Determination of unsaturated end groups in low molecular weight poly(vinyl chloride) by 1H NMR spectroscopy of the hydroxyphenyl substituted product

Poly(vinyl chloride) of low molecular weight (the fraction extracted with a hexane/acetone mixture (vol.-ratio 3:2)) was substituted by hydroxyphenyl groups and then analyzed by ¹H NMR spectroscopy. It was established that the ¹H NMR spectra of hydroxyphenyl substituted poly(vinyl chloride) prepared by removal of HCl, allows to determine the number of unsaturated end groups and to distinguish between the structures ? CHCl? CH₂? CH?CH? CH₂Cl and ? CH₂? CHCl? CH?CH? CH₂Cl, and even between their trans and cis forms. In addition the ¹H NMR spectra of hydroxyphenyl substituted poly(vinyl chloride) prepared without removal of HCl allow to determine the total number of unsaturated end groups.     

Bulk polymerization of styrene and methyl methacrylate using tetraphenylbisphosphine as an initiator

In this study a controlled polymerization of styrene (S) and methyl methacrylate (MMA) with tetraphenylbisphosphine (TPhBP) as the initiator in bulk was carried out, using UV light as the energy source. The yield of polymerization was up to 15% for PS and up to 62% for PMMA. TPhBP is decomposed to form ∗︁PPh₂ radicals, or is oxidized to form bisphosphine oxide. Only non-oxidized TPhBP initiates the photo-polymerization. For S and MMA an insignificant portion of photo- and thermal-polymerization was detected. In the presence of oxygen the phosphine end-groups of the polymer are oxidized to —PO(Ph)₂ groups. The molecular weights of PMMA were determined from ¹H NMR spectra and the molecular weights of PMMA and PS were determined by gel permeation chromatography (GPC) measurements. With increasing concentration of the initiator the molecular weight decreases and at a high concentration of the initiator the molecular weight decreases with conversion. The polydispersity decreases with increasing concentration of TPhBP. Termination occurs by combination of primary radicals ∗︁PPh₂, by combination of macroradicals, and by chain transfer to the initiator. Because of different types of termination the ratio between the tail —CH₂P(Ph)₂ and the head —C(CH₃,COOCH₃)P(Ph)₂ groups is about 4 to 1, and decreases with increasing concentration of the initiator.     

The effect of crosslinking in elastomers investigated by NMR analysis of 13C edited transverse 1H NMR relaxation

The transverse nuclear ¹H magnetization decay in poly(styrene-co-butadiene) (SBR) is investigated by editing ¹³C NMR spectra. This technique allows for the assignment of localized ¹H dynamical information by discriminating the chemical sites based on their chemical shift in the ¹³C dimension. Here, the homo- and heteronuclear dipolar couplings contribute to the ¹H NMR relaxation giving additional information to a homonuclear experiment. In this heteronuclear 2D experiment two prominent peaks are observed in the ¹³C dimension, which correspond to CH and CH₂ groups, respectively. The decay rate in the ¹H dimension is found for both groups to scale with the crosslink density. An additional ultra-fast magnetization decay is reported. The effect of the carbon black filler is investigated for this component. The analysis of the ¹³C NMR edited transverse ¹H magnetization relaxation is a useful tool in combining high resolution NMR spectra with information on molecular dynamics, providing insight into crosslink density and filler effects.     

Aliphatic-aromatic polyamide-imides from diisocyanates, 1. 1H and 13C NMR study of polymer structure

The reaction of a diisocyanate and an asymmetric aliphatic-aromatic diacid containing a preformed imide group was studied in order to obtain polyamide-imides. It is shown in this paper that combined ¹H and ¹³C NMR spectrometry will permit the quantitative evaluation of the proportions of head-tail, head-head, tail-tail additions, provided the content of urea in the polymer is low. In order to obtain unequivocal assignments and to thoroughly characterize the NMR spectra of the polymer, several model compounds resembling the polymer backbone were synthesized. A model polymer was synthesized with the same purpose, and its ¹H and ¹³C NMR spectra fully assigned. Unexpected chemical functions in the polymer, like urea and carboxylic acid, can also be easily detected and quantified by NMR.     

