Preparation and application of low molecular weight poly(vinyl chloride). I. Preparation and thermal stability

Poly(vinyl chloride) with relatively low molecular weight (LMW-PVC) was prepared by suspension polymerization in the presence of some chain-transfer agents, such as mercapto compounds. It is elucidated by means of thermogravimetry, dehydrochlorination, color difference, and discoloration that the resultant LMW-PVC has good thermal stability. The degree of dehydrochlorination of the LMW-PVC obtained by using n-dodecylmercaptan increases with increasing the content of component from the chain-transfer agent. It is found that the LMW-PVC obtained by using mercapto compounds shows better thermal stability (discoloration property) than does the one obtained without using these agents, at the same weight-average polymerization degree. © 1994 John Wiley & Sons, Inc.     

Preparation and application of low molecular weight poly(vinyl chloride). IV. Preparation and characteristics of poly(vinyl chloride) with broad molecular weight distribution

Poly(vinyl chloride) (PVC) with a broad molecular weight distribution (BMD-PVC) was prepared by suspension polymerization in the presence of PVC with relatively lower molecular weight (LMW-PVC), which was prepared by suspension polymerization in the presence of 2-mercaptoethanol as a chain-transfer agent. It is elucidated using porosity measurement, scanning electron microscopy (SEM), and energy dispersion X-ray microscopy (EDXM) that the resultant BMD-PVC grains have an interesting internal structure at the level of primary particles. Discoloration time and fusion time of the BMD-PVC was studied. Discoloration time and fusion time of BMD-PVC is particularly dependent on the polymerization degree (Pw) of LMW-PVC and LMW-PVC content in the BMD-PVC samples. © 1994 John Wiley & Sons, Inc.     

Vinyl polymerization: 414. Polymerization of vinyl monomer initiated by poly(N,N,N-trimethyl-N-2-methacryloxyethyl)ammonium chloride

The polymerization of vinyl monomer initiated by an aqueous solution of poly(N,N,N-trimethyl-N-2-methacryloxyethyl)ammonium chloride (poly(Q-DMAEM-CI) has been carried out at 85°C. The effects of the amounts of vinyl monomer, poly(Q-DMAEM-CI) and water on the conversion of vinyl monomer have been studied. The overall activation energy in the polymerization of MMA is estimated as 41.9 kJ mol^?1. The polymerization proceeds through a radical mechanism. The location in which the polymerization occurs is discussed. The selectivity for vinyl monomer is explained by ‘the concept of hard and soft hydrophobic areas and monomers’.     

The effect of additives on the thermal stability of poly(vinyl chloride)

The effect of a range of organic additives on the thermal stability of poly(vinyl chloride), both with and without a chloroparaffin extender, was studied using a number of experimental techniques. Of the additives used the best overall balance was provided by pentaerythritol, which increased stability when the extender was present and had no effect when it was absent. The congo red test emerged as the most suitable technique, being consistent and inexpensive and able to screen several additives simultaneously. Isothermal differential thermal analysis correlated with the congo red test but required more expensive equipment, was time-consuming and demanded good mixing of the poly(vinyl chloride) compound to give reproducible results. Thermogravimetry was not sufficiently sensitive and the heat stability test was the least useful of all.     

Continuous dosing of fast initiator during vinyl chloride suspension polymerization: Polymerization rate and PVC properties

Continuous dosing of a fast initiator during the suspension polymerization of vinyl chloride has been carried out in a pilot‐scale reactor. The kinetics course of this polymerization and the particle features of the resulting grains were discussed and compared to the conventional polymerization with the same conversion and maximum reaction rate. It was found for the system used that a suitable dosage trajectory allows the reaction rate to remain constant during polymerization. This decreases the polymerization time up to 53% compared with the conventional suspension polymerization, while the molecular weight distribution and molecular weight of the final grains remained almost unchanged. SEM micrographs revealed that PVC grains prepared using this polymerization process had irregularly shaped, uneven particle surfaces and larger particle sizes. The grains also featured high porosity with loosely aggregated smaller primary particles that led to low levels of residual unreacted monomer. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44079.     

