Curable resin as a substitute for phenolic resins and the applications thereof

Abstract

The invention relates to a curable resin that represents an excellent substitute for phenolic resins and is therefore able to replace phenolic resins in all applications in which they are used. Said resin is characterised in that it comprises: (1) at least one prepolymer resulting from the prepolymerisation of a compound A comprising at least one aromatic or heteroaromatic ring, a first group OCH2-CCH and at least one second group selected from the groups OCH2-CCH2 and CH2-CHCH2, said groups being carried by the at least one aromatic or heteroaromatic ring; and (2) a compound B comprising at least two thiol groups (SH). The invention also relates to a material obtained by curing said curable resin, and in particular to an ablative composite material. The invention further relates to a material obtained by curing said curable resin.

Claims

1. A curable resin, comprising: (1) at least one prepolymer resulting from a polymerization of a compound A, wherein compound A comprises at least one aromatic or heteroaromatic cycle, a first group which is a OCH.sub.2CCH group, and at least one second group which is a OCH.sub.2CCH or CH.sub.2CHCH.sub.2 groups, the first and second groups being borne by the aromatic cycle or heteroaromatic cycle; and (2) a compound B comprising at least two thiol groups, wherein the resin is cured by reacting the prepolymer with compound B.

2. The curable resin of claim 1, wherein compound A is a product of a propargylation of a compound A, wherein compound A comprises at least one aromatic or heteroaromatic cycle, a first group which is a hydroxyl or carboxyl group, and at least one second group which is a hydroxyl, carboxyl or CH.sub.2CHCH.sub.2 group, the first and second groups being borne by the aromatic or heteroaromatic cycle.

3. The curable resin of claim 2, wherein compound A is an allylated monophenol, a polyphenol, a phenolic acid or a polycarboxylic acid with one or more aromatic or heteroaromatic cycles.

4. The curable resin of claim 2, wherein compound A is derived from a biomass.

5. The curable resin of claim 4, wherein compound A is chavicol, eugenol, resorcinol, hydroquinone, pyrocathecol, phloroglucinol, pyrogallol, hydroxyquinol, resveratrol, an allylated monophenol dimer, parahydroxybenzoic acid, gallic acid, an isomer of gallic acid, vanillic acid, salicylic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, protocatechic acid, or an isomer of protocatechic acid.

6. The curable resin of claim 5, wherein compound A is resorcinol, phloroglucinol, gallic acid, pyrogallol, or a eugenol dimer of formula (I): ##STR00002##

7. The curable resin of claim 1, wherein compound B is derived from a biomass.

8. The curable resin of claim 7, wherein compound B is a product of a thiolation of a compound B, wherein compound B is obtained from the biomass and comprises at least a first and a second group selected from hydroxyl and carboxyl groups, and wherein the thiolation consists of replacing a hydrogen atom of the first and second groups with a (CH.sub.2).sub.3SH group.

9. The curable resin of claim 8, wherein compound B is resorcinol, hydroquinone, pyrocathecol, phloroglucinol, pyrogallol, hydroxyquinol, resveratrol, an allylated monophenol dimer, parahydroxybenzoic acid, gallic acid, an isomer of gallic acid, vanillic acid, salicylic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, protocatechic acid or an isomer of protocatechic acid, a lignin or a tannin.

10. The curable resin of claim 9, wherein compound B is resorcinol, phloroglucinol, gallic acid, pyrogallol, a lignin, or a eugenol dimer of formula (I): ##STR00003##

11. The curable resin of claim 1, wherein compounds A and B are derived from a biomass.

12. The curable resin of claim 11, wherein: the prepolymer is a prepolymer of propargylated resorcinol, a prepolymer of propargylated gallic acid, a prepolymer of a propargylated lignin or a prepolymer of a propargylated eugenol dimer, the eugenol dimer being of formula (I): ##STR00004## and compound B is a product of a thiolation of a compound B, wherein compound B comprises at least a first and a second group selected from hydroxyl and carboxyl groups, and is resorcinol, gallic acid, lignin or the eugenol dimer of formula (I), and wherein the thiolation consists of replacing a hydrogen atom of the first and second groups with a (CH.sub.2).sub.3SH group.

13. The curable resin of claim 1, comprising from 80 parts to 95 parts by mass of the prepolymer(s) and 5 parts to 20 parts by mass of compound B.

14. The curable resin of claim 1, further comprising a compound C which is a product of a propargylation of a polyphenol macromolecule derived from a biomass.

