Periodic ethylene-vinyl alcohol copolymers via ADMET polymerization: Synthesis, characterization, and thermal property

Article abstract of DOI:10.1016/j.polymer.2013.05.037

Periodic copolymers of ethylene and vinyl alcohol (EVA) were synthesized via acyclic diene metathesis (ADMET) polymerization of a series of structurally symmetric α,ω-diene monomers that containing two vinyl acetate (VAc) units, followed by exhaustive hydrogenation and subsequent hydrolysis. This synthetic methodology provided a new type of EVA copolymer with defined sequence and ever highest VA content via ADMET. These polymer samples were characterized by gel permeation chromatography (GPC), NMR, and matrix-assisted laser desorption/ionization time-of-fight mass spectroscopy (MALDI-TOF-MS). Thermal properties of EVAc and EVA copolymers were investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). EVAc copolymers exhibited two-stage decompositions on TGA traces and displayed a glass transition on DSC thermograms. Meanwhile, the EVA copolymers showed glass transition stages and sharp melting peaks on DSC thermograms, with the T _m values being comparable to that of high density polyethylene (HDPE).

Full text of DOI:10.1016/j.polymer.2013.05.037

Polymer 54 (2013) 3841e3849
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Periodic ethylene-vinyl alcohol copolymers via ADMET
polymerization: Synthesis, characterization, and thermal property
q
Zi-Long Li, An Lv, Lei Li, Xin-Xing Deng, Li-Jing Zhang, Fu-Sheng Du, Zi-Chen Li*
Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Polymer Chemistry & Physics of Ministry of Education,
Department of Polymer Science & Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 April 2013
Received in revised form
Periodic copolymers of ethylene and vinyl alcohol (EVA) were synthesized via acyclic diene metathesis
ADMET) polymerization of a series of structurally symmetric -diene monomers that containing two
vinyl acetate (VAc) units, followed by exhaustive hydrogenation and subsequent hydrolysis. This syn-
thetic methodology provided a new type of EVA copolymer with defined sequence and ever highest VA
content via ADMET. These polymer samples were characterized by gel permeation chromatography
(
a,u
10 May 2013
Accepted 14 May 2013
Available online 21 May 2013
(
GPC), NMR, and matrix-assisted laser desorption/ionization time-of-fight mass spectroscopy (MALDI-
TOF-MS). Thermal properties of EVAc and EVA copolymers were investigated by thermal gravimetric
analysis (TGA) and differential scanning calorimetry (DSC). EVAc copolymers exhibited two-stage de-
compositions on TGA traces and displayed a glass transition on DSC thermograms. Meanwhile, the EVA
Keywords:
Ethylene-vinyl alcohol copolymer
ADMET polymerization
Sequence
copolymers showed glass transition stages and sharp melting peaks on DSC thermograms, with the T
m
values being comparable to that of high density polyethylene (HDPE).
Ó 2013 Elsevier Ltd. All rights reserved.
1
. Introduction
and coatings [7]. Moreover, EVA copolymer represents one of the
important hydrophilic synthetic resins for applications in
biomedical fields [8e10]. However, EVA copolymers obtained by
free radical copolymerization usually exhibit a limited degree of
crystallinity and a wide melting temperature range due to their
ambiguous primary structures. Palladium-catalyzed coordination
copolymerization of ethylene and vinyl acetate was reported to
generate linear EVAc copolymer with rather low VAc molar content
[11]. Alternating EVAc polymer was attained via cationic group-
transfer polymerization (GTP) of 1,3-butadiene derivative fol-
lowed by multi-step post-modifications, but the branched struc-
tures were still unavoidable [12]. Therefore, to get a more precise
structureeproperty relationship of EVA copolymers and improve
the material performance, research on control over the composi-
tion, tacticity, and sequence of EVA copolymers has become
important.
Metathesis has been extensively applied in polymer synthesis as
one of the most efficient carbonecarbon bond formation reaction
to afford periodic vinyl copolymers. For instance, Ramakrishnan
et al. reported the ring-opening metathesis polymerization (ROMP)
of alkylboron-substituted cyclooctene, subsequent oxidation and
hydrogenation afforded EVA copolymers [13]. However, the
placement of the pendent hydroxyl groups in the final polymer
main chain is not in a regio-specific fashion, and the molar ratio of
the two monomers was fixed. Later on, based on the same strategy,
they conducted ROMP of different ring size cyclic olefins and
Copolymer of ethylene and vinyl acetate (EVAc) is commonly
used as hot melt adhesive, packing film, and rubbery toy. Due to its
wide applications, EVAc copolymer is the world’s largest ethylene
copolymer by volume, and is prepared industrially by radical
copolymerization of the two monomers at high temperature and
pressure [1,2]. Since ethylene and vinyl acetate exhibit nearly
identical reactivity ratio under the radical polymerization condi-
tions, the chemical composition of EVAc copolymers could be tuned
over a broad range by simply changing the feed ratio. However,
short branches are inevitably formed due to chain transfer re-
actions, thus disrupting the linearity of the polymer main chain.
The structureeproperty relationship of thus obtained EVAc co-
polymers has been thoroughly investigated [3e6].
Ethylene and vinyl alcohol copolymer (EVA) is routinely ob-
tained via saponification of the EVAc copolymer. Due to its excellent
barrier property to prevent hydrocarbon or gas diffusion through
membranes, EVA copolymers have been widely used as adhesives
q
This is an open-access article distributed under the terms of the Creative
Commons Attribution-NonCommercial-No Derivative Works License, which per-
mits non-commercial use, distribution, and reproduction in any medium, provided
the original author and source are credited.
*
Corresponding author. Tel.: þ86 10 6275 5543; fax: þ86 10 6275 1708.
E-mail address: zcli@pku.edu.cn (Z.-C. Li).
0
032-3861/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2013.05.037

3842
Z.-L. Li et al. / Polymer 54 (2013) 3841e3849
obtained EVA copolymers with the VA content varying from 16 to
0 mol% [14]. However, irregular placement of pendent hydroxyl
occurred for monomers M1 and M2. The other four monomers
(M3eM6) were polymerized with Grubbs-II catalyst in the pres-
ence of benzoquinone (BQ) to yield EVAc copolymers in high yields
and high molecular weights. After hydrogenation and hydrolysis of
those EVAc copolymers, EVA copolymers with defined-sequence
and tunable VA contents were obtained. The thermal properties
of the EVAc and EVA copolymers were investigated by thermal
gravimetric analysis (TGA) and differential scanning calorimetry
(DSC).
