Gel chromatographic investigation of p-benzoquinone and styrene products copolymerized in the presence of BF3·OEt2

The molecular weight distribution of copolymers of p-benzoquinone and styrene was studied by g.p.c.. It was shown that the products synthesized have low molecular weights and narrow MWD. p-Benzoquinone was found to be a copolymer macromolecule regulator.     

Radical copolymerization of N-vinylcarbazole and p-bromostyrene: determination of monomer reactivity ratios by SEC-multidetection

N-Vinylcarbazole (A)/p-bromostyrene (B) copolymers were prepared by radical copolymerization. Size exclusion chromatography (SEC) equipped with a refractometer and UV-vis spectrophotometer was found to be a very convenient technique to follow copolymerizations and to determine monomer conversions, copolymer composition, average molecular weights, polydispersity indexes versus time. The monomer reactivity ratios r_A (N-vinylcarbazole) and r_B (p-bromostyrene) were determined by using the Finemann-Ross (FR), the inverted Finemann-Ross (IFR), the Kelen-Tüdos (KT), and the fitting curve graphical methods. The four methods were in good agreement and led to very different values for r_A (0.55) and r_B (12.3) which induces a preference for the incorporation of B in the copolymer structure. Eventually, with these results the influence of initial feed on the microstructure of the copolymer has been predicted.     

Compatibility of poly(p-fluorostyrene-co-o-fluorostyrene) with poly(2,6-dimethyl-1,4-phenylene oxide) and polystyrene

The compatibility of blends prepared from random copolymers of p-fluorostyrene and o-fluorostyrene with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and blends of the copolymers with polystyrene (PS) has been examined using differential scanning calorimetry. It was found that compatibility in these systems depends on copolymer composition: copolymers containing from 10 to 38% of p-fluorostyrene are miscible with PPO in all proportions. The thermally induced phase separation in these systems was also studied and the existence of lower critical solution temperatures (LCST) was established for all compatible blends. The copolymers were found to be incompatible with PS regardless of composition.     

A theoretical study on the interaction between N-methylpyrrole and 3,4-ethylenedioxythiophene units in copolymer molecules

Quantum mechanical calculations at the density functional theory level have been used to examine the interaction between 3,4-ethylenedioxythiophene and N-methylpyrrole units when they are directly linked in copolymer chains. Specifically, in this study, which was motivated by experimental observations of electrochemically synthesized copolymers, the conformation and electronic properties of co-oligomers formed by two, three and four units have been examined in both neutral and radical cation states. Results reveal significant differences, especially in the radical cation state, between the co-oligomers and the corresponding individual homo-oligomers, which have also been explored considering the same theoretical method. Furthermore, electronic properties of oligomers have been used to estimate those of poly(3,4-ethylenedioxythiophene), poly(N-methylpyrrole) and the copolymer with alternated structure, which have been compared among them. The overall results allowed to understand the anomalous features detected in copolymers prepared by electrochemical techniques from 3,4-ethylenedioxythiophene and N-methylpyrrole mixtures, which were initially attributed to some type of unfavourable interaction between the two types of monomeric units.     

A novel biodegradable poly(p-dioxanone)-grafted poly(vinyl alcohol) copolymer with a controllable in vitro degradation

A novel biodegradable copolymer was synthesized from poly(vinyl alcohol) and poly(p-dioxanone) by ring-opening polymerization. The molecular structure of the copolymer was characterized by one- and two-dimensional NMR spectroscopy. The results of differential scanning calorimetry (DSC) show that the amphiphilic and comb grafted structure of the copolymer make its crystalline behavior different from that of the poly(p-dioxanone) homopolymer (PPDO). The in vitro degradation rate of the copolymers can be controlled via adjusting the number and length of PPDO segments of PVA-g-PPDO copolymers. The copolymer has a potential application in biomedical materials or in the controlled release of drug.     

