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RISS 인기검색어
- 검색키워드
- 저자 : Snijkers, F. (검색결과 3 건)
- 무료
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Architectural Dispersity in Model Branched Polymers: Analysis and Rheological Consequences
Snijkers, Frank,van Ruymbeke, Evelyne,Kim, Paul,Lee, Hyojoon,Nikopoulou, Anastasia,Chang, Taihyun,Hadjichristidis, Nikos,Pathak, Jai,Vlassopoulos, Dimitris American Chemical Society 2011 Macromolecules Vol.44 No.21
<P>We combine state-of-the-art synthetic, chromatographic, rheological, and modeling techniques in order to address the role of architectural polydispersity in the rheology of model branched polymers. This synergy is shown to be imperative in the field and leads to several important results. Even the best available synthesis is prone to “contamination” by side-products. The exact targeted macromolecular structure can be analyzed experimentally and statistically and eventually fractionated. Temperature-gradient interaction chromatography proves to be an indispensible tool in this process. All techniques are sensitive to the various macromolecular structures, but in different ways. In particular, the presence of side-products may or may not influence the linear rheology, due to competing contributions of the different relaxation processes involved, reflecting different structures at different fractions. Hence, combination of all these techniques is the key for fully decoding the architectural composition of branched polymers and its influence on rheology.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2011/mamobx.2011.44.issue-21/ma2013805/production/images/medium/ma-2011-013805_0019.gif'></P>
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Synthesis and Linear Viscoelasticity of Polystyrene Stars with a Polyketone Core
Polgar, L. M.,Lentzakis, H.,Collias, D.,Snijkers, F.,Lee, S.,Chang, T.,Sakellariou, G.,Wever, D. A. Z.,Toncelli, C.,Broekhuis, A. A.,Picchioni, F.,Gotsis, A. D.,Vlassopoulos, D. American Chemical Society 2015 Macromolecules Vol.48 No.18
<P>We report on a novel synthetic route to synthesize relatively large quantities of polystyrene (PS) star polymers with targeted arm functionality and molar mass and their rheological properties in the molten state. The synthetic route involves grafting styrene monomers onto a modified (aliphatic, alternating) polyketone backbone with a specific number of initiating grafting sites using controlled atom transfer radical polymerization (ATRP). Several polyketone precursors were used. This resulted in a large array of star polystyrenes with nonspherical cores and varying average arm length and number of arms. Their linear viscoelasticity was investigated and discussed in the context of the known response of anionically synthesized stars. Using a powerful characterization toolbox, including state-of-the-art interaction chromatography, rheometry, and tube modeling via the branch-on-branch (BoB) algorithm, we have assessed the viscoelasticity of these star polymers quantitatively. In particular, we have demonstrated a variability in molecular structure, which differs substantially from their anionically synthesized counterparts. Hence, whereas this new family of star polymers is not recommended for fundamental studies of polymer physics such as the molecular origin of relaxation mechanisms without prior extensive fractionation, they could be used in studies of mixtures as well as industrially relevant processing operations that require large amounts of polymeric stars.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2015/mamobx.2015.48.issue-18/acs.macromol.5b01434/production/images/medium/ma-2015-01434h_0012.gif'></P>
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van Ruymbeke, E.,Lee, H.,Chang, T.,Nikopoulou, A.,Hadjichristidis, N.,Snijkers, F.,Vlassopoulos, D. The Royal Society of Chemistry 2014 SOFT MATTER Vol.10 No.27
<P>An emerging challenge in polymer physics is the quantitative understanding of the influence of a macromolecular architecture (<I>i.e.</I>, branching) on the rheological response of entangled complex polymers. Recent investigations of the rheology of well-defined architecturally complex polymers have determined the composition in the molecular structure and identified the role of side-products in the measured samples. The combination of different characterization techniques, experimental and/or theoretical, represents the current state-of-the-art. Here we review this interdisciplinary approach to molecular rheology of complex polymers, and show the importance of confronting these different tools for ensuring an accurate characterization of a given polymeric sample. We use statistical tools in order to relate the information available from the synthesis protocols of a sample and its experimental molar mass distribution (typically obtained from size exclusion chromatography), and hence obtain precise information about its structural composition, <I>i.e.</I> enhance the existing sensitivity limit. We critically discuss the use of linear rheology as a reliable quantitative characterization tool, along with the recently developed temperature gradient interaction chromatography. The latter, which has emerged as an indispensable characterization tool for branched architectures, offers unprecedented sensitivity in detecting the presence of different molecular structures in a sample. Combining these techniques is imperative in order to quantify the molecular composition of a polymer and its consequences on the macroscopic properties. We validate this approach by means of a new model asymmetric comb polymer which was synthesized anionically. It was thoroughly characterized and its rheology was carefully analyzed. The main result is that the rheological signal reveals fine molecular details, which must be taken into account to fully elucidate the viscoelastic response of entangled branched polymers. It is important to appreciate that, even optimal model systems, <I>i.e.</I>, those synthesized with high-vacuum anionic methods, need thorough characterization <I>via</I> a combination of techniques. Besides helping to improve synthetic techniques, this methodology will be significant in fine-tuning mesoscopic tube-based models and addressing outstanding issues such as the quantitative description of the constraint release mechanism.</P> <P>Graphic Abstract</P><P>By coupling and confronting results obtained with different characterization techniques, a detailed description of the sample architectural dispersity is obtained. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4sm00105b'> </P>
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