Star-shaped polymers precursor

The synthesis of tailor-made star-shaped polymers can be performed in several ways by means of a plurifunctional organometallic initiator, or by reacting a living precursor polymer with a plurifunctional reagent, to build the centra] body, or by block copolymerization involving a diunsaturated monomer (Scheme 3). 

Figure 8.13 Convergent approach for the synthesis of 3-arm star-shaped polymers under nucleophilic phosphine-catalyzed conditions using RAFT-prepared precursor homopolymers. (Reprinted from Polymer, 50, 14, J.W. Chan, B. Yu, C.E. Hoyle and A.B. Lowe, The nucleophilic, phosphine-catalyzed thiol-ene click reaction and convergent star synthesis with RAFT-prepared homopolymers, 3158-3168, 2009, with permission from Elsevier.)...

A final arm-first method based on the preparation via anionic polymerization of star-shaped polymers will be mentioned. Here the anionic polymerization is only used to prepare a linear (D-fimctional polymer of controlled molar mass and functionality and not for the coupling reaction. In many cases, anionic polymerization is the only way to access these well-defined monofunctional precursor chains. In a second step, these functional polymers were reacted with plurifunctional compounds exhibiting antagonist functions. Some examples are given below. 

Riva R, l azzari W, Billiet L, Du Prez F, Jerome C, Lecomte P (2011) Fheparation of pH-sensitive star-shaped aliphatic poplyesters as precursors of polymersomes. J Polym Sci A Polym Chem 49 1552-1563... 

Star-shaped macromolecules have also been synthesized by using the monofunctional "living" precursor as an Initiator for the polymerization of a small amount of a divinyl monomer. A small crosslinked nodule is formed, which is connected with the p chains that have contributed to Its Initiation. It turns out that fluctuations on the value of p within a sample remain rather small, and consequently the star polymers obtained by this method can also be considered as tailor-made polymers. Recently star molecules with deuterium labeled central nodule have been synthesized according to the... 

Cyclic derivatives of type III include cyclic Mannich bases, such as dihydroben-zoxazines 497, employed as detergents for lubricating oils, - and cyclic urcides 498, precursors of crosslinking agents for fabrics, as well as other cyclic derivatives prepared by conversion of Mannich bases. Macromolecular derivatives of type IV are relatively small in size and have branched (star-shaped) structures they are of considerable importance as, for example, corrosion inhibitors 499, plastics stabilizers 500, - pre-polymers for epoxy-based electrophoretic paints, and polyols in polyurethane synthesis. ... 

A three-armed star telechelic precursor having cyclic ammonium salt groups was self-assembled with a tricarboxylate counteranion under dilution to form a one-to-one complex upon balancing the charges. The subsequent covalent fixation by heating produced a -shaped polymer very effectively (Scheme 18.3a) [14]. 

The combination of a linear bifunctional telechelic precursor with a tricarboxylate counteranion produced a self-assembly that consisted of three polymer units and two counteranions under dilution. Subsequent heat treatment produced a pair of covalently fixed constitutional isomers, namely manacle-shaped and 0-shaped polymers (Scheme 18.3b) [6, 15]. These relevant pairs of polymeric isomers were formed from a self-assembly of two units of a three-armed star telechelic precursor and three units of a dicarboxylate counteranion [16], as well as from the double-metathesis condensation of an H-shaped telechehc polymer precursor having four alkene end groups (Scheme 18.3c) [17]. 

An electrostatic self-assembly of two units of a linear telechelic precursor and a unit of a tetracarboxylate counteranion and subsequent covalent conversion produced a spiro-dicydic 8-shaped polymer effectively (Scheme 18.5a) [6, 9-11]. Alternatively, a four-armed star telechelic precursor having alkene end groups was subjected to a intramolecular metathesis condensation to form an 8-shaped... 

Figure 18.5 MALDI-TOF mass spectra of the precursors and product for the construction of a tricyclic paddle-shaped polymer topology, (a) Cyclic prepolymer having an alkyne functionality (b) Three-armed star prepolymer having azide termini (c) Tricyclic paddle-shaped product.

When 3-pinene was polymerized with BCI3 in the presence of p-dicumylchloride or p-tricumylchloride, polymers with two (Fig. 2.10) and three (Fig. 2.11) chlorinated end groups were obtained as potential precursors for linear and star-shaped multi-block copolymers [37]. 

More recently, the same photodimerization was exploited by Yagci et al, who functionalized linear or three-armed star-shaped poly(propylene oxide)s with two or three terminal benzoxazine coumarin functions, respectively [KIS 14], These products were used as multifunctional macromolecular precursors for the preparation of self-healing pol5mier films. Under irradiation at wavelengths over 300 nm, the formation of cyclobutane junctions from the chain-end chromophores of the macromonomers resulted in cross-linking. Regarding the recovery of mechanical properties, a healing efficiency up to 44% was obtained in the case of a cracked polymer sample studied in this work. 

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