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Thermophysical Properly Modifications in Functional Polymers via Lanthanide Trichloride Hydrates.

LAURENCE A. BELFIORE [*]

IZOLDA Y. RUZMAIKINA [**]

Polymer Physics & Engineering Laboratory Deportment of Chemical Engineering Colorado State University Fort Collins, CO 80523

Fourteen water-soluble trivalent metal chlorides from lanthanum to lutetium in the 1st-row of the f-block form complexes with poly(vinylamine) and increase the glass transition temperature from 57[degrees]C to well above 100[degrees]C at very low molar concentrations of the lanthanide. The large ionic radii of these hard-acid cations allow several hard-base amino sidegroups in the polymer to occupy sites in the first shell coordination sphere via ion-dipole (i.e., electrostatic) interactions, which leads to microclustering of the ligands about a single metal center. The enhancement in the glass transition temperature is explained in terms of multi-functional coordination crosslinking. f-Block salts induce larger increases in [T.sub.g], relative to transition metal-complexes from the d-block, however [CoCl.sub.2][([H.sub.2]O).sub.6] performs comparably to some of the more efficient lanthanides. Blends of poly(vinylamine) and trimethoxysilyl-propylpoly(ethylene imine)hydrochloride form complexes with europium(I II) and exhibit synergistic single [T.sub.g] response. Since lanthanides form very stable complexes with chelating (i.e., bidentate) oxygen ligands, it is possible to increase the elastic modulus of commercially important copolymers of ethylene and methacrylic acid via [Eu.sup.3+] complexation with the carboxylate anion. This claim is verified by infrared spectroscopy. Temperature and pH-sensitive applications for drug delivery and removal of contaminants from wastewater streams should increase the utility of these lanthanide complexes.

INTRODUCTION

Heavy metal complexes from the lanthanide series (i.e. f-block) enjoy several advantages relative to transition metal complexes from the d-block, when physical property modification of water-soluble polymers is the global objective. For example, lanthanide trichloride hydrates are water-soluble, non-toxic, and relatively inexpensive (i.e. [approximate] $1 to $5 per gram). The large ionic radius of [Ln.sub.3+] in general, allows the metal center to accomodate several ligands in its 1st shell coordination sphere [1, 2] via ionic, electrostatic and ion-dipole interactions. Hence, high coordination numbers (i.e., 6 to 12) are typical [1-3], and the potential for each metal center to interact with multiple polymeric ligands is attractive for physical property modification and compatibilization. With an eye toward future applications, there is a much greater tendency for actinides [3] to form complexes, in comparison with lanthanides. For example, uranium tetrachloride is water-soluble and coordinates to nitrogen-c ontaining ligands. such as pyridines [2] and amines [4]. Hence, future utilization of heavy metal complexes with water-soluble polymers could be significant.

Previous research in our laboratory has demonstrated that poly(vinylamine) complexes with europium(III) chloride hexahydrate produce either highly viscous solutions, complete gels or collapsed gels in aqueous media [5]. Transparent total gels with swelling ratios between 20 and 50 satisfy the "tilt" test because they do not flow under gravity when the mixture is inverted. To the best of our knowledge, this is the first example where lanthanides are responsible for gel formation in the research or patent literature.

The coordination group of the 4f trihalides is a tricapped trigonal prism, with a coordination number of nine [6], and bonding is primarily ionic in character [1]. Since lanthanide cations are classified as hard acids [1], it is not unreasonable that they form complexes with the nitrogen lone pair in the hard-base amino sidegroup of poly(vinylamine) [7, 8] via ion-dipole interactions. Previous investigations indicate that selected polymers form complexes with lanthanides via metal-nitrogen [9, 10] and metal-oxygen [10-l3] bonding.

EXPERIMENTAL CONSIDERATIONS

Materials. Poly(vinylamine) (PVA) was supplied by Dr. Lloyd M. Robeson of Air Products and Chemicals, Inc., in Allentown, Pa. It was synthesized from vinyl-formamide upon hydrolysis of the amide bond in the sidegroup of poly(vinylformamide). Linear PVA was provided in a free base aqueous solution (i.e., 32.5 wt% polymer, pH [approximate] 10) with. a weight-average molecular weight of 2.3 X [10.sup.4] daltons, and [T.sub.g] is 57[degrees]C. Infrared analysis of PVA [14, 15] yields a symmetric [NH.sub.2] stretch @ 3275 [cm.sup.-1], and an asymmetric [NH.sub.2] stretch @ 3331 [cm.sup.-1]. There is no evidence for protonated [[NH.sup.+].sub.3] sidegroups via NH stretches [14] below 2900 [cm.sup.-1]. This observation agrees with predictions from the Henderson-Hasselbalch equation [16] when pH [approximate] 10, and suggests that basic [NH.usb.2] sidegroups of poly(vinylamine) are not shielded from the metal cations. Poly(ethylene imine) (PEI) was purchased in aqueous solution (i.e., 50 wt% polymer) from Scientific Polymer Products, in Ontario, N.Y., with a viscosity-average molecular weight of 5.5 X [10.sup.4] daltons. Trimethoxysilylpropyl-poly(ethylene imine)hydrochloride (i.e., aziridine, 50 wt% in isopropanol) was purchased from Gelest in Tullytown, Pa., with 33 mol% quaternization of NH groups in linear poly(ethylene imine) via (3-chioropropyl)trimethoxysilane [i.e., C1[([CH.sub.2]).sub.3] Si[([OCH.sub.3]).sub.3]]. The molecular weight range for this functionalized poly(ethylene imine) is 2000-4000 daltons. Random copolymers of ethylene and methacrylic acid were obtained from DuPont in Wilmington, Del., courtesy of Drs. George Hoh and Donna L. Visioli, with 5.4 mol% (i.e., 15 wt%) methacrylic acid and a melting (i.e., peak) temperature of 94[degrees]C. Fourteen lanthanide trichloride hydrates from lanthanum to lutetium were obtained from Strem Chemicals in Newburyport, Mass.

