scholarly journals Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

2015 ◽  
Vol 11 ◽  
pp. 2261-2266 ◽  
Author(s):  
Stefan Naumann ◽  
Johannes Klein ◽  
Dongren Wang ◽  
Michael R Buchmeiser
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Anionic Polymerization ◽  
Heterocyclic Carbenes ◽  
Structure Activity ◽  
Convenient Preparation ◽  
High Molecular Weight Poly

The polymerization of octamethylcyclotetrasiloxane (D4) is investigated using several five-, six- and seven-membered N-heterocyclic carbenes (NHCs). The catalysts are delivered in situ from thermally susceptible CO2 adducts. It is demonstrated that the polymerization can be triggered from a latent state by mild heating, using the highly nucleophilic 1,3,4,5-tetramethylimidazol-2-ylidene as organocatalyst. This way, high molecular weight PDMS is prepared (up to >400 000 g/mol, 1.6 < Ð M < 2.5) in yields >95%, using low catalyst loadings (0.2–0.1 mol %). Furthermore, the results suggest that a nucleophilic, zwitterionic mechanism is in operation, in preference to purely anionic polymerization.

Living Anionic Polymerization in Continuous Flow: Facilitated Synthesis of High-Molecular Weight Poly(2-vinylpyridine) and Polystyrene

2014 ◽  
Vol 18 (11) ◽  
pp. 1408-1412 ◽  
Author(s):  
Adrian Natalello ◽  
Jan Morsbach ◽  
Andreas Friedel ◽  
Arda Alkan ◽  
Christoph Tonhauser ◽  
...  
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Anionic Polymerization ◽  
Continuous Flow ◽  
Living Anionic Polymerization ◽  
High Molecular Weight Poly

scholarly journals Achieving Good Protection on Ultra-High Molecular Weight Polythene by In Situ Growth of Amorphous Carbon Film

Coatings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 584
Author(s):  
Rui Dang ◽  
Liqiu Ma ◽  
Shengguo Zhou ◽  
Deng Pan ◽  
Bin Xia
Keyword(s):  
Molecular Weight ◽  
Epitaxial Growth ◽  
High Molecular Weight ◽  
Amorphous Carbon ◽  
Transition Layer ◽  
In Situ Growth ◽  
Good Protection ◽  
Ultra High Molecular Weight ◽  
Carbon Plasma

Ultra-high molecular weight polythene (UHMWPE), with outstanding characteristics, is widely applied in modern industry, while it is also severely limited by its inherent shortcomings, which include low hardness, poor wear resistance, and easy wear. Implementation of feasible protection on ultra-high molecular weight polythene to overcome its shortcomings would be of significance. In the present study, amorphous carbon (a-C) film was fabricated on ultra-high molecular weight polythene (UHMWPE) to provide good protection, and the relevant growth mechanism of a-C film was revealed by controlling carbon plasma currents. The results showed the in situ transition layer, in the form of chemical bonds, was formed between the UHMWPE substrate and the a-C film with the introduction of carbon plasma, which provided strong adhesion, and then the a-C film continued epitaxial growth on the in situ transition layer with the treatment of carbon plasma. This in situ growth of a-C film, including the in situ transition layer and the epitaxial growth layer, significantly improved the wetting properties, mechanical properties, and tribological properties of UHMWPE. In particular, good protection by in situ growth a-C film on UHMWPE was achieved during sliding wear.

Linear and high-molecular-weight poly-porphyrins for efficient photodynamic therapy

2021 ◽  
Author(s):  
Nan Zheng ◽  
Xiahui Li ◽  
Shangwei Huangfu ◽  
Kangkai Xia ◽  
Ruofei Yue ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Photodynamic Therapy ◽  
Quantum Yield ◽  
Singlet Oxygen ◽  
High Molecular Weight ◽  
Linear Poly ◽  
High Molecular Weight Poly

A linear poly-porphyrin with high Mw and conjugated by PEG and acetazolamide was developed with enhanced singlet oxygen quantum yield, improved photo-toxicity and excellent in vivo photodynamic therapy.

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