ROMP of acetoxy-substituted dicyclopentadiene to a linear polymer with a high Tg

Article abstract of DOI:10.1039/c5ra01855b

A polydicyclopentadiene derivative was obtained via ring-opening metathesis polymerization (ROMP) of acetoxy-substituted dicyclopentadiene (AcO-DCPD) using the Grubbs 1^st generation catalyst. Analyses of the polymer microstructures indicate that polymers are linear. The glass transition temperatures (T_g) of the linear polymers range from 136°C to 159°C, which are much higher than that of linear polydicyclopentadiene.

Full text of DOI:10.1039/c5ra01855b

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ROMP of acetoxy-substituted dicyclopentadiene to
a linear polymer with a high Tg†
Cite this: RSC Adv., 2015, 5, 26185
Laijiang Gong, Kun Liu, Encai Ou, Feng Xu, Yanbing Lu, Zhao Wang, Tao Gao,
Zhongkui Yang and Weijian Xu*
Received 30th January 2015
Accepted 6th March 2015
DOI: 10.1039/c5ra01855b
www.rsc.org/advances
1
A polydicyclopentadiene derivative was obtained via ring-opening instead of well-dened catalysts. It has been demonstrated that
metathesis polymerization (ROMP) of acetoxy-substituted dicyclo- the main advantages of the well-dened catalysts compared to
st
pentadiene (AcO-DCPD) using the Grubbs 1 generation catalyst. the binary catalytic ones are the relatively high catalyst stability,
Analyses of the polymer microstructures indicate that polymers are the elimination of co-catalyst or activators, and the lack of side
linear. The glass transition temperatures (T
g
) of the linear polymers reactions resulting from the high Lewis acidity of the older
ꢀ
ꢀ
16,17
range from 136 C to 159 C, which are much higher than that of linear systems.
polydicyclopentadiene.
Therefore, the method to obtain linear PDCPD derivative by
using Grubbs' 1 generation catalyst (G1) has been devised
crossed-linked PDCPD will be obtained with G1 (ref. 5)). A
st
(
Polydicyclopentadiene (PDCPD) is formed through ROMP of
dicyclopentadiene (DCPD) using a variety of transition-metal-
based metathesis catalysts.
feasible way to get linear PDCPD derivative is to selectively
inactivate the cyclopentene-type double bond of DCPD. It is well
known that the driving force for ROMP is the release of the ring
strain energy. Higher ring strain energy usually leads to higher
1–6
To date, the reaction mecha-
nism for endo-DCPD which is illustrated in Scheme 1 has been
4,5
widely accepted. DCPD contains two different carbon–carbon
double bonds: norbornene-type and cyclopentene-type. Both of
them are capable of binding with the catalyst to undergo
metathesis. Consequently, in the ROMP either both or one of
18
reactivity toward ROMP. As an electron-withdrawing group,
the acetoxy group has a large stabilizing effect on the rings due
19
20
to the anti-p double bond. It has also been reported that the
acetoxy group could lower the activity of ROMP of acetoxy-
substituted cycloolen (Scheme 2a and b). For example, no
polymerization was observed with acetoxy-substituted cyclo-
2
the double bonds from DCPD can be involved. In the rst case
a crossed-linked PDCPD (C-PDCPD) is the product while in the
second case linear PDCPD (L-PDCPD) can be obtained.
3
nd
pentene (Scheme 2d) using Grubbs 2 generation catalyst even
Furthermore, different cross-linking reaction mechanisms of
DCPD due to an olen addition reaction have also been repor-
if cyclopentene can be polymerized under the same
21
conditions.
6
ted. Up to now, with most of the catalytic systems, the poly-
merization is very fast and gives crossed-linked PDCPD, so that
the reaction can be only applied in reaction injection molding
(
RIM) techniques for manufacturing of impact-resistant and
7–9
tough molded parts.
Considering the L-PDCPD's good
thermal stability, good solubility and the promising application
in copolymerization, to polymerize DCPD into L-PDCPD will be
10,11
3,12–15
of value.
However, only a few of studies
in ROMP of
DCPD involving selectively ring-opening of the norbornene ring
in DCPD to L-PDCPD have been reported. Furthermore, most of
them employed certain selective binary catalytic systems
State Key Laboratory for Chemo/Biosensing and Chemometrics, Hunan University,
Changsha, 410082, P. R. China. E-mail: weijianxu59@gmail.com; gonglaijiang@
1
†
1
26.com; Fax: +86-0731-88821549; Tel: +86-0731-88821749
Electronic supplementary information (ESI) available. See DOI:
0.1039/c5ra01855b
Scheme 1 Reaction scheme of ROMP for endo-DCPD.
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Table 1 AcO-DCPD conversion at different catalyst loading; CH
solution; [M] ¼ 1.15 mmol; catalyst: Grubbs 1 catalyst; T ¼ 0 C
2
Cl
2
st
ꢀ
a
b
ꢀ
Entry [M]/[Cat.] Yield (%)
M
w
(kDa)
M
n
(kDa)
M
w
/M
n
T
g
( C)
#
#
#
#
#
#
1
2
3
4
5
6
70
130
350
900
1700
3850
96.0
96.1
95.8
95.9
91.3
87.5
29.0
53.7
69.2
80.7
223.2
619.0
22.3
34.2
46.0
58.6
115.4
274.1
1.24
1.48
1.45
1.37
2.01
2.44
136.4
137.5
141.1
146.8
152.7
159.1
Scheme 2 (A) Molecule structure: (a) 3-acetoxy-cyclooctene, (b) 3-
acetoxy-cycloheptene, (c) cyclopentene, (d) 3-acetoxy-cyclopentene,
a
b
Monomer (AcO-DCPD) to catalyst ratio. Isolated yield of polymer.
st
(
e) AcO-DCPD; (B) the synthesis of linear polymer and the Grubbs 1
generation catalyst (G1).
Synthesis of PAD from AcO-DCPD
In this communication, the acetoxy group was introduced to
the active methylene of the DCPD to lower the activity of the
ꢀ
All the experiments were performed at 0 C in a Schlenk ask
18–20
cyclopentene-type ring.
Then we successfully obtained
with a magnetic stirrer. The catalyst was rst dissolved in
dichloromethane and rapidly recrystallized using dry nitrogen
linear acetoxy-substituted PDCPD (PAD) by ROMP of AcO-DCPD
involving selectively ring-opening of norbornene-type ring

