Syndiotactic- and heterotactic-specific radical polymerizations of N-n-propyl-α-fluoroacrylamide and phase-transition behaviors of aqueous solutions of poly(N-n-propyl-α-fluoroacrylamide)

Article abstract of DOI:10.1002/pola.26024

Radical polymerization of N-n-propyl-α-fluoroacrylamide (NNPFAAm) was investigated in several solvents at low temperatures in the presence or absence of Lewis bases, Lewis acids, alkyl alcohols, silyl alcohols, or fluorinated alcohols. Different effects o

Full text of DOI:10.1002/pola.26024

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Syndiotactic- and Heterotactic-Specific Radical Polymerizations of N-n-
Propyl-a-fluoroacrylamide and Phase-Transition Behaviors of Aqueous
Solutions of Poly(N-n-propyl-a-fluoroacrylamide)
Tomohiro Hirano, Takahiro Furutani, Miyuki Oshimura, Koichi Ute
Department of Chemical Science and Technology, Institute of Technology and Science, The University of Tokushima,
Minamijosanjima 2-1, Tokushima 770-8506, Japan
Correspondence to: T. Hirano (E-mail: hirano@chem.tokushima-u.ac.jp)
Received 13 February 2012; accepted 25 February 2012; published online
DOI: 10.1002/pola.26024
ABSTRACT: Radical polymerization of N-n-propyl-a-fluoroacryla-
mide (NNPFAAm) was investigated in several solvents at low
temperatures in the presence or absence of Lewis bases, Lewis
acids, alkyl alcohols, silyl alcohols, or fluorinated alcohols. Dif-
ferent effects of solvents and additives on stereospecificity were
observed in the radical polymerizations of NNPFAAm and its
hydrocarbon analogs such as N-isopropylacrylamide (NIPAAm)
and N-n-propylacrylamide (NNPAAm); for instance, syndiotactic
(and heterotactic) specificities were induced in radical polymer-
ization of NNPFAAm in polar solvents (and in toluene in the
presence of alkyl and silyl alcohols), whereas isotactic (and syn-
diotactic) specificities were induced in radical polymerizations of
the hydrocarbon analogs under the corresponding conditions. In
contrast, heterotactic specificity induced by fluorinated alcohols
was further enhanced in radical polymerization of NNPFAAm.
The effects of stereoregularity on the phase-transition behaviors
of aqueous solutions of poly(NNPFAAm) were also investigated.
Different tendencies in stereoregularity were observed in aque-
ous solutions of poly(NNPFAAm)s from those in solutions of the
hydrocarbon analogs such as poly(NIPAAm) and poly
(NNPAAm). The polymerization behavior of NNPFAAm and the
phase-transition behavior of aqueous poly(NNPFAAm) are dis-
cussed based on possible fluorine–fluorine repulsion between
the monomer and propagating chain-end, and neighboring
C
V
monomeric units. 2012 Wiley Periodicals, Inc. J Polym Sci Part
A: Polym Chem 000: 000–000, 2012
KEYWORDS: heterotactic; hydrogen bonding; radical polymer-
ization; stereospecific polymers; stimuli-sensitive polymers;
syndiotactic
INTRODUCTION Fluorine-containing compounds play an im-
portant role in the stereospecificity of radical polymerization.
For example, fluorinated alcohols such as nonafluoro-tert-bu-
tanol (NFTB) induced or enhanced the stereospecificities
when used as the solvent for the radical polymerizations of
vinyl esters1,2 and methacrylates.3,4 The induced or
enhanced stereospecificity depended on the structures of the
monomers; syndiotactic specificity was induced in the radi-
cal polymerization of vinyl acetate and enhanced in those of
methacrylates, whereas heterotactic specificity was induced
in the radical polymerization of vinyl pivalate.
except in the radical polymerization of 2,2,2-trifluoroethyl
methacrylate, in which polymers with lower syndiotacticities
than that of poly(ethyl methacrylate) were obtained.9
The introduction of a fluorine atom at the a-position of the
vinyl group of an acrylic monomer also influenced stereospe-
cificity. For example, the radical polymerizations of methyl a-
fluoroacrylate (MFA),10 ethyl a-fluoroacrylate (EFA),11 a-fluo-
roacrylonitrile (FAN),11 and N-methyl-a-fluoroacrylamide
(NMFAAm)12 gave syndiotactic-rich polymers, whereas their
hydrocarbon analogs gave almost atactic polymers.
We reported that isotactic specificity was induced using
polar solvents in the radical polymerizations of N-monosub-
stituted acrylamides such as N-isopropylacrylamide
(NIPAAm).13 Furthermore, isotactic and syndiotactic specific-
ities were induced by adding Lewis bases14,15 or alkyl alco-
hols16,17 to the radical polymerizations of NIPAAm and N-n-
propylacrylamide (NNPAAm). Adding fluorinated alcohols
induced heterotactic specificity,18,19 indicating that fluorine-
containing compounds as additives also played a determin-
ing role in the stereospecificity of the radical polymerizations
Introducing fluorine atoms in the side groups of monomers
also affected the stereospecificity. For example, the radical
polymerizations of vinyl 2,2-bis(trifluoromethyl)propionate2,5
and vinyl pentafluorobenzoate6 gave polymers with higher
syndiotacticities than those of their hydrocarbon analogs.
The radical polymerization of nonafluoro-tert-butyl acrylate
also gave a polymer with higher syndiotacticity than that of
poly(tert-butyl acrylate).7,8 These results suggest that fluori-
nated side groups generally enhance syndiotactic specificity,
C
V
2012 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
1

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 1 Effects of fluorine atom at the a-position on stereospecificity of radical polymerization of N-monosubstituted acrylam-
ide derivatives.
of N-monosubstituted acrylamides. It is therefore assumed
that introducing fluorine atoms at the a-positions of N-mono-
substituted acrylamides further influences the stereospecific-
ity induced by polar solvents, Lewis bases, alkyl alcohols,
silyl alcohols, or fluorinated alcohols.
(35DMPNO), triisopropylsilanol (TIPSiOH), 2,2,2-trifluoroe-
thanol (TFE), samarium trifluoromethanesulfonate
[Sm(OTf)3] (Sigma-Aldrich Japan, Tokyo, Japan), 1,1,1,3,3,3-
hexafluoro-2-propanol (HFIP), MFA (supplied by Daikin
Industries, Osaka, Japan), n-propylamine, 2-propanol (iPrOH),
propylene carbonate (PC), N-ethylacetamide (NEtAcAm), trie-
thylsilanol (TESiOH), diethyl(isopropyl)silanol (DEIPSiOH),
NFTB, scandium trifluoromethanesulfonate [Sc(OTf)3], yt-
trium trifluoromethanesulfonate [Y(OTf)3], ytterbium tri-
fluoromethanesulfonate [Yb(OTf)3], (Tokyo Chemical Indus-
try, Tokyo, Japan), and lithium trifluoromethanesulfonate
(LiOTf) (Kishida Chemical, Osaka, Japan) were used as
received.
In this article, radical polymerization of N-n-propyl-a-fluoroa-
crylamide (NNPFAAm) was carried out under various condi-
tions, under which isotactic, syndiotactic, or heterotactic spe-
cificities were induced in the radical polymerizations of N-
monosubstituted acrylamides. A fluorine atom at the a-posi-
tion had a significant effect on the stereospecificity, as sum-
marized in Scheme 1.
Aqueous solutions of poly(NIPAAm) and poly(NNPAAm) are
known to show soluble-to-insoluble transitions.20–25 The
stereoregularity of a polymer significantly influences its
phase-transition behavior;16–18,26–28 therefore, the phase-
transition behaviors of aqueous solutions of the poly
(NNPFAAm)s obtained were also examined with respect to
tacticity effects.
