Synthesis and Purification of Tunable High Tg ElectroOptical Polymers by Ring Opening Metathesis 

Polymerization

by Robert H. Lambeth, Joseph M. Dougherty, Joshua A. Orlicki,

Adam M. Rawlett, Robert C. Hoffman, Timothy Pritchett, and 

Andrew G. Mott

ARL-TR-5651 September 2011

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Army Research Laboratory

Aberdeen Proving Ground, MD 21005

ARL-TR-5651 September 2011

Synthesis and Purification of Tunable High Tg ElectroOptical Polymers by Ring Opening Metathesis 

Polymerization

Robert H. Lambeth, Joseph M. Dougherty, Joshua A. Orlicki,

and Adam M. Rawlett

Weapons and Materials Research Directorate, ARL

4600 Deer Creek Loop

Aberdeen Proving Ground, MD 21005

Robert C. Hoffman, Timothy Pritchett, and Andrew G. Mott

Sensors and Electron Devices Directorate, ARL

Adelphi, MD 20783-1197

Approved for public release; distribution unlimited. 
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Synthesis and Purification of Tunable High Tg Electro-Optical Polymers by Ring 

Opening Metathesis Polymerization

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14. ABSTRACT

This report summarizes efforts to date toward preparing electro-optical polymer by ring opening metathesis polymerization. Initial work 

involved preparing model electro-optical polymers with tunable glass transitions. Random copolymerization of a norbornene ester tethered 

to E-O chromophore Disperse Red 1 (DR1) with various levels exo-N-Phenylnorbornene-5,6-dicarboxamide (NDI) and 5-carbomethoxy-2-

norbornene produced materials with controlled Tgs. The Tg could be varied from 89 to 189 °C by modifying the feed ratio of the 3 

monomers enabling materials to be produced according to desired processing conditions. The polymers were tested for electro-optical 

activity but displayed very little or no alignment along an electric field. The lack of activity is potentially the result of residual 

polymerization catalyst remaining in the final polymer product. To probe this further, a comprehensive investigation was performed to 

discover purification methods capable of reducing residual catalyst to acceptable levels. Initially, baseline levels were established for 

polymer purified via “traditional” methods involving multiple precipitations. The residual catalyst levels ranged from 240 to 140 ppm 

depending on the number precipitations. Several different strategies were employed to further reduce the trace metal remaining in the final 

polymer product. The first strategy involved the use of catalyst modifiers and various adsorbents. None of the methods explored reduced 

the catalyst level below 100 ppm while significantly reducing the yield of polymer due to adsorption of the polymer. The second strategy 

involved the use of heterogeneous functionalized particles to scavenge the catalyst from the solution. Filtration of the particles followed by 

precipitation produced polymers with 10–60 ppm residual catalyst, depending on the type of particle used, surface functional groups, and 

number of equivalents. The third strategy used small organic molecules that could coordinate to the metal species and modify the solubility 

of the catalyst, facilitating partitioning of the catalyst into the precipitation solvent. Several types of molecules with varied functionality 

reduced the residual catalyst level to 30–120 ppm, depending on the loading. Reducing the amount of trace catalyst significantly improved 

the oxidative stability of the polymer.

15. SUBJECT TERMS

ROMP, electro-optical polymers

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Robert H. Lambeth

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iii

Contents

List of Figures iv

List of Tables iv

1. Introduction 1

2. Experimental 2

3. Results and Discussion 3

4. Summary and Conclusions 12

5. References 14

List of Symbols, Abbreviations, and Acronyms 16

Distribution List 17
iv

List of Figures

Figure 1. Structures of monomers and catalyst used in this study..................................................5

Figure 2. Oxidative stability of polymer with varying levels of residual Ru. ..............................12

List of Tables

Table 1. Thermal data for E-O polymers prepared by ROMP........................................................4

Table 2. Yields and residual catalyst for various purification protocols. .......................................7

Table 3. Heterogeneous scavengers used in study..........................................................................8

Table 4. Residual Ru levels for ROMP polymers purified with catalyst solubilizing agents. .....11
1

1. Introduction

Organic/polymer electro-optical (E-O) materials have been heavily studied in recent years due to 

their potential use in high speed photonic devices (1). Compared to their inorganic counterparts, 

polymeric E-O materials offer significant advantages including: faster switching speeds, 

tunability, and processability (2). E-O properties arise from the non-centrosymmetric alignment 

of non-linear optical (NLO) chromophores during application of an electric field. One of the 

challenges in preparing materials for practical applications involves preventing decay of the 

poling-induced order during device operation (3). This can be achieved by incorporating the 

E-O chromophores into high glass-transition (Tg) polymers either as a guest or by covalent 

attachment. Covalent attachment is generally preferred as the motion of the chromophores is 

more restricted and phase separation from the matrix is not an issue (4). Covalent attachment 

can be achieved either by post-polymerization modification of a functionalized polymer 

backbone or direct polymerization of a chromophore containing monomer. Post-polymerization 

modification enables the incorporation of different chromophores with constant molecular 

weight. However, the procedure can be difficult to quantify and reproduce in terms of the 

number of chromophores incorporated per chain and their distribution along the backbone (5). 