5
groups on the polyethylene backbone remained unsolved due to
the non-selective nature of post-modification. Terpolymers of
ethylene, vinyl alcohol, and other vinyl monomer units were syn-
thesized using the same method [15,16]. Hillmyer and Grubbs et al.
reported the direct ROMP of hydroxyl-functionalized cyclooctene
using Ru-based Grubbs catalyst [17]. However, regioisomers were
still contained in the repeating unit of the periodic copolymers. EVA
copolymers with defined tacticity and predicted monomer
sequence were achieved via ROMP by Grubbs et al. [18,19]. Rather
high content of vinyl alcohol in the EVA copolymer was realized and
the effect of stereochemistry on the thermal property was
described. Very recently, Hillmyer et al. reported the synthesis of
sequence-regulated and stereo-specific periodic vinyl copolymers
containing vinyl acetate unit by the regio-selective ROMP of
substituted cyclic alkenes [20,21]. This elegant work opened a new
avenue for control over polymer microstructure from different
levels, thus providing important information for thorough eluci-
dating the structureeproperty relationship.
Acyclic diene metathesis (ADMET) polymerization shows
several advantages when adopted in periodic vinyl copolymer
synthesis [22e26]. At first, compared with that of ROMP, monomer
synthesis is generally simple especially when sequenced micro-
structure is to be built into the ADMET monomers. In order to
eliminate the uncertainty of regioselectivity, the only requirement
for monomer design is structural symmetry. Moreover, due to the
high tolerance to polar groups of Grubbs catalysts, sequence in-
formation encoded within the monomer can be completely trans-
formed into the repeating unit of the periodic copolymer via
ADMET polymerization. Therefore, this is a universal synthetic
pathway towards periodic vinyl copolymers via polycondensation.
In addition, polar group content can be tuned by varying the length
of methylene spacer that separating the functional group and the
terminal alkene. In this way, the effect of specific polar group
introduction on the thermal property can be elucidated, thus
providing better understanding of the structureeproperty rela-
tionship. Accordingly, Wagener et al. described the synthesis of EVA
copolymers using ADMET polymerization for the first time [27].
Vinyl alcohol content is another crucial parameter of EVA
copolymer since the barrier property of the copolymer significantly
decreases with reducing the hydroxyl group content [28]. However,
monomers suitable for ADMET polymerization usually contain
relatively long methylene spacers, thus making the hydroxyl group
content inherently low. On the other hand, monomers bearing too
short methylene spacers such as terminal allyl group are sluggish to
polymerize due to the negative neighboring group effect [29]. Thus,
we intended to solve this problem and get EVA copolymers with
defined-sequence and tunable VA contents based on our previous
works on ADMET polymerization [30e32].
2. Experimental
2.1. Materials
1,1,3,3-Tetramethoxypropane (>98.0%) was obtained from TCI.
Trans-1,2-cyclohexanediol (98%), hepta-1,6-dien-4-ol (95%), and
Grubbs catalysts (first and second generations) were purchased
from Aldrich. Tripropylamine (TPA, 98%) and ethyl vinyl ether
(stabilized with 0.1% N, N-diethylaniline) were used as received
from Alfa Aesar. 4-Methylbenzenesulfonhydrazide (TSH, 97%), 2,5-
dimethoxytetrahydrofuran (mixture of cis- and trans-isomers, 99%),
and 4-dimethylaminopyridine (DMAP, 99%) were from Acros. n-
Butyraldehyde (ꢀ98.5%) was purchased from Shanghai Shuang-
xiang Additives Factory. Acetic anhydride (ꢀ98.5%) and Glyoxal
solution (40%) were obtained from Sinopharm Chem. Reagent Co.,
Ltd. Glutaraldehyde solution (50%) was used as received from Bei-
jing Yili Fine Chem. Co., Ltd. Allyl bromide (ꢀ97.0%) and p-benzo-
quinone were from Beijing Chem. Reagent Co., Ltd. Ethyl acetate,
toluene, and methanol were obtained from Beijing Tongguang Fine
Chem. Co., Ltd. Tin dichloride dihydrate (ꢀ98.5%), potassium iodide
(A.R.), sodium hydroxide (NaOH), sodium carbonate (NaCO
anhydrous sodium sulfate (Na SO ), anhydrous calcium chloride
(CaCl ), sodium periodate (NaIO ), silica gel, tetrahydrofuran (THF),
petroleum ether, methylene dichloride (CH Cl ), chloroform
(CHCl ) were purchased from Beijing Chem. Works. Calcium hy-
dride (CaH ) was obtained from Tianjin Xuan’ang Trade and In-
dustry Co., Ltd. CH Cl , THF, and petroleum ether were refluxed
with CaH for 8 h and then redistilled. CH Cl was sonicated for half
3
),
2
4
2
4
2
2
3
2
2
2
2
2
2
an hour before use.
2.2. Characterization
Bruker ARX-400 spectrometer was utilized to measure the 1H
13
(400 MHz) and C (100 MHz) NMR spectra. EVA copolymers were
dissolved in d -DMSO while all the other samples were dissolved in
CDCl with tetramethylsilane (TMS) as the internal reference for
chemical shifts. Number- and weight-average molecular weights
(M and M /M ) were
6
3
n
w
) and polydispersity indices (PDI ¼ M
w
n
determined by gel permeation chromatograph (GPC). The mea-
ꢁ
surements were conducted in THF (flow rate: 1 mL/min) at 35 C
In this contribution, six structurally symmetric
a
,
u
-diene
with a Waters 1525 binary HPLC pump equipped with a Waters
2414 refractive index detector and three Waters Styragel columns
monomers bearing one (M1) or two (M2-M6) vinyl acetate units
were synthesized via Barbier reaction and subsequent acetylation.