Synthesis of NNPFAAm
MFA (29.60 g, 0.249 mol) in MeOH (200 mL) was added
dropwise at room temperature to a stirred solution of n-pro-
pylamine (29.32 g, 0.496 mol) in MeOH (400 mL). After stir-
ring the mixture for 24 h at room temperature, the solvent
was evaporated. The residue was distilled under reduced
ꢀ
pressure (6 mmHg, b.p. 113 C) to give 31.34 g of NNPFAAm
(96.14%). Using EFA instead of MFA gave NNPFAAm in
87.62% yield.
EXPERIMENTAL
NNPFAAm: colorless liquid; 1H NMR (400 MHz, CDCl3 at 35
Materials
Dimethyl 2,20-azobisisobutyrate (MAIB) (supplied by Otsuka
Chemical, Osaka, Japan) was recrystallized from methanol
(MeOH). Toluene (Kanto Chemical, Tokyo, Japan) was puri-
fied by washing with sulfuric acid, water, and 5% aqueous
NaOH, followed by fractional distillation. MeOH (Kanto
Chemical) was fractionally distilled. EFA was prepared
according to the literature.11 Anhydrous ethanol (EtOH), tert-
butanol (tBuOH) (Wako Pure Chemical Industries, Osaka,
Japan), tetrahydrofuran (THF), pyridine, acetone, acetonitrile,
N,N-dimethylformamide (DMF), chloroform (CHCl3) (Kanto
Chemical), 3-methyl-3-pentanol (3Me3PenOH), hexamethyl-
phosphoramide (HMPA), 3,5-dimethylpyridine N-oxide
3
ꢀC), d 6.30 (br, 1H), 5.67 (dd, 1H, 2J ¼ 3.2 Hz, JH,F trans
¼
2
3
48.5 Hz), 5.09 (dd, 1H, J ¼ 3.2 Hz, JH,F cis ¼ 15.5 Hz), 3.32
3
3
3
(q, 2H, J ¼ 7.0 Hz), 1.59 (sext, 2H, J ¼ 7.0 Hz, J ¼ 7.6 Hz),
0.96 (t, 3H, 3J ¼ 7.6 Hz); 13C NMR (100 MHz, CDCl3 at 35
2
1
ꢀC), d 159.69 (d, JC,F ¼ 30.66 Hz), 156.70 (d, JC,F ¼ 271.61
2
Hz), 98.67 (d, JC,F ¼ 15.09 Hz), 41.24, 22.79, 11.40.
Polymerization
The typical polymerization procedure was as follows.
NNPFAAm (0.6557 g, 5.0 mmol), NFTB (2.3604 g, 10 mmol),
and MAIB (0.0115 g, 5.0 ꢁ 10ꢂ2 mmol) were dissolved in
toluene to prepare 5 mL of solution. A total of 4 mL of this
2
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 1 1H, 13C, and 19F NMR spectra of poly(NNPFAAm) measured (a) in CDCl3 at 55 ꢀC and (b) in DMSO-d6 at 100 ꢀC.
ꢀ
solution was transferred to a glass ampoule and cooled to
ꢂ40 ꢀC. The glass ampoule was degassed and filled with
nitrogen three times. The mixture was irradiated at a dis-
tance of about 5 cm from a UV-LED lamp (k ¼ 375 nm,
Optocode, Tokyo, Japan) to initiate polymerization. After 12
h, the polymerization mixture was poured into diethyl ether
(400 mL). The precipitated polymer was collected by centrif-
ugation, and dried in vacuo. The polymer yield was deter-
mined gravimetrically.
minꢂ1 from 70 C to 2 ꢀC. The cloud point (Tc) in the heat-
ing and cooling processes was taken as the temperature at
which the transmittance was 50%. When some transparency
remained even above the phase-transition temperature, the
Tc was defined as the temperature at which the average
transmittance before and after the phase transition was
observed.
NMR Evaluation of Stereoregularity of Poly(NNPFAAm)
The stereoregularity of poly(NNPFAAm) was examined by
1H, 13C, and 19F NMR spectroscopy in CDCl3 at 55 ꢀC or in
Measurements
1H, 13C, and 19F NMR spectra were measured using an ECX-
400 spectrometer (JEOL, Tokyo, Japan) operated at 400 MHz
29
ꢀ
deuterated dimethyl sulfoxide (DMSO-d6) at 100 C. Proton
chemical shifts were referenced to internal TMS (d ¼ 0.00
ppm). Carbon chemical shifts were referenced to the solvents
(CDCl3: d ¼ 77.0 ppm DMSO-d6: d ¼ 39.6 ppm). Fluorine
chemical shifts were referenced to hexafluorobenzene (d ¼
ꢂ162.5 ppm) as an internal standard. The 1H NMR signals
of the methꢀylene groups in the main chain measured in
CDCl3 at 55 C showed poor splitting as a result of stereore-
gularity [Fig. 1(a)]. Those measured in DMSO-d6 at 100 ꢀC
showed splitting as a result of dyad tacticity similar to that
of poly(MFA)10 [Fig. 1(b)]. However, it was difficult to evalu-
ate the dyad tacticity because of overlapping of the signal
caused by the solvent.
1
for H, 100 MHz for 13C, and 376 MHz for 19F. The molecular
weights and molecular-weight distributions of the polymers
were determined by size-exclusion chromatography (SEC);
the chromatograph was calibrated using standard polysty-
rene samples. SEC was performed with an HLC 8220 chro-
matograph (Tosoh, Tokyo, Japan) equipped with TSK gel col-
umns (SuperHM-M and SuperHM-H, both 6.5 mm ID ꢁ 150
mm long; Tosoh). DMF containing LiBr (10 mmol Lꢂ1) was
used as the eluent at 40 ꢀC and a flow rate of 0.35 mL
minꢂ1. The polymer concentration was 1.0 mg mLꢂ1. The
transmittance of an aqueous solution of poly(NNPFAAm)
(0.1 w/v%) was monitored as a function of temperature at a
wavelength of 500 nm using a UV/VIS spectrophotometer
(V-550, JASCO, Tokyo, Japan) equipped with a Peltier thermo-
stated single-cell holder (ETC-505, JꢂA1SCO). The temperature
The 13C NMR signals of the quaternary carbon measured in
CDCl3 at 55 C also showed poor splitting as a result of ster-
eoregularity, but those measured in DMSO-d6 at 100 ꢀC
showed splitting as a result of triad tacticity, similar to those
of poly(MFA),10 poly(EFA),11 and poly(NMFAAm).12 The
ꢀ
ꢀ
ꢀ
was changed at a rate of 0.5 C min from 2 to 70 C, held
at 70 ꢀC for about 15 min, then changed at a rate of 0.5 ꢀC
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
3

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 1 Radical Polymerization of NNPFAAm in Various Solvents at 240 8C for 12 ha
Triad Tacticityb/%
r Dyadc/%
Mn ꢁ 10ꢂ4
Mw/Mn
Pm/r
Pr/m
Pm/rþ Pr/m
d
d
Run
Solvent
Yield/%
mm
mr
rr
1
2e
Toluene
Toluene
CHCl3
87
85
27
34
40
75
28
24
30
81
28
71
57
11
3
16.1
16.0
9.4
48.9
49.0
61.3
50.8
49.6
45.3
45.1
39.8
42.6
42.9
50.4
41.1
40.6
41.8
37.1
35.0
35.0
29.3
38.7
41.5
48.3
45.1
51.1
48.6
45.3
40.5
45.7
52.8
50.6
55.9
59.5
59.5
60.0
64.1
66.3
71.0
67.7
71.0
69.9
66.8
65.7
66.3
73.1
71.5
74.5
e
11.7
7.1
3.4
2.9
3.0
7.0
3.0
2.1
2.9
20.4
4.5
36.4
4.6
3.5
2.6
2.8
2.8
1.5
1.5
1.7
1.8
1.5
1.6
1.5
1.8
1.6
1.6
1.7
2.1
1.4
0.602
0.605
0.765
0.708
0.737
0.779
0.697
0.686
0.708
0.645
0.734
0.610
0.755
0.733
0.726
0.411
0.412
0.511
0.396
0.374
0.319
0.333
0.280
0.305
0.321
0.384
0.310
0.278
0.293
0.249
1.013
1.017
1.277
1.104
1.111
1.098
1.030
0.966
1.013
0.966
1.118
0.920
1.033
1.025
0.975
3
4
CH2Cl2
10.5
8.9
5
THF
6
Pyridine
Acetone
CH3CN
6.4
7
9.8
8
9.1
9
DMF
8.8
10
11
12
13f
14g
15h
a
PC
11.8
9.1
MeOH
NEtAcAm
CH3CNþpyridine
DMF
13.1
6.6
7.6
CH3CNþDMF
7.0
[NNPFAAm]0 ¼ 1.0 mol Lꢂ1, [MAIB]0 ¼ 1.0 ꢁ 10ꢂ2 mol Lꢂ1
.
