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Extrusion Foam of Polylactic Acid Using Stereocomplex Crystals
Published in S. T. Lee, Polymeric Foams, 2022
Daniele Tammaro, Fresia Alvarado Chacon, Gerald Schennink, Claudio Walker, Ulla Trommsdorff
Branched PLA architectures also show a distinctive crystallisation behaviour. Kim et al. discuss the lowering of the glass transition temperature for star-shaped polymers when compared to the linear counterparts. This is explained by the higher mobility of the polymer chains in star polymers due to the larger free volume. However, the poor folding property of the star polymers hinders crystallisation due to the limited mobility which hampers the transportation of chains to the crystal. This all results in slightly lower crystallinity and lower melting temperatures 179°C vs 182°C. In another study, the authors concluded that branching has no significant effect on the segmental mobility or glass transition temperature of PLA but disturbed the crystallisation during heating [55]. Here it was also confirmed that the crystalline form is not affected by the presence of branching. These studies have been performed with lab synthetised branched Poly(L-lactide) and compare star shape with linear counterparts. The effect of number of arms and their length on crystallisation was not studied. At this moment there is no commercially available branched PLA.
Structural Ordering in Polymer Solutions
Published in Kunio Esumi, Polymer Interfaces and Emulsions, 2020
The star-branched, or radial, polymers have the structure of linked-together linear polymers with a low-molecular-weight core. Generally, the star polymer has smaller hydrodynamic dimensions than that of a linear polymer with an identical molecular weight. The interest in star polymers arises not only from the fact that they are model branched polymers but also from their enhanced segment densities. Zimm and Stockmayer were the first to study the conformation of star-shaped polymers [1]. Recently, Daoud and Cotton [2] have studied the conformation and dimension of a star polymer consisting of three regions: a central core, a shell with semidilute density in which the arms have unperturbed chain conformation, and an outer shell in which the arms of the star assume a self-avoiding conformation. Stars with multiarms (the critical number of arms is estimated to be of order 102) are expected to form a crystalline array near the overlap threshold (C*) [3].
Star-Shaped Amphiphilic Polymers as Soluble Carriers for Drug Delivery
Published in Vladimir Torchilin, Handbook of Materials for Nanomedicine, 2020
Karolina A. Kosakowska, Scott M. Grayson
By the most general classification, star-shaped polymers consist of multiple linear polymer chains—i.e., “arms”—radiating from a central core. A minimum of 3 arms is required to achieve star-branching architecture, though the quantity of arms can number into the hundreds. The number of arms, as well as their relative length and density, represent the key structural parameters which enable the physical properties of the star polymers to be modulated. Even so, one feature common among all star-shaped polymer variants (and all non-linear polymers for that matter) is a more compact hydrodynamic volume and lower solution viscosity when compared to linear polymers of the same molecular weight and composition [11, 12].
Role of each part of cyanobiphenyl-containing polymers in porous-film preparation by using the breath-figure method
Published in Liquid Crystals, 2020
Yumiko Naka, Lisa Nagashima, Hiromu Takayama, Khoa Van Le, Takeo Sasaki
Monomers, 11-[4-(4-Cyanobiphenyl)oxy]undecyl methacrylate (11CB), 11-[(1,1ʹ-biphenyl)-4-yloxy]undecyl methacrylate (11B), 4-cyanobiphenyl methacrylate (0CB), and undecyl methacrylate (11), were synthesised using Williamson ether reaction and Schötten–Baumann reaction [18,19]. Methyl methacrylate (1) purchased from Kanto Chemical Co., Inc. was washed with an aqueous solution of sodium hydroxide (5%) to remove the stabiliser (hydroquinone). Monomer 1 was then dehydrated by stirring in anhydrous magnesium sulphate overnight, and then distilled under vacuum. Six-arm star polymers were prepared using compounds with 6-initiation sites (Aldrich) by atom-transfer radical polymerisation (ATRP) (Figure 1). The synthesised six-arm star homopolymers, P11CB, P1, P11B, P0CB, and P11, are composed of 11CB, 1, 11B, 0CB, and 11, respectively. Random copolymers, such as (P(0CB0.5–110.5)) comprising 0CB and 11 in the ratio of 1:1 and (P(11CBx–111-x)) containing 11CB and 11 in any ratio, were prepared to investigate the effects of alkyl chains in the polymers. In ATRP, the initiator, monomer, Cu(I)Br, 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA), and dried tetrahydrofuran (THF) were mixed in an ampule equipped with a reflux condenser, which was degassed and filled with nitrogen. In the synthesis of P1, no solvent was used as an exception. The monomers in the ampule were polymerised in an oil bath preheated to 80°C. After polymerisation, the catalyst was removed using a silica-gel column (spherical neutral, particle size 63–210 μm, Kanto Chemical Co., Inc.) considering chloroform as an eluent. The obtained polymers in chloroform were precipitated in a large excess of methanol and finally dried under vacuum. The product was white solids.