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. 2018 Mar 9;3(3):2909–2917. doi: 10.1021/acsomega.8b00081

Sugar-Functional Vinyl Addition Poly(norbornene)–Photopatternable Poly(norbornenyl gluconamide) Compositions Developed with Water

Steven Smith 1, Liladhar Paudel 1,*, Crystal Cyrus 1, Hugh Burgoon 1, Kazuyoshi Fujita 1, Jennifer Thoresen 1, Kim Thomas 1, Leah Langsdorf 1, Larry F Rhodes 1,*
PMCID: PMC6641349  PMID: 31458562

Abstract

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The norbornenyl gluconamide (NBGA) monomer can be polymerized by a number of palladium catalysts to give water-soluble, vinyl addition poly(NBGA). Depending on the catalyst used, the reaction conditions, and the chain-transfer additives employed, high-molecular-weight polymers can be obtained. These polymers can be thermally cross-linked at ca. 190 °C or at ca. 150 °C when the difunctional glutaraldehyde is added. A photopatternable composition is formed by the addition of a water-soluble diazide when the poly(NBGA) molecular weight is sufficiently high. After image-wise exposure, negative-tone patterns are revealed by water development. A detailed analysis of NBGA monomer structures by high-resolution nuclear magnetic resonance techniques including pure shift is reported showing that two diastereomers of each endo- and exo-isomer are formed from the reaction of norbornene methylamine and δ-gluconolactone.

Introduction

Solubility of macromolecules can be tailored by a judicious choice of the monomeric repeat units. For example, by incorporating heteroatoms in the repeat units, solubility of polymers generally increases in more polar solvents. The solubility is usually enhanced for lower-molecular-weight polymers; thus, molecular weight control is typically desired. Manipulation of the polymer microstructure of the backbone of the polymer can affect the solubility; more tactic polymers are usually less soluble than less tactic polymers.

In the case of ring-opening metathesis polymerization poly(norbornene), researchers have been successful in creating water-soluble polymers by incorporating cationic salts of norbornene monomers,1 ethylene oxide pendent groups,2−6 and saccharide-functional norbornene derivatives.7,8 Vinyl addition norbornene polymers are rendered water-soluble by the incorporation of pendent ammonium cations,9 derivatives of gluconolactone or lactobionic acid,10,11 or derivatives of galactopyranose,12 among others.13

Photoresists typically comprise a polymeric binder resin in an organic solvent along with other photosensitive additives.14 After coating a substrate, the organic solvent is removed in a post apply bake step forming a film. After image-wise exposure of the remaining film, a chemical reaction occurs that renders the exposed region soluble in a developer (positive tone) or insoluble in a developer (negative tone). The resulting three-dimensional relief image is then typically subjected to an etch step (either wet or dry), after which the relief pattern is transferred into the substrate. Because the majority portion of a photoresist consists of solvents, it would be prudent to use a solvent that is benign from a health and safety perspective.

In the late 1990s, two publications reported routes to both positive- and negative-tone chemically amplified photopolymer compositions that used water as a solvent and as a developer after imagewise exposure. Fréchet, Willson, and co-workers described a positive-tone system based on a pre-cross-linked poly(acrylic acid)/divinyl ether composition.15 Later, a negative-tone system based on a sugar-modified poly(acrylate) appeared.16

We aimed to develop water-soluble vinyl addition norbornene photopolymer compositions to take advantage of this benign solvent as well as the expected higher etch resistance that norbornene vinyl addition polymers provide.17 Although Puech, et al.10,11 and Hu, et al.12 had some success at forming norbornene-type vinyl addition polymers with saccharide pendent groups, such methods appear limited in that the polymers obtained had low-weight-average molecular weights (18 000 Da or less) or limited to a process having very high palladium catalyst loading (e.g., from 10:1 to 100:1 monomer to catalyst molar ratio). In this article, a method is developed for polymerization of norbornenyl gluconamide (NBGA) at low palladium catalyst concentration with molecular weight control in water as well as formulations which allow photopatterning with water development.

