Polymerization and Degradation of 1,5-Dioxepan-2-One

Abstract

1,5-Dioxepan-2-one was polymerized with stannous 2-ethylhexanoate as initiator and gave high molecular weight polymers, with MW > 150,000. The highest molecular weight was achieved at 110°C, and full conversion was reached after 20 hours. The polymerization rate increased with temperature. Transesterfication reactions and thermal degradation occurred above 130°C, which led to a decrease of the molecular weight. Polymerization with anion and cationic initiators led to low molecular weight polymers. Degradation of poly(1, 5-dioxepan-2-one) took place by the hydrolysis of ester bonds, and the initial molecular weight decreased by 30% during 46 weeks, starting from MW = 45,000.     

Photoinitiated polymerization of methacrylates comprising phenyl moieties

Investigation of photopolymerization kinetics of 4-(4-methacryloyloxyphenyl)-butan-2-one (1) in comparison with 2-phenoxyethyl methacrylate (2) and phenyl methacrylate (3) using a UV-LED emitting at 395 nm shows significantly faster polymerization of 1 compared to both 2 and 3 at 40°C. Vitrification affects photopolymerization kinetics of all methacrylates under investigation. Interestingly, quantitative final conversion is observed during photoinitiated polymerization of 1 and 2 whereas 3 shows limited conversion at about 80%. Furthermore, higher degree of polymerization is obtained by photoinitiated polymerization of 1 compared to 2 and 3. This shows that the 3-oxobutyl substituent at the phenyl ring of 1 significantly affects both polymerization kinetics and final conversion of the photoinitiated polymerization. Moreover, an additional higher molecular weight fraction is observed in case of polymerization of 1 at 85°C that is above the glass transition temperature of the polymer formed during photoinitiated polymerization. As a thermal polymerization at 85°C in the absence of light results in a high molecular weight polymer as well, an additional thermal process may be discussed as reason for the higher molecular weight polymer fraction in case of the photopolymer made at 85°C.     

Poly(lactic acid) brushes grow longer at lower temperatures

Poly(lactic acid) (PLA) brushes prepared by the ring opening of lactide were thicker when polymerized at a lower temperature (25 °C) than was typically used for polymerization in solution. The molecular weight of solution polymerized lactide was also higher when lactide was polymerized at 25 °C compared with polymerization at higher temperatures. However, the yield of PLA was low at this temperature. These results highlight the different requirements for solution polymerization and brush growth. In the former case, both percentage of conversion and molecular weight are important considerations. In the latter case, however, percentage of conversion is unimportant as a brush represents a very small amount of polymer. It was also shown during the course of these studies that the native hydroxy groups on silicon substrates and silanols in solution were equally good initiators when compared with hydroxy terminated self‐assembled monolayers on gold and alcohols, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3362–3367, 2010     

Olefin polymerization in liquid sulfur dioxide initiated by m-chloroperbenzoic acid. I. Homopolymerization of styrene and α-methylstyrene

Homopolymerizations of styrene (Sty) and α-methylstyrene (AMS) in liquid sulfur dioxide were carried out in the temperature range from ?10°C to ?78°C, using m-chloroperbenzoic acid as initiator. It is shown, through the effect of initiator concentration, temperature, and times of reaction on the conversion and molecular weight of the polymers, that AMS is more reactive than Sty because it requires a smaller amount of initiator for the same conversion to be reached, although the molecular weight of the resulting polymer is lower. A linear relationship has been observed for Sty between the degree of polymerization and the initiator concentration. Within the experimental conditions employed, the presence of polysulfones has been discarded by elemental analysis. The polymerization reactions are considered to be cationic in mechanism.     

Solvent-free polycondensation of 1,3-bis(hydroxyphenylmethyl)benzene. II. The dramatic difference in the polymerization behavior between meso and racemic isomers

The meso and racemic forms of 1,3-bis(hydroxyphenylmethyl)benzene underwent solvent-free polycondensation with the aid of an acid catalyst giving polyether. Very interestingly, the diastereoisomerism caused a considerable difference in the polymerization behavior. The meso isomer (mp = 96–98 °C) was polymerized even at 65 °C, whereas the racemic one (mp = 158–160 °C) required heating at 100 °C to undergo polymerization. However, the latter produced a much higher molecular weight than the former (30,000 vs 4000). The contamination of the meso isomer with the racemic one very sensitively reduced the polymerization temperature: the 98.5% meso monomer underwent polymerization at 50 °C. In contrast to solvent-free polymerization, two diastereomeric monomers showed almost identical behavior in solution polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3564–3571, 2003     

