Polymérisation de monomères carbonates de vinyle

Free-radical polymerizations of several aliphatic and aromatic N-substituted vinyl carbonates are described. The bulk polymerization was initiated at 35°C with di-tert-butylcylohexyl peroxydicarbonate yielding high-molecular-weight poly(vinyl carbonate)s. The structure of these polymers was examined by FTIR spectroscopy and the molecular weight by GPC. The effects of the substituents on the physical properties of the resulting polymers were studied. A comparison of the properties with those of similar compounds described in the literature was made.     

Polymerization of 1,2-epoxypropane and 1,2-epoxycyclohexane by diethylzinc-polyhydric phenol and/or phenol or 1-phenoxy-2-propanol as catalysts

1,2-Epoxypropane and 1,2-epoxycyclohexane were polymerized in the presence of catalysts derived from reactions of diethylzinc with a polyhydric phenol (4-tert-butylcatechol, pyrogallol) and/or phenol or 1-phenoxy-2-propanol in 1,4-dioxane solution, varying the polymerization temperature and time. The polymers formed in these polymerizations were analysed by means of ¹H NMR, ¹³C NMR and UV spectroscopy in terms of the polymer chain microstructure and chain end-groups. The poly(propylene oxide) (PPO) obtained appeared to be a high-molecular-weight polymer with prevailing isotactic diads (mole fraction in the range of 0,65–0,72). It was found to consist of a predominant amorphous (atactic) fraction and a crystalline (isotactic) fraction. An enhancement of both the crystallinity and the average molecular weight of PPO was observed with an elongation of the duration of the polymerization. Therefore, it was concluded that the catalyst enantioselectivity increases with progressing polymerization. The poly(cyclohexene oxide) (PCHO) obtained appeared to be a polymer with prevailing syndiotactic diads (mole fraction in the range of ca. 0,58–0,80) and threo-enchainement of monomeric units. This was explained in terms of inversion of the configuration at the carbon atom of the epoxide ring upon cleavage. A possible mechanism for the epoxide polymerization by the coordination catalysts studied is presented.     

Synthesis of poly(2-ethyl-2-hydroxymethyltrimethylene carbonate)

2-Ethyl-2-hydroxymethyltrimethylene carbonate (5-ethyl-5-hydroxymethyl-1,3-dioxan-2-one) ( 1 ) was treated with trimethylsilyl chloride, benzyl chloroformate and phenyl isocyanate to give the corresponding 5,5-disubstituted 1,3-dioxan-2-ones 2 , 3 and 4 . These monomers were subjected to anionic ring-opening polymerization reactions with lithium alcoholates as initiators. The polymers obtained usually exhibit linear structure; under special conditions slightly branched polymers were obtained. Poly( 2 ) and poly( 3 ) were subjected to polymer-analogous reactions—hydrolysis and hydrogenation—by which the protective groups are removed and poly( 1 ) was obtained. The hydroxyl groups in poly(1) are susceptible to a polymer-analogous reaction. Poly( 4 ) obtained by reaction of poly( 1 ) with phenyl isocyanate was identical with poly( 4 ) obtained by ring-opening polymerization of the corresponding monomer 4 . All these new monomers were characterized by means of ¹H and ¹³C NMR spectroscopy as well as elemental analysis. The polymers were analyzed with respect to their primary structure, their molecular weight and molecular weight distribution. The thermal properties of some of the polymers are discussed.     