We ruled out direct polymerization of the hydroxyl-functionalized
monomers due to the minimal solubility of the unprotected diols in
common organic solvents suitable for ADMET, and oligomers were
more likely to generate due to the sluggish diffusion in the highly
viscous polymerization mixture. On the other hand, not as in the
previous works to tune the length of methylene spacer separating
the pendent group and the terminal alkene [22e26], the monomers
4
3
ꢀ
(1 ꢂ 10 , 1 ꢂ 10 , and 500 A pore sizes). A family of narrowly
dispersed polystyrenes was used as the standards, and Breeze 3.30
SPA software was applied to calculate the molecular weight and
PDI. Electrospray ionization mass spectroscopy (ESI-MS) charac-
terizations were conducted using a Bruker APEX-IV Fourier trans-
form mass spectrometer in a positive ion mode. Matrix-assisted
laser desorption/ionization time-of-fight mass spectroscopy
(MALDI-TOF-MS) characterizations were performed on a Bruker
BIFLEX-III MALDI-TOF mass spectrometer in a linear mode. Thermal
gravimetric analysis (TGA) was carried out using a Q600-SDT
thermogravimetric analyzer (TA Co., Ltd.) with nitrogen purging
rate set at 50 mL/min. Measurements were conducted from room
(
M2-M6) were different in the length of methylene spacer con-
necting the two vinyl acetate units. ADMET polymerization of the
monomers and exhaustive hydrogenation were sequentially per-
formed to afford periodic EVAc copolymers. It was found that
intramolecular cyclization instead of ADMET polymerization
ꢁ
ꢁ
temperature to 600 C at a heating rate of 10 C/min. Calorimetric

Z.-L. Li et al. / Polymer 54 (2013) 3841e3849
3843
measurement was performed using a Q100 differential scanning
calorimeter (TA Co., Ltd.) with nitrogen purging rate set at 50 mL/
min. The program was set to finish two cycles in the temperature
1H NMR of preM4 (400 MHz, CDCl
3
),
d
(TMS, ppm): 5.83 (ddt,
J ¼ 17.1, 10.2, 7.2 Hz, 2H), 5.11 (m, 4H), 3.67 (m, 2H), 3.23 (m, 2H),
13
3
2.25 (m, 4H), 1.60 (m, 4H). C NMR (101 MHz, CDCl ): d 134.94,
ꢁ
ꢁ
range from ꢃ80e150 C for EVAc copolymers and from 0 to 180 C
117.68 (d, J ¼ 2.8 Hz), 70.89 (d, J ¼ 47.1 Hz), 42.01 (d, J ¼ 31.6 Hz),
þ
for EVA copolymers, respectively. The heating/cooling rate was set
32.95 (d, J ¼ 93.5 Hz) (Fig. S5). ESI-MS: [M þ H ] ¼ C10
H
19
O
2
, calcd:
ꢁ
þ
to 10 C/min. Data of the endothermic curve was acquired from the
171.13796, found: 171.13757; [M þ Na ] ¼ C10
18 2
H O Na, calcd:
second scan. TA Universal Analysis software was used for data
acquisition and processing in TGA and DSC measurements. IR
spectra were recorded on a Bruker Vector-22 Fourier transform
infrared spectrometer. Samples were dispersed by potassium bro-
mide (KBr), and OPUS/IR software was applied to manipulate the
spectra.
193.11990, found: 193.11947.
1
3
H NMR of preM5 (400 MHz, CDCl ), d (TMS, ppm): 5.83 (ddt,
J ¼ 17.3, 10.3, 7.1 Hz, 2H), 5.09 (dd, J ¼ 13.1, 5.3 Hz, 4H), 3.62 (m, 2H),
13
3
3.26 (m, 2H), 2.23 (m, 4H), 1.48 (m, 6H). C NMR (101 MHz, CDCl ):
d
135.08 (d, J ¼ 3.0 Hz), 117.33 (d, J ¼ 6.6 Hz), 70.52 (d, J ¼ 20.2 Hz),
41.95 (d, J ¼ 13.2 Hz), 36.38 (d, J ¼ 23.0 Hz), 21.56 (d, J ¼ 6.2 Hz)
þ
(
Fig. S6). ESI-MS: [M þ H ] ¼ C11
21 2
H O , calcd: 185.15361, found:
H O Na, calcd: 207.13555, found:
20 2
þ
2.3. Synthesis of adipaldehyde
185.15357; [M þ Na ] ¼ C11
2
07.13558.
The reported synthetic procedure was followed to prepare this
compound [33].
Silica gel (15 g), NaIO
4
(5.56 g, 26 mmol), deionized water
2.5. Synthesis of monomers via acetylation of the premonomers
(
15 mL), and CH
bottom flask. After vigorous stirring, a suspension was generated. A
solution of trans-1,2-cyclohexanediol (2.32 g, 20 mmol) in CH Cl
50 mL) was added dropwise to the suspension within 0.5 h. The
suspension was vacuum filtered after 6 h, and the silica gel was
washed with CH Cl
(100 mL ꢂ 3). The organic filtrate was dried
over anhydrous Na SO , filtered, and concentrated. Adipaldehyde
was obtained as viscous colorless liquid in 99% yield. H NMR
2 2
Cl (50 mL) were added into a 500 mL round
Monomer M1 was obtained by direct acetylation of the
1
2
2
commercially available hepta-1,6-dien-4-ol in 99% yield. H NMR
(
(400 MHz, CDCl
3
),
d
(TMS, ppm): 5.75 (ddt, J ¼ 17.2,10.2, 7.1 Hz, 2H),
13
5.08 (m, 4H), 4.97 (m, 1H), 2.32 (m, 4H), 2.03 (s, 3H). C NMR
2
2
3
(101 MHz, CDCl ): d 170.49, 133.51, 117.76, 72.27, 37.96,
2
4
21.07(Fig. S7).
1
All the other five monomers were synthesized by direct acety-
lating of the pre-monomers. Take the synthesis of M6 as an
example.
(
4
400 MHz, CDCl
H). C NMR (100 MHz, CDCl
3
),
d
(TMS, ppm): 9.75 (m, 2H), 2.47 (m, 4H),1.66 (m,
):
201.69 (d, J ¼ 2.7 Hz), 43.00, 20.99
13
3
d
(Fig. S1).
The diol preM6 (0.99 g, 5 mmol), acetic anhydride (3.06 g,
3
0 mmol), and DMAP (122 mg, 1 mmol) were sequentially weighed
and transferred into a 100 mL round bottom flask. Then 30 mL
CH Cl was added to generate a homogeneous solution, which was
vigorously stirred overnight at room temperature. The reaction
mixture was neutralized with Na CO solution, sequentially
washed with deionized water and brine, dried with anhydrous
Na SO , filtered, and evaporated to afford a yellowish liquid, which
2
.4. Synthesis of the diol pre-monomers via Barbier reaction
2
2
Take the synthesis of preM6 as an example.
In a 500 mL round bottom flask, a solution of adipaldehyde
2
3
ꢁ
(
2.28 g, 20 mmol) in THF (15 mL) was added within 0.5 h at 35 C to
a stirred mixture of SnCl
2
$2H
2
O (13.56 g, 60 mmol), KI (19.9 g,
2
4
1
20 mmol), and allyl bromide (5.2 mL, 60 mmol) in water (150 mL).
was further purified by silica gel column chromatography (petro-
ꢁ
The stirring was continued for 48 h at 30 C. The resulting mixture
was neutralized with Na CO solution and extracted with CH Cl
3 ꢂ 150 mL). The organic phase was washed with Na solution
SO , filtered, and
leum ether/ethyl acetate ¼ 20/1). Monomer M6 was obtained as a
1
2
3
2
2
colorless liquid in 99% yield. H NMR (400 MHz, CDCl
3
),
d
(TMS,
(
(
2
2
S O
3
ppm): 5.74 (dq, J ¼ 10.0, 7.1 Hz, 2H), 5.06 (m, 4H), 4.90 (m, 2H), 2.29
13
5% aq., 150 mL ꢂ 3), dried with anhydrous Na
2
4
(m, 4H), 2.03 (s, 6H), 1.53 (m, 4H), 1.32 (m, 4H). C NMR (101 MHz,
concentrated to afford a yellowish oil, which was further purified
CDCl
3
):
d
170.59, 133.65, 117.55, 72.99 (d, J ¼ 3.4 Hz), 38.59 (d,
þ
by silica gel column chromatography (petroleum ether/ethyl
J ¼ 3.0 Hz), 33.38, 25.05, 21.10. ESI-MS: [M þ Na ] ¼ C16
26 4
H O Na,
acetate ¼ 10/4). The diol preM6 was obtained as a pale yellow liquid
calcd: 305.17233, found: 305.17192.
