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Synthesis and characterization of aliphatic polyesteramides mainly composed of alternating diester diamide units from n,n-bis(2-hydroxyethyl)-oxamide and diacids.

This article provided a convenient method to synthesize aliphatic polyesteramides mainly composed of alternating diester diamide units by polycondensation and chain extension. Two kinds of polyesteramide pre-polymers were prepared through melt polycondensation from N,A/'-bis(2-hydroxyethyl)oxarnide and adipic acid or sebacic acid. Chain extension of them was conducted with 2,2'-(1,4-phenylene)-bis(2-oxazoline) and adipoyl biscaprolactamate as combined chain extenders. The chain extended polyesteramides (ExtPEAs) were characterized by IR, *H NMR, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray scattering, tensile test, and dynamic thermomechanical analysis. The results showed that the ExtPEA(0, m)s were mainly constituted with the diester oxamide alternating units. They had Tm above 140.8 C and the initial decomposition temperature above 298.0 C. They crystallized in similar crystallites to Nylon-66 and were thermoplastic materials with tensile strength up to 31.47 MPa. POLYM. ENG. SCI., 54:756765, 2014. 2013 Society of Plastics Engineers


With the increasing concern for white pollution, more and more researchers have focused their attention on the synthesis, properties, and biodegradation of the biodegradable polymers [l, 2), Currently, aliphatic polyesters such as polylbutylene succinate), polyl(3-hydroxybulyratc-co-3-hydroxyvalerate). and polylactic acid are the most important types of the synthetic biodegradable polymers and are gradually used as domestic plastics Meanwhile, aliphatic polyesteramides are also an important type of biodegradable polymeric materials. They are constituted with many ester groups and amide groups. The ester groups in the main chains ensure them susceptible to enzymes and microbes. The amide group! increase the intennolecular force and benefit the improvement of their thermal and mechanical properties. Polyesteramides become a promising type of biodegradable polymers because they have good processing and end-use properties. Polyesteramides are usually classified into three types: random, alternating, and segmented or block poly-esteramides. The random and block polyesteramides arc commonly synthesized through ring-opening polymerization and condensation polymerization directly from simple commercial monomers. Roda and Deshayes synthesized random or block polyesteramides from ring-opening copolymerizalion of j:-caprolactam wiih j:-capro-lactone or its polymer |4-6|. Bayer Company (7, K] patented random polyesteramides synthesized from adipic acid (AA), butanediol, and hcxanediamine or caprolactam. and commercialized them in the BAK series. Diamide-diols were also used as starting materials to synthesize aliphatic polyesteramides. Dijkstra and coworkers (9-11) synthesized random polyesteramides from dimethyl adi-pate. butanediol, and diamidediols. which were prepared through the reaction of butanediamine or elhanediumine with caprolactone.

Alternating polyesteramides usual]; show intennediatc properties between polyesters and polyamides. Serrano el al. (12-14) synthesized a series of semiaramatic aller-nating polyesteramides through melt and solid polycondensation from 1,4-butylene terephthalamide dimethyl with glycols. Luslon el al. (15) synthesized some semiaramatic alternating polyesteramides through polyaddition from aromatic bis(2-oxazoline)s wiih aliphatic dicarbox-ylic acids. Up lo now. aliphatic alternating polyesteramides are still seldom reported in the literal dies, Jamiolkows and Shalaby (16) had synthesized the random and alternating aliphatic polyesteramides from the reaction of diamidediols with dicarhowlic acid diestcrs at the presence or absence of the 1,6-hcxanediol. The diamidediols they used were A^-bisii-j-hydroxyalkyleneyoxa-mides, which were prepared by reacting diethyl oxalate with amino alcohols such as 3-amino- l-propanol, 5-ainino- I-pcntanol and 6-amino-l-hexanol. Alternating polyesteramides with high molecular weight were difficult lo be prepared. To increase the molecular weight, some 1,6-hexanediol needed to be added. But the alternating structure of the polyesteramides was destroyed.

In the literatures, polyesteramides having diesterdia-mide units are commonly prepared through transesterification from dicarboxylic acid dieslers with diamidediols and glycol in high vacuum system. Dicarboxylic acids are seldom used directly to react with diamidediols in their synthesis, maybe because high extent of the side reaction might be caused by the dicarboxylic acids. However, dicarboxylic acids had obviously higher reactivity than their dieslers. In this article, we studied the polycondensa-tion of a diamidediol directly with the dicarboxylic acids and synthesized two types of aliphatic alternating polyesteramides. The diamidediol N.N'-bis(2-hydroxyethyl)-ox-amide (HEOA) synthesized from the reaction of diethyl oxalate with 2-aminoalcohol was used as a starting male-rial. Two polyesteramide prepolymers (PrePEAs) with both HO- and HOOC- terminal groups were synthesized by reacting HEOA with AA or sebacic acid (SA) at moderate reaction conditions. The PrePEAs were chain extended with 2,2'-(l,4-phenylene)-bis(2-oxazoline) (PBOX) and adipoyl biscaprolaciamale (ABC) as combined chain extenders to increase the molecular weight. The chain extended polyesteramides (ExtPEAs) were characterized by 1R and 'H NMR spectra, differential scanning calorimetry (DSC), thcrmogravimetric analysis (TGA). wide-angle X-ray scattering (WAXS), tensile test, and dynamic thermomechanical analysis (DMTA).