Photoactive polymers containing vanadium: 1. Preparation,characterization and photoreactions

Photoactive polymers have been prepared by reaction of VOQ₂OH (Q = 8-quinolyloxo) with polymers of types A and B carrying pendant hydroxyl groups. Type A was represented by copolymers of methyl methacrylate and 2-hydroxyethyl methacrylate and type B by a copolymer of styrene and p-vinylbenzyl alcohol. The final copolymers are designated VA, VB, respectively. The copolymers were characterized by near u.v.—visible spectra. On irradiation (λ = 365 nm) the vanadium (IV) chelate VOQ₂ is formed; this is indicated by the u.v.—visible spectral changes, and also by e.s.r. spectroscopy. The infra-red spectra of the copolymers VA, VB show important differences, notably the presence of a strong band near 960 cm^?1 (attributable to V=O stretching vibrations) in the former and its absence from the latter. From this and other evidence it is concluded that the vanadium residues have different structures in the two types of copolymer, viz. O=VQ₂OR and (HO)₂VQ₂OR in VA and VB respectively, where R is the remainder of the copolymer molecule. Irradiation (λ = 365 nm) is considered to bring about scission of VOR bonds in copolymer VA with formation of a macroalkyloxy radical OR. This is consistent with spin-trapping experiments with benzylidene nitrone. On the other hand, photolysis of copolymer VB appears to give radicals identical with those from VOQ₂OH which are most probably OH.The formation of different types of radical on irradiation of copolymers VA, VB is also indicated by spin-trapping observations with nitrosodurene in benzene solution and also the occurrence of photografting when VA (but not VB) is irradiated in a monomer. The photolysis of VOQ₂OH to which we have referred above may provide a convenient source of hydroxyl radicals in non-aqueous solution.     

Preparation of poly(tert-butyl acrylate-g-styrene) as precursors of amphiphilic graft copolymers. 1. Kinetic study and thermal properties

Free radical copolymerizations of tert-butyl acrylate and a polystyrene macromonomer carrying a methacryloyloxy group at the chain end have been performed in benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator at 70 °C. The estimated values of the ‘lumped’ kinetic constant, k_p/k_t^1/2, have shown a clear dependency on the macromonomer concentration in the reaction medium. The obtained poly(tert-butyl acrylate-g-polystyrene) graft copolymers were characterized by size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). In addition, the thermal behavior of these copolymers was studied by thermogravimetric analysis (TGA). Subsequently, hydrolysis of precursor graft copolymer was performed to afford an amphiphilic graft copolymer. Characterization using FT-IR confirmed total hydrolysis of the ester group.     

Copolymerization of trimethylene carbonate and 2,2-dimethyltrimethylene carbonate by rare earth calixarene complexes

Rare earth (Nd, Y, La) p-tert-butylcalix[n]arene (n=4, 6, and 8) complexes alone have been developed to catalyze random and block copolymerizations of trimethylene carbonate (TMC) and 2,2-dimethyltrimethylene carbonate (DTC). The random or block structure and thermal behavior of the copolymers have been characterized by SEC, NMR, DSC, XRD and PLM. Random copolymer with M_w of 14,100 and M_w/M_n of 1.36 was prepared by neodymium p-tert-butylcalix[6]arene complex under the conditions: [TMC+DTC]₀/[Nd]=400, 80 °C, 8 h. The reactivity ratios of TMC and DTC are measured to be r_TMC=4.68 and r_DTC=0.163, respectively. Random copolymerization could be well designed by the feeding ratio to prepare copolymers with controlled T_m and T_g. Only 8% TMC units in the polymer chain destroyed the crystallization of PDTC showing no T_m of the copolymer in the DSC analysis.     

Self-assemblies formed by four-arm star copolymers with amphiphilic diblock arms in aqueous solutions

The self-assembly of two star copolymers, each consisting of four diblock arms of either poly(?-caprolactone)-block-poly(ethylene oxide), PCL-PEO, or polylactide-block-poly(ethylene oxide), PLA-PEO, with PEO blocks in the centers of the stars, have been studied by a combination of light scattering, atomic force microscopy, fluorometry and ¹H NMR spectroscopy. Results of the study show that despite the very similar architecture of both star copolymers, the structures of their self-assembled nanoparticles differ. Unlike the (PLA-PEO)₄ star copolymer which forms core/shell flower-like micelles, the association of the (PCL-PEO)₄ copolymer leads to large micellar aggregates in which individual micelles are interconnected by shared unimers, having joint coronas formed by hydrophilic centers of the stars.     

