Synthesis and characterization of novel amphiphilic telechelic polyoxetanes

Article abstract of DOI:10.1021/ma034846+

Alcohol-terminated telechelic polyoxetanes with semifluorinated (FOx) and alkyl ether pendant groups (ME2Ox) were synthesized and characterized. These are amphiphilic telechelics by virtue of incorporation of both hydrophilic and hydrophobic repeat units.

Full text of DOI:10.1021/ma034846+

Macromolecules 2003, 36, 9383-9389
9383
Synthesis and Characterization of Novel Amphiphilic Telechelic
Polyoxetanes
Tom ok o F u jiw a r a , Um it Ma k a l, a n d Ken n eth J . Wyn n e*
Department of Chemical Engineering, Virginia Commonwealth University,
Richmond, Virginia 23284-3028
Received J une 20, 2003; Revised Manuscript Received September 26, 2003
ABSTRACT: Alcohol-terminated telechelic polyoxetanes with semifluorinated (FOx) and alkyl ether
pendant groups (ME2Ox) were synthesized and characterized. These are amphiphilic telechelics by virtue
of incorporation of both hydrophilic and hydrophobic repeat units. The ME2Ox/FOx telechelic copolymers
were characterized by NMR spectroscopy for composition and molecular weight through end-group
g
analysis. Differential scanning calorimetry revealed decreasing T with increasing incorporation of ME2Ox
and provided evidence for copolymer structure. Monomer reactivity ratios were determined in two solvents
with different polarity. In methylene chloride, an active end derived from 5FOx monomer reacts
preferentially with ME2Ox whereas the ME2Ox-derived end shows no selectively. The reactivity ratios
are 0.97 for ME2Ox and 0.12 for 5FOx. In methylcyclohexane, the monomer reactivity ratios are more
characteristic of ideal copolymerization. The parameters are 1.65 for ME2Ox and 0.49 for 5FOx.
In tr od u ction
synthesis of polyurethanes containing semifluorinated
oxetane polymers.
1
5
Polyurethanes (PUs) constitute an important class of
polymers for materials and biomaterials applications.
1
To effect economical surface modification while re-
taining bulk properties, a surface-modifying additive
The solid-state structure is comprised of a hard or
reinforcing phase through hydrogen bonding and a soft
or low-Tg domain. The degree of phase mixing is wide-
ranging depending on the nature of hard and soft blocks.
Understanding the nature of the polyurethane-air
interface and changes that occur during the formation
of an aqueous interface is of importance for a broad
range of materials and biomaterials development. Our
work is aimed at new telechelic polymers that will
control the nature of these interfaces.
1
6,17
(
SMA) approach is attractive.
suggests, a specialized surface-active soft block PU
usually about 1%) is coprocessed with a standard bulk
As the term “additive”
(
polyurethane. Fluorinated polyoxetanes (FOx) have
been used as SMAs in blends, resulting in fluorinated
surfaces with characteristic hydrophobicity and oleo-
phobicity. Thomas and McGrath found that only 2 wt
%
3-trifluoroethoxymethyl-3-methyloxetane telechelic
polymer in a conventional polyurethane composition
resulted in 95% fluorinated oxetane surface composition
Recent results from tapping mode atomic force mi-
croscopy (TM-AFM) on polyurethanes utilizing poly-
1
8
(by ESCA at a 15° takeoff angle).
Considering the important role of soft blocks in
(
tetramethylene oxide) (PTMO) have refocused attention
2
controlling surface properties, modification of soft blocks
to effect surface functionalization is attractive. The
on the soft block as the predominant surface domain.
The AFM results reinforce and add a new dimension to
prior spectroscopic studies and contact angle measure-
1
9,20
surface exclusion of end groups
was coupled with
3
surface soft block concentration to generate PU-SMA
ments, such as the work of Andrade, that emphasized
the important interfacial role of the soft block. Interest-
ingly, PTMO was the first polyether used as a low-Tg
polyurethane soft block for elastomers and is utilized
in a variety of commercially available thermoplastics,
coatings, and foams. As the work of Runt demonstrates,
thermoplastics containing PTMO soft blocks continue
to be actively studied as biomaterials.1
compositions that are effective against protein adsorp-
1
6
tion. Functionalization of end groups has given SMAs
that favor growth of endothelial cells on a commercial
4
2
1
PTMO-based PU.
