Biodegradable lactone copolymers

Details Biodegradable lactone copolymers Biodegradable lactone copolymers

2000-05-10

2002-02-12

Hampton-Hightower, P. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S355000, C528S357000, C428S480000, C428S338000, C428S339000

Reexamination Certificate

active

06346599

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to lactone copolymers having suppressed crystallinity which can render them suitable for use, for example, in the manufacture of biodegradable films for trash bags.
BACKGROUND OF THE INVENTION
Current environmental concerns have generated interest in the use of biodegradable plastics for disposable items such as, for example, trash bags, packaging materials, eating utensils, and the like. A variety of biodegradable polymers have been proposed for such uses. Typical of such polymers include, condensation polymers, such as, for example, polyesters, polyester amides, polymers formed by ring open polymerization, e.g., lactone, lactide and lactam polymerizations, polyhydroxyalkonoates, polylactic acid and naturally occurring polymers, such as, polysaccharides, e.g., cellulosic, starch, and soy derivatives.
As used herein, the term “biodegradable”, as defined in ASTM D-883, is made with reference to degradable polymers in which the degradation results from the action of micro-organisms occurring naturally such as, for example, bacteria, fungi, and algae. The biodegradability may be evidenced, for example, by the production of CO
2
and associated reduction in mechanical properties, such as tensile strength and percent elongation at break. Further details are known to those skilled in the art.
Although many polymers such as those described above, are highly effective in terms of their biodegradability, they often suffer from inferior mechanical performance which has hindered their commercial viability. More specifically, when converted to film by blown film extrusion, for example, biodegradable polymers often do not have good machine direction (“MD”) Elmendorf Tear Strength as measured by ASTM D-1922, transverse direction (“TD”) Tensile Impact as measured by ASTM D-1822, Falling Dart Impact Resistance as measured by ASTM D-1709, MD and TD Secant Modulus as measured by ASTM D-882, and Puncture Resistance as measured by Union Carbide Test Method WC-68-L. On the other hand, when biodegradable polymers are modified to enhance their mechanical properties, their biodegradability often suffers.
As used herein, the terms “condensation polymerization” and “polycondensation” mean: (i) a polymerization reaction in which two or more molecules are combined with the generation of water, alcohol or other simple substances as by-products; and (ii) polymerization of monomers, e.g., ester and amide monomers, formed by ring opening polymerization, e.g., lactones, lactides and lactams, which do not generate water, alcohol or other simple substances as by-products.
Often, condensation polymers suitable for use as biodegradable materials are semi-crystalline in form, e.g., greater than about 30%, often greater than about 50% and more often greater than about 70% crystalline. Complete crystallization of polymers is often a slow process requiring minutes, hours or days to fully accomplish. When crystallization is desired, the temperature is held above the glass transition temperature (“Tg”) and below the crystalline melting point for a time sufficient to allow the molecules of the polymer to order themselves into crystal lattices. This process is also referred to in the art as “annealing”. If the crystallinity of the polymer becomes too high, the molded article from the polymer may not have sufficient toughness to be viable in a typical end use like trash bags, mulch film, molded parts and the like.
Accordingly, improved condensation polymers, e.g., lactone polymers, having enhanced mechanical properties are desired which can retain their biodegradable characteristics.
SUMMARY OF THE INVENTION
By the present invention, improved lactone polymers are provided. The improvement of the present invention is directed to the use of comonomers in the lactone polymerization which are effective to suppress the crystallinity of the copolymers. Without being bound to any particular theory, it is believed that the suppression of crystallinity can cause enhancements in the mechanical properties of films made from the copolymers compared to copolymers made without the crystallinity-suppressing monomers.
In accordance with the present invention, the suppression of crystallinity may be evidenced by one or more factors. For instance, the suppression of crystallinity may be evidenced by a reduction in the crystallization temperature of the copolymer, or by a reduction in the rate of crystallization of the copolymer, or by a reduction in the melt temperature of the polymer or by a reduction in the crystallinity of the copolymer. As used herein, the term “crystallization temperature” means the temperature at which formation of the crystalline phase occurs; the term “crystallization rate” means the rate at which formation of the crystalline phase occurs; the term “melt temperature” means the freezing point and the term “crystallinity” means the degree of crystallinity of the polymer. The crystallization properties of polymers can be readily determined by those skilled in the art, such as, for example, by differential scanning calorimetry (“DSC”).
DETAILED DESCRIPTION OF THE INVENTION
The first monomer suitable for use in accordance with the present invention is a lactone monomer. The first monomer can be ethylenically unsaturated or alternatively can have no ethylenic unsaturation. The molecular structure of the first monomer is not critical for the present invention and can have straight, e.g., normal, alkyl or branched, cyclic or aromatic substituents. In addition, the first monomer can have functional groups selected from the group consisting of esters, ethers, alcohols, acids, amines, amides, acid halides, isocyanates and mixtures thereof as may be determined by those skilled in the art. In addition, the first monomer can be comprised of a single molecular unit, an oligomer or a prepolymer and can have a molecular weight of typically from about 72 to 12,000 grams per gram mole (“g/gmol”), more typically, from about 72 to 10,000 g/gmol.
Unless otherwise indicated, as used herein, the term “molecular weight” means number average molecular weight. Techniques for determining number average molecular weight are known to those skilled in the art. One such technique is gel permeation chromatography (“GPC”).
In one aspect of the present invention, the lactone monomers include those having the formulas:
where X=nil, —O—, or —O—C=O; Z=1-3; Y=1-4; R
1
-R
4
=H—, —CH
3
, C
2
-C
16
alkyl group, —C(CH
3
), or HOCH
2−
, and where all R's are independent on each y or z carbon unit and independent of each other; or
where R
1
-R
4
=H—, —CH
3
, C
2
-C
16
alkyl group, or HOCH
2
—, and where all R's are independent of each other.
Examples of the lactones described above are, but not limited to, caprolactone, t-butyl caprolactone, zeta-enantholactone, deltavalerolactones, the monoalkyl-delta-valerolactones, e.g. the monomethyl-, monoethyl-, monohexyl-deltavalerolactones, and the like; the nonalkyl, dialkyl, and trialkyl-epsilon-caprolactones, e.g. the monomethyl-, monoethyl-, monohexyl-, dimethyl-, di-n-propyl-, di-n-hexyl-, trimethyl-, triethyl-, tri-n-epsilon-caprolactones, 5-nonyl-oxepan-2-one, 4,4,6- or 4,6,6-trimethyl-oxepan-2-one, 5-hydroxymethyl-oxepan-2-one, and the like; beta-lactones, e.g., beta-propiolactone, beta-butyrolactone gamma-lactones, e.g., gammabutyrolactone or pivalolactone, dilactones, e.g. lactide, dilactides, glycolides, e.g., tetramethyl glycolides, and the like, ketodioxanones, e.g. 1,4-dioxan-2-one, 1,5-dioxepan-2-one, and the like. The lactones can consist of the optically pure isomers or two or more optically different isomers or can consist of mixtures of isomers.
&egr;-caprolactone and its derivatives and other seven membered ring lactones are especially preferred for use as first monomers in accordance with the present invention.
In one aspect of the present invention, other monomers may be polymerized with the lactones to comprise the first monomer, such as, for example, one or more compounds which ca

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