Synthesis of Poly(1,3,4-oxadiazole-amide-ester) - Nature

Polymer Journal, Vol. 38, No. 9, pp. 940–948 (2006) #2006 The Society of Polymer Science, Japan

Synthesis of Poly(1,3,4-oxadiazole-amide-ester)s and Study of the Influence of Conformational Parameters on their Physical Properties Ion SAVA,1; y Inga R ONOVA,2 and Maria BRUMA1 1

2

‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Iasi 700487, Romania ‘‘Nesmeyanov’’ Institute of Element-Organic Compounds, Moscow 119991, Russia (Received May 15, 2006; Accepted June 8, 2006; Published August 4, 2006)

ABSTRACT: Aromatic poly(1,3,4-oxadiazole-amide-ester)s have been synthesized by low temperature solution polycondensation reaction of equimolar amounts of aromatic diamines containing preformed 1,3,4-oxadiazole rings with diacid chlorides containing preformed ester linkages. The polymers showed high thermal stability with initial decomposition temperature being above 365 C and glass transition temperature in the range of 215–260 C. The weight average molecular weight was in the range of 91,000–257,000 and polydispersity is in the range of 1.64–5. The polymer films showed good mechanical properties with tensile strength in the range of 40–91 MPa, elastic modulus in the range of 2.22–3.98 GPa and elongation at break in the range of 1.85–7.37%. Conformational parameters of polymers have been calculated by Monte Carlo method with allowance for hindered rotation and discussed in relation with some physical properties. [doi:10.1295/polymj.PJ2006033] KEY WORDS Poly(1,3,4-oxadiazole-amide-ester)s / Thermal Stability / Thin Films / Mechanical Properties / Conformational Parameters /

Fully aromatic poly(1,3,4-oxadiazole)s form a class of high performance polymers that are designated for use in small quantities, but with very high endvalue.1,2 High performances include electronic properties, electric conduction, optical properties, good hydrolytic stability, highly ordered systems, mechanical resistance and high thermal stability. But the applicability of these polymers is limited because they have rigid molecules due to the delocalization of -electrons along the polymer chain, which makes them insoluble in organic solvents and without glass transition or with too high glass transition temperature, and therefore their processing is very difficult. Research of poly(1,3,4-oxadiazole)s has considerably extended in the last years as can be seen from the large number of publications. Most of this research aims to improving solubility and processability of aromatic polyoxadiazoles by introduction of certain substituents on aromatic rings, flexible bridges in the chain like ether, amide, ester, isopropylidene, hexafluoroisopropylidene or voluminous units pendent to the chain, provided that the conjugation is not disturbed.3–10 We considered that the incorporation of ester together with amide groups in the macromolecular chain of aromatic poly(1,3,4-oxadiazole)s would result in products with enhanced solubility in organic solvents and reasonable glass transition temperature values, while maintaining a high thermal stability. Here we report the synthesis of poly(1,3,4-oxadiazole-amideester)s by solution polycondensation reaction of variy

ous aromatic diamines containing 1,3,4-oxadiazole ring with diacid chlorides containing preformed ester groups. We studied their thermal stability, glass transition, mechanical properties, weight average molecular weight, solubility, and film forming ability and have been compared these properties with those of related polymers. Also, some physical properties of these polymers such as solubility, glass transition temperature and initial decomposition temperature have been discussed in relation with the conformational rigidity of their chains and some relationships have been shown. EXPERIMENTAL Starting Materials N-methylpyrrolidinone (NMP) (Merck) was dried over phosphorous pentoxide and distilled under reduced pressure. Thionyl chloride (Riedel de Haen) was freshly distilled before use. 4-Hydroxybenzoic acid, 3-hydroxybenzoic acid, p-aminophenol, m-aminophenol, terephthalic acid and isophthalic acid were provided by different commercial sources and used as received. Aromatic Diamines, I 2,5-Bis(p-aminophenoxy-phenyl)-1,3,4-oxadiazole (Ia) and 2,5-bis(m-amino-phenoxy-phenyl)-1,3,4-oxadiazole (Ib) have been synthesized by starting from 4-fluorobenzoic acid that reacted with hydrazine hy-

To whom correspondence should be addressed (Tel: +40 232 217454, Fax: +40 232 211299, E-mail: [email protected]).

