ORIGINAL CONTRIBUTION
Preparation of two kinds of chloromethylated polystyreneparticle using 1,4-bis (chloromethoxy) butaneas chloromethylation reagent
Chunling Lü & Baojiao Gao & Qing Liu & Changsheng Qi
Received: 23 July 2007 /Revised: 9 October 2007 /Accepted: 8 November 2007 /Published online: 10 December 2007# Springer-Verlag 2007
Abstract By adopting “grafting from” manner, polystyrenewas grafted onto the surface of silica gel particles with anaverage size of 125 μm in a solution polymerizationsystem, and grafted particle PSt/SiO2 was prepared. Using1,4-bis (chloromethoxy) butane (BCMB, it is nontoxic.) aschloromethylation reagent, chloromethylation reaction forthe grafted particle PSt/SiO2 was performed in the presenceof Lewis acid catalyst SnCl4. At the same time, cross-linkedstyrene-divinylbenzene copolymer (CPS) microsphere alsowas chloromethylated with the same reagent as PSt/SiO2,so that two kinds of chloromethylated polystyrene particleswere obtained, and they are chloromethylated graftedparticle (CMPS/SiO2) and chloromethylated cross-linkedpolystyrene (CMCPS) microsphere, respectively. Thechemical structures and compositions of the two particleswere characterized using Fourier transform infrared andVolhard method. The effects of various factors on thechloromethylation reactions were mainly investigated. Theexperimental results show that the process to preparethe two kinds of chloromethylated polystyrene particlesnot only has the character of environment friendness andlow cost but also is convenient to control via adjustingvarious reaction conditions. The main reaction conditionsaffecting the chloromethylation reactions are reaction time,the added amount of BCMB, and the used amount ofsolvent and catalyst. They influence the reaction in tworespects: (1) the chloromethylation degrees of polystyreneare different under different conditions; (2) Friedel–Craftscross-linking reaction between polystyrene macromoleculesis accelerated or inhibited under different conditions (for
CPS microsphere, this cross-linking reaction also is calledthe additional cross-linking). Under suitable conditions, thetwo kinds of chloromethylated polystyrene particles with ahigh chlorine content (about 17%, this chlorine content wascalculated based on polystyrene weight) can be gainedusing SnCl4 as catalyst and CH2Cl2 as solvent at roomtemperature for 10 h and basically without cross-linking oradditional cross-linking.
Keywords Polystyrene . Chloromethylation .
Silica gel . 1,4-bis (chloromethoxy) butane .
Graft polymerization
Introduction
Chloromethylated cross-linked polystyrene (CMCPS) mi-crosphere is an important precursor of many functionalpolymer microspheres. Using CMCPS microspheres asstarting materials, various functional polymer microspherescan be obtained via further macromolecular reactions due tothe high chemical activity of chloromethyl groups(−CH2Cl). Therefore, CMCPS microsphere has wideapplications in various fields. For example, it can be usedas a support in solid-phase synthesis and combinatorialchemistry [1–3], it can be used to prepare ion-exchangingresin, chelating resin, and adsorption resin [4–7], it can beused as a support of catalysts and reagents in organicsynthesis [8–10], and it can be used in the preparation offunctional polymer microspheres used in the immobiliza-tion, separation, and purification of biomacromolecules, aswell as in chromatographic fixed phase [11–13], etc.Apparently, the preparation of CMCPS microsphere shouldbe developed greatly based on its wide applications.