The solid state 13C NMR studies of intermolecular hydrogen bonding formation in a blend of phenolic resin and poly(hydroxyl ether) of bisphenol A

The formation of intermolecular hydrogen bonds in blends of novolac type phenolic and poly(hydroxyl ether) of bisphenol A was investigated by studying its T_g behavior, excess volume, and solid state ¹³C NMR spectra. The T_g and parameters of solid state ¹³C NMR, such as the T_CH and spin‐lattice relaxation time in the rotating frame T^H_1ρ, indicate that the London dispersion force (entropically favored) significantly affects the intermolecular hydrogen bonding of the blend. The phenoxy chain forces opening of the intra‐association of phenolic and thus creates more free OHs. This strong entropic effect reduces the total hydrogen bonding of the system, especially when one of the polymer is the minor component. This also results in the reduction of T_g and free volume expansion, reflecting in the increase of cross‐polarization (C—H) time and molecular mobility within the phenolic/phenoxy blend.     

Sodium Poly(α,L‐glutamate)/Ethylene Oxide‐Propylene Oxide (Block and Random) Copolymer Macromolecular Complexes. Method of Preparation and Structure of Complex

Macromolecular complexes of sodium poly(α,L ‐glutamate) (PGNA) (molecular weight (MW) 1, 49 and 71 k) and ethylene oxide‐propylene oxide tri‐block copolymer (MW 8 400) have been prepared by a novel method involving dehydration of reverse micelles (DRM method). This series of complexes was compared with the complexes of PGNA (MW 1, 49 and 71 k)/ethylene oxide‐propylene oxide random and tri‐block copolymers prepared by the common method involving evaporation of aqueous mixtures (EAM method). By the DRM process fifteen times more copolymer was incorporated in the pure macromolecular complex than by the EAM process. CD spectra of the EAM series of complexes showed formation of α‐helical PGNA conformation as evidenced by the observation of +ve peak at 194 nm and two –ve peaks at 201 and 221 nm. Formation of the α‐helical conformation is further supported by FT‐IR spectroscopy. On the other hand, CD spectra of the DRM macromolecular complexes showed neither α‐helical nor random conformation, and the spectra may be attributed to a distorted helical PGNA conformation. DSC studies revealed that the copolymers in EAM macromolecular complexes were intimately blended with PGNA, while in the DRM series only 65% of the copolymer were blended at the molecular level, with the rest present as a pure copolymer domain. ²³Na NMR spectra of both series of complexes showed presence of free sodium ions indicative of dissociated Na⁺—O dipolar interactions in aqueous solution. Hydrophobic interaction between PGNA and copolymer remained intact even in very dilute solutions of both series of complexes as observed by strong 2D‐NOESY ¹H NMR correlation between β and γ CH₂ groups of PGNA and CH₂ groups of copolymers. However, in the DRM series, only the CH₂ groups of PEO blocks of the PEO‐PPO‐PEO copolymer showed the 2D‐NOESY ¹H NMR correlation indicating that only the PEO blocks are involved in the complex formation. The PPO block that had no interaction with PGNA may have formed pure PPO domains. NMR data combined with the DSC, CD and FT‐IR data suggest that the structure of both series of macromolecular complex is a composite composed of copolymer molecules intimately interacting with PGNA chains. Interactions between β and γ groups of PGNA side groups with CH₂ groups of the copolymer are involved in forming the complex. 2D‐NOESY ¹H NMR correlation further indicate that both the DRM and EAM series of macromolecular complexes are stable in water for at least seven weeks.     

