www.rsc.org/advances

RSC Advances

This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication.

Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. This Accepted Manuscript will be replaced by the edited, formatted and paginated article as soon as this is available.

You can find more information about Accepted Manuscripts in the Information for Authors.

Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.

View Article OnlineView Journal

This article can be cited before page numbers have been issued, to do this please use: M. Al-Hashimi, M.

Abu Bakar, K. elsaid, D. Bergbreiter and H. Bazzi, RSC Adv., 2014, DOI: 10.1039/C4RA08046G.

Soluble polymer bound second generation Grubbs Ru complex for ROMP that combines solution phase

chemistry and ease of separating the Ru

Page 1 of 8 RSC Advances

RS

CA

dvan

ces

Acc

epte

dM

anus

crip

t

Publ

ishe

d on

02

Sept

embe

r 20

14. D

ownl

oade

d by

Ast

on U

nive

rsity

on

08/0

9/20

14 0

8:01

:10.

View Article OnlineDOI: 10.1039/C4RA08046G

406x208mm (96 x 96 DPI)

Page 2 of 8RSC Advances

RS

CA

dvan

ces

Acc

epte

dM

anus

crip

t

Publ

ishe

d on

02

Sept

embe

r 20

14. D

ownl

oade

d by

Ast

on U

nive

rsity

on

08/0

9/20

14 0

8:01

:10.

View Article OnlineDOI: 10.1039/C4RA08046G

Journal Name RSCPublishing

ARTICLE

This journal is © The Royal Society of Chemistry 2013 J. Name., 2013, 00, 1-3 | 1

Cite this: DOI: 10.1039/x0xx00000x

Received 00th January 2012,

Accepted 00th January 2012

DOI: 10.1039/x0xx00000x

www.rsc.org/

Ring-Opening Metathesis Polymerization using

Polyisobutylene Supported Grubbs Second-

Generation Catalyst

Mohammed Al-Hashimi,*a M. D Abu Bakar,a Khaled Elsaid,b David E. Bergbreiter,c Hassan S. Bazzi,*a

Olefin metathesis is among the most powerful tool for the formation of regio - and steroselective

carbon-carbon double bonds. Appling the principles of Green Chemistry to the syntheses of

polymers, by developing useful strategies to facilitate catalyst and polymer product separation

after a polymerization is vital. In the present study, phase select ively soluble polymer bound

second generation Grubbs catalyst was successfully used to carry out ring-opening metathesis

polymerization (ROMP) on norbornene and a variety of different exo-norbornene derivatives.

Polymers with low ruthenium contamination levels were achieved in comparison to the non-

supported Grubbs catalyst which required multiple precipitations. Furthermore, the bound

catalyst exhibits similar catalytic activity to its homogenous counterpart.

Introduction

The development of well-defined and highly active ruthenium

metathesis catalysts having excellent functional group tolerance

has been fundamental to the widespread application of olefin

metathesis,1-4 in particular for the synthesis of natural products

and small molecules.5

Ring-opening metathesis polymerization (ROMP) has become

an extremely valuable tool for the preparation of functional

homopolymers 6 providing a wide range of polymers with unique

architectures.7 Grubbs (G1, G2 and G3) and Hoveyda–Grubbs

(HG1 and HG2) ruthenium based catalysts are among the widely

used complexes in both academia and industry (Figure 1).8-10

Despite these advances a relatively high price of these catalysts

and the removal of Ru from the reaction product predominantly

in the pharmaceutical industry represent an important

disadvantage for their practical application. 11

Figure 1 Ruthenium-based olefin metathesis catalysts

a Department of Chemistry, Texas A&M University at Qatar, P.O. Box

23874, Doha, Qatar. *Email: mohammed.al-hashimi@qatar.tamu.edu; bazzi@tamu.edu b Department of Chemical Engineering, Texas A&M University at Qatar,

P.O. Box 23874, Doha, Qatar. c Department of Chemistry, Texas A&M University, P.O. Box 30012,

College Station, Texas 77842-3012.†Electronic Supplementary

Information (ESI) available: Detailed experimental procedures, ICP-MS Digestion Procedure, NMR characterization, and assignment of polymers.

