Method of producing a thermally rearranged PBX, thermally rearranged PBX and membrane

Abstract

A method of producing a thermally rearranged polybenzoxazole, polybenzimidazole or polybenzothiazole (collectively denominated TR PBX), thermally arranged PBX and membranes including the same.

Claims

1. A method of producing a thermally rearranged polybenzoxazole, polybenzimidazole or polybenzothiazole (TR PBX), including the following method steps: preparing a polyimide or aromatic polyamide as a precursor polymer in a solution, wherein in each recurring monomer unit of the precursor polymer an aromatic ring is located adjacent to the nitrogen atom of the imide group or amide group of the monomer unit, wherein in some or all of the recurring monomer units the aromatic ring is functionalized with an XR group as a side chain at the ortho-position to the nitrogen atom, wherein XO, N or S; and performing a thermal treatment to carry out a thermal rearrangement resulting in the thermally rearranged polybenzoxazole, polybenzimidazole or polybenzothiazole, wherein R is an allyl group or an allyl-based group, wherein a processing temperature used during the thermal treatment for the thermal rearrangement is in a range of 0 C. and 350 C.

2. The method according to claim 1, wherein the allyl-based group is a group of the chemical formula CR.sub.1R.sub.2CR.sub.3CR.sub.4R.sub.5, wherein R.sub.1to R.sub.5 each is a hydrogen atom or a homo- or hetero-aliphatic or -aromatic structure, wherein at least one of R.sub.1 to R.sub.5 is a homo- or hetero-aliphatic or -aromatic structure.

3. The method according to claim 2, wherein each of the groups R.sub.1 to R.sub.5 may have up to 20 atoms.

4. The method according to claim 1, wherein a degree of functionalization is between 0.1% and 100%.

5. The method according to claim 1, wherein the precursor polymer is a polyimide synthesized through a reaction between a dianhydride and a diamine, through a reaction between a dianhydride and a diisocyanate or through the ester-acid route with a silylation pre-treatment.

6. The method according to claim 5, wherein the precursor polymer is synthesized through use of solid state thermal imidization, solution thermal imidization or chemical imidization.

7. The method according to claim 5, wherein 3,3-dihydroxy-4,4-diamino-biphenyl (HAB) is used as diamine and/or 2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) is used as dianhydride.

8. The method according to claim 1, wherein the functionalization with an allyl-group or an allyl-based group is performed on a monomer unit before polymerization, during polymerization or on the precursor polymer.

9. The method according to claim 1, wherein at least one of a functionalization agent and an activating agent is introduced during the step of preparing a polyimide or aromatic polyamide as a precursor polymer in a solution.

10. The method according to claim 9, wherein the functionalization agent is allyl halide and/or wherein the activating agent is K.sub.2CO.sub.3.

11. The method according to claim 1, characterized in that a solid-state object is produced from the precursor polymer solution prior to the thermal treatment and the thermal treatment resulting in the thermally rearranged polybenzoxazole, polybenzimidazole or polybenzothiazole is carried out on the solid-state object.

12. The method according to claim 11, wherein the solid-state object is a film.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described below, without restricting the general intent of the invention, based on exemplary embodiments, wherein reference is made expressly to the drawings with regard to the disclosure of all details according to the invention that are not explained in greater detail in the text. The drawings show:

(2) FIG. 1 a schematic representation of the production of a PBX by way of thermal rearrangement, according to the prior art,

(3) FIG. 2 a schematic representation of a known production of a TR-polymer,

(4) FIG. 3 different routes for obtaining conventional and functionalized TR PBO,

(5) FIG. 4 a schematic representation of an inventive route for the production of a TR-polymer,

(6) FIG. 5 a schematic representation of a possible inventive rearrangement process,

(7) FIG. 6 different routes for obtaining conventional and functionalized TR PBO from PHA,

(8) FIG. 7A and FIG. 7B idealized and measured TGA data on unmodified and functionalized PBO,

(9) FIG. 8 FTIR spectra of different unmodified and functionalized PBO and

(10) FIG. 9A-9D thermal characterization of unmodified and functionalized PBO,

(11) FIG. 10A-10D TGA measurements of various unmodified and functionalized PBO,

(12) FIG. 11 the synthesis of PBO derived from 6FDA-BisAPAF,

(13) FIG. 12 the synthesis of PBO derived from BTDA-BisAPAF and

(14) FIG. 13 the synthesis of PBO derived from PMDA-BisAPAF.

