Abstract: The homogeneous controlled/“living” free radical polymerization of methyl methacrylate (MMA) by atom transfer radical polymerization (ATRP) using a CuIX/4,4‘-di(5-nonyl)-2,2‘-bipyridine catalytic system (X = Cl, Br) with various initiators R−X was investigated. The rates of polymerization initiated by most of the systems exhibited first-order kinetics with respect to the monomer. A linear increase of number average molecular weight (Mn) versus monomer conversion was observed for most of these initiation systems. The benzhydryl chloride/CuICl system yielded the lowest rate of polymerization, which could be increased by slow addition of the initiator. The reduced rate of polymerization was due to an increase in the concentration of CuIICl, which results from the coupling of benzhydryl radicals during initiation. The slow addition of benzhydryl chloride prevented the formation of a large amount of benzhydryl radicals in the initiation step, thereby reducing radical−radical termination and CuII formation, and...

Abstract: The application of atom transfer radical polymerization (ATRP) to the homopolymerization of 2-hydroxyethyl acrylate, a functional monomer, is reported. The polymerizations exhibit first-order kinetics, and molecular weights increase linearly with conversion. Polydispersities remain low throughout the polymerization (Mw/Mn ≈ 1.2). Reactions were conducted in bulk and in 1 : 1 (by volume) aqueous solution; the latter demonstrates the resilience of ATRP to protic media. Analysis of poly(2-hydroxyethyl acrylate) by MALDI-MS and 1H-NMR shows Mn,exp to be much closer to Mn,th than those observed by SEC using polystyrene standards. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1417–1424, 1998

Abstract: The self-condensing vinyl polymerization of 4-(chloromethyl)styrene using metal-catalyzed living radical polymerization catalyzed by the complex CuCl/2,2′-bipyridyl has been attempted. Given the unequal reactivity of the two potential propagating species in this system, a variety of polymerization conditions were tested to optimize the extent of branching in the products. Typical reaction conditions included polymerization in the bulk, or preferably in chlorobenzene solution, with catalyst to monomer ratios in the range 0.01–0.30, temperatures of 100–130°C, and reaction times from 0.1 to 32 h. Polymers with weight average molecular weights between 3 × 103 and 1.6 × 105 and different extents of branching are formed as evidenced by size-exclusion chromatography, light scattering, and NMR analysis of the reaction products. The influence of reaction conditions on the molecular weight and branching of the resulting polymers is discussed in detail. In sharp contrast to an earlier report, the weight of evidence suggests that, at a catalyst to monomer ratio of 0.01, an almost linear polymer is obtained, while a high catalyst to monomer ratio favors the formation of a branched structure. As a result of the unequal reactivity of the primary and secondary benzylic halide reactive sites, growth occurs by a modified self-condensing vinyl polymerization mechanism that involves incorporation of the largely linear vinyl-terminated fragments formed early on in the polymerization into the vinyl polymer, to afford an irregularly branched structure. Chemical transformations involving the numerous benzylic halide functionalities of the highly branched polymer have been investigated. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 955–970, 1998

Abstract: The polymerization kinetics of photocurable compositions based on an epoxyacrylate oligomer and three analogous diacrylate monomers were investigated. The effects of the oligomer-to-monomer ratio, curing conditions, and monomer structure were considered. The polymerization is characterized by a synergistic effect observed in a wide temperature range and occurring for the polymerization rate both in air and Ar and for final conversions in air. The final conversion in Ar is determined by viscosity of a formulation. The presence of a heteroatom (S or O) in the ester group of the reactive diluent is beneficial for the polymerization course, especially in air atmosphere. The best results were obtained for the sulfur-containing monomer. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 665–673, 1998

Abstract: It is shown that the simple addition of FeCl 3 and triphenylphosphine to a bulk (or solution) polymeriation of methyl methacrylate initiated by AIBN allows the synthesis of polymers displaying precisely controlled high MW and very narrow MWD. The polymers obtained are α-functionalized by a nitrile group and ω-functionalized by an halide atom, which can then be used to obtain block copolymers by addition of a second monomer in a classical ATRP process

