High Grafting Degree Research Articles

POLY-L-LYSINE-GRAFT-PEG COMB-TYPE POLYCATION COPOLYMERS FOR GENE DELIVERY

ABSTRACT Polycations have been used for gene delivery in vitro quite successfully, however, in vivo applications suffered from serum effects that lower the overall gene drug efficiency. PEG polymers have been used extensively to minimize serum effects and create “stealth liposomes”, biocompatible materials, and proteins with extended circulation. Here, we report our efforts towards creating “stealth polyplexes”. A comb-type polycation, poly-L-lysine-graft-PEG copolymers were successfully prepared by ring opening of PEG-epoxide with e-amino lysine groups of linear poly-L-lysine. The ratios of PEG-epoxide to poly-L-lysine, PEG-epoxide size (2K, 3K, and 5K), and poly-L-lysine size (10K, 26K, and 38K) were varied. Copolymers with as little as 2% grafted PEG chains sterically stabilized DNA/copolymer complexes (polyplexes) even at charge neutrality. These polyplexes, formed with copolymers with various size of PEG chains grafted on various lenghths of poly-L-lysine backbone, remained relatively small, approximately 100 nm in saline With higher degree of grafting, the binding was significantly diminished. In addition, the morphology of polyplexes changed from thoroidal to more elongated, worm-like forms. Some globular structures were detected in cases of a lower degree of grafting. Finally, DNA release form polyplexes when exposed to negatively charged macromolecules, poly-L-aspartic acid sodium salt, is very structure dependant. Enhanced levels of luciferase expression observed with PLL-PEG polyplexes versus either free DNA or PLL polyplexes are encouraging and warrant further optimization of the polymeric gene delivery system.

An investigation on the modification of polypropylene by grafting of maleic anhydride based on the aspect of adhesion

Isotactic polypropylene was modified by a chemical grafting of maleic anhydride in a molten state. The degree of grafting, ranged from 0.078-0.368%, was determined by a titration method. Isotactic polypropylene modified by chemical grafting of maleic anhydride was used as an adhesive in bonding the cold-rolled steel sheets for the correlation of its bondability. It was found that the maximum adhesive strength 159 kg/cm 2 was obtained from a degree of grafting 0.217%. A higher degree of grafting was detrimental not only to the initial adhesive strength, but also to the durability aged in a wet environment. Electron spectroscopy for chemical analysis was used to analyze the failure loci, because the joint was separated by shearing.

An investigation on the modification of polypropylene by grafting of maleic anhydride based on the aspect of adhesion

Isotactic polypropylene was modified by a chemical grafting of maleic anhydride in a molten state. The degree of grafting, ranged from 0.078–0.368%, was determined by a titration method. Isotactic polypropylene modified by chemical grafting of maleic anhydride was used as an adhesive in bonding the cold-rolled steel sheets for the correlation of its bondability. It was found that the maximum adhesive strength 159 kg/cm2 was obtained from a degree of grafting 0.217%. A higher degree of grafting was detrimental not only to the initial adhesive strength, but also to the durability aged in a wet environment. Electron spectroscopy for chemical analysis was used to analyze the failure loci, because the joint was separated by shearing. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 383–387, 1998

Drug permeation through a temperature-sensitive poly( N- isopropylacrylamide) grafted poly(vinylidene fluoride) membrane

Poly( N-isopropylacrylamide) (poly(NIPAAm)) is a temperature sensitive polymer, which has been used in the development of thermally controlled devices. In the present study, poly(NIPAA)m grafted poly(vinylidene fluoride) (PVDF) membranes were prepared by an irradiation method and fluxes of model compounds across the various grafted membranes were measured. The effectiveness of various grafted membranes to control drug fluxes by temperature was studied using FITC-dextrans (molecular weights 4400–50 600) and mannitol as model compounds. Also, the effect of environmental conditions on the LCST of the membrane was evaluated. The fluxes of bigger molecules across a temperature sensitive, porous poly(NIPAA)m–PVDF membranes were effectively controlled by temperature, environmental ionic strength and degree of grafting of the membrane, while flux of the smaller molecules was not controlled thermally even at high degree of membrane grafting. These result indicates that the studied membranes are useful in controlling the permeation of high molecular weight compounds such as polynucleotides, peptides and proteins.

