Containing Aliphatic Backbones

Normally polymer structures containing aliphatic backbones are low in smokegenerating character and are generally not self-extinguishing. Additives to such systems to achieve flame-retardancy often enhances smoke generation Polymers with aromatic side groups such as polystyrene have a considerable tendency to generate smoke. 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acrylic (52). The acrylic—vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aliphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, solid epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

Abkowitz and Stolka (1990, 1991) compared hole mobilities of poly-silylanes and polygermylenes containing aliphatic pendants with compounds that contain only aromatic side groups. While transport occurred via states associated with the backbone chain in both compounds, the nature of the side groups was shown to influence the temperature dependence of the mobility. The results were described by a small-polaron argument, based on the assumption that the polarizability increases when an aromatic pendant group was substituted... 

The pre-polymers typically contain at least two epoxy groups spaced with an aromatic or aliphatic backbone or even by a fragment of chain including other functionalities. The most commonly used resin from this class is probably formed from epichlorohydrin and bisphenol A or 4-[1-(4-hydroxy-phenyl)-isopropyl]phenol under basic conditions to give a polymeric diglycidyl polyether as shown below ... 

Numerous studies have been performed on thermal stability and on pyrolysis of aliphatic poly(amides) [1-12], etc.. Similarly to other classes of polymers, there is a considerable difference in the thermal stability of the polymers with aliphatic segments in their backbone and those with aromatic groups. The compounds containing aliphatic segments decompose at lower temperatures, and it is not uncommon that in addition to the cleavage of other bonds, the C- bonds also are split. On the other hand, the aromatic rings are very resistant to thermal decomposition. The thermal decomposition of aliphatic poly(amides) was studied in connection to various practical purposes, such as the resistance of fibers to fire. Some information on thermal decomposition of aliphatic poly(amides) is summarized in Table 13.3.1 [13]. 

Lipids with a glycerol backbone containing aliphatic carbon chain(s) iV-[l-(2,3-dioley-... 

Poly(glycolic acid) (Figure 2.4) is an example of a polymer which contains a backbone ester linkage flanked by aliphatic groups on both sides. 

Epoxy resins are among the most important of the high performance thermosetting polymers and have been widely used as structural adhesives and matrix for fiber composites. Epoxy resins are characterized by the presence of epoxide groups before cure, and they may also contain aliphatic, aromatic, or heterocyclic structures in the backbone. The epoxy group can react with amines, phenols, mercaptans. 

MBPE-9. Macromolecules that contain aliphatic and aromatic sequences in their backbone structure have special possibiUties to exist as liquid crystals or as condis crystals (see Sect. 2.5). The thermal analysis of a polyether based on the semi-flexible mesogen l-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane is copied in Fig. 2.68. The computed vibration-only heat capacity is reached somewhat... 

Poly(a-ester)s, the most expansively studied class of biodegradable polymer, contain aliphatic ester linkages in their backbone which can be cleaved hydrolytically. It is reported that mere aliphatic polyesters with practically small aliphatic chains between ester bonds can decompose over the time needed for the majority of the biomedical applications. Poly(a-ester)s demonstrate enormous diversity and synthetic flexibility and, depending on the monomeric units, can be synthesized from a variety of monomers via condensation polymerization and ring-opening routes [19]. Poly(glycolic acid) and the stereoisomers of poly(lactic acid) are the most expansively investigated poly(a-ester)s polymers. 

There are also important differences in the nature of the polymer backbone formed by these processes. Olefin addition reactions lead to polymer chains containing aliphatic carbon as the backbone. Most step-growth reactions instead form polymer chains or rings containing heteroatoms (noncarbon atoms) in addition to aliphatic carbon in the backbone. The presence of heteratoms can provide remarkable enhancements in polymer performance and often leads to polymers with higher glass transition temperatures and thermal stability leading to such properties as conductivity or electroluminescence. 

The specialty class of polyols includes poly(butadiene) and polycarbonate polyols. The poly(butadiene) polyols most commonly used in urethane adhesives have functionalities from 1.8 to 2.3 and contain the three isomers (x, y and z) shown in Table 2. Newer variants of poly(butadiene) polyols include a 90% 1,2 product, as well as hydrogenated versions, which produce a saturated hydrocarbon chain [28]. Poly(butadiene) polyols have an all-hydrocarbon backbone, producing a relatively low surface energy material, outstanding moisture resistance, and low vapor transmission values. Aromatic polycarbonate polyols are solids at room temperature. Aliphatic polycarbonate polyols are viscous liquids and are used to obtain adhesion to polar substrates, yet these polyols have better hydrolysis properties than do most polyesters. 

Nearly all of the polymers produced by step-growth polymerization contain heteroatoms and/or aromatic rings in the backbone. One exception is polymers produced from acyclic diene metathesis (ADMET) polymerization.22 Hydrocarbon polymers with carbon-carbon double bonds are readily produced using ADMET polymerization techniques. Polyesters, polycarbonates, polyamides, and polyurethanes can be produced from aliphatic monomers with appropriate functional groups (Fig. 1.1). In these aliphatic polymers, the concentration of the linking groups (ester, carbonate, amide, or urethane) in the backbone greatly influences the physical properties. 

The SCLPs are defined as unbranched, aliphatic chains containing between nine and 18 carbon atoms, with up to three double bonds in the carbon backbone, and ending in an alcohol, aldehyde, or acetate functional group (Figure 12.5) [42]. Laboratory studies have demonstrated that there is no acute, subchronic, chronic, or developmental mammalian toxicity even with exposure to high doses of SCLPs or chemically similar compounds [39, 43]. 

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