Sample preparation methods. Polymer-metal complexes were prepared in aqueous media @ pH [approximate] 9-10 by (i) mixing the polymer and salt solutions, (ii) allowing the solvent to evaporate from a Petri dish in a fume hood at ambient temperature, and (iii) exposing the residual solids to further drying under vacuum @ ambient temperature for at least 24 hours, and an additional 24 hours between 80[degrees]C and 90[degrees]C. The cosolvent for ethylene/methacrylic-acid random copolymers was 90/10 (v/v) xylene/2-butanol, which was removed from the complexes @ 80[degrees]C under vacuum for 3 days. Sample compositions indicate the mole fraction of f-block cations with respect to the polymeric repeat unit. The average repeat unit molecular weight of DuPont's ethylene/methacrylic-acid random copolymers was determined as follows;

[less than] [MW.sub.repeat] [greater than] E- MAA = 0.946 [{[MW.sub.repeat]}.sub.PE] +

0.054 [{MW.sub.repeat]}.sub.MAA] [approximate] 31 daltons

where [{MW.sub.repeat]}.sub.PE] is 28 daltons for polyethylene, and [{[MW.sub.repeat]}.sub.MAA] is 86 daltons for poly(methacrylic acid). Hence, a complex of x mol% [Ln.sup.3+] with these ethylene/methacrylic-acid random copolymers implies that there are x moles of [Ln.sup.3+] per 100-x moles of copolymer repeat units, where the average repeat unit molecular weight of the copolymer is 31 daltons. For small values of x, this translates to approximately x moles of [Ln.sup.3+] per 5 moles of carboxlic acid groups in the copolymer. The average repeat unit molecular weight of trimethoxysilylpropylpoly(ethylene imine)hydrochloride, in which one-third of the NH groups are quarternized with (3-chloropropyl)trimethoxysilane, is;

[less than] [MW.sub.repeat] [greater than] Functionalized PEI [approximate]

{(43 + 13 + 242)/3} daltons = 109 daltons

Equimolar polymer-polymer blends are based on moles of repeat units, and the metal cation concentration in ternary complexes represents a ratio based on the total moles of both types of polymeric repeat units.

Differential scanning calorimetry and thermogravimetric analysis. Thermal analysis was performed on a Perkin-Elmer DSC-7 interfaced to a TAC-7/DX thermal analysis controller and a personal computer. Melting and dehydration/dehydrochlorination endotherms for the pure lanthanide salts were measured during the 1st heating scan at a rate of 20[degrees]C/min. After quenching polymer-lanthanide complexes from the molten state, [T.sub.g] was measured at a rate of 20[degrees]C/min during the 2nd or 3rd heating trace in the calorimeter. Thermogravimetric analysis was performed using a Seiko TGA/DTA. Granular powders of the undiluted lanthanide salts were heated from 50[degrees]C to 335[degrees]C at a rate of l0[degrees]C/min using a day nitrogen purge at a flowrate of 100 mL/min.

Mechanical properties. Engineering stress-strain response was measured at ambient temperature using an Instron model 8501 servohydraulic mechanical testing system. The strain rate was 25 mm/min (i.e., [approximate] 1 inch/min). Samples were cut into rectangular strips with average dimensions of 45 mm (length), 6.5 mm (width), and a thickness varying from 0.25 mm to 0.65 mm. At least three solid films were tested for reproducibility of each material. The elastic modulus was calculated from the initial slope of the stress-strain curve.

Infrared spectroscopy. Fourier transform infrared spectroscopy was performed on a Galaxy [TM] series model 5020 from Mattson Instruments at ambient temperature. The optical bench is interfaced to Mattson WinFIRST v.3.5 software on a personal computer for data acquisition and control. [Eu.sup.3+] complexes with ethylene/methacrylic-acid random copolymers were tested as thin films deposited on AgCl ciystals acquired from International Crystal Labs. Each spectrum was generated by signal averaging 64 interferograms at a resolution of 2 [cm.sup.-1], and a triangular apodization smoothing function was implemented prior to Fourier transformation.

RESULTS AND DISCUSSION

Thermal properties of pure lanthanide trichloride hydrates. Melting endotherms of the pure salts lie between 93[degrees]C and 180[degrees]C, as summarized above in Table 1. Except for the first four entries in Table 1 [i.e., lanthanum(III), cerium(III), praseodymium(III) and neodymium(III)], the other lanthanide trichlorides melt at much higher temperatures, between 158[degrees]C and 180[degrees]C. Promethium trichloride is the only lanthanide from the series that is missing in this investigation because (i) it is not available from rare earth ores (3) or a commercial distributor, and (ii) more than 100 mg cannot be handled safely because of its radioactivity (3). For each undiluted salt, dehydration and dehydrochlorination (3) endotherms above [T.sub.m] are verified by weight loss from therrnogravimetric analysis. In Table 1, [T.sub.Hcl] represents the highest measured dehydrochlorination endotherm which is furthest above [T.sub.m]. These hydrated salts probably lose hydrochloric acid more readily than they lose water upon heating (3), forming oxochlorides above 200[degrees]C. The formation of oxochlorides with a metal-oxygen double bond is represented by;

