Influence of additives on model emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as a protective colloid

To clarify the influence of additives on the grafting phenomenon as well as the particle behavior more precisely, we carried out a model emulsion polymerization of vinyl acetate (VAc) in a 1% aqueous solution with ammonium persulfate (APS) using poly (vinyl alcohol) (PVA) as a protective colloid in the presence of additives. The addition of alcohol to the system remarkably affected the particle formation, especially grafting. This is thought to be attributed to competition between hydrogen abstraction from PVA and alcohol with a sulfate radical. Especially, the addition of acetone to the system decreased grafting to a great extent, resulting in an increase in the particle size together with an increase in the number of polymer molecules in a polymer particle. This result is thought to arise from a combination of electron abstraction from acetone with a sulfate radical and the chain-transfer reaction of the propagation radical with acetone.     

Effect of initiators on grafting in the initial stage of the emulsion polymerization of methyl methacrylate using poly(vinyl alcohol) as a protective colloid

 To make clear the reason of unsuitability of poly(vinyl alcohol) (PVA) protective colloid for the emulsion polymerization of conjugated monomers, a model experiment of emulsion polymerization of methyl methacrylate (MMA) was carried out with ammonium persulfate (APS) or azobis(isobutyronitrile) (AIBN) initiators, where a small amount of MMA (1/100th of the concentration compared with ordinary emulsion polymerization) was employed. This corresponds to the initial stage of the emulsion polymerization. Grafting of MMA onto PVA took place remarkably irrespective of the kind of the initiators. Formation of homo-poly(MMA) was observed to a small extent. The formation of new emulsion particles smaller than 100 nm continued to increase to almost the end of the polymerization. PVA molecules in the grafted polymer are supposed to act as stabilizers of newly formed particles. From kinetic treatment using the experimental data, the important issues were derived as follows. Firstly, the sulfate anion radical from APS is much more reactive than the isobutyronitrile radical from AIBN in terms of hydrogen abstraction from PVA. Secondly, high grafting ability of the latter initiator system, notwithstanding the much lower reactivity in the hydrogen abstraction compared with the APS system, is attributed to the relative reactivity of the primary radicals, i.e., hydrogen abstraction reaction from PVA to initiation reaction with MMA. The much slower rate of addition of the isobutyronitrile radical to the monomer compared with that of hydrogen abstraction from PVA facilitates the grafting, although the rate constant of hydrogen abstraction is far smaller than that with the sulfate anion radical by 10⁻⁴ times. Received: 26 April 2001 Accepted: 6 September 2001     

Comparison of the different emulsion polymerization routes between acrylic and vinyl acetate monomers using poly(vinyl alcohol) as the sole stabilizer

The emulsion polymerization of acrylic and vinyl acetate monomers using poly(vinyl alcohol) (PVA) as protective colloid has been studied for a long time, whereas rare reports ranged over the lateral comparison of the two systems and the reason for the unstability of the PVA/MMA polymerization system was still indistinct. Here in this paper, a collection of experiments of methyl methacrylate (MMA) and vinyl acetate (VAc) were performed respectively with varied amount of PVA as the sole stabilizer. The grafting extent of the polymerisate was characterized through the fraction and FTIR and it was found that the grafted amount of PVA was even larger in the PVA/MMA copolymers than PVA/VAc copolymers, so the grafted mode of PVA was considered. Based on the kinetics, the slower initiation rate of sulfate radical towards MMA was found to be responsible for the unstability of corresponding colloids accompanied with the relatively quicker hydrogen abstraction of radical to PVA, which resulted in “layer-by-layer” grafting structure inside and the particle surface-grafting density was lowered thereof. This was proved with TEM and static contact angle measurements and a pseudo-homopolymer model was employed to describe the relationship of colloidal stability and the PVA density on surfaces.     

Fundamental studies of grafting reactions in free radical copolymerization. III. Grafting of styrene,acrylate, and methacrylate monomers onto cis-polybutadiene using benzoyl peroxide initiator in solution polymerization

Benzoyl peroxide (BPO), due to its higher radical reactivity as compared to AIBN, is known to promote grafting onto cis-polybutadiene. Switching from AIBN to BPO initiator made a dramatic difference in the extent of grafting for styrene and methacrylate monomers, but only a modest difference for acrylate monomer. For styrene and methacrylate monomers, graft site formation is due to BPO initiator radical attack onto the backbone via allylic hydrogen abstraction. Significant levels of grafting are achieved and depend upon the relative concentrations of monomer and backbone polymer but not upon the level of initiator. For acrylic monomer, graft site formation was found to be due to polymer radical attack at the double bond in the backbone. Abstraction of allylic hydrogen also occurs but results in retardation of the overall reaction rate. Graft level was dependent upon initiator and back-bone polymer concentrations but not upon monomer concentration. The effective role of the initiator is only to produce polymer radicals; the BPO has no direct role in the formation of effective graft sites. © 1995 John Wiley & Sons, Inc.     