Tailoring a Brush-Type Interface Favorable for Capturing Microbial Cells

A brush-type polymeric interface was prepared by grafting glycidyl methacrylate (GMA), an epoxy-group-containing vinyl monomer, onto a polyethylene (PE)-based backbone using the radiation-induced graft polymerization (RIGP) technique. PE was irradiated with an electron beam at a total dose ranging from 10 to 200 kGy before grafting. GMA was grafted and its epoxy ring was opened by diethylamine (DEA) to introduce tertiary amino groups. By irradiating PE before grafting at various total doses, the density of the graft chain was altered, and by controlling the degree of GMA grafting, the length of the graft chain was changed. As a result, a strategy for tailoring the characteristics of a “brush bed” on the polymeric interface to make it desirable for capturing microbial cells has been explored. The prepared brush-type interfaces were examined for their microbial-cell-capturing ability by contacting with aStaphylococcus aureusIFO 12732 cell suspension in batch mode. The capturing-rate constant of each interface is determined and used as a parameter for evaluation. The brush-type interface prepared at a high total dose with a high degree of GMA grafting was found to act as a fast-capturing interface forS. aureus.

Nondegradative melt functionalization of polypropylene with glycidyl methacrylate

The melt grafting of glycidyl methacrylate (GMA) onto powdered isotactic polypropylene (PP) in a Haake Rheocord RC90 mixer was studied. Grafting degrees were determined by nonaqueous back titration of trichloroacetic acid with sodium hydroxide. The extent of degradation and crosslinking of PP during grafting was indicated by the melt-flow rates (MFR) of the grafted samples. The influences of GMA concentration, initiator type and concentration on grafting degree, reaction efficiency, and degradation were evaluated. A novel method was developed to obtain a high grafting degree with little degradation of PP using acrylamide (AM) as the initiating agent. The grafting process occurred before or during the melting of PP (i.e., solid-state grafting), at which temperature crosslinking is preferred over chain scission. Primary free radicals generated from the rapid decomposition of AM have a higher tendency to attack GMA molecules than PP chains. At the same estimated amount of primary radicals, both grafting degree and grafting efficiency increase with decreasing decomposition temperature of the initiator (for the same decomposition half-life) in the order of AM > benzoyl peroxide (BPO) > 2,5-di(t-butylperoxy)-2,5-dimethyl-3-hexyne (LPO). FunctionalizedPP with the desired grafting degree and little degradation of PP could be obtained by the use of mixed initiators. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1957–1963, 1998

Characterization of interpolyelectrolyte complexes between double-stranded DNA and polylysine comb-type copolymers having hydrophilic side chains.

The polyionic interaction between DNA and polycations grafted with hydrophilic dextran side chains was evaluated. The comb-type copolymers, poly(L-lysine)-graft-dextran, were successfully prepared by employing a reductive amination reaction between epsilon-amino groups of poly(L-lysine) (PLL) and the reductive ends of dextran (Dex). A coupling efficacy on the order of 70% was obtained regardless of intrinsic philicities of the solvents used, either aqueous buffer or DMSO. The resulting graft copolymers, which varied in the degree of grafting and the length of hydrophilic side chains, formed a soluble complex with DNA. They also affected the melting behavior of double-stranded DNA (dsDNA) in different ways. Copolymers having a high degree of grafting thermally stabilized dsDNA without affecting its reversible transition between single-stranded and double-stranded forms. However, copolymers with a low degree of grafting or with a high degree of grafting of short dextran chains impeded the reversibility of this transition. Furthermore, highly grafted copolymers also accelerated the hybridization of DNA strands in a low-ionic strength medium. It is of particular note that these copolymers scarcely altered circular dichroismic signals of dsDNA even when the copolymers were added in excess. This suggested that the copolymer interacted with dsDNA without affecting its native structure or physicochemical properties. Finally, the copolymer even formed a stable complex with a short oligonucleotide (20 bases). We, therefore, concluded that, by regulating the degree of grafting and the molecular weight of grafted side chains, it would be possible to design novel different graft copolymers capable of acting as carriers of functional genes to target cells or tissue.

