Blend of Poly(ε-caprolactone) and 4,4′-Thiodiphenol: Hydrogen Bond Formation and Some Solid Properties

Macromol. Chem. Phys. 2001, 202, 1035–1043 1035

Blend of Poly(e-caprolactone) and 4,49-Thiodiphenol:

Hydrogen Bond Formation and Some Solid Properties

Yong He, Naoki Asakawa, Yoshio Inoue*

Department of Biomolecular Engineering, Tokyo Institute of Technology,Nagatsuta 4259, Midori-ku, Yokohama 226-8501, JapanFax: +81-45-924-5827; E-mail: [email protected]

Introduction

In the last few years, poly(4-vinylphenol) (PVPh) and a

variety of polymers with functional groups, such as car-

bonyl and ether groups have been reported to be miscible

or at least partially miscible over a wide range of compo-

sition in the amorphous state due to the formation of the

inter-associated hydrogen-bond between the hydroxyl

group of PVPh and functional groups of the second poly-

mers.[1–4] It was also reported that PVPh improved the

miscibility between the immiscible polymer pairs.[5–7]

Dihydric phenol is considered as a simplified dimmer

model of PVPh in terms of chemical structure and it pos-

sesses the potential ability to form a strong intermolecular

hydrogen bond with carbonyl, ether or other functional

groups. We have found that the two hydroxy groups in a

molecule of dihydric phenol could form two hydrogen

bonds at the same time with two carbonyl groups of dif-

ferent polymer chains.[8] We expect that dihydric phenol

could be used as a compatibilizer to improve the miscibil-

ity between the immiscible polymer pairs through the

intermolecular hydrogen bonds formed between dihydric

phenol and the immiscible polymer pairs.

On the other hand, nowadays a variety of low-molecu-

lar weight additives are included into industrial polymer

materials to modify their properties and then greatly

widen the application fields. For example, carbon black,

calcium carbonate and silicon dioxide are added as fillers

into rubber or plastics to improve the mechanical proper-

ties; Dialkyl phthalates are incorporated into poly(vinyl

chloride) materials as plasticizers to improve their pro-

cessability and flexibility. These additives have been

widely used in industry and the effects of these additives

on the properties of polymer are extensively studied.

However, little attention has been paid to the effect of

dihydric phenol as additive on the properties of polymer

so far. Just recently, Wu et al. have reported that the addi-

tion of dihydric phenol can greatly improve the damping

properties of polymer materials.[9] In a previous work, we

Full Paper: The formation of the inter-associated hydro-gen bond between poly(e-caprolactone) (PCL) and 4,49-thiodiphenol (TDP) was investigated as a function of com-position and temperature by temperature-variable Fouriertransform infrared spectroscopy. It was found that thefractions of associated carbonyl groups in PCL/TDPblends increased with the increase of TDP content anddecreased with the increase of temperature. The enthalpyof the inter-associated hydrogen bond was evaluated to be–5.30 kcal/mol. The molecular dynamics of PCL in theblends was also studied by high-resolution solid-state13C NMR. From the results, it was suggested that TDPmolecule exerted its influences on the molecular motionof PCL mainly through lowering the crystallinity of PCLrather than forming a hydrogen-bonded network with PCLchain.

Macromol. Chem. Phys. 2001, 202, No. 7 i WILEY-VCH Verlag GmbH, D-69451 Weinheim 2001 1022-1352/2001/0704–1035$17.50+.50/0

The FTIR spectra of the PCLTDP40 blend in the hydroxylvibration region recorded at different temperatures. From topto bottom, the temperatures are 26, 35, 45, 65, 90, 120 and1608C.

1036 Y. He, N. Asakawa, Y. Inoue

have also found that 4,49-thiodiphenol (TDP) is effective

for the modification of the thermal and mechanical prop-

erties of polyesters[8].

It is well known that the type and strength of interac-

tions between the low-molecular weight compounds and

polymers are crucial to the practical uses of low-molecu-

lar weight additives. In this paper, we will focus on the

formation of the inter-associated hydrogen bond between

poly(e-caprolactone) (PCL) and TDP and we will try to

elucidate the relationship between this specific interac-

tion and the properties of the blends. By employing Four-

ier transform infrared spectroscopy (FTIR), the formation

of the inter-associated hydrogen bond will be investigated

as a function of composition and temperature. Then, the

effect of TDP on the molecular mobility of PCL will be

also studied by high-resolution solid-state 13C NMR spec-

tra.