Results and Discussion

Synthesis and Characterization of NBGA

The NBGA monomer was synthesized by the reaction of δ-gluconolactone with norbornenyl methylamine (Scheme 1) using a procedure much similar to what has been published by Puech, et al.10,11 In this reaction, the nucleophilic amine ring opens the lactone to form the amide linkage in NBGA. The monomer was obtained in moderate yield as a white solid.

Scheme 1. Reaction of Norbornenyl Methylamine with δ-Gluconolactone to Form NBGA.

Scheme 1

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The synthesis of NBGA should produce both endo- and exo-products because the norbornenyl methylamine starting material is a mixture of both isomers (endo-/exo- mol ratio, ca. 80/20). However, the potential product stereochemistry is not limited to just endo- and exo-isomers; each endo- and exo-isomers exist as pairs of enantiomers and should produce diastereomers of both endo- and exo-isomers because the starting δ-gluoconolactone is isomerically pure. Thus in principle, the NBGA product should exist as four different isomers, a diastereomeric pair of endo-isomers (Scheme 1, structures 1A, 1B), and a diastereomeric pair of exo-isomers (Scheme 1, structures 2A, 2B). The coexistence of these structures and their complex multiplet patterns in the proton nuclear magnetic resonance (1H NMR) spectrum impeded plausible assignment of chemical sites; even with the aid of conventional two-dimensional (2D)-NMR methods, a significant problem in the characterization was experienced. Such a complexity rendered misassignment and/or incomplete analysis in the past.10 Herein, we tackled the assignment problem by taking advantage of the improvement in spectral resolution offered by pure shift nuclear magnetic resonance (NMR) techniques.18−21 The Supporting Information Tables S1 and S2 show 1H (reported from the 1D-1H pure shift spectrum) and 13C (reported from 1D-13C spectrum) NMR chemical shifts of these structures, respectively.

Endo- and exo-isomers (endo-/exo- mol ratio, 80/20) of NBGA were evident from 1H NMR spectrum (Figure S1), in particular, from the amide proton (H-9) and olefinic proton (H-5 and H-6) resonances. They can be further distinguished from one another by comparing relative strengths of couplings between H-1 and H-2. The distinction is based on a very different H–C-1–C-2–H dihedral angle between the endo- and exo-isomers. In endo-isomers, the coupling constant JH-1H-2 is ca. 3.66 Hz, large enough to be observed as H-1/H-2 correlation spectroscopy (COSY) correlations (the dihedral angle is ca. 47°). However in exo-isomers, the coupling constant JH-1H-2 is ca. 0.55 Hz, causing a very weak or a complete disappearance of H-1/H-2 COSY correlations (the dihedral angle is ca. 72°).22 (In complete agreement with the result of double quantum filter (DQF)-COSY NMR (Figure S13) showing correlations between H-1 (2.77 ppm) and H-2 (ca. 2.21 ppm) for endo-isomers, but no such correlations between H-1 (ca. 2.75 ppm) and H-2 (ca. 1.51 ppm) for exo-isomers) (Karplus equation used to compute dihedral angle is J = 8.5 cos2 φ – 0.28 (0° < φ < 90°) where φ = dihedral angle).23 However, this analysis does not indicate the formation of diastereomeric pairs of endo-(1A and 1B) and exo-(2A and 2B) isomers.

Figure 1 shows the olefinic section of the pure shift heteronuclear single quantum coherence (HSQC)19 spectrum of the NBGA monomer in dimethyl sulfoxide (DMSO)-d6. Spectral resolution was improved by the combination of pure shifting (homo-decoupling) in the 1H dimension and spectral aliasing in the 13C dimension. Projected onto the 1H (F2) axis is the corresponding region from a conventional 1H NMR spectrum, where overlapping multiplets (giving the appearance of unoverlapped multiplets) are clearly seen. However, in pure shift, the proton multiplets collapsed to singlets, thereby improving the resolution and component-signal discernment (as shown in Figure 1, the CH chemical sites (5 and 6) of four NBGA isomers are resolved in both the 1H and 13C dimensions, the lone exception being CH site 6 of the exo-isomers where 1H chemical shifts occurred at a single spot as well as the 13C chemical shifts).