See DOI: 10.1039/b000000x/

The development of supported Ru catalysts for olefin metathesis

has attracted increasing interest, both from the view of

environmental (removal of heavy metal impurities) and

economic benefit (high ruthenium cost). We 12-14 and several

research groups 15-26 have reported the use of polymeric and solid

supports for immobilizing ruthenium based catalysts. Among the

several approaches the majority of articles report on using

supported Grubbs second generation catalysts G2 for ring

closing metathesis (RCM). Barrett et al. were the first to report

the immobilization of G2 on vinyl modified poly(styrene) beads,

the so called “boomerang” polymer supported catalyst was used

up to three times in RCM almost without loss of any activity.27

Blechert et al. reported the synthesis of supported G2 on

poly(styrene) Merrifield resin, the catalyst was used in RCM,

cross and enyne metathesis affording near quantitative

conversions.15 Fürstner et al. prepared hydroxyalkyl-

functionalized G2 complex and was shown to catalyze a serious

of RCM. The catalyst was recycled up to three times, but it

showed lower catalytic activity than its homogenous

counterpart.28 Weck et al. utilized poly(norbornene) as a support

for Grubbs second generation catalyst. The reactivity of the

supported NHC ruthenium complex were studied for RCM, the

authors reported good conversions yielding Ru free products. 29

Buchmeiser’s group are among the few that have reported the

use of supported G2 catalyst for ROMP. They used a monolithic

support to immobilize G2 complex, the catalyst was easily

removed by filtration at the end of the reaction. Reasonable

yields and high activity were obtained in both RCM and ROMP,

while the ruthenium residue in the products for RCM was found

to be 70 ppm.16 Grubbs et al. published the use of polyethylene

glycol (PEG) supported G2 complex. The water soluble catalyst

efficiently carried out the ROMP of norbornene derivatives,

however, low turnover numbers (TONs) for RCM was reported.

Page 3 of 8 RSC Advances

RS

CA

dvan

ces

Acc

epte

dM

anus

crip

t

Publ

ishe

d on

02

Sept

embe

r 20

14. D

ownl

oade

d by

Ast

on U

nive

rsity

on

08/0

9/20

14 0

8:01

:10.

View Article Online

DOI: 10.1039/C4RA08046G

ARTICLE Journal Name

2 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 2012

After phase separation

In order to expand the scope of our work using soluble supports

we now wish to report the synthesis of polyisobutylene

supported Grubbs second-generation catalyst and its application

in Ring-Opening Metathesis Polymerization.

Results and discussions

Synthesis of soluble PIB-supported 2nd generation Ru

complex 6 and Characterization

Recently, we elaborated a simple synthetic protocol for

preparation of polyisobutylene (PIB)-supported N-heterocyclic

carbene (NHC) ligand 5.12 Using this methodology we

synthesized the new soluble PIB-supported 2nd generation Ru

complex 6. The synthetic routes to complex 6 are outlined in

Scheme 1. Accordingly, to a solution of N-heterocyclic carbene

ligand 5 in THF at room temperature was added potassium tert-

butoxide, resulting in the deportation of the corresponding NHC

salt to form the free carbene. In situ the free carbene was reacted

with Cl2Ru(CHPh)(PCy3)2 G1 in toluene at room temperature

and the reaction was heated to 80 °C. After purification a waxy

brown-pink oil in 60% yield was obtained.

Scheme 1 Synthesis of PIB-supported second-generation Grubbs

complex 6.

The structure of complex 6 was verified by 1H NMR, 31P NMR

and 13C NMR spectroscopy (Figure 2). As one might expect, the 1H NMR spectrum of complex 6 (Figure 2a) shows a shift for the

benzylidene proton peak from δ = 20.02 ppm (shift for the first-

generation Grubbs G1 complex) to δ = 19.05 ppm, consistent

with the parent none supported 2nd generation Grubbs complex

G2. However, at first 31P NMR spectroscopy indicated that some

triphenyl phosphine oxide was still present 31P δ = 50.04 ppm.

Using the heptane-phase selective solubility of complex 6 due to

the polyisobutylene-containing ligand to our advantage a

liquid/liquid separations using heptane/methanol was introduce

which ultimately resulted in removal of the phosphine oxide

affording the pure complex as depicted in Figure 2b.

a) 1H NMR spectrum of complex 6

b) 31P NMR spectrum of complex 6

Figure 2 NMR spectra (1H and 31P NMR) of PIB supported

complex 6.