[NNPFAAm]0 ¼ 0.5 mol Lꢂ1, [MAIB]0 ¼ 1.0 ꢁ 10ꢂ2 mol Lꢂ1
CH3CN þ pyridine ¼ 1:1 vol/vol.
.
b
c
f
Determined from 19F NMR signals.
g
h
Calculated from the triad tacticities with the equation: r ¼ mr/2þrr.
At –60 ꢀC.
d
Determined by SEC (polystyrene standards).
CH3CN þ DMF ¼ 1:1 vol/vol, at –80 ꢀC, for 48 h.
resolution, however, was low compared with those in the
NMR spectra of other polymers.
poly(MFA) (34%),10 poly(EFA) (34%),11 poly(FAN) (29%),11
and poly(NMFAAm) (34%).12 The first-order Markovian
probabilities of m-addition by r-ended radicals (Pr/m) and of
r-addition by m-ended radicals (Pm/r) were calculated using
The 19F NMR signals of the fluorine atom at the a-position
showed splitting as a result of stereoregularity longer than
triad stereosequences, regardless of the type of solvent used.
The spectral pattern observed in DMSO-d6 at 100 ꢀC was
similar to those for poly(MFA),10 poly(EFA),11 and poly
(FAN).11 The signals were therefore assigned in terms of
triad stereosequences, as shown in Figure 1(b), according to
the assignments in the literature.10,11 The triad tacticity
determined from the 19F NMR signals was in good agree-
ment with that determined from the 13C NMR signals. How-
ever, in the 19F NMR spectrum in CDCl3 at 55 ꢀC, the signal
intensity distribution did not explain the triad tacticity deter-
mined from the 13C NMR signals. This suggests that the
spectral pattern observed in CDCl3 at 55 ꢀC was more com-
plicated than that in DMSO-d6 at 100 ꢀꢀC. 19F NMR analysis
of poly(NNPFAAm) in DMSO-d6 at 100 C was therefore cho-
sen to determine the tacticity at the triad level.
the following equations: Pr/m ¼ mr/(2mm þ mr) and Pm/r
¼
mr/(2rr þ mr). The sums of Pr/m and Pm/r were quite close
to unity, indicating that the stereoregularities of the obtained
polymers almost obeyed Bernoullian statistics. The probabil-
ities of r-addition by m-ended and r-ended radicals were cal-
culated to be about 0.60 and 0.59, respectively. Taking into
account that a polymer with r ¼ 53% was obtained by
NNPAAm polymerization under the corresponding condi-
tions,17 it seems that introducing a fluorine atom at the a-
position of NNPAAm slightly enhanced the syndiotactic
specificity.
As reported previously,13,30 using polar solvents increases
the m-dyad contents of the polymers obtained by radical po-
lymerization of NIPAAm at low temperatures. Radical poly-
merization of NNPFAAm was carried out in several solvents
more polar than toluene (Table 1, runs 3–12). Unlike the
NIPAAm polymerizations, the syndiotacticities increased
when polar solvents such as pyridine, CH3CN, and DMF, but
not CHCl3, were used. In particular, a polymer with rr ¼
51.1% was obtained by NNPFAAm polymerization in CH3CN.
Using a mixed solvent (CH3CN/pyridine ¼ 1:1, v/v) slightly
increased the rr-triad content compared with those obtained
using CH3CN and pyridine individually (Table 1, runs 6, 8,
and 13). Lowering the temperature enhanced the syndiotac-
tic specificity slightly (Table 1, runs 9 and 14). Polymeriza-
tion was therefore carried out in a mixed solvent (CH3CN/
RESULTS AND DISCUSSION
Radical Polymerization of NNPFAAm in Various
Solvents at 240 8C
Radical polymerization of NNPFAAm was carried out in tolu-
ene at ꢂ40 ꢀC for 12 h (Table 1, runs 1 and 2). Polymers
slightly rich in syndiotacticity (rr ¼ 35.0%) were obtained,
regardless of the monomer concentration. The rr content
(35.0%) agreed well with those observed for a-fluorinated
acrylic polymers prepared by radical polymerization, such as
4
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
ꢀ
DMF ¼ 1:1, v/v) at ꢂ80 C. A polymer with an rr-triad con-
tent of 55.9% was obtained, although the polymer yield was
reduced [Table 1, run 15 and Fig. 2(b)]. It is assumed that
polar solvents enhance the syndiotactic specificity of radical
polymerization of NNPFAAm, although the reason is not at
present clear.
Radical Polymerization of NNPFAAm in the
Presence of Lewis Bases or Lewis Acids
We reported that adding phosphoric acid derivatives such as
HMPA to the NIPAAm and NNPAAm polymerizations induced
syndiotactic specificity through formation of a hydrogen-
bonding-assisted 1:1 complex of the monomer and the Lewis
base.14,17 The effect of HMPA on the stereospecificity of radi-
cal polymerization of NNPFAAm was therefore examined in
toluene at low temperatures (Table 2, runs 1–3). Adding
HMPA increased the syndiotacticities of the polymers and
decreased the polymer yields significantly (Table 1, run 1
and Table 2, run 1). This tendency corresponds with those
observed in both NIPAAm and NNPAAm polymerizations.
The syndiotacticity gradually increased with decreasing poly-
merization temperature, and a polymer with rr ¼ 50.7%
was obtained at ꢂ80 ꢀC. This result differed from the ten-
dencies in NIPAAm and NNPAAm polymerizations, in which
HMPA most effectively induced syndiotactic specificity at
14,17
ꢀ
ꢂ60 C under the corresponding conditions.
Radical polymerization of NNPFAAm was also examined in
the simultaneous presence of HMPA and MeOH (Table 2, run
4), because isotactic specificity was induced in NIPAAm poly-
merization by a combined effect of HMPA and the less bulky
alcohol.31 The rr-triad content decreased slightly, but
isotactic specificity was not induced. The effect of 35DMPNO
was then examined (Table 2, run 5) because 35DMPNO
induced isotactic specificity in NIPAAm and NNPAAm
FIGURE 2 19F NMR spectra of poly(NNPFAAm)s prepared (a) in
toluene at ꢂ40 ꢀC (Table 1, run 1), (b) in CH3CN þ pyridine at
ꢂ80 ꢀC (1:1, v/v) (Table 1, run 15), and (c) in toluene at ꢂ40 ꢀC
in the presence of NFTB (Table 4, run 7).
