A calorimetric investigation of suspension and emulsion polymerization of vinyl chloride

An isothermal calorimeter for studying radical polymerization in heterogeneous systems is presented. The calorimeter was used for investigation of suspension and emulsion polymerization of vinyl chloride at 50°C. The results from the suspension polymerization experiments showed that the termination rate constant in the PVC phase was diffusion controlled and very sensitive to the vinyl chloride activity. During suspension polymerization the pressure started to drop at a much lower conversion than in emulsion polymerization. Mass balance calculations showed that this was due to entrapment of a large amount of liquid vinyl chloride in the fine capillary system of the suspension particles. The results from emulsion polymerization experiments in which the particle number spanned the range from 0.094.10¹⁸ to 1.7.10¹⁸ dm^?3, were analyzed according to the kinetic model developed by Ugelstad et al. Using the concentration-dependent termination rate constant obtained from the suspension experiments and assuming proportionality between the radical adsorption and desorption rate constants, this model gave a very good fit of the experimental rate over the entire interval II and most of interval III. The results strongly indicated that termination in the aqueous phase was of measurable importance during interval II and became the dominating termination in interval III.     

Co γ-irradiation-initiated RAFT polymerization of VAc at room temperature

In this work, the reversible addition-fragmentation chain transfer (RAFT) polymerization of vinyl acetate (VAc) was successfully performed at room temperature using ⁶⁰Co γ-irradiation as the initiation source. Under the dose rate of 10 Gy/min irradiation, the polymerization proceeded smoothly and converted approximately 90% of the monomer within 7 h. The molecular weight distribution (M_w/M_n) remained narrow (M_w/M_n < 1.35) up to 90% conversion. Compared to AIBN-initiated RAFT polymerization at 60 °C, ⁶⁰Co γ-irradiation-initiated RAFT polymerization is a technique that can better control the molecular weight, especially at high conversion. The ¹H NMR spectra and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry confirmed that most of the chain ends of poly(VAc) (PVAc) from γ-irradiated RAFT polymerization were living and can be reactivated for chain-extension reactions. The microstructures of PVAc from ⁶⁰Co γ-irradiated RAFT polymerization (almost head-to-tail addition) and AIBN-initiated RAFT polymerization (5% tail-to-tail addition) were different, as revealed by the ¹³C NMR spectra. For the first time, ⁶⁰Co γ-irradiation was used as an initiation source for RAFT polymerization of VAc at room temperature.     

Microemulsion polymerization of butyl acrylate initiated by γ rays

Radiation polymerization of butyl acrylate was carried out in a microemulsion stabilized with sodium 12-butinoyloxy-9-octadecenate (SBOA). The stable and reddish latex with high polymer content and low emulsifier content was successfully produced in this way. It was found that, for most cases, the polymerization rate shows three intervals: the increasing period, the plateau period, and the decreasing period. The length of the nucleation period becomes longer at a higher dose rate (D) and lower emulsifier content (E). The plateau region of polymerization rate is lengthened with the increase of monomer and emulsifier content and shortened with the increase of dose rate. It was shown that monomer content, emulsifier content, and dose rate have great effects on R_p (the polymerization rate in the plateau region, or the maximum polymerization rate during polymerization) and M_n (the molecular weight of the polymer). R_p ∞ [M^0.93D^1.27[E]^−1.07; M_n ∞ [M]^0.65D^0.28[E]^−1.66. The polymerization mechanism is discussed based on these results. © 1996 John Wiley & Sons, Inc.     

Aqueous polymerization of protonated 4-vinylpyridine in montmorillonite

The polymerization of protonated 4-vinylpyridine (4-VPH⁺X⁻) in the interlayer zone of montmorillonite was studied. Polymerization is critically affected by the degree of surface coverage with a threshold value twice the cation exchange capacity of the mineral. Montmorillonite surfaces show selectivity for protonated 4-vinylpyridine favoring the formation of the quaternized form of the polyvinylpyridine polyelectrolyte. In situ polymerization of 4-VPH⁺X⁻ in the presence of 10 wt.% or lower sodium montmorillonite in aqueous solution yields exfoliated montmorillonite–polyelectrolyte heterostructures. The rate of polymerization in the presence of delaminated montmorillonite is much faster than in the absence. Mechanisms for intergallery and exogallery polymerization of 4-VPH⁺X⁻ are described.     