Colloid Polym Sci (2008) 286:553–561DOI 10.1007/s00396-007-1800-z
C. Lü : B. Gao (*) :Q. Liu : C. QiDepartment of Chemical Engineering, North University of China,Taiyuan 030051, People’ s Republic of Chinae-mail: [emailprotected]
At present, there are mainly two methods to prepareCMCPS microsphere. One is the reaction of cross-linkedstyrene-divinylbenzene copolymer (CPS) microsphere withchloromethyl ether (CME) or bis-chloromethyl ether(BCME) in the presence of a Lewis acid [14, 15], andanother is the copolymerization of p-chloromethyl styrene(CMS), styrene, and divinylbenzene [16, 17]. However,CME and BCME have serious carcinogenic toxicity, and infact, the first method has been limited for a long time overthe world. The second method is expensive because of highprice of CMS (400$ per kg [15]), and large-scalepreparation of CMCPS microsphere with CMS is thereforeunattractive. Considering these drawbacks of the twomethods, some new ways to prepare chloromethyltedpolystyrene microsphere need to be developed. In thiswork, using 1,4-bis (chloromethoxy) butane (BCMB) aschloromethylation reagent, which is non-carcinogenic andinexpensive [18], two kinds of chloromethylted polystyreneparticles were prepared: (1) In the presence of Lewis acidcatalyst, CPS microspheres were allowed to be reacted withBCMB, and CMCPS microspheres were obtained; (2) first,styrene was grafted onto the surface of silica gel particleswith “grafting from” manner resulting in formation ofgrafting particles PSt/SiO2, then, the grafted polystyrenewas chloromethylated using BCMB as the chloromethyla-tion reagent, and finally, the composite particles CMPS/SiO2 were obtained, on which chloromethylated polysty-rene (CMPS) was attached chemically. The compositeparticle CMPS/SiO2 not only has chemical modificabilitylike as CMCPS microspheres but also has the excellentmechanical property and thermal stability, which areattributed to SiO2 particles. It can be predicted that thecomposite particle CMPS/SiO2 will replace CMCPS mi-crosphere in various application fields, and furthermore, itwill display better service performance.
To obtain the two kinds of the chloromethylated particleswith high chloromethylation degree and without obviouscross-linking caused by Friedel–Crafts reaction, which isdisadvantageous to the application performance of thechloromethylated particles, in this study, a detailed researchon the chloromethylation reaction process was carried out.To our knowledge, the new way to obtain chloromethylatedpolystyrene particles described in this work has not beenreported up to now.
Experimental
Materials and equipment
Cross-linked polystyrene (CPS) microsphere (TenlongChemical Ltd, Changchou, China), namely, cross-linkedstyrene-divinylbenzene copolymer microsphere, with 4% of
crosslinking degree and 0.315–0.45 mm in diameter, wasreceived. Silica gel with an average diameter of 125 μm (120–160 mesh) was supplied by Ocean Chemical Ltd (Qingdao,China). Styrene (St, Denfeng Chemical reagent Plant,Tianjing, China) was of analytical grade and was purified bydistillation under vacuum before use. Azo-diisobutyronitrile(AIBN, Shanghai Chemical reagent plant), γ-methacryloyl-propyl trimethoxysilane (MPS, Chuangshi Chemical Aux Ltd,Nanking, China), and anhydrous tin tetrachloride (SnCl4,Yuanli Chemical Ltd, Tianjin, China) were all of analyticalgrade. Other reagents were all commercial chemicals withanalytical pure grade. BCMB was prepared by us [18].
A Perkin-Elmer 1700 infrared spectrometer (Perkin-Elmer, USA) was used for Fourier transform infrared(FTIR) analyses, A 438VP scanning electron microscope(SEM, LEO, UK) was used for observing the morphologyof the grafting particles, a Netzsch STA449 thermogravi-metric analyzer (GTA, Netzsch, Germany) was used forGTA analysis, and a calorimetric meter of oxygen-bombtype made in China was used for analysis of chlorineelement with Volhard method.
Preparation and characterization of CMCPS microsphere
The chloromethlation reaction of CPS microsphere wascarried out in a thermostatic four-necked flask of 100 mlfitted with a reflux condenser, stainless-steel stirrer, andthermometer. Accurately weighted CPS microspheres(about 3 g) and a certain amount of solvent CH2Cl2 wereadded, and the CPS microspheres were allowed to be fullyswelled for a period of time. Then, a certain amount ofBCMB and catalyst SnCl4 were added (the status of theused amounts of various reagents will be discussed in the“Results and discussion”). The reaction was conducted withstirring at room temperature (25°C) for a certain period oftime. After ending the reaction, the product mixture wastreated with diluted hydrochloric acid and filtrated toremove the catalyst. The product microspheres werewashed adequately with dioxane to remove residual organicsolvent and then washed repeatedly with distilled wateruntil without chloride ions. After being dried undervacuum, CMCPS microspheres were obtained. The infraredspectra of CMCPS microspheres and CPS microsphereswere measured with KBr pellet method, respectively, toconfirm the structure changes. To determined chlorinecontents, the sample of CMCPS microspheres was firstburned out in an oxygen bomb [19] and chlorine elementcontained in the sample was fully transformed into chlorideions. Volhard method was adopted to analyze the chlorinecontents (wt%).
