US20120237704A1

US20120237704A1 - Controlled lowering of a polymers glass transition temperature

Info

Publication number: US20120237704A1
Application number: US13/422,888
Authority: US
Inventors: Daniel E. Bowen, III
Original assignee: Honeywell Federal Manufacturing and Technologies LLC
Current assignee: Honeywell Federal Manufacturing and Technologies LLC
Priority date: 2011-03-17
Filing date: 2012-03-16
Publication date: 2012-09-20
Also published as: US8609752B2; US20120238669A1

Abstract

Processes for lowering the glass transition temperature of a polymeric compound relative to the glass transition temperature of a control polymeric compound are disclosed. The methods include the formation of a precursor composition comprising precursor compounds to the polymeric compound dispersed or dissolved in a solvent system. The compounds are partially or fully cured in the presence of the solvent system, which is then substantially removed. After further curing, where necessary, the resulting cured polymeric compound is essentially free of plasticizers, but still has a decreased glass transition temperature relative to the glass transition temperature of a control polymeric compound. Articles of manufacture comprising such polymeric compounds are also disclosed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the priority benefit of U.S. Provisional Patent Application Ser. No. 61/453,579, filed Mar. 17, 2011, entitled CONTROLLED LOWERING OF A POLYMER'S GLASS TRANSITION TEMPERATURE WITHOUT THE USE OF PLASTICIZERS, incorporated by reference in its entirety herein.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under contract #DE-NA0000622, awarded by the United States Department of Energy. The United States government has certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to methods of lowering the glass transition temperature of a polymer, and articles formed thereby.
2. Description of Related Art
One of the more important fundamental properties of a polymer is its glass transition temperature (Tg). The exact temperature of a polymer's Tg is dictated by a wide variety of factors, including the monomers used to make the polymers, the presence of large molecular moieties attached to the polymer's main chain, the amount and type of cross-links found within the polymers, and the presence of a plasticizer, etc. Above its Tg, a polymer is relatively soft and pliable. Below its Tg, a polymer behaves like a glassy solid. Plasticizers are well known to lower the Tg of a given polymer by creating an environment within the polymer matrix where the polymer chains can slide past one another more easily. The use of plasticizers is ubiquitous throughout the world of commercial polymers, with their addition to a polymer matrix being common for reducing a polymer's Tg. However, in many instances it would be useful to lower the Tg of a given polymer matrix without needing to use a plasticizer or without the need for the plasticizer to be present in the polymer matrix. Plasticizers can be volatile, evaporating over time and thus also changing the performance of the polymer into which it has been incorporated. Other plasticizers have been shown to, or are suspected to be, toxic. The elimination of such plasticizer from polymer products would be beneficial, if there was a way to controllably lower the Tg of a polymer without the need for a plasticizer in the end product.

SUMMARY OF THE INVENTION

The present invention is broadly concerned with a method of lowering the glass transition temperature of a polymeric compound (polymer) relative to a control, wherein the control has a first glass transition temperature. The method comprises providing a precursor composition, which comprises a precursor compound dispersed or dissolved in a solvent system. The precursor compound is selected from the group consisting of monomers (including chain extenders), oligomers, pre-polymers, polymers, and combinations thereof. The precursors to the polymeric compound are cured in the presence of the solvent system to yield a cured polymer network or partially cured polymer resin. The cured polymer network or partially cured polymer resin is swollen with the solvent. The solvent system is then substantially removed to yield a cured polymeric compound or dried polymer resin, which may be further cured to yield the polymeric compound, if desired. The resulting fully cured polymeric compound (polymer) has a second glass transition temperature that is lower than the first glass transition temperature.
An article of manufacture comprising a polymeric compound is also provided. Advantageously, the polymeric compound has a decreased glass transition temperature relative to a control, and is essentially free of plasticizer.
The present invention is applicable in a wide variety of polymeric compounds. Nearly anything made or manufactured from such polymers could effectively have its glass transition temperature lowered without the need for the plasticizer to be present in the final article.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 is a graph of the rheology data from the Model Epoxies prepared in Example 1;

FIG. 2 is a graph of the rheology data from the Model Epoxies prepared in Example 1, after being subjected to additional heating under vacuum;

FIG. 3 is a graph of thermogravimetric analysis (TGA) results of the samples from Example 1;

FIG. 4 is a graph of the rheology data from the Model Epoxies prepared in Example 1, and subjected to various cure times;

FIG. 5 is a graph showing the % weight loss of the Model Epoxies prepared in Example 1, and subjected to various cure times;

FIG. 6 is a graph of the rheology data from the EN8 urethanes prepared in Example 2; and

FIG. 7 is a graph of the rheology data from the EN8 urethanes prepared in Example 2, and subjected to various cure times.

