Poly polymerization techniques

As previously described, all microspheres discussed in this chapter were synthesized from AB type diblock copolymers. Precursor block copolymers, poly(styrene-b-4-vinyl pyridine) (P[S-b-4VP]) diblock copolymers, were synthesized using the additional anionic polymerization technique [13]. The basic properties of the block copolymers were determined elsewhere [24,25] and are listed... 

As these block copolymers were synthesized using the anionic polymerization technique, their molecular weight distributions were narrow. The microspheres with narrower size distribution are better for well-ordered self-organization. Actually, all block copolymers synthesized for these works formed poly(4-vinyl pyridine) (P4VP) spheres in the PS matrices with narrow size distributions. 

The poly(styrene-b-isoprene) (P(S-b-IP)) and poly(-styrene-b-2-vinyl pyridine) (P(S-b-2VP)) block copolymers with narrow molecular weight distributions for blending with the microspheres were also synthesized using the additional anionic polymerization technique. The number-average molecular weights (Mns) and PS contents are also shown in Table 1. 

The structure-property relationship of graft copolymers based on an elastomeric backbone poly(ethyl acry-late)-g-polystyrene was studied by Peiffer and Rabeony [321. The copolymer was prepared by the free radical polymerization technique and, it was found that the improvement in properties depends upon factors such as the number of grafts/chain, graft molecular weight, etc. It was shown that mutually grafted copolymers produce a variety of compatibilized ternary component blends. 

Figure 7. Chromatographs of three samples of poly(dichlorophosphazene) prepared by three different polymerization techniques...

An overview of the synthesis and characterization of a unique class of polymers with a phosphorus-nitrogen backbone Is presented, with a focus on poly(dichloro-phosphazene) as a common Intermediate for a wide variety of poly(organophosphazenes). Melt and solution polymerization techniques are Illustrated, Including the role of catalysts. The elucidation of chain structure and molecular weight by various dilute solution techniques Is considered. Factors which determine the properties of polymers derived from poly(dichlorophos-phazene) are discussed, with an emphasis on the role that the organic substituent can play In determining the final properties. 

The temperature-sensitive poly(A-isopropyl acrylamide) and pH-sensitive poly(methacrylic acid) were used as the two component networks in the IPN system. Since both A-isopropyl acrylamide (NIPAAm) (Fisher Scientific, Pittsburgh, PA) and methacrylic acid (MAA) (Aldrich, Milwaukee, Wl) react by the same polymerization mechanism, a sequential method was used to avoid the formation of a PNIPAAm/PMAA copolymer. A UV-initiated solution-polymerization technique offered a quick and convenient way to achieve the interpenetration of the networks. Polymer network I was prepared and purified before polymer network II was synthesized in the presence of network I. Figure I shows the typical IPN structure. 

Although block copolymers do not occur naturally, synthetic block copolymers have been prepared by all known classical polymerization techniques. The first commercial block copolymer was a surfactant (Pluronics) prepared by the addition of propylene oxide to polycarbanions of ethylene oxide. While neither water-soluble PEO nor water-insoluble poly(propylene oxide) exhibits surface activity, the ABA block copolymer consisting of hydrophilic and lyophilic segments, is an excellent surfactant. Each block has 20 plus repeat units of that variety. 

Poly(hexamethylenesebacamide) (Nylon 6-10) by an Interfacial Polymerization Technique... 

In poly(AAm-co-BMA)/PAAc IPNs (BMA is butyl methacrylate), the synthetic procedure applied was the sequential polymerization technique shown in Fig. 10. A monomer or set of comonomers is polymerized into a polymer gel. A second monomer is introduced and subsequently polymerized and crosslinked within the initial gel (AAm-co-BMA) matrix to form the IPN. 

Commodity Chain-Growth Polymers. Two of the largest commodity wafer-soluble polymers are poly(vinyl alcohol) (PVA) and polyacrylamide (PAM). They are prepared by the free-radical initiation of vinyl monomers, a chain-growth polymerization technique. 

Poly(VP) containing azo groups, prepared as described above, has been employed for preparing block copolymers with acrylonitrile using a precipitation polymerization technique in t-butyl alcohol (see Table 4.10). 

Core-shell polymers were commercially introduced as impact modifiers for poly(vinyl chloride) PVC, in the 1960s. They are produced by a two-stage latex emulsion polymerization technique (Cruz-Ramos, 2000). The core is a graftable elastomeric material, usually crosslinked, that is insoluble in the thermoset precursors. Typical elastomers used for these purposes are crosslinked poly(butadiene), random copolymers of styrene and butadiene,... 

The -conjugated polyselenophene named PEDOS (182) the analog of poly-3,4-ethylenedioxythiophene (PEDOT) [281], one of the most successful conductive polymers, was obtained from 3,4-ethylenedioxyselenophene (89) using different polymerization techniques. These were oxidative chemical polymerization, solid-state polymerization, transition metal-mediated polymerization, and electrochemical polymerization (Scheme 46) [293, 294], The derivatives of PEDOS having the... 

Anionic polymerization techniques and naphthalene chemistry were used by Teyssie et al. to prepare A2B miktoarm stars, where A is poly(ethylene oxide) (PEO) and B is PS, PI, poly(a-methyl styrene) or poly(tert-butyl styrene) [25]. The reaction sequence is shown in Scheme 7. 

Star polymers having several PS branches and only one poly(2-vinyl naphthalene), PVN branch were prepared by Takano et al. using anionic polymerization techniques [31]. Sequential anionic block copolymerization of (4-vinyl-phenyl) dimethylvinylsilane (VS) and VN was employed. The double bonds attached to silicon have to remain unaffected during the polymerization of VS. This was ac-... 

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. 

As polymeric model fillers with specific surface groups and narrow size distribution, different microgel types, e.g., poly(styrene)-microgel, PS(m), and poly(methoxy-styrene)-microgel, PMS(m), are applied. They can be prepared by emulsion polymerization techniques as described, e.g., in [48]. 

---