EUROPEAN

European Polymer Journal 41 (2005) 823–829

www.elsevier.com/locate/europolj

POLYMERJOURNAL

Functionalization of syndiotactic polystyrene withsuccinic anhydride in the presence of aluminum chloride

Juan Li, Hua-Ming Li *

Department of Chemistry, Institute of Polymer Science, Xiangtan University, Xiangtan 411105, Hunan Province, PR China

Received 8 October 2004; accepted 29 October 2004

Available online 13 January 2005

Abstract

Syndiotactic polystyrene has been chemically modified with succinic anhydride by use of Friedel–Crafts acylation

reaction in the presence of anhydrous aluminum chloride in carbon disulfide. The modified syndiotactic polystyrene

containing –COCH2CH2COOH fragments in side phenyl rings, named succinoylated syndiotactic polystyrene

(s-sPS), was characterized by FTIR and 1H NMR spectroscopy. The effects of reaction conditions on the degree of suc-

cinoylation of s-sPS were investigated. In addition, the effects of incorporation of carboxyl groups into syndiotactic

polystyrene on the thermal behavior were studied by differential scanning calorimetry in comparison with pure syndio-

tactic polystyrene. It was found that the crystallization temperature, melting temperature, and degree of crystallinity of

the modified polymer decreased with increasing the degree of succinoylation, while the glass transition temperature

increased.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Syndiotactic polystyrene; Acylation; Succinic anhydride; Modification

1. Introduction

Since the first synthesis of syndiotactic polystyrene

(sPS) by Ishihara [1], this new semicrystalline polymer

has been the subject of intense investigation. Along with

high melting temperature (�270 �C), high crystallinity

and rapid crystallization rate, sPS exhibits low dielectric

constant, high modulus, and good chemical resistance,

which has been made an attractive engineering ther-

moplastic for many applications in the electronic, packag-

ing, and automotive industries. However, sPS resembles

0014-3057/$ - see front matter � 2004 Elsevier Ltd. All rights reserv

doi:10.1016/j.eurpolymj.2004.10.048

* Corresponding author. Tel.: +86 732 8293606; fax: +86 732

8293264.

E-mail address: yfhuamingli@126.com, huamingli8@

163.com (H.-M. Li).

atactic polystyrene (aPS) polymer with poor impact

strength, inherent brittleness, and low surface energy. Re-

cently, attempts have been made to improve the physical

properties and processability of sPS through several pro-

cedures. Physical bending with other polymers or sub-

strates (e.g., engineering thermoplastics and elastomers)

may extend the commercial utility of sPS [2,3]. Except

for a few polymers such as aPS and PPO, blending with

other polymers (e.g., polyamides) usually leads to phase

separation due to lack of compatibility. Therefore, chemi-

cal modified sPS polymer with functional groups was

expected to be a very desirable material.

In previous articles dealing with the preparation of

functionalized sPS, experimental observations were

interpreted as two aspects. One involves direct polymeri-

zation of styrenic monomer or copolymerization with a

second monomer by using metallocene catalyst systems

ed.

824 J. Li, H.-M. Li / European Polymer Journal 41 (2005) 823–829

to produce syndiotactic polystyrene derivatives contain-

ing functional groups [4–8]. For example, Chung devel-

oped a route to prepare functionalized sPS through the

direct copolymerization of styrene with a borane-con-

taining styrenic monomer and extended this sPS to pre-

pare functionalized sPS and sPS graft copolymers [7].

Chung also demonstrated a family of syndiotactic poly-

styrene derivatives containing primary amino groups via

stereospecific polymerization of a styrene derivative con-

taining a masking N,N-bis(trimethylsilyl)amino group

followed by acid hydrolysis leading to the complete

recovery of primary amino groups in sPS derivatives

[8]. On the other hand, functionalization of sPS can also

be achieved by introducing other types of functional

groups into the polymer or by modifying existed func-

tional groups. From a research and development point

of view, the latter one is usually more efficient and less

expensive. So far, there are only a few reports on dis-

cussing the modification of sPS-based polymer, such re-

ports including sulfonated sPS [9,10], brominated sPS

[11], acetylated sPS [12], maleated sPS [13,14], and a ser-

ies of sPS graft copolymers synthesized using ATRP

technique with brominated sPS as initiator [15]. In

addition, Liu et al. used a mixture of [Ni(p-methal-

lyl)(Br)]2and AlCl3, to graft branched oligoethene onto

the pendant aromatic groups of sPS [16].

