Photoinitiation, 6. Copolymerization of styrene with maleic anhydride photoinitiated by the excited charge-transfer complex styrene-maleic anhydride

The kinetics of styrene (St) copolymerization with maleic anhydride (MA) initiated by light (at λ = 365 nm) was studied in acetone, acetonitrile, chloroform, and N,N-dimethyl formamide at 30°C. With the exception of the chloroform containing system, the copolymerizations took place in homogeneous reaction media. The copolymerization rate R_p = ?d([St] + [MA])/dt was found to be a function of the mole ratio of the comonomers in the reaction mixture. For a given ratio of comonomers R_p and the molecular weight of the resulting copolymer were found to be a function of the donor number of the solvent used for a given rate of initiation. Due to the dependence of R_p on the concentration of an equimolar mixture of both comonomers in acetone on [St] (at constant [MA]), and on [MA] (at constant [St]) the participation of the exciplex {St…acetone}^* in the initiation reaction can be expected. The ratio of the overall rate constants for the propagation (k?_p) and termination (k?_t) reactions, k?_p/2k?_t, determined by a rotating sector technique, was found to depend on the composition of the comonomer mixture. The copolymerization rate is proportional to the square root of the intensity of incident light, which, together with the observed inhibition effect of oxygen points to a radical mechanism of the photoinitiated copolymerization of St with MA. In the presence of the photosensitizer benzophenone in the system St/MA/acetone an increase in R_p was observed, accompanied by a decrease in molecular weight of the copolymer in comparison with the system without benzophenone.     

Controlled delivery of paclitaxel from stent coatings using novel styrene maleic anhydride copolymer formulations

The controlled release of paclitaxel (PTx) from stent coatings comprising an elastomeric polymer blended with a styrene maleic anhydride (SMA) copolymer is described. The coated stents were characterized for morphology by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and for drug release using high-performance liquid chromatography (HPLC). Differential scanning calorimetry (DSC) was used to measure the extent of interaction between the PTx and polymers in the formulation. Coronary stents were coated with blends of poly(b-styrene-b-isobutylene-b-styrene) (SIBS) and SMA containing 7% or 14% maleic anhydride (MA) by weight. SEM examination of the stents showed that the coating did not crack or delaminate either before or after stent expansion. Examination of the coating surface via AFM after elution of the drug indicated that PTx resides primarily in the SMA phase and provided information about the mechanism of PTx release. The addition of SMA altered the release profile of PTx from the base elastomer coatings. In addition, the presence of the SMA enabled tunable release of PTx from the elastomeric stent coatings, while preserving mechanical properties. Thermal analysis reveled no shift in the glass transition temperatures for any of the polymers at all drug loadings studied, indicating that the PTx is not miscible with any component of the polymer blend. An in vivo evaluation indicated that biocompatibility and vascular response results for SMA/SIBS-coated stents (without PTx) are similar to results for SIBS-only-coated and bare stainless steel control stents when implanted in the non-injured coronary arteries of common swine for 30 and 90 days.     

High pressure copolymerization of styrene with maleic anhydride

The radical copolymerization of styrene with maleic anhydride was investigated in an acetone solution at 40°C under high pressure up to 4000 kg/cm². Effects of pressure on the monomer reactivity ratio considering the influence of the penultimate monomer unit were studied from kinetic data and IR spectra. It has been found that the radical copolymerization rate increases with pressure, especially concerning the reaction of maleic anhydride with a polymer chain possessing a maleic anhydride unit preceding the active styrene chain end.     

The applicability of copolymer composition and sequence distribution data to the mechanistic study of the alternating copolymerisation of maleic anhydride with substituted styrene derivatives

The composition and sequence distribution of copolymers of maleic anhydride (MA) with p-methoxystyrene (p-MST) and p-chlorostyrene (p-CST) prepared in ethyl methyl ketone at 50 ± 0,1°C were analysed using ¹³C DEPT NMR techniques, in order to compare the applicability of composition and sequence distribution data to the study of the mechanism of copolymerisation using the terminal, penultimate and complex-participation models. In the case of the strongly alternating copolymerisation of p-MST with MA, the comparison of models on the basis of sequence distribution data was found to be better at separating each model in terms of its applicability, with the complex-participation model providing the best fit to the data. In the case of the less strongly alternating copolymerisation of p-CST with MA, neither method of comparison could clearly distinguish between the penultimate and complex-participation models.     

Kinetics of the copolymerization of styrene with maleic anhydride in ethyl methyl ketone

The copolymerization of styrene and maleic anhydride in ethyl methyl ketone as solvent and with benzoyl peroxide as initiator at 60–80°C in the entire feed composition range was studied. The resulting copolymers appear to have negative and positive deviations from alternation as determined by use of elemental analysis. The experimental data were found to fit a three-reactivity-ratio copolymer composition equation from the penultimate model. The inclusion of the reactivity ratio, k_SM (=k_SMM/k_SMS), in addition to r_SS (=k_SSS/k_SSM) and r_MS (=k_MSS/k_MSM), allows prediction of a positive deviation from the alternation, i.e. the mole fraction of maleic anhydride in the copolymer being higher than 0,5.     

