Poly(dimethylaminoethyl methacrylate) grafted natural rubber from seeded emulsion polymerization

SYNTHESIS AND TEMPERATURE-RESPONSIVE BEHAVIOR OF N-VINYLCAPROLACTAM-GRAFTED NR

Temperature-responsive polymers are smart materials that respond to changes in temperature, making them suitable for a range of applications. We report the synthesis and temperature-responsive behavior of N-vinylcaprolactam-grafted natural rubber. The grafting reaction was carried out using deproteinized natural rubber (DPNR) latex, with 2,2′-azoisobutyronitrile (AIBN) as the free radical initiator. The temperature responsiveness of the graft copolymers was investigated using water swelling and contact angle measurement and compared with that of pure DPNR. The graft copolymer was found to be temperature responsive in the range 32–34 °C, whereas the DPNR was not responsive to temperature. Since the temperature responsiveness of graft copolymer is near the human body temperature, it can be used to fabricate biomedical and sensing materials. Dye adsorption studies revealed the Langmuir isotherm, indicating monolayer coverage. The novel temperature-responsive natural rubber demonstrated in this study has potential uses in a wide range of applications.

Deproteinised natural rubber latex grafted poly(dimethylaminoethyl methacrylate) - poly(vinyl alcohol) blend membranes: Synthesis, properties and application

Natural rubber latex was initially deproteinised (DNRL) and then subjected to physicochemical modifications to make high functional membranes for drug delivery applications. Initially, DNRL was prepared by incubating with urea, sodiumdodecylsulphate and acetone followed by centrifugation. The deproteinisation was confirmed by CHN analysis. The DNRL was then chemically modified by grafting (dimethylaminoethyl methacrylate) onto NR particles by using a redox initiator system viz; cumene hydroperoxide/tetraethylenepentamine, followed by dialysis for purification. The grafting was confirmed by dynamic light scattering, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The grafted system was blended with a hydrophilic adhesive polymer PVA and casted into membranes. The membranes after blending showed enhanced mechanical properties with a threshold concentration of PVA. The moisture uptake, swelling and water contact angle experiments indicated an increased hydrophilicity with an increased PVA content in the blend membranes. The grafted DNRL possessed significant antibacterial property which has been found to be retained in the blended form. A notable decrease in cytotoxicity was observed for the modified DNRL membranes than the bare DNRL membranes. The in-vitro drug release studies using rhodamine B as a model drug, confirmed the utility of the prepared membranes to function as a drug delivery matrix.

CHLOROHYDRINATION OF NR LATEX BY USING SODIUM HYPOCHLORITE FOR FUEL-RESISTANT MATERIALS

NR is hydrophobic and cannot be used to store, transfer, or make contact with hydrocarbon compounds. We report a simple method to increase the hydrophilicity of NR: a chlorohydrination reaction of NR latex by using sodium hypochlorite is described. It was found that only chlorohydrinated NR was obtained and side products were unnoticeable. The effects of sodium hypochlorite concentration, hydrochloric acid concentration, surfactant concentration, and reaction time on chlorohydrin content in NR were investigated. The swelling resistance of chlorohydrinated NR with 11% chlorohydrin content in diesel and gasohol fuels was improved nearly 3-fold and 4-fold, respectively, compared to that of the unmodified NR. The thermal and mechanical properties of the chlorohydrinated NR were characterized and found to be similar to those of pristine NR, indicating that the chlorohydrinated NR can be an excellent substitute for NR. This method has merits such as low cost of raw materials, easier and greener production processes than traditional methods, and scaling-up possibilities for the fabrication of chlorohydrinated NR for a variety of applications.

Effects of Type and Concentration of Initiator on Grafting of Acrylic Monomer onto Depolymerized Natural Rubber