In our previous paper, we have reported a method for

preparing acetylated syndiotactic polystyrene (AsPS) by

Friedel–Crafts reaction [12]. The outstanding virtue of

this method lies in that it is well suited for the prepara-

tion of high molecular mass of styrenic polymer based

ionomers with substituted groups situated randomly

along the polymer chain under mild conditions [12,

17,18]. In addition, all the reagents used in the reaction

are commercially available. Following our previous

work, the present work is design to introduce carboxyl

groups onto pendant aromatic groups of sPS through

Friedel–Crafts acylation reaction. There is limited infor-

mation about the preparation of sPS bearing pendant

carboxyl groups in the side phenyl rings. Pendant func-

tional groups, such as carboxyls, will be potentially

interesting for preparing amphiphilic copolymers and

ion-containing sPS. The aim of this work is to modify

sPS with succinic anhydride via Friedel–Crafts acylation

reaction. Furthermore, differential scanning calorimetry

(DSC) was used to investigate the thermal properties of

functionalized polymers in view of the crystallization

and melting behavior along with the neat sPS.

2. Experimental

2.1. Materials

The sPS used in these studies was synthesized by bulk

polymerization of styrene with a Cp*Ti (OCH2C6H5)3/

MAO catalytic system at 80 �C [19]. The resulting poly-

mer was stirred in a 10 wt.% methanol solution of HCl

for 5 h to remove the residual metal catalyst, the poly-

mer was then filtered and dried under vacuum at 70 �Cfor 72 h after which was extracted with methylethyl ke-

tone (MEK) to remove the atactic component. The puri-

fied polymer was characterized to have a very high steric

purity (>99% in syndio units) and its number average

molecular weight and polydispersity were 210,000 and

2.2, respectively. Succinic anhydride (SA) was purified

by recrystallization from chloroform before used. Car-

bon disulfide was dried overnight with anhydrous cal-

cium chloride, filtered and fractionally distilled in the

presence of phosphorus pentoxide before used. All the

other reagents and solvents were commercially available

and of analytical grade.

2.2. Modification

In a typical run, 0.50 g (5 mmol) of SA and 2.00 g

(15 mmol) of finely powdered anhydrous aluminum

chloride (AlCl3) was treated with 50 ml of carbon disul-

fide in a 150 ml three-neck round-bottom flask equipped

with condenser, dropping funnel, gas inlet/outlet, and a

magnetic stirrer. After being rapidly stirred for 2 h,

0.52 g (5 mmol based on benzene ring) of sPS (200 mesh)

was added to the mixture. The reaction was continued

under nitrogen atmosphere until the product turned to

a dark red. Then, the product was decomposed with

ice water followed by dilute hydrochloric acid, thor-

oughly washed with water to remove any residual acid,

filtered and dried overnight under vacuum at 70 �C.The modified polymer thus obtained was refined with

1,1,2-trichloroethane/methanol mixture (99/1, v/v), then

precipitated with methanol, filtered, and subsequently

dried under vacuum.

2.3. Characterization

Fourier transform infrared (FTIR) spectra were re-

corded on a Perkin–Elmer Spectrum One spectrometer.

Samples films were cast in aluminum pans from a

1.0 wt.% solution in chloroform/methanol mixture (99/

1, v/v) and dried under vacuum at 70 �C, which is suffi-

ciently high for removal of residual solvent.1H NMR spectra were obtained at 25 �C on a Bruker

AV 400 NMR spectrometer. Samples for 1H NMR spec-

troscopy were prepared by dissolving about 10 mg of

products in 5 ml of deuterated chloroform. Tetramethyl-

silane was used as an internal reference.

