Synthesis and Characterization of Novel Networks with Nano-Engineered Structures:  Cross-Linked Star Homopolymers

Abstract

Group transfer polymerization was used for the one-pot preparation of a network structure comprising cross-linked star homopolymers. The structure contains many dangling chains (constituting the arms of the primary stars), whose number is approximately equal to the number of the elastic chains. 2-(Dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were used as the monomer and cross-linker, respectively. The synthesis involved a four-step sequential addition of monomer/cross-linker/monomer/cross-linker, which produced linear polymer, "arm-first" star polymer, "in-out" star polymer, and cross-linked star polymer network, respectively. The products of the first three steps of the synthesis were characterized in terms of their relative molecular weights by gel permeation chromatography, and in terms of their absolute molecular weights by static light scattering, which indicated that the number of arms in the "arm-first" stars is about 50, whereas that in the "in-out" stars is about 100. Seven networks were prepared in total, covering a range of degrees of polymerization of the primary and the secondary arms. The degrees of swelling of all the networks were measured in water and were found to increase by lowering the pH, a result of the ionization of the tertiary amine group of the monomer repeat unit.

Synthesis and Characterization of Polymer Networks and Star Polymers Containing a Novel, Hydrolyzable Acetal-Based Dimethacrylate Cross-Linker

“…For the star polymers with structure MMA n -b-DMOEM 4 -star, Table 3 shows that the calculated numbers of arms decreased from 41 to 5, as n increased from 10 to 40, respectively, manifesting the effect of steric hindrance of the arm on star polymer formation. The numbers of arms calculated for the above star polymers were at the lower end of the spectrum of values for numbers of arms of "arm-first" star polymers with EGDMA cores also prepared by GTP with reported values of 20, 28 30,29 50, 30 and 15-40. 31 Table 3 shows that as the cross-linker/initiator molar ratio (m) of the MMA 20 -b-DMOEM m -star star polymers increased from 4 to 8, the M w s increased from 32 400 to 1 350 000 g mol -1 , and the calculated number of arms also increased from 8 to 540.…”

Microphase separation under constraints: a molecular thermodynamic theory for polyelectrolytic amphiphilic model networks in water

“…To understand the coefficient of 2/3 in the Symbols. Constants: f 0 , polymer volume fraction in unperturbed state, taken as that upon synthesis; set equal to 0.2 [14,16]; b, number of arms per cross-link, taken to be equal to 20 throughout the manuscript [16,[40][41][42]; c B , Flory-Huggins interaction parameter between water and the hydrophobic units; set equal to 2.0 [16,43]; c A , Flory-Huggins interaction parameter between water and the hydrophilic units; set equal to 0.45 [15,44]. Independent variables: i, degree of ionization of ionizable groups: varied between 0.001 and 1; z, number of units in the hydrophobic block (or one half of the hydrophobic units between crosslinks; each elastic chain has two hydrophobic blocks); varied between 2 and 238; h, number of units in the hydrophilic semi-block (or one half of the hydrophilic units between cross-links; only one half of each hydrophilic block is located within the unit cell); varied between 238 and 2.…”

“…f 0 , the polymer volume fraction in the unperturbed state was taken equal to 0.2, the same as the volume fraction upon synthesis in our experimental system [14,16]. b, the number of arms at the cross-links was fixed to 20, close to the values determined by static light scattering for star polymers prepared by analogous methods [16,[40][41][42]. c B , the FloryHuggins interaction parameter between the hydrophobic block and water, was set equal to 2.0, typical for the value of the propylene oxide-water pair [16,43].…”

A Cleavable Network Based on Crosslinked Star Polymers Containing Acid‐Labile Diacetal Crosslinks: Synthesis, Characterization and Hydrolysis

“…One of the special types of polymer model networks are crosslinked star polymer17–20 model networks (CSPMNs), whose synthesis was developed recently by our research team 21–28. These networks can be prepared by sequential additions of monomer‐crosslinker‐monomer‐crosslinker, using the “living” polymerization technique group transfer polymerization (GTP) 29–33.…”

“…To date, both non‐hydrolyzable21–28 and hydrolyzable24, 25, 27 CSPMNs have been prepared by our group. The non‐hydrolyzable CSPMNs were prepared using the commercially available non‐hydrolyzable crosslinker ethylene glycol dimethacrylate (EGDMA), and the hydrolyzable ones using either hydrolyzable crosslinkers with different ease of degradation that were prepared in our laboratories or combinations of hydrolyzable and non‐hydrolyzable (EGDMA) crosslinkers.…”