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Controlled Polymerization
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
In this section, we lay out the kinetic scheme that describes a living polymerization, and thereby derive the resulting distribution of chain lengths. This scenario is most closely approached in the anionic case, but because it is not limited to anionic polymerizations, we will designate an active polymer of degree of polymerization i by Pi* and its concentration by [Pi*], where * represents the reactive end. A living polymerization is defined as a chain-growth process for which there are no irreversible termination or transfer reactions. There has been some controversy in the literature about the precise criteria for “livingness” [1], and whether they can ever be met in practice, but we will not dwell on this.
Hydrogenated Styrene–Diene Copolymer Viscosity Modifiers
Published in Leslie R. Rudnick, Lubricant Additives, 2017
Isabella Goldmints, Sonia Oberoi
Linear hydrogenated diene copolymers are produced by anionic polymerization with subsequent hydrogenation that results in a saturated carbon–hydrogen backbone with pendant alkyl groups (methyl or ethyl) similar to OCP produced from ethylene/propylene or ethylene/1-butene [11,25,46]. The anionic living polymerization ensures narrow molecular weight distribution of the polymer. The gel permeation chromatograph (GPC) traces of the hydrogenated diene block copolymer and the OCPs produced by metallocene process are shown in Figure 13.2a.
Innovative industrial technology starts with iodine
Published in Tatsuo Kaiho, Iodine Made Simple, 2017
Polymers which have been synthesized by additional polymerization such as polyethylene, PVC (polyvinyl chloride), polyvinyl acetate, polyacrylic ester, etc. are abundantly around us. However, in the process of normal additional polymerization, along with the initiation reaction and growth response, side reactions referred to as transfer and termination reactions occur, resulting in a mixture of polymers of varying molecular weight. However, according to a precise polymerization method called living polymerization, only the initiation reaction and growth response occurs, without any side reactions. Living polymerization shows the following characteristics: (1) molecular weight increases in proportion to the rate of polymerization; (2) molecular weight of the generated polymer can be controlled based on the charged molar ratio or rate of polymerization of the monomer and initiator; (3) polymers of basically the same molecular weight with a narrow molecular weight distribution can be obtained; (4) all generated polymer ends have an initiator section introduced, to allow functional transformation.
Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices
Published in Science and Technology of Advanced Materials, 2022
Copolymerization with polyhydric-hydroxyl-substituted aromatic monomers has recently been studied (Figure 7(b)) [104]. Because polyhydric-hydroxyl-substituted aromatic compounds have large radical chain transfer constants, they exhibit poor addition polymerization ability and do not increase in molecular weight. However, this has been overcome using solvents and initiators. Living polymerization techniques can also be applied, and polymers with well-defined structures have been successfully synthesized [112,113]. There are also methods to create more stable and highly functional surfaces, such as introducing reactive polymers to dopamine by forming an oxidative polymerization film on the base material (Figure 7(c)) [105], or graft polymerization by introducing an initiator for living radical polymerization (Figure 7(d)) [106]. These have potential as methods for modifying the surfaces of medical devices, and further research is expected.
A review on surface modification methods of poly(arylsulfone) membranes for biomedical applications
Published in Journal of Biomaterials Science, Polymer Edition, 2021
Vahid Hoseinpour, Laya Noori, Saba Mahmoodpour, Zahra Shariatinia
Atom transfer radical polymerization (ATRP) is one of efficient techniques concerning grafting polymers, which is accomplished in rather gentle conditions and permits a diversity of vinyl monomers to be polymerized with well-defined shapes in a controllable way. Generally, three kinds of grafting techniques are employed using ATRP for the preparation of grafted copolymers, which are (1) grafting-from, (2) grafting-to, and (3) grafting-through. For the surface modification, the ATRP was used to change the functionality of the sample so that the chloromethylation of poly(aryl sulfone) under gentle circumstances afforded surface benzyl chloride groups as the active initiators. By employing surface-initiated ATRP, hydrophilic polymers were grafted onto the poly(aryl sulfone) samples. Other controlled living polymerization techniques such as iodine transfer polymerization, free radical-mediated polymerization (SFRP), and reversible addition-fragmentation chain transfer (RAFT) polymerization may also be employed to modify the poly(aryl sulfone) membranes [29].
Syntheses of biodegradable and biorenewable polylactides initiated by aluminum complexes bearing porphyrin derivatives by the ring-opening polymerization of lactides
Published in Journal of Biomaterials Science, Polymer Edition, 2019
In summary, we reported a number of new aluminum complexes based on modified porphyrins, which were used as catalysts for the stereoselective polymerization of rac-LA. The microstructure analysis of the polymers catalyzed by these complexes revealed that the porphyrin ligand had a certain ability to affect the tacticity of the polymer, and this ability depended on the hindrance of substituents on the phenyl/pyrrolyl rings moieties. The bigger the steric hindrance, the higher the selectivity. And the substituent on the pyrrolyl group have a greater influence on the bulk of the phenyl ring. It is speculated that the substituent on the pyrrolyl group is closer to the central metal. Kinetic studies showed that the polymerization using aluminum complex as catalyst was a living polymerization with narrow PDI.