Structure Of Graft Copolymers Research Articles

Preparation and Characterization of Melt Grafted Acrylamide Tertiary Butyl Sulfonic Acid onto Polypropylene

Grafting of acrylamide tertiary butyl sulfonic acid (ATBS) onto polypropylene (precisely, ethylene/propylene random copolymer containing 8% ethylene content) was carried out by melt extruding with addition of dicumyl peroxide (DCP) as an initiator. The structure of graft copolymer was characterized by using WAXS, FT-IR, ESCA and DSC. Improved thermal stability was observed for graft copolymer. The effect of monomer and initiator concentration, reactive temperature and srew speed on degree of grafting efficiency of grafting has been investigated.

Synthesis and characterization of hydroxyl terminated poly(butadiene)-g-poly(glycidyl azide) copolymer as a new energetic propellant binder

Poly(glycidyl azide), PGA, was grafted onto Hydroxyl Terminated Poly(butadiene), HTPB, via free radical mechanism. PGA-macro azoinitator and HTPB polymer mixture was casted from solution and the polymer film was kept at 90°C for 4 hours. The grafted polymer was isolated from the product by fractional precipitation and characterized by NMR and FT-IR spectroscopy. Graft copolymer structure was also confirmed that volume ratio of nonsolvent to the solution of the graft copolymer was between those of corresponding homopolymers. TGA traces of the block polymers were containing two different maxima at 253°C (for PGA units) and 469°C (for HTPB units). Because of the incompatibility of the blocks, DSC curve showed two Tg's which belong to the related segments.

On the macro- and microphase separation of compatibilizers in immiscible polymer blends

Macro- and microphase separation of compatibilizing graft copolymers in melt-mixed polystyrene/polyamide-6 blends was studied by transmission electron microscopy and thermal analysis. Three different graft copolymers with main chains of polystyrene and side chains of poly(ethylene oxide) were used as additives at various concentrations. The polyamide-6 domain sizes decreased with increasing amounts of compatibilizing graft copolymers in the blends up to a saturation concentration, after which no further reduction was noted. Macrophase separation of the graft copolymers into discrete macrodomains 20–200 nm in size occurred at concentrations equal to or slightly lower than the saturation concentration. The macrodomains of the graft copolymers were microphase separated, and the sizes and shapes of the microdomains were found to largely depend on the graft copolymer structure and composition. As a consequence of microphase separation, poly(ethylene oxide) crystallinity was noted in blends with sufficiently high macrophase contents. Observations of a graft copolymer interphase between the polystyrene matrix and the polyamide-6 domains confirmed that the graft copolymer was present at the blend interfaces in some of the compatibilized blends. © 1996 John Wiley & Sons, Inc.

Butyl rubber graft copolymers: synthesis and characterization

This paper discusses four closely related themes, (a) First, we present the synthesis of new butyl rubber graft copolymers that have a polyisobutylene backbone and several free-radical polymerized polymers, such as poly(methyl methacrylate), in the side chains. The chemistry involves commercial butyl rubber, poly(isobutylene- co-isoprene) and free-radical graft-from reaction using a borane reagent. (b) The selective autoxidation reaction of secondary alkyl-9-borabicyclononane offers the conditions for producing desirable polymeric radicals in graft-from polymerization with high grafting efficiency and controllable copolymer compositions. (c) The structure of graft copolymers is characterized. Several techniques, especially gel permeation chromatography measurement with on-line refractive index, photodiode-array and light scattering detectors, were used to provide detailed microstructural information. (d) Finally, compatibility is studied using graft copolymers as the compatibilizers in polyisobutylene blends.

