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Miscibility and properties of new poly(propylene succinate)/poly(4-vinyl phenol) blends George Z Papageorgiou, Ifigenia Grigoriadou, Eleftherios Andriotis, Dimitrios N. Bikiaris, and Costas Panayiotou Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie4011657 • Publication Date (Web): 30 Jul 2013 Downloaded from http://pubs.acs.org on August 12, 2013

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Industrial & Engineering Chemistry Research

Miscibility and properties of new poly(propylene succinate)/poly(4-vinyl phenol) blends George Z. Papageorgiou, Ifigenia Grigoriadou, Eleftherios Andriotis, D.N. Bikiaris, Costas Panayiotou

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Miscibility and properties of new poly(propylene succinate)/poly(4-vinyl phenol) blends

George Z. Papageorgiou1*, Ifigenia Grigoriadou1, Eleftherios Andriotis1, D.N. Bikiaris1, Costas Panayiotou2

1

Department of Chemistry, Laboratory of Organic Chemical Technology, Aristotle

University of Thessaloniki, GR-541 24, Thessaloniki, Macedonia, Greece 2

Department of Chemical Engineering, Laboratory of Physical Chemistry, Aristotle

University of Thessaloniki, GR-541 24 Thessaloniki, Greece

*

Corresponding author: Tel: +30 2310 997812 Fax: +30 2310 997769 E-mail address: [email protected] (G.Z. Papageorgiou).


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ABSTRACT: Poly(propylene succinate) PPSu is a biodegradable polyester with fast biodegradation

rate.

New

semicrystalline/amorphous

blends

by

mixing

poly(propylene succinate) and poly(4-vinyl phenol) were prepared by solution casting. Single composition dependent glass transition temperature was observed over the entire composition range in DSC traces of the quenched blend samples showing miscibility in the amorphous phase. The blends were also found to be miscible in the melt phase as melting point depression evidenced. The Flory-Huggins interaction parameter was found to be χ1,2=-1.21. In FTIR spectra a small shift in the characteristic absorbance peaks for the ester carbonyl and hydroxyl groups of PVPh, supported the hypothesis of intermolecular interactions due to hydrogen bonding. Crystallization rates of PPSu in the blends were slower for the neat polymer. WAXD patterns showed that the final degree of crystallinity decreased with increasing PVPh content. Blends with intermediate composition were amorphous. The multiple melting behaviour of the blends was studied with standard and Step Scan DSC.

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Introduction Poly(4-vinyl phenol) (PVPh) is able to interact with proton-accepting functional groups of other polymers1. In literature, a number of studies reported miscible blends of PVPh with other polymers including poly(ethylene oxide), polymethacrylates, poly(vinyl alkyl ethers)2 (e.g., poly(vinyl methyl ether) and poly(vinyl ethyl ether)), poly(vinyl methyl ketone). Furthermore, PVPh forms miscible blends with aliphatic polyesters like poly(D,L-lactide)3, 4, (e.g., poly(εcaprolactone)5-9, poly(butylene succinate) (PBSu)10,

11

, poly(ethylene succinate)

(PESu)12, poly(β-hydroxybutyrate), poly(ethylene adipate), and poly(butylene adipate)13-16 or with aromatic polyesters (e.g., poly(ethylene terephthalate), poly(butylene

terephthalate)

(PBT),

poly(trimethylene

terephthalate),

and

17, 18

poly(ethylene 2,6-naphthalene dicarboxylate)

. Besides, blends of biodegradable

polyesters gained attention recently. Published works mainly deal with blends of the well-known aliphatic polyesters poly(ε-caprolactone), poly(lactic acid), poly(ethylene succinate) and poly(butylene succinate)19-23 or others 24-27. In past, 1,3-propanediol (1,3-PD) was not available in the market at low cost and in sufficient amounts and purity for polymerization, so polyesters of 1,2ethyleneglycol and 1,4-butanediol dominated