The reaction was first evaluated using kinetic studies at room

temperature in deuterated THF (0.5 mL) using 1 mol% catalyst.

Conveniently the polymerizations were conducted in NMR tubes

at a spinning rate of 20 Hz. The conversion of monomer M7 to

polymer P8 was monitored using 1H NMR spectroscopy (Figure

3a-b). Interestingly, a marked difference in reactivity profiles is

observed for complex 6 and G2. The NB M7 was 93% converted

to polynorbornene P8 using complex 6 in 60 min resulting in a

colorless solution of polynorbornene P8 with low viscosity. In

comparison to the ROMP of NB with the parent Grubbs complex

G2, complex 6 exhibited a faster ROMP initiation with greater

than ca. 70% conversion occurring at 25 0C within the first 10

min (Figure 3c) and progressed to ca.90% in 30 min. Whereas

initiation was significantly slower with the non-supported

Grubbs complex G2 ca.31% conversion was achieved after

10min and ca.76% after 30 min. However, 99% conversion was

achieved within a 60 min. Both complexes G2 and 6 achieved

the same conversion in the 46 min 92%. Increasing the catalyst

loading of complex 6 to 1.5 mol% results in 99% conversion

after 20 min. The results for the kinetic studies obtained using

complex G2 agree well with previous published data in the

literature.30

Before phase separation

Page 4 of 8RSC Advances

RS

CA

dvan

ces

Acc

epte

dM

anus

crip

t

Publ

ishe

d on

02

Sept

embe

r 20

14. D

ownl

oade

d by

Ast

on U

nive

rsity

on

08/0

9/20

14 0

8:01

:10.

View Article Online

DOI: 10.1039/C4RA08046G

Journal Name ARTICLE

This journal is © The Royal Society of Chemistry 2012 J. Name., 2012, 00, 1-3 | 3

a) 1H NMR spectra for non- b) 1H NMR spectra PIB- supported

complex G2 supported complex 6

c) Percentage conversion vs reaction time.

Figure 3 Rates of conversion of NB monomer to

polynorbornene- complexes G2 and 6.

The trans/cis double bond ratio in the polymer chain was

determined from 1H NMR spectroscopy as depicted in Figure 4.

The olefinic peaks of the monomer at δ = 5.85 ppm are replaced

by new signals at δ = 5.26 and 5.09 ppm, which correspond to

the cis and trans double bonds of the polymer, respectively. In

accord with previous reports, both complexes resulted in

polymer P8 having a slight excess of trans ratio (trans:cis ∼ 59:

41 complex G2, 51:49 complex 6).31

a) PIB supported complex 6 b) non-supported complex G2

Figure 4 1H NMR spectra in THF-d8 of trans/cis double bond

of polymer P8 using supported and non-supported Ru complex.

A slight difference in the trans/cis double bond ratio was found

between the polymers prepared using the PIB supported Ru

complex and non-supported complex (Table 1). The ratio of the

trans double bond in polymer P8 prepared with the supported

complex was lower. This small difference in stereoselectivity

corresponds to a ca. 0.17 kcal/mol difference in activation energy

for the stereoselectivity in trans/cis isomer formation for catalyst

G2 versus 6. Accounting for such small differences is

necessarily speculative. One possibility is that there is some sort

of steric effect of the PIB group. However, other studies by our

group have shown that terminally functionalized polymer

supports have no significant steric effect.32-35

Moreover, prior work did not show any significant difference in

trans/cis isomer ratio for polymerizations of a functionalized

norbornene using a low molecular weight or a PIB-bound

Grubbs-Hoveyda ROMP catalyst.12 We speculate that the PIB

groups that are associated with the active Ru alkylidene chain

growth site may produce a local solvent effect wherein they

interact with this relatively hydrophobic polynorbornene chain.

Even a modest such effect could easily account for the observed

small change in stereoselectivity for the non-supported complex

G2 versus the PIB-supported complex 6.

