Polymer conformation and NMR chemical shifts, 8. Monomer- and stereo-sequence dependences of 13C NMR spectrum of poly(methyl acrylate-co-styrene)

The ¹³C NMR spectra of poly(methyl acrylate-co-styrene) are interpreted by a theoretical procedure which consists of conformational analysis of the random copolymer chain and shielding calculation. The conformational probabilities of the diad sequences constituting poly(methyl acrylate-co-styrene) are calculated by a matrix method which is conducted by the statistical mechanics of polymer chains. All the elements of the matrices are determined by the force field method. As significant shielding factors for ¹³C nuclei, paramagnetic, diamagnetic, and anisotropic terms are taken into account. The calculation is used to assign the observed split peaks for the carbonyl carbon and methoxyl carbon in the copolymer. A good agreement between calculation and observation of the peak splittings due to the distribution of the monomer sequence as well as that of the stereo sequence was obtained by considering the feasibility of rotational isomerization at the side chain ester group in two successive MA units.     

Polymer conformation and NMR chemical shifts, 6. Alternating copolymer of α-methylene-γ-butyrolactone with styrene

In view of the structural resemblance of α-methylene-γ-butyrolactone to methyl methacrylate, conformation and NMR chemical shifts of poly(α-methylene-γ-butyrolactone-alt-styrene). are calculated and compared with those of poly(methyl methacrylate-alt-styrene). The conformational energy surfaces for the dyad sequence models of the both copolymers are analogous to each other, as is expected from the similarity in the constituting monomeric units. Agreement of calculation with observation is satisfactory with respect to the cotacticity-dependent splittings in the ¹³C NMR spectra and is improved by the fixation of a substituent in poly(α-methylene-γ-butyrolactone-alt-styrene). Calculation of ¹H chemical shifts gives an alignment of NMR signals which is in accordance with the observation.     

Calculation of domain sizes in block copolymers with broad interphase

The domain dimensions of poly(styrene-b-isoprene) diblock copolymers with polyisoprene spheres in a continuous polystyrene matrix, in which the interphase is broadened by a random poly(isoprene-co-styrene) copolymer block, are significantly smaller than in unmodified block copolymers. The depression of domain sizes and the reduced exponent of the molecular weight dependence in these systems are calculated on the basis of Helfand's theory in which the surface and the conformational entropy were appropriately modified. The domain dimensions of unmodified block copolymers, for which hitherto larger than experimental radii were predicted by the original theory, are also in good agreement if calculated by the proposed phenomenological approach.     

Polymer conformation and NMR chemical shifts, 4. Contrast of 13C NMR spectra between poly(methyl acrylate-alt-styrene) and poly(methyl methacrylate-alt-styrene)

The presence of the α-methyl group in the alternating methyl methacrylate-styrene copolymer produces a remarkable difference in its ¹³C NMR spectra as compared with the spectra of the alternating methyl acrylate-styrene copolymer; cotacticity-dependent splittings occur only in the former spectrum. A theoretical interpretation was attempted for this characteristic spectral variation in terms of the calculated time-averaged chemical shifts for carbons in the dyads constituting the alternating copolymers. Each (meso or racemic) dyad sequence is considered to exist in several conformational states which are mutually exchanging rapidly and the probabilities of which are determined by a statistical mechanical procedure. The calculation of cotacticity-dependent chemical shifts is conducted for the side chain carbonyl, aromatic C¹ and methoxyl carbons as well as for some main chain carbons to give good agreement with the observed peak splittings, especially with respect to the side chain carbons. In accordance with the reported assignment, the calculated differences in shielding factors between meso and racemic dyads for the side chain carbons of poly(methyl methacrylate-alt-styrene) are positive, i.e. the meso or isotactic peak appears at higher field than the racemic or syndiotactic peak. Furthermore, the resulting values are relatively large (≈0,63 ppm) in conformity with the experiment. The calculation for the carbons in poly(methyl acrylate-alt-styrene) gives a very small shielding difference (?0,04 to 0,06 ppm) by the dyad cotacticity, being consistent with the observation, i. e. absence of peak splittings.     

Sequence distribution and glass transition of vinyl alcohol/n-alkyl vinyl carbonate copolymers

¹³C NMR spectroscopy was used for the determination of the sequence distribution in vinyl alcohol-ethyl vinyl carbonate copolymers prepared by reaction of poly(vinyl alcohol) with ethyl chloroformate. The ¹³C NMR spectra of the methylene carbons in the main chain show three split peaks whose intensities change with copolymer composition. These peaks can be assigned to the three dyad sequences. The obtained results show that ethyl vinyl carbonate units have an alternating tendency in the copolymer chain. The T_g values of the vinyl alcohol-ethyl vinyl carbonate and vinyl alcohol-butyl vinyl carbonate copolymers are influenced by both the overall copolymer composition and the monomer sequence distribution.     

