MXPA97010097A - Flexible acrylic light duct, and better photo-thermal stability - Google Patents

Abstract

An acrylic light conduit has a thermal and photothermal stability for many purposes, but it is deficient in maintaining clarity, color and good optical properties under exposure conditions at high temperatures, especially in combination with exposure for long periods to the passage of light. The improved thermal stability, as reflected in the reduced color formation, can be imparted by adjusting the polymerization conditions to produce the uncured core polymer of the core / shell construction with a very low terminal vinyl content, preferably below of 0.5 vinyl groups / 1000 monomer units. This process improvement, in combination with the selected addition of a combination of certain hindered phenols and hydrolytically stable organic phosphites, produces a substantial improvement in the resistance to fading under photothermal conditions, while maintaining the fading resistance under thermal conditions. The known process conditions, which do not produce a lower terminal vinyl content, in combination with the selected additives, also produce acrylic light conduits with a much better photothermal stability

Description

Flexible Acrylic Light Duct, and Enhanced Thermal-Thermal Stability The present invention relates to processes, continuous processes and related compositions to produce a photothermally more stable flexible light conduit ("TFL") based on polymerized units of one or more acrylic esters, and the improved product of TFL that produces the process. In the patents of Bigley et al., U.S. Patent Nos. 5,406,641 and 5,485,541 an effective process for the preparation of a flexible light conduit, based on acrylic, is disclosed. In a preferred aspect of this process, a cross-linked core mixture comprising a non-crosslinked copolymer formed primarily from acrylic monomers and esters with functionally reactive alkoxysilane groups, together with a reactive additive for curing the non-crosslinked polymer is present. reticulated by cross-linking, the reactive additive is preferably water and a silane condensation reaction catalyst, such as an organic tin dicarboxylate. Preferably, the core mixture is polymerized by means of a (non-solvent) process in bulk, more preferably by a continuous mass process, the non-crosslinked copolymer is preferably devolatilized prior to co-extrusion with a coating, preferably a fluoropolymer, in a core / coating compound that is then cured separately until the final flexible light conduit is obtained. The process based on a monomer such as ethyl acrylate, taught by Bigley et al., Produces a flexible light conduit or optical conduit that has high transmission of white light, flexibility and acceptable hardness for a variety of uses where light it will be transported from a remote source to a target, and where the conduit needs to be flexible to follow a tortuous path, and hard enough to retain its critical geometry. The existing process also produces a TFL of thermal stability (exposure to heat in the absence of visible light that is conducted through the light pipe) and photothermal (exposure linked to heat and visible light conducted through the light pipe, which can containing light of wavelength known as "ultraviolet-like") suitable even after exposure to many hours of light and environmental heat. The polymer of the prior art has adequate stability for exposure to high temperatures, including those of about 90 ° C, for lower usage times. However, there is a long potential market for light conduit that is thermally and photothermally stable at high temperatures and longer periods of exposure, such as in automotive applications where light is conducted near the engine compartment, and can reach temperatures of 120 ° C or higher. Other potential uses where high temperatures may be encountered may be when the light source is not adequately covered from the connection with the TFL or where the light source is of extremely high intensity. Photothermal stability becomes important when light is transported through the TFL for long periods of time, accompanied by exposure to temperatures above room temperature. Bigley et al. it teaches in general the use of stabilizers as part of the core component but does not teach or specifically suggest an acceptable response to this important stabilization problem. We have discovered an improved process by which to prepare a cross-linked acrylic core for a TFL, which, after being cured to be cross-linked, exhibits a surprisingly improved stability to thermal or photothermal aging, while retaining its other desired properties of good initial clarity, lack of initial color, good flexibility and adequate hardness to prevent physical deformation. An improved product, especially with respect to thermal aging in the absence of light passing through the core, can be prepared by carefully controlling the temperature of the process, preferably shortening some of the residence time in the reactor, and controlling the nature of the initiator, so as to decrease the number of terminal vinyl groups in the polymer. This invention is specifically directed to the provisional US application filed on October 8, 1996 with no. in series 60 / 27,942, filed by several of the present inventors. However, the photothermal stability conferred by the process changes is not sufficient to allow the TFL to be used under certain conditions of end use demand. By means of a specific choice of a combination of antioxidants and thermal stabilizers, preferably in combination with process improvements, the objective of acceptable photothermal stabilization has been achieved.