Branching process of the grafting reaction between two reactive polymers

Graft coupling between two reactive polymers can lead to the formation of compatibilized blends. There is a need to control the extent of graft coupling if the grafting system is capable of gelation, not just for the control of phase size and morphology, which depend on the amount and structures of graft copolymers in a ternary blend. In this paper, we give a thorough analysis of the molecular characteristics of the grafting system of two reactive polymers each having a large number of reactive groups. A kinetic approach is employed to quantify the molecular characteristics: concentration of individual species, molecular-weight averages and gel point. It is found that the percentage conversions of the reactive polymers to copolymers are quite limited in order to avoid a weight-average molecular weight of the system that is too high. The presence of a high-molecular-weight tail in the polydisperse reactive polymers further limits the extent of the grafting reaction, an undesirable factor in such a grafting system.

Structure of graft copolymers based on SVM fibre and polytetrafluoroethylene

1. It has been found that grafting PTFE to SVM reduces the degree of crystallinity of the starting fibre; the depth of grafting depends on the radiation dose. 2. The formation of water clusters in swollen fibres on grafting the hydrophobic PTFE to SVM is caused mainly by water—water interaction, which depends on the grafted PTFE content.

Effects of reaction conditions on the structure of graft copolymer

In order to advance the studies of radiation graft copolymerization, we have presented the theory of coupling graft copolymerization and apply it to the investigation of the grafting of methylmethacrylate on to pre-irradiated polystyrene.

Structure and properties of graft copolymers of polyethylene terephthalate with polytetrafluoroethylene

-- Using IR-spectroscopy, x-ray diffraction, and electron microscopy, we have investigated the change in supermolecular structure of graft copolymers of PET with PTFE.

Peculiarities of phase and supermolecular structure of graft copolymers of polycaproamide with poly(methacrylic acid)

AbstractThe structure of graft copolymers of PCA with PMAA obtained by the methods of chemically initiated liquid‐phase grafting polymerization has been investigated with the use of electron microscopy, electron‐probe microanalysis, and X‐ray radiography. The concentration profiles of the graft copolymer distribution along the fiber cross section and diffusion coefficients of the monomer solutions correlated with the kinetics of the graft layer penetration inside the polymeric matrix have been determined. The concentration profile of the graft polymer distribution has been shown to have drops down to the zero level. Grafting proceeds both in the amorphous regions and on the surface of imperfect crystals. The structure of the graft layer, in which the segregated chains of graft PMAA constitutes the dispersed medium and the PCA inclusions represent the dispersed phase, has been found to be heterogeneous.

Structure of graft copolymers of polycaproamide with polymethacrylic acid

Electron microscopy and electron-probe microanalysis, contrasting and etching have been used to investigate the structure of graft copolymers of PA-6 with polymethacrylic acid obtained by chemically initiated liquid phase graft polymerization. The authors have determined the concentration distribution profiles of the grafted polymer over a section of the fibre and the diffusion coefficients of monomer solutions which were compared with the kinetics of penetration of the grafted layer into the polymeric matrix. The concentration distribution profile of the grafted polymer is of a termination character. Grafting occurs both in the interfibrillar space and on the surface of the fibre. The heterogeneous character of the structure of the grafted layer in which the disperse medium is the segregated phase of the grafted acid and the disperse phase the PA-6 inclusions has been established.

Drug permeability of modified silicone polymers. II. Silicone—Organic graft copolymers

Polydimethylsiloxane (PDMS)/poly(ethylene oxide) (PEO) graft copolymers were synthesized and the effect of the size and the degree of grafting of the hydrophilic pendent PEO segments were systematically investigated with respect to drug permeabilities and physical properties of the graft copolymers. It was found that increasing the size and the degree of grafting of the pendent PEO segments resulted in little, if any, change in the permeability of a lipophilic steroid (progesterone), but a dramatic increase in those of hydrophilic steroids (testosterone and hydrocortisone). Changes in the drug permeabilities of greater than three orders of magnitude were achieved by varying the graft copolymer structure. Grafting higher levels of the shorter pendent PEO segments was found to be more effective in enhancing the testosterone permeability than grafting fewer of the longer ones. Modification of PDMS using the graft copolymer approach was also shown to be more effective in enhancing the testosterone permeability than using the block copolymer approach. The water absorption of the graft copolymers increased with an increase in the size and the degree of grafting of the pendent PEO segments. The tensile strength of the graft copolymers, however, was fairly low. The quantitative relationships between the graft copolymer structures and the permeabilities of these steroids, as well as their physical properties, were established.