AA was purchased from Beijing Chemical Factory. China and SA from Tianjtn Fuchen Chemical Reagent Plant. China. AA and SA were purified by crystallization in de-ionized water before used. Sn[CL.sub.2] was purchased from Beijing Shuanghuan Weiyi Reagent Co. Ltd. Other materials such as ether, dimethylfonnamide (DMF). dimethyl sulfoxide (DMSO). and p-toluenesulfonic acid (p-TSA) are all obtained as reagent grade and used directly. HEOA (m.p.: 175[degrees]C) was prepared through condensation of diethyl oxalate with ethanolamine and purified by crystallization in absolute methanol (17). The chain extender PBOX (m.p.;249 C) was prepared according to the procedure described by Nery et al. (18). ABC (m.p.: 73"C) was prepared according to the procedure b> Wilfong et al. (19).

Synthesis of the PrePEAs

In a 250-ml three-necked flask equipped with mechanical stirrer, the polycondensation of HEOA with AA or SA was carried out at 160-170[degrees]C under [N.sub.2] atmosphere for 2-3 h with SnCI; 2[H.sub.2]0 as a catalyst. Water was removed by distillation from the reaction mixture. Afterward the temperature was increased about I0[degrees]C, and the pressure in the reaction system was slowly decreased from atmosphere to 5 mm Hg abs. over a period of 3 h and kept 2 h. PrePEAs with different acid value (AJ and hvdroxyl number {[Q.sub.v]) were obtained.

Chain Extension of the PrePEAs

In a l(K)-ml three-necked flask equipped with mechanical stirrer. 6 g PrePEAs was added, stirred, and heated under [N.sub.2] to 180-200[degrees]C. Chain extenders such as PBOX and ABC were added at molar ratios of (1/2) PBOX/-COOH = 1.0 and (l/2)ABC/-OH = 1.0, and the reaction mixture was homogeneously mixed. The chain extension was conducted at normal pressure for 1 h and at reduced pressure to 5 mm Hg for 3 h. The ExtPEAs were poured out ami cooled al room Temperaiure.


The acid value and the hvdroxyl number of PrePEAs were detected according in the procedure described in the literature (20). One gram of PrePEA was dissolved in 15 ml DMF and titrated with 0.05 N NaOH ethanol solution lo delect ihe acid values. The intrinsic viscosity of the PrePEAs and the ExtPEAs was detennined at 30[degrees]C by Ubbelohde viscometer using 1:1 (v/v) DMF:DMSO as mixture solvents. Some PrePEAs and the ExtPEAs were also characterized by gel permeation chromalograplu (GPC). Their Mn, Mw. and molecular weight distribution were measured on Agilent 26(X) Series equipped with PLgel 5 /nn 1000 A column and a refractive index detector al 25[degrees]C. DMF was used as eluent with a low rale of 1 ml/min. and polystyrene was used as standards.

The ExtPEAs used for the IR and NMR detection were purified three times through dissolving-precipitation cycles using 20 ml DMSO as solvent and 2(X) ml ether as nonsolvent. FTIR spectra were recorded on NICOLET 60SXB FTIR spectrometer. The 'H-NMR spectra were recorded on Bruker AC-600 spectrometer using DMSO-d6 as the solvent and tetramelhylsilane as ihe labeling compound.

DSC spectra of the polymers were performed on a Q2(X) V24.2 Build 107 DSC analyzer under nitrogen atmosphere. The samples were firsi heated from room temperature to 250 C at a heating rate of 60[degrees]C/min and kept for 5 min to eliminate thennal history. Then the samples were cooled to -90[degrees]C al the rale of 40[degrees]C/min. In the second heating scan, the samples were healed from -90 to 250[degrees]C at the rate of 10[degrees]C/min. The cooling DSC scans of the PrePEAs and ExtPEA were also recorded on a Q200 V24.2 Build 107 DSC analyzer under nitrogen atmosphere. The samples were first heated from room temperature lo 250[degrees]C al a heating rate of 60" C/min and kept for 5 min lo eliminate thermal history. Then the samples were cooled to -100[degrees]C at the rate of 10 C/min.

The TGA was carried oul employing TA TGAQ50 analyzer in the temperature range of 20-500[degrees]C at a healing rate of 10[degrees]C/min under nitrogen atmosphere. The WAXS measurements of the polymer samples were delected using Rigaku D/Max 2300 VB2+/PC diffraclomeler with Cu Ky.radiation. The samples were continuously scanned over the 20 ranging from 5 lo 50[degrees].