DETAILED DESCRIPTION

(15) FIGS. 1 and 2 show the known path for obtaining PBX from precursor polyimides according to H. B. Park et al., Science, 2007, and were explained above. In FIG. 3, this known reaction corresponds to the route A-A1, arriving at the unmodified TR PBO.

(16) The skilled person will understand that multiple routes may be used. For example, several methods are possible to prepare polyimides, among them the reaction between a dianhydride and a diamine and the reaction between a dianhydride and a diisocyanate. The substitution can take place in other positions and even multi-substitutions.

(17) Four exemplary synthesis procedures for obtaining inventively functionalized TR PBO are shown in FIG. 3, namely according to the routes a. A-A1-B1-functionalized TR PBO, b. A-B-B1-functionalized TR PBO, c. A-B-B1-C1-functionalized TR PBO and d. A-B-C-C1-functionalized TR PBO. In each case in the exemplary embodiment of FIG. 3, the starting monomers are 3,3-dihydroxy-4,4-diamino-biphenyl (HAB)

(18) ##STR00001##
and 2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)

(19) ##STR00002##

(20) In order to obtain the functionalized polymers, shown in FIG. 4, the reaction is carried out either on the monomers (routes B and C in FIG. 4, same as routes B to D in FIG. 3) or on the polymer (route A of FIG. 3, same as route A of FIG. 4).

(21) The thermal rearrangement temperature for the PBX production may be lowered even if the Claisen rearrangement has already taken place and the moiety facing the imide group is XH (X being O, N or S), as in compound C1 of FIG. 3 or route C of FIG. 4. There are two possible reasons for this. The first idea is that the oxygen is already activated (like O) and then it is easy to start the process. The second possibility is that when the allyl chain moves to the aromatic ring, the flexibility of the polymers changes. It is then more flexible so that the glass transition temperature Tg of the polymer is lower. In that case, the thermal rearrangement process occurs at lower temperatures. Thereby the rearrangement occurs at lower temperatures while the separation properties of the materials are kept, since the main chain of the polymer is not or hardly changed. In addition, the amount of modification needed is low.

(22) As an example, the reaction described in FIGS. 3 and 4 uses allyl-bromide (AllylBr) as functionalization agent. Furthermore, an activating agent, for example K.sub.2CO.sub.3 is added, and the temperature is raised to 60 C. Then, the corresponding amount of the allyl-derivate is added, and the reactions are left to complete for 24 hours, resulting in an ortho-functionalized poly(amic acid). Chemical or thermal imidization leads to ortho-functionalized polyimide which then is thermally rearranged to PBO.

(23) The steps of the Claisen rearrangement of the allyl group in the case of an aromatic polyimide monomer unit functionalized according to the present invention are shown in FIG. 5. In the beginning, the oxygen and allyl group form an open ring with the phenyl ring which is prone to electron hopping, affording the oxygen atom with a double electron binding to the aromatic ring, whereas the allyl group is bound to the next carbon atom of the aromatic ring. The following steps complete the rearrangement in the course of which the two oxygen atoms of the imide group are lost and a heterocycle oxazole ring is formed on the homocyclic aromatic ring. Here, the allyl group serves as a catalyst for the formation of the benzoxazole unit.

(24) FIG. 6 shows an alternative route, starting from 2,2-Bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (bisAPAF) and terephthaloyl chloride monomers. In this case, it is the OH-moieties of bisAPAF that are functionalized with allyl groups. Thermal cyclodehydration of the functionalized polyhydroxyamide (PHA) leads to the creation of the functionalized PBO, with allyl groups present at the homocyclic rings of the benzoxazole units.

(25) FIG. 7A shows an idealized version of a TGA (thermogravimetric analysis) scan of a polymer that is thermally rearranged and degraded in two different temperature ranges. This is described in the above-mentioned Calle et al., Polymer 53 (2012) reference, where three temperatures with significant changes in the first slope in the TGA curve are defined. T.sub.TR1 is the initial temperature of the weight loss defining the temperature at which polymer chains start the cyclization process. T.sub.TR2 is the temperature at the maximum point of weight loss or maximum amount of CO.sub.2 evolution and T.sub.TR3 is the final temperature, end of the weight loss, marking the completion of the rearrangement process. The degradation starts quantitatively at even higher temperatures.

