|M.Sc Student||Shulamit Livshin|
|Subject||High Internal Phase Emulsion Polymers Based on Monomers|
with Long Side Chains: Structure and Properties
|Department||Department of Materials Science and Engineering||Supervisor||Full Professor Silverstein Michael|
|Full Thesis text|
A high internal phase emulsion (HIPE) is an emulsion in which the dispersed phase occupies more than 74 % of the volume. PolyHIPE are cross-linked porous polymers synthesized by polymerizing a monomer and crosslinking comonomer in the continuous phase of a HIPE. PolyHIPE have an open-cell structure and a low bulk density. In polymers comprising long n-alkyl side-chains a part of the side-chain is able to crystallize beyond a minimal side-chain length. Incorporation of monomers bearing long n-alkyl sidechains could be used to produce crystallinity within a polyHIPE. The objectives of this research were to synthesize crystallizable polyHIPE based on nalkyl acrylates and methacrylates and to characterize and describe the effects of the chemical structure of the backbone, side-chain length, degree of crosslinking, chemical structure and flexibility of the cross-linking comonomer, and locus of initiation on the structure and properties.
PolyHIPE were synthesized using lauryl acrylate and methacrylate (n=12) and stearyl acrylate and methacrylate (n=18) using divinylbenzene as the cross-linking comonomer. Two series of polyHIPE with varying comonomer contents were synthesized based on stearyl acrylate (A18) with two different of cross-linking comonomers, divinylbenzene and ethylene glycol dimethacrylate (EGDMA). The influence of the locus of initiation on polyHIPE morphology and properties was investigated by using either a water-soluble initiator or an oil-soluble initiator. In addition, three types of reference materials were synthesized: homopolymers, copolymers synthesized using bulk polymerization, and model non-cross-linked copolymers using styrene as an equivalent comonomer.
The polyHIPE densities were between 0.10-0.18 g/cm3. The divinylbenzene cross-linked polyHIPE exhibited highly interconnected open-pore structures. However, crosslinking with the more hydrophilic EGDMA destabilized the HIPE producing structures whose closed-cell nature increased with increasing EGDMA content. Organic-phase initiation yielded a highly interconnected porous structure. All the polyHIPE exhibited melting endotherms but only the A18-based polyHIPE had melting temperatures above room temperature. The melting temperatures and crystallinities increased with side-chain length. Melting temperatures and crystallinities were higher for the acrylates than for the methacrylates and they decreased with increasing comonomer content. The EGDMA crosslinked polyHIPE exhibited higher melting temperatures and higher crystallinities than the divinylbenzene crosslinked polyHIPE. Organic-phase initiation produced polyHIPE with lower melting temperatures and crystallinities compared to interfaced initiation. The mechanical properties of the polyHIPE cross-linked with divinylbenzene depended both on the degree of crystallinity and on the degree of cross-linking. PolyHIPE with relatively closed-cell structures exhibited higher moduli as expected from the analysis of the elastic mechanical behavior of open-cell and closed-cell foams.