POLYMERIZABLE COMPOSITION BASED ON ALLYL CARBONATE MONOMERS, POLYMERIZED PRODUCT OBTAINABLE FROM SAID COMPOSITION AND USES THEREOF

Abstract

The present invention relates to a polymerizable composition based on allyl carbonate monomers comprising: from 40% to 90% of a first reactive component (component A) comprising at least 50% by weight of diethylene glycol bis(allyl carbonate); from 10% to 60% of a second reactive component (component B) consisting of at least one compound having general formula (II)

##STR00001## or having general formula (III)

##STR00002## from 0.4 to 10.0 phm (parts by weight per 100 parts of the total weight of components A and B) of at least one peroxide radical initiator. The present invention also relates to the polymerized products that can be obtained from the above composition, their preparation process and their use as organic glass.

Claims

1. Polymerisable composition based on allylcarbonate monomers comprising (percentages by weight referred to the total weight of components A and B): from 40% to 90% of a first reactive component (component A) of general formula (I) ##STR00015## where n is an integer from 1 to 6, said component A comprising at least 50% by weight of a compound of general formula (I) wherein n is equal to 1; from 10% to 60% of a second reactive component (component B) consisting of at least one compound of general formula (II) ##STR00016## or of general formula (III) ##STR00017## where in the above formulas (II) and (III): p is equal to 0 or 1, R, equal or different from each other, are selected from: a group having formula (IV) ##STR00018## or a group having formula (V) ##STR00019## wherein m is an integer from 1 to 3; R, equal or different from each other, are selected from: hydrogen, methyl, ethyl or a group ##STR00020## from 0.4 to 10.0 phm (parts by weight per 100 parts of the total weight of components A and B) of at least one peroxide radical initiator.

2. Polymerisable composition according to claim 1, wherein said component A is obtained by reacting diallylcarbonate (DAC) and diethylene glycol (DEG) in a molar ratio DAC/DEG from 2.5/1 to 5/1, preferably from 2.75/1 to 4.0/1, more preferably from 2.5/1 to 3.5/1.

3. Polymerisable composition according to claim 1, wherein said component B is obtained by reacting diallylcarbonate (DAC) and at least one aliphatic polyol having at least 4 alcoholic hydroxyl groups in a molar ratio DAC/polyol from 4/1 to 24/1.

4. Polymerisable composition according to claim 3, wherein said molar ratio DAC/polyol is from 4/1 to 16/1, preferably from 8/1 to 14/1, more preferably from 10/1 to 14/1.

5. Polymerisable composition according to claim 3, wherein said aliphatic polyol having at least 4 alcoholic hydroxyl groups is selected from: di(trimethylolpropane), pentaerythritol, di(pentaerythritol) and tri(pentaerythritol).

6. Polymerisable composition according to claim 1, wherein said component B is obtained by reacting diallylcarbonate (DAC) and pentaerythritol in a molar ratio DAC/pentaerythritol from 5/1 to 16/1, preferably from 8/1 to 14/1, more preferably from 10/1 to 14/1.

7. Polymerisable composition according to claim 1, wherein said peroxide radical initiator is selected from: peroxymonocarbonate esters, peroxydicarbonate esters, diacylperoxides, peroxyesters and mixtures thereof.

8. Polymerisable composition according to claim 1, wherein said peroxide radical initiator is selected from the compounds of formula (VI), the compounds of formula (VII) and mixtures thereof ##STR00021## where R1 and R2, equal or different from each other, are selected from: C1-C20 alkyl, C1-C20 alkenyl or C1-C20 cycloalkyl.

9. Polymerisable composition according to claim 1, wherein the concentration of said peroxide radical initiator is within the range 0.4-5.0 phm, more preferably within the range 0.5-3.5 phm.

10. Polymerised product, in particular, organic glass, obtained by means of thermal treatment of a polymerisable composition according to claim 1.

11. Process for preparing a polymerised product comprising the step of thermally treating a polymerisable composition based on allylcarbonate monomers comprising (percentages by weight referred to the total weight of components A and B): from 40% to 90% of a first reactive component (component A) of general formula (I) ##STR00022## where n is an integer from 1 to 6, said component A comprising at least 50% by weight of a compound of general formula (I) wherein n is equal to 1; from 10% to 60% of a second reactive component (component B) consisting of at least one compound of general formula (II) ##STR00023## or of general formula (III) ##STR00024## where in the above formulas (II) and (III): p is equal to 0 or 1, R, equal or different from each other, are selected from: a group having formula (IV) ##STR00025## or a group having formula (V) ##STR00026## wherein m is an integer from 1 to 3; R, equal or different from each other, are selected from: hydrogen, methyl, ethyl or a group ##STR00027## from 0.4 to 10.0 phm (parts by weight per 100 parts of the total weight of components A and B) of at least one peroxide radical initiator.