COMPARISON EXAMPLE 1

(26) An example of this procedure is described below. A polyhydroxyimide (PHI) of the general structure

(27) ##STR00003##
was prepared by a precursor polyamic acid of the general structure

(28) ##STR00004##
formed from the reaction of the previously shown monomers 3,3-dihydroxy-4,4-diamino-biphenyl (HAB) and 2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA).

(29) HAB and dry N-methyl-2-pyrrolidone (NMP) (15 wt %) were added to a flame-dried 3-neck flask equipped with a mechanical stirrer, a 2-purge, and a condenser. The HAB was dissolved in the NMP solvent, and the resulting solution cooled to 0 C. Then an equimolar amount of a representative dianhydride-6FDA, and solvent was added, giving a 15% (w/v) mixture. The mixture was stirred and gradually heated to room temperature, forming a poly(amic acid).

(30) The imidization route followed in this case was the solution thermal imidization. To achieve this, a co-solvent was added to the reaction solution (ortho-xylene) and the temperature of the solution raised to 180 C. for 6 hours to complete the imidization. Once the polymer was imidized completely, the polyimide was precipitated in water. The solid was washed three times in methanol/water solutions, recovered by vacuum, filtered, washed with methanol and dried under vacuum at 160 C. for 24 hours.

(31) The obtained pristine polymer was named 6FDA-pHAB or 6FDA-HAB.

EXAMPLE 1

(32) In this example, allyl-bromide was used as functionalization agent. The reaction conditions were similar to those of Comparison Example 1 in all cases. Once the monomer or polymer was dissolved in dimethylformamide (DMF), an activating agent, for example K.sub.2CO.sub.3, was added and the temperature raised to 60 C. Then, the corresponding amount of the allyl-derivate was added and the reactions were left to complete for 24 hours. The process was followed by thin layer chromatography (TLC).

(33) After the reaction was completed, the reaction solution was cooled down to room temperature and then precipitated in water. The solid was washed at least 3 times in methanol/water solutions, vacuum filtered, washed with methanol and dried under vacuum at 160 C. for 24 hours. The nomenclature used herein for the precursor polymer thus obtained is 6FDA-HAB-allyl, the general monomer unit structure of which is

(34) ##STR00005##

(35) The examples were prepared following route A of FIG. 4, wherein the polymer was functionalized as was explained previously. After the functionalization reaction, the polymer was dissolved in N,N-dimethylacetamide (DMAc) and cast as a film for testing and different thermal treatment purposes.

(36) In a series of experiments, different samples of the obtained film were in turn heated up to

(37) 160 C. to eliminate the main part of the solvents from the membranes (6FDA-pHAB-allyl-160 C);

(38) 200 C., 12 hours under vacuum to activate the Claisen rearrangement and to begin the rearrangement in at least some groups in the polymer (6FDA-pHAB-allyl-200 C);

(39) 250, 12 hours under vacuum (6FDA-pHAB-allyl-250 C);

(40) 251 275 C., 1 hour in a furnace under Argon flux (6FDA-pHAB-allyl-275 C);

(41) 300, 1 hour in a furnace under Argon flux (6FDA-6FpDA-allyl-300 C);

(42) 301 325 C., 0.5 hours in a furnace under Argon flux (6FDA-pHAB-allyl-325 C); and

(43) 350 C., 5 minutes in a furnace under Argon flux (6FDA-pHAB-allyl-350 C).

(44) Outlay of Experimental Testing of Example 1

(45) The inventive samples were tested in two different ways. A well-known system was selected (6FDA-pHAB) and the results compared with those found in references in the literature, a. o. those published in D. F. Sanders et al., Gas permeability, diffusivity, and free volume of thermally rearranged polymers based on 3,3-dihydroxy-4,4-diamino-biphenyl (HAB) and 2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), Journal of Membrane Science 409 (2012) 232-241, representing the pristine, i.e., unmodified, polymer used in Example 1 of the present application.

(46) At first, the polymer structure and physical behaviour was characterized. The structural characterization was conducted with the techniques of nuclear magnetic resonance (.sup.1H-NMR, .sup.13C-NMR) and spectroscopy (FT-IR). By NMR the formation of functionalization in the samples was confirmed. The structures with and without functionalization were compared using FTIR, and it was possible to determine the degree of functionalization in the same way that it was described in previous works. The amount of the conversion was determined by following the peaks at 1255 cm.sup.1 (CF bonds that are thermally stable and do not change during the thermal treatments), 1778 cm.sup.1 (CO stretching in imide I), 1720 cm.sup.1 (asymmetric CO stretching, imide I) and 1380 cm.sup.1 (CNC stretching, imide II). Following a formula mentioned by the group of Professor Freeman in US 2012/0305484 A1 it was possible to determine the amount of conversion. The imide I and imide II are two different vibrational modes in the imide group.