Polymer conformation and NMR chemical shifts, 2. Methoxyl protons NMR spectra of alternating copolymers of methyl (meth)acrylate with (α-methyl)styrene

¹H NMR spectra of alternating copolymers of methyl acrylate with styrene, methyl acrylate with α-methylstyrene, and methyl methacrylate with α-methylstyrene show triplet splittings at the methoxyl protons regions, which apparently reflect the cotacticity of triad sequences having a (meth)acrylate unit in the center. The two intervals between two neighboring peaks of the triplet are nearly equivalent for each alternating copolymer, whereas the absolute value of the splitting width is significantly different from one alternating copolymer to another. A theoretical interpretation is given for this observation by calculating the chemical shifts of the methoxyl protons in combination with a conformational analysis of the copolymers. The chemical shift of the protons in meso or racemic type dyad sequence is assigned by averaging the shieldings over all the preferred conformations for the dyad and is accumulated to give the shifts in triad sequences: iso = meso + meso, hetero = meso + racemic, syndio = racemic + racemic. The cotacticity-dependent splittings thus calculated are quantitatively in accordance with the observed spectra and discussed in terms of conformational variation of the copolymers depending on the presence of α-methyl group(s) in neither, either, or both of the monomeric unit(s).     

Enzymes in polymer chemistry, 6. Lipase-catalyzed acylation of comb-like methacrylic polymers containing OH groups in the side chains

The enzymatically catalyzed acylation of poly[N-(2-hydroxypropyl)-11-methacryloylaminoundecanamide-co-styrene] and the corresponding monomer was performed in the presence of a lipase, with vinyl acetate, phenyl acetate, 4-fluorophenyl acetate and phenyl stearate as acylating agents. The kinetics of the enzymatically catalyzed reaction was followed by ¹H NMR spectroscopy and correlated with sterical and chemical effects. The reactivity of monomer towards acylation is higher than that of the copolymer, and that of the copolymer depends on copolymer composition, pointing at steric and hydrophobic effects.     

Le poly(α-acétoxystyrène) et les copolymères de l'α-acétoxystyrène avec le styrène et styrènes substitués obtenus par polymérisation thermique. Etude de la microstructure et de la stabilité thermique des polymères

The microstructure of poly(α-acetoxystyrene), prepared from α-acetoxystyrene by bulk thermal polymerization, was studied by ¹H and ¹³C NMR spectroscopy. Anomalies observed in the NMR spectra could be ascribed to fragmentations with formation of benzoxy and acetoxy radicals followed by re-initiation. The thermal degradation of the polymer, resulting in the formation of polyphenylacetylene, rules out certain types of transfer. α-Acetoxystyrene was copolymerized with styrene or substituted styrenes and the NMR study (¹H and ¹³C) was limited to α-acetoxystyrene. The composition of the copolymer could be ascertained by means of the resonances of the quaternary carbons of the aromatic cycle. The copolymers were characterized by viscometry, GPC, and thermal degradation. Their compositions, except that of poly(α-acetoxystyrene-co-styrene) were determined by elemental analysis.     

Copolymers of L- and D,L-lactide with 6-caprolactone: synthesis and characterization

L - and D ,L -lactide copolymers with 6-caprolactone were synthesized and characterized in a wide range of compositions. The polymerizations were carried out in batch at 130°C, with Sn(II) octoate as a catalyst, a monomers/initiator mole ratio of 5000/1 and a reaction time of 48 h. The copolymers having from 5 to 40 wt.-% of 6-caprolactone are characterized by higher values of non-reacted monomers and deviations of the polymer composition from the feed ratio. In the same interval of compositions, L -lactide copolymers showed progressive hardening with time at room temperature, attributable to the tendency to crystallization of homopolymeric sequences. This behaviour was more deeply studied in the case of poly(L -lactide-co-6-caprolactone) with 30 wt.-% of 6-caprolactone. ¹H NMR at 300 MHz appeared to be a suitable method for the determination of the monomer sequence.     

Preparation and properties of new photo-functional polymers, 1. N-substituted maleimide/styrene copolymers containing pendant para-nitrobenzyl groups

A new photo-functional copolymer was designed by etherification or esterification of poly-[N-(4-hydroxyphenyl)maleimide-co-styrene] or poly[N-(4-carboxyphenyl)maleimide-co-styrene] with p-bromomethylnitrobenzene using 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) as the base in an aprotic solvent. The chain-stiffening effect of the N-substituted maleimide group provided good thermal stability. It was observed that the photosensitivity of the copolymer is enhanced by the addition of a base like tributylamine.     