DETAILED DESCRIPTION

The present invention is concerned with the controlled manipulation of the Tg of a polymeric compound, methods of carrying out the same, and articles of manufacture prepared therefrom. Suitable polymeric compounds that can be modified using the invention include those with precursor compounds that are substantially soluble in a solvent system and can be cured in the presence of the solvent system. In addition, after being cured, the resulting polymeric network preferably remains swollen by the solvent system, which can then be substantially removed, as discussed in more detail below. Suitable polymeric compounds would include many thermoplastic polymers and most thermosetting polymers (i.e., prepolymer materials or compounds that undergo an irreversible change upon fully curing—typically from a soft solid or viscous state to an infusible, insoluble polymer network, once fully cured). Exemplary thermosetting compounds (i.e., A-stage, unreacted resins) for use in the inventive methods include, without limitation, monomers, oligomers, pre-polymers and/or polymers of epoxies, urethanes, silicones, cyanoacrylates, vulcanized rubber, phenol-formaldehyde, melamine-formaldehyde, urea-formaldehyde, imides, esters, cyanate esters, allyl resins, and combinations thereof. Suitable chain extenders that can be used to prepare the polymeric compound include diols, dicarboxylic acids, diamines, diacrylates, and the like. Exemplary thermoplastic compounds for use in the inventive methods include acrylonitrile butadiene styrene, polymethylmethacrylate, cyclic olefin copolymer, ethylene vinyl acetate, ethylene vinyl alcohol, fluoroplastics, liquid crystal polymers, polyacrylates, polyacrylonitrile, polyamide, polyamide-imide, polyaryletherketone, polybutadiene, polyisoprene, styrene butadiene rubber, conjugated diene elastomers, polybutylene, polybutylene terephthalate, polycaprolactone, polychlorotrifluoroethylene, polycyclohexylene dimethylene terephthalate, polycarbonate, polyhydroxyalkanoates, polyketone, polyester, polyethylene, polypropylene, polystyrene, polyetheretherketone, polyetherketoneketone, polyetherimide, polyethersulfone, polysulfone, chlorinated polyethylene, polyimide, polylactic acid, polymethylpentene, polyphenylene oxide, polyphenylene sulfide, polyphthalamide, polysulfone, polytrimethylene terephthalate, polyurethane, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, styrene acrylonitrile, and the like.
In one aspect of the inventive method, the precursor compounds (i.e., monomers, chain extenders, oligomers, pre-polymers, polymers, and combinations thereof) are dispersed or dissolved in a solvent system to form a precursor composition. The precursor composition is preferably formed by mixing the ingredients together under ambient conditions (˜25° C., ˜14.7 psi or ˜1 atm) for a sufficient time period to uniformly disperse or dissolve the compounds in the solvent system. The level of precursor compounds used in the composition will vary, but will typically range from about 50% to about 99.9% by weight, preferably from about 70% to about 99.5% by weight, and more preferably from about 75% to about 99% by weight, based upon the total weight of the composition taken as 100% by weight. The solvent system can be present in the composition at a level of from about 0.1% to about 50% by weight, preferably from about 0.5% to about 30% by weight, and more preferably from about 1% to about 25% by weight, based upon the total weight of the composition taken as 100% by weight.
Suitable solvent systems will depend upon the compounds used in the precursor composition. A preferred solvent system will be one in which the precursors to the polymeric compound can be dissolved or dispersed (i.e., the polymer material, before curing, is relatively, and preferably substantially, soluble in the solvent system), and one in which, after being cured, the resulting polymeric compound remains swollen by the solvent system. A preferred solvent system will also contain one or more solvents that have a sufficiently high boiling point to be workable without evaporating (i.e., not too volatile), but will ultimately volatize (evaporate) at a temperature below the degradation temperature of the polymeric compound. More specifically, a suitable solvent system will have a boiling point of from about 25° C. up to about the T₅temperature of the polymeric compound, preferably from about 35° C. up to a temperature that is about 20° C. lower than the T₅temperature of the polymeric compound, and more preferably from about 50° C. up to a temperature that is about 50° C. lower than the T₅temperature of the polymeric compound. The “T₅temperature” of a polymeric compound is a measure of its thermally stability, which is defined as the temperature at which less than 5% weight loss is observed in the polymeric compound by TGA, when heated to that temperature for at least about 10 minutes (under nitrogen). For example, the Model Epoxy formed in Example 1 has a T₅temperature of about 190° C. Thus, preferred solvent systems for use with the Model Epoxy will have a boiling point of from about 25° C. to about 190° C., preferably from about 35° C. to about 170° C., and more preferably from about 50° C. to about 140° C. Similarly, the T₅temperature of the EN8 polyurethane formed in Example 2 is about 280° C. Thus, preferred solvent systems for use with the EN8 polyurethane will have a boiling point of from about 25° C. to about 280° C., preferably from about 35° C. to about 260° C., and more preferably from about 50° C. to about 230° C.
Exemplary solvents and their boiling points include, without limitation, acetic acid (118° C.), acetic acid anhydride (139° C.), acetone (56.3° C.), acetonitrile (81.6° C.), benzene (80.1° C.), iso-butanol (107.7° C.), n-butanol (117.7° C.), tert-butanol (82.5° C.), carbon tetrachloride (76.5° C.), chlorobenzene (131.7° C.), chloroform (61.2° C.), cyclohexane (80.7° C.), cyclopentane (49.3° C.), dichloromethane (39.8° C.), dioxane (101° C.), ethanol (78.3° C.), ethyl acetate (77.1° C.), ethylene dichloride (83.5° C.), heptane (98.4° C.), n-hexane (68.7° C.), hydrochloric acid (84.8° C.), methyl ethyl ketone (79.6° C.), methanol (64.7° C.), methyl tert-butyl ether (55.2° C.), iso-propanol (82.3° C.), n-propanol (97.2° C.), pyridine (115.3° C.), tetrahydrofuran (66° C.), toluene (110.6° C.), trifluoroacetic acid (71.8° C.), water (100° C.), dimethyl acetamide (166.1° C.), dimethyl formamide (153° C.), pentane (36.1° C.), diethyl ether (34.6° C.), dimethyl sulfoxide (189° C.), ethyl ether (34.6° C.), ethylene glycol (197.5° C.), petroleum ether (35-60° C.), and the like. Solvent mixtures may also be used in the solvent system.
Additional optional ingredients can be dispersed or dissolved in the solvent system with the compound. Such optional ingredients include curing (crosslinking) agents, including diols, fillers, nanofillers, catalysts, processing aids, binders, pigments, antioxidants, antifungal agents, metal oxides, plasticizer, and the like. Exemplary curing agents will also depend on the polymeric compound used in the composition, but includes amines, peroxides, and sulfur for vulcanization. When present, the level of curing agent will typically range from about 0.001% to about 10% by weight, preferably from about 0.01% to about 8% by weight, and more preferably from about 0.1% to about 6% by weight, based upon the total weight of the composition taken as 100% by weight. When present, the level of fillers will typically range from about 0.1% to about 25% by weight, preferably from about 0.5% to about 20% by weight, and more preferably from about 1% to about 15% by weight, based upon the total weight of the composition taken as 100% by weight. When present, the level of nanofillers will typically range from about 0.1% to about 20% by weight, preferably from about 0.5% to about 15% by weight, and more preferably from about 1% to about 10% by weight, based upon the total weight of the composition taken as 100% by weight.
