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Transworld Research Network37/661 (2), Fort P.O., Trivandrum-695 023, Kerala, India

Polymeric Materials, 2009: 29-48 ISBN: 978-81-7895-398-4

Editor: Aleksandra B. Nastasovi

2Thermoplastic elastomersbased on poly(butylene

terephthalate) and various

siloxane prepolymers

Vesna V. Anti1, Marija V. Vukovi1, Milica R. Balaban1

Milutin N. Govedarica1 and Jasna Djonlagic2

1

Polymer Department, Center of Chemistry, Institute of ChemistryTechnology and Metallurgy, Studentski trg 12-16, 11000 Belgrade, Serbia2Faculty of Technology and Metallurgy, Karnegijeva 4, 11000 Belgrade, Serbia

AbstractThermoplastic poly(ester-siloxane)s (TPES)

and poly(ester-ether-siloxane)s (TPEES), based on

poly(butylene terephthalate) (PBT) as the hard

segment and different siloxane-containing prepolymers

as the soft segments were synthesized by catalyzedtwo-step transesterification/polycondensation reaction.

Incorporation of disilanol- or dicarboxypropyl-

terminated poly(dimethylsiloxane)s (PDMS-OH and

PDMS-CP) into the polar poly(butylene terephthalate)

Correspondence/Reprint request: Dr. Vesna V. Anti, Polymer Department, Center of Chemistry, Institute of

Chemistry, Technology and Metallurgy, Studentski trg 12-16, 11000 Belgrade, Serbia

E-mail: [email protected]


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Vesna V. Antiet al.30

chains resulted in rather inhomogeneous TPES copolymers. The inhomogeneity

was a consequence of a pronounced phase separation of the polar and non-polar

reactants during the synthesis. In order to avoid or reduce phase separation,

siloxanecontaining triblock prepolymers with hydrophilic terminal blocks, such

as ethylene oxide (EO), poly(propylene oxide) (PPO) or poly(caprolactone)(PCL), were investigated in order to improve the compatibility of corresponding

prepolymer with the polar reactants, dimethyl terephthalate (DMT) and 1,4-

butanediol (BD). Homogeneity was significantly improved in the case of

copolymers with poly(caprolactone)-poly(dimethylsiloxane)-poly(caprolactone)

soft segments, but the melting temperatures and degrees of crystallinity of the

resulting copolymers were much lower in comparison with all the previous

synthesized series of copolymers. Thermal stability of the obtained copolymers

was higher in comparison with PBT homopolymer, with exception of PDMS-CP

based samples, which were somewhat less stable.

IntroductionThermoplastic elastomers represent polymeric materials that combine the

elasticity and flexibility of chemically cross-linked elastomers and the easinessof processability of thermoplastic materials. Combined thermoplastic and

elastomeric behavior is characteristic for block copolymers, as well as for

mixtures of elastomers and thermoplasts. Block copolymers belonging to theclass of thermoplastic elastomers consist of two types of chemically incompatible

segments: hard, glassy or crystalline blocks, which provide for physical

crosslinking, and soft, flexible blocks with a low glass transition temperature,which provide for elasticity. The chemical incompatibility of the hard and

soft blocks leads to phase segregation and the formation of a two-phasemicrostructure. Due to the two-phase microstructure, thermoplastic elastomers

possess excellent mechanical properties, such as low-temperature flexibility,impact strength, toughness and high modules in the rubbery plateau region.

At elevated temperatures, the physical crosslinking disappears, allowing the

copolymer to soften and flow like thermoplastic materials thus enabling it to

be processed in the melt by techniques such as injection molding [1, 2].

The properties of thermoplastic elastomers depend on the chemical nature of

the two types of segments, hard and soft, as well as on their mass ratio andrespective lengths [1, 2]. Organic-siloxane block copolymers, due to the presenceof poly(siloxane) chains, show lower glass transition temperatures, higher thermal

and thermo-oxidative stability, as well as higher resistance to UV-radiation,

atomic oxygen and ozone, enhanced permeability to many gases, hydrophobicity, biocompatibility and resistance to many solvents in comparison to common

organic polymers. As a result of the mentioned properties, organic-siloxane


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Thermoplastic elastomers based on siloxane prepolymers 31

copolymers have received special attention as elastomers, protective coatings,

photoresists, biomaterials, gas separation membranes, emulsifiers, etc [3].Reactive, telechelic siloxane oligomers are the most important starting

material for the synthesis of siloxane-containing copolymers which behave as

thermoplastic elastomers. Step-growth polymerization is usually used for thesynthesis of such organo-siloxane copolymers, mainly due to the availability

of a wide variety of well-defined, organofunctionally terminated reactive

siloxane oligomers (,-telechelic siloxanes).

