1H and 13C NMR spectra of poly(propyl α-bromoacrylate) and poly(methyl α-bromoacrylate)

The ¹³C NMR spectra measured at 25 MHz of the methyl and propyl esters of isotactic and syndiotactic poly(α-bromoacrylate) were sufficiently resolved to be analysed for pentad tacticity sequences. The pentad tacticity of the syndiotactic polymers prepared with free radical initiators at ?40°C agreed with those calculated for Bernoullian sequence distributions based on P_r values of 0,83–0,87. The tacticities of the isotactic polymers prepared with heterogeneous catalysts were determined on the basis of these assignments. Good internal consistency was obtained between the calculated and observed pentad proportions from the quaternary and carbonyl carbon peaks in the spectra of these polymers. The order of chemical shifts for the meso and racemic dyads and tetrads in these polymers were opposite to those found in the equivalent methacrylate polymers, but as with the latter, the ¹³C-T₁ values were longer in the isotactic than in the syndiotactic polymers.     

Investigation on the microstructure of poly(cyclohexyl α-chloroacrylate)s using 500 MHz 1H and 25 MHz 13C NMR

The tacticity of poly(cyclohexyl α-chloroacrylate) (PCCA) was studied by 500 MHz ¹H and 25 MHz ¹³C NMR spectroscopy. The influence of the polymer configuration was observed at three different carbon resonances: The backbone methylene carbon, the carbonyl carbon and the quaternary carbon. Tetrad tacticities of PCCA measured from the resonance of the backbone methylene carbon were in good agreement with tetrad values obtained by ¹H NMR. The polymer obtained was syndiotactic rich and obeyed Bernoullian statistics in its tacticity distribution.     

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.     

13C cross polarization/magic-angle spinning NMR and infrared spectroscopic study of poly(ε-caprolactam) and of poly(ε-caprolactam)/polystyrene blends

Infrared and ¹³C cross polarization/magic-angle spinning nuclear magnetic resonance (¹³C CP/MAS NMR) spectra and T relaxation times of differently treated poly(ε-caprolactam) 1

1 Systematic IUPAC name: poly[imino(1-oxohexamethylene)].

(PCL) and of poly(ε-caprolactam)/polystyrene blends were measured and the fractions of the α- and α-crystalline and mesomorphous PCL forms were determined. The amounts of the α-form obtained from the infrared and ¹³C CP/MAS NMR spectra are in agreement. In the blends, the fraction of the PCL α-crystalline form is higher as compared with extruded pure PCL. The existence of a single T parameter for PCL in each of the samples indicates small dimensions of the crystalline regions; the obtained T values correspond to the PCL phase composition.     

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.     

1H and 13C NMR determination of the hydroxy end-groups in poly(oxypropylene)s

¹H and ¹³C NMR signals of tri(propylene glycol) and of its benzoate and phenyl urethane were assigned by means of 1D and 2D NMR methods such as super-selective long-range INEPT, H-H COSY, H-C COSY and H-H-C RCT spectra. Both ¹H and ¹³C NMR were used as methods for the determination of primary and secondary hydroxy end-groups and of their degree of conversion. ¹³C NMR was found to be a reliable and universal method of end-group determination even for cases where ¹H NMR fails due to the presence of water in the sample or to the nature of the reactant. The results are applied to the analysis of poly(oxypropylene)s with two or three hydroxy end-groups and their derivatives.     

A novel synthetic route to poly(β-ketone)s via poly(alkoxyethyne)s

Isopropoxyethyne (1a) and tert-butoxyethyne (1b) were polymerized using group 5 and 6 transition metal catalysts to give poly(isopropoxyethyne) (2a) and poly(tert-butoxyethyne) (2b) , respectively. The weight-average molecular weight (M?_w) of the resulting poly(alkoxyethyne)s was up to 1.0 × 10⁴. Among the transition metal catalysts, a tungsten alkoxide or a molybdenum alkoxide having low Lewis acidity were found to effectively promote the polymerization without causing side reactions. Poly(tert-butoxyethyne) was successfully converted to poly(β-ketone) 3 by acid hydrolysis of the tert-butyl vinyl moiety.     