The precursor composition is then subjected to a curing process. In particular, the precursor compounds are first cured in the presence of the solvent system (i.e., the solvent system is not substantially removed during the curing process; rather, the polymeric compound remains swollen by the solvent system during the curing reaction). Depending upon the boiling point of the solvent system and the polymeric compound materials involved, initial curing can take place under ambient temperatures and/or pressures or elevated temperature (˜25-300° C.) and/or vacuum pressure (˜1E⁻⁹−200 psi). Preferably, the precursor compounds are cured under ambient conditions. Curing is preferably carried out for a time period of from about 0.001 to about 48 hours, more preferably from about 0.01 to about 24 hours, and even more preferably from about 0.1 to about 16 hours. The polymeric compound does not need to completely cure in the presence of the solvent and may be partially cured, meaning that the reacting ingredients in the precursor composition cure to the point of vitrification (i.e., B-stage thermoset). In other instances, the polymeric compound may be completely cured in the presence of the solvent system, but will remain swollen with solvent. It will also be appreciated that references herein to “fully” or “completely” curing refer to substantially complete (approaching 100%) curing of the resin, although those skilled in the art will appreciate that 100% curing does not actually occur; rather, the cure reaction continues over time in many polymer systems, including the formation of new crosslinks as aging of the resin begins taking place.
The solvent system is then substantially removed from the fully cured polymeric compound or partially cured polymer resin. As used herein, “substantially removed,” means that at least about 99% by weight of the solvent system is removed, and preferably at least about 99.9% by weight removed, based upon the total weight of the initial solvent system amount in the precursor composition, taken as 100% by weight. It will be appreciated that the solvent system can be removed from the cured polymeric compound or resin using heat (to speed up evaporation), vacuum pressure, CO₂extraction, freeze-drying, lyophilization, sublimation, centrifugation, and the like, and any combination thereof. In one aspect, the solvent system is removed/evaporated by heating to a temperature greater than or equal to the boiling point of the solvent system (preferably from about 25 to about 300° C.), for a time period of from about 0.5 to about 48 hours (and preferably for about 1 to about 16 hours).
The substantially dried polymer resin, if only partially cured in the above process, can then be subjected to further curing to fully cure the composition (i.e., C-stage, cross-linked polymer network). This further curing may also aid in the removal of residual solvent remaining in the polymeric compound. It will be appreciated that these parameters may vary greatly depending upon the solvent system and the polymeric compounds involved. Typical curing temperatures will range from about 25° C. to about the T₅temperature of the polymeric compound, preferably from about 25° C. to about 300° C., and more preferably from about 30° C. to about 200° C., at time periods of from about 0.1 to about 48 hours, preferably from about 0.1 to about 10 hours, and more preferably from about 0.5 to about 5 hours. Those of ordinary skill in the art will appreciate that during this process, the polymeric compound can be cooled for a period of time (about 0.1 to about 24 hours) under ambient conditions, and then reheated (according to the ranges above), depending upon the polymeric compound involved. In other words, the various stages of the curing process may be repeated, as desired for the particular polymeric compound being formed. Any stage of the curing process may also be carried out under vacuum to further facilitate removal of the solvent system. The fully cured polymeric compound can also be subjected to further heat and/or vacuum treatments for a time period of from about 0.1 to about 48 hours to remove residual solvent, as desired. It will be appreciated that although the present invention is described primarily with respect to heat curing, at any stage of the process described herein, curing may be carried out using any suitable alternative cure mechanism, including e-beam, radiation, and/or vulcanization.
It will be appreciated that during curing, the precursor composition can be formed into the desired shape and/or size, depending upon the final article to be formed, using any suitable technique, such as molding (e.g., resin transfer molding, compression molding, injection molding, etc.), extrusion, and/or pultrusion. The precursor composition can also be laminated and/or used to impregnate a fiber (woven or nonwoven) reinforcement before fully curing.
Advantageously, the cured polymeric compound will have a modified Tg that has been decreased relative to the Tg of a control polymeric compound. Preferably, the modified Tg is at least about 5° C. lower than the Tg of a control polymeric compound, more preferably at least about 10° C. lower, and even more preferably at least about 15° C. lower than the Tg of a control polymeric compound. A “control” polymeric compound, as used herein, refers to the same polymeric compound as the polymeric compound modified according to the invention, but in its native, non-modified state, formed without the use of plasticizers or other agents or special processing parameters that modify the Tg of the polymeric compound. In other words, the Tg of a control polymeric compound is what the Tg of the polymeric compound according to the invention would have been, had that polymeric compound not been subjected to the inventive methods. Thus, one advantage of the invention is that the Tg-lowering effects of the inventive process remain, even after the solvent has been substantially removed from the system. Accordingly, another advantage of the present invention is that the fully cured polymeric compound is essentially free of plasticizer, which means that the fully cured polymeric compound comprises less than about 1% by weight plasticizer, more preferably less than about 0.5% by weight plasticizer, and even more preferably less than about 0.1% by weight plasticizer, based upon the total weight of the fully cured polymeric compound taken as 100% by weight. The present invention achieves the benefits of polymeric compounds conventionally formulated using plasticizers, without the drawbacks of plasticizer in the final polymeric compound.
Exemplary articles of manufacture that can benefit from the present invention include, without limitation, molded articles, pads, o-rings, gaskets, mats, cushions, foams, fibers, fabric, hoses, tubing, belts, tires, bladders, and the like.
Additional advantages of the various embodiments of the invention will be apparent to those skilled in the art upon review of the disclosure herein and the working examples below. It will be appreciated that the various embodiments described herein are not necessarily mutually exclusive unless otherwise indicated herein. For example, a feature described or depicted in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the present invention encompasses a variety of combinations and/or integrations of the specific embodiments described herein.
As used herein, the phrase “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing or excluding components A, B, and/or C, the composition can contain or exclude A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.
The present description also uses numerical ranges to quantify certain parameters relating to various embodiments of the invention. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claim limitations that only recite the upper value of the range. For example, a disclosed numerical range of about 10 to about 100 provides literal support for a claim reciting “greater than about 10” (with no upper bounds) and a claim reciting “less than about 100” (with no lower bounds).

