Monomer residues

Any of the four monomer residues can be arranged in a polymer chain in either head-to-head, head-to-tail, or tail-to-tail configurations. Each of the two head-to-tail vinyl forms can exist as syndiotactic or isotactic stmctures because of the presence of an asymmetric carbon atom (marked with an asterisk) in the monomer unit. Of course, the random mix of syndiotactic and isotactic, ie, atactic stmctures also exists. Of these possible stmctures, only... 

In the crystalline region isotactic polystyrene molecules take a helical form with three monomer residues per turn and an identity period of 6.65 A. One hundred percent crystalline polymer has a density of 1.12 compared with 1.05 for amorphous polymer and is also translucent. The melting point of the polymer is as high as 230°C. Below the glass transition temperature of 97°C the polymer is rather brittle. 

The classical representation of a homopolymer chain, in which the end groups are disregarded and only one monomer residue is considered, allows no possibility for structural variation. However, possibilities for stercoscqucnce isomerism arise as soon as the monomer residue is considered in relation to its neighbors and the substituents X and Y are different. The chains have tacticity (Section 4,2.1). Experimental methods for tacticity determination are summarized in 4.2.2 and the tacticity of some common polymers is considered in 4.2.3. 

When the configurational series of the monomer residues is known, D- or L- may be included as a prefix to the name. 

PVA can be crosslinked with a crosslinker present in a molar concentration, relative to monomer residues, of 0.01% to 1.0%. The crosslinker may be formaldehyde, acetaldehyde, glyoxal, glutaraldehyde, maleic acid, oxalic acid, dimethylurea, polyacrolein, diisocyanate, divinyl sulfonate, or a chloride of a diacid [89-91]. 

Upon complexation, shifts in the UV-visible spectra of cupric chloride are manifested as a shoulder at approximately 370 nm, and a shift in the visible absorption from 865 to 850 nm. The method of continuous variation7 (Job s Method) was employed using the new, 370 nm, absorption. The results indicate one monomer residue (pyridine... 

Another important property which affects biocompatibility is permeability to low molecular weight solutes, since it is usually required that all extractable materials be leached from the device prior to use. These extractables include lower molecular weight species such as unreacted monomer, residual initiators,... 

The overwhelming majority of synthetic polymers is organic in nature, and it is on these that we will concentrate. The simplest and most common synthetic polymer is polyethylene, which will be our first example. Figure 1.1 shows the basic chemical structure of polyethylene. Pairs of hydrogen atoms are attached to the carbon atoms that make up the backbone. The repeat unit in this structure contains two carbon atoms and is derived from the ethylene monomer. In the case of polyethylene, the number of monomer residues, which is known as the polymerization... 

The term tactidty refers to the configuration of polymer chains when their constituent monomer residues contain a steric center. Figure 1.8 illustrates the three principal classes of tacticity as exemplified by polypropylene. In isotactic polypropylene, the methyl groups are all positioned on the same side of the chain, as shown in Fig. 1.8 a). In syndiotactic polypropylene, the methyl groups alternate from one side to the other, as shown in Fig. 1.8 b). Random placement of the methyl groups results in atactic polypropylene, which is shown in Fig. 1.8 c). We can readily observe the effects of tacticity on the properties of polypropylene isotactic polypropylene is hard and stiff at room temperature, syndiotactic polypropylene is soft and flexible, and atactic polypropylene is soft and rubbery. 

We can create thermoplastic polymers by chain growth or step growth reactions. In either case the polymer chains consist of a string of monomer residues, each of which is attached to two other monomer residues. The polyethylene molecule shown in Fig. 1.1 is an example of a thermoplastic polymer made via chain growth polymerization, as shown in Fig. 1.7,... 

We use hydrogen NMR spectrometry to measure the relative concentrations of the hydrogen atoms that are part of the different monomer residues making up copolymers. We can measure monomer residue concentrations directly by comparing the relative areas of the various peaks with which they are associated. 

We have some evidence that this theoretical problem is a genuine limitation in the case of a quaternised styrenic monomer which is block copolymerised with NaVBA. This problem can be circumvented in two ways. Firstly, the polymerisation sequence can be simply reversed so that the longer block is synthesised first. If this is the quaternised block, the resulting copolymer cannot exhibit an isoelectric point because the major block is permanently cationic, thus no charge compensation can occur. On the other hand, if the longer block is anionic, then addition of HCl will protonate the acidic monomer residues and at some point an isoelectric point will be attained (unless the acidic block is strongly acidic, e.g. 4-styrenesulfonic acid). 

To keep the probe specifically at the primary amine side chains, we have used pyrenecarboxaldehyde and attached it covalently to polyethylenimine by reduction with sodium borohydride of the Schiff base formed between the probe aldehyde and the polymer primary amine. Such reductive alkylation has been used widely with primary amines of enzymes.43,44 For three different adducts to the polymer, the extent of coupling with pyrene, expressed relative to units of monomer residues,... 

Fig. 12. Fluorescence emission spectra at different pH values [(a) pH <1 (6) pH 6.15 (c) pH 9.6)] for pyrene covalently attached to polyethylenimine. Percentages designate the fractional number of monomer residues with attached pyrene moieties.

I have no substantive disagreement with Dr. Mandel. It was my impression from his previous comment that he viewed the addition of a CH, group to the acrylate residue as trivial. For reasons that I just described I consider the addition of 1 CH3 to a three-carbon monomer as a substantial change in the context of a polymer (comparable to adding 1 C12H25 group to 10% of the monomer residues in polyethylenimine). 

---