Experimental Part

Materials

Poly(e-caprolactone) (PCL) sample (M—

n = 5.35 N 104, M—

w/M—

n

= 1.47; Celgreenm-PH4) was supplied by the courtesy of Dai-cel Chemical Industries, Ltd., Japan. 4,49-thiodiphenol (TDP)was purchased from Tokyo Kasei Kogyo Co., Japan. Boththe PCL and TDP samples were used as received.

Preparation of Blend Samples

PCL and 4,49-thiodiphenol in appropriate weight ratios werefirstly dissolved in 1,4-dioxane (total polymer concentrationis about 5 wt.-%). Then, the solution was cast on the glassPetri dish and the solvent was evaporated at room tempera-ture over night. The cast films were placed in an oven at608C under vacuum for two days to remove the residual sol-vent. After that, the films were further aged at room tempera-ture for more than four weeks before the NMR measure-ment.

Fourier Transform Infrared (FTIR) Spectra

Films of the blends with a thickness suitable for FTIR meas-urements were prepared by directly dropping the polymer1,4-dioxane solution (polymer concentration is about1.5 wt.-%) on the surface of a silicon wafer. The siliconwafer is transparent for IR incident beam and was used asthe substrate. The thickness of the cast film was carefullycontrolled to be thin enough to ensure that the studied IRabsorption was within the linearity range of the detector.

IR measurements were carried out on a single-beam IRspectrometer of Perkin Elmer Spectra 2000, equipped with adigital temperature controller. All FTIR spectra wererecorded under a given temperature at a resolution of 4 cm–1

with an accumulation of 16 scans.

High-Resolution Solid-State 13C NMR

The high-resolution solid-state 13C NMR spectra were meas-ured at room temperature on a Varian Unity 400 NMR spec-

trometer (100 MHz for 13C nucleus). The DD/MAS (dipolar-decoupling/magic angle spinning) spectra of pure PCL andthe blends were measured under high-power proton dipolar-decoupling (ca. 59.5 kHz). Their CP (cross-polarization)/MAS spectra were recorded under a 1H-13C cross-polariza-tion time of 2.2 ms. The pulse repetition time was set at 5 sand the magic angle spinning rate was optimized at 5000 l 2Hz.

The CP/MAS spectrum of pure TDP was measured with a1H-13C cross-polarization time of 2.5 ms and a pulse repeti-tion time of 90 s. In order to simplify the CP/MAS spectrumof TDP, the TOSS (total side band suppression) techniquewas used to eliminate the spinning side bands.[10]

For the determination of the cross-polarization time con-stant (TCH), the CP/MAS spectra of PCL and the blends werealso generated as a function of the cross-polarization time.For each spectrum at least 512 transients were accumulated.The chemical shifts of the 13C nuclei were referenced to theCH3 resonance of hexamethylbenzene (HMB) as the externalstandard (17.4 ppm from TMS).

Lineshape Analysis of FTIR and NMR Spectra

A curve-fitting program was used to separate the PCL carbo-nyl vibration bands into three components: the amorphous,crystalline and hydrogen bonded components. This programis based on the least-squares parameter adjustment criterionusing the Gauss-Newton iteration procedure.[11] The fitadjusts the peak position, the lineshape (a Gaussian fractionwhereby 0 represent a pure Lorentzian and 1 represent a pureGaussian), peak width and height in such a way that a best fitis obtained. This program was also used to resolve the carbonresonances in the high-resolution solid-state 13C NMR spec-tra of PCL/TDP blends.

Results and Discussion

Hydrogen Bond Between PCL and TDP

Observed by FTIR and Solid-State NMR

FTIR spectroscopy is a particularly suitable technique for

the investigation of the inter-associated hydrogen bond.

