Assignment of 13C nuclear magnetic resonance spectra of poly(methacrylonitrile)

¹³C Nuclear magnetic resonance (NMR) spectra of atactic and syndiotactic-rich poly(methacrylonitrile) (PMAN) were determined. In addition, 2D (¹H-¹³C COSY)

1 COSY = COrrelated SpectroscopY.

NMR spectra of α-methyl and methylene regions of atactic PMAN were measured. Values of tetrads and pentads were calculated from triads obtained from α-methyl carbon absorptions of the samples. By comparing calculated values with the observed ones, and by taking 2D NMR spectra into consideration, both α-methyl carbon and proton absorptions were assigned by pentads, and methylene carbon absorptions by tetrads (partly by hexads).     

1H and 13C NMR Full Assignment of a Series of Precursor Polymers Derived from the Sulfinyl Route Towards Poly(p‐phenylene vinylene)

A series of precursor polymers towards poly(p‐phenylene vinylene) is analyzed by different complementary NMR techniques. Resonance assignments were achieved by the use of one‐ and two‐dimensional NMR techniques, such as ¹H, ¹³C, APT, 2D‐HETCOR, FLOCK, COSY and INADEQUATE. The series consists of the sulfinyl precursor poly[p‐phenylene(1‐butylsulfinyl)ethylene] and the derived sulfanyl (poly[p‐phenylene(1‐butylsulfanyl)ethylene] and sulfonyl derivative (poly[p‐phenylene(1‐butylsulfonyl)ethylene]). Chiral induction during polymerization of sulfinyl monomers was quantified by high resolution ¹³C NMR.     

NMR evidence of the block structure of poly(methyl methacrylate)-block-poly(ethyl acrylate) prepared by group transfer polymerization

The structure of poly(methyl methacrylate)-block-poly(ethyl acrylate) prepared by group transfer polymerization was studied by ¹H and ¹³C 1 D and 2D NMR methods including SINEPT, COSY, LR H-H-C RELAY and COLOC using model homopolymers of methyl methacrylate (MMA) and ethyl acrylate (EA) of a length equal to that of the blocks and prepared under the same conditions. The ¹H and ¹³C spectra of the copolymer are shown to be a superposition of the respective spectra of the homopolymers, with the exception that the copolymer lacks the terminal group present in the MMA homopolymer and the initiating group of the EA polymer. Moreover, a new minor signal is found in the CH₂ region of the copolymer which is shown to belong to the link of the blocks. The existence of a direct link between the blocks is further supported by the results of 1D and 2D coherence transfer methods, especially, those using the newly modified DS INEPT and H-C-C RELAY pulse sequences.     

Polylactones, 24. Polymerizations of racemic and meso-D,L-lactide with Al?O initiators. Analyses of stereosequences

Racemic D ,L -lactide and meso-D ,L -lactide were polymerized with four different initiators: Al(isopropoxide)₃, AIEt₃/neopentyl alcohol (1 : 1, mole ratio), AIEt₃/(+)-menthol (1 : 1, mole ratio) and methylaumoxane. Most polymerizations were conducted in xylene at 60, 90 and 120°C, but at 60°C the yields were below 10%. ¹H NMR end-group analyses revealed the formation of alkyl ester end-groups from all Al-alkoxide initiators, in agreement with an insertion mechanism. The highest molecular weights were obtained with the methylalumoxane initiator. The stereosequences of the isolated poly(D ,L -lactide)s were analyzed by ¹H and ¹³C NMR spectroscopy on the basis of tetrad effects. poly(D ,L -Iactide)s prepared from racemic D ,L -lactide suggest a stereospecific polymerization favoring syndiotactic growing steps. In the case of meso-D ,L -lactide all polymerizations follow Bernoullian statistics. Transesterification is poor or absent at temperatures ≤ 120°C. However, random stereosequences may be obtained by bulk polymerizations at 180°C. DSC measurements revealed that the glass transition temperature mainly depends on the molecular weight and not on slight differences in the stereosequences.     