The importance of the soft block in defining the nature
of the PU surface has led us to explore a new architec-
ture that may be useful in SMAs. We have focused on
telechelic polyoxetanes incorporating differing func-
tional groups pendant to the main chain. In one model,
we are interested in using “air-philic” fluorinated groups
to bring functional groups to the polymer surface. The
resulting “dual functional telechelics” (DFTs) have side
chains with contrasting driving forces at the polymer-
air and polymer-water interfaces (Figure 1). Using
DFT-containing polyurethanes as PU-SMAs is ex-
pected to lead to PUs with novel combinations of surface
and bulk properties.
,5-7
A number of approaches have been pursued to modify
the surface properties of polyurethanes. Changing the
soft block changes surface properties but creates an
entirely new material so that the whole gamut of bulk
properties must be evaluated. The introduction of
fluorinated functionality is well-known for providing
polymer surfaces that are oleophobic as well as hydro-
8
-11
phobic.
In a series of patents, Malik et al. reported
the synthesis of semifluorinated oxetanes useful as soft
1
2,13
blocks (Tg ∼ -40 °C) in polyurethanes.
We reported
polyurethanes incorporating the poly(3-heptafluorobu-
In initiating work on DFT containing polyurethanes,
we have reported wetting behavior of polyurethane
surfaces containing a bromomethyl-substituted poly-
toxymethyl-3-methyloxetane) as the soft block (Tg ∼ -50
°
C) with a hard block generated conventionally using
2
2
benzenedimethanol (BDM)-methylene diphenyl isocy-
anate (MDI). McGrath confirmed and extended the
oxetane. The present report focuses on the synthesis
of DFTs with hydrophobic semifluorinated and hydro-
1
4
1
0.1021/ma034846+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/20/2003

9
384 Fujiwara et al.
Macromolecules, Vol. 36, No. 25, 2003
Sch em e 1
philic alkyl ether (methoxyethoxyethoxy) pendant groups.
Synthesis via cationic ring-opening polymerization
was utilized as previously described for semifluorinated
polyoxetanes by Malik.13 Ring-opening polymerization
of oxetane monomers using BF3 catalyst is well-known.
Saegusa et al. have investigated reactivities of differ-
ently substituted oxetanes in polar and nonpolar sol-
Exp er im en ta l Section
Ma ter ia ls. 3-(2,2,3,3,3-Pentafluoropropoxymethyl)-3-meth-
yloxetane (5FOx), 3-(2,2,3,3,4,4,4-heptafluorobutoxymethyl)-
3
-methyloxetane (7FOx), and 3-bromomethyl-3-methyloxetane
(BrOx) were synthesized from published procedures13 or
generously provided by Gencorp Aerojet (Sacramento, CA) or
Omnova Solutions (Akron OH). All monomers were distilled
under vacuum before use: 5FOx and 7FOx at 100 °C/5 mmHg
and BrOx at 85 °C/5 mmHg. 2-(2-Methoxyethoxy)ethanol from
Aldrich and 1,4-butanediol from Acros Organics were distilled
2
3
vents. Bucquoye and Goethals determined copolymer-
ization reactivity ratios for oxetane and 3,3-dimethyl-
oxetane and analyzed microstructure of the copolymer
by triad abundances.24 Manser and Ross have demon-
strated the living-like character of oxetane oligomeriza-
tion using BF3/1,4-butanediol initiation at a molar ratio
of 2/1.25 Prud’homme et al. recently reported the copo-
lymerization of 3,3-bis(chloromethyl)oxetane and ꢀ-ca-
prolactone and modification to poly(3,3-bis(azidomethyl)-
oxetane-co-ꢀ-caprolactone).26 Kubisa summarized the
propagation mechanisms of cyclic ethers with hydroxyl
under vacuum before use. Boron trifluoride dietherate [BF
3
O-
(
C
2
H
5
)
2
, BF ] and tetrabutylammonium bromide (TBAB)
3
-OEt
2
were used as received. Methylene chloride and other organic
solvents were used as received or kept with molecular sieves
4
A.
