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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 4 2023 63
ISSN 0005-2531 (Print)
UDC 54.057
SYNTHESIS AND PROPERTIES OF BROMINE-CONTAINING BICYCLIC
UNSATURATED POLYESTERS
A.M.Mustafayev\ Y.N.Gahramanli2, B.N.Babanly2, RXIsmailova1
institute of Polymeric Materials, Ministry of Science and Education of the Republic of Azerbaijan Azerbaijan State Oil and Industry University
Received 01.02.2023 Accepted 14.03.2023
A method for obtaining bromine-containing bicyclic unsaturated polyesters by the interaction of 1,4,5,6,7,7-hexabromobicyclo-[2,2,1]-hept-5-ene-2,3-dicarboxylic acid anhydride, propanetriol and ma-leic anhydride was developed. It was found that unsaturated polyethers synthesized by a two-step method have a higher molecular weight (3130), density (1.461 g/cm3), viscosity (105 St) and ether number (400 ml KOH/g). It was found that the compositions of epoxy resin ED-20 with unsaturated polyether obtained by method III possess higher tensile strength (90 MPa), higher relative elongation (9%), higher Vicat resistance (2500C) than unmodified epoxy resin. It was shown that in comparison with pure epoxy resin ED-20, its composition with unsaturated polyester synthesized by method I and cured in the presence of polyethylene polyamine (ED-20: unsaturated polyester: polyethylene polyamine), has flame retardant properties, high tensile strength, higher relative elongation and thermal resistance by Vicat. The best results are achieved when the content of unsaturated polyester in the composition is 20%.
Keywords: 1,4,5,6,7,7-hexabromobicyclo-[2,2,1]-hept-5-ene-2,3-dicarboxylic acid anhydride, propanetriol, maleic anhydride, epoxy resin ED-20, styrene.
doi.org/10.32737/0005-2531-2023-4-63-70 Introduction
In modern times, the demand for polymer materials with high operational properties is constantly increasing, and this problem is solved by the synthesis of new high-molecular compounds or chemical modification of the known polymers, development of various composite materials on the basis of them. Among these polymers, unsaturated polyesters are in the center of attention due to their high mechanical properties, adhesion ability, chemical stability, etc. So, they have found wide application as a binding component for obtaining various paint materials, glues, casting and hermetic compositions [1-13].
Unsaturated polyester resins are generalpurpose thermosetting materials that are synthesized by the curing reaction of a mixture of precursors from unsaturated polyesters and styrene [14]. These materials are widely used in electronics, marine, aerospace, automotive and load-bearing structures due to their high adhesion, chemical resistance, low cost and high
processability [15-17]. Despite this, the good flammability of thermosetting materials severely limits their application in some engineering applications, such as electronic equipment and instruments [18]. Due to the increasing degree of commercial application of thermosetting materials, the development of new flame retardant and self-extinguishing systems to reduce the flammability of polyester resins has attracted increasing attention in recent years.
The synthesis of cyclic unsaturated polyesters containing hydrocarbon fragments and the study of fire-retardant materials based on them are of both scientific and practical interest [19-26]. Currently, close attention is being paid to the research of chlorine-free flame retardant thermosetting resins. For example, bromine [25, 26], metal hydroxide [27], boron [28], silicon [29], nitrogen [30] and phosphorus [31, 32] containing flame retardants. Among these different flame retardants, one of the promising ways to improve the fire resistance of thermo-setting materials is the addition of phosphorus-
containing flame retardants because of their environmental friendliness and excellent catalytic charring properties of polyester resins. Pan et al. [33] included ammonium polyphosphate (APP) and triphenyl phosphate (TPP) in thermosetting materials based on unsaturated polyester resins. The results showed that this flame retardant system mainly plays a role in the condensed phase, and the decomposition of APP and TPP produced phosphoric acid and polyphosphoric acid, which effectively contributed to the cross-linking and barrier layer. However, as electronic devices become miniaturized and mutually integrated, the effectiveness of the flame retardant requires further improvement [34]. In this regard, it was decided to study brominated un-saturated polyethers and their properties.
The paper was dedicated to the development of a method for obtaining bicyclic unsatu-rated polyesters containing many bromine atoms and the study of the methods for using them as modifiers in ED-20 epoxy resin.
Experimental part
1,4,5,6,7,7-hexabromobicyclo-[2.2.1]-hept-5-ene-2,3-dicarboxylic acid anhydride was synthesized by the known method and it was determined that physical-chemical properties correspond to the literature data.
Synthesis of polyester of a, co-maleinate-(bis-propionate)hexabromobicyclo[2.2.1]-hept-5-ene-2,3-dicarboxylic acid.
