were recrystallized three times from methanol. The free-radical initiator, 1,1
0 -azobis
(isobutyronitrile), AIBN, was purified by recrystallization twice from methanol. A
typical copolymerization involved dissolving the monomers and initiator in
1,4-dioxane, degassing the solution with a dry nitrogen purge for 30 min and running
the reaction for ~24 h at 60
C. The solution was then cooled to room temperature,
and the copolymer product was recovered by precipitation in excess diethyl ether or
hexane, filtering the solids and drying them under vacuum at 50–150
C, depending
on the glass transition temperature of the dry copolymer.
Reactivity ratios have been reported for the copolymerizations of DMA with
FOSA and FOSM [26]. In both cases, the products were statistical copolymers. For
the DMA/FOSA reaction r DMA ¼ 1.126 Æ 0.031 and r FOSA ¼ 1.624 Æ 0.048, which
indicates that the copolymerization was nearly random, i.e., neither monomer has a
much greater propensity for adding one of the two monomers during polymerization.
In contrast, for the DMA/FOSM reaction r DMA ¼ 0.859 Æ 0.026 and
r FOSM ¼ 2.876 Æ 0.083, which indicates that both monomers prefer to react with
FOSM, so that it is more difficult to incorporate the fluoroacrylate in those polymers.
As a result, the DMA-FOSM copolymers are somewhat blocky in sequence distribution. However, no detailed characterization of the sequence distributions of those
or of any of the other amphiphilic copolymers discussed here has been reported.
The composition and characteristics of the amphiphilic copolymers that are
considered in this chapter are summarized in Table 1. The sample notation of the
copolymers or hydrogels includes two or three letters and a number, where the
sample designation letters D, N, H, F, and Fm represent DMA, NIPA HEA, FOSA,
and FOSM, respectively. The number x provides the F or Fm concentration in mol%.
Thus, DF21 indicates a hydrogel based on a DMA/FOSA copolymer with a composition of 79 mol% DMA and 21 mol% FOSA.
Small-angle X-ray scattering (SAXS) data, Fig. 2, show that the DF9 and NF5
copolymers (curves labeled (0)) were microphase-separated, with a morphology
consisting of fluoroacrylate-rich nanodomains dispersed in a continuous matrix of
the hydrophilic polymer. All the other copolymers exhibited similar microphaseseparated morphologies. The formation of the nanodomains arises from the strong
repulsive interactions between the fluoroacrylate and alkyl acrylamide groups that
produce aggregation of the fluorinated groups and the formation of hydrophobic
supramolecular bonds. Additional evidence for the microphase separation of the
DF21 hydrogel is provided by the transmission electron micrograph shown in
Fig. 3a. A comparison of the scattering intensity I(q), where q is the scattering
vector, measured by SAXS and calculated from a fast Fourier transform of the TEM
image shown in Fig. 3b indicates good agreement with the peak position, which
represents the characteristic separation distance between the fluoroacrylate
nanodomains.
168
B. D. Vogt and R. A. Weiss
0 -azobis
(isobutyronitrile), AIBN, was purified by recrystallization twice from methanol. A
typical copolymerization involved dissolving the monomers and initiator in
1,4-dioxane, degassing the solution with a dry nitrogen purge for 30 min and running
the reaction for ~24 h at 60
C. The solution was then cooled to room temperature,
and the copolymer product was recovered by precipitation in excess diethyl ether or
hexane, filtering the solids and drying them under vacuum at 50–150
C, depending
on the glass transition temperature of the dry copolymer.
Reactivity ratios have been reported for the copolymerizations of DMA with
FOSA and FOSM [26]. In both cases, the products were statistical copolymers. For
the DMA/FOSA reaction r DMA ¼ 1.126 Æ 0.031 and r FOSA ¼ 1.624 Æ 0.048, which
indicates that the copolymerization was nearly random, i.e., neither monomer has a
much greater propensity for adding one of the two monomers during polymerization.
In contrast, for the DMA/FOSM reaction r DMA ¼ 0.859 Æ 0.026 and
r FOSM ¼ 2.876 Æ 0.083, which indicates that both monomers prefer to react with
FOSM, so that it is more difficult to incorporate the fluoroacrylate in those polymers.
As a result, the DMA-FOSM copolymers are somewhat blocky in sequence distribution. However, no detailed characterization of the sequence distributions of those
or of any of the other amphiphilic copolymers discussed here has been reported.
The composition and characteristics of the amphiphilic copolymers that are
considered in this chapter are summarized in Table 1. The sample notation of the
copolymers or hydrogels includes two or three letters and a number, where the
sample designation letters D, N, H, F, and Fm represent DMA, NIPA HEA, FOSA,
and FOSM, respectively. The number x provides the F or Fm concentration in mol%.
Thus, DF21 indicates a hydrogel based on a DMA/FOSA copolymer with a composition of 79 mol% DMA and 21 mol% FOSA.
Small-angle X-ray scattering (SAXS) data, Fig. 2, show that the DF9 and NF5
copolymers (curves labeled (0)) were microphase-separated, with a morphology
consisting of fluoroacrylate-rich nanodomains dispersed in a continuous matrix of
the hydrophilic polymer. All the other copolymers exhibited similar microphaseseparated morphologies. The formation of the nanodomains arises from the strong
repulsive interactions between the fluoroacrylate and alkyl acrylamide groups that
produce aggregation of the fluorinated groups and the formation of hydrophobic
supramolecular bonds. Additional evidence for the microphase separation of the
DF21 hydrogel is provided by the transmission electron micrograph shown in
Fig. 3a. A comparison of the scattering intensity I(q), where q is the scattering
vector, measured by SAXS and calculated from a fast Fourier transform of the TEM
image shown in Fig. 3b indicates good agreement with the peak position, which
represents the characteristic separation distance between the fluoroacrylate
nanodomains.
168
B. D. Vogt and R. A. Weiss