940

Synthesis and Properties of Poly(1,3,4-oxadiazole-amide-ester)s

N PPA

COOH + H2N NH2 .H2O

2F

F

N

C

F

C O 2 HO

Ar

NH2

NMP, K2CO3 o

180 C

N H2N Ar O

N

C

C

O Ar NH2

O I Ia: Ar =

;

Ib: Ar =

N 2 H2N

COOH + H2N NH2 .H2O

PPA

H2N

N

C

C

NH2

O Ic

Scheme 1. Synthesis of aromatic diamines containing 1,3,4-oxadiazole rings, I.

2 HO - Ar - COOH

+

ClOC - Ar' - COCl

SOCl2 HOOC - Ar - OOC - Ar' - COO - Ar - COOH - SO2 II' - HCl ClOC - Ar - OOC - Ar' - COO - Ar - COCl II II'a; IIa: Ar = II'b; IIb: Ar =

; Ar' = ; Ar' =

Scheme 2. Synthesis of the diester-diacid chlorides, II.

drate in polyphosphoric acid to give 2,5-bis(p-fluorophenyl)-1,3,4-oxadiazole which further reacted with p- or m-aminophenol, respectively, following the reaction sequence shown in Scheme 1, according to the method previously reported.11 The resulting diamines Ia and Ib were recrystallized from ethanol. mp Ia: 225–227 C; 1 H NMR (DMSO-d6 , 400 MHz, ppm): 8.00 (d, 4H); 7.02 (d, 4H); 6.85 (d, 4H); 6.67 (d, 4H); 5.09 (s, 4H); mp Ib: 190–192 C; 1 H NMR (DMSOd6 , 400 MHz, ppm): 8.08 (d, 4H); 7.16 (d, 4H); 7.08 (t, 2H); 6.45 (d, 2H); 6.33 (s, 2H); 6.25 (d, 2H); 5.33 (s, 4H). 2,5-Bis(p-aminophenyl)-1,3,4-oxadiazole (Ic) has been prepared by the reaction of p-aminobenzoic acid with hydrazine hydrate in polyphosphoric acid (PPA), according to a published method.12 It was rePolym. J., Vol. 38, No. 9, 2006

crystallized from ethanol. mp: 259–262 C; 1 H NMR (DMSO-d6 , 400 MHz, ppm): 7.87 (d, 4H); 6.78–6.63 (d, 4H); 4.64 (s, 4H). The values of the melting points of these three diamines were identical with those reported in the literature.12,13 Diacid Chlorides with Ester Groups, II The diacid chlorides containing ester groups namely isophthaloyl-bis(4-oxybenzoyl-chloride), IIa, and terephthaloyl-bis(3-oxybenzoyl-chloride), IIb, were prepared by treating with thionyl chloride the corresponding diester-dicarboxilic acids, II0 a and II0 b, which had been obtained from the reaction of 4hydroxybenzoic acid or 3-hydroxybenzoic acid with terephthaloyl- or isophthaloyl chloride, respectively, by following a procedure previously reported (Scheme 2).14,15 The diacid chlorides IIa and IIb were recrystallized from chloroform. mp of IIa: 208–210 C; 1 H NMR (DMSO-d6 , 400 MHz, ppm): 8.60 (s, 1H); 8.36 (d, 4H); 8.10 (d, 2H); 7.48 (m, 1H); 7.31 (d, 4H); mp IIb: 239–241 C; 1 H NMR (DMSO-d6 , 400 MHz, ppm): 8.35 (d, 4H); 7.92 (m, 2H); 7.90 (s, 2H); 7.64 (d, 4H). The values of the melting points were identical with those reported in the literature.15 Synthesis of the Polymers The poly(1,3,4-oxadiazole-amide-ester)s III have been prepared by low temperature solution polycondensation reaction of equimolar amounts of different aromatic diamines I with diacid chlorides incorporating ester linkages IIa and IIb in N-methylpyrrolidinone (NMP) as a solvent using pyridine as acid accep941

