Terminal and Internal Unsaturations in Poly(ethylene-co-1-octene

Jun 16, 2014 - Unsaturated structures in polyolefin polymers are important in many respects. In this work, new vinyl and vinylidene structures were id...
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Terminal and Internal Unsaturations in Poly(ethylene-co-1-octene) Yiyong He,*,† XiaoHua Qiu,*,† Jerzy Klosin,*,‡ Rongjuan Cong,§ Gordon R. Roof,‡ and David Redwine† †

Corporate R&D, The Dow Chemical Company, 1897 Building, Midland, Michigan 48667, United States Corporate R&D, The Dow Chemical Company, 1776 Building, Midland, Michigan 48667, United States § Performance Plastics R&D, The Dow Chemical Company, Freeport, Texas 77541, United States ‡

S Supporting Information *

ABSTRACT: Unsaturated structures in polyolefin polymers are important in many respects. In this work, new vinyl and vinylidene structures were identified in poly(ethylene-co-1octene) copolymers. The combination of careful sample selection and model compounds provided clear evidence for the assignment of these structures. More importantly, a new method was developed to differentiate and quantify for the first time terminal and internal unsaturations in ethylene-co-1octene copolymers. The method described here will be generally applicable to many different polyolefins.

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INTRODUCTION Molecular olefin polymerization catalysts (metallocene, constrained geometry, non-metallocene) have become important industrially because of their ability to produce very high molecular weight ethylene/α-olefin copolymers with a narrow composition distribution.1,2 Some of the most important catalytic events during olefin polymerization reactions are various chain termination reactions as they control the ultimate molecular weight of produced polyolefins. Under hydrogen-free polymerization conditions, all polymer chains are terminated with unsaturated groups, as a result of β-H transfer to either the catalyst metal or the incoming monomer. The main unsaturation in homopolyethylene formed by coordination catalysis is the vinyl group (V1); however, the complexity of unsaturation increases significantly in ethylene−α-olefin copolymers due to the occurrence of chain termination events after inserted ethylene, 1,2- and/or 2,1-inserted α-olefin as well as various isomerization pathways. Analysis of unsaturated structures in polyolefins is crucial to understand the nature and the relative importance of the various possible chain termination pathways. The knowledge obtained from such analysis can be used to fine-tune catalysts and process conditions for better molecular weight control. The significance of unsaturation analysis in polyolefins is not limited to molecular weight control.3 For example, polymers with vinyl chain ends can act as macromers and are one of the prerequisites for generating long-chain branching.4 Unsaturations, as the functional groups of polyolefins, can be useful for further functionalization5 or be disadvantageous in the undesired case of oxidation reactions.6 Unsaturations in polyolefin chains have been widely studied in the past two decades by NMR spectroscopy.7,8 For poly(ethylene-co-1-octene) (EO) copolymers, a family of polymers with tremendous commercial significance, the most © XXXX American Chemical Society

comprehensive study on unsaturated structures was reported by Busico and co-workers.8 However, the assignments made of various unsaturation structures were based on resonances in a 1 ppm 1H NMR spectral region from a single polymer sample. Because of heavy peak overlapping, some structures were tentatively proposed based on simulations or peak deconvolution. Another complexity of unsaturation analysis arises from frequent and simultaneous occurrence of both terminal and internal unsaturations. The position of unsaturations along a polyolefin chain was usually presumed based on proposed reaction mechanisms. 9 Busico et al. proposed several mechanisms leading to internal trisubstituted unsaturations in EO copolymers, which involve allylic CH activation of metal bound terminal unsaturated group, followed by isomerization of the resulting allyl species, ethylene propagation, and chain termination. Wasserman and coauthors used an ozonolysis method to cleave polyolefin chains at each internal double bond.10 This approach demonstrated for the first time the presence of internal unsaturations, but its main limitation was that different types of unsaturations could not be differentiated. The accuracy of the quantification was also not satisfactory. Without a reliable method to determine the ratio between terminal and internal unsaturations in polyolefins, the precise measurement of total unsaturations has limited utility. The first objective of this work is to provide an updated understanding of unsaturations in EO copolymers. The results obtained in this work are not limited to EO copolymers as most of the reported unsaturated structures in EO copolymers have closely related analogues in other ethylene/α-olefin copolymers. We overcame the previous peak overlap challenge by Received: May 13, 2014 Revised: May 25, 2014

