Star-shaped architecture polymerization

In this study, lactide was polymerized by Sn-oct in the presence of polyfunctional alcohols such as glycerol or pentaerythritol. The resulting PLA had multi-armed chains to yield a star-shaped architecture. The microstructure, thermal properties, and degradation behaviour were studied to compare the effect of the different architecture, linear PLA with starshaped one. In addition, it was very beneficial to study the effect of various chain end groups on the thermal and hydrolytic stability of this multi-armed PLA. Therefore, OH terminal groups of PLA were converted into Cl, NH2 or COOH groups. 

A change of architecture is another route that enables diversification of the properties of aliphatic polyesters. This review will focus on star-shaped, graft, macrocyclic, and crosslinked aliphatic polyesters. It must be noted that the ROP of lactones has been combined with several other polymerization mechanisms such as ROP of other heterocyclic monomers, ionic polymerization, ROMP, and radical polymerization. Nevertheless, this review will not cover these examples and will focus on polymers exclusively made up of poly(lactone)s. 

Copolymerization of TMC with e-CL or L-lactide has been reported to be useful for modifications of the polymer properties [144,218,280,283]. The molecular architecture presents a powerful tool for obtaining new materials with interesting properties. For instance, a star-shaped rubbery poly(TMC-co-CL) was synthesized. d,L-LA/GA polymerization was then initiated from the hydroxy terminated arms to yield a poly(TMC-co-CL)-block-PLGA [284]. 

Living polymerization processes pave the way to the macromolecular engineering, because the reactivity that persists at the chain ends allows (i) a variety of reactive groups to be attached at that position, thus (semi-)telechelic polymers to be synthesized, (ii) the polymerization of a second type of monomer to be resumed with formation of block copolymers, (iii) star-shaped (co)polymers to be prepared by addition of the living chains onto a multifunctional compound. A combination of these strategies with the use of multifunctional initiators andtor macromonomers can increase further the range of polymer architectures and properties. 

Figure 8 Formation of ID hydrogen-bonded polymeric strnctnre in [Cu2(L56)2(H20)2]-2(CH3)2C0, 77, and 3D coordination polymeric network architecture with star-shaped channels in [Cn2(L56)2], 78, in a single-pot crystallization of 76 indicating the effect of solvents.

Six J-L, Gnanou Y (1995) From star-shaped to dendritic poly(ethylene oxide)s toward increasingly branched architectures by anionic polymerization. Macromol Symp 95 137-150... 

With the significant progress in the living polymerization techniques , in the design of multifunctional initiators and the control in coupling reactions a large variety of block copolymers with sophisticated architecture became available such as cyclic, H and star shaped, multiarm and pahn-tree or dumbell structures, dendritic blocks linked to linear blocks, etc. 

Living polymerizations afford a variety of options to control polymer size, dispersity, composition, and shape (architecture), as well as allowing specific and defined placement of useful chemical functionalities within these macromolecules. Common strategies for attaching chemical functionalities include the use of functional initiators and post-polymerization reactions. In addition, the absence of chain termination allows access to complex polymeric architectures, which may include block copolymers, multiblock polymers, star polymers, and bottlebrush copolymers. 

This result proves that well-defined structures with low degree of heterogeneity of the multiarm star-shaped polymers can be synthesized. Moreover, the method reported herein can also provide a synthetic pathway for the introduction of block copolymers synthesized via different polymerization routes (RAFT, ROP, etc.) onto the anthracene-end-functionalized multiarm star-shaped polymers. Although the Diels-Alder cycloaddition between anthracene and maleimide derivatives has proven to provide good results in the formation of complex architectures, the major drawback of this method remains the requirement of high temperature and relatively long reaction times. 

Reversible deactivated radical polymerization processes, which have been referred to as living/controlled radical polymerizations, allow for producing polymeric materials with controlled molecular masses, low dispersities, and complex maaomolecular architectures, such as block and comb-like copolymers as well as star-shaped (co)polymers. In addition to nitroxide-mediated polymerization (NMP) ° and atom-transfer radical polymerization (ATRP), ° reversible addition fragmentation chain-transfer (RAFT) polymerization is an attractive new method. " ... 

TEMPO-terminated PS and subsequent deprotection. Interestingly, when DVB was used as a cross-linking agent upon chain extension with glycomonomer G7 or G8, core-glycoconjugated star-shaped PS architectures were obtained. From a difiinctional TEMPO-based alkoxyamine, polymerization of glycomonomer G7 at 125 °C for 5h followed by chain extension afforded the corresponding triblock... 

Several others methods also exhibiting a living character are now being used for the construction of branched macromolecular architectures. One of them, group transfer polymerization, is briefly mentioned in the text. Special efforts are being made presently to apply living radical polymerization to the synthesis of star-shaped polymers. The performance of the different methods has been compared recently [94]. 

Multifunctional initiators based on, for example, cyclotriphosphazine [106], silesquioxane [107], porphyrin [108] and bipyridine metal complex [109, 110] cores were also successfully used for the living cationic ring-opening (co)polymerization of 2-oxazolines, resulting in star-shaped (co)polymers. The use of polymeric initiators also allowed the construction of well-defined complex macro molecular architectures, such as triblock copolymers with a non-poly(2-oxazo-line) middle block that is used to initiate the 2-oxazoHne polymerization after functionalization with tosylate end-groups [111-113]. In addition, poly(2-oxazoline) graft copolymers can be prepared by the inihation of the CROP from, for example, poly(chloromethylstyrene) [114, 115] or tosylated cellulose [116]. 

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