28, 29

. However, in recent years, more

attractive processes have been developed for the production of 1,3-PD, including selective hydration of acrolein followed by catalytic hydrogenation of the intermediate 3-hydroxypropionaldehyde, hydroformylation of ethylene-oxide, and various other biotechnological methods. Polyesters of 1,3-PD are characterized by excellent properties and are most promising, e.g. poly(propylene terephthalate) (PPT) or the aliphatic polyester poly(propylene succinate) (PPSu) 30-33. PPSu has attracted considerable attention, because of its biodegradability and biocompatibility, combined with its physical and chemical properties. The properties of PPSu can be modified by blending, and the application field of PPSu can also be extended. However, as it is a relatively new polymer, very few works on PPSu blends have been published

34, 35

.As was reported previously PBSu/PVPh and PESu/PVPh

blends proved to be miscible.19-23 PESu, PPSu and PBSu are only different in their numbers of methylene groups between the two ether groups, namely 2, 3 and 4 for PESu, PPSu and PESu, respectively. Thus PPSu/PVPh blends may be a new miscible 2 ACS Paragon Plus Environment

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crystalline/amorphous polymer blends model since the carbonyl group of PPSu is likely to form a hydrogen bond with the hydroxyl group of PVPh as in the case of PBSu/PVPh and PESu/PVPh blends. To the best of our knowledge, in contrast to PESu/PVPh and PBSu/PVPh blends which have been extensively studied, PPSu/PVPh blends have not been reported so far in the literature. Therefore, the purpose of this manuscript is to investigate the miscibility and crystallization of PPSu/PVPh blends. This pair leads to miscibility and finally to amorphous materials on cooling from the melt. Given the characteristics of PPSu, fast biodegradation, biocompatibility, production from monomers from renewable resources and low crystallinity, its blends and copolymers are of special interest for applications in medicine and pharmaceutics. Biodegradation and biocompatibility studies of PPSu copolymers have been already studied,30,31 however relevant studies on PPSu/PVPh blends have been scheduled and will be part of a future work on PPSu/blends. As a matter of fact, polymer blends where one of the component is biodegradable, like polyethylene/starch blends, are also very interesting and can be used in practical applications. Furthermore, this is the first time that hydrogen bonding in PPSu blends is studied. O

(CH2)3

O

C

(CH2)2

C O n

O

Poly(propylene succinate) CH2

CH n

OH

Poly(4-vinyl phenol) Scheme 1. Repeating units of Poly(propylene succinate) and Poly(4-vinyl phenol).

The chemical structures of PPSu and PVPh are shown in Scheme 1. According to the chemical structures of the two polymers hydrogen-bonding is expected to occur between the two polymers. So, the miscibility of the polymer pair in the amorphous phase is investigated using DSC. Interactions are analyzed by FTIR. Miscibility of the polymer pair in the melt phase and polymer-polymer interaction parameter have been studied according to the melting point depression method. 3 ACS Paragon Plus Environment


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Experimental Section Materials. Succinic acid (purum 99 %) was purchased from Aldrich Chemical Co. 1,3-Propanediol (1,3-PD) (CAS Number: 504-63-2, Purity: > 99,7 %) was kindly supplied by Du Pont de Nemours Co. Tetrabutyl titanate catalyst of analytical grade and polyphosphoric acid (PPA) used as heat stabilizer were purchased from Aldrich Chemical Co. Amorphous Poly(4-vinyl phenol) (PVPh), with Mn=22,000 g mol-1, was obtained from Aldrich Chemical Co. All the other materials and solvents which were used for the analytical methods were of analytical grade. PPSu was prepared by the two-stage melt polycondensation method (esterification and polycondensation) in a glass batch reactor. Proper amount of succinic acid and 1,3-PD in a acid/diol molar ratio 1/1.1 and the catalyst Ti(OBu)4 were charged into the reaction tube of the polyesterification apparatus. The apparatus with the reagents was evacuated several times and filled with argon in order to remove the whole oxygen amount. The reaction mixture was heated at 180oC under argon atmosphere and stirring at a constant speed (500 rpm). This first step (esterification) is considered to complete after almost all the theoretical amount of water was collected (about 3.5 h) as the reaction by-product of esterification. In the second step PPA was added (5x10-4 mol PPA/mol SA), which is believed to prevent side reactions such as etherification and thermal decomposition. A vacuum (5.0 Pa) was applied slowly over a period of time of about 30 min, to avoid excessive foaming and to minimize oligomer sublimation, which is a potential problem during the melt polycondensation. The temperature was slowly increased to 230oC while stirring speed was increased at 720 rpm. Such high speed is necessary in order to create a thin film of viscous polymer on the reaction tube surface and thus the diffusion of formed oligomers from the polyester melt to be easier. The polycondensation continued for about 60 min. Blend preparation. Methyl ethyl ketone (MEK) with b.p.=79.6 oC was used as a mutual solvent of the two polymers. Each polymer was dissolved in separate. After complete dissolution, the two solutions were mixed.