A

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Scheme 1. Some Unsaturated Structures Identified in Ethylene−1-Octene Copolymers

Figure 1. Fragments of 1H NMR spectra showing the unsaturation region for EO copolymers. (See structure notations in Table 1. The peaks labeled with an asterisk come from an antioxidant in these samples.)

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studying a variety of samples synthesized with different catalysts and selecting the spectra with the least interference for unsaturations present. This approach allowed us not only to identify structures previously misassigned but also to identify new unsaturations in EO copolymers. The second objective of this work is to address the longstanding challenge of differentiating internal and terminal unsaturations in polyolefins. This work details a new approach to differentiate and quantify internal and terminal unsaturations through preparative scale fractionation according to molecular weight followed by high sensitivity 1H NMR analysis. Conclusive determination of internal vs terminal unsaturations will contribute to our mechanistic understanding of polyolefin synthesis.

RESULTS AND DISCUSSION

Spectral Assignments for Unsaturation Structures in EO Copolymers. The unsaturations in EO copolymers have been studied previously.8 One limitation of that work is that only one copolymer sample was studied, and it is possible that some unsaturation structures were not present in that particular sample. Another limitation is that there was severe overlap in NMR resonances due to a wide variety of unsaturation structures, which led to ambiguity in a few assignments. To overcome these two limitations, we studied many EO copolymers that were synthesized by different catalysts under different reactor conditions. Since the identity and relative abundance of unsaturation structures are catalyst dependent, B

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Table 1. Summary of Unsaturated Structures, Notations, Chemical Shifts (δ) in 1H NMR Spectra (Figure 1), Their Splitting Patterns, and Coupling Constants (J)

“P” represents a polymer chain, R1 and R2 can be aliphatic segments of any length. bDetermined experimentally. See details in the Terminal vs Internal Unsaturations section.

a

we had the opportunity to select the sample that not only best highlights the resonances of interest for a given unsaturation structure but also reveals more unsaturation structures than reported previously. The 1H NMR spectra of the unsaturation region for five selected EO copolymers are shown in Figure 1. These spectra clearly demonstrate the catalyst-dependent unsaturations in EO copolymer chains. For each spectrum, only a few unsaturation structures with unambiguous peak splitting patterns are

highlighted. The summary of various unsaturation structures, their notations,11 chemical shifts for typical 1H NMR resonance peaks, splitting patterns, and coupling constants are listed in Table 1. Our assignment of the three vinylene structures (Vy1, Vy2, Vy3) is the same as that reported in ref 8. The Vy3 structure is especially manifested in the sample EO-1. The gCOSY spectrum shows the coupling of the two groups of Vy3 peaks and supports this assignment (see Figure S1 in Supporting Information). The trisubstituted unsaturation (T) C

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the complete overlapping of the right peak of Vd1 with the singlet of Vd2 makes the peak assignment challenging. The signals of Vd1 and Vd2 in sample EO-1 can be separated through gCOSY experiments (see Figure S1 in Supporting Information). A third vinylidene structure, Vd3, is also present in the EO copolymers, which to our knowledge has not previously been reported for EO copolymers. Vd3 shows two distinct singlets at 4.83 and 4.76 ppm (Figure 1, sample EO-5), indicating that it is a locally asymmetric structure. The structure Vd3 was determined based on the comparison of 1H NMR spectrum of EO-5 and that of a lab-made polypropylene (Figure 3). Both samples were studied under identical