Radiation grafting of acrylamide onto starch-filled low density polyethylene

Acrylamide (AAm) was grafted on the surface of starch-filled low density polyethylene (SLDPE) and low density polyethylene (LDPE) films by the mutual irradiation technique at doses from 0.75 to 5 kGy. The effect of dose, solvents and dihydroxybenzoquinone on the degree of grafting was studied by Fourier transform infrared spectroscopy and the weight measurement method of extracted films at a constant monomer concentration (10% w/w). An ultraviolet spectrophotometer was also used to elucidate the results of the above methods. Grafting on SLDPE and LDPE samples reaches a maximum followed by a slight decrease with increasing dose. A higher degree of grafting was obtained on SLDPE samples compared with that on LDPE. An induction period was observed in the case of the samples prepared in tetrahdyrfuran (THF) as the solvent compared with those in chloroform. Addition of benzene to chloroform and THF (50% v/v) accelerates the rate of AAm grafting on the samples. Dihydroxybenzoquinone inhibits the grafting reactions of the samples especially in the THF solutions. The water uptake measurement of the samples correlates with the degree of grafting.

Graft Copolymers of Polypropylene Films. 1. Radiation-induced Grafting of Mixed Monomers

Radiation graft copolymerization of comonomer mixtures of acrylic acid (AAc) and styrene (S) onto polypropylene (PP) films by the mutual method has been investigated. The effect of different factors that may affect the grafting yield, such as inhibitor concentration (Mohr’s salt), solvent composition (MeOH and H2O), radiation dose and dose rate, was studied. It was found that Mohr’s salt was very effective when the content of AAc in the comonomer mixtures was low. However, the addition of 1·25wt% of Mohr’s salt reduced homopolymer formation and enhanced the grafting process. Graft copolymerization in the presence of a solvent mixture composed of methanol and water was found to afford a higher grafting yield than in pure methanol, regardless of the composition of the comonomer mixture used. However, the highest degree of grafting was obtained at a solvent composition of 20% H2O: 80% MeOH and a comonomer mixture of 20% AAc: 80% S. An attempt was made to determine each PAAc and PS fraction by different methods in the graft copolymer obtained. Elemental analysis indicated that the PAAc fraction with respect to PS in the graft copolymer decreased with increasing AAc ratio in the comonomer feed solution. The rough assessment of these fractions by IR spectroscopy showed similar trends. The reactivity ratios of AAc and S monomers determined in the present graft copolymerization system were found to be 0·45 and 1·3, respectively. © of SCI.

Amphiphilic Graft Copolymers as Phase-Transfer Catalysts in a Solid-Liquid System

Abstract Amphiphilic graft copolymers consisting of a hydrophobic backbone and poly(oxyethylene) (PEO) side chains were employed as solidliquid phase-transfer catalysts (PTC) in the substitution of octylbromide by solid potassium phenoxide in toluene. A wide variety of structures were synthesized via ester substitution of poly(phthalimidoacrylate) (PPIA) or poly(phthalimidoacrylate-co-styrene) [poly(PIA-co-St)] with amino-functionalized methoxy-PEO (MPEO-NH2). The phase-transfer catalytic activity (PTA) of these soluble graft copolymers was studied as a function of the structure of the backbone, the length of the side chains, and the graft density. The graft copolymers of a high degree of grafting showed PTA higher than that of parent PEOs. GPC was used to study the behavior of the graft copolymers in toluene at 90°C. It is believed that the phase-transfer reaction is accelerated in the PEO microphase.

Emulsifier free grafting of styrene and methyl methacrylate concurrently onto polybutadiene and determination of the copolymer microstructure

Styrene/methyl methacrylate ( 75 25 ) monomer mixtures were copolymerized at 323 K in the presence of a polybutadiene seed latex using either a water soluble (potassium persulfate) or an oil soluble (cumene hydroperoxide) initiator. The polybutadiene seed latex was made via an emulsifier free emulsion polymerization process. The graft copolymerizations were performed over a range of emulsifier concentrations. The emulsifier free polymerization with cumene hydroperoxide shows a very high degree of grafting while neither secondary nucleation nor coagulation was observed. Furthermore, the graft polymers have been extensively studied in terms of intra- and intermolecular microstructure. For this purpose, the breaking of the polymer backbone by means of ozonolysis was necessary. The grafted styrene/methyl methacrylate copolymer is less rich in styrene than the free copolymer. The chemical composition distributions of the graft copolymer were broader than those of the free copolymer.