15. The curable resin of claim 14, wherein the polyphenol macromolecule is a lignin or a tannin.

16. The curable resin of claim 14 comprising: at least one prepolymer which is a prepolymer of propargylated resorcinol, a prepolymer of propargylated gallic acid or a prepolymer of a propargylated eugenol dimer; a thiolated resorcinol, a thiolated gallic acid, a thiolated lignin or a thiolated eugenol dimer; and a propargylated lignin.

17. The curable resin of claim 14 comprising from 30 parts to 94 parts by mass of the prepolymer(s), from 5 parts to 20 parts by mass of the compound B, and from 1 part to 50 parts by mass of the compound C.

18. A material obtained by curing a curable resin of claim 1.

19. A composite material, comprising a matrix and a reinforcement in the matrix, in which the matrix is obtained by curing a curable resin of claim 1.

20. The composite material of claim 19, wherein the material is an ablative composite material for thermal protection.

21. A curable resin, comprising: (1) at least one prepolymer resulting from a polymerization of a compound A, wherein compound A comprises at least one aromatic or heteroaromatic cycle, a first group which is a OCH.sub.2CCH group, and at least one second group which is a OCH.sub.2CCH or CH.sub.2CHCH.sub.2 group, the first and second groups being borne by the aromatic cycle or heteroaromatic cycle; and (2) a compound B comprising at least two thiol groups, wherein compound B is a product of a thiolation of a compound B, wherein compound B comprises at least a first and a second group selected from hydroxyl and carboxyl groups, and wherein the thiolation consists in replacing a hydrogen atom of the first and second groups with a (CH.sub.2).sub.3SH group; wherein the resin is cured by reacting the prepolymer with compound B.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 illustrates the conditions of the heat treatment that has been applied to resins according to the invention for their curing in the experiments which are reported in Examples 1 to 4 which follow; the temperature, denoted and expressed in C., is indicated on the ordinate axis while the time, denoted t and expressed in hours, is indicated on the abscissa axis.

(2) FIG. 2 illustrates the thermogravimetric analysis curve (or TGA curve) obtained for a sample of a first resin according to the inventionhereinafter called resin R4after curing; the residual mass of the sample, denoted M.sub.r and expressed in % of the initial mass, is indicated on the ordinate axis while the temperature, denoted and expressed in C., is indicated on the abscissa axis.

(3) FIG. 3 illustrates the differential scanning calorimetry curve (or DSC curve) obtained during curing of a sample of the R4 resin (dashed line); for comparison, also shown is the DSC curve obtained, under the same conditions, during the curing of a control sample, which differs from the sample of the resin R4 only in that it does not include the compound B (curve in solid line); the heat flux, denoted and expressed in W/g, is indicated on the ordinate axis while the temperature, denoted and expressed in C., is indicated on the abscissa axis.

(4) FIG. 4 illustrates the conservation module curve, denoted E and expressed in MPa (solid line curve), and the curve of the loss factor or tan (dashed curve) as obtained by dynamic mechanical analysis (or DMA) for a sample of the R4 resin after curing; the conservation modulus and the tan are indicated on the ordinate axes, respectively of left and right, while the temperature, denoted and expressed in C., is indicated on the abscissa axis.

(5) FIG. 5 illustrates the evolution of the dynamic viscosity, denoted and expressed in Pa.s (solid line curve), of the resin R4, as a function of the temperature, denoted and expressed in C. (dashed curve).

(6) FIG. 6 illustrates the evolution of the dynamic viscosity, denoted and expressed in Pa.s, of the resin R4, as measured at the temperature of 55 C., as a function of the shear rate, denoted D and expressed in s.sup.1, which has been applied to it during a charge cycle (x) and a discharge cycle (o).

(7) FIG. 7 illustrates the evolution of the dynamic viscosity, denoted and expressed in Pa.s, of the resin R4, as determined at the temperature of 55 C. and for a shear rate of 10 s.sup.1, as a function of the time, denoted t and expressed in hours.

(8) FIG. 8 illustrates the reaction scheme that has been followed for the preparation of a thiolated resorcinol which is reported in Example 2 below.

(9) FIG. 9 illustrates the TGA curve obtained for a sample of a second resin according to the inventionhereinafter called resin R6after curing; the residual mass of the sample, denoted M.sub.r and expressed in % of the initial mass, is indicated on the ordinate axis while the temperature, denoted and expressed in C., is indicated on the abscissa axis.

(10) FIG. 10 illustrates the DSC curve obtained during curing of a sample of resin R6 (dashed line); for comparison, also shown is the DSC curve obtained under the same conditions, during the curing of a control sample, which differs from the sample of the resin R6 only in that it does not include the compound B (curve in solid line); the heat flux, denoted and expressed in W/g, is indicated on the ordinate axis while the temperature, denoted and expressed in C., is indicated on the abscissa axis.

