We combine state-of-the-art synthetic, chromatographic, rheological, and modeling techniques in order to address the role of architectural polydispersity in the rheology of model branched polymers. This synergy is shown to be imperative in the field and leads to several important results. Even the best available synthesis is prone to “contamination” by side-products. The exact targeted macromolecular structure can be analyzed experimentally and statistically and eventually fractionated. Temperature-gradient interaction chromatography proves to be an indispensible tool in this process. All techniques are sensitive to the various macromolecular structures, but in different ways. In particular, the presence of side-products may or may not influence the linear rheology, due to competing contributions of the different relaxation processes involved, reflecting different structures at different fractions. Hence, combination of all these techniques is the key for fully decoding the architectural composition of branched polymers and its influence on rheology.

An emerging challenge in polymer physics is the quantitative understanding of the influence of a macromolecular architecture (i.e., branching) on the rheological response of entangled complex polymers. Recent investigations of the rheology of well-defined architecturally complex polymers have determined the composition in the molecular structure and identified the role of side-products in the measured samples. The combination of different characterization techniques, experimental and/or theoretical, represents the current state-of-the-art. Here we review this interdisciplinary approach to molecular rheology of complex polymers, and show the importance of confronting these different tools for ensuring an accurate characterization of a given polymeric sample. We use statistical tools in order to relate the information available from the synthesis protocols of a sample and its experimental molar mass distribution (typically obtained from size exclusion chromatography), and hence obtain precise information about its structural composition, i.e. enhance the existing sensitivity limit. We critically discuss the use of linear rheology as a reliable quantitative characterization tool, along with the recently developed temperature gradient interaction chromatography. The latter, which has emerged as an indispensable characterization tool for branched architectures, offers unprecedented sensitivity in detecting the presence of different molecular structures in a sample. Combining these techniques is imperative in order to quantify the molecular composition of a polymer and its consequences on the macroscopic properties. We validate this approach by means of a new model asymmetric comb polymer which was synthesized anionically. It was thoroughly characterized and its rheology was carefully analyzed. The main result is that the rheological signal reveals fine molecular details, which must be taken into account to fully elucidate the viscoelastic response of entangled branched polymers. It is important to appreciate that, even optimal model systems, i.e., those synthesized with high-vacuum anionic methods, need thorough characterization via a combination of techniques. Besides helping to improve synthetic techniques, this methodology will be significant in fine-tuning mesoscopic tube-based models and addressing outstanding issues such as the quantitative description of the constraint release mechanism.

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

A number of well‐defined complex macromolecular architectures have been synthesized using an efficient macromonomer technique. Styrenic triple‐tailed polybutadiene (PBd) macromonomers (sTMMB), synthesized by selective reaction (titration) of living PBd tails with the SiCl groups of 2‐(dichloromethylsilyl)ethylchloromethylsilyl‐4‐styrene (TCDSS), were polymerized in situ without isolation of sTMMB with s‐BuLi, using high vacuum techniques. Taking advantage of the living character of the anionic polymerization of sTMMB, the following complex macromolecular architectures were prepared: PBd‐g‐(PBd)3 (triple‐combs), PS‐g‐(PBd)3 (triple‐grafts), [PBd‐g‐(PBd)3]3 (3‐arm triple‐comb stars), and triple molecular brushes (tmbPBd) or triple polymacromonomers (tPMMB). Characterization carried out by size exclusion chromatography (SEC), equipped with refractive index and light scattering detectors, indicated that the synthesized novel architectures have a high degree of molecular and compositional homogeneity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3513–3523, 2007

We report upon the characterization of the steady-state shear stresses and first normal stress differences as a function of shear rate using mechanical rheometry (both with a standard cone and plate and with a cone partitioned plate) and optical rheometry (with a flow-birefringence setup) of an entangled solution of asymmetric exact combs. The combs are polybutadienes (1,4-addition) consisting of an H-skeleton with an additional off-center branch on the backbone. We chose to investigate a solution in order to obtain reliable nonlinear shear data in overlapping dynamic regions with the two different techniques. The transient measurements obtained by cone partitioned plate indicated the appearance of overshoots in both the shear stress and the first normal stress difference during start-up shear flow. Interestingly, the overshoots in the start-up normal stress difference started to occur only at rates above the inverse stretch time of the backbone, when the stretch time of the backbone was estimated in analogy with linear chains including the effects of dynamic dilution of the branches but neglecting the effects of branch point friction, in excellent agreement with the situation for linear polymers. Flow-birefringence measurements were performed in a Couette geometry, and the extracted steady-state shear and first normal stress differences were found to agree well with the mechanical data, but were limited to relatively low rates below the inverse stretch time of the backbone. Finally, the steady-state properties were found to be in good agreement with model predictions based on a nonlinear multimode tube model developed for linear polymers when the branches are treated as solvent. V C 2016 The Society of Rheology.