About morphology in ethylene-propylene(-diene) copolymers-based latexes

Delphine L. Tillier, Jan Meuldijk, Günther W.H. Höhne, Peter M. Frederik, Oren Regev, Cor E. Koning

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

Coatings and engineering plastics often require high impact strength. This property can be achieved with tougheners. For the present paper, core-shell impact modifiers were synthesized using ethylene-propylene copolymers (EPM), ethylene-propylene-diene copolymers (EPDM) or a mixture of both types (EP(D)M) as core material, as well as poly(methyl methacrylate) (PMMA) as shell material. EP(D)M-based polymers were dispersed in water using an Ultra-Turrax ® and a high pressure homogenizer. The prepared artificial latexes were used, either without further treatment or after crosslinking, as seed latexes in the emulsion polymerization of methyl methacrylate (MMA). The free radical seeded emulsion polymerization of MMA was investigated in the presence of an oil-soluble initiator, i.e. cumene hydroperoxide (CHP), combined with a redox system, i.e. sodium formaldehyde sulfoxylate hydrate (SFS), disodium salt of ethylenediamine tetra-acetic acid (EDTA), iron (II) sulfate heptahydrate (FeSO4). This initiation system promotes polymerization of MMA near the surface of the seed particles, partially suppressing homogeneous secondary nucleation and polymerization in the aqueous phase. Kinetic and thermodynamic considerations were used to predict the particle morphology. The monomer type, the monomer-to-rubber ratio, the monomer feed type, and crosslinking of the seed latex particles were investigated, to optimize the polymerization kinetics and the properties of the resulting dispersions. The particle morphology was determined by cryo-transmission electron microscopy (cryo-TEM). Monomer-flooded conditions led to the formation of inverted core-shell particles, whereas starved-feed MMA or MMA/styrene mixtures gave rise to partially engulfed structures, i.e. snowman-like. Crosslinking of the EP(D)M seed particles was found to be required to provide the desired core-shell structures. Finally, the obtained core-shell structured particles were used to toughen a PMMA matrix. The tensile properties of the modified PMMA matrix were investigated. The micro-morphology of modified PMMA was studied by scanning electron microscopy (SEM). Tensile tests as well as TEM and SEM analyses demonstrated that the main mechanism of deformation operating in the EP(D)M-toughened PMMA matrix is shear yielding, accompanied by debonding and cavitation processes.

Original languageEnglish
Pages (from-to)7094-7108
Number of pages15
JournalPolymer
Volume46
Issue number18
DOIs
StatePublished - 23 Aug 2005

Keywords

  • Impact modifier
  • Morphology
  • Seeded emulsion polymerization of methyl methacrylate (MMA)

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