More specifically, we have discovered a cross-linked core mixture for a curing, subsequent cure compound, which mixture contains a thermoplastic core polymer, the thermoplastic core polymer has a weight average molecular weight of from about 2,000 to about 250,000 daltons, and preferably a final vinyl group content below 0.5 per 1000 monomer units, the core mixture comprises: (a) a thermoplastic core polymer, comprising: (i) from 80 to 99.9 weight percent units polymerized from a C.sub.1 -C.sub.18 alkyl acrylate or mixtures thereof with up to 50 weight percent of the components of (a) (i) of polymerized units of a C.sub.1 -C.sub.4 alkyl methacrylate; (Ii) 0.1 to 18.2 weight percent of polymerized units of a functionally active monomer, and (iii) 0 to about 10 weight percent of polymerized units of a monomer of increased refractive index selected from styrene, acrylate of benzyl, benzyl methacrylate, phenylethyl acrylate or phenylethyl methacrylate; (iv) from 0.002 to 0.3, preferably 0.01 to 0.3, percent residual molecules, or decomposition products, of a polymerization initiator, including end groups in the thermoplastic core polymer, the initiator preferably having a half-life at 60 ° C, from 20 to 400 minutes, more preferably from 100 to 250 minutes; (v) from 0.2 to 2.0, preferably 0.6 to 1.5, weight percent of residual molecules, or from decomposition products, of a chain transfer agent, including end groups in the thermoplastic core polymer; (b) from 0.1 to 10 weight percent, based on the weight of the crosslinkable core mixture, of a reactive additive; and (c) from 0.01 to 1.0 weight percent, based on the weight of the crosslinkable core mixture, of a stabilizer / antioxidant combination comprising from 20 to 80 weight percent, based on the combination, of an organic phosphite is hydrolytically stable, and 80 to 20 weight percent, based on the combination, of a hindered phenol, the phenol preferably exhibiting separately an absorption of less than 1 in 5% ethyl acetate solution in a cell of 10 cm at a wavelength of 400 Á. The word "hindered" appears in many ways in the definition of the invention, but is maintained because terms such as "hindered phenol" are well known to those skilled in the art which are related to polymer stabilization. The following define terms used in the description and claims: (a) hindered phenol: a phenol having in the ortho position, relative to the hydroxyl group of the phenol, at least one alkyl group, preferably at least one (t) -alkyl group tertiary, more preferably having two alkyl groups, and still more preferably having two t-alkyls, such as two t-butyl groups, and further, when there is only one substitution in the ortho position, at least there is more of an alkyl group, preferably a t-alkyl group, in the meta position; (b) hydrolytically stable organic phosphite: an organic phosphite having at least one, preferably two, and more preferably three, aryl groups, preferably phenyl, added through carbon-oxygen-phosphorus bonds, wherein the group aryl has in the ortho position, relative to the phenolic group, at least one alkyl group, preferably at least one tertiary (t) -alkyl group, more preferably having two alkyl groups, and more preferably having two t-groups alkyl, such as two t-butyl groups. It is known that said materials are hydrolytically stable in contrast, for example, to the trisalkyl phosphites.

