A collection of solid-state 13C CP/MAS NMR spectra of common polymers

A collection of high resolution solid-state ¹³C NMR spectra was recorded in a standard way employing cross polarization (CP), magic angle spinning (MAS), and high power proton decoupling. The collection will be useful for reference purposes in case of unknown or partly unknown samples such as polymer blends, block copolymers, or polymeric latexes. The collection is available via internet at http://www.mpip-mainz.mpg.de/documents/aksp/spektrensammlung.     

Orientational distribution in stretched poly(methyl methacrylate) from 13C NMR spectroscopy

The orientational distribution in drawn amorphous poly(methyl methacrylate) extended to the ratio λ = 3 was measured with one- and two-dimensional carbon-13 NMR spectroscopy. In the analysis, signals from the carboxyl carbons were used as a probe of the orientational distribution. The angular-dependent line shapes were analyzed to determine the orientational distribution function and the order parameter 〈P₂〉. The analysis yielded 〈P₂〉 = 0,21. A two-dimensional rotor-synchronized magic angle spinning experiment was also used to measure the order parameter. The obtained value 〈P₂〉 = 0,22 is in excellent agreement with the 1D result. The experimental results obtained for 〈P₂〉 are compared to those proposed by the pseudo-affine model. 〈P₂〉 predicted by theory is reduced due to conformational disorder present in the glassy state.     

Secondary structure of peptides, 14. FT-IR and 13C NMR CP/MAS investigation of the helix stability of solid poly(L-proline)s

Primary amine and pyridine-initiated polymerizations of L-proline-N-carboxyanhydride (Pro-NCA) at 20 or 100°C yield exclusively or predominantly 10₃-helices. Only primary amine-initiated polymerizations in 1,4-dioxane at 100°C result in partial formation of 3₁-helices. The stability of both 10₃- and 3₁-helices against conformational transitions was investigated in various organic non solvents or salt solutions at 100 or 150°C. A 10₃ → 3₁ transition was only observed in protic non solvents such as formamide, water, or propionic acid, but not in alcohols. A 3₁ → 10₁ helix transition was observed in alcohols and most aprotic solvents but not in formamide, water, or propionic acid. Hence, it is concluded that the formation of 3₁ helices by primary amine-initiated polymerizations in 1,4-dioxane at 100°C is a kinetically controlled consequence of the reaction mechanism. The usefullness of ¹³C NMR CP/MAS spectra and Fourier-Transform IR spectra for the quantitative analysis of composed secondary structures is compared and discussed.     

Stereoregularity of poly(methyl vinyl ketone) and poly(isopropenyl methyl ketone) determined by 13C NMR spectroscopy

¹³C NMR spectra of poly(methyl vinyl ketone)s (PMVK) and poly(isopropenyl methyl ketone)s (PIPMK) obtained by radical and anionic catalysts were measured. The ¹³C resonances of the CH₂ carbon of PMVK were tentatively assigned to diad tacticities. The spectra of carbonyl carbon and methyl carbon of the CH₃CO group of PIPMK were assigned to pentad and triad tacticities, respectively. It is shown that radically obtained PMVK and PIPMK have atactic and syndiotactic-rich structure, respectively. The stereoregularity of radically obtained PIPMK obeys Bernoullian statistics, while that of anionically obtained PIPMK conforms to first-order Markov statistics.     

Determination of the microstructure of poly(chlorophenyl methacrylates) by 13C NMR spectroscopy

Poly(chlorophenyl methacrylate)s with varying number and positions of the chloro substituent were prepared and investigated using ¹³C NMR spectroscopy. The tactic sequence distribution was determined from the signals of the carbonyl carbon (pentads) and the α-methyl carbon atoms (triads). It was found that the polymers are predominantly syndiotactic with an average sequence length of between 3 and 4. The isotactic sequences accounted for a very small fraction of the polymer chain with an average sequence length of between 1,3 and 1,5. As for the signals of the aromatic carbon atoms it could be demonstrated that, depending on the substitution pattern of the aromatic ring, the sensitivity on sequence distribution was more or less pronounced.     