To explore the effects of various factors on thechloromethylation reaction, the reactions were performed
554 Colloid Polym Sci (2008) 286:553–561
under various conditions, respectively, such as with thedifferent added amounts of chloromethylation reagentBCMB and with the different used amounts of the solventand catalyst.
Preparation and characterization of CMPS/SiO2 particle
Preparation and characterization of grafting particlePSt/SiO2
According to the procedure described in [20], graftedparticle PSt/SiO2 was prepared in the manner of “graftingfrom” in a solution polymerization system. The typicalprocess is as follows: first, silica gel particles were activatedwith aqueous solution of methane sulfoacid at 102°C for4 h; then, activated silica gel particles were allowed to bereacted with coupling agent MPS at 50°C for 24 h usingethanol as solvent, and surface-modified silica gel particleswere obtained denoted as MPS–SiO2; finally, the graftpolymerization of styrene onto the surface of MPS–SiO2
particles was carried out. The grafting polymerization wasconducted in a four-necked flask equipped with a refluxcondenser, mechanical stirring, thermometer, and N2 inlet.Solvent toluene, styrene, and MPS–SiO2 particles wereadded in turn, and the mixture was stirred and the particleswere fully dispersed. As the temperature increased up to80°C, initiator AIBN was added to this mixture. Under inertgas of N2, the graft polymerization was carried out at aconstant temperature of 80°C for 7 h while being stirred.After finishing the reaction, the product particles wereextracted for 20 h in a soxhlet to remove the free polymerphysically adsorbed on the surface of the product particles.After drying, grafted particles PSt/SiO2 were gained. Thegrafting degree (g/100 g) of PSt/SiO2 was determined withthermogravimetry. The PSt/SiO2 particles used in this studyhave a grafting degree of 17.30/100 g. The infraredspectrum of PSt/SiO2 particle was measured, and itsmorphology was observed with scanning electron micro-scope (SEM).
Chloromethylation of grafting particles PSt/SiO2
and characterization
Accurately weighted PSt/SiO2 microspheres (about 3 g) andsolvent CH2Cl2 were added into a four-necked flaks fittedwith a mechanical stirrer, reflux condenser, and thermom-eter, and the PSt/SiO2 particles were allowed to be fullyswelled for a period of time, followed by the additions ofBCMB and SnCl4 (the status of the used amounts ofvarious reagent will be discussed below). The chlorome-thalation reaction was carried out at room temperature(25°C) for a certain period of time. After finishing thereaction, the product mixture was washed with diluted
hydrochloric acid to remove the catalyst. After filtrated, theproduct particles were washed adequately with dioxane toremove organic solvent and then washed repeatedly withdistilled water until in the absence of chloride ions. Afterbeing dried under vacuum, CMPS/SiO2 particles weregained on which chloromethylated polystyrene was at-tached chemically. The chlorine content of CMPS/SiO2
particle was determined with the combination of oxygenbomb combustion and Volhard method, and the chlorinecontent was calculated based on the weight of graftedpolystyrene. At the same time, the FTIR of CMPS/SiO2
particle was measured with KBr pellet method.To explore the effects of various factors on the
chloromethylation reaction of the grafted particle PSt/SiO2, the reactions were conducted under various con-ditions, such as with the different added amounts ofchloromethylation reagent BCMB and with the differentused amounts of the solvent and catalyst.