Progress of Polymerization of D,L-Lactide Through Differential Scanning Calorimetry and Gel Permeation Chromatography

Melt polymerization conditions for D,L-lactide initiated with tetraphenyltin were studied with regard to polymer molecular weight. The present study was undertaken to investigate the progress of polymerization of D,L-lactide through differential scanning calorimetry (DSC), and also to explore the correlation between melt polymerization conditions and molecular weight. The physical characteristics, such as glass transition temperature (Tg) of the polymer and melting transition (Tm) of D,L-lactide are correlated with GPC data. DSC data shows that the Tm of D,L-lactide is 122.8 at 150°C polymerization time. ΔHf is 83.2 J g-1, and Tg of polymer is untraceable. At 180°C the Tm is 101.4°C, ΔHf is 34 J g-1, and Tg is around 29.5°C. The drop in Tm and ΔHf clearly shows the conversion of D,L-lactide to polymer. The maximum increment to molecular weight of polymer is achieved at 160°C and 8 h. After a short induction period, the slow polymerization of D,L-lactide resulted in maximal molecular weight followed by an almost constant value of molecular weight. This revised version was published online in July 2006 with corrections to the Cover Date.     

High‐molecular‐weight poly(1,5‐dioxepan‐2‐one) via enzyme‐catalyzed ring‐opening polymerization

To avoid organometallic catalysts in the synthesis of poly(1,5‐dioxepan‐2‐one), the enzymatic ring‐opening polymerization of 1,5‐dioxepan‐2‐one (DXO) was performed with lipase CA (derived from Candida antarctica) as a biocatalyst. A linear relationship between the number‐average molecular weight and monomer conversion was observed, and this suggested that the product molecular weight could be controlled by the stoichiometry of the reactants. The monomer consumption followed a first‐order rate law with respect to the monomer, and no chain termination occurred. Water acted as a chain initiator, but it could cause polymer hydrolysis when it exceeded an optimum level. An initial activation via the heating of the enzyme was sufficient to start the polymerization, as the monomer conversion occurred when samples were left at room temperature after an initial heating at 60 °C. A high lipase content led to a high monomer conversion as well as a high molecular weight. An increase in the monomer conversion and molecular weight was observed when the polymerization temperature was increased from 40 to 80 °C. A further increase in the polymerization temperature led to a decrease in the monomer conversion and molecular weight because of the denaturation of the enzyme at elevated temperatures. The polymerization behavior of DXO under lipase CA catalysis was compared with that of ε‐caprolactone (CL). The rate of monomer conversion of DXO was much faster than that of CL, and this may have been due to differences in their specificity toward lipase CA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4206–4216, 2005     

Binary Mixtures of Liquid Crystalline Ester Bismaleimides

Abstract

A binary system consisting of a chlorohydroquinone-based ester bismaleimide (3-Cl), T _m = 238°C, and a methylhydroquinone-based ester bismaleimide (3-Me), T _m = 251°C, was investigated for the purpose of improving processability by widening the nematic phase range before polymerization. Calculations based on the Schroeder-van Laar equation predicted a system eutectic composition of 41% 3-Me monomer and a eutectic temperature of 202°C. Experiments found the eutectic composition at 35% 3-Me and the eutectic temperature at 218.5°C. Discrepancies between experimental results and theoretical predictions are likely due to error in measured heats of fusion either due to impurities in the samples or due to the reactive nature of the components being considered. Thermal cycling was also found to have a significant melting point depression effect. While significant depression of the system melting point was achieved, polymerization still occurred immediately after melting in all systems evaluated. All mixtures could be polymerized from the nematic phase to yield a solid which retained the nematic orientation of the starting polymer melt.     

Anionic Polymerization of α-Methylstyrene. IX. Nature of the Propagating Species

Abstract

The nature of the initiating and propagating species involved in the anionic polymerization of α-methylstyrene has been explored. The earlier hypothesis that multimodal GPC molecular weight distributions in polymers arise solely out of different reaction steps or different ion-pair mechanisms being involved has been modified for poly-α-methylstyrene. Multimodal GPC molecular weight distributions in poly-α-methylstyrene initiated with potassium at 25°C and polymerized at 25°C or higher in THF, p-dioxane, or cyclohexane as solvents have been ascribed to the presence of two different types of tetramers which grow simultaneously but at different rates, each responding to its own well-defined thermodynamic equilibrium and yielding dormant and living polymers. Reaction schemes describing the initiation (at 25°C) and propagation reactions (between -25 and 60°C) in the polymerization (in solution of THF as well as in bulk) of α-methylstyrene initiated with potassium-naphthalene, butyl-lithium, and butyllithium-tetramethylethylenediamine (TMEDA) have been presented. The role of coordinating agents naphthalene and TMEDA in changing irreversible propagations into reversible ones has been emphasized.     