The FTIR spectra of PCL/TDP blends in the hydroxyl

vibration region and in the carbonyl vibration region are

shown in Figure 1 as a function of TDP composition. As

can be seen in Figure 1a, three vibration bands centered

at 3318, 3265 and 3183 cm–1 appears in the spectrum of

pure TDP. For pure PCL, only a very weak band centered

at 3447 cm–1 is observed in this region, which should be

attributed to the vibration of the hydroxy group in the

chain terminal of PCL. In the spectra of PCL/TDP blends,

a broad band appeared at 3383 cm–1 and its relative

absorbance increased with increasing content of TDP. As

the vibration band of pure PCL in this region was very

weak, the differences (in wave number and shape),

between the bands of pure TDP and PCL/TDP blends,

should indicate that the hydroxyl group of the TDP form

inter-associated hydrogen bond with the carbonyl group

Blend of Poly(e-caprolactone) and 4,49-Thiodiphenol ... 1037

of PCL chain in PCL/TDP blends. As shown in Figure

1b, the carbonyl vibration band of pure PCL is observed

at 1727 cm–1. Blending with TDP, a second band appears

at a lower wave number (1706 cm–1) beside the band cen-

tered at about 1727 cm–1. The second band should be

attributed to the associated carbonyl vibration, and con-

firm the formation of inter-associated hydrogen bonds

between PCL and TDP. It is clearly seen that, with

increasing TDP content in the blends, the relative absor-

bance of the associated carbonyl vibration increases,

while that of the ‘free’ carbonyl band decreases, indicat-

ing the reduction of ‘free’ carbonyl groups relative to the

associated ones.

Another useful tool to study hydrogen bonds is the

high-resolution solid-state 13C NMR. In general, the for-

mation of a hydrogen bond usually leads to the downfield

shifts of the 13C nucleus.[12–14] As expected, a significant

downfield shift of about 2 ppm and 0.8 ppm is observed

for the carbonyl and C6 carbon resonances, respectively

(Figure 2). Thus, the formation of inter-associated hydro-

gen bonds was further confirmed by high-resolution

solid-state 13C NMR.

Dependence of Composition

Employing the Beer-Lambert law permits a quantitative

analysis of the fraction of the carbonyl groups involved in

the inter-associated hydrogen bond by using FTIR spec-

troscopy.[1, 15–19] The spectra of PCL/TDP blends in the

carbonyl region exhibit three distinct components. The

components at about 1736 cm–1 and 1724 cm–1 are attrib-

uted to PCL in the amorphous and crystalline phases,

respectively.[20, 21] The contribution observed at 1706 cm–1

can be attributed to the associated carbonyl vibration as

referred above. According to the Beer-Lambert law the

integrated intensities of the amorphous Aa, the crystalline

Ac and the hydrogen-bonded part Ab can be expressed as:

Ai ¼ bci

Z þv

0

eiðmÞd m ð1Þ

here the subscript i is a, b or c, which denote the crystal-

line, hydrogen bonded and the amorphous carbonyl

groups part, respectively; ei (m) is the absorption coeffi-

Figure 1. The FTIR spectra of pure PCL, TDP and their blendsrecorded at room temperature. a: the hydroxyl vibration regionand b: the carbonyl vibration region. A: PCL; B: PCL/TDPblend with TDP content of 10 wt.-% (PCLTDP10); C: 20 wt.-%(PCLTDP20); D: 30 wt.-% (PCLTDP30); E: 40 wt.-%(PCLTDP40); F: TDP.

Figure 2. The 13C chemical shift of the PCL carbonyl (0) andC6 carbon resonances (9) at different TDP contents. The chemi-cal shifts were determined from the high-resolution 13C DD/MAS NMR spectra of the blends.


cient; b is the thickness; c is the concentration; m is the

wave number.

On the other hand, the fraction of hydrogen-bonded

carbonyl groups Fb can be determined from cb and c

(c = ca + cc + cb) as:

Fb = cb/(ca + cc + cb) (2)

On the basis of Equation (1)–(2) and appointing:

ci=j ¼Z þv

0

eiðmÞ d m

�Z þv

0

ejðmÞ dm ð3Þ

here the subscript j is a, b or c. Then Fb can be expressed

by Ai and ci/j as:

Fb = Ab/(Ab + cb/a Aa + cb/c Ac) (4)

From Equation (4), it can be seen that the problem

associating with calculating Fb is how to determine Ai and

ci/j. cc/a was accurately measured to be 1.46 in a previous

work,[11] cb/a was determined to be 1.95, which will be dis-

cussed in the next section; cb/c can be calculated to be

1.34 from cc/a and cb/a (cb/c = cb/a/cc/a). By using a curve-fit-

ting program,[11] the integrated intensities of the three

components were also obtained.

