Emulsion polymerization of hydrophobia monomers

Emulsion polymerization is the most important industrial polymerization process for manufacturing water based polymers. The heterogeneous nature of the process requires the diffusion of monomers from the emulsified droplets, through the aqueous medium, into the polymer particles where the polymerization takes place. Adequate solubility of the monomer is necessary for the diffusion process to occur effectively. Consequently, very hydrophobic monomers cannot be readily incorporated by emulsion polymerization. The use of a catalytic level of cyclodextrin allows the use of very hydrophobic monomers in emulsion polymerization.^[1] The mechanism of the process is believed to involve a catalytic cycle in which cyclodextrin acts as a “Phase Transport Catalyst”, continuously complexing and solubilizing the hydrophobic monomers and releasing them to the polymer particles. The kinetics and thermodynamics are favorable for the reaction to proceed.     

Aqueous Catalytic Polymerization of Olefins

Catalytic conversions in aqueous environments by transition metal complexes have become a well‐established field over the past two decades. However, the vast majority of investigations have focussed on small‐molecule synthesis. This may appear somewhat surprising as water is a particularly attractive reaction medium, especially for polymerization reactions. For example, aqueous emulsion and suspension polymerization is carried out today on a large scale by noncatalytic free‐radical routes. Polymer latices can be obtained as a product, that is, stable aqueous dispersions of polymer particles in the size range of 50 to 1000 nm. Such latices possess a unique property profile. Amongst other advantages, the use of water as a dispersing medium is particularly environmentally friendly. In comparison to these free‐radical reactions, aqueous catalytic polymerizations of olefinic monomers have received less attention. However, considerable advances and an increased awareness of this field have emerged during the past few years. A variety of high molecular weight polymers ranging from amorphous or semicrystalline polyolefins to polar‐substituted hydrophilic materials have now been prepared by catalytic polymerization of olefinic monomers in water. Polymer latices based on a number of readily available monomers are accessible and catalytic activities as high as 10⁵ turnovers per hour have already been reported. As another example, materials prepared by aqueous catalytic polymerization have been investigated as protein inhibitors. A versatile field spanning colloids, polymer, and coordination chemistry has emerged.     

Stereoselective Polymerization of Aromatic Vinyl Polar Monomers

Polar vinyl polymers, a class of polymers with polar groups as side chains, have significant advantages over conventional nonpolar polyolefin materials in terms of viscosity, toughness, interfacial properties (dyeability and printability), and compatibility with solvents or other polymers. Among them, aromatic polar vinyl polymers are of interest because of their good heat resistance properties. In addition, stereoselective polymerization of aromatic polar vinyl monomers has been rapidly developed because the steric structure of the polymer has a significant impact on its physical properties. In this paper, we review the research progress of stereoselective polymerization catalysts for aromatic polar vinyl monomers in recent years, discuss in detail the influence of ligand structure, electronic effect of substituents, spatial site resistance effect, central rare earth metal species and polymerization solvents on the activity and stereoselectivity of polymerization reactions, and explore the possible mechanism of polymerization reaction.     

超临界CO2在高分子合成与制备中的应用

介绍超临界二氧化碳流体作为介质在高分子合成与制备中的研究进展。文中表明，可在超临界二氧化碳中实施氟代单体的自由基溶液聚合、甲基丙烯酸甲酯的分散聚合、丙烯酸的沉淀聚合、丙烯酰胺的反相乳液聚合以及异丁基乙烯基醚的阳离子聚合等多种聚合反应，可用超临界二氧化碳溶胀聚合法制备梯度共混物。此外，超临界二氧化碳还可用于聚合物分级和聚合物微孔、微纤与微球材料的制备等，显示出超临界二氧化碳是一种对环境无污染且价廉的     

乳液聚合法制备水分散有机硅聚合物

乳液聚合法是制备水性有机硅聚合物的最有效、最常用的方法。本文从乳液聚合所采用的有机硅单体或预聚物、乳液聚合工艺、乳液体系的稳定性等方面，论述了采用乳液聚合法合成水性有机硅聚合物领域所面临的问题及所取得的研究进展。     