TABLE 2 Radical Polymerization of NNPFAAm in the Presence of Lewis Base or Lewis Acida
Triad
Tacticityb/%
d
d
Run Additive
Solvent Temp. (ꢀC) Yield/% mm mr
rr
r Dyadc/% Mn ꢁ 10ꢂ4 Mw/Mn Pm/r
Pr/m
Pm/rþ Pr/m
1e
2e
3e
4f
5g
6h
7h
8h
9h
HMPA
HMPA
HMPA
Toluene –40
Toluene –60
Toluene –80
23
8
9.8 46.5 43.7 67.0
8.8 45.6 45.6 68.4
8.0 41.3 50.7 71.4
9.8 49.7 40.5 65.4
10.0 51.5 38.5 64.3
12.2 51.9 35.9 61.9
13.1 52.7 34.2 60.6
11.8 52.2 36.0 62.1
10.1 51.6 38.3 64.1
9.0 58.5 32.5 61.8
f
3.9
2.9
2.3
3.5
3.5
6.6
6.7
6.8
5.8
4.0
2.3
2.4
1.5
1.5
1.5
1.8
1.6
1.7
1.7
2.3
0.702 0.347 1.049
0.721 0.333 1.054
0.722 0.290 1.012
0.717 0.380 1.097
0.720 0.401 1.121
0.679 0.420 1.099
0.668 0.436 1.104
0.689 0.421 1.110
0.719 0.402 1.122
0.764 0.474 1.237
3
HMPAþMeOH Toluene –80
35DMPNO
Sc(OTf)3
Y(OTf)3
7
CHCl3
MeOH
MeOH
MeOH
MeOH
MeOH
–60
–20
–20
–20
–20
–20
21
20
54
62
45
63
Yb(OTf)3
Li(OTf)
10h Sm(OTf)3
a
[NNPFAAm]0 ¼ 1.0 mol Lꢂ1, [MAIB]0 ¼ 1.0 ꢁ 10ꢂ2 mol Lꢂ1
.
[HMPA]0 ¼ [MeOH]0 ¼ 2.0 mol Lꢂ1
.
b
c
g
h
Determined from 19F NMR signals.
[35DMPNO]0 ¼ 2.0 mol Lꢂ1
.
Calculated from the triad tacticities with the equation: r ¼ mr/2þrr.
[NNPFAAm]0 ¼ 0.5 mol Lꢂ1, [MAIB]0 ¼ 0.5 ꢁ 10ꢂ2 mol Lꢂ1, [M(OTf)x]0
d
e
Determined by SEC (polystyrene standards).
¼ 0.5 ꢁ 10ꢂ1 mol Lꢂ1
.
[HMPA]0 ¼ 2.0 mol Lꢂ1
.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
5

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 3 Radical Polymerization of NNPFAAm in Toluene in the Presence of Alkyl Alcohol or Silyl Alcohola
Triad
Tacticityb/%
r Dyadc/% Mn ꢁ10ꢂ4 Mw/Mn
Pm/r
Pr/m
Pm/rþ Pr/m
d
d
Run Additive
Temp. (ꢀC) Yield/% mm mr
rr
1
None
0
90
86
44
68
69
85
>99
91
91
48
76
84
91
17.8 50.1 32.1 57.2
16.1 49.0 34.9 59.4
9.1 58.4 32.5 61.7
8.4 60.6 31.0 61.3
7.8 63.8 28.4 60.3
7.2 65.5 27.3 60.1
7.7 65.2 27.1 59.7
6.4 65.9 27.7 60.7
5.8 65.3 28.9 61.6
6.3 65.6 28.1 60.9
6.7 62.8 30.4 61.8
6.8 59.1 34.0 63.6
4.0 69.0 27.0 61.5
c
11.8
8.2
4.9
5.3
4.9
6.2
5.1
5.4
6.9
5.1
6.6
6.3
5.4
3.7
2.4
1.7
1.8
1.8
1.7
2.2
2.0
1.9
1.9
2.1
2.1
2.1
0.585 0.438 1.023
0.604 0.413 1.017
0.762 0.473 1.235
0.783 0.494 1.276
0.804 0.529 1.332
0.819 0.546 1.365
0.810 0.546 1.356
0.837 0.543 1.380
0.848 0.531 1.379
0.838 0.539 1.377
0.824 0.508 1.332
0.812 0.465 1.277
0.896 0.561 1.457
2
None
–40
–40
–40
–40
–40
0
3
MeOH
EtOH
4
5
iPrOH
6
tBuOH
3Me3PenOH
7
8
3Me3PenOH –20
3Me3PenOH –40
3Me3PenOH –60
9
10
11
12
13
a
TESiOH
–40
–40
–40
DEIPSiOH
TIPSiOH
[NNPFAAm]0 ¼ 0.5 mol Lꢂ1, [MAIB]0 ¼ 0.5 ꢁ 10ꢂ2 mol Lꢂ1, [Alcohol]0
Calculated from the triad tacticities with the equation: r ¼ mr/2þrr.
¼ 2.0 mol Lꢂ1
.
Determined by SEC (polystyrene standards).
d
b
Determined from 19F NMR signals.
polymerizations.15,30 However, induction of isotactic specific-
ity was not observed. Radical polymerizations of NNPFAAm
in MeOH in the presence of catalytic amounts of metal tri-
flates were carried out (Table 2, runs 6–10) because metal
triflates such as Y(OTf)3 were reported to catalyze isotactic-
specific radical polymerization of NIPAAm to give polymers
with over 90% m-dyads.32,33 The mm-triad content of the
obtained polymers increased slightly compared with that in
MeOH in the absence of metal triflates (see Table 1, run 11),
but were much lower than those of poly(NIPAAm)s prepared
under the corresponding conditions. These results suggest
that NNPFAAm does not readily give isotactic polymers,
probably because of repulsion between fluorine atoms at the
a-positions of the propagating chain-end, penultimate, and
antepenultimate monomeric units, and/or the incoming
monomers in the propagation reaction.
Silyl alcohols also induced syndiotactic specificity in NIPAAm
polymerization.34 The effects of silyl alcohols were examined.
Silyl alcohols, as well as alkyl alcohols, induced heterotactic
specificity in NNPFAAm polymerization. The induced hetero-
tactic specificity was further enhanced. A polymer with mr ¼
ꢀ
69.0% was obtained by NNPFAAm polymerization at ꢂ40 C
in the presence of TIPSiOH. This value (69.0%) is close to
70%, which is the highest heterotacticity obtained for poly
(NIPAAm)s prepared by radical polymerization in the pres-
ence of fluorinated alcohols.18
Radical polymerization of NNPFAAm was then investigated
in the presence of fluorinated alcohols (Table 4). A further
improvement in the heterotactic specificity was observed for
NNPFAAm polymerization compared with NIPAAm polymer-
ization under the corresponding conditions. In particular, a
polymer with mr ¼ 82.6% was obtained in the presence of
ꢀ
NFTB at ꢂ40 C [Table 4, run 7 and Fig. 2(c)]. To the best of
our knowledge, this is the highest level of heterotacticity so
far reported for homopolymers prepared by radical
polymerization.18,35
Radical Polymerization of NNPFAAm in the Presence of
Alkyl, Silyl, or Fluorinated Alcohols
We reported that adding alkyl alcohols such as 3Me3PenOH
to NIPAAm and NNPAAm polymerizations induced syndiotac-
tic specificity.16,17 The effects of alkyl alcohols on the stereo-
specificity of radical polymerization of NNPFAAm were there-
fore examined in toluene at low temperatures (Table 3).
Unlike the cases of NIPAAm and NNPAAm polymerizations,
adding alkyl alcohols induced heterotactic specificity in the
radical polymerization of NNPFAAm. The induced heterotac-
tic specificity increased with increasing bulkiness of the
added alcohols (Table 3, runs 3–6 and 9), but was scarcely
affected by polymerization temperature (Table 3, runs 7–10).