Preparation and solubility of a partial ladder copolymer from p-phenylenediamine and o-phenetidine

A series of copolymers were synthesized by chemically oxidative polymerization of p-phenylenediamine (PPD) and o-phenetidine (PHT) in acidic aqueous media. The polymerization yield, intrinsic viscosity, and solubility of the copolymers were comprehensively studied by changing the comonomer ratio, polymerization time and temperature, oxidant, monomer/oxidant ratio, and acidic medium. As-prepared fine powder of the PPD/PHT copolymers was characterized by FT-IR, UV-vis, high-resolution ¹H-NMR, and DSC techniques. A circular dichroism technique was firstly used to characterize the macromolecular structure of the copolymers. The results showed that the oxidative copolymerization from PPD and PHT is exothermic and the resulting copolymers exhibit an enhanced solubility in most of the organic solvents as compared with poly(p-phenylenediamine), sometimes also with poly(o-phenetidine). The polymer obtained is a real copolymer containing PPD and PHT units, and the actual PPD/PHT ratio calculated by ¹H-NMR spectra of the polymers is very close to the feed ratio. The DSC measurement indicates that the copolymers are amorphous and chemically instable at elevated temperature.     

Kinetics of water absorbency in AA/AMPS copolymers: applications of a diffusion-relaxation model

Superabsorbent copolymers, based on acrylamide, 2-acrylamido-2-methyl-propanosulfonic acid and a divinyl crosslinker, N,N′-methylenebisacrylamide, have been synthesized by free radical solution and inverse emulsion polymerization. The copolymerization has been carried at different pH values of the monomer mix reaction medium.The copolymers were characterized by their dynamic swelling behavior in deionized water, i.e. the mass of water absorbed by a sample of copolymer was measured vs time. The results were analyzed in terms of the Berens-Hopfenberg non-Fickian equation, leading to a one-only-term relaxation. These kinetics were interpreted by the diffusion-relaxation model and offer quantitative information by diffusivity at 20°C of water in the copolymers. In this investigation, the results have been confirmed within experimental error as the sample of the copolymer is swollen.     

A unique phase behavior of random copolymer of N-isopropylacrylamide and N,N-diethylacrylamide in water

Thermosensitive phase separation of aqueous solutions of the random copolymers of N-isopropylacrylamide (iPA) and N,N-diethylacrylamide (dEA) (PiPA-dEA) and of iPA and N-isopropylmethacrylamide(iPMA) (PiPA-iPMA) with different compositions has been investigated by using calorimetry, turbidimetry and infrared spectroscopy. Though the phase transition temperature (T_p) of PiPA-iPMA is a linear function of its composition, a deviation from additivity is observed for that of PiPA-dEA, that is, it has a minimum value at iPA/dEA = 1 (mol/mol). IR spectrum at the amide II mode of the copolymer suggests that part of N-H groups of iPA units form a hydrogen bond with CO groups of dEA units at T > T_p as well as with those of the iPA units. Effects of methanol on T_p of these copolymers have also been studied.     

Compatibilising action of random and triblock copolymers of poly(styrene-butadiene) in polystyrene/polybutadiene blends: A study by electron microscopy, solid state NMR spectroscopy and mechanical measurements

Scanning electron microscopy, solid-state proton NMR spectroscopy and static mechanical analysis have been performed in order to evaluate the compatibilising action of random copolymers of polystyrene and polybutadiene and triblock copolymers of poly(styrene-butadiene-styrene) in incompatible polystyrene/polybutadiene (PS/PB) blends. Scanning electron microscopic examination of the cryofractured and etched surfaces showed high degree of compatibilising action of the triblock copolymers as evidenced by the very sharp decrease of the domain size of the dispersed phase followed by an increase at higher concentrations. This is a clear indication of interfacial saturation. These results were in agreement with the theoretical predictions of Noolandi and Hong. The random copolymer was not effective in compatibilising the system. Solid-state proton NMR experiments were performed on the uncompatibilised and compatibilised blends. The proton spin-lattice relaxation times in the laboratory frame, T₁(H), and in the rotating frame, T_1ρ(H), and spin-spin relaxation times, T₂(H), were carefully measured for the systems. Significant changes were observed for the systems compatibilised with triblock copolymers due to the preferential localisation of the copolymers at the PS/PB interface. However, the random copolymer did not have any compositional drift and is not an effective interface modifier in agreement with microscopy study. The static mechanical properties of the blends have also been analysed. The addition of triblock copolymers increased the mechanical properties of the blends. Finally, attempts have been made to correlate the NMR results with the microstructure and mechanical properties of the blends.     