Mon om er Syn th esis. 3-(Methoxyethoxyethoxymethyl)-3-
methyloxetane (ME2Ox) was synthesized using phase transfer
catalysis (PTC) (Scheme 1). A mixture of 2-(2-methoxyethoxy)-
ethanol (60.1 g, 0.5 mol), BrOx (82.5 g, 0.5 mol), TBAB (8.0 g,
0.025 mol), and water (20 mL) was stirred and heated to 75
groups.2
7,28
°
C. Then, a solution of KOH (35.5 g, 87%, 0.55 mol) in water
In preparing polyoxetanes with hydrophobic semi-
fluorinated and hydrophilic alkyl ether (methoxyethoxy-
ethoxy) pendant groups, we provide telechelic polymers
that can be used to explore surface properties of
polymers incorporating these DFTs. The novel DFTs
described herein were characterized by NMR spectros-
copy to analyze composition and molecular weight, and
their thermal properties were determined by DSC
analysis.
(
50 mL) was added. The reaction mixture was stirred vigor-
ously at 80-85 °C for 7 h. The mixture was cooled to room
temperature, filtered, and diluted with water. The product was
extracted with methylene chloride and distilled at 100 °C/8
mmHg. ME2Ox monomer. H NMR (CDCl
1
3
): δ 1.32 (-CH
CH O-, 4H, m),
-, 2H, m), δ 4.35 (ring
3
,
3
H, s), δ 3.39 (-OCH
δ 3.67 (-OCH CH O-, 4H, and -CH
CH -, 2H, d), δ 4.52 (ring CH , 2H, d). C NMR (CDCl
1.5 (-CH ), δ 40.0 (-C-), δ 59.1 (-OCH ), δ 70.7, 71.1, and
2.1 (-OCH CH O-), δ 76.6 (-CH -), δ 80.2 (ring -CH -).
FOx monomer was prepared from BrOx and 2,2,3,3,4,4,4-
heptafluorobutanol by the same procedure used for ME2Ox
3
3H, s), δ 3.55 (-OCH
2
2
2
2
2
1
3
-
2
7
2
2
3
): δ
3
3
2
2
2
2
We use ME2Ox to designate the oxetane made from
-(2-methoxyethoxy)ethanol and 3-bromomethyl-3-
7
2
1
methyloxetane. ME2Ox is also used for the derived
polymer segment. This acronym is a shortened version
from that previously utilized.29 We do so in anticipation
of work with longer oligomeric side chains such as
ME3Ox.
monomer. 7-FOx monomer. H NMR (CDCl
3H, s), δ 3.67 (-CH -, 2H, s), δ 3.99 (-CH
4.34 (ring -CH -, 2H, d), δ 4.50 (ring -CH -, 2H, d).
Telech elic P olyoxeta n e Syn th esis. Homo- and copolym-
erization of ME2Ox and FOx monomers were carried out by a
modification of a published procedure for FOx and 3-bromo-
methyl-3-methyloxetane.13 Cationic ring-opening polymeriza-
3
): δ 1.31 (-CH
3
,
2
2
CF -, 2H, t), δ
2
2
2
3
tion was employed using BF and 1,4-butanediol as catalyst
and cocatalyst, respectively. Methylene chloride (10 mL) was
poured into a round-bottom flask under nitrogen. 1,4-Butane-
diol (165 mg, 1.84 mmol) and BF
3
2
-OEt (520 mg, 3.67 mmol)
in methylene chloride (10 mL) were added and stirred at room
temperature for 45 min under nitrogen. Then the solution was
cooled to 0-5 °C in ice bath, and a mixture of ME2Ox and
FOx monomers (e.g., total 36.7 mmol) in methylene chloride
(10 mL) was added dropwise at the rate of 0.5 mL/min. The
reaction was kept at 0-5 °C for 4 h with stirring. The reaction
mixture was then brought to room temperature and quenched
with 30 mL of water. The organic phase was separated and
washed with 0.2% HCl and NaCl aqueous solution, and then
solvent was evaporated. The product (a viscous, opaque liquid)
was redissolved in acetone and reprecipitated in water. The
resulting viscous liquid was separated and dried in a vacuum
oven at 70 °C, 5 Torr overnight to give a transparent oily
product with >80% yield.