Figure 1.

Figure 1

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Olefinic regions of the pure shift HSQC spectrum of a sample of NBGA monomers showing the assignments of four isomers, two each for endo-(1A/1B) and exo-(2A/2B) isomers.

After each chemical site was discerned (Tables S1 and S2), the atomic connectivity was confirmed by HMBC. Figure 2 shows various sections of a band-selective HMBC spectrum at the amide carbonyl carbon (C-10). The correlations observed in the spectrum are multiple bond (usually between those separated by 2- and 3-bonds) correlations between 1H and 13C (in this spectrum, 1Hs are from H-8, H-9, H-11, OH-11, and OH-12, and 13Cs are from C-10 sites). Correlations to four distinct C-10 sites, one from each of the four isomers (two endo- and two exo-) of NBGA, are observed. As for example, all of these four C-10s show correlations to their respective H-8s (protons from the norbornene side of the amide bond) and H-11s (protons from the saccharide side of the amide bond), and thereby confirm that the saccharide and methylnorbornenyl groups of these four isomers are connected to each other via the amide bond. The results from pure shift total correlation spectroscopy (TOCSY) and 1H selective TOCSY (full details of the analysis are given in the Supporting Information) reveal correlations between all protons in a chain with unbroken proton–proton couplings confirming atomic connectivity within each of the saccharide and methylnorbornenyl groups.

Figure 2.

Figure 2

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Different regions of a band-selective HMBC spectrum of a sample of NBGA monomers showing 1H–13C multiple-bond correlations to amide carbonyl carbons (C-10).

Using the resolving power of the pure shift NMR technique, we have been able to show that the product from the reaction of norbornenyl methylamine and δ-gluconolactone yields a pair of diastereomers of both the endo- and exo-isomers. While four sets of chemical shifts due to these four isomers have been identified, the assignment of these sets of chemical shifts to the individual structures is not possible. Nevertheless, δ-gluconolactone is essentially acting as a chiral derivatization reagent, much similar to Mosher’s ester, rendering the enantiomeric norbornenyl methylamine discernible by NMR techniques as diastereomers.24

Polymerization of NBGA Using [(Allyl)PdCl]2 and TPPTS

Puech and co-workers10,11 initially reported the polymerization of NBGA using PdCl2 modified by the water-soluble phosphine [triphenylphosphine-m-trisulfonic acid trisodium salt (TPPTS)]. We have shown that polymerization of norbornene monomers could be obtained at high yield with low catalyst loading using phosphine derivatives of allyl palladium compounds.25 The high activity also translated to suspension and emulsion polymerization in water with added TPPTS and surfactant. The particle size of the 5-butyl-2-norbornene homopolymer made in emulsion was determined to be about 181 nm with a polydispersity of 2.6.26 Later, similar behavior was reported by Chemtob and Gilbert.27 Because of the high activity of the allyl palladium compounds, we initially tried polymerization of NBGA with the TPPTS derivative in water in an attempt to obtain the polymer at a lower catalyst loading.

The results of the first polymerization (Table 1, experiment 1), gave reasonable conversion and molecular weight (58% and 14 100 Mw). The 1H NMR spectrum (Figure S62) shows no olefinic resonances consistent with the presence of a vinyl addition poly(norbornene).

Table 1. Polymerization Results for NBGA in the Presence of Formic Acid Using [(Allyl)PdCl]2, TPPTS, and LiFABA.

experiment % formic acid conversion (%) Mw Mw/Mn
1 0 58 14 100 1.33
2 9.1 89 10 100 1.33
3 23.0 80 8000 1.28
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About 10 years ago, we discovered that formic acid could be used to enhance the conversion of norbornene polymerizations and can act as a chain-transfer agent.28,29 Given the solubility of formic acid in water, we investigated the performance of this additive in the polymerization of NBGA. The conversion increased as the concentration of formic acid increased (Table 1). As expected, the molecular weight decreases. In each case, the polymerization is carried out in the presence of LiFABA which forms the active, cationic catalyst in situ.25