A curve-fitting program was used to resolve the carbo-

nyl vibration region of the PCL/TDP blend into three

bands: the amorphous, crystalline and associated carbonyl

group vibration bands. During the curve-fitting, the peak

positions of the amorphous and crystalline bands were

fixed to be 1736 cm–1 and 1724 cm–1, respectively,

which were the same to that reported in literatures,[20, 21]

but left the peak widths and heights of the three bands

and the peak position of the hydrogen bonded carbonyl

bands as the adjustable parameters. Figure 3 illustrates

the experimental and fitting spectra in the carbonyl vibra-

tion region of PCL/TDP blends. The excellent agreement

between the experimental and fitting spectra indicated the

reliability of this curve-fitting technique. In this way,

quantitative data regarding the relative integrated inten-

sity of the amorphous, crystalline and associated bands

were obtained (Table 1). It is interesting to note here that

the crystalline band disappears in the spectra of PCL/

TDP blend with TDP content of 40 wt.-% (PCLTDP40)

under this fitting procedure. This suggests that

PCLTDP40 blend is a fully amorphous elastomer (which

has also been conformed by DSC[8]).

The fractions of associated carbonyl groups in PCL/

TDP blends are summarized in Table 1. It is clear that Fb

increases as the TDP content increases. The value of Fb

(0.50) in PCLTDP40 blend seems relatively high while it

is lower than that (0.71) reported for the PCL/PVPh blend

with PVPh content of 40%.[20]

Dependence of Temperature

As an example, the FTIR spectra of the PCLTDP40 blend

in the hydroxyl and carbonyl vibration region at different

temperature are depicted in Figure 4. Two changes in the

hydroxyl vibration region with the increase of tempera-

ture can be observed from Figure 4a: (i) the absorbance

decreases and (ii) the band shifts to a higher wave num-

ber. These changes indicate that the inter-associated

hydrogen bond between PCL and TDP weakens as the

temperature increases. In Figure 4b, the integrated inten-

sity of the ‘free’ carbonyl vibration band increases at the

expense of the associated band with the increase of tem-

perature, which suggests that the fraction of associated

carbonyl groups decreases with the temperature.

Before a further discussion, a determination of the

absorption coefficient ratio cb/a is needed. From Equation

(1), (3) and c = ca + cc + cb, Equation (5) can be easily

derived:

Ab ¼ bc

Z þv

0

ebðmÞd mÿ cb=a Aa ÿ cb=c Ac ð5Þ

For an amorphous blend system (cc = 0, Ac = 0), Equa-

tion (5) can be simplified as:

Ab ¼ bc

Z þv

0

ebðmÞ dmÿ cb=aAa ð6Þ

Figure 3. The experimental and fitted FTIR spectra in the car-bonyl vibration region of PCL/TDP blends. expt.: experimentalspectrum; amor.: amorphous; crys.: crystalline; bond.: hydro-gen-bonded component; base.: baseline; fitt.: fitted spectrum,the sum of amorphous, crystalline, hydrogen-bonded componentand baseline.

Table 1. FTIR peak intensities Aa, Ac and Ab, the fraction ofassociated carbonyl groups Fb and the crystallinity Xc of PCLand PCL component in PCL/TDP blends.

Blends Aa Ac Ab Fb Xc

%

PCL 14.2 21.6 0 0 51.1CPLTDP10 11.6 15.4 5.36 0.110 42.3PCLTDP20 8.65 12.9 11.6 0.253 37.8PCLTDP30 10.5 1.70 16.5 0.421 5.81PCLTDP40 10.2 0.00 20.0 0.501 0.00


All the FTIR experiments in this work were carried out

on polymer films that cast on silicon wafers. There was

no movement of the films during the measurement.