The main factors determining the reactivity of telechelic siloxane oligomers

toward other reactants are the type and nature of the terminal functional groups.Due to the fundamental differences in their structures, chemical reactivities and

overall properties, it is possible to divide functionally terminated siloxane

oligomers into two groups. The first group consists of oligomers with Si-Xterminal units and the other with Si-R-X units, where Xand R represent the

reactive functional group and a short organic moiety, respectively.In most of the published reports concerning siloxane containing

copolymers, the soft segment was almost exclusively poly(dimethylsiloxane).

Poly(dimethylsiloxane) has one of the lowest values of glass transition

temperature (Tg = -123 C) and the largest molar volume (75.5 cm3/mol). Chain

flexibility and low intermolecular forces are also responsible for its low surface

tension, low solubility parameters and low dielectric constant. Moreover, theseproperties show only a very small variation over a wide range of temperatures,

which is also an important characteristic of poly(siloxane)s [3, 4]. Theextremely non-polar nature of PDMS, together with the very low level of inter-

and intramolecular attractions, leads to the formation of thermodynamically and

mechanically incompatible blends with virtually all other polymers. This is

reflected in the very low value of the solubility parameter of PDMS [ =15

(J/cm3)

1/2] [3, 5], when compared with other polymers [ =15.4-28.0 (J/cm

3)

1/2]

[6]. This is the most important driving force in the formation of a two-phasemicrostructure in PDMS containing copolymers. Another very important factorwhich makes the morphology and structure-property relationships of siloxane

copolymers somewhat unusual when compared with conventional organic block copolymers is the fact that at room temperature (20-25 C), at which

most of polymer experiments are conducted, PDMS is about 150 C above itsglass transition temperature. At these temperatures, due to the absence of inter

and intramolecular interactions, PDMS behaves like a non-polar viscous liquid,thus providing perfect conditions for the formation of phase separated

copolymer structures. In many cases, a siloxane molar mass as low as 500-600g/mol (6-8 siloxane repeat units) and an organic segment having only a single

repeat unit are sufficient to obtain two-phase morphologies [3].


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Several studies on thermoplastic elastomers based on soft

poly(organosiloxane)-based segments and hard poly(butylene terephthalate)

segments have been presented and described in the literature since 1990 [7-

26]. Poly(organosiloxane)s exhibit many important and interesting properties,

such as low-temperature flexibility, high thermal and thermo-oxidative

stability, good biocompatibility, low surface energy, ultraviolet resistance and

high permeability to many gases [3, 4]. The incorporation of poly(organosiloxane)-containing segments into a PBT-backbone results in

improved clarity, surface smoothness and non-sticking properties, as well as

good film, fiber and hydrophobic properties of the resulting copolymers [7-16].

Our research in the field of siloxane containing copolymers commenced withthe synthesis of poly(estersiloxane)s (TPES) based on poly(butylene terephthalate)

(PBT) as the hard segment and poly(dimethylsiloxane) prepolymers as the softsegments. The TPES copolymers were synthesized by catalyzed two-step

transesterification, from dimethyl terephthalate, (DMT), 1,4-butanediol, (BD) andpoly(dimethylsiloxane)s with either disilanol- (PDMS-OH) or dicarboxypropyl-

(PDMS-CP) terminal groups. Incorporation of PDMS-OH or PDMS-CP

homopolymers into the polar PBT chains resulted in rather inhomogeneous TPES

copolymers, because of the pronounced phase separation of the polar and non-

polar reactants during synthesis [21-24]. All the copolymers prepared werepartially soluble in chloroform, as a consequence of their significant structural

and compositional inhomogeneity. Siloxane-containing triblock prepolymers

with hydrophilic terminal blocks (which served as a compatibilizer between the

extremely non-polar PDMS and the polar DMT and BD), such as ethylene oxide(EO), poly(propylene oxide) (PPO) or poly(caprolactone) (PCL) [25, 26], wereused in further investigations to avoid phase separation during copolymer

synthesis and to increase the miscibility of the polar and non-polar reactants.The structure, composition and size of the poly(ester-siloxane)s and poly(ester-

ether-siloxane)s macromolecules were investigated by1H NMR and

13C NMR

spectroscopy and the viscosity of dilute solutions. The thermal properties ofsamples from all the synthesized series were investigated by differential

scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

Experimental1. Siloxane-containing prepolymers

,-Dicarboxypropyl-poly(dimethylsiloxane)s (PDMS-CP, nM =1030

g/mol) and their dimethyl-esters were prepared as described previously [21,

27]. ,-Disilanol-poly(dimethylsiloxane) (PDMS-OH, nM =2400 g/mol),

,-dihydroxy-poly(ethylene oxide-dimethylsiloxane-ethylene oxide (EO-


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PDMS-EO), ,-dihydroxy-poly(propylene oxide-dimethylsiloxane-propylene

oxide) (PPO-PDMS-PPO) and ,-dihydroxy-poly(caprolactone-dimethylsiloxane-caprolactone) (PCL-PDMS-PCL) were supplied from