ME2Ox homopolymer. H NMR (CDCl
F igu r e 1. Depiction of synergistic dual functionality by which
1
a fluorinated group [CF
3
(CF
2
)
n
] brings desired surface func-
3
): δ 0.91 (-CH
3
, 3H,
tionality to the elastomer (polyurethane) surface.
s), δ 3.19 (backbone -CH
2
-, 4H, m), δ 3.30 (-CH -, 2H, s), δ
2

Macromolecules, Vol. 36, No. 25, 2003
Novel Amphiphilic Telechelic Polyoxetanes 9385
1
F igu r e 2. Typical H NMR spectrum of ME2Ox/5FOx (1/1)
copolymer.
F igu r e 4. Plot of degree of polymerization as a function of
monomer/cocatalyst ratios.
In str u m en ts. The chemical structures of synthetic materi-
1
13
als were established by H and C NMR (Varian, Inova 400
MHz) in CDCl . The molecular weight and composition were
3
1
determined from the integration of specific peaks in H NMR
spectra. Gel permeation chromatography (GPC) was performed
on a Viscotek TriSEC triple detector system in THF with
sample concentrations of 3-6 mg/mL and a flow rate of 1 mL/
min. Universal calibration by polystyrene standards was used
n w
for calculation of molecular weight (M , M ) and polydispersity.
A TA-Q Series (TA Instruments) differential scanning calo-
rimeter (DSC) was used for obtaining glass transition tem-
peratures of polyoxetanes. The measurements were made
using indium for calibration at a heating rate of 20 °C/min
from -80 °C.
Resu lts a n d Discu ssion
Ch a r a cter iza tion a n d Molecu la r Weigh t An a ly-
sis. A new series of oxetane polymers have been
prepared containing hydrophobic fluoroalkyl groups and
a hydrophilic alkyl ether group (Scheme 1). A typical
1
F igu r e 3. Structure and H NMR spectrum of trifluoroacetyl
end groups of copolymers.
1
H NMR spectrum for ME2Ox/5FOx (1/1) copolymer is
shown in Figure 2. The composition ratios of ME2Ox
and FOx monomers in copolymer were determined from
integration of the H NMR peaks for the methylene
group b next to the alkyl ether chain (3.30 ppm) and
the methylene group g next to the semifluoroalkyl ether
chain (3.44 ppm).
Table 1 lists the molar ratios of monomer feed as well
as the compositions of polymers. Monomer/1,4-butane-
diol ratios were varied in order to make polyoxetanes
with differing molecular weights. The BF3-OEt2/1,4-
butanediol ratio was kept constant at 2.2/1, and in all
compositions in Table 1, the reactions were done under
a nitrogen atmosphere with a temperature at 0-5 °C.
Monomer ratios in copolymers are very close to feed
ratios.
GPC results are also listed in Table 1. The number-
average molecular weights (Mn) correlate well with end-
group analysis results for ME2Ox homopolymers and
ME2Ox/FOx copolymers but show higher values for
3
(
(
.38 (-OCH
-OCH CH
-CH ), δ 40.8-41.3 (backbone -C-), δ 58.9 (-OCH
CH O-), δ 70.9-71.3 (-CH -), δ 74.0
-).
ME2Ox/5FOx (ME2Ox/7FOx) copolymer. H NMR (CDCl
δ 0.91 (-CH for ME2Ox and FOx, 3H, s), δ 3.19 (backbone
CH -, 4H, m), δ 3.30 (-CH - for ME2Ox, 2H, s), δ 3.38
- for FOx, 2H, s), δ 3.55
O-, 4H, m), δ 3.64 (-OCH CH O-, 4H, m), δ 3.85
): δ 16.9-17.8 (-CH for
3
3H, s), δ 3.55 (-OCH
2
CH
2
O-, 4H, m), δ 3.64
): δ 17.3-17.9
), δ 70.4
1
1
3
2
2
O-, 4H, m). C NMR (CDCl
3
3
3
and 71.9 (-OCH
2
2
2
(backbone -CH
2
1
3
):
3
-
2
2
(
(
(
-OCH
3
3H, s), δ 3.44 (-CH
CH
CF -, 2H, t). C NMR (CDCl
2
-OCH
2
2
2
2
1
3
-CH
2
2
3
3
ME2Ox and FOx), δ 40.8-41.5 (backbone -C-), δ 58.6
-OCH ),δ68.0 (-CH CF -,t),δ70.4 and 71.9 (-OCH CH
δ 70.9-71.3 (-CH - for ME2Ox), δ 73.4 (backbone -CH
(
3
2
2
2
2
O-),
2
2
-
-
for FOx), δ 74.0 (backbone -CH
for FOx), δ 110.0-123.3 (-(CF
Molecu la r Weigh t Deter m in a tion . The degree of polym-
erization (D ) and equivalent molecular weight are determined
by end-group analysis. End-group analysis was performed by
the reaction of trifluoroacetic anhydride (TFA) with the
hydroxyl end group of polyoxetanes. A molar excess of TFA
2
- for ME2Ox), δ 75.3 (-CH
CF ).