Improving the electrochemical performance of polyaniline electrode for supercapacitor by chemical oxidative copolymerization with p-phenylenediamine

A series of poly(aniline-co-p-phenylenediamine) (P(ANI-co-PPDA)) copolymers were synthesized via the chemical oxidative polymerization of aniline with p-phenylenediamine (PPDA) as the comonomer. The structure and morphology of the P(ANI-co-PPDA) copolymers prepared with different feeding ratio of PPDA under different polymerizing temperature were compared with the two homopolymers polyaniline (PANI) and poly(p-phenylenediamine) (PPPDA). It is interesting to find that the electrical conductivity, specific capacitance and cycling stability of the P(ANI-co-PPDA) copolymer electrode materials were obviously improved with certain feeding ratio of PPDA, compared with those two homopolymers.     

ABA triblock copolymers from poly(p‐dioxanone) and poly(ethylene glycol)

Poly(p‐dioxanone)–poly(ethylene glycol)–poly(p‐dioxanone) ABA triblock copolymers (PEDO) were synthesized by ring‐opening polymerization from p‐dioxanone using poly(ethylene glycol) (PEG) with different molecular weights as macroinitiators in N₂ atmosphere. The copolymer was characterized by ¹H NMR spectroscope. The thermal behavior, crystallization, and thermal stability of these copolymers were investigated by differential scanning calorimetry and thermogravimetric measurements. The water absorption of these copolymers was also measured. The results indicated that the content and length of PEG chain have a greater effect on the properties of copolymers. This kind of biodegradable copolymer will find a potential application in biomedical materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1092–1097, 2006     

Synthesis and characterization of hydrophilic copolymers of maleimide derivatives with 2‐hydroxyethyl methacrylate: electrochemical and thermal behavior

BACKGROUND: The high‐technology industries have been the driving force in the development of new synthetic polymers that combine thermal stability with specific functional properties. In this study p‐chlorophenylmaleimide, p‐hydroxyphenylmaleimide and p‐nitrophenylmaleimide (R‐PhMI) with 2‐hydroxyethyl methacrylate (HEMA) were synthesized by free radical polymerization to obtain hydrophilic polymers, in order to study the effect of the p‐chloroaryl, p‐hydroxyaryl or p‐nitroaryl group on the copolymer composition, electrochemical behavior and thermal properties. RESULTS: The thermal behavior was correlated with the copolymer composition and functional groups, maleimide derivatives, on the copolymers. Thermal decomposition temperature (TDT) and glass transition temperature (T_g) were influenced by the functional groups of R‐PhMI moiety on the copolymer. The polymers showed an electrochemically irreversible reduction process under the conditions tested. CONCLUSION: Poly[(p‐chloromaleimide)‐co‐(2‐hydroxyethyl methacrylate)] copolymer shows a higher TDT than poly[(p‐hydroxymaleimide)‐co‐(2‐hydroxyethyl methacrylate)] or poly[(p‐nitromaleimide)‐co‐(2‐hydroxyethyl methacrylate)] (NPHE). T_g decreases in going from nitro to hydroxyl to chloro groups. The NPHE copolymer shows a lower stability, losing weight at 200 °C. The NPHE copolymer shows a well‐defined reduction wave which is similar to those of the other copolymers and it also shows an additional quasi‐reversible reduction wave corresponding to the nitrobenzene group. Copyright © 2009 Society of Chemical Industry     

Thermal properties of poly(tetramethyl-p-silphenylene siloxane) and (tetramethyl-p-silphenylene siloxane-dimethyl siloxane) copolymers