ABCR (Germany). The number-average molar masses of the EO-PDMS-EO,

PPO-PDMS-PPO and PCL-PDMS-PCL, were determined by 1H NMR

spectroscopy. The nM of the prepolymer EO-PDMS-EO was 1200 g/mol,

the molar mass of central poly(dimethylsiloxane) (PDMS) block was

1080PDMSM = g/mol, and the terminal ethylene oxide, (EO) consisted of

one unit. The number-average molar mass of the PPO-PDMS-PPO was 2900g/mol, with a molar mass of the central poly(dimethylsiloxane) (PDMS)

block of 1100PDMSM = g/mol and a molar mass of the terminal

poly(propylene oxide) (PPO) blocks of 900PPOM = g/mol. The nM of the

PCL-PDMS-PCL was 6100 g/mol, the molar mass of the centralpoly(dimethylsiloxane) (PDMS) block was 2000PDMSM = g/mol. The molar

mass of the terminal poly(caprolactone) (PCL) blocks was 2050PCLM = g/mol.

2. Poly(ester-siloxane) and poly(ester-ether-siloxane) synthesisThe poly(ester-siloxane)s and poly(ester-ether-siloxane)s were

synthesized by catalyzed two-step reactions involving transesterification

and polycondenzation in the melt, under the optimal conditions [21-25].

The reactants were dimethyl terephthalate (DMT), 1,4-butanediol (BD), and

the corresponding siloxane prepolymer (PDMS-OH, PDMS-CP, EO-PDMS-EO, PPO-PDMS-PPO or PCL-PDMS-PCL). The catalyst was tetra-n-butyl-titanate (1.0-2.5 mmol / mol DMT), whilst the thermal stabilizer

was N,N-diphenyl-p-phenylenediamine. The first step, transesterification,was performed from 160 to 230-240 C, at atmospheric pressure, whereby

the formed methanol was distilled off. The second step, polycondensation,

was performed for 1.5 to 4.5 h (depending on which prepolymer was used)

at 230-250 C, under reduced pressure. In this manner, three series of

TPESs and two of TPEESs, with different soft segments and hard-to-softweight ratios in the range from 90/10 to 40/60, were obtained. The

synthesized TPESs (except for the copolymers based on PCL-PDMS-PCL)and the TPEESs were extracted with chloroform and the obtained soluble

and insoluble fractions were analyzed by1H NMR spectroscopy [21-26].

3. Characterization of the copolymers1H NMR (200 MHz) spectra were obtained on a Varian Gemini-200

instrument. The TPES samples based on PDMS-OH and PDMS-CP, as well


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as the TPEES samples, were measured as solutions in CF3COOD. The

solvent was simultaneously used as the internal standard. The TPES samplesbased on PCL-PDMS-PCL prepolymer were measured as solutions in CDCl3.

The inherent viscosities (inh) of the TPES and TPEES samples weremeasured in a mixture of phenol/trichloroethylene/toluene (1:1:2 by vol.) at

30 C, using an Ubbelohde viscometer.Gel permeation chromatography (GPC) was conducted on a Waters 600E

instrument equipped with a refractive index detector, on three Supelco Pl-Gel

columns connected in line (cross-linked polystyrene with pore sizes of 10-5

,10-6 and 10-7 m) at 30 C. Twenty l of a sample solution in chloroform (10 mass

%) were injected in all cases. The flow rate was 1.5 m3

min1. The system was

calibrated with a number of high and low molecular weight siloxanes [27].Differential scanning calorimetry (DSC) was performed using a Perkin

Elmer DSC2 thermal analyzer. The DSC scans were recorded under a dynamic

nitrogen atmosphere (flow rate 25 cm3

min1

) at a heating and cooling rate of 10

C min1

(two scans were run for each sample). The weight of the samples

was approximately 10 mg. The samples were analyzed between 50 and 250 C.Thermogravimetric analysis (TGA) was performed using a TA Instruments

SDT Q600 analyzer in the temperature range from 30 to 750 C. The heating

rate was 10 C min1. The TGA scans were recorded under a dynamic nitrogen

atmosphere with a gas flow rates of 100 cm3

min1. The sample mass was about

10 mg.

