Handbook of Solvents - George Wypych - ChemTech - Ventech!

6.4 Influence of structure on equilibrium swelling 335
#
ρ
kg/m 3
QV (ve/V0)
Toluene
QV (ve/V0)
THF
QV (ve/V0)
MEK
QV (ve/V0)
1,4-Dioxane
QV (ve/V0)
TBP
8 972 2.42 0.35 1.84 0.36 1.01 0.54 2.08 0.34 1.48 0.35
9 979 2.26 0.39 1.72 0.37 0.98 0.54 1.97 0.35 1.62 0.31
10 990 2.00 0.63 0.47 0.99 0.55 2.42 0.29 2.19 0.24
11 991 4.11 0.18 2.79 0.18 3.98 0.17 3.42 0.18 2.54 0.17
12 997 2.42 0.50 1.00 0.32 2.68 0.12 4.06 0.13 4.32 0.08
(ve/V0), kmol/m 3
To understand the restrictions to swelling of SPU caused by the physical network containing
hard domains, the following experiments were carried out. Segmented
polybutadiene urethane urea (PBUU) on the base of oligobutadiene diol urethane
prepolymer with functional NCO-groups (M ≈ 2400), cured with MOCA, and SPU-10
based on prepolymer cured with the mixture of MOCA and oligopropylene triol (M ≈5000)
were used. The chemical network densities of PBUU and SPU were 0.05 and 0.08 kmol/m 3 ,
respectively. The physical network density of initial sample, (ve/V0) d, of PBUU was 0.99
kmol/m 3 and of SPU-10 was 0.43 kmol/m 3 .
Samples of PBUU and SPU-10 were swollen to equilibrium in solvents of different
polarity: dioctyl sebacate (DOS), dioctyl adipate (DOA), dihexyl phthalate (DHP), transformer
oil (TM), nitrile of oleic acid (NOA), dibutyl carbitol formal (DBCF), and tributyl
phosphate (TBP).
The values of equilibrium swelling of elastomers in these solvents, Q1, (ratio of the
solvent mass to the mass of the unswollen sample) are given in Table 6.4.4. After swelling
in a given solvent, samples were swollen in toluene to equilibrium. The obtained data for
T
swelling in toluene, QV , indicate that the physical networks of PBUU and SPU-10 do not
change on swelling in most solvents. Equilibrium swelling in toluene of initial sample and
the sample previously swollen in other solvents is practically identical. Several other observations
were made from swelling experiments, including sequential application of different
solvents. If preliminary disruption of the physical network of PBUU and SPU-10 by TBP
occurs, swelling of these materials in toluene strongly increases. Similarly, samples previously
swollen in TBP have higher equilibrium swelling, Q2, when swollen in other solvents.
The value of Q2 is likely higher than equilibrium swelling Q1 of initial sample (Table 6.4.4).
Q2 for PBUU is closer to the value of equilibrium swelling of a single-phase crosslinked
polybutadiene urethane, PBU, having chemical network density, (ve/V0) x = 0.04 kmol/m 3 .
Thus, the dense physical network of polyurethane essentially limits the extent of equilibrium
swelling in solvents, which do not breakdown the domain structure of a material.