The Effect of Chain Length Distribution on Elastomeric Properties. III. Non-Random Networks Prepared with a Partially Vinyl-Selective Bis(Alkylperoxy)Diisopropylbenzene

1980 ◽  
Vol 53 (4) ◽  
pp. 988-993 ◽  
Author(s):  
M. A. Llorente ◽  
J. E. Mark
Keyword(s):  
Reaction Time ◽  
Benzoyl Peroxide ◽  
Crosslinking Agent ◽  
Length Distribution ◽  
Random Networks ◽  
Silicon Hydride ◽  
Chain Length Distribution ◽  
Γ Radiation ◽  
Close Proximity ◽  
Effective Degree

Abstract The reactant α,α′-bis(t-butylperoxy)diisopropylbenzene was used to crosslink PDMS polymers containing vinyl side groups with varying degrees of segregation along the chains. On the basis of the elongation moduli of the resulting networks, this reactant was found to be moderately selective for vinyl groups, falling approximately midway between the essentially non-selective benzoyl peroxide and γ-radiation and a highly selective silicon hydride crosslinking agent. As expected, a significant amount of the selectivity was lost at longer reaction time. Placing crosslinks in close proximity decreases the effective degree of crosslinking, and may affect the swelling response more than the modulus in elongation.

THE DEGRADATION OF POLYSTYRENE: II. THE SYNTHESIS AND DEGRADATION OF POLYSTYRENE POSSESSING THE KUHN–SCHULZ CHAIN LENGTH DISTRIBUTION

1950 ◽  
Vol 28b (7) ◽  
pp. 416-428
Keyword(s):  
Molecular Weight ◽  
Benzoyl Peroxide ◽  
Chain Length ◽  
Average Molecular Weight ◽  
Length Distribution ◽  
Chain Scission ◽  
Limited Range ◽  
Number Average Molecular Weight ◽  
Chain Length Distribution ◽  
Synthesis And Degradation

By polymerizing styrene in emulsion it was possible to synthesize polystyrenes of known number average molecular weight, the chain length distributions of which corresponded closely to the Kuhn–Schulz relation Ny = N0py−1(1 − p)2. This enabled a relation between intrinsic viscosity and number average molecular weight to be established for polystyrenes with chain length distributions of this functional form. Assuming this form of chain length distribution to remain unaltered on degradation, it was possible to estimate the average number of scission points per structural unit from viscosimetric measurements. The extent of thermal scission of polystyrene after one week at 144 °C. was shown to be negligible while benzoyl peroxide caused appreciable chain scission at 80 °C. and 100 °C. The number of scission points estimated from viscosimetric measurements was directly proportional to the mass of benzoyl peroxide added to the system, and the scission appeared to be essentially random over the limited range investigated.

THE DEGRADATION OF POLYSTYRENE: III. THE SCISSION OF POLYSTYLENE BY A VARIETY OF AGENTS AND THE ROLE PLAYED BY THE SOLVENT IN THIS PROCESS

1950 ◽  
Vol 28b (7) ◽  
pp. 429-440 ◽  
Author(s):  
D. S. Montgomery ◽  
C. A. Winkler
Keyword(s):  
Thermal Degradation ◽  
Linear Function ◽  
Benzoyl Peroxide ◽  
Chain Length ◽  
Intrinsic Viscosity ◽  
Structural Unit ◽  
Length Distribution ◽  
Relative Viscosity ◽  
Chain Length Distribution

For a number of polystyrenes possessing the Kuhn–Schulz chain length distribution but of different mean chain length, the relation was established between the intrinsic viscosity and the corresponding relative viscosity of a 16% solution in toluene, to facilitate the study of the scission process under conditions similar to those employed by Mesrobian and Tobolsky. It was found that this relation failed to distinguish between those scission points introduced during polymerization and those due to the subsequent degrading action of benzoyl peroxide and air. Assuming polystyrene prepared in a similar manner to that described by Mesrobian and Tobolsky possessed the Kuhn–Schulz chain length distribution it was possible to show that the average number of scission points per structural unit was a linear function of the mass of benzoyl peroxide added to the system and the number of hours exposure to light. The thermal degradation of polystyrene was studied both in the presence and the absence of toluene, and the role of the solvent in the scission of polystyrene by benzoyl peroxide and air was investigated.