Results and discussionStructure and composition of synthesized TPESs and TPEESsOur work on thermoplastic, siloxane-containing copolymers commenced

with the synthesis and characterization of poly(estersiloxane)s based on

PBT as the hard segment and PDMS prepolymers with either silanol- or

carboxypropyl- terminal groups as the soft segment [21]. The series of

copolymers prepared with PDMS-OH is denoted as TPES-OH, whilst theseries obtained with PDMS-CP is denoted as TPES-CP. The structures of the

employed prepolymers and the synthesized copolymers are presented in

Scheme 1 and 2, respectively. Poly(butylene terephthalate) was chosen as the

hard segment for the thermoplastic elastomers because of its high structuralregularity, rapid crystallization and high degree of the crystallinity [28, 29].

After the optimal reaction conditions had been established [21], the effect ofthe length of the carboxypropyl-terminated PDMS prepolymers (5502170

g/mol) on some characteristic properties of the TPES-CP was examined,while the mass ratio of the hard and soft segments was kept constant (57/43)

[22]. The weight fractions of PBT segments in the poly(ester-siloxane)s were


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Scheme 1. Molecular structure of the prepolymers that were used as the soft segments

in thermoplastic poly(ester-siloxane)s and poly(ester-ether-siloxane)s

C

O

C

O

O CH2 O4

p

SOFT SEGMENT

q n

Scheme 2. Molecular structure of the synthesized copolymers based on hard PBTsegments and different siloxane-based soft segments

in the range from 5 9 to 63 % and the average lengths of the PBTsegments lay between 3.8 and 16.9, calculated on 1 mole of the soft

segment, indicating an increase in the length of the hard segments with

increasing length of the soft poly(dimethylsiloxane) segments. As a


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consequence of the increase in the length of the hard PBT segments, the

melting temperature, the enthalpy of melting and the hardness of the

poly(ester-siloxane)s increased. The degree of crystallinity calculated from

DSC data was in the range from 18.5 to 22.6 %, while the degree of

crystallinity from WAXS data was from 37 to 40 %. The glass transitiontemperatures of the poly(ester-siloxane)s increased with decreasing PDMS

segment length, which indicates that the amorphous domains are a mixture of

PDMS and non-crystallized PBT segments [22]. Further investigations wererelated to the investigation of the effect of the mass ratio of hard and soft

segments, with a constant length of the carboxypropyl-PDMS prepolymers

(1030 g/mol) on some properties of the obtained thermoplastic poly(ester-

siloxane)s (Table 1) [23]. The mass fraction of PBT segments in poly(ester-

siloxane)s, calculated from their1H NMR spectra, were in the range 39 to 76

%, while the average degree of the polymerization of the PBT segments

increased from 3.1 to 15.4, with respect to 1 mol of soft segments. Theinherent viscosity of the copolymers increased from 0.35 to 0.45 dl g

-1, as the

molar mass of the TPES increased from 11500 to 35000 g mol-1

. It appeared

that there was a pronounced molar mass maximum when the PBT content of

the copolymers was approximately 60 mass %, whereby all the samples wereconsiderably inhomogeneous with respect to the distribution of the lengths of

the hard segments. Extraction with chloroform confirmed the multiblockstructure of both the soluble and insoluble fractions.

Analysis of the homogeneity of the synthesized TPESs and

TPEESsAll the samples of poly(ester-siloxane)s based on PDMS-OH or PDMS-

CP prepolymers exhibited considerable inhomogeneity with respect to thedistribution of the lengths of the hard segments. Due to the high

incompatibility of the employed extremely non-polar siloxane prepolymers

with the polar reactants, DMT and BD, phase separation occurred during thereaction in the melt. It was observed that the PDMS prepolymers floated to

the surface of the reaction mixtures when the stirring was stopped during the

first, transesterification step. Hence, it was obvious that the reaction mixturewas not homogeneous. As a consequence, the incorporation of

dicarboxypropyl- and disilanol-terminated PDMS into the polar poly(butylene

terephthalate) chains resulted in rather inhomogeneous TPES copolymers.The effectiveness of the incorporation of PDMS prepolymers into the

copolymer chains was examined by Soxhlet extraction with chloroform. It is

well known that PBT homopolymer is insoluble, while the PDMS

prepolymers are soluble in chloroform. The obtained results showed that allTPES-OH and TPES-CP samples were comprised of a soluble, as well as of an


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insoluble fraction (Table 1). The TPES-OH samples lost 6-40 %, while the