Results and discussion
Preparation process and characterization of CMCPSmicrospheres
Using 1,4-bis(chloromethoxy) butane as chloromethylationreagent and in presence of SnCl4, cross-linked polystyrene(CPS) microspheres were chloromethylated at para-positionof benzene ring to form CMCPS microspheres, and thereaction process is expressed schematically in Scheme 1.
Chloromethyl group is a chemically active group. Alongwith the chloromethylation reaction of CPS microspheres,Friedel–Crafts reaction between polystyrene macromole-cules will occur, leading to additional cross-linking, asshown in Scheme 2. This additional cross-linking is areaction process to lose chlorine due to the deprivation ofHCl during the cross-linking reaction. The possibility of theadditional cross-linking increases with enhancement ofchloromethylation degree of CPS microspheres. The addi-tional cross-linking reaction not only leads to the decreaseof chloromethylation degree of CPS microspheres but alsoincreases the cross-linking degree, which will influence thesubsequent functional modification reaction for the CMCPSmicrospheres. Therefore, it is necessary to control reactionconditions to avoid the occurrence of the additional cross-linking as far as possible.
Figure 1 gives the FTIR spectra of CPS and CMCPSmicrospheres. In the spectrum of CPS, the bands at 3,024,1,600, 1,492, 1,452, 756, and 700 cm−1 are the character-istic absorptions of polystyrene, and the band at 828 cm−1 isthe vibration absorptions of =C–H bond of benzene ringafter binary substituting caused by the incorporation ofdivinyl benzene. After chloromethylating reaction, some
Colloid Polym Sci (2008) 286:553–561 555
absorption changes have occurred in the spectrum ofCMCPS: (1) Two new bands at 1,421 and 670 cm−1 haveappeared, and they are the characteristic absorptions of thechloromethyl group –CH2Cl. The band at 670 cm−1
corresponds to the stretching vibration of C–Cl bond, andthe band at 1,419 cm−1 is corresponding to the bendingvibration of –CH2 in –CH2Cl. (2) Besides, a new band at1,263 cm−1 have appeared, and the band at 828 cm−1 isstrengthened, which is attributed to the vibration absorp-tions of =C–H bond of benzene ring after binary substitut-ing caused by the substitution of hydrogen atoms at thepara-position of benzene rings by groups –CH2Cl. Theseabsorption changes indicate that the hydrogen atoms at thepara position of benzene ring of polystyrene have beensubstitutes by chloromethyl groups, fully confirm that CPSmicrosphers have been chloromethylated, and suggest thatCMCPS microsphers have been prepared.
Preparation process and characterization of CMPS/SiO2
particles
After being activated for silica gel particles, a great quantityof silanol groups is produced on their surfaces, and thenMPS reacts with these silanol groups to form modifiedsilica gel, designated as MPS–SiO2 on which polymerizabledouble bonds are attached chemically. In the presence ofinitiator, polystyrene is grafted onto silica gel in the mannerof “grafting from” to form grafted particles PSt/SiO2. Byusing BCMB without carcinogenic toxicity [18] as chlor-omethylation reagent and in the presence of Lewis acidcatalyst, the chloromethylation reaction of the grafted
polystyrene of PSt/SiO2 is carried out, resulting in theformation of composite particles CMPS/SiO2. The totalprocess to prepare CMPS/SiO2 particles is shown inScheme 3.
As mentioned above, chloromethyl group is an activegroup. In addition, Lewis acid catalyst also is the catalyst ofFriedel–Crafts reactions. Therefore, along with the chlor-omethylation reaction of particles PSt/SiO2, the Friedel–Crafts reaction between the grafted polystyrene macro-molecules will occur as shown in Scheme 2, leading to theformation of cross-linking (but it is not the additional cross-linking like as in the case of CMCPS). The cross-linkingbridge between macromolecules will affect subsequentfunctional modification of CMPS/SiO2. Therefore, theFriedel–Crafts reaction also needs to be controlled.
Figure 2a and b shows the SEM images of SiO2 particlesand the grafted particles PSt/SiO2, respectively. It can beseen from Fig. 2a that, before graft polymerization, thesurface of the bare SiO2 particles is rough and irregular,whereas after graft polymerization, the surface of particlePSt/SiO2 becomes smooth because of the effect of filling upand covering of the grafted polymer layer as Fig. 2b shown.