(11) FIG. 11 illustrates the conservation modulus curve, denoted E and expressed in MPa (solid line curve), and the curve of the loss factor or tan (dashed curve) as obtained by DMA for a sample of the resin R6 after curing; the conservation modulus and the tan are indicated on the ordinate axes, respectively of left and right, while the temperature, denoted and expressed in C., is indicated on the abscissa axis.

(12) FIG. 12 illustrates the evolution of the dynamic viscosity, denoted and expressed in Pa.s (solid curve), of the resin R6, as a function of the temperature, denoted and expressed in C. (dashed curve).

(13) FIG. 13 illustrates the evolution of the dynamic viscosity, denoted and expressed in Pa.s, of the resin R6, as measured at the temperature of 65 C., as a function of the shear rate, denoted D and expressed in terms of s.sup.1, applied to it during a charge cycle (x) and a discharge cycle (o).

(14) FIG. 14 illustrates the evolution of the dynamic viscosity, denoted and expressed in Pa.s, of the resin R6, as determined at the temperature of 65 C. and for a shear rate of 10 s.sup.1, as a function of time, denoted t and expressed in hours.

(15) FIG. 15 illustrates the chemical structures of the propargylated resorcinol, denoted 5, of a phenylpropanoid unit, denoted 6, of a propargylated lignin (the rest of the propargylated lignin being symbolized by the letter L inscribed in a circle), of a propargylated eugenol dimer, denoted 7, and of propargylated gallic acid, denoted 8.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

EXAMPLE 1

Preparation and Characteristics of a First Type of Curable Resins According to the Invention

(16) The present example relates to a first type of resins according to the invention which comprise: a mixture of prepolymers obtained by prepolymerization of propargylated resorcinol (compound A); and pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) as compound B.

(17) 1.1Preparation of the Resins:

(18) *Preparation of Propargylated Resorcinol:

(19) Propargylated resorcinol is prepared according to a protocol based on that described in reference [1] above.

(20) To this end, 100 g of resorcinol (SIGMA-ALDRICH) are solubilized in 1.7 L of N,N-dimethylformamide (DMF) to which 1.27 kg of potassium carbonate (K.sub.2CO.sub.3) are added with mechanical stirring. Then, 115 mL of propargyl bromide in 80% solution in toluene is added to the solution. Mechanical agitation is maintained for 12 hours. After filtration and dilution in ethyl acetate, the medium is washed 3 times with brine and twice with deionized water. The organic phase is dried over anhydrous magnesium sulfate (MgSO.sub.4), filtered and concentrated under reduced pressure. 156 g of resorcinol propargylated, denoted 5 in FIG. 15, are thus obtained (yield: 92%).

(21) *Prepolymerization of Propargylated Resorcinol:

(22) 50 g of the propargylated resorcinol obtained above are introduced into a two-necked 250 ml flask containing a magnetic bar. The flask is surmounted by a water cooler. The medium is subjected to a heat treatment comprising steps of 2 hours at 180 C. separated from each other by a return to ambient temperature under a stream of nitrogen. After 10 stages at 180 C., a viscous material, which is fluidized by raising the temperature, is obtained and which corresponds to a mixture of resorcinol propargyl prepolymers (yield: 100%).

(23) *Mixture of Propargylated Resorcinol Prepolymers and PETMP:

(24) Five resins, hereinafter called R1, R2, R3, R4 and R5 resins, are prepared by adding the mixture of propargylated resorcinol prepolymers obtained above to PETMP (available from SIGMA-ALDRICH), with simple manual stirring and prepolymer ratios of propargylated resorcinol/PETMP of 95/5, 90/10, 85/15, 80/20 and 75/25 respectively.

(25) 1.2Curing of the Resins:

(26) For their curing, samples of the resins R1 to R5 are placed in an oven previously heated to 100 C. and subjected to the heat treatment whose conditions modalities are illustrated in FIG. 1.

(27) As visible in this figure, this heat treatment comprises 7 stages located respectively at 100 C., 120 C., 140 C., 160 C., 180 C., 200 C. and 220 C., each of 2 hours and separated from each other by a rise in temperature of 1 C./minute.

(28) 1.3Coke Rate after Curing:

(29) The coke rates of the resins R1 to R5 after curing are determined by a TGA which is carried out using a TA Instruments Q500 thermogravimetric analyzer and by applying to samples of these cured resins a rise in temperature between room temperature and 900 C., at 5 C. per minute and under nitrogen flow.