To assist homogenization

sonication for 10 min was applied. Solutions of 0.01 g/ml were formed. Films were 4 ACS Paragon Plus Environment

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prepared by solution-casting. Removal of solvent was achieved by evaporation at room temperature for two weeks. Usually, as was found by mass loss measurements, the weight of the films did not change after 10 days. The PPSu/PVPh w/w compositions of the blends were 100/0. 95/5, 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80 and 0/100. Characterization Intrinsic viscosity measurement. Intrinsic viscosity measurements of the synthesized PPSu were performed using an Ubbelohde viscometer Oc at 25oC in chloroform, at a solution concentration of 1 wt%. The intrinsic viscosity of the sample was found to be 0.5 dL/g.

Gel permeation chromatography (GPC). GPC analysis was performed using a Waters 150C GPC equipped with differential refractometer as detector and three ultrastyragel (103, 104, 105 A) columns in series. CHCl3 was used as the eluent (1 mL/min) and the measurements were performed at 35°C. Calibration was performed using polystyrene standards with a narrow molecular weight distribution. Results showed that the number average molecular weight (Mn) of PPSu was equal to 13,130 Da and weight average molecular weight (Mw) was 32,210 Da and the polydispersity Mw/Mn=2.45. Differential Scanning Calorimetry (DSC). A Perkin–Elmer, Pyris Diamond differential scanning calorimeter (DSC), calibrated with Indium and Zinc standards, was used for the study the thermal behaviour of the blends. Samples of 5±0.1 mg were used in tests. They were sealed in aluminium pans and heated at a heating rate 20°C/min to 220°C. To obtain amorphous samples, rapid cooling from the melt at a rate 200oC/min was applied in the instrument. For isothermal crystallizations the sample was first rapidly cooled (cooling rate 200oC/min) from the melt to a temperature, 20oC above the crystallization temperature. Finally, the sample was cooled to Tc, at a rate 50oC/min. This final slower cooling aimed to achieve equilibration of the instrument. Then, the sample was left to crystallize isothermally at Tc and the crystallization exothermic peak was recorded. Subsequent heating scans were performed at a rate of 20°C/min. If some



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other procedure was followed in specific tests this will be described in the corresponding part.

FTIR spectroscopy. FTIR spectra were obtained using a Perkin–Elmer FTIR spectrometer, model Spectrum 1000 using KBr tablets. The resolution for each spectrum was 2 cm−1 and the number of co-added scans was 64. The spectra presented were baseline corrected and converted to the absorbance mode.

Wide Angle X-ray Diffractometry (WAXD). WAXD study of the blends, in the form of powder, were performed over the range 2θ from 5 to 60o, at steps of 0.05o and counting time of 5 seconds, using a MiniFlex II XRD system from Rigaku Co.

Results and Discussion

Blend

preparation.

PPSu

was

prepared

by

the

two-stage

melt

polycondensation method (esterification and polycondensation). GPC measurements showed that the number average molecular weight (Mn) of PPSu was equal to 13,130 Da and weight average molecular weight (Mw) was 32,210 Da and the polydispersity Mw/Mn=2.45. PPSu/PVPh blends were prepared by solution casting using methyl ethyl ketone (MEK) as a mutual solvent of the two polymers.

Glass transition. Glass transition behavior is often used as criterion to judge miscibility of polymer blends. Miscible polymer pairs show a single glass transition temperature (Tg), intermediate between those of the pure polymers. In the DSC heating traces of the PPSu/PVPh blends after melt quenching, single glass transition was observed for the whole range of blend composition as can be seen in Fig 1a. To investigate details, Step Scan DSC was also used. Tg values are summarized in Table 1. Although a single glass transition was observed for all blends in the DSC traces and the reversing signal curves of the Step Scan DSC, the width of the Tg region within some blends was increased. This has been observed in literature and as a matter of fact recent research on blends has shown that in fact even miscible blends 6 ACS Paragon Plus Environment

