Microstructure determination of styrene/ethyl acrylate copolymers by NMR spectroscopy and its correlation with glass transition temperature

Styrene/ethyl acrylate (S/E) copolymers of different compositions were prepared by bulk polymerization using benzoyl peroxide as an initiator. Copolymer compositions were determined from NMR spectra and reactivity ratios r₁ and r₂ were calculated using a non-linear least-squares errors-in-variables method (EVM) which gives more reliable values of r₁ and r₂. The copolymerization parameters such as terminal, penultimate reactivity ratios, diad concentrations, conditional probabilities, number-average sequence lengths and run numbers in the copolymers were calculated by evaluating ¹³C{¹H} NMR spectra. The observed sequence concentrations of triads as determined from ¹³C{¹H} NMR spectra were in good agreement with those calculated from the reactivity ratios. The coisotacticity parameter (σ) was calculated from NMR spectroscopy data using the oxymethylene resonance signal in ¹H NMR spectra. The glass transition temperatures (T_g) of various copolymers were obtained from Barton's equation (using diad relation) and are in agreement with those determined by means of differential scanning calorimetry.     

Copolymerization via zwitterion, 5. β-butyrolactone and 2-methyl-2-oxazoline

The zwitterionic copolymerization of 2-methyl-2-oxazoline (MOX) as nucleophilic monomer with β-butyrolactone (BUL) as electrophilic monomer was investigated in bulk and in solution (CH₃CN) at 45°C. The copolymer composition was around 1,5/1,0 (BUL/MOX) as was established by ¹H NMR. ¹H and ¹³C NMR spectroscopy were used to identify the copolymers. The IR spectroscopy supported the NMR results. On the other hand, the copolymers behave as polyelectrolytes, according to viscosity determinations. A copolymerization mechanism through a zwitterion species is suggested.     

Kinetic and Copolymer Composition Investigations of the Free Radical Copolymerization of 1‐Octene with Glycidyl Methacrylate

Kinetic and copolymer composition investigations of the free radical copolymerization of 1‐octene with glycidyl methacrylate are reported. The chemical structure of the obtained copolymers is elucidated by ¹H, ¹³C, heteronuclear single quantum coherence nuclear magnetic resonance (NMR) and infrared spectroscopies. ¹H NMR measurements indicate that a maximum statistical incorporation of 1‐octene in the copolymer chain of 32 mol% is obtained when 90 mol% of this comonomer is used in the initial monomer feed of the copolymerization reaction. Furthermore, the reactivity ratios of this comonomer system are estimated using the obtained experimental data, which are fitted to the integral form of the copolymerization equation utilizing a nonlinear least squares approach. To the best of knowledge, this is the first report on the reactivity ratios of this specific comonomer system. To evaluate the potential of the obtained materials as dispersants, the effect of the polymer concentration on the dispersion of copper nanopowders in organic solvents is studied for a copolymer with a 1‐octene composition of 25 mol%.     

Copolymerization reactivities,electron structure and nuclear magnetic resonance spectra of vinylazoles

Data obtained on the electronic structure of a series of C- and N-vinylazoles using the SCF MO method in MNDO approximation and analysis of the ¹³C and ¹H NMR data as well as their copolymerization reactivity ratios in the copolymerization with styrene have shown individual correlations between the relative activity 1/r (r is the copolymerization reactivity ratio of styrene) and the chemical shifts of the terminal vinyl carbon atoms in ¹³ C NMR spectra, between 1/r and chemical shifts of the protons in trans-position towards the substituent in ¹H NMR spectra, and between 1/r and the net effective charges on the terminal vinyl carbon atoms for each type of monomers considered. The correlations obtained and the analyses obtained from the monomers studied within the modified Alfrey-Price scheme indicate that the reactivity of vinylazoles in copolymerization is mainly influenced by two factors: the acceptor inductive effect of a substituent in the vinyl bond and the conjugation effect. These factors operate in a different manner for C- and N-vinylazoles and determine their different reactivity in radical copolymerization with styrene.     