A polymer with mr ¼ 65.9% was obtained by NNPFAAm po-
NMR Analysis of Hydrogen-Bonding Interactions
Between NNPFAAm and Alkyl Alcohols
Both alkyl and fluorinated alcohols induced heterotactic
specificity in NNPFAAm polymerization, although the former
induced syndiotactic specificity in NIPAAm polymerization.
To investigate the reason for this difference in the induced
stereospecificities, we conducted an NMR analysis ofꢀa mix-
ture of NNPFAAm and 3Me3PenOH in toluene-d8 at 0 C.
The 13C NMR signal of the carbonyl carbon showed a down-
field shift on addition of 3Me3PenOH [Fig. 3(a,b)]. This sug-
gested that the carbonyl oxygen formed hydrogen bonds
ꢀ
lymerization at ꢂ20 C in the presence of 3Me3PenOH.
6
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 4 Radical Polymerization of NNPFAAm in the Presence of Fluorinated Alcohol (RfOH)a
Triad
Tacticityb/%
[NNPFAAm]0 Temp.
Run Additive (mol Lꢂ1
)
(ꢀC)
Yield/% mm mr
rr
r Dyadc/% Mn ꢁ10ꢂ4 Mw/Mn
Pm/r
Pr/m
Pm/rþ Pr/m
d
d
1
2
3
4
5
6
7
8
TFE
1.0
0.5
0.5
0.5
1.0
0.5
0.5
1.0
–40
0
60
77
47
23
60
17
29
73
11.4 64.8 23.8 56.2
14.1 70.9 15.0 50.5
13.2 72.7 14.1 50.5
12.3 74.4 13.3 50.5
13.7 73.9 12.4 49.4
11.9 71.8 16.3 52.2
3.0 82.6 14.4 55.7
3.7 82.1 14.2 55.3
c
4.5
3.0
2.3
2.4
4.8
1.8
2.7
8.0
2.1
1.4
1.5
1.3
2.2
1.3
2.3
3.5
0.739 0.576 1.315
0.716 0.702 1.418
0.733 0.720 1.453
0.752 0.737 1.488
0.730 0.749 1.479
0.751 0.688 1.440
0.932 0.741 1.674
0.917 0.743 1.660
HFIP
HFIP
HFIP
HFIP
HFIP
NFTB
NFTB
–20
–40
–40
–60
–40
–40
a
[NNPFAAm]0/[MAIB]0 ¼ 100. [RfOH]0 ¼ 2.0 mol Lꢂ1
.
Calculated from the triad tacticities with the equation: r ¼ mr/2þrr.
b
d
Determined from 19F NMR signals.
Determined by SEC (polystyrene standards).
with 3Me3PenOH. The 1H NMR signal of the amide proton
showed a down-field shift on addition of 3Me3PenOH. This
suggested that the amide proton also formed hydrogen
bonds with the oxygen in 3Me3PenOH. The 19F NMR signal
of the a-fluorine also showed a down-field shift. It has been
reported, however, that covalently bonded fluorine atoms
hardly act as hydrogen-bonding acceptors.36 Consequently,
NNPFAAm and 3Me3PenOH formed a 1:2 complex through
cooperative hydrogen bonding, OAHꢃꢃꢃO¼¼CAN AHꢃꢃꢃO(H)
(Scheme 2), as in the case of NIPAAm and tBuOH.16 This
means that not the complex structure, but rather the fluorine
atom at the a-position should be responsible for inducing
heterotactic specificity.
Table 5 summarizes the Pr/m and Pm/r data for the radical
polymerizations of NNPFAAm, NNPAAm, and NIPAAm in tol-
uene in the presence of 3Me3PenOH. The Pm/r for the
NNPFAAm polymerization indicates that 3Me3PenOH signifi-
cantly increases r-selectivity by m-ended radicals in the
NNPFAAm polymerization, even more than in the NNPAAm
and NIPAAm polymerizations. Propagation by m-ended radi-
cals was considered to occur in a mechanism similar to that
proposed for syndiotactic-specific NIPAAm polymerization in
previous papers.14,16 The Pr/m value for NNPFAAm polymer-
ization was higher than those for the NNPAAm and NIPAAm
polymerizations. This indicates that the m-selectivity by the
r-ended radicals in the NNPFAAm polymerization is higher
than those in the NNPAAm and NIPAAm polymerizations. It
is therefore believed that the conformation near the propa-
gating chain-end of the r-ended radicals was particularly
affected by repulsion between the fluorine atoms at the a-
positions of the chain-end, penultimate, and antepenultimate
monomeric units, resulting in enhanced m-selectivity by the
r-ended radicals in a mechanism similar to that proposed for
FIGURE 3 1H, 13C, and 19F NMR spectra of NNPFAAm (0.125
mol Lꢂ1) measured in toluene-d8 at 0 ꢀC in the absence or pres-
ence of alcohols: (a) none, (b) 3Me3PenOH (0.125 mol Lꢂ1),
and (c) NFTB (0.125 mol Lꢂ1).
SCHEME 2 Proposed structures for 1:2 complexes of
NNPFAAm and NIPAAm with alkyl alcohol (ROH).
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
7

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 5 Pm/r and Pr/m for Polymerizations of NIPAAm,
NNPAAm, and NNPFAAm in Toluene in the Presence of
3Me3PenOH or NFTB
Monomer
Added Alcohol
Temp. (ꢀC)
Pm/r
Pr/m
NIPAAma
NNPAAmb
NNPFAAm
NIPAAmc
NNPFAAm
a
3Me3PenOH
3Me3PenOH
3Me3PenOH
NFTB
–60
–40
–20
–40
–40
0.733
0.694
0.837
0.814
0.932
0.314
0.259
0.543
0.614
0.741
NFTB
Calculated with mm ¼ 8%, mr ¼ 44%, and rr ¼ 48%.18
Calculated with mm ¼ 8.3%, mr ¼ 37.7%, and rr ¼ 54.0%.37
Calculated with mm ¼ 8%, mr ¼ 70%, and rr ¼ 22%.18
b
c
heterotactic-specific NIPAAm polymerization in a previous
paper.18
NMR Analysis of Hydrogen-Bonding Interactions
Between NNPFAAm and Fluorinated Alcohols
NMR analysis of a mixture of NNPFAAm and NFTB was also
carried out [Fig. 3(a,c)]. Adding NFTB caused a down-field
shift of the 13C NMR signal of the carbonyl group, indicating
that the carbonyl oxygen formed hydrogen bonds with NFTB.
In contrast, the 1H NMR signal of the amide proton showed
an up-field shift on addition of NFTB. These results sug-
gested that the amide proton was free from hydrogen bond-
ing, as was seen for the combination of NIPAAm and
NFTB.18 This was also supported by a significant up-field
shift of the 19F NMR signal because formation of C¼¼OꢃꢃꢃHAO
hydrogen bonds would increase the electron density at the
a-position in the a,b-unsaturated carbonyl moiety.
FIGURE 4 (a) Changes in the chemical shifts of the vinylidene
proton trans to the fluorine atom (HC¼CH; trans) of NNPFAAm
in the presence of NFTB (l), ([NNPFAAm]0 þ [NFTB]0 ¼ 0.25
mol Lꢂ1, in toluene-d8 at 0 ꢀC) and (b) Job’s plots for the asso-
ciation of NNPFAAm with NFTB. The plot marked (h) denotes
the chemical shift of NNPFAAm alone at the corresponding
concentration.
