טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLivshin Shulamit
SubjectHigh Internal Phase Emulsion Polymers Based on Monomers
with Long Side Chains: Structure and Properties
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Michael Silverstein
Full Thesis textFull thesis text - English Version


Abstract

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.