Polymerization of NBGA Using [(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4]

Bell, Protasiewicz, and co-workers reported the synthesis of a family of cationic palladium compounds from their neutral precursors by reaction with salts of weakly coordinating anions.30 These cationic compounds have found utility in the polymerization of norbornene monomers.31 In general, these compounds generated high conversions of polymer with very high molecular weight. Because the molecular weights of poly(NBGA) reported by Puech using the TPPTS derivative of palladium dichloride and [(allyl)PdCl]2 shown above were low, we investigated the ability of one member of this cationic catalyst family to generate poly(NBGA) with higher molecular weight.

In Table 2, experiment 1 shows that, as expected, the polymerization of NBGA using [(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4] gave a modest conversion in the absence of formic acid. However, the molecular weight of the polymer was approximately 10-fold higher than when [(allyl)PdCl]2 was employed. As shown in experiments 2–5, when the formic acid concentration increased, the conversion increased initially and leveled-off, and the molecular weight decreased; the effect of formic acid on NBGA polymer weight-average molecular weight is presented graphically in Figure 3.

Table 2. Polymerization Results for NBGA in the Presence of Formic Acid Using trans-[(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4] and LiFABA.

experiment mol % formic acid conversion (%) Mw Mw/Mn
1 0 64 122 800 1.60
2 2.9 79 87 500 1.73
3 4.8 77 82 300 1.68
4 7.4 78 76 200 1.66
5 10 71 75 000 1.59
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Figure 3.

Figure 3

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Effect of formic acid on weight-average molecular weight of poly(NBGA).

A detailed investigation of mechanism of norbornene polymerization initiated by [(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4] in the presence of formic acid indicated that the reason for the increased polymer conversion was due to the formation of a palladium hydride complex which initiates polymerization.29 Results of a deuterium-labeling study supported the supposition that chain-transfer occurs after the β-hydride elimination from a palladium formyl intermediate. It is likely that a similar mechanism is operative for the polymerization of NBGA.

Thermal Reaction of Poly(NBGA)

The thermal stability of poly(NBGA) was investigated by thermogravimetric analysis (TGA). In the TGA trace (Figure S63), the polymer experiences a gradual weight loss from room temperature to about 175 °C. This is likely because of the loss of absorbed and adsorbed water in this very hydrophilic polymer. A similar behavior has been observed for gluconamide functional poly(acrylates).32 Above about 175 °C, a substantial weight loss occurs. This is likely because of dehydration and condensation reactions of the gluconamide pendent functionality in the polymer which typically occurs for sugars.

Guided by the TGA results, the thermal cross-linking of a film of poly(NBGA) was tested. In this series of experiments, a film of poly(NBGA) was spun onto a silicon wafer. The wafer was baked for 5 min at 130 °C to remove the water. The film thickness was determined. Then, the film was exposed to water for 5 min. In this case, the film was dissolved off the wafer (experiment 1, Table 3). Another wafer was prepared in the same fashion except that the film was heated to 130 °C for 5 min twice. Again, water exposure dissolved the poly(NBGA) film (experiment 2 in Table 3). Identical results were obtained for experiment 3 in which the wafer was baked at 130 °C for 5 min and then at 150 °C for 5 min. Not until the wafer was heated at 190 °C for 5 min did the poly(NBGA) film remain, after exposure to water (experiment 4). The film thickness remained essentially unchanged after a third bake (1.28 μm), indicating that there was no significant swelling during the water-exposure step. These results are consistent with cross-linking occurring for poly(NBGA) near or at 190 °C as a consequence of dehydration and condensation, as reflected in the weight loss occurring above about 175 °C in the TGA trace.