The reaction mixture containing the polymer and Ru catalyst

residue in THF was concentrated in vacuo then the Ru residue

was separated by dissolving the crude mixture in minimum

amount of DCM and precipitating the mixture in hexane. Thus,

the homoploymer was isolated as a white solid, while the PIB-

Ru complex remains in the hexane layer. The results obtained by

GPC analysis show that the number average molecular weight

(Mn) of 488,900 g/mol with a monomodal polydispersity index

(PDI) of 2.79, while using the non-supported Ru resulted in a

polymer having an Mn of 456,400 g/mol and PDI 2.85 as depicted

in Table 1.

Encouraged by the promising result and to examine the scope of

complex 6 we decided to investigate the performance of the new

complex on a wider range of substrates. Substituted exo-

norbornene imides were selected as the monomers due to their

ability to undergo living ROMP, as well as their ability to be

easily functionalized. We therefore prepared a variety of

monomers from Exo-oxabicyclo-[2.2.1] hept-5-ene-2,3-

dicarboximide M9. Monomers M11–M14 were synthesized

according to our previously reported method12 Mitsunobu

coupling of imide M9 with methoxy-terminated poly(ethylene

glycol) (average Mw = 2000) afforded monomer M10 (scheme

2). Monomers M17-M21 illustrated in Scheme 2 were prepared

according to the reported procedure with slight modifications.36

Reaction of exo-anhydride M16 with the appropriate

diamine(butane-1,4-diamine) or amino alcohol, 6-amino-1-

hexanol and 3-amino-1-propanol afforded monomer M17, M18

and M19 in 50-60% yield. Oxidation of the primary alcohol

M19 with CrO3 afforded the carboxylic acid derivative M20,

respectively. Coupling of monomer M20 with N-

hydroxysuccinimide (NHS) in the presence of 1-ethyl-3-(3-

(dimethylamino)propyl)carbodiimide (EDC) afforded the ester

M21.

0

20

40

60

80

100

0 5 10 15 20 25 30 35 40 45 50 55 60

% C

on

vers

ion

Time (Min)

Grubbs 2nd Gen. PIB Grubbs 2nd Gen.

Page 5 of 8 RSC Advances

RS

CA

dvan

ces

Acc

epte

dM

anus

crip

t

Publ

ishe

d on

02

Sept

embe

r 20

14. D

ownl

oade

d by

Ast

on U

nive

rsity

on

08/0

9/20

14 0

8:01

:10.

View Article Online

DOI: 10.1039/C4RA08046G

ARTICLE Journal Name

4 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 2012

Scheme 2 Synthetic pathway for the synthesis of ROMP Monomers.

Table 1 Results for the Ru contamination and ROMP catalyzed by complex G2 and supported complex 6.

Entrya Polymers Product Yield

c (%) M

n

d (g/mol) PDI

d trans:cis Ru content

(%) ppm

1 P8 80 488,900 2.79 51:49 3.45 464

2 P8b 81 456,400 2.85 59:41 46.4 6134

3 P11 78 345,900 1.71 52:48 2.09 130

4 P12 63 821,600 1.83 46:54 0.98 71

5 P13 60 170,0000 1.11 44:56 1.82 139

6 P13b 71 125,500 2.34 46:54 16.6 1083

7 P14 80 737,600 2.0 43:57 3.41 156

8 P15 74 163,800 2.16 44:56 6.1 252

9 P17 65 Insoluble - - 9.25 543

10 P19 60 Insoluble - - 4.8 361

a 1 mol% catalyst; b Using non-supported Grubbs 2nd Generation complex G2; c Isolated yield; d Molecular weight and PDI were

determined by GPC; e Measurements were done using ICP-MS analysis, the mol % Ru is the % leached into the polymer.

Page 6 of 8RSC Advances

RS

CA

dvan

ces

Acc

epte

dM

anus

crip

t

Publ

ishe

d on

02

Sept

embe

r 20

14. D

ownl

oade

d by

Ast

on U

nive

rsity

on

08/0

9/20

14 0

8:01

:10.