To investigate the stoichiometry of the NNPFAAm–NFTB
complex, 1H NMR analysis was carried out on solutions of
[NNPFAAm]0 þ [NFTB]0 ¼ 0.25 mol Lꢂ1 in toluene-d8 at 0
ꢀC. Figure 4(a) shows the changes in the chemical shift of
the vinylidene proton ‘‘trans’’ to the fluorine atom (HC¼¼CF;
trans) of NNPFAAm resulting from variations in the initial
proportion of NNPFAAm. The plots roughly obeyed a quad-
ratic equation. The stoichiometry of the complex was eval-
uated by the Job’s method via eq 1:38
initial proportion of NNPFAAm ¼ 0.5 [Fig. 4(b)]. This result
indicates that NNPFAAm and NFTB formed a 1:1 complex
through hydrogen bonding, C¼¼OꢃꢃꢃHAO (Scheme 3), as in
½NNPFAAm ꢂ NFTBꢄ
dðHC ¼¼ CF; transÞ ꢂ dðHC ¼¼ CF; transÞf
dðHC ¼¼ CF; transÞcꢂdðHC ¼¼ CF; transÞf
¼
ꢁ ½NNPFAAmꢄ0
(1)
where d(HC¼¼CF; trans) and d(HC¼¼CF; trans)f are the chemi-
cal shifts of the sample mixture and NNPFAAm alone, respec-
tively. We reported that the chemical shift of NIPAAm varied
with [NIPAAm]0 as a result of self-association. The chemical
shift of NNPFAAm alone at the corresponding concentration
was equated to d(HC¼¼CF; trans)f [Fig. 4(a)]. The chemical
shift for the saturated mixture, d(HC¼¼CF; trans)c, was calcu-
lated from the intercept of the quadratic fit to the data in
Figure 4(a) since the saturation value should be independent
of NNPFAAm concentration. A maximum was observed at an
SCHEME 3 Proposed structures for 1:1 complexes of
NNPFAAm and NIPAAm with NFTB.
8
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 6 Equilibrium Constants (K) for the Interaction Between
NNPFAAm and NFTB, and Degree of Association (a) in the
Polymerization Systema
ab [NNPFAAm]0
Temperature
(ꢀC)
K (L molꢂ1
)
0.5 mol Lꢂ1
1.0 mol Lꢂ1
60
45
25
0
56.4
72.1
0.99
0.99
0.99
1.00
1.00
1.00
0.98
0.99
0.99
0.99
1.00
1.00
105
171
–20
–40
a
(281)c
(498)c
NMR conditions: [NIPFAAm]0 ¼ 5.0 ꢁ 10ꢂ2 mol Lꢂ1, in toluene-d8.
Calculated with [NFTB]0 ¼ 2.0 mol Lꢂ1
.
b
c
FIGURE 5 Changes in the chemical shifts of the vinylidene pro-
ton trans to the fluorine atom (HC¼CF; trans) of NNPFAAm in
toluene-d8 at various temperatures, resulting from variations in
the [NFTB]0/[NNPFAAm]0 ratio.
Calculated from van’t Hoff relationship.
Application of the K values for the polymerization conditions
gives the values shown in Table 6 for the degree of associa-
tion (a) of NNPFAAm. The K values for the NNPFAAm–NFTB
complex were smaller than those for the NIPAAm–NFTB
complex, regardless of the temperature.18 This is probably
because the basicity of the C¼¼O group of NNPFAAm, which
has an electron-withdrawing fluorine atom, is weaker than
that of NIPAAm. However, NNPFAAm formed the complex
quantitatively in the presence of NFTB (2.0 mol Lꢂ1) at ꢂ40
ꢀC, regardless of the NNPFAAm concentration.
the case of a combination of NIPAAm and NFTB, and the po-
lymerization proceeded by a mechanism similar to that pro-
posed in a previous paper for heterotactic-specific NIPAAm
polymerization, in which the monomer formed a 1:1 complex
with fluorinated alcohols.18
The equilibrium constant (K) of the NNPFAAm–NFTB com-
1
plex was determined from the changes in the H NMR chem-
ical shift of the vinylidene proton trans to the fluorine atom
(HC¼¼CF; trans) of NNPFAAm. Figure 5 shows the relation-
ship between the change in the chemical shift and the
[NFTB]0/[NNPFAAm]0 ratio at constant [NNPFAAm]0 (5.0 ꢁ
10ꢂ2 mol Lꢂ1) in toluene-d8 at several temperatures. K was
determined from the data in Figure 5 by nonlinear least-
squares fitting of the data to eq 2:39
NFTB significantly increased Pr/m and Pm/r for NNPFAAm po-
lymerization compared with those for NIPAAm polymeriza-
tion (Table 5). This suggested that m-selectivity by the r-
ended radicals and r-selectivity by the m-ended radicals
were enhanced simultaneously by repulsion between the flu-
orine atoms at the a-positions of the monomeric units near
the propagating chain-end and at the incoming monomer, in
addition to repulsion between fluorine atoms in the hydro-
gen-bonded alcohols.
Dd0 ꢀ
ꢁ
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Dd ¼
b ꢂ b2 ꢂ 4X
2
1
(2)
ꢂ
ꢃ
b ¼ 1 þ X þ
K½NNPFAAmꢄ0
X ¼ ½NFTBꢄ0=½NNPFAAmꢄ0
where Dd and Dd0 are the changes in the chemical shift of
the vinylidene proton trans to the fluorine of NNPFAAm
for the given solution and a saturated solution, respectively
(Table 6).
A van’t Hoff plot of the K values obtained is shown in Fig-
ure 6. The enthalpy (DH) and entropy (DS) of complex for-
mation were evaluated as ꢂ14.0 6 0.3 kJ molꢂ1 and ꢂ8.5 6
0.9 J molꢂ1
K
ꢂ1, respectively, from eq 3:
DS DH
ln K ¼
ꢂ
(3)
R
RT
where R is the gas constant and T is the absolute tempera-
ture. The K values at temperatures below 0 ꢀC were calcu-
lated on the assumption that DH was constant.
FIGURE 6 van’t Hoff plot for 1:1 complex formation between
NNPFAAm and NFTB in toluene-d8.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
9

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
obey Bernoullian statistics from the beginning of the poly-
merization reaction, the r-selectivity of dimer and trimer rad-
icals is calculated to be 0.71. This value agreed well with
those of the m-ended (0.755) and r-ended (0.722) propagat-
ing radicals. This suggests that the dimer radicals already
prefer r-addition rather than m-addition under the given
conditions (Scheme 4).
Heterotactic poly(NNPFAAm) with mr ¼ 82.6% (Table 4, run
7) also showed major peaks assignable to rr-triads. This
means that dimer radicals and r-trimer radicals favor r-addi-
tion, even in the heterotactic-specific polymerization system.
The peaks assignable to the rr-triad further split into more
than three peaks. This indicates that the splitting reflects
stereostructures longer than pentad sequences near the ini-
tiating chain-end. In fact, the highest peak in the spectrum of
the heterotactic polymer differs from that of the syndiotactic
polymer [Fig. 7(b,c)]. These results suggest that the addition
of fluorinated alcohols should in principle enhance syndio-
tactic specificity. However, the stereoselectivity of the r-
ended radicals is inverted after the chain length of the prop-
agating radicals is longer than at least a tetramer. In a previ-
ous paper,18 we proposed that repulsion of fluorine atoms in
fluorinated alcohols bound to the amide groups at the ante-
penultimate and chain-end monomeric units was responsible
for conformational change near the propagating chain-end,
resulting in the m-addition of r-ended radicals. The reason
FIGURE 7 1H NMR spectra of methoxy groups in the MAIB
fragments of poly(NNPFAAm)s prepared at ꢂ40 ꢀC (a) in tolu-
ene (Table 1, run 2), (b) in CH3CN þ pyridine (Table 1, run 13),
and (c) in toluene in the presence of NFTB (Table 4, run 7),
measured in DMSO-d6 at 100 ꢀC.
