Macromonomers, siloxane

Interestingly, the first example of a macromonomer, long before the names Macro-mer or macromonomer have been coined 94), is a styrene terminated polydimethyl-siloxane synthesized by the reaction of a Grignard derivative of p-ch loro styrene and an co-chlorodimethylsiloxane oligomer 90) as shown in Reaction Scheme IX. Later, these macromonomers have been reacted with different vinyl monomers such as styrene and acrylates, and relatively well defined graft copolymers have been synthesized. 

Surprisingly, after this very first example, there was a 20 year delay in the literature in the appearance of the second report on siloxane macromonomers. However, during this period there have been numerous studies and developments in the vinyl and diene based macromonomers91 -94). The recent approach to the synthesis of siloxane macromonomers involves the lithiumtrimethylsilanolate initiated anionic polymerization of hexamethyltrisiloxane in THF 95,123). The living chain ends were then terminated by using styrene or methacrylate functional chlorosilanes as shown in Reaction Scheme X. 

Optimization of geometry 180-182 Organofunctional siloxane oligomers see Macromonomers... 

In our own research, the functional termination of the living siloxanolate with a chlorosilane functional methacrylate leading to siloxane macromonomers with number average molecular weights from 1000 to 20,000 g/mole has been emphasized. Methacrylic and styrenic monomers were then copolymerized with these macromonomers to produce graft copolymers where the styrenic or acrylic monomers comprise the backbone, and the siloxane chains are pendant as grafts as depicted in Scheme 1. Copolymers were prepared with siloxane contents from 5 to 50 weight percent. 

Investigation of the thermal decomposition of the novel architectures of POSS macromonomers and POSS siloxane co-polymers was reported.598 Novel, thermally stable polysiloxanes with bulky side-chain tris(trimethylsilyl)hexyl, and reactive glycidoxypropyl substituents, were recently described.599... 

Hydrosilylation was also applied to the preparation of thiophene-terminated dimethyl-siloxane macromonomer, which is used for the synthesis of thiophene-dimethylsiloxane graft copolymers by oxidative polymerization281. Polycarbosilanes have been prepared by hydrosilylation-polymerization of l,4-bis(ethenylmethylphenylsilyl)benzene with 1,4-bis(methylphenylsilyl)benzene in various ratios282. 

Poly(methyl methacrylate)-g-poly(dimethylsiloxane) copolymers have been prepared by free radical copolymerizations of acrylate-functional siloxane macromonomers (29) with methyl methacrylate. Siloxane macromonomers (29) of between 1,000 and 20,000 molecular weight were utilized to give a range of copolymers with between 4 and 17 wt% silicone115. 

O Neill, M. L. Yates, M. Z. Johnston, K. P. Smith, C. D. Wilkinson, S. P. Dispersion Polymerization in Supercritical C02 with a Siloxane-Based Macromonomer The Particle Growth Regime. Macromolecules 1998a, 31, 2838-2847. 

We have obtained silsesquioxane-based polymer (HS-Polymer) by using the hydro-silylation reaction of vinyl-functionalized macromonomer (DD-2V) with some SiH-functionalized siloxanes (Scheme 4). 

Fig. 5. Tapping Mode pictures of a thin solvent-cast copolymer film with 20 (left) and 30 (right) wt% of a siloxane macromonomer. Clearly seen is the transition fi om a segregated domain stmeture to an interpenetrating sponge morphology.

Allyllithium was used to polymerize hexamethylcyclotrisiloxane, D3 (eq. 16). Subsequent termination (eq. 17) with chlorotrimethylsilane yielded polydimethyl-siloxane (PDMS) macromonomers carrying allyl end groups (55). 

In the macromonomer approach, polymeric chains (of monomer Mi) end-functionalized with a vinyl group are homopolymerized (with Mi) or copolymerized (with M2) to produce branched (co)polymers. Thus, poly(ethylene glycol) methyl ether methacrylate (CJien et al., 2003) and poly(dimethyl siloxane) methacrylate (Shinoda and Matyjaszewski, 2001) have been homo- or copolymerized to yield graft (co) polymers with the corresponding pendant chain. 

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