The sample plates (50 X 50 X I [mm.sup.3)) were hot pressed with 709II-24B powder press machine (Tianjin New Technical Instrument Com.). The polymer samples were healed al I60[degrees]C for 5 min under 15 MPa and cooled to room temperature under the same pressure, and then cut into dumbbell-shaped bars (50 X 4 X 1 [mm.sup.3)). Mechanical properties were detennined on lnstron 11X5 tensile testing machine with erosshead speed at 50 mm/min.

Five measurements were performed for each sample, and the results were averaged to obtain a mean value.

The dynamic thennomechanical properties of ihe ExtPEAs were detennined wilh Rheomelric Scientific DMTA V dynamic thermomechanical analyzer. The testing specimens were prepared by cutting the central pans of the dumbbell-shaped samples (50 X 4 X I [mm.sup.3)), The measuremenls were performed at the frequency of I Hz. The specimens were healed from -50 to 150[degrees]C al the scanning rate of 5 C/min.


Synthesis and Chain Extension of the PrePEA(0.m)s

Two types of aliphatic polyesteramides mainly composed of alternating diester diamide (DE-all-DA) unils were synthesized by a melt polycondensaiion and a chain extending reaction wilh PBOX and ABC as combined chain extenders. The PrePEAs PrePEAs with both HO- and HOOC- tenninal groups at the ends were prepared through polycondcnsation of A/Jv"-bis(2-hydroxye-thyDoxamide with AA or SA. The synthesis reaction of the PrePEA(0.m)s was described in Scheme 1.

Table 1 shows the properties of ihe PrePEA(0.4)s and their chain extension. PrePEA(0.4)s were synthesized by ihe poly condensation of HEOA with AA at A A: HEOA molar raiios of 1.2 or 1.3. Higher AA/HEOA molar raiios than 1.0 made ihe PrcPEA(0,4)s mainly lenninaied with the HOOC- lenninal groups, and the HO- terminal groups were in less amount. The [A.sub.v] of ihe PrePEA(0.4)s ranged from 47.1 lo 54.3 mg-KOH/g. and the hydroxy! number ranged from 2.8 to 14.9 mg KOH/g. From Table I. it was also found thai [SnCl.sub.2] was an effective calalyst. Sn[Cl.sub.2] promoted the condensation between the -COOH groups and -OH groups, resulting in obvious decrease of ihe [A.sub.v] and [Q.sub.v]. But higher amount of SnCU than 0.10 wt% often resulted in the amorphous PrePEA(0.4>s. which hardly crystallized when they were cooled. Reaction temperature and reaction time were oiher important influencing factors to synthesize crystallizable PrePEA(0,4)s. If the reaction temperature was above 180T and the reaction lime was too long, amorphous PrePEA(0,4)s were often obtained. The reason might be that during the polycondensalion of AA with HEOA. the HOOC- reacting groups had acid characteristics. They had higher reactivity than the ester groups in the starting materials such as dicarboxylic acid diesters and benefited the condensation with the HO-groups in the HEOA. But it was likely that the HOOC-groups also catalyzed the ester-amide interchanging side reaction and led to the amorphous PrePEA(0.4)s. So, lower reaction temperature and shorter reaction time were adopted to reduce the ester-amide interchanging reaction and lo obtain ihe crystallizable PrePEA(0.4)s. As the erysiallizable PrePEA(0,4)s were insoluble in THF. iheir intrinsic viscosity was deiennined al 30[degrees]C by Ubbelohde viscometer using 1:1 (v/v} DMFtDMSO as mixture solvents. The intrinsic viscosity of the PrePEA(0.4)s ranged from 0.081 lo 0.097 dl/g.

TABLE 1. Cham extension of PrePEA (0. 4)s wilh
different Av/Qv.
AA/HEOA  [SnCl.sub.2]  Av/Qv (mg  [M.sup.c]
               (molar   (wt%)           .KOH/g)
PrePEA(0.4)-1  1.20     --              50.0/14.9  1728.8
PrePEA(0.4)-2  1.20     0.05            47.1/11.3  1921.2
PrePEA(0.4)-3  1.30     0.05            54.3/11.5  1705.2
PrePEA(0.4)-4  1.30     0.05            51.8/2.8   2054.9
               ([(eta]))  [T.sub.p][d.sup.d]  [SnCl.sub.2]
               (dl/g)       ([degrees]C)          (wt%)
PrePEA(0.4)-1  0.081        200                     --
                            200                     0.30
                            180                     0.30
PrePEA(0.4)-2  0.097        180                     0.20
PrePEA(0.4)-3  0.083        180                     0.20
PrePEA(0.4)-4  0.097        200                     0.15
               TSA    ([(eta]))
               (wt%)  (dl/g)
PrePEA(0.4)-1  0.1    0.18
               --     0.32
               --     0.20
PrePEA(0.4)-2  0.05   0.43
PrePEA(0.4)-3  0.05   0.44
               0.05   0.47
PrePEA(0.4)-4  0.05   0.36