Use of controlled radical polymerization of butadiene with AIBN and TEMPO for the determination of the NMR characteristics of hydroxymethyl groups

The controlled radical polymerization of butadiene initiated with 2,2′-azoisobutyronitrile (AIBN) and in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) is presented. The produced oligomers which have number average degrees of polymerization ranging between 3 and 12 were characterized by NMR. This led to the determination of both the end-groups and the functionality. The hydrolysis of these oligomers yields α-hydroxy-ω-cyano-polybutadiene. ¹³C and ¹H NMR spectra of these products exhibit two characteristic signals of hydroxymethyl groups. The mechanism of the polymerization allows the assignments to cis- and trans-CH₂CH=CH—CH₂OH groups. In fact, this method also shows that geraniol end-groups are negligible in commercially available products obtained by the polymerization initiated with hydrogen peroxide.     

Haloaldehyde polymers, 34. 1H and 13C NMR spectra of chloral oligomers prepared by lithium tert-butoxide initiation and the assignment of the meso/racemo addition products of the dimers

¹H and ¹³C NMR spectra of the mixture of chloral oligomers prepared by initiation with lithium tert-butoxide were examined in detail. ¹H and ¹³C NMR signals due to meso and racemo diastereomers of the dimer fraction were unequivocally assigned through the ¹³C-¹H COSY spectrum and the ¹³C NMR spectra with low-power selective ¹H-decoupling. The two-dimensional NOESY spectrum showed correlation peaks between the signals due to the methine (acetal) protons of the neighbouring chloral monomeric units of the most abundant isomers in the trimer and tetramer fractions. The ¹H NOE enhancements and ³J_CH coupling constants were measured for the dimers; the results confirmed the meso/racemo assignments based on earlier conformational analysis.     

NMR Characterization of Carbazole‐Substituted Norbornene Comonomer 9‐(Bicyclo[2.2.1.]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) and Poly(ethylene‐co‐BHMCZ) Copolymer

Carbazole‐substituted norbornene comonomer 9‐(bicyclo[2.2.1.]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) can be copolymerized with ethylene using the [Ph₂C(Ind)(Cp)ZrCl₂] catalyst and methylaluminoxane (MAO) cocatalyst system. The microstructures of BHMCZ comonomer and of ethylene–BHMCZ copolymer containing 4.6 mol‐% BHMCZ units in the chain were characterized by one‐dimensional ¹³C DEPT and two‐dimensional homonuclear ¹H‐¹H COSY and heteronuclear ¹H‐¹³C HXCO NMR spectroscopy. The BHMCZ comonomer appears as endo and exo stereoisomers, which were identified on the basis of chemical shifts, signal multiplicities, and coupling in the 2D NMR spectra. The NMR information on the BHMCZ isomers was used to assist in the determination of the chemical shifts and microstructure of ethylene–BHMCZ copolymer. The NMR analysis of ethylene–BHMCZ copolymer indicated that exo‐BHMCZ polymerizes with ethylene slightly more readily than does endo‐BHMCZ under the polymerization conditions employed.

Isolated segments of exo(2)‐exo(5)‐exo(6) and endo(2)‐exo(5)‐exo(6) ethylene‐BHMCZ copolymer showing carbon atom numbering.     

New polymer syntheses, 81 . Poly(3-oxybenzoate) randomly branched with 3,5-dihydroxybenzoic acid or 5-hydroxyisophthalic acid

Randomly branched (hyperbranched) Poly(3-hydroxybenzoate), poly(3-Hybe), was prepared by polycondensation of silylated 3-acetoxybenzoic acid with either silylated 3,5-diacetoxybenzoic acid or bis(trimethylsilyl) 5-acetoxyisophthalate. The number of branching points was varied by changing the feed ratio of difunctional and trifunctional monomers. ¹H NMR and ¹³C NMR spectroscopy proved the nearly random incorporation of the trifunctional “branching units”. Cocondensations with small amounts of acetylated bisphenol-P allowed one to control the degree of polymerization (DP) and to determine the DP by ¹H NMR spectroscopy. However, analogous copolycondensations with silylated 2-(4-tert-butylphenoxy)terephthalic acid failed. According to GPC measurements, weight-average molecular weights above 10⁵ were obtained. DSC measurements revealed that the glass transition temperatures (T_g's) vary largely with the degree of branching (DB) and with the nature of the end-groups. In the case of phenolic OH and acetate end-groups, the relationship T_g vs. number of branching points passes through a minimum.     