[Ln.sup.3+][Cl.sub.3][([H.sub.2]O).sub.x][equivalence][Ln.sup.3+]Ocl[ ([H.sub.2]O).sub.x-1] + 2 HCl(g)

Actually, all of the undiluted lanthanide trichloride hydrates lose [H.sub.2]O or HCl continuously over a temperature range that encompasses all of the endotherms, beginning at [T.sub.m], as evidenced by thermogravimetric analysis. Higher hydration and dehydrochlorination temperatures represent a measure of the difficulty of removing lattice waters and chloride anions from the 1st-shell coordination sphere of the lanthanide (5) in potential ligand exchange reactions, as described below.

Lanthanide complexes with poly(vinylamine). Poly(vinylamine) complexes with all of the lanthanide trichlorides investigated herein produce optically transparent films with enhanced glass transition temperatures. At 0.5 mol% lanthanide, poly(vinylamine)'s [T.sub.g] increases by a minimum of 3[degrees]C for gadolinium (III), to a maximum of 55[degrees]C for thulium(III) and lutetium(III). When all fourteen lanthanides are considered, except promethium trichloride, there is no simple explanation for [T.sub.g] enhancement in terms of, for example, (i) cation size, (ii) number of f-electrons, (iii) ligand field stabilization, or (iv) the "gadolinium break" (4). Ten of the fourteen lanthanide trichlorides investigated herein form complexes with poly(vinylamine) that exhibit [T.sub.g]'s above 100[degrees]C when the [Ln.sup.3+] concentration is only 0.5 mol%. Consider lanthanum(III), which exhibits a melting transition at 93[degrees]C. It should be obv**********ious that thermal synergy is operative because 0.5 mol% [La.sup.3+] and poly(vinylamine) form a complex with a glass transition of 104[degrees]C, as indicated by the first entry in the far right column of Table 1. in this case, [T.sub.g] of the complex is higher than [T.sub.g] of the pure polymer (i.e., 57[degrees]C) and [T.sub.m] of the pure lanthanide.

Microclustering of several ligands about a single metal center--the concept of multi-functional coordination crosslinks. Based on experimental [T.sub.g] data in the far-right column of Table 1 and the rather large coordination numbers for f-block complexes [1-3], the best explanation for these significant increases in poly(vinylamine)'s [T.sub.g] focuses on the formation of "coordination crosslinks" [18, 19] via ion-dipole interactions between the metal center and the lone pair of electrons on the amino nitrogen in PVA's side-group. Coordination crosslinks occur when amino side-groups displace waters of hydration in the 1st shell and the lanthanide forms a complex with at least two [NH.sub.2] sidegroups on different chains. This is illustrated by the following neutral ligand substitution reaction:

[Ln.sup.3+][Cl.sub.3][([H.sub.2]O).sub.6] + y Polymer [equivalence] [Ln.sup.3+][Cl.sub.3][(Polymer).sub.y][([H.sub.2]O).sub.6-y] + y [H.sub.2]O

where the number (i.e., y) of amino sidegroups from the polymer that occupy sites in the 1st-shell coordination sphere of the metal cation could span the range from 1 to 6 if only lattice waters are displaced. However, one might also envision multifunctional metal centers [19] in which some anionic chloride ligands (i.e., x) are displaced to the 2nd shell and more than six amino sidegroups coordinate to the lanthanide;

[Ln.sup.3+][Cl.sub.3][([H.sub.2]O).sub.6] + (6 + x) Polymer [equivalence] [Ln.sup.3+][Cl.sub.3-x][(Polymer).sub.6+x] + x [Cl.sup.-] + 6 [H.sub.2]O

where x varies from one to three. The fact that ionic lanthanide complexes undergo rapid ligand exchange [31] supports the two previous substitution reactions. The concept of 9 polymeric ligands occupying sites in the 1st-shell of a lanthanide cation has been simulated for complexes of lanthanum triflate [La[([CF.sub.3][SO.sub.3]).sub.3]] with poly(ethylene oxide) [20]. Neither of the ligand substitution schemes illustrated above is driven by hard-and-soft acid-base considerations [7, 8] because the trivalent lanthanide cation is a hard Lewis acid [1], and all of the possible ligands (i.e., amino sidegroups, lattice waters and chloride anions) are classified as hard bases. However, the energetics of these ligand substitution reactions are favorable because primary amines (i.e., [RNH.sub.2], [pK.sub.b] [approximate] 3.3) are much stronger bases [21] relative to lattice waters ([pK.sub.b] [approximate] 14) [22] or chloride anions ([pK.sub.b] [approximate] 21) [22]. Hence, weaker metal-ligand bonds are broken an d stronger ones form when amino sidegoups in the polymer displace either lattice waters or chloride anions.