Radiation-induced ionic polymerization of isobutyl vinyl ether in bulk

The radiation-induced ionic polymerization of isobutyl vinyl ether was investigated under conditions where the monomer was dried with molecular sieves. The investigation covered the temperature range from ?16°C to 90°C, and the dose-rate range from 10¹⁵ to 10²⁰ eV/g-sec, using both γ-rays and electrons. A very high overall activation energy of 15.9 kcal/mole was found for the process below 30°C. Above 30°C, however, the value of the overall activation energy dropped to 4.9 kcal/mole, a phenomenon which is ascribed to the solvation of the propagating carbonium ion below 30°C. The dose-rate dependence of the rate of polymerization was found to be 0.58 over the entire dose-rate range investigated. The molecular weight of the polymer was found to be far less sensitive to trace amounts of water than the rate of polymerization. The molecular weight of the polymer depended strongly on the irradiation temperature, reaching a maximum value of about 120,000 at 35°C. It is shown that at temperatures above 20°C regenerative chain transfer processes play an important role in determining the molecular weight of the polymer.     

Molecular weight distributions in radiation-induced polymerization. VI. γ-ray-induced polymerization of “dry” styrene in the solid state

The γ-ray-initiated polymerization of styrene in the solid state has been studied over the temperature range ?35°C to ?55°C for samples exhaustively purified and dried to remove residual water (“dry” samples). Comparison with kinetic results previously reported for dry samples in the liquid state indicates a sharp decrease in the rate of polymerization resulting from the liquid to solid state transition. The molecular weight distributions for in-source polymerization at ?35°C and ?40°C are bimodal in nature, and the appearance of a third peak is noticeable at ?47°C and ?55°C. In the case of postpolymerization at ?35°C the molecular weight distribution is bimodal as in the case of in-source samples. In the former case, however, the high molecular weight peak is predominant whereas the low molecular weight peak predominates in the latter. These results have been tentatively attributed to the postulated coexistence of two distinct propagating species which are radical and cationic in nature.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. VII. Effect of pretreatment temperature of silica gel on styrene–silica gel system

To investigate the reaction mechanism of radiation-induced polymerization of styrene adsorbed on silica gel, the effect of pretreatment temperature of silica gel was studied. Preheating of silica gel was carried out at 200, 500, and 800°C. The number of silanol groups of silica gel surface decreased as preheating temperature increased. The rate of polymerization on the silica gel preheated at 500°C was faster than that at 200°C, but the polymerization rate on the silica gel preheated at 800°C was the lowest. These results suggest that rate of polymerization on the silica gel is affected by the conditions of silica gel surface such as the number of silanol groups and the pore size. At the same monomer conversion, percent grafting decreased as preheating temperature of silica gel increased. The GPC spectra of both graft polymers and homopolymers have two peaks at all preheating temperatures. The monomer conversion of low molecular weight peaks of graft polymers decreased as preheating temperature of silica gel increased. This result suggests that there is a probability that the grafting sites of low molecular weight peaks of graft polymers somehow interact with silanol groups.     

Lipase‐Catalyzed Ring‐Opening Polymerization of 3(S)‐sec‐Butylmorpholine‐2,5‐dione

Lipase‐catalyzed ring‐opening bulk polymerizations of 3(S)‐sec‐butylmorpholine‐2,5‐dione (BMD) were investigated. Selected commercial lipases were screened as catalysts for BMD polymerization at 110°C. Polymerizations catalyzed with 10 wt.‐% of lipase PPL and PC result in BMD conversions of about 70% and in molecular weights of the products ranging from 5 500 to 10 700. Lipases MJ, CR and ES showed lower catalytic activities for the polymerization of BMD. Poly(3‐sec‐butylmorpholine‐2,5‐dione) has a carboxylic acid group at one end and a hydroxy group at the other end. During the polymerization racemization of the isoleucine residue takes place. Lipase PPL was selected for a more detailed study. The apparent rate of polymerization increases with increasing PPL concentration when the polymerization temperature is 110°C. When the PPL concentration is 5 and 10 wt.‐% with respect to the monomer, a conversion of about 70% is reached after 5 d and 3 d, respectively, while for a PPL concentration of 1 wt.‐% the conversion is less than 7% even after 6  d. High concentrations of PPL (10 wt.‐%) result in high M_n values (< 4  d). The highest molecular weight poly(BMD), M_n = 19 900, resulted from a polymerization conducted at 120°C with 5 wt.‐% PPL for 6 d. The general trend observed by varying the polymerization temperature is as follows: (i) monomer conversion and M_n increase with increasing reaction temperature from 110 to 125°C, (ii) monomer conversion and M_n decrease with an increase in reaction temperature from 125 to 130°C. Water content was found to be an important factor that controls both the conversion and the molecular weight. With increasing water content, enhanced polymerization rates are achieved while the molecular weight of poly(BMD) decreases.     