Living ring‐opening polymerization of cyclic carbonates mediated by bulky titanium bisphenolates

Dichlorotitanium {2,2′‐methylenebis(6‐tert‐butyl‐4‐methylphenolate)} ( 2 ) brought about living homopolymerization and copolymerization of cyclic carbonates with 6‐ and 7‐membered rings to give the corresponding polycarbonates with narrow molecular weight distribution. ¹H and ¹³C NMR studies of the polycarbonates obtained by 2 showed the presence of terminal hydroxy groups at both polymer ends, although no signals assignable to a chlorobutyl group or bisphenolate group were observed. ¹H and ¹³C NMR spectroscopy of the polymerization system showed that the cyclic carbonate molecule is coordinated to the titanium complex, whereas the structure of the titanium complex was almost unchanged throughout the polymerization. The polymerization is considered to proceed via a nucleophilic attack of hydroxy groups at the polymer ends on the cyclic carbonates activated by 2 .     

One-step synthesis of functional polymers by polycondensation: Polyesters with pendant hydroxyl side groups from potassium malate or tartrate and 1,4-dibromobutane

Polyesters with pendant hydroxyl side groups such as (R,S)- and (S)-poly(tetramethylene malate)s and (R,R)-poly(tetramethylene tartrate)s of moderately high molecular weights were prepared by polycondensation, at 105°C in 1-methyl-2-pyrrolidone for 16 to 80 h, from potassium malate or tartrate and 1,4-dibromobutane. It was shown by a detailed analysis of the ¹H and ¹³C NMR spectra of the prepared polyesters that no branching occurs in the course of the reaction. The nature of the end-groups was also clearly established by NMR spectroscopy. The presence of large cycles in the final products cannot be completely excluded.     

Assignment of finely resolved 13C NMR spectra of poly(methyl methacrylate), 2. Methylene carbon

The ¹³C methylene carbon absorptions of poly(methyl methacrylate) with a random structure were assigned in terms of tetrad sequences using the 2D COSY (¹H-¹³C) NMR spectrum and by comparison with the absorptions of isotactic-rich and syndiotactic-rich poly(methyl methacrylate)s. The rrr, rmr and mmr tetrads were further assigned in terms of hexad sequences.     

Synthesis of Novel Polymers via ROMP of Benzyne-Derived Monomers and Their NMR Spectroscopic Properties

Dehydrohalogenation of 1,4-dihalobenzenes and 1,2,4-trichlorobenzene is performed using n-BuLi to form benzynes. These benzynes are used as dienophiles in a Diels–Alder reaction with the dienes furan and 2,5-dimethylfuran to prepare new benzonorbornadiene derivatives. The cycloadducts of furan are polymerized by a ring-opening metathesis reaction using a Hoveyda–Grubbs ruthenium catalyst. The polymers are characterized by ¹H NMR (nuclear magnetic resonance), and unambiguous proton chemical shift assignments are based on the multiplicity pattern of proton resonances. This is confirmed by 2D NMR data from HSQC(Heteronuclear Single Quantum Coherence) and COSY (Correlation Spectroscopy) spectra. The polybenzonorbornadienes have both cis and trans conformation in their chemical structure. The trans conformation is qualitatively in greater proportion observed at ¹H NMR experiments. These materials may have syndiotactic microstructure by the lack of correlations in COSY.     

Addition of the 1-cyano-1-methylethyl radical to α-methylstyrene

1-Cyano-1-methylethyl end-groups in copolymers of α-methylstyrene (MST) with methyl methacrylate (MMA) and with styrene (STY) have been examined by ¹³C NMR; the end-groups have been derived from initiators suitably enriched with carbon-13. It has been shown that at 60°C MST closely resembles STY in reactivity towards the 1-cyano-1-methylethyl radical. MST is 1,89 times as reactive as MMA towards the radical at 40°C; the corresponding factors at 60 and 100°C are 1,69 and 1,55, respectively. There is no evidence for reversibility in the reaction of MST with the 1-cyano-1-methylethyl radical.     