PBOX and ABC were effective chain extenders in the chain extension of ihe HOOC- or HO- tenninated polymers such as polyesters and polyamides to increase the molecular weight in short lime (18. 2l-24|. PBOX and ABC were also used as combined chain exlenders in the chain extension of the aliphatic polyesters and random polyesteramides having both HOOC- and HO- lenninal groups (25. 26). PrePEA(0,4)s were tenninated by both HO- and HOOC- groups, so PBOX and ABC were chosen as combined chain exlenders. The chain extension was showed in Scheme 2.

Table 1 shows the chain extension of the PrePEA(0,4)s with PBOX and ABC as combined chain exlenders. As p-TSA was an effective catalyst in the chain extension of the aliphatic polyesters (20), it was also chosen as a catalyst in the chain extension of the PrePEA(0,4)s. Meanwhile, the catalysis of ihe [SnCl.sub.2] was also studied. From Table 1. it was found that SnCN was more effective than ihe p-TSA. When [SnCI.sub.2] and p-TSA were used as combined catalysis, the chain extension showed the best chain extension efficiency, and ihe ExtPEA (0, 4) with [eta] up lo 0.47 dl/g was obiained. Maybe the complexalion and the protonalion between [SnCl.sub.2] or p-TSA and the oxazo-line groups in PBOX or the carbonyl groups in ABC promoted Ihe chain extension. Chain extension at I80-200[degrees]C for 4 h did not influence the crystallization of Ihe ExtPEA (0, 4)s seriously. After chain extension was completed, when the ExlPEA(0, 4)s were poured out and cooled, they crystallized rapidly. So ExtPEA (0, 4)s wilh easy crystallization characteristics were obtained at the chain extension conditions mentioned above (see also in the DSC characterization). Serious ester-amide interchanging reaction often resulted in amorphous polyesteramides. which crystallized very slowly when they were cooled after synthesis reaction.

Similarly. PrePEA(0. 8)s were also synthesized from polycondensalion of HEOA wilh SA. Table 2 shows the properties of the PrePEAtO, 8)s and their chain extension with PBOX and ABC. From Table 2, it was found that at the SA/HEOA molar ratio of 1.3 with 0.1 wt% [SnCl.sub.2] as catalyst. PrePEA(0, 8)s having HO- and HOOC- terminal groups were synthesized. The [A.sub.v] of the PrePEAK). 8)s ranged from 48.S to 75.8 mg KOH/g, and their ((7.sub.V] ranged from 0 lo 21.5 mg-KOH/g. As the reaction temperature increased, ihe A%and ihe decreased obviously. The [y] increased from 0.093 or 0.1 to 0.20 dl/g. Increasing the reaction lemperaiure resulted in the increase of the molecular weight of the PrePEAtO. 8). PrePEA(0. 8)s with easy crystallization characteristics were obtained at ihe reaction lemperaiure of 160-I80[degrees]C. From Table 2. it was also found ihat when the [SnCl.sub.2] and p-TSA were used as combined catalysts, the chain extension showed the best chain extension efficiency. The ExtPEA(0, 8) with [eta) up to 0.43 dl/g was obtained al molar ratios of (l/2)PBOX/-COOH= 1.0 and (l/2>ABC/-OH = 1.0 using 0.20 wt% [SnCl.sub.2] and 0.05 wt% p-TSA as combined catalysis.

TABLE 2. Cham extension of PrePEAlO. tf)s
with ditterei[c] Av/Qv.

               [T.sub.1]     [T.sub.2]     Av/Qv       ([(eta]))
               ([degrees]C)  ([degrees]C)  (mg-KOH/g)  (dl/g)
PrePEA(0.8)-1  160             170             75.8/21.5   0.10
PrePEA(0.8)-2  170             180             48.8/3.9    0.20
PrePEA(0.8)-3  160             170             73.9/0      0.093
               [SnCl.sub.2]  TSA    ([(eta]))
               (wt%)           (wt%)  (dl/g)
PrePEA(0.8)-1  0.20            --     0.25
PrePEA(0.8)-2  0.20            --     0.25
               0.30            --     0.24
               0.20            0.05   0.43
PrePEA(0.8)-3  0.15            0.05   0.36

Meanwhile, some PrePEAs and the ExlPEAs were also characterized by GPC method (Table 3). The PrcPEAsK). 4)-3 and PrePEAs(0. 4)-4 had Mn of 1280 and 1270, respectively. As PrePEA(0,8)-3 was not soluble in DMF. its Mn and Mw could not be detected. After chain extension, ihe Mn and Mw increased obviously. ExtPEAs having Mn from 30.500 to 50.140 and Mw from 57.680 to 92.970 were prepared.