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show two distinct Tgs, which can be observed most frequently by other techniques such as dielectric relaxation or fluorescence spectroscopy.36 Table 1. Figure 1b shows the dependence of the glass transition temperature (Tg) of quenched samples of the blends. As can be seen Tg values increased monotonically with PVPh content, between the two values for the neat polymers, i.e. -33oC for PPSu and 183oC for PVPh. Among the equations proposed to describe the Tg-composition dependence of miscible polymer blends the Fox equation is the often used

37

. In the

equation of Fox 37 w w 1 = 1 + 2 Tg Tg 1 Tg 2

(1)

w1 and w2 are the weight fractions of the comonomers and Tg1 and Tg2 the glass transition temperatures of the respective homopolymers. In the Kwei equation 38 Tg = ( w1Tg1 + kw2Tg ) /( w1 + kw2 ) + qw1w2

(2)

k and q are fitting constants. k is the ratio of ∆αΒ/∆αΑ where ∆αΑ and ∆αΒ are the changes in the thermal expansion coefficients at Tg. The first term on the right-hand side of eq. 2 is the widely used Gordon-Taylor equation

39

. The second term

corresponds to the strength of hydrogen bonding in the blend, reflecting a balance between the breaking of the self-association interactions and the forming of the interassociation interactions through hydrogen bonding. In systems with a highly symmetric deviation from linearity, it is common practice to set k=1; fitting to a single parameter, with a simplified Kwei equation 38 Tg = w1Tg1 + kw2Tg + qw1w2

(3)

The fit of experimental data to the Kwei equation is also shown in Figure 1. Large negative values for q suggest weak specific interactions responsible for miscibility. The Gordon-Taylor and the Fox equation do not fit well the experimental values. Furthermore the Couchman-Karasz (C-K) equation was tested

40

. The

Couchman-Karasz equation is given by 40

ln Tg =

wI ∆C pI ln TgI + w II ∆C pII ln TgII wII ∆C pI ln TgI + wII ∆C pII ln TgII

(4)



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The C-K shows slight deviation from the experimental values as can be seen in Figure 1. As can be seen best fit can be achieved by the Kwei model.

Figure 1.

The above is, of course, a rather crude approach that accounts for the “similarity” principle of miscibility but disregards entirely the “complementarity” principle of miscibility.41, 42 A sound discussion of miscibility of the PPSu – PVPh blend should account for the fact that PPSu is a proton acceptor or electron donor (Lewis base) via its ester groups while PVPh has both acidic and basic character via its hydroxyl groups. As a consequence, PVPh has the capacity to self-associate (OH--OH hydrogen bonding interactions) as well as the capacity to cross-associate (OH--COO interactions). It is, primarily, the interplay of these two competing interactions that will dictate ultimately the extent of miscibility in the blend. A thermodynamically consistent treatment of miscibility along these lines is postponed to a forthcoming publication after we determine the Partial Solvation Parameters (PSPs)

43, 44

of the

pure polymers.

FTIR spectra. It is well known that miscibility of PVPh with aliphatic polyesters is induced by hydrogen bonding between hydroxyl groups of PVPh and carbonyl groups of the polyester

3, 4, 45

. For the study of specific interactions in polymer blends in

which the miscibility driving force is hydrogen bonding between components, infrared spectroscopy has been widely used. Miscibility between PVPh and biodegradable aliphatic polyesters, such as poly(hydroxybutyrate) and poly(εcaprolactone) (PCL), has also been reported, and hydrogen bonding has been confirmed by FTIR in these systems

16, 25

. So in this work the FTIR spectra of the

blend samples were recorded and the study focused on the hydroxyl and ester groups absorption band regions.

In the spectra of PVPh there is a characteristic peak which is attributed to the hydroxyl groups absorption, appearing at around 3359 cm-1 of –OH and a shoulder at 3525 cm-1 (Figure 2). In the spectra of the blends, these peaks shifted at progressively higher wavenumbers. This is an indication that the chemical environment of –OH 8 ACS Paragon Plus Environment

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group has changed after blending with PPSu. Actually it is expected that, in pure PVPh, OH are likely to be self-associated. As PPSu is added, cross H-bonding form and another peak emerges at higher wavenumbers, associated to OH interacting with carbonyls. Hence, in the blend coexist the signals generated by the self-associated OH and the signals generated by the cross-associated OH, the latter increasing as the amount of PPSu increases. Since the energy of self-association is expected to be greater than that of cross-association, the peak related to cross-associated OH groups is located at higher wavenumbers.

