1. Field of the Invention
This invention relates to novel acetal terpolymers. More particularly, this invention relates to novel ultraviolet (UV) curable terpolymers of trioxane, 1,3-dioxolane and certain formals of monoethylenically unsaturated aliphatic diols. These terpolymers are non-crystalline at room temperature (about 25.degree. C.) or above by virtue of having higher dioxolane contents than copolymers or terpolymers hitherto contemplated by the prior art, although they can be made to crystallize at temperatures below room temperature. They can be admixed with multifunctional acrylates or similarly - performing multifunctional crosslinking monomers and a photosensitizer or UV initiator and cured to an insoluble, non-tacky, rubbery state using UV radiation. The resulting cured polymeric materials form useful crosslinked films, and can also be cryogenically ground to a suitable small particle size and then blended with conventionally prepared crystalline oxymethylene homo-, co- and terpolymers to improve the impact properties of molded articles made therefrom.
2. Description of the Prior Art
Commonly-assigned copending U.S. patent application Ser. No. 07/096,187, filed of even date herewith in the names of George L. Collins, Paul Zema and William Pleban and entitled "Low Tg Non-Crystalline Acetal Copolymers", discloses and claims low Tg (glass transition temperature) trioxane/ 1,3-dioxolane copolymers which are also non-crystalline at room temperature or above (although they too can be made to crystallize at temperatures below room temperature) and which have a dioxolane content greater than 65 mol percent and less than about 75 mol percent and an IV (intrinsic viscosity) of from about 1.00 to about 2.3, as measured by standard viscometric measurements, e.g., in o-chlorophenol. These copolymers contain no unsaturated sites for subsequent crosslinking, and are not disclosed as being curable by reaction with multifunctional crosslinking monomers under UV curing conditions.
Trioxane/1,3-dioxolane/unsaturated diol formal terpolymers are disclosed in U.S. Pat. No. 3,297,647, issued January 10, 1967 to Schott et al. The unsaturated diol formals disclosed in the Schott et al patent include 2-butene-1,4-diol formal, 2-hexane-1,4-diol formal and 2-(2-ethyl)butene-1,4-diol formal (column 2, lines 11-14), the amounts of monomers disclosed are as follows:
"(t)he cyclic ether or saturated cyclic formal is advantageously used in an amount of 0.1 to 59.9% by weight, calculated on the total monomer mixture. The formal of the unsaturated diol is advantageously used in an amount of 59.9 to 0.2% by weight, calculated on the total monomer mixture. The trioxane is advantageously used in an amount of 40 to 99.8% by weight, calculated on the total monomer mixture", PA0 "The physical properties of the terpolymers can be varied within wide limits and depend, on the one hand, on the nature and concentration of the saturated cyclic formal or saturated cyclic ether and, on the other hand, on the concentration of the formal of an unsaturated cyclic diol. PA0 For example, when 0.1 to 10% by weight, calculated on the total monomer mixture, of unsaturated cyclic formal and 0.1 to 10% by weight, calculated on the total monomer mixture, of saturated cyclic formal or ether are used highly crystalline products are obtained, whereas with 40 to 59.9% by weight, calculated on the total monomer mixture of unsaturated cyclic formal or ether, amorphous elastic glass-clear products are obtained. The more voluminous the second comonomer, the lower is the crystallinity and the higher is the elasticity. The decrease in crystallinity can be well measured by means of X-rays. PA0 Low molecular weight terpolymers which constitute waxes or oils can easily be obtained with the use of high concentrations of catalyst, that is about 0.1 to 1% by weight, calculated on the total monomer mixture. PA0 The above statements are intended to indicate the wide limits within which the properties of the terpolymers obtained by the process of the invention may be varied, the incorporation of different comonomers having, of course, different effects on the properties of the terpolymers and the transitions being fluid", PA0 "(v)ery interesting properties are imparted to the terpolymers of the invention by the double bonds contained in the main chain, which double bonds enable the terpolymers to be crosslinked by known methods. For example, the terpolymers may be vulcanized by kneading with sulfur", PA0 ". . . such that at least 30% of the polymer composition remains undissolved when a film thereof of 5-8 mils thickness is immersed in one hundred times its weight of boiling dimethylformamide for two minutes", PA0 ". . . at least one covalently bonded linkage [is present] between catenarian carbon atoms of different polyoxymethylene chains for each for polyoxymethylene polymer molecules",
column 2, lines 17-24, and the patentees had this to say about the interrelationships between monomer contents and polymer properties:
column 2, lines 25-52.
The Schott et al patent does not disclose terpolymers having 1,3-dioxolane contents in excess of 59.9% by weight, based on the total weight of monomers present, or blends of its terpolymers with crystalline oxymethylene polymers. And while Schott et al do disclose that their olefinic unsaturation-containing terpolymers can be crosslinked:
column 2, lines 53-58, there is neither a disclosure of crosslinking with multifunctional crosslinking monomers nor a disclosure of UV curing.
U.S. Pat. No. 3,215,671, issued Nov. 2, 1965 to Melby, discloses crosslinking oxymethylene homopolymers using, in one embodiment, from 0.5 to 20% by weight of a polyunsaturated compound (multifunctional acrylates are disclosed) and a photoinitiator under UV light. See, e.g., column 2, lines 21-25 and 63-72. The crosslinked product is characterized as having an extent of crosslinking:
column 2, lines 30-39, or such that:
column 2, lines 40-44. Melby's crosslinked oxymethylene homopolymers appear to be crystalline materials; see from column 5, line 67 to column 8, line 10. In no case are they characterized as noncrystalline.