12. (canceled)

13. Method for producing an organic glass comprising the steps of: a) injecting at least the polymerizable composition according to claim 1 into at least one mould having the shape desired for said organic glass; b) thermally treating the composition injected into said mould to obtain said organic glass.

Description

EXAMPLES

[0134] 1. Preparation of Components A and B and of the Polymerizable Mixtures

[0135] The reactive component A was prepared by reacting diallyl carbonate (DAC) and diethylene glycol (DEG), in a DAC/DEG molar ratio of 3/1 in a reactor equipped with a stirrer and distillation column to remove the allyl alcohol produced during the reaction.

[0136] The reagents were charged into the reactor according to the required molar ratio and the mixture obtained was deaerated before the addition of the catalyst (sodium methylate in a concentration of 100 ppm by weight with respect to the weight of DEG). After bringing the pressure inside the reactor to about 150-200 mbar, the heating was started, until the temperature of the beginning of the distillation of allyl alcohol, within the range of 95-100 C., was reached.

[0137] The theoretical quantity of allyl alcohol which develops with the total conversion of DEG is equal to 2 moles per mole of DEG. The reaction is considered as being complete when the theoretical quantity of allyl alcohol has been collected.

[0138] The pressure inside the reactor was then gradually reduced to remove the excess DAC. The residual quantity of DAC depends on the degree of vacuum: by operating at 10 mbar, a product is obtained with a residual quantity lower than 1%.

[0139] Through HPLC analysis, it was determined that component (A) is composed of the monomer (diethylene glycol bis(allyl carbonate) in a quantity of about 63% by weight with respect to component A, the remaining percentage consisting of oligomers having formula (I) wherein the average value of n is equal to about 2.5. The HPLC analysis of component A was carried out under the following conditions: temperature=25 C.; sample of A subjected to analysis in the form of a 10% by weight solution of acetonitrile; sample injected=5 microliters; eluent: a mixture of acetonitrile/water (45/55% by volume); UV detector.

[0140] Component B was obtained by reacting diallyl carbonate (DAC) and pentaerythritol in a DAC/pentaerythritol molar ratio of 12/1, under the same conditions and using the same equipment described above for the preparation of component A.

[0141] HPLC analysis revealed that component (B) is composed of a mixture containing about: [0142] 55% by weight of compounds having formula (II) wherein the radical R is the group having formula (IV) (monomer): [0143] 45% by weight of compounds having formula (II) wherein the radical R is the group having formula (V) (average value of m in formula (V) equal to about 2.5) (oligomers).

[0144] The HPLC analysis of component B was carried out under the following conditions: temperature=25 C.; sample of A subjected to analysis in the form of a 10% by weight solution of acetonitrile; injected sample=5 microliters; eluent: mixture of acetonitrile/water (70/30% by volume); UV detector.

[0145] Mixtures containing 75% by weight of component A and 25% by weight of component B, were prepared starting from the reactive components A and B. A radical initiator and a UV absorber were then added to the mixtures, in the quantities indicated hereunder.

[0146] The radical initiator of the group of the peroxydicarbonate esters is the commercial product Trigonox ADC-NS30 by Akzo Nobel. This product contains about 70% by weight of diethylene glycol bis(allyl carbonate) and 30% by weight of a mixture of isopropyl peroxydicarbonates, sec butyl and isopropyl/sec-butyl.

[0147] The radical initiator of the group of the diacylperoxides is dibenzoil peroxide (BPO), commercial product Perkadox CH-50L by Akzo Nobel. This product contains about 50% by weight of benzoil peroxide and 50% by weight of dicyclohexyl phtalate.

[0148] The UV absorber is 2-hydroxy,4-methoxybenzophenone (Lowilite 20 by Addivant).

[0149] The viscosity at 25 C. of the mixture of components A and B, before the addition of the initiator, is equal to 55 cStokes and the specific weight at 20 C. is 1.184 g/cm.sup.3.