has the most structural variations among the four families of unsaturations. At least six different resonance peaks appeared in the samples we studied. However, without model compounds, it is impossible to determine the exact structures of these trisubstituted unsaturations. One of the focuses of this work is to update the structure assignments for vinyl and vinylidene groups. In the literature only the V1 structure was reported for vinyl unsaturation in EO copolymers.8 This is the case for samples EO-2 through EO-5, where two doublets around 5.05 ppm of the same intensity are observed in the 1H NMR spectra. The 1H NMR spectrum for sample EO-1 is somewhat different in that the left doublet (5.07 ppm) is obviously larger than the right doublet (5.01 ppm). A shoulder peak between the two doublets is resolved. It is clear that there are peaks underneath the left doublet (5.07 ppm) of sample EO-1 which do not belong to the structure V1. After comparing newly identified resonances to the NMR spectra of model olefinic compounds (small molecules),12 the structure V3 was proposed. To further confirm the assignment, a poly(1-butene) was made, and its 1H NMR spectrum is shown in Figure 2. The chemical shifts and peak splitting

Figure 3. Comparison of 1H NMR spectra for polypropylene (PP) and EO-5 to confirm the assignment of Vd3 structure.

conditions. The two singlets at 4.83 and 4.76 ppm in the EO-5 sample match those of polypropylene perfectly, indicating the same structure. The structure Vd3 was well-known in polypropylene as the end group13 but was not previously reported in ethylene-based copolymers or any other polyolefins. There is a further evidence to support the Vd3 assignment in EO copolymers. In the upfield region of the spectrum in Figure 3, there is a doublet at 2.15 ppm (J = 6.8 Hz) and a singlet at 1.80 ppm. Based on the TOCSY spectrum (see Figure S2 in Supporting Information), these two peaks are correlated to the protons d and c in the structure Vd3, respectively. The peak at 2.15 ppm is a doublet, indicating d is next to a methine group, while the 1.80 ppm peak is a singlet, indicating c is a methyl group. All of these observations are consistent with the proposed structure Vd3. The origin of Vd3 unsaturation in EO copolymers is not known yet. Terminal vs Internal Unsaturations in EO Copolymers. The key question is whether polymer unsaturated structures are located in the middle of polymer chains (internal) or at chain ends (terminal) with the latter being a result of chain termination step. The frequency of terminal and internal unsaturation formation is governed by the appropriate set of rate constants during catalysis and both type of unsaturations are uniformly distributed during polymerization.14 This means that the frequency of internal unsaturations should be independent of polymer molecular weight. On the other hand, by definition, the frequency of terminal unsaturations will have a linear correlation with the polymer number-average molecular weight (Mn). If a polyolefin sample is fractionated based on molecular weight, the absolute concentration of internal unsaturations in each fraction should be the same whereas the concentration of terminal unsaturations should vary depending on polymer Mn. This means that the ratio

Figure 2. 1H NMR spectra of poly(butadiene) (PBd) and poly(1butene) (PB) to explicitly show the peak patterns of V2 and V3 structures (R1 = ethyl for the sample PB).

pattern of the structure V3 in this poly(1-butene) exactly match those of sample EO-1 in Figure 1. For EO copolymers, V3 arises from β-H elimination/transfer after ethylene which followed an inserted 1-octene. In Figure 2, another vinyl structure (V2) is presented, which is dominant in a lab-made poly(butadiene). The structure V2 was proposed for EO copolymers in ref 8 but was not experimentally detected. In this paper we summarize the three possible vinyl unsaturations (V1, V2, V3) with clear resonance peaks shown for each structure, so that quantification of each structure is feasible. Three vinylidene structures were identified in EO copolymers as shown in Figure 1 and Table 1. Structure Vd2 is a locally symmetric structure. Therefore, its two geminal protons on the unsaturated carbon are equivalent in the 1H NMR spectrum and appear as a singlet, which is the same assignment as in ref 8. However, we believe that ref 8 inappropriately simulated a singlet for the structure Vd1. Vd1 is a locally asymmetric structure; therefore, its two geminal protons a and b should not be equivalent. In the 1H NMR spectrum of sample EO-5 (Figure 1), we indeed observed two peaks for protons a and b. For many EO copolymers (such as EO-1 and the copolymer in ref 8), Vd1 and Vd2 coexist, with the result that D