An especially preferred stabilizer / antioxidant combination is from 500 to 3000 parts per million (ppm), that is, from 0.05 to 3 weight percent, of 3,5-di-t-butyl-4-hydroxyhydrocinnamate octadecyl, and 500 to 1500 ppm of tris (2,4-di-t-butylphenyl) phosphite. It is preferred that crosslinkable core mixtures exhibit the percentage of polymerized units of a C-C18 alkyl acrylate as 80 to 99.5 weight percent ethyl acrylate, it is also preferred that the chain transfer agent be a mercaptan aliphatic of one to twenty carbon atoms, such as butyl mercaptan, dodecyl mercaptan and the like, in addition to preferring that the polymerization initiator be an azo compound. It is also preferred that the crosslinkable core mixes maintain the functionally reactive monomer as present at a level of from about 0.5 to about 12 weight percent, more preferably from 2 to 12 weight percent, and that it be selected from 2 to 12. methacryloxyethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, or mixtures thereof, preferably 3-methacryloxypropyltrimethoxysilane. In addition, it is preferred that the reactive additive be water and a silane condensation reaction catalyst, preferably a dialkyl tin dicarboxylate, such as dibutyltin diacetate. In the initial work described in U.S. Patent 5,485,541, the curing of the functionally reactive alkoxysilane monomers is carried out by injecting water, an organic tin catalyst and, optionally, a solvent for the catalyst after the polymerization is complete but before of coextrusion with the coating. It has been found that a curable core can be prepared when the organic tin catalyst and the solvent for the catalyst are present during the polymerization, and then there is either an addition of water just before co-extrusion or else it is conducted, then of extrusion, in the presence of diffused water in the environment. The last process has been accelerated to a practical level using a humidification oven or curing it in a highly humid controlled atmosphere. The advantage that the separation of water from the other components until the polymerization and coating have been completed, is that premature crosslinking does not occur, where there are subsequent effects on the extrusion and on the surface between the core and the coating. Useful coatings are the fluorinated polymers, and two especially useful are the terpolymers of perfluoroalkyl vinyl / ether / tetrafluoroethylene / hexafluoropropylene (FEP) and of vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene (THV). The THV coating samples, which are more water permeable than the FEP, can be cured externally, fast enough for the present purposes (without absorbing much water and fog present) at temperatures of 80 ° C. and 50% relative humidity, while the FEP coating samples can be cured fast enough for the present purposes at 85 ° C. and 85% relative humidity. This crosslinkable core mixture may further contain a coating polymer, such as a fluoropolymer surrounding the core mixture, and preferably the crosslinkable core mixture within the fluoropolymer extrudate coating and the extruded fluoropolymer coating are in substantially complete contact. It should be recognized that the crosslinkable thermoplastic core polymer and the coating do not form a chemical or physical mixture, but are adjacent to one another in construction where the core mixture is surrounded by the coating. Similarly, we have discovered, based on the crosslinkable core polymers described above, a flexible light conduit product containing the above-described crosslinkable core mixture, wherein the product has: a good light transmission, wherein the loss of differential transmission between the wavelength of light of 400 nm and 600 nm, is equal to or less than 1.0 decibels per meter, according to the measurement by means of a non-destructive interference filter method; excellent thermal stability, when the final vinyl group content is below 0.5 per 1000 units of monomer, where a change in differential transmission loss between the light wavelengths of 400 nm and 600 nm is equal to or less 1.0 decibles per meter, after 150 hours of exposure to a temperature of 120 ° C, according to the measurement by means of a non-destructive interference filter method; excellent photothermal stability, where a change in the differential transmission loss between the wavelengths of light from 400 nm to 600 nm is equal to or less than 1.0 decibles per meter, after 100 hours of exposure at a temperature of 110 ° C , simultaneously with the exposure of 12 to 15 lumens / square millimeters of light, according to the measurement by means of a non-destructive interference filter method; good flexibility, where the product, at 20 ° C, survives without a core fracture at 180 ° of flexion in a bend radius that is less than or equal to five times the diameter of the cured core; and good hardness properties, where Shore "A" hardness is less than 90 after 50 days of exposure at 120 ° C. In addition we have discovered a process for preparing a crosslinkable core mixture for a subsequently cured composite comprising a coextruded coating polymer and a coextruded crosslinkable core mixture, said mixture containing a thermoplastic core polymer having a weight average molecular weight of about 2,000 to about 250,000 daltons, and preferably a final vinyl group content of less than 0.5 per 1000 monomer units, said process comprising: a) preparing a mixture of (i) about 80 to about 99.9 weight percent of a mass monomer mixture selected from an alkyl acrylate or mixtures thereof with up to 50 weight percent of the bulk monomer mixture of a C 1 -C 18 alkyl methacrylate; (ii) about 0.1 to about 18.2 weight percent of a functionally reactive monomer, and (iii) about 0 to about 10 weight percent of a refractive index increase monomer, selected from styrene, benzyl acrylate, benzyl methacrylate, phenylethyl acrylate or phenylethyl methacrylate; b) adding from 0.002 to 0.3 weight percent, based on the weight of the non-crosslinked copolymer, of an azo polymerization initiator, which preferably has a half life at 60 ° C. from 20 to 400 minutes, preferably from 100 to 250 minutes; c) before, simultaneously or after the addition of the initiator, add 0.2 to 2.0 percent by weight, preferably 0.75 to 1.5 percent by weight, based on the weight of the non-crosslinked copolymer, of a chain transfer agent; d) charging the monomer mixture, initiator and reaction mixture of the chain transfer agent in a constant flow stirred reactor heated to 70-120 ° C, preferably 85-100 ° C, with a preferred residence time of 5 hours. at 30 minutes, preferably 20 to 28 minutes, to form a non-crosslinked and polymerized cross-linked core mixture; e) devolatilizing the polymerized and uncrosslinked mixture of crosslinkable core to remove unreacted monomers; f) before, during or after the devolatilization, add from 0.1 to 10 weight percent, based on the crosslinkable core mixture, of a reactive additive; g) before, during or after devolatilization, add from 0.01 to 1.0 weight percent, based on the weight of the crosslinkable core mixture, of a stabilizer / antioxidant combination comprising from 20 to 80 weight percent, based on the combination, of a hydrolytically stable organic phosphite, of 80 to 20 weight percent, based on the combination, of a hindered phenol, the phenol preferably exhibiting separately an absorption of less than 1 in 5% of the Ethyl acetate solution at a wavelength of 400 Á; h) coextruding the crosslinkable core mixture and the coating polymer to form a curable compound.

In this process, it is preferred, separately, that the coextruded coating polymer and a co-extruded crosslinkable core mixture be continuously, concurrently and coaxially extruded, that the coating polymer be a molten fluoropolymer as described above, that the extruded mixture of The crosslinkable core, which is within the fluoropolymer extrudate coating and the fluoropolymer extrudate coating, is in substantially complete contact after filling the extruded tubular coating with the extruded crosslinkable core mixture, and further that the curing is conducted subsequently and separately from the Extrusion and coating operation. In addition, a portion of the reactive additive may be added to the core mixture after extrusion, for example, by diffusion of water through the coating. We have also discovered a flexible duct-i light product prepared by the above process, wherein the product has a good light transmission where the loss of differential transmission between the wavelengths of light of 400 nm and 600 nm is equal or less than 1.0 decibels per meter, according to the measurement by means of a "trimming" interference filter method; excellent thermal stability, wherein a change in the differential transmission loss between the wavelengths of light of 400 nm and 600 nm is equal to or less than 1.0 decibels per meter after 150 hours of exposure at a temperature of 120 ° C, according to the measurement by means of a non-destructive interference filter method; excellent photothermal stability, where a change in the loss of differential transmission between the wavelengths of light from 400 nm to 600 nm is equal to or less than 1.0 decibels per meter after 150 hours of exposure at a temperature of 120 ° C, according to the measurement by means of a non-destructive interference filter method; excellent photothermal stability, wherein a change in differential transmission loss between wavelengths of 400 nm to 600 nm is equal to or less than 1.0 decibels per meter after 100 hours of exposure at a temperature of 110 ° C. simultaneously with exposure to 12-15 lumens / square millimeters of light, according to the measurement by means of a non-destructive interference filter method; good flexibility, where the product, at 20 ° C, survives without a core fracture at 180 ° of flexion in a bend radius that is less than or equal to five times the diameter of the cured core; and good hardness properties, where Shore "A" hardness is less than 90 after 50 days of exposure at 120 ° C.