Table 3. Effect of Bake Temperature on Film Thickness Retention after Water Immersion.

      film thickness (μm)
experiment 2nd bake temp/time water immersion time (min) after 2nd bake after water immersion after 3rd bake
1   5 1.00 0  
2 130 °C/5 min 5 0.93 0  
3 150 °C/5 min 5 1.09 0  
4 190 °C/5 min 5 1.21 1.22 1.28
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Reaction of Poly(NBGA) with Glutaraldehyde

The reaction of poly(vinyl alcohol) with butyraldehyde forms poly(vinyl butyral) which is used in safety glass applications, among others.33 Hydrogels of poly(vinyl alcohol) can be prepared by cross-linking with difunctional aldehydes such as gluraldehyde.34 The plethora of alcohol groups in poly(NBGA) suggested that cross-linking of this polymer with a difunctional aldehyde such as glutaraldehyde to form acetal linkages would be favorable (Scheme 2).

Scheme 2. Representation of Cross-linked Poly(NBGA) by Reaction with Glutaraldehyde and Formation of Acetal Linkages.

Scheme 2

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To test this concept, mixtures of poly(NBGA) with increasing concentration of glutaraldehyde ranging from 0 to 20 gphr (grams of additive per hundred grams of poly(NBGA)) were made. Films of these mixtures were prepared on silicon wafers by spin-coating. After baking at 150 °C for 5 min, the film thickness was determined by profilometry at 22 °C and 50% relative humidity. The films were then immersed in water. In the case of 0 gphr glutaraldehyde, the film was completely washed away with water (experiment 1, Table 4). However, for 10 and 20 gphr glutaraldehyde, the majority of the film was retained after water immersion. The determination of film thickness after water immersion and a second bake (190 °C for 3 min) to remove residual water show that little swelling of the films occurred during water immersion (experiments 2 and 3, Table 4). In contrast to these results in which cross-linking occurred at 150 °C with glutaraldehyde, the thermal reaction presented above without glutaraldehyde at 150 °C was insufficient to produce cross-linked films. The addition of glutaraldehyde effectively cross-links poly(NBGA) at a lower temperature.

Table 4. Effect of Glutaraldehyde on Thermal Cross-linking of Poly(NBGA).

      film thickness (μm)
experiment glutaraldehyde (gphr) bake temperature/time after bake after water immersion after 2nd bake
1 0 150 °C/5 min 1.09 0  
2 10 150 °C/5 min 1.44 1.34 1.31
3 20 150 °C/5 min 1.68 1.47 1.62
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Photopatterning of Poly(NBGA)

To create a photopatternable composition from poly(NBGA), a photoactive compound was needed that was soluble in water. Disodium 4,4′-diazidostilbene-2,2′-disulfonate (DAZST-Na) has been shown to be a suitable photoactive cross-linker for poly(vinylpyrrolidone), a water-soluble polymer.35 An added bonus is the maximum absorption of DAZST-Na, which is near the maximum output of an i-line exposure unit: 365 nm.36 Diazide extrudes dinitrogen upon exposure to create chemically reactive nitrenes that can insert into C–H/O–H bonds of the polymer, thereby cross-linking the film.

Poly(NBGA) (Mw = 60 000) gave good-quality films as thick as 5 μm on silicon. The polymer was formulated with DAZST-Na in water. Films of this formulation were exposed with increasing dose at 365 nm and developed with water. The remaining film thickness after development was determined. From this data, a contrast curve (film thickness remaining after development vs dose) was constructed (Figure 4). At a relatively low exposure dose (ca. 10 mJ/cm2), the film thickness retention begins to climb until ca. 100% is retained at ca. 30 mJ/cm2. From this curve, the contrast γ was determined to be 3.35 using eq 1 (Experimental Section).

Figure 4.

Figure 4

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Effect of dose on normalized film thickness after development with water.

Next films of the poly(NBGA) formulation with DAZST-Na were imagewise exposed at 365 nm and developed with water. The resulting negative-tone 3D patterns were examined by scanning electron microscopy (SEM), the results of which are presented in Figure 5. At a dose of 46 mJ/cm2, 50 μm trenches were produced after water development. A cross-sectional SEM photomicrograph showed that the side walls of the patterns were sloped.

Figure 5.

Figure 5

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SEM micrograph of negative-tone patterns obtained from poly(NBGA) and DAZST-Na at a dose of 46 mJ/cm2: top-down view (top) and side view (bottom).