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uncertainty of ±5%, whichever is larger. The EO copolymer composition was calculated from the peak intensity of methyl protons relative to that of the methylene and methine protons in 1H NMR spectra. This is because most methyl groups in EO copolymers originate from the 1-octene units. For samples with relatively low molecular weight (Mn < 22 kg/mol), a slight correction15 is needed to compensate for the contribution of methyl groups arising from chain ends. This 1H NMR method for EO copolymer composition analysis was validated by comparing it to the 13C NMR method. After the chain end correction, the 1H NMR method is able to provide 1-octene content with accuracy within ±0.5 mol % for any EO copolymers with Mn > 5 kg/mol. Molecular Weight Dependent Unsaturation Levels in EO Copolymers. For each of the two commercial EO copolymers in Table 2, two fractions and its original resin were studied. Thus, the data sets cover a low, the average, and a high molecular weight fraction for each commercial sample. This selection allowed us unambiguously to investigate the unsaturation dependence on molecular weight. Several observations are apparent: (1) within the 1H NMR measurement uncertainty (±0.5 mol %), the low and high molecular weight fractions have the same 1-octene content as that of the original EO resin. This ensures that the two fractions are essentially the same EO copolymer as the original, but with different molecular weights. (2) The concentration of unsaturation groups of (Vy1 + Vy2), (V1 + V3), Vd1, and Vd2 shows significant dependence on the molecular weight with higher molecular weight fractions showing lower levels of unsaturations. This indicates that these unsaturations are terminal and is consistent with mechanistic understandings regarding the origin of these unsaturations. (3) Vy3 and trisubstituted unsaturations T exhibit only moderate molecular weight dependence, as compared to other unsaturated groups. This is strong evidence that some of the Vy3 and T unsaturations are in the middle of a polymer chain. The visual comparison of unsaturations for each EO fraction is shown in Figures 6 and 7. In each figure, the three spectra are normalized to the intensity of the polymer backbone peak, which is equivalent to normalization to the total sample mass. Quantitative Analysis of Terminal and Internal Unsaturations in EO Copolymers. The probability of a growing chain to terminate in different ways (e.g., termination after inserted ethylene, a normally inserted 1-octene, an inversely inserted 1-octene) is a function of the local chemical structure of the growing chain, the catalyst, and the reaction conditions. It is not a function of the degree of polymerization of this growing chain, as long as the chain is long enough (typically more than 100 repeating units). Therefore, the distribution of various unsaturation groups should only be a function of the catalyst used and the reaction conditions but not a function of molecular weight. In other words, the ratio of terminal groups (Vy1 + Vy2):Vy3:T:(V1 + V3):Vd2:Vd1 should be the same in different fractions of the same polymer. The above assumption is valid only if the catalysis exhibits single site behavior. The samples selected for this study are all believed to be made by single-site catalysts. Without involving any assumptions of termination/chain transfer mechanisms, the vinyl group is undoubtedly a terminal group due to the nature of its structure. All other unsaturation groups could be terminal or internal. The following equation can be established for single-site catalysis:

between terminal to internal unsaturations should vary in various molecular fractions with the largest ratio value anticipated for the lowest molecular weight fraction. This idea is illustrated in Figure 4.

Figure 4. Schematic drawing showing the occurrence of unsaturations relative to the polyolefin chain length.

We decided to explore this idea and investigate if polymer fractionation followed by detailed unsaturation analysis can be used to differentiate and quantify terminal vs interval unsaturations in ethylene−1-octene copolymers. Quantitative Analysis of Unsaturated Structures in EO Copolymers. Two commercial EO copolymers (ENGAGE 8180 and Dex EXACT 0210) were fractionated based on molecular weight and separated into eight fractions. For the ENGAGE sample, fractions 1−3 did not produce enough material for further analysis; thus, fraction 4 was the lowest molecular weight fraction that yielded high quality NMR spectra. The lowest and the highest molecular weight fractions of the two commercial resins were characterized using GPC. The elution traces are shown in Figure 5. There is only slight overlap between the high and low molecular weight fractions of each sample.