I. S AVA, I. R ONOVA, and M. B RUMA N

H2N

Ar

N

C

Ar

C

NH2 + ClOC

Ar

OOC

O N

Ar

COO

Ar

COCl

II

I OCHN

Ar'

N

C

Ar

C

NH OC

Ar'

OOC

Ar"

COO

Ar'

O

n

III

IIIa: Ar =

O

Ar' =

Ar" =

IIIb: Ar =

O

Ar' =

Ar" =

Ar' =

Ar" =

IIIc: Ar = IIId: Ar =

O

Ar' =

Ar"=

IIIe: Ar =

O

Ar' =

Ar" =

Ar' =

Ar" =

IIIf: Ar =

Scheme 3.

Synthesis of the polymers, III.

tor, as shown in Scheme 3. Part of the resulting polymer solution was cast into thin films and heated gradually from 80 C to 220 C to evaporate the solvent and the other part of polymer solution was poured into water to precipitate the solid polymer. Preparation of Thin Films Approximately 10 mL of polymer solution as resulted from the polycondensation reaction were cast onto glass plates (100 mm 100 mm) and dried gradually in an oven at 80 C, 120 C, 160 C and 220 C, each for 1 h. The resulting films were stripped off the plates by immersion in water followed by drying in a vacuum oven at 105 C. Films of various thicknesses from 20 to 40 mm, were thus prepared and were used afterwards for measurements. Measurements Melting points of the monomers were measured on a Melt-Temp II (Laboratory Devices) apparatus without correction. The 1 H NMR spectra were recorded on a Bruker Avancel DRX 400 spectrometer at 400 MHz for solution in dimethylsulfoxide-d6 using tetramethylsilane as internal standard. Inherent viscosities were determined at 20 C for solutions of polymers (0.5 g/dL) in NMP, using an Ubbelohde viscometer. The IR spectra were recorded on a Perkin-Elmer spectrometer using polymer films of 5–6 mm thickness or KBr pellets. Thermogravimetric analysis (TGA) was performed on a MOM-type Derivatograph made in Budapest, Hungary, operating in air at a heating rate of 942

12 C/min. The glass transition temperature (Tg ) was measured on a Mettler DSC 12E apparatus in nitrogen with a heating rate of 20 C/min. The mid-point of the inflection curve resulting from the typical second heating cycle was assigned as the Tg of polymers. Model molecules for a polymer fragment were obtained by molecular mechanics (MM+) by means of the Hyperchem program, Version 6.16 The same program was used to visualize the structures obtained after energy minimization. The calculations were carried out with full geometry optimization (bond lengths, bond angles and dihedral angles). X-Ray diffraction experiments were performed on a TURMG2 diffractometer (Dresden, Germany). Nickel filtered CuK radiation was used. The wide-angle Xray diffraction traces were recorded by a scintillation counter system with a 1.0 mm diameter pin-hole collimator. The samples were used as powders or films. Weight-average molecular weights (Mw ) and number-average molecular weights (Mn ) were determined by means of gel permeation chromatography (GPC) using a Waters GPC apparatus, provided with Refraction and Photodiode array Detectors and PhenomenexPhenogel MXN column. Measurements were carried out with polymer solutions having 0.2% concentration, using dimethylformamide as eluent. Polystyrene standards of known molecular weight were used for calibration. Mechanical properties of the polymer films were analyzed by cold drawing of solution cast films and testing with an Instron 5566 universal testing machine (UTM). The samples in the form of Polym. J., Vol. 38, No. 9, 2006