In certain cases, the chemistry to couple the chromophore to backbone is incompatible with 

chromophore itself. Direct polymerization of a chromophore containing monomer is easier to 

quantify and reproduce and requires less synthetic steps. However, many of the materials 

prepared in this regard require either demanding reaction conditions unsuitable for the E-O 

chromophores and produce polymers with broad molecular weight distributions (6, 7). Thus, 

preparation of thermally stable E-O materials via direct polymerization of chromophore 

containing monomers under mild reaction conditions is highly desirable. Ring opening 

metathesis polymerization (ROMP) is an attractive alternative to other modes of polymerization 

because well-defined, high molecular weight polymers can be obtained under mild reaction 

conditions with excellent functional group tolerance (8). Thus, ROMP would be a viable route 

to directly produce E-O polymers where the desired chromophore is incompatible with other 

polymerization methods. 

Another important factor to consider is the processing and poling conditions of the material 

produced. In general, the poling induced order of the chromophores is better preserved with 

higher Tg. However, with higher Tg, the material becomes more difficult to process and thermal 

stability of the chromophores itself is an issue. Such constraints could limit the temperature 

range over which the materials would be applicable and necessitates control over the Tg. 

Varying comonomer feed ratios is a convenient method to control Tg and is easily employed in 

ROMP. In this report, we explain the synthesis, characterization, and purification of tunable 

high Tg E-O polymers by ROMP. 
2

2. Experimental

General Methods and Materials. All solvents and reagents were purchased from Aldrich and 

used as received. Compounds 2, 3, 4, 4-(dimethylamino) pyridinium 4-toluenesulfonate (DPTS) 

and cis-5-norbornene-exo-2,3-carboxylic anhydride were prepared according to the literature

(9–13). 

1H NMR and 13C NMR data were recorded on a Bruker 600 MHz instrument. All 

chemical shifts are reported in ppm relative to residual CHCl3 or DMSO. Coupling constants (J) 

are expressed in hertz (Hz). The molecular weight and polydispersity of the polymers was 

estimated in THF at rt with a Waters 515 HPLC pump, Thermo Separations Products AS300 

autosampler, Waters 2487 Dual wavelength absorbance detector, Wyatt Optilab DSP refractive 

index detector, Wyatt Dawn EOS MALLS detector, and two Polymer Laboratories PLgel 5 μm 

mixed D columns at a flow rate of 1.0 mL/min. Glass-transitions were obtained on a TA 

Instruments DSCQ1000 with a heat-cool-heat cycle from 25 to 250 °C at 10 °C/min.

2-(ethyl(4-((E)-(4-nitrophenyl)diazenyl)phenyl)amino)ethyl bicyclo[2.2.1]hept-5-ene-2-

carboxylate (1). 5-norbornene-2-carboxylic acid (2.02 g, 15.94 mmol), Disperse Red 1 (5.51 g, 

17.52 mmol), and DPTS (0.50 g, 1.59 mmol) were dissolved in CH2Cl2 (100 mL) and cooled in 

an ice bath. In a separate flask, DCC (3.94 g, 19.12 mmol) was dissolved in CH2Cl2 (25 mL) and 

transferred via cannula to the above mixture. The reaction mixture was allowed to gradually 

warm to rt and was stirred overnight (~18 h). The reaction mixture was filtered by vacuum 

filtration to remove dicyclohexylurea (DCU) and concentrated by rotary evaporation. The crude 

mixture was dissolved in ethyl acetate (100 mL) and placed in an ice bath for 1 h to crystallize 

any remaining DCU. Vacuum filtration, concentration and recrystallization from ethanol 

produced the title compound (6.1 g, 88 %) as a red solid. m.p. 86–88 °C; endo-norbornyl isomer: 

1H NMR (600 MHz, CDCl3): δ 1.27-130 (m, 4H), 1.37-1.47 (m, 2H), 1.93 (td, J = 3.7, 9.4, 1H), 