Biodegradable Polymers for Orthopedic Applications: Synthesis and Processability of Poly (l-Lactide) and Poly (Lactide-co-€-Caprolactone)

Abstract

The synthesis of poly(l-lactide) (PLLA), poly(l-lactide-co-e-caprolactone), and poly(DL-lactide-co-e-caprolactone) by ring-opening bulk polymerization was investigated. Polymerization temperature had a significant effect on the PLLA molecular weight. At 184°C a polymer with a molecular weight of only 10 × 10⁴ resulted. This was lower by a factor of 2 than that obtained at 103 and 145°C. The stannous octoate (SnOct) concentration, with a monomer/SnOct molar ratio in the range of 1,000 to 10,000, was not found to have a significant effect on the PLLA molecular weight. A heterogeneous structure in polymerized PLLA was observed. The intrinsic viscosity of poly(lactide-co-€-caprolactone), obtained at 130°C, monomer/SnOct molar ratio 5,000, and polymerization time of 30 hours, decreased with increasing €-caprolactone content within the first 9 wt% and then leveled off. Die-drawing of PLLA cylinders, for the purpose of increasing the polymer's mechanical strength, was unsuccessful due to the brittleness of the polymer. The drawability of poly(l-lactide), however, was greatly improved by copolymerization with €-caprolactone. With only 3 wt% of €-caprolactone, for example, the tensile strength of die-drawn poly(l-lactide-co-e-caprolactone) was increased by a factor of more than 3. Polymer processing temperature was also investigated. The requirement for low processing temperatures in melt manufacture of controlled release matrix devices containing thermal sensitive drugs was accomplished by three methods: through the use of low molecular weight poly(DL-lactide), adding (DL-lactic) acid oligomer to high molecular weight PDLLA, and copolymerizing DLLA with €-caprolactone. The glass transition temperatures of the modified high molecular weight PDLLA decreased significantly. Melt extrusion below 100°C could be performed.     

Kinetic Aspects of Styrene Polymerization with an Acyloxyamine

The present paper evaluates largely unstudied kinetic aspects of styrene polymerization with a (relatively new) acyloxyamine over several temperature levels and contrasts these features with regular styrene polymerization and styrene polymerization with TEMPO. These comparisons show that the system behaves rather like regular thermal polymerization of styrene at temperatures between 120–180°C. However, at higher temperatures (> 180°C), acyloxyamine has an initiator-like contribution, giving the rate of polymerization an extra boost while decreasing molecular weights. This is further corroborated by mathematical modeling for both conversion and molecular weight averages.     

The Effect of Active Carbon on the Kinetics of Polymerization of Methyl Methacrylate

Rates of 2–2¹?azobisisobutyronitrile initiated polymerization of methyl methacrylate in benzene were determined at 77.2, 65.0, and 50.0°C. The variation of molecular weight of the polymer with temperature and conversion was also studied. At a fixed conversion of 2.0%, the molecular weight decreased from 2.05 × 10⁵ at 50°C to 1.4 × 10⁵ at 77.2°C. The ratio of the propagation rate coefficient to the square root of the termination rate coefficient was found to be 0.61, 0.397, and 0.374 at 77.2, 65.0, and 50.0°C, respectively, with an uncertainty of ±0.5°C in temperature. The effect of active carbon on the rates of polymerization at 77.2°C was measured. Rates of polymerization decreased in the presence of active carbon. For example, the initial rate of polymerization decreased from 7.8 × 10^?4 mole/(liter min) to 4.6 × 10^?4 mole/(liter min) when the carbon concentration was varied from 0 to 9.65 g/liter. The molecular weight of the polymer increased from an average of 1.4 × 10⁵ in the absence of carbon to 1.5 × 10⁵ when carbon was present.     

