MXPA97007688A - Acrylic and flexible light tube with better thermal stability - Google Patents

Abstract

An acrylic light tube, as described in the U. A. Patents of Bigley et al., Nos. 5,406,641 and 5,485,541, has adequate thermal stability for many purposes. It has been found that improved thermal stability can be imparted, as reflected in the color formation, by adjusting the polymerization conditions, to produce the uncured core polymer of the core / shell construction with a very low terminal vinyl content.

Description

ACRYLIC AND FLEXIBLE LIGHT TUBE. WITH IMPROVED THERMAL STABILITY This invention relates to processes, continuous processes and related compositions to produce a more thermally stable light tube ("FLP"), based on polymerized units of one or more acrylic esters, and to the improved FLP product, which produces the process An effective process for the preparation of light flexible tubes, acrylic-based, is described in two patents of Bigley et al. , the patents of E. U. A., Nos. 5,406,641 and 5,485,541. In a preferred aspect of this process, a crosslinkable core mixture is present, which comprises a non-interlaced copolymer, formed mainly of acrylic esters and monomers with functionally reactive alkoxysilane groups, together with a reactive additive to cure the non-core polymer. interlaced by their entanglement, this reactive additive is preferably water and a silane condensation reaction catalyst, such as an organic tin dicarboxylate. The mixture of the core is preferably polymerized by a volumetric process (without solvent), more preferably by a continuous volumetric process, the non-interlaced copolymer is preferably devolatilized before co-extrusion with a coating, preferably a fluoropolymer, in a compound of core / coating, which is then separately cured to the flexible and lightweight end tube. The process based on a monomer, such as ethyl acrylate, taught by Bígley et al. , provides a flexible tube of light or an optical conduit, which has a high transmission of white light and an acceptable flexibility and hardness for a variety of uses, where the light is going to be transported from a remote source to a target and where the conduit needs to be flexible to follow a tortuous path, and still hard enough to retain its critical geometry. The existing process also produces an FLP of adequate thermal and photothermal stability (exposure of joints to heat to visible light, which can contain light with wavelengths known as "near the ultraviolet"), even after exposure to many hours of light and environmental heat. The prior art polymer has adequate stability for exposure to higher temperatures, including those up to about 90 ° C, for shorter periods of use. However, there is a large potential market for a light tube, which is thermally and photothermally stable at higher temperatures and longer exposure periods, such as in automatic applications, where light is conducted near the engine compartment and temperatures of 150 ° C or higher can be reached. Other potential uses, where high temperatures can be found, can be when the light source is not adequately protected from the connection with the FLP or where the light source is of an extremely high intensity. Bigley et al. , 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 problem of stabilization. We have discovered an improved process by which an interlacing acrylic core is prepared for an FLP, which, during the healing for interlacing, exhibits a surprisingly improved stability to thermal aging, which retains its other desirable properties of good initial clarity, lack of color initial, good flexibility, adequate or somewhat improved photothermal stabilization and adequate hardness to prevent physical distortion. An improved product, especially towards thermal aging in the absence of light, passed through the core, can be prepared by carefully controlling the temperature of the process, preferably shortening somewhat the residence time in the reactor and controlling the nature of the initiator, thus decrease the number of terminal vinyl groups in the polymer.