TPES-CP samples lost 1942 % during extraction. The content of the soluble

fraction increased with increasing mass fraction of soft segments in both the

TPES-OH and TPES-CP series, however the increase was more pronounced in

the first series (Fig. 1A). This meant that the amount of soluble fraction washigher in the TPES-OH in comparison to the TPES-CP series, at the same

hard to soft segments ratio.The composition and structure of the soluble and insoluble fractions were

investigated by1H NMR spectroscopy. The spectra of both fractions contained

signals of aromatic protons from the PBT segments, as well as signals of theSiCH3 protons from the PDMS segments. The spectra also showed that the

extracted and insoluble fractions differed in both their composition and structure,

containing considerably different amounts of PDMS and PBT segments. Themass fraction of soft segments was significantly larger in the soluble than in

insoluble fractions in both TPES-OH and TPES-CP series (Table 1). Thecalculated value ofp (the average degree of butylene terephthalate units in the

hard segments, Scheme 2) was very small in the soluble fractions in both series(psol = 1.02.9). In the insoluble fractions,p was much higher, especially for the

TPES-OH series (pinsol = 63300 for TPES-OHs and pinsol = 432 for TPES-

CPs, Table 1). It can be concluded that both the extracted and insoluble fractions

have a segmented (multiblock) structure, but with much more shorter PBTblocks in the soluble than in the insoluble fractions. Based on these results, it is

obvious that the TPES-OH samples were more inhomogeneous regarding their

structure and composition in comparison with the PDMS-CP samples. It seems

that the PDMS-CP prepolymers had better miscibility with DMT and BD thanthe PDMS-OH ones, due to the presence of polar carboxyl-end groups.

In order to avoid or reduce phase separation during the synthesis of TPES-OH and TPES-CP, hydroxyl-terminated triblock prepolymers of the ABA type,

with hydrophilic terminal blocks, i.e., ethylene oxide (EO), poly(propylene

oxide) (PPO) or poly(caprolactone) (PCL) and with central PDMS block, wereused in further investigations (Scheme 1). It was expected that the terminal EO,

PPO or PCL blocks would serve as a compatibilizer between the extremely

non-polar PDMS and the polar DMT and BD. The results of solubility andextraction in chloroform, as well as analysis of the

1H NMR spectra of the

obtained fractions showed that the presence of ether chains, either EO or PPO,did not improve the homogeneity of the prepared poly(ester-ether-siloxane)s, in

comparison with the TPES-OH and TPES-CP copolymers. The TPEESsamples from both series (TPEES-EO and TPEES-PPO) were partially soluble

in chloroform, as well as the previously synthesized TPESOH and TPESCP

samples. The compositions of the chloroform soluble and insoluble fractions

of the TPEES samples are also presented in Table 1.


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Table1.Inherentviscosities(inh)and1HNMRanalysisofthechloroformsolubleandinsolublefractionsofsomeof

theTPES

andTPEESsamples.


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Figure 1. Change in the content of the soluble fraction with changing mass fraction of

soft segments for the poly(ester-siloxane)s based on PDMS-OH and PDMS-CP prepolymers (A) and the poly(ester-ether-siloxane)s based on EO-PDMS-EO and

PPO-PDMS-PPO prepolymers (B).

The TPEES-EO samples lost 356 mass % during extraction. The soluble

fractions of the TPEES-EO samples contained 8186 mass % of soft

segments, while the insoluble ones contained 424 mass %. It can beconcluded that the length of the EO block (only 1 repeating unit) was too

short to be an efficient compatibilizer between PBT and PDMS, in spite of

the high solubility parameter of poly(ethylene oxide) [PEO = 20.2 (J/cm3)

1/2]

[5], which is close to the solubility parameter of PBT[PBT = 23.0 (J/cm3)

1/2]

[6]. The TPEES-PPO samples lost 3960 mass % during extraction. The

sample TPEES-PPO2, with a mass fraction of PBT of 52.8 %, lost 43 %during extraction, while the sample TPEES-EO5, with a very similar

content of the hard segment (53.4 mass %), but with shorter soft segments,

lost 34 % during extraction. This result indicates a relationship between thelength of the soft segments and the amount of soluble fraction: the longer

the soft segments, the higher is the amount of extracted fraction. The

relationship between the mass fraction of soft segments and amountof thesoluble fraction for the series TPEES-EO and TPEES-PPO is presented in

Fig. 1B.The soluble fractions of the TPEES-PPO samples contained 8589 mass

% of soft segments, while the insoluble ones contained 1928 mass %. In thecase of the TPES-PPO copolymers, it can be concluded that compatibilizing

effect between PBT and PDMS was not achieved, because of the rather low

solubility parameter of PPO [PPO = 15.4 (J/cm3)

1/2] [6, 30],

which is very

similar to that of PDMS [PDMS = 15 (J/cm3)1/2][3].