1
in 76% yield. H NMR (400 MHz, CDCl
3
),
d
(TMS, ppm): 5.82 (m, 2H),
Monomers M2eM5 were prepared in a similar way as colorless
5
2
.10 (dd, J ¼ 12.2, 5.8 Hz, 4H), 3.62 (d, J ¼ 1.9 Hz, 2H), 2.79 (s, 2H),
liquids in nearly quantitative yields.
13
1
.21 (m, 4H), 1.46 (m, 8H). C NMR (101 MHz, CDCl
3
):
d
135.02,
3
H NMR of M2 (400 MHz, CDCl ), d (TMS, ppm): 5.72 (tdt,
1
17.48, 70.55 (d, J ¼ 9.2 Hz), 41.90, 36.57, 25.54 (d, J ¼ 11.1 Hz)
J ¼ 12.3, 10.3, 6.0 Hz, 2H), 5.07 (m, 6H), 2.35 (m, 4H), 2.05 (d,
þ
13
(
2
Fig. S2). ESI-MS: [M þ Na ] ¼ C12
22
H O
2
Na, calcd: 221.15120, found:
J ¼ 15.1 Hz, 6H). C NMR (101 MHz, CDCl
3
): d 170.03, 132.88 (d,
21.15148.
J ¼ 43.6 Hz), 117.99 (d, J ¼ 39.8 Hz), 72.47 (d, J ¼ 24.9 Hz), 34.75 (d,
The syntheses of preM2-preM5 were essentially the same as for
J
¼
111.2 Hz), 20.76 (d,
J
¼
4.5 Hz) (Fig. S8). ESI-MS:
þ
preM6 except that different starting materials were used (glyoxal
for preM2, 1,1,3,3-tetramethoxypropane for preM3, 2,5-
dimethoxytetrahydrofuran for preM4, and glutaraldehyde for pre
M5) [34,35].
[M þ Na ] ¼ C12
H
18
O
4
Na, calcd: 249.10973, found: 249.10938.
), (TMS, ppm): 5.73 (dddd,
1
H NMR of M3 (400 MHz, CDCl
3
d
J ¼ 16.9, 14.0, 7.1, 2.7 Hz, 2H), 5.08 (m, 4H), 4.98 (dq, J ¼ 11.3, 5.8 Hz,
13
2H), 2.33 (m, 4H), 2.02 (m, 6H), 1.82 (m, 2H). C NMR (101 MHz,
CDCl ):
170.36 (d, J ¼ 8.3 Hz), 133.10 (d, J ¼ 7.7 Hz), 118.07 (d,
1H NMR of preM2 (400 MHz, CDCl
),
d
(TMS, ppm): 5.85 (ttd,
d
3
3
J ¼ 14.1, 7.0, 2.5 Hz, 2H), 5.11 (m, 4H), 3.69 (d, J ¼ 34.3 Hz, 2H), 3.51
J ¼ 10.6 Hz), 69.56 (d, J ¼ 124.2 Hz), 38.77 (d, J ¼ 69.1 Hz), 37.20 (d,
13
(
s, 2H), 2.29 (m, 4H). C NMR (101 MHz, CDCl
J ¼ 38.3 Hz), 117.35, 73.11 (d, J ¼ 52.1 Hz), 37.11 (d, J ¼ 180.4 Hz)
Fig. S3).
1H NMR of preM3 (400 MHz, CDCl
.12 (m, 4H), 3.92 (dddd, J ¼ 17.3, 15.0, 13.0, 8.8 Hz, 3H), 3.32 (s, 1H),
3
):
d
134.83 (d,
J
¼
35.5 Hz), 21.03 (d,
J
¼
11.7 Hz) (Fig. S9). ESI-MS:
þ
[M þ Na ] ¼ C13
H
20
O
4
Na, calcd: 263.12538, found: 263.12530.
), (TMS, ppm): 5.73 (ddt,
1
(
H NMR of M4 (400 MHz, CDCl
3
d
3
),
d
(TMS, ppm): 5.81 (m, 2H),
J ¼ 17.3, 10.3, 7.1 Hz, 2H), 5.08 (dd, J ¼ 13.2, 5.6 Hz, 4H), 4.89 (m, 2H),
13
5
2
CDCl
3
2.30 (m, 4H), 2.03 (s, 6H), 1.58 (m, 4H). C NMR (101 MHz, CDCl ):
13
.27 (ddt, J ¼ 13.5, 7.1, 6.7 Hz, 4H), 1.57 (m, 2H). C NMR (101 MHz,
):
134.56 (d, J ¼ 36.9 Hz), 117.81 (d, J ¼ 11.3 Hz), 71.73, 68.03,
1.85 (dd, J ¼ 66.9, 23.4 Hz) (Fig. S4).
d
170.55, 133.40 (d, J ¼ 2.5 Hz), 117.77 (d, J ¼ 1.3 Hz), 72.79 (d,
3
d
J ¼ 25.0 Hz), 38.47 (d, J ¼ 3.7 Hz), 29.18 (d, J ¼ 9.0 Hz), 21.09 (d,
þ
4
J ¼ 10.8 Hz) (Fig. S10). ESI-MS: [M þ H ] ¼ C14
23 4
H O , calcd:

3844
Z.-L. Li et al. / Polymer 54 (2013) 3841e3849
þ
þ
2
2
55.15909, found: 255.15906; [M þ Na ] ¼ C14
22
H O
4
Na, calcd:
J ¼ 8.1 Hz) (Fig. S18). ESI-MS: [M þ Na ] ¼ C10
14 4
H O Na, calcd:
77.14103, found: 277.14106.
221.07843, found: 221.07824. The GPC traces are displayed in
Fig. S19. The synthesis of cM2 has been reported [36], and the NMR
data are essentially the same.
Dimerization of M0 was performed similarly to the RCM reac-
tion mentioned above. Three reaction conditions were tested: (a)
Grubbs-I catalyst; (b) Grubbs-II catalyst; (c) Grubbs-II catalyst with
benzoquinone (Scheme S1). The amount of catalyst or benzoqui-
none was the same as that used in the ADMET polymerization
1
H NMR of M5 (400 MHz, CDCl ), d (TMS, ppm): 5.73 (ddt,
3
J ¼ 17.2, 10.3, 7.1 Hz, 2H), 5.07 (dd, J ¼ 13.4, 5.8 Hz, 4H), 4.90 (m, 2H),
13
2
.28 (m, 4H), 2.03 (s, 6H), 1.54 (m, 4H), 1.32 (m, 2H). C NMR
(
101 MHz, CDCl ):
3
d
170.61, 133.56, 117.63 (d, J ¼ 1.2 Hz), 72.89,
3
8.54 (d, J ¼ 4.6 Hz), 33.22 (d, J ¼ 1.6 Hz), 21.05 (d, J ¼ 10.8 Hz)
þ
(
2
2
Fig. S11). ESI-MS: [M þ H ] ¼ C15
25 4
H O , calcd: 269.17474, found:
þ
69.17457; [M þ Na ] ¼ C15
24 4
H O Na, calcd: 291.15668, found:
1
91.15644.
described above. See Fig. S20 for the H NMR spectra of the olefin
signals region and Fig. S21eS23 for the ESI-MS spectra of the
2.6. Synthesis of the mono-alkene compound M0
products.