Highly crosslinked epoxy resin for engineering applications is normally stiff but brittle. Therefore, many attempts have been made to improve its toughness. Nowadays, several studies have been done on toughening epoxy resin using natural rubber (NR) because it is abundant and comes from renewable resource. In the present work, NR was subjected to depolymerize in order to achieve molecular dispersion of NR in epoxy matrix. Depolymerized natural rubber (DNR) was prepared by adding a carbonyl compound to natural rubber latex solution and subjecting the mixture to air oxidation in the presence of a radical forming agent at 70°C. In addition, the interfacial adhesion between rubber and matrix must be present to achieve a significant increase in toughness. Hence, DNR was further functionalized by grafting with monomer mixture of methyl methacrylate (MMA)/glycidyl methacrylate (GMA) (90/10 wt/wt%) in an amount of 50% based on rubber content. Solution polymerization was used to graft such monomers using 2 hours reaction times at a reaction temperature of 80oC. Two types of initiator used were benzoyl peroxide (BPO) and azo-bisisobutyronitrile (AIBN). The amounts of initiator in the grafting process were 1, 2, and 3 parts per hundred of DNR. Effects of type and concentration of initiator on grafting efficiency of MMA/GMA monomer mixture onto depolymerized natural rubber were studied by proton nuclear magnetic resonance (1H-NMR) analysis. The molecular weight of DNR was characterized by gel permeation chromatography (GPC). The results indicated good evidence for the formation of graft co-polymers in the presence of both initiators, AIBN or BPO. However, the amounts of grafted MMA/GMA on DNR backbone using BPO was higher than those on DNR backbone using AIBN.

Synthesis of natural-synthetic hybrid materials from cellulose via the RAFT process

The synthesis and characterization of a novel natural-synthetic hybrid material based on cellulose is reported. The reversible addition-fragmentation chain-transfer (RAFT) process was used to graft poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) onto a cellulosic substrate. The weight ratio was increased with an increase in monomer concentration, polymerization time and degree of polymerization (DP). We found that the addition of free chain-transfer agent has a pronounced effect on the weight ratio, chain length of grafted polymer, monomer conversion and homopolymer formation in solution. The cellulose-graft-poly(2-(dimethylamino)ethyl methacrylate) copolymers were characterized by gravimetry, elemental analysis, attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, thermal analysis and atomic force microscopy. The dithioester end-group present at the chain end of PDMAEMA was removed via aminolysis. The livingness of the process was utilized to block-copolymerize styrene from the grafted PDMAEMA chains. The hydrophilic/hydrophobic properties of the novel cellulose-g-(PDMAEMA-b-polystyrene) material were illustrated by contact-angle measurements.

Wet STEM: A new development in environmental SEM for imaging nano-objects included in a liquid phase

Environmental scanning electron microscopy (ESEM) enables wet samples to be observed without potentially damaging sample preparation through the use of partial water vapour pressure in the microscope specimen chamber. However, in the case of latices in colloidal state or microorganisms, samples are not only wet, but made of objects totally submerged in a liquid phase. In this case, under classical ESEM imaging conditions only the top surface of the liquid is imaged, with poor contrast, and possible drifting of objects. The present paper describes experiments using a powerful new Scanning Transmission Electron Microscopy (STEM) imaging system, that allows transmission observations of wet samples in an ESEM. A special device, designed to observe all sorts of objects submerged in a liquid under annular dark-field imaging conditions, is described. Specific features of the device enable to avoid drifting of floating objects which occurs in the case of a large amount of water, thus allowing slow-scan high-definition imaging of particles with a diameter down to few tens of nm. The large potential applications of this new technique are then illustrated, including the imaging of different nano-objects in water. The particular case of grafted latex particles is discussed, showing that it is possible to observe details on their surface when submerged in water. All the examples demonstrate that images acquired in wet STEM mode show particularly good resolution and contrast, without adding enhancing contrast objects, and without staining.

A Method for Preparing Low-Allergen Natural Rubber Latex

The free radical polymerization of dimethylaminoethyl methacrylate (DMAEMA) on the surface of particles in natural rubber latex (NRL) was carried out using an iron(ii)/tetraethylenepentamine (TEPA) redox couple initiation system, which results in significant grafting of poly(DMAEMA) to the surface of the particles. Because poly(DMAEMA) functions as an electrosteric stabilizer, this leads to increased colloidal stability, which suggests that the proteinaceous material which normally provides the colloidal stability in NRL can be displaced. This opens the way to preparing barrier products of low allergenicity, because the allergic response from NRL products arises from this proteinaceous material. Dipped and cast films were prepared from the modified NRL and were shown to be of low allergenicity using the IgE-ELISA inhibition assay. Vulcanized films prepared from the modified latex were also found to be of low allergenicity compared to a compounded film of unmodified NRL prepared under similar conditions. The barrier integrity, tensile strength, and elongation at break values of vulcanized films prepared from the modified latex were also equivalent to the unmodified film, and their water sensitivity and ageing characteristics were not significantly different. This suggests that this modified NRL can be used as an effective low-allergy latex for personal barrier products such as surgical gloves.