ow to obtain the catalyst in smaller and more soluble form, in
(Scheme 2B). Evidence for the success of linear PAD synthesis
2
3
order to accelerate the dissolution of the catalyst powder. In
was provided by using a variety of characterization techniques,
ꢁ1
the glove box, estimated amount of G1 (2.0 mg mL in CH
2
Cl
2
)
1
13
1
13
including H NMR, C NMR and H– C HMQC.
was added into 10 mL Schlenk asks by pipettor. Then the

asks were sealed with airtight stoppers, taken out of the glove
ꢀ
box and cooled down to 0 C under continuous stirring. Five
minutes later, 0.20 g AcO-DCPD was added by a 1.0 mL Ham-
Synthesis of acetoxy-
dicyclopentadiene
2
ilton glass syringe under N atmosphere. Aer 4 h the reaction
mixtures were quenched with ethyl vinyl ether and stirred for
additional 15 min. The solvent was removed and the product
was dried under vacuum. Yields are given in Table 1.
The AcO-DCPD was synthesized referring to the modied Mir-
22
onov's method. To a solution of 50 g of DCPD in 110 mL of
acetic anhydride, 30 mL of acetic acid and 40.2 g of SeO were
2
added. The mixture was stirred at room temperature for 24 h.
Aer cooling, the mixture was ltered through a celite pad,
The successful synthesis of linear PAD
diluted with H
times. The extract was separated by distillation. Yield: 35.2 g CHCl
2
O and extracted with 100 mL of hexane three The PAD can be easily dissolved in several solvents (CH
2 2
Cl ,
3
, THF and toluene) at room temperature. This means that
(
49%). The structures of the AcO-DCPD were characterized by the PAD may be linear. The NMR studies were fully carried out
1
1
13
H NMR spectrum (Fig. 1). H NMR (CDCl
3
): d ¼ 6.06 (1H, dd, J for a sample (entry #3). The analysis of C NMR spectrum
¼
5.4, 2.4 Hz), 5.84–5.89 (1H, m), 5.83 (1H, dd, J ¼ 5.4, 2.4 Hz), indicates that only four kinds of signals at a high eld region
5
.55 (1H, dt, J ¼ 5.9, 1.8 Hz), 4.92–4.95 (1H, m), 3.33–3.40 (1H, (138.0 ppm, 132.0 ppm, 131.2 ppm, 130.6 ppm) are C]C
m), 3.88 (1H, br s), 2.80 (1H, br s), 2.57 (1H, dq, J ¼ 6.9, 2.2 Hz), carbons while a higher signal at 170.5 ppm is C]O carbon
2.03 (3H, s), 1.57 (1H, d, J ¼ 8.4 Hz), 1.38 (1H, d, J ¼ 8.4 Hz).
1
13
Fig. 1 H NMR spectrum of AcO-DCPD (in CDCl
3
).
Fig. 2
3
C NMR spectrum of PAD (in CDCl ).
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13
3
Fig. 3 H– C HMQC spectrum of PAD (in CDCl ).
Fig. 5 Determination of T
g
of PADs by differential scanning calorim-
etry (DSC).
that the PAD displays two degradation steps and the rst
ꢀ
degradation step loses nearly 32% weight (from 221 C to
ꢀ
3
17 C), which is attributed to the degradation of acetoxy unit
(
in conformity with the weight percentage of acetoxy group in
ꢀ
PAD). The other one begins around 426 C which is similar to
cross-linked PDCPD.
24,25
Fig. 4 TG curves of the PAD #1 and C-PDCPD (C-PDCD was prepared
under the same condition as the PAD #1).
DSC analyses of PAD
The thermal transition temperatures of PAD is examined by
(