Comparision of [T.sub.g] enhancement in poly(vinylamine) with lanthanide and transition metal complexes. The amino sidegroup in poly(vinylamine) forms a complex with several metal cations from the d-block [23] and the f-block [5]. Table 2 provides a summary of the enhancement in [T.sub.g] per mol% metal cation, which is averaged over the range of salt concentrations that were investigated. In most of the lanthanide complexes, any differences between the reported [T.sub.g] enhancements in Table 1 and Table 2 are due to the range of salt concentrations. For example, [Tb.sup.3+] exhibits an extrapolated 106[degrees]C increase in poly(vinylamine)'s [T.sub.g] per mol% metal cation between 0 and 0.5 mol% [Tb.sup.3+], as indicated in Table 1. However, when this [T.sub.g] modification is averaged between 0 and 2 mol% metal cation in Table 2, the enhancement is 50[degrees]C per mol% [Tb.sup.3+]. Conversely, [GdCl.sub.3][([H.sub.2]O).sub.x] produces a 6[degrees]C increase in PVA's [T.sub.g] per mol% [Gd.sup.3+] betwee n 0 and 0.5 mol% metal cation, as indicated in Table 1, whereas this [T.sub.g] modification is reported as 27[degrees]C per mol% [Gd.sup.3+] between 0 and 2 mol% metal cation in Table 2. Cobalt chloride hexahydrate from the d-block functions similarly to [Eu.sup.3+] and [Tb.sup.3+] from the f-block, by inducing a significant enhancement in poly(vinylamine)'s [T.sub.g]. [Ni.sup.2+] and [Ru.sup.2+] function similarly to [GdCl.sub.3][([H.sub.2]O).sub.x], and these two d-block complexes are not as effective in modifying PVA's [T.sub.g] relative to most of the lanthanide complexes, except for gadolinium acetate tetrahydrate. All three transition metal complexes in Table 2 exhibit pseudo-octahedral symmetry with a coordination number of 6. Each acetate ligand is monodentate in nickel acetate tetrahydrate [24, 25], dichlorotricarbonylruthenium(II) exists as a dimer with a dichloride bridge between both of the metal centers [26, 27], and only four waters of hydration occupy sites in the 1st shell coordination sphere of cobalt chloride hexahydrate [28-30]. Hence, it is understandable that 6-coordinate [Ni.sup.2+] and [Ru.sup.2+] are not as efficient thermophysical property modifiers for poly(vinylamine) as most of the lanthanides, which exhibit higher coordination numbers. However, [CoCl.sub.2] [([H.sub.2]O).sub.6] is unusual because this 6-coordinate complex is comparable to 9-coordinate [Eu.sup.3+] and [Tb.sup.3+] based on [T.sub.g] enhancement of poly(vinylamine).

[T.sub.g] enhancement in poly(ethylene imine) and other nitrogen-containing polymers via europium trichloride hexahydrate. Europium(III) was chosen for further studies of polymer/lanthanide complexation because [Eu.sup.3+] has had tremendous commercial importance as a red phosphor in color monitors since the mid-1960s, when it replaced transition metal complexes for this application (31). Poly(ethylene imine) exhibits a [T.sub.g] at -18[degrees]C, which increases to 49[degrees]C @ 5 mol% [Eu.sup.3+] and 108[degrees]C 25 mol% [Eu.sup.3+]. Relative to Eu.sup.3+]/poly(vinylamine), [EuCl.sub.3][([H.sub.2]O).sub.6] is not as efficient a thermophysical property modifier for poly(ethylene imine), and a similar claim is justified for [CoCl.sub.2][([H.sub.2]O).sub.6] based on [T.sub.g] enhancement of these two polymers (i.e., 45[degrees]C/mol% for PVA/[Co.sup.2+] vs. [20[degrees]C/mol% for PEI/[Co.sup.2+]) (23). Contrary to low molecular-weight amines, poly(vinylamine) is a stronger base than poly(ethylene imine) bec ause less conformational reorganization of the chain backbone is required to accomodate nitrogen bond-angle distortions when the [NH.sub.2] sidegroup of PVA is protonated, compared to protonation of nitrogen's lone pair in the backbone of PEI. Hence, [Co.sup.2+] and [Eu.sup.3+] induce larger increases in the [T.sub.g] of PVA, relative to that of PEI, as a consequence of stronger metal-ligand [sigma]-bonds with [Co.sup.2+] and stronger ion-dipole interactions with [Eu.sup.3+].

The efficiency of [EuCl.sub.3][([H.sub.2]O).sub.6] as a [T.sub.g] enhancer for eight nitrogen-containing polymers is summarized in Table 3. In comparison with the results for [Eu.sup.3+]/poly(ethylene imine) described above, the 82[degrees]C in crease in [T.sub.g] per mol% [Eu.sup.3+] for trimethoxysilylpropylpoly(ethylene imine)hydrochloride is attributed to (i) quaternization of the secondary main-chain nitrogen via Cl[([CH.sub.2]).sub.3]Si[([OCH.sub.3]).sub.3] and (ii) [Eu.sup.3+] complexation to several methoxy sidegroups. Two mol% [Eu.sup.3+] increases [T.sub.g] from 10[degrees]C to 173[degrees]C, as illustrated in Fig. 1 for a low-molecular-weight silicon modified polymer with approximately 18-36 PEI repeat units. These solid state results are consistent with the fact that this functionalized poly(ethylene imine) forms a total gel with 2 mol% [Eu.sup.3+] in 90/10 (v/v) THF/ethanol, and passes the "tilt" test because it does not flow under gravity when the mixture is inverted. At most, [Eu.sup.3+] can f orm a complex with four or five functionalized sidechains of PEI, where approximately 12-14 methoxy oxygens occupy sites in the 1st-shell of the lanthanide. This model for "coordination crosslinks" in functionalized PEI via [Eu.sup.3+] complexation with several methoxy oxygens in rather flexible sidegroups is consistent with the measured [T.sub.g] enhancement of 82[degrees]C per mol% [Eu.sup.3+]. Poly(4-vinylpyridine)'s [T.sub.g] is depressed by [Eu.sup.3+], which is attributed to the fact that it is not favorable for borderline-base pyridine sidegroups in P4VP to displace hard-base lattice waters and chloride anions in the 1st shell coordination sphere of the hard-acid lanthanide cation. There is only one previous example from our laboratory where a transition metal complex (i.e., zinc laurate) depresses the glass transition temperature of poly(4 vinylpyridine) (32) between 0 and 30 mol% [Zn.sup.2+]. Zinc acetate dihydrate (32, 33), copper acetate dihydrate (33), nickel acetate tetrahydrate (18, 33), cobalt chloride hexahydrate (34). and dichlorotricarbonylruthenium(II) dimer (34) all induce significant increases in P4VP's [T.sub.g].