Figure 2. Figure 3. On the other hand the characteristic absorbance of ester groups of PPSu appears at about 1745 cm-1 while the other characteristic band of carboxylic group is recorded at 1737 cm-1. However, in the blends both a broadening of the band towards lower wavenumbers and an increase of intensity of absorbance of shoulder are observed with higher PVPh content (Figure 3). This is also an indication that the ester carbonyl groups and the carboxyl end groups of PPSu participate at hydrogen bonding with -OH groups of PVPh inducing miscibility.

Crystallization and melting behavior. Figure 4a shows the WAXD patterns of neat PPSu and the PPSu/PVPh 80/20 blend. Crystalline reflections prove that the blend had some crystallinity. Furthermore, no change in peak position or appearance of new peaks was observed in the WAXD patterns of the blends. This means that PPSu crystals of the same modification formed in the blends. In fact PPSu is slowly crystallizing polyester 47. So, it can either be obtained as glassy or semicrystalline material. PVPh is an amorphous polymer. As expected all of the blends are also amorphous after melt quenching. The isothermal crystallization of neat PPSu or PPSu in the blends was studied at various temperatures after melting at 90oC and fast cooling from the melt. However, the crystallization was slow and took long time as can be realized from the isothermal crystallization half times plots of Figure 4b. Crystallization of blends got slower with increasing the PVPh content. Subsequent heating scans of the crystallized samples were recorded on heating at 20oC/min. Figure 5 shows the melting traces of PPSu/PVPh 95/5 and 90/10 blends after isothermal crystallization from the melt. 9 ACS Paragon Plus Environment


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Figure 4. Figure 5. Figure 6. In DSC traces of Figure 5, multiple melting peaks are observed. This behaviour is similar to that of neat PPSu.47 A thorough study of the melting behaviour of the blends was conducted to understand the nature of each endotherm in DSC traces. Thus, the effect of the crystallization time on the subsequent melting behaviour and the effect of the heating rate were investigated. Furthermore, Step Scan studies of the melting behaviour were performed. In the standard DSC traces of the blends, like for neat PPSu, first appeared the so-called annealing peak, at about 7-10oC above the crystallization temperature. A middle endothermic peak and an ultimate peak also appeared at higher temperatures. In Figure 6a it is clear that the low temperature peak rises after significant crystallinity has already formed and its heat of fusion increases at a slower rate than the other two peaks. This fact in combination with the low peak temperature, prove that the low temperature peak has to do with secondary crystals. The temperature of the annealing peak and the middle melting peak temperature steadily increase with crystallization temperature. On the other hand, the high temperature melting peak is about constant. In the traces showing the melting behaviour after crystallization at high temperature close to the melting region, for example at Tc=30oC, the middle and high temperature melting peaks coincided, leaving only one peak of increasing temperature. Figure 6b shows the Step Scan DSC traces for PPSu/PVPh 95/5 blend after isothermal crystallization from the melt at 10oC for 90 min. In the non-reversing signal curve of Figure 6b, the recrystallization exothermic peak is obvious. So, it is clear that recrystallization takes place on heating the isothermally crystallized blend samples. Recrystallization most often plays important role in appearance of multiple melting behaviours of polymers.47 Recrystallization during heating isothermally crystallized PPSu/PVPh blends samples was also verified by DSC traces on heating at different heating rates, not shown here for briefness. The above findings verified that the melting-recrystallization-final melting scheme, is appropriate for interpretation of the melting behaviour of the blends. Multiple melting has also been reported for other biodegradable polyester/PVPh blends

10-12, 36

and in most cases the phenomenon was interpreted in the context of 10 ACS Paragon Plus Environment

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partial melting recrystallization. After all, it was concluded that the middle melting peak appearing in the DSC traces of the PPSu/PVPh blends is associated with melting of primary crystals. On the other hand the ultimate temperature melting peak was attributed to the melting of the recrystallized material. Finally, the triple melting behaviour is more pronounced for PPSu/PVPh 95/5 compared to the 90/10 sample (Figure 6). Thus with increasing the content of the minor component in blends recrystallization is limited.

