Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Reversible photodimerization of coumarin derivatives dispersed in poly(vinyl acetate) (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 2705-2714 
    Details
    ISSN: 0887-624X
    Keywords: coumarin derivatives ; photodimerization ; photocleavage ; reversible ; pho-tosensitizer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four photoreactive coumarin derivatives were successfully synthesized from 7-hydroxy-coumarin and 7-hydroxy-4-methylcoumarin, i.e., 7-propionyloxy-4-methylcoumarin (M1), 7-palmitoyloxy-4-methylcoumarin (M2), 7-propionyloxycoumarin (M3), and 7-palmitoy-loxycoumarin (M4). Reversible photodimerization (350 or 300 nm) and photocleavage (254 nm) of these coumarin derivatives dispersed in poly(vinyl acetate) (PVAc) were investigated by tracing their UV absorbance variations at 310 nm. The M2 and M4 with long palmitoyl chain show much better photoreaction reversibility than M1 and M3 with short propionyl chain. Moreover, photodimerization rate (under 350 nm) of M2 is greater than 200 times of that of M1. This has been explained by the formation of suitable conformation for revers-ible photodimerization due to the hydrophobic interactions. Photodimerization of M2 is ca. 3 times quicker than that of M4, indicating 4-methyl substitution enhances pho-todimerization. The influence of photodimerization wavelength (350 and 300 nm) and photosensitizer (benzophenone) have also been investigated in detail. © 1995 John Wiley & Sons. Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1995.080331604
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Preparation and photoreaction of copolymers derived from N-(1-phenylethyl)acrylamide and 7-acryloyloxy-4-methyl coumarin (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1867-1875 
    Details
    ISSN: 0887-624X
    Keywords: N-(1-phenylethyl)acrylamide ; 7-acryloyloxy-4-methyl coumarin ; copolymerization ; monomer reactivity ratio ; photocrosslinking ; photocleavage ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The copolymers containing photoreactive 4-methyl coumarin pendant groups have been prepared by radical copolymerization of N-(1-phenylethyl)acrylamide (M1) and 7-acryloyloxy-4-methyl coumarin (M2) in DMF at 70°C. The monomer reactivity ratios (MRR) of M1 and M2 are estimated by Finenam-Ross, Kelen-Tüdos, Mayo-Lewis, and YBR methods to be about r1 = 0.12-0.16 and r2 = 1.13-1.28. Dilute dioxane solutions of the copolymers (10-4-10-5 M of 4-methyl coumarin chromophores) are first photocrosslinked intramolecularly by irradiating 350 nm light (dimerization of 4-methyl coumarin) and then photo-cleaved at 254 nm (symmetric cleavage of cyclobutane). Tracing by an UV-visible spectrophotometer, it is found that photocrosslinking and photocleavage proceed simultaneously when 254 nm is the light source and finally reaches to a dynamic equilibrium. However, only photocrosslinking can be observed under 350 nm light. Kinetic results show that both photocrosslinking and photocleavage are first-order reactions. Moreover, photocrosslinking rate constant increases with mole fraction of M2 in the copolymer (F2). On the contrary, rate constant of photocleavage decreases with increasing F2. © 1994 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321007
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Preparation and photocrosslinking behaviors of polyesters derived from trans-2,2′-dihydroxystilbene (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 1319-1327 
    Details
    ISSN: 0887-624X
    Keywords: coumarin dimer ; photocleavage ; trans-2,2′-dihydroxystilbene ; interfacial polycondensation ; photocrosslinking ; characteristic curve ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The monomer, trans-2,2′-dihydroxystilbene (DHS), has been prepared by asymmetric photocleavage (254 nm) of coumarin dimer acid derived from coumarin dimer. Four new polyesters are successfully synthesized by interfacial polycondensation of the DHS with adipoyl chloride, azelaoyl chloride, sebacoyl chloride, and dodecanedioyl dichloride, respectively. The reduced viscosities of the polyesters decrease from 0.32 to 0.11 dL/g as the number of methylene unit in diacid chlorides increases from 4 to 10. From DSC investigation, it is found that the polyesters are semi-crystalline polymers with Tm = 39-192°C. Under 350 nm light, photocrosslinking behavior in solution and film-state is investigated by UV spectral change with irradiation time (350 nm). The photoreactive stilbene chromophores in the main chain dimerize to form cyclobutane derivatives, and lead to crosslinking of the polyesters. Photosensitivity in the film state has also been evaluated by their characteristic curves. Polyester from dodecanedioyl dichloride (5d) exhibits the highest initial reaction rate and ultimate crosslinking ratio. © 1995 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1995.080330814
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Synthesis and reversible photocleavage of novel polyurethanes containing coumarin dimer components (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 613-624 
    Details
    ISSN: 0887-624X
    Keywords: anti head-to-head 7-hydroxycoumarin dimer ; anti head-to-tail 7-hydroxy-4-methylcoumarin dimer ; polyurethane ; photocleavage ; photopolymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Six polyurethanes containing coumarin dimer components in the main chain have been prepared by polyaddition of diisocyanates with anti head-to-head 7-hydroxycoumarin dimer or anti head-to-tail 7-hydroxy-4-methylcoumarin dimer. 7-Acetoxycoumarin and 7-acetoxy-4-methylcoumarin were first prepared and then photodimerized under 350 nm UV light to give anti head-to-head 7-acetoxycoumarin dimer and anti head-to-tail 7-acetoxy-4-methylcoumarin dimer, respectively. After hydrolyzing under acidic conditions to 7-hydroxycoumarin dimer and anti head-to-head 7-hydroxycoumarin dimer, they were polymerized with aliphatic and aromatic diisocyanates in N,N-dimethylacetamide to give the polyurethanes. Addition of dibutyltin dilaurate (T-12) as catalyst increases the polymer yield with the viscosity remaining almost unchanged. It was also found that lithium chloride enhances both the yield and viscosity of the polyurethanes by increasing their solubility possibly through complexation. The polyurethanes are symmetrically photocleaved at cyclobutane rings under 254 nm UV light to dicoumarins. Reversible photodimerization of the photocleaved compounds have also been investigated under 300 and 350 nm UV light. The polyurethanes from aromatic diisocyanates or with 4-methyl substituent exhibit greater reactivity in the photocleavage reaction. © 1997 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...