More specifically, we have discovered a crosslinkable core mixture for a cured composite, which is subsequently cured, which mixture contains a thermoplastic core polymer, this thermoplastic core polymer has a weight average molecular weight of approximately 2,000 to 250,000 daltons and a content of vinyl end groups below 0.5 per 1000 monomer units, this core mixture comprises: (a) a thermoplastic core polymer, which comprises: (i) from 80 to 99.9 weight percent of polymerized units of a alkyl acrylate C ^ -C ^ g, or mixtures thereof, with up to 50 weight percent of the components of (a) (i) of polymerized units of an alkyl methacrylate C ^ -C ^ g; (ii) from 0.1 to 18.2 weight percent of polymerized units of a functionally reactive monomer, and (iii) from 0 to 10 weight percent of polymerized units of a monomer with increasing refractive index, selected from styrene, acrylate of benzyl, benzyl methacrylate, phenylethyl acrylate or phenylethyl methacrylate; (iv) from 0.002 to 0.3, preferably from 0.01 to 0.3, weight percent of residual molecules of, or decomposition products of, a polymerization initiator, which includes end groups in the thermoplastic core polymer, this initiator has a half life at 60 ° C from 20 to 400 minutes, preferably from 100 to 250 minutes; (v) from 0.2 to 2.0, preferably from 0. 6 to 1.5 weight percent of residual molecules of, or decomposition products of, a chain transfer agent, including end groups in the thermoplastic core polymer; (b) 0.1 to 10 weight percent, based on the weight of the crosslinkable core mixture, of a reactive additive. It is preferred that the crosslinkable core blends exhibit the percentage of polymerized units of a C?-C? G alkyl acrylate, such as 80 to 99.5 percent by weight, of the ethyl acrylate, it is further preferred that the The chain is an aliphatic mercaptan with one to twenty carbon atoms, such as butyl mercaptan, dodecyl mercaptan, and the like, and it is further preferred that the polymerization initiator be an azo compound. It is also preferred that crosslinkable core blends keep the reactive monomer functionally present at a level of about 0.5 to 12 weight percent, more preferably 2 to 12 weight percent, and be selected from 2-methacryloxy-ethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, or mixtures thereof, preferably is 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 the patent of US, No. 5,485,541, the cure for the reactive monomers of alkoxysilane functionality, is carried out by injecting water, an organic tin catalyst and (optionally) a solvent for the catalyst, after completing the polymerization, but before the -Extrusion 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 addition of water just before conducting co-extrusion or curing, after extrusion, in The presence of diffuse water ennment. The latter process has been accelerated to a practical level using a humidified furnace or by curing in a highly controlled atmosphere in humidity. The advantage of separating the water from the other components until the polymerization and coating is complete is that premature entanglement does not occur, with subsequent effects on the extrusion and on the surface between the core and the coating. Samples coated with THV, which is more permeable to water than FEP, can be cured externally quickly enough for the present purposes (without absorbing as much water as fogging occurs) at temperatures of 80 ° C and 50% relative humidity, while coated samples with FEP they can be cured quickly enough for the present purposes, at 85 ° C and 85% relative humidity. The crosslinkable core mixture may further contain a coating polymer, such as a fluoropolymer, which surrounds the core mixture, and preferably the mixture of the crosslinkable core within the coating of the extruded fluoropolymer and this coating of the extruded fluoropolymer are in substantially complete contact . It should be recognized that the thermoplastic core polymer and the coating do not form a chemical or physical mixture, but are adjacent to each other in the construction, in which the mixture of the core is surrounded by the coating. We have also discovered, based on the interlacing core polymers, described above, a flexible light tube product, containing the interlaced core mixture described above, in which the product has: good light transmittance, in which the loss of The differential transmission between the wavelengths of light of 400 nm and 600 nm is equal to or less than 1.0 decibel per meter, as measured by a non-destructive interference filter method; excellent thermal stability, in which a change in the loss of differential transmission between the wavelengths of light of 400 nm and 600 nm is equal to or less than 1.0 decibel per meter after more than 100 hours of exposure to a temperature of 120 ° C, as measured by a non-destructive interference filter method; good flexibility, in which the product, at 20 ° C, survives without core fractures, at 180 ° C, bent with a bend radius which is less than or equal to five times the diameter of the cured core; and good hardness properties, in which Shore "A" hardness is less than 90, after 50 days of exposure at 120 ° C. We have also 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, this mixture contains a thermoplastic core polymer having a weight average molecular weight of about 2,000 to 250,000 daltons and a content of vinyl end groups below 0.5 per 1000 monomer units, this process comprises: a) preparing a mixture of: i) about 80 to 99.9 weight percent of a volumetric monomer mixture , selected from an alkyl acrylate or mixtures thereof, with up to 50 percent by weight of the bulk monomer mixture of an alkyl methacrylate C ~ Cl8 '* 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 , benzyl methacrylate, phenylethyl acrylate or phenylethyl methacrylate; b) adding from 0.002 to 0.3 percent by weight, based on the weight of the non-interlaced copolymer, of a polymerization initiator, which has a half-life, at 60 ° C, from 20 to 400 minutes, preferably 100 250 minutes; c) before, simultaneously with, or after the addition of the initiator, add from 0.2 to 2.0 percent by weight, preferably from 0.75 to 1.5 percent by weight, based on the weight of the non-interlaced copolymer, of an agent of chain transfer; 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, preferably at 85-100 ° C, with a preferred residence time from 5 to 30 minutes, more preferably from 20 to 28 minutes, to form a crosslinkable, polymerized core mixture, which is not yet interlocked; e) discharging the mixture of the interlaced, polymerized, non-interlaced core, to a devolatilization apparatus,, to remove the unreacted monomers; f) before, during or after the 