Polymer conformation and NMR chemical shifts, 5 1H and 13C NMR spectra of poly(methyl methacrylate)

Tacticity-dependent splittings observed in ¹H and ¹³C NMR spectra of poly(methyl methacrylate) are elucidated by a theoretical procedure which consists of conformational analysis of the polymer chain and shielding calculation. The conformation is analyzed by the statistical mechanical method combined with the force field energy calculation on the dyad sequence models. As significant shielding factors, diamagnetic, anisotropic, and electrostatic terms are taken into account for the chemical shifts of ¹H NMR, while paramagnetic, diamagnetic, and anistropic terms are considered for ¹³C NMR. The calculation is used to assing the α-methyl proton, methoxyl proton, methylene proton, quaternary carbon, methylene carbon, α-methyl carbon, carbonyl carbon, and methoxyl carbon peaks split due to dyad and triad cotacticities. The results are generally consistent with the observed spectra. Especially, the calculated splitting widths are in quantitative agreement with the observed splittings of the methoxyl and α-methyl protons resonances as well as of the carbonyl and α-methyl carbons resonances. Effects of temperature and stereoregularity on the spectra are also discussed.     

Polymerization of α,α-disubstituted β-propiolactones and lactams, 12. Properties and crystalline structure of poly(β-propiolactam)s

A series of α,α-disubstituted β-propiolactams (substituted nylon 3 polymers) was prepared from non-optically active lactams. Their thermal characteristics, densities, and x-ray fiber diffraction patterns were recorded. One of the α-substituents was always a methyl group while the other was either CH₃, C₂H₅, n-C₃H₇, or n-C₄H₉. The melting point for the dimethyl substituted polymer was 268°C; the others were respectively 76, 74, and 72°C. X-ray fiber diffraction data on all four samples yielded the same fiber repeat of ≈8,4 Å. A minimum energy based conformational analysis for the α,α-dimethyl derivative indicates that two conformations correspond to this repeat, each of which is a 2₁ helix.     

Preparation and 13C NMR spectra of model compounds for poly(4-bromostyrene)

The preparations of 2,4-bis(4-bromophenyl)pentane ( 1b ) and 2,4,6-tris(4-bromophenyl)heptane ( 2b ) are described. The study of the different isomers of 1b and 2b by ¹³C NMR allows a comparison of the various configurational sequences of these compounds in terms of their chemical shifts. Methyl, methylene, and aromatic C¹ carbons of 1b and 2b could be deduced from the values obtained from corresponding polystyrene model compounds by a mere translation. From the aromatic C¹ chemical shifts it was possible to propose an assignment of the corresponding triads of poly(4-bromostyrene).     

Structural analyses of poly(m-xylene-α,α′-diyladipamide) and nylon 66 by 15N solid state NMR

¹⁵N solid state NMR, viz. both ¹⁵N cross polarization (CP) NMR and ¹⁵N CP/magic angle spinning (MAS) NMR, is applied to the structural determination—including molecular orientation—of uniaxially oriented poly(m-xylene-α,α′-diyladipamide) film and nylon 66 fiber on the basis of the chemical shift tensors. In the spectrum of a poly(m-xylene-α,α′-diyladipamide) block sample whose fiber axis was set up parallel to the applied magnetic field, a single main peak with 20% powder pattern (non-crystalline domains) was observed. The small difference in the structure of the main chain between these two uniaxially stretched polyamides was clarified from the chemical shift data of the parallel spectra which reflect the angle between the NH bond and the fiber axis. Determinations of the angles between various molecular-fixed axes and the axis of polymer alignment were tried.     

Propriétés viscoélastiques de la poly(α,α-diéthyl-β-propiolactone)

The viscoelastic properties of poly(α,α-diethyl-β-propiolactone) were investigated in the linear range using stress relaxation and dynamic mechanical methods. Using Ferry's reduction method, a horizontal shift factor was determined at each temperature, that satisfactorily agreed with the WLF equation in the transition zone. No vertical shift was required to superimpose different relaxation curves. The apparent activation energy was temperature dependent and passed through a maximum near T_g whose value is (311 ± 2)K. The relaxation spectrum has been calculated according to the first method of approximation of Schwarzl and Staverman. It consists of a high intensity plateau at shorter times, a wedge type portion with a slope of ?0,15 and a low intensity plateau at longer times. Dynamical mechanical measurements revealed a β relaxation peak at 333 K and yielded the evidence of a γ peak around 120 K.     

13C NMR study of the tacticity of poly(propylene oxide)s prepared by polymerization with α,β,γ,δ-tetraphenylporphyrin/AlEt2Cl as initiator system: An example of first-order markovian statistics in ring-opening polymerization

Racemic and enantiomerically enriched poly(propylene oxide)s were prepared using α, β, γ, δ-tetraphenylporphyrin/AlEt₂Cl as initiator system. Triad tacticity of the polymers was analyzed by ¹³C NMR spectroscopy (62,89 MHz). A predominance of isotactic triads was observed in the case of the racemic polymer, corresponding to a non-random distribution of configurational units in the polymer chain. A model correlating tacticity with enantiomeric excess of starting monomer in the case of a first-order Markovian distribution was established. Good agreement between experimental results and calculated triad contents (according to the model previously described) was observed for enantiomerically enriched polymers. This indicates a steric control by the last unit of the growing chain end. The influence of the size of the substituent was examined for the case of poly(1,2-epoxybutane). The origin of the chain-end effect is discussed.     

