Abstract: Polymer−clay nanocomposites of styrene and methyl methacrylate have been prepared by bulk, solution, suspension, and emulsion polymerization as well as by melt blending. Two different organic modifications of montmorillonite have been used: one contains a styryl monomer on the ammonium ion while the other has no double bond. The organic modification as well as the mode of preparation determines if the material will be exfoliated or intercalated. Exfoliation is more likely to occur if the ammonium ion contains a double bond which can participate in the polymerization reaction, but the mere presence of this double bond is not sufficient to always produce an exfoliated system. Solution polymerization always produced intercalated systems. Neither thermogravimetric analysis nor the tensile modulus can be used to evaluate the type of nanocomposite that has been formed.

Abstract: Styrene was polymerized under a source of ultraviolet radiation in the presence of certain thiocarbonylthio compounds. Use of 1-phenylethyl phenyldithioacetate (1-PEPDTA) produced well-defined polymers with molecular weights close to those predicted from theory, up to conversions of 30%. The mechanism of polymerization was examined and shown to proceed via reversible addition-fragmentation chain transfer, as opposed to reversible termination with a thiocarbonylthiyl radical. UV-induced decomposition of the dithioester moiety in 1-PEPDTA and 1-phenylethyl dithiobenzoate (1-PEDB) mediated RAFT polymerizations was followed using UV/vis spectrophotometry, 1-PEPDTA decomposed much slower than 1-PEDB. Analysis of the decomposition products of 1-PEPDTA with gas chromatography/mass spectrometry was used to elucidate a possible mechanism for its degradation, suggesting that both 1-phenylethyl and benzyl radicals are decomposition products.

Abstract: Bulk polymerizations of e-caprolactone (CL) were conducted at 130 °C, in which the structure and amount of initiator were varied. Polymerization induction periods were observed and attributed to slow heat transfer and to the type of alcohol used as initiator. Induction periods persisted until virtually complete consumption of both ethylene glycol (EG) and 1,3-propanediol (PD). 1-Butanol displayed no detectable induction. 1H NMR suggested that induction was a result of strong and unique interactions between the diols and stannous octoate, which lead to the formation of more stable, less reactive stannous alkoxides compared to stannous alkoxides derived from the polymer chain end. Only after virtually all free diol was consumed did chain propagation commence at the normal rate. The rate of polymerization was insensitive to the [CL]/[EG] ratios chosen for this study. The results were consistent with a mechanism in which stannous alkoxide initiator is formed in situ via reaction between stannous octoate and a...

Abstract: Poly(e-caprolactone)/clay nanocomposites were prepared by in-situ ring-opening polymerization of e-caprolactone by using dibutyltin dimethoxide as an initiator/catalyst. A nonmodified Na+−montmorillonite and two montmorillonites surface-modified by dimethyl 2-ethylhexyl (hydrogenated tallow alkyl) and methyl bis(2-hydroxyethyl) (hydrogenated tallow alkyl) ammonium cations, respectively, were used. The evolution of molecular weights was followed in relation to silicate surface modification and clay concentration. The alcohol-bearing organo-modified clay was a co-initiator for the polymerization reaction and thus controlled the molecular weight of the PCL chains. Furthermore, the number-average molecular weight of the growing PCL chains linearly increased with the monomer conversion. Nanocomposites were analyzed by small-angle X-ray diffraction, transmission electron microscopy, and thermogravimetry. The clay dispersion depended on the structure of the alkylammonium used to make the clay more hydrophobic. E...

Abstract: Following a previous work (J. L. Luna-Xavier et al., Colloid Polym. Sci.279, 947 (2001)), silica-poly (methyl methacrylate) (PMMA) nanocomposite latex particles have been synthesized in emulsion polymerization using a cationic initiator, 2,2'-azobis (isobutyramidine) dihydrochloride (AIBA), and a nonionic polyoxyethylenic surfactant (NP30). Silica beads with diameters of 68, 230, and 340 nm, respectively, were used as the seed. Coating of the silica particles with PMMA was taking place in situ during polymerization, resulting in the formation of colloidal nanocomposites with a raspberry-like or a core-shell morphology, depending on the size and nature of the silica beads. The amount of surface polymer was quantified by means of ultracentrifugation and thermogravimetric analysis as extensively described in the first article of the series (see above reference). The influence of some determinant parameters such as the pH of the suspension, the initiator, silica, monomer, or surfactant concentration on the amount of coating polymer and on the efficiency of the coating reaction was investigated in details and discussed in light of the physicochemical properties of the seed mineral. Electrostatic attraction between the positive end groups of the macromolecules and the inorganic surface proved to be the driving force of the polymer assembly on the seed surface at high pH, while polymerization in adsorbed surfactant bilayers (so-called admicellar polymerization) appeared to be the predominant mechanism of coating at lower pH. Optimal conditions have been found to reach high encapsulation efficiencies and to obtain a regular polymer layer around silica.