Synthetic antigens. II. Immunogenic, antigenic and adjuvant properties of a copolymer of styrene and maleic anhydride.

Immunogenic, antigenic and adjuvant properties of a polyanionic copolymer of styrene and maleic anhydride (PSM) are described. The results obtained showed that PSM was immunogenic in BALB/c mice when administered without adjuvant, the optimal dose being 0.01 mug/mouse. Antibodies could be detected only by precipitation in gel but not by agglutination. High molecular weight polymer (290 000 daltons) was a stronger immunogen and antigen than copolymers of lower molecular weights (85 000-210 000 daltons). PSM also showed adjuvant activity and enhanced the humoral response of mice against sheep red blood cells. Adjuvanticity was found only when 1 mug of PSM/mouse was applied. The results obtained suggest that PSM interacts with B rather than T cells.     

Some products of interaction of p-benzoquinone with styrene

Using equimolar concentrations of p-benzoquinone and styrene at 100°C, a compound consisting of one molecule of benzoquinone, one molecule of hydroquinone and one molecule of styrene was separated from the complex reaction mixture in a small yield. Quinhydrone was separated at short reaction time and hydroquinone at prolonged reaction times. Reaction mechanisms for the formation of these compounds are proposed. Solvent extraction, fractional precipitation, thin layer chromatography, IR and UV spectrophotometry, elementary analysis, and molecular weight determination were applied for separation and identification.     

Terpolymerization of maleic anhydride,styrene and electron-acceptor monomers

The free-radical terpolymerization of maleic anhydride, styrene, and acrylic monomers such as acrylonitrile, methyl acrylate and methyl methacrylate was studied. The alternating copolymerization of maleic anhydride with styrene was found to be favored in those systems. Contrary to theoretical predictions, maleic anhydride is more reactive than styrene in ternary systems. The relative reactivity of the acrylic monomers studied was found to decrease in the order: methyl methacrylate ≥ methyl acrylate > acrylonitrile. In the presence of a Lewis acid, such as ZnCl₂ or C₂H₅AlCl₂, the relative reactivity of acrylic monomers increases and at the respective complexing agent concentration the copropagation of the acrylic monomer with styrene can dominate. On the basis of the results obtained, some aspects of the mechanism of alternating propagation in systems comprising an electron-donor monomer and two electron-acceptor monomers are discussed.     

Discussion on the mechanism of alternating copolymerization of styrene and maleic anhydride

To clear up the detailed mechanism of the alternating copolymerization of styrene (St) and maleic anhydride (MAn) concerning the initiation species, the propagation species, the tendency of the chain transfer reaction as well as the directional tendency of the reaction between copolymer radicals and monomer complexes, the role of the charge transfer complexes, characterization of end groups and additional donor effects were examined. The equilibrium constant of the St/MAn (1 : 1) complex was determined to be 0.31 by NMR spectroscopy, that suggested considerable amounts of complexes existing in the system. As expected, a small quantity of initiator (¹⁴C-azobisisobutyronitrile (AIBN)) was incorporated into the St/MAn copolymer. Chlorine atoms were scarcely incorporated into the copolymer synthesized in CCl₄ with AIBN or benzoyl peroxide (BPO) as an initiator. Hence the copolymerization was considered to be induced only by attacke of initiator radicals to the monomer or the complexes, contrary to the usual conception of telomerization. When the electron donor monomer was added to the system, the terpolymerization could be treated as a copolymerization of the two complexes, i.e., St/MAn and Donor/MAn. By adding naphthalene the rate maximum point shifted from higher concentration of MAn to the equivalent concentration of St and MAn. Degradative chain transfer to N.N-dimethylaniline was observed, confirming the existance of poly-MAn radicals. It was suggested from these results that the charge transfer complex and uncomplexed MAn took part in the copolymerization of St and MAn. This was proved kinetically. The whole mechanism was discussed.     

The terpolymerisation of styrene,methyl methacrylate and maleic anhydride

Application of the Alfrey-Goldfinger equations to data from terpolymerisations of styrene, methyl methacrylate and maleic anhydride leads to values of the relative reactivity (R) of styrene and methyl methacrylate towards the maleic anhydride radical that are dependent upon the concentrations of the monomers in the feeds. It is shown that it is unlikely that this effect arises from the influence of maleic anhydride-comonomer complexes but may indicate the importance of a penultimate group effect involving styryl radicals.     

Solvent effect on the asymmetric induction copolymerization of styrene with maleic anhydride in the presence of lecithin

The asymmetric induction radical copolymerization of styrene (St) with maleic anhydride (MAn) was studied in various solvents with different dielectric constants in the presence of lecithin as a chiral surfactant. The observed specific rotation of the resulting alternating copolymer decreased with an increase in the dielectric constant of the solvent used. It was concluded that the asymmetric induction depends mainly upon the incorporation of MAn within the reversed lecithin micelles.     