The desired photothermal stability is preferably achieved when the polymer to be stabilized has a final vinyl group content, as measured by NMR of below 0.5 per 1000 units of monomer, while this adjustment is also It leads to improved thermal stability. An alternative way to express the photothermal stability achieved by the invention is that the lifetime, judged by a 50% change in the differential transmission loss between the wavelengths of light from 400 nm to 600 nm in exposure to a temperature of 110 ° C, simultaneously with the exposure of 12 to 15 lumens / square millimeter of light, according to the measurement of a non-destructive interference filter method, is at least 150%, preferably 200%, for a material similar that lacks the stabilizer / antioxidant combination. It is preferable that the photothermally stable light conduit of the present invention be mounted in such a manner as to be with respect to the illumination source so that the heat of the source is removed by means of ventilation or isolation, such as by the use of glass-based connectors that are between the light source and the near end of the TFL. Separately, it is preferred that the light from the light conduit be filtered to eliminate the shorter wavelengths of 370 nm. Although you do not want to relate to any theory of polymer stability, is believed to be detrimental to thermal stability and, to a much lesser degree, to photochemical stability, if the crosslinkable core polymer contains oligomers or polymers with terminal vinyl groups. Said oligomers or polymers, in the presence of heat and / or light, can form molecules with conjugated double bonds that eventually, with sufficient conjugation, form species that are absorbent of color in the visible region of the spectrum, as well as can lower the amount of light which is sent by the light conduit to the final source. Said double vinyl bonds, apart from the residual monomer that can be reduced by bringing the reaction to a greater conversion and / or devolatilization of the crosslinkable core before curing or crosslinking, can be formed by hydrogen abstraction followed by a chain splitting or other forms of radical attack. For example, these radicals may be from the initiator, some reaction product of the initiator or from hydroperoxides formed in the presence of oxygen. The double bonds can also be formed by some form of termination reaction during the polymerization, even in the presence of a chain transfer agent used to reduce the molecular weight, and keep the crosslinkable core polymer fluid in the mixture before coating and curing Surprisingly, it has been found that the reduction of the reaction temperature and the amount of initiator, preferably accompanied by a low residence time in the continuous reactor, is sufficient to achieve significant improvements in the initial color of the polymer core before and after curing, and to increase the thermal lifetime, as defined below, at 120 ° C, in the absence of any thermal-oxidative or thermal stabilizing additive. These results, especially in relation to the residence time in the reactor and the polymerization temperature, would not have been expected by a person skilled in the art of mass polymerization of acrylate monomers. Although it is known to stabilize methyl methacrylate polymers against photodegradation by the use of selected antioxidants, the technique is poor in teaching appropriate stabilizers against photodegradation of optically clear polymers comprising exclusively or predominantly polymerized monomers of alkyl acrylate. There is still less teaching about the combination and selection of stabilizer combinations against photothermal degradation, and in the prior art it is not predicted which binary or tertiary combination would be effective. For example, alkyl sulfides and disulfides, which are very effective in thermal stabilization of polymethacrylates, are not particularly effective in photothermal stabilization of these acrylate polymers. Although one can predict the general mode of action of an individual stabilizer, such as the absorption of light, the conversion of a degradation product into a molecule that does not absorb visible light or interfere with chain reactions caused by chain abstraction or unfolding primary, its interaction with a poly (alkyl acrylate) is difficult to predict. In addition, the technique does not discuss the potential mode of response for active stabilizer combinations in different ways such as those applied to poly (alkyl acrylates). As seen in the Examples, there are effective individual stabilizers only in combination with others, as well as combinations that are not efficient enough to achieve the stabilization goal that can be achieved by means of certain selected additives. EXPERIMENTS The various antioxidant stabilizers studied are classified to continued in Table I by trade name, provider, class and by the best structure available from the descriptive literature.

Table I: Stabilizers and antioxidants considered in this application of photothermal stabilizers for a flexible light conduit, based on acrylate.