The influence of molecular interaction on polymerization, 5. Copolymerization of benzyl methacrylate with maleic anhydride

Copolymerization of benzyl methacrylate (BMA) with maleic anhydride (MA), initiated by 2,2′-azoisobutyronitrile at 70°C in chloroform or acetonitrile, were investigated. The complex formation between the two monomers in chloroform was studied by ¹H NMR spectroscopy. The stability constant of the complex was found to be 0,25 l.mol^?1. The following copolymerization reactivity ratios were found: in chloroform: r_BMA = 0,188 ± 0,035 and r_MA = 0,003 ± 0,005, in acetonitrile: r_BMA = 0,116 ± 0,093 and r_MA = 0,231 ± 0,027. By ¹H NMR investigations it could be shown that the results correlate with the changes of the reactivity ratios depending on the solvent used.     

Synthesis and characterization of new siloxane-modified addition polyimides

A new series of polyimides was synthesized by addition polymerization of 4,4′-(bismaleimido)-diphenylmethane, 1,4-piperazine and an amino-terminated polydimethylsiloxane. The synthesis was carried out in m-cresol solution following a two-step procedure. Copolymers containing 15 and 20 wt.-% of the polydimethylsiloxane elastomer were prepared, together with the unmodified base copolymer. Infrared spectroscopy, ¹³C and ¹H NMR, thermal and thermogravimetric analyses were used to characterize the copolymers. The DSC curves of all the samples showed an exotherm in the temperature range 230–280°C, attributable to curing and addition reactions involving the chain-end groups. Different glass transition temperatures (T_g) were observed, depending on the elastomer content. Thermogravimetric analysis indicated that no significant changes occur in the thermal stability of rubber-modified copolymers.     

Copolymerization of ethylene with propene in the presence of Ti-Mg catalysts of different compositions

Comonomer reactivity ratios (from kinetic and ¹³C NMR data), compositional homogeneity of ethylene-propene copolymers, and molecular structure of individual fractions of the copolymers obtained with supported Ti-Mg catalysts of different compositions were determined. The copolymerization reactivity of these systems was found to increase upon introduction of ethyl benzoate and dibutyl phthalate to the catalyst system. It was found that both lowly stereospecific and highly stereospecific catalysts have a broad distribution of active sites with respect to copolymerization reactivity. The composition of the catalysts (titanium content and stereoregulating additives) was shown to influence the reactivity ratios of the comonomers and the microstructure of the copolymers.     

Radically initiated polymerization of a methacryloylamido-terminated saccharide, 2. Copolymerization with 2-hydroxyethyl methacrylate

Kinetics of radically initiated copolymerization of 6-deoxy-6-methacryloylamido-D -glucopyranose (MAG) with 2-hydroxyethyl methacrylate (HEMA) was investigated at 60°C in water using 4,4′-azobis(4-cyanopentanoic acid) as initiator. Reactivity ratios of the binary system were determined to be r_HEMA = 3.50 and r_MAG = 0.60, indicating a strong copolymerization drift as polymerization proceeds. Copolymers with homogeneous composition were prepared using a simple and easy method based on the knowledge of the consumption rate of each monomer. These copolymers were then characterized with regard to composition (by ¹H NMR) and physicochemical properties in aqueous media (using SEC with MALLS and refractometry detection and viscosimetric measurements).     

Zwitterionic Copolymerization of β‐Butyrolactone with Styrene

The hybrid copolymerization of vinyl monomers with cyclic esters endows the formed copolymers new features, such as biodegradability and functionality. However, the recently reported hybrid copolymerizations are mainly based on polar vinyl monomers and cyclic esters catalyzed by organocatalysts. The copolymerization of non‐polar vinyl monomers with cyclic esters is still a challenge. In this work, the copolymerization of β‐butyrolactone (β‐BL) with styrene catalyzed by B(C₆F₅)₃ in the absence of coinitiators is reported. The density functional theory studies suggest the formation of zwitterion between β‐BL and B(C₆F₅)₃. It is found that β‐BL and styrene are concurrently copolymerized through the macro‐zwitterion intermediates. The obtained copolymers are carefully examined by ¹H NMR, 2D ¹H‐¹³C HMBC, differential scanning calorimetry, thermogravimetric analysis, hydrolysis experiments, as well as Brady's reagents.     

