Content Of Copolymers Research Articles

High-throughput analysis of bulk and contact conductance of polymer layers on electrodes

An approach for high-throughput analysis of bulk and contact conductance of polymer layers is described and evaluated. The approach, based on s24-technique (simultaneous two- and four-point conductance measurements), was realized as a high-throughput method and applied for investigation of conductive polymers on an array of interdigital platinum electrodes. Several examples demonstrate distinctive influence of combinatorially varied conditions of polymer synthesis (polymerization charge, content of copolymers) as well as chemical treatment of the synthesized polymers in bulk and contact resistance of metal/polymer/metal systems. The developed high-throughput s24-technique can be widely applied to material research for investigation of bulk and contact electrical properties.

Conformational Transition between Random Coil and Helix of Copolymers of N‐Propargylamides

AbstractSummary: Copolymerization of two N‐propargylamides bearing pendent groups with different lengths [monomer 4, HCCCH2NHCO(CH2)4H; monomer 8, HCCCH2NHCO(CH2)8H] was carried out and the conformational transition behavior of copolymers with different compositions was examined systematically. The copolymers could form relatively stable helices even though both of the corresponding homopolymers, poly(4) and poly(8), could not take a stable helical conformation under the same conditions. The helix content of copolymers reached a maximum when the content of monomer 8 was 61%. These results are explained in terms of the idea that the copolymers have higher cis‐content and that the intramolecular hydrogen bonding is more effective in these copolymers compared with the corresponding homopolymers.image

Efeitos da temperatura e do tipo de iniciador na redução do teor de monômero residual durante reações de copolimerização em emulsão

Reduzir o teor de monômero residual é uma preocupação de qualquer produtor de polímeros, pois produtos sem, ou com teores muito baixos de monômero residual, apresentam um apelo comercial diferenciado. Neste trabalho são apresentadas e testadas experimentalmente diversas estratégias para reduzir o teor de monômero residual de copolímeros estireno/acrilato de butila produzidos em reações semicontínuas de polimerização em emulsão, que são amplamente utilizados nas indústrias de papel e tintas. Estas estratégias envolvem a adição contínua de iniciador e/ou o aumento da temperatura do reator durante a última etapa da reação, além da adição de um agente redutor e/ou de um iniciador solúvel na fase orgânica. Verificou-se que a combinação adequada de diferentes técnicas pode levar a uma redução significativa no teor residual de monômeros no látex.

Properties and biocompatibility of polypropylene graft copolymer films.

Modifying the surfaces of polymers has received a great deal of attention, because it could bring about specific surface characteristics such as antithrombogenic property. Therefore, N-vinyl pyrrolidone/sodium acrylate (NVP/Na-AAc) binary monomers were introduced onto polypropylene (PP) films by a radiation grafting method. The effect of solvent and comonomer composition on the degree of grafting was determined. Studies of the mechanical properties and water content of such graft copolymers showed that as the grafting yield increases the elongation percent decreases. However, the water content increases with increasing grafting yield. The blood compatibility of the original PP and PP-g-NVP/Na-AAc films was evaluated by determination of the extent of platelet adsorption and thrombus formation. The blood compatibility of PP-g-NVP/Na-AAc seems to be better than that of original PP.

Synthesis and properties of amphiphilic copolymers of butyl acrylate and methyl methacrylate with uniform polyoxyethylene grafts

AbstractAmphiphilic copolymers of butyl acrylate (BA) and methyl methacrylate (MMA) with uniform polyoxyethylene (PEO) grafts were synthesized by the copolymerization of BA and MMA with a methacrylate‐terminated PEO macromer in benzene with azobisisobutyronitrile as an initiator. The effects of various copolymerization conditions on the grafting efficiency and molecular weight of the copolymers, as well as the effect of the copolymerization time on the conversions of the macromer and the monomers, were reported. The copolymers, with uniform PEO grafts, were purified by successive extractions with water and ether/acetone (3/7) to remove unreacted macromer and ungrafted copolymers of MMA and BA, respectively. The purified graft copolymers were characterized with IR, 1H‐NMR, membrane osmometry, gel permeation chromatography, and differential scanning calorimetry. The highest grafting efficiency was about 90%, and molecular weight of the copolymers varied around 105. The average grafting number of the copolymer was about 10. A study of the crystalline properties, emulsifying properties, phase‐transfer catalytic ability, and mechanical properties of the graft copolymers showed that the emulsifying volume decreased with the increasing molecular weight of the PEO grafts but increased with the PEO content. The conversion of potassium phenolate in the Williamson solid–liquid reaction obviously increased with an increasing PEO content of the graft copolymers. The crystallinity of the graft copolymers increased with the PEO content of the graft copolymers or the molecular weight of the macromer used. The copolymers, prepared under certain conditions, behaved as thermoplastic elastomers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2982–2988, 2003