[0150] 2. Characterization of the Polymerized Products

[0151] The polymerizable compositions were polymerized in the form of flat sheets having a thickness ranging from 3 mm to 5 mm and neutral lenses having a thickness of 2 mm, by casting in glass moulds. The moulds are composed of two glass half-moulds joined to each other by means of a spacer gasket made of plasticized polyvinylchloride (sheets) or low-density polyethylene (LDPE) (lenses), forming a cavity suitable for containing the polymerizable composition.

[0152] The polymerization was carried out by means of thermal treatment in a forced-air-circulation oven, with a gradual temperature rise as indicated hereunder. At the end of the thermal treatment, the moulds were opened and the lenses were kept at 110 C. for 1 hour in order to decompose the possible residual peroxide initiator.

[0153] The following characterization tests were carried out on the polymerized products obtained in order to determine their physico-mechanical and optical properties.

[0154] The following characteristics were determined on the flat sheets:

[0155] (a) Optical Characteristics [0156] Refractive index (n.sup.D.sub.20): measured with an Abbe refractometer (ASTM D-542); [0157] Yellow index (YI), (ASTM D-1925), determined with a GretagMacbeth 1500 Plus spectrophotometer and defined as: YI=100/Y.Math.(1.277X-1.06Z); [0158] Haze % and Light Transmittance (ASTM D-1003) determined with a Haze-gard plus instrument;

[0159] (b) Physico-Mechanical Characteristics [0160] Specific weight: determined with a hydrostatic balance at 20 C. (ASTM D-792); [0161] Volume contraction in polymerization (shrinkage) calculated with the formula:

[00001]$\mathrm{Shrinkage}.Math..Math.\left(\%\right)=\frac{\mathrm{Polymer}.Math..Math.\mathrm{density}-\mathrm{Monomer}.Math..Math.\mathrm{density}}{\mathrm{Polymer}.Math..Math.\mathrm{density}}100$ [0162] Rockwell Hardness (M) measured with a Rockwell durometer (ASTM D-785); [0163] Impact strength (Ball Drop TestAmerican National Standard Z87.1-2003); [0164] Distortion temperature under load 1.82 MPa (HDT) (ASTM D-648).

[0165] The following properties were determined on the neutral lenses:

[0166] (c) Tintability

[0167] The capacity of the polymerized product of superficially adsorbing a colouring agent was determined by immersing a neutral lens in an aqueous bath in which the commercial dye BPI gray diluted at 10% by weight in demineralized water, was dispersed.

[0168] The lens was immersed in the tinting bath for 20 minutes at a temperature of 90 C. After rinsing with demineralized water, the Transmittance % of the lens was determined under the terms of the standard ASTM D-1003.

[0169] (d) Abrasion Resistance

[0170] The capacity of the polymerized product of resisting surface abrasion was determined with a Taber oscillating abrasimeter, according to the method ASTM F-735. This method involves contemporaneously subjecting the sample lens and a reference lens made of diethylene glycol bis(allyl carbonate) (CR39) to 600 oscillating cycles with the abrasive material Alundum ZF-12.

[0171] The ratio between the increase in Haze measured with the instrument Haze-gard plus according to ASTM D-1003 after the abrasion cycles on the sample lens and on the reference lens represents the Bayer abrasion resistance value (BA).

[00002]$\mathrm{Bayer}.Math..Math.\mathrm{Abrasion}=\frac{.Math..Math.\mathrm{Haze}\left(\mathrm{reference}.Math..Math.\mathrm{lens}\right)}{.Math..Math.\mathrm{Haze}\left(\mathrm{sample}.Math..Math.\mathrm{lens}\right)}$

[0172] Values or the BA jcate an abrasion resistance higher than that of the reference material; values of the BA index lower than 1 indicate an abrasion resistance lower than that of the reference material.

[0173] 3. Polymerizable Compositions Nr. 1-6

[0174] The chemical composition of the polymerizable compositions nr. 1-3 according to the present invention is indicated in Table 1.

TABLE-US-00001 TABLE 1 Polymerizable compositions nr. 1-3 according to the invention Composition N 1 2 3 Component (A) + 93.05.sup.a 93.25.sup.a 93.45.sup.a Component (B) Peroxide 6.9.sup.b 6.7.sup.b 6.5.sup.b initiator (2.22).sup.c (2.16).sup.c (2.09).sup.c UV absorber 0.05.sup.a 0.05.sup.a 0.05.sup.a .sup.aweight percentage referring to the total weight of the polymerizable composition; .sup.bweight percentage of the commercial product Trigonox ADC-NS30 referring to the total weight of the polymerizable composition; .sup.cOverall concentration of peroxide compounds expressed as phm (parts by weight per 100 parts of the total weight of components A and B).