Oxidation of Poly(dimethylbutadiene) Popcorn Polymer

Poly(dimethylbutadiene) popcorn polymer oxidizes readily in the presence of oxygen at room temperature. Quantitative data are presented for the production of the major volatile product, 2,5-hexanedione, as well as for the secondary products: water, acetic acid, and acetaldehyde. Three reaction mechanisms formerly proposed for polyisoprene oxidation are considered for their applicability to poly(dimethylbutadiene) popcorn oxidation. Of these, one that assumes the formation of a Bevilacquatype peroxyalkoxy radical followed by hydrogen abstraction to form an alcohol group, double bond migration, formation of a peroxide radical adjacent to the alcohol, then elimination of a hydroxy radical and scission, can explain the experimental data.     

Styrene-assisted free radical grafting of glycidyl methacrylate onto polyethylene in the melt

Glycidyl methacrylate (GMA) is a very useful monomer as it bears an epoxy group which is capable of reacting with various other functional groups. However, its melt free radical grafting reactivity onto a polymer backbone is low. In this study, we show that the use of styrene (St) as a comonomer greatly promotes both GMA's grafting yield and grafting rate onto polyethylene (PE). It is proposed that, in the presence of St, the dominant mechanism of the free radical grafting of GMA onto PE is that St reacts first with PE secondary macroradicals and the resulting styryl macroradicals then copolymerize with GMA leading to grafted GMA. We also show that the contribution of St is not related to an improved solubility of GMA in the molten PE. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2763–2774, 1998     

Novel emulsion graft copolymerization onto the silylmethyl group of poly(dimethylsiloxane)

The influence of radical initiators upon the emulsion graft copolymerization of styrene and acrylonitrile onto poly(dimethylsiloxane) (PDMS) was studied. As initiators, a series of peroxides and hydroperoxides were coupled with ferrous sulfate, among which the tert-butyl peroxylaurate system gave the highest grafting efficiency (30%). The tert-butyl peroxylaurate initiator fulfills the criteria for efficient radical grafting by generating only the tert-butoxy radical, which is reluctant to form a carbon radical via β-scission, being highly hydrophobic, and not carrying a tertiary hydrogen that may be abstracted by a radical. ¹³C-NMR analysis of the products showed that the grafting occurred on the silylmethyl groups of PDMS to give 10–25 grafts per polymer and graft ratio in the range 44–140%. The PDMS graft copolymers thus obtained could be used as surface-modifying agents to improve the lubricity and water-repellency of ABS [poly(styrene-co-acrylonitrile)-graft-polybutadiene]. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2607–2617, 1997     

A Rare Example of the Formation of Polystyrene‐Grafted Aliphatic Polyester in One‐Pot by Radical Polymerization

The radical copolymerization of cyclic ester β‐propiolactone (β‐PL) with styrene (St) at 120 °C, with a complete range of monomer ratios, is a rare example of a system providing graft copolymers (PSt‐g‐β‐PL) in one pot. The structure of the resulting β‐PL–St copolymers was proven by using a combination of different characterization techniques, such as 1D and 2D NMR spectroscopy and gel permeation chromatography (GPC), before and after alkaline hydrolysis of the polymers. The number of grafting points increased with an increasing amount of β‐PL in the feed. A significant difference in the reactivity of St and β‐PL and radical chain‐transfer reactions at the polystyrene (PSt) backbone, followed by combination with the active growing poly(β‐PL) chains, led to the formation of graft copolymers by a grafting‐onto mechanism.     

Synthesis,Characterization and Application of Amphiphilic Copolymer Poly(vinyl alcohol)-g-Poly(butyl acrylate)

An amphiphilic graft copolymer poly(vinyl alcohol)-g-poly(butyl acrylate) (PVA-g-PBA) was synthesized by grafting butyl acrylate (BA) onto poly(vinyl alcohol) (PVA) with potassium persulfate (KPS) as free radical initiator in N₂ atmosphere and aqueous medium. The formation of graft copolymer was confirmed by means of infrared spectroscopy (IR). The influences of initiator, monomer concentration and reaction time on the percentage of monomer conversion(C _M), graft degree(Gd) and graft efficiency(Ge) have been discussed in detail. PVA-g-PBA was used as compatibilizer in blends of chlorinated polyethylene (CPE)/ poly(acrylic acid-co-acrylamide)[P(AA-AM)], and the compatibility between CPE and P(AA-AM) was also investigated.     

