Determination of the distribution of acrylic comonomers in free radicals polymers

Article abstract of DOI:10.14233/ajchem.2013.13194

Some acrylate monomers have been synthesized and copolymerized by means of free radical polymerization with methyl methacrylate and butyl methacrylate. These monomers are known to introduce the desired functionality and tune the properties of the resulting polymer. The synthesized monomers and the polymers have been characterized with NMR spectroscopy. The latter is utilized to study the polymer composition and verify the distribution of the monomers in the copolymer chain. The reactivity ratios have been estimated and concluded moderately random distribution of the monomers in the copolymer chain.

Full text of DOI:10.14233/ajchem.2013.13194

Asian Journal of Chemistry; Vol. 25, No. 1 (2013), 475-479
http://dx.doi.org/10.14233/ajchem.2013.13194
Determination of the Distribution of Acrylic Comonomers in Free Radicals Polymers
1
,*
2
1
1
1
ADELAIDA ANDONI , JASPER J. MICHELS , EFROSINI KOKALARI (TELI) , KRENAIDA TARAJ and ARMAND ÇOMO
1
2
Department of Chemistry, Faculty of Natural Sciences, Blv. "Zog I", 1001, University of Tirana, Tirana, Albania
TNO Science and Industry, P.O. Box 6235, 5600 HE Eindhoven, The Netherlands
*
Corresponding author: E-mail: adelaida.andoni@unitir.edu.al; adelaida.andoni@fshn.edu.al
(
Received: 7 December 2011; Accepted: 30 July 2012)
AJC-11903
Some acrylate monomers have been synthesized and copolymerized by means of free radical polymerization with methyl methacrylate
and butyl methacrylate. These monomers are known to introduce the desired functionality and tune the properties of the resulting polymer.
The synthesized monomers and the polymers have been characterized with NMR spectroscopy. The latter is utilized to study the polymer
composition and verify the distribution of the monomers in the copolymer chain. The reactivity ratios have been estimated and concluded
moderately random distribution of the monomers in the copolymer chain.
Key Words: Acrylate monomers, Free radical polymerization, Reacitivity ratios.
O
INTRODUCTION
O
CO H
2
CO2
O
N
H
One of the most common and useful reactions to make
O
polymers is free radical polymerization. This polymerization
is used to make polymers from monomers containing carbon-
carbon double bonds such as acrylates, vinyl monomers, allylic
monomers etc. Some acrylate monomers have been used by
1
4
O
OH
O
N
H
N
H
1
2
O
Voss et al. and Wouters et al. to study the effect of pendant
functionality on the thermal and physical properties of polymers
obtained by the reversible addition-fragmentation chain-transfer
2
5
(
RAFT) polymerization. The methacrylate copolymers studied
O
by these authors contained n-butyl-methacrylate and methyl
methacrylate (MMA) to control the glass transition temperature
of the final polymer and a minor fraction of one of the mono-
mers displayed in Fig. 1. These monomers were chosen for
their particular interacting capabilities (H-bonding or π-π
interaction). In this study, the authors assumed that the distri-
bution of comonomers in the RAFT polymers is random and
nevertheless no further investigation was done to prove this
supposition.
3
Fig. 1. Chemical structures of the monomers 1, 2, 3, 4 and 5
Free radical polymerization: Three main kinetic steps
occur during free radical polymerization: (1) initiation, (2)
propagation and (3) termination. Free radicals are usually gene-
rated by the addition of an initiator. The latter forms radicals
when heated or irradiated. Two common examples of compounds,
which afford free radicals are benzoyl peroxide (BPO) (Fig.
1
2
We extended the work of Voss et al. and Wouters et al.
by performing free radical copolymerization of monomers 3
and 5 with methyl methacrylate and butyl-methacrylate with
the aim to estimate the reactivity ratios, giving though insight
in the monomer distribution in the polymer chain. The copoly-
merizations of monomers 3 and 5 with both methyl methacrylate
and butyl methacrylate were carried out. Subsequently, the
reactivy ratios are determined and the compositions of the
2
a) and 2-2'-azo-bis-isobutyrylnitrile (AIBN) (Fig. 2b).
a)
b)
O
O
C
CH3
C
CH3
CH3
H C C +
N
2
∆
C O
:
O
H
3
C
N N
C
C
N
CH
3
2
.