2.93 (s, 1H), 2.97 (dt, J = 3.9, 9.4, 1H), 3.03 (s, 1H), 3.56 (dd, J = 7.1, 14.3, 2H), 3.68 (t, J = 6.3, 

2H), 4.27 (t, J = 6.3, 2H), 5.91 (dd, J = 2.8, 5.6, 1H), 6.21 (dd, J = 2.9, 5.6, 1H), 6.83 (d, J = 9.1, 

2H), 7.93 (m, 4H), 8.33 (d, J = 8.8, 2H) 13C NMR (150 MHz, CDCl3) δ 12.33, 29.33, 30.47, 

41.65, 42.56, 43.11, 43.34, 45.74, 46.42, 46.59, 48.83, 49.72, 61.20, 111.51, 122.67, 124.69, 

126.28, 132.20, 135.65, 138.05, 138.17, 143.86, 147.43, 151.33, 156.79, 174.74.

exo-N-(p-Carboxyphenyl) nadimide. cis-5-norbornene-exo-2,3-carboxylic anhydride (19.14 g, 

0.117 mol) was dissolved in acetone (70 ml) with slight heating. p-aminobenzoic acid (16.05g, 

0.117 mol) was added in one portion and the mixture was allowed to stir for 30 min during 

which a white precipitate formed. The precipitate was collected by vacuum filtration and dried 

under high vacuum to yield 29.13 g of the amic acid. 

The amic acid was dissolved in DMF (100 mL) at 100 °C. Acetic anhydride (14.8 g, 0.145 mol) 

and anhydrous sodium acetate (0.8 g, 0.01 mol) were added and the mixture was allowed to stir 

at 100 °C for 2 h. The solution was allowed to gradually cool to rt during which the product 
3

crystallized. The crystals were collected by vacuum filtration, washed thoroughly with water, 

and dried under high vacuum at 80 °C to yield 20.96 g (63 %) of the title compound. m.p.

265–268 °C; 1H NMR (600 MHz, CDCl3): δ 1.46 (q, J = 9.9, 2H), 2.87 (s, 2H), 3.22 (s, 2H), 

6.36 (s, 2H), 7.42 (d, J = 8.5, 2H), 8.05 (d, J = 8.5, 2H), 13.13 (bs, 1H) 13C NMR (150 MHz, 

CDCl3) δ 42.55, 44.86, 47.47, 126.73, 129.71, 130.032, 135.73, 137.63, 166.40, 176.29.

exo-N-[(E)-2-(ethyl(4-((4-nitrophenyl)diazenyl)phenyl)amino)ethyl benzoate] nadimide (5). 

DPTS (0.44 g, 1.41 mmol), exo-N-(p-Carboxyphenyl) nadimide (2.0 g, 7.06 mmol) and Disperse 

red 1 (2.26 g, 7.20 mmol) were dissolved in a mixture of THF (40 mL) and CH2Cl2 (40 mL) 

under N2 atmosphere and cooled in an ice bath. In a separate flask, DCC (1.75 g, 8.47 mmol) 

was dissolved in CH2Cl2 (10 mL) and transferred via cannula to the above mixture. The reaction 

mixture was allowed to gradually warm to rt and was stirred overnight (~18 h). The reaction 

mixture was filtered by vacuum filtration to remove dicyclohexylurea (DCU) and concentrated 

by rotary evaporation. The product was purified by column chromatography (SiO2: 1:1 ethyl 

acetate:hexanes). The product crystallized in the fraction tubes and was collected by vacuum 

filtration to yield 0.89 g (22 %) of the title compound as a deep red solid. m.p. 184 – 187 °C; 1H 

NMR (600 MHz, CDCl3): δ 1.28 (t, J = 7.1, 14.16, 3H), 1.45 (d, J = 9.9, 1H), 1.62 (d, J = 10.0, 

1H), 2.87 (s, 2H), 3.41 (s, 2H), 3.58 (q, J = 7.0, 2H), 3.83 (t, J = 6.2, 2H), 4.56 (t, J = 6.2, 2H), 

6.36 (s, 2H), 6.86 (d, J = 8.5, 2H), 7.93 (m, 4H), 8.11 (d, J = 8.4, 2H), 8.32 (d, J = 8.9, 2H) 13C 

NMR (150 MHz, CDCl3) δ 12.39, 43.08, 45.80, 45.98, 47.97, 48.89, 62.28, 111.58, 122.71, 