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) co-extrude the interlayer core mixture and the coating polymer to form a curable compound. In this process, it is separately preferred that the coextruded coating polymer and the co-extruded crosslinkable core mixture be continuously, concurrently and coaxially extruded, that the coating polymer be a molten fluoropolymer, as described above, than the mixture of the extruded interlayer core , within the coating of the extruded fluoropolymer and this coating of the extruded fluoropolymer is in substantially complete contact, after filling the extruded tubular coating with the extruded crosslinkable core mixture, and that the cure is subsequently and separately conducted from the extrusion and coating operation . In addition, a portion of the reactive additive can be added to the core mixture after extrusion, such as by diffusion of the water through the coating. Likewise, a flexible light tube product has been discovered by any of the above processes, in which the product has good light transmittance, in which the loss of the differential transmission between the wavelengths of the light of 400 nm and 600 nm is equal to or less than 1.0 decible, per meter, as measured by the "clipping" interference filter method; excellent thermal stability, in which a change in the loss of differential transmission between the wavelengths of light of 400 nm and 600 nm is equal to or less than 1.0 decibel, per meter after more than 100 hours of exposure to a temperature of 120 ° C, as measured by a non-destructive interference filter method; good flexibility, in which the product, at 20 ° C, survives without core fracture, at a bend of 180 °, with a bend radius which is less than or equal to five times the diameter of the cured core; and good hardness properties, in which Shore "A" hardness is less than 90, after 50 days of exposure at 120 ° C. Although it is not desired to be bound by any theory of polymer stability, it is believed to be detrimental to thermal stability and, to a much lesser extent, photochemical stability, if the crosslinkable core polymer contains oligomers or polymers with vinyl groups terminals. Such oligomers or polymers can, in the presence of heat and / or light, form molecules with conjugated double bonds, which, finally,, with sufficient conjugation, they form species that are absorbent of color in the visible region of the spectrum, as well as they diminish the amount of light that is delivered by the tube of light to the final source. Such vinyl double bonds, apart from the residual monomer, which can be reduced by bringing the reaction to a greater conversion and / or devolatilization of the crosslinkable core, before curing or interlacing, can be formed by the extraction of the hydrogen, followed by the splitting chain, or other forms of radical attack. These radicals may be, for example, the initiator, some reaction product of the initiator or of the 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 in the melt fluid, before the coating and healing. It has been found, surprisingly, that the reduction of the reaction temperature and the amount of the initiator, preferably accompanied by a decrease in the residence time in the continuous reactor, is sufficient to make significant improvements in the initial color of the polymer core before and after after curing and increasing the thermal lifetime, as defined below, at 120 ° C, in the absence of any thermal or oxidative-thermal stabilization additive. These results, especially in relation to residence time in the reactor and at the polymerization temperature, were not expected by a person skilled in the art of volumetric polymerization of acrylate monomers. Experimentation in the study of thermal stability was conducted by a tube filling process, but the process can easily be adapted to the continuous method described by Bigley et al. , to prepare a flexible tube of light. A standard laboratory process is used as the control, followed by the method of Example 1 (tube filling) and Example 29 (details of the compositions) of the E. ü patent. A., No. 5,485,541. The monomer composition is 95% EA (purified through acid alumina) and 5% MATS (3-methacryloxypropyltrimethoxysilane). Vazo 67 (DuPont) uses the 2, 2'-azobis (2-methylbutyronitrile) initiator at a level of 0.064% of the monomer. A chain transfer agent, n-dodecyl mercaptan, is used at a level of 1% of the amount of the monomer. The standard reactor temperature is 125 ° C and the standard residence time is 28 minutes. After devolatilization, the polymer is used to fill FEP / polyethylene tubes. The catalyst (20 ppm dibutyltin diacetate, based on the polymer) and water (0.40%) are mixed in the polymer as it is pumped into the tubes. Various variations in this polymer are used. These variations are summarized in the following Table 1, together with the initial color measurements. The following indicates the details for the standard polymerization, which is used as the basis for the process changes listed in Table I. Mixtures of monomers are prepared as follows: to a 316 stainless steel vessel, 19 liters, were added and mixed 9500 g of ethyl acrylate, 500 grams of the functionally reactive monomer, 3-methacryloxypropyltrimethoxysilane (MATS) (5% by weight based on the weight of the monomer, 5.4 g of the initiator (recrystallized from 2, 2'-azobis ( 2-methylbutyronitrile) (0.064% by weight) and 100 g of n-dodecyl mercaptan (1% by weight) The mixture was sprayed for at least 15 minutes with nitrogen and degassed under a vacuum of 711 mm Hg , as it is pumped into the reactor, the monomer mixture was fed through a 0.045 micron PTFE membrane cartridge filter to a 2000 ml stirred stainless steel constant flow tank reactor (CFSTR). the polymerization, the flow regimes for this 2000 ml CFSTR were approximately 70 g / min, to produce a residence time of 28 minutes. The CFSTR was equipped with turbine agitators, with 45 ° pitch, of multiple (6) blades. During the polymerization, the reactors were maintained at 125 ° C and were stirred at 225 rpm under a pressure of 1035 kPa. The reactor effluent (copolymer and residual monomer) was fed through a back-pressure valve, nominally set at 1035 kPa in a devolatilization column comprising a non-moving blender, twisted ribbon, stainless steel (60 cm length, with a shirt about 50 cm long) mounted on a stainless steel collector of 39 liters. The heating oil was recirculated through the column jacket and maintained at 200 ° C at the entrance of the jacket. The collector was maintained at 100-110 ° C and a vacuum of approximately 300 to 400 mm, during devolatilization. Upon completion of the polymerization, the collector was again filled with filtered nitrogen.