3
slow
C
N
C
Benzoyl peroxide
O
N
2
C O'
1
present polymers are presented. H NMR spectroscopy is
employed to study the polymer composition.
Fig. 2. Generation of the free radicals by thermal decomposition of (a)
benzoyl peroxide; (b) AIBN to form free radicals

476 Andoni et al.
Asian J. Chem.
The process starts with the initiation, which involves two
reactions. The first one is the production of the free radicals.
The low concentrations of the radical chain-ends in the
systems are difficult to be determined experimentally. For this
reason a steady state approximation is applied for species
ˆ
The initiator will split to give a pair of radicals R :
ˆ
ˆ
kd
•
I →2R . The carbon-carbon double bond, for instance,
1 2
......M and ......M to remove the corresponding factors from
2
the eqn. (3). The interconversion between the two species must
be equal in order for the concentrations of each to remain
constant and hence the rates of reactions with rate constant k12
of an acrylate has a pair of electrons, which is attacked by the
free radicals. The unpaired electrons of the radical combine
with one of the electrons of the carbon-carbon double bond
by creating a new pair of electrons and therefore making a
new chemical bond between the free radical and the double
•
•
4
and k21 must be equal: k21
[L LM
]
[M
]
= k12
[L LM
]
[M
]
(4) .
2
1
1
2
Rearrangement of eqn. (4) and combination with eqn. (3) gives
eqn. (5):
bond of the monomer:
H
•
2
•
ki
R + M →M
•
i
.
.
R +CH =CHX
2
R-CH -C
2
k
11
k
21
[
LLM
2
]
[
M
1
]
•
+ k21
+ k21
[
LLM2
]
[
M1
]
,
d
[
M1
]
]
k12
[
M2
]
X
=
(5)
•
•
The unpaired electron created after the double bond has
been attacked associates itself with the carbon atom which is
not bonded to the initiator fragment. Therefore the chain ends
with a free radical can be combined with another carbon-
carbon double bond of the next monomer and the process
results in propagation. Thus a polymer is formed. As propa-
gation continues and each monomer unit is added, the radical
has the same identity as the radical before except it is larger
d
[
M2
k22
[
LLM2
]
[
M2
]
[
LLM2
]
[
M1
]
This equation can be further simplified by dividing the
4
right side (nominator and denominator by k21
•
[
LLM2
]
[
M1
]
and r
.
,
The results are then combined with the parameters r
which are defined to be the reactivity ratios: r
1
2
1
= k11/k12 and r
2
= 22/k21 (6). The most familiar form of the copolymerization
composition equation is then obtained:
k
•
1
kP
•
2
by unit: M + M →M . Propagation with growth of the
d
[
M2
M1
]
]
[
M1
]
(
r
1[M1
]
M1 + r2
+
[
[
M2
]
)
])
=
3,5
(
7)
chain to higher molecular weight polymer takes place rapidly
but at some point the propagating radical at the end of the
polymer chain stops growing and terminates.
d
[
[
M2
]
(
[
]
M2
At low conversion, where the concentration of monomers
does not change appreciably equation (7) can be approximated
Reactivity ratios: In a free radical copolymerization of
by equation (8): m m = M
(
r M + M
)
M2
is the mole fraction of monomer 1 in the reaction
system (amount in the feed) and M is the mole fraction of
monomer 2 in the reaction system (amount in the feed). m1
and m are the mole fractions of monomer 1 and 3 in the
(
M + r M
)
,
1
2
1
1
1
2
1
2
2
1 2
two monomers M and M four competing propagation steps
3
are considered (Fig. 3):
where, M
1
2
•
k11
•
LLM + M →LLM
1
1
1
•
k12
•
LLM + M   →LLM
2
1
2
2
polymer composed entirely of the two monomers (estimated
from the NMR spectra after short polymerizations). The
copolymer composition equation defines the molar ratios of
the two monomers that are incorporated into the copolymer. A
reactivity ratio expresses the ratio of the reactivity of a growing
•
k21
•
LLM + M   →LLM
2
1
1
•
k22
•
LLM + M   →LLM
2
2
2
1 2
Fig. 3. Reaction scheme of the copolymerization of M and M
ˆ
chain end towards its own monomer and that towards the other
3
monomer . Lastly, if r
The propagating chain that ends with M
with a monomer of type M or of type M
can react with a monomer unit of
. The rate constant for the reaction of the
1
can either react
1
= 1 and r
2
= 1 the monomers are
1
2
. The propagating
ˆ
randomly distributed: − − M M M M M M M M M − − . If
chain that ends with M
type M or of type M
propagating chain that ends with M
to the end of the chain is k11 and the rate constant for the
2
1
1
2
2
2
1
2
1
1
1 2
r << 1 and r << 1 the copolymer contains one or more long
1
2
ˆ
uninterrupted sequences of each of the comonomer species
1
and reacts with another
M
1
giving a block copolymer: − − M M M M − M M M M − − .