Block copolymers of narrow molecular-weight distribution with a side-chain liquid-crystalline polymeric block as one component

Syntheses of block copolymers have been undertaken by photo-polymerization of 6-{4-[4-(butoxyphenoxy)carbonyl]phenoxy}hexyl methacrylate ( 1 ) using the living propagating chain end of poly(methyl methacrylate) as an initiating species. The latter was derived from photo-polymerization of methyl methacrylate (MMA) in the presence of methyl(5,10,15,20-tetraphenylporphinato)aluminium. The polymerization of 1 proceeded from the propagating end of poly(MMA) with high blocking efficiency to produce poly(MMA)-block-poly( 1 ) with narrow molecular-weight distribution. The length of the block chain could be controlled by varying the amounts of monomers. An endothermic peak of the block copolymer with higher mass of liquid-crystalline chain was observed at almost the same temperature region as that of poly( 1 ) on differential scanning calorimetric analyses, which suggests that the former has a structure with microphase separation.     

Ethylene‐co‐Norbornene Copolymers Grafted Carbon Nanotube Composites by In Situ Polymerization

Vinyl functionalized multiwalled carbon nanotubes (MWCNT‐vinyl) are synthesized and used as monomers to prepare poly(ethylene‐co‐norbornene)‐grafted carbon nanotube composites by in situ polymerization with [Ti(η⁵‐C₅Me₅)(N?C^tBu₂)Cl₂] activated with methylalumoxane (MAO). The glass transition temperatures (T_g) of grafted MWCNT composites are more than 30 °C higher than those of copolymers. This difference is rationalized by the immobilization of the copolymer chain to the MWCNT surface by a covalent bond. The Young's modulus is shown to increase by more than 200% compared to poly(ethylene‐co‐norbornene) by incorporating 3.4 wt% functionalized MWCNT.     

Etude diélectrique de deux copolymères du méthylcyanure de vinylidène avec le 4‐fluorostyrène et le 4‐chlorostyrène

The dielectric properties of 2 copolymers poly[(methyl vinylidene cyanide)‐co‐(4‐chlorostyrene)] and poly[(methyl vinylidene)‐co‐(4‐fluorostyrene)] have been studied. These products are chiefly alternating and have relatively high glass transition temperatures, respectively at 145°C and 160°C. α relaxation phenomena have been characterised around to these temperatures. The values of dielectrical increment Δε have been calculated and compared to those of similar copolymers synthesized from vinylidene cyanide with various substituted styrenes. The low values are due to the steric effect of the bulky aromatic cycles. The orientation abilities of CN dipoles decrease comparatively to that of the copolymer of vinylidene cyanide with vinylacetate and this could explain the low piezo or pyroelectric properties.     

Polymer conformation and NMR chemical shifts, 3. Calculation of conformational energies on alternating acrylate-styrene copolymers

Conformational energies of meso and racemic dyads of four alternating copolymers composed of methyl methacrylate or methyl acrylate with styrene or α-methylstyrene are computed by an empirical force field method as a function of the rotational angles about the skeletal bond pair within each of the dyads. The patterns of the energy contour surfaces of poly(methylacrylate-alt-styrene) and poly(methyl methacrylate-alt-α-methylstyrene) resemble respectively those of the corresponding homopolymers, i.e. poly(styrene) or poly(methyl acrylate) and poly(α-methylstyrene) or poly(methyl methacrylate). On the other hand the energy maps of poly(methyl methacrylate-alt-styrene) and poly(methyl acrylate-alt-α-methylstyrene) containing an α-methyl group in either of the monomeric units, greatly differ from those of the homopolymers of the component monomers. For all the alternating copolymers, the ? state is more than 5 kcal/mol higher in energy than the lowest energy state, as it was for the homopolymers. The cutoff distance, employed as a tentative measure of the solvent effect in the calculation of nonbonded interaction, gives a significant effect on the conformational energy, especially of the meso-tt state. Bond interaction parameters for various pairs of substitutents in the copolymers are evaluated from the calculation and they are compared with those determined from the conformational analysis of the homopolymers to check whether or not they are generally applicable to conformational analysis of polymers. Furthermore, conformational probabilities are calculated by the matrix method using the data of the energy calculation.     