[0175] For comparative purposes, the following polymerizable compositions nr. 4*-6* also containing 0.05% of UV absorber, were also prepared: [0176] nr. 4*: composition containing 93.05% by weight of diethylene glycol bis(allyl carbonate) (RAV 7AT) as sole monomer, 0.05% by weight of UV absorber (Lowilite 20) and 6.9% by weight of peroxide initiator (Trigonox ADC-NS30); [0177] nr. 5*: composition containing 88.95% by weight of diethylene glycol bis(allyl carbonate) (RAV 7AT) as sole monomer, 0.05% by weight of UV absorber (Lowilite 20) and 11% by weight of peroxide initiator (Trigonox ADC-NS30); [0178] nr. 6*: composition containing:

[0179] (i) 65.28% by weight of the product obtained from the reaction between DAC and DEG, in a molar ratio equal to 2/1; said product contains 54% by weight of oligomers and 46% of monomer (diethylene glycol bis(allyl carbonate));

[0180] (ii) 27.97% by weight of the product obtained from the reaction between DAC and pentaerythritol in a molar ratio equal to 24/1 (comonomer); said product contains 73% by weight of monomer having formula (II) wherein the radical R is the group having formula (IV) and 27% of compounds having formula (II) wherein the radical R is the group having formula (V) (average value of m in formula (V) equal to about 1.3) (oligomers); HPLC analysis of component (ii) was carried out under the same conditions used for the analysis of component B of the present invention (see previous item 1);

[0181] (iii) 0.05% by weight of UV absorber (Lowilite 20);

[0182] (iv) 6.7% by weight of peroxide initiator (Trigonox ADC-NS30).

[0183] The chemical composition of the polymerizable compositions nr. 4*-6* is indicated in Table 2.

TABLE-US-00002 TABLE 2 Comparative polymerizable compositions nr. 4*-6* Composition N 4* 5* 6* Monomer + possible 93.05.sup.a 88.95.sup.a 93.25.sup.a comonomer Peroxide initiator 6.9.sup.b 11.0.sup.b 6.7.sup.b (2.22).sup.c (3.71.sup.)c (2.09).sup.c UV absorber 0.05 0.05 0.05 .sup.aweight percentage referring to the total weight of the polymerizable composition; .sup.bweight percentage of the commercial product Trigonox ADC-NS30 referring to the total weight of the polymerizable composition; .sup.cOverall concentration of organic peroxide expressed as phm (parts by weight per 100 parts of the total weight of the monomer and possible comonomer).

[0184] The polymerizable compositions Nr. 1-6 were subjected to polymerization by means of thermal treatment in a forced-air-circulation oven, with a gradual temperature rise from 40 C. to 80 C. according to the following curve: maintaining at 40 C. for 3 hours; temperature rise from 40 C. to 50 C. in 7 hours; temperature rise from 50 C. to 80 C. in 9 hours; maintaining at 80 C. for 1 hour.

[0185] At the end of the thermal treatment, the polymerized products (neutral lenses and flat sheets) were recovered from the moulds and heated to 110 C. for hour (in order to decompose the possible residual radical initiator).

[0186] The results of the characterization of the polymerized products are indicated in Tables 3 and 4.

TABLE-US-00003 TABLE 3 Properties of the polymerized products according to the invention Composition N 1 2 3 Refractive index (n.sup.D.sub.20) 1.500 1.500 1.500 Yellow index (5 mm) 1.30 1.22 1.20 Haze, % 0.13 0.14 0.11 Transmittance, % 93.3 93.3 93.3 Specific weight, g/cm.sup.3 1.329 1.329 1.329 Shrinkage, % 11.0 11.0 11.0 Rockwell hardness (5 mm), M 103 102 100 Drop Ball Test (68 g) Passed Passed Passed HDT, C. 110 95 85 Bayer Abrasion resistance- 1.1 1.1 1.1 Dyeability: Transmittance, % 31 29 28 Colour homogeneity Yes Yes Yes

TABLE-US-00004 TABLE 4 Properties of the comparative polymerized products Composition N 4* 5* 6* Refractive index (n.sup.D.sub.20) 1.500 1.500 1.500 Yellow index (5 mm) 0.56 1.20 1.20 Haze, % 0.11 0.10 0.12 Transmittance, % 93.3 93.3 93.3 Specific weight, g/cm.sup.3 1.314 1.314 1.334 Rockwell hardness (5 mm), M 73 95 95 Drop Ball Test (68 g) Passed Passed Passed HDT, C. 41 59 50 Bayer Abrasion resistance 0.5 1.0 1.2 Dyeability: Transmittance % 2 28 8 Colour homogeneity No Yes No *comparative composition

[0187] From a comparison of the data indicated in Tables 3 and 4, it can be observed that, even in the presence of a low concentration of radical initiator, the polymerized products obtained starting from the polymerizable compositions of the present invention (compositions 1-3) have optical and physico-mechanical properties similar to or significantly higher than those of the homopolymer of RAV 7AT polymerized in the presence of a conventional quantity of initiator (composition 5*).