(30) For each resin, the coke rate corresponds to the residual mass presented by the sample of this resin at the end of the TGA, expressed as a percentage of the mass initially presented by this sample.

(31) The coke rates thus obtained for the resins R1 to R5 after curing are shown in Table I below while the TGA curve obtained for the resin sample R4 is illustrated in FIG. 2.

(32) TABLE-US-00001 TABLE I Resins Coke rate R1 62% (95/5) R2 58% (90/10) R3 55% (85/15) R4 52% (80/20) R5 49% (75/25)

(33) This table shows that the presence of PETMP up to 20% by mass or less in a resin comprising a mixture of prepolymers of resorcinol propargylated gives a coke rate greater than 50% to the resin after curing.

(34) 1.4Calorimetric Monitoring of Curing:

(35) The influence of the presence of PETMP in the resin R4 on the reactivity of the mixture of propargylated resorcinol prepolymers is assessed by a DSC analysis which is carried out using a Q100 calorimeter from TA Instruments and by subjecting a sample of the uncured R4 resin at a temperature rise between 0 C. and 300 C., at 3 C./minute and under nitrogen flow.

(36) The DSC curve obtained for this sample is illustrated in FIG. 3 (dashed curve). By way of comparison, this figure also shows in the DSC curve obtained, under the same conditions, a control sample comprising the same mixture of propargylated resorcinol prepolymers as the resin R4 but free of PETMP.

(37) This figure shows that the presence of PETMP at a level of 20% by mass in the resin R4 allows the polymerization/crosslinking of the mixture of prepolymers of propargylated resorcinol:

(38) (1) to start at a lower temperature: 110 C. versus 160 C.;

(39) (2) to take place in a wider temperature range: 110-270 C. versus 160 C.-280 C.; and

(40) (3) to have a lower enthalpy: 770 J/g versus 880 J/g.

(41) The presence of PETMP at a level of 20% by mass in the resin R4 thus allows better control of the reactivity of the mixture of propargylated resorcinol prepolymers and a less violent course of the polymerization/crosslinking of this mixture of prepolymers.

(42) 1.5No Runaway During Curing:

(43) No runaway was observed during the curing of resins R1 to R5.

(44) On the other hand, the curing of resins comprising the same mixture of propargylated resorcinol prepolymers as resins R1 to R5 but free of PETMP resulted in runaway, in which case the material chars with strong smoke release.

(45) 1.6Loss of Mass During Curing:

(46) The mass lost by the resin R4 during its curing is determined by subjecting a sample of this resin to a rise in temperature between 100 and 220 C. and comparing the mass of this sample before and after this heat treatment. The mass loss is 10%.

(47) 1.7Glass Transition Temperature:

(48) The glass transition temperature of the resin R4 after curing is determined by a DMA which is carried out by means of a TA Instruments Q800 dynamic mechanical analyzer (simple lever mode, frequency of 1 Hz, amplitude of 30 m) and by subjecting a parallelepipedic sample (17.5 mm2 mm10 mm) of the cured resin R4 to a temperature rise between 0 C. and 350 C. at a rate of 3 C./minute.

(49) The results of this analysis are illustrated in FIG. 4 which shows the conservation modulus curve (solid curve) and the curve of the loss factor or tan (dashed curve) obtained for this sample as a function of temperature.

(50) As shown in this figure, the drop of the conservation modulus of the cured resin R4 occurs at 315 C. The glass transition temperature of this resin is therefore 315 C.

(51) 1.8Rheological Characteristics Before Curing:

(52) Samples of the uncured resin R4 are subjected to rheological measurements which are carried out by means of an ARES rheometer from TA Instruments (cone/plane geometry =50 mm, air gap=50 m) equipped with a calibration system. Peltier effect temperature control (APS from TA Instruments).

(53) The results of these measurements are illustrated in FIGS. 5 to 7 which show:

(54) FIG. 5: the evolution of the dynamic viscosity of the resin R4 (curve in solid line) as a function of the temperature (dashed curve);

(55) FIG. 6: the evolution of the dynamic viscosity of the resin R4 at constant temperature (55 C.) as a function of the shear rate, during a charge cycle (x) and a discharge cycle (o);

(56) FIG. 7: the evolution of the dynamic viscosity of the resin R4 at constant temperature (55 C.) and constant shear rate (10 s.sup.1) as a function of time.