EXAMPLES

The following examples set forth methods in accordance with the invention. It is to be understood, however, that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.

Example 1

Model Epoxy

A. Increasing Amounts of THF Added to Model Epoxy

A series of model epoxy formulations were prepared with increasing amounts of tetrahydrofuran (THF) solvent (boiling point 66° C.). A control sample without THF was also made. The samples were prepared by weighing the desired amount of EPON® 828 (standard Bisphenol-A epoxy resin) into a small aluminum weighing dish, to which was added the desired amount of THF (Table 1). The THF was carefully mixed into the EPON® 828 using a wooden tongue depressor that had been split the long way. Care was taken in mixing to minimize the evaporation of THF. To the EPON® 828/THF mixture was added the desired amount of EPIKURE® 3270 (a modified aliphatic amine curing agent). All materials were thoroughly mixed and care was taken to ensure that even the material along the sides of the aluminum foil weighing dish was dispersed and mixed. THF was added in increasing amounts by weight at 1.0%, 5.0%, 10.0%, and 25%, respectively. The total amount of material mixed was kept at ≦17.5 g to minimize the loss of material from the small aluminum weighing dish when being stirred/mixed. Before the material had cured, small amounts were poured into disk shaped RTV silicone molds (diameter=11 mm, by 3.4 mm deep). The material in the RTV mold and the material that remained in the aluminum weighing dish was partially cured at ca. 25° C. overnight in a fume hood. This also allowed most of the THF to volatilize from the samples. All of the samples were then cured at ˜110° C. for 5 hours. The samples were cooled to ca. 25° C. overnight in a fume hood. All of the samples were then fully cured at ˜110° C. for 5 hours under vacuum. The long cure times, high cure temperatures, and exposure to vacuum facilitated substantially complete removal of the THF from the polymer resin. The samples were finally cooled to ca. 25° C., and tested over a period of 2 weeks.

