Precise Synthesis and Characterization of Fourth-Generation Dendrimer-like Star-Branched Poly(methyl methacrylate)s and Block Copolymers by Iterative Methodology Based on Living Anionic Polymerization

Abstract

International audienceA series of the fourth-generation (4G) dendrimer-like star-branched poly(methyl methacrylate)s, (PMMA)s, with high branch densities have been synthesized by the iterative "arm-first" divergent methodology. It involves a two-reaction sequence in each iterative process: (1) a linking reaction of alpha-functionalized living anionic PMMA with either two or four tert-butyldimethylsilyloxymethylphenyl (SMP) groups with benzyl bromide (BnBr)-chain-end-functionalized PMMA and (2) a transformation reaction of the SMP groups into BnBr functions. Accordingly, the branch segments are introduced by the (1) linking reaction based on termination reaction using premade living anionic polymers. The two-reaction sequence has been repeated four times to build up the 4G dendrimer-like star-branched polymers composed of four branch junctures in three generations and two branch junctures in one generation. Likewise, three block copolymers with the same dense 4G branched architectures have been synthesized by the linking reaction of the 3G brominated PMMA with either of living anionic polymers of tert-butyl methacrylate, (2,2-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate, and 2-vinylpyridine. Unfortunately, however, the synthesis of a highly dense 4G polymer composed of four branch junctures in all generations was not successful possibly due to steric hindrance. The resulting dendrimer-like star-branched (PMMA)s have been analyzed by RALLS, SAXS, and viscosity measurements to obtain their hydrodynamic radii, radii of gyration, intrinsic viscosities, and g' values. The relationship between either of such values and the branched structures, generation, or molecular weight will be discussed. The observation of the largest and most dense 4G polymer by AFM was attempted in order to directly visualize the dendrimer-like star-branched polymer

Synthesis and temperature gradient interaction chromatography of model asymmetric star polymers by the “macromonomer” approach

“…Star polymers with varying numbers of arms have been widely produced and studied [1][2][3][4][5][6][7][8] and branched polymers of increasing complexity and diverse structures have evolved. These include H-shaped polymers [9][10][11][12][13][14][15], comb-shaped polymers [16][17][18][19][20][21][22][23][24][25][26][27][28] and more recently dendritically branched polymers [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. Fundamental to all these studies is the ability of the synthetic polymer chemist to control structural homogeneity and produce branched ...…”

Dendrimer-like star-branched polymers: novel structurally well-defined hyperbranched polymers

“…Furthermore, with the appropriate choice of a-functionalized living PMMA having either two or four SiOMP groups in each iterative process, the structural variations lead to significant changes in the branched architectures of the 3G and 4G dendrimer-like star-branched PMMAs, as shown in Figure 3. 24 A new 1,1-diphenylethylene (DPE) derivative substituted with four SiOMP moieties was needed to prepare the above a-(SiOMP) 4 -functionalized living PMMA. This was readily synthesized in 100% yield by a reaction of 1,1-(3-bromomethylphenyl)ethylene (2) with the functionalized DPE anion derived from 1 and sec-BuLi, as shown in Scheme 6.…”

“…Several attempts were not successful at synthesizing the 4G polymer. 23,24 In this section, a new methodology using a living anionic AB diblock copolymer as a building block is proposed for the synthesis of higher molecular weight and more densely branched DSPs, as illustrated in Scheme 9. 27 Similar to the methodologies introduced in the preceding sections, the new methodology is based on the 'arm-first' divergent approach.…”

“…2,24 The results are summarized in Table 4. These polymers are four branched at the core and two branched at each junction and are abbreviated as A 4 (1G), (A-A 2 ) 4 (2G), (A-A 2 -A 4 ) 4 (3G), (A-A 2 -A 4 -A 8 ) 4 (4G) and (A-A 2 -A 4 -A 8 -A 16 ) 4 (5G).…”

“…24 This polymer possesses four branches at the core, as well as in the 2G and 3G layers, but has three branches on average in the 4G layer. Contrary to the expectation, however, flattened objects with an average square size close to 100 nm and a height of only 1.6 nm were observed as isolated molecules on the AFM image.…”