Synthesis of end-functionalized polymers by means of living anionic polymerization, 3. Synthesis of polystyrene and polyisoprene with 1,3-butadienyl termini by reaction of their anionic living polymers with 6-bromo-3-methylene-1-hexene

Both polystyrenes and polyisoprenes with 1,3-butadienyl end-groups were synthesized by the reactions of polystyryl and polyisoprenyl anions with 6-bromo-3-methylene-1-hexene ( 3 ). The 1,3-butadienyl end-group was further transformed to an anhydride function by Diels-Alder reaction with maleic anhydride. These end-functionalized polymers were characterized by size exclusion chromatography (SEC), infrared spectroscopy, elemental analysis, ¹H and ¹³C NMR, and thin layer chromatography coupled with a flame ionization detector. All analytical deta indicate that the polymers are quantitatively end-functionalized with 3 and then with maleic anhydride. Polymers with one or two end-functions are obtainable.     

Poly(arylazophosphonate)s: New Arylazophosphonate‐Containing Monomers for Synthesis of Laser‐Structurable Polymers

In this paper we report the preparation of new hydroxy‐functionalized arylazophosphonate‐containing monomers for the synthesis of poly(arylazophosphonate)s by means of a polycondensation reaction with suitable comonomers (e. g., isocyanates, acid chlorides). The monomers were synthesized from hydroxy‐functional diazonium salts and bifunctional phosphoric diesters via N—P coupling reactions. Six new monomers were synthesized, and in addition four poly(arylazophosphonate)s have been prepared by polycondensation techniques using diisocyanate comonomers. Monomers, as well as polymers, were characterized by common methods such as ¹H, ¹³C and ³¹P NMR, FT‐IR and UV/visible spectroscopies, DSC and GPC measurements. In addition, an example of the polymer structuring via laser ablation with a XeCl excimer laser is given.     

Synthesis and Characterization of Novel Alcohol‐Soluble Ladderlike Poly(silsesquioxane)s Containing Side‐Chain Hydroxy Groups

Two novel kinds of alcohol‐soluble ladderlike poly(silsesquioxane)s containing side‐chain hydroxy groups ( OH‐T₁ and OH‐T₂ ) were prepared successfully for the first time by hydrolysis of ladderlike poly(silsesquioxane)s with side‐chain ester groups ( Ester‐T₁ and Ester‐T₂ ), which were synthesized by stepwise coupling polymerization. A variety of characterization methods including FT‐IR, ¹H NMR, ¹³C NMR, ²⁹Si NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vapor pressure osmometry (VPO), gel permeation chromatography (GPC), and X‐ray diffraction (XRD) were combined to demonstrate that the obtained alcohol‐soluble polymers have ladderlike structures, although some structural defects still existed.     

Influence of thionoesters on the degree of polymerization of styrene,methyl acrylate,methyl methacrylate and vinyl acetate

The aromatic thionoester 3 (benzyl thionobenzoate) was an effective chain transfer agent in polymerizations of styrene (C_x = 1,0) and methyl acrylate (C_x = 1,2) at 60°C. This activity was close to the ideal for obtaining narrow molecular-weight distributions in batch polymerizations. The thionoester 3 showed no activity in polymerizations of methyl methacrylate, but was too reactive to be useful in vinyl acetate polymerizations. Ring-substituted thionoesters 9-11 and 14 and ¹H NMR spectroscopy of the resulting polymers were used to establish the type and quantity of end-groups. The thionoester 12 was used to produce low-molecular-weight polystyrene that was terminated at one end with a hydroxy group and at the other end by a thioloester moiety.     

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.     

Assignment of finely resolved 13C NMR spectra of polyacrylates

¹³C NMR spectra of poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA), poly(isopropyl acrylate) (PIPA), poly(butyl acrylate) (PBA), and poly(isobutyl acrylate) (PIBA) with various tacticities were determined. It was found that methine carbon resonances of PIPA split into triad sequences and those of PEA, PBA and PIBA show a mm triad at high field. Methylene carbon spectra of polyacrylates were assigned in terms of hexad sequences using HECTOR (¹³C-¹H COSY) spectra.     

Polylactones 26. Lithium alkoxide-initiated polymerizations of L-lactide

Lithium alkoxide-initiated polymerizations of L -lactide were conducted in toluene at 50°C. The initiator solutions were prepared in situ from butyllithium and benzyl alcohol, 1-tetradecanol, diethylene glycol monobutyl ether or poly(ethylene glycol) monomethyl ether. These lithium alkoxides initiate the polymerization via nucleophilic attack, forming alkyl ester end-groups as evidenced by ¹H NMR spectroscopy. High yields, high molecular weights and a relatively high optical purity (up to 95%) of the isolated poly(L -lactide) may be obtained.