(47) Physico-chemical properties were studied by differential scanning calorimetry (DSC) experiments, and extensively thermogravimetric analysis (TGA). By analysing the DSC results the glass transition temperature (Tg) of the polymers treated at different temperatures was determined. This technique was not considered crucial for the determination, but was used complementary.

(48) By TGA, the thermal stability was determined along with the effect of different thermal treatments followed by the determination of degree of rearrangement for the samples treated at different temperatures (160, 200, 250, 275, 300, 325, and 350 C.).

(49) Three different experimental protocols were followed. The first one was the analysis of the thermal stability of the samples. In this case, the rearrangement temperature for the unmodified and functionalized polymers was determined. The difference between the pristine polymer and the functionalized samples was significant. For the unmodified samples the process begins at temperatures around 350 C., and the maximum weight lost can be found at temperatures around 450 C., while for the functionalized samples the process starts at temperatures around 200 C. and the maximum weight loss was around 340 C. In both cases the resulting PBO starts degradation above 500 C.

(50) The second one was the isothermal treatment for different temperatures in order to fully understand the mechanism the rearrangement followed and calculate the degree of conversion. The time of treatment was constant.

(51) The last experiment was the analysis of the thermal stability of the samples after the corresponding thermal treatments. In this case, it was possible to determine the amount of polyimide remaining in the polymers by following the weight loss.

(52) The second way to characterise the samples was by analyzing the separation properties of the samples. The results obtained at different temperatures and for degree of conversion to PBOs were compared with the ones of previous works found in the literature.

(53) Results for Example 1

(54) FTIR and TGA for all the samples were measured in order to determine the degree of conversion of the aromatic polyimide to PBO.

(55) In FIG. 7B, the rearrangement temperatures for the unmodified and functionalized polymers are presented. For the samples treated at 160 C. there was some solvent remaining as the solvent (DMAc) has a boiling point of 165 C., causing the first knee in the curve. Beyond 200 C. effectively all DMAc is evaporated.

(56) The further differences between the unmodified and functionalized samples are very clear. For the unmodified or pristine sample (6FDA-HAB) the rearrangement process begins at 350 C. and the maximum weight loss is around 450 C., overlapping with the degradation which starts even below 500 C. For the functionalized samples (6FDA-HAB-allyl) the rearrangement starts shortly over 200 C. and finishes at 340 C. The steepest slope is observed around 360 C. for the functionalized polymer and at 450 to 460 C. in the pristine polymer. The thermal stability of the resulting PBO remained similar in both cases; the main degradation temperature could be found above 500 C. in both cases.

(57) FIG. 8 depicts the FTIR spectra for samples treated at different temperatures. It was possible to determine the amount of the conversion by following the peaks at 1255 cm.sup.1 for normalization (CF bonds that are thermally stable and do not change during the thermal treatments), 1778 cm.sup.1 (CO stretching in imide I), 1720 cm.sup.1 (asymmetric CO stretching in imide I) and 1380 cm.sup.1 (CNC stretching in imide II). These bands decrease with temperature according to the progressing conversion of the imide to benzoxazole units. The further bands that are observed and marked up are other typical vibrational modes occurring in the polymer which strengthen or disappear with progressing functionalization.

(58) From these measurements, it was possible to determine the extent of conversion (rearrangement) following a formula put forward in US 2012/0305484 A1, the entire content is incorporated herein by reference. For this, the observed weight loss is compared with a theoretically calculated weight loss representing 100% conversion. Furthermore, all monomers and polymers are suitable for allyl-functionalization according to the present invention, under the premise that R mentioned therein is replaced by an allyl group or an allyl based group.

(59) FIGS. 9A to 9D illustrate the results for the TGA experiments. Different experimental protocols for TGA were carried out. The first one was the analysis of the thermal stability of the samples, i.e., the residual mass of the polymer was measured as a function of time at various fixed temperatures (isotherms).