(57) These figures show: on the one hand, that the dynamic viscosity of the resin R4 is less than 2 Pa.s above 39 C. (FIG. 5); on the other hand, that the resin R4 has a Newtonian behavior, i.e. that its dynamic viscosity is independent of the shear rate (FIG. 6); and finally, that the dynamic viscosity of the resin R4 is very stable over time and may be maintained at a value of less than 2 Pa.s for at least 4 hours at a temperature which is below 80 C. (FIG. 7), which makes it possible to envisage a use of this resin in methods for manufacturing composite materials by impregnation without the use of organic solvents.

EXAMPLE 2

Preparation and Characteristics of a Second Kind of Curable Resin According to the Invention

(58) The present example relates to a second type of resin according to the invention, which comprises: a mixture of prepolymers obtained by prepolymerization of resorcinol propargylated (compound A); and thiolated resorcinol as compound B.

(59) 2.1Preparation of the Resin:

(60) The mixture of propargylated resorcinol prepolymers is prepared as described in point 1.1 of Example 1 above while the thiolated resorcinol is prepared according to the reaction scheme illustrated in FIG. 8, which is based on that described in reference [5] above.

(61) *Preparation of Thiolated Resorcinol:

(62) As may be seen in FIG. 8, the first step of this preparation consists in subjecting resorcinol, denoted 1, to an allylation reaction.

(63) To this end, 11.61 g of resorcinol are solubilized in 465 ml of DMF in a 2.5 L reactor whose contents are stirred mechanically. Then, 150 g of K.sub.2CO.sub.3 and 19 ml of allyl bromide are added successively to the medium. The reaction takes place over 12 hours at room temperature. The reaction medium is then diluted in ethyl acetate and filtered. The washing is carried out by extraction with brine and permuted water. The organic phase is dried over anhydrous MgSO.sub.4 and concentrated under reduced pressure. 13.18 g of the compound denoted 2 in FIG. 8 are thus obtained (yield: 66%).

(64) The second step is to subject the compound 2 to a radical addition reaction with thioacetic acid to replace the allyl groups with thioester groups.

(65) To this end, 13.06 g of compound 2 and 5.56 g of azobisisobutyronitrile (AIBN) are solubilized in 59 ml of 1,4-dioxane. The medium is degassed for 40 minutes by bubbling argon in the medium. Excess thioacetic acid (18 mL) is added to the medium left under argon. The temperature is raised to 63 C. After 24 hours of stirring and return to ambient temperature, the medium is diluted in diethyl ether. The organic phase is washed with a solution of saturated sodium bicarbonate (NaHCO.sub.3), with brine and finally with deionized water. After evaporation of the diethyl ether, 15.52 g of the compound denoted 3 in FIG. 8 are obtained in the form of white crystals (yield: 66%).

(66) The third step consists of subjecting the compound 3 to solvolysis in an aqueous-alcoholic medium to transform the two thioester groups into thiol groups.

(67) To do this, 15.50 g of compound 3 are introduced into a 250 ml two-neck flask surmounted by a water cooler. Then, 150 ml of methanol and 18 ml of concentrated hydrochloric acid (HCl) are added to the flask. The medium is placed under magnetic stirring and the temperature is raised to 70 C. for 3 hours. After returning to ambient temperature, 200 mL of chloroform and 200 mL of deionized water are added to the medium. The aqueous phase is extracted 4 times with 200 mL of chloroform. The organic phase fractions are combined and concentrated under reduced pressure.

(68) Thus 8.19 g of a product are obtained (yield: 70%), whose infrared spectrum (which shows the absence of the absorption band of the resorcinol OH groups and the appearance of a signal at 2565 cm.sup.1 indicating the presence of SH groups), elemental analysis (calculated: 55.8% C, 7.02% H, 24.8% S found: 55.6% C, 7.21% H, 24.8% S) and the .sup.13C and .sup.1H NMR spectra confirm that it is indeed thiolated resorcinol, denoted 4 in FIG. 8.

(69) *Mixture of Propargylated Resorcinol Prepolymers and Thiolated Resorcinol:

(70) A resin, hereinafter referred to as resin R6, is prepared by adding the mixture of propargylated resorcinol prepolymers and thiolated resorcinol with manual stirring and in a mass ratio allowing the introduction of a quantity of thiol groups identical to that present in the resin R4 of Example 1 above, which gives a mass ratio of propargylated resorcinol prepolymers/thiolated resorcinol of 79/21.

(71) 2.2Curing of the Resin:

(72) The curing of the resin R6 is carried out under conditions identical to those described in point 1.2 of Example 1 above.

(73) 2.3Coke Rate after Curing:

(74) The coke rate of the resin R6 after curing is determined by subjecting a sample of this cured resin to TGA which is carried out under conditions identical to those described in point 1.3 of Example 1 above.