When the experiment was repeated with a lower-molecular-weight poly(NBGA) (Mw = 18 000), the exposed film washed off the wafer during water development. This indicates that such a lower-molecular-weight polymer was insufficiently cross-linked and exhibited a fast dissolution rate in water, thereby failing to form negative-tone features. Without the development of methods for making high-molecular-weight poly(NBGA) presented herein, the formation of negative-tone features under the conditions described would have been unsuccessful.

Conclusions

Using the pure shift NMR technique, two diastereomers of both endo- and exo-isomers of NBGA have been identified. Methods for making higher-molecular-weight poly(NBGA) are developed by using alternative catalysts than those disclosed earlier along with methods for controlling molecular weight by the addition of formic acid. Poly(NBGA) films are cross-linked at 190 °C. Cross-linking occurs at lower temperatures if glutaraldehyde is present. Photoactive compounds similar to DAZST-Na can cross-link poly(NBGA) upon exposure and form negative-tone features if the molecular weight is sufficiently high.

Experimental Section

General

All polymerization manipulations were carried out under an atmosphere of nitrogen using standard airless techniques. Solvents were deoxygenated by sparging with nitrogen prior to its use.

δ-Gluconolactone was purchased from Sigma. Norbornenyl methylamine was prepared previously.37 DAZST-Na (Chart 1 was obtained from Toyo Gosei. Lithium tetrakis(pentafluorophenyl)borate etherate (LiFABA) was sourced from Boulder Scientific Company. trans-[(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4] (see Chart 1) was prepared as reported in the prior literature.30 [(Allyl)PdCl]2 (see Chart 1) and TPPTS (Chart 1) were purchased from Strem and Sigma, respectively. Formic acid (98%) from Sigma was used.

Chart 1. Structure of Catalysts ([(Allyl)PdCl]2 and trans-[(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4]) and Phosphine (TPPTS) Used to Polymerize NBGA, and Photoactive Cross-linker (DAZST-Na) Used for Photopatterning of Poly(NBGA).

Chart 1

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All NMR measurements were performed at 298 K in DMSO-d6 ((CD3)2SO) or pyridine-d5 (C5D5N) using a Bruker AVANCE IIIHD 500 MHz spectrometer equipped with a double-resonance pulse-field-gradient BBFO probe (5 mm). For the analysis of monomers, both 1D- (1H, 1H Sel-TOCSY, 13C) and 2D- (DQF-COSY, TOCSY, HSQC, HMBC, and HSQC-TOCSY) NMR measurements were conducted; pure shift18−21 NMR (both 1D- and 2D-) measurements were also carried out. For samples dissolved in (CD3)2SO, the 1H NMR spectral window (centered at 3.961 ppm) was ca. 6250 Hz. For samples dissolved in C5D5N, the 1H NMR spectral window (centered at 4.596 ppm) was ca. 7002.801 Hz. The 13C NMR spectral window (centered at 102.000 ppm) was ca. 20 000.00 Hz (however, for high-resolution band-selective HMBC and aliased HSQC, narrow band 13C NMR spectral window was used). In general, the relaxation delay was 1–2 s, and 32k–64k data points (2k–4k data points in 2D experiments) per scan were averaged over 4–16 scans (256–4k t1 data points were acquired in the indirect dimension of 2D experiments). Relevant parameters used in the quantitative NMR are 13C: 30° flip angle (90° pulse duration was 10 us), 64k data points, 1.05 s acquisition time, 840 scans, 16 s relaxation delay (with gated 1H decoupling), and experiment time of ca. 4 h, 1H: 30° flip angle (90° pulse duration was 12 μs), 64k data points, 5.24 s acquisition time, 16 scans, 20 s relaxation delay, and experiment time of ca. 7.5 min. 1H and 13C NMR chemical shifts data were recorded relative to ((CD3)2SO) (residual internal CD3CD2HSO (δ1H = 2.5000 ppm) and δ13C = 39.93 ppm).