Figure 5. Molecular weight distributions for the fractions with the lowest and highest molecular weights of the two commercial samples.

The unsaturation levels in EO copolymers, 1-octene contents, and molecular weights are summarized in Table 2 for selected samples and their fractions. The level of unsaturation was determined from 1H NMR based on the unsaturation signals and total olefinic signals after converting their intensities to the number of carbons. Since each unsaturation structure has a CC double bond, in this work the molar concentration of unsaturation is presented in parts per million of C2H4 units (ppm). The reported unsaturation levels have an absolute uncertainty of ±3 ppm or a relative E

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Table 2. Level of Unsaturation Structures in EO Copolymers (in Units of parts per million C2H4), 1-Octene Content, and Molecular Weighta level of unsaturation sampleb

Vy1 + Vy2

Vy3

T

V1 + V3

Vd2

Vd1

octene (mol %)

Dex EXACT_1 Dex EXACT_original Dex EXACT_8 ENGAGE_4 ENGAGE_original ENGAGE_8

732 294 137 227 120 56

164c 102c 89c 23c 16c 18c

975 581 336 215 190 124

626 201 42 53 25 11

703 214 41 89 41 16

257d 182d 140d 29 13 5

6.0 5.9 5.5 14.1 14.2 13.9

Mn (kg/mol)

Mw (kg/mol)

5.4

17.1

67 33

142 53.1

152

241

a

Molecular weight was measured by GPC. bThe number attached to each name represents the fraction number. cDue to significant overlap with the trisubstituted unsaturation peaks, the relative uncertainty can be up to 50%. dThese results will be discussed separately in Figure 8 and related context.

Figure 6. 1H NMR spectra of the EO copolymer Dex EXACT 0210 and its fractions. (The peak “∗” comes from solvent impurity.)

Uterminal h Uterminal l

=

Utotal h − Uinternal Utotal l − Uinternal

=

Vh Vl

Figure 7. 1H NMR spectra of the EO copolymer ENGAGE 8180 and its fractions. (The peaks “∗” come from solvent impurity.)

detection uncertainty, some calculated internal unsaturations have negative values. These uncertainties are simply caused by signal overlap and/or noise. From Table 3, we can conclude that vinyl (V1 + V3), Vd2, and Vd1 unsaturations are exclusively terminal groups within experimental uncertainty. Vinylenes (Vy1 + Vy2) could have 10−30% contribution from internal unsaturations, depending on the sample studied. ENGAGE 8180 has fewer internal vinylenes (Vy1 + Vy2) than Dex EXACT 0210. Both resins have approximately 50% internal trisubstituted unsaturation (T) groups. The data interpretation for the Vy3 structure is somewhat challenging. Due to severe overlap with neighboring peaks, the results for the Vy3 unsaturation are less reliable than the others. Because of this, we can only qualitatively state that the majority of Vy3 unsaturations are internal. These conclusions are summarized in the last column of Table 1. Internal Vinylidene. In the ENGAGE sample, strong molecular weight dependences for unsaturations Vd2 and Vd1 were observed (Figure 7), consistent with the conclusion that Vd2 and Vd1 are terminal groups. However, the Dex EXACT

(1)

where “U” represents the absolute concentration of any given unsaturation group (or combined unsaturation groups) and “V” represents the absolute concentration of total vinyl groups. The subscript describes that the unsaturation group of interest is terminal, internal, or the total amount. The superscript “h” denotes that the data is obtained from the high molecular weight fraction, and “l” denotes that it is from the low molecular weight fraction. “Uinternal” is the only unknown in eq 1. It has no superscript because internal unsaturations have no molecular weight dependence, as mentioned previously. By solving eq 1 with the inputs from Table 2, we calculated the amount of internal unsaturation for each structure in each of the two commercial EO copolymers. The results are included in Table 3 as “internal”. The total amount of unsaturation (terminal + internal) for each structure is copied from Table 2 and included in Table 3 as “total”. The percentage of internal unsaturation (within total unsaturation) was calculated for each structure in each EO copolymer. Because of the NMR F