The conversion of the monomer to the polymer of the effluent was about 87-88%, as measured gravimetrically. The solids content, determined gravimetrically, of the devolatilized polymer was typically 99.5% by weight. It should be noted that in the latter operations, the conditions were changed as follows: 2.08 grams of 2,2'-azobis (2,4-dimethylvaleronitrile); 150 grams of n-dodecyl mercaptan; reaction temperature of 95 ° C; 90 grams / min, load regime; residence time of 22.2 minutes; conversion from 79 to 80%, before devolatilization. The color and loss measurements in these samples were made by the methods taught in the U.A. Patent No. 5,485,541, that is, monitored with a non-destructive interference filter method. This method uses sections of the 1.8 m long light tube and the source, which integrate sphere and interference filters. For measurements of white light, excitation was restricted mainly to the visible spectrum through the use of a heated mirror. The length of the sample was measured, its transmission was monitored with several filters, it was aged and then measured again. The changes were monitored through the ratio of the transmission values of short wavelength in relation to the transmission at 600 nm; absorption at such long wavelengths was relatively unaffected by degradation, except in the most severe cases. Because only changes in the transmission were studied, the reflection losses and the scattering effects of the refractive index can not be neglected. The decreases in the percentage in the ratio of the short wavelength to the absorbance of 600 nm were treated as percentages of loss in the length of the sample; the resulting values are named "changes in differential loss". Table 1 Polymer Composition and Initial Color Table 1 (Continued) ETEMA = ethylthioethyl methacrylate Vazo 52 = DuPont 2,2'-azobis (2,4-dimethylvaleronitrile), a lower temperature initiator (half-life at 60 ° C approximately 188 minutes); Vazo 67, DuPont 2,2'-azobis (2-methylbutyronitrile, initiator; half-life at 60 ° C approximately 1880 minutes; MATS = 3-methacryloxypropyltrimethoxysilane; 4-OH-TEMPO = 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, an inhibitor for the premature polymerization of MATS during purification; nDDM = n-dodecyl-mercaptan; t-BuSH = t-butyl mercaptan; BMA = butyl methacrylate.