Name Type Formula Provider name HP-l hindered phenol / tris (3,5-di-t-butyl-hydroxy-Irganox 311 isocyanurate benzyl) isocyanurate HP-2 hindered phenol hydroxytoluene (2,6-di-t-butyl-BHT-methylphenol) butylated HP-3 phenol hindered l, 3,5-triraethyl-2,4,6-tris (3,5-di-Ethanox 330 tert-butyl-4-hydroxybenzyl) enene HP- A hindered phenol. tetrakis (3, 5-di-t-butyl-4-hydro-Irganox 1010 xihydrocin ate) methylene) ethane HP-4B phenol hindered tetrakis ((3,5-di-t-butyl-4-hydro-Ultranox 210 methylene xihydrocinnamate) methane HP-5A phenol hindered 3, 5-di-t-butyl-hydroxyhydro-Irganox 1076 octadecyl cinnamate HP-5B phenol hindered 3,5-di-t-butyl-hydroxyhydro-Ultranox 276 cinnamate of octadecyl HP-6 hindered phenol 3/1 condensate of 3-methyl-6-t-Topanol CA butylphenol and crotonaldehyde; it is believed that mainly l, l, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane HP-7 hindered phenol and benzenepropanoic acid, 3,5-bis (l, Irganox 1035 organic sulfur 1- dimethylethyl) -4-hydroxy-, thiodi-2, 1, ethanediyl ester or tiodiethylene bis (3, 5, -di-tert -butyl-4-hydroxy-hydrocinnamate) HSP-1 organic phosphite 2,2'-Ethylidenebis (, 6-di-t-Ethanox 398 hydrolytically butylphenyl) stable fluorophosphonate HSP-2 organic phosphite tris (2, -di-tert-butylphenyl) Irgafos 168 hydrolytically stable phosphite HSP-3 organic phosphite Phosphorus trichloride, P-EPQ products hydrolytically reaction with l, 1-biphenyl and stable 2,4-bis (1, 1-dimethylethyl) phenol HUSP-1 organic phosphite bis (2,4-di-t-butylphenyl) pentaeriUltranox 626 hydrolytically tritol unstable HUSP-2 organic phosphite Diisodecyl-pentaerythritol diphosphite Weston XR hydrolytically 2806 unstable NHP phenol unimpeded hydroquinone monomethyl ether MEHQ OS-1 organic sulfide thiodipropi Dilauryl Oatone DLDTP ODS-1 organic disulfide di (t-dodecyl) disulfide DTDDS A standard laboratory process was used as a control, following the method of Example 1 (filling the duct) and Example 29 (details of composition) of U.S. Pat. 5,485,541. The monomer composition was 95% EA (purified through acid alumina) and 5% distilled MATS (3-methacryloxypropyltrimethoxysilane). An initiator Vessel 67, (DuPont) 2, 2'-azobis (2-methylbutyronitrile) was used at a level of 0.064% of the monomer. A chain transfer agent, n-dodecyl mercaptan, was used at a level of 1% of the amount of monomer. The standard temperature of the reactor was 125 ° C. and the standard residence time of 28 minutes. After devolatilization, the polymer was used to fill the FEP / polyethylene ducts. The catalyst (20 ppm dibutyltin diacetate, based on the polymer, butyl acetate) and water (0.40%) were mixed separately into the polymer while it was pumped into the conduits. A third solution, containing the selected antioxidants or stabilizers, was added at a rate of 2.4 ce. of solution per 100 grams of polymer. The variations used (in addition to the stabilizer / antioxidants) are summarized in Table 2 below. The following highlights the details of the standard polymerization that is used as the basis for the process changes listed in Table I: the monomer mixtures were prepared as follows: a 196-gallon stainless steel container, 19 liters, was added and they mixed 9500 gr. of ethyl acrylate, 500 grams of functionally reactive monomer, 3-methacryloxypropyltrimethoxysilane (MATS) (5 weight percent, based on the weight of monomer (bom), 6.4 grams of initiator (2, 2'-azobis (2- methylbutyronitrile) recrystallized (0.064 percent by weight)) and 100 g of n-dodecyl mercaptan (1 percent by weight) The mixture was sprayed for at least 15 minutes with nitrogen, and the gas was eliminated under 28 inches (711 mm) of vacuum, while it was being pumped into the reactor. The monomer mixture was fed through a 0.045 micron PTFE membrane cartridge filter to a stainless steel constant flow stirred tank reactor (RTAFC). During the polymerization, the reactors were maintained at 125 ° C, and were stirred at 225 rpm under a pressure of 1035 kPa (150 psi). The reactor jet (copolymer and residual monomer) was fed through a back-pressure valve set nominally at 1035 kPa (150 psi) in a devolatilization column comprising a non-moving mixer, twisted ribbon, stainless steel (60 cm long with a shirt approximately 50 cm long) mounted in a 30 liter stainless steel container (ca. 9 gallons). The heating oil, recirculated through the jacket of the column, was maintained at 200 ° C at the entrance of the jacket. The container was maintained at 100 110 ca.300 40 mm. of vacuum during devolatilization. Upon completion of the polymerization, the vessel was filled back with filtered nitratene. The conversion of monomer to polymer from the jet was approximately 87 to 88%, according to the gravimetric measurement. The solids content, determined gravimetrically, of the devolatilized polymer is 99.5 by weight. The polymer variations used in the evaluation of antioxidants are summarized in Table 2.

Table 2 Process / polymer variations Variable Standard Variations Composition of 95% EA / 5% MATS 66.5% EA / 28.5% BMA / 5% MATS monomer 95% EA / 5% MATS + 0.5% ETEMA 66.5% EA / 28.5% BMA / 5% MATS + 0.5% ETEMA Purification EA Acid alumina Basic alumina and molecular sieve Initiator 0.064% Vazo 67 0.032% Vazo 67 0.0208% Vazo 52 0.0104% Vazo 52 1.0% agent n-DDM 1.5% n-DDM (n-dodecyl mercaptan ) 0.6% t-BuSH (t-butyl mercaptan) 0.97% MPTMS (mercaptopropyl trimethoxysilane) MATS Distillation 5 ppm of 4-hydroxyTEMPO (2,2,6,6-tetramethyl-4-hydroxy-piperidine-N-oxyl), in MATS Temperature of 125 ° C 95 ° C reaction 10 ° C Time of 28 minutes 22 minutes home MAB = butyl methacrylate MAETE = ethylthioethyl methacrylate Vazo 52 DuPont 2,2'bisazo (2,4-dimethylaleronitrile), a lower temperature initiator. Table 3 lists the same polymers that were prepared and evaluated. They produced 15 to 35 kg. Of polymer in each preparation. This was enough to develop six FEP / polyethylene (5.1 mm id) ducts two meters long for each 3-12 antioxidant combinations. In addition, 6 to 12 ducts were prepared with curative additives but no antioxidants were added.