TABLE 1

Model Epoxy with Increasing Amounts of Added THF - Samples
Cured at 110° C. for 5 hours and then at 110°
C. for 5 hours under vacuum.

	Amount (g)

1	0% by weight THF
	EPON ® 828	9.90
	EPIKURE ™ 3270	7.43
	Total	17.33
	THF	0
	Sum All	17.33
2	1% by weight THF
	EPON ® 828	9.90
	EPIKURE ™ 3270	7.43
	Total	17.33
	THF	0.17
	Sum All	17.50
3	5% by weight THF
	EPON ® 828	9.50
	EPIKURE ™ 3270	7.13
	Total	16.63
	THF	0.88
	Sum All	17.50
4	10% by weight THF
	EPON ® 828	9.00
	EPIKURE ™ 3270	6.75
	Total	15.75
	THF	1.75
	Sum All	17.50
5	25% by weight THF
	EPON ® 828	7.50
	EPIKURE ™ 3270	5.63
	Total	13.13
	THF	4.38
	Sum All	17.50

B. Increasing Amounts of THF Added to Model Epoxy—Additional Heating Under Vacuum

Model epoxy formulations, prepared according to the procedure described in 1A above, were subjected to further testing. Before the material had cured, small amounts were poured into disk shaped RTV silicone molds, as described above. The material in the RTV mold and the material that remained in the aluminum weighing dish was cured at ca. 25° C. overnight in a fume hood. This also allowed most of the THF to volatilize. All of the samples were then cured at ˜110° C. for 5 hours. The samples were then cooled to ca. 25° C. overnight in a fume hood, followed by curing at ˜110° C. for 5 hours under vacuum. After a period of 2 weeks at ca. 25° C., all of the samples were then heated at ˜110° C. for 48 hours under vacuum. The excessive cure times, high cure temperatures, and exposure to vacuum facilitated substantially complete removal of the THF from the polymer.
C. Increasing Cure Times for Model Epoxy without Added THF
A series of identical model epoxy formulations were prepared and subjected to increasing cure times from 1 to 9 hours at 110° C. THF was not added to these samples. The samples were prepared by weighing the desired amount of EPON® 828 into a small aluminum weighing dish, to which was added the EPIKURE® 3270 (Table 2). The materials were thoroughly mixed and care was taken to ensure that even the material along the sides of the aluminum foil weighing dish was dispersed and mixed. The total amount of material mixed was kept at ≦17.5 g to minimize the loss of material from the small aluminum weighing dish when being stirred/mixed. Before the material had cured, small amounts were poured into disk shaped RTV silicone molds. The material in the RTV mold and the material that remained in the aluminum weighing dish was partially cured at ca. 25° C. overnight in a fume hood. All of the samples were then cured at ˜110° C. from 1 to 9 hours. The sample cured for 7 hours was cured under vacuum for the last 2 hours of the 7 hours of total cure time. The sample cured for 9 hours was cured under vacuum for the last 4 hours of the 9 hours of total cure time. The samples were then cooled to ca. 25° C. overnight in a fume hood. The samples were tested over a period of 2 weeks.

TABLE 2

Model Epoxy cured from 1 to 9 hours 110° C.

	Amount (g)

1	1 hr at 110° C.
	EPON ® 828	10.00
	EPIKURE ™ 3270	7.50
	Total	17.50
2	2 hrs at 110° C.
	EPON ® 828	10.00
	EPIKURE ™ 3270	7.50
	Total	17.50
3	3 hrs at 110° C.
	EPON ® 828	10.00
	EPIKURE ™ 3270	7.50
	Total	17.50
4	5 hrs at 110° C.
	EPON ® 828	10.00
	EPIKURE ™ 3270	7.50
	Total	17.50
5	7 hrs (2 under vacuum) at 110° C.
	EPON ® 828	10.00
	EPIKURE ™ 3270	7.50
	Total	17.50
6	9 hrs (2 under vacuum) at 110° C.
	EPON ® 828	10.00
	EPIKURE ™ 3270	7.50
	Total	17.50