124.70, 126.23, 126.32, 129.50, 130.52, 136.15, 138.05, 143.97, 147.48, 151.25, 156.783, 

165.62, 176.53

Representative Polymerization Procedure. A solution of 4 (11.1 mg, 0.013) in CH2Cl2 (1 mL) 

was rapidly injected via syringe into a vigorously stirred solution of 1 (150 mg, 0.34 mmol), 2

(75 mg, 0.49 mmol), and 3 (275 mg, 0.68 mmol) in CH2Cl2 (9 mL) at rt. After 30 min, a large 

excess of ethyl vinyl ether was added to quench the polymerization. The reaction mixture was 

poured into stirred methanol, and the resulting precipitate was collected by vacuum filtration and 

dried under high vacuum.

3. Results and Discussion

As stated previously, our goal is to explore the use of ROMP to directly prepare tunable, high Tg

E-O polymers that would otherwise be difficult to prepare using polymerization methods where 

high temperatures or free-radicals are required. We envisioned copolymerizing an E-O 

chromophore tethered monomer such as 1 with norbornyl-monomers 2 and 3 via ROMP as a 

method for preparing polymers with controllable Tg values under mild reaction conditions. 

Polymers derived from nadimide 3 are thermally robust with Tg values exceeding 200 °C and are 

soluble in common organic solvents (10). Modification of the feed ratio between monomers 2
4

and 3 with constant 1 should enable the preparation of polymers with pre-determined Tg values, 

allowing the material to be tuned according to the desired processing conditions.

Commercially available Disperse Red 1 (DR1) was used as a model chromophore for this study,

which is attached to the polymerizable norbornene unit via DCC/DPTS coupling. Acrylic 

monomers containing DR1 are difficult to polymerize to high molecular weights by free radical 

polymerization (14). Lambeth and Moore have previously shown that similar azobenzenetethered norbornyl-monomers are readily polymerized in a controlled fashion by complex 4 (15).

Monomers 1, 2, and 3 were initially homo-polymerized in the presence of complex 4 with target 

molecular weights of 40 kDa. Five copolymer samples were also prepared with target molecular 

weights of 40 kDa where the weight fraction of monomer 1 in the feedstock was held constant at 

30% while the ratios of monomers 2 and 3 were varied. GPC characterization indicated the 

polymers were well-defined as evidenced by nearly mono-modal peak shapes and low PDIs 

(1.1-1.2).

The polymers were characterized by DSC heating from 25 to 250 °C at 10 °C/min with two 

heating cycles. The Tg values reported were taken from the 2nd heating scan. The Tgs of the 

homopolymers (Samples P1–P3, table 1) were used to estimate the Tg values of the copolymers 

(Samples P4–P8, table 1) using the Fox equation (16). As anticipated, the Tg of the copolymers 

increased as the ratio of monomer 2 to 3 was decreased. For a copolymer with 30 wt% of 

monomer 1, the Tg can be manipulated from 89 to 189 °C simply by varying to ratios of 2 and 3

in the monomer feedstock. The measured Tg values are higher by 5–11% then those predicted by 

the Fox equation. The polymers are also soluble in a variety of common organic solvents and are 

easily processed under bulk conditions. 

Table 1. Thermal data for E-O polymers prepared by ROMP.

Monomer 

Feedstock

Sample w1 w2 w3

Tg (°C) 

(calc)a

Tg (°C) 

(DSC)b

P1 1 0 0 – 103.8

P2 0 1 0 – 78.8

P3 0 0 1 – 234.8

P4 0.3 0.7 0 84.9 89.3

P5 0.3 0.55 0.15 95.1 106.64

P6 0.3 0.35 0.35 113.3 132.9

P7 0.3 0.15 0.55 140.1 163.1

P8 0.3 0 0.7 170.3 189.2

aCalculated according to the Fox equation. bValue reported is from 2nd heating cycle.
5

To further enhance the possible Tg range that could be accessed, a polymer where the entire 

backbone was derived from a nadimide type monomer was synthesized. To this end, exo-N-(pcarboxyphenyl) nadimide was prepared which provided an attachment point for DR1 (17). The 

chromophore was added via DCC/DPTS coupling to produce nadimide monomer 5. 

Co-polymerization with nadimide 3 (70 wt%) was conducted at room temperature in the 

presence of complex 4 to produce P9 in quantitative yield after 15 min. The polymer was not 

able to be characterized by GPC due to insolubility in THF. The material was characterized 

thermally by DSC giving a value of 212 °C for Tg. The polymer was also soluble in chlorinated 

solvents such as CH2Cl2 or CHCl3 and polar, aprotic solvents such as DMF, NMP, or 

cyclopentanone. The structures of the various monomers and catalyst used are summarized in 

figure 1.