strips (thickness of 0.03 mm, gang length of 50 mm and width of 15 mm) were drawn with a rate of 1 mm/min at room temperature and 50% humidity. The tensile stress (MPa) versus tensile strain (%) dependencies were recorded. The Kuhn segments were calculated by using the Monte Carlo method as described earlier.17,18 RESULTS AND DISCUSSION Aromatic poly(1,3,4-oxadiazole-amide-ester)s (III) have been synthesized with the aim to have highly thermostable, easy soluble and processable products. The structures of these polymers were identified by IR spectra. All polymers III showed a wide absorption band at 3440 cm1 and a sharp peak at 1540 cm1 characteristic for N–H, and another peak at 1670 cm1 due to C=O in amide groups. The absorption band at 1760 cm1 is characteristic for COO groups. The weak absorption peaks at 1025 cm1 and 965 cm1 were attributed to the 1,3,4-oxadiazole ring. The polymers, except for IIIc and IIIf, are easily soluble in polar aprotic solvents such as NMP, dimethylformamide (DMF) and dimethylacetamide (DMA). The good solubility of these polymers is due to the presence of ester, amide and ether bridges which make the macromolecular chains more flexible and thus their shape is very different from a linear rigid rod which is characteristic to wholly aromatic polyamides and poly(1,3,4-oxadiazole)s. The polymer IIIc, after precipitation from NMP solution resulting from polycondensation reaction, became insoluble in NMP. Therefore, the viscosity of the polymer IIIc could not be measured. By molecular modeling we observe that in the case of polymers IIIc and IIIf the length of one macromolecular chain (four repeating units) is ˚ and 95.50 A ˚ , respectively. That means that 100.129 A the degree of planarity is higher for IIIc than in the case of polymer IIIf, and this fact can be a possible explanation for a slightly better solubility of polymer IIIf in comparison with polymer IIIc. Model molecules of the polymers IIIa and IIIe are shown in Figure 1. It can be seen that there is a large distance between the macromolecular chains which prevents the tight interchain packing through hydrogen bonds between amide groups and thus facilitates the diffusion of small molecules of solvent. For comparison, molecular models of an aromatic polyamide and a polyoxadiazole are also shown in Figure 1. Due to their good solubility, most of these polymers could be easily processed from their NMP solutions, by casting onto glass plates. Thin films were thus obtained, having the thickness in the range of tens of micrometers. These films were flexible, tough and creasable, meaning that they maintained their integrity after repeated Polym. J., Vol. 38, No. 9, 2006

bendings, except for polymers IIIe and IIIf which gave brittle films. Also, due to their good solubility, the molecular weight of these polymers was easily determined by using their solutions. Inherent viscosity values of these polymers are in the range of 0.26–0.45 dL/g (Table I). The molecular weight of the polymers was determined by gel permeation chromatography (GPC), by using polymer solutions in DMF. The polymers IIIc and IIIf were not soluble in DMF and therefore GPC measurements could not be performed with these two polymers. The weight average molecular weight values, Mw , of the measured polymers are in the range of 91,000– 257,000 g/mol, the number average molecular weight values, Mn , are in the range of 41,300–86,000 g/mol and the polydispersity Mw =Mn is in the range of 1.6–5.0 (Table I). All these values indicate that these polymers have fairly high molecular weight and a broad polydispersity. In any case these values have to be taken as indicative only, since calibration with polystyrene may give questionable results when the polarity and backbone stiffness of the studied polymers deviate strongly from those of polystyrene. The thermal stability of these polymers was studied by thermogravimetric analysis (TGA) performed in air at a heating rate of 12 C/min. All the polymers show fairly high thermal stability. Their decomposition in air begins in the range of 365–390 C (onset on the TGA curves) and the temperature of 10% weight loss (T10 ) is in the range of 395–420 C. These results indicate that the thermostabilities of these polymers are quite similar to each other; the thermal degradation occurs approximately in the same range of temperatures (around 400 C). TGA curves are presented in Figure 2. The thermal stability of the present polymers is very similar to that of related polyoxadiazoles which contain pendent phenoxy groups,19 but slightly lower (by approximately 40–50 C) than that of poly(1,3,4-oxadiazole-ether)s20 and poly(1,3,4-oxadiazole-amide)s which contain pendent phthalimide groups.5,21 That proves that the ester groups in the present polymers are more vulnerable to thermal degradation. However the incorporation of ester together with amide groups into these polymer backbones effectively enhances the solubility while maintaining a fairly high thermal stability. These polymers do exhibit a glass transition when studied by DSC analysis, while, as it is known, wholly aromatic polyoxadiazoles and polyamides do not show any Tg . The Tg values of the present polymers are in the range of 215–260 C, being comparable with that of related poly(1,3,4-oxadiazole-amide)s which contain pendent phenoxy groups.19 The polymers IIIc and IIIf had the highest values of Tg (260 C and 245 C, respectively) (Table I). It can be 943

