Study of the Molecular Dynamics of Multiarm Star Polymers with a Poly(ethyleneimine) Core and Poly(lactide) Multiarms

Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin

Two different commercial hyperbranched poly(ethyleneimine)s (HBPEI), with molecular weights (MW) of 800 and 25,000 g/mol, and denoted as PEI800 and PEI25000, respectively, as well as the mixtures with a Diglycidyl Ether of Bisphenol-A (DGEBA) epoxy resin, have been studied using thermal analysis techniques (DSC, TGA), dielectric relaxation spectroscopy (DRS), and dynamic mechanical analysis (DMA). Only a single glass transition is observed in these mixtures by DSC. DRS of the HBPEIs shows three dipolar relaxations: γ, β, and α. The average activation energy for the γ-relaxation is similar for all HBPEIs and is associated with the motion of the terminal groups. The β-relaxation has the same average activation energy for both PEI800 and PEI25000; this relaxation is attributed to the mobility of the branches. The α-relaxation peak for all the HBPEIs is an asymmetric peak with a shoulder on the high temperature side. This shoulder suggests the existence of ionic charge trapped in the PEI. For the mixtures, the γ- and β-relaxations follow the behaviour of the epoxy resin alone, indicating that the epoxy resin dominates the molecular mobility. The α-relaxation by DRS is observed only as a shoulder, as a consequence of an overlap with conductivity effects, whereas by DMA, it is a clear peak.

Preparation of Porous Poly(Styrene-Divinylbenzene) Microspheres and Their Modification with Diazoresin for Mix-Mode HPLC Separations

By using the two-step activated swelling method, monodisperse porous poly(styrene-divinylbenzene) (P(S-DVB)) microparticles were successfully synthesized. The influence of porogens, swelling temperatures and crosslinking agents on the porosity of porous microparticles was carefully investigated. Porous P(S-DVB) microparticles were used as a packing material for high performance liquid chromatography (HPLC). Several benzene analogues were effectively separated in a stainless-steel column as short as 75 mm due to the high specific surface area of the porous microparticles. Porous P(S-DVB) microparticles were further sulfonated and subsequently modified with diazoresin (DR) via electrostatic self-assembly and UV (ultraviolet) radiation. After treatment with UV light, the ionic bonding between sulfonated P(S-DVB) and DR was converted into covalent bonding through a unique photochemistry reaction of DR. Depending on the chemical structure of DR and mobile phase composition, the DR-modified P(S-DVB) stationary phase performed different separation mechanisms, including reversed phase (RP) and hydrophilic interactions. Therefore, baseline separations of benzene analogues and organic acids were achieved by using the DR-modified P(S-DVB) particles as packing materials in HPLC. According to the π-π interactional difference between carbon rings of fullerenes and benzene rings of DR, C₆₀ and C₇₀ were also well separated in the HPLC column packed with DR-modified P(S-DVB) particles.