Study of the hydrodynamic properties of high molecular weight conjugates of a copolymer based on N-vinylpyrrolidone with the protein streptokinase

The paper reports the results of study of the hydrodynamic properties by velocity sedimentation and diffusion of conjugates of the protein streptokinase with a hydrophilic linear copolymer based on N-vinylpyrrolidone as a function of different ratios of the components in the reaction medium and also on the MW of the polymer-modifier. The authors apply to systems of the protein-polymer type the approach used to study the structure of synthetic graft copolymers consisting in comparative investigation of the molecular parameters of the end product (graft-polymer) and the components constituting it.

Study of the structure of graft dextran (dialdehyde dextran)-Polyacrylamide copolymers

Velocity sedimentation, translational diffusion and viscometry have been used to investigate the structure of graft copolymers of dextran-polyacrylamide and dialdehyde dextran-polyacrylamide. Introduction of the aldehyde groups into the main chain raises the frequency of grafting. However, because of the degradation of the main chain, greater in the case of dialdehyde dextran, the number of side chains in the graft copolymers synthesized on bases with different contents of the aldehyde groups is roughly the same.

Structure and properties of enzyme graft copolymers: effects of using dissolved agarose on horseradish peroxidase immobilization.

The immobilization of horseradish peroxidase (HRP) onto dissolved agarose by a photochemically initiated graft copolymerization reaction, carried out at room temperature, was studied. Enzyme immobilization parameters such as the catalyst (FeCl3) and the enzyme concentration were considered. Using hexhydro-1,3,5-triacryloyl-s-triazine (HTsT) as vinyl monomer, the agarose/HTsT ratio was the main reaction parameter controlling the copolymer characteristics. By increasing the polymer content of the sample better stability properties were obtained. For the samples with agarose/HTsT ratios of 20/40 and 40/20 (S 20-40, S 40-20) the residual activities after 240 min at 60 degrees C were respectively 47 and 18%. The residual activity in continuous working was 33% for S 40-20 (after 20 h) and 64% for S 20-40 (after 70 h). For both the synthesized copolymers no limitation to substrate diffusion was found but the flexibility of immobilized enzyme decreased with the increase of polymer content as indicated by the Km values that were 0.90 X 10(-4) mol/liter for the sample S 40-20, and 1.50 X 10(-4) mol/liter for the sample S 20-40. Other enzymes (glucose oxidase, alpha-chymotrypsin, and lipoxidase), besides HRP, were immobilized with good yields, showing the wide applicability of the proposed methodology for the preparation of a solid biocatalyst which can be conveniently stored in water suspension or as lyophilized material.

Structure and properties of enzyme graft copolymers: Temperature effects on HRP immobilization mechanism

The possibility of obtaining immobilized horseradish peroxidase (HRP) materials with K'(m) values close to that of the native enzyme, but with good thermal stability, was investigated. The photochemical reaction was used as the immobilization methodology. Temperature and catalyst concentration were found to be the main parameters able to control the immobilization reaction mechanism more than type of functional monomer, polymer-matrix, and enzyme-polymer ratios. By carrying out the immobilization reaction at 35 degrees C and using either bisacryloylpiperazine (BAP) or hexhydro-1,3,5-triacryloyl-s-triazine (HTsT) as the functional monomer, materials with a good thermal stabilization (the retained activity after 240 min at 60 degrees C was between 65-25%) as well as kinetic constants (0.6-0.8 x 10(-4)M) similar to that of the free enzyme (0.57 x 10(-4)M) were obtained. Since low K'(m) values were obtained also using a high polymer content (pBAP copolymers, 25%; pHTsT copolymers, 30%) and neither limitation to substrate diffusion nor a reduction of the enzyme mobility was found, the enzyme should be linked to the matrix during the last steps of monomer polymerization, and it should have an external disposition with respect to the support.