Determination of Equilibrium Melting Temperature. The most popular method for the estimation of the equilibrium melting point of polymers is that of HoffmannWeeks.48 According to this procedure, the measured melting temperatures (Tm) of samples isothermally crystallized at various temperatures (Tcs) are plotted against the crystallization temperatures. Linear extrapolation to the line Tm = Tc gives an intercept equal to Tmo. The associated equation is

1 T Tm = Tmo (1− ) + c r r

(5)

Tm is the observed melting temperature of a crystal formed at a temperature Tc, r is the thickening coefficient equal to lc/lg* where lc is the thickness of the grown crystal and lg* is the initial thickness of a chain-folded lamellar crystal.48 The prerequisite for the application of this theory is the isothermal thickening process of lamellar crystals at a specific crystallization temperature and the dependence of the thickening coefficient on the crystallization temperature. For the determination of the Tmo of PPSu in the blends the middle peak temperature values were plotted vs the crystallization temperature (Figure 7). A decrease in Tmo values was observed for the blends (Table 1).

Figure 7. Equilibrium Melting Point Depression. Thermodynamic considerations predict that the chemical potential of a polymer will be decreased by the addition of miscible diluents. If the polymer is crystallizable, this decrease in chemical potential will result in a decreased equilibrium melting point. The equilibrium melting temperatures can be analyzed by the Flory-Huggins equation 49



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1 o m ( blend )

T

−

1 o m ( pure )

T

=

 − R V2  ln φ 2  1 1  φ1 + χ 12φ1 2  +  −  0 ∆H V1  m 2  m 2 m1  

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(6)

where the subscripts 1 and 2 refer to the amorphous and the crystalline polymer, respectively. T0m(pure) and T0m(blend)) denote the equilibrium melting points of the pure crystallizable component and that of the blend, respectively. V1, V2 are the molar volumes of the repeating units of the polymers, R is the universal gas constant, ∆Η0 is the heat of fusion of the perfectly crystallizable polymer, m is the degree of polymerization, φ is the volume fraction of the component in the blend, and χ12 is the polymer-polymer interaction parameter. The molecular volume is 126.1 cm3/mol for PPSu and 100 cm3/mol for PVPh. The enthalpy of fusion is ∆Ηmo = 22.12 kJ/mol for PPSu. For high molecular weight polymers, both m1 and m2 are large and the related terms can be neglected:

−

∆H 0V1  1 1 − 0 0  RV2  Tm ( blend ) Tm ( pure )

  = x12φ12  

(7)

If χ12 is assumed to be independent of composition, a plot of the left-hand side of eq 7 versus φ12 should give a straight line passing through the origin. The interaction parameter is implicitly referred to a reference volume, Vr, usually defined in terms of the molar volume of the amorphous component in the mixture. However, since the monomer volumes of polymers 1 and 2 are usually significantly different from each other, different systems cannot be compared by using χ12. In contrast, the interaction energy density can be used. The interaction energy density is a different form to express the Flory-Huggins interaction parameter eliminating the reference volume:

RTx12 (8) Vr where Vr is a reference volume, usually defined in terms of the molar volume of the B=

amorphous component in the mixture. Substituting φ12 from this equation in the Flory-Huggins equation yields the Nishi-Wang equation50


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o Tmo − Tmb = Tmo

BV2 2 φ1 ∆H m

(9)

The equilibrium melting temperatures for pure PPSu and blends of given compositions were used prior to eliminate the morphological effect from the melting point depression. The plot of

∆H 0V1  1 1  vs φ12 can be seen in Figure 8. − 0 0   RV2  Tm ( blend ) Tm ( pure ) 

The resulting values were χ12=-1.21 and B=-33 J/cm3. A moderately negative interaction parameter value indicates miscibility of the blend components. Similar findings were reported for other pairs of biodegradable polymers and PVPh, like PLLA/PVPh, PCL/PVPh, PESu/PVPh or PBSu/PVPh or PESeb/PVPh.3-8, 10-16, 36

Figure 11.