Direct Observation of Chain Lengths and Conformations in Oligofluorene Distributions from Controlled Polymerization by Double Electron-Electron Resonance

2019 ◽  
Author(s):  
Dennis Bücker ◽  
Annika Sickinger ◽  
Julian D. Ruiz Perez ◽  
Manuel Oestringer ◽  
Stefan Mecking ◽  
...  
Keyword(s):  
Chain Length ◽  
Length Distribution ◽  
Catalyst System ◽  
Chain Conformation ◽  
Controlled Polymerization ◽  
Chain Length Distribution ◽  
Electron Resonance ◽  
Double Electron ◽  
The Individual ◽  
Double Electron Electron Resonance

Synthetic polymers are mixtures of different length chains, and their chain length and chain conformation is often experimentally characterized by ensemble averages. We demonstrate that Double-Electron-Electron-Resonance (DEER) spectroscopy can reveal the chain length distribution, and chain conformation and flexibility of the individual n-mers in oligo-(9,9-dioctylfluorene) from controlled Suzuki-Miyaura Coupling Polymerization (cSMCP). The required spin-labeled chain ends were introduced efficiently via a TEMPO-substituted initiator and chain terminating agent, respectively, with an in situ catalyst system. Individual precise chain length oligomers as reference materials were obtained by a stepwise approach. Chain length distribution, chain conformation and flexibility can also be accessed within poly(fluorene) nanoparticles.

Natural variation in rice starch synthase IIa affects enzyme and starch properties

2004 ◽  
Vol 31 (7) ◽  
pp. 671 ◽  
Author(s):  
Takayuki Umemoto ◽  
Noriaki Aoki ◽  
Hongxuan Lin ◽  
Yasunori Nakamura ◽  
Naoyoshi Inouchi ◽  
...  
Keyword(s):  
Amino Acid ◽  
Natural Variation ◽  
Oryza Sativa L ◽  
Length Distribution ◽  
Starch Synthase ◽  
Rice Starch ◽  
Nucleotide Polymorphisms ◽  
Cultivated Rice ◽  
Chain Length Distribution ◽  
Starch Properties

The natural variation in starch synthase IIa (SSIIa) of rice (Oryza sativa L.) was characterised using near-isogenic lines (NILs). SSIIa is a candidate for the alk gene regulating the alkali disintegration of rice grains, since both genes are genetically mapped at the same position on chromosome 6 and related to starch properties. In this study, we report that the alkali-susceptible cultivar Nipponbare lacked SSIIa activity in endosperm. However, the activity was detected with NILs having the alk allele of alkali-tolerant Kasalath. SSIIa protein was present even in Nipponbare endosperm, but it was not associated with starch granules at the milky stage of endosperm. Three single-nucleotide polymorphisms (SNPs) predicting amino acid substitutions existed between the cDNA sequences of SSIIa of Nipponbare and Kasalath were genotyped with 65 rice cultivars and four wild relatives of cultivated rice. The results obtained explain the potential importance of two of the amino acid residues for starch association of rice SSIIa. An analysis of the chain-length distribution of β-limit dextrin of amylopectin showed that without SSIIa activity, the relative number of A-chains (the short chains without branches) increased and that of B1-chains (the short chains with branches) decreased. This suggests that, given the SSIIa defect, short A-chains could not reach a sufficient length for branching enzymes to act on them to produce B1-chains.

scholarly journals Miniaturized Analysis of Amylopectin Chain Length Distribution by Fluorescence-Assisted Capillary Electrophoresis (FACE) down to Single Starch Granules