Abstract: The kinetics of bulk polymerization of 6-, 7-, 9-, 12-, 13-, 16-, and 17-membered lactones initiated with a zinc 2-ethylhexanoate/butyl alcohol system at 100 °C was studied and compared with that of lipase-catalyzed polymerization. Instantaneous concentrations of the lactone monomers were determined on the basis of the relative intensities of signals in the 1H NMR spectra (500 MHz, CDCl3 as a solvent, room temperature) from the ω-methylene protons (−(CH2)x-1CH2OC(O)−) (where x = 4, 5, 7, 10, 11, 14, and 15) in the lactone monomer and the polyester repeating units, respectively. Linearity of the semilogarithmic kinetic dependencies (ln([lactone]0/[lactone]) vs time), revealed a first order of propagation in monomer for all of the polymerizations studied. This kinetic behavior, pointing to the constant concentration of the involved active centers and thus to the practical elimination of termination side reaction, allowed the relative polymerization rates to be determined. The following order of polymerizati...

Abstract: A new metal-free synthetic approach to the controlled ring-opening polymerization (ROP) of lactide with nucleophilic phosphines as transesterification catalysts is described. P(Bu)3, PhPMe2, Ph2PMe, PPh3, and related phosphines are commercially available, inexpensive catalysts that generate narrowly dispersed polylactides with predictable molecular weights. These organic catalysts must be used in combination with an initiator, such as an alcohol, to generate an alcoholate ester α-end group upon ROP. A likely polymerization pathway is through a monomer-activated mechanism, with minimal active species, facilitating narrow molecular weight distributions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 844–851, 2002; DOI 10.1002/pola.10168

Abstract: The polymerizations of styrene (St), methyl acrylate (MA), and butyl acrylate (BuA), carried out under UV irradiation at room temperature in the presence of dibenzyl trithiocarbonate (DBTTC) were found to display living free-radical polymerization characteristics as evidenced by: narrow molecular weight distribution, linear increase of molecular weight with increasing conversion, well-controlled molecular weight, and first-order polymerization kinetics. The triblock copolymer, PMA-PSt-PMA, with narrow polydispersity and well-defined structure was successfully prepared using PMA-S-C(=S)-S-PMA as macro-photoinitiator under UV irradiation at room temperature. Based on GPC, NMR and FT-IR analyses, the structures of the polymers were obtained and the mechanism of the polymerization was proposed.

Abstract: Chain-length-dependent termination rate coefficients of the bulk free-radical polymerization of styrene at 80degreesC are determined by combining online polymerization rate measurements (DSC) with living RAFT polymerizations. Full k(t) versus chain-length plots were obtained indicating a high k(t) value for short chains (2 x 10(9) L . mol(-1) . s(-1)) and a weak chain-length dependence between 10 and 100 monomer units, quantified by an exponent of -0.14 in the corresponding power law [k(t)(i,i)] = k(t)(0) . P(-b).

Abstract: a Bifuctional Iniator M eer, U rula; Palm ans, Anja R A.; Lotjens, Ton; H ese, Areas Pulished n: M arom olcules D O I: 10021/m a01929m IM PO R AN T N O E: ou re avised to csult he puisher's vrsion (pulisher's PD F) if ou w sh to ite rom it. Pase ceck he dcum nt vrsion blow . D ocum nt Vrsion Puisher's PD F, lso know n as Vrsion of rcord Puication dte: 2002 ink to puication in U niersity of G rongen/U M C G reearch dabase C ittion or pulished vrsion (APA): M eer, U ., Palm ans, A. R . ., Lotjens, ., & H ese, A. (202). Ezym tic R ig-O pning Polym eration nd Atom Trnsfer R aical Polym eration rom