Dithiocarbamate telechelic polymers: Synthesis and block copolymerization

The iniferter method of Otsu was studied for the synthesis of polyvinyl block copolymers of relatively low molecular weight using tetramethylthiuram disulfide (TD) and benzyl N,N-diethyldithiocarbamate (BDC) as initiator. Considering the low quantum yield of dissociation (?_d) of TD (2,5 · 10^?3 in cyclohexane), TD was used as thermal initiator (95°C) for the synthesis of dithiocarbamate-polystyrene (TD-PS) telechelics. ¹³C NMR analysis of this TD-PS shows two ¹³C?S signals corresponding to two different end-groups: Et₂N? CS? S? CH(C₆H₅)? CH₂? and Et₂N? CS? S? CH₂? CH(C₆H₅)? . Several styrene polymerizations were also carried out in presence of azoisobutyronitrile (AIBN) as thermal initiator and TD as chain-transfer reagent. Depending on the mole ratio AIBN/TD, mono- and difunctional TD-PS's are formed, as evidenced by NMR analysis. These TD-PS's were used for the photochemical initiations of ethyl acrylate (EA), acrylic acid (AA) and methyl methacrylate (MMA). It is assumed that the quantum yield of dissociation of the dithiocarbamate end-group is equal to that of BDC (?_d : 0,06). TD-PS nonfunctional polymers were also prepared, either photochemically by dissociation of BDC, or thermally in presence of AIBN and BDC as transfer agent. They were used for block copolymerization with MMA. Inversely, TD-PMMA's were prepared in a first step; in this case ?_d = 0,026. They were then used for the polymerization of EA. The block copolymers were fractionated; their composition and molecular weights were determined by ¹H NMR and gelpermeation chromatography, respectively.     

Synthesis of Alkyl‐Substituted Quinoxaline‐Based Copolymers Along with Photophysical Property Modulation for Polymer Solar Cells

A series of alkyl‐substituted quinoxaline‐based copolymers are prepared and their properties are studied. Stille copolymerization of 2,5‐bis(trimethylstannyl)thiophene (M3) with different ratios of 2,7‐dibromo‐9,9‐dioctyl‐9H‐fluorene (M4) and 5,8‐dibromo‐6,7‐difluoro‐2,3‐didodecylquinoxaline (M1) affords five new random copolymers, labeled P1–P5. Suzuki copolymerization of 4,5,5‐tetramethyl‐2‐[2‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐9,9‐dioctyl‐9H‐fluoren‐7‐yl]‐1,3,2‐dioxaborolane (M5) and 5,8‐bis(5‐bromothiophen‐2‐yl)‐2,3‐didodecyl‐6,7‐difluoroquinoxaline (M2) yielded a new alternating copolymer, labeled P6. All copolymers show high thermal stability, and the 5% weight loss temperature is above 400 °C. The estimated optical bandgap (E _g) values of random copolymers P1–P5 (E _g ≈ 1.93, 1.97, 1.97, 2.02, and 2.08 eV, respectively) are found to be relatively lower than that of alternating copolymer P6 (E _g ≈ 2.14 eV). All copolymers P1–P6 exhibit deep highest occupied molecular orbital (HOMO) energy levels, and the determined HOMO levels are ?5.65, ?5.67, ?5.67, ?5.60, ?5.59, and ?5.66 eV, respectively. The maximum power conversion efficiencies of polymer solar cells made with individual copolymers P1–P6 as a donor materials and PC₇₀BM as an acceptor are 3.98, 2.91, 3.33, 3.55, 3.07, and 2.78%, respectively.     

Glycidyl Cinnamate: Copolymerization with Glycidyl Ethers,In-Situ NMR Kinetics,and Photocrosslinking

The copolymerization of glycidyl cinnamate (GC) as a hitherto non-polymerizable, photoreactive epoxide structure to aliphatic polyether copolymers is described, using the monomer-activated epoxide ring-opening polymerization (MAROP). Ethoxyethyl glycidyl ether (EEGE) and GC are copolymerized employing triisobutylaluminum (i-Bu₃Al) as a catalyst and tetraoctylammonium bromide (NOctBr₄) as an initiator. The amount of GC varies from 3 mol% to 100 mol%, which results in apparent molecular weights in the range of 2600 to 4600 g mol⁻¹ and dispersities (Đ) below 1.34. Studies of the microstructure by in-situ ¹H NMR kinetics indicate a gradient-like distribution of EEGE and GC (reactivity ratios: r_EEGE = 0.28; r_GC = 3.6), applying the ideal copolymerization model for evaluation. A tentative explanation relies on differing bond lengths in the respective epoxide rings, as suggested by density functional theory (DFT) calculations. Mild and selective cleavage of the acetal protecting groups of EEGE is achieved using the acidic ionic resin Dowex, leaving the GC ester bonds intact (M_n = 1900–3700 g mol⁻¹, Đ < 1.34). Thermal properties of the copolymers and the PGC homopolymer are investigated by differential scanning calorimetry (DSC). The crosslinking of P(G-co-GC) copolymers by UV irradiation allows hydrogel formation, which is confirmed by IR spectroscopy.     