甲基丙烯酸缩水甘油酯/苯乙烯固相接枝聚丙烯

以苯乙烯(St)为共单体，过氧化苯甲酰(BPO)为引发剂，采用固相接枝反应将甲基丙烯酸缩水甘油酯(GMA)接枝到聚丙烯(PP)大分子链上。研究了反应时间、单体用量、引发剂用量等因素对接枝率的影响。采用凝胶渗透色谱(GPE)测定了PP和接枝物PP-g-(GMA-St)的分子量和分子量分布。结果 表明固相接枝PP反应条件为[GMA／[St]=2，反应3．5h，加入GMA 10份，BPO 5份。St的加入有助于GMA与PP的接枝，同时在一定程度上抑制了PP的降解。     

Fundamental studies of grafting reactions in free radical copolymerization. II. Grafting of styrene,acrylate, and methacrylate monomers onto cis-polybutadiene using AIBN initiator in solution polymerization

Grafting can be initiated by primary and/ or polymer radical attack on the backbone polymer and it is well known that AIBN does not readily promote grafting, even when using poly-butadiene. We have studied the grafting of several different monomers onto cis-polybuta-diene using AIBN initiator and find dramatically different results among the monomers. As expected, styrene grafts at very low levels due to the inactivity of the initiator radicals and the polystyryl radicals. Methacrylate monomer grafts at a slightly higher level due to its more reactive polymer radical, while acrylate monomer readily grafts onto the poly-butadiene because polyacrylate radicals are quite reactive. The use of a kinetic model allowed the evaluation of rate coefficients for graft site initiation to be in the relative order of 0.1 : 1.0 : 10.0 (L/mol/s) for styrene:methacrylate:acrylate monomers. The model also pro-vided successful interpretations of the grafting data and its dependence upon the concen-trations of monomer, initiator, and backbone polymer. Due to the relatively higher reactivity of the polyacrylate radicals, the benzene solvent acted as a chain transfer agent in this system. This affected the molecular weight of both free and grafted acrylate polymer and also surpressed the graft level. Polyacrylate radicals attack the cis-polybutadiene backbone by abstracting an allylic hydrogen and also adding across the residual double bond. The latter mechanism is responsible for the majority of the grafting; the hydrogen abstraction leads to relatively inactive radicals which cause a retardation in the overall reaction rate. © 1995 John Wiley & Sons, Inc.     

Kinetic investigations on the photopolymerization of di- and tetrafunctional (meth)acrylic monomers in polymeric matrices. ESR and calorimetric studies. I. Reactions under irradiation

The photopolymerization of several di- and tetrafunctional (meth)acrylic monomers in the presence of a styrene–butadiene–styrene polymeric matrix (SBS) has been studied. Electron spin resonance spectroscopy (ESR) and differential scanning photocalorimetry (photo-DSC) were used as monitoring techniques to identify the photogenerated radicals and analyze photopolymerization profiles, radical environments, and radical secondary reactions. The study of the photopolymerization and/or photocrosslinking reactions of these monomers in the solid media was carried out by taking into consideration different factors, such as the influence of both monomer and photoinitiator structures on the hydrogen abstraction in the binder with formation of benzylic and allylic radicals, the polymerization of the monomers itself and the hydrogen abstraction reaction in the polymerized acrylic chains. Finally, irradiation of the system SBS/photoinitiator in the absence of monomer was also accomplished. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2775–2783, 1998     

Poly(propylene imine) dendrimers as hydrogen donor in Type II photoinitiated free radical polymerization

Three generations of poly(propylene imine) dendrimers, namely (PPI-16, PPI-32 and PPI-64; 16, 32 and 64 for generations 3, 4 and 5, respectively) were used as hydrogen donors in photoinitiated free radical polymerization of methyl methacrylate by using one of the following photosensitizers; benzophenone and thioxanthone. The effect of generation number of the dendrimer on photoinitiation efficiency and molecular weight of the resulting polymers was investigated. Glass transition temperatures and particle size measurements of the resulting polymers indicated the presence of nearly stretched polymer chains around the dendrimers. The location of hydrogen donating sites was evaluated by photolysis studies in the absence of monomer by using a stable radical namely, 2,2,6,6-tetramethylpiperidine-N-oxyl free radical (TEMPO) and showed that hydrogen abstraction occurs from the inner tertiary amino groups. The TEMPO attached dendrimers were further used in the nitroxide mediated radical polymerization (NMP) of styrene to yield star polymers.     