Polymerization of vinyl chloride in presence of substituted olefins: Effects on molecular weight and melt rheology

Vinyl chloride (VCM) was polymerized by free-radical suspension procedures in presence of methyl-substituted olefins such as propylene, isobutylene, cis-2-butene, trimethylethylene, and tetramethylethylene. Dilute solution viscosities of polymer formed in the presence of these olefins were measured and compared to that of trichloroethylene, a chlorinated chain-transfer agent. A pseudo-chain-transfer coefficient for these olefins was calculated based on solution viscosity determinations and found to be exponentially proportional to the number of allylic hydrogens. The effects on melt flow of the olefin distribution in the polymer chain were examined. Olefins at the ends of polymer chains were found to have no effect on melt rheology, whereas those in internal portions of chains were found to significantly increase melt flow.     

Preparation and application of low molecular weight poly(vinyl chloride). II. Thermal stability of blended poly(vinyl chloride)

The blending effect of poly(vinyl chloride) (PVC) with relatively higher molecular weight (HMW-PVC) and relatively lower molecular weight (LMW-PVC) has been investigated by measuring various thermal stability and fusion times. The thermal stability of the blended PVC is improved when the small amount of LMW-PVC obtained using mercapto compounds as a chain-transfer agent is blended into PVC with HMW-PVC. At the LMW-PVC content from about 5–30 wt %, the thermal stability of the blended PVC is much more improved. Furthermore, the blended PVC with LMW-PVC, obtained using mercapto compounds, exhibits significant improvement in the discoloration time. The fusion time of the blended PVC is related to the weight-average polymerization degree of LMW-PVC and the LMW-PVC content. © 1994 John Wiley & Sons, Inc.     

Control of main chain structure and possibility of molecular weight control of polymer on polymerization of vinyl chloride with tert-butyllithium

The controlled polymerization of vinyl chloride (VC) with tert-butyllithium (tert-BuLi) was investigated. The polymerization of VC with tert-BuLi at −30 °C proceeded to give a high molecular weight polymer in good yield. In the polymerization of VC −30 to 0 °C under nearly bulk, the relationship between the M_n of polymers and polymer yields gave a straight line passed through the origin, but the M_w/M_n of PVC was not narrow. When CH₂Cl₂ was used as polymerization solvent, the M_n of PVC increased with the polymer yield, and the M_w/M_n of 1.25 was obtained. Structure analysis of the resulting polymers indicates that the main chain structure could be regulated in the polymerization of VC with tert-BuLi. Accordingly, a control of molecular weight of polymer and main chain structure is possible in the polymerization of VC with tert-BuLi.     

Primary particle stability in bulk polymerization of vinyl chloride at high ion strength

Tetrabutyl ammonium tetrafluoroborate and tetrabutyl ammonium chloride dissociate completely in vinyl chloride (VCM). These salts, when added to colloidal dispersions of PVC primary particles in VCM prepared by bulk polymerization, cause the particles to flocculate, showing that the primary particles were electrostatically stabilized. When bulk polymerizations were carried out in the presence of the same quarternary ammonium salts, smaller primary particles were obtained than in additive-free polymerizations. Addition of tetrabutylammonium tetrafluoroborate to a suspension polymerization increased the porosity of the resin.     

Studies on the thermal stability of poly/vinyl chloride/ and vinyl chloride - carbon monoxide copolymers

Thermal stability of vinyl chloride/carbon monoxide copolymers synthetized in the presence of different proportions of carbon monoxide was studied in nitrogen, oxygen or air stream at 180°C. Dehydrochlorination rate increases proportionally to the incorporated carbonyl content. Effect of air and oxygen on acceleration of the decomposition is higher for PVC samples of regular structure than for the vinyl chloride/carbon monoxide copolymers. In the infra-red spectra recorded after the thermal oxidative decomposition, a broad absorption band appears between 1600 and 1800 cm^?1. Two peaks show the most emphasized increase: one at 1720 to 1730 cm^?1 assigned to the carbonyl group and another at about 1770 cm^?1 of unidentified origin. Additional oxidation products from the polyene yield a “shoulder” in the spectrum between 1600 and 1690 cm^?1.     