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The calculated values ofpsolfor the samples of both TPEES series were

very small (psol =1.0-2.4) and similar to thepsol of the previous TPES-OH and

TPES-CP series. The calculated value ofpinsol was much higher in the

TPEES-PPO series than in the TPEES-EO series at a similar PBT content

(pinsol was 62 for TPEES-PPO2 and 18 for TPEES-EO5). This result showsthat the length of the PBT segments in the insoluble fraction is directly

related to the length of the prepolymer used, at a fixed mass ratio of hard-to-soft segments.

The relationships between the content of PBT segments in the

copolymers and the length of the hard segment in the insoluble fraction arepresented in Fig. 2. It is obvious that increasing the content of PBT leads to

an increase ofpinsol. The longest hard segments were founded in the insoluble

fractions of the TPES-OH series. This indicates that the prepolymer mostimmiscible with PBT within the prepolymers used in this work was PDMS-

OH. At a fixed PBT content, the increase of the length ofpinsol in the differentseries was as follows: TPEES-PPO > TPEES-EO > TPES-CP (Fig. 2). The

differences inpinsol for TPEES-EO and TPES-CP were not very pronounced,probably because of the similar length of the soft segments (1200 and 1030

g/mol, respectively). The values ofpinsol in the TPEES-PPO series were

higher, probably as a consequence of the much longer soft segment (2930

g/mol).The series of poly(ester-siloxane)s based on PBT and poly(caprolactone)-

poly(dimethylsiloxane)-poly(caprolactone), TPES-PCL, with hard-to-soft

segment ratios in the range from 74/26 to 51/49, were completely soluble in

chloroform, which enabled their molar masses to be determined by gel- permeation chromatography. The chromatograms showed the presence of

only one peak, the shape of which corresponded to a typical high-molecularweight product of step-growth polymerization. The values of the number

average molar masses, nM , the weight average molar masses, wM , the

polydispersity index, wM / nM and of the molar masses which corresponded

to the maximum of the peak,peak

M are given in Table 2. The values of the

inherent viscosities of the TPES-PCLs and of the number of repeating units

within the hard segments are also given in Table 2. The values of nM werein the range from about 20000 to almost 50000 g/mol. It is obvious that the

presence of the longer (18 repeating units), polar poly(caprolactone) blocks

[PCL = 20.0 (J/cm3)]

1/2][31, 32] played a significant role in the improvement

of the miscibility of the prepolymer with the polar reactants and PBT. The

reaction mixture was homogeneous, as were the synthesized copolymers with

respect to their structure and composition.


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Figure 2. Change in the length of the hard segment in the insoluble fraction (pinsol)

with changing mass fraction of PBT segments for the synthesized poly(ester-siloxane)s and poly(ester-ether-siloxane)s.

Table 2. Inherent viscosities (inh),1H NMR and GPC analysis of the TPES-PCL

samples, based on PCL-PDMS-PCL prepolymer ( nPCL PDMS PCLM = 6100 g/mol).

SamplePBT

Soft segment

mass % mass %

(NMR)

p

(NMR)inh

(dl/g)nM

(g/mol)

wM (g/mol)

w

n

M

M

peakM

(g/mol)

TPES-PCL1 70/30 74/26 80 0.52 22470 43200 1.9 36700

TPES-PCL2 60/40 68/32 59 0.65 21170 45160 2.1 39480

TPES-PCL2 55/45 63/37 48 0.62 22540 45830 2.0 39480

TPES-PCL4 50/50 59/41 41 0.60 26610 49850 1.9 42500

TPES-PCL5 40/60 51/49 30 0.89 49340 91890 1.9 83950

DSC analysis of the TPESs and TPEESs

The synthesized TPES and TPEES were semi-crystalline polymers. Themelting temperatures (Tm) of the hard segments were observed by DSC. The

DSC measurements were performed between 50 and 250 C to determined

the melting temperatures (Tm), the enthalpy of melting (Hm) and the degree

of crystallinity (wc) of the TPES and TPEES samples.The values ofTm of the synthesized copolymers were in the following

ranges: 224-226 C for TPES-OH; 214-223 C for TPEES-EO; 208-218 C


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for TPES-CP; 175-181 C for TPEES-PPO and 103-196 C for TPES-PCL. It

was obvious that the copolymers from the different series, with the same

mass fraction of PBT segments, have different melting temperatures in the

previously given order, as is presented in Fig. 3. From Fig. 3, it can also be

seen that with increasing mass fraction of PBT segments, the meltingtemperatures mostly shifted to higher values. This phenomenon was the most

pronounced in the TPES-PCL series.The enthalpies of melting were calculated from the corresponding

thermograms. The total degree of crystallinity, i.e., the mass fraction of

crystallities in the TPES and TPEES copolymers, were calculated from the

determined Hm using the equation:

wc = Hm / Hm

where Hm

= 144.5 J/g is the enthalpy of melting of perfectly crystalline

PBT homopolymer[6].