Abstract: e-Caprolactone was polymerized in bulk at 80°C with 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) as initiator. The reaction time was varied for monomer/initiator molar ratios of 20, 100 and 500. A rapid and complete conversion of the monomer and only slight transesterification or back-biting degradation were found after longer reaction times. However, significant acceleration of these side reactions was observed at 180°C. Regardless of the M/I ratios and of the reaction time the polydispersities were nearly constant. Number average molecular weights (M n 's) as obtained from GPC measurements are larger than the values obtained from end-group analyses by 15-25% and increase with increasing molar ratio M/I (at 100% conversion). The living character of the Sn-O end-groups was demonstrated by acylation with 4-nitrobenzoyl chloride and by the synthesis of a macrocyclic block copolyester containing β-D,L-butyrolactone.

Abstract: Arrhenius parameters for the transfer constant to monomer (CM) for the free-radical polymerization of butyl acrylate (BA) are determined by a combination of techniques. A seeded emulsion polymerization with conditions designed so that “zero−one” kinetics are obeyed, i.e., where entry of a radical into a particle causes instantaneous termination, such that transfer to monomer can be shown to be the dominant chain-stopping event. The seed comprised small polystyrene particles, which reduces the likelihood of chain transfer to polymer provided the polymer:monomer ratio is sufficiently low. Since the dominant chain-stopping events are then entry and transfer to monomer, CM can then be obtained from the number molecular weight distribution for different initiator concentrations and conversions and isolating the component due to transfer to monomer. The transfer constant so obtained, over the temperature range 50−72 °C, fits CM = (0.016 ± 0.003) exp(−(15.2 ± 0.6) kJ mol-1/RT).

Abstract: Living polymerizations occur without termination or transfer reactions and have the advantage of being able to form well-defined polymers with predictable molecular weights and narrow polydispersities. The first examples of this were living anionic polymerizations,1 which require the exclusion of moisture and oxygen and are run at low temperatures. Radical polymerization methods have the advantage of being insensitive to the presence of water and have even been carried out in aqueous media. This allows for less rigorous reaction conditions and is convenient for industrial application. Free radical polymerizations typically have slow initiation and form a high molecular weight polymer limited by transfer and termination reactions leading to poorly controlled molecular weights and broad molecular weight distributions.2 Also, in contrast to living ionic polymerization, it is very difficult to prepare well-defined homopolymers and block copolymers. In recent years, radical polymerizations have been developed into controlled/“living” polymerizations yielding well-defined polymers. Currently, nitroxide-mediated,3 metal-mediated,4 and either rutheniumor coppercatalyzed atom transfer radical polymerization (ATRP)5 are at the forefront of controlled radical polymerizations. Improvements to these processes have been aimed toward application to new monomers, new initiators and new architectures, compositions, and functionalities.6 In ATRP, recent advances have also been in the direction of new ligands7 and new metals8 which affect the activity and selectivity of the ATRP catalysts for various monomers. Also, improvements have been made in ATRP by the addition of small amounts of zerovalent metal.9 Up to this point, radical polymerizations need to be carried out in an oxygen-free environment. ATRP, in fact, requires less stringent conditions since O2 can react with the catalyst as opposed to reacting with the free organic radicals which should be present in a much lower concentration. However, oxidation reduces the active catalyst concentration. For example, the Cu(I) catalyst is oxidized to a Cu(II) species which is not an active ATRP catalyst and can even be a deactivating species, if a halogen ligand is present, and further slow the polymerization.7b In this communication, we report that controlled radical polymerizations with polymers having low polydispersities (Mw/Mn < 1.2) can be prepared without any removal of oxygen or inhibitor and does not require purging with inert gas, if a sufficient amount of zerovalent metal is present. If Cu(I)Br/dNbpy complex is added (in excess), the polymerization occurs but at a slow rate. This is due to two factors: first, the amount of Cu(I) is reduced by oxidation to Cu(II), second, the concentration of Cu(II), which is a deactivator, is increased further slowing the polymerization.7b Adding Cu(0) to the system, reduces the Cu(II) to Cu(I) and allows for a smaller concentration of catalyst to be added initially.