Hept-1-en-4-ol (regarded as preM0) was synthesized similarly
2.8. Exhaustive hydrogenation
as for preM6 by using n-butyraldehyde and allyl bromide in 92%
yield. Acetylation of hept-1-en-4-ol afforded M0 in 99% yield.
Take the synthesis of EVAc6 as an example.
1
H NMR of preM0 (400 MHz, CDCl
3
)
d
(TMS, ppm): 5.84 (m, 1H),
Polymer P6 (200 mg), TSH (614 mg, 3.3 mmol), and TPA (572 mg,
4.0 mmol) were weighed and transferred into a 100 mL round bot-
tom flask. Subsequently, toluene (30 mL) was added to obtain a pale
blue suspension. The flask was connected to a reflux condenser that
5
.12 (m, 2H), 3.64 (dt, J ¼ 16.5, 5.8 Hz, 1H), 2.45 (s, 1H), 2.24 (m, 2H),
13
1.41 (m, 4H), 0.94 (m, 3H). C NMR (101 MHz, CDCl
3
): d 135.01,
1
17.49, 70.40, 41.89, 38.87, 18.76, 13.97 (Fig. S12).
1
H NMR of M0 (400 MHz, CDCl
3
),
d
(TMS, ppm): 5.75 (ddt,
equipped with an anhydrous CaCl
2
loaded drying tube. Under
ꢁ
J ¼ 17.2, 10.2, 7.1 Hz, 1H), 5.06 (m, 2H), 4.93 (m, 1H), 2.31 (m, 2H),
vigorous stirring, the reaction proceeded at 130 C for 12 h, and tiny
bubbles were observed during that time. Then, the reaction was
stopped upon cooling to room temperature to generate an opaque
solution with white precipitates. An equal supply of TSH and TPA
was re-added, and the reaction was allowed to proceed for another
13
2
.02 (s, 3H), 1.53 (m, 2H), 1.32 (m, 3H), 0.91 (t, J ¼ 7.3 Hz, 3H).
NMR (101 MHz, CDCl ): 170.50, 133.73, 117.36, 72.92, 38.62, 35.68,
0.99, 18.48, 13.76 (Fig. S13).
C
3
d
2
ꢁ
2.7. ADMET polymerization
12 h at 130 C. The mixture was washed with water for three times,
and then toluene in the organic layer was removed in vacuo. Chlo-
roform (1 mL ꢂ 3) was used to dissolve the crude hydrogenated
product. The viscous solution was poured into cold petroleum ether
(100 mL) to generate a pale brown suspension. Pale brown precip-
Take the synthesis of P6 as an example.
Monomer M6 (282 mg, 1.0 mmol), p-benzoquinone (2.16 mg,
0 mmol), and Grubbs-II catalyst (8.4 mg, 10 mmol) were weighed
and transferred sequentially into a 25 mL Schlenk flask equipped
with a Teflon valve. Subsequently, 1.0 mL of CH Cl (degassed by
2
ꢁ
itate could be observed via storage at 4 C overnight. After filtration
2
2
and vacuum dryness, EVAc6 was obtained in 90% yield.
All the other EVAc copolymers were obtained in a similar way,
and their NMR spectra are shown in Figs. S24eS26.
sonication for half an hour) was added to dissolve the mixture to
obtain a homogeneous blue solution. The flask was connected to a
reflux condenser which was equipped with an anhydrous CaCl
2
loaded drying tube. Then the flask was placed in an oil bath set at
2.9. Hydrolysis
ꢁ
6
0 C. Nitrogen gas was continuously purged in through the Teflon
valve during ADMET polymerization. As the polymerization pro-
ceeded, the solvent CH Cl was gradually evaporated and the re-
Take the synthesis of EVA6 as an example.
Polymer EVAc6 (150 mg), NaOH (0.4 g, 10 mmol), and CH OH
3
2
2
action mixture became highly viscous in a couple of hours as the
magnetic bar was sluggish to stir. Polymerization was stopped after
(10 mL) were added into a 25 mL round bottom flask. The reaction
mixture was vigorously stirred at room temperature overnight and
an opaque suspension was generated. The mixture was poured into
3
120 h via adding CHCl (5 mL) followed by a large excess of ethyl
ꢁ
vinyl ether. The concentrated dark blue polymer solution was
poured into cold petroleum ether (about 100 mL) to generate a pale
cold deionized water (100 mL) and stored at 4 C for 3 h. The
generated white precipitate was vacuum-filtered, washed with
deionized water, and vacuum dried. Copolymer EVA6 was obtained
in 90% yield as a white solid.
blue suspension. Dark blue precipitate was obtained via storage at
ꢁ
4
C overnight. After filtration and vacuum dryness, P6 was ob-
tained in 95% yield as a brownish semi-solid.
Unsaturated copolymers of P3-P5 were synthesized similarly,
and the NMR spectra are shown in Figs. S14eS16.
All the other EVA copolymers were prepared via the similar
synthetic procedure, and their NMR spectra are shown in Figs. S27e
S29.
Cyclized monomers cM1 and cM2 could be obtained via a
similar synthetic procedure with nearly quantitative yields. The
RCM reactions were allowed to proceed for 24 h. The mixture
became heterogeneous in that blue precipitate coexisted with a
very small amount of liquid, which was not viscous. The mixture
2.10. Synthesis of re-generated EVAc copolymers
Take the synthesis of re-generated EVAc6 as an example.