Properties of dendronized acrylic polymers: Effect of composition and structure of peripheral groups

Two series of new acrylic polymers carrying L-aspartic acid-based dendrons in side chains with terminal hexyloxycarbonyl groups that are both directly and indirectly, via a rigid spacer, attached to polymer chains have been synthesized by the free-radical polymerization of monomers. The polymerization ability of the monomers has been studied. The properties of new polymers are compared with the properties of polymer analogs containing terminal methoxycarbonyl groups of dendrons. Upon incorporation of the rigid spacer, the shielding of reactive centers decreases and the polymerizability of the monomers increases. The replacement of terminal methyl groups in dendrons with hexyl groups in spacer-free polymers leads to a reduction in the degree of polymerization, while in the case of polymers containing spacers, high-molecular-mass products arise. This phenomenon is facilitated by the amphiphilic nature of the polymers and the additional enhancement in the rigidity of chains. A polymer carrying a third-generation dendron has been synthesized only for the latter series.     

INVERSE EMULSION POLYMERIZATION OF ACRYLAMIDE: POLYMERIZATION KINETICS AND PROCESS DEVELOPMENT

Inverse emulsion polymerization confers the benefits of emulsion polymerization kinetics — rapid polymerization rates combined with high polymer molecular weights — on water-soluble polymers, particularly polyacrylamide and its copolymers and derivatives, and allows easy dissolution of the polymer in water by inversion of the latex. The mechanism and kinetics of the inverse emulsion polymerization of acrylamide in o-xylene containing Tetronic 1102 emulslfier and benzoyl peroxide initiator are described, particularly the formation of 10-200nm multiple emulsion droplets resulting from the particulate emulsifier, and their effect on the polymerization process     

The wettability of polymer films depends on the polymerization conditions

The polymerization conditions have a strong influence on the properties and time-dependent behavior of a sessile water drop on polymer films. For a given copolymer composition, the recipe components of emulsion copolymer films clearly influence the initial static water contact angle. Common emulsifiers such as sodium dodecyl sulfate lead to lower contact angles than poly(ionic liquid) dispersions which are a new class of stabilizers for emulsion polymerization. In contrast to the static contact angle, the time-dependent properties of the water contact angle reflect the particular conditions during the polymerization. It is a general conclusion of this study that waterborne emulsion copolymers show a distinctly different time-dependent behavior of the contact angle than bulk polymers of the same molecular composition regardless of the initial static contact angle.     

Trends in Structural Polymer Science in Industry

Plastics production has grown rapidly in the past 30 years. The versatility of plastics which is not exceeded by any other class of materials, guarantees that polymers will continue to be very important in the future. However, at present a distinct change is taking place in polymer research and development. While in the pioneering days of plastics new polymer properties were determined by the choice of suitable monomers, today the commercialization of polymers from new monomers is restricted to a few specialities with a rather modest production volume. On the other hand, the number of new polymers derived from old monomers is increasing very rapidly. The development of highly selective catalysts and advances in reactor technology have provided the means for producing new tailor-made polymers. The same is true regarding new polymer blends and alloys based on old polymers: blending immiscible polymers yields materials with property profiles superior to the features of the individual components. Using selected examples, this paper will discuss trends, possibilities and challenges for structural polymer research in industry. © 1997 John Wiley & Sons, Ltd.     

Block polymers of isocyanates and vinyl monomers by homogeneous anionic polymerization

The “living” polymer method was used to prepare block polymers of vinyl monomers and isocyanates at low temperatures in toluene–tetrahydrofuran mixtures. Vinyl monomers and diisocyanates, which have one hindered isocyanate group, as in 2,4-toluene diisocyanate, form block polymers which contain pendant reactive isocyanate groups. These block polymers can be crosslinked with water, diols, diamines, etc. The polymerization is apparently limited to block polymer formation, since the polyisocyanate anion is incapable of initiating the polymerization of common vinyl monomers.     