Figure 3 displays the FTIR spectra of PSt/SiO2 andCMPS/SiO2 particles. In the spectrum of PSt/SiO2, inaddition to the absorption bands of SiO2, there are thecharacteristic absorptions of polystyrene, such as the bandsat 3,028, 1,580, 1,499, 1,450 and 710 cm−1. Only becausethe strong background of the absorption bands of SiO2
exists, all the characteristic absorptions of polystyrenebecome weaker, and so much as some bands cannot bedisplayed. As compared with the spectrum of PSt/SiO2, inthe spectrum of CMPS/SiO2, there are two new bands to be
SnCl4+
CH2Cl
CH CH2 CH CH2 CH CH2
CH CH2
CH CH2 CH CH2
CH CH2
CH CH2
CH2
Scheme 2 Schematic illustra-tion of Friedel–Crafts cross-linking reaction between PStchains
+ ClCH2OCH2CH2CH2CH2OCH2ClSnCl4
+HOCH2CH2CH2CH2OH
CH CH2 CH CH2
CH2Cl
CH2Cl
CH CHCH2
CH CH2 CH CH2
CH CH2 CH CH2
CH2
Scheme 1 Schematic illustra-tion of preparing process ofCMCPS microsphere
556 Colloid Polym Sci (2008) 286:553–561
produced, and they are at 1,423 and 818 cm−1. The formeris ascribed to the characteristic absorptions of chloromethylgroup –CH2Cl, and the later is attributed to the vibrationabsorptions of =C–H bond of benzene ring after binarysubstituting caused by the substitution of hydrogen atoms atthe para-position of benzene rings by groups –CH2Cl. Theabove changes of the absorptions reveal that the graftedpolystyrene on PSt/SiO2 has been chloromrthylated and thecomposite particles CMPS/SiO2 have been obtained.
Effect of various factors on chloromethylation reactionof CPS microsphere
Effect of the used amount of BCMB
By varying the used amount of the chloromethylationreagent BCMB, chloromethylation reactions of CPS micro-spheres were carried out, and Fig. 4 shows the dependenceof chlorine content of CMCPS microspheres on time asdifferent amounts of BCMB are used.
It can be found that, at the initial stage, the chlorinecontent increase rapidly with reaction time; then, theincrease becomes smooth as after a certain time; finally,the chlorine content turn to decrease. A vertex appears onthe curve, and this is a signal that indicates that theadditional cross-linking reaction between polystyrene mac-romolecules has been occurred obviously. At the initialstage, because the concentration of BCMB is very high, thechloromethylation reaction at para-position of benzene ringfor CPS microspheres is carried out with a high rate,resulting in rapid enhancement of the chlorine content.However, along with the increase of the chlorine content,Friedel–Crafts cross-linking reaction between macromole-cules turns to be easy to occur. As described before, theFriedel–Crafts cross-linking reaction is a process to losschlorine. Therefore, after a certain reaction time, theincrease of the chlorine content tends to be smooth becauseof the neutralization of chlorine loss. When the process to
(1) CH2CH2CH2OC
O
+ C
CH3
SiO2 CH3O
OCH3
OCH3
OSiO2 CH2CH2CH2OC
O
C
CH3
+
OCH3
O
OCH3 H
CH2
CH2
Si
Si
OH
(2)+OSiO2 Si CH 2CH2CH2OC CH2
O
C
CH3OCH3
OCH3
n
CH=CH2
) nCH2CH(OSiO2 Si CH2CH 2CH 2 OC
O
C
CH 3
CH2
OCH3
OCH3
AIBN
SiO2(3)
+HOCH2CH2CH2CH2OH
SiO2
+ ClCH2OCH2CH2CH2CH2OCH2ClSnCl4CH CH 2 CH CH 2
CH CH 2 CH CH 2
ClCH2ClCH2
Scheme 3 Schematic illustra-tion of preparing process ofCMPS/SiO2 particles
4000 3000 2000 1000
828
CPS
14211261
828
670
700
7561452
1492
1600
3024
CCPS
T(%)
Wavenumber/cm-1
Fig. 1 FTIR spectra of CPS and CMCPS microsphere
Colloid Polym Sci (2008) 286:553–561 557
loss chlorine turns to be predominant over the chlorome-thylation process, the chlorine content will began todecrease. This above reason leads to the character with amaximum for the curve of chlorine content vs time. Thevertex occurrence implies that Friedel–Crafts cross-linkingreaction has occurred obviously. Therefore, to obtain theCMCPS microspheres with high chloromethylation degreeand without obvious additional cross-linking, the reactiontime needs to be control effectively.