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Table 3. Percentage of Internal Unsaturation within Total Unsaturation Groups sample

unsaturation

Vy1 + Vy2

Vy3

T

V1 + V3

Vd2

Vd1

Dex EXACT 0210

total (ppm) internal (ppm) internal (%)b uncertainty (%)d total (ppm) internal (ppm) internal (%)b uncertainty (%)d

294 94 32 ±10 120 11 9 ±5

102 84 82 −c 16 17 104 −c

581 290 50 ±5 190 100 53 ±5

201 0 0 ±3 25 0 0 ±3

214 −7 −3 ±5 41 −3 −8 ±10

−a −a −a −a 13 −1 −10 ±15

ENGAGE 8180

Will be discussed in a later section. bInternal (%) = internal/total × 100%. cDue to severe peak overlap, the uncertainty is hard to determine. dThe uncertainty was estimated from repeated experiments and data processing and the extent of peak overlap. a

molecular structure identification. The variety of samples studied allowed us not only to select the sample that best highlight the resonance peaks of interest for a given unsaturation structure but also to identify more unsaturation structures than previously reported in the literature. This study clarifies some ambiguity in the literature and provides an updated understanding of unsaturation groups in EO copolymers, especially for vinyl and vinylidene structures. The clear spectral patterns presented in this work will be a good reference for quantitative analysis when peak deconvolution is needed. The results will further facilitate the understanding of catalyst-dependent chain termination and transfer mechanisms. In the second part of the work, we fractionated ethylene−1octene copolymers by molecular weight and measured the amount of unsaturation groups in each fraction by 1H NMR. Such a method is necessary to deconvolute the contribution from terminal and internal unsaturation groups. This approach is feasible because, for single-site catalysts, terminal unsaturation groups will strongly depend on molecular weight while internal unsaturation groups should have no molecular weight dependence. Based on the results of the two studied EO copolymers, vinyl and vinylidene groups are terminal. The exception is the Dex EXACT resin, which has a small amount of internal vinylidene. For the vinylene structures, depending on the catalyst, only 10−30% of Vy1 and Vy2 are internal groups, while Vy3 are predominantly internal. Trisubstituted unsaturations have the most structural variation, and approximately 50% of them are terminal groups. Our new method was demonstrated to have the capability to differentiate internal and terminal unsaturation groups in polyolefins. Some of our findings are different from previous assumptions based only on proposed reaction mechanisms.

sample in Figure 6 shows some complexity in the molecular weight dependence of vinylidene. In the vinylidene region, there are two small peaks at 4.85 and 4.81 ppm that remain nearly unchanged across the studied molecular weight range. The vinylidene region is expanded in Figure 8. In the low

Figure 8. 1H NMR spectrum of the vinylidene region for the Dex EXACT 0210 copolymer. The right peak of Vd1 completely overlaps with Vd2 and thus is not visible.

molecular weight fraction 1, three sets of vinylidene peaks were resolved. There are significant peak overlaps among the peaks of these vinylidene strutures; therefore, lines were drawn to indicate their chemical shifts. Two sets of peaks belong to the assigned Vd1 and Vd2 structures. As discussed above, their intensities have significant molecular weight dependences. The third set of peaks is designated by the dashed lines, and their intensities remained unchanged from the low molecular weight fraction 1 to the high molecular weight fraction 8. This indicates that it comes from an internal vinylidene structure. Its structure remains to be determined. Here we simply called it “internal Vd” to differentiate it from Vd1 and Vd2. Internal Vd is less common than Vd1 and Vd2 in the samples we studied. Resconi proposed a mechanism for the formation of internal vinylidene for some metallocene catalysts in propylene polymerization. It involved a 6-member ring intermediate and hydrogen transfer.16 A similar mechanism is possible for the Dex EXACT sample.