(75) The TGA curve obtained for the resin R6 sample is illustrated in FIG. 9.

(76) This figure shows that the coke rate of the resin R6 is 54%.

(77) 2.4Calorimetric Monitoring of Curing:

(78) The influence of the presence of thiolated resorcinol in the resin R6 on the reactivity of the mixture of resorcinol propargylated prepolymers may be appreciated by subjecting a sample of uncured resin R6 to a DSC analysis which is carried out under conditions identical to those described in point 1.4 of Example 1 above.

(79) The DSC curve obtained for this sample is illustrated in FIG. 10 (dashed curve). By way of comparison, this figure also shows the DSC curve obtained, under the same conditions, for a control sample comprising the same mixture of propargylated resorcinol prepolymers as the resin R6 but free of thiolated resorcinol.

(80) This figure shows that the presence of thiolated resorcinol at 21% by mass in the resin R6 produces the same effects as those produced by the presence of PETMP in the resin R4.

(81) The presence of thiolated resorcinol at 21% by mass in the resin R6 thus allows better control of the reactivity of the mixture of propargylated resorcinol prepolymers and a less violent course of the polymerization/crosslinking of this mixture of prepolymers.

(82) 2.5No Runaway During Curing:

(83) No runaway was observed during the curing of the R6 resin.

(84) 2.6Loss of Mass During Curing:

(85) The mass lost by the resin R6 during its curing is determined under the same conditions as those previously described in point 1.6 of Example 1 above. The mass loss is 12%.

(86) 2.7Glass Transition Temperature:

(87) The glass transition temperature of the resin R6 after curing is determined by subjecting a sample of this cured resin to a DMA which is carried out under the same conditions as those previously described in point 1.7 of Example 1 above.

(88) The results of this analysis are illustrated in FIG. 11 which shows the conservation modulus curve (solid curve) and the curve of the loss factor or tan (dashed curve) obtained for this sample as a function of temperature.

(89) This figure shows that the drop of the conservation modulus of the cured resin R6 occurs at 312 C. The glass transition temperature of this resin is therefore 312 C.

(90) .2.8Rheological Characteristics Before Curing:

(91) Samples of the uncured resin R6 are subjected to rheological measurements which are carried out using the same apparatus as that described in point 1.8 of Example 1 above.

(92) The results of these measurements are illustrated in FIGS. 12 to 14 which show:

(93) FIG. 12: the evolution of the dynamic viscosity of the resin R6 (curve in solid lines) as a function of the temperature (dashed curve);

(94) FIG. 13: the evolution of the dynamic viscosity of the resin R6 at constant temperature (65 C.) as a function of the shear rate, during a charge cycle (x) and a discharge cycle (o);

(95) FIG. 14: the evolution of the dynamic viscosity of the resin R6 at constant temperature (65 C.) and constant shear rate (10 s.sup.1) as a function of time.

(96) These figures show: on the one hand, that the dynamic viscosity of the resin R6 is less than 2 Pa.s above 51 C. (FIG. 12); on the other hand, that the resin R6 has a Newtonian behavior (FIG. 13); and finally, that the dynamic viscosity of the resin R6 is very stable over time and may be maintained at a value of less than 2 Pa.s for at least 4 hours at a temperature which is below 80 C. (FIG. 14).

EXAMPLE 3

Preparation and Characteristics of a Third Kind of Curable Resin According to the Invention

(97) The present example relates to a third type of resin according to the invention, which comprises: a mixture of prepolymers obtained by prepolymerization of propargylated resorcinol (compound A); and a thiolated lignin as compound B.

(98) 3.1Preparation of the Resin:

(99) The mixture of propargylated resorcinol prepolymers is prepared as described in point 1.1 of Example 1 above while the thiolated lignin is prepared following a protocol based on that described in reference [5] above.

(100) *Preparation of Thiolated Lignin:

(101) The first step of this preparation is to subject a lignin to an allylation reaction.

(102) To do this, 40 g of a lignin (Kraft Indulin AT lignin) are solubilized in 800 ml of a solution of sodium hydroxide (NaOH) at 0.5 mol/L in a reactor equipped with a lid allowing the passage of a stirring blade and the installation of a water cooler. Then 62 ml of allyl bromide are added and the temperature of the medium is raised to 60 C. for 4 hours. After stopping the stirring, the majority of the allylated lignin is in the form of sediments while the still dispersed allyl lignin may be recovered by centrifugation. The allylated lignin thus obtained is then washed with osmosis water until neutrality of the washing water. It is then lyophilized.