[0188] In particular, the yellow index and dyeability of the polymerized products according to the present invention are substantially identical to those of the homopolymer of RAV 7AT that have been polymerized using a conventional quantity of initiator, i.e. a higher quantity compared to that used with the polymerizable compositions according to the present invention.

[0189] This result is completely unexpected, as it is well known that higher values of the Rockwell hardness and HDT are normally associated with a deterioration in the dyeability properties and yellow index.

[0190] It can also be observed from Table 4 that the homopolymer obtained starting from the commercial monomer RAV 7AT in the presence of a reduced quantity of initiator (composition 4*) with respect to the quantities normally used in the state of the art has worse physico-mechanical and dyeability properties with respect to the polymerized products of the present invention.

[0191] The results also show that the polymerization of the comparative composition 6*, effected in the presence of a quantity of radical initiator identical or comparable to that used with the polymerizable compositions according to the present invention (compositions 2 and 3), produces polymerized products having worse characteristics with respect to the polymerized products of the present invention, in particular a lower HDT value and unacceptable dyeability properties.

[0192] 4. Polymerizable Compositions Nr. 7-10

[0193] Additional polymerizable compositions according to the present invention have been prepared using the same components A and B of the compositions 1-3 in combination with the peroxidic initiator BPO (Perkadox CH-50L) and optionally methyl methacrylate as reactive comonomer (component C). The chemical composition of the polymerizable compositions nr. 7-10 is indicated in Table 5.

TABLE-US-00005 TABLE 5 Polymerizable compositions nr. 7-10 according to the invention Composition nr. 7 8 9 10 Component (A) + 98.0.sup.a 96.9.sup.a 88.4.sup.a 83.6.sup.a Component (B) Component (C) 9.8.sup.a 14.8.sup.a (11.09).sup.b (17.70).sup.b Peroxidic 1.9.sup.c 3.0.sup.c 1.7.sup.c 1.5.sup.c initiator (0.97).sup.d (1.55).sup.d (0.87).sup.d (0.86).sup.d UV Absorber 0.1.sup.a 0.1.sup.a 0.1.sup.a 0.1.sup.a Viscosity.sup.e (cSt) 55 55 23.1 15.4 .sup.aweight percentage referring to the total weight of the polymerizable composition; .sup.bConcentration of the comonomer C expressed in phm (parts by weight per 100 parts of the total weight of the components A and B); .sup.cweight percentage of the commercial product Perkadox CH-50L referring to the total weight of the polymerizable composition; .sup.dOverall concentration of peroxide compounds expressed as phm (parts by weight per 100 parts of the total weight of the components A, B and C, where the latter is present; .sup.ecinematic viscosity (before the addition of the initiator) expressed in centiStokes, measured according to ASTM D446.

[0194] The polymerizable compositions Nr. 7-10 were subjected to polymerization by means of thermal treatment in a forced-air-circulation oven, with a gradual temperature rise from 60 C. to 93 C. according to the following curve: initial temperature 60 C.; temperature rise from 60 C. to 78 C. in 12 hours; temperature rise from 78 C. to 93 C. in 4 hours; maintaining at 93 C. for 5 hour.

[0195] At the end of the thermal treatment, the polymerized products (neutral lenses and flat sheets) were recovered from the moulds and heated to 120 C. for hour (in order to decompose the possible residual radical initiator).

[0196] The results of the characterization of the polymerized products are indicated in Table 6.