2
2
)
n
3
p
5
FOx homopolymer. The molecular distribution has a
trend that the polydispersity (Mw/Mn) decreases as
monomer/cocatalyst ratio increases for all polymer
series. When the monomer/cocatalyst ratio is above 22,
the polydispersities are 1.9-2.2.
As shown in Table 1, the Dp of polymer is not directly
related to the monomer/cocatalyst ratios. Figure 4 is a
plot of Dp of polymers as a function of monomer/
3
was added to the polymer solution in CDCl . The solution was
1
stirred at room temperature for 1 h before measuring the H
NMR spectrum. Figure 3 shows the signals of methylene
protons next to the fluoroacetyl group for ME2Ox (a), FOx (b),
and butanediol (c) end groups. D and molecular weight are
p
calculated from the sum of those peaks against the methyl
peak of all oxetane repeat units.

9
386 Fujiwara et al.
Macromolecules, Vol. 36, No. 25, 2003
Ta ble 1. Cop olym er iza tion of ME2Ox a n d F Ox Mon om er s via BF 3-OEt2 Ca ta lyst System a t 0 °C in Meth yen e Ch lor id e
monomer feed ratio
polymers
equiv MWb
[
monomer]/
a
Dpb
c
3
Mw/Mnc
sample
ME2Ox
5FOx
7FOx
[cocatalyst]
ME2Ox/FOx
Mn (/10 )
M-1
M-2
M-3
M-4
M5F-1
M5F-2
M5F-3
M5F-4
F-1
F-2
F-3
F-4
M7F-1
M7F-2
1
1
1
1
0.5
0.5
0.5
0.5
5.5
11
22
33
5.5
11
22
33
5.5
11
22
33
22
22
12.4
16.9
18.6
18.2
16.8
17.9
20.8
20.6
20.1
27.3
31.9
36.8
18.6
14.9
2540
3450
3810
3710
3680
3910
4570
4520
4720
6390
7470
8620
4550
3440
3.4
3.6
3.0
3.3
4.0
4.8
4.7
4.8
8.7
11.6
11.8
12.9
5.3
2.7
3.2
2.1
2.2
2.6
2.8
1.9
1.9
2.4
2.1
1.9
2.0
2.2
1.9
0.5
0.5
0.5
0.5
1
1
1
1
0.53/0.47
0.54/0.46
0.53/0.47
0.52/0.48
0.5
0.67
0.5
0.33
0.55/0.45
0.66/0.34
4.5
a
Monomer to cocatalyst (1,4-butanediol) molar ratio, [BF3-OEt2]/[1,4-butanediol] ) 2.2 (constant). Determined by 1H NMR end-
b
c
group analysis. Determined by GPC.
cocatalyst ratio. The Dp of ME2Ox homopolymer, 5FOx
homopolymer, and their copolymer are not dependent
on the monomer/1,4-butanediol ratios. At low monomer/
(chloromethyl)oxetane and THF using BF3-OEt2 is also
nearly nonselective, with the r1 and r2 equal 0.82 and
3
4
1.00, respectively. Thus, in these cases cyclic ether
reactivities are close to unity and copolymerization gives
random sequences. Near-ideal selective copolymeriza-
tion is observed for tetrahydrofuran and 3,3-dimethyl-
oxetane with the r1 and r2 equal 0.13 and 8.1, respec-
1
,4-butanediol ratio, all polymers have higher molecular
weight than calculated values. However, when the
monomer/1,4-butanediol ratio is increased, the increase
of Dp is small. The insensitivity of Dp to monomer/1,4-
butanediol ratio is especially noteworthy for ME2Ox
homo- and copolymers, where Dp plateaus at a monomer/
cocatalyst ratio of 20/1.