Novel synthesis of photocrosslinkable polymers

A new preparative route to photocrosslinkable polymers in which the polymers are produced directly from the polymerization of vinyl monomers having photocrosslinkable groups has been investigated. The photosensitive resins thus produced have higher sensitivity and resolution than conventional photosensitive resins. The monomers were synthesized from the esterification of vinylphenols or vinyl β-chloroethyl ether with cinnamic acid, β-styrylacrylic acid, and their homologs, and from the etherification of vinyl β-chloroethyl ether with hydroxychalcones. Homopolymerizations of these monomers and their copolymerizations with other comonomers were investigated with the use of both radical and ionic initiators. It is shown that radical polymerization of the monomers gave soluble polymers only at low conversion. Anionic initiators did not initiate polymerization. Cationic polymerization imparted soluble polymers in high yield, except for the monomers bearing cyano groups, which generally gave insoluble polymers. Infrared and NMR spectroscopic investigation of the cationically obtained soluble polymers and comparative investigation by cationic polymerization of model compounds indicated that polymerization of the monomers proceeds through the vinyl double bond without affecting the photosensitive unsaturated bond. Thus, linear photocrosslinkable polymers with an intact photoreactive group may be produced by cationic polymerization. In general, these polymers have uniform structure and modifiable physical properties depending on the monomer used. The polymer thus obtained from β-vinyloxyethyl cinnamate has been shown to have excellent properties for use as a photo-resist.     

季铵盐型阳离子聚合物的合成及其应用

介绍季铵盐型阳离子聚合物的合成方法,主要包括二甲基二烯丙基氯化铵、甲基丙烯酰氧乙基二甲基氯化铵、表氯醇和丙烯酰胺等单体直接聚合方法,及天然高分子和聚乙烯醇的改性制备方法等。同时总结了季铵盐型阳离子聚合物在涂料、环境、水处理等领域的应用。     

可逆加成-断裂链转移(RAFT)聚合在星形聚合物合成中的应用

可逆加成-断裂链转移(RAFT)聚合作为一种新型活性自由基聚合,由于其具有单体适用面广、操作条件温和、实施聚合的方法多--本体、溶液、乳液、悬浮聚合均可的优点已经在分子设计方面取得了广泛的应用.星形聚合物作为一种特殊结构的聚合物,由于其具有较低的结晶度、较小的流体动力学体积等独特的性质,越来越引起研究者的重视.本文综述了近几年来采用RAFT法合成星形聚合物的研究进展.根据合成星形聚合物所用的RAFT多官能团试剂种类,对RAFT法合成星形聚合物的反应进行了分类.     

New trends in industrial polymer research

In the past decades a shift in paradigm took place in industrial polymer research. Only a few new polymers were developed based on new monomeric building blocks. The main focus is now on tailoring “new polymers” with well-defined structure and properties based on a set of low cost “old” monomers using controlled polymerization mechanisms.     

Thiol‐Ene Step‐Growth as a Versatile Route to Functional Polymers

A new use of the thiol‐ene reaction to generate functional, redox‐tunable polymers is described. To illustrate the versatility of this approach, tailored divinyl ether monomers were polymerized with triethylene glycol dithiol to yield polymers containing either a carbonate or zwitterionic phosphocholine within the polymer backbone. Similarly, dithioerythritol was polymerized with triethylene glycol divinyl ether to yield a polymer with pendant diols and show how functional groups can be designed into either the divinyl ether or dithiol monomer. Using the thioether functional group inherent to this polymerization, all three polymers were selectively and quantitatively oxidized to either sulfoxides or sulfones by treatment with dilute hydrogen peroxide or mCPBA, respectively. With these illustrative examples, it is shown that the thiol‐ene polymerization is a broad‐reaching method to access a class of new redox‐active polymers which contain varied and dense functional‐group compositions.     