Kinetics and thermal properties of polydiethylsiloxane initiated by potassium trimethylsilanolate

This work reports the kinetics of anionic ring-opening polymerization of hexaethylcyclotrisiloxane (D₃^Et) with potassium trimethylsilanolate as initiator and diglyme and N,N-dimethylformamide (DMF) as promoters. The polymerization rate of D₃^Et is influenced by the nature of promoters and the reaction temperatures. With the use of DMF as a promoter, the polymerization activation energy is 107.89 kJ/mol, and the polymerization rate constant at 110°C is 0.08466 min⁻¹ with [P]/[I] = 3.0. Gel permeation chromatography and ²⁹Si NMR spectra showed that the intermolecular redistribution occurred during the late stage of polymerization, which facilitated the synthesis of high-molecular-weight polydiethylsiloxane (PDES). Differential scanning calorimetry analysis showed that PDES exhibited a glass transition temperature of −142°C and complex crystallization phenomena. Thermogravimetric analysis illustrated that the PDES that was prepared using this method had good thermal stability with onset decomposition temperatures of 483 and 452°C under nitrogen and air conditions, respectively. This work presents innovative approaches for achieving a more energy-efficient synthesis of PDES to meet the demands of industrial-scale production.     

Polymerization of – Phenylmaleimide Initiated by 9-Borabicyclo[3.3.1]nonane

N-Phenylmaleimide (N-PMI) was polymerized by 9-borabicyclo[3.3.1] nonane (9-BBN) in tetrahydrofuran under argon at 0°C. The molecular weight distributions of the resulting polymers were around 1·1. The rate of poly-merization was proportional to [9-BBN]^1·18 and [N-PMI]^1·24. Hydroquinone had little effect on the rate of polymerization and on the molecular weight of the polymers obtained. Triethylamine completely inhibited the polymerization, and aniline with a relatively small pK_a value and zinc iodide effectively retarded the polymerization. The polymerization did not proceed either in polar dimethylformamide or in non-polar toluene. In polymerizations at temperatures higher than 60°C the conversions decreased. On the basis of the results, a non-radical mechanism was proposed for this polymerization. © of SCI.     

Ring-opening polymerization of γ-benzyl-l-glutamate-N-carboxyanhydride in ionic liquids

This work deals with ring-opening polymerization of a representative N-carboxy-α-amino acid anhydride (NCA) in ionic liquids. The polymerization of γ-benzyl-l-glutamate-N-carboxyanhydride (BLG-NCA) with n-butylamine as an initiator in an ionic liquid ([BMI][PF₆]) proceeded as a milky white dispersion with no evidence of macroscopic precipitation. The polymerization with the primary amine under suitable conditions afforded poly(amino acid) having narrow polydispersity, molecular weights close to the theoretical values, and helical secondary structure. The polymerization rate was slightly affected by the nature of the anion and hydrophobicity of the ionic liquids, while poly(BLG)s having low polydispersities were obtained regardless of the kind of the ionic liquids. Several parameters, such as the existence of organic solvent as a co-solvent and monomer concentration, had also clear effects on the polymerization rate and/or the polydispersity of the resulting poly(BLG)s. The possible interactions between the ionic liquid and NCA monomer or the ionic liquid and the initiator were characterized using FT-IR, ¹H and ¹³C NMR measurements. The character of this polymerization process was also studied by performing kinetic investigations. We believe that this represents the first report on amine-initiated ring-opening polymerization of NCA in ionic liquid.     

Polymerization of propylene over titanium exchanged Y-zeolite

Summary It was found that isotactic polymerization of propylene took place over titanium ion-exchanged Y-zeolite without organometallic compounds. The results obtained have led to the conclusions that Ti⁴⁺ species as well as Ti³⁺ species are active for the polymerization and that neither Ti-alkyl bonds nor Cl ligands are necessarily essential for polymerization of propylene.     

Functionalization of wool with L‐cysteine: Process characterization and assessment of antimicrobial activity and cytotoxicity

In this study, we show that the plasma-initiated polymerization (PIP) can be carried out at ambient pressure using the dielectric barrier discharge (DBD) technology. The structure of styrene-maleic anhydride copolymer (SMA) is analyzed by ¹H and ¹³C-NMR. The effects of initiation time, gas flow rate, post-polymerization time, and temperature on yield are also discussed. The results show that SMA exhibits a dominant alternating structure. The yield of SMA increases with the increase of initiation time and polymerization temperature, remains unchanged with the increase of flow rate, and decreases rapidly with the increase of St-MAH molar ratio. The PIP in this experiment is shown to follow the free-radical polymerization mechanism and the process of the polymerization is also discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Kinetic modeling of commercial scale mass polymerization of vinyl chloride

The kinetic model for the mass polymerization has been developed for a commercial scale mass polymerizer, which shows an anomalous polymerization rate behavior. Non-equilibrium of the refluxed monomer between monomer and polymer phase was proposed to account for this anomaly. Monomer conversion and polymer average molecular weights can be predicted with this mathematical model. The developed model has been successful in simulating a commercial mass polymerizer of 60 m³ size for the optimization of production recipe with respect to the productivity and quality of polyvinyl chloride (PVC).     