38 g (0,06 mole) hexabromobicyclo [2.2.1]-hept-5-ene-2,3-dicarbonic acid anhydride + 12 g (0.13 mol) propanetriol, 6 g (0.06 mol) ma-leic anhydride, 100 ml o-xylene, 1 g hydroqui-none are placed into a four-necked reaction flask equipped with a mechanical stirrer, thermometer, counter-cooler, Dean-Stark apparatus and a glass tube through which nitrogen gas is released. The reaction mixture is stirred rapidly and heated. At this time, water releases as a result of the reaction at 115-1200C. A sample of the reaction mixture is taken in every 30 minutes, titrated by 0,1N solution of KOH and acid number is determined.
The reaction is completed when water release is stopped and acid number makes up 4050 mg KOH/g.
Further, the reaction mixture is washed and dried by MgSO4. Solvent is fed by a water pump
(31-320C/mm) and 150 g (81%) of a,ra-maleinate-(bis-propionate)hexabromobicycle-[2.2.1]-hept-5-ene-2,3-dicarboxylic acid unsatu-rated polyester is obtained.
Modification of ED-20 epoxy resin by the synthesized polyester.
2.8 g of synthesized polyester, 2.14 g of maleic anhydride are added to a chemical beaker. The mixture is heated until melting. 100 g of ED-20 epoxy resin and 0.1 g of dimethylaniline are added and heated to 80-850C in a water bath. The mixture is poured into a mold. First of all, the mold is kept at room temperature for 12 hours, then heated step by step at 800C for 12 hours, at 1200C for 89 hours and finally at 1500C for 8 hours. Obtained samples are subjected to physical-mechanical testing and the average value is taken in Table 5.
Result and discussion
The methods of obtaining of bromine- and maleate fragments-containing bicyclic unsaturat-ed polyester by polycondensation of propanetri-ol, maleic anhydride and 1,4,5,6,7,7-hexabromo-bicyclo-[2.2.1]-hept-5-ene-2,3-dicarboxylic acid anhydride (BED-anhydride) obtained by the condensation of maleic anhydride with hexa-bromocyclopentadiene via Diels-Alder reaction were developed [20].
Unsaturated polyester was synthesized using 3 methods [21, 22]. According to the first method, BED-anhydride, propanetriol and ma-leic anhydride are mixed in a 0.5:1.1:0.5 mol ratio in a reaction flask and heated at 160-1800C in nitrogen gas medium.
The unsaturated polyester obtained by this method possesses a regular structure, because maleic anhydride is more active than BED-anhydride, and the amount of maleate fragments in the obtained polyester is high, but the amount of BED-anhydride fragments is little. Besides that, the maleate fragment is more likely to be located in the center of the molecule
[22, 24]. According to the second method unsaturated polyester is synthesized by two stages. In the first stage, oligoester (II) containing only hydroxyl group at the end of the molecule is
synthesized by mixing maleic anhydride and propanetriol in a ratio of 1.1:0.5 mol and heating in toluene medium:
.CO
Hor°H + C >
H
OH
OOC - CH = CH -co
OH
OH
ai)
The oligoester (II) obtained by the second containing fragment in the center of the molestage reacts with BED anhydride as a diol and cule and hexabromine bicycloheptene fragment as a results of the reaction the unsaturated poly- at the edge of the molecule: ester (III) is obtained. It contains maleate-
H
OH
o
OOC - CH = CH -CO
OH
Br*
OH +
.o
o
o o
OH
—c c—o-s ^ooc-ch = ch-co-o-s o—c <:—
J n
OH o
(HI)
The essence of the third method is that in this case the process is carried out by two stages too. In the first stage, by heating of propanetriol and BED anhydride in a xylene medium in a
0.5:1.1 mole ratio an oligoester (IV) with a hy-droxyl group at the end of the molecule is obtained:
HO. HO
OH +
H
oA0_
OH
OH (IV)
The oligoester (IV) synthesized in the second stage, reacts with maleic anhydride as a diol and as a results of the reaction the unsatu-rated polyester (V) of a regular structure con-
of the molecule and maleic fragment at the edge of the molecule is obtained:
Solution of synthesized unsaturated polyesters in styrene may be stored for a long time.
taining BED anhydride fragment in the center The reaction of copolymerization (solidification) of styrene with unsaturated polyester was
studied. It is known from the literature that unsaturated polyesters and styrene are easily co-polymerized in the presence of radical-forming catalysts.
Benzoyl peroxide was used during the copolymerization reaction between the synthesized unsaturated polyester and styrene. The copolymerization reaction is carried out in the following way. Unsaturated polyester and styrene (30%) are mixed, then 3% of benzoyl peroxide and 5% of dimethylaniline are added to the mixture, mixed and poured into special molds. The obtained specimens, at first, are heated at room temperature for 24 hours, then at 800C for 8 hours and finally at 1200C for 4
Table 1. Physicochemical properties of unsaturated polyesters
hours. The kinetics of styrene copolymerization reaction with unsaturated polyesters was studied. Such kinetic parameters of copolymerization reaction of unsaturated polyester with styrene as activation energy, reaction order and the amount of heat released in the reaction (Q) were determined by differential thermal analysis (Table 2).