Fig. 2). This has also proven the obtainment of the linear PAD. DSC analyses. Note that the PAD is amorphous, which only
1
13
The structure of PAD was also characterized by H– C HMQC exhibits a sharp T without any melting temperature (Fig. 5). A
g
(
Fig. 3).
range of T values has been reported for PDCPD that depends
g
1
13
1
Through the analysis of the H– C HMQC spectrum, the H on and characterizes the amount of cross-linking. For reference,
ꢀ
26
NMR signals are assigned unambiguously. The acetoxyl group DSC measurements of linear PDCPD yielded a T of 53 C. As
g
proton signals are clearly observed around 2.0 ppm as a singlet. would be expected, Tg is dependent on several parameters,
1
In the H NMR of the PAD, ve signals existed in the region of including comonomer, molecular weight, and functionality. In
1
ꢀ
ꢀ
the double bond, while only four signals in the H NMR of the this communication, the measured T range of 136 C to 159 C
g
AcO-DCPD (Fig. A, ESI†). The signal at 5.6 ppm can be easily (Tg values are compiled in Table 1 and Fig. 5) for the PAD
1
13
assigned to a methane proton labelled with “9” in the H– C obtained in our experiments indicates more excellent thermal
HMQC spectrum (Fig. 3 carbon 9). As a result, there are only performance than the L-PDCPD. As mentioned before, the only
1
four kinds of signals labelled with C]C carbons in the H NMR difference between the PAD and the L-PDCPD is whether to be
spectra. This is the additional evidence in support of the substituted by acetoxy group. Hence, the acetoxy added to the
product of the linear PAD. Other signals are assigned one by one chain of L-PDCPD should be responsible for the higher T
g
27,28
in Fig. 3. From the above, the structure of PAD is proved to be values of the PADs.
3,11
linear by using analogous experiments.
Conclusions
Thermogravimetric analyses of PAD
We successfully synthesized a derivative of DCPD, AcO-DCPD,
The thermal stability of PAD was studied by TGA (Fig. 4). The which can be polymerized into acetoxy-substituted PDCPD
onset degradation temperatures (T ) are dened by the using rst well-dened ruthenium catalyst. The microstructures
temperatures of 5% weight loss in TGA curves. It's quite obvious of the polydicyclopentadiene derivative were analyzed by
d
1
H
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1
3
1
13
14
NMR, C NMR and H– C HMQC and proved to be linear.
13 K. Dono, J. Huang, H. Ma and Y. Qian, J. Appl. Polym. Sci.,
2000, 14, 3247–3251.
The thermal stability of PAD is not good enough, because the
onset of PAD degradation temperatures is around 220 C. 14 V. Dragutan, A. Demonceau and I. Dragutan, A Selective
ꢀ
However, the Tg of the polymers obtained from AcO-DCPD
range from 136 C to 159 C, which are much higher than
that of L-PDCPD. PAD can be recycled easily with its good
Route for Synthesis of Linear Polydicyclopentadiene[M],
Green Metathesis Chemistry, Springer Netherlands,
Rumania, 2010, pp. 369–381.
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