Since the discovery of simple polymers many years ago, polymers of all kinds have emerged for a variety of uses, including manufacture of textiles, paints, plastics, synthetic rubbers, insulation, adhesives to name only a few. Polymers exist in two primary forms, thermoplastic polymers, which may be recurred, and thermosetting polymers, such as polystyrene, epoxies, etc., which cannot be recurred.
A common phenomenon occurring as a monomer is polymerized involves volumetric shrinkage of up to 15% based on the resulting polymer formed. This shrinkage represents an undesirable feature of polymers, as there exist many applications in which 0% shrinkage or "zero shrinkage," and even volume expansion upon polymerization are desirable.
Several "oxa-spiro" monomers have been identified that expand during polymerization. See, e.g., W. J. Bailey, et al.: J. Polym. Sci., Polym. Lett. Ed., 18: 771-773 (1980); J. Polym. Sci., Polym. Symp., 64: 17-26 (1978); J. Rubber Res., Inst. Sci. Lanko., 54: 566-75 (1977); J. Polym. Sci., Polym. Symp., 56: 117-27 (1976); J. Polym. Sci., Polym. Chem. Ed., 14: 1735-41 (1976); Makromol. Chem., 177, No. 11: 3231-5(1976); Polym. Prepr., ACS Polym. Chem. Div., 15:445-50 (1974); J. Macromol Sci., Chem. Publ., A9, No. 5: 849-65 (1975); J. Polym. Sci., Polym. Chem. Ed., 13: 2525-30 (1975); Makromol. Chem., 176: 2897-903 (1975); J. Poly. Sci., Polym. Lett. Ed., 13: 193-5 (1975); Polym. Prepr., ACS Polym. Chem. Div., 14: 1169-74 (1973); Polym. Prepr., ACS Polym. Chem. Div., 13: 281-6 (1972); W. J. Bailey and T. Endo, J. Polym. Sci., Polym. Lett. Ed., 18: 25-27 (1980); and W. J. Bailey, R. L. Sun, H. K. Endo, H. Iwana, R. Teushima, K. Saigou, and M. M. Bitritto, ACS Symp. Ser., Ring-Opening Polym., Int. Symp., 59: 38-59 (1977). Typical of these bicyclic oxa-spiro monomer structures are those shown below: ##STR1##
These bicyclic oxa-spiro monomers polymerize through a ring opening mechanism in the presence of cationic initiators such as boron trifluorde etherate (BF.sub.3.OEt.sub.2). ##STR2##
The predominant change which produces expansion is the breaking of two covalent bonds of the monomer for every new covalent bond formed. Several oxa-spiro monomers have been identified that exhibit between 0 and 17% expansion during polymerization. See Bailey, et al., supra. Some of these materials have been evaluated as comonomers with epoxy resins for controlling shrinkage and voids in insulation materials used in electrical equipment.
There are various organo-phosphorus monomers which undergo cationic ring-opening polymerization. For example, phospholanes and deoxophostones (5-membered ring monomers), phosphorinanes (6-membered monomers) and phosphocane (8-membered ring) all undergo cationic ring opening polymerization. See Kobayashi, et al., "Cationic Ring-Opening Polymerization of 2-Phenyl-1,3,2-dioxaphosphepane, a Seven Membered Cyclic Phosphonite, 19 Macromolecules 466-469 (1986). Cyclic phosphonites will polymerize to produce polyphosphinates as follows: ##STR3## X=(CH.sub.2).sub.2, (CH.sub.2).sub.3, (CH.sub.2).sub.2 O(CH.sub.2).sub.2 R=Ph
Polymerization of deoxophostone produces poly(phosphine oxide) ##STR4## and the polymerization of 2-phenyl - 1,3,2-dioxaphosphepane (7-membered ring) produces polyphosphinates as follows: ##STR5##
The stereochemistry of these monomers is such that during polymerization significant volume expansion occurs as the cyclic ring opens up. This "uncoiling" effect during polymerization has been observed with certain cyclic keto-dilactones. See S. Klaus and W. S. Knowles, 10 J. App. Poly. Sci. 887 (1966).
Although the oxa-spiro and organo-phosphorus materials discussed above do exhibit zero shrinkage and even expansion upon polymerization, they exhibit less than desirable properties for certain applications. For example, these polymers exhibit low thermal stability at temperatures above about 120.degree. C., and thus have only limited use in high voltage insulation applications.
Another drawback with the oxa-spiro compounds is that they tend to exhibit undesirable electrical properties, such as allowing high electrical losses stemming from having dielectric constants and dissipation factors which are too high for high voltage insulation applications.
Yet another problem associated with these oxa-spiro compounds is their tendency to burn rapidly, which is of great significance for polymers used in high voltage, high temperature situations.
Still further problems exhibited by these polymers are the fact that they exhibit less than desirable mechanical properties, including low tensile (modulus and strength) properties. Additionally, these polymers are frequently slow-curing, requiring very strong acid catalysts to cure.
Attempts to solve these problems by blending these polymers with other materials such as epoxies have improved some properties moderately, but have not resulted in any improvement in flame retardant and electrical properties.
Accordingly, it would be desirable to develop a high temperature polymer exhibiting zero shrinkage, and solving some or all of the above problems, such as the need for flame retardance.