Quantitative analysis corresponding to the amount of

pendant carboxyl groups incorporated onto sPS was

done by a titration method as follows: 0.2 g of modified

polymer was put in 50 ml refluxing chloroform/metha-

nol mixture (99/1, v/v) for 2 h. Then the hot solution

was directly titrated without permitting it to cool to

J. Li, H.-M. Li / European Polymer Journal 41 (2005) 823–829 825

a phenolphthalein end point using sodium hydroxide

(0.05 molL�1) in methanol. Results were expressed as

the degree of succinoylation, which is defined as the

mole percentage of the styrene units succinoylated. Sam-

ple without modification was also titrated, yielding the

blank value.

Thermal analysis was performed using a TA instru-

ments Q10 differential scanning calorimeter equipped

with a RCS accessory under nitrogen atmosphere. For

all samples, the standard procedure is as follows: the

samples (about 5 mg) were heated at 300 �C for 5 min

in order to eliminate the influence of thermal history

and the effect of heat treatment on the crystalline struc-

ture of the materials, then cooled down to 50 �C to

record the crystallization temperatures, and then re-

heated to 300 �C to record the melting temperatures,

all at a rate of 20 �Cmin�1. The recorded temperatures

were calibrated using Indium as standard.

3. Results and discussion

3.1. Acylation reaction

Friedel–Crafts acylation reactions are aromatic sub-

stitution reactions in which benzene (or a substituted

benzene) undergoes acylation when treated with carboxy-

lic acid derivatives (usually acyl halide or anhydride)

and a Lewis acid catalyst, such as AlCl3 [20]. These reac-

tions were widely used to modify polystyrene through

the side groups (phenyl rings) of macromolecules [21].

However, crosslinking reaction of acylated macromole-

cules usually occurs in Friedel–Crafts acylation reac-

tions, which leads to changes in the molecular mass

and the solubility of the modified polymers. In order

to overcome this problem, Hird and Eisenberg [18] re-

ported a simple method for the preparation of partial

p-carboxylation of linear polystyrene without degrada-

tion or crosslinking of the polymer. It is well established

that, in Friedel–Crafts acylation reactions, when alumi-

num chloride and acetyl chloride are allowed to react to-

gether prior to addition to the substrate, the ratio of

catalyst to acyl component remains constant throughout

the reaction, and the results are reproducible.

In this study, Friedel–Crafts acylation reaction was

used to prepare slightly succinoylated syndiotactic poly-

styrene (s-sPS) in a heterogeneous process. However,

conducting the succinoylation reaction in the solution

state proved to be difficult, since sPS only dissolves in

high-boiling chlorinated solvents, such as 1,2,4-trichlo-

robenzene and 1,1,2-trichloroethane, at elevated temper-

atures. It is well known that chlorinated solvents and

high temperatures will have opposite influences on the

acylation procedure [20]. Thus, in the first stage of the

heterogeneous sPS succinoylation experiments, a

charge–transfer complex is formed between AlCl3 and

succinic anhydride in carbon disulfide. After stirring this

complex about 30 �C for 2 h, powder sPS (200 mesh)

was added, then a formation of HCl occurred and the

polymer was functionalized (Scheme 1). The following

parameters, such as the amount of AlCl3, reaction tem-

perature and reaction time, were changed in order to

optimize the process. The work-up procedure involves

treatment with ice water followed by dilute hydro-

chloride acid to decompose the complex and dissolve

the aluminum salts. The degree of succinoylation corre-

sponding to carboxylic acid value of the polymers was

determined by chemical titration, and the data are pre-

sented in Table 1.

As shown in Table 1, a noticeable increase of the de-

gree of succinoylation can be observed initially with

increasing catalyst concentration. The results indicate

that a relatively higher equimolar catalyst concentration

which depends on the [AlCl3]/[SA] molar ratio is desired

to promote succinoylation efficiency. Data for the succi-

noylation reactions at different temperature show an in-

crease in the succinoylation efficiency with increasing

reaction temperature. On the other hand, a high reaction

temperature would lead to crosslinking of sPS. As well,

time plays an important role on the succinoylation per-

centage in the Friedel–Crafts reactions. When succinic

anhydride and AlCl3 was first added as to form a

charge–transfer complex in the reaction medium to elimi-

nate undesirable side reactions, crosslinking was still ob-

served in the presence of high levels of AlCl3, i.e.,

[AlCl3]/[SA] molar ratio above 3/1, in parallel with high

reaction temperature, i.e., above 40 �C. This is attrib-

uted to a low reactivity between succinic anhydride

and AlCl3 generated on the sPS backbone, which is be-

lieved to be responsible for the increased crosslinking.

