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Special Issue "Advanced Polymer Architectures"

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A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (30 September 2010)

Special Issue Editor

Guest Editor
Dr. Vikas Mittal

BASF SE, Polymer Research, G201, 67056 Ludwigshafen, Germany
Phone: +49 176 967 07435
Interests: organic-inorganic nanocomposites; polymer colloids; surface chemistry; barrier properties; modeling

Published Papers (4 papers)

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Research

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Open AccessArticle New Biocompatible Polyesters Derived from α-Amino Acids: Hydrolytic Degradation Behavior
Polymers 2010, 2(4), 418-439; doi:10.3390/polym2040418
Received: 20 September 2010 / Revised: 2 October 2010 / Accepted: 8 October 2010 / Published: 13 October 2010
Cited by 11 | PDF Full-text (809 KB) | HTML Full-text | XML Full-text
Abstract
New polymers were synthesized from α-hydroxy acids derived from the natural amino acids Ile, Leu, Phe, and Val, combined with lactic acid, glycolic acid and 6-hydroxyhexanoic acid by direct condensation. The toxicity was determined and the degradation process of these polyesters was [...] Read more.
New polymers were synthesized from α-hydroxy acids derived from the natural amino acids Ile, Leu, Phe, and Val, combined with lactic acid, glycolic acid and 6-hydroxyhexanoic acid by direct condensation. The toxicity was determined and the degradation process of these polyesters was investigated under physiological conditions by analyzing the composition of the degraded polymers and the oligomers cleaved in the buffer medium. The polymers were found to be non toxic to two cell lines. Polymers displayed a biphasic degradation behavior. In most cases, a linear relationship was found between the weight loss constant and the hydrophobicity of the polymers, Log P. Regarding the second stage of weight loss, it is apparent that polymers derived from α-hydroxy(L)isoleucine ((L)HOIle) and α-hydroxy(L)Valine ((L)HOVal) degraded much faster than those derived from α-hydroxy(L)leucine ((L)HOLeu) and α-hydroxy(L)phenylalanine ((L)HOPhe), probably due to different spatial orientation of the side chains. Copolymers of 6-hydroxyhexanoic acid displayed slow degradation rates as expected, whereas the degradation profile of copolymers of lactic acid was similar to the other homopolymers. These new polyesters may serve as potential biocompatible materials for medical applications. Full article
(This article belongs to the Special Issue Advanced Polymer Architectures)
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Open AccessArticle Chemically Induced Dynamic Nuclear Polarization during the Thermolysis of Alkoxyamines: A New Approach to Detect the Occurrence of H-Transfer Reactions
Polymers 2010, 2(4), 364-377; doi:10.3390/polym2040364
Received: 30 August 2010 / Revised: 23 September 2010 / Accepted: 26 September 2010 / Published: 28 September 2010
Cited by 5 | PDF Full-text (1000 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Thermal decomposition of alkoxyamines in the presence of scavengers was found to proceed with the formation of chemically induced nuclear polarization detected by 1H NMR. The distinctive Chemically Induced Dynamic Nuclear Polarization (CIDNP) features were studied using the example of three alkoxyamines: [...] Read more.
Thermal decomposition of alkoxyamines in the presence of scavengers was found to proceed with the formation of chemically induced nuclear polarization detected by 1H NMR. The distinctive Chemically Induced Dynamic Nuclear Polarization (CIDNP) features were studied using the example of three alkoxyamines: 4-nitrophenyl 2-(2,2,6,6-tetramethylpiperidin-1-yloxy)-2-methylpropanoate (1a), 4-nitrophenyl 2-(2,2-diphenyl-3-phenylimino-2,3-dihydroindol-1-yloxy)-2-methylpropanoate (2a) and 4-nitrophenyl 2-(2,2,5,5-tetramethyl-4-phenyl-2H-imidazol-1-oxy)-2-methylpropanoate (3a) in the presence of PhSH. The analysis of CIDNP signs of methacrylate protons allows us to conclude on the occurrence of hydrogen atom transfer reaction in geminate radical pair formed in alkoxyamine thermolysis. Thus, CIDNP is a fast and sensitive method to detect the occurrence of intra/intermolecular hydrogen transfer in alkoxyamine thermolysis. Full article
(This article belongs to the Special Issue Advanced Polymer Architectures)
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Open AccessArticle Diasteromeric Effect on the Homolysis of the C–ON Bond in Alkoxyamines: A DFT Investigation of 1,3-Diphenylbutyl-TEMPO
Polymers 2010, 2(3), 353-363; doi:10.3390/polym2030353
Received: 2 September 2010 / Revised: 16 September 2010 / Accepted: 16 September 2010 / Published: 27 September 2010
Cited by 3 | PDF Full-text (575 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The rate constants kd of the homolysis of the C–ON bond in styryl dyads TEMPO-based alkoxyamines have recently been published (Li et al. Macromolecules 2006, 39, 9201). The diastereoisomers exhibited different values which were higher than for the unimer [...] Read more.
The rate constants kd of the homolysis of the C–ON bond in styryl dyads TEMPO-based alkoxyamines have recently been published (Li et al. Macromolecules 2006, 39, 9201). The diastereoisomers exhibited different values which were higher than for the unimer TEMPO-styryl alkoxyamine 1. At a first glance, the localization of the steric strain was not obvious. To decipher this problem, diastereoisomer models 2 (RR/SS) and 3 (RS/SR), as well as the released alkyl radicals, were calculated at the \B3LYP/6-31G(d) level. It was revealed that the increase in kd from 1 to 3 was due to the compression (buttressing effect) of the reactive center by the second styryl moiety. The difference in kd for the diastereoisomer was clearly an activation entropy effect DS because the alkyl fragment of the RS/SR diastereoismer exhibited the same conformation as the released radical whereas the conformation for the RR/SS diastereoisomer was quite different and thus required the rotation of several bonds to reach the correct TS, which cost DS, and thus lowers kd. Full article
(This article belongs to the Special Issue Advanced Polymer Architectures)