[T.sub.g] enhancement in ternary complexes of poly(vinylamine), functionalized poly(ethylene imine) and europium trichloride hexahydrate. A 50/50 molar ratio (i.e., 28/72 wt. ratio) of PVA and functionalized PEI, prepared from a 90/10 (v/v) THF/ethanol mixture, exhibits a single glass transition near 20[degrees]C, as illustrated in Fig. 1. This measurement agrees well with predictions from the Fox equation, because an equimolar blend of poly(vinylamine) (i.e., [T.sub.g] = 57[degrees]C) and trimethoxysilylpropylpoly(ethylene imine)hydrochloride (i.e., [T.sub.g] = 10[degrees]C) should exhibit a glass transition at 22[degrees]C if the morphology is consistent with single phase behavior. The 50/50 (mol/mol) complex of PVA and functionalized PEI with 1 mol% [Eu.sup.3+] reveals a single [T.sub.g] at 140[degrees]C (i.e., uppermost thermogram in Fig. 1), which reflects the fact that [Eu.sup.3+] induces remarkable increases in [T.sub.g] for each polymer in binary complexes (i.e.. PVA/[Eu.sup.3+] and functionalized P EI/[Eu.sup.3+]), as illustrated in Fig. 1 and summarized in Table 3.

Mechanical property modification In [Eu.sup.3+] complexes with random copolymer of ethylene and methacrylic acid. It is well-documented that lanthanide cations form very stable complexes with oxygen-containing ligands (3). Macroscopic consequences of this concept are illustrated in Fig. 2 via stress strain data for [Eu.sup.3+] complexes with random copolymers of ethylene and methacrylic acid. Progressive addition of [Eu.sup.3+] increases the elastic modulus (i.e., 5-fold increase @ 3 mo1% [Eu.sup.3+]), but decreases the fracture strain. Some important mechanical properties of these lanthanide complexes are summarized in Table 4, together with the effects of [Na.sup.+] and [Zn.sup.2+] neutralizing cations on the secant modulus of ethylene/methacrylic-acid ionomers. Complexation occurs between the lanthanide metal cation and the carboxylate anion in the methacrylic segments of the random copolymer via ionic interactions. A simple one-step mechanism, similar to ionomer neutralization, is proposed in which carbo xylate anions displace anionic chloride ligands in the 1st-shell coordination sphere of [Eu.sup.3+];

[Eu.sup.3+] [Cl.sub.3][([H.sub.2]O).sub.6] + x RCOOH [equivalence]

[([RCOO.sup.-]).sub.x] [Eu.sup.3] [Cl.sub.3-x] [({H.sub.2]O)].sub.6] + x HCl

where R represents the remainder of the ethylene/methacrylic-acid random copolymer and x varies from one to three. When x is greater than one, the [Eu.sup.3+] complex on the right side of the previous anionic lig-and exchange reaction could bridge more than one copolymer chain. This type of structural modification is consistent with the enhancement in elastic modulus reported in Fig. 2 and Table 4.

Infrared spectroscopy in Fig. 3 reveals that the C=O stretch in the methacrylic acid segments of the undiluted copolymer absorbs strongly near 1700 [cm.sup.-1], which is characteristic of hydrogen-bonded carboxylic acid dimers [35]. The non hydrogen-bonded C=O stretch absorbs @ 1750 [cm.sup.-1] [35], and it is essentially absent in both spectra of Fig. 3. When the carboxylate anion in the methacrylic acid segments forms an ionic complex with 5 mol% [Eu.sup.3+], most likely in bidentate fashion, the asymmetric [RCOO.sup.-] stretch appears between 1660 [cm.sup.-1] and 1670 [cm.sup.1], as illustrated in the upper spectrum of Fig. 3. This is reasonable because the asymmetric stretch of the free acetate anion absorbs @ 1578 [cm.sup.-1] [36], and metal complexation shifts this asymmetric stretch to higher frequency [36]. Lattice waters (i.e., HOH bending vibrations) in undiluted [EuCl.sub.3][([H.sub.2]O).sub.6] absorb between 1625 [cm.sup.-1] and 1635 [cm.sup.-1] [36], and this signal is essentially nonexistent in the [Eu.sup.3+] / copolymer complex, as illustrated in the upper spectrum of Fig. 3. Hence, two different environments are detected by infrared spectroscopy for carboxylic acid groups in the methacrylic acid segments of the random copolymers; (i) hydrogen-bonded carboxylic acid dimers and (ii) carboxylate anions that are complexed to [Eu.sup.3+]. As mentioned above, this latter structure is responsible for the enhancement in elastic modulus reported in Fig. 2.