Polymerization mechanisms and molecular weight distributions. III. Gamma-radiation-initiated polymerization of methyl methacrylate

The termination mechanism in gamma-radiation-initiated polymerization of methyl methacrylate was investigated. The termination mechanism and the associated rate constants were determined by comparing the theoretical molecular weight distribution (MWD) and the experimental MWD, which was determined by gel permeation chromatography. Disproportionation occurs 1.2 times as frequently as combination at 30°C and 0.5 times as frequently at 0°C. The activation energy for disproportionation is 5.5 kcal/mole greater than that for combination. The rates of initiation were determined by a new method and were found to compare well with those reported in the literature. It is also suggested that it is necessary for the theoretical MWD to have the same shape as the experimental MWD before a mechanism can be authenticated.     

Synergistic effect of metal soaps and natural zeolite on poly(vinyl chloride) thermal stability

The synergistic effect of metal soaps (zinc stearate and calcium stearate) and/or natural zeolite (clinoptilolite) on PVC thermal stability was investigated. For this purpose, PVC plastisol was prepared by mixing poly(vinyl chloride) (PVC) and dioctyl phthalate (DOP) and stabilized with different amounts of metal soaps and zeolite. Kinetic studies of dehydrochlorination at 140 and 160°C were done for unstabilized and stabilized PVC plastigels using 763 PVC Thermomat equipment. The stabilizing effect of zeolite on the increase in the induction period of the sample was considered to result from the absorption of HCl, a property that was thought to reduce the autocatalytic effect of HCl evolved at the initial stages of dehydrochlorination. Since the induction time of the sample having 0.53% of zinc stearate and 0.53% of zeolite was higher than those of the PVC plastigels having only zinc stearate or zeolite, the synergistic effect on thermal stability was observed at low levels of these additives. J. VINYL. ADDIT. TECHNOL., 11:47–56, 2005. © 2005 Society of Plastics Engineers     

Poly(vinyl chloride), Part II: Effect of polymerization temperature and molecular weight on the glass transition and melting point of poly(vinyl chloride)

A detailed study was made of the thermal behavior of poly(vinyl chloride) (PVC) homopolymers, whose chain length and structure were independently manipulated. Normal PVC polymerizations are made at temperatures, the selection of which determines the polymer chain length. In the case of PVC, this choice of temperature also determines its syndiotacticity, and so, its glass transition temperature, and in many ways, its processibility. The ability to understand how to control chain structure and length in PVC is critical in designing polymers for selected specific end use conditions. The thermal spectrum is known to be one measure of how polymers will perform. This study reveals how such controlled chain length/structure PVCs are characterized by thermal methods, and how one can separate individually the effects of syndiotacticity and molecular weight on thermal properties of poly(vinyl chloride).     

Polymerization mechanisms and molecular weight distribution. II. AIBN-initiated polymerization of styrene at 60°C

An experimental study was carried out on the AIBN-initiated polymerization of styrene at 60°C. The kinetic rate constants were determined by the method of moments and the MWD method, which was proposed in a previous paper. The results compared favorably with the data in the literature and the MWD method was noted to yield more consistent results than the method of moments, which indicates the importance of considering the whole molecular weight distribution. The theoretical MWD was found to approximate the experimental MWD well. The chain-transfer constant to AIBN was found to be between 0.09 and 0.14.     