Characterization of the structure of the stereocomplex of poly(methyl methacrylate) in solution from NMR relaxation data

From the values of relaxation times T₂ determined on a pulse spectrometer, and from the shape of bands in high resolution (HR-) and broad line (BL-) NMR spectra, two types of protons, different in mobility, were found to exist in the associated stereocomplex of isotactic (it-) and syndiotactic (st-) poly(methyl methacrylate) (PMMA). From the analysis of NMR spectra, measured at magic angle rotation (MAR-NMR), the mobility of the ester groups in the stereocomplex is shown to be greatly hindered. Temperature changes of HR-NMR spectra of mixed solutions of it- and st-PMMA in benzene indicate that the associated segments of the stereocomplex can be characterized as junctions of a network of nonassociated sequences.     

Internal mobility of PMMA in concentrated CDCl3 solutions, 2. 13C NMR spectra

The ¹³C NMR relaxation parameters (T₁, line widths and NOE factors) were measured and analyzed for two samples of atactic poly(methyl methacrylate) (PMMA) of molecular weight M_w 4,20·10⁴ and 1,76.10⁶ in CDCl₃ solutions in the concentration range 11 to 54% (by weight) of polymer, at 297 and 323 K. By this analysis it was found that the backbone segmental motion of PMMA is spatially isotropic in the whole measured concentration range; the motion of the α-CH₃ group may be approximated by the double reorientation model; the motion of the ester CH₃ group can be approximated by the isotropic model only at concentrations lower than 12%; in more concentrated solutions, a satisfactory approximation is obtained neither by the isotropic, nor by the double reorientation models. The reasons of this behaviour are discussed.     

Synthesis and radical polymerization of allenyl ethers with oligo(oxyethylene) moieties

Synthesis and radical polymerization of allenyl ethers with oligo(oxyethylene) moieties ( 1a–1c : CH₂?C?CH? O? (CH₂CH₂O)m? CH₃, m = 3 ? 1) were examined. The polymerization of 1a (m = 3) in bulk with 2,2′-azoisobutyronitrile as initiator at 60°C gives the polymer 2a in 51% yield with 75% of the double bonds remaining in the polymer chain (estimated by ¹H NMR). The polymers 2a–2c are hydrophilic, soluble in protic solvents such as water and methanol, and are subject to crosslinking upon storage in the air.     

NMR investigation of UV‐cured vinyl ether networks

The structure of the networks obtained by UV curing of the triethylene‐glycol divinyl ether (DVE3) and its mixtures with diethylene‐glycol monovinyl ether (HDVE2) was investigated by high resolution ¹H and ¹³C NMR spectroscopy. By working in swelled systems, signals with good resolution were obtained and were assigned to the different structures. The signals attributable to the CH₃ end groups of the poly(vinyl ether) together with the CH₂ and CH groups of the chain could be distinguished. The CH₃ groups signal is stronger in the case of the DVE3/HDVE2 mixture as a consequence of the chain transfer reaction. Hydrolysis reactions occur in the systems giving rise to the formation of acetaldehyde and aldehydic end groups.     

End-group characterization of poly(methylphenylsilane) by alkali metal salts doped MALDI-TOF mass spectra

The end groups of a sample of poly(methylphenylsilane) (PMPS) obtained by the Wurtz coupling reaction of diorganodichlorosilane were characterized by MALDI-TOF mass spectrometry. Three fractions were obtained by fractionation of a PMPS sample with methanol, in order to get information on the distribution of end groups as a function of the molecular weight. The MALDI mass spectra of these fractions showed well-resolved signals up to 2500 Da corresponding to open chain oligomers of PMPS bearing four different types of end groups:  Si (CH₃)₃,  O Si (CH₃)₃,  O CH₃,  H. Six different types of linear oligomers were identified together with a sizeable amount of cyclic oligomers, most likely generated during the polymerization step. The problem of isobar mass series in the MALDI spectra due to clusters of oligomers with Li⁺, Na⁺, K⁺ was solved by comparing the MALDI spectra of PMPS fractions with and without the addition of a specific alkaline salt (KCl or Nal) to the solution containing the sample and matrix. The intensity of the oligomer clusters with the specific cation were enhanced with respect to the others. The mass shifts observed in the MALDI-TOF doped spectra with respect to the undoped ones allowed the unambiguous assignments of the isobar peaks corresponding to PMPS oligomers.     