By comparing the three curves in Fig. 4, it can beobserved that on the left side of the vertex, in the sameperiod of time, the chlorine content of the product is higheras the concentration of BCMB is greater. This fact accordswith general kinetics rule, namely, the higher the reactantconcentration, the rapider the reaction rate. It still can befound that the higher BCMB concentration, the shorter thetime when the vertex occurs. This is caused by rapidFriedel–Crafts cross-linking reaction. Therefore, to obtainthe CMCPS microspheres with high chloromethylationdegree and without obvious additional cross-linking, theused amount of BCMB should be controlled. Basing onexperimental results, we consider that the suitable addedamount of BCMB should be 1.5 times more than theoreticamount (i.e., expected chlorine content) or lower. In this
study, with the suitable amount of BCMB, the CMCPSmacrospheres with about 16 wt% of chlorine content can beobtained in 10 h as displayed in Fig. 4 (13 ml of BCMB).
Effect of the used amount of solvent
By varying the used amount of CH2Cl2 and fixing otherreaction conditions, chloromethylation reactions of CPSmicrospheres were carried out, and Fig. 5 gives thedependence of chlorine content of CMCPS microsphereson time as different amounts of CH2Cl2 are used.
It can be seen clearly that for 3 g of CPS microspheres,the chlorine content of the product in the same period andthe time when the maximum appears are different for thedifferent used amounts of solvent CH2Cl2: (1) the chlorinecontent of the product is the highest as 30 ml of solventCH2Cl2 is used, and the chlorine content maximum appearsin 8–12 h; (2) whereas as 20 ml of CH2Cl2 is used, thechlorine content is lower; (3) the chlorine content of theproduct is the lowest as 40 ml of CH2Cl2 is used, andthe chlorine content maximum appears in 15–18 h.
As the used amount of solvent is lower (20 ml), thecross-linking networks of CPS microspheres cannot be
100µm b 100µm a
Fig. 2 TEM photographs ofSiO2 and PSt/SiO2 particles
4000 3000 2000 1000
15
20
25
30
35
40
45
50
1450PS/SiO2
CMPS/SiO2
710
8181423
149915802852
29263028
T(%)
Wavenumber(cm-1)Fig. 3 FTIR spectra of PSt/SiO2 and CMPS/SiO2 particles
0 5 10 15 20 25
10
12
14
16
Chl
orin
e C
onte
nt/%
T/h
13mL10mL7mL
Fig. 4 Plot of chlorine content of CMCPS microsphere vs time withdifferent BCMB amounts. CPS microsphere, 3 g; temperature, 25°C;CH2Cl2, 30 ml; SnCl4, 1.5 ml (0.013 mmol)
558 Colloid Polym Sci (2008) 286:553–561
fully swelled; the chloromethalation reaction is nor easy tobe carried out, resulting in the lower chlorine content in thesame period. As the used amount of solvent is greater(30 ml), the cross-linking networks of CPS microspheresthecan be fully swelled, and they become adequately extended.This enables the active reaction sites to be fully exposed,and it is greatly advantageous to the chloromethylationreaction, resulting in the highest chlorine content in thesame period. Whereas as the used amount of solvent isincreased further (40 ml), the chlorine content in the sameperiod turns to decrease because of diluted effect for thereactant BCMB. The above described reason leads to theinterlacing up and down for the three curves as shown inFig. 4. It also can be found that the greater the used amountof solvent is, the longer the period in which the maximumchlorine content is attained, namely, the time when Friedel–Crafts cross-linking reaction obviously occur is prolonged.This is another display of the diluted effect. As the solventamount is very great, the networks of CPS are swelledenough and become quite extended so that the spacebetween chains becomes greater, and it makes the addi-tional cross-linking reaction difficult to occur, resulting inthe longer time when vertex appears. By this token, toobtain the CMCPS microsphere with high chloromethyla-tion degree and without obvious additional cross-linking,the used amount of the solvent also needs to be selectedrightly. Apparently, for the studied system, the suitable usedamount of CH2Cl2 is 30 ml.