Polyethers for biomedical applications. Polymerization of propylene oxide by organozinc/organotin catalysts

The polymerization of propylene oxide to obtain a high-molecular-weight polymer with an atactic structure required for the application as artificial blood vessels was investigated using combinations of organozinc and organotin compounds as catalyst. The composition of the most active catalyst, resulting from the reaction of diphenyltin sulfide with bis(3-dimethyl-aminopropyl)zinc, was found to be R(C₆H₅)₂Sn(SZn)₂R with R = (CH₂)₃N(CH₃)₂. Using this catalyst, an anionic coordination polymerization was observed with neither stereoselectivity nor living type or cationic features. At low catalyst concentration (0,03 mol-% Zn) a high-molecular-weight poly(propylene oxide) (PPOX) was obtained in 80–90% yield (M _w = 500000; 40% isotactic). Lowering of the catalyst concentration and increasing the polymerization temperature changed the kinetics and the stereochemistry of the polymerization leading to polymers of lower molecular weight and to a decrease in the isotactic PPOX fraction to 20%, probably due to an association of the catalytic species.     

Anionic polymerization of alkyl methacrylates in the presence of diethylzinc

The anionic polymerizations of methyl methacrylate (MMA), isopropyl methacrylate (IPMA), and tert-butyl methacrylate (TBMA) in THF in the presence of diethylzinc were investigated. The addition of diethylzinc to the reaction mixture remarkably lowers the polymerization rates of the methacrylates initiated with potassium diphenylmethanide to afford polymers with the predicted molecular weights and very narrow molecular weight distributions, while PMMA and poly(IPMA) produced with potassium diphenylmethanide in the absence of diethylzinc have rather broad molecular weight distributions. The stereospecificities of PMMA, poly(IPMA) and poly(TBMA) are not affected by diethylzinc. From the result of the block copolymerization of MMA with TBMA, it was found that the presistency of the anionic propagating end of PMMA is significantly enhanced by the addition of diethylzinc. The retardation of the polymerization rates and the enhancement of the persistency of the propagating end in the presence of diethylzinc may be caused by the weak coordination of diethylzinc toward the enolate anions at the propagating end groups.     

Synthesis, characterization, biodegradation, and drug delivery application of biodegradable lactic/glycolic acid polymers: I. Synthesis and characterization

A series of lactic/glycolic acid polymers with various molar ratios of lactic to glycolic acid and various molecular weights were synthesized using the ring-opening polymerization method. The polymerization conditions for the lactic/glycolic acid polymer synthesis were as follows: 150 degrees C, 700 microm Hg, 3 h, 0.03 wt% of catalyst (stannous 2-ethyl-hexanoate) concentration. The molecular weight of these polymers was controlled by using a molecular weight controller, lauryl alcohol. The synthesized polymers have been characterized with respect to polymer composition, molecular weight, inherent viscosity, and glass transition temperature. The characterization experiments show a good correlation between the polymer compositions and the feed ratios of lactic to glycolic acid. The molecular weight of the lactic/glycolic polymers, ranging from 10,876 to 166,630 D and the intrinsic viscosity of the polymers, ranging from 0.16 to 0.86 dl g(-1), are controlled by the amount of molecular weight controller used. The effect of the amount of the molecular weight controller on the polymer molecular weight and the polymer inherent viscosity was studied. Results indicate that the molecular weight and inherent viscosity of the polymers have a log-log linear relationship with the amount of molecular weight controller used. The lactic/glycolic acid polymers are amorphous, glassy, and transparent. The glass transition temperature of the polymers range from 21.95 to 51.29 degrees C, depending on the polymer molecular weight and the composition.     

Radical polymerization and copolymerization of some vinyl phosphates

Diethyl vinyl phosphate ( 1 ), diphenyl vinyl phosphate ( 2 ), and phenyl divinyl phosphate ( 3 ) were prepared, and their polymerization and copolymerization behaviors as well as the hydrolysis of the polymers obtained were investigated. The monomers 1 and 2 were homopolymerized to give low molecular weight polymers, probably as a result of high chain transfer reactivity to monomer. Although the monomer 3 gave a cross-linked polymer, this polymerization was found to proceed mainly by a cyclopolymerization mechanism to give a polymer with a five-membered ring unit which was readily hydrolyzed. The alkaline hydrolysis of poly( 1 ) occurred only partly and thus pure polyvinyl alcohol was not obtained. From the copolymerizations of 1 and 2 with vinyl monomers such as vinyl chloride, the reactivities of these monomers were found to be somewhat lower than that of vinyl acetate.     