1
1
1
1
2
2
2
2
ˆ
reaction of the propagating chain that ends with M
reacts with M to the end of the chain is k21 and so on. Mono-
mers 1 and 2 are consumed as indicated by the reaction scheme
2
and
1 2
If r << 1 and r << 1 the polymer has equimolar compositions
1
with a regularly perfect alternating distribution of monomer
units. These are alternating copolymers: - - M M M M M
1
1
2
1
2
in Fig. 3. The change in monomer concentrations M
3
is expressed by equation (1) and (2) :
1
and M
2
2 1 2
M M M -- .
EXPERIMENTAL
Monomer synthesis: All the chemicals used for the
d
[
dt
M1
]
= k11
•
•
−
[
LLM1
]
[
M1
]
+ k21
[
LLM
]
[
M1
]
2
(1)
(2)
synthesis of monomers 3 and 5 were purchased from Aldrich
and used as received. Monomers 3 and 5 were synthesized as
described below. NMR spectra were recorded on a Varian
Mercury 400 spectrometer.
d
[
M2
]
= k12
•
•
−
[
LLM1
]
[
M2
]
+ k22
[
LLM
]
[
M2
]
2
dt
Equation (1) is divided by eqn. (2) to give the copolymer
composition equation (3):
Synthesis of monomer 3 (Fig. 4)
pyridine (dropwise)
•
•
Cl
HO
d
[
M1
]
]
k11
k12
[
LLM1
[
]
[
M1
]
]
+ k21
[
LLM
[
]
[
M1
]
3
2
+
THF, RT
=
•
•
2
(3)
d
[M2
LLM1
]
[
M2
+ k22
LLM
]
[
M2
]
O
Fig. 4. Reaction scheme for the synthesis of the monomer 3

Vol. 25, No. 1 (2013)
Determination of the Distribution of Acrylic Comonomers in Free Radicals Polymers 477
Reaction: 4-Phenyl phenol (C12
H
10O, M
w
= 170.22 g/mol,
used as eluent comparing the reaction mixture with the starting
material 2-methacryloyl oxyethyl isocyanate as a reference.
Reaction was completed after 48 h.
2
0 g, 117 mmol) was dissolved in 100 mL tertrahydrofuran
in a 250 mL 3-neck flask, equipped with a dropping funnel
preferably positioned at the middle neck), nitrogen inlet and
a stopper. Methacryloyl chloride (C ClO, M = 104.54
(
Work up: The organic layer was washed with 0.1 M HCl
in a separating funnel till the pH of the aqueous layer remained
acidic. The aqueous layer was extracted with 200 mL
dichloromethane and the combined organic layers were dried
4
H
5
w
g/mol, 13.94 mL, 15 g, d = 1.076 g/mL, 141 mmol) was added
to the stirring solution using a syringe. The dropping funnel
was charged with pyridine (C
5
H
5
N, M
w
= 79.11 g/mol, 11.34
4
on MgSO followed by filtration and evaporation under
mL, d = 0.97 g/mL, 11 g, 141 mmol). The whole set-up was
kept under nitrogen atmosphere. Pyridine was added dropwise
to the stirring solution while maintaining the reaction mixture
at ºC. Upon addition of the pyridine a white precipitate formed.
The mixture was stirred over night at room temperature under
nitrogen atmosphere. The reaction was monitored by TLC
using chloroform as eluent. The reaction was over after 24 h.
Work up: 100 mL water and 200 mL ethyl acetate were
added to the reaction mixture. The layers were mixed by
shaking properly in a separating funnel. The organic layer was
separated and washed with 100 mL water and HCl (0.001 M)
to remove pyridine residues. The combined aqueous layers
were extracted with ethyl acetate. The organic layers were dried
on magnesium sulphate followed by filtration and evaporation
of the solvent under reduced pressure. The purity of the crude
product was checked by TLC (chloroform used as solvent)
reduced pressure to remove the solvent. The obtained product
was a white powder (yield = 80 %).