Example 2

Polyurethane

A. Increasing Amounts of THF Added to Polyurethane

A series of urethane formulations were prepared with increasing amounts of THF. A control sample without THF was also made. The samples were prepared by weighing the desired amount of diol chain extenders (Cytec CONATHANE® EN-8 Part B) into a small aluminum weighing dish, to which was added the desired amount of THF (Table 3). The THF was carefully mixed into the EN8 Part B using a wooden tongue depressor that had been split the long way. Care was taken in mixing to minimize the evaporation of THF. Next, a polyurethane (Cytec CONATHANE® EN4 Part A) was added to the EN8 Part B/THF mixture. All materials were thoroughly mixed and care was taken to ensure that even the material along the sides of the aluminum foil weighing dish was dispersed and mixed. THF was added in increasing amounts by weight at 1.0%, 2.5%, 5.0%, 10.0%, and 25%. The total amount of material mixed was kept at ≦17.5 g to minimize the loss of material from the small aluminum weighing dish when being stirred/mixed. Before the material cured, small amounts were poured into disk-shaped RTV silicone molds. The material in the RTV mold and the material that remained in the aluminum weighing dish was partially cured at ca. 25° C. overnight in a fume hood. This also allowed most of the THF to volatilize. All of the samples were then cured at ˜110° C. for 5 hours. The samples were then cooled to ca. 25° C. overnight in a fume hood, and then cured at ˜110° C. for 5 hours under vacuum. The long cure times, high cure temperatures, and exposure to vacuum facilitated substantially complete removal of the THF. The samples were then cooled to ca. 25° C. and tested over a period of 2 weeks.

TABLE 3

Polyurethane with Increasing Amounts of Added THF.

	Amount (g)

0	0% by weight THF
	EN4 (Part A)	14.58
	EN8 (Part B)	2.74
	Total	17.32
	THF	0
	Sum All	17.32
1	1% by weight THF
	EN4 (Part A)	14.58
	EN8 (Part B)	2.74
	Total	17.32
	THF	0.17
	Sum All	17.50
2	2.5% by weight THF
	EN4 (Part A)	14.36
	EN8 (Part B)	2.70
	Total	17.06
	THF	0.44
	Sum All	17.50
3	5% by weight THF
	EN4 (Part A)	14.00
	EN8 (Part B)	2.63
	Total	16.63
	THF	0.88
	Sum All	17.51
4	10% by weight THF
	EN4 (Part A)	13.25
	EN8 (Part B)	2.49
	Total	15.74
	THF	1.75
	Sum All	17.49
5	25% by weight THF
	EN4 (Part A)	11.05
	EN8 (Part B)	2.08
	Total	13.13
	THF	4.38
	Sum All	17.50

B. Increasing Cure Times for Polyurethane without Added THF

A series of identical EN8 urethane formulations were prepared and subjected to increasing cure times from 1 to 9 hours at 110° C. THF was not added to these samples. The samples were prepared by weighing the desired amount of EN8 Part B into a small aluminum weighing dish, to which was added the desired amount of EN4 (Table 4). The materials were thoroughly mixed and care was taken to ensure that even the material along the sides of the aluminum foil weighing dish was dispersed and mixed. The total amount of material mixed was kept at ≦17.82 g to minimize the loss of material from the small aluminum weighing dish when being stirred/mixed. Before the material had cured, small amounts were poured into disk shaped RTV silicone molds. The material in the RTV mold and the material that remained in the aluminum weighing dish was cured at ca. 25° C. overnight in a fume hood. All of the samples were then cured at ˜110° C. from 1 to 9 hours. The sample cured for 7 hours was cured under vacuum for the last 2 hours of the 7 hours of total cure time. The sample cured for 9 hours was cured under vacuum for the last 4 hours of the 9 hours of total cure time. The samples were cooled to ca. 25° C. overnight in a fume hood. The samples were tested over a period of 2 weeks.

TABLE 4

Cytec EN8 Polyurethane Encapsulant
cured from 1 to 9 hours at 110° C.

	Amount (g)

1	1 hr at 110° C.
	EN4 (Part A)	15.00
	EN8 (Part B)	2.82
	Total	17.82
2	2 hrs at 110° C.
	EN4 (Part A)	15.00
	EN8 (Part B)	2.82
	Total	17.82
3	3 hrs at 110° C.
	EN4 (Part A)	15.00
	EN8 (Part B)	2.82
	Total	17.82
4	5 hrs at 110° C.
	EN4 (Part A)	15.00
	EN8 (Part B)	2.82
	Total	17.82
5	7 hrs (2 under vacuum) at 110° C.
	EN4 (Part A)	15.00
	EN8 (Part B)	2.82
	Total	17.82
6	9 hrs (2 under vacuum) at 110° C.
	EN4 (PartA)	15.00
	EN8 (Part B)	2.82
	Total	17.82

Example 3

Material Characterization

A. Rheology

All rheology testing was performed on a TA Aries 2000 or AR-G2 rheometer under torsion between 25-mm parallel plates. As much as possible, disks (diameter ˜11 mm, by ˜3.4 mm) of uniform size were used as samples. Samples that where thicker than ˜3.2 mm were sanded with an ultra-fine grit sand paper. All samples were subjected to a temperature sweep from low to high temperatures at strains of 0.025% and a frequency of 1 Hz. All experiments where performed under normal force control at 5.0 N, with a 0.5 N tolerance (gap=+/−500,000 nm). The temperature range varied depending on the locations of the expected transitions, but a 5 minute equilibration time was used once a sample reached the minimum temperature. A temperature ramp rate of 3° C./min. was used. Rheology is used to determine, among other things, the glass transition temperature (Tg) of a given material. The Tg is determined as being the maximum Tan δ peak height.