Mesogen-jacketed liquid crystalline polymers via stable free radical polymerization

Stable free radical polymerization has been used in the controlled synthesis of poly(2,5-bis[(4-butylbenzoyl)oxy]styrene), PBBOS. This “mesogen-jacketed liquid crystalline polymer”, which has mesogenic units attached directly to the backbone in a side-on mode, has been found to exhibit thermotropic liquid crystallinity similar to more conventional main-chain architectures. Stable free radical polymerization of PBBOS consistently produced molecular weight distributions below the theoretical limiting polydispersity of 1.5 calculated for a conventional free radical polymerization process. Surprisingly, a comparison of the synthesis of polystyrene to the polymerization of PBBOS under nearly identical conditions showed that the PBBOS polymerized with a significantly higher reaction rate and monomer conversion efficiency. The nematic phase of these polymers was determined to be stable over the temperature range spanning the polymer glass transition temperature up to the temperature for thermal decomposition. The molecular arrangement of the PBBOS polymers was examined by wide-angle X-ray diffraction and is described here.     

Protection and polymerization of functional monomers, 22. Synthesis of well-defined poly(4-vinylbenzoic acid) by means of anionic living polymerization of N-(4-vinylbenzoyl)-N′-methylpiperazine,followed by deprotection

Anionic polymerizations of N-(4-vinylbenzoyl)-N′-methylpiperazine ( 3a ) and N-(4-vinylbenzoyl)morpholine ( 3b ) were carried out in tetrahydrofuran at ?78°C with oligo(α-methylstyryl)-dilithium, -disodium, and -dipotassium. The polymerizations of both 3a and 3b proceeded quantitatively to give stable living polymers having predicted molecular weights and narrow molecular weight distributions. Novel block copolymers, poly( 3a )-block-polystyrene-block-poly( 3a ) and poly( 3b )-block-polystyrene-block-poly( 3b ), were synthesized by using these living polymerization systems. Under acidic conditions (6 N HCl in 1,4-dioxane-water), quantitative hydrolysis of the amide linkage of the poly( 3a ) was achieved to give a well-defined poly(4-vinyl-benzoic acid).     

Evaluation of polyphosphates and polyphosphonates as degradable biomaterials.

A series of polymers, bisphenol A-based poly(phosphoesters), were evaluated as degradable biomaterials. Degradation was observed for the four polymers studied under both in vitro and in vivo conditions. The rate of degradation was affected by polymer side-chain structure and correlated with the swelling behavior. The ethyl side-chain polymers absorbed more water than their phenyl counterparts. Among the sterilization methods, UV irradiation followed by antibiotic treatment was the most suitable, as steam autoclave and ethylene oxide treatments altered the properties of several of the poly (phosphoesters). Tissue response to the poly(phosphoesters) in rabbits was characterized by minor encapsulation and slight or no lymphocyte, giant cell, or macrophage activity. No evidence of edema or necrosis was found. The elastic moduli of these materials varied from 488 MPa for poly(bisphenol A-ethylphosphate) (BPA/EOP) to 627 MPa for the more rigid poly(bisphenol A-phenylphosphonate) (BPA/PP). The ultimate strength, modulus, and energy to failure of BPA/PP were lower than those of similarly compression molded high-molecular-weight poly(L-lactic acid) (PLLA).     