2021 ◽  
Author(s):  
amandine pruvost ◽  
stanislas helle ◽  
nicolas szydlowski ◽  
Christian ROLANDO
Keyword(s):  
Capillary Electrophoresis ◽  
Chain Length ◽  
Solid Phase ◽  
Potato Starch ◽  
Relative Proportion ◽  
Length Distribution ◽  
Fluorescence Analysis ◽  
Starch Granules ◽  
Chain Length Distribution ◽  
Single Granule

In the present work, we developed a miniaturized method for determining amylopectin chain length distribution (CLD) by fluorescence-assisted capillary electrophoresis (FACE). The method relies on single granule entrapping into capillaries followed by direct starch gelatinization and amylopectin debranching on carbograph-based solid phase extraction (SPE) cartridges. Sample desalting on HypersepTM tips following APTS-labelling and the use of nanovials allowed for the fluorescence analysis of weakly diluted samples. Consequently, method sensitivity was improved by 500-fold which is compatible with the analysis of single potato starch granules. The method was implemented to determine CLD profiles of single starch granules ranging from 50 to 100 µm in diameter. In these experiments, the relative proportion of starch glucans of up to 30 degrees of polymerization (DP) could be quantified.

scholarly journals Production of very-high-amylose cassava by post-transcriptional silencing of branching enzyme genes

2018 ◽  
Author(s):  
Wenzhi Zhou ◽  
Shanshan Zhao ◽  
Shutao He ◽  
Qiuxiang Ma ◽  
Xinlu Lu ◽  
...  
Keyword(s):  
Amylose Content ◽  
Length Distribution ◽  
Constitutive Expression ◽  
Raw Material ◽  
Distribution Analysis ◽  
Starch Granules ◽  
Storage Roots ◽  
Chain Length Distribution ◽  
Transgenic Cassava ◽  
High Amylose

AbstractHigh amylose starch, a desired raw material in the starch industry, can be produced by plants deficient in the function of branching enzymes (BEs). Here we report the production of transgenic cassava plants with starches containing up to 50% amylose due to the constitutive expression of hair-pin dsRNAs targeting the BE1 or BE2 genes. A significant decrease in BE transcripts was confirmed in these transgenic plants by quantitative real-time RT-PCR. The absence of BE1 protein in the BE1-RNAi plant lines (BE1i) and a dramatically lower level of BE2 protein in the BE2-RNAi plant lines (BE2i) were further confirmed by Western blot assays. All transgenic plant lines were grown up in the field, but with reduced biomass production of the above-ground parts and storage roots compared to wild type (WT). Considerably high amylose content in the storage roots of BE2i plant lines was achieved, though not in BE1i plant lines. Storage starch granules of BE1i and BE2i plants had similar morphology as WT, however, the size of BE1i starch granules were bigger than that of WT. Comparisons of amylograms and thermograms of all three sources of storage starches revealed dramatic changes to the pasting properties and a higher melting temperature for BE2i starches. Glucan chain length distribution analysis showed a slight increase in chains of DP>36 in BE1i lines and a dramatic increase in glucan chains between DP 10-20 and DP>40 in BE2i lines, compared to that of WT starch. Furthermore, BE2i starches displayed a B-type X-ray diffraction pattern instead of the A-type pattern found in BE1i and WT starches. Therefore, cassava BE1 and BE2 function differently in storage root starch biosynthesis; silencing of cassava BE1 or BE2 caused various changes to starch physico-chemical properties and amylopectin structure. We also report that remarkably high amylose content in cassava starch has been first obtained in transgenic cassava by silencing of BE2 expression, thus showing a high potential for future industrial utilization.

Chain Length Distribution of Amylopectins of Double- and Triple-Mutants Containing the Waxy Gene in the Inbred Oh43 Maize Background

1987 ◽  
Vol 39 (9) ◽  
pp. 295-298 ◽  
Author(s):  
H. Fuwa ◽  
D. V. Glover ◽  
K. Miyaura ◽  
N. Inouchi ◽  
Y. Konishi ◽  
...  
Keyword(s):  
Chain Length ◽  
Length Distribution ◽  
Waxy Gene ◽  
Chain Length Distribution
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