Abstract: Chain transfer to polymer in free-radical bulk and emulsion polymerization of vinyl acetate has been studied using 13C NMR spectroscopy. The poly(vinyl acetate) (PVAc) spectra have been fully inter...

Abstract: The polymerization of D,L-lactide in the presence of zinc metal was investigated for low values of the monomer/catalyst ratio in order to allow end-group characterization of the growing chains by high resolution 360MHz 1H NMR. The results showed that the polymerization was moisture sensitive and that only a fraction of zinc was active. Small quantities of a side-product were detected and identified as zinc lactate. This compound appeared to be an efficient initiator of the ring-opening polymerization in the bulk. Zinc lactate is thus proposed as the actual initiator of the polymerization of 1,4-dioxane-2,5-diones in the presence of zinc metal. A polymerization mechanism based on a cationic process co-catalysed by lactic acid is also proposed, which accounted very satisfactorily for experimental data. Initiation by zinc lactate yielded high molecular weight polymers with a high degree of conversion and rather high polymerization rates. Therefore, zinc lactate appears to be an attractive alternative to the initiations by zinc metal and stannous octoate, the latter being suspected of some toxicity. © 1998 SCI.

Abstract: The invention provides a production process of a water-absorbent resin, by which process the polymerization temperature can be controlled in static aqueous solution polymerization. The production process of a water-absorbent resin comprises the step of polymerizing statically an aqueous solution with a thickness of 10˜50 mm including a hydrophilic monomer, and is characterized in that the polymerization heat is removed using both cooling due to heat conduction transfer and cooling due to the latent heat of vaporization, thereby controlling the maximum attained temperature of the polymerization system in the range of 60˜95°C. or controlling the increase in solid content in the range of 0.2 to 10 weight %.

Abstract: 1,4-Dioxan-2-one (DOXA) was polymerized by means of Zn L-lactate (ZnLac 2 ) as catalyst in bulk. Upon systematic variation of the temperature, the reaction time and the monomer/catalyst (M/C) mole ratio the highest molecular weights were obtained at 100°C and M/C ratios between 2000 and 4000. However, long reaction times (8-14d) were required to obtain optimum results. Zinc chloride proved to be a somewhat less reactive catalyst, whereas zinc bromide proved to be as efficient as ZnLac 2 . Addition of benzyl alcohol as a coinitiator at a fixed DOXA/ZnLac 2 ratio allowed a systematic control of the molecular weight. Furthermore the formation of benzyl ester endgroups was detected. Moreover, ZnLac 2 allows the incorporation of various bioactive alcohols or phenols (e.g. testosterone, stigmasterol, ergocalciferol, cortisone, α-tocopherol) in the form of ester endgroups. Finally several properties of polydioxanone are reported and discussed, such as solubilities, IR, 1 H NMR and 13 C NMR spectroscopic data and thermogravimetric analysis.

Abstract: Enzymatic ring-opening polymerization of medium-size lactones, e-caprolactone (e-CL) and 6-valerolactone (δ-VL). was performed by using a lipase as a catalyst. For the polymerization of e-CL in bulk, a lipase derived from Pseudomonas fluorescens (lipase PF) showed the highest catalytic activity among the powdery lipases examined, i.e., the highest molecular weight was achieved by using lipase PF. The polymerization behavior depends on the lipase origin as well as on the polymerization condition. From 1 H and 13 C NMR analyses the polymer was found to possess one terminal carboxylic acid group and one hydroxyl group, 6-VL was enzymatically polymerized. yielding the corresponding polyester. The polymerization rate of δ-VL catalyzed by lipase PF is larger than that of e-CL. whereas the molecular weight of poly(6-VL) is lower than that of poly(e-CL) obtained under similar reaction conditions. These lactones were also enzymatically polymerized in organic solvents. The relationship between the type of the solvent and the polymerization behavior was investigated. An immobilized lipase derived from Candida antarctica causes a much faster polymerization of the lactones than the powdery lipases. The immobilized lipase can be reused as a catalyst for the polymerization of e-CL.