Anionic polymerization of monomers containing functional groups, 11. Anionic polymerizations of alkynyl methacrylates

Anionic polymerization of 2-propynyl methacrylate ( 1 ), 3-trimethylsilyl-2-propynyl methacrylate ( 2 ), 2-butynyl methacrylate ( 3 ), and 3-pentynyl methacrylate ( 4 ) was carried out in tetrahydrofuran at −78°C for 1 h. The employed initiator systems were (diphenylmethyl)potassium/diethylzinc (Et₂Zn) and 1,1-bis(4′-trimethylsilyphenyl)-3-methylpentyllithium/lithium chloride (LiCl). Although poly( 1 ) was obtained quantitatively with each initiator system, the observed molecular weights were always higher than the predicted values and the molecular weight distributions were rather broad (M̄_w/M̄_n > 1.3), indicating a side reaction at the acidic acetylenic proton. On the other hand, the polymerization of 2–4 , i.e., methacrylate monomers having no terminal acetylenic protons in the ester moieties, proceeded quantitatively under similar conditions. The resulting poly( 2–4 )s were found to possess the predicted molecular weights and narrow molecular weight distributions (M̄_w/M̄_n < 1.1), indicating the living character of the polymerization systems. The trimethylsilyl protecting group of poly( 2 ) was completely removed to form a poly( 1 ) having well-defined chain structures by treating it with potassium carbonate in a mixed solvent of THF and methanol at room temperature for 1 h.     

Préparation et étude des propriétés chiroptiques de poly(tert-butyloxiranne)s optiquement actifs

Optically active poly(tert-butyloxirane)s of various molecular weights were prepared by polymerization of R(–)-tert-butyloxirane with different initiators or by stereoelective polymerization of the racemic monomer. Using identical conditions of polymerization (initiator, temperature etc.) it was found that the pure enantiomer polymerizes much faster than the racemic monomer. The chiroptical properties of the obtained polymers showed similarities in behaviour with those of a synthetized linear model molecule representative for a monomeric unit of the polymer. The enhanced optical activities of low molecular weight polymers were correlated with the presence of chelated hydroxylic end-groups.     

Synthesis and properties of novel block copolymers containing poly(lactic-glycolic acid) and poly(ethyleneglycol) segments

A synthetic process for obtaining high-molecular-weight block copolymers containing poly(lacticglycolic acid) and poly(ethylene glycol) segments has been established. This process involves the reaction of poly(ethylene glycols) with phosgene, followed by polycondensation of the resulting ,ω-bis (chloroformates) with poly(lactic-glycolic acid) oligomers. The copolymers have been characterized for their molecular weight, solubility properties, water absorption and preliminarily thermal behaviour. All evidence points to the conclusion that the process described is a general one, enabling biodegradable polymers to be obtained tailor-made according to specific requirements.     

The stereoregularity of poly(methyl methacrylate)s formed in the presence of highly syndiotactic poly(methyl methacrylate)s

Methyl methacrylate (MMA) was radically polymerized in the presence of highly syndiotactic deuterated or undeuterated poly(methyl methacrylate)s. In contrast to observations found in the literature no increase in isotacticity was observed. The stereoregularity of the polymers formed in the presence of an undeuterated PMMA as matrix was found by ¹H NMR spectroscopy to be about the same as that in polymers prepared without any matrix, except the polymers formed in the early stage of polymerization which show a little lower syndiotacticity. Determinations of triad tacticities of polymers formed in the presence of deuterated PMMA, gave values of syndiotacticity a little higher than in the case of undeuterated matrixes. The polymer formed in the graft copolymerization of MMA onto pre-irradiated syndiotactic PMMA was fractionated by GPC. The high molecular weight fraction showed a lower syndiotacticity than that of lower molecular weight.     

