Chemically Designed, UV Curable Polycarbosilane Polymers

1992 ◽  
Vol 271 ◽  
Author(s):  
Kevin J. Thorne ◽  
Stephen E. Johnson ◽  
Haixing Zheng ◽  
John D. Mackenzie ◽  
M. F Hawthorne
Keyword(s):  
Molecular Weight ◽  
Inert Atmosphere ◽  
Uv Exposure ◽  
Cross Linking ◽  
Substitution Reactions ◽  
High Solubility ◽  
Chemical Route ◽  
Uv Curable ◽  
Polymer Precursors ◽  
C Nmr

ABSTRACTTo prepare new polycarbosilane polymer precursors with high solubility and the capability of UV cross-linking, commercial polycarbosilane was modified by a chemical route. These modifications involved AlCl3 catalyzed chlorination reactions of polycarbosilane's Si-H bonds. The resultant Si-Cl bonds were substituted by a reaction with sodium acetylyde to form Si-C=CH ligands. These ligands are suitable for controlled, free radical initiated cross-linking of the polycarbosilane polymers. The increase in molecular weight should allow for increased Tg's and the retention of polymer pre-forms. In this report, the chlorination of the polycarbosilane polymer and the substitution reactions of polycarbosilane were examined with IR, 29Si and 13C NMR spectroscopy. In addition, the retention of polymer pre-forms were analyzed after UV exposure and inert atmosphere pyrolysis.

Alkynyl Substituted Carboranes as Precursors to Boron Carbide Thin Films, Fibers and Composites

1992 ◽  
Vol 271 ◽  
Author(s):  
Stephen E. Johnson ◽  
Xiaoguang Yang ◽  
M. F. Hawthorne ◽  
Kevin J. Thorne ◽  
Haixing Zheng ◽  
...  
Keyword(s):  
Thin Films ◽  
Molecular Weight ◽  
Boron Carbide ◽  
Inert Atmosphere ◽  
Uv Exposure ◽  
Derivatives Of

ABSTRACTThe use of alkynyl substituted derivatives of o-carborane as precursors to boron containing ceramics is described. These compounds undergo a thermally or photochemically induced polymerization to afford cross linked polyakynyl-o-carborane derivatives. The increase in molecular weight should allow for increased Tg's and the retention of modelled polymer preforms. In this report, these modification reactions are described. In addition, the retention of molded polymer preforms were analyzed after UV exposure and inert atmosphere pyrolysis.

Phenolic Resins (II) – Influence of the Chemical Structure of High Molecular Weight Molecules on the Mechanisms of Cross-linking and on the Final Structure of the Resins

2003 ◽  
Vol 11 (4) ◽  
pp. 233-262 ◽  
Author(s):  
J. Bouajila ◽  
G. Raffin ◽  
H. Waton ◽  
C. Sanglar ◽  
J.O. Païsse ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Chemical Structure ◽  
Physicochemical Characterization ◽  
Cross Linking ◽  
Phenolic Resins ◽  
Molar Ratios ◽  
Synthesis Parameters ◽  
Fragmentation Mechanisms ◽  
C Nmr

The physicochemical characterization of the structures of the oligomers (n < 4) in resols has been carried out by fragmenting monomers in LC/UV/MS and LC/UV/MS/MS. Fragmentation mechanisms are related to the numbers and positions of substituents on the aromatic ring and to the types of oligomer junctions. It was more difficult to determine the structures of phenol hemiacetals and dimer hemiacetals because of the large number of position isomers. The resols were prepared with differing molar ratios R = Formaldehyde/Phenol and catalysts. They were cross-linked using two industrially recommended heat cycles. The progression of resin cross-linking was determined by solid state 13C NMR (CP/MAS). The residual percentage of monomers and oligomers at n < 4 was determined in leachates (water and methanol) and characterized by LC/UV/MS. The results for cross-linking advancement were correlated with the various synthesis parameters (ratio R, type of catalyst and heat cycle).

Cross-Linked αsγt-Chain Hybrids in Plasma Clots Studied by 1D- and 2D Electrophoresis and Western Blotting

1993 ◽  
Vol 70 (03) ◽  
pp. 438-442 ◽  
Author(s):  
B Grøn ◽  
C Filion-Myklebust ◽  
S Bjørnsen ◽  
P Haidaris ◽  
F Brosstad
Keyword(s):  
Molecular Weight ◽  
Monoclonal Antibodies ◽  
Human Plasma ◽  
Western Blotting ◽  
Isoelectric Point ◽  
Factor Xiii ◽  
Cross Linking ◽  
2D Electrophoresis ◽  
Complex Phenomenon ◽  
Fibrinopeptide A

SummaryFibrinogen and fibrin related chains in reduced human plasma as well as the bonds interlinking partially cross-linked fibrin from plasma clots have been studied by means of 1D- and 2D electrophoresis and Western blotting. Immunovisualization of reduced plasma or partially cross-linked fibrin with monoclonal antibodies specific for the α-chains or the γ-chains have shown that several bands represent material belonging to both chains. In order to decide whether these bands constitute αγ-chain hybrids or superimposed α- and γ-chain dimers, the cross-linked material was separated according to both isoelectric point (pI) and molecular weight (MW) using Pharmacia’s Multiphor II system. Western blotting of the second dimension gels revealed that partially cross-linked fibrin contains αsγt-chain hybrids and γ- polymers, in addition to the well-known γ-dimers and α-polymers. The main αsγt-chain hybrid has a pI between that of the α- and the γ-chains, a MW of about 200 kDa and contains Aα-chains with intact fibrinopeptide A (FPA). It was also observed that soluble fibrinogen/fibrin complexes as well as partially cross-linked fibrin contain degraded α-dimers with MWs close to the γ-dimers. These findings demonstrate that factor XIII-catalyzed cross-linking of fibrin is a more complex phenomenon than earlier recognized.