Poly(D,L-lactic acid)-poly(ethylene glycol)-monomethyl ether diblock copolymers control adhesion and osteoblastic differentiation of marrow stromal cells.

Biodegradable polymers, such as poly(lactic acid) (PLA) and poly(lactic-coglycolic acid) (PLGA), are attractive materials for tissue engineering because of their degradative and mechanical properties, which permit scaffolds to be tailored to the individual requirements of different tissues. Although these materials support tissue development, their chemical properties offer no control of cell adhesion or function because their surfaces become immediately masked by adsorbing serum proteins when the materials come into contact with body fluids. Furthermore, adhesion proteins undergo conformational changes and a decrease in bioactivity when adsorbed to hydrophobic materials, such as PLA. To overcome these limitations, we modified the properties of PLA by synthesizing a diblock copolymer with poly(ethylene glycol) (PEG), which is known to reduce the amount of adsorbed proteins and to modify their conformation. By altering the PEG content of these diblock copolymers we were able to control the adsorption of adhesion proteins and, because cell adhesion takes place only in the presence of serum proteins, to control cell adhesion and cell shape. Marrow stromal cell differentiation to the osteoblastic phenotype was strongly improved on PEG-PLA compared with PLA, PLGA and tissue culture polystyrene and led to a 2-fold increase in alkaline phosphatase activity and mineralization.

A study of solvent exchange process in (ethylene–vinyl alcohol) copolymer gels by a proton nuclear magnetic resonance spectroscopy imaging method

AbstractThe proton nuclear magnetic resonance (1H NMR) image patterns of (ethylene–vinyl alcohol) copolymer (EVOH)/dimethylsulfoxide (DMSO) gels with various ethylene contents were measured to elucidate the process of solvent exchange between DMSO and water in the gels soaked in water. The results of these experiments indicate that the rate of solvent exchange between DMSO and water in the gels increased with an increase in the ethylene content of EVOH copolymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 504–508, 2002

SYNTHESIS OF POLY(METHYL METHACRYLATE)-SILICA NANO-COMPOSITE

ABSTRACT Transparent organic/pre-ceramic composite films of poly(methyl methacrylate) [PMMA] and perhydropolysilazane [PHPS] were synthesized by blending poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) [P(MMA-co-HEMA)] random copolymers and PHPS. In the blend films, P(MMA-graft-PHPS) graft copolymers were formed, PMMA and PHPS were microscopically phase-separated in the solid state. Morphology of the microphase separation was investigated by transmission electron microscopy by changing HEMA content of the random copolymers and blend ratio of PHPS to HEMA. To convert PHPS to silica glass, the blend films were calcinated at 100°C. The morphology of the microphase separation of the films was not changed by the calcinations; the calcinated films were transparent. When the molar content of HEMA of P(MMA-co-HEMA) and the molar content of PHPS to HEMA in feed were 14.5% and 150%, respectively, the morphology was well ordered lamellae of PMMA and silica.

Side-chain liquid-crystalline poly(ketone)s: effect of spacer length, mesogen type and mesogen density on mesomorphic behavior

Novel side-chain liquid-crystalline copolymers (SCLCPs) were synthesized via the Pd(II) catalyzed alternating copolymerization of mesogenic 1-alkenes and carbon monoxide. For methoxybiphenyl mesogens, these copolymers exhibited highly ordered smectic E mesophases and high glass transition temperatures. The transition temperatures of these polymers were tuned by altering the spacer length or by dilution of mesogen-containing alkenes with 1-hexene. Polymers with cyanobiphenyl or methoxyazobenzene mesogens exhibited nematic mesophases. These polymers were the first ever nitrogen containing copolymers of this type. Increase of the spacer length or the 1-hexene content of methoxybiphenyl-containing copolymers resulted in a decrease of the surface polarity of spincoated films. The decomposition temperature of these SCLCPs started far above the isotropization temperature of the polymers.