Secondary structure of peptides, 10. FT-IR and 13C NMR CP/MAS study on tacticity and secondary structure of poly(D,L-leucine)s

A series of poly (L -leucine)s with average degrees of polymerization in the range between 10 and 100 and various poly (D,L -leucine)s were prepared by polymerization of L -leucine-N-carb-oxyanhydride (NCA) or D,L -Leu-NCA. The FT-IR spectra measured in KBr show that the amide I and II bands are exclusively sensitive to the secondary structure of the poly (leucine)s and not to their tacticity. The tacticities of the poly(D,L -leucines) were determined in solution of trifluoroacetic acid by means of ¹³C NMR spectra, while ¹³C NMR CP/MAS spectra of the solid polymers revealed that the poly(D,L -leucine)s contain 40 – 60 wt.- % α-helix structure. For this reason the broad amide I and II bands do not enable one to distinguish isotactic and more or less atactic poly(leucine)s. However, the IR-bands between 500 and 900 cm^?1 allow a differentiation between poly(L -leucine) and poly(D,L -leucine)s and also between poly(D,L -leucine)s of different tacticity. The IR-spectra confirm that primary amine-initiated polymerizations of D,L -Leu-NCA do not lead to long stereo blocks.     

The 13C NMR spectra of poly(1-pentenylene) and poly(1,3-cyclopentylenevinylene)

¹³C NMR spectra were obtained for polymers made by ring-opening polymerization of cyclopentene and bicyclo[2.2.1]hept-2-ene respectively. The fraction of cis double bonds could be determined with much greater precision from ¹³C NMR spectra than from IR spectra and varied from 0,66 to 0,31 for the samples of poly(1-pentenylene), ( 2 ), and from 1,0 to 0,14 for the samples of poly(1,3-cyclopentylenevinylene), ( 4 ). This is the first time an all-cis polymer of 4 has been reported. The spectra of 2 showed a cis (upfield) and trans (downfield) peak for each of ?CH and α-CH₂, but only one peak for β-CH₂. The spectra of 4 showed multiple fine structure, the main splittings corresponding to a cis (upfield) and trans (downfield) peak for α-CH, and a reverse line order for the other three carbons; subsidiary splittings were observed for all but the olefinic carbons, interpreted in terms of sensitivity of the chemical shifts to the cis/trans structure at the next nearest double bond. A complete interpretation of the line orders in 4 is given in terms of steric compression effects. The possibility that ring tacticity accounts for some of the fine structure cannot be entirely discounted. The stereochemistry of 4 is discussed in relation to the four possible modes of addition of monomer to a carbene chain carrier during polymerization.     

Investigation of poly(arylenevinylene)s, 24. High-resolution solid-state 13C NMR spectroscopy of poly(1,4-phenylenevinylene)s

High-resolution ¹³C NMR spectra of solid poly(1,4-phenylenevinylene), poly(1,4-phenylene-1,2-diphenylvinylene) and of three related, substituted polymers (? CN, ? OCH₃, ? O? ) were obtained with a combined technique of heteronuclear decoupling, cross-polarization and magic angle spinning. The reported chemical shifts were assigned by means of solid model compounds (trans-stilbene, trans, trans-1,4-distyrylbenzene, tetraphenylethylene). Utilizing the high sensitivity of ¹³C NMR chemical shifts to chemical structure, this method is applied to structure confirmation, the determination of sp³-defects in poly(phenylenevinylene)s PPV, and the determination of sterical and electronical effects of phenyl and phenylene groups.     