Use of germanium initiators in ring‐opening polymerization of L‐lactide

Three different, new germanium initiators were used for ring‐opening polymerization of L ‐lactide. Chlorobenzene and 120 °C was a usable polymerization system for solution polymerization, and the results from the polymerizations depended on the initiator structure and bulkiness around the insertion site. The average molecular weights as measured by size exclusion chromatography increased linearly with the monomer conversion, and the molecular weight dispersity was around 1.2 for initiators 1 and 2 , whereas it was around 1.4 for initiator 3 . The average molecular weight of poly(L ‐lactide) could be controlled with all three initiators by adding different ratios of monomer and initiator. The reaction rate for the solution polymerization was, however, overall extremely slow. With an initial monomer concentration of 1 M and a monomer‐to‐initiator ratio of 50, the conversion was 93% after 161 h for the fastest initiator. In bulk polymerization, 160 °C, the conversion was 90% after 10 h. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3074–3082, 2003     

Copolymerization of Alpha‐Methyl Styrene with Butyl Acrylate: Parameter Estimation Considerations

Abstract

The kinetics of the copolymerization of alpha‐methyl styrene (AMS) and butyl acrylate (BA) have been revised to include both the bulk and solution systems. Reactivity ratios and other kinetic parameter estimates based upon a copolymerization model developed by Kruger have been ascertained for a range of temperatures (60–140°C) and at a single solvent level (23?wt%). Full conversion range studies have been completed at two different solvent levels to determine the effects of feed composition, solvent, and chain transfer agent (CTA) on the rate of polymerization, copolymer composition, and the resulting molecular weight.     

Cationic polymerization of isobutylene coinitiated by AlCl3 in the presence of ethyl benzoate

<正>The cationic polymerizations of isobutylene(IB) coinitiated by AlCl_3 were carried out in solvent mixture of n-hexane /methylene dichloride(n-hex/CH_2Cl_2) of 60/40 V/V in the presence of ethyl benzoate(EB) at various temperatures range from-80℃to-30℃.The effects of EB concentration([EB]) and polymerization temperature on monomer conversion,weight-average molecular weight(M_w) and molecular weight distribution(MWD,M_w/M_n) of polyisobutylene (PIB) products were investigated.The rate of polymerization decreased while M_w of PIB products increased with increasing [EB].The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB.Significantly, the polymers with high M_w of 80.2×10~4 and 65.4×10~4 could be produced at-80℃and-70℃at[EB]=0.24×10~(-3) mol/L respectively,which were much higher than that(M_w=57.9×10~4) of PIB prepared at-100℃in the absence of EB.A simple but effective method for preparing the high molecular weight polyisobutylenes was developed in this work.It has been also found that the activation energy for propagation(E_p) depended on the polymerization temperature range in the presence of EB.An obvious inflection of the linear plots of lnX_n versus 1/T_p occurred at the temperature range from-60℃to-50℃at four different concentrations of EB from 0.19×10~(-3) mol/L to 0.33×10~(-3) mol/L,and thus the inflection temperature(T_(inf)) was in the range of-60℃to-50℃.When[EB]was in the range of 0.24×10~(-3) mol/L to 0.33×10~(-3) mol/L,E_p was determined to be around-12 kJ/mol when the polymerization was carried out at temperatures from-80℃to T_(inf) and to be around-28 kJ/mol at temperatures from T_(inf) to-15℃respectively.     

Polymerization of aromatic aldehydes. II. Cationic cyclopolymerization of phthalaldehyde

Phthalaldehyde was found to undergo cyclopolymerization with ease by several cationic catalysts and by γ-ray irradiation. The polymer was composed entirely of the dioxyphthalan unit, as confirmed by infrared spectroscopy and ready decomposition to monomer. The enhanced polymerizability of phthalaldehyde as compared with other aromatic aldehydes was explained in terms of the intermediate-type or, preferably, concerted propagation scheme. The conversion reached a saturation value of 87% in about 1 hr in methylene chloride at ?78°C, indicating an equilibrium polymerization. The ceiling temperature of the polymerization was ?43°C, as estimated from the relation between the saturation yield and polymerization temperature. The enthalpy and entropy of propagation were ?5.3 kcal/mole and ?23.0 eu, respectively. Since the molecular weight of the polymer was proportional to conversion, the propagating chain end was considered to be “living” in this system. The rate constant for propagation was calculated to be 0.18 1/mole-sec in methylene chloride at ?78°C with BF₃OEt₂ catalyst.