1
Purification: H NMR and TLC indicated 99 % purity,
therefore no purification was carried out.
1
Characterization: H NMR, (400 MHz, CDCl
3
) δ (ppm),
), 4.59 (s, 1H, NHCONH), 4.36 (s,
1H, NHCONH), 4.24 (t, 2H, 3 J = 5.4 Hz, COOCH CH ),
NH), 3.16 (t, 2H, J = 7.2
6.12, 5.59 (s, 2H, CCH
2
2
2
3
3
3.51 (t, 2H, J = 5.2 Hz, OCH
Hz, CONHCH CH ), 1.95 (s, 3H, CH
J = 7.1 Hz, NHCH CH CH ), 1.35 (seq, 2H, J = 7.4 Hz,
CH CH CH ), 0.92 (t, 3H, J = 7.2 Hz, CH
(400 MHz, CDCl ) δ (ppm), 167.20 (HNCONH), 159.08
(COO), 135.86 (CCH ), 125.64 (=CH ), 64.04, 39.75, 38.86,
32.20, 19.86, 18.03, 13.59. Elementary analysis calculated for
: C, 57.86 %; H, 8.85 %; N, 12.27 %. Found: C,
2 2
CH
3
2
2
3 2
CCH ), 1.48 (p, 2H,
3
2
2
2
3
13
2
2
3
2 2 3
CH CH ); C NMR
3
3
2
11 20 3 2
C H O N
57.58 %; H, 8.63 %; N, 11.99 %.
1
and H NMR.
Polymer syntheses: All the chemicals used for the
synthesis of polymers were purchased from Aldrich and used
as received. NMR spectra were recorded on aVarian Mercury
400 spectrometer. A typical polymerization involves 50 mmol
of monomer and 25 mmol of 2-2'-azo-bis-isobutyrylnitrile
(AIBN). 8 Sets of experiments were carried out for 8 copoly-
merizations. Samples were taken from the reactions mixture
at low conversion (typically below 10 %). The conversions
were estimated by dividing the polymer weight with the
theoretical weight of the monomers present in 1 mL of reaction
mixture multiplied by 100 (assuming the density of the
monomers to be 1 g/mL).
Purification: The obtained crude product was dissolved
in methanol in a three neck flask equipped with a reflux
condenser stirred and heated (with heating gun) till the solution
becomes clear. The solution cooled down and crystallization
occurred. The solution was afterwards filtrated. The fine white
crystals were dried under reduced pressure to remove traces
of methanol. Yield of product was 70 %.
1
Characterization: H NMR (400 MHz, CDCl
3
) δ (ppm)
OCO), 6.37, 5.77 (s, 2H, CCH ),
C); C NMR (400 MHz, CDCl ) δ (ppm)
65.91 (ArOCO), 150.31 (CCH ), 140.37, 138.86, 135.82,
28.77, 128.13, 127.30, 127.10, 126.75 (=CH ), 121.85, 18.40
). Elementary analysis calculated for C16
7
2
1
1
.61-7.18, (m, 9H, C
6
H
5
C
H
6 4
2
1
3
.08, (s, 3H, CH
3
3
3
2
Polymerizations of monomer 5 with methyl methacrylate
(CH
3
H O
12 2
, C, 80.63
Experiment 1: 3.35 g methyl methacrylate (33.5 mmol),
.76 g monomer 5 (16.5 mmol) and 41 mg AIBN initiator
%
; H, 14.14 %. Found C, 80.65 %; H, 5.69 %.
Synthesis of monomer 5 (Fig. 5)
3
were dissolved in 7 mL dioxane in a 100 mL flask equipped
with a stirrer bar. The reaction mixture was purged with
nitrogen for 20 min and heated afterwards at 60 ºC. 1 mL
sample was taken from the reaction mixture after 40 min of
polymerization and precipitated in the solution of methanol/
water = 70 %/30 %. The polymer was dried under reduced
pressure and weighed afterwards (0.013 g). Conversion =
ca. 3 wt %.