Copolymer EVA6 (50 mg), acetic anhydride (3 mL), DMAP (cat-
alytic amount) were sequentially weighed and transferred into a
was dissolved in CHCl
gel was washed with CHCl
evaporated to generate pale yellow oil. H NMR of cM1 (400 MHz,
CDCl ),
(TMS, ppm): 5.71 (d, J ¼ 7.7 Hz, 2H), 5.37 (t, J ¼ 6.9 Hz, 1H),
.74 (dd, J ¼ 16.8, 6.9 Hz, 2H), 2.39 (d, J ¼ 18.0 Hz, 2H), 2.04 (d,
3
and filtered through a pad of silica. The silica
3
, and the combined organic phase was
3
100 mL round bottom flask. Then CHCl (30 mL) was added to
1
generate a pale yellow suspension, which was vigorously stirred
ꢁ
3
d
and refluxed at 90 C overnight. The mixture was cooled to room
2
temperature, neutralized with Na
deionized water, dried over anhydrous Na
2
CO
3
solution, washed with
SO , filtered, and evap-
13
J ¼ 6.2 Hz, 3H). C NMR (101 MHz, CDCl
3
):
9.68, 21.30 (Fig. S17). H NMR of cM2 (400 MHz, CDCl
ppm): 5.59 (m, 2H), 5.12 (m, 2H), 2.31 (m, 4H), 2.05 (d, J ¼ 4.5 Hz,
d
171.00, 128.27, 74.16,
2
4
1
3
3
), (TMS,
d
orated to afford highly viscous brownish liquid. The re-generated
EVAc6 copolymer was obtained in 80% yield.
All the other re-generated EVAc copolymers were synthesized
similarly.
13
6
H). C NMR (101 MHz, CDCl
3
):
d
170.32 (d, J ¼ 21.2 Hz), 123.54 (d,
J ¼ 8.4 Hz), 69.34 (d, J ¼ 95.0 Hz), 29.14 (d, J ¼ 148.2 Hz), 21.01 (d,

Z.-L. Li et al. / Polymer 54 (2013) 3841e3849
3845
3
. Results and discussions
reaction mixtures did not increase as in the case of normal ADMET
polymerization. After quenching the reaction, we filtered the
mixtures through a pad of silica and analyzed the concentrated
crude products. The NMR spectra (Figs. S17 and S18) revealed that
only cyclic products were generated in both cases with no high
molecular weight product as confirmed by the GPC traces (Fig. S19).
Not surprisingly, ring-closing metathesis (RCM) reactions occurred
to afford cM1 and cM2 due to the Thorpe-Ingold effect [41].
We then followed our previous reported conditions for the
3.1. Monomer synthesis and characterization
Grignard reaction between aldehyde and organomagnesium
compound is a well-known CeC bond formation reaction [37].
Anhydrous anaerobic operation at low temperature is basically
required. However, if one substrate is allyl bromide or its derivative,
the reaction can be conducted even in water and in a one-pot
manner at room temperature with the assistance of metals or
metal salts. This can be roughly regarded as the characteristics of
Barbier reaction [38]. We selected five linear aliphatic dialdehyde
compounds (or their acetal precursors) to undergo Barbier re-
actions with allyl bromide in water at room temperature for 48 h in
ADMET polymerization of the other four monomers M3-M6
ꢁ
[30,31]. The polymerization was conducted in CH
120 h under continuous N
2
Cl
2
at 60 C for
2
purge. After a couple of hours, the re-
action mixtures became highly viscous, indicating formation of
high molecular weight polymers. These unsaturated copolymers
(designated as P3eP6, respectively) were separated and charac-
terized (Scheme 2). Following the previously reported hydrogena-
tion conditions [42], we got four saturated EVAc copolymers (from
EVAc3 to EVAc6). Hydrolysis of these copolymers by saponification
finally generated the EVA copolymers (from EVA3 to EVA6). For the
copolymer sample EVA3, the theoretical vinyl alcohol molar con-
tent reaches 57%, being the EVA copolymer with ever highest vinyl
alcohol content by ADMET polymerization.
2
the presence of tin dichloride (SnCl ) and potassium iodide (KI). For
acetal substrates, they hydrolyzed gradually in acidic medium so
that dialdehyde formed in situ. Five structurally symmetric diols as
pre-monomers were obtained with yields up to 83%. Subsequent
acetylation of these diols generated the ADMET monomers M2-M6
bearing two vinyl acetate units in nearly quantitative yields
(Scheme 1). M1 was obtained by direct acetylation of the
commercially available hepta-1,6-dien-4-ol in 99% yield. All the
1
13
monomers were characterized by ESI-MS, and H, C NMR spectra
Fig. 1 and Figs. S8eS11). These characterizations confirmed the
The molecular weight (M
(PDI ¼ M /M ) of all the unsaturated and EVAc copolymers were
measured by GPC (Fig. 2). All the polymers had high M values
n w
and M ) and polydispersity index
(
w
n
expected monomer structures, monomers M1-M6 were all mix-
n
tures of stereoisomers.
ranging from 11 800 to 20 800. The PDI values of the EVAc co-
polymers were in the range of 1.68e1.92, in accordance with the
step-growth mechanism. Elevated molecular weights and slightly
reduced PDI values were observed after the unsaturated samples
were hydrogenated, which can be attributed to the increase in
theoretical molecular weights and the decreased molar fraction of
low molecular weight components due to additional selective
precipitation. The final EVA copolymers were not subjected to GPC
measurements due to their insolubility in THF. However, these EVA
copolymers could be re-acetylated and transformed into EVAc co-
polymers. The GPC traces of the re-generated EVAc copolymers
were essentially the same, and the NMR spectra were also consis-
tent with the original EVAc copolymers (data not shown).
The unsaturated and EVAc copolymers were then characterized
by NMR measurements. Fig. 3 shows the spectra of P6 and EVAc6,
the NMR spectra of P3-P5 and the corresponding EVAc copolymers
are shown in Figs. S14eS16 and Figs. S24eS26, respectively. The
signals of terminal alkenes (5.0e5.1 and 5.7e5.8 ppm) of the
monomers disappeared completely in the unsaturated copolymers,
while the signals of internal alkenes (5.4e5.5 ppm) appeared,
suggesting that the ADMET of these monomers were successful
with the formation of high molecular weight copolymers.
3.2. ADMET polymerization, hydrogenation, and hydrolysis
In general, Grubbs-I catalyst is preferentially chosen for ADMET
polymerization due to its ability in suppressing olefin isomeriza-
tion. However, a large number of olefins are inert for metathesis
reaction if Grubbs-I catalyst is adopted [39]. Indeed, Grubbs-I
catalyst is efficient enough for
a,u-diene monomers with long
methylene spacers in that negative neighboring group effect is not
severe. For the monomers in this study, acetoxy group is very close
to the terminal alkene so that steric repulsion cannot be overseen
when Grubbs catalyst approaches are adopted. As we expected,
moderate molecular weight products were generated if Grubbs-I
catalyst was utilized for ADMET polymerization (data not shown).
Therefore, more active Grubbs-II catalyst was chosen for ADMET
polymerization in this study.
In order to examine whether olefin isomerization takes place
using Grubbs-II catalyst for ADMET polymerization, we synthesized
a model compound hept-1-en-4-yl acetate (M0, see Scheme S1)
through Barbier reaction between n-butyraldehyde and allyl bro-
mide followed by acetylation. It was found that olefin isomerization
was clearly resolved from the NMR (Fig. S20) and the ESI-MS
After exhaustive hydrogenation to transform the unsaturated
copolymers into EVAc copolymers, the signals of the internal al-
kenes and the allylic protons (2.1e2.3 ppm) completely dis-
appeared, indicating that 100% saturation of the internal alkenes
was achieved using the selected method. In addition, in the NMR
spectra of both the unsaturated copolymers and the EVAc
(Figs. S21eS23) spectra of the dimerized product of M0. Never-
theless, this side reaction could be suppressed by adding two
equivalents of benzoquinone (BQ) into metathesis system [40].