Effect of catalyst amount
By varying the used amount of catalyst (1, 1.5, and 2 ml)and fixing other reaction conditions, chloromethylationreactions of CPS microspheres were performed, and Fig. 6
gives the dependence of chlorine content of CMCPSmicrospheres on time as different amounts of catalyst wereused. By comparing the three curves in Fig. 6, it can beobserved that on the left side of the vertex, the chlorinecontent in the same period is higher as the catalyst amountis greater. This accords with the general kinetics rule,namely, the greater the catalyst concentration is, the rapiderthe reaction rate. It still can be found from Fig. 6 that thegreater the catalyst amount is, the shorter the timecorresponding to the maximum, namely, the time whenFriedel–Crafts cross-linking reaction has occurred obvious-ly. The reason for this is that the catalysis action of SnCl4for Friedel–Crafts cross-linking reaction is stronger as morecatalyst is used. Interleaving up ad down for the curves alsohappened in Fig. 6. Obviously, for the studied system, thesuitable used amount of SnCl4 is 1.5 ml, as displayed inFig. 6. Therefore, to obtain the CMCPS microsphere withhigh quality, the catalyst amount also needs to be selectedsuitably.
Effect of various factors on chloromethylation reactionof PSt/SiO2 particles
Effect of the used amount of BCMB
The chloromethylation reactions for the grafted particlesPSt/SiO2 were conducted with the different used amount ofBCMB and with fixed other conditions. Figure 7 displaysthe dependence of the chlorine content of the productparticles CMPS/SiO2 on time.
The status in Fig. 7 is the same as in the case in Fig. 4.The chlorine content exhibits the variation trend of first arising and then a declining with reaction time. The reasonfor this is similar to that described in section Effect of the
0 5 10 15 20 25
8
10
12
14
16
chlo
rine
cont
ent/%
T/h
30ml20ml40ml
Fig. 5 Plot of chlorine content of CMCPS vs time with differentsolvent amounts. CPS microsphere: 3 g; Temperature: 25 °C; BCMB:13 ml; SnCl4: 1.5 ml (0.013 mmol)
0 5 10 15 20 25
8
10
12
14
16
Chl
orin
e C
onte
nt/%
T/h
1.5mL2mL1mL
Fig. 6 Plot of chlorine content of CMCPS vs time with differentcatalyst amounts. CPS microsphere, 3 g; temperature, 25°C; BCMB,13 ml; CH2Cl2, 30 ml
Colloid Polym Sci (2008) 286:553–561 559
used amount of BCMB “Effect of the used amount ofBCMB.” In comparison with the chloromethylation sys-tems of CPS, the only difference is that the Friedel–Craftscross-linking reaction along with the chloromethylationreaction is the cross-linking reaction between graftedpolystyrene macromolecules in the chloromethylation sys-tem of PSt/SiO2, and it cannot be called “additional cross-linking reaction.” The appearance of the maximum meansthat the Friedel–Crafts cross-linking reaction betweengrafted macromolecules has been produced obviously.
As three amounts of BCMB, 9, 13 and 17 ml, were used,the cholromethylation results are distinctly different, al-though the relationship between the reaction rate and theamounts of BCMB as well as the relationship between thetime corresponding to the maximum and the amounts ofBCMB are the same as in the chloromethylation system ofCPS. There appears curve interleaving as shown in Fig. 7.For the studied system, 13 ml of BCMB is an appropriateamount. Therefore, for the chloromethylation system ofPSt/SiO2, the used amount of BCMB also should be choicecorrectely.
