Polyarylates crystallinity

Figure 19.12 Relationship between the heat distortion temperature (HDT) (at 1.82 MPa) and Tg for the amorphous polyarylates of HBA/Ph-HQ or fBu-HQ/HQ/ BB and the crystalline polyarylate of Ph-HQ/BB [33]...

Ph-HQ/HQ/BB (50/50) is a crystalline polyarylate and its HDT is 297 °C. We found that copolymerization involving small amounts of the third unit (HBA) into this system could improve its crystallinity (Figure 19.13) and HDT finally, the HDT of the copolyarylate Ph - HQ/HQ/BB/p-hydroxy benzoic acid (HBA) (47.5/47.5/5) increased to above 300 °C. 

More recent developments involve the preparation of liquid crystalline polyarylates and liquid crystal polyesters in general. 

Jackson and co-workers reported in 1976 [21,22] (on work carried out in 1971) that poly-p-oxybenzoyl-modified poly(ethylene terephthalate) was found to exhibit thermotropic liquid crystalline characteristics. A variety of thermotropic liquid crystalline polyarylates have since been described, and some of these also contain flexible spacer units [23-30]. 

D. N. Schulz, J. Bock, J. Maurer, E. Berluche, J. Kaladas, I. Duvdevani 257 Thermotropic Liquid Crystalline Polyarylates... 

I would like to acknowledge the numerous contributions of M.Okamoto,T.Yamanaka and N.Goto who prepared the thermotropic liquid crystalline polyarylates. 

Uses Prod, of liq. crystalline polyarylate Manuf./Distrib. Aldrich http //www.sigma-aldrich.com... 

Creed, D., Griffin, A.C., Hoyle, C.E., and Venkataram, K., The role of aggregates in the wavelength dependent photochemistry of a main-chain liquid crystalline polyaryl cinnamate, Proc. SPIE-Int. Soc. Opt. Eng., 1213, 184, 1990. 

PC is more resistant to strong acids but is less stable than polyterephthalates (PET, PBT) to benzene and methanol. PET, polyethylene terephthalate, is a hard, stiff homopolymer, whilst PBT, polybutylene terephthalate is somewhat softer. Further materials in this group include, i) thermoplastic poly (ether) ester elastomers, included in the TPE grouping, ii) amorphous polyarylates, and Hi) self-reinforced crystalline polyarylates (LCP). Polycarbonate may be blended with various styrenics (PC/ABS, PC/ASA, PC/SMA). 

Fig. 1. Engineering resins cost vs annual volume (11) (HDT, °C) A, polyetheretherketone (288) B, polyamideimide (>270) C, polyarylether sulfone (170- >200) D, polyimide (190) E, amorphous nylons (124) F, poly(phenylene sulfide) (>260) G, polyarylates (170) H, crystalline nylons (90—220) I, polycarbonate (130) J, midrange poly(phenylene oxide) alloy (107—150) K, polyphthalate esters (180—260) and L, acetal resins (110—140).

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

This polyester class comprises amorphous high-Tg copolyesters, known as amorphous polyarylates, and semicrystalline polyesters that often exhibit anisotropic hquid crystalline (LC) melts. Liquid crystalline polyesters are often termed as polyester LCPs. 

TABLE 2.13 Topical Properties of Ardel D-100 Bisphenol-A Polyarylate and of Liquid Crystalline Polyesters Vectra A-950 and Xydar SRT-500... 

Amorphous bisphenol-A polyarylates are soluble in dioxane and in chlorinated solvents such as CH2C12, 1,2-dichlororethane, 1,1,2-trichloroethane, and 1,1,2,2-tetrachloroethane while semicrystalline and liquid crystalline wholly aromatic polyesters are only sparingly soluble in solvents such as tetrachloroethane-phenol mixtures or pentafluorophenol, which is often used for inherent viscosity determinations. 

Many researchers have reported the structure-thermal property correlations in LCPs from substituted hydroquinones (HQs) and dicarboxylic acids. Lenz and co-workers have investigated the liquid crystallinity of the polyarylates obtained from substituted HQs and terephthalic acid (TA) [6-10], substituted HQs and l,10-bis(phenoxy)decane-4,4/-dicarboxylic acid [8], and substituted HQs and a,oo-bis(phenoxy)alkane-4,4/-dicarboxylic acid [11], Kricherdorf and Schwarz [12] and Osman [13] reported the liquid crystallinity of the polyarylates obtained from substituted HQs and 1,4-cyclohexanedicarboxylic acid, while Krigbaum el al. [14], Heitz and co-workers [15] and Kricherdorf and Engelhardt [16] investigated the liquid crystallinity of the polyarylates synthesized from substituted HQs and substituted TAs. In addition, Jackson reported the liquid crystallinity and the moduli of fibers and injection molded specimens of the polyarylates... 