Table 1 shows the actual polymers that were prepared and evaluated. The fourth column lists the terminal vinyl content measured from the nuclear magnetic resonance (NMR) spectrum of the devolatilized but uncured polymer. The vinyl content refers to the group where P represents the polymer chain and R ^ is -COO-C2H5. Vinyl content has been associated with increased stability. Low temperature conditions give lower vinyl contents. The presence of this type of terminal unsaturation is quite unexpected for the degraded polymer; the technique strongly suggests that an internal double bond, such as P-CH = CR? -P, is more likely to be formed, but it will not be detected in the spectrum. The initial color was used as a measure of the polymer. The color was measured in a 1.83 meter piece by the standard method. The color was measured by the difference in absorption at 450 and 600 nm (450-A600). Similarly, the color at 400 nm is equal to 4oo ~ A600- The results indicate that the low color polymers are obtained by a process of low temperature.

Thermal Degradation Absorption vs. the wavelength of a section of 1. 83 meters from a light tube. The sample was thermally vented in a forced air oven at 120 ° C. Periodically, the light tube was removed from the oven and the spectrum of absorption was measured. We have calculated the life time with four different criteria: Increase of A40 = 1 The lifetime is the time in which the increase in absorption at 400 nm (A400-A600) = 1 dB / m. This is the criterion that has been used historically A = 2 dB / m The life time is the time in which the absorption at 400nm (A400 - AQOO) = 2 dB / m- Increase of A450 = The lifetime is the time in which the increase in absorption at 450 nm (A450-A500) = ° -3 dB / m. 0 3 dB / m A = 0. 6 dB / m The lifetime is the time at which the absorption at 450 nm (A450-A600) = ° -6 dB / m.

Previous tests measured the failure by an increase in odor. Since the light tubes vary in the initial color, depending on the process and the chemicals, this was an attempt to remove this factor. We have added criteria that measure the absolute amount of color, that is, the point of failure is the same color for all. The results for the polymers for all four criteria are listed below.

Table 2 Effect of Polymer Composition and Process in the Durability Vinyl contents above about 0.5 per 1000 units of monomers give low stability.

Vinyl contents below 0.5 give high durability. An initial color (A450-A500) of less than about 0.5 gives very good durability. The photothermal stability of the previous polymers was equivalent to or slightly better than the standard polymers, as measured by the transmission ratios of the aged and non-aged samples exposed to 100 ° C and to 12-15 lumens / square millimeter of light, from a XMH-60 lamp from General Electric, with an Optivex filter.

Claims (11)

