromophores by just changing the aldehyde structure. Importantly, two polymers (P3 and P4) even exhibit NIR degradability due to the two‐photon absorption, and their nanoparticles formulated by the single emulsion method have been used as the NIR‐responsive nanocarriers for hydrophobic dyes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 334–341 Three aromatic aldehydes are used for the preparation of photodegradable polymers with different sensitive wavelengths by the Passerini multicomponent polymerization. Polymers P3 and P4 are even sensitive to NIR due to the two‐photon absorption, and are used to fabricate NIR‐responsive nanoparticles for hydrophobic dye release. [ABSTRACT FROM AUTHOR]

Published
2019
Full Text
View/download PDF

103. Thermally Degradable Polyesters with Tunable Degradation Temperatures via Postpolymerization Modification and Intramolecular Cyclization

Author

Lv, An, Cui, Yang, Du, Fu-Sheng, and Li, Zi-Chen

Abstract

We report the novel synthesis of thermally degradable polyesters through the postpolymerization modification of an unsaturated aliphatic polyester from maleic acid via Michael addition reaction with β-amino mercaptans. A high molecular weight polyester (P0) was synthesized by the acyclic diene metathesis (ADMET) polymerization of a diene monomer, di(10-undecenyl) maleate. Postpolymerization modification of P0with three β-amino mercaptans (2-aminoethanethiol, l-cysteine methyl ester, and 2-(butylamino)ethanethiol) and 2-mercaptoethanol via the selective and quantitative thiol–Michael addition reaction with the maleate vinylic double bonds afforded four polyesters (P1–P4). All the polyesters were characterized by 1H NMR, GPC, and MALDI-TOF-MS, and their thermal properties were studied by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The three polymers with pendant amino groups (P1–P3) subjected to thermal-induced degradation in the solid state, the driving force of which is the intramolecular cyclization at elevated temperatures with the formation of six-membered lactam derivatives. Degradation kinetics of P1–P3in the solid states at different temperatures was studied in detail. It was found that increase of the steric hindrance and decrease of the nucleophilicity of the pendent amino groups could increase the degradation temperatures from 0 °C (P1) to 50 °C (P3). Alternatively, protonation of the amino groups of P1and P2with trifluoroacetic acid (TFA) could decrease the nucleophilicity of the primary amino groups, and the polymers P1-Bocand P2-Bocshowed enhanced thermal stability up to 80 °C. Degradation of these two polymers via intramolecular cyclization occurred only when TFA was removed at higher temperatures. When the pendant group was a hydroxyl group as in polymer P4, no intramolecular cyclization occurred, and the polymer was thermally stable up 130 °C. Thus, the results highlight the importance of sequence, functional group, and nucleophilicity of the amino groups in determining the intramolecular cyclization and thermal degradation of these polyesters.

Published
2024
Full Text
View/download PDF

104. Special Issue: Celebrating the 70th Anniversary of the Establishment of Polymer Program at Peking University.

Author

Li, Zi-Chen

Subjects
*POLYMERS, *POLYMER liquid crystals, *SCIENTISTS' attitudes, *BIOPOLYMERS
Abstract

This document is a preface to a special issue of the Chinese Journal of Polymer Science, celebrating the 70th anniversary of the establishment of the polymer program at Peking University. The program, founded by Prof. Xinde Feng in 1953, is the earliest polymer educational and research organization in China. The preface highlights the program's history, including its early graduates, the initiation of postgraduate education, and the development of research areas such as polymer chemistry and bioactive and biomedical polymer materials. The document also mentions the establishment of the Department of Polymer Science and Engineering in 1996 and the program's current research focus areas. The special issue features 18 publications showcasing the latest progress in polymer chemistry, physics, materials, and related interdisciplinary fields. [Extracted from the article]

Published
2023
Full Text
View/download PDF

106. Generalized group signature scheme

Author

Dai Yiqi, Wu Xu-dong, and Li Zi-chen

Subjects
Discrete mathematics, Multidisciplinary, Theoretical computer science, Ring signature, Merkle signature scheme, Digital signature, Computer science, Blind signature, ElGamal signature scheme, Group signature, Secret sharing, Computer Science::Databases, Schnorr signature
Abstract

The concept of generalized group signature scheme will be present. Based on the generalized secret sharing scheme proposed by Lin and Harn, a non-interactive approach is designed for realizing such generalized group signature scheme. Using the new scheme, the authorized subsets of the group in which the group member can cooperate to produce the valid signature for any message can be randomly specified.

Published
2001

110. Seasonal Variation and Vertical Distribution of Salinization in Tianjin Coastal Reservoirs

Author

Ma Bin, Li Hai-ming, Li Zi-chen, and Zhao Xue

Subjects
geography, geography.geographical_feature_category, Soil salinity, Environmental engineering, chemistry.chemical_element, Soil science, Seasonality, medicine.disease, Total dissolved solids, Chloride, Ion, chemistry, Electrical resistivity and conductivity, Spring (hydrology), medicine, Chlorine, Environmental science, medicine.drug
Abstract

Field investigation and sampling analysis method was conducted to seasonal variation and vertical distribution of salinization for Beidagang reservoir and Beitang reservoir in the coastal region of Tianjin. Results show that the reservoirs had a serious problem of salinization. In different sites of reservoirs, the average level of Electric conductivity, Chlorine ion and Total Dissolved Solids (TDS) of reservoir water was 1797.5µs/cm, 4.291 g/L and 10.062 g/L respectively, and pH was essentially stable in the range of 8.2 and 9.4, and was weak alkaline. Seasonal variation characteristics of salinization indicators, such as Electric conductivity, chloride ion and TDS in reservoir were obviously, and showed that in winter was higher than in spring. Vertical variation characteristics of the reservoir water of pH underneath the surface were not obvious. Vertical variation characteristics of the reservoir water of Electric conductivity, chloride ion and TDS vertical changed significantly, and presented that the Electric conductivity, chloride ion and TDS increases with the increase of depth, but also presented the opposite rule for some sites.

Published
2013

111. Notice of Retraction: Permeability Loss of Substrate in High Salinity Landscape Water Constructed Wetland

Author

Li Hai-ming, Li Zi-chen, Xu Xiao-mei, and Tong Qi

Subjects
Salinity, Hydrology, Permeability (earth sciences), Materials science, Initial permeability, Constructed wetland, Soil science, Permeability coefficient, Water pollution
Abstract

Considering the characteristics of high salinity landscape water in Tianjin coast area, column experiments were conducted to elucidate the permeability changes of substrate under high salinity environment in the performance of constructed wetland. The effect of particles diameter on permeability of substrate in constructed wetland were identified, and the mathematical model of the correlative relations between the maximum of permeability loss ratio and particles diameter of substrate were analyzed. Results showed that the permeability of constructed wetland's substrate decreased with runtime until it steadied in some scale, when the permeability was less than initial permeability. In addition, the variety range of permeability coefficient of substrate varied depending on particles diameter. The maximum of permeability loss ratio of different substrates ranged from 60% to 98%, and the correlation between the maximum of permeability loss ratio and particles diameter follows the Guess equation. The particles diameter of substrates made a big different in the change of permeability. The results suggested that particles diameter had great impact on the permeability of substrate for constructed wetland.

Published
2011

Catalog

Books, media, physical & digital resources
See catalog results