Rate coefficient for radical desorption in emulsion polymerization

Investigators have proposed the rate coefficient for radical desorption from polymer particles to explain the kinetic deviation of the emulsion polymerization of water-soluble monomers such as vinyl acetate and vinyl chloride from the classical Smith and Ewart theory.⁶ In this article, the rate coefficient for radical desorption is theoretically derived by a different approach, and its applicability to vinyl acetate and vinyl chloride emulsion polymerization is examined in detail using experimental data available in the literature. The theory developed here predicts the average number of radicals per polymer particle in the emulsion polymerization of vinyl acetate and vinyl chloride.     

Polymerization of α,β-unsaturated carbonyl monomers initiated by 9-borabicyclo [3.3.1] nonane

9-Borabicyclo[3.3.1]nonane (9-BBN) initiated the polymerization of α,β-unsaturated carbonyl monomers such as ethyl acrylate (EA) without an oxidant at low temperatures (to −90°C) under argon. Hydroquinone and 2,6-di-tert-butyl-p-cresol had little effect on the polymerization, indicating that the propagating chain end is not a free radical. The rate of polymerization was found to be proportional to [9-BBN]^1.0 and [EA]^1.5. Electron spin resonance measurements using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap showed the absence of any radical species under polymerization conditions. No copolymerization of EA with styrene occurred. On the basis of the results obtained, this polymerization was assumed to proceed via a non-radical mechanism.     

Silica–alumina catalysts for polymerization of cyclic siloxanes

Silica–alumina catalysts of varying acidity were used for polymerization of hexamethyl cyclotrisiloxane and octamethyl cyclotetrasiloxane monomers (cyclic trimer and tetramer, respectively). Acidic sites of silica–alumina are responsible for the polymerization and variation in the acidity of the catalyst were shown to influence the polymerization significantly. Mordenite type zeolites with low silica-to-alumina ratio (∼5) gave low yields of polymer from tetramer and zeolite ZSM-5 with a much higher silica-to-alumina ratio (∼40) was found to be a very efficient catalyst for polymerization. Studies on the effect of water on the polymerization suggested that the polymerization (rate and yield) depended to some extent on the amount of water present in the system. The products were characterized using FTIR, ¹H-NMR, ²⁹Si-NMR, and GPC techniques. A plausible mechanism for polymerization of cyclic siloxane monomers on silica–alumina catalysts was proposed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 629–635, 1998     

Einfluß der Änderung des Ordnungsgrades des Ethylens mit der Druckerhöhung auf den Verlauf der radikalischen Polymerisation

According to Kargin and Kabanov¹ the polymerization of monomers in a higher degree of order is characterized by the phenomena: induction period, self-acceleration of the reaction, low energy of activation and absence of a chain termination reaction. In this article it is shown that all these phenomena are detected in the radical polymerization of ethylene under such a pressure and a temperature where ethylene is in a higher degree of order, as taught by our model of ethylene behaviour at high pressure². This article supports our model of ethylene behaviour at high pressure and contributes to closer understanding of the radical polymerization of ethylene.     

High-pressure polymerization of ethylene using methyl isobutyl ketone peroxide as initiator

An investigation was carried out into the suitability of methyl isobutyl ketone peroxide (MIKP) as initiator for the high pressure polymerization of ethylene. For this purpose, polymerization tests were carried out in a stirred autoclave at a pressure of 1000 to 2000 bar and a temperature of 195 to 310°C. The initiator concentration of the feed was varied between 6.5 and 42 mol ppm while the residence time was kept at a constant 30 s. Apart from the rate of polymerization, the conversion and the initiator consumption were also determined. The characteristic properties of polyethylene (PE) were determined by measuring the melt flow index, the density and, in some cases, the molecular weight distribution. Conversion levels of 5 to 27% were achieved with rates of polymerization between 1 and 5.5 kg PE l^?1 h^?1. The initiator consumption at 1700 bar was in the region of 1 to 2 g I kg^?1 PE^?1 over a temperature range of 220 to 315°C. In view of these results, MIKP can be considered as suitable to initiate ethylene high pressure polymerization at 220 to 310°C, particularly in the tubular reactor. The density of the polyethylene thus prepared is ranging between 0.910 and 0.927 g ml^?1. Without the addition of modifiers or cross-linking agents, the melt flow index varies considerably. The polydispersity of the polymers prepared at a pressure of 1700 to 2000 bar was between 6 and 8 and therefore within the range to be expected for stirred autoclaves. Reducing the pressure to 1000 bar resulted in surprisingly low polydispersity values of 2.4 to 3.7.     