With respect to the sPS acetylation reactions [12], it is

worth noting that the low sPS succinoylation efficiency

was achieved due to the lower reactivity of succinic

anhydride and aluminum chloride complex in compari-

son with acetyl chloride.

3.2. FTIR analysis

To aid in the structural elucidation of the succinic

anhydride-functionalization chemistries, sPS with car-

boxyl moieties along the backbone was analyzed using

FTIR spectroscopy, and assignments for the characteris-

tic groups were developed.

FTIR spectra of pure sPS and the s-sPS with a degree

of succinoylation of 3.7 mol% in the range 2000–

1500 cm�1 are given in Fig. 1a and b, respectively. Com-

pared with Fig. 1a, two new bands appeared at 1685 and

1713 cm�1 in Fig. 1b, which confirmed the presence of

carbonyl groups in the s-sPS. In the s-sPS molecule,

two different carbonyl functional groups separated by

two carbon atoms do not lie in the same plane and

can be assigned to individual keto and acid groups.

O

O

O

AlCl3

AlCl3O

O

O

H2C CH CH2 CH

O

O

O

AlCl3

H2C CH CH2 CH

H2C

H2C O

O

OH

O

O

O

AlCl3H2C CH CH2 CH

H+/H2O

m

m

n

n

m n

(1)

(2)

Scheme 1.

Table 1

Synthesis of s-sPS by Friedel–Crafts reactiona

Run [AlCl3]/[SA]

(molar ratio)

Timeb

(h)

Temperature

(�C)DSc

(mol%)

1 2 2 20 0.5

2 2 2 30 1.5

3 2 2 40 4.1

4 3 2 30 2.8

5 4 2 30 4.6

6 3 4 30 3.7

7 3 6 30 5.9

a Conditions: sPS, 0.52 g (5 mmol); SA, 0.50 g (5 mmol);

CS2, 50 ml.b The reaction time are refereed to duration of reaction

between the AlCl3–SA charge–transfer complex and sPS

polymer.c DS referred to the degree of succinoylation obtained by

titration analysis.

2000 1900 1800 1700 1600 1500

Tran

smitt

ance

Wavenumber (cm-1)

a

b

Fig. 1. FTIR spectra of pure sPS (a) and s-sPS (b) with

degree of succinoylation of 3.7 mol% in the range of 2000–

1500 cm�1.

826 J. Li, H.-M. Li / European Polymer Journal 41 (2005) 823–829

Conjugation with an aromatic group leads a lower fre-

quency, the keto absorbs at 1685 cm�1, while the free

acid exhibited bands at 1713 cm�1 which attributed to

absorbance of isolated and hydrogen-bonded carbonyl

groups [22].

J. Li, H.-M. Li / European Polymer Journal 41 (2005) 823–829 827

3.3. NMR analysis

Supporting evidence for the structural elucidation

was revealed by 1H NMR analysis. Fig. 2 shows the1H NMR spectra of starting sPS and the s-sPS with de-

gree of succinoylation of 3.7 mol%. The resonances at

about 1.8 and 1.3 ppm are assigned to CH and CH2

units in the sPS backbone, respectively. After succi-

noylation, two new broad peaks at about 2.8 ppm and

3.2 ppm, due to methylene (CH2) proton of –COCH2-

CH2COOH moiety, are observed. Furthermore, in the

aromatic region, a new peak due to the protons ortho

to the succinoyl group appears around 7.6 ppm [23]. A

similar chemical shift was observed for the published

acetylated sPS [12].

