Synthesis of exact comb polybutadienes with two and three branches

Abstract

Two methodologies, based on living star polymers and anionic polymerization high vacuum techniques, were used for the synthesis of exact comb polybutadienes (PBds) with two (C‐2 or H‐type) and three identical branches (symmetric, sC‐3, H‐type with an extra identical branch at the middle of the connector and asymmetric, aC‐3, H‐type with the extra identical branch at any other position along the connector). The first methodology involves (a) the selective replacement of the two chlorines of 4‐(dichloromethylsilyl)diphenylethylene (DCMSDPE, key molecule) with 3‐arm star PBds, by titration with identical (C‐2, sC‐3) or different (aC‐3) living 3‐arm star PBds, (b) the addition of s‐BuLi to the double bond of DPE, and (c) the polymerization of butadiene from the newly created anionic site (sC‐3, aC‐3).The second methodology involves the reaction of living stars with dichlorodimethylsilane (C‐2) or the selective replacement of the three chlorines of trichloromethylsilane with star and linear chains (sC‐3, aC‐3). Intermediate and final products were characterized via size exclusion chromatography, low angle laser light scattering and 1H‐NMR. The first methodology does not require fractionation, but in contrast to the second methodology, cannot afford polymers with branches of identical molecular weight. Both methods are general and can be extended to combs with two or three different branches at controllable positions along the backbone. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2597–2607, 2009

Anionic Synthesis and Rheological Characterization of Poly(p‐methylstyrene) Model Comb Architectures with a Defined and Very Low Degree of Long Chain Branching

“…the distance between them is unknown, which can have a significant effect on the rheological properties. Recent attempts for the synthesis of exact combs with equidistant branches [30][31][32] could provide a better insight into the rheology of branched polymers.…”

Combining Living Anionic Polymerization with Branching Reactions in an Iterative Fashion to Design Branched Polymers

“…[122] As illustrated in Scheme 14, a living star PB with an anion at the v-terminus was first prepared in the same manner mentioned above and then coupled with either MeSiCl 3 or 1-(4-dichloromethylsilyl)phenyl-1-phenylethylene. The resulting coupled product having one residual Si-Cl bond was reacted with PBLi to give an exact graft PB having three PB branches.…”

Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution

“…Briefly, the synthetic methodology involves the selective replacement of the three chlorines of trichloromethylsilane with two different 3-arm star {(10 K) 2 87 K and (10 K) 2 48 K} and linear (10 K) chains, using appropriate coupling chemistry. The total weight-average molar mass M w , as measured by low-angle laser light scattering (LALLS) in cyclohexane at 25 C, was reported to be 186.5 kg/mol and the polydispersity index (PDI ¼ M w /M n , with M n the number average molar mass) of the exact comb was found to be 1.08, as determined by size-exclusion chromatography (SEC) in CHCl 3 at 25 C [14]. The microstructure of the exact comb, determined by 1 H NMR in CDCl 3 at 25 C, was 87%-90% 1,4 and 13%-10% 1,2.…”

“…1) was reported in detail in [14]. The term exact comb is chosen to indicate that the polymer has the overall structure of a comb and that the position of the branches on the backbone are exactly known in contrast with random-branched combs for which the positions of the branches on the backbone are random.…”

“…The issue remains however open and the current lack of understanding of the experimental conditions for homogeneous flow or shear banding [6][7][8][9][10] leave the issue of experimental and theoretical analysis of polymeric response in strong nonlinear flows wide open [8,9,11]. (ii) The syntheses of model polymers are mainly performed by anionic polymerization high-vacuum techniques resulting in well-defined molecular structures, which however come in very small quantities (typically <1 g) [12][13][14]. When theoretical models are being evaluated, such well-defined architecturally complex structures are indispensable, even though some disparity in molecular structure is unavoidable albeit not always problematic, and advanced characterization is often called for [15,16].…”