Polyesters obtained by the catalytic ringopening polymerization of macrolactones in many aspects resemble the properties of polyethylene. However, the molecular weight distribution is intrinsically different and equals the molecular weight distribution observed for a stepgrowth process even though macrolactone ring-opening polymerization follows a chain-growth mechanism. The concurrent occurrence of transesterification reactions leading to the formation of cyclic polymers is responsible for the deviation from the molecular weight distribution characteristic for chain-growth polymerization. To explain and extent on the theoretical principles forming the basis of this peculiar molecular weight distribution, in this work the cyclization process during the polymerization of the 17-membered macrolactone ambrettolide has been analyzed. Liquid chromatography under critical conditions has been applied to semiquantitatively analyze the fractions of cyclic and linear products. In addition, low molecular weight size exclusion chromatography has been used to independently quantify the fractions of the smallest cyclics. Using the combination of these techniques it has been shown that cyclics are present during the whole polymerization process. Furthermore, the thermodynamics of the polymerization reaction were determined. The negligible ΔH ⊖ p = 0.9 ± 1.9 kJ•mol −1 and a positive ΔS ⊖ p = 38.5 ± 6.5 J•mol −1 •K −1 clearly demonstrate the absence of significant ring strain and proofs that the polymerization is driven by entropy. Individual equilibrium concentrations of the cyclics, from monomer to pentamer, were determined and these values were used in combination with the Jacobson and Stockmayer theory to calculate the effective molarity of the cyclic monomer, B = 0.087 M. This value subsequently yields a critical monomer concentration of 0.155 M, for which it was also experimentally determined that polymerizations having a monomer concentration below this value only yield cyclic polymers. Finally, B was used in combination with the monomer and initiator concentration to successfully predict the molecular weight distribution, which shows that real M n 's are far lower and dispersities far higher than predicted from often-applied theories.

Polymeric nanoparticles have become indispensable in modern society with a wide array of applications ranging from waterborne coatings to drug-carrier-delivery systems. While a large range of techniques exist to determine a multitude of properties of these particles, relating physicochemical properties of the particle to the chemical structure of the intrinsic polymers is still challenging. A novel, highly orthogonal separation system based on comprehensive two-dimensional liquid chromatography (LC × LC) has been developed. The system combines hydrodynamic chromatography (HDC) in the first-dimension to separate the particles based on their size, with ultrahigh-performance size-exclusion chromatography (SEC) in the second dimension to separate the constituting polymer molecules according to their hydrodynamic radius for each of 80 to 100 separated fractions. A chip-based mixer is incorporated to transform the sample by dissolving the separated nanoparticles from the first-dimension online in tetrahydrofuran. The polymer bands are then focused using stationary-phase-assisted modulation to enhance sensitivity, and the water from the first-dimension eluent is largely eliminated to allow interaction-free SEC. Using the developed system, the combined two-dimensional distribution of the particle-size and the molecular-size of a mixture of various polystyrene (PS) and polyacrylate (PACR) nanoparticles has been obtained within 60 min.

A range of poly­(ethylene glycol) (PEG)-based polyacrylate networks with two different topological properties were synthesized by photoinitiated free-radical polymerization and analyzed by mechanical, chromatographic, and NMR methods. Comparison between networks with ziplike and pointlike junctions pinpointed the critical role of network topology in generating the so-called “short chain abnormality” in polymer dynamics. In particular, double quantum (DQ) NMR analysis of the ziplike networks identified strong topological constraints on isotropic movement of network chains directly resulting in increased effective functionality of the system. The failure of classical rubber elasticity theory in treating networks with ziplike cross-links is found to arise primarily from non-Gaussian behavior of these network chains caused by the topological constraints.