3
5
tively. Similar behavior is observed for 3-methyltetra-
3
6
hydrofuran and 3,3-dimethyloxetane. Finally, a case
of alternating tendency has been shown for an oxetane
copolymerization with caprolactone. The r1 and r2 for
3,3-bis(chloromethyl)oxetane and ꢀ-caprolactone are
From the literature, polyoxetane molecular weight is
2
6,27,30-32
controllable in favorable cases.
It is known that
2
6
ring-opening propagation of heterocyclic monomers us-
ing BF3 catalyst proceeds via two different mecha-
0.26 and 0.48, respectively.
To estimate copolymer composition, the reactivity
3
0
nisms. The active chain-end mechanism is typical for
cationic polymerizations. Alternatively, polymerization
may occur by an activated monomer mechanism. That
is, in the presence of alcohol or diol, monomers compete
with alcohol groups, [OH], as transfer agents. Which
mechanism predominates depends on the kinetics of
each process. An important factor influencing the mech-
anism is the instantaneous [M]/[OH], which depends on
the rate of monomer addition and/or temperature. Well-
controlled living-like polymerization of cyclic ethers
using the BF3-OEt2/1,4-butanediol system has been
reported to occur only through the activated monomer
ratios r1 and r2 for ME2Ox and 5FOx, respectively, were
3
7
determined using Finemann-Ross (F-R) and Kelen-
3
8
Tudos (K-T) methods. The values of r1 ) k11/k12 and
r2 ) k22/k21 are the ratio of homopropagation/cross-
propagation rate constant for each monomer species. All
polymerizations were performed in methylene chloride
at the same conditions described in the Experimental
Section and terminated below 10% monomer conversion
to minimize errors due to changes in the feed ratio. The
1
copolymer compositions were calculated from each H
NMR spectrum for methylene groups next to the ME2Ox
and 5FOx side chains, that is, peaks b and g (Figure
2).
2
6,27
mechanism.
For ME2Ox and FOx polymers, 1H NMR analysis
vide infra) indicates the polymerization proceeds via
The F-R plot shown in Figure 5a was fitted to a
2
(
straight line with R ) 0.990. Two separate data sets
mixed mechanisms. Chain transfer or chain termination
may be favored for ME2Ox monomer due to competition
from oxygen in ether side groups. Whatever the cause,
under the reaction conditions used, Dp reaches a maxi-
mum value for ME2Ox-containing polyoxetanes. For-
tunately, the molecular weights obtained approximate
those required for utilization as PU soft blocks. Chang-
ing reaction conditions, such as lowering temperature,
may be necessary for gaining a stronger dependency of
molecular weight on the monomer-to-catalyst ratio.
Mon om er Rea ctivity Ra tios. The majority of co-
polymerization studies to determine reactivity ratios
involve vinyl monomers.33 However, there are a few
reports applying this classic method to the evaluation
of reactivity ratios for ring-opening polymerizations
where one comonomer is an oxetane. For example, the
copolymerization of oxetane and 3,3-dimethyloxetane
using BF4-OEt3 in methylene chloride is almost ideally
nonselective with the r1 and r2 equal to 1.19 and 0.95,
respectively.24 Also, the copolymerization of 3,3-bis-
were collected demonstrating reproducibility. The values
of r1 and r2 obtained from this plot are 0.97 for ME2Ox
and 0.12 for 5FOx, respectively. Similar values are
calculated by the K-T method (r1 ) 0.98, r2 ) 0.28).
These r1 and r2 values indicate that the active end
derived from ME2Ox reacts with both monomers equally,
whereas the 5FOx-derived end favors reaction with the
ME2Ox monomer. Generally, the reactivity of the cyclic
ether itself depends on basicity and ring strain. One
might expect similar reactivities for ME2Ox and 5FOx
monomers because of the similar nucleophilicity re-
1
flected in similar chemical shifts of ring-methylene H
NMR peaks for both monomers. However, the result
obtained indicates that the 5FOx growing species has
clear monomer selectivity. The values show r1 ≈ 1 > r2
and r1r2 () k11k22/k12k21) ) 0.12, much smaller than
unity.