View Article Online

DOI: 10.1039/C4RA08046G

Journal Name ARTICLE

This journal is © The Royal Society of Chemistry 2012 J. Name., 2012, 00, 1-3 | 5

The reactivity of the PIB supported complex 6 with the

appropriate ROMP substrates M10 to M20 was evaluated

(Scheme 3). The reactions were carried out using 1 mol %

complex 6 under rigorously inert conditions in dry THF at room

temperature. The rate of monomer conversion was monitored

using 1H NMR spectroscopy recorded in CDCl3. Monomers

M11 to M15 were fully converted to the desired polymers P11-

P15 within 1 h, wherein resonances at δ 6.53 ppm for the

cyclic olefin were not observed. Interestingly, complex 6

exhibits very low activity for the ROMP of M10, M18 and M20,

showing just 7% conversion after 1.5 h at 25 °C in THF. Even

after the reaction time was extended to 24 h this showed no

particular change in the conversion. We infer the low monomer

conversion due to the decomposition of the Ru complex, yielding

the phosphonium oxide as the sole 31P product as analyzed by

NMR spectroscopy. Furthermore, interestingly, M17 and M19

resulted in formation of a white solid precipitate within minutes.

This was found to be essentially insoluble in common organic

solvents, Moreover, the analysis of the polymers by NMR

spectroscopy and GPC was made very difficult.

Scheme 3 Synthesis of homo-polymers via ROMP.

Homopolymers P11-15 were separated from the Ru residue as

described previously. GPC analysis of polymers P11-15 showed

broad PDI’s 1.2 to 1.9, which is relatively broader in comparison

to polymers synthesized by living polymerization using other

Grubbs initiators. Previously it has been shown that G2 complex

affords polymers with broad polydispersities and high molecular

weights, this can be attributed to the basicity of the tricyclohexyl

phosphine ligand.30, 37 and high catalyst loading.

Inductively coupled plasma mass spectrometry (ICP-MS)

analysis was used to determine the content of Ru leaching in the

polymer products (Table 1) by dissolving the polymers in

concentrated HNO3. As expected the Ru leaching levels are

substantially lower when using the supported complex 6 ranging

from 0.98% to 3.45%, in comparison to the non-supported

complex G2 which had a higher Ru contamination of 16.6% to

46.6% (entries 1 to 8) even after multiple precipitations with

hexane. The results compare favorably well with other systems

for the removal of ruthenium residues.

Conclusions

In summary, we have synthesized a soluble polymer bound

second generation Grubbs Ru complex for ROMP. The

supported catalyst can be easily obtained from commercially

available starting materials. The catalytic activity of the

supported complex is comparable to those of its homogenous

counterpart. In addition the supported catalyst combines solution

phase chemistry with the ease of separating the Ru form the final

product. Importantly, the ruthenium contamination in the

product was very low without the need for further purification in

comparison to the parent Grubbs catalyst that required multiple

precipitations. Currently further investigations in various types

of metathesis reactions using the supported Grubbs catalyst is

underway.

Acknowledgements

The authors gratefully acknowledge support of this work from

the Qatar National Research Fund project number: NPRP 4-

081-1-016.

Notes and references

1 A. Furstner, Angew. Chem. Int. Ed., 2000, 39, 3012-3043.

2 T. M. Trnka and R. H. Grubbs, Acc. Chem. Res., 2001, 34, 18-29.

3 Y. Vidavsky, A. Anaby and N. G. Lemcoff, Dalton Trans., 2012, 41,

32-43.

4 S. J. Connon and S. Blechert, Angew. Chem. Int. Ed., 2003, 42, 1900-

1923.

5 R. H. Grubbs, Angew. Chem. Int. Ed., 2006, 45, 3760-3765.

6 P. Schwab, R. H. Grubbs and J. W. Ziller, J. Am. Chem. Soc., 1996,

118, 100-110.

7 S. Sutthasupa, M. Shiotsuki and F. Sanda, Polym. J., 2010, 42, 905-

915.

8 S. B. Garber, J. S. Kingsbury, B. L. Gray and A. H. Hoveyda, J. Am.

Chem. Soc., 2000, 122, 8168-8179.

9 M. Scholl, S. Ding, C. W. Lee and R. H. Grubbs, Org. Lett., 1999, 1,

953-956.

10 C. A. Busacca, D. R. Fandrick, J. J. Song and C. H. Senanayake, Adv.

Synth. Catal., 2011, 353, 1825-1864.

11 C. Samojlowicz, M. Bieniek and K. Grela, Chem Rev, 2009, 109, 3708-

3742.

12 M. Al-Hashimi, C. Hongfa, B. George, H. S. Bazzi and D. E.

Bergbreiter, J. Polym. Sci. Part A: Polym. Chem., 2012, 50, 5211-

5212.