B. Thermogravimetric Analysis (TGA)

Thermogravimetric analysis was performed on clean Pt pans using a TA Q1000 instrument. All experiments were performed using a ramp rate of 10° C./min. over the desired temperature range. All experiments where performed under nitrogen.

Example 4

Observations

A. Model Epoxy (EPON® 828+EPIKURE® 3270)

1. Example 1A-Rheology
Even though the samples from Example 1A were cured at 110° C. for 5 hours and then at 110° C. for 5 hours under vacuum to remove THF, the Tg steadily decreased as the amount of THF present during the partial curing process was increased. The Tg decreased by up to about 20° C. when 25 wt % THF is added to the epoxy formulation compared to the control. The vast majority of the THF originally present while the epoxy cured is removed under these curing parameters, although trace amounts may still remain. The results are shown in FIG. 1.
2. Example 1B-Rheology
The samples from Example 1B were subjected to an additional 48 hours under vacuum at 110° C., in addition to being cured at 110° C. for 5 hours and then at 110° C. for 5 hours under vacuum. This curing process was designed to remove even more of any residual THF that may be present. However, the Tg of the polymer was still steadily decreased as the amount of THF present during the partial curing process was increased. The Tg still decreased by about 15° C. when 25 wt % THF is added to the epoxy formulation compared to the control. The results are shown in FIG. 2.
3. Example 1B-TGA
When the Model Epoxy samples from Example 1B, were tested by TGA, no discernible increase in weight loss was observed for the samples that had been treated with THF compared to the control. If anything, the samples that had been treated with THF exhibited less weight loss compared to the control. The presence of any residual THF did not appear to change the thermal stability of the model epoxies. The results are shown in FIG. 3.
4. Examples 1A and 1B-Mass Spectrometry for Residual THF Analysis
Although not quantitative, Mass Spectrometry was used to determine if residual THF was present in both the Model Epoxy samples from Examples 1A and 1B. The samples were outgassed over a temperature range of 35° C. to 400° C. and analyzed by direct insertion probe mass spectrometry. For the samples from Example 1A, no THF or just the mass of THF was detected in sample treated with <1 wt % THF. At 5 wt %, THF could be detected in the total ion chromatogram. At >10 wt %, THF was clearly detected. However, for the samples from Example 1B, no THF or just the mass of THF was detected in samples treated with <5 wt % THF. At 10 wt % THF, THF could be detected in the total ion chromatogram. At 25 wt % THF, THF was clearly detected. It was surprisingly determined that the Tg of the resulting polymers prepared in Example 1 was permanently lowered through this inventive process even though only trace amounts (if any) THF remained in the sample.
5. Example 1C-Rheology
Curing the Model Epoxy samples from Example 1C for increasing amounts of time at 110° C. caused only a small drop in the Tg. However, the Tg appears to have stopped dropping after 5 hours at 110° C. and the total drop in the Tg (<10° C.) is smaller than the drop in the Tg when 25 wt % of THF is present during partial curing and then later almost entirely removed upon heating and the application of vacuum. This establishes that the curing regimen itself is not responsible for the change in Tg. The results are shown in FIGS. 4-5.

B. Cytec Conathane® EN8 Polyurethane

1. Example 2A-Rheology
The Tg of EN8 urethane behaves similarly to the Model Epoxy, although the drop in the Tg is smaller and only appears to significantly affect one of EN8's two main transitions. The lower temperature Tg, which is caused by the soft polybutadiene segments within EN8, is not affected by the addition and subsequent removal of THF. However, the higher temperature transition, which is due to the urethane component of EN8, does exhibit a lowering of its Tg. It is especially noticeable on the high temperature tail of the transition. This edge of the Tg can be seen to be moving to lower and lower temperatures as the amount of THF present when the urethane cures, but is later almost entirely removed upon heating and the application of vacuum. The results are shown in FIG. 6.
2. Example 2B-Rheology
When EN8 urethane is cured for increasing amounts of time at 110° C., no discernible change, including a decrease, is observed for either of EN8's two main Tan δ transitions. This establishes that the curing process itself is not responsible for the change in Tg. The results are shown in FIG. 7.