CONCLUSIONS

Essentially, the complete set of lanthanide trichloride hydrates has been investigated in complexes with poly(vinylamine), and all of them increase the glass transition temperature of the polymer. The enhancement in [T.sub.g] is due to microclustering of several amino sidegroups about a single metal center via ion-dipole interactions and the formation of multi-functional coordination crosslinks. Microclustering induces a significant reduction in polymer mobility near each lanthanide cation and a large increase in the glass transition. f-Block salts induce larger increases in poly(vinylamine)'s [T.sub.g], relative to transition metal complexes from the d-block; however, [CoCl.sub.2][([H.sub.2]O).sub.6] performs comparably to some of the more efficient lanthanides. When relatively low-molecular-weight poly(ethylene imine) is functionalized with (3-chloropropyl) trimethoxysilane, 2 mol% [Eu.sub.3+] increases [T.sub.g] dramatically from 10[degrees]C to 173[degrees]C. Blends of poly(vinylamine) and trimethoxysilyl propylpoly(ethylene imine) hydrochloride form complexes with [Eu.sup.3+] and exhibit synergistic single [T.sub.g] response. Europium(III) forms an ionic complex with the carboxylate anion in commercially important ethylene/methacrylic-acid random copolymers and induces a 5-fold increase in elastic modulus when the metal cation concentration is 3 mol%. There are several advantages of employing f-block complexes, instead of d-block complexes, as thermophysical property modifiers for polymeric materials.

ACKNOWLEDGMENTS

The research described herein is supported by the National Science Foundation's Division of Materials Research, Polymers Program, through grant #DMR-9902657. The authors are grateful to Professor Don Radford in the Department of Mechanical Engineering at Colorado State University for providing facilities to perform thermogravimetric analysis.

(*.) Corresponding author. belfiore@engr.colostate.edu

(**.) Permanent address: Institute of Macromolecular compounds, St. Petersburg. Russia.