Table 3 Polymer composition and process Run # ID Polymer Variables RM Process variables 1A AB2441 1.5% of nDDM Standard IB AB2457 1.5% of nDDM Standard 2 AB2468 Standard Standard 3 AB2480 0.5% of MAETE Standard 4 AB2488 28.5% of MAB + 0.5% of AETE Standard 5 AB2601 28.5% of MAB Standard 6 AB2620 Standard 22 '7 AB2628 0.6% t-BuSH Standard 8 AB2643 Y- 11700 MATS Standard 9 AB2842 Standard Standard 10 AB2610 Standard 95 ° C 11 AB2637 0.32% Vazo 67 105 ° C 12 AB2651 0.6% of t-BUSH 105 ° C 13 AB2661 0.0208 Vazo% 52 95 ° C, 22 '1 AB2669 0 0208% Vazo 52, 1.5% aDDM 95 ° C, 22' 15 AB2689 Y-11700 MATS 105 ° C 16 AB2811 0.0208% Vazo 52 95 ° C, 22 '17 AB2817 0 0205% of Vazo 52, 1.5% of nDDM 95 ° C, 22' 18 AB2822 0 0208% of Vazo 52, 0.97% of 3-MPTMS 95 ° C, 22 '19 AB2826 0.0104% of Vazo 52 95 ° C, 22 '20 AB2850 0.0208% Vazo 52 95 ° C 21 AB2858 0 0208% Vazo 52, EA purified 95 ° C, 22' through Basic alumina and molecular sieve Thermal degradation The light conduit was evaluated to determine the thermal stability by measuring the time required for the transmitted light to turn yellow. The wavelength spectrum vs. absorption of a six-foot section of the light conduit. The difference in absorption at 400 nm and 600 nm (A40 - A600) was calculated from the spectrum. Because thermal aging causes an increase in the absorption of short wavelengths (400 nm) but a small change in long wavelengths (600 nm), the changes in this difference (A400-A600) are a measure of increases in the yellowness of the transmitted light. The light pipe was thermally aged in a forced air oven at 120 ° C. Periodically, the light pipe was removed from the furnace, the absorption spectrum measured and A400-A600 calculated. The thermal lifetime was calculated as the time required for the absorption to increase by 1 dB / m from its initial value. The thermal life times (in hours) of the light conduits containing antioxidants are recorded in Tables 3 and 4. By way of comparison, the thermal life times of the controls, that is, light conduits prepared from the same core polymer but not containing antioxidant, are also included in said tables. The hindered phenols having low color tone, especially the Irganox 1076 and Ultranox 276 (HP-5A-HP-5B), increase the thermal lifetime of the light conduit. Even larger increases are observed with the combinations of these hindered phenols and aromatic phosphites with ortho-alkyl substituents, especially HSP-2. The light conduits prepared from a hindered phenol and diisodecyl-pentaerythritol-diphosphite (HUSP; see table 3) were not tested since they acquired a hazy appearance when stored. We have observed a similar nebulous phenomenon in light conduits containing trisisooctyl-phosphite, phenyl-neopentylene-glycol-phosphite and tris (dipropylene glycol) phosphite. The large light losses associated with this nebulosity make the formulations containing these aliphatic or partially aliphatic phosphites not suitable for the applications of light conduits.

Photothermal degradation Photothermal durability studies were developed using the General Electric XMH-60 lamp, and the filter was replaced with an Optivex filter. The light was passed through a mixing bar (11.5 mm square coupler) to provide a uniform light output of 12-15 lumens per square millimeter. Four light conduits of 5 mm. they were shrunk by heating in glass bars, and these shrunk by heat in the square coupler. The light conduits were then passed through an oven at 110 ° C. The fibers were connected to a filter / photodiode holder. Periodically, during the test, the response of the photodiode was measured through filters of 400 nm, 450 nm and 600 nm. The data were treated by dividing the 400 nm reading by reading 600 nm, and normalizing the initial index. A graph of (% TP400 /% Tt600) / (% T0400 /% T ° 600) vs. weather where (% TP.00 /% T 00) is the voltage index at time t, and (% T ° 400 /% T 00) is the initial voltage index. The life time is defined as the time in which this index falls to 0.5, and was determined by interpolation. This corresponds to a 50% loss in the initial transmission at 400 nm. This correlates fairly well with the time in which the light transmitted through five feet of light conduit appears yellow. One of the four light conduits in each set was a control, that is, a light conduit made with the same polymer but that did not contain added antioxidants. The durability recorded for each formulation in the following tables is the life time index of the light conduit containing antioxidants to that of the control conduit. Therefore, this represents the increase in the life time due to the presence of antioxidants. The lifetime of the controls varies from 35 to 110 hours, depending on the polymer formulation and the conditions of the particular aging experiment (light intensity).