A novel polymer chain growing mode and styrene copolymer prepared with low molecular weight copolymer of α‐methylstyrene and styrene as macroinitiator

A new polymer chain growth mode, having multiple potential chain propagation sites, initiated by oligomer of α‐methylstyrene (AMS) and styrene (St) (PAS) is presented in this article. The effects of PAS content, AMS fraction in PAS and reaction temperature on bulk polymerization of St have been investigated. It is demonstrated that the PAS performed as macroinitiator in the polymerization of St. The average molecular weights of products increase significantly with the evolution of the polymerization, which is different from conventional free radical polymerization. With 20 wt % macroinitiator, the molecular weights increase from 1.21 × 10⁵ to 3.00 × 10⁵ with the monomer conversion increasing from 15.3 to 83.0%. This unique feature is tentatively attributed to both the reversible polymerization–depolymerization of AMS segments at high temperature which could generate more than one propagation sites in a polymer chain and the combination termination of St free radical polymerization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41460.     

Radical-induced ionic polymerization in the presence of maleic anhydride. III. Polymerization of isobutyl vinyl ether initiated by trapped radicals in poly(maleic anhydride)

In a previous paper¹ it was mentioned that trapped radicals in poly(maleic anhydride) (Poly-MAH) have the ability to initiate cationic polymerization. In this paper, the cationic polymerization of isobutyl vinyl ether (IBVE) is described using Poly-MAH as the initiator. These radicals show different behavior during polymerization depending upon their structure. In particular, large conjugated radicals initiate ionic polymerizations.     

Polymerization of allyl methacrylate with nylon 6 using benzoyl peroxide as initiator

Polymerization of allyl methacrylate with nylon 6 using benzoyl peroxide as initiator was carried out under different conditions. The polymer add-on was dependent upon allyl methacrylate and benzoyl peroxide concentrations, polymerization time and temperature as well as addition of metallic salts or organic solvents. The polymer add-on increased by increasing benzoyl peroxide concentration up to 0.5 mmol/l then decreased by further increase in peroxide concentration, whereas it increased as the allyl methacrylate concentration increased from 80 – 300 mmol/l. A polymerization temperature of 85°C constituted the optimal temperature, below or above this temperature resulted in lower polymer add-on. The effect of polymerization time was related to the polymerization temperature, no induction period occured at 95°C in contrast to 15 and 30 minutes at 85°C and 75°C, respectively. The incorporation of Cu^{+ +}ions in the polymerization system improved the magnitude of polymer add-on. A similar situation was encountered with Fe^{+ + +} and Li⁺ ions. Using a water/organic solvent mixture as a polymerization medium was advantageous in enhancing polymer add-on provided that the organic solvent did not exceed 1% in case of ethanol and isopropanol and 4% in case of methanol.     

Radiation-induced polymerization of water-saturated styrene in a wide range of dose rate

Radiation-induced polymerization of water-saturated styrene (water content 3.5 × 10^-2 mole/liter) was carried out in a wide range of dose rate between 1.2 × 10³ and 1.8 × 10⁷ rad/sec, and compared with the polymerization of the moderately dried styrene (water content 3.2 × 10^-3 mole/liter). Molecular weight distribution curves of the polymerization products showed that they were generally consisted of four parts, namely, oligomers, radical, cationic, and super polymers. Contributions of the four constitutents to the polymerization and the number average degrees of polymerization (DP) of the four kinds of polymers were calculated by the graphical analysis of the curves. The rate of radical polymerization and DP of radical polymers are independent of the water content; the dose rate dependences of the polymerization rate and DP agree with the well known square root and inverse square root laws, respectively, of the radical polymerization of styrene. The rate of ionic polymerization is directly proportional to the dose rate, but it decreases, at a given dose rate, inversely proportional to the water content of styrene. DP of ionic polymer is independent of the dose rate but decreases with increasing water content. The super polymer of DP about 10⁴ is not formed in the case of the moderately dried styrene. G values for the initiating radical and ion formation are calculated to be, independently of the dose rate and water content, 0.66 and 0.027, respectively. It was suggested that oligomer was formed in the early stage by the interaction of cation with anion and only those cations which had survived underwent polymerization.