End-reactive

Fig. 11. The variation of the threshold toughness Gy with S when an end-reactive PDMS chain was coupled into a PDMS network (H.R. Brown, W. Hu, J. Koberstein, unpublished work).

The polymerization of 2-methyl-2-oxazoline is a clean reaction, which is not disturbed by chain transfer and termination. In this polymerization, the propagating species having the structure of an oxazolinium salt is not fragile, which is conveniently utilized for syntheses of block copolymers and end-reactive polymers [28],... 

At present, the most frequently used methods for PEGylation are chemical conjugation between reactive groups in the drug, such as the primary amine of lysine in protein, and end-reactive PEG derivatives, such as the A-hydroxysuccinimide-... 

New Telechelic Polymers and Sequential Copolymers by Polyfunctional Initiator-Transfer Agents (Inifers) End Reactive Polyisobutylenes by Semicontinuous Polymerization... 

The inifer technique is a most convenient route for the preparation of well-defined end-reactive polyisobutylenes (PIB)(1). These materials may be linear or three-arm star telechelics carrying exactly 2.0 or 3.0 end-functions, respectively. The inifer technique yields tert.-chlorine-telechelic product, for example,... 

The purpose of this paper is to outline semicontinuous reaction conditions under which perfectly symmetrical end-reactive materials can be obtained with close to theoretical molecular weight dispers-ities, i.e., M M l.5 for linear and 1.33 for three-arm star products, even at complete monomer conversions. 

Table II. Comparison between Conventional Batch and Semicontinuous Inifer Techniques for the Preparation of End-Reactive Polyisobutylenes...

While it can be expected that a number of physical properties of hyperbranched and dendritic macromolecules will be similar, it should not be assumed that all properties found for dendrimers will apply to hyperbranched macromolecules. This difference has clearly been observed in a number of different areas. As would be expected for a material intermediate between dendrimers and linear polymers, the reactivity of the chain ends is lower for hyperbranched macromolecules than for dendrimers [125]. Dendritic macromolecules would therefore possess a clear advantage in processes, which require maximum chain end reactivity such as novel catalysts. A dramatic difference is also observed when the intrinsic viscosity behavior of hyperbranched macromolecules is compared with regular dendrimers. While dendrimers are found to be the only materials that do not obey the Mark-Houwink-Sakurada relationship, hyperbranched macromolecules are found to follow this relationship, albeit with extremely low a values when compared to linear and branched polymers [126]. 

By controlled thermal degradation of PIB, end-reactive oligomers can be prepared (53). For example, the resulting end-reactive polymers having one or two tertiary chloro groups can be converted to terminal-unsaturated polymers bearing an isopropenyl group by dehydrochlorination... 

For PIB, a method resulting in end-reactive polymers, however, based on chain transfer reactions during polymerization, was addressed as the cationic inifer method (54). 

T. Sawaguchi and M. Seno, Preparation and characterization of end-reactive oligomers by thermal degradation of polyisobutylene, Polymer, 37(16) 3697-3706, August 1996. 

The method adopted for the synthesis of these stars can be considered as a macromonomer method, since end-reactive vinyl groups were used for the linking of the PS arms. There is a possibility that the silyl vinyl anion formed after the addition of the living PS chains reacts with silyl vinyl groups this effect was minimized using short VS blocks and a large excess of PS anions. 

Synthesis of branched and network state polymers. End-reactive polymer [Y. Tezuka, K. Imai, Kohunshi 1991, 40(5), 314-317],... 

The scope of MACROMER has been extended to generally designate the end-reactive oligomers of various monomers. A variety of MACROMERS have been reported. Hydroxy end-reactive oligomers were esterified with methacroyl chloride to yield methacrylate end-reactive MACROMERS 41,43) ... 

Another type of one-end reactive oligomers are oligomeric initiators which have an end group capable of initiating the polymerization of other monomers. Polymeric azo compounds of the type 52 and 53 were prepared by reaction of anionic living polymers with azo-bis-isobutyronitrile 9) ... 

This review covers mainly the scientific literature that has appeared in relevant journals until early 2001 concerning the metal-catalyzed (or atom-transfer) living radical polymerization. The word living employed here simply refers to polymerizations that provide control over the molecular weights, the molecular weight distributions, and the chain end reactivity as do other living polymerizations. Its definition and use criteria, along with the word controlled , are still under discussion and have recently been discussed elsewhere.39 Thus, the discussion on the difference between these words is not to be treated here. 

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