1. CLAIMS A crosslinkable core mix for a subsequently cured composite, this blend contains a thermoplastic core polymer, this thermoplastic core polymer has an average molecular weight of approximately 2,000 to 250,000 daltons, and a vinyl end group content below 0.5 per cent. 1000 monomer units, this core mixture includes: (a) a thermoplastic core polymer, which comprises: (i) from 80 to 99.9 weight percent of polymerized units of an alkyl acrylate C ^ -C ^ g, or mixtures thereof, with up to 50 percent by weight of the components of (a) (i) of polymerized units of an alkyl methacrylate C] _ C] _8 '(ii) from 0.1 to 18.2 percent by weight of polymerized units of a functionally reactive monomer, and (iii) from 0 to 10 weight percent of polymerized units of a monomer with increasing refractive index, selected from styrene, benzyl acrylate, benzyl methacrylate, phenylethyl acrylate or phenylethyl methacrylate; (iv) from 0.002 to 0.3, preferably from 0.01 to 0.3, weight percent of residual molecules of, or decomposition products of, a polymerization initiator, which includes end groups in the thermoplastic core polymer, this initiator has a half life at 60 ° C from 20 to 400 minutes; (v) from 0.2 to 2.0, preferably from 0. 6 to 1.5 weight percent of residual molecules of, or decomposition products of, a chain transfer agent, including end groups in the thermoplastic core polymer; (b) 0.1 to 10 weight percent, based on the weight of the crosslinkable core mixture, of a reactive additive.
2. 2. The crosslinkable core mixture of claim 1, further containing a coating polymer which surrounds the core mixture.
3. 3. The crosslinkable core mixture of claim 2, wherein the coating polymer is a fluoropolymer and wherein the crosslinkable core mixture, within the coating of the extruded fluoropolymer and this coating of the extruded fluoropolymer are in substantially complete contact.
4. 4. The crosslinkable core mixture of claim 3, wherein the percentage of the polymerized units of an alkyl acrylate Ci to Cig is 80 to 99.5 weight percent of the vinyl acrylate, where the chain transfer agent is a mercaptan aliphatic with about twenty carbon atoms, and in which the initiator of the polymerization is an azo compound.
5. 5. The crosslinkable core mixture of claim 3, wherein the functionally reactive monomer is present at a level of about 0.5 to 12 weight percent and is selected from 2-methacryloxy-ethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyl triethoxysilane,. or mixtures thereof, and wherein the reactive additive is water and a silane condensation reaction catalyst.
6. 6. The crosslinkable mixture of the core of claim 5, wherein the silane condensation reaction catalyst is a dialkyl tin dicarboxylate.
7. 7. The crosslinkable core mixture of claim 6, wherein the non-interlaced copolymer is formed of polymerized units of 94 to 98 weight percent of ethyl acrylate and about 2 to 6 weight percent of 3-methacryloxypropyltrimethoxysilane, and the silane condensation reaction catalyst is dibutyl tin diacetate.
8. 8. A flexible light tube product, containing the intertwined core mixture of claim 2, wherein the product has a good light transmittance, where the loss of the differential transmission between the wavelengths of the light of 400 nm at 600 nm is equal to or less than 1.0 decibel per meter, as measured by a "trimming" interference filter method; excellent thermal stability, in which a change in the loss of differential transmission between the wavelengths of light from 400 to 600 nm is equal to or less than 1.0 decibel, per meter, after more than 100 hours of exposure to a temperature of 120 ° C, as measured by a non-destructive interference filter method; a good flexibility, in which the product, at 20 ° C, survives without core fracture, a bend of 180 ° at a bend radius which is less than or equal to five times the diameter of the cured core; and good hardness properties, in which Shore "A" hardness is less than 90, after 50 days of exposure at 120 ° C.
9. 9. A process for preparing a crosslinkable core mixture for a subsequently cured composite, comprising a coextruded coating polymer and a coextruded crosslinkable core mixture, this blend contains a thermoplastic core polymer having a weight average molecular weight of about 2,000 to 250,000 daltons, and a final vinyl group content below 0.5 per 1000 monomer units, the process comprises: a) preparing a mixture of: i) about 80 to 99.9 weight percent of a volumetric monomer mixture, selected from a C -C 8 alkyl acrylate / or mixtures thereof, with 50 weight percent of the bulk monomer mixture of an alkyl methacrylate Ci-C ^ g; ii) from about 0.1 to 18.2 weight percent of a functionally reactive monomer and 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 percent by weight, based on the weight of the non-interlaced copolymer, of a polymerization initiator, which has a half-life, at 60 ° C, from 20 to 400 minutes; c) before, simultaneously with, or after the addition of the initiator, add from 0.2 to 2.0 percent by weight, based on the weight of the non-interlaced 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 crosslinked, polymerized core mixture, which is not still interlaced; e) discharging the interlaced, polymerized, non-interlaced core mixture to a devolatilization apparatus to remove unreacted monomers; f) before, during or after the 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) co-extrude the interlayer core mixture and the coating polymer to form a curable compound.
10. 10. The process of claim 9, wherein the co-extruded coating polymer and a co-extruded, interlaxable core mixture are extruded continuously, concurrently and co-axially, where this coating polymer is a molten fluoropolymer, the interlayer core mixture extruded within the coating of the extruded fluoropolymer and this extruded fluoropolymer coating, is in substantially complete contact after filling the extruded tubular sheath with the extruded interlayer core mixture, wherein the cure is conducted subsequently and separately from the extrusion of the coating operation, and where a portion of the reactive additive is added to the core mixture after co-extrusion.
11. 11. A light tube product, obtained by the process of claim 9 or 10, wherein the product has a good light transmittance, where the loss of the differential transmission between light wavelengths of 400 nm to 600 nm is equal to or less than 1.0 decibel per meter, as measured by the "clipping" interference filter method; excellent thermal stability, where a change in the loss of differential transmission between the wavelengths of light from 400 to 600 nm is equal to or less than 1.0 decibel per meter after more than 100 hours of exposure at a temperature of 120 ° C, as measured by the non-destructive interference filter method; good flexibility, in that the product, at 20 ° C, survives without a core fracture at a bend of 180 °, at a bend radius, which is less than or equal to five times the diameter of the cured core; and good hardness properties, in which Shore "A" hardness is less than 90, after 50 days of exposure at 120 ° C.