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Assessing the stability of molecular bonds in polymer architectures is of critical importance for determining conditions for extrusion, molding, and processing. The topological complexity of branched polymers defines their strain hardening and consequently their melt strength properties, critical parameters for their exploitation in applications. Their molecular architecture is defined by the grafting density and the chain length of the backbone as well as branches. Herein, we introduce a set of polymer combs to establish an understanding of the above parameters on the stability of the popular triazole linkage—often exploited in tethering the branches to the backbone—during thermal treatment and shearing. We exploit a combination of reversible deactivation radical polymerization (RDRP) and copper-catalyzed alkyne–azide cycloaddition (CuAAC) to construct comb polymers (ranging in backbone number-average molecular weight from 39.9 to 55.6 kg mol–1 and a branch length from 3.3 to 18 kg mol–1) with statistically located branches tethered via triazole-based ligation to the backbone. These polymer combs were subsequently thermally challenged at 150 °C (or 180 °C) in an inert atmosphere as well as subjected to shearing at the same temperature. The resulting molecular cleavage processes were analyzed via size exclusion chromatography (SEC) as well as SEC coupled to high-resolution electrospray ionization mass spectrometry (SEC-HR ESI MS) to establish a mechanistic image of branch debonding when it occurs. In addition, by virtue of this approach, we establish an in-depth understanding of how the comb architecture dictates its stability under otherwise unchanged chemical bonding conditions via triazole units, allowing to adopt design criteria for generating thermally and mechanically stable comb structures.

Although controlled/living radical polymerization processes have significantly facilitated the synthesis of well-defined low polydispersity polymers with specific functionalities, a detailed and systematic knowledge of the thermal stability of the products-highly important for most industrial processes-is not available. Linear polystyrene (PS) carrying a trithiocarbonate mid-chain functionality (thus emulating the structure of the Z-group approach via reversible addition-fragmentation chain transfer (RAFT) based macromolecular architectures) with various chain lengths (20 kDa ≤ Mn,SEC ≤ 150 kDa, 1.27 ≤ Crossed D sign = Mw/Mn ≤ 1.72) and chain-end functionality were synthesized via RAFT polymerization. The thermal stability behavior of the polymers was studied at temperatures ranging from 100 to 200 C for up to 504 h (3 weeks). The thermally treated polymers were analyzed via size exclusion chromatography (SEC) to obtain the dependence of the polymer molecular weight distribution on time at a specific temperature under air or inert atmospheres. Cleavage rate coefficients of the mid-chain functional polymers in inert atmosphere were deduced as a function of temperature, resulting in activation parameters for two disparate Mn starting materials (Ea = 115 ± 4 kJ·mol-1, A = 0.85 × 109 ± 1 × 109 s-1, M n,SEC = 21 kDa and Ea = 116 ± 4 kJ·mol -1, A = 6.24 × 109 ± 1 × 109 s-1, Mn,SEC = 102 kDa). Interestingly, the degradation proceeds significantly faster with increasing chain length, an observation possibly associated with entropic effects. The degradation mechanism was explored in detail via SEC-ESI-MS for acrylate based polymers and theoretical calculations suggesting a Chugaev-type cleavage process. Processing of the RAFT polymers via small scale extrusion as well as a rheological assessment at variable temperatures allowed a correlation of the processing conditions with the thermal degradation properties of the polystyrenes and polyacrylates in the melt. © 2013 American

The detailed characterization of poly(styrene)-b-poly(tetrahydrofuran) (pS-b-pTHF) multiblock copolymers (17800 g mol -1≥ M n ≥ 46800 g mol -1) generated via urethane linkages is presented. The synthesis of the block copolymers is enabled via a mechanistic switch of the thiocarbonyl thio end group of a poly(styrene) to dihydroxyl terminated polymers that subsequently react with a diisocyanate terminated polytetrahydrofuran based prepolymer to form multiblock copolymer structures. The characterization of the multiblock copolymers and their substructures includes size exclusion chromatography (SEC), liquid chromatography at critical conditions (LCCC), nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy as well as matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. To obtain even further details of the polymer size and its composition, SEC with triple detection as well as newly developed SEC coupled online to IR spectroscopy was carried out. The quantification of the average block fractions via online SEC-IR (41-61 mol % pTHF) is in very good agreement with the results obtained via NMR spectroscopy (39-66 mol % pTHF). © 2012 American Chemical Society.