The degree of crystallinity of the TPES and TPEES samples increased

with increasing mass fraction of the hard PBT segments in all theinvestigated series, as can be seen in Fig. 4. Also, the copolymers from the

TPES-OH, TPES-CP and TPEES-PPO series have the highest degrees ofcrystallinity at a fixed content of PBT (17-28, 11-23 and 10-17 %,

respectively). The trend of changing wc with mass fraction of PBT in the

copolymer was almost the same in all of these series. The samples from theTPEES-EO series had a somewhat lowerwc (3-28 %). The samples from the

TPES-PCL series (3-15 %) had the lowest degrees of crystallinity. This can

be explained by the high miscibility of PCL-PDMS-PCL prepolymer with

PBT, which leads to poor phase segregation of soft and hard segments in the

TPES-PCL copolymer, and also to the obstruction of the crystallization of thePBT segments.

The ratio of the total degree of crystallinity and the determined mass

fraction of PBT segments (1H NMR) gave the mass fraction of hard

segments which were incorporated into the crystallites, wcPBT

. The degrees ofcrystallinity, w

c

PBT, were in the range 28 to 31 % for the synthesized TPES

and in the range 27 to 30 % for the TPEES-EO and TPEES-PPO. This means

that less than 30 mass % of the PBT segments in all the TPES and TPEESsamples crystallized. These results show that not all of the hard segments in

these segmented copolymers could crystallize completely due to their partial

incorporation into the amorphous phase. The degree of crystallinity of PBT

homopolymer was wc=wcPBT

= 35.7 %.


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Figure 3. Change in the melting temperature (Tm) measured by DSC with changingmass fraction of PBT segments for the synthesized poly(ester-siloxane)s andpoly(ester-ether-siloxane)s.

Figure 4. Change in the degree of crystallinity (wc) measured by DSC with changing

mass fraction of PBT segments for the synthesized poly(ester-siloxane)s and

poly(ester-ether-siloxane)s.

PBT homopolymer is a fast-crystallizing polymer. By comparing the

supercooling, i.e., the difference between melting and crystallizationtemperature, it is possible to analyze the rate of crystallization of different

segmented copolymers. PBT has a supercooling of 32oC. Supercooling of the

hard segments, Th = Tm - Tc , of the poly(ester-siloxane)s and poly(ester-


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ether-siloxane)s was in the range from 38 to 45oC, respectively, indicating

that the rate of crystallization of the copolymers TPES and TPEES was lower

than that of PBT, due to the presence of the soft polysiloxane segments. The

results show that the crystallization rates of the TPES and TPEES were

dependent both on structure and composition in the examined range.Poly(ester-ether-siloxane)s, TPEES-PPO, exhibited two glass transition

temperatures. The glass transition temperatures of the amorphous PDMSphase, Tg

PDMS, were between -121 and -124

oC, which are very close to that of

PDMS homopolymer, i.e., -123oC. The glass transition temperatures of the

amorphous PPO phase, TgPPO

, decreased from -21 to -43oC with increasing

content of soft segments in the copolymers. PPO homopolymer has a glass

transition temperature of -75oC, which is lower than those of the TPEESs,

and indicates that the amorphous fraction of the hard PBT segments wasmixed with PPO-PDMS-PPO segments.

Thermal stability of the TPESs and TPEESsThe results of thermogravimetric analysis under a nitrogen atmosphere

of the samples from different series, but with very similar content of PBT

segments (about 60 mass %), are given in Table 3 and shown in Figure 5.

The thermal stability and degradation behavior of the copolymers wascompared to the behavior of PBT homopolymer, synthesized in the same

way and stabilized with the same heat stabilizer[21-23]. It can be seen thatall copolymers, as well as PBT homopolymer, with exception of TPES-CP3

sample, commenced to degrade above 360 C (Table 3). It seems that thethermal stabilities of the TPES-OH, TPEES-EO, TPEES-PPO and TPES-

PCL copolymers were somewhat higher in comparison to that of the PBThomopolymer. The thermal stability of the TPES-CP3 sample was lower

than those of all the other copolymers and the PBT homopolymer (Fig. 5A).