13 C. Hongfa, H. L. Su, H. S. Bazzi and D. E. Bergbreiter, Org. Lett.,

2009, 11, 665-667.

14 C. Hongfa, J. H. Tian, H. S. Bazzi and D. E. Bergbreiter, Org. Lett.,

2007, 9, 3259-3261.

15 S. C. Schurer, S. Gessler, N. Buschmann and S. Blechert, Angew.

Chem. Int. Ed., 2000, 39, 3898.

16 M. Mayr, B. Mayr and M. R. Buchmeiser, Angew. Chem. Int. Ed.,

2001, 40, 3839.

17 J. Dowden and J. Savovic, Chem. Commun., 2001, 37-38.

18 S. J. Connon, A. M. Dunne and S. Blechert, Angew. Chem. Int. Ed.,

2002, 41, 3835-3838.

19 S. Varray, R. Lazaro, J. Martinez and F. Lamaty, Organometallics,

2003, 22, 2426-2435.

Page 7 of 8 RSC Advances

RS

CA

dvan

ces

Acc

epte

dM

anus

crip

t

Publ

ishe

d on

02

Sept

embe

r 20

14. D

ownl

oade

d by

Ast

on U

nive

rsity

on

08/0

9/20

14 0

8:01

:10.

View Article Online

DOI: 10.1039/C4RA08046G

ARTICLE Journal Name

6 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 2012

20 N. Audic, H. Clavier, M. Mauduit and J. C. Guillemin, J. Am. Chem.

Soc., 2003, 125, 9248-9249.

21 Q. W. Yao and A. R. Motta, Tetrahedron Lett., 2004, 45, 2447-2451.

22 S. T. Nguyen and R. H. Grubbs, J. Organomet. Chem., 1995, 497, 195-

200.

23 M. Ahmed, A. G. M. Barrett, D. C. Braddock, S. M. Cramp and P. A.

Procopiou, Tetrahedron Lett., 1999, 40, 8657-8662.

24 S. Zaman and A. D. Abell, Tetrahedron Lett., 2009, 50, 5340-5343.

25 S. Cetinkaya, E. Khosravi and R. Thompson, J. Mol. Catal. A-Chem.,

2006, 254, 138-144.

26 B. H. Lipshutz and S. Ghorai, Tetrahedron, 2010, 66, 1057-1063.

27 M. Ahmed, T. Arnauld, A. G. M. Barrett, D. C. Braddock and P. A.

Procopiou, Synlett., 2000, 1007-1009.

28 S. Pruhs, C. W. Lehmann and A. Furstner, Organometallics, 2004, 23,

280-287.

29 W. J. Sommer and M. Weck, Adv. Synth. Catal., 2006, 348, 2101-

2113.

30 R. Tuba, R. C. da Costa, H. S. Bazzi and J. A. Gadysz, ACS Catal.,

2012, 2, 155-162.

31 C. W. Bielawski, D. Benitez, T. Morita and R. H. Grubbs,

Macromolecules, 2001, 34, 8610-8618.

32. D. E. Bergbreiter and R. Chandran, J Org Chem, 1986, 51, 4754-4760.

33. D. E. Bergbreiter and R. Chandran, J. Am. Chem. Soc., 1987, 109, 174-

179.

34. D. E. Bergbreiter and Y. C. Yang, J. Org. Chem., 2010, 75, 873-878.

35. C. Hongfa, J. H. Tian, J. Andreatta, D. J. Darensbourg and D. E.

Bergbreiter, Chem., Commun, 2008, 975-977.

36. N. B. Sankaran, A. Z. Rys, R. Nassif, M. K. Nayak, K. Metera, B. Z.

Chen, H. S. Bazzi and H. F. Sleiman, Macromolecules, 2010, 43, 5530-

5537.

37. J. Vargas, E. S. Colin and M. A. Tlenkopatchev, Eur. Polym. J., 2004,

40, 1325-1335.

Page 8 of 8RSC Advances

RS

CA

dvan

ces

Acc

epte

dM

anus

crip

t

Publ

ishe

d on

02

Sept

embe

r 20

14. D

ownl

oade

d by

Ast

on U

nive

rsity

on

08/0

9/20

14 0

8:01

:10.

View Article Online

DOI: 10.1039/C4RA08046G