Synthesis and Characterization of End-Linked Amphiphilic Copolymer Conetworks Based on a Novel Bifunctional Cleavable Chain Transfer Agent

Synthesis of New Type Polymers by Quasi-Living Atom Transfer Radical Polymerization

Thanks to the polymer revolution of the 20th century, plastics are now part of our everyday lives. We use plastics as naturally as if they had always been an integral part of our lives. However, in the recent past, we were still predominantly using wood, metal, and glass objects, which were replaced by plastic products at an explosive rate. In many cases, this replacement has resulted in products with better physical, chemical, or biological properties. The changeover was too rapid, and the consequences were not recognized in time. This is evidenced by the huge scale of plastic pollution worldwide today. It is therefore in the interests of the future of both humans and animals that we must pay particular attention to the direct and indirect environmental impact of plastics introduced in animal husbandry. Starting from the tetrafunctional initiator produced as the first step of my work, poly(n-butyll acrylate) star polymers of different molecular weights were synthesized by atom transfer radical polymerization, using the so-called “core first” method. The bromine chain end of the produced star polymers was replaced by an azide group using a substitution reaction. Propalgyl telechelic PEGs were synthesized as a result of lattice end modification of poly(ethylene glycol) with different molecular weights. The azidated star polymers were connected with propalgyl telechelic PEGs using Huisgen’s “click” chemical process, and as a result of the “click” connection, amphiphilic polymer networks with several different structures were obtained.

Effect of Polyethylene Glycol on Properties and Drug Encapsulation-Release Performance of Biodegradable/Cytocompatible Agarose-Polyethylene Glycol-Polycaprolactone Amphiphilic Co-Network Gels

We synthesized agarose-polycaprolactone (Agr-PCL) bicomponent and Agr-polyethylene glycol-PCL (Agr-PEG-PCL) tricomponent amphiphilic co-network (APCN) gels by the sequential nucleophilic substitution reaction between amine-functionalized Agr and activated halide terminated PCL or PCL-b-PEG-b-PCL copolymer for the sustained and localized delivery of hydrophilic and hydrophobic drugs. The biodegradability of the APCNs was confirmed using lipase and by hydrolytic degradation. These APCN gels displayed good cytocompatibility and blood compatibility. Importantly, these APCN gels exhibited remarkably high drug loading capacity coupled with sustained and triggered release of both hydrophilic and hydrophobic drugs. PEG in the APCNs lowered the degree of phase separation and enhanced the mechanical property of the APCN gels. The drug loading capacity and the release kinetics were also strongly influenced by the presence of PEG, the nature of release medium, and the nature of the drug. Particularly, PEG in the APCN gels significantly enhanced the 5-fluorouracil loading capacity and lowered its release rate and burst release. Release kinetics of highly water-soluble gemcitabine hydrochloride and hydrophobic prednisolone acetate depended on the extent of water swelling of the APCN gels. Cytocompatibility/blood compatibility and pH and enzyme-triggered degradation together with sustained release of drugs show great promise for the use of these APCN gels in localized drug delivery and tissue engineering applications.

Disulfide bonds-containing amphiphilic conetworks with tunable reductive-cleavage

The disulfide bonds-containing amphiphilic conetworks were presented with tunable reduction-cleavage via click reaction of azide terminated poly(ε-caprolactone) and alkyne-terminated polyethylene glycol.

Self-Sealing and Puncture Resistant Breathable Membranes for Water-Evaporation Applications

Breathable and waterproof membranes that self-seal damaged areas are prepared by modifying a poly(ether ester) membrane with an amphiphilic polymer co-network. The latter swells in water and the gel closes punctures. Damaged composite membranes remain water tight up to pressures of at least 1.6 bar. This material is useful for applications where water-vapor permeability, self-sealing properties, and waterproofness are desired, as demonstrated for a medical cooling device.

Degradable/cytocompatible and pH responsive amphiphilic conetwork gels based on agarose-graft copolymers and polycaprolactone

Amphiphilic conetwork gels based on graft copolymers of agarose and polycaprolactone exhibited desirable cytocompatibility/blood compatibility and pH responsive release of hydrophilic and hydrophobic drugs, and may be suitable for biomedical applications.

A polyester–polystyrene hybrid connected by dynamic covalent bonds prepared via radical polymerization of styrene in a “RAFT gel”

We cross-linked the polyester chains with 1,1-thiocarbonyldiimidazole to form a reversible addition–fragmentation chain-transfer (RAFT) gel, in which the trithiocarbonate moiety acted as a cross-linker. The “RAFT gel” was then swollen in vinyl monomers and styrene was radically polymerized within the gel, in which the polyester and polystyrene segments were miscible at the segment level.

Amphiphilic conetworks and gels physically cross-linked via stereocomplexation of polylactide

Amphiphilic conetworks (APCNs), consisting of hydrophilic poly[poly(ethylene glycol) methyl ester acrylate] (PPEGMEA) and hydrophobic stereocomplex of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), were prepared by free radical copolymerization of PEGMEA with acrylate macromonomer of the PLA stereocomplex. The effects of stereocomplexation and the amount of PLA stereocomplex on the rheology properties of APCNs were investigated. The results indicated that the APCNs was stronger in the presence of stereocomplexation compared with the that of nonstereocomplex system, and the strength of the APCNs increased with the increasing of the amount of PLA stereocomplex. The storage modulus of the APCNs could be easily tuned from 1200 to 4300 Pa by incorporating 2-10% of stereocomplex PLA. On the other hand, the swelling behavior of APCNs decreased with the increasing content of hydrophobic PLA cross-linker.

Self-consistent field approach for cross-linked copolymer materials

A generalized self-consistent field approach for polymer networks with a fixed topology is developed. It is shown that the theory reproduces the localization of cross-links, which is characteristic for gels. The theory is then used to study the order-disorder transition in regular networks of end-linked diblock copolymers. Compared to diblock copolymer melts, the transition is shifted towards lower values of the incompatibility parameter χ (the Flory-Huggins parameter). Moreover, the transition becomes strongly first order already at the mean-field level. If stress is applied, the transition is further shifted and finally vanishes in a critical point.

Investigations on diffusion limitations of biocatalyzed reactions in amphiphilic polymer conetworks in organic solvents

The use of enzymes as biocatalysts in organic media is an important issue in modern white biotechnology. However, their low activity and stability in those media often limits their full-scale application. Amphiphilic polymer conetworks (APCNs) have been shown to greatly activate entrapped enzymes in organic solvents. Since these nanostructured materials are not porous, the bioactivity of the conetworks is strongly limited by diffusion of substrate and product. The present manuscript describes two different APCNs as nanostructured microparticles, which showed greatly increased activities of entrapped enzymes compared to those of the already activating membranes and larger particles. We demonstrated this on the example of APCN particles based on PHEA-l-PDMS loaded with α-Chymotrypsin, which resulted in an up to 28,000-fold higher activity of the enzyme compared to the enzyme powder. Furthermore, lipase from Rhizomucor miehei entrapped in particles based on PHEA-l-PEtOx was tested in n-heptane, chloroform, and substrate. Specific activities in smaller particles were 10- to 100-fold higher in comparison to the native enzyme. The carrier activity of PHEA-l-PEtOx microparticles was tenfold higher with some 25-50-fold lower enzyme content compared to a commercial product.