Therefore, the number of molecules in the infrared beam

remained constant; that is, bc is a constant quantity for a

given sample. Then, the first term in the right side of

Equation (6) can be seen as a constant for a given sample

(in strict, ei (m) changes with the temperature and so does

ci/j. But as an approximation, ei (m) and ci/j can be assumed

as a constant independent of temperature in a narrow tem-

perature range[22]). Thus, there should be a linear relation-

ship between Ab and Aa in a narrow temperature range

and then the value of ratio cb/a can be determined from the

slope of the line.

Employing the fitting procedure as referred before, the

values of Ab and Aa at the temperature range from 26 to

458C were determined for the PCLTDP40 blend. The plot

of Ab vs. Aa is depicted in Figure 5 and cb/a was calculated

to be 1.95 from the slope of the line.

From Equation (4), Fb’s at different temperatures were

calculated and are summarized in Table 2. Obviously, Fb

decreases as the temperature increases while Fb retains a

relatively high value of 0.33 even at 1608C.

From the Fb’s, the equilibrium constants K of the

hydrogen bond formation at different temperature can be

obtained. ln(K) as a function of temperature is plotted in

Figure 6. From the slope of this plot, the enthalpy of

hydrogen bond (DH) was here calculated to be

Figure 4. The FTIR spectra of the PCLTDP40 blend in thehydroxyl vibration region (a) and the carbonyl vibration region(b) recorded at different temperatures. From top to bottom, thetemperatures are 26, 35, 45, 65, 90, 120 and 160 8C.

Figure 5. The relationship between the integrated intensity ofthe hydrogen-bonded (Ab) and amorphous (Aa) bands forPCLTDP40 blend at different temperatures ranging from 26 to458C. The regression line and correlation coefficient R2 were:Ab = 39.855–1.950 Aa, R2 = 0.999.

Table 2. FTIR peak intensities Aa, Ac and Ab, and the fractionof associated carbonyl groups Fb at different temperatures forPCLTDP40 blend.

Temperature�C

Aa Ac Ab Fba)

26 10.2 0.0 20.0 0.501

30 10.5 0.0 19.4 0.48635 10.9 0.0 18.5 0.46540 11.2 0.0 18.1 0.45445 11.3 0.0 17.7 0.44565 11.8 0.0 17.2 0.42890 12.1 0.0 16.6 0.413

120 11.4 0.0 14.4 0.392160 12.2 0.0 11.8 0.331

a) It should be noted that there may be a larger error for Fb attemperatures higher than 45 8C.


–5.30 kcal/mol. This value of DH is similar to those

reported for binary blend systems of PVPh with natural

poly(3-hydroxybutyrate) and chemosynthetic atactic

poly(3-hydroxybutyrate).[23]

The Crystallinity of the PCL Component

Similar to Fb as indicated in Equation (4), the crystallinity

of the PCL component (Xc) in the blend can be expressed

by the following equation, assuming that associated PCL

segments via hydrogen bonds exist in the amorphous

phase:

Xc = Ac /(Ac + cc/a Aa + cc/b Ab) (7)

Thus the determined values for Xc are listed in Table 1.

The data indicates that the crystallinity of PCL compo-

nent in the blend decreases drastically with increasing

TDP content.

Mobility of PCL Chain

The 13C CP/MAS NMR spectra of PCL/TDP blends are

shown in Figure 7 as a function of TDP content. In the

spectrum of pure PCL, both C6 and C2 resonances split

into two peaks: the upfield peak of the C6 resonance and

the downfield peak of the C2 resonance were assigned to

the amorphous component (C6a and C2a), whereas the

counter part peaks of both resonances were ascribed to

the crystalline component (C6c and C2c).[24] With increas-

ing TDP content, the intensities of C6c and C2c resonances

weakens relative to those of C6a and C2a, and C6c and C2c

disappears at a TDP content of 40%. The resonances of

other carbons also become narrower as the TDP content

increases. This fact indicates that the crystallinity of PCL

component in the blends decreases with the TDP content,

which is in accordance with the FTIR result.