TABLE 3. The GPC data of the PrePEAs and ExtPEAs.
                                PrePEAs                          EkiPEAs
               Mn               Mw       Mw/Mn  Mn               Mw
               ([GPC.sup.b])  (GPC)    (GPC)  ([GPC.sup.b])  (GPC)
PrcPEA(0.4)-3  1280             1290     1.01   50140            92970
PrePEA(0.4)-4  1270             1280     1.01   38470            67890
PrePEAlO.*     --               --       --     30500            57680
PrcPEA(0.4)-3  1.82
PrePEA(0.4)-4  1.76
PrePEAlO.*     1.89

'H NMR and FT IR Characterization of the ExtPEA (0,m)s

The PrePEAs and ExlPEAs were characterized by FTIR and 'H NMR spectra. Figure I shows the 'H NMR spectrum of the PrePEA(0. 4)-3. In Fig. 1. the peaks at 4.09 and 3.38 ppm corresponded to l-[CH.sub.2]- and 2-[CH.sub.2]-hydrogens in the alternating oxamide adipate units (I). The peak at 8.86 ppm corresponded to the 3-NH hydrogen in the same alternating oxamide adipate units (1). Peaks at 2.26 and 1.49 ppm corresponded lo the 4-CH;- and 5-CH;- hydrogens, respectively, in the adipale linkages. These peaks verified the major alternating and crysiallizahle polyloxamide adipale) structure. Meanwhile, some esler-amide interchanging side reaction was observed in Fig. I. The peaks at 3.99. 3.26. and 2.06 ppm corresponded the 1'-, 2'-, and 4'-[CH.sub.2];- hydrogens in the esteramide units (11) formed because of the ester-amide interchanging side reaction. The peak at 7.90 ppm corresponded to the 3'-NH hydrogen in the same esteramide units (II). By comparison of the area ratios with those of the normal alternating oxamide adipale units (I), the amount of the ester-amide interchanging reaction was about 16.9%. Figure 2 shows the 'H NMR spectrum of ihe ExtPEAtf). 4>-3 with the ["/| of 0.47 dl/g. In Fig. 2. the peaks at 4.13 and 3.32 ppm corresponded lo 1-CH--and 2-CH;- hydrogens, respectively, in the alternating oxamide adipate units (I). The peak at 8.75 ppm corresponded lo the 3-NH hydrogen in the same alternating oxamide adipale units (I). The peaks at 2.25 and 1.48 ppm corresponded to the 4-CH;- and 5-CH;- hydrogens, respectively, in the adipate linkages. These peaks .dsn verified the major alternating and crystallizable poly(oxa-mide adipate) structure. The peaks at 3.90. 3.20. and 2.(X) ppm corresponded the 1'-, 2'-. and 4'-CH;- hydrogens, respectively, in the esteramide units (II) formed through the ester-amide interchanging side reaction. The amount of the ester-amide interchanging reaction increased lo I8.5(r. In Fig. 2. the peaks corresponding to the tereph-thalamide diesters units (III) were also observed. The peaks at 4.20 and 3.50 ppm corresponded to l"-CH;- and 2"-CH;- hydrogens, respectively, in the lerephlhalamide diesiers unils (III). The pc.ik ut 8.7(1 ppm corresponded lo he 3"-NH hydrogen in the same lerephthalamide diesters unils. Peak at 7.86 ppm corresnonded to 6-CH4- benzene hydrogens and the 3'-NH hydrogens in the esteramide units (II). It verified that chain extension look place between the HOOC- tenninal groups of the PrePBA(t), 4 is and the chain extender PBOX. As chain extension between the HO- terminal groups of the PrePEA(0. 4)s and ABC resulted in the adipale linkages, which were the same as ihose in Ihe alternating oxamide adipate unils (1), they showed the same chemical shifts and no other peaks were observed. Similarly, the PrePEA(0,4)-4 and ExtPEA(0.4)-4 were also characterized with 'H NMR spectra. The amount of the ester-amide interchanging reaction of them was 21.3% and 23.0%, respectively. Chain extension led lo the amount of the esteramide unils (II) increased slightly.

Figure 3 shows the FTIR spectra of ihe ExlPEA(0. 4) and ExtPEA(0, 8). In Fig. 3. the strong absorption peaks at 3401 and 3306 [cm.sup.-1) were assigned lo ihe N-H stretch-ing vibration of the amide groups in the alternating oxamide adipate units (I) or the esleramide unils (II) fonned by the esier-amide interchanging reaction, and the amide groups in the lerephihalamide dieslers units (III) fonned in the chain extension between the HOOC- terminal groups of the PrePEA(0. m)s and the chain ex-lender PBOX. The weak peak at 3071 cm1corresponded lo the H-C stretching vibration of the aromatic -ChHu units in the lerephthalamide dieslers units (III). Two peaks at 2946 and 2872 cm-1 corresponded lo the stretching vibration of C-H bonds in the -CH:- groups. There were two characteristic peaks corresponded lo the amide groups: one al 1658 cm-1 was assigned to the C=0 stretching vibration of the amide groups and the other at 1540 cm-1 was assigned to the N-H bending vibration in the secondary amide groups (amide II hand). Meanwhile, the characteristic peak al 1732 cm-1 corresponded to the stretching vibration of the ester C=0 groups in the oxamide adipate units (It in the main chains and those in the lerephthalamide diesters units (III) formed during the chain extension of PBOX.

