Amphiphilic Polymer Conetwork Gel Films Based on Tetra-Poly(ethylene Glycol) and Tetra-Poly(ε-Caprolactone)

Abstract

The preparation and investigation of gel films from a model amphiphilic polymer conetwork (ACN) grant a deeper control and understanding of the structure–property relationship in the bulk phase and at the interface of materials with promising applications. In order to allow the simultaneous transport of hydrophilic and hydrophobic substances, polymeric networks with finely distributed hydrophilic and hydrophobic components are very suitable. When designing new soft materials such as coatings, in addition to the structure in the bulk phase, the structure at the interface plays a critical role. In this study, two alternating tetra-arm star polymers poly(ε-caprolactone) (tetra-PCL-Ox) and amino-terminated poly(ethylene glycol) (tetra-PEG-NH2) form an amphiphilic polymer conetwork. The correlation between different synthesis strategies for gel films of this ACN model system and their resulting properties will be described. Through various spin coating techniques, control over film thickness and roughness is achievable and highlights differences to macroscopic gel samples. Atomic force microscopy (AFM) measurements reveal the effect of solvents of different polarities on the swelling ability and surface structure. This correlates with AFM investigations of the mechanical properties on ACN gel films, demonstrating a strong effect on the resulting elastic modulus E, depending on the presence or absence of a good solvent during synthesis. Furthermore, a higher E modulus is obtained in the presence of the selective solvent water, compared to the non-selective solvent toluene. This observation is explained through selective swelling of the tetra-arm star polymers displaying a different hydrophobicity.

Amphiphilic Model Networks Based on PEG and PCL Tetra-arm Star Polymers with Complementary Reactivity

“…Hagmann et al previously analyzed the surface structure of thin films of these ACN gels using atomic force microscopy and compared this with their bulk structure. 44 Our main concern is to show how the reaction conditions influence the course of the reaction and thus the microstructure and homogeneity of ACNs. In particular, we study the influence of the reaction conditions (solvent, concen-tration, and temperature) on the cross-linking process and the occurrence of associated network defects.…”

“…The moderate rate of the cross-linking reaction allows the precursor star polymers to mix and diffuse and, moreover, the monitoring of this process by NMR spectroscopy and oscillatory shear rheology. Hagmann et al previously analyzed the surface structure of thin films of these ACN gels using atomic force microscopy and compared this with their bulk structure …”

Model Amphiphilic Polymer Conetworks in the Bulk: Dissipative Particle Dynamics Simulations of Their Self-Assembly and Mechanical Properties

“…However, the presence of the cross-links or/and the nonideal structure of the APCN building blocks lead to the formation of frustrated/distorted morphologies, with much less regularity than the morphologies observed with (non-cross-linked) linear block copolymers . Thus, the APCN electron micrographs or atomic force micrographs usually exhibit morphologies with spheroidal domains, and the corresponding small-angle X-ray scattering (SAXS) or small-angle neutron scattering (SANS) profiles present a single broad peak. − ,,− However, recent synthetic developments, involving sparser and more regular cross-linking, e.g., end-linking, as well as the utilization of near-ideal building blocks (well-defined linear or star polymers), resulted in APCN nanophase-separated morphologies of high regularity, e.g., wavy lamellae, and SAXS and SANS profiles with a number of higher order peaks. , The experimental recording of these more regular morphologies in self-assembled APCNs renders their modeling/simulation more worthwhile. In particular, current state-of-the-art simulations and self-consistent field theories (SCFT) very successfully reproduce the experimentally observed morphologies of linear diblock melts and are, consequently, expected to accurately predict the morphologies formed by APCNs comprising well-defined building blocks .…”

Amphiphilic tetra-PCL-b-PEG star block copolymers using benzoxazinone-based linking groups

“…Our interest in tetra-PCL-b-PEG micelles stems from investigations on model amphiphilic co-networks based on tetra-arm PEG and PCL star polymers. [23][24][25] Here, soluble amphiphilic star block copolymers containing the same building blocks are needed to structure the material prior to network formation.…”