Coordination polymerization of lactides, 1. Structure determination of obtained polymers

Racemic lactide was polymerized with various initiators containing Zn and Al, and the structures of the obtained polymers were determined by means of ¹³C NMR spectroscopy. The extent of transesterification reactions was calculated on the basis of the analysis of the methine carbon signal in the polymer ¹³C NMR spectra. Three groups of initiators can be distinguished in view of their influence on transesterification: ZnCl₂ exhibits the strongest transesterification activity, ZnEt₂ and ZnEt₂/Al(OiPr)₃ are among those of medium activity, and Al(acac)₃ does not show transesterification activity at all.     

Molecular dynamics of new thermoplastic elastomers based on hydrogen bonding complexes: a deuteron nuclear magnetic resonance investigation

4-(4-Carboxyphenyl)-3,5-dioxo-1,2,4-triazolidin-1-yl moieties resulting from 4-(3,5-dioxo-1,2,4-triazolin-4-yl)benzoic acid (U4A) randomly attached to 1,4-polybutadiene form supramolecular aggregates which act as effective junction zones in new thermoplastic elastomers. Deuteron nuclear magnetic resonance (²H NMR) spectroscopy was used to investigate the molecular dynamics of the polymer backbone and the junction zones in selectively labelled samples. The spectra show motional heterogeneity along the polymer chain as well as in the supramolecular domains. Polybutadiene segments which are adjacent to these polar clusters are restricted in their mobility, even at temperatures 100 K above the glass transition temperature T_g. The immobilized regions are estimated to involve about two monomeric units. The functional groups in the supramolecular structures are rigid or exhibit 180° -phenyl flips dependent on their location in the middle or in the edges, respectively. Polar units which are not enclosed in the clusters and dispersed in the polymer matrix undergo fast isotropic motions.     

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 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.     

2H NMR study of solvent and solute mobility in polymer solution,gel and glass states

²H spin relaxation times, T₁ and T₂ and solid echo line shapes were investigated in 2-propanol (2-POH) solutions of poly(butyl methacrylate) (PBMA) in a wide concentration and temperature range, covering the solution, gel and glass states. From the results in deuterated 2-POH-d₆ we found that the polymer influence upon solvent mobility is largely suppressed in the gel and glass states in contrast to normal polymer solutions where below the glass transition an increasing amount of solvent slows down with decreasing temperature. From ²H NMR of deuterated butyl side groups in the PBMA-d₉/2-POH system we found that the side group motion is anisotropic and largely independent of solvent concentration in the gel and glass states which confirms that polymer-polymer interaction via side group interpenetration should be considered as the main cause for gel formation in this system.     

Polymer conformation and NMR chemical shifts, 9. Poly(α-methylene-γ-butyrolactone)

The conformational energies of poly(α-methylene-γ-butyrolactone) are calculated and compared with those of poly(methyl methacrylate). In spite of the structural resemblance of these two polymers, the patterns of the energy contour maps are clearly distinguishable from each other; the energy barriers between rotational isomeric states are appreciably higher in the former than in the latter polymer. The calculation indicates large non-bonded interactions between the protons in one lactone ring and those in the adjacent lactone rings. The broad NMR spectrum of poly(α-methylene-γ-butyrolactone) apparently reflects its rigid conformational structure. ¹H and ¹³C NMR chemical shifts are calculated by theoretical shielding calculations based on conformational analysis. Much lower magnetic field resonances of the O? CH₂ and α-CH₂ carbons in poly(α-methylene-γ-butyrolactone) as compared with those of the O? CH₃ and α-CH₃ carbons in poly(methyl methacrylate) are well reproduced by the calculation. The shift to lower magnetic field is mainly attributed to paramagnetic shielding derived from the interaction between O? CH₂ carbon and α-CH₂ carbon. Tacticity- and conformation-dependent ¹H and ¹³C NMR chemical shifts of poly(α-methylene-γ-butyrolactone) are well interpreted on the basis of the conformational analysis.     