Synthesis and characterization of α-hydroxy, α-thiol and α-chloroformyl oligomers of poly(butylene terephthalate)

α-Hydroxy and α-chloroformyl oligomers of poly(butylene terephthalate) (PBT) were prepared in 1,1,2,2-tetrachloroethane by condensing terephthaloyl chloride and 1,4-butanediol and using benzoyl chloride and 4-hydroxybutyl benzoate as chain limitator. The average molecular weight was determined by ¹H NMR analysis, and thermal properties were assessed by differential scanning calorimetry (DSC). Preparation of α-thiol oligomers of PBT was also investigated by esterification of α-hydroxy oligomers with thioglycolic acid and using p-toluenesulfonic acid as catalyst. The DSC and TGA analyses pointed out that the introduction of a thiol group by esterification has no influence on the thermal properties of the PBT oligomers.     

Controlled synthesis of α,β-difunctional poly(hexafluoropropylene oxide)

An improved method is described for the preparation of difunctional poly(hexafluoropropylene oxide) of moderate molecular weight (M _n ≈ 6000) in good yield (>80 wt.-%). With the dependence of chain transfer constant on initiator concentration known, at least under controlled conditions, good molecular-weight control can be achieved.     

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.     

13C NMR studies of thermotropic liquid crystalline poly(γ-alkylaryl L-glutamate)s

The molecular motions of three kinds of poly(γ-alkylaryl L -glutamate)s ( 1 – 3 ) having a phenylene or a biphenylylene group and alkyl groups with various length, containing 6 to 22 carbon atoms, were investigated by means of ¹³C NMR spectroscopy as a function of temperature. The observed range of temperature covers the “crystal-to-liquid-crystal” phase transition temperature, T_m. It was found that these phase transitions are caused by an increase of the motions of aromatic or alkyl groups in the side chain, depending on the samples, and that the motion of main chains of polymers 1 – 3 with α-helical conformation does not occur on the NMR time scale at least up to 160°C. The degree of the mobility of the alkyl chain in the side chain of 1 – 3 depends on their length above T_m.     

Investigation of γ-irradiated syndiotactic poly(2-methylheptyl methacrylate) using NMR spectroscopy

Syndiotactic poly(2-methylheptyl methacrylate) which was γ-irradiated at room temperature to a dose of 1600 kGy was investigated by NMR spectroscopy. The ¹H and ¹³C resonances for the macromolecular chain were assigned by using the 2D and the DEPT (distortionless enhancement by polarization transfer) technique. The spin-echo modified 2D NMR pulse sequence was used to investigate the small molecules and new structures which were formed during γ-irradiation. The radiation mechanisms for cleavage of the side chain from the main chain and formation of double bonds from both the main chain and the side chain have been formulated based upon the NMR analysis.     

Crystallization of polypeptides in the course of polymerization, 7. Crystallization of poly(γ-methyl-L-glutamate), poly(γ-benzyl-L-glutamate) and poly(β-benzyl-L-aspartate)

Heterogeneous polymerizations of γ-methyl-L -glutamate N-carboxy anhydride (NCA), γ-benzyl-L -glutmate NCA, and β-benzyl-L -aspartate NCA were carried out using butylamine as initiator in acetonitrile at 30°C. The oligomer chains formed in the beginning of the polymerization crystallized into the antiparallel β-form and thereafter the α-helical chains grew from the active sites of the β-chains. The polymerization of γ-methyl-L -gultamate NCA proceeded to 100% conversion and accordingly gave rise to high molecular weight poly(γ-methyl-L -glutamate). The polymerizations of γ-benzyl-L -glutamate NCA and β-benzyl-L -aspartate NCA stopped at 54% and 16%, resp. The levelling-off of the conversion at such low values, in spite of the α-helical chain growth, may be due to the occlusion of the active chain ends of the resultant poly(γ-benzyl-L -glutamate) and poly(β-benzyl-L -aspartate) into the crystals. It was concluded that the interlamellar crystallization was induced by the intermolecular interaction between the benzyl groups of the polymer side chains, giving rise to the occlusion of the active growing chain ends into the interstices of the crystal formed during the polymerization.