Synthesis and characterization of dextran grafted with poly(N‐isopropylacrylamide‐co‐N,N‐dimethyl‐acrylamide)

Graft copolymers consisting of dextran as a main chain and poly(N‐isopropylacrylamide‐co‐N,N‐dimethylacrylamide) (poly(NIPAAm‐co‐DMAAm)) as graft chains were synthesized. For the synthesis of the graft copolymers, a semitelechelic poly(NIPAAm‐co‐DMAAm) with an amino end‐group was obtained by radical copolymerization with ethanethiol as a chain transfer agent, followed by a coupling reaction of its hydroxyl end‐group with ethylenediamine. Graft copolymers with various length of the grafts were obtained from coupling reactions between carboxymethyl dextran and poly‐(NIPAAm‐co‐DMAAm) in the presence of a water‐soluble carbodiimide. The graft copolymers in phosphate buffer exhibit lower critical solution temperatures due to thermosensitivity of their grafts. There is no significant change in the hydration‐dehydration behavior of the poly(NIPAAm‐co‐DMAAm) chain after the grafting reaction. The existence of such grafts in dextran may play an important role for modulated degradation in synchronization with temperature.     

Sequencing analysis and study of substituent effects in aromatic poly(amide-thioether)s by 13C NMR spectroscopy

Poly(amide-thioether)s with different microstructures are studied by ¹³C NMR spectroscopy. Alternating copolymers with head-to-head or tail-to-head arrangement of amido groups in the chain give quite different NMR spectra which are assigned. The spectra of statistical copolymers exhibit resonances which are not present in the spectra of alternating copolymers due to the existence of new triads. The study of chemical shift differences between the alternating copolymers and copolymers with 4-iminobenzoyl, terephthaloyl or 1,4-diiminophenylene units show that these sequencing effects are transmitted through ? S? links but not through ? CONH? links. This was explained by the participation of the sulfur atom in the mesomeric system of the two neighbouring 1,4-phenylene groups.     

13C NMR spectroscopy of 2-formamido-2-methylpropyl acrylate and poly(2-formamido-2-methylpropyl acrylate)

The synthesis and characterization of 2-formamido-2-methylpropyl acrylate (FMPA) is reported. ¹³C NMR spectra of FMPA in CDCl₃, CD₃OD, DMSO-d₆, DMF-d₇, and D₂O exhibit two pairs of lines for all seven carbon atoms at room temperature; the ratio of the two conformers varies moderately with solvent (21 : 79 to 41 : 59). The conformers are believed to involve strong internal hydrogen bonding which is not completely broken even by the addition of trifluoroacetic acid to CDCl₃ (1/1, v/v). However, the pairs of lines coalesce in turn as the temperature is raised to 120°C in DMSO-d₆. FMPA was polymerized at 35°C in DMF and CHCl₃, using a free radical initiator and the polymer was characterized by ¹³C NMR spectroscopy.     

Poly(allylamine)‐graft‐poly(N‐isopropylacrylamide)/Poly(styrene sulfonate) Sodium Salt Multilayers: Buildup,Wettability, and Mechanical Properties

Poly(allylamine)‐graft‐poly(N‐isopropylacrylamide) (PAH‐g‐PNIPAAm)/poly(styrene sulfonate) sodium salt (PSS) multilayer films are prepared using electrostatic layer‐by‐layer assembly. Buildup of the PAH/PSS and PAH‐g‐PNIPAAm/PSS multilayers under different salt concentrations and different temperatures is compared by using ellipsometry and scanning force microscopy. All the film thicknesses increase linearly with the increase of layer number regardless of their assembly conditions. However, the average layer thickness of the PAH‐g‐PNIPAAm/PSS multilayers is larger than that of the PAH/PSS multilayers under the same assembling conditions. Their surfaces also become rougher and show higher water contact angles. In contrast to the apparent loss transition in the friction force curve of the PAH/PSS multilayers, the PAH‐g‐PNIPAAm/PSS multilayers with PAH‐g‐PNIPAAm as the outmost layer do not undergo a pressure‐induced glass transition in water. Nanoindentation tests show that the elastic modulus of the PAH‐g‐PNIPAAm/PSS multilayers is only 75% of that of the PAH/PSS multilayers.