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Table 1.
Melting (i.e., [T.sub.m]) and Dehydrochlorination (i.e.,
[T.sub.HCL] of Several Undiluted Lanthanide Trichlorides. (i.e.,
[T.sub.g]) are Reported for Poly(vinyalamine) Complexes With
0.5 mol% [Ln.sup.3+].
 Electr. Config.
 [Ln.sup.3+]
Metal salt (Xe)4[f.sup.n]
La[Cl.sub.3][([H.sub.2]O).sub.6] 4[f.sup.0]
Ce[Cl.sub.3][([H.sub.2]O).sub.x] 4[f.sup.1]
Pr[Cl.sub.3][([H.sub.2]O).sub.7] 4[f.sup.2]
Nd[Cl.sub.3][([H.sub.2]O).sub.6] 4[f.sup.3]
Sm[Cl.sub.3][([H.sub.2]O).sub.6] 4[f.sup.5]
Eu[Cl.sub.3][([H.sub.2]O).sub.6] 4[f.sup.6]
Gd[Cl.sub.3][([H.sub.2]O).sub.x] 4[f.sup.7]
Tb[Cl.sub.e][([H.sub.2]O).sub.6] 4[f.sup.8]
Dy[Cl.sub.3][([H.sub.2]O).sub.6] 4[f.sup.9]
Ho[Cl.sub.3][([H.sub.2]O).sub.6] 4[f.sup.10]
Er[Cl.sub.3][([H.sub.2]O).sub.x] 4[f.sup.11]
Tm[Cl.sub.3][([H.sub.2]O).sub.7] 4[f.sup.12]
Yb[Cl.sub.3][([H.sub.2]O).sub.6] 4[f.sup.13]
Lu[Cl.sub.3][([H.sub.2]O).sub.6] 4[f.sup.14]
 [T.sub.m] ([degrees]C)
Metal salt [literature.sup.17]
La[Cl.sub.3][([H.sub.2]O).sub.6] 91-92
Ce[Cl.sub.3][([H.sub.2]O).sub.x] 90 **
Pr[Cl.sub.3][([H.sub.2]O).sub.7] 115
Nd[Cl.sub.3][([H.sub.2]O).sub.6] 124-127
Sm[Cl.sub.3][([H.sub.2]O).sub.6] 147
Eu[Cl.sub.3][([H.sub.2]O).sub.6] 152
Gd[Cl.sub.3][([H.sub.2]O).sub.x] 148, 158 ***
Tb[Cl.sub.e][([H.sub.2]O).sub.6] 158-159
Dy[Cl.sub.3][([H.sub.2]O).sub.6] 162
Ho[Cl.sub.3][([H.sub.2]O).sub.6] 164
Er[Cl.sub.3][([H.sub.2]O).sub.x] 164 ***
Tm[Cl.sub.3][([H.sub.2]O).sub.7] 162
Yb[Cl.sub.3][([H.sub.2]O).sub.6] 154
Lu[Cl.sub.3][([H.sub.2]O).sub.6] 157
 [T.sub.m])[degrees]C)
Metal salt measured *
La[Cl.sub.3][([H.sub.2]O).sub.6] 93 {3}
Ce[Cl.sub.3][([H.sub.2]O).sub.x] 97 {4}
Pr[Cl.sub.3][([H.sub.2]O).sub.7] 112 {5}
Nd[Cl.sub.3][([H.sub.2]O).sub.6] 129 {4}
Sm[Cl.sub.3][([H.sub.2]O).sub.6] 163 {23}
Eu[Cl.sub.3][([H.sub.2]O).sub.6] 158 {7}
Gd[Cl.sub.3][([H.sub.2]O).sub.x] 164 {7}
Tb[Cl.sub.e][([H.sub.2]O).sub.6] 169 {7}
Dy[Cl.sub.3][([H.sub.2]O).sub.6] 171 {10}
Ho[Cl.sub.3][([H.sub.2]O).sub.6] 172 {16}
Er[Cl.sub.3][([H.sub.2]O).sub.x] 180 {13}
Tm[Cl.sub.3][([H.sub.2]O).sub.7] 168 {10}
Yb[Cl.sub.3][([H.sub.2]O).sub.6] 162 {9}
Lu[Cl.sub.3][([H.sub.2]O).sub.6] 159 {10}
 [T.sub.HCl] ([degrees]C)
Metal salt measured *
La[Cl.sub.3][([H.sub.2]O).sub.6] 219 {4}
Ce[Cl.sub.3][([H.sub.2]O).sub.x] 200 {20}
Pr[Cl.sub.3][([H.sub.2]O).sub.7] 209 {20}
Nd[Cl.sub.3][([H.sub.2]O).sub.6] 219 {20}
Sm[Cl.sub.3][([H.sub.2]O).sub.6] 207 {20}
Eu[Cl.sub.3][([H.sub.2]O).sub.6] 181 {6}
Gd[Cl.sub.3][([H.sub.2]O).sub.x] 218 {5}
Tb[Cl.sub.e][([H.sub.2]O).sub.6] 178 {8}
Dy[Cl.sub.3][([H.sub.2]O).sub.6] 236 {5}
Ho[Cl.sub.3][([H.sub.2]O).sub.6] 218 {6}
Er[Cl.sub.3][([H.sub.2]O).sub.x] 213 {11}
Tm[Cl.sub.3][([H.sub.2]O).sub.7] 238 {14}
Yb[Cl.sub.3][([H.sub.2]O).sub.6] --
Lu[Cl.sub.3][([H.sub.2]O).sub.6] 224 {4}
 [T.sub.g]
Metal salt ([degrees]C)
La[Cl.sub.3][([H.sub.2]O).sub.6] 104
Ce[Cl.sub.3][([H.sub.2]O).sub.x] 102
Pr[Cl.sub.3][([H.sub.2]O).sub.7] 102
Nd[Cl.sub.3][([H.sub.2]O).sub.6] 103
Sm[Cl.sub.3][([H.sub.2]O).sub.6] 74
Eu[Cl.sub.3][([H.sub.2]O).sub.6] 79
Gd[Cl.sub.3][([H.sub.2]O).sub.x] 60
Tb[Cl.sub.e][([H.sub.2]O).sub.6] 110
Dy[Cl.sub.3][([H.sub.2]O).sub.6] 107
Ho[Cl.sub.3][([H.sub.2]O).sub.6] 105
Er[Cl.sub.3][([H.sub.2]O).sub.x] 74
Tm[Cl.sub.3][([H.sub.2]O).sub.7] 112
Yb[Cl.sub.3][([H.sub.2]O).sub.6] 106
Lu[Cl.sub.3][([H.sub.2]O).sub.6] 112
(*)Melting and dehydration/
dehydrochlorination temperatures
are calculatled from the
endothermic peak.
(**)Literature value for cerium
trichloride hepptpppppahydrate
(i.e., x = 7)
(***)Literature values for gadolini
trichloride hexahydrate and erbium
trichloride and erbium trichloride
(i.e., x = 6).
Table 2.
Effect of Some d-Block and f-Block Metal Complexes on
[T.sub.g] Enhancement in Poly(vinylamine). In All
Cases, Complexes Were Prepared fromAqueous Solution (pH
[approximate] 9-10).
 Electronic
 d-block complexes Configuration
Ni[([CH.sub.3]COO).sub.2] [Ar][3d.sup.8]
[([H.sub.2]O).sub.4]
[{[RuCl.sub.2][(CO).sub.3]}.sub.2] [Kr][4d.sup.6]
[CoCl.sub.2][([H.sub.2]O).sub.6] [Ar][3d.sup.7]