N

N

N

NO2

Ru

N

N

Br

Br

Cl

Cl

MesN NMes

1

2

3

4

O

O

O

O

5

N

O

O

N

O

O

O

O

N N

O2N N

Figure 1. Structures of monomers and catalyst used in this study.

Having demonstrated the ability to prepare tunable high Tg E-O polymers in a mild fashion by 

ROMP, the polymerization method was scaled up (10 g) to test the material for E-O activity. 

The polymer was prepared from a feed ratio of 10 % 1, 45 % 2, and 45 % 3 target Tg of 140 °C. 

Characterization by DSC confirmed a Tg of 141 °C. The material was spin-coated from solution 

to form a thin film on an ITO coated glass substrate. The top surface was coated with gold and 

the material poled in the range of 200–400 V with peak temperatures ranging from 142 to 145 

°C. Teng-Man analysis of the films indicated very low poling efficiency with the E-O 

coefficient r33 ranging from 0.3 to 1.1 pm/V at 1320 nm. For comparison, the highest recorded 

value for a DR1 tethered polymer system is 7.5 pm/V at 810 nm. 
6

We postulate the very low poling efficiency could be due to several factors including residual 

catalyst from the polymerization or oxidative instability of the polymer backbone. In ROMP, the 

polymerization involves initial coordination of the monomer to catalyst followed by a [2+2] 

cycloaddition between the strained double bond in the monomer and the metal alkylidene in the 

catalyst forming a metallocyclobutane intermediate. This intermediate ring opens to form a new 

metal alkylidene complex which can undergo reaction with another monomer. This process 

continues until all the monomer is consumed. Reaction with a terminating agent such as ethyl 

vinyl ether liberates the metal complex from the polymer chain and produces a metathesis 

inactive catalyst species (18). The polymer is then typically purified and isolated by multiple 

precipitations in a non-solvent for the polymer. Despite the many reports of the use of ROMP to 

prepare a wide variety of materials for various applications, authors rarely analyze the amount of 

residual Ru present. The presence of trace levels of Ru could be detrimental in a number of 

applications, especially for biomedical or optoelectronic applications. In our own application, 

the presence of trace metal species increases the conductivity of the material reducing the poling 

efficiency of the material. In an effort to increase the poling efficiency, we quantitated the 

amount of residual Ru present after standard purification procedures and explored alternative 

approaches to removing trace Ru.

Model polymers where prepared from monomers 2 and 3, which mimicked the structure of the 

E-O polymers. Initially, the polymers where purified by repeated precipitation from methanol 

and the level of residual Ru analyzed by inductively coupled plasma mass spectrometry (ICPMS). The analysis indicated significant levels of Ru present after three precipitations (140 ppm). 

This suggested the poor poling efficiency observed may have been the result of the presence of 

trace Ru species. To reduce the levels of Ru further, new purification protocols were 

investigated, some of which had been shown to be effective for the removal of Ru from products 

produced by ring closing metathesis in small molecule synthesis.

To further decrease the residual Ru, Soxhlet extraction was performed with MeOH. The 

resulting material contained 110 ppm Ru, an improvement over repeated precipitations but still 

relatively high for many applications. In small molecule organic synthesis, a variety of methods 

have been employed to remove trace Ru from the final product in reactions such as ring closing 

metathesis (RCM). Several authors reported successfully scavenging Ru based metathesis 

catalysts with activated carbon (19, 20). After isolation of the polymer by precipitation, the 

material was redissolved in CH2Cl2 and stirred with activated charcoal for 24 h. Filtration of the 

charcoal and precipitation in MeOH yielded polymer with 160 ppm Ru indicating the charcoal 

had no effect relative to simple repeated precipitation. Use of charcoal also significantly reduced 

the yield of polymer isolated suggesting the polymer is adsorbed.

Maynard and Grubbs used a polar, water soluble phosphine ligand to bind Ru and partition the 

complex into water via extraction (21). Alternatively, the solubility enhanced catalyst can be 

absorbed onto silica gel with heating and subsequently filtered (22). For our material, we choose 

to explore the second method employing silica gel to scavenge the catalyst from solution prior to 
7

precipitation. The resulting material contained 100 ppm Ru in the final product accompanied 

with a reduction in isolated yield. The yield could be improved with additional washing of the 

filtered silica gel. However, we observed the colored Ru complex to slowly migrate from the 

silica gel to the filtrate resulting in increased residual catalyst in the final product.