(103) The infrared spectrum of this lignin shows a decrease in the signal associated with the OH groups at 3450 cm.sup.1 and the appearance of a new absorption band at 3078 cm.sup.1 corresponding to the functionalization of part of the lignin OH groups by allyl groups (CH.sub.2CHCH.sub.2).

(104) .sup.31P NMR analysis after derivatization of the lignin with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (TMDP) indicates that the aromatic OH groups of the lignin were quasi-quantitatively functionalized: 3.7 mmol of aromatic OH groups/g of lignin before allylation versus 0.4 mmol of remaining aromatic OH groups/g of lignin after allylation.

(105) The second step is to subject the allylated lignin to a radical addition reaction with thioacetic acid in order to replace the allyl groups in thioester groups.

(106) To this end, 10 g of dried allylated lignin are solubilized in 50 ml of 1,4-dioxane using a vortex mixer. Then, 2 g of AIBN are solubilized in 21 ml of 1,4-dioxane and added to the allylated lignin solution. Oxygen is removed from the reaction chamber by bubbling argon in the solution for 40 minutes. After addition of 20 ml of thioacetic acid, the medium is heated to 70 C. for 24 hours under an inert atmosphere. The product is then recovered by precipitation in a large volume of diethyl ether, filtered and immediately dispersed in a saturated solution of NaHCO.sub.3. The thioesterified lignin thus obtained is washed to neutrality of the washing water and freeze-dried.

(107) The infrared spectrum of this lignin shows the disappearance of the signal at 3078 cm.sup.1 and the appearance of a very intense aborption band at 1689 cm.sup.1 corresponding to the presence of the thioester groups.

(108) The third step is to subject the thioesterified lignin to deprotection to convert the thioester groups to thiol groups.

(109) To do this, 8.16 g of this lignin are solubilized in 75 ml of DMF with vortex stirring. The solution is degassed by bubbling argon in the medium. Then, 3.3 mL of acetic acid and 2.8 mL of hydrazine monohydrate are introduced successively and dropwise. After stirring for 1 hour, the thiolated lignin may be precipitated in a large volume of water and washed with osmosis water.

(110) The infrared spectrum of this lignin shows the disappearance of the signal centered at 1689 cm.sup.1 as well as the appearance of an absorption band at 2564 cm.sup.1 attributed to the presence of thiol groups. Elemental analysis indicates that the mass percentage of sulfur is 11% versus 1.5% for raw lignin before any modification.

(111) *Mixture of Propargylated Resorcinol Prepolymers and Thiolated Lignin:

(112) A resin, hereinafter referred to as R7 resin, is prepared by adding the mixture of propargylated resorcinol prepolymers to the thiolated lignin, with simple manual stirring and in a mass ratio of prepolymers of resorcinolpropargylated/thiolated lignin of 86/14.

(113) 3.2Curing of the Resin:

(114) The curing of the resin R7 is carried out under conditions identical to those described in point 1.2 of Example 1 above.

(115) 3.3Characteristics of the Resin:

(116) The resin R7 is subjected to analyses to determine its coke rate after curing, its loss of mass during curing and its glass transition temperature, which is carried out in the same way as described in points 1.3, 1.6 and 1.7. of Example 1 above.

(117) The results are shown in Table II below.

(118) TABLE-US-00002 TABLE II Coke rate 62% Loss of mass 4% Glass transition temperature >330 C.

EXAMPLE 4

Preparation and Characteristics of a Fourth Type of Curable Resin According to the Invention

(119) The present example relates to a fourth type of resin according to the invention, which comprises: a mixture of prepolymers obtained by prepolymerization of propargylated resorcinol (compound A); PETMP as compound B; and a propargylated lignin as compound C.

(120) 4.1Preparation of the Resin:

(121) The mixture of propargylated resorcinol prepolymers is prepared as described in point 1.1 of Example 1 above while the propargylated lignin is prepared as described below.

(122) *Preparation of Propargylated Lignin:

(123) 20.1 g of lignin (Kraft Indulin AT lignin) are solubilized in 400 ml of a 0.5 mol/l NaOH solution. Then 22 ml of propargyl bromide in 80% solution in toluene are added to the solution and the temperature of the medium is raised and maintained at 75 C. for 4 hours. The propargylated lignin is then recovered by centrifugation and washed with osmosis water until neutrality of the washing water. It is then lyophilized.