On‐Line SEC‐NMR Analysis of the Stereocomplex of Uniform Isotactic and Uniform Syndiotactic Poly(methyl methacrylate)s

Mixtures of uniform isotactic (it‐) and uniform syndiotactic (st‐) 46mers of methyl methacrylate (C₂₃₄H₃₇₈O₉₂; molecular weight (M) = 4 663) in acetone/acetone‐d₆ at –15°C were analyzed by size exclusion chromatography coupled to 750 MHz ¹H NMR spectroscopy (on‐line SEC‐NMR). Each SEC‐NMR chromatogram of the mixtures showed two elution peaks corresponding to the stereocomplex and the dissociated 46mers. When a detection temperature (the temperature of the flow NMR cell) was adjusted to the column temperature of –15°C, SEC‐NMR spectra of the stereocomplex showed significant broadening of resonances due to the restricted segmental mobility of polymer chains. On the other hand, a detection temperature of 45°C permitted us to observe the it‐ and st‐sequences in the OCH₃ and α‐CH₃ resonances as well‐resolved signals. The st‐/it‐compositions of the stereocomplex were determined to be 1.61–1.94. Accordingly, at least two types of stereocomplexes with different compositions (e. g. st‐/it‐ = 1/1 and 2/1) should coexist in the mixtures. Both the complexes with 1/1 (M = 9 326) and 2/1 (M = 13 989) compositions were suggested to have the hydrodynamic volumes corresponding to that of it‐PMMA with M ≈ 7 000. Multivariate curve resolution was successfully applied to the post‐analysis of the SEC‐NMR experiments to extract component‐resolved spectra of the complex and the dissociated 46mers.     

Radical Copolymerization of N‐Vinylformamide with Methylvinylketone: An Approach to Iminium/Imine Ring Containing Polymers

The free radical copolymerization of N‐vinylformamide (NVF) with methylvinylketone in water and the subsequent alkaline or acidic hydrolysis produce iminium structures containing polymers. It can be concluded from the copolymerization parameters (r_{N ‐vinylformamide} = 0.02, r _{methylvinylketone} = 0.50) that alternating copolymers are formed which contain few amounts with statistically arranged monomer sequences. The acidic hydrolysis of the copolymer results in a water‐soluble polymer bearing five‐membered iminium rings along the polymer chain. A water‐insoluble polymer is generated under alkaline conditions also containing five‐membered imine rings. The formation of the iminium ring polymer is attributed to the fact that generated free amino groups derived from NVF immediately react with the keto groups in the vicinity. The molecular structures of the obtained polymers are characterized by ¹H‐NMR, ¹³C‐NMR, and IR spectroscopy. The assignment of the signals in the novel polymers are confirmed by model compounds.     

Solid-state 13C nuclear magnetic resonance studies of side-group conformations in the rigid-rod polyester poly[1,4-phenylene 2,5-bis(hexadecyloxy)terephthalate]

The ¹³C solid-state NMR spectra of the aromatic polyester 1 with flexible hexadecyloxy side chains are measured at temperatures below and above its solid-solid phase transition in order to study the conformation of the side chains. The signals due to the CH₂ carbons reflect the ratio of trans and gauche conformations at the various positions along the chain. An increase in the gauche content was observed towards the end of the side chain in both phases, however, in the low temperature phase the spectra are dominated by all-trans sequences. The solid-solid transition, as detected by differential scanning calorimetry corresponds to a large increase in the gauche content at all positions on the side chain, except near to the rigid polymer backbone. Above the solid-solid transition a small residual concentration of all-trans sequences was detectable.