This analysis indicates that, while the instantaneous
monomer ratio is 1:1, the copolymer units being formed
have a composition in which the 5FOx-5FOx dyad mole

Macromolecules, Vol. 36, No. 25, 2003
Novel Amphiphilic Telechelic Polyoxetanes 9387
F igu r e 6. F-R plot (a) and composition diagram (b) for
ME2Ox/5FOx copolymerization in methylcyclohexane.
F igu r e 5. F-R plot (a) and composition diagram (b) for
ME2Ox/5FOx copolymerization in methylene chloride.
hexane, resulting in an ideal random copolymer com-
position.
fraction is well below the statistically predicted amount.
That is, most 5FOx exists in dyads combined with
ME2Ox. Also, there is a greater than statistical amount
of ME2Ox-ME2Ox dyads. However, the telechelic poly-
oxetanes isolated at the completion of the batch syn-
theses are expected to have dyad compositions that are
not very different from a statistical copolymer.
Figure 5b shows the composition diagram, which is a
plot of mole fraction for 5FOx in copolymer (f2) as a
function of its mole fraction in the monomer feed (F2)
for 11 experiments. The dashed line corresponds to ideal
random copolymerization (r1 ) r2 ) 1). The solid line,
the theoretical curve for r1 ) 0.97, r2 ) 0.12, does not
intersect the ideal line.
There are relatively few studies of oxetane copolym-
erization. In the polymerization of oxetane with 3,3-
dimethyloxetane, the reactivity ratios are both close to
2
4
unity. That may also be the case in the copolymeri-
zation of 3,3-bis(hydroxymethyl)oxetane with 3-ethyl-
4
0
3-(hydroxymethyl)oxetane and in the reaction of 3,3-
bis(azidomethyl)oxetane with either 3-azidomethyl-3-
(2,5-dioxaheptyl)oxetane or 3-azidomethyl-3-(2,5,8-trioxa-
4
1
decyl)oxetane. In the solution-phase copolymerization
of 3,3-bis(chloromethyl)oxetane with 3-ethyl-3-(chloro-
4
2
methyl)oxetane and the reaction of 3,3-bis(azido-
methyl)oxetane with 3-chloromethyl-3-(2,5,8-trioxadecyl)-
4
3
oxetane, selectivity is inferred from the composition
of products at high conversion. The selectivity observed
for the ME2Ox-5FOx system in methylene chloride
may be somewhat unusual. However, the effect on the
structure and composition of the telechelic polyoxetanes
isolated from synthetic procedures is confounded be-
cause these reactions are run to high conversion.
To investigate the monomer sequence issue further,
monomer reactivity ratios in a nonpolar solvent were
examined. Methylcyclohexane has a solvent polarity
parameter of 0.563 compared to 0.875 for methylene
chloride from the solvent polarity/polarizability (SPP)
3
9
calculation by Catal a´ n. The F-R plot and the compo-
sition diagram are shown in Figure 6a,b. Ratios r1
and r2 are 1.65 for ME2Ox and 0.49 for 5FOx, with
Ta cticity. Polymer tacticity is often affected by
catalyst, counteranion, monomer substituent, solvent
polarity, and reaction temperature. Stereoregularity in
cationic polymerization in homogeneous systems has
been investigated for poly(vinyl ether)s. Isotactic-rich
polymer was obtained using BF3-OEt2 in nonpolar
2
R ) 0.998. In methylcyclohexane r1 > 1 > r2, and r1r2
(
) k11k22/k12k21) is closer to unity (0.81), indicating near-
ideal copolymerization.
Generally, solvent polarity shows an effect on reactiv-
ity in ionic polymerization when the structures or
basicities of two monomers are different. Basicities of
ME2Ox and 5FOx are presumably similar but might
have slight differences caused by electron-donating alkyl
ether group vs the electron-accepting fluoro group. This
substituent effect can be larger in a polar solvent than
that in a nonpolar solvent, accounting for the results
in methylene chloride. However, monomer selectivity of
the growing species decreases in nonpolar methylcyclo-
4
4,45
solvent at low temperature.
Tacticity of polyethers
obtained from cyclic ethers by cationic polymerization
has not been reported.