DSC and TGA Characterization

The thermal behavior of ihe PrePEA(0.m)s and ihe ExtPEA((),m)s was characterized by DSC spectra. Figure 4 shows the second heating DSC curves of the PrePEA(0. 4)-3. PrePEA(0. 8)-2. ExiPEA(0. 4>-3. and the ExtPEA(0, 8)-2. The glass transition temperature (TA, crystallization temperaiure [(T.sub.t]). enthalpy of crystallization (A[H.sub.c]). melting point ([delta][H.sub.m]). and enthalpy of melting ([delta]H.m) of them were compiled in Table 4. From Fig. 4. and Table 4, it was found that the prepolyesteramides PrcPEA(0, 4)-3 and PrePEA(0. 8>-2 and the ExlPEAs ExtPEA(0. 4)-3 and ExtPEA(0. 8)-2 were all Ihe crystallized polymers. They all had iwo melting points ([T.sub.m]). a predominant exothermic peak and a small additional peak. These multiple fusion peaks showed similar characteristics to the polya-mides (27) and were usually associated wilh different populations of lamellar crystals. The higher melting points ([T.sub.m]) of the PrePEAtO. 4)-3 and PrePEA(t), 8)-2 were 155.3[degrees] and 150.1[degrees]C. respectively, but lhal of the ExtPEA(0. 4)-3 and ExtPEAtO. 8)-2 were 143.8[degrees]C and 140.8[degrees]0. respectively. After the chain extension, the [T.sub.m] decreased. The reason was that the chain extension between the HOOC- lenninal groups of the PrePEAtO. mis and the chain extender PBOX brought about the lerephthalamide dieslers unils (III), which were different from the major alternating oxamide adipate units (I) in the prepolyeste ram ides. After the chain extension, the regularity of the ExtPEA(0, 4)-3 and ExtPEA(0. 8)-2 decreased. Hence, the 7",,, also decreased. From Fig. 4 and Table 4. it was also found thai ihe ExtPEAs ExlPEAtO. 4)-3 and ExtPEA(0. 8)-2 had a obvious [T.sub.t] at 76."9[degrees]C and 54.97 C, respectively, but the prepolyesteramides PrePEAlO. 4)-3 and PrePEAlO. 8)-2 had not. Meanwhile, the [T.sub.t] of the ExtPEA(0. 4)-3 and ExiPEA(0. 8)-2 was much more obvious than thai of the PrePEA(0. 4)-3 and PrePEAlO. 8)-2. It meant that the amorphous ponion in the ExlPEA(0. 4)-3 and ExtPEA((), 8>-2 increased compared with lhal of the PrePEA(0, 4)-3 and PrePEA (0. 8)-2. Afler Ihe chain extension, the crystallization of the ExtPEAs lowered. As the PrePEA(0, 4>-3 and PrePEAlO. 8)-2 were all mainly terminated by HOOC- lenninal groups, chain extending reaction between the HOOC- lenninal groups and the PBOX was the major chain extension. The ter-ephihalamide dieslers unils (III) formed lowered the regularity of the ExtPEA(0. 4)-3 and ExlPEA(0. 8)-2. So the crystallization became difficult lo some extent. Meanwhile. the [T.sub.t] of ihe ExiPEA(0. 4)-3 and ExtPEA(0, 8)-2 was obviously higher lhan that of the PrePEA(0. 4)-3 and PrePEA(0, 8)-2, because Ihe lerephthalamide dieslers unils (III) fonned during ihe chain extension were rigid unils. Figure 5 showed the second heating DSC curves of the PrePEAtO. 4)-4. ExtPEA(0. 4)-4. and ExtPEA(0, 8)-3. Their [T.sub.g] [T.sub.c] and [T.sub.m] were also compiled in Table 4. Although PrePEA((). 4)-4 had higher molecular weight than PrePEA(0. 4)-3 as showed in Table I, the former had obviously lower [T.sub.m], than the latter. PrePEAtO. 4)-4 showed an obvious [T.sub.c] but not PrePEAlO. 4)-3. It meant that molecular weight had little effect on their thermal propenies. PrePEA(0. 4)-4 crystallized more difficultly than the PrePEA(0. 4)-3 maybe because PrePEAtO. 4)-4 had higher amount of the esleramide units (II) unils. which resulted from the ester-amide interchanging reaction as showed in the 'H NMR characterization. Similarly. ExtPEA(0. 4)-4 also showed lower [T.sub.m] and crystalling than ihat of the ExtPEA(0, 4)3 because ExiPEA(0, 4)-4 had higher amouni of esier-amide interchanging reaction.