The degree of succinoylation of the resultant polymer

can be estimated from the ratio of the integrated area

under the peaks resulting from the aliphatic and aro-

matic protons in the 1H NMR. The signals of respective

protons in the modified polymer were assigned as a, b, c

and d as shown in Fig. 2. Aa, Ab, Ac and Ad denote inte-

grated area under the signals of respective protons maxi-

mum at d = 1.80, 1.29, 3.22 and 2.84 ppm. The degree of

succinoylation (DS) of partially succinoylated sPS was

calculated from the relative intensities of the respective

signals in 1H NMR spectra according to the following

equation:

DS ¼ f½3� ðAc þ AdÞ�=½4� ðAa þ AbÞ�g � 100%

The value obtained by a NMR quantitative analyti-

cal method through the equation (4.0 mol%) was found

to be in agreement with the titration analysis (3.7 mol%).

3.4. Thermal analysis

The random incorporation of small quantities of

noncrystallizable comonomer units into the backbone

10 9 8 7 6 5 4 3 2 1 0

H2C CH CH2 CH

H2C

H2C O

O

OH

a

c

d

b

m n

dc

b

a

B

A

ppm

Fig. 2. 1H NMR spectra pure sPS (A) and s-sPS (B) with

degree of succinoylation of 3.7 mol%.

of a semicrystalline polymer has a dramatic effect on

the thermodynamics and kinetics of crystallization. Rela-

tive to the behavior observed with homopolymer, crys-

tallizable copolymers usually exhibit low melting

temperature, low degrees of crystallinity, and a signifi-

cant decrease in the overall rate of crystallization [24].

In attempt to understand the link between succinoyl

moieties and crystallization of s-sPS, the thermal beha-

vior of s-sPS was investigated by means of DSC.

The sample subjected to the DSC experiments are

used the following protocol: equilibrium at 300 �C and

kept at this temperature for 5 min, then cooling from

300 to 50 �C, and finally reheating from 50 to 300 �C,both the heating and cooling rate are 20 �Cmin�1. Figs.

3 and 4 exhibit DSC scans of sPS (a) and related s-sPS

with different degree of succinoylation ((b) 0.5 mol%,

(c) 1.5 mol%, (d) 3.7 mol% and (e) 5.9 mol%). Table 2

lists the thermal data for each of the samples shown in

Figs. 3 and 4.

From crystallization temperature (Tc) recorded from

the cooling scans of the samples (Fig. 3), the crystalliza-

tion endotherm of pure sPS occurs at the highest tem-

perature and has the sharpest crystallization exotherm,

while crystallization temperature (Tc) and enthalpy of

cryatallization (DHc) for s-sPS samples from the melt de-

creased with increasing degree of succinoylation. Fur-

thermore, a more broadened transition temperature

range has been observed for all succinoylated samples

with increasing degree of succinoylation, which indicates

that the nonisothermal crystallization rate decreases

with increasing degree of succinoylation. This suggests

that the crystallization rate can be retarded by the pres-

ence of covalently attached carboxyl groups.

Generally, the degree of crystallinity of crystallizable

polymer materials can be estimated by measuring the

50 100 150 200 250 300Temperature (°C)

a

b

c

d

e

Endo

Fig. 3. DSC cooling scans of pure sPS (a) and s-sPS with

different degree of succinoylation, (b) 0.5 mol%, (c) 1.5 mol%,

(d) 3.7 mol% and (e) 5.9 mol%.

50 100 150 200 250 300Temperature (°C)

a

b

c

d

e

Endo

Fig. 4. DSC heating scans of pure sPS (a) and s-sPS with

different degree of succinoylation, (b) 0.5 mol%, (c) 1.5 mol%,

(d) 3.7 mol% and (e) 5.9 mol%.

828 J. Li, H.-M. Li / European Polymer Journal 41 (2005) 823–829

enthalpic changes at melt. The melting enthalpy of 100%

crystalline sPS has been reported to be 53 Jg�1 [25].

Using this value, the degree of crystallinity (Xc) of the

samples was calculated. The data in Table 2 exhibits a

systematic trend of degree of crystallinity (Xc) depres-

sion with increasing degree of succinoylation. For the

sample with degree of succinoylation of 5.9 mol%, its

Xc value is 23%, much lower than that of neat sPS

(56%).

