Aromatic units

Sources, structure elucidation and syntheses of aromatic units are summarized in Table 3. It is of interest that some orsellinic acid 

Methyl orsellinate 208-210 From methyl acetoace-tate and -BuLi with NaFl in THF and subsequent acidification (70) 

Orsellinic acid (2- C) Phthalic acid Rhizonic acid 

Di-O-methylorsellinic acid, R = Me Di 0-mefiiyldivaric acid, R = 11-C3H7 Di-0-me hyk)livctotearbo3Q lic acid, R = 11-C5H1 j Di OmethylsphaaophorolcafboTQ Iic acid, R = 11 1 15 

Neither the carboxylic acid I nor the benzylated P-orcinol II did react trifluoroacetic anhydride to the wanted benzophenones. 

---

One class of aromatic polyethers consists of polymers with only aromatic rings and ether linkages ia the backbone poly(phenylene oxide)s are examples and are the principal emphasis of this article. A second type contains a wide variety of other functional groups ia the backbone, ia addition to the aromatic units and ether linkages. Many of these polymers are covered ia other articles, based on the other fiinctionahty (see Polymers containing sulfur, POLYSULFONES). 

Benzene derivatives. Tbe nomenclature is a combination of the lUPAC system and traditional names. Many of the derivatives are named by the substituent group appearing as the prefbt. These may be considered a subclass of the aliphatic-aromatic hydrocarbon family, which contains both aliphatic and aromatic units in its structures. Thus, alkylbenzenes are made up of a benzene ring and alkane units alkenylbenzenes are Composed of a benzene ring and alkene units and alkynylbenzenes comprise a benzene ring and alkyne units. Examples of alkylbenzenes include... 

Partially aromatic PAs have a higher glass transition temperature and a higher melting temperature dian their aliphatic counterparts thus these polymers have a better dimensional stability.18 Due to the high Tg and the low water absorption as a result of die presence of die aromatic unit, the effect of water on the properties at room temperature is small. The barrier properties of partially aromatic PAs are also better. However, despite all these favorable properties, their commercial market is relatively small. 

Calixarenes are cyclophane-type molecules, in which at least four aromatic units are joined via methylene or related groups [9]. It is known that calix[4]arenes with hydroxy groups in the 2-position normally prefer a conelike conformation, however, depending on the substituents a more or less rapid dynamic interconversion with three possible partial cone conformations is possible (Fig. 1) [9, 10]. 

Functionalized copolymers from dienes and p-alkylstyrenes can serve as dispersants and viscosity index improvers. The functionalities are introduced via the aromatic units [233,234]. The polymers are selectively hydrogenated to produce polymers that have highly controlled amounts of unsaturation, permitting a highly selective functionalization. The dispersant substances may also include a carrier fluid to provide concentrates of the dispersant. 

Here, however, it is possible to obtain stabilization of the low-dense lattice build-up of bulky molecules via intermolecular adhesion and orientation forces. Molecules with planar structural elements are advantageous in this respect since they are apt to support the lattice aggregate, and at the same time they are able to partition off cavities effectively. It is very convenient to use aromatic units. 

The synthesis of block polymers of diacetylene-silarylene and diacetylene-carboranylenesiloxane polymers (99a-e) (Fig. 61) by the polycondensation reaction of 1,4-dilithiobutadiyne with l,4-bis(dimethylchlorosilyl) benzene and/or l,7-bis(tetramethylchlorodisiloxane)-m-carborane have been reported by Sundar and Keller.129 These polymers are a hybrid between the carboranylenesiloxane and silarylene-siloxane polymers and have high char yields (up to 85%) at 1000°C in N2 and in air, reflecting the thermal stabilizing effects of the carborane and aromatic units in the polymeric backbone. 

LBADH also catalyzed the asymmetric reduction of a broad variety of differently substituted acetylenic ketones, including aromatic alkynones and a number of aliphatic derivatives [71]. For example, methyl alkynones bearing an aromatic unit attached to the triple bond were reduced to the corresponding (7 )-propargylic alcohols with >99% ee. Similarly, alkylsilyl-substituted... 

Further transformation of 62 to the ansa chain (+ )-66 is briefly summarized in Scheme 7-14 without a detailed discussion. Compound ( )-66 has now been properly functionalized for coupling with the aromatic unit of rifamycin. 

The macrocydic polyether BPP34C10 and 1,1 -dimethyl-4,4-bipyridiniumbis(hexafluorophosphate) give rise to colorless solutions when they are dissolved by them-sdves in MeCN. The sudden appearance of a color, upon mixing the two compounds in MeCN, is indicative of complex formation and is a result of chaige transfer interadions between the complementaiy aromatic units of the host and guest. 

X-ray diffraction measurements have shown that Bisphenol-AF-derived poly(aryloxydiphenylsilane) is amorphous.28 The Tg value of 106°C is higher than that of the poly(aryloxydiphenylsilane)s derived from dianilinodiphenylsilane and bisphenols such as 4,4 -biphenol, 2,7-dihydroxynaphthalene, and hydroqui-none.28 The aromatic units in poly(aryloxy-diphenylsilane(s) have a remarkable effect on the Tg. The thermal stability of this polymer is somewhat lower than those of poly(aryloxydiphenylsilane)s derived from dianilinodiphenylsilane and bisphenols such as 4,4 -biphenol, 2,7-dihydroxynaphthalene, and hydroquinone. The DT10 is 362°C and the residual weight at 500°C in air is 54%. 

Figure 3.3 Partial structure (16 aromatic units) of a spruce lignin fragment.

Linking the central ring via NH bridges to aromatic units, i.e., formation of the 2,5-diarylamino-l,4-benzoquinones (116), and... 

Polyphenylene oxide and polyphenylene ether are oxides or ethers like polyoxymethylene but an aromatic unit replaces the methylene group leading to — ( — C6H4 — O—) — Polyphenylene ether has too high a glass transition temperature to be easily processed and is marketed in the form of alloys with other resins, such as ... 

---