THE EXTRACTION OF ORGANIC MATTER FROM SELECTED SOILS AND PARTICLE SIZE FRACTIONS WITH 0.5 M NaOH AND 0.1 M Na4P2O7 SOLUTIONS

1989 ◽  
Vol 69 (2) ◽  
pp. 253-262 ◽  
Author(s):  
M. SCHNITZER ◽  
P. SCHUPPLI
Keyword(s):  
Molecular Weight ◽  
Organic Matter ◽  
Humic Acids ◽  
Nmr Spectra ◽  
Attractive Alternative ◽  
Particle Size Fractions ◽  
Molecular Weights ◽  
Naoh Solution ◽  
C Nmr ◽  
Medium Silt

Organic matter (OM) in the Bainsville and Melfort soils, and in coarse clay and medium silt fractions separated from these soils, was extracted under N2 with 0.5 M NaOH and unadjusted 0.1 M Na4P2O7 solutions. pH ranges of the soils and fractions in contact for 24 h with 0.5 M NaOH and 0.1 M Na4P2O7 solutions extended from 12.2 to 12.6 and 9.0 to 9.4, respectively. Slightly greater proportions of the soil-carbon were extracted by 0.5 M NaOH than by 0.1 M Na4P2O7 solution. The differences, however, did not appear to be significant and may vary from soil to soil. The efficiency of extraction and the characteristics of the extracted materials were assessed on humic acids (HAs), which were isolated from the extracts. From the Bainsville soil and fractions, 0.1 M Na4P2O7 solution extracted more high-molecular weight and more deeply colored HAs than did 0.5 M NaOH solution. But HAs extracted from the Melfort soil and fractions had similar molecular weights and colours. 13C NMR spectra showed that HAs extracted by 0.1 M Na4P2O7 solution tended to be more aromatic than HAs extracted by 0.5 M NaOH solution. Well defined solid-state 13C NMR spectra of HAs, containing up to 69.0% ash, could be recorded. Unadjusted 0.1 M Na4P2O7 solution under N2 was found to be an attractive alternative to 0.5 M NaOH solution as an extractant for soil OM. Key words: Humic acids, E4:E6 ratios, IR spectra, 13C NMR spectra, aromaticity

scholarly journals Pulsed UV Laser Processing of Carbosilane and Silazane Polymers

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 372 ◽  
Author(s):  
Samuel Ligon ◽  
Gurdial Blugan ◽  
Jakob Kuebler
Keyword(s):  
Laser Beam ◽  
Laser Processing ◽  
Scanning Speed ◽  
Inert Atmosphere ◽  
Laser Wavelength ◽  
Uv Laser ◽  
Glass Substrates ◽  
Polymer Precursors ◽  
Laser Systems ◽  
Pre Treatment

Freestanding SiCNO ceramic pieces with sub-mm features were produced by laser crosslinking of carbosilane and silazane polymer precursors followed by pyrolysis in inert atmosphere. Three different pulsed UV laser systems were investigated, and the influence of laser wavelength, operating power and scanning speed were all found to be important. Different photoinitiators were tested for the two lasers operating at 355 nm, while for the 266 nm laser, crosslinking occurred also without photoinitiator. Pre-treatment of glass substrates with fluorinated silanes was found to ease the release of green bodies during solvent development. Polymer crosslinking was observed with all three of the laser systems, as were bubbles, surface charring and in some cases ablation. By focusing the laser beam several millimeters above the surface of the resin, selective polymer crosslinking was observed exclusively.

scholarly journals Potential Effects of Corneal Cross-Linking upon the Limbus

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Johnny E. Moore ◽  
Davide Schiroli ◽  
C. B. Tara Moore
Keyword(s):  
Stem Cells ◽  
Potential Risk ◽  
Ocular Surface ◽  
Ex Vivo ◽  
Uv Exposure ◽  
Cross Linking ◽  
Clinical Complications ◽  
Cellular Dna ◽  
Pathological Consequence

Corneal cross-linking is nowadays the most used strategy for the treatment of keratoconus and recently it has been exploited for an increasing number of different corneal pathologies, from other ectatic disorders to keratitis. The safety of this technique has been widely assessed, but clinical complications still occur. The potential effects of cross-linking treatment upon the limbus are incompletely understood; it is important therefore to investigate the effect of UV exposure upon the limbal niche, particularly as UV is known to be mutagenic to cellular DNA and the limbus is where ocular surface tumors can develop. The risk of early induction of ocular surface cancer is undoubtedly rare and has to date not been published other than in one case after cross-linking. Nevertheless it is important to further assess, understand, and reduce where possible any potential risk. The aim of this review is to summarize all the reported cases of a pathological consequence for the limbal cells, possibly induced by cross-linking UV exposure, the studies donein vitroorex vivo, the theoretical bases for the risks due to UV exposure, and which aspects of the clinical treatment may produce higher risk, along with what possible mechanisms could be utilized to protect the limbus and the delicate stem cells present within it.

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