Ahn et al. and Haack et al. found treatment of the catalyst with DMSO and/or PPh3=O followed 

by silica gel filtration to be an effective method for catalyst removal (23, 24). This method has 

the advantage of using cheap, readily available compounds. For our material, the quenched 

polymerization medium was treated with DMSO and silica gel followed by filtration over a pad 

of silica. Surprisingly, the resulting material contained a higher level of residual Ru (260 ppm) 

then a single precipitation. This may have been partially the result of using a more polar mobile 

phase (4 % MeOH in CH2Cl2) to effectively elute the polymer from the silica. 

Paquette and coworkers used Pb(OAc)4 to aid in the removal of the Grubbs 1st generation 

catalyst from a variety of products prepared by RCM (25). Treatment of the polymerization 

medium with 1.5 eq Pb(OAc)4 followed by filtration over a pad of silica and precipitation gave a 

polymer containing 100 ppm residual catalyst accompanied with a reduction in the isolated yield. 

As before, continued washing of the silica gel caused migration of the colored Ru byproduct 

from the silica gel to the filtrate. The results are summarized in table 2. 

Table 2. Yields and residual catalyst for various purification protocols.

Entry Method Yield Residual Ru 

(ppm)

1 Once precipitated 97 240

2 Twice precipitated 91 160

3 Thrice precipitated 77 140

4 Precipitate, Soxhlet extraction, precipitate 86 110

5 Precipitate, activated charcoal, precipitate 53 160

6 P(CH2OH)3 and SiO2 at 40 °C, filter over SiO2, precipitate 69 100

7 DMSO and SiO2, filter over SiO2, precipitate 63 260

8 Pb(OAc)4, filter over SiO2, precipitate 65 100

Despite the success of several of the methods for removing the catalyst to a satisfactory content 

in small molecule synthesis, none of the preceding methods employed reduced the remaining 

metal below 100 ppm. For many applications, this amount would present several issues for 

product stability and toxicity. We subsequently explored new strategies to further reduce the 

level of residual catalyst. The first strategy explored involved using heterogeneous particles 

bearing various functional groups. The functional groups on the surface of the particle can 

coordinate to the metal species, allowing the metal to be removed by a simple filtration of the 

particles from the reaction mixture. The polymer is then isolated by precipitating the polymer 

from the filtrate. The second method involves post-polymerization addition of a solubility 

modifier to enhance the solubility of the Ru catalyst in a particular solvent. Upon precipitation 

of the polymer in a non-solvent, the modified solubility of the Ru species will allow it to stay in 

solution and be washed away from the polymer during filtration. These two methods have been 
8

used by chemists to remove metal catalysts used to effect various chemical transformations in 

small molecule synthesis for the pharmaceutical industry (21, 26, 27). However, these 

techniques have yet to be applied in the removal of residual catalyst species in polymer 

synthesis.

The effectiveness of heterogeneous scavengers depends on a number of factors such as the 

affinity of the surface functional group toward the metal, the spatial arrangement of the 

functional groups, and compatibility of the particle with reaction conditions. Thus, a wide range 

of scavengers were tested with different surface functionalities and compositions at 500 eq 

relative to catalyst. Several different particle types were investigated, consisting of silica 

particles, polystyrene beads, polysiloxane beads, and grafted polyolefin fibres. Surface 

functional groups consisted of imidazole, thiourea, dimercaptotriazine (DMT), pyridine, amine, 

triaminetetraacetic acid (TAAcOH), tetrasodium triaminetetraacetate (TAAcONa), and 

isothiouronium. From our initial screening, four candidates were identified for further 

investigation. Three of the four candidates consisted of silica functionalized with DMT, thiol, or 

TAAcONa. The fourth candidate was thiol-functionalized polysiloxane beads. The scavengers 

were tested at two additional levels: 100, and 50 molar equivalents to catalyst. The results are 

summarized in table 3. 

Table 3. Heterogeneous scavengers used in study.

Additive Name Structure Residual Ru Level (ppm)

500 eq 100eq 50 eq

Siliabond® imidazole

Si

H

N N

N

20

Siliabond® thriourea 20

Siliabond® DMT

Si N

H

N

N N

SH

SH

10 30 20

Siliabond® thiol 20

Smopex-105 Pyridine

NH Cl

20
9

Table 3. Heterogeneous scavengers used in study (continued).