The melting point (Tm) of succinoylated polymers in

Fig. 4, as expected, exhibits a systematic trend of depres-

sion with increasing degree of succinoylation. The Tm of

neat sPS is around 270 �C, similar to the value previ-

ously obtained [26]. For the 5.9 mol% succinoylated

polymer sample, the Tm decreases to about 255 �C. Thisresult is quite different from the acetylated syndiotactic

polystyrene. For the 42.6 mol% acetylated syndiotactic

polystyrene sample, the Tm is about 265 �C [12]. This

phenomenon may be explained by comparing the size

of acyl substituents between the acylated styrene units.

It is expected that in s-sPS due to the larger size of the

Table 2

Summary of DSC results for sPS and s-sPS

Run DSa (mol%) Tgb (�C) Tm

b (�C) DHm

1 0 92.7 270.7 29.5

2 0.5 97.2 269.8 27.5

3 1.5 97.1 268.0 19.6

4 3.7 98.3 263.8 16.0

5 5.9 95.1 255.6 13.4

a DS referred to the degree of succinoylation.b The glass transition temperatures, Tgs were determined as the mi

crystallization, Tc temperatures were selected as the peak maximum orc The degree of crystallinity in the sample, Xc is determined by the

enthalpy of the sample and DH 0m is the melting enthalpy of 100% cry

substituent group, the chain mobility, which is required

for significant crystallization, would be less in s-sPS rela-

tive to the acetylated sPS. Thus, based on this chain

mobility argument, the succinoylated styrene units may

interrupt or retard crystal growth, limiting the size of

the crystallites achievable and resulting in the depression

of melting point.

The glass transition temperature (Tg) data also helps

in understanding the effects of succinoyl groups on the

movement of the polymer chains. It is clear from Table

2 that the Tg value of the modified polymer increases

with increasing the degree of succinoylation. For exam-

ple, as degree of succinoylation increases, Tg increases

from 93 �C for neat sPS to 98 �C for the 3.7 mol% s-

sPS sample. As mentioned above, the substituent groups

result in reducing the mobility of the polymer chains and

therefore raising Tg values. Furthermore, compared with

neat sPS, due to the interactions between the acid

groups, e.g., hydrogen bonding, the mobility of the poly-

mer chains is also reduced, thus raising Tgin the modi-

fied samples. This result also coincides with the results

presented in Refs. [9,12].

4. Conclusions

The succinoylated syndiotactic polystyrene was

accomplished by Friedel–Crafts reaction in a heteroge-

neous process by using carbon disulfide as dispersing

agent, succinic anhydride as succinoylating agent and

aluminum chloride as catalyst. An optimum reaction

should be carried out at 30 �C with a molar ratio of alu-

minum chloride to succinic anhydride of 3/1. The succi-

noylated syndiotactic polystyrene was confirmed by

FTIR and 1H NMR spectroscopy. Moreover, it is found

that thermal behavior of the succinoylated syndiotactic

polystyrene exhibits considerable differences in compari-

son to the neat sPS. The melting temperature (Tm), crys-

tallization temperature (Tc), and degree of crystallinity

of the succinoylated polymer samples decreases with

increasing the degree of succinoylation, while the glass

(Jg�1) Xcc (%) Tc

b (�C) DHc (Jg�1)

55.7 239.5 30.4

51.9 236.7 26.9

37.0 225.8 20.3

30.2 213.0 16.7

25.3 197.6 16.0

dpoint of the step change in the heat flow. The melting, Tm and

minimum in endothermic or exothermic transition, respectively.

equation: X c ¼ ðDHm=DH0mÞ � 100%, where DHm is the melting

stalline sPS (53 Jg�1 [25]).

J. Li, H.-M. Li / European Polymer Journal 41 (2005) 823–829 829

transition temperature increases. The functionalized sPS

offers possibility for the development of novel sPS-based

polymer blends and composites, thus extending the

application field of sPS.

Acknowledgments

The authors thank the Key Project of Scientific Re-

search Funds of Hunan Provincial Education Depart-

ment (02A011) for support of this work.

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