Synthesis and characterization of hydrogels from graft copolymers

Well-defined graft copolymers composed of a hydrophilic clyceryl methacrylate backbone and hydrophobic monodisperse molecular weight polystyrene branches were prepared by the macromonomer technique. The swelling behaviour and the oxygen permeability of hydrogels prepared from these graft copolymers were studied. It was found that equilibrium water content of these hydrogels was considerably high and depended on both the graft copolymer structure and the microphase separated structure of the prepared hydrogel. Oxygen permeability of the hydrogels was directly related to their water content. Hydrogel membranes prepared from the graft copolymers have also well-defined structures which can be easily controlled by the graft copolymer structure.

Influence of the molecular structure of cellulose triacetate-polymethyl methacrylate graft copolymers and the degree of compatibility of the components on the properties of their solutions

The method of light scatter has been used to determine the MM, mean square radii of inertia and the second virial coefficient of cellulose triacetate-PMMA graft copolymers. The effect of the number and MM of the grafted chains, degree of compatibility of the components on the conformation of the macromolecules, the hydrodynamic and thermodynamic properties and microstructure of the copolymers has been studied.

Effect of the structure of cellulose graft copolymers containing antimicrobic substances on properties

Cellulose derivatives were synthesized which contain antimicrobic substances attached by an ester bond to various chains graft to cellulose. It was shown that the rate of hydrolysis of ester bonds under conditions for determining the antibacterial activity of fibrous materials (pH 7·2, 37°) dependes to a large extent on the structure of chains grafted to cellulose and the chemically combined antimicrobic substanees, and increases markedly by the anchimeric action of ionized carboxyl groups arranged in the β-position to the ester bond. The antimicrobic activity of polymers synthesized depends on the structure of cellulose derivative, the proportion and activity of chemically combined antimicrobic substance.

Supermolecular structure of graft copolymers of cotton and cellulose hydrate fibres with certain fluorine-containing polymers

The results of a study of the supermolecular structure of graft copolymers of cotton and viscose cellulose hydrate fibres with certain fluorine-containing polymers are presented in the present paper. It has been observed by a study of IR spectroscopic data that, in all the fluorine-containing copolymers from the cellulose fibres, a reduction occurs in the absorption band regions related to bonded hydroxyl groups and deformation vibrations of water (adsorbed on the cellulose) and new characteristic absorption bands for the fluorine-containing polymers appear. Optical and electron-microscopic observations have revealed a number of features of the supermolecular structure of graft fluorine-containing copolymers formed by cellulose fibres.

Cationic polymerization of α‐methyl styrene from polydienes. II. Tensile properties of poly(butadiene‐g‐α‐methyl styrene) and poly(styrene‐b‐butadiene‐g‐α‐methyl styrene) copolymers

AbstractTensile properties of poly(butadiene‐g‐α‐methyl styrene) copolymers have been investigated on molded samples. These graft copolymers show thermoplastic elastomer behavior because of their graft copolymer structure. Both modulus and strength increase with increasing α‐methyl styrene content and tensile strength is highest at the 45–50% by weight α‐methyl styrene level. Tensile strength at elevated test temperatures is considerably higher for these poly(butadiene‐g‐α‐methyl styrene) copolymers than for styrene‐butadiene‐styrene triblock polymers. This is attributed to the higher glass transition temperature for poly(α‐methyl styrene) segments compared to polystyrene segments. The oil acceptance of these graft copolymers appears to depend on the number of loose polybutadiene chain ends. Thus, the tensile strength of oil‐extended poly(butadiene‐g‐α‐methyl styrene) copolymers was considerably lower than oil‐extended poly(styrene‐b‐butadiene‐g‐α‐methyl styrene) copolymers even though both copolymers contained equal hard segment contents.