SynopsisReactive microspheres suitable for binding proteins were prepared using emulsifier-free emulsion copolymerizations of styrene (St) and acrolein (AL) with various molar ratios of monomers St and AL. A maximum polymerization rate was obtained when the molar ratio of the monomers was 1 : 1. The diameter of the latex particles increased with increase in the amount of monomer AL. The amounts of aldehyde groups on the latex particle surfaces were determined by conductometric titration. The binding capacity of the copolymer latexes with spacer molecules was also examined. INTRODUCTIONImmunomicrospheres have been widely used in the biomedical and biochemical fields.' Several types of polymeric microspheres with various functional groups on their surfaces have been synthesized as carriers of protein^.^-^ Recently polyacrolein (PA) microspheres were synthesized by aqueous polymerization under alkaline conditions and by aqueous radical p~lymerization.~.~ PA microspheres have many aldehyde groups on their surfaces, and aldehyde groups can be used for the covalent binding of amino group-carrying biological materials, e.g., proteins, drugs, and enzymes, by the formation of Schiff base a t room temperature. Polyacrolein microspheres, however, have some problems: Monodisperse particle size cannot be achieved easily, and the specific gravity of the particles is too high to keep them in suspension for a long time without sedimentation.A copolymerization of acrolein with styrene seems to be, on the contrary, advantageous, because the copolymer particles obtained have a lower specific gravity than the polyacrolein particles, and are expected to be highly monodisperse. In this paper, poly(styrene-co-acrolein) latex particles were synthesized by emulsifier-free emulsion copolymerization. The amount of aldehyde groups localized on the latex particle surfaces (surface -CHO) was determined by conductometric titration. The polymerization process was examined in detail. The binding capacity of the latex particles with spacer molecules (6-amino-n-caproic acid) was also examined.*To whom all correspondence should be addressed. EXPERIMENTALS MaterialsStyrene (St) and acrolein (AL) were purified by distillation in vacuo. 6-Amino-n-caproic acid (8ACA), hydroxylamine hydrochloride and sodium borohydride were of analytical grade, and used without further purification. Sodium borohydride was used as a reducing agent for the introduction of spacer groups into latex particles. l-Ethyl-3-(3-dimethylamino-propyl) carbodiimide hydrochloride (EDC) was used for the coupling of proteins with latex particles? Other reagents were commercially available. Water was doubly distilled before use. Preparation of Latex ParticlesA series of poly(styrene-co-acrolein) (PSt/AL) latexes were prepared by an emulsifier-free emulsion copolymerization. The polymerization recipes are listed in Table I. All polymerization reactions were carried out in a 250-mL round-bottomed four-necked flask. The prescribed amounts of St and AL were copolymerized in 125 mL of water...
SYNOPSISPoly(N-isopropylacrylamide) (PIPA) was synthesized by radical polymerization with 2,2'-azobisisobutyronitrile (AIBN) as an initiator and 3-mercaptopropionic acid (MPA) as a chain-transfer reagent in methanol (MeOH) at 70°C for 7 h. The resultant PIPA was grafted to polyallylamine hydrochloride (PAlAm -HCl) by amide formation under the influence of water-soluble carbodiimide l-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC). The graft polymer was made into microspheres (MS) by chemical crosslinking. The pH-responsive drug release of the graft polymer microspheres was examined by releasing phenobarbital natrium (PN), which was carried on the microspheres by physical adsorption. A dynamic dialysis technique was used in the drug-release experiment and the drug-release-rate constants reflecting the drug release characteristic of polymer microspheres were obtained by constituting a mathematical model. The results indicated that the homopolymer PAlAm microspheres and the copolymer PAIAm-g-PIPA microspheres are both pH responsive to release P N and that in the neutral pH condition the release rate is the slowest. 0 1995 John Wiley & Sons, Inc. INTRODUCTIONThe external signal-responsive drug-delivery system has been paid more and more attention. The obvious advantage of this system is the "on-off" switching control release of a drug from a drug carrier by surrounding signals such as heat, chemical compounds, electric field, and pH. Many polymers such as polyacrylamide,' poly(N-acryloylpyrrolidine),2 poly(N-alkyl-substituted acrylamides)? and some liposomes4 can be used to achieve this "onoff'' drug-control release as a drug-carrier martrix. Among these polymers, poly(N-isopropylacrylamide)5 (PIPA) has demonstrated noticeable thermosensitivity in terms of water swelling. Okahata et a1.6 even used a large nylon capsule membrane with a surface-grafted poly(N-isopropylacrylamide) to regulate reversily the permeation of NaCl and dyes by ambient temperature change. Recently, Schild7 reported a detailed review of the specificity, synthesis, and application of PIPA. Changes in the swelling states of PIPA gels can influence the diffusion of solutes from within the gels to the outside aqueous media. The changes were mainly thermosensitive. However, the review reported also a novel e x t e n~i o n~'~ of the PIPA system in which acrylic acid as a comonomer was introduced consequently, the copolymer possessed not only a thermal response but also pH sensitivity. The lower critical solution temperature (LCST) shifts to higher temperature at higher pH due to repulsion between the ionized groups. Yan" also utilized PIPA to obtain controllable catalytic activity of the enzyme immobilized by the medium temperature. According to Yan's work, the phase transition of the graft copolymer polyallylamine hydrochloride (PAlAm) -g-PIPA was influenced not only by the temperature but also by the pH of the dissolution medium. Extensively, we carried out drug-release experiments with PAIAmg-PIPA as a drug carrier at various pH's....
Polyallylamine-graft-poly(N4sopropylacrylamide) was prepared by coupling polyallylamine with poly(N4sopropylacrylamide) (the latter with an end-standing carboxyl group). The graft polymer obtained showed a temperature-responsive phase transition under alkaline conditions, whereas the starting poly(N-isopropylacrylamide) with end-standing carboxyl group showed temperature-sensitivity under acidic conditions. With an increase in the degree of grafting the temperature-sensitivity of the polymer under weakly alkaline conditions increases. Microspheres were prepared by cross-linking the graft polymers with glutaraldehyde in water-in-oil emulsion. Trypsin immobilized to the microspheres showed temperature-responsiveness in its catalytic activity. The graft polymer can be used as a component of temperature-sensitive devices in various forms.
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