Comparison of Facially Amphiphilic versus Segregated Monomers in the Design of Antibacterial Copolymers

A direct comparison of two strategies for designing antimicrobial polymers is presented. Previously, we published several reports on the use of facially amphiphilic (FA) monomers which led to polynorbornenes with excellent antimicrobial activities and selectivities. Our polymers obtained by copolymerization of structurally similar segregated monomers, in which cationic and non‐polar moieties reside on separate repeat units, led to polymers with less pronounced activities. A wide range of polymer amphiphilicities was surveyed by pairing a cationic oxanorbornene with eleven different non‐polar monomers and varying the comonomer feed ratios. Their properties were tested using antimicrobial assays and copolymers possessing intermediate hydrophobicities were the most active. Polymer‐induced leakage of dye‐filled liposomes and microscopy of polymer‐treated bacteria support a membrane‐based mode of action. From these results there appears to be profound differences in how a polymer made from FA monomers interacts with the phospholipid bilayer compared with copolymers from segregated monomers. We conclude that a well‐defined spatial relationship of the whole polymer is crucial to obtain synthetic mimics of antimicrobial peptides (SMAMPs): charged and non‐polar moieties need to be balanced locally, for example, at the monomer level, and not just globally. We advocate the use of FA monomers for better control of biological properties. It is expected that this principle will be usefully applied to other backbones such as the polyacrylates, polystyrenes, and non‐natural polyamides.     

Simple polymerization through oxygen at reduced volumes using oil and water

An enduring question is: what is the simplest and easiest way to obtain tailored polymers? This communication explores a robust photoiniferter polymerization with only two active ingredients that requires no prior deoxygenation and can be performed on the milliliter scale or sub-milliliter scale. Rather than leaving headspace in the polymerization vessel or scaling reactions up to fill the vessel, this approach fills the headspace of the reaction vessel with mineral oil or inert solvents. This approach can also be applied to polar monomers in aqueous media, using oil as the inert solvent, or to hydrophobic monomers with water as the inert solvent. This method removes enough ambient oxygen that the photoiniferter reaction proceeds with no deoxygenation step, and achieves high conversion and good molecular weight control in 10–20 h in both aqueous and organic solvents. Complex polymer architectures such as multiblock copolymers and gradient polymers were successfully synthesized by this approach.     

Molecular Watchmaking: ab initio Emulsion Polymerization by RAFT-controlled Self-assembly

Controlled radical polymerization using RAFT has the potential to make polymers with virtually any desired molecular architecture. For this to be implemented on an industrial scale, it must be performed by polymerization in disperse media. However, simply adding a RAFT agent to a conventional emulsion polymerization recipe leads to a loss of molecular weight control and formation of coagulum, probably because of nucleation in droplets, which is normally an unlikely phenomenon in emulsion polymerizations. Recently, a method has been devised for implementing RAFT in ab initio emulsion polymerization that avoids droplets in the particle formation stage. The molecular weight distribution of the polymer thus formed shows that molecular weight control is maintained throughout the polymerization. A model is developed to predict the particle size formed in this new type of emulsion polymerization. The new methodology enables synthesis of novel dispersions where molecular architecture can be precisely controlled, such as structured core-shell particles.     

Trends in industrial polymer research

In the past decades a shift in paradigm took place in industrial polymer research for structural materials. Only a few new polymers based on new monomeric building blocks were developed. The main focus is now on tailoring improved “old polymers” with well-defined structure and properties based on a set of low cost “old” monomers using controlled polymerization mechanisms.     

Polymerization of water soluble cationic vinyl monomers

This paper summarizes investigations on the radical polymerization of cationic vinyl monomers with respect to the peculiarities of the reaction in aqueous solution, the synthesis of model polymers and polyelectrolytes with regular structure as well as to a new process of stabilized precipitation polymerization. The rate of polymerization depends on the ionic strength of the solution. Random copolymers of diallyldimethylammonium chloride and acrylamide with variable charge density but equal molecular weight were synthesized by a feeding technique. Block copolymers consisting of charged and uncharged monomelic units with different hydrophilicity are available using macroazoinitiators. The novel polymers are powerful stabilizers in the precipitation polymerization of water soluble cationic vinyl monomers in aqueous salt solution leading to a dispersion of fine polymer particles. Polyampholytes with alternating positively and negatively charged monomelic units in the backbone were obtained by cyclocopolymerization of diallylanmine compounds and derivatives of maleic acid.