TABLE-US-00006 TABLE 6 Properties of the polymerized products according to the invention Composizione N 7 8 9 10 Refractive index (n.sup.D.sub.20) 1.502 1.503 1.500 1.500 Yellow index (5 mm) 1.50 2.20 1.30 1.20 Haze, % 0.11 0.14 0.10 0.10 Transmittance, % 93.3 93.2 93.3 93.3 Specific weight, g/cm.sup.3 1.329 1.329 1.316 1.308 Shrinkage, % 10.5 10.5 12.3 13.0 Rockwell hardness 102 103 101 102 (5 mm), M Drop Ball Test (68 g) Passed Passed Passed Passed HDT, C. 75 90 70 66 Bayer Abrasion resistance 1.2 1.0 1.0 0.8 Dyeability: Trasmittance 26 40 29 26 % Colour Yes Yes Yes Yes homogeneity *comparative composition

[0197] The data reported in Table 6 shows that the cured product obtained from the polymerizable composition n. 7 according to the present invention containing reduced amounts of the peroxidic initiator BPO exhibits yellow index values and dyeability properties significantly better compared to those of the cured product obtained from the polymerizable composition n. 8 containing a conventional amount of the same initiator.

[0198] The addition of the reactive comonomer (component C) in the polymerizable compositions n. 9 and 10 allows to operate a further reduction of the concentration of the peroxide initiator, without however substantially altering the properties of the polymerized products, but improving the yellow index.

[0199] The addition of the reactive comonomer, besides further reducing the amount of the radical initiator, has a positive influence on the cost of the polymerizable compositions since it allows to prepare polymerizable compositions containing lower concentrations of components A and B.

[0200] 5. Preparation of Optical Lenses

[0201] Semi-finished optical lenses having a diameter of 80 mm were prepared with the polymerizable composition nr. 3 described in the previous item 3, using moulds having different geometries, assembled with adhesive tape (Okamoto Y1).

[0202] The polymerization was carried out in a forced-air-circulation oven, with a gradual temperature rise from 36 C. to 78 C. in 20 hours according to the following curve: maintaining at 36 C. for 3 hours, temperature rise from 36 C. to 50 C. in 11 hours, temperature rise from 50 C. to 60 C. in 3 hours, temperature rise from 60 C. to 78 C. in 3 hours.

[0203] Some characteristics of the lenses obtained at the end of the polymerization are indicated in Table 7.

TABLE-US-00007 TABLE 7 Polymerizable compositions according to the invention Lens Mould Mould Lens Lens Streaks/ N (base)* opening breakage edge Flow lines 1 cx 6; cc 6 Good No Good Absent 2 cx 6; cc 6 Good No Good Light 3 cx 6; cc 6 Good No Good Absent 4 cx 6; cc 6 Good No Good Absent 5 cx 6; cc 6 Good No Good Absent 6 cx 6; cc 6 Good No Good Absent 7 cx 6; cc 6 Good No Good Absent 8 cx 6; cc 6 Good No Good Absent 9 cx 6; cc 6 Good No Good Absent 10 cx 4; cc 4 Good No Good Absent 11 cx 4; cc 4 Good No Good Absent 12 cx 4; cc 4 Good No Good Absent 13 cx 4; cc 4 Good No Good Absent 14 cx 4; cc 4 Good No Good Absent 15 cx 4; cc 6 Good No Good Absent 16 cx 4; cc 6 Good No Good Absent 17 cx 4; cc 6 Good No Good Absent 18 cx 4; cc 6 Good No Good Absent 19 cx 4; cc 6 Good No Good Absent 20 cx 4; cc 6 Good No Good Absent *cx = curvature of the front half-mould; cc = curvature of the rear half-mould.

[0204] The data of Table 7 shows that, with the polymerizable compositions of the present invention, high-quality lenses substantially free of optical defects such as streaks and flow lines, are easily obtained, also in the presence of a low quantity of radical initiator. The yield of the production process (breakage of lenses) is also good.

[0205] 6. Aging Tests

[0206] The polymerized products obtained from compositions nr. 2 and 3 described in the previous item 3, were subjected to aging tests in order to verify the stability of the properties of the polymerized products with time.

[0207] The polymerized products in the form of flat sheets having a thickness of 5 mm were continuously exposed to the open air for 90 days. The Yellow Index values (YI) of the two products, measured at certain time intervals, are indicated in Table 8 compared with the values measured on the polymerized product obtained starting from the commercial monomer RAV 7AT (composition nr. 5*).

TABLE-US-00008 TABLE 6 Days of exposure 0 24 63 90 Composition 2 1.20 1.18 1.28 1.26 Composition 3 1.30 1.28 1.32 1.30 Composition 5* 1.00 1.08 1.10 1.04 *comparative composition

[0208] The data of Table 6 show that the polymerized products of the present invention have an aging resistance equivalent to that of the commercial homopolymer RAV 7AT.