The effects of PC‐PMMA block copolymer on the compatibility and interfacial properties of PC/SAN blends

AbstractBlock copolymers of polycarbonate (PC) and polymethylmethacrylate (PMMA), PCb‐PMMA, were examined as compatibilizers for blends of PC with styrene‐co‐acrylonitrile (SAN) copolymer. PC‐b‐PMMA was added to blends of PC with SAN containing various amounts of AN. The average diameter of the dispersed particles was measured with an image analyzer, and the interfacial properties of the blends were analyzed with an imbedded fiber retraction (IFR) test and an asymmetric double cantilever beam fracture test. The average particle size and interfacial tension of the PC/SAN blends reached a minimum value when the SAN copolymer contained about 24 wt% AN. A maximum in the adhesion energy was also observed at the same AN content. Interfacial tension and particle size were further reduced by adding PC‐b‐PMMA to the PC/SAN blends. Fracture toughness of the blends was also improved by enhancing the interfacial adhesion by the addition of PC‐b‐PMMA. The addition of PC‐b‐PMMA copolymer was more effective at improving the interfacial properties of PC/SAN blends than was varying the AN content of the SAN copolymers. The interfacial properties of the PC/SAN blends were optimized by adding a block copolymer and using an SAN copolymer that had minimum interaction energy with PC.

POLY(ETHYLENE-CO-VINYL ACETATE) (EVA) COPOLYMERS AS MODIFIERS OF OIL WAX CRYSTALLIZATION

ABSTRACT This work describes the performance of poly(ethylene-co-vinyl acetate) (EVA) copolymers as pour point reducer and organic deposits inhibitor. The molecular weight, molecular weight distribution and vinyl acetate content of the EVA copolymers were determined by gel permeation chromatography and thermogravimetric analyses, respectively. The copolymer with the highest vinyl acetate content (within the range analyzed, 28-41 wt %) exhibited the best performance as organic deposits inhibitor. Results from differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) suggest that the EVA copolymer acts modifying the morphology of the wax crystals.

Direct determination of vinyl acetate content of ethylene-vinyl acetate copolymers in thick films by infrared spectroscopy

An infrared spectroscopic method was developed for the determination of vinyl acetate content in thick films of ethylene-vinyl acetate copolymers. The A3460/A3610 ratio was used for the quantitative analysis. The technique is simple, quick and does not require a complicated sample preparation procedure.

Cation exchange membranes by radiation-induced graft copolymerization of styrene onto PFA copolymer films. I. Preparation and characterization of the graft copolymer

PFA-g-polystyrene graft copolymers were prepared by simultaneous radiation-induced graft copolymerization of styrene onto poly(tetrafluoroethylene-co-perfluorovinyl ether) (PFA) films. The effects of grafting conditions such as monomer concentration, dose, and dose rate were investigated. Three solvents, i.e., methanol, benzene, and dichloromethane, were used as diluents in this grafting system. Of the three solvents employed, dichloromethane was found to greatly enhance the grafting process, and the degree of grafting increased with the increase of monomer concentration until it reached its highest value at a styrene concentration of 60 (vol %). The dependence of the initial rate of grafting on the monomer concentration was found to be of the order of 1.2. The degree of grafting was found to increase with the increase in irradiation dose, while it considerably decreased with the increase in dose rate. The formation of graft copolymers was confirmed by FTIR analysis. The structural investigation by X-ray diffraction (XRD) shows that the degree of crystallinity content of such graft copolymers decreases with the increase in grafting, and consequently, the mechanical properties of the graft copolymers were influenced to some extent. Both tensile strength and elongation percent decreased with the increase in the degree of grafting. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2095–2102, 1999

