Positronium annihilation in amine‐cured epoxy polymers

Abstract

synopsisPoeitronium annihilation spectroscopy (PAS) has been used to study the microstructural properties of aminecured epoxy polymers. We have determined the free-volume "hole" sizes in these polymers by comparing the observed ortho-positronium lifetimes with the known lifetime-free volume correlation for low-molecular-weight systems. The free volumes for four epoxies with different crosslink densities are found to vary significantly over the temperature range between -7V and 250%. The free-volume holes for these polymers are found to range from 0.0% to 0.220 rims. Two important transition temperatures were found: one corresponds to the glass transition temperature T, determined by differential scanning calorimetry (DSC), and the other occurs about 80-130T below T,. The subT, transition temperature is interpreted tentatively as being where hole size reaches dimensions adequate for poeitronium trapping or else the onset temperature for local mode or sidechain motions. These two transition temperatures plus two additional onset temperatures are found to be correlated with crosslink densities calculated from stoichiometry.

Free volume dependence of polymer viscosity

“…The total free volume fraction, f PALS , has been expressed as (Jean et al 1986;Wang et al 1990;Liu and Jean 1995):…”

“…One of the exceptions is a study of cured epoxy resin at different of T and P (below and above T g ) (Jean et al 1986;Wang et al 1990;Liu and Jean 1995). The published graphs reporting variations of t 3 and I 3 with T and P were digitalized and from the extracted data V 3 , and f PALS (Eq.…”

Positron annihilation lifetime studies of changes in free volume on cross-linking cis-polyisoprene, high-vinyl polybutadiene, and their miscible blends

“…(1) to o-Ps annihilation data for molecular solids of known pore size. In addition to the o-Ps lifetime, 3 , the total fraction of positrons that form o-Ps, I 3 , is also determined by PALS. The probability of o-Ps formation is assumed to be proportional to the number of regions of low electron density in which o-Ps can locate.…”

“…The lifetime of o-Ps is sensitive to its local molecular environment and in particular increases with the size of the free-volume region in which it is localized. A semiempirical correlation between the free-volume hole radius, R, and the o-Ps lifetime, 3 , has been established 7 :…”

Degradation of polymer coating systems studied by positron annihilation spectroscopy. II. Correlation with free radical formation

“…For example, smaller percentages of Ps formation are seen in a series of epoxy polymers at higher crosslink densities. 21 The decrease of free volume and holes due to the increased crosslinking by UV-irradiation can also result in a decrease in the S parameter. The initial formation of free radicals (measured by ESR) leads to permanent defects, which are detected by current positron annihilation method.…”