Abstract: Novel end-chain and midchain functional macrophotoinitiators of poly(-caprolactone) have been synthesized. For this purpose, mono- and dihydroxy functional photoinitiators namely, benzoin (B) and 2-hydroxy-2-methyl-1-phenyl propan-1-one (HMPP), Darocure 1173, and 2-hydroxy-1-(4-(2-hydroxy- ethoxy)phenyl)-2-methyl propan-1-one (HE-HMPP), Irgacure 2959, respectively, were used as initiators for the stannous-2-ethylhexanoate (Sn(Oct)2) catalyzed living ring-opening polymerization of -caprolactone. The gpc and IR, H NMR, UV, and fluorescence spectroscopic studies revealed that low-polydispersity poly(-caprolactone) with desired photoinitiator functionality at the end or in the middle of the chain were obtained. These prepolymers were used to induce radical polymerization of methyl methacrylate (MMA) upon irradiation via R-cleavage of the incorporated phenyl ketone groups. While end-chain functional macrophotoiniators led to the formation of both homo and block copolymers, only block copolymers of -CL and MMA were formed with midchain functional macrophotoinitiator. Successful blocking has been confirmed by a strong change in the molecular weight of the prepolymer and the block copolymer as well as by NMR spectral measurements.

Abstract: A kinetic model incorporating effects of diffusion-controlled reactions on atom-transfer radical polymerization (ATRP) was developed. The reactions considered to be diffusion-controlled are monomer propagation, bimolecular radical termination, chain transfer between propagating radical and catalyst, and transfer to small molecules. Model predictions indicate that a diffusion-controlled propagation reduces the “living” behavior of the system, whereas a diffusion-controlled termination enhances its livingness. When diffusion-controlled transfer between chains and catalyst is considered the same in the forward and backward directions, the livingness of the system is enhanced, but if one of them is kept unchanged while the other is increased, the livingness of the system is reduced. When diffusion-controlled termination is important, our simulations show that the overall effect of diffusion-controlled phenomena in ATRP is to enhance the livingness of the system. Experimental data from the literature for styrene, methyl methacrylate, and methyl acrylate ATRP homopolymerizations validate the kinetic model.

Abstract: A novel experimental procedure is presented that allowed probing of reversible addition-fragmentation chain-transfer (RAFT) free-radical polymerizations for long-lived species The new experimental sequence consisted of gamma irradiation of a mixture of initial RAFT agent (cumyl dithiobenzoate) and monomer at ambient temperature, a subsequent predetermined waiting period without initiation source also at ambient temperature, and then heating of the reaction mixture to a significantly higher temperature After each sequence step, the monomer conversion and molecular weight distribution were determined, indicating that controlled polymer formation occurs only during the heating period The results indicated that stable intermediates (either radical or nonradical in nature) are present in such experiments because thermal self-initiation of the monomer can be excluded as the reason for polymer formation (C) 2002 Wiley Periodicals, Inc

Abstract: A novel experimental procedure is presented that allowed probing of reversible addition-fragmentation chain-transfer (RAFT) free-radical polymerizations for long-lived species. The new experimental sequence consisted of gamma irradiation of a mixture of initial RAFT agent (cumyl dithiobenzoate) and monomer at ambient temperature, a subsequent predetermined waiting period without initiation source also at ambient temperature, and then heating of the reaction mixture to a significantly higher temperature. After each sequence step, the monomer conversion and molecular weight distribution were determined, indicating that controlled polymer formation occurs only during the heating period. The results indicated that stable intermediates (either radical or nonradical in nature) are present in such experiments because thermal self-initiation of the monomer can be excluded as the reason for polymer formation. © 2002 Wiley Periodicals, Inc. J. Polym. Sci. Part A: Polym. Chem.