Some physical properties of poly(tetramethyl-p-silphenylene siloxane) homopolymer and random block copolymers of tetramethyl-p-silphenylene siloxane-dimethyl siloxane have been determined and correlated with polymer structure. Differential scanning calorimetry (d.s.c.), differential thermal analysis (d.t.a.), density gradient column measurements and optical hot stage melting point determination and diluent techniques were used. The thermodynamic melting temperature of the homopolymer was estimated to be 160°C and its heat of fusion, ΔH_u, found to be 54.4 J/g (13 cal/g or 2710 cal/mol of monomer repeat units). Its limiting glass transition temperature, T_g, was ?20°C. T_g of the copolymer was found to vary almost monotonically with increasing dimethyl siloxane (DMS) content ranging from ?20° (0% DMS) to just above ?123°C, for pure DMS polymer. The copolymer melting temperature was found to increase as the fraction of the crystalline (hard) TMPS constituent was increased. Based upon copolymer theory and extrapolated melting point data, it was estimated that the block size of soft DMS component in the copolymer most probably consists of twelve monomer units distributed amongst TMPS sequences of varying length.     

Thermal degradation of polymers. XIV. Thermal analysis studies in air on homopolymers of m-N,N-dimethylaminostyrene and p-N,N-diethylaminostyrene and their copolymers with styrene

Homopolymers of m-N,N-diethylaminostyrene and p-N,N-diethylaminostyrene and their copolymers with styrene have been subjected to thermal analysis studies in air. Molecular weight and copolymer composition have been shown to influence the stability of the polymers and the shape of the TG and DSC curves in the case of polymers containing m-N,N-dimethylaminostyrene. Polymers containing p-N,N-diethylaminostyrene show TG and DSC curves essentially independent of molecular weight and copolymer composition. The behavior of the two systems is discussed in terms of the antioxidant effect of the chain-bound N,N-dialkylamino substituents and their secondary reactions.     

Simple and facile synthesis of aryl benzoates from stabilized arenediazonium tetrafluoroborate using a recyclable polymer-supported benzoate ion

Temperature-responsive P(NIPAM-co-HMAM)-b-PEO-b-P(NIPAM-co-HMAM) triblock copolymers were synthesized by an atomic transfer radical polymerization (ATRP) method without freeze?Cpump?Cthaw cycles. The composition, structure, and molecular weight of the synthesized block copolymer were characterized by ¹?H NMR and GPC. The phase transitions induced by temperature for different copolymers in dilute aqueous solutions have been studied using transmittance measurements, laser particle size measurements, viscosity analysis, and surface tension measurement, which showed that the HMAM content and the PEO (or PEG) chain length in the synthesized triblock copolymer affects the copolymer??s lower critical solution temperature (LCST). The micellization behavior of each temperature-responsive triblock copolymer was investigated by fluorescence probe measurements and transmission electron microscopy (TEM), which showed that the triblock copolymers form stable micelles above the LCST. The introduction of the HMAM component and the formation of micelles represent the first steps in the development of an injectable gel that forms in situ through chemical and physical crosslinking.     

Synthesis and characterization of novel functionalized polylactides with pendent hydroxyl arms

A class of polyesters have been synthesized by the ring-opening copolymerization of dl-lactide (DLLA) and RS-benzyloxyethyl-β-malolactonate (MABE) using different monomer feeding doses. The compositions and structures of poly(dl-lactide-co-RS-benzyloxyethyl-β-malolactonate) (poly(DLLA-co-MABE)) were determined by ¹H and ¹³C NMR measurements. GPC measurement showed that the molecular weight of the copolymers decreased as the MABE content increases. After catalytic hydrogenation of the benzyl ether functions, the desired copolymers with pendent hydroxyl arms, poly(dl-lactide-co-RS-hydroxyethyl-β-malolactonate) (poly(DLLA-co-MAHE)), were recovered. Thermal properties of poly(DLLA-co-MABE) and poly(DLLA-co-MAHE) copolymers were examined by differential scanning calorimetry (DSC) measurement. Single glass transition temperature appeared in the DSC spectra, which confirmed that the copolymers were true copolymers and not blends. The hydrophilicity of poly(DLLA-co-MAHE) copolymer was tunable, which increased with the increase in MAHE content. Furthermore, the hydrolytic degradation of poly(DLLA-co-MAHE) material was investigated and the results showed that faster degradation was observed in the copolymer film containing more MAHE content.