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EXPERIMENTAL SECTION

Materials. Two commercial poly(ethylene-co-1-octene) (EO) copolymers and five EO lab samples were selected for this study. The first sample, ENGAGE 8180, is a commercial product offered by The Dow Chemical Company and has higher molecular weight (melt index MI = 0.5). The second sample, Dex Plastomers EXACT 0210, is a commercial product from ExxonMobil Chemical Company and has lower molecular weight (MI = 10). Samples EO-1 through EO-5 were synthesized in our core R&D lab. Lab Synthesis of EO Copolymers. Continuous flow, solution polymerizations were carried out in a 0.1 L pressure vessel equipped with an internal stirrer and a single, stationary baffle. The reactor set points were maintained via a Camile data acquisition and control system, an externally heated circulating oil jacket, external heat tapes, and an internal thermocouple. All liquid components, solvent, a purified mixed alkanes solvent (Isopar E available from ExxonMobil, Inc.), 1-octene, catalyst, activator, and aluminoxane solutions were fed into the reactor with positive displacement pumps. Isopar-E, 1-octene,

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CONCLUSIONS We revisited 1H NMR assignments of unsaturation structures in poly(ethylene-co-1-octene) (EO) copolymer by studying a series of EO copolymers made with different catalysts. 1H NMR, COSY, and TOCSY experiments were performed for G

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Table 4. Solvent/Nonsolvent Ratio of Preparative Scale CRYSTAF fraction no.

1

2

3

4

5

6

7

8

solvent (mL) nonsolvent (mL)

54.0 126.0

63.0 117.0

72.0 108.0

81.0 99.0

90.0 90.0

99.0 81.0

108.0 72.0

126.0 54.0

Table 5. Temperature Profile for Preparative CRYSTAF in Molecular Separation Mode first dissolution first stabilization dissolution up dissolution down redissolution stabilization

temp (°C)

rate (°C/min)

time (min)

stirring rate (rpm)

stirrers

on/off time (s)