I. S AVA, I. R ONOVA, and M. B RUMA

IIIa

IIIe

Poly(p-phenylene-1,3,4-oxadiazole)

Poly(p-phenylene-terephthalamide) Figure 1. Model molecules (4 repeating units) of polymers IIIa, IIIe, poly(p-phenylene-1,3,4-oxadiazole) and poly(p-phenyleneterephthalamide).

Table I.

Properties of the polymers III

Polymer

Inherent viscosity (dL/g)

Mw (g/mol)

Mn (g/mol)

Mw =Mn

Tg b ( C)

IDT c ( C)

T5 d ( C)

T10 e ( C)

IIIa IIIb IIIc IIId IIIe IIIf

0.26 0.29 — 0.33 0.30 0.45

91,000 206,500 — 215,000 257,000 —

55,500 41,300 — 86,000 65,900 —

1.64 5 — 2.5 3.9 —

235 225 260 232 215 245

375 365 390 375 390 384

385 375 395 390 400 390

400 395 410 415 420 415

a

a Measured with polymer solutions in NMP, conc. 0.5 g/dL, at 20 C. b Determined from DSC curves. c Initial decomposition temperature = onset on TGA curve. d Temperature of 5% weight loss. e Temperature of 10% weight loss.

seen that there is a large interval, of more than 130 C, between Tg and the decomposition temperature which can be advantageous for the processing of these polymers by thermoforming techniques, as well. A typical DSC curve is shown in Figure 3. The small angle X-ray scattering patterns of two 944

polymers are given in Figure 4. The polymer IIId, which contains two m-catenations in one repeating unit, is amorphous, while the polymer IIIa, which contains only one m-catenation, showed a slight crystallinity. The amorphous nature of these polymers was also reflected in a good solubility in organic solvents. Polym. J., Vol. 38, No. 9, 2006


Table II. Mechanical properties of the polymers III 0

Tensile strength Elastic modulus Elongation at break (MPa) (GPa) (%)

Polymer Weight loss, %

-10

IIIa IIIb IIIc IIId


-20

-30

40.32 47.49 91.13 84.14

2.83 2.22 3.98 3.24

1.85 2.99 7.37 5.20

-40

100

-50

0

100

200

300

400

500

600

Temperature, °C

Figure 2. TGA curves of polymers III.

Tensile stress [MPa]

-60

80

60

40

20

0 0

1

2

3

4

5

6

Tensile strain [%]

Figure 5.

Figure 3.

DSC curve of polymer IIIa.

Figure 4. X-Ray traces of poly(1,3,4-oxadiazole-ester-amide)s IIIa and IIId.

We expected these polymers to show more significant crystallinity since it is known that, from spectral and electronic points of view, the 1,3,4-oxadiazole ring is similar to a p-phenylene structure, which is a planar, rigid unit.22 However, due to the presence of flexible ester and amide groups, these polymers are amorphous. Polym. J., Vol. 38, No. 9, 2006

Tensile test of the polymer IIId (two experiments).