DURABILITY OF THE LIGHT TUBE PREPARED AT 125 ° C (THERMAL LIFE TIME / PHOTOTERMAL LIFETIME / VTT TIME INDEX.? 3 DURABILITY OF LIGHT TUBE PREPARED AT 95-105 ° C (THERMAL LIFE TIME / PHOTOTERMAL LIFE TIME / TOTAL TIME TENSION) V VTDA FO G.TFI? AT. 36 The results in Tables 4 and 5 indicate: That hindered phenolic antioxidants at a level of 0.075-0.5% (750-5000 ppm) increase the photothermal lifetime by approximately 50-200%. Phosphite antioxidants (0.05-0.25%) increase the photothermal life time by approximately 30 to 500%. Phosphites resistant to hydrolysis (such as Irgafos 168 (HSP-2), P-EPQ (HSP-3), Ethanox 398 (HSP-1) and those of similar structure) are required since those that are not resistant, the hydrolysis leads to the nebulosity of the luminous DUCT and to large losses of white light (see the results with Weston XR2806 (HUSP-2)).

Thioether antioxidants increase photothermal lifetime by approximately 50%. The combinations of hindered phenols and phosphites resistant to hydrolysis consistently result in large increases in photothermal lifetime (approximately 150-700%). The combinations of hindered phenols and thioethers provide an increase in photothermal lifetime of about 30-130%.

Example 22 The absorption spectrum of a series of phenols disabled was measured. 'A solution of 5% of the phenol hindered in ethyl acetate. The spectrum of absorption was recorded in a 10 cm cell .. The absorption at 400 nm is recorded in Table 6. Absorption varies from very low to more than 3. The absorption at 400 nm can not occur due to the electronic absorption of phenol prevented, but can result from impurities in the commercial product.

Table 6 Comparison of hindered phenols Antioxidant Absorption Time Time of 400 nm thermal life life (1) (hours) phototherm (hours) None .._ 126-183 44-75 Irganox 0.053 329 179 1076 (HP-5A) Irganox 0.160 236 142 1010 (HP-4A) Topanol CA 0.625 271 138 (HP-6) Irganox 0.163 235 131 1035 (HP-7) Cyanox 425 3.303 37 not measured (2) (HP) Cyanox 2246 3.048 39 not measured (3) (HP) Ethanox 0.164 without sample without 330 (HP-3) sample (1) 5% hindered phenol in ethyl acetate, 10 cm cell. (2) Cyanox 425: 2, 2 '-methylenebis (4-ethyl-6-tert-butylphenol) (3) Cyanox 2246: 2,2'-methylenebis (4-methyl-6-tert-butylphenol) The thermal and photothermal data of the DUCTS of light prepared with 750 ppm of hindered phenols and 1000 ppm of Irgafos 168 of Table 4, are summarized in Table 6. The data indicate that those with a 400 nm absorption of less than 1 , provided thermal and photothermal stability increased. The measured thermal lifetimes are 235-329 hours, and photothermal life times are 131-179 hours. The two most absorbent antioxidants (used if possible, without purification) that were tested resulted in thermal life times of less than 40 hours, significantly less than those of control with no added antioxidant. Preferred hindered phenols are those having an absorption of less than 1 at 400 nm (5% solution in ethyl acetate, 10 cm cell). This low absorption is also beneficial by minimizing any color change in the transmitted light.

Claims (9)