Styrene-assisted melt free radical grafting of glycidyl methacrylate onto polypropylene

The free radical grafting reactivity of glycidyl methacrylate (GMA) onto polypropylene (PP) in the molten state is low. This article shows that adding styrene as a second monomer (or comonomer) increases both the rate and yield of GMA grafting and reduces PP chain scission. The proposed mechanism is that when St is added to the PP/GMA/peroxide grafting system, St reacts first with PP macroradicals to form stable styryl macroradicals. These latter then react (or copolymerize) with GMA to form GMA grafted PP. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1053–1063, 1998     

马来酸酐-苯乙烯多组分单体熔融接枝高密度聚乙烯机理及性能研究

用单螺杆挤出机制备了马来酸酐-苯乙烯(MAH-St)多单体熔融接枝高密度聚乙烯(HDPE)体系,研究发现添加St共同接枝,可以显著提高接枝物的接枝率.随着St的增加,接枝率先增大后有所降低.当两种单体物质的量比约为1:1时,接枝物的接枝率最高,此时接枝物的熔体流动速率(MFR)最小.即MAH接枝率越高,接枝物的MFR越...     

Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.     

Free radical polymerization of glycidyl methacrylate in plasticized Poly(vinyl chloride)

Kinetic of free radical in-situ polymerization of glycidyl methacrylate (GMA), was studied in a complex evolutionary system: poly(vinyl chloride) (PVC) plastisols. A predictive model of conversion-time profile based on free radical mechanism was proposed and structure of the modified PVC system developed was investigated by NMR analyses. In order to elucidate the mechanism of the reaction, model molecules for PVC were used with NMR and MALDI-TOF characterization. It was found that in-situ polymerization of GMA in PVC plastisols leads to both homopolymerization and grafting of GMA onto PVC backbone by hydrogen abstraction. For 33 wt% GMA loaded, grafting efficiency is 67% with an amount of grafted poly-glycidyl methacrylate (pGMA) equals to 22 wt%. Thus, this article discloses a new type of PVC plastisols called reactive plastisols where, in addition to usual plasticizers, PVC is modified by polymerizable GMA monomer.     

Preparation and characterization of a strong basic anion exchanger by radiation-induced grafting of styrene onto poly(tetrafluoroethylene) fiber

A novel anion-exchange fiber with strong basic groups has been prepared by grafting styrene onto poly(tetrafluoroethylene) fibers via irradiation. Experiments were carried out to analyze the effects of synthesis conditions on the grafting degree and to characterize the physicochemical properties of the anion-exchange fibers. The experimental results showed that preirradiation grafting styrene onto poly(tetrafluoroethylene) fiber could significantly reduce the waste of raw material and the formation of homopolymer, although the grafting degree was relatively low. The grafting reaction could be effectively enhanced through the addition of magnesium powder into the reaction system. The optimal temperature and time for preirradiation grafting were 80 degrees C and 6 h, respectively. The experimental results also showed that the anion-exchange fibers had excellent mechanical properties and thermal stability at a temperature up to 420 degrees C. The fibers were stable in acidic, alkali, and oxidative solutions. The static ion-exchange capacity of the fibers was as high as 6.08 mmol/g. The static adsorption capacities for Cr(2)O(2-)(7) and MnO(-)(4) ions were 214.08 and 290.98 mg/g, respectively.     

PREPARATION OF PARTICLE SIZE NARROWLY DISTRIBUTED LOW-DENSITY STYRENE DIVINYLBENZENE COPOLYMER MICROBEADS

1. INTRODUCTION Micro-particle polymers have found their application in bioengineering, electronic and chemical industry [1~3], chemical analysis and some other fields. As a kind of carrier both the density, the particle sizes are very important char…     

马来酸酐-苯乙烯熔融接枝聚丙烯的影响因素及其性能研究

用单螺杆挤出机制备了马来酸酐 (MAH) 苯乙烯 (St)对聚丙烯 (PP)的多组分单体自由基熔融接枝体系 .研究证实了当两种单体物质的量比约为 1∶1时 ,接枝物的接枝率最高 ,而熔体流动速率 (MFR)最大 .对反应体系影响因素的研究表明单体用量和引发剂用量对不同单体用量比的系列接枝物的接枝率会产生不同的影响 ;另外 ,单体用量增加 ,接枝物的MFR减小 ,过氧化二异丙苯 (DCP)用量增加 ,接枝物的MFR增加 .对多单体熔融接枝聚丙烯PP g (MAH co St)的力学性能研究发现 ,选用合适的单体用量比、单体用量和DCP用量时 ,所制备的接枝物可具有与纯PP相当或更佳的力学性能