Abstract: The monomer chain transfer constant (CM) has been evaluated for three monomers in bulk polymerization, viz, methyl methacrylate (MMA), styrene (STY) and α-methyl styrene (AMS). The new chain length distribution (CLD) analytical method was utilized to determine values for CM at the low initiation limit and compared to the traditional Mayo method. The values for CM obtained at 50 °C using the CLD method were (CM × 105) 5.15, 5.27, and 412 for MMA, STY, and AMS, respectively. The extremely high value for AMS originates in the low propagation rate coefficient for AMS. The values for the chain transfer rate coefficients (ktr) were calculated were (ktr × 102 dm3·mol-1·s-1), 3.34, 1.25, and 0.711 for MMA, STY, and AMS, respectively. The similarity of the values for ktr are discussed in terms of possible mechanisms for the chain transfer to monomer reaction. The strong influence of transfer to monomer as a chain-stopping mechanism in AMS polymerization was confirmed by end group studies using matrix-assisted lase...

Abstract: Polymerization of orthopedic cements makes use of a peroxide initiator which is decomposed by an accelerator to provide free radicals. Free radicals which act on the monomer molecules are also known to induce cell lesions and cell death. We used an in vitro model of cement polymerization to study the effects of free radicals release on osteoblast-like cells. Initiation of methylmethacrylate was done with benzoyl peroxide and acceleration by N,N-dimethylaniline. Bulk polymerization was done in calibrated test tubes which were left aging until use. Polymers (aged from J1 to J31 days after completion of the polymerization process) were sawed to produce slices. Slices were rinsed in distilled water and free radical release was measured by spectrophotometric titration with p-iodonitrotetrazolium. Saos-2 osteoblast-like cells were cultured in parallel on the slices. Cells appeared to be round and were altered when grown on slices prepared freshly after polymerization. Cytomorphometric analysis of the cell shape surface area and form-factor polyethylene confirmed that they spread and flatten on slices prepared a long time after polymerization. Free radical release from polymethylmethacrylate cements is a long-lasting event that can induce bone cells alterations in their neighborhood. Two cytotoxic mechanisms were evidenced: (a) polymer slices released a stable toxic component which could be removed by extensive washing; (b) they released free radicals which were still detectable several days after the end of polymerization. The titration curve was a negative exponential. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 124–131, 1998.

Abstract: A new method for determining the relative efficiencies of free-radical photoinitiators is reported. Called the fluorescence probe technique (FPT), the method has been used to determine the relative initiation efficiencies of several commercial photoinitiators and new phenyl glyoxylate derivatives in the photopolymerization of a model monomer, triethylene glycol diacrylate. The reactivity of each initiator was measured in reference to that of a standard commercial initiator, 2,2-dimethoxy-2-phenylacetophenone, Irgacure 651. Efficiencies differ widely among the acetophenone derivatives studied, and the phenylglyoxylate initiators are somewhat less reactive than the standard.

Abstract: We have investigated the reaction mechanism of the radical polymerization of diethyl (Z,Z)-2,4-hexadienedioate (EMU) in the crystalline state under UV irradiation to yield a polymer of ultrahigh molecular weight with a highly regulated stereochemical structure. The molecular weight of poly(EMU) was estimated to be much higher than 106 by gel permeation chromatography and viscometry, irrespective of the polymerization temperature, in contrast to the polymerization rate, which significantly depended on the temperature. The crystal structural change monitored by X-ray diffraction during the polymerization has evidenced the crystal-to-crystal reaction process yielding the poly(EMU) crystals. The results of X-ray diffraction and NMR spectroscopy confirmed that the propagation proceeded under a crystal-lattice control, leading to the meso-diisotactic-trans-2,5-polymer as a completely regulated structure. The ESR measurement has revealed the radical chain mechanism and the formation of a long-lived propagating r...

Abstract: The activity of camphorquinone (CQ) in the photoinitiation of polymerization at various conditions (in the presence or absence of atmospheric oxygen or a coinitiator) has been studied by UV spectroscopy and differential scanning calorimetry. In the latter case the polymerization kinetics of six multifunctional (meth)acrylates of various structures was followed under isothermal conditions. In the absence of a coinitiator the rate of polymerization was found to depend on the chemical structure of the monomer and its ability to donate hydrogen to exited CQ. For most of the monomers the polymerization rate in air exceeds markedly the polymerization rate in nitrogen, which is in contrast to the situation observed for the polymerization in the presence of a coinitiator (aromatic amine). The increase in the polymerization rate in the presence of atmospheric oxygen is discussed in terms of additional formation of initiating species due to *CQ-assisted decomposition of some oxidation products arising from monomer, polymer or CQ during irradiation.