The mechanical properties of the polymer films are listed in Table II. The films made from polymers IIIe and IIIf could not be measured because they were brittle. For the other polymers, tensile strength, elastic modulus, and elongation to break have been determined as averages of two or three drawing experiments. All polymers showed similar type of behavior with respect to the elastic deformation range at small strains. The values of tensile strength are in the range of 40–91 MPa, elastic modulus in the range of 2.22– 3.98 GPa and elongation to break in the range of 1.85–7.37%. A representative tensile test is shown in Figure 5. As can be seen in Table II, the values of tensile strength are similar with those of related polyamides obtained from the same diamines but with other diacid chlorides.10 Comparison with mechanical properties reported for polyoxadiazole-ketones which have tensile strength of 48 MPa, elastic modulus of 1.46 GPa23 shows that the present polymers exhibit higher values indicating that they are strong materials (Table II, Figure 5). The Kuhn segment (Afr ) and the number of aromatic rings in the Kuhn segment (p) were chosen as the conformational parameters and were discussed in correlation with some physical properties of the present polymers. The parameter p was included because in previous work the correlation of physical properties with the number of aromatic rings in Kuhn segment was shown.24,25 945


Table III.

Conformational parameters of the polymers III

Glass transition, °C

260

250

240

230

y = 197.1 + 5.17x 220

Polymer

l0

Afr

C1

p

Tg d ( C)

IDT b ( C)


42.85 42.84 32.98 42.58 42.58 32.69

45.12 27.77 68.12 23.80 34.09 40.67

1.053 0.648 0.801 0.559 2.065 1.244

8.424 5.186 12.393 6.405 4.472 7.465

235 225 260 232 215 245

375 365 390 375 390 384

l0 = contour length of the repeat unit; Afr = Kuhn segment; p = parameter of rigidity. b Initial decomposition temperature = onset on TGA curve. d Determined from DSC curves.

R = 93.65%

210 4

6

8

10

12

14

p

Figure 6. The dependence of glass transition temperature on rigidity parameter.

As is known, the Kuhn statistical segment can be writen as: 2 hR i A ¼ lim n!1 nl0 where hR2 i=nl0 is the ratio of the average square endto-end distance of a chain to its contour length; n is the number of repeat units; l0 is the contour length of a repeat unit. In the case of polyheteroarylenes in which the macromolecular unit contains virtual bonds with different length and different angles between them, the length of the zig-zag line connecting the mid-points of the virtual bonds is taken as the contour length. The Kuhn segment lengths were calculated by Monte Carlo method.26 We used the Volkenstein rotational isomeric state approximation by consideration of only discrete values of rotation angles, and the Flory approximation by the assumption that rotations around virtual bonds are independent.27 The term hhvirtual bondsii is used to indicate a rigid section of a chain approximated by a straight line about which rotation is possible. In a particular case, it can be an ordinary valence bond; more generally, it can contain rings, as well. The conformational energy maps for several aromatic polyesters and polycarbonates were calculated and the minimum energy structures were found, in which the rotation angles about virtual bonds passing through aromatic rings were 0 and 180 , both values being equally probable.28 Knowing the value of Kuhn segment allows one to calculate the parameter of conformational rigidity p: p¼

A k l0

where k is the number of aromatic rings in a polymer structural unit. The conformational parameter p takes into account both factors: aromatic character of poly946