(60) A first set of TGA measurements is presented in FIGS. 9A and 9B for the pristine polymer (FIG. 9A) and the functionalized polymer (FIG. 9B). These figures show the weight loss as a function of the time at one specific temperature. These isotherms were measured at different temperatures in order to follow the rearrangement process and calculate the degree of conversion. The isotherms were carried out at different temperatures for a constant period of time of more than 13 hours (800 minutes).

(61) During the process, the pristine polymer is expected to suffer a loss of 14.096% of weight until completing a full rearrangement, i.e., changing from polyimide to PBO. The functionalized polymer is expected to lose 13.246% of weight. In this way it is possible to estimate the percentage of rearrangement for each thermal treatment by subtracting the measured percentage of weight loss from the initial weight. It is also possible to identify completion of the conversion when 100% conversion is reached.

(62) In FIGS. 9A and 9B, the order of the curves is the same as in the inlays. The first step in all curves corresponds to the reimidization of the polymers and the weight loss is similar for all the samples (close to 4%). The beginning of the curves shows a loss of weight that is due to other factors, so this is taken into account by adding this initial percentage of lost weight (2-3% due to solvents a.o.) to the total. In FIG. 9A, for the pristine polymer, and FIG. 9B, for the functionalized polymer, the weight loss for the samples can be compared. It is observed, e.g., that at the 350 C. isotherm the pristine polymer has the same weight loss as the functionalized polymer at 250 C., indicating that the functionalized polymer rearranged at much lower temperatures. This is the similar for the other isotherms. The effect is especially important for the last temperatures, 450 and 350 C., respectively. In the 450 C. isotherm of the pristine polymer, a rapid decrease in the weight due to the degradation in the polymer is observed, while for the functionalized polymer the same weight loss is achieved at lower temperature and the degradation process does not occur. This stability in the 350 C. isotherm of the functionalized polymer after less than two hours indicates higher stability and less amount of oxidation.

(63) From these curves, the degree of conversion from polyimide to polybenzoxazole may be analyzed. It is possible to calculate the theoretical one and then estimate the real one. It was shown that for the functionalized polymer, 350 C. for the complete conversion while for the pristine polymer 450 C. are needed.

(64) Results of a second type of measurements are present in FIGS. 9C and 9d). After producing the isothermals of FIGS. 9A and 9B, a normal thermogravimetric characterization, namely TGA measurements with temperature ramp-up were performed on the same samples that were isothermally treated for 12 hours at different temperatures. The results are shown for the pristine polymer in FIG. 9C and for the functionalized polymer in FIG. 9D. Herein, the order of the curves is inverse to that in the inlays, i.e, the highest isotherm temperatures correspond to the uppermost curves. Those curves that are designated no thermal treatment underwent the 160 C. pretreatment regime.

(65) The TGA curves in FIGS. 9C and 9D range from room temperature to 800 C. for the samples treated with different temperature protocols to different functionalization extents. As can be discerned from FIG. 9D, those functionalized samples that underwent isotherm pretreatment at elevated temperatures are stable up to the degradation temperature. Others that were pretreated at 250 C. or 275 C. experience some residual rearrangement under loss of CO.sub.2. In this case, it was also possible to determine the amount of polyimide remaining in the polymers by following the weight loss.

(66) The curves of FIG. 9C show that only those samples that were pretreated at at least 400 C. are thermally stable up to degradation temperature, whereas those that were pretreated at 350 C. or lower exhibit the mass loss due to rearrangement above 400 C. It is clearly visible that the rearrangement temperatures differ from FIG. 9C (pristine polymer) to FIG. 9D (allyl-functionalized polymer) by between 50 C. and 100 C.

(67) In a comparison between the theoretical weight loss for the thermal rearrangement and the weight loss that was found, the degree of conversion can be estimated. In this context, the deviation from the first part of the isotherm in FIGS. 9A and 9B can be eliminated. It is observed that no more weight loss was found for the functionalized sample treated at 350 C., since the conversion was already completed. Another important finding is that, although the temperature for the rearrangement is lower, the thermal stability is the same. After the conversion, both samples (pristine and functionalized) start to degrade at temperatures above 500 C.

(68) Comparing the obtained results with the results from the existing bibliography, it is possible to observe that with the inventive functionalization similar conversion degrees can be obtained at temperatures between 100 C. and 200 C. lower. E.g., for the functionalized sample treated at 350 C., the degree of conversion was higher than 90%, while for the pristine polymer at the same thermal treatment, the conversion was 11%. A similar degree of conversion was only obtained when the pristine polymer was thermally treated at 450 C.