Study of the DTA curve shows that the reactions carried out on the basis of one-step or two-step polycondensation are both the first order reactions. However, the activation energy and the amount of released heat are different. These indicators are clearly shown in Table 2.
(V)
Unsaturated polyesters Molecular weight n 20 nD d420 Ester number ml.KOH/g Viscosity, 200C, St Acid number, ml. KOH/g
One-step (the I method) 1830 1.5510 1.0800 300 50 60
Two-step (the II method) 2030±50 1.5070 1.0993 320 68 55
Two-step (the III method) 3130 1.5610 1.4610 400 105 43
*30% styrene solution was determined.
Table 2. Some kinetic parameters of copolymerization reaction
Unsaturated polyesters Reaction order Activation energy, kJ/mol Heat release, GJ/g
One-step (the I method) 1.09 36 88
Two-step (the II method) 1.26 78.21 290.8
Two-step (the III method) 1.17 77.31 290.8
H-
OH o
A 1
Br,
OH
OH
,co
/ "CO
o o
II II
-C-CH=CH -c
OH o
A 11
Br,
o
II c
A II II
—öS ^o-c-ch=ch-c----
OH o
Physicochemical properties of obtained unsaturated polyesters are set into Table 1.
Table 3. Thermal properties of the obtained compositions
Unsaturated polyesters EXP decomposition energy, J/mole Half-life period of decomposition, / min. Thermogravimetric index, 0C
(the I method) 179.2 57.2 106
(the II method) 176.3 55.6 100
(the III method) 172.4 55.8 99
Epoxy resin + polyethylene polyamine 198.53 60.8 127
Table 4. Physical-mechanical properties of the obtained compositions
Properties Unsaturated polyesters Unmodified epoxy resin
I II III
Tensile strength, MPa 80 85 90 43
Relative elongation, %, during tensile 5 7 9 1.8
Thermal resistance according to Vicat, 0C 200 230 250 91
Brunel hardness, MPa 50 57 65 -
As is evident from Table 2, activation energy of the one-step polycondensation reaction is equal to 36 kJ/mole and it's less than activation energy of the two-step 2nd and 3rd methods. The low activation energy is related to structure. The presence of such a difference also becomes apparent at releasing of the heat. It should be noted that there are many maleate residues in the oligoester chain obtained by one-step polycondensation. Therefore, it interacts very actively during the copolymerization reaction.
In order to study of plasticizing and self-extinguishing properties of synthesized unsatu-rated polyesters in epoxy resins composition their modification was carried out.
10, 20 and 30% mixtures based on unsaturated polyester: epoxy resin: polyethylene polyamine were prepared, poured into a glass, and then 14% polyethylene polyamine was added to them at room temperature. The mixtures were poured into special molds to get the composition and stored at room temperature for one day. Then the mixtures were heated at 800C for 6 hours and at 1200C for 4 hours. After complete solidification, the mixtures were removed
from the mold and physical-mechanical properties were determined. The 20% mixture had the best result.
Heat stability, decomposition energy and half-life decomposition period of the obtained compositions were studied by derivatography. Thermophysical characteristics of the compositions are represented in Table 3.
As is evident from the Table, decomposition energy and half-life decomposition period of the composition obtained by the solidification of polyethylene polyamine and epoxy resin is higher than the decomposition energy and half-life decomposition period of the compositions obtained on the basis of unsaturated polyester and epoxy resin. Physical-mechanical properties of compositions obtained on the basis of the synthesized unsaturated polyesters and epoxy resin are shown in Table 4. As is seen from the table, when modifying, the obtained compositions have high physical-mechanical properties due to good solubility of unsaturated polyesters in epoxy resin. Tensile strength, relative elongation, heat resistance and strength of the obtained compositions are higher than unmodified epoxy resin.
Table 5. Physical-mechanical properties of solidified compositions
ED-20 polyester:solidifier (PEPA) Tensile strength, MPa Relative elongation, % Thermal resistance to Vicat, 0C Combustion duration, sec
Modifier 90:10:20 80 7 135 extinguishes
80:20:20 110 15 155 extinguishes
70:30:20 86 10 130 extinguishes
ED-20+PEPA 37 1.8 90 extinguishes
As a result of the experiments, it's concluded that unsaturated polyesters may be used as modifier-plasticizers in epoxy resins due to the functional groups (C=O, -CH=CH-, etc.) contained in the unsaturated polyesters.
A chemical reaction occurs between the functional groups and the epoxy resin during the modification and as a result of the reaction the cross-linked insoluble polymers are obtained.
