Aliphatic Main-Chain Polymers

PEIs derived from AT-(4-carboxyphenyl) trimellitimide and aliphatic spacers (11) are not thermotropic, irrespective of whether the spacer is chiral or not. If the spacers are semi-aliphatic and contain a benzene ring, then thermotropic PEIs may be formed with both a smectic and nematic phase. If chiral spacers are then used a chiral smectic A or C phase may additionally be obtained. Such phases may be ferroelectric, which is extremely rare for main-chain polymers [26]. Examples of chiral and non-chiral spacers used in the copolymers (12) are ... 

Aromatic imide groups are known to be nearly planar, rigid, polar, and thermostable. However, aromatic imide structures are also known to be non-mesogen in nature. Poly(ester-amide) (PEI) derived from N- (4 -carboxyphenyl) trimellitimide and aliphatic spacers are not thermotropic, whether the spacer used is chiral or not. Semi-aliphatic spacers are observed to exhibit both a smectic and a nematic LC phase in the resultant thermotropic PEIs. The semi-aliphatic chiral spacers exhibit both chiral smectic phase (A or C ) and cholesteric phase. Such a chiral smectic LC-phase, which may be ferroelectric in nature, is extremely rare for LC-main-chain polymers [27]. It is a particular advantage of polar imide mesogens to favor the formation of layer-structures when combined with non-polar species [28]. 

The polymer matrices used in HEMs can be divided by chemical structure into two major categories aromatic main-chain polymers and aliphatic main-chain... 

Jang, W., Kim, D., Choi, S., Shul, Y.G., Han, H. (2006) Synthesis and characterization of sulfonated polyimides containing aliphatic linkages in the main chain. Polymer International, 55, 1236-1242. 

Viscosity additives are aliphatic polymers of high molecular weight whose main chain is flexible. It is known that in a poor solvent, interactions between the elements making up the polymer chain are stronger than interactions between the solvent and the chain (Quivoron, 1978), to the point that the polymer chain adopts a ball of yarn configuration. The macromolecules in this configuration occupy a small volume. The viscosity of a solution being related to the volume occupied by the solute, the effect of polymers on the viscosity in a poor solvent will be small. 

Incorporation of cyclic aliphatic (aUcycHc) side groups markedly improves the plasma etch resistance of acryhc polymers, without reduciag optical transparency at 193 nm (91). Figure 32 presents stmctures of some acryhc polymers currendy under study for use ia 193-nm CA resists (92—94). Recendy, polymers with main-chain aUcycHc stmctures have been described that offer similar properties (95,96). 

Carothers also produced a number of aliphatic linear polyesters but these did not fulfil his requirements for a fibre-forming polymer which were eventually met by the polyamide, nylon 66. As a consequence the polyesters were discarded by Carothers. However, in 1941 Whinfield and Dickson working at the Calico Printers Association in England announced the discovery of a fibre from poly(ethylene terephthalate). Prompted by the success of such a polymer, Farbenfabriken Bayer initiated a programme in search of other useful polymers containing aromatic rings in the main chain. Carbonic acid derivatives were reacted with many dihydroxy compounds and one of these, bis-phenol A, produced a polymer of immediate promise. 

Several factors related to chemical structure are known to affect the glass transition tempera lure. The most important factor is chain stiffness or flexibility of the polymer. Main-chain aliphatic groups, ether linkages, and dimethylsiloxane groups build flexibility into a polymer and lower Tg Aliphatic side chains also lower Tg, (he effect of the length of aliphatic groups is illustrated by the methacrylate series (4,38) ... 

Due to the unsaturation present in the main chain, protection is required against oxygen, UV and ozone. Oil resistance is poor and the polymer is not resistant to aromatic, aliphatic and halogenated hydrocarbons. 

Polymide polymers contain amide group NH CO in the main chain. The most important are linear aliphatic Polyamides. These are known as nylons. Polyamides are also used as adhesives, coatings and in engineering applications. 

The general correlations of structure and properties of homopolymers are summarized in Table 2.13. Some experiments which demonstrate the influence of the molecular weight or the structure on selected properties of polymers are described in Examples 3-6 (degree of polymerization of polystyrene and solution viscosity), 3-15, 3-21, 3-31 (stereoregularity of polyisoprene resp. polystyrene), 4-7 and 5-11 (influence of crosslinking) or Sects. 4.1.1 and 4.1.2 (stiffness of the main chain of aliphatic and aromatic polyesters and polyamides). 

Shigematsu et al. (3) prepared aliphatic polymers containing ketone and ether components in the main chain, (III), by the dehydration of glycerol followed by treatment with 1,10-decane diol and sulfuric acid at 165°C. 

By using this method, the chemical shifts of the resonances in the spectra of a sulfur vulcanized natural rubber (Fig. 32 expanded aliphatic region in shown in Fig. 33 [top]) are assigned to various units of the polymer network, which arise from structural modifications induced by the vulcanization 194,196 200). Different sulfidic structures are found for unaccelerated and accelerated sulfur vulcanizations, respectively. With increasing amount of accelerator (as compared to the sulfur), the network structure exhibits less crosslinking, fewer main chain structural modifications, and fewer cyclic sulfide structures 197). 

The catalyst [Pd(Me-DUPHOS)(MeCN)2](BF4)2 was also effective in the alternating asymmetric copolymerization of aliphatic a-olefins with carbon monoxide [27,28]. The polymer synthesized in a CH3N02-CH30H mixture has both 1,4-ketone and spiroketal (10) units in the main chain. The propylene-CO copolymer consisting only of a 1,4-ketone structure shows [ ]D +22° (in (CF3)2CHOH), and the optical purity of the main chain chiral centers is over 90% as estimated by NMR analysis using a chiral Eu shift reagent. 

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