Vinyl polymers description

The problem is further complicated for vinyl polymers with their problems of stereoisomerism. The first descriptions of the conformational state of isotactic polypropylene in solution go back 25 years (178, 179, 192, 193). Corradini, Allegra, and Ganis proposed a model, still essentially valid today, according to which macromolecules possess a local helical structure analogous to that observed in the crystalline state. The helix segments are rather short, only a few monomer units, after which an inversion of the helix sense occurs, with simultaneous alteration of its direction (Figure 15). As a whole this disordered con-... 

While the situation with respect to simple vinyl polymers is straightforward, the tacticity and geometrical arguments are more complicated for more complex polymers. Here we will only briefly consider this situation. Before we move to an illustration of this let us view two related chloride-containing materials pictured below. We notice that by inserting a methylene between the two chlorine-containing carbons the description of the structure changes from racemic to meso. Thus, there exists difficulty between the historical connection of meso with isotactic and racemic with syndiotactic. 

Carboxypolymethylene. Carbomer cnrbopol car -boxyviny] polymer. A vinyl polymer with active carboxyl groups. Description Chern. Eng. News 36, 64 (Sept. 29, 1958). 

At least one other possibility exists. Assume, for example, that a very small amount of BPA is used with an excess of ECH under conditions that favored homopolymerisation of ECH (which may be different than conditions used to copolymerise the two). BPA would not be a monomer because it would not occur as a repeat unit, but rather would become a locus of initiation for a homopolymer of ECH. The most accurate description of the substance would be oxirane, (chloromethyl)-, homopolymer, ether with 4,4 -(l-methylethylidene) bis[phenol] (2 1), CASRN 139873-26-0. This principle also applies for cases in which a reactant such as a peroxide is used as a free radical initiator for a vinyl polymer. For example, a copolymer of monomers A, B, and C made using a free-radical initiator D may be called A, copolymer with B and C, D-initiated. Before 1989, the EPA had not informed industry of the need to include free-radical initiators as part of a polymer name, and therefore polymers placed onto the TSCA Inventory before 1989 do not have to include the free-radical initiator in the polymer name, even if it is used at a level of greater than two percent. In the latter case, the polymer would be named as A, polymer with B and C, without reference to the initiator. 

Vinyl polymers, for which pol5rpropylene serves as a prototype, present some additional issues not encountered in chains with symmetric torsions. The physical properties of these chains depend on the stereochemical composition and stereochemical sequence of the chain, and this dependence must be reflected in Z. Two equivalent methods have been used for description of the stereochemistry of vinyl polymers. One approach uses pseudoasymmetric centers [67]. Although the fragment denoted by -CH2-CHR-CH2- does not contain a chiral center, it can be treated as though it were chiral if one CH2 group is distinguished from the other. This distinction is drawn when the bonds in the... 

Here the probabilities in each matrix are normalised to make the highest probability unity in each. In the more general theory, the factor x is re-expressed in terms of the rotational constraints on individual bonds, and one typically needs five such variables for an acceptable description of an un-symmetrical vinyl polymer in which each bond has three rotational states. In the above case it may simply be defined as the relative probability of the gg state in the racemic dyad. 

The potential use of solid-state CPMAS NMR to detail the molecular structure of PP is demonstrated by many authors and is nicely reviewed in a recent paper by ToneUi [3]. The key parameter in such an analysis is the -y-gauche effect which enables the NMR chemical shifts of vinyl polymers to be assigned and provides an opportunity to test or derive rotational isomeric state (RIS) model descriptions of their conformational characteristics. 

As we can see, the y-gauche effect prediction of NMR chemical shifts in vinyl polymers permits assignment of their NMR spectra, provides an opportunity to test or derive an RIS model description of their conformational characteristics, and may also permit a test of their polymerization statistics. 

Effect of Solubility Parameter Differences. The polymer of major interest for the initial blend research was poly(2-vinyl naphthalene), an aryl vinyl polymer whose conformational energetics are very similar to polystyrene but with a higher quantum yield. In this first series of studies no attempt was made to develop a quantitative description of the absolute value of R rather, this ratio v s simply assumed to be proportional to the local segment density of aromatic rings. An increase in the local segment concentration of fluorescence guest polymer, due either to an increase... 

Emulsion Polymerization. Poly(vinyl acetate)-based emulsion polymers are produced by the polymerization of an emulsified monomer through free-radicals generated by an initiator system. Descriptions of the technology may be found in several references (35—39). 

Fig. 3. Schematic description of self-condensing vinyl polymerization used for the synthesis of of hyperbranched polymers based on vinyl monomers as presented by Frechet [52] -(represents a reactive site which can initiate polymerization)...

Note 3 In most cases, the polymer can actually be made by direct polymerization of its parent monomer but in other cases, e.g., poly(vinyl alcohol), the description conceptual denotes that an indirect route is used because the nominal monomer does not exist. 

Latexes are usually copolymer systems of two or more monomers, and their total solids content, including polymers, emulsifiers, stabilizers etc. is 40-50% by mass. Most commercially available polymer latexes are based on elastomeric and thermoplastic polymers which form continuous polymer films when dried [88]. The major types of latexes include styrene-butadiene rubber (SBR), ethylene vinyl acetate (EVA), polyacrylic ester (PAE) and epoxy resin (EP) which are available both as emulsions and redispersible powders. They are widely used for bridge deck overlays and patching, as adhesives, and integral waterproofers. A brief description of the main types in current use is as follows [87]. 

All paper samples for the poly (vinyl acetate)/paper and glue/paper studies were Whatman chromatography paper 1, basis weight 87 g/m2, thickness 0.16 mm, medium flow rate, supplied in 0.5-in. X 300-ft rolls, cut in 6-in. lengths. The materials used to prepare the polymer-paper composite systems are listed in Table I. Complete descriptions including suppliers7 comments are provided in earlier studies (1,2,3). 

From recent investigations()( 5 ), it is generally concluded that polymerization tcdces place exclusively in the polymer particles in vinyl acetate emulsion polymerization. As a detailed description of the role of polymer particles was presented in the previous paper(4 ), a brief explanation will therefore be reviewed here. 

A recent study on poly(2-vinyl naphthalene) P2VN has also concluded that the simple scheme 1 is inappropriate for the description of excimer kinetics in this polymer, and on the basis of comparison with isomers of 1, l -di-2-naphthyldiethyl ether (III), explanations of behaviour which emphasize conformational aspects (see ) have been proposed. In the polymer, monomer fluorescence decays... 

Treatment of solid wood over the years for increased utility included many chemical systems that affected the cell wall and filled the void spaces in the wood. Some of these treatments found commercial applications, while some remain laboratory curiosities. A brief description of the earlier treatments is given for heat-stabilized wood, phenol-formaldehyde-treated veneers, bulking of the cell wall with polyethylene glycol, ozone gas-phase treatment, ammonia liquid- and gas-phase treatment, and p- and y-radiation. Many of these treatments led to commercial products, such as Staybwood, Staypak, Im-preg, and Compreg. This chapter is concerned primarily with wood-polymer composites using vinyl monomers. Generally, wood-polymers imply bulk polymerization of a vinyl-type monomer in the void spaces of solid wood. 

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