Polymer molecular weights were determined by gel permeation chromatography (GPC) according to the following procedure. Approximately 50 mg of polymer was dissolved in 20 mL of N,N-dimethylacetamide (0.05 M NaNO3). The samples were gently shaken to dissolve. The solution was filtered through a 0.2 μm PTFE disposable syringe filter prior to addition to the autosampler. The GPC system (Waters 2695 Separations Module) was equipped with a PL 10 μm Guard + PLgel 10 μm Mixed B × 2 column set. Eluant was N,N-dimethylacetamide (0.05 M NaNO3) at a flow rate of 1.00 mL/min. The temperature of the column was 60 °C. Measurements were made using a Waters 2414 refractive index detector and were reported relative to narrow molecular weight polystyrene standards. In some experiments, conversion of polymerizations was reported as a ratio of the area percent of the polymer peak relative to the area percent of the monomer peak from the GPC measurements. TGA measurements were made using a TA Q500 instrument. Samples were heated at a ramp rate of 10 °C/min under nitrogen from 30 to 500 °C.

Synthesis of NBGA

NBGA was prepared largely according to a procedure (Scheme 1), published by Puech, et al.10,11 Norbornenyl methylamine (69.2 g, 0.562 mol) was added to a methanol solution (approximately 1L) of δ-gluconolactone (100 g, 0.562 mol). The solution was stirred at room temperature for 23 h, resulting in a clear, pale-yellow solution. The solution was added to ether (approximately 3.0 L) to yield a precipitate which was filtered, rinsed with ether (approximately 1.0 L), and dried under vacuum at 70 °C overnight, giving 107 g (63%). Fourier transform infrared (FT-IR) (diamond cell): ν(amide NH and sugar OH, H-bond, s br) at 3327 cm–1; ν(=CH, m) at 3061 cm–1; ν(amide C=O, s) at 1640 cm–1; δ(amide NH, m) at 1548 cm–1 (see Figure S61). NMR characterization of NBGA monomer is described in the Results and Discussion section.

Representative Polymerization of NBGA Using [(Allyl)PdCl]2 and (TPPTS)

NBGA (45 g, 0.15 mol), [(allyl)PdCl]2 (0.030 mg, 0.082 mmol), LiFABA (0.40 mg, 0.46 mmol), and TPPTS (0.20 mg, 0.35 mmol) were added to a glass vial equipped with a magnetic stir bar in a glovebox. The vial was sealed with a septum, and sufficient water (sparged with nitrogen) was added to the vial outside of the glovebox using a syringe to form ca. 30% by weight solution of NBGA. After the components dissolved in water, the solution was sparged with nitrogen for 25 min. Then, formic acid (0.687 g) was added to the vial and the mixture was heated to 60 °C for 18 h. The reaction mixture was cooled and the polymer was precipitated from 3 L of acetone. The solid was filtered, and the filter cake was rinsed with methanol (1 L). The polymer was then dried in a vacuum oven at 70 °C for 16 h. Yield 21.5 g (48%). GPC: Mw = 12 300; Mn = 9180. For a representative sample of the polymer, 1H NMR data were obtained in the same manner as that of the NBGA monomer. 1H NMR ((CD3)2SO) δ (ppm): 7.51 (br s, NH), 5.35 (br s, OH-11/–C(O)–CH(OH)−), 4.50 (br m, OH-12, 13, 14, 15/>CHOH), 4.00 (br m, H-11,12/>CHOH), 3.50 (m, H-13,14/>CHOH), 3.30 (m, H-15/–CH2OH), 3.1 (br s, aliphatic H including H-8/–CH2–NHCO−), 2.5–0.5 (br m, aliphatic H).

Representative Polymerization of NBGA Using trans-[(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4]

The palladium complex trans-[(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4] (0.012 g, 0.010 mmol) and solid NBGA monomer (3.01 g, 10.0 mmol) were added to a vial equipped with a magnetic stir bar. In the glovebox, lithium tetrakis(pentafluorophenyl)borate etherate (0.026 g, 0.030 mmol) was added. On the bench, a water (6.95 g) and formic acid (0.37 g, 0.8 mmol) solution was sparged with nitrogen and then added to the monomer and catalyst mixture. The solution was heated to 80 °C for 18 h. Conversion: 78% (by GPC). GPC: Mw = 76 200; Mn = 45 920.