Claims

1. A method of lowering the glass transition temperature of a polymeric compound relative to a control polymeric compound, said control polymeric compound having a first glass transition temperature, said method comprising:

(a) providing a precursor composition, said composition comprising precursor compounds to said polymeric compound dispersed or dissolved in a solvent system, said precursor compounds being selected from the group consisting of monomers, chain extenders, oligomers, pre-polymers, polymers, and combinations thereof;

(b) curing said precursor compounds in the presence of said solvent system to yield a cured polymer network or partially cured polymer resin;

(c) substantially removing said solvent system from said cured polymer network to yield a cured polymeric compound or from said partially cured polymer resin to yield a dried polymer resin; and

(d) optionally, further curing said dried polymer resin to yield a cured polymeric compound,

wherein said cured polymeric compound has a second glass transition temperature that is lower than said first glass transition temperature.

2. The method of claim 1, said cured polymer network or partially cured polymer resin being swollen with said solvent system.

3. The method of claim 1, wherein said precursor compound is selected from the group consisting of epoxies, urethanes, silicones, cyanoacrylates, vulcanized rubber, phenol-formaldehyde, melamine-formaldehyde, urea-formaldehyde, imides, esters, cyanate esters, allyl resins, and combinations thereof.

4. The method of claim 1, wherein said precursor composition comprises from about 50% to about 99.9% by weight of said precursor compounds, based upon the total weight of the composition taken as 100% by weight.

5. The method of claim 1, wherein said solvent system has a boiling point that is from about 25° C. to about the T₅temperature of said cured polymeric compound.

6. The method of claim 1, wherein said solvent system includes a solvent selected from the group consisting of acetic acid, acetic acid anhydride, acetone, acetonitrile, benzene, iso-butanol, n-butanol, tert-butanol, carbon tetrachloride, chlorobenzene, chloroform, cyclohexane, cyclopentane, dichloromethane, dioxane, ethanol, ethyl acetate, ethylene dichloride, heptane, n-hexane, hydrochloric acid, methyl ethyl ketone, methanol, methyl tert-butyl ether, iso-propanol, n-propanol, pyridine, tetrahydrofuran, toluene, trifluoroacetic acid, water, dimethyl acetamide, dimethyl formamide, pentane, diethyl ether, dimethyl sulfoxide, ethyl ether, ethylene glycol, petroleum ether, and mixtures thereof.

7. The method of claim 1, wherein said precursor composition comprises from about 0.1% to about 50% by weight of said solvent system, based upon the total weight of the composition taken as 100% by weight.

8. The method of claim 1, wherein said precursor composition further comprises an additional ingredient selected from the group consisting of curing agents, fillers, nanofillers, catalysts, processing aids, binders, pigments, antioxidants, antifungal agents, metal oxides, plasticizer, and combinations thereof.

9. The method of claim 1, wherein said curing (a) comprises subjecting said composition to ambient temperature and pressure for a time period of from about 0.1 to about 10 hours.

10. The method of claim 1, wherein said further curing (d) comprises subjecting said composition to elevated temperature for a time period of from about 0.5 to about 48 hours.

11. The method of claim 1, wherein said removing (c) comprises heat, vacuum pressure, CO₂extraction, freeze-drying, lyophilization, sublimation, centrifugation, or any combination thereof to remove said solvent system.

12. The method of claim 1, wherein said removing (c) comprises heating said cured polymer network or partially cured resin to a temperature greater than or equal to the boiling point of said solvent system for a time period of from about 0.5 to about 48 hours.

13. The method of claim 1, wherein said further curing (d) comprises heating said dried polymer resin to a temperature of from about 25° C. to about 300° C., for a time period of from about 0.5 to about 48 hours.

14. The method of claim 13, wherein said curing (b) further comprises cooling said polymer resin or network under ambient conditions for a time period of from about 0.1 to about 24 hours to yield a cooled resin or network.

15. The method of claim 14, further comprising reheating said cooled resin or network to a temperature of from about 25° C. to about the T₅temperature of the polymeric compound, for a time period of from about 0.5 to about 48 hours to yield said cured polymeric compound.

16. The method of claim 1, further comprising subjecting said cured polymeric compound to heat, vacuum pressure, or a combination thereof.

17. The method of claim 1, further comprising pouring said precursor composition into a mold prior to said curing.

18. The method of claim 1, wherein said cured polymeric compound is essentially free of plasticizer.

19. An article of manufacture comprising a polymeric compound, said polymeric compound having a decreased glass transition temperature relative to the glass transition temperature of a control polymeric compound, wherein said polymeric compound is essentially free of plasticizer.

20. The article of claim 19, wherein said polymeric compound is a thermoset selected from the group consisting of epoxies, urethanes, silicones, cyanoacrylates, vulcanized rubber, phenol-formaldehyde, melamine-formaldehyde, urea-formaldehyde, polyimides, polyesters, cyanate esters, allyl resins, and combinations thereof.

21. The article of claim 19, wherein said article of manufacture is selected from the group consisting of molded articles, pads, o-rings, gaskets, mats, cushions, foams, fibers, fabric, hoses, tubing, belts, tires, and bladders.