Viscous properties of butadiene/styrene triblock copolymer solutions

Viscosities of dilute and concentrated solutions of a styrene-butadiene-styrene triblock copolymer in solvents of different thermodynamic quality and at different temperatures were studied. In 1,4-dioxane (theta solvent for butadiene blocks) the viscosity derived polymer-polymer interaction parameter has been found to be much smaller than in decalin (theta solvent for styrene blocks) or in tetralin (good solvent for both blocks). The dynamic viscosity and the enthalpy of activation of viscous flow, ΔH, increase much faster for 1,4-dioxane solutions with increasing concentration than those for decalin or tetralin. The different properties of solutions in different solvents are discussed in terms of the physical structure of the systems.     

Antigen-binding activity of antibodies immobilized on styrene copolymer beads

An important element of the Kodak thin-film immunoassay is antibody immobilized on small polymer beads. Monodisperse styrene copolymer beads offer a well-defined, high surface area substrate for covalent immobilization of monoclonal antibodies. The authors have used the ability of an immobilized monoclonal antibody directed against phenobarbitol, Phe 1.9, to recognize an antigen-enzyme conjugate to determine the extent of antibody activity retention and find that the packing density of antibody at the surface and the copolymer composition are important variables. For polystyrene homopolymer and some copolymers, antibody retention is greater as the packing density at the surface increases. Small changes in the copolymer composition, such as addition of 1% acrylamide or 10% acrylic acid, significantly increase the retention of binding activity of the antibody. The chemistry for covalent coupling of the antibody to the surface is also important. Phe 1.9 coupled to chloromethyl styrene copolymer beads retains less activity than when coupled to vinyl sulfone copolymer beads. Monodisperse sytrene copolymer beads provide great flexibility in the design of rapid immunoassays since a copolymer bead can be tailored to the specific requirements of the antibody and the analyte.     

Synthesis of antitumor-active conjugates of adriamycin or daunomycin with the copolymer of divinyl ether and maleic anhydride

Polymeric conjugates of adriamycin (ADR) ( 2 ) or daunomycin (DM) ( 3 ) were synthesized by reaction of the drugs with the copolymer of divinyl ether and maleic anyhdride (DIVEMA) ( 1 ). The content of ADR moieties in the DIVEMA conjugate ( 4 ) could be varied depending on the reaction conditions up to 35,8 wt.-%. Considering the low toxicity and the high possibility of renal excretion, DIVEMA with M?_w of 7000 and M?_w/M?_n = 1,6 was used for the conjugation. The rate of drug release from the conjugate was determined under physiological conditions by reversed phase HPLC. Within 14 days only 15% of the attached ADR was released from conjugate 4 . The antitumor activity of the conjugates was tested in vitro and in vivo against mouse P388 leukemia. Conjugate 4 proved to be 28 times less active than ADR in vitro, which could be explained from the slow drug-release. On the contrary 50% of the leukemic mice treated by 4 survived more than 60 days, whereas no mice given ADR alone or the admixture of ADR and DIVEMA survived 30 days. An antitumor activity of the polymeric conjugate better than that of the free drug was also observed in vivo with DM. Such a polymeric effect can be attributed either to the change in body distribution, the difference in pharmacokinetics, or the slow drugrelease.     

Kinetic and structural studies of the copolymerization of the cleavable bismaleimide p-maleimidobenzoic anhydride and styrene

The polymerization of a bismaleimide-styrene system was studied by using a model compound, p-maleimidobenzoic anhydride, that can be split by simple hydrolysis. Compared to known divinyl systems, a decreased reactivity of the pendant double bonds is observed, probably as a result of cyclization and the steric excluded volume effect. The use of a solvent causes an additional shift of the gel point towards higher conversion. Hydrolysis of gelled material affords soluble p-maleimidobenzoic acid-alt-styrene copolymers. Compared to a linear system, methyl p-maleimidobenzoate and styrene, the primary chains obtained by hydrolysis show an increased polydispersity, probably due to retardation of bimolecular termination of the free radicals that are attached to the polymer network (gel effect).     

Photoinitiation, 7. Terpolymerization of the system acrylonitrile/maleic anhydride/styrene

The photoinitiated (at wavelength λ = 365 nm) terpolymerization of acrylonitrile, maleic anhydride and styrene in the presence and/or absence of additives such as ZnCl₂ or N,N-dimethylaniline (DMA) in acetone was studied, and the relative reactivities R of maleic anhydride and acrylonitrile towards a styryl radical were determined. In the presence of ZnCl₂ and/or DMA, the relative reactivities R are by about 40% lower than the value of R (= 13,3 ± 2,1) for the terpolymerization system without additives.     

Copolymerization of styrene,maleic anhydride and acrylonitrile up to high conversion

Terpolymers of styrene, maleic anhydride and acrylonitrile were synthesized by variation of the molar ratios of the three monomers at total monomer conversion up to 90 mol-%. Polymerizations were performed with total initial monomer concentrations of 0,25 g/mL in benzene at 60°C with AIBN as initiator. The composition of the terpolymers was determined by elemental analysis. Although this ternary system comparises only one electron-donor monomer and two electron-acceptor monomers, maleic anhydride is the most reactive monomer and is incorporated in higher proportions than the other monomers.