Abstract: Poly(lactide) is synthesized by ring-opening copolymerization of various combinations of l-lactide, d-lactide, and meso-lactide. The influence of the stereochemical differences of the three lactides on the kinetics of melt copolymerization was determined by monitoring the change in the polymer stereosequence distribution as a function of conversion. The living stereo-copolymerization catalyzed by Sn(II) bis2-ethylhexanoate (Sn(II) octoate) in 1:10 000 molar ratio at 180 °C was investigated by comparing to the values predicted by a reversible polymerization scheme that achieves equilibrium at ∼95% conversion. The stereosequence distribution was measured by high-resolution 500 MHz 1H NMR. A preference for syndiotactic addition was observed and is thought to be due to steric hindrance at the growing site of the polymer. Furthermore, the syndiotactic preference decreased as the polymerization proceeded in a batch process. Similar behavior was observed during lactide polymerization catalyzed by butyl Sn(IV) tr...

Abstract: An enzymatic approach to combine ring-opening polymerization of e-caprolactone and regioselective acylation of methyl glycopyranosides has been investigated. Candida antarctica lipase B (Novozym 435) catalyzed the regiospecific acylation of methyl galacto- and glucopyranoside and the ring-opening polymerization of e-caprolactone to give methyl 6-O-poly(e-caprolactone)glycopyranosides. The synthetic strategy led to the synthesis of methyl 6-O-poly(e-caprolactone)-β-d-glucopyranoside with a Mw of 3750 and a polydispersity of 1.3. The best results were obtained by drying the system and carrying out the polymerization at 60 °C in bulk, without solvent. The overall conversion from methyl β-d-glucopyranoside was 80%.

Abstract: Polymerization of lactones such as δ-valerolactone (VL) and e-caprolactone (CL) with protic compounds proceeded in the presence of an aluminosilicate mesoporous zeolite Al−MCM-41 (pore diameter of 27 A, surface area = 1010 m2 g-1, and Si/Al = 17), to give polyesters with a narrow molecular weight distribution. A sequential two-stage polymerization of VL and CL with Al−MCM-41/butanol gave a block copolymer. NMR and GPC studies showed that the produced polymer carries a terminal group originating from the protic compound. In contrast with Al−MCM-41, pure silicate MCM-41, an MCM-41 with masked SiOH functionalities, and a “microporous” aluminosilicate with much narrower pores (zeolite-Y; pore diameter = 8 A) were not effective for the polymerization under similar conditions. Infrared spectroscopy of an inclusion adduct of Al−MCM-41 with VL suggested a possible interaction of the monomer onto the aluminosilicate surface. Al−MCM-41, isolated from the polymerization mixture, could be used again for the polymeriz...

Abstract: Isobutylene polymerization is initiated by Cp*TiMe2(μ-Me)B(C6F5)3, formed by combining Cp*TiMe3 and B(C6F5)3 in a 1:1 ratio. The polymerization process exhibits the signature of a carbocationic mechanism, as molecular weights generally increase with decreasing temperature, polydispersities are ∼2, and polymers contain vinylidene end groups. Initiation probably occurs via η1-coordination of a molecule of monomer to the cationic species [Cp*TiMe2]+, while propagation and chain transfer proceed as with conventional Lewis acid initiators. Although addition of the proton trap 2,6-di-tert-butylpyridine does have an adverse effect on polymerization, this is not because traces of possible protic initiators are being scavenged but rather because the 2,6-di-tert-butylpyridine coordinates to the titanium cation and inhibits activation of monomer. Further evidence that [Cp*TiMe2]+ behaves as a carbocationic initiator is that the system induces dimerization of 1,1-diphenylethylene to 1,3,3-triphenyl-3-methylindan and ...