Review

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Open AccessReview Photo-Induced Micellization of Block Copolymers
Polymers 2010, 2(4), 623-648; doi:10.3390/polym2040623
Received: 30 September 2010 / Revised: 16 November 2010 / Accepted: 25 November 2010 / Published: 26 November 2010
PDF Full-text (448 KB) | HTML Full-text | XML Full-text
Abstract
We found novel photo-induced micellizations through photolysis, photoelectron transfer, and photo-Claisen rearrangement. The photolysis-induced micellization was attained using poly(4-tert-butoxystyrene)-block-polystyrene diblock copolymer (PBSt-b-PSt). BSt-b-PSt showed no self-assembly in dichloromethane and existed as isolated copolymers. Dynamic [...] Read more.
We found novel photo-induced micellizations through photolysis, photoelectron transfer, and photo-Claisen rearrangement. The photolysis-induced micellization was attained using poly(4-tert-butoxystyrene)-block-polystyrene diblock copolymer (PBSt-b-PSt). BSt-b-PSt showed no self-assembly in dichloromethane and existed as isolated copolymers. Dynamic light scattering demonstrated that the copolymer produced spherical micelles in this solvent due to irradiation with a high-pressure mercury lamp in the presence of photo-acid generators, such as bis(alkylphenyl)iodonium hexafluorophosphate, diphenyliodonium hexafluorophosphate, and triphenylsulfonium triflate. The 1H NMR analysis confirmed that PBSt-b-PSt was converted into poly(4-vinylphenol)-block-PSt by the irradiation, resulting in self-assembly into micelles. The irradiation in the presence of the photo-acid generator also induced the micellization of poly(4-pyridinemethoxymethylstyrene)-block-polystyrene diblock copolymer (PPySt-b-PSt). Micellization occurred by electron transfer from the pyridine to the photo-acid generator in their excited states and provided monodispersed spherical micelles with cores of PPySt blocks. Further, the photo-Claisen rearrangement caused the micellization of poly(4-allyloxystyrene)-block-polystyrene diblock copolymer (PASt-b-PSt). Micellization was promoted in cyclohexane at room temperature without a catalyst. During micellization, the elimination of the allyl groups competitively occurred along with the photorearrangement of the 4-allyloxystyrene units into the 3-allyl-4-hydroxystyrene units. Full article
(This article belongs to the Special Issue Advanced Polymer Architectures)

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