Jl. Mateo et al., Photoinitiated polymerization of methacrylic monomers in a polystyrene matrix: Kinetic, mechanistic, and structural aspects, J POL SC PC, 39(12), 2001, pp. 2049-2057
Citations number
23
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY
The kinetics and mechanism of the photoinitiated polymerization of tetrafun
ctional and difunctional methacrylic monomers [1,6-hexanediol dimethacrylat
e (HDDMA) and 2-ethylhexyl methacrylate (EHMA)] in a polystyrene (PS) matri
x were studied. The aggregation state, vitreous or rubbery, of the monomer/
matrix system and the intermolecular strength of attraction in the monomer/
matrix and growing macro-radical/matrix systems are the principal factors i
nfluencing the kinetics and mechanism. For the PS/HDDMA system, where a rel
atively high intermolecular force of attraction between monomer and matrix
and between growing macroradical and matrix occurs, a reaction-diffusion me
chanism takes place at low monomer concentrations (< 30 - 40%) from the beg
inning of the polymerization. For the PS/EKMA system, which presents low in
termolecular attraction between monomer and matrix and between growing macr
oradical and matrix, the reaction-diffusion termination is not clear, and a
combination of reaction-diffusion and diffusion-controlled mechanisms expl
ains better the polymerization for monomer concentrations below 30-40%. For
both systems, for which a change from a vitreous state to a rubbery state
occurs when the monomer concentration changes from 10 to 20%, the intrinsic
reactivity and k(p)/k(t)(1/2) ratio (where k(p) is the propagation kinetic
constant and k(t) is the termination kinetic constant) increase as a resul
t of a greater mobility of the monomer in the matrix (a greater k(p), value
). The PS matrix participates in the polymerization process through the for
mation of benzylic radical, which is bonded to some extent by radical-radic
al coupling with the growing methacrylic radica, producing grafting on the
PS matrix. (C) 2001 John Wiley & Sons, Inc.