Vinyl-type monomers, block copolymers

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

A large variety of AB- and ABA-type block copolymers have been prepared from vinyl ethers via sequential living cationic polymerizations. For example, as shown in Scheme 2 (A), isobutyl vinyl ether (IBVE) is first polymerized with the HI/ZnI2 or HCl/ZnCl2 initiating system, and from the resulting living polymer, the second monomer, 2-acetoxyethyl vinyl... 

Polysilanes are connected with carbon polymers to form A-B and A-B-A type block pol5uners. Reaction of Li-terminated polyst5Tene with cyclotetrasilanes (73) or halogen-terminated polysilanes (74), photolysis of polysilanes in carbon monomers (methacrylic monomers) (75), or reaction of halogen-ended polysilanes with poly(ethylene glycol) affords A-B and/or A-B-A type Block Copolymers (qv) (76) (Fig. 8). Comb-like Graft Copolymers (qv) have also been prepared by reaction of triflate-substituted poly(methylphenylsilane) with THF, 2-methyl-2-oxazoline, or isobutyl vinyl ether (77). 

The methods described above are applicable to the preparation of block copolymers from vinyl and diene monomers and, in the case of anionic polymerization, to certain cyclic monomers such as ethylene oxide. These methods are not in general appropriate to the preparation of condensation-type and rearrangement-type block copolymers. For such materials a number of methods may be envisaged. As an example a polymer with carboxyl end-groups may be allowed to react with a polymer containing hydroxyl end-groups ... 

If (P ) is terminated by a chain transfer to a solvent or a monomer, a graft copolymer is formed, or, if the termination is from a combination, a crosslinked network polymer is formed. If the pre-existing polymer (B) contains an end group that itself is photosensitive (or can produce a radical by interacting with photoinitiator) and in the presence of a vinyl monomer (A), block copolymer of type AB can be produced if the photosensitive group is on one end of the polymeric chain. Type ABA block copolymer can be produced if the polymer chain (B) contains a photosensitive group on both ends. 

The copolymerization of multimonomers with vinyl monomers such as acrylic acid, styrene, or acrylonitrile results in semi-ladder copolymers soluble in many common sol-vents. Such products consist of ladder-type blocks created from multimonomer molecules and blocks of repeated units formed from vinyl monomer, both connected with branching points and fastened together by fragments of the molecule with ladder structure. Semi-ladder copolymer (multimethacrylate-acrylic acid, partially crosslinked) has the following structure ... 

Homopolymers of polybutadiene can consist of three basic isomeric forms (czs-1,4, trans-1,4, and 1,2 vinyl), and these can be present in different sequential order. Copolymers may obtain a variety of co-monomers, such as styrene, acrylonitrile, etc. Depending on their distribution in the chain, random copolymers or block copolymers of different types and perfection can be produced. There are many synthetic elastomers based on butadiene available commercially. 

Three arm amphiphilic star block copolymers of IBVE and 2-hydroxyethyl vinyl ether (HOVE) were prepared using the trifunctional initiator 8 with sequential cationic polymerization of two hydrophobic monomers, IBVE and AcOVE. Subsequent hydrolysis of the acetates led to the hydrophilic poly(HOVE) segments [38]. Two types of stars were prepared depending on which monomer was polymerized first three arm star poly(IBVE-h-HOVE), with the hydrophobic part inside and three arm star poly(HOVE-h-IBVE), with the hydrophobic part outside. When IBVE was polymerized first, the experimental conditions were the same as described in Sect. 2.2.1. After reaching quantitative monomer conversion, AcOVE was added and temperature was raised from 0 to 40 °C to accelerate the reaction since this monomer is less reactive than IBVE. When starting with AcOVE as a first block, both polymerizations were carried out at 40 °C. SEC analysis showed that MWDs were narrow for the two steps whatever the se-... 

So far we have discovered very few polymerization techniques for making macromolecules with narrow molar mass distributions and for preparing di-and triblock copolymers. These types of polymers are usually made by anionic or cationic techniques, which require special equipment, ultrapure reagents, and low temperatures. In contrast, most of the commodity polymers in the world such as LDPE, poly(methyl methacrylate), polystyrene, poly(vinyl chloride), vinyl latexes, and so on are prepared by free radical chain polymerization. Free radical polymerizations are relatively safe and easy to perform, even on very large scales, tolerate a wide variety of solvents, including water, and are suitable for a large number of monomers. However, most free radical polymerizations are unsuitable for preparing block copolymers or polymers with narrow molar mass distributions. 

Catalysts of the Ziegler-Natta type are applied widely to the anionic polymerization of olefins and dienes. Polar monomers deactivate the system and cannot be copolymerized with olefins. J. L. Jezl and coworkers discovered that the living chains from an anionic polymerization can be converted to free radicals by the reaction with organic peroxides and thus permit the formation of block copolymers with polar vinyl monomers. In this novel technique of combined anionic-free radical polymerization, they are able to produce block copolymers of most olefins, such as alkylene, propylene, styrene, or butadiene with polar vinyl monomers, such as acrylonitrile or vinyl pyridine. 

To obtain a high molecular weight block or random copolymer of the oxonium ion type monomer and carbonium ion type monomer, experimental conditions must be such that termination or transfer reactions are minimized. The living nature of the cationic polymerization of THF (7) is well established, but it has been difficult to obtain a high polymer of styrene or DOL by cationic mechanism. In this paper we demonstrate the living nature of the polymerization of DOL and the high polymer of St-DOL copolymer. Using this technique, we were able to obtain a block copolymer of vinyl monomer and cyclic monomer. 

The following sections detail the literature reports pertaining to the synthesis of block copolymers using nitroxide-mediated polymerization techniques. The sections are organized according to monomer type and generally follow the historical development of the particular subsection. Most literature on nitroxide mediated preparation of block copolymers is found for the styrene-based monomers, and is summarized first. This is followed by acrylates and dienes, as they were the next monomers to be studied. These sections are followed by more recent work with vinyl pyridine, acrylamides, and maleic anhydride. The final section deals with methacrylates. This is presented last to stress the importance of developing new nitroxides that can successfully be used for the homopolymerization of methacrylate-based monomers. 

Prepolymers of this type can also act as inisurfs for dispersion polymerizations in organic solvents by using prepolymers soluble in the particualr solvent. This can be determined by appropriate choice of the monomer in the polymerizations forming the prepolymer. So for instance the vinyl acetate prepolymer can be used to obtain stable polyacrylamide dispersions with a solid content of upto 50% by polymerization in methanol [47]. Another application of this type of polymeric azoinitiator mentioned very briefly is the preparation of graft and block copolymers [55,5Q. The chemical composition of the blocks as well as the polymerization technique employed can be matched over a wide range to obtain polymers with desired properties. 

Polymerizations of isobutylene and/or vinyl ethers with appropriate catalysts. This includes formation of block copolymers from the two types of monomers. ... 

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