Date of Award
Doctor of Philosophy
Chemical and Biological Engineering
Eric W. Cochran
This dissertation report focuses on block copolymers derived from biomass along with a model methacrylate system to study the gelation behavior during reversible addition-fragmentation chain transfer (RAFT) polymerization due to the multi-functionality of bio-derived monomers. There are two bio-based block copolymer systems disclosed in this report. One is poly(styrene-blockacrylated epoxidized soybean oil) (PS-PAESO) derived from soybean oil. Thanks to the architecture of triglycerides, PS-PAESO block copolymers are found to resemble star block copolymers at low degree of polymerization (DP) and bottlebrush block copolymers at high DP. The long aliphatic chains of AESO act as the star arms in the former case while they become the side chain brushes in the latter case. At high DP, these PAESO brushes stiffen the primary chain and cause crowding. The self assembly of PS-PAESO block copolymers thus have unusual microdomain expansion without paying a severe entropy penalty. The domain spacing of the microstructures
can be in the submicron scale. The investigation of PS-PAESO self assembly is conducted by small angle x-ray scattering (SAXS), transmission electron microscopy (TEM), and rheology. Understanding the structure-property relationship of PS-PAESO block copolymers reveals that the incorporation of bio-based materials in polymers has the potential for novel applications for their
Another bio-based block copolymers covered in this dissertation is the glycerol-based block copolymers. Glycerol, the byproduct of biodiesel production is cheap and abundant. Developing new applications out from glycerol is therefore appealing. In this dissertation we used glycerol derivatives, acrylated glycerol and solketal acrylate to develop pressure sensitive adhesives (PSAs). Two (meth)acrylate-based block copolymers, poly(methyl methacrylate-block-acrylated glycerol) (MMAAG) and poly(isobornyl acrylate-block-solketal acrylate-block-isobornyl acrylate) (IBASA) were synthesized via RAFT polymerization. The formulation of PSAs includes only plasticizer and the elastomers without any tackifier thanks to elastomers self tack. The structureproperty relationship of these formulations was studied by rheology and peel tests. PSAs were conditioned at different humidity, adherends, and peel rates to test their peel adhesion. IBASA formulations showed comparable performance as commercial 3M ScotchTM magic tape after plasticized by benzoate esters. This result indicates that substituting petroleum-based PSAs with biobased PSAs are feasible.
Since monomers of block copolymer systems revealed in this report tend to crosslink owing their multi-functional features, understanding their gelation behavior during synthesis becomes important. A model system composed of methyl methacrylate and ethylene glycol dimethacrylate was introduced to study the gelation behavior at high DP. A new parameter, the crosslinking
tendency (CT) was introduced to predict the gelation conversion of controlled radical polymerization systems including RAFT and atom transfer radical polymerization. The CT analysis takes the system concentration into account which gives a better prediction than the conventional FloryStockmayer gelation theory. Through CT correlation, the reaction condition of intramolecular and intermolecular crosslinking can be distinguished. That is, the gelation suppression due to intramolecular crosslinking is accounted for in CT analysis. CT quantitatively describes many RAFT and ATRP systems implying that factors including monomer architectures and radical controlling mechanisms may not be as vital in gelation suppression.
Lin, Fang-Yi, "Gelation mechanism, synthesis, characterization, and applications of bio-based and model thermoplastic elastomers via RAFT polymerization" (2019). Graduate Theses and Dissertations. 17500.