Figure 8 shows the resonances of the C6 carbon in pure

PCL recorded under a series of contact time, ranging

from 50 to 8000 ls. By the fitting procedure, the overlap-

ping signals were described well by two Lorentzian

curves corresponding to the amorphous and crystalline

components. The resonance intensities of the two compo-

nents were integrated and are depicted in Figure 9. It is

obvious that the resonance intensities increases first and

then decreases with increasing contact time. Compared to

the resonance of pure PCL, the resonances of the C6 car-

bon in the PCLTDP40 blend as a function of contact time

Figure 6. Plot of ln (K) vs. 1000/T. The regression line and cor-relation coefficient R2 are: ln (K) = 2677/T–9.658, R2 = 0.991.

Figure 7. 100 MHz 13C CP/MAS NMR spectra of PCL/TDPblends. SSB denotes the spinning side band.

Figure 8. The resonance lines of C6 carbon in pure PCL as afunction of contact time: 1: 50 ls; 2: 100 ls; 3: 150 ls; 4: 200ls; 5: 300 ls; 6: 400 ls; 7: 600 ls; 8: 900 ls; 9: 1200 ls; 10:1500 ls; 11: 1800 ls; 12: 2200 ls; 13: 3000 ls; 14: 4000 ls;15: 5000 ls; 16: 6000 ls; 17: 7000 ls; 18: 8000 ls.


are displayed in Figure 10 and the plot of the intensity vs.

the contact time was illustrated in Figure 11. Clearly, the

initial increase of the intensity was much slower while

the following decrease was much faster comparing with

that of pure PCL.

In principle, under the matched Hartmann-Hahn pre-

scription, the 1H and 13C magnetization locked in their

individual channels are mixed, and the magnetization of

naturally abundant proton will transfer to that of rare 13C

nucleus through the near static 1H-13C dipolar interac-

tion.[25] According to the theory of the cross polarization

process, the 13C magnetization enhanced through this pro-

cess is expressed as a function of the contact time t when

TCH s T1qH a T1qC:[26]

M(t) = M0 [exp (–t/T1qH)–exp (–t/TCH)] (8)

Here, M0 is the maximum 13C magnetization which can

be obtained during cross polarization, TCH represents the

characteristic time for the build up of the carbon magneti-

zation, and T1qH and T1qC are the 1H and 13C spin-lattice

relaxation times in the rotating frames, respectively.

The spotted curves in Figure 9 and 11 indicate the fit-

ting results based on Equation (8) obtained by the compu-

ter-aided least-squares method. The experimental data

seem to be in good accord with the theoretical curves.

The TCH and T1qH values thus obtained are listed in Table

3. The same analysis was also carried out for the PCL/

TDP blends with TDP contents of 10%, 20% and 30%

(Table 3). With increasing TDP, TCH of the amorphous

component increases while T1qH of the amorphous compo-

nent decreases. In contrast, no marked change was

observed for those of the crystalline component. This

increase of TCH and decrease of T1qH for the amorphous

component can be directly used as the measure of the

increase of the PCL molecular mobility in the amorphous

phase with increasing TDP content.

It was well known that the molecular mobility of poly-

mers is affected by many factors: such as chemical struc-

ture, stereo structure, crystallization, crosslink and so on.

For the blend system studied here, it has been found that

Figure 9. The plot of the signal intensity M(t)vs. the contacttime t for the CP/MAS NMR signals of the C6 carbon in purePCL.

Figure 10. The 13C CP/MAS NMR signals of the C6 carbon inthe PCLTDP40 blend as a function of the contact time: 1: 50 ls;2: 100 ls; 3: 150 ls; 4: 200 ls; 5: 300 ls; 6: 400 ls; 7: 600 ls;8: 900 ls; 9: 1200 ls; 10: 1500 ls; 11: 1800 ls; 12: 2200 ls;13: 3000 ls; 14: 4000 ls; 15: 5000 ls; 16: 6000 ls; 17: 7000ls; 18: 8000 ls.

Figure 11. Signal intensity M(t) vs. the contact time t for theCP/MAS NMR signals of C6 in the PCLTDP40 blend.

Table 3. 1H spin-lattice relaxation times in the rotating frame(T1qH) and cross-polarization times (TCH) of PCL/TDP blends.The experimental error was estimated to be l10%.