Figure 7 shows a typical 13C NMR spectrum of
ME2Ox/5FOx (1/1) copolymer. Of all polyoxetane car-
bons, three carbons (-CH3 (a , a ′) and -CH2- (d , d ′)
side groups and -C- for main chain (b, b′)) give
multiple peaks. Peaks for -CH3 (a , a ′) are shown in the

9
388 Fujiwara et al.
Macromolecules, Vol. 36, No. 25, 2003
F igu r e 7. Typical 13C NMR spectrum of ME2Ox/5FOx (1/1) copolymer. The expanded spectra are the part of ME2Ox homopolymer,
5
FOx homopolymer, and copolymer.
Ta ble 2. Gla ss Tr a n sition Tem p er a tu r es (Tg) for
P olyoxeta n es
homo- or
homo- or
copolymers
Tg (°C)
copolymers
Tg (°C)
ME2Ox
-67.3
-43.5
-52.7
ME2Ox/5FOx (1/1)
ME2Ox/7FOx (1/1)
ME2Ox/7FOx (2/1)
-56.9
-55.6
-58.3
5
7
FOx
FOx
expanded insert. To understand the origin of these
multiple peaks, the spectra of homo-ME2Ox and homo-
5
FOx were examined. The methyl carbon peaks of
homo-ME2Ox (a M) and homo-5FOx (a F ′) are shown in
the inset. ME2Ox homopolymer has multiple peaks
whereas 5FOx homopolymer shows a single peak with
a small second peak. This pattern is also observed for
the methylene carbon (d M and d F ′) peaks for ME2Ox
and 5FOx homopolymers, respectively.
For ME2Ox homopolymer the origin of the three
peaks may be different carbon environments in isotactic,
syndiotactic, and atactic configurations. In contrast, one
dominant peak is seen for 5FOx. This suggests that the
F igu r e 8. Typical DSC curves of polyoxetanes with heating
rate of 20 °C/min: (a) ME2Ox homopolymer, (b) physical
mixture of ME2Ox and 5FOx homopolymers, (c) 5FOx homo-
polymer, and (d) ME2Ox/5FOx (1/1) copolymer.
5
FOx polymer may have a dominant tacticity or that
the carbon peaks are accidentally degenerate.
For the ME2Ox/5FOx (1/1) copolymer, broad multiple
peaks (a , a ′) are observed. The 5FOx methyl group peak
is notably broadened compared to the homopolymer,
consistent with a copolymer structure vs a mixture of
homopolymers.
Tacticity is a very important determinant for proper-
ties (e.g., Tg) of polymers. Further investigation of
polyoxetanes synthesized under varying reaction condi-
tions will be required for confirmation of tacticity effects
in this cationic ring-opening polymerization.
homopolymers. This mixture has two Tg’s because the
two homopolymers are completely immiscible. In con-
trast, ME2Ox/5FOx (1/1) copolymer gives one Tg at -57
°
C in between the Tg’s of the homopolymers. This result
supports the composition study of the copolymer that
indicates a random or alternating tendency but not
blocky sequence. The Tg of copolymer can be estimated
by the Fox equation using the Tg’s of homopolymers:
Th er m a l An a lysis. Glass transition temperatures
(
Tg’s) of the polyoxetanes were measured using subam-
-
1
-1
-1
Tg(cal) ) w T
+ w T
2 g2
bient DSC. Table 2 shows Tg of ME2Ox and FOx
homopolymers and their copolymers. ME2Ox homopoly-
mer has the lowest Tg (-67 °C) close to the Tg of PTMO
1
g1
where w1 and w2 are the weight fraction of each
component. Using w(ME2Ox) and w(5FOx) and homopolymer
Tgs, Tg(cal) is -54 °C for ME2Ox/5FOx (1/1). Similarly,
Tg(cal) of ME2Ox/7FOx (1/1) and ME2Ox/7FOx (2/1) is
(
ca. -70 °C). Typical DSC curves are shown in Figure
. The Tg of 5FOx homopolymer is -44 °C. Curve b is
the scan of a physical mixture of ME2Ox and 5FOx
8

Macromolecules, Vol. 36, No. 25, 2003
Novel Amphiphilic Telechelic Polyoxetanes 9389
-
58 and -60 °C, respectively. Calculated Tgs are close
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(
(
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(
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