Protection and polymerization of functional monomers, 23. Synthesis of well-defined poly(2-hydroxyethyl methacrylate) by means of anionic living polymerization of protected monomers

Anionic polymerizations of 2-[(trimethylsilyl)oxy]ethyl methacrylate ( 1 ), 2-[(tert-butyldimethylsilyl)oxy]ethyl methacrylate ( 2 ), and 2-[(methoxymethyl)oxy]ethyl methacrylate ( 3 ), the protected forms of 2-hydroxyethyl methacrylate (HEMA), were carried out in THF at ?78°C with 1,1-diphenylhexyllithium or 1,1-diphenyl-3-methylpentyllithium in the presence of LiCl. The resulting poly( 1–3 )s were found to possess predictable molecular weights and very narrow molecular weight distributions. The sequential polymerizations of tert-butyl methacrylate with the anionic propagating ends of poly( 1–3 ) gave block copolymers in quantitative efficiency. Thus, the anionic polymerizations of 1–3 proceeded without transfer and termination reactions to afford stable living polymers. Complete hydrolysis of the protective groups of poly( 1–3 )s produced linear poly(HEMA) quantitatively. Novel well-defined di- and triblock copolymers containing hydrophobic [polystyrene, poly(4-octylstyrene), polyisoprene] and hydrophilic segments [poly(HEMA)] were also prepared by sequential polymerization of the corresponding hydrophobic comonomers with 1 , followed by deprotection.     

Synthesis of novel cholic acid functionalized branched oligo/poly(epsilon-caprolactone)s for biomedical applications

Novel cholic acid functionalized branched oligo/poly(epsilon-caprolactone)s were synthesized through the ring-opening polymerization of epsilon-caprolactone initiated by cholic acid with hydroxyl groups. The molecular weight of the branched polymers can be adjusted by controlling the feed ratio of the initiator cholic acid to the monomer epsilon-caprolactone. Comparing with linear homopolymer poly(epsilon-caprolactone) (PCL), these branched oligo/poly(epsilon-caprolactone)s show much faster hydrolytic degradation rates, implies that our approach provides a convenient and effective strategy to accelerate degradation of the biodegradable polymers with slow degradation rates such as PCL. The cell culture experiment indicates the incorporation of cholic acid moiety to the polymer chain can improve both cell adherence and proliferation obviously.     

Polymer characterization by temperature gradient interaction chromatography

Thermodynamic principles and some applications of the temperature gradient interaction chromatography (TGIC) recently developed for the characterization of synthetic polymers are described. TGIC is a form of high performance liquid chromatography (HPLC) that varies column temperature in a programmed manner to control the retention of polymeric species during isocratic elution. The retention of polymers strongly depends on their molecular weights, and the polymers are well separated by TGIC in terms of their molecular weights. TGIC is superior to size exclusion chromatography (SEC) in resolution and sample loading capacity, and has higher sensitivity to molecular weight in the analysis of nonlinear polymers. TGIC has an advantage over solvent gradient HPLC because it permits the use of refractive index sensitive detection method such as differential refractometry and light scattering due to the isocratic elution. In addition, temperature provides finer and more reproducible retention control than the solvent composition, which is important in determining the molecular weight distribution by secondary calibration methods. With TGIC analysis, we found that the molecular weight distribution of anionically polymerized polymers is much narrower than has been generally accepted from SEC analysis. We also found the TGIC separation conditions for polystyrene, polyisoprene, poly(methyl methacrylate), poly(vinyl chloride), and poly(vinyl acetate) over wide molecular weight range. Because of its sensitivity to the molecular weight alone, TGIC was successfully applied to the characterization of star shaped polystyrene, and the detailed linking kinetics between living polystyrene anions and a chlorosilane linking agent was investigated.     