1. Re ivindi falls 1. ions A mixture of crosslinkable core for a compound subsequently cured which mixture contains a thermoplastic polymer core, thermoplastic polymer core has an average molecular weight of about 2,000 to about 250,000 daltons, the core mixture comprising (a) a thermoplastic core polymer comprising: (i) from 80 to 99.9 weight percent of polymerized units of a C 1 -C 18 alkyl acrylate or mixtures thereof with up to 50 weight percent of the components of (a) (i) of polymerized units of a C 1 -C 18 alkyl methacrylate; (Ii) 0.1 to 18.2 weight percent of polymerized units of a functionally active monomer, and (iii) 0 to about 10 weight percent of polymerized units of a monomer of increased refractive index selected from styrene, acrylate of benzyl, benzyl methacrylate, phenylethyl acrylate or phenylethyl methacrylate; (Iv) from 0.002 to 0.3, preferably 0.01 to 0.3, percent residual or decomposition products molecules, a polymerization initiator, including end groups on the thermoplastic polymer core, the initiator preferably having a half-life 60 ° C. from 20 to 400 minutes, more preferably from 100 to 250 minutes; (v) from 0.2 to 2.0, preferably 0.6 to 1.5, weight percent of residual molecules or decomposition products, of a chain transfer agent, including end groups in the thermoplastic core polymer; (b) from 0.1 to 10 weight percent, based on the weight of the crosslinkable core mixture, of a reactive additive; and (c) from 0.01 to 1.0 weight percent, based on the weight of the crosslinkable core mixture, of a stabilizer / antioxidant combination comprising from 20 to 80 weight percent, based on the combination, of an organic phosphite which is hydrolytically stable, and 80 to 20 weight percent, based on the combination, of a hindered phenol.
2. 2. The crosslinkable core mixture according to claim 1, wherein the thermoplastic core polymer has a final vinyl group content below 0.5 per 1000 monomer units.
3. 3. The crosslinkable core mixture according to claim 1 or 2, further comprising at least one fluorocarbon coating polymer surrounding the core mixture.
4. 4. The crosslinkable core mixture according to claim 1 or 2, wherein the percentage of the polymerized units of a C1-C18 alkyl acrylate is from 80 to 99.5 weight percent ethyl acrylate, wherein the Chain transfer agent is an aliphatic mercaptan of one to twenty carbon atoms, and wherein the polymerization initiator is an azo compound having a half-life at 60 ° C. from 20 to 400 minutes.
5. 5. The mixture of crosslinkable core according to claims 1 or 2 wherein the functionally reactive monomer is present at a level of about 0.5 to about 12 percent by weight and is selected from 2-metacriloxietiltrimetoxisilano, 3-methacryloxypropyltrimethoxysilane , 3-acryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, or mixtures thereof, wherein the reactive additive is water and a condensation reaction catalyst silane, wherein the hindered phenol is from 500 to 3000 parts per million of 3, 5-di- t-butyl-4-hydroxyhydrocinnamate, and the hydrolytically stable organic phosphite is 500 to 1500 parts per million of tris (2,4-di-t-butylphenyl) phosphite.
6. 6. The mixture crosslinkable core according to claim 3 wherein the functionally reactive monomer is present at a level of about 0.5 to about 12 percent by weight and is selected from 2-metacriloxietiltrimetoxisilano, 3-methacryloxypropyl-trimethoxysilane, 3 -acyloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane or mixtures thereof, wherein the reactive additive is water and a silane condensation reaction catalyst, wherein the hindered phenol is from 500 to 3000 parts per million of octadecyl 3, 5-di-t-butyl-4-hydroxyhydrazinacin, and the hydrolytically stable organic phosphite is from 500 to 1500 parts per million of tris (2,4-t-butylphenyl) phosphite.
7. 7. A flexible light DUCT product, containing the crosslinkable core mixture formed by the curing of the crosslinkable core mixture of claim 3, wherein the product has good light transmission where the loss of differential transmission between the lengths Wavelength of 400 nm to 600 nm is equal to 1.0 decibels per meter, according to the measurement by means of an interference filter method of "trimming"; excellent thermal stability, wherein a change in the differential transmission loss between the wavelengths of light from 400 nm to 600 nm is equal to or less than 1.0 decibels per meter after 150 hours of exposure at a temperature of 120 ° C, according to the measurement by a non-destructive interference filter method; excellent photothermal stability, where a change in differential transmission loss between light wavelengths from 400 nm to 600 nm is equal to or less than 1.0 decibles per meter after 100 hours of exposure at a temperature of 100 ° C, simultaneously with exposure between 12 to 15 lumens / square millimeter of light, according to the measurement by means of a non-destructive interference filter method; good flexibility, where the product, at 20 ° C, survives without a core fracture at a flexion of 180 ° at a bend radius that is less than or equal to five times the diameter of the cured core; and good hardness properties, where the hardness of Shore "A" is less than 90 after 50 days of exposure to 120 ° C.
8. 8. A process for preparing a crosslinkable core mixture for a subsequently cured compound comprising a Coextruded coating polymer and a co-extruded crosslinkable core mixture, this mixture contains a thermoplastic core polymer having a weight average molecular weight of from about 2,000 to about 250,000 daltons, the process comprising: a) preparing a mixture of: i) from 80 to 9
9. 9.9 weight percent of a bulk monomer mixture, selected from a C 1 -C 18 alkyl acrylate, or mixtures thereof, with 50 weight percent of the mass monomer mixture of an alkyl methacrylate C1 -C18; ii) from about 0.1 to 18.2 weight percent of a functionally reactive monomer and iii) from about 0 to 10 weight percent of a monomer which increases the refractive index, selected from styrene, benzyl acrylate, methacrylate benzyl, phenylethyl acrylate or phenylethyl methacrylate; b) adding from 0.002 to 0.3 weight percent, based on the weight of the non-crosslinked copolymer, of an azo polymerization initiator; c) before, simultaneously, or after the addition of the initiator, add from 0.2 to 2.0 percent by weight, based on the weight of the non-crosslinked copolymer, of a chain transfer agent; d) charging the monomer mixture, initiator and reaction mixture of the chain transfer agent to a stirred, constant flow reactor, heated to 70-120 ° C, to form a crosslinkable, polymerized core mixture, which is not still reticulated; e) devolatilizing the crosslinkable core mixture, which is not yet crosslinked, polymerized, to remove unreacted monomers, f) before, during or after devolatilization and / or coextrusion, add from 0.1 to 10 weight percent, based on the mixture of the crosslinkable core, of a reactive additive; g) before, during or after the devolatilization add from 0.01 to 1.0 weight percent, based on the weight of the crosslinkable core mixture, of a stabilizer / antioxidant combination comprising from 20 to 80 weight percent, based on in the combination, of a phosphite that is hydrolytically stable, and 80 to 20 weight percent, based on the combination, of a hindered phenol; h) coextruding the crosslinkable core mixture and the coating polymer to form a curable compound. The process according to claims 7 or 8, wherein the co-extruded coating polymer and a co-extruded crosslinkable core mixture are coextruded continuously, concurrently and coaxially, wherein the coating polymer is a molten fluoropolymer, wherein the mixture of extruded crosslinkable core within the extruded fluoropolymer coating and the extruded fluoropolymer coating are in substantially complete contact before filling the extruded tubular coating with the extruded crosslinkable core mixture, wherein further the curing is conducted subsequent and separately from the operation of extrusion and coating, and wherein the hindered phenol is from 500 to 3000 parts per million of octadecyl 3, 5-dit-butyl-4-hydroxyhydrocinnamate, and the hydrolytically stable organic phosphite is from 500 to 1500 parts per million of tris ( 2,4-di-t-butylphenyl) phosphite.