In order to compare the crystallinities of the polyarylates, X-ray diffraction patterns were observed in the temperature range of 25-250 °C, with the relative degree of crystallinity (I/I0) being calculated according to the following equation ... 

The liquid crystallinity and the moduli of as-spun fibers of polyarylates from substituted HQs and substituted PECs could be controlled by the substituents shown in Table 19.1. Polyarylates derived from /-butyl HQ (fBu-HQ) and PEC (fBu-HQ/PEC), and phenyl-HQ (Ph-HQ) and PEC (Ph-HQ/PEC), showed decreased liquid crystallinity when compared to chloro-HQ (Cl-HQ) and PEC (Cl-HQ/PEC), and methyl-HQ (Me-HQ) and PEC (Me-HQ/PEC), because of the bulky substituents on the HQ units. 

Polyarylates prepared from cyclohexyl-HQ (Ch-HQ) and PEC (Ch-HQ/PEC) did not show liquid crystallinity due to the more bulky substituent on the HQ unit compared to those on f Bu-HQ and Ph-HQ. As-spun fibers of Ch-HQ/PEC exhibited lower moduli than those of fBu-HQ/PEC and Ph-HQ/PEC. Therefore, in order to obtain high-modulus as-spun fibers, the stability of the liquid crystalline state (7j — 7j,) is an influential factor, as shown in Table 19.1. 

Polyarylates derived from various substituted HQs and l,2-bis(methoxy-phenoxy) ethane-4,4/-dicarboxylic acid or l,2-bis(2,6-dichlorophenoxy)ethane-4,4 -dicarboxylic acid exhibited low moduli because of the lack of liquid crystallinity resulting from the steric hindrance of the substituents on the PEC units. 

Therefore, we expected that the polyarylates synthesized from substituted HQs and BB would show higher stabilities of the liquid crystalline state and higher moduli than those produced from substituted HQs and substituted PEC. 

However, in spite of the higher rigidity of the polymer chains, many pol-yarylates derived from substituted HQs and BB exhibited liquid crystallinity and lower Tms when compared to the polyarylates derived from substituted HQs and TA. 

The reason for the lower liquid crystalline (LC) temperature of the BB model compound seems to be that the biphenyl unit of this compound was adopting a twisted structure in the LC state [26], Therefore, we prepared various polyarylates containing the BB unit and determined their thermal properties and the moduli of the as-spun fibers, as shown in Table 19.3. 

On the other hand, the HDT is affected by the crystallinity of the polyarylates. Thus, polyarylates with a high crystallinity are predicted to have a high HDT. 

The moduli of as-spun fibers of polyarylates depend highly upon the stability of the liquid crystalline state, the rigidity of the polymer chain, and the degree of elongational flow orientation (F-value). On the other hand, the moduli of injection molded specimens of polyarylates depend upon the stability of the liquid crystalline state, and the rigidity and packing density of the polymer chain. 

Polyarylates derived from BB show a high 7 g, while their HDT values depend upon both the Tt and the crystallinity. 

Statistical copolymerization of ethylene glycol and 1,4-butanediol with dimethyl ter-ephthalate results in products with improved crystallization and processing rates compared to poly(ethylene terephthalate). Polyarylates (trade names Ardel, Arylon, Durel), copolymers of bisphenol A with iso- and terephthalate units, combine the toughness, clarity, and proce-sibility of polycarbonate with the chemical and heat resistance of poly(ethylene terephthalate). The homopolymer containing only terephthalate units is crystalline, insoluble, sometimes infusible, and difficult to process. The more useful copolymers, containing both tere- and isophthalate units, are amorphous, clear, and easy to process. Polyarylates are used in automotive and appliance hardware and printed-circuit boards. Similar considerations in the copolymerization of iso- and terephthalates with 1,4-cyclohexanedimethanol or hexa-methylene diamine yield clear, amorphous, easy-to-process copolyesters or copolyamides,... 

Aromatic polyesters having an amorphous molecular structure. Compared with other amorphous engineering plastics in terms of heat resistance, polyarylates are generally positioned between polycarbonate on the low side and sulfone and polyether polymers on the high side. Compared with crystalline and semi-crystalline engineering plastics, polyarylate resins offer better resistance to warping, and generally comparable mechanical properties. 

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