Polyanhydrides V. Branched polyanhydrides

The objective of the present study was to investigate the properties of branched polyanhydrides and compare them to the corresponding linear polymers. Sebacic acid was polymerized with 1,3,5 benzenetricarboxylic acid and poly(acrylic acid) to yield random and graft-type branched polyanhydrides. The polymerization was followed until the gel point and the resulting polymers were evaluated for their physico-chemical properties and degradation behaviour. Drug release from these polymers was studied using morphine as a model drug. The experiment showed that the molecular weights of branched polyanhydride were significantly higher (mol wt 250 000) than the molecular weight of linear poly(sebacic anydride) (mol wt 80 000). In the case of poly(acrylic acid) branched polymers, the molecular weight increased linearly with increasing concentration of poly(acrylic acid). The specific viscosities of the branched polyanhydrides were lower than linear polyanhydrides with similar molecular weights. Except for the difference in molecular weights, there were no noticeable changes in the physico-chemical or thermal properties of the branched polymers and the linear poly(sebacic anhydride). The degradation of the branched polyanhydride was triphasic and the degradation rates were faster than for linear poly(sebacic anhydride). The release of morphine from the branched polymers was lower than the corresponding poly(sebacic anydride). Release of morphine was much higher from the poly(acrylic acid) branched polymers compared to the 1,3,5 benzenetricarboxylic acid branched polymers and increased with increasing concentrations of the branching agent. However, in both cases the release rates and the total amounts of morphine released approached that of poly(sebacic anhydride).     

Synthesis of Optically Active Helical Poly(2-methoxystyrene). Enhancement of HeLa and Osteoblast Cell Growth on Optically Active Helical Poly(2-methoxystyrene) Surfaces

Poly(2-methoxystyrene)s (P2MS) were synthesized using n-BuLi in THF and toluene at various temperatures. At ?20°C and higher temperatures, toluene was an effective polymerization solvent for synthesizing poly(2-methoxystyrene). Under these conditions, polymers with good yields and reasonable molecular weight distributions were obtained. Polymers synthesized under all conditions were isotactic; the most highly isotactic polymer was obtained in toluene at ?20°C. The m (isotactic dyad) content of the polymers synthesized in toluene at 0°C and ?20°C was 0.65 and 0.74, respectively. Optically active helical (+) and (?) P2MS were synthesized by asymmetric polymerization utilizing (+) or (?) [2,3-dimethoxy1,4(dimethylamino)butane] (DDB)/tolyl lithium initiating complex in toluene. Asymmetric polymerizations were also carried out at 0°C to synthesize optically active polymers. The optical rotations of the polymers were found to be dynamic and reversible, strongly suggesting contribution of the chiral higher ordered structure to the overall optical rotation. Geometry optimization carried out using various force fields such as MM+, AMBER and CHARMM suggests that isotactic P2MS form low energy stable helical conformations. HeLa cells showed better growth on surfaces prepared using chiral polymers compared to the surfaces prepared with achiral polymers. Similarly, chiral P2MS surfaces were also more effective as supports for mouse and human osteoblast cells. The cell attachment and growth data demonstrate that chiral P2MS surfaces were better supports compared to achiral P2MS surfaces. Atomic force microscopy (AFM) studies on surfaces prepared using chiral poly(2-methoxystyrene) showed more discrete topography features compared to surfaces prepared with achiral polymers. Thus, the surface topography may play a role in determining polymer–cell interactions.     

Polymerization and quaternization of 1-(2-diethylaminoethyl)-4-vinylbenzene: A new cationic polyelectrolyte

Diethylamination of 1,4-divinylbenzene catalyzed by lithium diethylamide gave rise to 1-(2-diethylaminoethyl)-4-vinylbenzene ( 3 ), quantitatively. Subsequent quaternization of 3 with ethyl bromide gave a cationic monomer, 4-vinylphenethyltriethylammonium bromide ( 7 ). High molecular weight polymers, poly[1-{4-[2-(diethylamino)ethyl]phenyl}ethylene] ( 5 ) and poly[1-{4-[2-(triethylammonio)ethyl]phenyl}ethylene bromide] ( 8 ), were prepared from 3 and 7 , respectively, by using radical initiators, especially with redox-type ones. Anionic polymerization of 3 was also carried out. The relationship between the polymerization condition and the stereoregularity of the polymer was studied by Carbon-13 NMR spectroscopy. A polyion complex ( 10 ) was prepared from 8 in combination with poly(sodium 4-vinylbenzenesulfonate) ( 9 ) to evaluate its properties as biomedical material.