At first, we tried the ADMET polymerization of M1 and M2 in
bulk, respectively. It was observed that the viscosities of the
ꢁ
Scheme 1. Monomer Synthesis. Reagents and Conditions: (a) 3 equiv. allyl bromide, 3 equiv. SnCl
2
, 6 equiv. KI, H
2
O, 30 C, 48 h (b) 6 equiv. acetic anhydride, 0.2 equiv. DMAP, CH
2
Cl
2
,
rt, overnight.

3846
Z.-L. Li et al. / Polymer 54 (2013) 3841e3849
Fig. 1. 1H and 13C NMR spectra of M6 in CDCl
.
3
2 2
Scheme 2. EVAc and EVA Copolymers via ADMET Polymerization, Hydrogenation, and Hydrolysis. Reagents and Conditions: (a) Grubbs-II catalyst (1.0 mol %), BQ (2.0 mol %), CH Cl ,
ꢁ ꢁ
2 3
N purge, 60 C, 120 h (b) 3.3 equiv. TSH, 4.0 equiv. TPA, toluene, 130 C, 24 h; (c) 5 equiv. NaOH, CH OH, rt, overnight.
copolymers, the signals of
a
-methine (4.8e4.9 ppm) and methyl
limited solubility of the copolymer in DMSO. Fortunately, the sig-
nals of the terminal methyl groups (0.9 ppm) could be clearly
(
2.0e2.1 ppm) protons of the acetoxy groups were maintained, thus
the acetoxy groups can endure both the ADMET polymerization
and hydrogenation. In the NMR spectra of the EVAc copolymers, the
signals of the terminal methyl groups (0.9 ppm) could be resolved,
resolved, thus, the M
integration ratios between the
n
values could be calculated based on the peak
-methine protons of hydroxyl
a
group (4.2 ppm) and terminal methyl protons. These data are also
collected in Table 1, and they coincided well with those of the EVAc
precursors. We also conducted IR characterization to confirm the
existence of pendent hydroxyl groups in the EVA copolymers, and
thus permitting the calculation of absolute M
copolymers by comparing the peak area integration ratios between
the -methine protons of acetoxy groups and the terminal methyl
n
values of the EVAc
a
ꢃ1
ꢃ1
protons. These calculated data are summarized in Table 1.
peaks at 1100 cm and 3300 cm were ascribed to the stretching
vibrations of the CeO and OeH bonds, respectively (Fig. S30).
As shown in Fig. 5, the fine chemical structures of the periodic
EVAc copolymers were further characterized by MALDI-TOF-MS
spectra. A series of peaks with regular intervals that equal to the
theoretical repeating unit mass of each copolymer were observed
in all these spectra, indicating the integrity of the periodic
The final EVA copolymers were generated from hydrolysis of
1
their EVAc precursors. The H NMR spectrum of EVA6 in d
6
-DMSO
1
is shown in Fig. 4. The H NMR spectra of the other EVA copolymers
are shown in Figs. S27eS29. The signals of the hydroxyl groups and
residual water in d
6
-DMSO were partially overlapped. The resolu-
tion of the main chain methylene protons is also low due to the
Fig. 2. GPC traces of P3-P6 and the EVAc copolymers.

Z.-L. Li et al. / Polymer 54 (2013) 3841e3849
3847
Fig. 3. 1H and 13C NMR spectra of P6 and EVAc6 in CDCl
.
3
microstructures as expected. However, a minor series of peaks
deviating from the major peaks by several methylene units due to
the olefin isomerization could still be observed. Such a slight
contamination of the isomerized copolymers may somehow affect
the precise elucidation of the structureeproperty relationship.
These observations also confirmed that olefin isomerization could
not be completely prevented in Grubbs-II catalyst assisted ADMET
polymerization even if inhibitor such as benzoquinone was added
[43e47]. Hence, in this study, the chemical structures of the co-
polymers can only reflect the average chemical composition in a
single repeating unit.
3.3. Thermal properties
Table 1
The thermal stability of the EVAc and EVA copolymers were
Molecular weights and thermal data of the copolymers.
evaluated by TGA. As shown in Fig. 6, the TGA traces of all the EVAc
c
M c
/M c
d
d
d
e
Polymer
M
n
M
n
w
M
w
n
T
(
g
ꢁ
T
m
ꢁ
D
(J/g)
H
m
T
d
copolymers displayed typical two-stage decomposition. The first
ꢁ
C)
( C)
( C)
ꢁ
ꢁ
stage occurred at the temperature range from 250 C to 350 C,
P3
P4
P5
P6
EVAc3
EVAc4
EVAc5
EVAc6
EVA3
EVA4
EVA5
EVA6
e
e
e
e
12 200 23 700 1.94
11 700 20 900 1.79
18 200 37 300 2.05
10 200 18 000 1.76
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
12 800a 14 500 27 300 1.89
ꢃ4.4 n.d.
ꢃ17.1 n.d.
ꢃ21.3 n.d.
ꢃ32.6 n.d.
n.d.
n.d.
n.d.
n.d.
301
312
317
317
210
282
308
299
11 400a 13 300 23 000 1.73
a
18 200
20 800 39 900 1.92
9 600a 11 800 19 800 1.68
7 100b
6 600b
9 500b
6 100b
e
e
e
e
e
e
e
e
e
e
e
e
48.3 144.7 23.0
47.1 145.3 42.7
46.5 135.1 29.9
43.9 136.9 42.5
a
Calculated according to the peak area integration ratios between the
a
-methine
protons of the acetoxy group (S
for each sample. Then M
¼ (theoretical repeating unit mass) ꢂ 3S
Calculated according to the peak area integration ratios between the
protons of the hydroxyl group (S
each sample. Then M
1
) and the main chain terminal methyl protons (S
2
)
n
1 2
/S .
b
a
-methine
) for
1
) and terminal main chain methyl protons (S
/S
2
n
¼ (theoretical repeating unit mass) ꢂ 3S
1
2
.
c
Determined by GPC (1 mL/min) using polystyrene calibration.
d
ꢁ
Determined by DSC, 10 C/min scan rate, the values recorded from the second
scan data. T
m
is defined as the peak value.
e
ꢁ
Determined by TGA, 10 C/min scan rate. T
d
is defined as the temperature at 5%
weight loss.
Fig. 4. 1H NMR spectrum of EVA6 in d
-DMSO.