Abstract: Highly (S)-enriched substituted poly(e-caprolactone)s were synthesized from 4-methyl-e-caprolactone (4-MeCL) and 4-ethyl-e-caprolactone (4-EtCL) by lipase Novozym-435 (from Candida antarctica) catalyzed ring-opening polymerizations. The polymerizations were performed in bulk, thus eliminating the need for solvents in the polymerization process. Poly(4-EtCL) and poly(4-MeCL) having >95% enantiomeric purity (eep) have been prepared. Number-average molecular weights of the poly(4-EtCL) and poly(4-MeCL) were 4400 and 5400, respectively. The effect of reaction temperature on enzyme enantioselectivity, polymer molecular weight, and monomer conversion was also investigated at 45 and 60 °C. Contrary to many literature reports and conventional wisdom, the enantioselectivity of the lipase was greater at 60 °C, the higher reaction temperature. The solventless polymerization process appeared to be diffusion-controlled in which the monomer conversion and polymer molecular weight increased at higher reaction temperature.

Abstract: A continuous process for producing water-insoluble, water-swellable polymers comprises subjecting a monomer and initiator to polymerization conditions in a reactor system having at least 3 zones.

Abstract: Ring-opening polymerization of ϵ-caprolactone was carried out smoothly and effectively with constant microwave powers of 170, 340, 510, and 680 W, respectively, with a microwave oven at a frequency of 2.45 GHz. The temperature of the polymerization ranged from 80 to 210 °C. Poly(ϵ-caprolactone) (PCL) with a weight-average molar mass (Mw) of 124,000 g/mol and yield of 90% was obtained at 680 W for 30 min using 0.1% (mol/mol) stannous octanoate as a catalyst. When the polymerization was catalyzed by 1% (w/w) zinc powder, the Mw of PCL was 92,300 g/mol after the reaction mixture was irradiated at 680 W for 270 min. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1749–1755, 2002

Abstract: A double metal-cyanide catalyst based on Zn 3 [Co(CN) 6 ] 2 was prepared. This catalyst is very effective for the ring-opening polymerization of propylene oxide. Polyether polyols of moderate molecular weight having low unsaturation (<0.015 meq/g) can be prepared under mild conditions. The molecular weight of polymer is entirely controlled by a reacted monomer-to-initiator ratio. The polymers prepared with stepwise addition of monomer exhibit a narrower molecular weight distribution as compared with those prepared with one-step addition of monomer. Various compounds containing active hydrogen, except basic compounds and low-carbon carboxylic acid, may be used as initiators. The reaction rate increases with increasing catalyst amount and decreases with rising initiator concentration. Polymerization involves a rapid exchange reaction between the active species and the dormant species. It was also proven that, to a certain extent, the chain termination of this catalytic system is reversible or temporary. 13 C NMR analysis showed that the polymer has a random distribution of the configurational sequences and head-to-tail regiosequence. It is assumed that the polymerization proceeds via a cationic coordination mechanism.

Abstract: The tetrameric titanium alkoxide (MeC(CH 2 -μ 3 -O)(CH 2 -μ-O) 2 ) 2 Ti 4 (O-i-Pr) 10 (1) catalyzes the ring-opening polymerization (ROP) of lactide (LA) in toluene solution at various polymerization temperatures, and its bulk ROP at 130 °C. Compound 1 facilitated reasonably controlled polymerization characteristics via a coordination/insertion mechanism in solution, whereas the bulk polymerization products displayed broad molecular-weight distributions. The stereochemical microstructure of PLA was determined from homonuclear decoupled 1 H NMR spectroscopic studies.

Abstract: The importance of kinetic chain length on termination kinetics has been investigated in cross-linking free radical polymerizations both experimentally and using a kinetic model. The model differs f...

Abstract: The kinetics of the free radical bulk polymerization of methyl methacrylate (MMA) was studied by DSC, using the benzoyl peroxide (BPO)/amine initiation system. N,N dimethyl-4-aminophenethyl alcohol (DMPOH), which is a newly synthesized and used amine in the preparation of acrylic dental resins and bone cements was examined, and the results compared to the most commonly used in these applications amine, the N,N dimethyl-p-toluidine (DMT). For both amines, the effect of the molar ratio of BPO/amine and of the reaction temperature, on the polymerization kinetics was investigated. The prepared polymers were characterized by determination of the average molecular weights (M¯ n and M¯ w ) and molecular weights distribution (M¯ w /M¯ n ) using Gel Permeation Chromatography. DMPOH was found to lead in slightly higher polymerization rates, lower gel times and lower molecular weights than DMT. The values of these parameters for both amines were influenced by the molar ratio of BPO to amine, when the produc...