1H NMR Analysis of Stereosequences Near
the Initiating Chain-End
End-group analysis of polymers by NMR spectroscopy often
provides important information for understanding the poly-
merization mechanism.40,41 The 1H NMR signals of the
methoxy groups in the MAIB fragments exhibited splitting,
probably as a result of stereosequences near the initiating
chain-end (Fig. 7). Although the present polymerization did
not proceed in a living manner, this splitting should provide
stereoselectivities of the initiating species, such as dimer and
trimer radicals.
The signals of the methoxy groups split roughly into four
peaks, probably as a result of triad stereosequence near the
initiating chain-end. The intensities of the peaks at the low-
est and highest magnetic fields increased and decreased,
respectively, in the spectrum of poly(NNPFAAm) with r ¼
73.1% (Table 1, run 13), compared with that with r ¼
59.5% (Table 1, run 2). This suggests that the peaks at the
lowest and highest magnetic fields are at least assignable to
rr- and mm-triads at the initiating chain-end. The fraction of
the peaks of the rr-triad of poly(NNPFAAm) with r ¼ 73.1%
was evaluated to be about 50%. If the stereoselectivities
SCHEME 4 Formation of rr-tetramer radicals by r-addition of
dimer radicals, followed by r-addition of r-trimer radicals.
10
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 8 Temperature dependences of the light transmittance
(k ¼ 500 nm) of aqueous solutions of (a) poly(NNPFAAm) with
r ¼ 59.5% and (b) poly(NNPAAm) with r ¼ 60.4% (0.1 w/v%,
heating and cooling rates ¼ 0.5 ꢀC minꢂ1).
FIGURE 9 Temperature dependences of the light transmittance
(k ¼ 500 nm) of aqueous solutions of (a) poly(NNPFAAm)s
with r ¼ 59.5% and (b) with r ¼ 74.5% (0.1 w/v%, heating and
cooling rates ¼ 0.5 ꢀC minꢂ1).
for the r-selectivity of r-trimer radicals was probably that
the MAIB fragment on the r-trimer radicals was not bulky
enough to significantly induce repulsion between the fluo-
rine atoms, as compared with the polymer chain.
content greater than 67.3% exhibited large hysteresis (ca. 15
ꢀC) under the same conditions.44 The effects of the r-dyad
content of poly(NNPFAAm) on the phase-transition behaviors
were examined. Figure 9 shows the temperature dependen-
ces of the transmittances of aqueous solutions of poly
(NNPFAAm)s with r-dyad contents of 59.5% (Table 1, run 2)
and 74.5% (Table 1, run 15). Unlike the case of aqueous pol-
y(NNPAAm), as the r-dyad content increased, the tempera-
ture and sharpness of the phase transition in the heating
Phase-Transition Behaviors of Aqueous Solutions of
Poly(NNPFAAm)
The phase-transition behaviors of aqueous solutions of poly
(NNPFAAm)s were examined. Figure 8 shows the tempera-
ture dependences of the transmittances of aqueous solutions
of poly(NNPFAAm) with an r-dyad content of 59.5% (Table
1, run 2) and of poly(NNPAAm) with an r-dyad content of
60.4%.42 In the heating process, the Tc of poly(NNPFAAm)
was observed at a higher temperature than that of poly
(NNPAAm), indicating that introducing fluorine atoms at the
a-position of the monomeric units slightly increased the
phase-transition temperature, as does the introduction of
methyl groups.43 In contrast, in the cooling process, the Tc of
poly(NNPFAAm) was observed at a slightly lower tempera-
ture than that of poly(NNPAAm). The hysteresis, which is a
retardation in the cooling process versus the heating process,
was larger than that for poly(NNPAAm), because the differ-
ences in Tc between the hꢀeating and cooling processes (DTc)
were calculated to be 5.6 C for the poly(NNPFAAm) and 1.5
ꢀC for the poly(NNPAAm).
The temperature and sharpness of the phase transition of
aqueous poly(NNPAAm)s increased with increasing r-dyad
content, and syndiotactic poly(NNPAAm)s with an r-dyad
FIGURE 10 Relationship between DTc and nr in syndiotactic-
rich poly(NNPFAAm)s and poly(NNPAAm)s.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
11

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
process decreased, and some transparency remained even
above the Tc. Furthermore, poly(NNPFAAm) with an r-dyad
ꢀ
content of 74.5% exhibited smaller hysteresis (13.7 C) than
those of poly(NNPAAm)s with lower r-dyad contents.
Figure 10 shows the relationship between DTc and the aver-
age r-dyad length (nr), calculated from nr ¼ (rr þ mr/2)/
(mr/2),45 in syndiotactic-rich poly(NNPFAAm)s. The relation-
ship for syndiotactic-rich poly(NNPAAm)s is also plotted.
The hysteresis increased gradually with increasing nr, and
increased moderately above nr ¼ 3.57. This result is in con-
trast with that observed for poly(NNPAAm)s, in which the
hysteresis increased greatly at nr ¼ 3.06. In a previous pa-
per,44 we proposed that formation of intramolecular hydro-
gen bonds by monomeric units in syndiotactic stereosequen-
ces made dehydrated polymers more hydrophobic when the
nr was longer than about 3 (Scheme 5). This caused large
hysteresis by strong aggregation of syndiotactic polymers in
dehydrated states. In the dehydrated state, the polymer was
believed to adopt a helical conformation. This was supported
by quantum-chemical calculations for a syndiotactic octa-
mer.37 In the case of dehydrated poly(NNPFAAm)s, however,
repulsion between fluorine atoms at the a-positions in neigh-
boring monomeric units may arise. This repulsion is
assumed to influence the stability of the ordered structure in
the dehydrated state, which is formed by cooperative hydro-
gen-bonding, as shown in Scheme 5. As a result, the depend-
ences of the nr values on hysteresis in the phase transitions
of aqueous poly(NNPFAAm)s would differ from those of
poly(NNPAAm)s.
FIGURE 11 Temperature dependences of the light transmittan-
ces (k ¼ 500 nm) of aqueous solutions of (a) poly(NNPFAAm)s
with mr ¼ 73.9% and (b) with mr ¼ 82.1% (0.1 w/v%, heating
and cooling rates ¼ 0.5 ꢀC minꢂ1).
decreased in the cooling process. Furthermore, the hysteresis
was larger than that for mr ¼ 73.9%. The reason is not at
present clear. However, these results suggest that highly het-
erotactic polymers exhibit large hysteresis, or a fluorine
atom at the a-position in highly heterotactic poly
(NNPFAAm)s influences the aggregation states of the dehy-
drated polymers.
We previously reported that the sharpness of the phase tran-
sition increased and also hysteresis was significantly reduced
when the content of heterotactic stereosequences in poly(NI-
PAAm)s increased.18 The effects of heterotacticity in poly
(NNPFAAm)s on the phase-transition behaviors were there-
fore examined. Figure 11 shows the temperature dependen-
ces of the transmittances of aqueous solutions of poly
(NNPFAAm)s with mr-triad contents of 73.9% (Table 4, run
5) and 82.1% (Table 4, run 8). In the case of poly
(NNPFAAm) with mr ¼ 73.9%, the sharpness of the phase
transition in both the heating and cooling processes
increased, and the hysteresis was significantly reduced (see
Fig. 9). These results correspond to the tendencies observed
for heterotactic poly(NIPAAm)s. In contrast, in the case of
poly(NNPFAAm) with mr ¼ 82.1%, the sharpness of the
phase transition increased in the heating process, but
CONCLUSIONS
Radical polymerization of NNPFAAm was investigated in sev-
eral solvents at low temperatures in the presence or absence
of Lewis bases, Lewis acids, alkyl alcohols, silyl alcohols, or
fluorinated alcohols; these were reported to induce syndio-
tactic, isotactic, or heterotactic specificity in NIPAAm poly-
merization. Syndiotactic-rich poly(NNPFAAm)s were obtained
in polar solvents such as CH3CN, whereas isotactic-rich poly-
mers were obtained by NIPAAm polymerization under the
corresponding conditions. Isotactic specificity was not
induced in NNPFAAm polymerization, even when Lewis acids
or Lewis bases, which induced isotactic specificity in
NIPAAm polymerization, were added. Alkyl alcohols induced
heterotactic specificity, although they induced syndiotactic
specificity in NIPAAm polymerization. Furthermore, hetero-
tactic specificity was enhanced by fluorinated alcohols in
NNPFAAm polymerization compared with that in NIPAAm
polymerization. These results indicate that the fluorine atom
at the a-position significantly influences the stereospecificity
of radical polymerization of N-monosubstituted acrylamides.