(124) The infrared spectrum of this lignin, denoted 6 in FIG. 15, shows the appearance of the characteristic signals of the alkyne function at 3283 cm.sup.1 and 2120 cm.sup.1. A .sup.31P NMR analysis after derivatisation by the TMDP shows that the aromatic groups of the lignin have been modified in a quasi-quantitative manner: 3.7 mmol of aromatic OH groups/g of lignin before propargylation versus 0.5 mmol of remaining aromatic OH groups/g of propargylated lignin.

(125) *Mixture of Propargylated Resorcinol Prepolymers, Propargylated Lignin and PETMP:

(126) A resin, hereinafter referred to as resin R8, is prepared by adding the mixture of propargylated resorcinol prepolymers and propargylated lignin to PETMP after fine grinding of the propargylated lignin to ensure homogeneous dispersion thereof, with simple manual stirring in a mass ratio of propargylated resorcinol prepolymers/PETMP/propargylated lignin of 75/10/15.

(127) 4.2Curing of the Resin:

(128) The curing of the resin R8 is carried out under conditions identical to those described in point 1.2 of Example 1 above.

(129) 4.3Characteristics of the Resin:

(130) The resin R8 is subjected to analyses to determine its coke rate after curing, its mass loss during curing and its glass transition temperature, which is carried out in the same way as described in points 1.3, 1.6 and 1.7. of Example 1 above.

(131) The results are shown in Table III below.

(132) TABLE-US-00003 TABLE III Coke rate 58% Loss of mass 4% Glass transition temperature >330 C.

EXAMPLE 5

Preparation of a Propargylated Eugenol Dimer Useful as Compound A According to the Invention

(133) *Preparation of the Eugenol Dimer of Formula (I) Above:

(134) The eugenol dimer is prepared by metathesis of eugenol according to a protocol based on that described in reference [4] above.

(135) To do this, 24 ml of eugenol (SIGMA-ALDRICH) are placed in the presence of 0.530 g of Grubbs first-generation catalyst, under an inert atmosphere and magnetic stirring, at room temperature. Once the medium has become thicker and frozen, the system is placed under reduced pressure (100 kPa) for 48 hours. The solid obtained is solubilized in 1l of a 1 mol/l aqueous NaOH solution and filtered on celite to remove the catalyst. The filtrate is acidified by adding concentrated HCl until precipitation of a pale gray solid. The solid is collected by filtration on a Bchner funnel and washed with deionized water until neutrality of the washing water. The product is then dispersed in a minimum volume of a water-ethanol mixture (50:50 v/v), solubilized by raising the temperature (40 C.) and then placed at 5 C. until precipitation. The solid obtained is filtered on a Bchner funnel and washed with water-ethanol solution. The recovered compound is solubilized in dichloromethane and washed with water. The organic phase is concentrated under reduced pressure to obtain 3.0 g of eugenol dimer (yield: 13%).

(136) *Propargylation of Eugenol Dimer:

(137) 1.5 g of the eugenol dimer is solubilized in 24 ml of DMF in which 7.5 g of K.sub.2CO.sub.3 are introduced with magnetic stirring. Then 1.2 ml of propargyl bromide in 80% solution in toluene is then introduced. Magnetic stirring is maintained for 12 hours. After filtration and dilution in ethyl acetate, the medium is washed 3 times with brine and twice with deionized water. The organic phase is dried over MgSO.sub.4, filtered and concentrated under reduced pressure.

(138) There is thus obtained 1.62 g of propargylated eugenol dimer, denoted 7 in FIG. 15 (yield: 86%).

EXAMPLE 6

Preparation of Propargylated Gallic Acid Useful as Compound A According to the Invention

(139) 5.0 g of gallic acid (SIGMA-ALDRICH) are solubilized in 317 ml of DMF in which 101 g of K.sub.2CO.sub.3 are introduced with magnetic stirring. Then, 32.7 mL of propargyl bromide in 80% solution in toluene is added to the solution. Magnetic stirring is maintained for 12 hours. After filtration and dilution in ethyl acetate, the medium is washed 3 times with brine and twice with deionized water. The organic phase is dried over MgSO.sub.4, filtered and concentrated under reduced pressure.

(140) 7.4 g of propargylated gallic acid, denoted 8 in FIG. 15 are thus obtained (yield: 78%).

REFERENCES CITED

(141) [1] M. C. Joshi et al., Bioorg. Med. Chem. Lett. 2007, 17(11), 3226-3230 [2] WO-A-2006/044290 [3] WO-A-01/071020 [4] H. E. Blackwell et al., J. Am. Chem. Soc. 2000, 122, 58-71 [5] S. Chatani et al., Macromol. 2014, 47(15), 4894-4900