O
N
+
NH2
5
DCM, RT, 2d
O
O
Fig. 5. Reaction scheme for the synthesis of the monomer 5
Reaction: 30 mL of 2-methacryloyl oxyethyl isocyanate
Experiment 2: 1.65 g methyl methacrylate (16.5 mmol),
7 9 9 w
(C H NO , M = 145 g/mol, 33.83 g, d = 1.098 g/mL, 233
7
.65 g monomer 5 (33.5 mmol) and 41 mg AIBN were
dissolved in 14 mL dioxane (the larger amount of the monomer
used in this case required twice amount of the solvent for
mmol) was dissolved in 250 mL dichloromethane in a 500
mL 3-neck flask equipped with a dropping funnel, nitrogen
inlet and a stopper. The dropping funnel was filled with
5
proper dissolution of the monomer in dioxane), followed by
purging for 20 min with nitrogen and heating afterwards at 60
ºC. 1 mL sample was taken after 40 min of polymerization
followed by the precipitation of the polymer in the solution of
methanol/water = 70 %/30 %. Polymer was dried under
reduced pressure and weighed afterwards (0.027 g). Conver-
sion = ca. 6.75 wt %.
4 w
n-butyl amine (C H11N, M = 73.16 g/mol, 27 mL, d = 0.74
g/mL, 20 g, 273 mmol) using a syringe. The whole set-up was
kept under nitrogen atmosphere. The reaction mixture was
cooled to 0 ºC using an ice bath. n-Butyl amine was added
dropwise while maintaining the reaction mixture at 0 ºC. Subse-
quently, the reaction mixture was stirred for 2 days at room
temperature. The reaction was monitored with chloroform was

478 Andoni et al.
Asian J. Chem.
Polymerizations of monomer 5 with butyl-methacrylate
indicated with arrows in the structures of Fig. 6 were analyzed
in the NMR spectra.
Experiment 3: 2.35 g butyl-methacrylate (16.5 mmol),
.65 g monomer 5 (33.5 mmol) and 42 mg AIBN were
7
O
dissolved in 7 mL dioxane.After 20 min purging with nitrogen
the reaction mixture was heated at 60 ºC. 1.5 mL sample was
taken after 25 min of polymerization. The polymer was preci-
O
O
N
H
N
H
Methyl methacrylate
5
2
pitated in the solution of MeOH/H O = 70 %/30 %, dried
under reduced pressure and weighed afterwards (0.068 g).
Conversion = ca. 7.5 wt %.
Fig. 6. Chemical structure of methyl methacrylate and monomer 5 where
protons analyzed in the NMR spectra are indicated with arrows
Experiment 4: 4.76 g butyl-methacrylate (33.5 mmol),
.76 g monomer 5 (16.5 mmol) and 42 mg AIBN were dissol-
Polymers obtained from the experiments 3 and 4 were
3
dissolved in CD
3
OD as well. For the butyl-methacrylate and
ved in 7 mL dioxane followed by 20 min purging with nitrogen.
The reaction mixture was heated at 60 ºC afterwards. 1 mL
monomer 5 the protons indicated with arrows in the structures
of Fig. 7 were analyzed for the calculations (m
1
2
and m ) in the
sample was taken after 15 min and precipitated in CH
O = 70 %/30 %. The polymer was dried under reduced
pressure and weighed afterwards (0.025 g). Conversion = ca.
.63 wt %.
3
OH/
NMR spectra.
H
2
O
4
O
O
N
H
N
H
Polymerizations of monomer 3 with methyl methacrylate
Experiment 5: 0.42 g methyl methacrylate (4.2 mmol),
.99 g monomer 3 (8.4 mmol) and 10.5 mg AIBN were
Buty methacrylate
5
1
dissolved in 7 mL dioxane (the amounts were divided by 4
due to the lack of the starting material). The same procedure
was followed as in the former experiments. 1 mL sample was
taken after 45 min of polymerization and precipitated in
hexane. The polymer was dried under reduced pressure and
weighed afterwards (0.013 g). Conversion = ca. 5.09 wt %.
Experiment 6: 0.84 g methyl methacrylate (8.4 mmol),
Fig. 7. Chemical structure of butyl-methacrylate and monomer 5 where
protons analyzed in the NMR spectra are indicated with arrows
Polymers obtained from the experiments 5 and 6 were
dissolved in CD
protons in the region of the aromatic groups (9H) and the
protons of the OCH (3H) group of the methyl methacrylate
2 2 1 2
Cl . For the calculation of m and m the
3
were analyzed in the NMR spectra (Fig. 8 as well).