6

3848
Z.-L. Li et al. / Polymer 54 (2013) 3841e3849
Fig. 5. MALDI-TOF-MS spectra of EVAc3 (A), EVAc4 (B), EVAc5 (C), and EVAc6 (D), respectively.
corresponding to the thermo-induced release of acetic acid from
aromatic compounds (due to polymer chain pyrolysis) followed by
the EVAc copolymers [48,49]. The second stage occurred at above
sharp decomposition to 100% weight loss [50e53]. All the data are
also collected in Table 1, where T is defined as the temperature at
d
5% weight loss.
Glass transition and melting behaviors were measured by DSC
for the EVAc and EVA copolymers. EVAc copolymers only exhibited
typical glass transition stages in the DSC thermograms of Fig. 7, and
ꢁ
3
80 C being the catastrophic decomposition, and the EVAc co-
ꢁ
polymers decomposed completely at about 480 C. For the four
EVAc copolymers, the percentage weight loss due to acetic acid
pyrolysis could be calculated, and the predicted values were
marked in all the corresponding TGA traces, respectively. Much to
our delight, each of the inflection points that connecting the two
stages coincided well with the theoretical values, further confirm-
ing the integrity of periodic sequences of EVAc copolymers. Like-
wise, the TGA traces of the EVA copolymers also exhibited two-
stage decomposition (Fig. S31), with copolymer EVA3 being the
most pronounced one. This can be explained as residual water
entrapped within the EVA copolymer and/or the thermal elimina-
tion of water (due to intermolecular etherification), carbonyls, and
no melting peak or other transition was observed even when
ꢁ
heated to 150 C. The T
m
value of poly(vinyl acetate) is absent since
this polymer decomposes before it melts. Wagener et al. reported
ꢁ
that EVAc copolymers exhibited T
m
values lower than 57 C [54].
However, in their copolymers, the repeating unit contained rather
long methylene spacers so that polyethylene chains govern the
crystallinity, therefore, the T
m
values increased as increasing the
ethylene content [55,56]. It can be obviously seen from Fig. 7 that
the T
g
values of the EVAc copolymers decrease with decreasing
ꢁ
vinyl acetate contents (from EVAc3 to EVAc6, ꢃ4.4 C for EVAc3
ꢁ
and ꢃ32.6 C for EVAc6). This is reasonable if considering that the
ꢁ
T
g
values of polyethylene and poly(vinyl acetate) are ꢃ125
C
ꢁ
[57,58] and 30 C [58], respectively. On the other hand, the EVA
copolymers displayed both glass transition stages and melting
peaks in the DSC thermograms. Based on the data collected in
Table 1, the T values of the EVA copolymers increase slightly as
g
increasing the vinyl alcohol content (from EVA6 to EVA3).
Fig. 6. TGA traces of the EVAc copolymers.
Fig. 7. DSC thermograms of the EVAc and EVA copolymers.

Z.-L. Li et al. / Polymer 54 (2013) 3841e3849
3849
Additionally, the T
than those of EVA5 and EVA6 due to the higher content of vinyl
alcohol [12]. It is reported that a large number of copolymers
containing ethylene and polar monomers exhibit lower T
than that of HDPE since the pendent group incorporation should
disturb the main chain crystallinity. However, for EVA copolymers,
extra hydrogen bonding between the hydroxyl groups should
m
values of EVA3 and EVA4 are obviously higher
[5] Chowdhury F, Haigh JA, Mandelkern L, Alamo RG. Polym Bull 1998;41:
63e70.
4
[
[
6] Bistac S, Kunemann P, Schultz J. Polymer 1998;39:4875e81.
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Yamamoto T, et al. Macromolecules 2003;36:9467e76.
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values
[
[
9] Moroi H. Br Polym J 1988;20:335e43.
[
10] Bruzaud S, Levesque G. Macromol Chem Phys 2000;201:1758e64.
[11] Ito S, Munakata K, Nakamura A, Nozaki K. J Am Chem Soc 2009;131:14606e7.
[
[
12] Mori Y, Sumi H, Hirabayashi T, Inai Y, Yokota K. Macromolecules 1994;27:
051e6.
13] Ramakrishnan S, Chung TC. Macromolecules 1990;23:4519e24.
compensate such decrease in T
surprising that the T
60]. In our case, the EVA copolymers showed T
m
values [59]. Therefore, it is not
1
ꢁ
m
value of poly(vinyl alcohol) reaches 220
C
ꢁ
[
m
values from 135 C
m
value of HDPE [58]. This result sug-
[14] Ramakrishnan S. Macromolecules 1991;24:3753e9.
[15] Yang HL, Islam M, Budde C, Rowan SJ. J Polym Sci Part A Polym Chem 2003;41:
ꢁ
to 145 C, very close to the T
2107e16.
gests that these EVA copolymers could share the same processing
technique as that applied for HDPE. Importantly, the melting peaks
of these EVA copolymers are quite sharp compared to those of the
industrially synthesized sequence random counterparts. The lower
[
16] Schellekens MAJ, Klumperman B. J Macromol Sci Rev Macromol Chem Phys
2000;40:167e92.
[
[
[
17] Hillmyer MA, Laredo WR, Grubbs RH. Macromolecules 1995;28:6311e6.
18] Scherman OA, Kim HM, Grubbs RH. Macromolecules 2002;35:5366e71.
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[20] Zhang JH, Matta ME, Hillmyer MA. ACS Macro Lett 2012;1:1383e7.
[21] Zhang JH, Matta ME, Martinez H, Hillmyer MA. Macromolecules 2013;46:
DH
m
values of EVA3 and EVA5 were ascribed to the hampered
crystallinity caused by more severe olefin isomerization as dis-
cussed above.
2535e43.
[
[
[
22] Lindmark-Hamberg M, Wagener KB. Macromolecules 1987;20:2949e51.
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4
. Conclusions
2006;44:4981e9.
[
25] Opper KL, Wagener KB. J Polym Sci Part A Polym Chem 2011;49:821e31.
We have demonstrated a facile synthetic method for periodic
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[27] Valenti DJ, Wagener KB. Macromolecules 1998;31:2764e73.
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Macromolecules 1997;30:7363e9.
EVAc and EVA copolymers with controllable sequence and
composition via ADMET polymerization and clearly showed a
relationship between the sequence and content of EA units and the
thermo properties of the EVA copolymers. A series of
a
,
u
-diene
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013;51:2900e9.
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4
monomers were obtained in high yields from commercial available
materials. Among them, monomer M1 and M2 underwent RCM
reaction instead of ADMET polymerization. Monomers M3eM6
could be polymerized by Grubbs-II catalyst in the presence of BQ to
generate high molecular weight polymers, hydrogenation of which
afforded a series of EVAc copolymers with regular sequence and
tunable VAc contents. Subsequent hydrolysis of these EVAc co-
polymers generated EVA copolymers with EVA-3 containing the
ever highest VA content (57 mol%) via ADMET polymerization. The
VA contents play crucial roles in determining the thermo properties
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This work was financially supported by National Natural Science
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