heteroarylenes and their rigidity. In the case of the present polymers we have found that the Kuhn segment values calculated under the assumption of free rotation (Afr ) and under the assumption of hindered rotation (Ahin ) are equal.29 It means that the ester or oxadiazole groups do not cause a significant hindrance, since they allow rotation around virtual bond going through phenyl ring in meta-position despite the narrow distance between the hydrogen of phenyl and hydrogen of amide group. The solubility of the polymers correlates well with their conformational rigidity. All these polymers are soluble in polar amidic solvents such as NMP and DMF. The solubility is due to the relatively high flexibility of the macromolecular chains of these polymers having low values of Kuhn segment (23.8–68.12). The flexible ester groups together with ether and oxadiazole units do not allow the macromolecular chains to pack tightly through hydrogen bonds between amide groups and thus increase the solubility of the polymers (Table III). However, the polymer IIIc having the highest Kuhn segment value was not soluble in DMF after precipitation. The other polymers having lower Kuhn segment values are more flexible and are soluble in neat polar aprotic solvents. The polymers containing meta-disubstituted phenylene rings have lower Kuhn segment values and hence better solubility than the corresponding polymers containing para-disubstituted phenylene rings. The glass transition temperature (Tg ) and the initial decomposition temperature values (IDT) are known to be significantly dependent on the presence of aromatic rings in the polymeric chain. In the case of the present polymers, Tg values increased while increasing the value of the conformational rigidity parameter. Previously,29 it was shown that there was a relationship between glass transition temperature and initial decomposition temperature for several polymers: Td ¼ aTg . The value of a for polyamides and polyimides lies in the range of 1.15–1.25 depending on the structure of the polymer repeating unit. Since the dependence between Polym. J., Vol. 38, No. 9, 2006


the glass transition temperature and the conformational rigidity exists, it would be reasonable to assume the existence of a correlation between the initial decomposition temperature and the conformational rigidity. At first glance, the onset temperature must depend entirely upon thermal stability of groups forming the monomer. However, the decrease in mass at the early stages of heat destruction depends on conformational mobility of the elements of the chain in the surface layer of the polymer because this is where the destruction takes place initially. As soon as the entire sample is heated (mass losses exceeding 5%) no dependence between decomposition temperature and the conformational stiffness of the polymers are observed probably because the nature of amide and ester groups dictate the thermal stability. It is known that Tg and IDT values are to an essential degree dependent on the presence of aromatic rings in the polymeric chain. Therefore, one can try to find a correlation between these parameters and the number p of aromatic rings in the fragment of polymeric chain equivalent to Kuhn segment. The dependence of glass transition temperature (determined from DSC curves) on p value for polymers III is shown in Figure 6. Using the least-squares method, the dependence of Tg on conformational parameter p can be described by a linear equation. The factor of convergence R is relatively high (R ¼ 93:65%). As is mentioned in the literature,26 if the dependence is linear with a good factor of convergence, this equation can be used for the theoretical estimation of glass transition temperature for polymers having similar structures. CONCLUSIONS By introducing ester together with amide groups into the aromatic backbone of polyoxadiazoles, polymers with substantially increased solubility where obtained which could be processed into thin flexible films by casting their solutions. The films, showed good mechanical properties, with tensile strength in the range of 40–91 MPa, elastic modulus in the range of 2.22–3.98 GPa and elongation to break in the range of 1.85–7.37%. These polymers show high thermal stability with decomposition temperature being above 365 C and reasonably high glass transition temperature, being in the range of 215–260 C. The polymers have fairly high molecular weights with Mw being in the range of 91,000–257,000 g/mol and polydispersity of 1.64–5. The solubility and the glass transition temperature of the polymers correlate well with the values of conformational rigidity parameter. The initial decomposition temperature is not visibly influenced by the conformational rigidity parameter. Polym. J., Vol. 38, No. 9, 2006

Acknowledgment. The financial support for part of this work was provided through CEEX 29/2005 Project and it is gratefully acknowledged. Our warm thanks also go to M. Bierbauer at the Institute of Thin Film Technology and Microsensors in Teltow, Germany, for GPC analyses. REFERENCES 1.

2. 3. 4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

19. 20. 21. 22. 23. 24.