TABLE 4. The second healing DSC data Of the
PrePEAtO. 41-3. Pre-PEA(0. 8)-2, ExtPEAtO. 4)-3.
and ihe ExiPEAlO. 8)-2.
                          [T.sub.g]     [T.sub.c]
Sample                    ([degrees]C)  ([degrees]C)
PrePEA(0,4)-3             1.64            -
PrePEA(0,8)-2             -7.32           -
ExtPEA(0,4)-(3.sup.b]   22.52           76.99
ExtPEA(0,8)-(2.sup.c]   9.89            54.97
PrcPEA(0,4)-4             1.84            55.09
ExtPEA(0,4)-(4.sup.d]'  25.84           91.54
ExtPEA (0,8)-(3.sup.e]  14.01           69.84
                          [DELTA][H.sub.c]  []
Sample                    (J/g)                 ([degrees]C)
PrePEA(0,4)-3             -                     118.70
PrePEA(0,8)-2             -                     133.42
ExtPEA(0,4)-(3.sup.b]   19.53                 119.39
ExtPEA(0,8)-(2.sup.c]   14.25                 127.62
PrcPEA(0,4)-4             25.X7                 116.35
ExtPEA(0,4)-(4.sup.d]'  20.76                 121.44
ExtPEA (0,8)-(3.sup.e]  21.38                 124.27
                          [DELTA][]  [T.sub.m2)
Sample                    (J/g)                  ([degrees]C)
PrePEA(0,4)-3             3.59                   155.30
PrePEA(0,8)-2             17.52                  150.10
ExtPEA(0,4)-(3.sup.b]   2.34                   143.83
ExtPEA(0,8)-(2.sup.c]   37.62                  140.83
PrcPEA(0,4)-4             -                      149.27
ExtPEA(0,4)-(4.sup.d]'  4.59                   136.68
ExtPEA (0,8)-(3.sup.e]  13.7                   137.12
Sample                    (J/g)
PrePEA(0,4)-3             2.3.34
PrePEA(0,8)-2             16.84
ExtPEA(0,4)-(3.sup.b]   11.78
ExtPEA(0,8)-(2.sup.c]   -
PrcPEA(0,4)-4             23.24
ExtPEA(0,4)-(4.sup.d]'  3.05
ExtPEA (0,8)-(3.sup.e]  1.69

The thermal properties of the PrePEAl(0, m)s and the ExlPEAt(0, m)s were also characterized by the cooling DSC spectra. Figure 6 shows the cooling DSC curves of ihe PrePEAlO. 4)-3. PrePEAtO. 8)-2, ExtPEA(0. 4)-3. and the ExtPEAfO. 8,-2. The cooling crystallization temperature ([] and the ccxiling crystallization enthalpy ([delta][]) daia were compiled in Table 5. From Fig. 6 and Table 5. it was found lhal the PrePEA(0. 4)-3 and PrePEAt(0. 8)-2 showed one or two [T.sub.m] peaks. ExlPEAtO, 4>-3 and ExtPEAtO. X)-2 just showed one [] peak. After the chain extension, the [T.sub.m] and the [delta[]] decreased. The crystallization of the ExlPEAs were also lowered because of the lerephthalamide dieslers units (III> introduced by the chain extension between the major HOOC- tenninal groups of Ihe PrePEAtO. m>s and the PBOX.

TABLE 5. The cooling DSC data of the PrePEA(0. 4)-?.
PrcPEA(0. 8)-2. ExiPEAlO. 4|-3. and ihe ExlPEA(0. 8)-2.
Sample'                  []    [DELTA][]
                         ([degrees]C)  (J/g)
PrePEA(0,4)-3            103.63          26.48
PrePEA(0.8)-2            59.27. 119.52   12.35, 35.25
ExtPEA(0.4)-(3.sup.b]  82.37           20.61
ExtPEA(0.8)-(2.sup.c]  109.37          36.50

Figure 7 shows the TGA curves of the ExtPEA(0, 4)-3 and the ExlPEAtO. 8)-2. The initial decomposition lemperaiure ([T.sub.i],) of the ExlPEAtO. 4)-3 and the ExlPEAtO, 8)-2 were 298.0[degrees]C and 3II.2[degrees]C. respectively. They had similar thermal stability and high enough to be processed with normal ihennally processing machines.