Polymers obtained from the experiments 7 and 8 were
0
.98 g monomer 3 (4.2 mmol) and 10.5 mg AIBN were
dissolved in 7 mL dioxane. The same procedure was carried
out as above mentioned. 1 mL sample of polymer was taken
after 1 h of polymerization and precipitated in hexane. The
polymer was dried under reduced pressure and weighed
afterwards (0.021 g). Conversion = ca. 10 wt %.
2 2 1 2
dissolved in CD Cl as well. For the calculation of m and m
the protons indicated with arrows in the structures of Fig. 8
were analyzed in the NMR spectra.
O
O
Polymerizations of monomer 3 with butyl-methacrylate
O
Experiment 7: 1.19 g butyl-methacrylate (8.4 mmol),
.98 g monomer 3 (4.2 mmol) and 10.5 mg AIBN were
0
Butyl methacrylate
3
dissolved in 7 mL dioxane. The reaction mixture was purged
for 20 min with nitrogen and heated afterwards at 60 ºC. 0.5 mL
sample of polymer was taken after 20 min of polymerization
and precipitated in hexane. The polymer was dried under
reduced pressure and weighed afterwards (0.019 g). Conver-
sion = ca. 15 wt %.
Fig. 8. Chemical structure of butyl-methacrylate and monomer 3 where
protons analyzed in the NMR spectra are indicated with arrows
RESULTS AND DISCUSSION
Determination of reactivity ratios: Reactivity ratios were
determined for the copolymerization of monomers 3 and 5
with methyl methacrylate and butyl-methacrylate. Eight reac-
tivity ratios were determined in all the 8 experiments. These
determinations were done in accordance with the equation:
Experiment 8: 0.59 g butyl-methacrylate (4.2 mmol),
.99 g (8.4 mmol) monomer 3 and 10.5 mg AIBN were
1
dissolved in 5 mL dioxane. The reaction mixture was purged
for 20 min with nitrogen and heated afterwards at 60 ºC. 1 mL
sample of polymer was taken after 50 min of polymerization
and precipitated in hexane. The polymer was dried under
reduced pressure and weighed afterwards (0.018 g). Conver-
sion = 4.78 wt %.
m m = M
(
r M + M
)
M2
(
M + r M . Although free
)
radical polymerization was used instead of RAFT polymer-
1
2
1
1
1
2
1
2
2
ization, the effect of the latter on the reactivity ratios is known
6
to be negligible . One set of two experiments is needed to
NMR spectroscopy: NMR spectra for the copolymers
1
were recorded 400 MHz NMR spectrometer. H NMR
determine two reactivity ratios (r ). In the equation,
m m = M r M + M M2 M + r M , m and m are
2
1
, r
2
13
chemical shifts were given relative to TMS (0.00 ppm). C
Chemical shifts are given relative to CDCl (77.00 ppm).
(
)
(
)
1
2
1
2
1
1
1
2
1
2
3
determined from the NMR spectra as noted in the experimental
part. M and M are, as mentioned, the mole fractions of the
NMR spectroscopy of polymers: Polymer 1 and 2
obtained from experiment 1 and 2 respectively were dissolved
1
2
monomer 1 and 2 in the reaction system. Therefore there are
two equations with two unknowns r and r .