Determination of the Reactivity Ratios for the Oxidative Copolymerizations of Indene with Methyl,Ethyl and Butyl Acrylates

The copolyperoxides of various compositions of indene with methyl acrylate, ethyl acrylate and butyl acrylate have been synthesized by the free‐radical‐initiated oxidative copolymerization. The compositions of copolyperoxide obtained from ¹H and ¹³C NMR spectra have been used to determine the reactivity ratios of the monomers. The copolyperoxides contain a greater proportion of the indene units in random placement. The NMR studies have shown irregularities in the copolyperoxide chain due to the cleavage reactions of the propagating peroxide radical. The thermal analysis by differential scanning calorimetry suggests alternating peroxide units in the copolyperoxide chain. From the activation energy for the thermal degradation, it was inferred that degradation occurs via the dissociation of the peroxide (O—O) bonds of the copolyperoxide chain. The flexibility of the polyperoxides in terms of glass transition temperature (T_g) has also been examined.     

On the structure of radically obtained maleic anhydride/C4-alkene copolymers

The radical heterophase copolymerization of maleic anhydride ( 1 ) with isobutene ( 2 ), 1-butene ( 3 ) or with a petrochemical C₄-fraction free from butadiene ( C ₄) yielded copolymers with a molecular weight of 424 · 10³, 291 · 10³ and 190 · 10³ g/mol, respectively. The structures of poly( 1 -co- 2 ), poly( 1 -co- 3 ) and poly( 1 -co- C ₄) obtained were elucidated by ¹³C NMR, ¹H NMR and IR spectroscopy. Irrespective of whether 2 , 3 or C ₄ was used as comonomer, the appropriate ¹³C NMR, ¹H NMR and IR spectra proved to be essentially identical. These spectra confirm the presence of the 1,1-dimethylethylene structural units in the repeating units of each of the copolymers investigated. Thus, the radical copolymerization of 1-butene with maleic anhydride is accompanied by a rearrangement within the 1-butene molecule due to hydrogen and methyl shift.     

Radical Copolymerization of α‐Trifluoromethylacrylic Acid with Vinylidene Fluoride and Vinylidene Fluoride/Hexafluoropropene

Summary: The radical copolymerization of α‐trifluoromethylacrylic acid (TFMAA) with vinylidene fluoride (VDF), initiated by tert‐butyl 2,2‐dimethyl peroxypropanoate (or tert‐butyl peroxypivalate) is presented. The kinetics of copolymerization were investigated from a series of eight reactions for which the initial [VDF]₀/[TFMAA]₀ molar ratios ranged between 15.0/85.0 and 89.4/10.6. The compositions of the copolymers, i.e. the molar ratios of VDF and TFMAA monomeric units, were determined mainly by ¹⁹F and ¹H NMR spectroscopy. According to the Tidwell and Mortimer method, the reactivity ratios, r_i, were assessed to be: r_VDF = 0.33 ± 0.09 and r_TFMAA = 0 at 55 °C, leading to copolymers of mainly alternating structure. Then, the radical terpolymerization of TFMAA with VDF and hexafluoropropene (HFP), initiated by 2,5‐bis(tert‐butylperoxy)‐2,5‐dimethylhexane is described and the thermal properties of the materials produced are discussed.