     

13C NMR spectra of poly(alkyl α-chloroacrylate)s

¹³C NMR spectra of isotactic and syndiotactic poly(ethyl α-chloroacrylate)s and poly(isopropyl α-chloroacrylate)s were measured in toluene-d₈ at 25 MHz. The spectra were analyzed for triad, tetrad and pentad tacticities comparing the spectra with the results previously obtained by ¹H NMR spectroscopy. Tetrad tacticities of the polymers were measured from the resonance of the backbone methylene carbon and favorably compared with tetrad values obtained by ¹H NMR. The resonance of the carbonyl carbon showed the peaks corresponding to the tactic triad with a pentad splitting in mm resonance. The triad values obtained from the carbonyl carbon resonance were in good agreement with those calculated from the tetrad values as well as the triad tacticities obtained by ¹H NMR. The quaternary carbon reconances were very complicated because the chemical shift differences for the different tactic triads were of the comparable magnitude with those for the pentads, and a tentative peak assignment was made with the aid of the statistical calculation of pentad values assuming first-order Markovian statistics for the isotactic polymer and Bernoullian statistics for the syndiotactic polymer.     

13C NMR spectroscopical sequence analysis of poly(ethylene terephthalate-co-oxybenzoate)s

The sequence distribution of liquid-crystalline poly(ethylene terephthalate-co-oxybenzoate)s was determined by ¹³C NMR spectroscopical investigations of samples with different compositions. All possible oxybenzoate- and terephthalate-centered triads could be identified and assigned. The analysis of NMR substituent effects confirms the assignment. The comparison of the calculated statistical with the experimentally determined triad distribution shows a tendency for the formation of oxybenzoate blocks in the polymer chain.     

13C NMR relaxation studies of poly(vinyl alcohol) and its derivatives

Spin-lattice relaxation times (T₁) have been measured by ¹³C NMR for poly(vinyl alcohol), poly(vinyl benzoate), poly(vinyl cinnamate) and poly(vinyl acetate) in dimethyl sulfoxide as a function of temperature and concentration. As expected, T₁ increases with increasing temperature and decreases with increasing polymer concentration. The influence of the microstructure (tacticity) of the polymers on the relaxation times is negligible. T₁ for the methine carbon of the polymer main chain is observed to serve as a measure of the rigidity and/or mobility of the chain. Assuming isotropic motion of the polymer chains, the activation energies for the protonated carbons were determined using the calculated correlation times.     

13C NMR spectroscopic analysis of poly(electrolyte) cement liquids.

13C NMR spectroscopy has been applied to the analysis of carboxylic poly-acid cement liquids. Monomer incorporation, composition ratio, sequence statistics, and stereochemical configuration have been considered theoretically, and determined experimentally, from the spectra. Conventionally polymerized poly(acrylic acid) has an approximately random configuration, but other varieties may be synthesized. Two commercial glass-ionomer cement liquids both contain tartaric acid as a chelating additive but the composition of their poly-acids are different. Itaconic acid units, distributed randomly, constitute 21% of the repeating units in one of these polyelectrolytes.     

Stabilization in Water of Polymer/Cu2+ Complexes Using Poly(sodium acrylate)‐graft‐poly(N,N‐dimethylacrylamide) Graft Copolymers

The formation of complexes between Cu²⁺ ions and graft copolymers built from a PANa backbone and non‐ionic hydrophilic PDMAM side chains is investigated by means of turbidimetry, viscometry, DLS, ζ‐potential measurements, and UV‐vis spectrophotometry. The macroscopic phase separation which accompanies complexation is gradually depressed with increasing PDMAM content x, and water‐soluble complexes are formed for x = 70 mol‐%. The polymer/Cu²⁺ complexation is a charge neutralization process that leads to the formation of water‐soluble, compact, hybrid polymer/metal ion nanostructures. UV‐vis data indicate that this graft copolymer could possibly serve as a water‐soluble sensor for Cu²⁺ ions.

     

13C NMR chemical shifts and stereochemical structures in poly(vinyl chloride)

The ¹³C NMR chemical shifts of triad and tetrad configurations in poly(vinyl chloride) have been calculated by the average excitation energy approximation using the CNDO/2 MO method. On the basis of these calculations, both Inoue's and Carman's assignments for the observations of the triad and tetrad configurations have been examined and the partial discrepancy between them ascribed to the solvent effect. Further, the tacticity dependences of the calculated chemical shifts for triad and tetrad configurations are discussed.