Synthesis,Characterization and In Vitro Cytotoxicity of Poly[(5‐benzyloxy‐trimethylene carbonate)‐co‐(trimethylene carbonate)]

The ring‐opening copolymerization of 5‐benzyloxy‐trimethylene carbonate (BTMC) with trimethylene carbonate (TMC) was described. The polymerization was carried out in bulk at 150°C using stannous octanoate as initiator. The influence of reaction conditions such as polymerization time and initiator concentration on the yield and molecular weight of the copolymers were investigated. The poly(BTMC‐co‐TMC)s obtained were characterized by FT‐IR, ¹H NMR, ¹³C NMR, GPC and DSC. NMR results of copolymer showed no evidence for decarboxylation occurring during the propagation. The relationship between the copolymer glass transition temperature and composition was in agreement with the Fox equation. The in vitro cytotoxicity studies of the poly(BTMC‐co‐TMC) (50 : 50) using 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay demonstrated that the copolymer has low cytotoxicity compared to poly[(lactic acid)‐co‐(glycolic acid)] (75 : 25).     

Triblock copolymer based thermoplastic elastomeric gels of a large service temperature range: preparation and characterization

Poly(methyl methacrylate)-block-polybutadiene-block-poly(methyl methacrylate) (MBM) triblock copolymers and their hydrogenated counterparts with poly(ethylene-co-1,2-butylene) midblock (MEBM) were swollen by an aliphatic oil of high boiling point which is a selective solvent for the central block. Thermoreversible gels are accordingly formed by both MBM and MEBM copolymers above a critical polymer content (Cr), which depends on the nature of the midblock and not on the copolymer molecular weight, at least in the investigated range. Cr has been found to be 5 wt.-% for an MBM block copolymer and 2 wt.-% for MEBM copolymers of various molecular weights. Gels of MEBM triblock copolymers exhibit interesting mechanical properties, such as high elongation at break (up to 870%) and high tensile strength (32 kPa). The most interesting feature of the MEBM gels is an upper service temperature as high as 170°C, thus more than 100°C higher than the value (47°C) reported for gels of an SEBS copolymer (S = polystyrene) of comparable molecular weight (100000) and composition (ca. 30 wt.-% hard block). The morphology of MEBM gels was studied by scanning electron microscopy (SEM) and found to be cocontinuous in case of a gel containing 20 wt.-% copolymer.     

On‐line coupling of gradient‐HPLC and 1H NMR for the analysis of random poly[(styrene)‐co‐(ethyl acrylate)]s

Random poly[(styrene)‐co‐(ethyl acrylate)]s can effectively be analysed with respect to the chemical composition distribution by on‐line coupled HPLC/¹H NMR. The separation of the copolymers is conducted on a reversed‐phase column using acetonitrile/tetrahydrofuran as the eluent mixture. Via on‐line coupling, the chromatographic peaks are directly transferred into the NMR spectrometer and analysed on‐flow. Information on the chemical composition and the chemical heterogeneity of copolymers with high conversion is obtained. The experiments have been carried out using conventional HPLC‐grade solvents and no deuterium lock. The results of the on‐line HPLC/¹H NMR investigation have been correlated with a HPLC procedure based on calibration with narrow‐distributed copolymer standards.     

Influence of the block length on the structure of micelles formed by polystyrene-block-poly(ethylene-co-propene) in octane and 5-methyl-2-hexanone

The influence of molar mass and chemical composition of the copolymer on the structural parameters of copolymer micelles was investigated. Two polystyrene-block-poly(ethylene-co-propene) copolymers with the same polystyrene block length but different poly(ethylene-co-propene) length were used. The micelles were studied in solutions of octane and 5-methyl-2-hexanone, selective solvents for poly(ethylene-co-propene) (PEP) and polystyrene (PS) blocks, respectively. Static light scattering and viscosity measurements were carried out in order to determine the weight-average molar mass, radius of gyration, second virial coefficient and hydrodynamic radius of the micelles. The association number of the micelles depends on the location of the largest copolymer block in the micelle structure. An influence of the copolymer structure on the micelle dimensions was also found.     

The Synthesis of Liquid Crystalline Copolymers with Block Copolymer Grafts

The synthesis of novel copolymers consisting of a side‐group liquid crystalline backbone and poly(tetrahydrofuran)‐poly(methyl methacrylate) block copolymer grafts was realized by using cationic‐to‐free‐radical transformation reactions. Firstly, photoactive poly(tetrahydrofuran) macroinimers were prepared by cationic polymerization of tetrahydrofuran and subsequent termination with 2‐picoline N‐oxide. Secondly, the macroinimers and acrylate monomers containing different spaced cyanobiphenyl mesogenic groups were copolymerized to yield the respective graft copolymers. Eventually, these were used for indirect photochemical polymerization of methyl methacrylate by UV irradiation in the presence of anthracene as a photosensitizer leading to the final copolymers with block copolymer grafts. The liquid crystalline, semicrystalline, and amorphous blocks were micro‐phase separated in the graft copolymers.