Additive Name Structure Residual Ru Level (ppm)

500 eq 100eq 50 eq

Smopex-110

S

NH2

NH2

Cl

100

QuadrapureTM IMDAZ

Si

H

N N

N

20

QuadraSilTM MP

Si SH

<10 10 20

QuadraSilTM AP

Si NH2

20

Siliabond® diamine

Si N

H

NH2

110

Siliabond® TAAcOH

Si N

O

OH

N

O

OH

N

O

OH

OH

O

30

Siliabond® TAAcONa

Si N

O

ONa

N

O

ONa

N

O

ONa

ONa

O

10 10 <10

PhosphonicSTM SPM36 20

PhosphonicSTM SEA 20
10

Table 3. Heterogeneous scavengers used in study (continued).

Additive Name Structure Residual Ru Level (ppm)

500 eq 100eq 50 eq

PhosphonicSTM STA3 30

Deloxan® MP 

O

Si

Si

O

O CH2CH2CH2SH

CH2CH2CH2SH

O

O

<10 40 60

Deloxan® THP II 

O

Si

Si

O

O CH2CH2CH2S

CH2CH2CH2S

O

O

NH

NH

C S

30

The selected scavengers significantly reduced the residual catalyst levels compared to multiple 

precipitations in MeOH. Of the selected scavengers, the TAAcONa- and thiol-functionalized 

silica particles were the most effective, reducing the residual Ru level to 10 and 20 ppm, when 

100 and 50 eq, respectively, relative in G3, were added to the polymerization medium after 

quenching the polymerization. 

For the second strategy, several compounds were investigated that had been previously 

successfully employed as solubilizing agents for Ru or Pd catalysts in small molecule synthesis. 

The results are summarized in table 4. 2-mercaptonicotinic acid (MNA) was previously shown 

to be an effective solubilizing agent for a Ru-based catalyst when extracted with aqueous sodium 

bicarbonate (28, 29). We reasoned that MNA could enhance the solubility of the metathesis 

inactive G3 catalyst in MeOH. After precipitation of the polymer in MeOH, the residual catalyst 

would be effectively washed away with the filtrate. Gratifyingly, the Ru level was reduced from 

190 ppm to 30 ppm in a single precipitation when 50 eq of MNA relative to G3 was added to the 

polymerization medium prior to precipitating the polymer in MeOH. Tris(hydroxymethyl) 

phosphine (THP) was previously shown to be an effective compound for modifying the 

solubility of metathesis catalysts to facilitate removal of the residual catalyst during purification 

in both RCM and ROMP processes (21, 22). For comparison, THP was also used in this study. 

The addition of 100 eq THP relative to G3 to the polymerization medium prior to precipitation 

resulted in a polymer containing 50 ppm Ru.
11

Table 4. Residual Ru levels for ROMP polymers purified with catalyst solubilizing agents.

Scavenger Structure Residual Ru Level 

(ppm)

100 eq 50 eq

Tris(hydroxymethyl) phosphine 50 110

2-mercaptonicotinic acid 30 30

N-acetyl-L-cysteine 70 120

Diethylphenylazothioformamide 30 30

Next, we turned our attention to solubilizing agents that had previously shown efficacy in 

reducing residual catalyst levels in Pd-catalyzed reactions. N-acetyl-L-cysteine was 

demonstrated to be an effective scavenging agent for Pd during the crystallization of an active 

pharmaceutical ingredient intermediate from ethanol (30). N,N-diethylphenylazothioformamide 

(DEPATF) was shown to be an effective solubilizing agent for Pd(0) during the precipitation of 

conjugated polymers in MeOH (31). Given the success of other thiol-functionalized compounds 

and particles in scavenging Ru, we reasoned N-acetyl-L-cysteine and DEPATF could be 

effective solubilizing agents for metathesis inactive G3 as well. As anticipated, both compounds 

were effective in reducing the residual catalyst level compared to simple precipitation in MeOH. 

The addition of 100 eq of N-acetyl-L-cysteine reduced the Ru level to 70 ppm while the addition 

of 50 eq DEPATF reduced the Ru level to 30 ppm. 

When the two strategies investigated in this report are compared, each method has advantages 

and disadvantages. The surface functionalized particles were more effective in removing Ru as 

evidenced by lower levels of residual catalyst at similar equivalents. However, removal of the 

particles by filtration added an extra step to the process. Use of solubilizing agents is a simple 

modification to the traditional purification process but is not as effective as using functionalized 

heterogeneous particles at comparable equivalents. 