DNA complexes with block and graft copolymers of N-(2-hydroxypropyl)methacrylamide and 2-(trimethylammonio)ethyl methacrylate

Block and graft copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) with 2-(trimethylammonio)ethyl methacrylate (TMAEM) were synthesized for the preparation of polyelectrolyte complexes with calf thymus DNA intended for targeted delivery of genes in vivo. In this study, the effects of the poly(HPMA) content of copolymers on the parameters of the interpolyelectrolyte complexes is investigated. Static and dynamic light scattering methods were used as a main tool for characterization. The ability of the copolymers to condense DNA was studied by the ethidium bromide displacement method. The stability of the complexes against precipitation in 0.15 M NaCl and the resistance of the complexed DNA to the action of nucleases was also studied. It was found that the presence of poly(HPMA) in the copolymers has not significantly affected the ability of poly(TMAEM) parts of the copolymers to form complexes with DNA, but has an effect on molecular parameters and aggregation (precipitation) of the complexes. The size of the complexes increases with increasing poly(HPMA) content while their apparent molecular weight decreases. The complex stability against precipitation in 0.15 M NaCl strongly depends on the amount of poly(HPMA) in the copolymer structure. The presence of a sufficiently high content of poly(HPMA) is a prerequisite for achieving good stability. The structure of the complexes changes with increasing poly(HPMA) content from 'soft balls' to the polymer coil. The density of the complexes decreases with increasing poly(HPMA) content independently of the copolymer structure. The DNA complexes of all copolymers showed very good nuclease stability.

Modification of poly(styrene- [formula omitted]-acrylonitrile) to promote polymer blend miscibility through hydrogen-bonded (2,4-diamino-1,3,5-triazine)maleimide interactions

The acrylonitrile units in poly(styrene- stat -acrylonitrile) (SAN) have been partially converted to the 2,4-diamino-1,3,5-triazine (DAT) moiety by the reaction with dicyandiamide in dry dimethyl sulfoxide, containing catalytic amounts of potassium hydroxide. This produced a range of terpolymers of poly(styrene- stat -acrylonitrile- stat -vinyl 2,4-diamino-1,3,5-triazine) with mol% composition in the range (54.3:43.0:2.7) to (54.3:25.0:20.7). Copolymers of methyl acrylate (MA) and maleimide (MI) were also synthesised and used to prepare blends with the modified SAN terpolymers. Here the triazine rings and the maleimide units can form complementary pairs of donor-acceptor-donor (DAD) and (ADA), triple hydrogen bonding sites. It was found that miscible, one-phase, polymer blends could be formed if the DAT content of the modified SAN terpolymers was ⩾ 10 mol% and the MI content of the (MA–MI) copolymers was > 22 mol%, or alternatively if the MI content was 9–14 mol% and the corresponding DAT content in the modified SAN was ⩾ 21 mol%. Once formed these secondary interactions were stable up to the onset of degradation of the blends and there was no evidence of a lower critical temperature for phase separation.

Poly(ethylene glycol)-block-poly(butyl acrylate). II. Characterization and properties

Poly(ethylene glycol)-block-poly(butyl acrylate) synthesized by radical polymerization in a one-step procedure were characterized by gel permeation chromatography, infrared, 1H-NMR spectroscopy, and differential scanning calorimetry (DSC). The crystalline property, emulsifying property, and phase transfer catalytic effect in the Williamson reaction were studied. It was found that the crystallinity of the copolymer increased with an increase in both the content and molecular weight of poly(ethylene oxide) (PEO) sequences. DSC curves showed two distinct crystallization temperature due to the heterogeneous nucleation and homogeneous nucleation crystallization. The casting solvent significantly affected the morphology and crystallinity of the solvent cast films. Both the emulsifying volume and the phase transfer catalytic efficiency in the Williamson reaction increased with the amount and PEO content of the block copolymers used, but decreased with an increase in the molecular weight of PEO sequences. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1427–1436, 1998

The compatibilizing effect of poly(styrene-co-4-vinylpyridine) copolymers on the polystyrene-polyethylene-based ionomer blends