Thus, it should be noted that unsaturated polyesters synthesized on the basis of BED anhydride, propanetriol, and maleic anhydride may be used as a self-extinguishing component in epoxy resins.
Fire resistant properties of the compositions obtained by solidification were also studied. Fire resistant property of the samples was determined by "Fire-Tube" method. As a result of the experiments, it was determined that the tested samples possess self-extinguishing property [25, 26].
It was determined that physical-mechanical properties of the composites based on the synthesized polyester (I) are superior than physical-mechanical properties of the composites based on the pure ED-20 epoxy resin.
It's evident, that physical-mechanical properties of the obtained composites have higher results due to the chemical reactions occurring between polyester and epoxy resin ED-20 during solidification.
Physical-mechanical parameters of the composition solidified in the presence of unsaturated polyester PEPA were shown in Table 5.
An appropriate amount of the modifier (I) and ED-20 epoxy resin were taken in a chemical beaker, then heated at 40-500C until becoming a homogeneous mass and mixed well. It was cooled to room temperature, then PEPA is added and mixture is mixed well. Obtained mass is poured into molds. Solidification time made up 24 hours at room temperature, 6 hours at 800C, 4 hours at 1200C and 2 hours at 1400C. Obtained specimen was removed from the mold and studying its physical-mechanical properties was carried out.
Solidification degree of the composition was determined by extraction in acetone for 6-8
hours in a Soxhlet apparatus. Thus, it should be noted that solidification degree of the samples made up 98-99%.
Synthesized a, ra-maleate-(bispropanate hexabromo)-bicyclo-[2,2,1]-hept-5-ene-2,3-dicarbonate unsaturated polyester is well soluble in ED-20 epoxy resin by heating up to 60-650C and forms a polymer composition with high physico-mechanical properties.
The results of the carried out experiments prove that physical-mechanical properties of the compositions based on synthesized unsaturated polyester and PEPA are superior to properties of the compositions based on ED-20 epoxy resin and PEPA.
It was determined that although the amount of modifier is 10, 20, 30% in all samples, but the best result is obtained at 20% content of modifier.
Conclusions
A method of obtaining of unsaturated polyester contains a bicyclic fragment and bromine atoms and based on hexabromobicyclo-[2.2.1]-hept-ene-2,3-dicarboxylic acid anhydride and maleic anhydride was developed and physicochemical properties were studied.
Solidification of the obtained unsaturated polyester by styrene was studied by deri-vatographic method and some kinetic regularities were calculated.
The obtained unsaturated polyester was tested as self-extinguishing modifier in ED-20 resin and it was determined that the obtained compositions possess high physical-mechanical and self-extinguishing properties.
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BROM TORKÎBLi BiTSiKLiK DOYMAMI§ POLiEFiRLORiN SiNTEZi VO XASSOLORi
A.M.Mustafayev, Y.N.Qahramanh, B.N.Babanli, R.i.ismayilova
1,4,5,6,7,7-heksabrombitsiklo-[2,2,1]-hept-5-en-2,3-dikarboksil turçusunun anhidridinin, propantriolun va malein anhidridinin reaksiyasi naticasinda brom tarkibli bitsiklik doymamiç poliefirlarin alinmasi üsulu içlanib hazirlambdir. Müayyan edilib ki, iki marhalali üsul ila sintez olunmuç doymamiç poliefirlar daha yüksak molekul çakisina (3130), sixliga (1,461 q/sm3), özlülüya (105 St) va efir adadina (400 ml KOH/q) malikdir. Müayyan edilib ki, modifikasiya olunmamiç epoksid qatrani ila müqayisada, III-cü üsul ila sintez olunmuç doymamiç poliefirlarin ED-20 epoksid qatram ila olan kompozisiyasi daha yüksak dartilmada möhkamlik haddina (90 MPa), nisbi uzanmaya (9%) va Vika üzra termiki stabilliya (2500C) malikdir. Göstarilib ki, tamiz ED-20 epoksid qatranindan farqli olaraq, onun polietilen poliaminin içtirakmda barkimiç va I-ci üsula göra sintez olunmuç doymamiç poliefir ila olan kompozisiyasi (ED-20:doymamiç poliefir:polietilen poliamin) oddan qoruyucu xassalara, yüksak dartilmada möhkamlik haddina, daha yüksak nisbi uzanma va Vika üzra termiki davamliliga malikdir. Kompozisiyada doymamiç poliefirin miqdari 20% saviyyasinda olduqda an yaxçi naticalar alda olunur.
Açar sözlzr: 1,4,5,6,7,7-heksabrombitsiklo-[2,2,1]-hept-5-en-2,3-dikarboksil turçusunun anhidridi, propantriol, malein anhidridi, epoksid qatrani ED-20, stirol