Amorphous phase Crystalline phaseT1qH

ms

T1CH

ms

T1qH

ms

TCH

ms

PCL 28.5 0.10 10.6 0.029PCLTDP10 25.6 0.14 8.2 0.026PCLTDP20 15.1 0.24 9.6 0.027PCLTDP30 13.4 1.4 9.2 0.024PCLTDP40 6.1 2.0


the addition of TDP resulted in the decrease of the PCL

crystallinity and the formation of a hydrogen bonded net-

work,[8] so we shall focus on the factors of the crystalli-

nity and the density of the hydrogen bonded network.

Huang et al. have found that the T1qH correlated linearly

with the crystallinity rather well for poly(ethylene ter-

ephthalate).[27] Fulber et al. have reported that the cross

polarization rate (1/TCH) depended linearly on the cross-

link density for poly(styrene-co-butadiene) elastomer.[28]

For PCL/TDP blends, the T1qH and TCH of the amorphous

component are plotted as a function of PCL crystallinity

(Xc) in Figure 12 and 13, respectively. T1qH increases with

the crystallinity as expected and there should be a linear

relationship between T1qH and Xc within the experimental

errors as can be seen from Figure 12. Furthermore, as

shown in Figure 13, the change of ln(TCH) with Xc follows

a linear relationship rather well. These facts strongly sug-

gested that the crystallinity of PCL was one of the main

factors that affected the molecular motion of PCL in the

amorphous region. As to the hydrogen-bonded network,

it should constrain the molecular motion and the increase

of its density should cause the reduction of the molecular

motion for a general case. In PCL/TDP blends, with the

increase of the TDP content, the density of hydrogen

bonded network increases while T1qH and the cross polari-

zation rate (1/TCH) in the amorphous region decreases.

This result should imply that the density of the hydrogen-

bonded network was not a significant factor influencing

the molecular motion of PCL in the amorphous region.

Therefore, it seems clear that the addition of TDP leads a

decrease of the PCL crystallinity and the formation of a

hydrogen bonded network simultaneously, but TDP

exerts its influence on the molecular motion of PCL

mainly through lowering the crystallinity of PCL rather

than forming a hydrogen-bonded network with the PCL

chain.

Conclusion

As detected by FTIR and high-resolution solid-state13C NMR, there are strong inter-associated hydrogen

bonds between PCL and TDP. The quantitative analysis

of the FTIR spectra revealed that the fractions of asso-

ciated carbonyl groups in PCL/TDP blends increases with

the increase of TDP content and decreases with the

increase of temperature. The enthalpy of the inter-asso-

ciated hydrogen bond between PCL and TDP was evalu-

ated to be –5.30 kcal/mol. The crystallinity of PCL in the

blends was also found to decrease with increasing TDP

content.

With the increase of TDP, the TCH of PCL in the amor-

phous region increases while the T1qH of that decreases,

which indicates the increase of a PCL molecular mobility

in the amorphous phase with increasing TDP content.

Furthermore, ln(TCH) and T1qH of the amorphous compo-

nent were found to correlate linearly with the PCL crys-

tallinity in the blends. These facts strongly suggests that

the crystallinity of PCL is one of the main factors that

affects the molecular motion of PCL in the amorphous

region.

Acknowledgement: This work was partly supported by aGrant-in-Aid for Scientific Research on Priority Area, “Sustain-able Biodegradable Plastics”, No. 11217204(2000) from the

Figure 12. T1qH of the amorphous component as a function ofPCL crystallinity in the PCL/TDP blends.

Figure 13. The value of ln(TCH) as a function of PCL crystal-linity in the PCL/TDP blends. The regression line and correla-tion coefficient R2 were: ln (TCH) = 0.693–0.059 Xc, R2 = 0.995.


Ministry of Education, Science, Sports and Culture (Japan). Theauthors are grateful to Daicel Chemical Industries, Ltd., Japan,for kindly supplying the PCL sample.

Received: May 8, 2000Revised: September 18, 2000

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Documents

Blend of Poly(ε-caprolactone) and 4,4′-Thiodiphenol: Hydrogen Bond Formation and Some Solid Properties