(69) Even a small amount of modification with functional units can result in the reduction of the rearrangement temperature. This behaviour indicates that the Claisen rearrangement occurring between the allyl attached to the O in ortho-position and the aromatic ring works catalytically for the system rearrangement. Recent experiments eliminate the possibility of the rearrangement occurring via an intermolecular reaction mechanism and are consistent with an intramolecular process denominated [3,3]-electrocyclic reaction. This mechanism produces an activation of the oxygen in ortho-position so that the rearrangement of the polyimide to polybenzoxazole occurs at lower temperatures.

(70) The required temperatures are affected by the structure of the polymers, solvent and degree of functionalization, among other factors. The formation of a double bond attached to the aromatic ring after the Claisen rearrangement probably also favours the process. This functional group may be able to delocalize the charge around the aromatic ring, thereby possibly reducing the rearrangement temperature.

(71) The behaviour was confirmed by checking permeability properties of the functionalized samples. Table 1 shows the results for the permeability of the samples. It is simple to observe that at lower temperatures, separation properties are similar than for the samples in the bibliography, e.g., those published in D. F. Sanders et al., Gas permeability, diffusivity, and free volume of thermally rearranged polymers based on 3,3-dihydroxy-4,4-diamino-biphenyl (HAB) and 2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), Journal of Membrane Science 409 (2012) 232-241, representing the pristine, i.e., unmodified, polymer used in the first example of the present application. In fact, similar permeabilities and higher selectivities were found.

(72) The D. F. Sanders reference results for the PHI 6FDA-HAB precursor polymer are abbreviated by FG (Freeman's group) in the following, followed by the treatment temperature used to initiate the thermal rearrangement. The results for the inventively functionalized precursor polmyer 6FDA-HAB-allyl are named Modified PHI, followed by the pretreatment temperature.

(73) TABLE-US-00001 TABLE 1 Permeability Selectivity (Barrer) (dimensionless) Sample H.sub.2 O.sub.2 CO.sub.2 O.sub.2/N.sub.2 CO.sub.2/CH.sub.4 FG (300 C.) 11 0.64 2.9 6.4 48.3 FG (350 C.) 55 3.9 17 6.3 65.4 FG (400 C.) 115 13 58 4.8 38.7 FG (450 C.) 155 21 95 4.7 31.4 Modified PHI (200 C.) 47 3.48 15 7.0 48.9 Modified PHI (250 C.) 41 3.2 13.9 5.9 47.0 Modified PHI (350 C.) 130 18 83 5.6 35.8

(74) A very important effect has to be taken in account: this reduction on the rearrangement temperatures produces at the same time samples with wonderful separation properties and excellent mechanical properties. This effect could be observed in the samples, and explained by TGA. As it was shown, the rearrangement finishes at temperature much lower than degradation temperatures. In this way, the degradation process is not initiated, and the samples are stable, living up to their full capacity.

(75) The inventive method to obtain low temperature rearrangement from ortho-functional polyimide can be applied to all the structures precursor of thermally rearrangement polymers, understanding by this, all kinds of structure capable of reorganizing (as much in solid and in solution).

FURTHER EXAMPLES

(76) FIGS. 10A to 10D show TGA measurements for four different pristine and functionalized polybenzoxazoles, of which the functionalized version in each case is an example according to the present invention.

(77) FIG. 10A shows a TGA temperature scan for pristine and functionalized PBO derived from 6FDA-HAB after thermal treatment at 350 C. for 12 hours, as described in Example 1 above. This precursor corresponds to precursor compound A1 in FIG. 3, whereas the pristine PBO corresponds to final compound A1 in FIG. 3 and the functionalized PBO to the Modified TR PBO derived from B1 in FIG. 3.

(78) Low-level thermal rearrangement can be observed in the functionalized PHI at a temperature as low as ca. 200 C., picking up pace at higher temperatures. Thermal rearrangement is finished at slightly above 400 C. Thermal degradation does not set in until ca. 500 C. The temperature ranges of thermal rearrangement and thermal degradation have no significant overlap in this case.

(79) In contrast, the curve for the pristine PHI only bends down above ca. 430 C., directly connecting to the even steeper slope of thermal degradation. The temperature ranges of thermal rearrangement and thermal degradation overlap significantly in this case.