P. E. Cassidy, T. M. Aminabhavi, and V. S. Reddy, in ‘‘Kirk-Othmer Encyclopedia of Chemical Technology,’’ 2nd ed, J. I. Kroschwitz, Ed., Wiley, New York, 1994, vol. 12, p 1045. B. Schulz, M. Bruma, and L. Brehmer, Adv. Mater., 9, 601 (1997). C. J. Thaemlitz, W. J. Weikel, and P. E. Cassidy, Polymer, 33, 3278 (1992). E. R. Hensema, M. Sena, M. H. V. Mulder, and C. A. Smolders, J. Polym. Sci., Part A: Polym. Chem., 32, 527 (1994). C. Hamciuc, E. Hamciuc, I. Sava, A. Stoleriu, F. W. Mercer, and M. Bruma, Polym. Adv. Technol., 7, 847 (1996). G. Maglio, R. Palumbo, M. Tortora, M. Trifuoggi, and G. Varricchio, Polymer, 39, 6407 (1998). S. H. Hsiao, L. R. Dai, and M. H. He, J. Polym. Sci., Part A: Polym. Chem., 37, 1169 (1999). M. D. Iosip, M. Bruma, Y. Kaminorz, and B. Schulz, High Perform. Polym., 13, 133 (2001). I. Sava, M. D. Iosip, M. Bruma, C. Hamciuc, J. Robison, L. Okrasa, and T. Pakula, Eur. Polym. J., 39, 725 (2003). M. D. Iosip, M. Bruma, I. A. Ronova, M. Szesztay, and P. Muller, Eur. Polym. J., 39, 2011 (2003). M. Bruma, C. Hamciuc, E. Hamciuc, and B. Schulz, Rev. Roum. Chim., 45, 677 (2000). A. E. Siegrist, E. Maeder, and M. E. Duenenberger, Swiss Patent 383985 (1965), Chem. Abstr., 62, 14867 c (1965). F. W. Mercer, High Perform. Polym., 5, 73 (1992). A. Bilibin, A. Tenkovtsev, and O. Piraner, Vysokomol. Soedin., Ser. A, 26, 2570 (1984). I. Sava, C. Hamciuc, M. Bruma, and E. Hamciuc, Rev. Roum. Chim., 46, 1161 (2001). Hypercube Inc. (Ontario), Hyperchem, 2000, Version 6.0. S. A. Pavlova, G. I. Timofeeva, I. A. Ronova, and L. A. Pankratova, J. Polym. Sci., Polym. Phys. Ed., 18, 1 (1980). I. A. Ronova, L. B. Eylshina, A. N. Vasilyuk, A. L. Rusanov, and E. G. Bulycheva, Russ. Chem. Bull., 51, 820 (2002). C. Hamciuc, E. Hamciuc, and M. Bruma, M., High Perform. Polym., 8, 507 (1996). F. A. Bottino, G. D. Pasquale, and P. Iannelli, Macromolecules, 34, 33 (2001). C. Hamciuc, I. A. Ronova, E. Hamciuc, and M. Bruma, Angew. Macromol. Chem., 254, 67 (1998). S. H. Hsiao and J. H. Chiou, J. Polym. Sci., Part A: Polym. Chem., 39, 2271 (2001). C. Hamciuc, E. Hamciuc, M. Bruma, M. Klapper, and T. Pakula, Polym. Bull., 47, 1 (2001). S. A. Pavlova, I. A. Ronova, G. I. Timofeeva, and L. V. Dubrovina, J. Polym. Sci., Part B: Polym. Phys., 31, 1725 947


25. 26. 27.

948

(1993). I. A. Ronova and S. A. Pavlova, High Perform. Polym., 10, 309 (1998). I. A. Ronova, A. N. Vasilyuk, C. Gaina, and V. Gaina, High Perform. Polym., 14, 195 (2002). P. J. Flory, ‘‘Statistical Mechanics of Chain Molecules,’’

28. 29.

Interscience: New York, 1969. A. E. Tonneli, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 13, 1023 (1972). E. P. Krasnov, V. P. Aksenova, and S. N. Khar’kov, Vysokomol. Soedin., Ser. A, 15, 2093 (1973).

Polym. J., Vol. 38, No. 9, 2006