3 1 2
in CD OD. For the calculation of m and m the protons
1
2

Vol. 25, No. 1 (2013)
Determination of the Distribution of Acrylic Comonomers in Free Radicals Polymers 479
TABLE-1
OVERALL RESULTS OF REACTIVITY RATIOS. RESULTS OF DUPLO EXPERIMENTS ARE SHOWN IN BRACKETS
Monomer 1
MMA
MMA
BMA
Monomer 2
M1
M2
m1
m2
r1
0.79
r2
1.27
BMA
MAA
1.18/2.61
1.20
0.63/0.43
0.75
MAA
MMA
BMA
HEMA
0.824
-
0.63
HEMA
-
MMA
MMA
BMA
3
3
3
3
5
5
5
5
0.33
0.67
0.33
0.67
0.33
0.67
0.33
0.67
0.67
0.33
0.67
0.33
0.67
0.33
0.67
0.33
0.25
0.64
0.75
0.36
1
0
.17
.64
1.84
0.22
0.78
1.80
BMA
0.40
0.60
MMA
MMA
BMA
0.18 (0.22)
0.58 (0.52)
0.37 (0.35)
0.62 (0.65)
0.82 (0.78)
0.42 (0.48)
0.63 (0.65)
0.38 (0.39)
1
0
.13 (0.47)
.54 (0.53)
2.99 (1.66)
0.57 (0.66)
BMA
The initial feed ratios of the monomers in the reaction
mixture are estimated from the equations: M21 ≅ r1 2 + r1
. M21 is the initial feed ratio of the
monomer 2 in the first experiment, whereas M22 is the initial
feed ratio of the monomer 2 in the second experiment. r
and r are the reactivity ratios. Assuming r = r = 1 (for a
completely random polymerization), we get: M21 = 1/3 and
22 = 2/3. In this context, two reaction mixtures were prepared,
Free radical polymerization was employed to copolymerize
monomers 3 and 5 with methyl methacrylate and butyl-
methacrylate. NMR spectroscopy was utilized to study the
composition of these copolymers at low conversion. In addition
reactivity ratios were calculated. The reported values are in
the range 0.6-3 and indicate rather random composition. This
conclusion proves that the supposition made by former
(
)
6
and M22 ≅ 2
(2 + r2
)
1
2
1
2
1,2
researchers regarding random composition of the polymers
obtained by RAFT- copolymerization is justified.
M
one containing ca. 33 mol % of monomer 1 and ca. 67 mol %
of monomer 2 (as seen in the experimental part, polymer
synthesis).
REFERENCES
1
.
R.W.J. Voss, G.A. Roescher and H.A.M. Biemans, Crosslinkable Poly-
meric Materials with Controlled Melt-Flow Behaviour. Report of TNO
Industrial Technology Eindhoven, Polymer Products and Coatings,
Eindhoven, The Netherlands (2000).
The overall results of the obtained reactivity ratios are
given in Table-1. The reactivity ratios for the copolymerizations
of butyl-methacrylate-methyl methacrylate, methyl methacrylate-
butyl-methacrylate and methyl methacrylate-HEMA (2-
7
) are included as well .
2. M.E.L. Wouters, H.A.M. Biemans, R. Voss and M.J. Monteiro, Effect of
Pendant Functionality and Molecular Weight on Some Thermal Properties
of RAFT-Polymers. Unpublished manuscript. TNO Industrial Techno-
logy Eindhoven, The Netherlands. Dutch Polymer Institute (DPI), 5600
AX, Eindhoven, The Netherlands (2004).
hydroxyethyl methacrylate, C
H
6 10
O
3
Despite the moderate accuracy of some numbers all the values
displayed in Table-1 for r and r are suitably close to 1 and
1
2
therefore, suggest random copolymerization in all cases. In
the experiments of the copolymerizations of monomer 3 and
3. G. Challa, Polymer Chemistry; An Introduction, Ellis Horwood Limited
(
1993).
4
.
K.B. Wiles, Determination of Reactivity Ratios for Acrylonitrile/Methyl
Acryalte Radical Copolymerization via Non-linear Methodologies
Using Real Time FTIR, Master's Thesis in Chemistry, Faculty of Virginia
Polytechnic and State University, August 2002, Blacksburg, Virginia;
http://scholar.lib.vt.edu/theses/available/etd-09022002-112751/.
P.W. Tidwell and G.A. Mortimer, J. Polym. Sci. Part A, 3, 369 (1965).
K. Matyjaszewski and T.P. Davis, Handbook of Radical Polymerization,
John Wiley & Sons, Inc. Canada (2002).
5
with either methyl methacrylate and butyl-methacrylate r
2
>
r
1
, meaning that k22/k21 > k11/k12. This result indicates that 3
and 5 are preferred in the propagation if the chains end with
these same monomers. This preference may be explained by
specific interaction between the radical chain end and the new
reacting monomer. In the case of 3 this interaction stems from
π-π stacking, while hydrogen bonding is involved in the case
of 5.
5
6
.
.
7. J. Brandrup and E.H. Immergut, Editors with the Collaboration of W.
McDowell; Polymer Handbook, Jonh Wiley & Sons, Inc. New York,
edn 2 (1975).
Conclusion
1
2
We extended the work of Voss et al. and Wouters et al.
and presented a full characterization of monomers 3 and 5.