To demonstrate the effect of the residual catalyst on material properties, the oxidative stability of 

a polymer purified by simple precipitation was compared to a polymer purified with DEPATF by 

differential scanning calorimetry (DSC). It was previously suggested that the presence of 
12

residual Ru in polymers prepared by ROMP limited the oxidative stability of the polymer (32). 

Samples were heated from room temperature to 300 °C under an atmosphere derived from a 

compressed air tank. The DSC curves are shown in figure 2. The first sample was purified by a 

single precipitation in MeOH and contained 190 ppm Ru. During heating under an air 

atmosphere, the sample began to decompose ca. 86 °C. The second sample was purified using 

the solubility agent DEPATF and contained 30 ppm Ru. During heating under an air 

atmosphere, the sample began to decompose ca. 107 °C. Reduction of the residual Ru level from 

190 ppm to 30 ppm resulted in a 21 °C increase in the oxidation induction temperature. This 

simple experiment demonstrates the importance of considering the presence of trace catalyst 

species on materials properties and performance. 

Figure 2. Oxidative stability of polymer with varying levels of residual Ru. 

4. Summary and Conclusions

We report a new method for directly preparing tunable, thermally stable E-O polymers via 

ROMP. Polymers containing 30 wt% DR1 were prepared in quantitative yields under 

undemanding reaction conditions. The materials were characterized by DSC indicating that the 

Tg could be controlled from 89 to 189 °C by varying the feed ratio of monomers 1, 2, 3. The Tg

could be increased above 200 °C by using a backbone derived entirely from nadimide type 

monomers. The materials were soluble in a range of solvents and could easily be processed in 

the bulk. These characteristics make ROMP a highly attractive method for preparing E-O 

polymers. Preparation of materials that combine high thermal stability and processability were 

previously difficult to obtain without post-polymerization modification or lattice hardening 

procedures during poling. The use of ROMP should greatly simplify the overall process and 

provide materials capable of realizing stable E-O coefficients. Unfortunately the polymers did 

not display the anticipated poling behavior. This was potentially attributed to residual 

polymerization catalyst present in the final product. A comprehensive study was undertaken to 
13

determine levels of residual catalyst present in ROMP based materials when isolated using 

typical protocols. Catalyst levels ranged from 240 to 140 ppm depending on the number of 

precipitations. The difficulty in complete removal of the catalyst may be the result of 

coordination of the metal species to double bonds located along the polymer backbone. 

Hydrogenation of the double bonds in the polymer backbone using diimide generated in-situ 

produced polymer containing 10 ppm residual Ru upon precipitation. Since saturation of the 

polymer backbone may not always be a suitable strategy to facilitate removal of residual metal, 

additional strategies were explored. Several methods were explored that previously had been 

used in small molecule synthesis to remove residual Ru that were based on the use of various 

catalyst modifiers and adsorbents. None of these methods succeeded in reducing the level of 

trace metal below 100 ppm while also significantly reducing the yield of the polymerization. 

Various functionalized heterogeneous particles and fibers were tested, several of which 

successfully reduced the catalyst levels to 10–30 ppm using 50–100 equivalents relative catalyst. 

The use of solubility agents was also explored, which could coordinate to the metal species and 

help partition the catalyst into the precipitation solvent, facilitating removal during isolation of 

the polymer via filtration. The presence of residual catalyst on the oxidative stability of ROMPbased polymer was also explored to demonstrate the detrimental effects the presence of the metal 

can have on material properties. A 20 °C increase in the oxidative induction temperature was 

observed when the level of Ru was reduced from 190 ppm to 30 ppm. Recently, we have 

prepared a series of ROMP based polymers containing various E-O chromophores where some 

of the methods previously described were used to remove any residual catalyst from the final 

polymer product. These materials are currently undergoing testing for E-O activity. 
14

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22. Grubbs, R. H.; Maynard, H. D. Method of Removing Transition Metals U. S. Patent 

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16

List of Symbols, Abbreviations, and Acronyms

DCU dicyclohexylurea

DEPATF diethylphenylazothioformamide

DMT dimercaptotriazine

DPTS (dimethylamino) pyridinium 4-toluenesulfonate

DR1 Disperse Red 1

DSC differential scanning calorimetry

E-O electro-optical

Hz hertz

ICP-MS inductively coupled plasma mass spectrometry

MNA mercaptonicotinic acid

NLO non-linear optical

RCM ring closing metathesis

ROMP ring opening metathesis polymerization

TAAcOH triaminetetraacetic acid

TAAcONa tetrasodium triaminetetraacetate

Tg glass-transition

THP Tris(hydroxymethyl) phosphine
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