氯乙烯聚合安全设计与安全生产控制

介绍了聚氯乙烯装置中存在的大量危险化学品,在氯乙烯聚合安全设计中如何优化技术方案以及采取的安全可靠措施。     

In-silico vinyl chloride suspension polymerization: Kinetic modelling,thermal runaway prediction,and prevention

In the present study, a combined kinetic and heat transfer model was developed to study the kinetics and predict thermal runaway of vinyl chloride (VC) suspension polymerization. Reactor temperature, monomer conversion, mole of initiator, radical concentrations in the two phases (i.e., VC-rich phase and PVC-rich phase), and average molecular properties were mapped during non-isothermal processes. Meanwhile, the risk of thermal runaway was evaluated using S–Z (divergence) and H–J criteria. Simulation results show that a lower jacket temperature T_j and a larger heat transfer coefficient U are able to postpone or even avoid the risk of thermal runaway. Both of the criteria serve well for the prediction of thermal runaway during non-isothermal processes. To prevent the occurrence of thermal runaway to the greatest extent, model-based design of strategies for an isothermal polymerization process was done. Specifically, either jacket temperature T_j or heat transfer coefficient U can be fine-tuned to maintain a 50°C isothermal process.     

The effect of pentaerythritol‐aluminum on the thermal stability of rigid poly(vinyl chloride)

Pentaerythritol‐aluminum (PE‐Al) was synthesized by a solid‐phase reaction in this study. The formation and characteristics of PE‐Al were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). SEM images showed that the shapes of PE‐Al particles were spherical and the average size was around 23 nm. The thermal properties of rigid poly(vinyl chloride) (PVC) with PE‐Al were tested by Congo red test, thermal aging test, conductivity test, thermogravimetric analysis (TGA), and UV–visible spectroscopy test. The results showed that combination of PE‐Al, in comparison with commercial thermal stabilizers, presented an obvious improvement in stabilization efficiency of PVC. Moreover, addition of PE‐Al could significantly prolong static stability time of PVC, reduce weight loss, and improve the initial color of PVC films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3704–3709, 2013     

Radiation-induced cationic polymerization of vinyl ethers in solution: 3. The influence of monomer and solvent concentrations on the rate of polymerization of ethyl vinyl ether in ether solvent

The influence of the monomer concentration on the rate of propagation of the radiation-induced polymerization of super-dry ethyl vinyl ether has been examined in detail in two ether solvents, diethyl ether and diglyme, chosen for their different dielectric constants and their different abilities to solvate ions. Estimations of the rate of initiation and of the rate of termination have made possible the evaluation of the rate constants of polymerization. Very similar values were obtained in both ethers. Experiments were also performed in benzene-diglyme and diglyme-methylene chloride mixtures. The results are in good agreement with the previous studies, made in benzene and methylene dichloride, and confirm the important role of the solvation of the free propagating species concerning the reactivities observed in the radiation-induced polymerization of EVE in solution.     

Influences of molecular weight on photodegradation of poly(vinyl chloride)

2-Dicyanomethylene-1,3-indandione forms colourless adducts with higher molecular derivatives of N,N-Diethanolaniline which thermally decompose to dark blue dyes. The rate of the dye formation is determined UV-photometrically and is compared with rates for monomeric model compounds. It is shown that reaction rates can be correlated with the solvent polarity parameter E_T′ (r = 0,928). Due to kinetic data a carbanionic mechanism is suggested.     

The effect of sodium stearate‐modified hydrocalumite on the thermal stability of poly(vinyl chloride)

Hydrocalumite as a new‐type of thermal stabilizer used in poly(vinyl chloride) resin had been well prepared by using precipitation transformation method. The as‐prepared hydrocalumite was then modified by sodium stearate in different condition including temperature, stirring time, and the amount of sodium stearate. Scanning electron microscopy tests demonstrate that hydrocalumite had been well modified. Illustrated by activation grade, the static oven heat aging experiments and the rate of thermal weight loss, it turns out that the best modification condition is when the addition of sodium stearate is 6% of hydrocalumite (wt), the reacting temperature is 90 °C, and the stirring time is 100 min. Static thermal aging test shows that the aging time got improved at least 30 min under the high temperature of 190 °C, and the time when Congo red test paper began to turn blue for modified hydrocalumite is 20 min longer than that of unmodified hydrocalumite. All results turn out to be that the hydrocalumite modified by sodium stearate in such condition had good compatibility with poly(vinyl chloride) and presented better thermal stability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45758.