 Electronic
 f-block complexes Configuration
Gd[([CH.sub.3]COO).sub.3] [Xe][4f.sub.7]
[([H.sub.2]O).sub.4]
[GdCl.sub.3][([H.sub.2]O).sub.x] [Xe][4f.sub.7]
[ErCl.sub.3][([H.sub.2]O).sub.x] [Xe][4f.sub.11]
[SmCl.sub.3][([H.sub.2]O).sub.6] [Xe][4f.sub.5]
[EuCl.sub.3][([H.sub.2]O).sub.6] [Xe][4f.sub.6]
[TbCl.sup.3][([H.sub.2]O).sub.6] [Xe][4f.sub.8]
 [T.sub.g] enhancement
 d-block complexes ([degrees]C) per mol% salt
Ni[([CH.sub.3]COO).sub.2] 17
[([H.sub.2]O).sub.4]
[{[RuCl.sub.2][(CO).sub.3]}.sub.2] 25
[CoCl.sub.2][([H.sub.2]O).sub.6] 45
 [T.sub.g] enhancement
 f-block complexes ([degrees]C) per mol% salt
Gd[([CH.sub.3]COO).sub.3] 4
[([H.sub.2]O).sub.4]
[GdCl.sub.3][([H.sub.2]O).sub.x] 27
[ErCl.sub.3][([H.sub.2]O).sub.x] 31
[SmCl.sub.3][([H.sub.2]O).sub.6] 38
[EuCl.sub.3][([H.sub.2]O).sub.6] 49
[TbCl.sup.3][([H.sub.2]O).sub.6] 50
 salt mol%
 d-block complexes
Ni[([CH.sub.3]COO).sub.2] 0-3
[([H.sub.2]O).sub.4]
[{[RuCl.sub.2][(CO).sub.3]}.sub.2] 0-1
[CoCl.sub.2][([H.sub.2]O).sub.6] 0-3
 salt mol%
 f-block complexes
Gd[([CH.sub.3]COO).sub.3] 0-2
[([H.sub.2]O).sub.4]
[GdCl.sub.3][([H.sub.2]O).sub.x] 0-2
[ErCl.sub.3][([H.sub.2]O).sub.x] 0-2
[SmCl.sub.3][([H.sub.2]O).sub.6] 0-2
[EuCl.sub.3][([H.sub.2]O).sub.6] 0-2
[TbCl.sup.3][([H.sub.2]O).sub.6] 0-2
Table 3.
Efficiency of [EuCl.sub.3][(H.sub.2]O).sub.6] as a [T.sub.g]
Enhancer for Serveral Nitrogen-Containing Polymers.
 pH during preparation
Polymer in aqueous media
Trimethoxysilylpropyl
 poly(ethylene imine)hydrochloride
Poly(vinylamine), PVA pH=10
Poly(ethylene imine), PEI pH=10
Poly(vinylpyrrolidone)
Poly(acrylamide) pH=6
Poly(2-ethyl-2-oxazoline), pH=6
Poly(diphenoxyphosphazene)
Poly(4-vinylpyridine), PAVP
 [T.sub.g] enhancement ([degrees]C)
Polymer per mol% [Eu.sup.3+]
Trimethoxysilylpropyl
 poly(ethylene imine)hydrochloride 82
Poly(vinylamine), PVA 49
Poly(ethylene imine), PEI 14
Poly(vinylpyrrolidone) 5
Poly(acrylamide) 1
Poly(2-ethyl-2-oxazoline), 0
Poly(diphenoxyphosphazene) 0
Poly(4-vinylpyridine), PAVP -7
Polymer [Eu.sup.3+] mol%
Trimethoxysilylpropyl
 poly(ethylene imine)hydrochloride 0-2
Poly(vinylamine), PVA 0-2
Poly(ethylene imine), PEI 0-5
Poly(vinylpyrrolidone) 0-5
Poly(acrylamide) 0-10
Poly(2-ethyl-2-oxazoline), 0-5
Poly(diphenoxyphosphazene) 0-5
Poly(4-vinylpyridine), PAVP 0-5
Table 4.
Summary of the MechanicalProperties of [Eu.sup.2+]
Complexes with Random Copolymers ofEthylene and Methacrylic
Acid at an Engineering Strain Rate of 25mm/minute. Effects of
[Na.sup.+] and [Zn.sup.2+]Neutralization on the
Secant Moduli of These Copolymers AreAlso included for
Comparison.
 Elastic Yield
 Modulus Stress
Polymer/Complex (N/[m.sup.2]) (N/[m.sup.2])
Ethylene/methacrylic-
acid random copolymer 6.2 x [10.sup.7] 3.0 x [10.sup.6]
(5.4 mol% acid content)
EIMAA w/1 mol% [Eu.sup.3+] 2.2 x [10.sup.8] 7.0 x [10.sup.6]
EIMAA w/2 mol% [Eu.sup.3+] 2.7 x [10.sup.8] 9.0 x [10.sup.6]
EIMAA w/3 mol% [Eu.sup.3+] 3.6 x [10.sup.8] 1.1 x [10.sup.7]
EIMAA
(5.4 mol% acid content) 3.1 x [10.sup.8*]
50% neutralized w/ Na+
EIMAA
(5.4 mol% acid content) 2.4 X [10.sup.8*]
25% neutralized w/ [Zn.sup.2+]
E/MAA
(5.4 mol% acid content) 4.0 x [10.sup.8*]
60% neutralized w/ [Zn.sup.2+]
 Fracture Fracture
 Stress Strain
Polymer/Complex (N/[m.sup.2]) (%)
Ethylene/methacrylic-
acid random copolymer 1.0 X [10.sup.7] 400
(5.4 mol% acid content)
EIMAA w/1 mol% [Eu.sup.3+] 1.0 x [10.sup.7] 95
EIMAA w/2 mol% [Eu.sup.3+] 1.1 x [10.sup.7] 90
EIMAA w/3 mol% [Eu.sup.3+] 1.3 x [10.sup.7] 80
EIMAA
(5.4 mol% acid content)
50% neutralized w/ Na+
EIMAA
(5.4 mol% acid content)
25% neutralized w/ [Zn.sup.2+]
E/MAA
(5.4 mol% acid content)
60% neutralized w/ [Zn.sup.2+]
(*)Secant module via ASTM method D-882(courtesy of the DuPont
Company).


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Author:BELFIORE, LAURENCE A.; RUZMAIKINA, IZOLDA Y.; DAS, PRONAB K.
Publication:Polymer Engineering and Science
Article Type:Statistical Data Included
Geographic Code:1USA
Date:Jul 1, 2001
Words:7054
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