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A matter of phis: The size of macromolecules is determined by the "universal calibration" based on the Flory-Fox equation (see scheme). The effect of the segmental density of real branched systems on this equation is investigated. To study this effect, accurately prepared polymers with discrete molecular properties were characterized in detail and precisely evaluated.

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The synthesis and characterization of aromatic−aliphatic polyesters with tailored degree of branching (DB), i.e. hyperbranched (hb), gradually branched, and linear polymers, are described. The dilute solution properties of polymers resulting from two different synthetic approaches are compared. The ABB*/AB2 approach leads to homopolymers with different DB based on the same AB2 monomer, 4,4-bis(4′-hydroxyphenyl)pentanoic acid, employing the protection of one phenolic group (B*) in the AB2 monomer followed by copolymerization with AB2 monomer at different molar ratios. Because of their identical chemical origin, well-tunable DB, comparable molar masses, an absence of aggregation in common solvents, and high refractive index increments, they are suitable as model systems in branching characterization. Their solution properties are compared to those of polymers obtained by the AB/AB2 approach. In order to study the influence of the end-groups on thermal and solution polymer properties, all terminal OH groups were modified with tert-butyldimethylsilyl chloride (SY-Cl). A different dependence of the thermal properties on branching was found for OH- and SY-terminated samples produced by the ABB*/AB2 approach. While the difference in the T g values between linear and hb structures was found to be 16 °C for SY-terminated samples, nearly identical values were obtained for OH-terminated linear and hb polyesters due to strong effect of hydrogen bond formation.

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The retention behavior of aromatic polyesters possessing different degrees of branching was studied in gradient liquid adsorption chromatography (gradient chromatography), liquid adsorption chromatography (LAC), and liquid chromatography at the critical conditions (LCCC). The chromatographic experiments revealed that retention of linear and branched polyesters is influenced by the degree of branching as well as the molar mass of the polymer samples in all enthalpy-dominated chromatographic modes such as LAC, LCCC, and gradient chromatography. At critical conditions of the linear polymer, the corresponding branched structures elute in the adsorption mode, indicating a stronger adsorptive interaction between the stationary phase and the branched polymer molecule. In gradient chromatography, polymer samples with higher degrees of branching are retarded longer on the stationary phase. A clear dependence between the degree of branching and the elution volume was found in both chromatographic modes, which clearly demonstrates a pronounced effect of topology on retention behavior. The results suggest the use of gradient chromatography as a first separation step for a two-dimensional characterization method of branched polymers in order to separate by both degree of branching and molar mass.

The effect of the degree of branching (DB) of a hyperbranched polyester (GBPEX) added as a modifier of new thermosets obtained from diglycidylether of bisphenol A has been studied. The use of ytterbium triflate as cationic initiator allows the hydroxyl chain‐ends in the GBPEX to become covalently linked to the matrix through the monomer activated propagation mechanism. The curing process has been studied by DSC and rheology. The DB of the modifier does not affect appreciably the thermal stability and the chemical reworkability but shrinkage exhibits a significant reduction on increasing the DB. Thermomechanical characteristics are also improved with increasing the DB of the modifier.magnified image

SANS measurements in THF-d 6 were carried out at the D11 instrument at ILL, Grenoble with two aliphatic aromatic hyper-branched (hb) samples with nearly the same degree of polymerization (DP ≈ 90), containing hydroxyl (OH) and silyl-ether (SY) terminal groups. The choice of a large region of momentum transfer q permitted probing the global shape and the local structure. The scattering of both samples showed pronounced concentration dependence. Using Zimm's well-known scattering equation the true size and shape of the macromolecules at finite concentration were derived. Agreement of the data and curves at finite concentration with those at c = 0 was obtained. The scattering curves were analyzed on the basis of the Sinha et al.'s refinement of fractals. Complete agreement with the experimental scattering curves was achieved. The apparent anomalous behavior at very large qvalues was shown to arise from the monomer and segmental contributions. Molecular dynamics (MD) simulation of an uniform hb sample (DP 35) revealed the monomer contribution in agreement with the experiment. The discrepancy of the experimental curve at small q-values is shown to arise from the broad molar mass distribution. When Flory's molar mass distribution was combined with the MD simulation data, the experimental results were described well.