The compatibilizing effect of styrene-co-4-vinylpyridine (SVP) random copolymers on the immiscible polystyrene (PS)–polyethylene-based ionomer (Surlyn) blends was examined by means of scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and tensile test. For the binary SVP–Surlyn and ternary PS–Surlyn–SVP blends, the domain size of dispersed phase decreases dramatically with the increase in the vinyl pyridine (VP) content of the SVP copolymers. The mechanical properties are improved with increasing the VP content in copolymers. FTIR results suggest that the compatibilization in this blend system is attributed to the ion–dipole interaction between the polar VP groups of SVP copolymer and ionic groups of Surlyn. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 807–816, 1998

Effect of methyl acrylate composition on the microstructure changes of high molecular weight polyacrylonitrile for heat treatment

The acrylate comonomer in polyacrylonitrile (PAN) precursor markedly influences the microstructure of PAN fiber and its resulting carbon fiber. In this study, the change occurring during the heat treatment of PAN copolymers (acrylonitrile-co-methyl acrylate) in the presence of air up to 260°C has been examined using both physical and chemical techniques. Considering the effect of the methyl acrylate content of PAN copolymers on the cyclization mechanism and fine structural changes in polymer chains under various heat treatment conditions, the composition of acrylonitrile and methyl acrylate = 98 : 2 to 97 : 3 mol % was suitable for the precursor preparation because the cyclization mechanism and fine structural changes in the boundary of this composition of copolymers were significantly different. With increasing MA content, the exothermic onset and peak in the thermogram was found to shift toward higher temperatures, and the aromaticity index decreased. This evidence indicates that MA was believed not to activate at all but to interfere with the cyclization. Additionally, by means of 13C nuclear magnetic resonance (13C-NMR) analysis, the tacticities of copolymers were nearly same, regardless of the copolymer composition, and the cyclization occurred nonstereospecifically during the initial heat treatment at 240°C for 1 h. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2205–2213, 1998

Synthesis and thermal behavior of triblock copolymers fromL-lactide and ethylene glycol with long center PEG block

In this study, poly( L-lactide) -poly (ethylene glycol) (PLLA-PEG) ABA triblock copolymers with the PEG mole fraction ranging from 27 to 57% have been synthesized, and their thermal properties were investigated. Differential scanning calo- rimetric thermograms of copolymers obtained from specimens dissolved in CH2Cl2 solu- tion and precipitated with hexane exhibit no crystallization exotherms, but those cast from CHCl3 solution show some crystallinity. Water absorption depended on the PEG content of copolymers; thus, with a PEG mole fraction of 57, the water absorption was 82%. q 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1949-1954, 1998

Modification of Polychloroprene by Graft Copolymerization and its Application as an Adhesive

Graft copolymerization of ethyl acrylate (EA) and methyl methacrylate (MMA) onto polychloroprene (PCP) were carried out in toluene using benzoyl peroxide (BPO) as an initiator. The polychloroprene-g-poly (ethyl acrylate) (PCP-g-P(EA)) and polychloroprene-g-poly (methyl methacrylate) (PCP-g-P(MMA)) were isolated from the homopolymers of poly(ethyl acrylate) (P(EA)) and poly (methyl methacrylate) (P(MMA)) by a selective solvent extraction technique using diisopropyl ether and acetic acid as solvents, respectively. The infrared (IR) spectra of PCP-g-P(EA) and PCP-g-P(MMA) showed an absorption band at 1730 cm−1, a characteristic of the carbonyl band (>C═O) of P(EA) or P(MMA) which is not present in PCP. The NMR spectrum of PCP-g-P(EA) copolymer showed the —OCH2 proton peak at 4.12 ppm, the methylene proton peak at 2.28 ppm and the methyl proton peak at 1.25 ppm. The NMR spectrum of PCP-g-P(MMA) copolymer shows the α—CH3 proton at 0.95 ppm and —OCH3 proton at 3.5 ppm. The IR and NMR studies on the graft copolymer showed the occurrence of grafting. The mechanism of the grafting seems to be by chain transfer as evidenced by the decrease in chlorine content of the graft copolymers. These graft copolymers were blended with tackifier and filler for adhesive applications. The peel and shear strength of the above adhesives with respect to upper leather to sole leather were investigated.