Polymeric carriers for covalent immobilization of amino groups containing compounds

Graft copolymers of acryloylchloride (AC) with polyethylene (PE) and polyethyl eneterephtalate (PET) have been synthesized by grafting of AC from the vapor phase under mutual γ-irradiation. It has been shown that both the amount of grafted reactive chains and their structure was determined by the polymer: monomer ratio and the total irradiation dose. The high grafting degree of reactive groups and their ability to interact with free amino groups of biological molecules both in organic media and in water solutions make these functionalized polymers suitable as reactive carriers for covalent immobilization of various amino groups containing compounds.

Modification of natural rubber by different grafting techniques

An attempt has been made to graft a hydrophylic monomer of N,N.dimethyl acrylamide (DMAA) onto natural rubber (NR) tube by simultaneous, per-oxidation and preirradiation grafting techniques. It was found that the grafting by simultaneous grafting technique results a maximum 29 wt% degree of grafting and by peroxidation and preirradiation techniques, results the maximum 42 wt% and 13 wt% degree of grafting, respectively. It was concluded that the peroxidation technique is the most appropriate to obtain a high degree of grafting in radiation copolymerization of DMAA onto NR.

Functionalization of polyethylene and ethylene propylene diene terpolymer in the bulk through dibutyl maleate grafting

AbstractFunctionalization of polyethylene (PE) and ethylene propylene diene terpolymer (EPDM) in the bulk through dicumyl peroxide (DCP) initiated grafting of dibutyl maleate (DBM) has been studied in the temperature range from 140 to 200°C. The degree of grafting has been determined by infrared spectrophotometry and DSC. The concentration of DBM and DCP has been optimized. 0.5 wt.‐% and 0.2 wt.‐% DCP for PE and EPDM, respectively, and 10% DBM for both have been found to be the optimum. The kinetics of the grafting reaction is comparable for PE and EPDM. The activation energy of grafting is ca. 145 kJ/mol for PE and ca. 130 kJ/mol for EPDM. The influence of structure of polyolefins on the degree of grafting has also been studied. A higher degree of grafting is obtained for PE than for EPDM. For PE/EPDM blends, the degree of grafting increases with increasing PE content in the blends. A through discussion and proposed mechanism for grafting and other competitive secondary reactions has been provided.

Rubber toughening of poly(methyl methacrylate). Part I: Effect of the size and hard layer composition of the rubber particles

AbstractPoly(methyl methacrylate) (PMMA) is a brittle material which can be reinforced by the incorporation of acrylic particles, which do not spoil the transparency but which considerably increase the toughness of the material. In that study, we have varied the particle size and the outer layer for anchoring with the matrix. The proportion of reinforcing material is kept constant and the particles have an elastomeric core structure and a hard outer layer of PMMA. Monitoring of the two parameters, the critical stress intensity factor KIC and the critical energy release rate GIC, which are given by the fracture mechanics under static and dynamic (impact) loading, has made it possible to establish an optimum size of the reinforcement of the order of 200 to 250 nanometers. This optimum size can be explained as being the best compromise between the initiation of the damage and the control of its propagation, and that makes it possible to avoid a premature catastrophic failure. It also appears that a higher degree of grafting and a higher molecular mass of the hard layer result in an improved toughness.

Preparation and properties of cationic membranes obtained by radiation grafting of methacrylic acid onto PTFE films

AbstractCationic membranes were prepared by direct radiation grafting of methacrylic acid (MAA) onto poly(tetrafluoroethylene) (PTFE) films followed by alkaline treatment to confer ionic character in the graft copolymer. The complete inhibition of homopolymerization of MAA by using ammonium ferreous sulfate (Mohr's salt) failed. However, the addition of 0.5 wt % FeCl3 to the monomer solution effectively inhibited the homopolymerization process and higher grafting yield was obtained. It was found that the graft polymerization proceeded successfully in presence of methanol/water mixture (30/70 wt %), and much higher degrees of grafting were obtained as compared with those in the presence of other diluents used here. The influence of irradiation atmosphere (air, N2 gas, and vacuum) on the grafting process was investigated. The dependence of the grafting rate on MAA concentration was found to be of orders 2.9 and 0.72 in the presence of 0.5 wt % Mohr's salt or 0.5 wt % FeCl3, respectively. This grafting system proceeds by the front mechanism. Investigation of mechanical properties, electrical conductivity, and swelling behavior of the grafted films revealed that such a copolymer could be acceptable in practical use as a cation‐exchange membrane.