WAXS Analysis

The crystalline structure of the chain-extended polyesteramides was also determined by WAXS measurements. Figure 8 shows WAXD curves of ihe ExlPEAtO. 4)-3 and ExtPEAtO. 8)-2. The peaks corresponding lo ExtPEA(0. 4)-3 occurred at 20 of 21.16[degrees] and 22.24[degrees]. and those corresponding to ExlPEAtO. 8)-2 occurred at 2(7 of 21.28[degrees] and 22.11 . These ExlPEAs crystallized in the similar crystallites to those of the nylon-66 J28. 29) and polyesteramides having similar structure (301. The peak intensity relates to the crystalliniiy of them.

Tensile Testing

The mechanical properties of the ExlPEA(0, 4)-4 and ExlPEAtO, X)-3 were conducted and shown in Fig. 9. The tensile strength of the ExtPEAt(0, 4)-4 and ExlPEAt(0, 8)-3 was 31.47 and 23.70 MPa. respectively. The strain at break of them was 1.07%and 10.42 respectively. ExlPEAtO. 4)-4 showed higher lensile strength than the ExlPEAtO, 8)-3. They were all brittle and rigid plastics. They were also characterized by DMTA. ExtPEAtO. 4)-4 and ExtPEAtO, 8)-3 showed storage modulus (E') of 950.9 and 1108.4 MPa and loss modulus E" of 140.8 and 124.5 MPa (in Figs. 10 and 11). respectively. As storage modulus was directly related with ihe rigidity and loss modulus related with the impact toughening of ihe materials 131J, ExtPEAt(0, 4)-4 showing lower E' and higher E" meant lhal it had lower stiffness and higher flexibility. The reason might be thai ExtPEAt(0, 4)-4 had lower crystallinity or [[delta]H.sub.m]," as showed in Table 4 Different from Nylon-66, which had [T.sub.m] of 265[degrees]C and tensile strength up to 77 MPa (32), polyesteramides often showed much lower [T.sub.m] and tensile sirength. In our previous work, we had synthesized two random polyesteramides composed of hexylene adipamide and butylencs adipale units (33|. They showed [T.sub.m] up to 159.9. Their [T.sub.m] was just detected in the first heating DSC scan at heating rale of 20'C/min bul could nol be showed in ihe second heating DSC scan. They crystallized slowly and nol well. The polyesieramide having 40 mol9r amide showed tensile strength of 22.42 MPa. We also synthesized two types of alternating polyesteramides (ExtPEA (4, 4) and ExlPEA (4. 8)1 from A.A,-bis(2-hydroxyethyl)-adipamide and AA or SA ihrough polycondensalion and chain extension 130). Their T", detected in the first heating DSC scan al heating rate of 10[degrees]C/min was 83.8'C and 85.8[degrees]C. respectively, but could not be showed in the second healing DSC scan. They crystallized slowly. They had lensile strength up to 25.64 MPa. Their mechanical propenies were sensitive to ihe environments. Compared with those reported earlier, these two types of ExtPEAs synthesized here were all thermoplastic materials with better thermal properties and higher tensile strength.


PrePEAs PrePEA(0.m)s with both HO- and H0OC-lenninal groups were prepared through polycondensalion of HEOA wilh AA or SA. Under the catalysis of SnCh at reaction temperature nol higher than 180 C and reaction time no longer than X h. crystallizable PrePl:A(0,m)s were prepared through polycondensalion from HEOA and AA or SA. with low ester-amide interchanging side reaction occurred. Through chain extension of the Pre-PEA((),m)s with PBOX and ABC as combined chain exlenders. the ExtPEA (0. m)s wilh [eta] up lo 0.47 dl/g were obtained. The chain extension showed the best chain extending efficiency when the [SnCl.sub.2] and p-TSA were used as the combined catalysts. FT-IR and 'H NMR characterization showed that the ExtPEA (0. m)s were mainly constituted with the alternating diester oxamide unils. The ExtPEA (0. 4) and ExtPEA (0. 8) had [T.sub.m] of 143.8[degrees]C and 140.8[degrees]C, respeclively. and initial decomposition tempera lure above 298.OX. They crystallized in ihe similar crystallites lo Nylon-66. They were thennoplastic materials with good tensile strength. This methixi provides a promising way to synthesize aliphatic polyesteramides mainly composed of alternating diester diamide units through polycondensalion and chain extension directly from diamidediols and diacids as starting materials.


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Corresi>ondent c la: Jing Bo Zhao: e-mail: / and Wan Tai Yang: e-mail:

Contract grant sponsor: National Natural Science Foundation of China: contract grant numbers: 2124400ft Mti 50X73013.

DOI I0.1002/pen.236l2

Published online in Wiley Online Library

[C] 2013 Society of Plastics Engineers

Tiao Yin, (1),(2) Hui Yun Sun, (1),(2) Jing Bo Zhao, (1),(2) Zhi Yuan Zhang, (1),(2) Wan Tai Yang (1),(2)

(1) Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China

(2) State Key Laboratory of Chemical Resource Engineering, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China
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