EXAMPLE 2

(80) FIG. 10B shows TGA temperature scan results for a pristine and a functionalized precursor PHI which were obtained according to the method described above in Example 1 and Comparison Example 1, but with 2,2-Bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (BisAPAF) instead of HAB. All other reaction parameters were kept the same. The poly(hydroxyimide) precursor is called 6FDA-BisAPAF.

(81) The reaction path is shown in FIG. 11, leading to a functionalized PBO after a functionalization with AllylBr, and to a pristine PBO without the functionalization step.

(82) The TGA scans of the pristine and functionalized PHI in FIG. 10B show that the thermal rearrangement sets in gradually in the pristine case, whereas in the functionalized case, the steep slope causes the function to arrive at a plateau at about 400 C. No such plateau is seen in the pristine case.

(83) As in the case of Example 1 in FIG. 10A, the temperature ranges of thermal rearrangement and thermal degradation have no significant overlap in case of functionalized 6FDA-BisAPAF, while they overlap significantly for the unmodified 6FDA-BisAPAF.

EXAMPLE 3

(84) FIG. 10C shows TGA temperature scan results for a pristine and a functionalized precursor PHI which were obtained according to the method described above in Examples 1 and 2 and Comparison Example 1. In contrast to Example 2, the dianhydride is 3,3,4,4-benzophenone tetracarboxylic dianhydride (BTDA). All other reaction parameters were kept the same. The intermediate poly(hydroxyimide) is named BTDA-BisAPAF.

(85) The reaction path is shown in FIG. 12, leading to a functionalized PBO after a functionalization with AllylBr, and to a pristine PBO without the functionalization step.

(86) The TGA scans of the pristine and functionalized PHI in FIG. 10C show that the thermal rearrangement sets in earlier (ca. 260 C.) in the functionalized case than in the pristine case (ca. 320 C.). Both cases develop a plateau-like shallow slope leading into the steep slope of thermal degradation. However, the temperature ranges of thermal rearrangement and thermal degradation have less overlap in case of functionalized BTDA-BisAPAF than in the case of the unmodified BTDA-BisAPAF.

EXAMPLE 4

(87) FIG. 10D shows TGA temperature scan results for a pristine and a functionalized PHI which were obtained according to the method described above in Examples 1, 2 and 3 and Comparison Example 1. In contrast to Examples 2 and 3, the dianhydride is pyromellitic dianhydride (PMDA). All other reaction parameters were kept the same. The intermediate poly(hydroxyimide) is named PMDA-BisAPAF.

(88) The reaction path is shown in FIG. 12, leading to a functionalized PBO after a functionalization with AllylBr, and to a pristine PBO without the functionalization step.

(89) The TGA scans of the pristine and functionalized PHI in FIG. 10D show that the thermal rearrangement sets in earlier (ca. 230 C.) in the functionalized case than in the pristine case (ca. 330 C.). Both cases develop a plateau-like shallow slope leading into the steep slope of thermal degradation. However, the temperature ranges of thermal rearrangement and thermal degradation have much less overlap in case of functionalized PMDA-BisAPAF than in the case of the unmodified PMDA-BisAPAF.

(90) The comparison of the TGA scan results shown in FIGS. 10A, 10B, 10C and 10D with each other shows that in each case, weight loss indicating the thermal rearrangement towards the final PBO sets in and is concluded substantially earlier in the functionalized PBO than in the pristine product. FIG. 10B shows the smallest observed temperature difference, but the slope of the weight loss curve in the functionalized case is much steeper than in the pristine sample, indicating that the completion of the thermal rearrangement still occurs at lower temperatures than in the unmodified case.

(91) This slope of the curve could be an indication to how rapidly the thermal rearrangement takes place. The steeper the slope, the more rapidly the thermal rearrangement is carried out.

(92) Accordingly, in each example according to the present invention, the TGA scan of the functionalized PHI shows a plateau which is much more pronounced than in the corresponding unmodified PHI, indicating that there is much less overlap between the temperature ranges for thermal rearrangement on the one hand and thermal degradation on the other hand, showing a benefit of the inventive method in a wide variety of compounds.

(93) All named characteristics, including those taken from the drawings alone, and individual characteristics, which are disclosed in combination with other characteristics, are considered alone and in combination as important to the invention. Embodiments according to the invention can be fulfilled through individual characteristics or a combination of several characteristics. Features which are combined with the wording in particular or especially are to be treated as preferred embodiments.