130 120 120 105 120 120

20.0 30.0 20.0 20.0 20.0 30.0

60 30 35 100 60 30

200 150 150 150 150 150

continuous discontinuous discontinuous discontinuous discontinuous discontinuous

30/5 30/5 30/5 30/5 30/5

hydrogen, and ethylene were passed through purification columns of activated alumina and Q-5 (Engelhard Corporation) prior to introduction to the reactor. Brooks 5840E mass flow controllers were used to deliver ethylene and hydrogen to the reactor as required. The two separate fed streams were introduced into the bottom of the reactor via two eductor tubes. The reactor was run liquid-full at 400− 500 psig (2.7−3.4 MPa) with vigorous stirring while the products were removed through an exit line at the top of the reactor. The reactor effluent passed through an optical spectrometer cell monitoring exit stream composition as it exited the electrically heat traced and insulated system. The reactor pressure was controlled with a Badger Research Control valve. Polymerization was quenched by the addition of a small amount of water and 2-propanol introduced into the exit line along with polyolefin stabilizers and additives in a toluene solution. Polymer samples were collected after more than 4.5 average residence times after steady state conditions were established and observed by an optical spectrometer. Polymer samples were collected under an inert nitrogen atmosphere and dried in a temperature ramped vacuum oven for approximately 10 h with a final high temperature set point of 140 °C and 4 h soak interval. NMR Spectroscopy. All EO copolymers were dissolved in 8 mm NMR tubes in a 1:1 mixture of tetrachloroethane-d2 and perchloroethylene containing 0.001 M Cr(acac)3.17 The sample concentration is 0.10 g/1.8 mL. The tubes were purged with nitrogen gas and then heated in a heating block set at 115 °C. The sample tubes were repeatedly vortexed and heated to achieve a homogeneous flowing fluid. The heating time was minimized to avoid sample degradation and is normally less than 4 h. The 1H NMR experiments were performed on a Varian Inova 600 MHz spectrometer. For each sample, two experiments were performed. The first is a standard single pulse 1H NMR experiment to quantify the polymer peak relative to the solvent peak. The second is a presaturated 1H NMR experiment to suppress the polymer backbone peak. The unsaturation signals were then quantified by referencing to the same solvent peak. The following acquisition parameters were used: 12.5 s relaxation delay, 0.5 s presaturation (satpwr = 1) on backbone (CH2) protons, 90° pulse of 7.9 μs, 16 scans for normal spectra, and 128−256 scans for presaturated spectra. Each spectrum was centered at 4 ppm with a spectral width of 16 ppm. All measurements were taken without sample spinning at 110 ± 1 °C. The 1 H NMR spectra were referenced to 5.99 ppm for the resonance of the solvent (residual protonated tetrachloroethane). For 2D gCOSY NMR with homodecoupling, the following acquisition parameters were used: 4.8 kHz spectral width, 10 s relaxation delay, 0.21 s acquisition time, 199 increments in F1 dimension, rf irradiation on the backbone CH2 protons (dpwr = 10), 90° pulse of 7.9 μs, and 16 scans. P1 was set to 45° pulse to suppress diagonal peaks and emphasize off-diagonal coupling peaks. Molecular Weight Separation. Separation at the preparative scale was performed with a commercial preparative CRYSTAF instrument (PolymerChAR, Spain) in the molecular weight separation mode. The total polymer loading was 1000 mg for the ENGAGE sample and 714 mg for the Dex Plastomers EXACT sample. o-Xylene

(reagent grade) containing 0.97 mg/mL of butylated hydroxytoluene (BHT) was used as solvent. Di(ethylene glycol) monobutyl ether (DEGMBE) (Fisher Scientific) was used as nonsolvent. The solvent/ nonsolvent ratio is shown in Table 4. The temperature profile of this fractionation is shown in Table 5. The online filtration condition is shown in Table 6.

Table 6. Online Filtration Conditions for Preparative CRYSTAF in Molecular Weight Separation Mode N2 pressure (psi) pressurizing time (s) maximum flow rate (mL/s) maximum time (min)

15 90 2.0 30

filtration stirrer speed (rpm) extra time stirring off (s) extra time stirring on (s)

150 15 15

Each fraction was recovered by adding a large quantity of acetone at room temperature. The solution was kept at room temperature overnight to ensure complete precipitation and facilitate the subsequent filtration. The solution was then filtered. Extensive washing with acetone was performed on the precipitates. The precipitates were dried in a vacuum oven under N2 at 90 °C for several hours. Fractions 1−3 for the ENGAGE sample did not yield enough material, so fraction 4 is the lowest molecular weight fraction for this sample. Size Exclusion Chromatography. The chromatographic system consists of either a Polymer Laboratories (current Agilent Technology) Model PL-210 or Model PL-220. The column and carousel compartments were operated at 140 °C. Three Polymer Laboratories 10 μm Mixed-B columns were used with the solvent of 1,2,4trichlorobenzene, which contained 200 ppm of BHT as antioxidant. The samples were prepared at a concentration of 0.1 g polymer/50 mL solvent. Samples were prepared by agitating lightly for 4 h at 160 °C. The injection volume was 100 μL, and the flow rate was 1.0 mL/min. Calibration of the column set was performed with 21 polystyrene standards purchased from Polymer Laboratories. The polystyrene molecular weights were converted to polyethylene molecular weights using the equation

M polyethylene = A(M polystyrene)B

(2)

where M is the molecular weight, A has a value of 0.4316, and B is equal to 1.0. A third-order polynomial was determined to build the logarithmic molecular weight calibration as a function of elution volume. Polyethylene equivalent molecular weight calculations were performed using Viscotek TriSEC software (Version 3.0). The precision error bar of the weight-average molecular weight Mw is