     

15N NMR spectroscopy, 13. Copolymerization of glycine-N-carboxyanhydride and β-alanine-N-carboxyanhydride

In contrast to ¹³C NMR spectra, ¹⁵N NMR spectra allow one to characterize the sequence of copolypeptides built up by glycyl and β-alanyl residues, because the shifts of the Gly-Gly, β-Ala-Gly, Gly-β-Ala, and β-Ala-β-Ala bonds differ from each other by several p.p.m. Hence, the copolymerization of glycine-NCA and β-Alanine-NCA can be investigated by quantitative evaluation of the ¹⁵N NMR spectra obtained from the resulting copolymers. The copolymerization of these two amino acid NCAs initiated by primary amines leads to random sequences; the copolymerization is azeotropic in nature, and both copolymerization reactivity ratio parameters are near 1. If aprotic bases like pyridine and triethylamine are used as catalysts, the rate of incorporation of glycine is higher than that of β-alanine and the copolymers possess a block structure.     

Syntheses and Properties of Novel Copolymers of Poly(1,4‐dioxane‐2‐one) and Aliphatic Polycarbonate Based on Ketal‐Protected Dihydroxyacetone

Novel random copolymers of 1,4‐dioxane‐2‐one (DON) and 2,2‐ethylenedioxy‐1,3‐propanediol carbonate (EOPDC) are synthesized in bulk at 120 °C using Sn(Oct)₂ as a catalyst. The effects of different molar feed ratios of EOPDC/DON on the yield and molecular weight of the copolymers are investigated. The copolymers are obtained with a yield of 55.4–98%. The number‐average molecular weight of the copolymer is 0.49–4.18 × 10⁴ g mol^?1 with a polydispersity of 1.52–1.68. The poly(DON‐co‐EOPDC)s obtained are characterized by FTIR, ¹H NMR, and ¹³C NMR spectroscopy, gel‐permeation chromatography (GPC), and DSC. The hydrolytic degradation of the copolymer in phosphate buffered saline (PBS) is also investigated. The results show that both the hydrophilicity and the degradation rate of the copolymers increase with increasing copolymer DON content.     

The cyclo-copolymerization of diallyl compounds and sulfur dioxide, 5. Copolymerization of some 4-substituted 1,6-heptadiene derivatives with sulfur dioxide

Copolymers of sulfur dioxide with N-substituted 4-(1,6-heptadiene-4-yl)pyridinium chlorides and bromides ( 1 ) and N-substituted 4-(3-butenyl)pyridinium chlorides and bromides, and some other 1,6-heptadiene derivatives 3 substituted in 4-position were prepared. The effects of the copolymerization conditions on the conversions and viscosities of the copolymers were studied and their structures by elemental analyses, IR and ¹H NMR spectroscopy. The thermal stabilities of the copolymers were also examined.     

Synthesis and characterization of polymers bearing pyrazole groups, 1. Methacrylic derivatives

The synthesis of new methacrylic monomers H₂C? C(CH₃)? COOCH₂? G where G is a pyridine, a pyrazole or a bipyrazole group has been achieved. Their homopolymerization was studied and gave fairly low molecular mass polymers. Their copolymerization with styrene gave copolymers tending to be alternating when the bulkiness of group G increased. Moreover, in the presence of Lewis acids the monomers were complexed. With ZnCl₂, they were complexed through nitrogen atoms and were shown to be inactive in copolymerization. With SnCl₄, they were complexed through the carbonyl group and gave alternating copolymers. The homopolymers exhibited low glass transition temperatures (50–76°C) and moderate thermal stability (decomposition begins at ca. 200–280°C and is complete at 550°C). In the copolymers with styrene the thermal properties showed to be improved.     

Potentiometric Behavior of Polyampholytes Based on N,N′‐diallyl‐N,N′‐dimethylammonium Chloride and Maleamic Acid Derivatives

Strongly alternating copolymers (PalH, PalPh, PalPhBisCarb) composed of N,N′‐diallyl‐N,N′‐dimethyl‐ammonium chloride (DADMAC) and maleamic acid derivatives (MAD) are synthesized by a water‐based free radical copolymerization using 4,4‐azobis(4‐cyanovaleric acid) (V501) as the initiator. The structure of the copolymers is verified by ¹H‐NMR, elemental analysis, and thermogravimetric measurements, and the physicochemical properties are investigated by viscometric and potentiometric techniques. Potentiometric titration curves show that the acidity of the carboxylic groups strongly depends on the degree of dissociation and the ionic strength. Since all copolymers behave as polycations at low degree of dissociation, a transition from an extended chain to a coil conformation can be identified by reaching the isoelectric point (IEP).