These results are in a agreement with the fact that the thermal stability of

the poly(ester-siloxane)s TPES-CPs decreased slightly with increasingconcentration of ester-bonds between the hard and soft segments, which are

the weakest bonds in the copolymer chains [23]. From Fig. 5B, it can beseen that the temperatures of the maximal rate of degradation of the

copolymers were higher than the corresponding value for PBThomopolymer. This means that when the degradation of the PBT

homopolymers starts, it proceeds faster than the degradation of the

copolymers. The residual masses were between 6.0 and 10.9 % at 450 C,

originating probably from the PBT fraction, since the PDMS chainsdegrade through depolymerization under a nitrogen atmosphere, with the

formation of cyclosiloxanes [4].


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Figure 5. TGA (A) and DTGA (B) curves for the TPES-CP5, TPEES-EO4, TPEES-

PPO1 and PBT homopolymerunder a nitrogen atmosphere.

Table 3. Thermal gravimetric analysis data of some TPESs and TPEESs samples andPBT homopolymerunder a nitrogen atmosphere.

SampleT for 5 % mass

loss (oC)

T for 50 %

mass loss (oC)

T for maximal rate of

degradation (oC)

Residue

at 450 oC

PBT 361 389 389 10.3

TPES-OH5 364 403 407 6.0

TPES-CP3 343 389 387/398 6.0

TPEES-EO4 362 402 385/405/407 9.4

TPEES-PPO1 365 409 389/400/408 6.8

TPES-PCL4 367 404 394/407 10.9

Thermogravimetric analysis of the synthesized TPES and TPEES in

oxygen gave more pronounced differences between the samples, including

that of the PBT homopolymer. The thermo-oxidative stability of thecopolymers decreased with decreasing PBT content. Under a thermo-

oxidative atmosphere, the degradation of the PDMS chains or segments


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commences with the formation of peroxy structures in the side-chains, which

leads to the occurrence of different free radical reactions and results in the

formation of gaseous silicon compounds, CO, CO2, H2, H2O, HCHO and

HCOOH, leaving as a residue SiO2[4]. Therefore, the residues at 500oC in

oxygen for TPES and TPEESs were higher compared to PBT, due to theincreased amount of SiO2 formed.

ConclusionsThermoplastic elastomers with hard segments based on poly(butylene

terephthalate) (PBT) and soft segment based on: a) ,-dicarboxypropyl-

poly(dimethylsiloxane)s (PDMS-CP); b) ,-disilanol-

poly(dimethylsiloxane) (PDMS-OH); c) ,-dihydroxy-ethylene oxide- poly(dimethylsiloxane)-ethylene oxide (EO-PDMS-EO); d),-dihydroxy-

poly(propylene oxide-dimethylsiloxane-propylene oxide) (PPO-PDMS-PPO)and e) ,-dihydroxy-poly(caprolactone-dimethylsiloxane-caprolactone)(PCL-PDMS-PCL) were synthesized by two-step transesterification in themelt. The obtained poly(estersiloxane)s based on PDMS-OH (TPES-OH)

and PDMS-CP (TPES-CP) and poly(esterethersiloxane)s based on EO-

PDMSEO (TPEES-EO) and PPO-PDMSPPO (TPEES-PPO) were rather

inhomogeneous. After extraction with chloroform, soluble and insolublefractions of different structure and composition were obtained. Both the

soluble and insoluble fractions had multiblock structures. Due to the presenceof long, polar PCL sequences, the miscibility of the PCL-PDMSPCL

prepolymer with the polar monomers in the reaction mixture wassignificantly improved, in comparison with all the other examined systems.

As a result, the obtained PCL-PDMSPCL based copolymers (TPES-PCL)were structurally and compositionally homogeneous and completely soluble

in chloroform. The semi-crystalline nature of the poly(estersiloxane)s andpoly(esterethersiloxane)s was confirmed by DSC analysis. With increasing

mass fraction of hard PBT segments, the melting temperature and the degree

of crystallinity of the TPES and TPEES increased. Copolymers from theTPES-OH, TPES-CP and TPEES-PPO series had the highest degrees of

crystallinity. Copolymers from TPES-PCL series had the lowest degrees of

crystallinity. This was a consequence of the increased miscibility of PCL-PDMS-PCL with PBT, which on the other hand led to reduced crystallization

of the hard segments in the copolymers. The thermal stability of thecopolymers was somewhat higher than that of the PBT homopolymer, with

exception of the TPES-CP samples, which were less stable due to the

presence of ester-bonds between the hard and soft segments, which are the

weakest bonds in copolymer chains.


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AcknowledgementThis work was financially supported by the Ministry of Science of the

Republic of Serbia (Project No. 142023).

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