SCHEME 5 Cooperative hydrogen-bonds formed between con-
tiguous monomeric units in syndiotactic stereosequences in
dehydrated poly(NNPAAm).
12
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
19 Hirano, T.; Yamaoka, R.; Miyazaki, T.; Ute, K. J. Polym. Sci.
Part A: Polym. Chem. 2010, 48, 5718–5726.
The phase-transition behaviors of aqueous solutions of poly
(NNPFAAm)s with different tacticities were also examined. It
appeared that the tacticity effect was quite different from
those observed for poly(NIPAAm)s and poly(NNPAAm)s. This
result suggests that the fluorine atoms at the a-position of the
monomeric units also influence the phase-transition behaviors
of aqueous solutions of poly(N-monosubstituted acrylamide)s.
20 Fujishige, S.; Kubota, K.; Ando, I. J. Phys. Chem. 1989, 93,
3311–3313.
21 Schild, H. G. Prog. Polym. Sci. 1992, 17, 163–249.
22 Ito, S. Kobunshi Ronbunshu 1989, 46, 437–443.
23 Ito, D.; Kubota, K. Macromolecules 1997, 30, 7828–7834.
24 Ito, D.; Kubota, K. Polym. J. 1999, 31, 254–257.
This work was supported in part by KAKENHI [a Grant-in-Aid
for Young Scientists (B) (23750130)].
25 Maeda, Y.; Nakamura, T.; Ikeda, I. Macromolecules 2001, 34,
1391–1399.
26 Ray, B.; Okamoto, Y.; Kamigaito, M.; Sawamoto, M.;
Seno, K.-I.; Kanaoka, S.; Aoshima, S. Polym. J. 2005, 37,
234–237.
REFERENCES AND NOTES
27 Kitayama, T.; Shibuya, W.; Katsukawa, K.-I. Polym. J. 2002,
34, 405.
1 Yamada, K.; Nakano, T.; Okamoto, Y. Macromolecules 1998,
31, 7598–7605.
28 Ito, M.; Ishizone, T. J. Polym. Sci. Part A: Polym. Chem.
2006, 44, 4832–4845.
29 The polymer was prepared in toluene at 0 ꢀC in the absence
2 Yamada, K.; Nakano, T.; Okamoto, Y. J. Polym. Sci. Part A:
Polym. Chem. 1999, 37, 2677–2683.
3 Isobe, Y.; Yamada, K.; Nakano, T.; Okamoto, Y. Macromole-
cules 1999, 32, 5979–5981.
of additives (see Table 3, run 1).
30 Hirano, T.; Ishizu, H.; Yamaoka, R.; Ute, K.; Sato, T. Polymer
2009, 50, 3522–3527.
4 Isobe, Y.; Yamada, K.; Nakano, T.; Okamoto, Y. J. Polym. Sci.
Part A: Polym. Chem. 2000, 38, 4693–4703.
31 Hirano, T.; Morikami, A.; Fujioka, Y.; Ute, K. Polymer 2011,
52, 629–634.
5 Yamada, K.; Nakano, T.; Okamoto, Y. Polym. J. 1998, 30, 641–645.
6 Liu, W.; Koike, Y.; Okamoto, Y. Polymer 2004, 45, 5491–5495.
32 Isobe, Y.; Fujioka, D.; Habaue, S.; Okamoto, Y. J. Am. Chem.
Soc. 2001, 123, 7180–7181.
7 Uryu, T.; Shiroki, H.; Okada, M.; Hosonuma, K.; Matsuzaki, K.
J. Polym. Sci. Part A-1: Polym. Chem. 1971, 9, 2335–2342.
33 Habaue, S.; Isobe, Y.; Okamoto, Y. Tetrahedron 2002, 58,
8205–8209.
8 Liu, W.; Nakano, T.; Okamoto, Y. J. Polym. Sci. Part A:
Polym. Chem. 2000, 38, 1024–1032.
34 Hirano, T.; Kamikubo, T.; Fujioka, Y.; Ute, K. Polym. Int., in
press.
9 Liu, W.; Tang, K.; Guo, Y.; Koike, Y.; Okamoto, Y. J. Fluorine
Chem. 2003, 123, 147–151.
35 Hatada, K.; Kitayama, T.; Hirano, T. Polym. News 2005, 30,
277–283.
10 Majumdar, R. N.; Harwood, H. J. Polym. Bull. 1981, 4,
391–397.
36 Dunitz, J. D.; Taylor, R. Chem. Eur. J. 1997, 3, 89–98.
11 Victor, M. W.; Saffariannour, M.; Reynolds, J. R. J. Macro-
mol. Sci. Part A: Pure Appl. Chem. 1994, 31, 721–736.
37 Mori, T.; Hirano, T.; Maruyama, A.; Katayama, Y.; Niidome,
T.; Bando, Y.; Ute, K.; Takaku, S.; Maeda, Y. Langmuir 2008, 25,
48–50.
12 Sato, T.; Maeda, Y.; Seno, M.; Hirano, T. J. Polym. Sci. Part
A: Polym. Chem. 2001, 39, 2196–2205.
38 Gil, V. M. S.; Oliveira, N. C. J. Chem. Educ. 1990, 67,
473–478.
13 Hirano, T.; Kamikubo, T.; Fujioka, Y.; Sato, T. Eur. Polym. J.
2008, 44, 1053–1059.
39 Macomber, R. S. J. Chem. Educ. 1992, 69, 375.
14 Hirano, T.; Miki, H.; Seno, M.; Sato, T. Polymer 2005, 46,
3693–3699.
40 Kitayama, T.; Hirano, T.; Hatada, K. Polym. J. 1996, 28,
61–67.
15 Hirano, T.; Ishizu, H.; Sato, T. Polymer 2008, 49, 438–445.
41 Kitayama, T.; Hirano, T.; Hatada, K. Polym. J. 1996, 28,
1110–1111.
42 Mn ¼ 5.5 ꢁ 104, Mw/Mn ¼ 1.9.
43 Tang, Y.; Ding, Y.; Zhang, G. J. Phys. Chem. B 2008, 112,
16 Hirano, T.; Okumura, Y.; Kitajima, H.; Seno, M.; Sato, T. J.
Polym. Sci. Part A: Polym. Chem. 2006, 44, 4450–4460.
17 Hirano, T.; Nakamura, K.; Kamikubo, T.; Ishii, S.; Tani, K.;
Mori, T.; Sato, T. J. Polym. Sci. Part A: Polym. Chem. 2008, 46,
4575–4583.
8447–8451.
44 Hirano, T.; Yamamoto, H.; Ute, K. Polymer 2011, 52,
5277–5281.
18 Hirano, T.; Kamikubo, T.; Okumura, Y.; Bando, Y.; Yamaoka,
R.; Mori, T.; Ute, K. J. Polym. Sci. Part A: Polym. Chem. 2009,
47, 2539–2550.
45 Randall, J. C. Macromolecules 1978, 11, 592–597.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
13