Thermal Cross-linking Experiments

Poly(NBGA) (Mw = 9800) was dissolved in water (20 weight percent solution). The solution was spin-coated onto four quartz wafers (500 rpm for 5 s followed by 1500 rpm for 40 s). The wafers were then baked for 5 min at 130 °C. The thickness of the film was determined by profilometry. One wafer was not baked; the remaining three wafers were baked at 130, 150, or 190 °C for 5 min. The wafers were immersed in water for 5 min. The film thickness was then again determined by profilometry. The wafers were baked a third time at 190 °C for 3 min, and the film thickness was measured again by profilometry.

Cross-linking of Poly(NBGA) with Glutaraldehyde

Poly(NBGA) (Mw = 12 300) was dissolved in a water/propylene glycol methyl ether (50/50) solution (20 wt % percent polymer). A second and third solution was made, but with 10 phr (part per hundred) and 20 phr glutaraldehyde, respectively. Three quartz wafers were spin-coated separately with each solution (500 rpm for 5 s followed by 1500 rpm for 40 s). The three wafers were then baked for 5 min at 150 °C. The thickness of the resulting film on each wafer was determined by profilometry. The wafers were immersed in water for 5 min. The film thickness was then determined again by profilometry. If the film remained on the wafer, the wafer was baked a second time at 190 °C for 3 min, and the film thickness was measured again.

Photopatterning

Poly(NBGA) (Mw = 60 000) was dissolved in deionized water (10 wt %) along with DAZST-Na (3 wt % on the polymer). The solution, after filtration, was spin-coated onto a thermal oxide silicon wafer (500 rpm for 10 s followed by 1000 rpm for 60 s). The wafer was then baked at 130 °C for 2 min. The film thickness was determined to be 1.3 μm by profilometry. Using a variable density mask and an i-line band-pass filter, the polymer film was exposed using an AB-M mask aligner (medium-pressure Hg lamp) and developed using water (60 s puddle development). The thickness was then determined as a function of dose, determined at 365 nm. From these data, the contrast (γ) of the formulation was determined using the following formula:

graphic file with name ao-2018-00081t_m001.jpg 1

where Df is the minimum dose at which the film thickness is retained and Do is the maximum dose at which the film thickness is removed by the developer.38

The experiment was repeated but the film was imagewise exposed through a chrome on glass mask using an AB-M mask aligner using an i-line band-pass filter. After water development, patterns on the wafer were examined using SEM.

Acknowledgments

We acknowledge “http://nmr.chemistry.manchester.ac.uk” for the macro used to produce one-dimensional pure shift NMR spectra.

Glossary

Abbreviations

ROMP

ring-opening metathesis polymerization

NBGA

norbornenyl gluconamide

DAZST-Na

disodium 4,4′-diazidostilbene-2,2′-disulfonate

LiFABA

lithium tetrakis(pentafluorophenyl)borate etherate

TPPTS

triphenylphosphine-m-trisulfonic acid trisodium salt

GPC

gel permeation chromatography

TGA

thermogravimetric analysis

NMR

nuclear magnetic resonance

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b00081.

  • Detail NMR analysis and FT-IR analysis of NBGA and 1H NMR, TGA and GPC elution curves of poly(NBGA) (PDF)

Author Present Address

† S.S.: Gabriel Performance Products, Research, 725 State Rd., Ashtabula, Ohio 44004, United States.

Author Present Address

‡ K.F.: Sumitomo Bakelite Co., Ltd., 5-8 Higashi-Shinagawa 2-chome, Shinagawa-ku, Tokyo 140-0002, JP.

Author Present Address

§ C.C.: The Lubrizol Corporation, 9911 Brecksville Rd., Brecksville, Ohio 44141, United States

The authors declare no competing financial interest.

Supplementary Material

ao8b00081_si_001.pdf (4.1MB, pdf)

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Supplementary Materials

ao8b00081_si_001.pdf (4.1MB, pdf)

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