Macromonomer synthesis, addition

Scheme 59 Synthesis of macromonomers through addition-fragmentation processes...

Depending on the choice of transfer agent, mono- or di-cnd-functional polymers may be produced. Addition-fragmentation transfer agents such as functional allyl sulfides (Scheme 7.16), benzyl ethers and macromonomers have application in this context (Section 6.2.3).212 216 The synthesis of PEG-block copolymers by making use of PEO functional allyl peroxides (and other transfer agents has been described by Businelli et al. Boutevin et al. have described the telomerization of unsaturated alcohols with mercaptoethanol or dithiols to produce telechelic diols in high yield. 

The third route for the synthesis of PIB macromonomer was based on the addition of p-hydroxy-thiophenol onto the PIB double bonds followed by esterification with methacryloyl chloride (Scheme 14). 

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. 

A similar synthetic route was adopted by Stadler et al. for the synthesis of (PS)(PB)(PMMA) stars [54] as shown in Scheme 21. Living PS chains were end-capped with l-(4-bromomethylphenyl)-l-phenyl ethylene to produce the macromonomer. The capping reaction with DPE was employed in order to reduce the reactivity of the PSLi chain ends thus avoiding several side reactions (trans-metallation, addition to the double bond of the DPE derivative). The next step involved the linking of living PB chains, prepared in THF at -10 °C to the end double bond of the macromonomer. This produces a new active center which was used to initiate the polymerization of MMA leading to the formation of the desired product. 

The ability of these macromonomers to participate in free-radical copolymerization was not tested. They were used28b) for the synthesis of tri- and multiblock copolymers by means of hydrosilylation, i.e. an addition reaction between vinylsilyl groups and the —Si — H functions at the chain end of poly(dimethylsiloxane)mole-cules. 

The use of an unsaturated nucleophile to introduce into the chain end of the macromolecule a double bond has also proved successful for the synthesis of poly-THF macromonomers. The oxolane polymerization is started with any efficient initiator. When the growing chains have reached the desired length, the unsaturated deactivator is added. The reaction between the oxonium sites and the nucleophile should be fast and free of side reactions. Various unsaturated nucleophiles have been employed, e.g. p-vinylphenoxide used by Asami50). The THF polymerization was initiated with triethyloxonium tetrafluoroborate and carried out atO °C. Addition of the nucleophile (obtained by reaction of the phenol with NaH) yields the corresponding macromonomer the structure of which was characterized by various techniques ... 

Depending on the composition of the monomer feed and the polymerization procedure, different types of heterogeneities may become important. For example, in the synthesis of tailor-made polymers telechelics or macromonomers are frequently used. These oligomers or polymers usually contain functional groups at the polymer chain end. Depending on the preparation procedure, they can have a different number of functional end groups, i.e. be mono-, bifunctional, etc. In addition, polymers can have different architectures, i.e. they can be branched (star- or comb-like), and they can be cyclic. 

Our team also realized the synthesis of macromonomers with a polymerizable double bond by using peculiar transfer agents. For instance, telomeriza-tions of (meth)acrylates were performed in the presence of cysteamine, i.e., thiol with an amine group, leading to PMMAs with an amine at the chain end [253]. However, amines enable the Michael addition onto the double bond activated by the carbonyl group. Hence, before performing the telom-erization, the amine group is protected (chlorhydrate salt) and recovered by a simple basification of the solution (Scheme 48). 

The synthesis of numerous macromonomers can be performed by two methods through radical polymerization in the presence of various addition-fragmentation CTAs [292-295] or catalytic CTAs [69,70,296]. 

The general form [56] for CTAs involved in addition-fragmentation for the synthesis of macromonomers is described in Scheme 58. The CTA will undergo a /1-scission to lead to the corresponding macromonomer (Scheme 59). 

Various macromonomers made from an addition-fragmentation process have been employed as precursors of graft copolymers [292,297-300]. But Krstina et al. [301] also characterized the use of such macromonomers in the synthesis of block copolymers. They explained that for macromonomers based on methacrylic monomers (Scheme 60,1), fragmentation of the adduct (Scheme 60, 2) (formed by addition of the methacrylate monomer onto the methacrylate macromonomer) always dominates over reaction with the monomer. This fragmentation leads to block copolymers and graft copolymerization does not occur. 

Addition-fragmentation and CCT are of great interest for the synthesis of macromonomers. Indeed, unlike other radical techniques, they lead to macromonomers in a one-step reaction by directly introducing the chain-end double bond. This double bond is very reactive because it is activated by... 

Finally, Chiefari et al. [315-317] suggested another technique leading to the synthesis of addition-fragmentation-type macromonomers but without the use of any CTA. This method, clean, easy, and economical, involves heating a mixture of acrylate or styrene monomer in an appropriate solvent with an azo or peroxy initiator. High temperatures (typically up to 150 °C) are required. To prove the expected mechanism, the authors studied the poly(alkyl acrylate) reactions in the presence (or not) of monomers and by using different conditions. They showed the reaction does not occur without the monomer. Moreover, an increase of the temperature leads to a better yield and a decrease of the molar mass. Macromonomers have been synthesized by this technique withMn between 103 and 104 gmol... 

After synthesis, the methacryloxy-terminated PDMS macromonomers were purified, and the macromonomers were copolymerized with methyl methacrylate using free-radical, anionic, and group transfer polymerization. Detailed descriptions of the polymerization are provided by DeSimone (1990) and Hellstern (1989). In addition to well-defined graft copolymers, there is... 

Fig. 19 Mechanism and synthesis of photohealable metallosupramolecular polymers, (a) Proposed optical healing of a metallosupramolecular, phase separated network, (b) Synthesis of macromonomer 3 and polymerizatiMi by addition of Zn(NTf2)2. DEAD, diethyl azodicarboxylate. Reproduced with ptamission from 75]...

Figure 10.4 Schematic illustration of the synthesis of brush block copolymers through the sequential addition (upper row) and brush random copolymer through random copolymerization (lower row) of macromonomers [39]. (Reproduced with permission of the American Chemical Society.)...

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