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RISS 인기검색어
- 검색키워드
- 저자 : Lentzakis, Helen (검색결과 2 건)
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Constraint Release Mechanisms for H-Polymers Moving in Linear Matrices of Varying Molar Masses
Lentzakis, Helen,Costanzo, Salvatore,Vlassopoulos, Dimitris,Colby, Ralph H.,Read, Daniel Jon,Lee, Hyojoon,Chang, Taihyun,van Ruymbeke, Evelyne American Chemical Society 2019 Macromolecules Vol.52 No.8
<P>We investigate the influence of the environment on the relaxation dynamics of well-defined H-polymers diluted in a matrix of linear chains. The molar mass of the linear chain matrix is systematically varied and the relaxation dynamics of the H-polymer is probed by means of linear viscoelastic measurements, with the aim to understand its altered motion in different blends, compared to its pure melt state. Our results indicate that short unentangled linear chains accelerate the relaxation of both the branches and the backbone of the H-polymers by acting as an effective solvent. On the other hand, the relaxation of the H-polymer in an entangled matrix is slowed-down, with the degree of retardation depending on the entanglement number of the linear chains. We show that this retardation can be quantified by considering that the H-polymers are moving in a dilated tube at the rhythm of the motion of the linear matrix.</P> [FIG OMISSION]</BR>
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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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