Conclusions

PPSu is slow crystallizing aliphatic polyester with fast biodegradation and most promising polymer. Copolymers and blends of such materials are of special interest. In this work PPSu/PVPh blends were found to show single composition dependent glass transition and thus miscibility. The FTIR spectra of the blends evidenced hydrogen bond interactions between the two blend components. Equilibrium melting points calculated with application of the HoffmannWeeks extrapolation were found to decrease with increasing the PVPh content. The analysis of the melting point depression by using the Nishi-Wang equation resulted in a negative value for the interaction parameter (χ12=-1.21), indicating miscibility in the melt phase. Crystallization rates got slower with increasing the PVPh content, while the ultimate crystallinity of the blends decreased as WAXD patterns and DSC traces showed. The multiple melting behavior of the blends after isothermal crystallization was studied with standard DSC as well as with Step Scan DSC. The non reversing 13 ACS Paragon Plus Environment


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signal clearly evidenced recrystallization at the melting temperatures region. Thus the phenomena were interpreted in the context of the partial melting, recrystallization and final melting.

References

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CAPTIONS TO TABLES AND FIGURES Table 1 Glass transition temperature (Tg), Cp increase in glass transition (∆Cp), melting point (Tm), heat of fusion (∆Hm), degree of crystallinity (Xc), equilibrium melting point (Tmo).

Figure 1. a) DSC traces for melt quenched blend samples. b) Experimental Tg values vs PVPh content and theoretical predictions using the Fox, Gordon-Taylor, Kwei and Cauchman-Karasz models.

Figure 2. FTIR spectra of the blends in the hydroxyl group absorbance region. Figure 3. FTIR spectra of the blends in the carbonyl absorbance region. Figure 4. a) WAXD patterns of neat PPSu and the PPSu/PVPh 80/20 blend and b) isothermal crystallization half times for neat PPSu and PPSu/PVPh 95/5 and 90/10 blends.

Figure 5. DSC heating traces of a) PPSu/PVPh 95/5 and b) PPSu/PVPh 90/10 blend after isothermal crystallization from the melt. Heating rate 20oC/min.

Figure 6. DSC heating traces of a) PPSu/PVPh 95/5 samples crystallized for different times at 10oC and b) Step Scan DSC traces for PPSu/PVPh 95/5 blend after isothermal crystallization from the melt at 10oC for 90 min.

Figure 7. Hoffmann-Weeks plots for the PPSu/PVPh blends. Figure 8. Determination of parameter B (plot of

∆H 0V1  1 1  vs. φ12 ). − 0 0  RV2  Tm ( blend ) Tm ( pure ) 



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Table 1. Glass transition temperature (Tg), Cp increase in glass transition (∆Cp), melting point (Tm), heat of fusion (∆Hm), degree of crystallinity (Xc), equilibrium melting point (Tmo). 37x30mm (600 x 600 DPI)



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Fig. 1. a) DSC traces for melt quenched blend samples. b) Experimental Tg values vs PVPh content and theoretical predictions using the Fox, Gordon-Taylor, Kwei and Cauchman-Karasz models.


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Fig. 2. FTIR spectra of the blends in the hydroxyl group absorbance region. 168x134mm (600 x 600 DPI)



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Fig. 3. FTIR spectra of the blends in the carbonyl absorbance region. 166x130mm (600 x 600 DPI)


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Fig. 4. a) WAXD patterns of neat PPSu and the PPSu/PVPh 80/20 blend and b) isothermal crystallization half times for neat PPSu and PPSu/PVPh 95/5 and 90/10 blends. 203x290mm (96 x 96 DPI)



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Fig. 5. DSC heating traces of a) PPSu/PVPh 95/5 and b) PPSu/PVPh 90/10 blend after isothermal crystallization from the melt. Heating rate 20oC/min. 203x290mm (96 x 96 DPI)


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Fig. 6. DSC heating traces of a) PPSu/PVPh 95/5 samples crystallized for different times at 10oC and b) Step Scan DSC traces for PPSu/PVPh 95/5 blend after isothermal crystallization from the melt at 10oC for 90 min. 203x290mm (96 x 96 DPI)



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Fig. 7. Hoffmann-Weeks plots for the PPSu/PVPh blends. 169x130mm (600 x 600 DPI)


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Fig. 8. Determination of parameter B. 229x182mm (300 x 300 DPI)


Poly(4

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