Synthesis and characterization of bigraft copolymers based on grafted type peracid polymer

AbstractIn this study, a radiation‐induced copolymer, namely, polyethylene‐g‐acrylic acid and EVA‐g‐acrylic acid, in the form of a membrane, particulate, or tube was used as a substrate. The carboxyl groups of the grafted acrylic chains were oxidized into peracids. Optimal conditions for the oxidation, including the catalyst, reaction time, and temperature were investigated. Novel bigraft copolymers were then synthesized from the grafted polymeric peracid. A third component (e.g., 2‐hydroxyethyl methacrylate) was grafted through the decomposition of peracid groups. Abnormality in morphology of the acrylic acid grafted and HEMA bigraft membrane was investigated by SEM and TEM observation, which showed the levelling effect of the third component and manifested a third circular domain generated inside the membrane at high degree of grafting.

Acid‐ and base‐functionalization of ethylene‐propene rubbers, 3. Mechanical and dynamic‐mechanical characterization of the elastomer networks

AbstractInfluences of type and content of functional groups on the mechanical response of various functionalized (grafted) ethylene‐propene rubbers (EPRs) are reported. Grafted molecules include succinic anhydride (SA), monomethyl succinate (MMS) and 2‐(dimethylamino)ethylsuccinimide (DAESI). A semiquantitative correlation between the decrease of the mechanical properties at high grafting degree and degradation of the polyolefinic backbone is given. Also a study of the dynamic‐mechanical properties of the functionalized rubbers is reported. A rubbery plateau is found, the strength and temperature dependence of which is a function of the type and content of the grafted molecules.

Bulk functionalization of ethylene–propylene copolymers. II. Influence of the initiator concentration and of the copolymer composition and chain microstructure on the reaction kinetics

AbstractThe effect of the dicumylperoxide (DCPO) concentration on the kinetics of the bulk functionalization of an ethylene‐propylene copolymer (EPR) has been studied. It has been found that, enhancing the DCPO initial concentration in the reaction mixture, results in both increased initial reaction rate and grafting process efficiency. DCPO content also affects degradation, which always accompanies the grafting reaction. At high DCPO content, products with a high degree of grafting and intrinsic viscosity close to that of the parent copolymer can be obtained. Furthermore, the influence of the EPR composition and chain microstructure on the functionalization as well as on the degradation processes has been investigated. By increasing the C2 content in EPRs prepared by using vanadium‐based conventional catalysts, obtains faster functionalization kinetics and a less pronounced degradation of the products. At fixed experimental conditions, the highest grafting degrees have been obtained by using EPRs prepared by high‐yield titanium catalysts and characterized as a block‐like microstructure. The experimental results have been interpreted on the basis of a proposed reaction mechanism.

Modification of natural rubber tubes for biomaterials I. Radiation‐induced grafting of N,N‐dimethyl acrylamide onto natural rubber tubes

AbstractRadiation‐induced simultaneous grafting of N,N‐dimethyl‐acrylamide (DMAA) onto natural rubber (NR) tubes has been studied to improve blood compatibility of the NR tubes. Concerning grafting of DMAA onto NR tubes, it was found that the grafting proceeds effectively in the presence of carbon tetrachloride (CCl4) as a solvent. The degree of grafting was found to be saturated at about 26 wt%, but a higher degree of grafting can be obtained by either “so called two‐step grafting” or “putting a standing time for a while before irradiation.” The initial grafting rate was proportional to 0.85 power of dose rate. The apparent activation energy of the graft‐copolymerization was 7.42 kcal/mol. Evaluation of blood compatibility of DMAA‐grafted NR tubes has been carried out by ex vivo test. According to the results, significant improvement of blood compatibility was obtained for the samples in which degree of grafting is higher than 30 wt%.