Effect of the used amount of solvent
By varying the used amount of CH2Cl2 and fixing otherreaction conditions, the chloromethylation reactions forPSt/SiO2 particles were performed. Figure 8 displays thedependence of the chlorine content of grafted polystyreneon time.
It is seen from Fig. 8 that, for 3 g of PSt/SiO2 particles,the chlorine content is the highest as 40 ml of CH2Cl2 isused, compared with 30 ml and 50 ml of CH2Cl2, and themaximum appears after 10 h. This fact indicates that, in
40 ml of CH2Cl2, the grafted polystyrene macromoleculescan be well swelled and extended so that the active reactionsites can be adequately exposed and the chloromethylationreaction can be carried out favorably. The less and moresolvent than 40 ml are disadvantageous for preparingCMPS/SiO2 with high quality. As 30 ml of CH2Cl2 isused, the rate of the chloromethylation reaction is slowerdue to un-enough swelling of grafted polystyrene, and thecross-linking reaction occurs prematurely owing to ashorter distance between the grafted macromolecules. As50 ml of CH2Cl2 is used, the rate of the chloromethylationreaction is also slower due to the diluted effect, and thecross-linking reaction occurs lingeringly owing to a distantinterval between the grafted macromolecules.
5 10 15 20 25
6
8
10
12
14
16C
hlor
ine
Con
tent
(%
)
t (h)
13ml 9ml 17ml
Fig. 7 Plot of chlorine content of CMPS/SiO2 particle vs time withdifferent BCMB amounts. PSt/SiO2 particle, 3 g; temperature, 25°C;CH2Cl2, 40 ml; SnCl4, 1.5 ml (0.013 mmol)
6
8
10
12
14
16
Chl
orin
e co
nten
t (%
)
40ml 30ml 50ml
5 10 15 20 25
t /hFig. 8 Plot of chlorine content of CMPS/SiO2 particle vs time withdifferent solvent amounts. PSt/SiO2 particle, 3 g; temperature, 25°C;BCMB, 13 ml; SnCl4, 1.5 ml (0.013 mmol)
7
8
9
10
11
12
13
14
15
16
Chl
orin
e co
nten
t(%
)
1.5ml 2ml 1ml
5 10 15 20 25t /h
Fig. 9 Plot of chlorine content of CMPS/SiO2 particle vs time withdifferent catalyst amounts. PSt/SiO2 particle, 3 g; temperature, 25°C;BCMB, 13 ml; CH2Cl2, 40 ml
560 Colloid Polym Sci (2008) 286:553–561
Effect of the used amount of catalyst
By varying the used amount of SnClB4 (1, 1.5, and 2 ml)and fixing other reaction conditions, the chloromethylationreactions for PSt/SiO2 particles were performed. Figure 9displays the dependence of the chlorine content of graftedpolystyrene on time. The curve interleaving status also canbe found in Fig. 9. For 3 g of PSt/SiO2 particles, 1.5 ml ofSnClB4 is optimal as compared with 1 and 2 ml of SnCl4 asdisplayed in Fig. 9. The less catalyst will lead to slowerchloromethylation reaction rate, whereas the more catalystwill result in prematurely occurring of the cross-linkingreaction and lower chlorine content.
About reaction temperature
The reaction temperature is an important factor for nearly allchemical reactions. The effect of temperature on thechloromethylation reaction of polystyrene was examined. Itwas found that Friedel–Crafts cross-linking reaction is verysensitive to temperature. If the temperature goes up to above20°C, the rate of the cross-linking reaction will be enhanceddistinctly. Hence, higher temperature is not suitable tochloromethylation reaction. In this study, the reaction wasconducted at room temperature (25°C) to avoid Friedel–Crafts cross-linking reaction as far as possible.
Conclusion
In this work, the chloromethylation reaction of cross-linking styrene-divinyl styrene copolymer microsphereswas realized in the presence of Lewis acid catalyst byusing BCMB as chloromethylation reagent, and chlorome-thylated cross-linking polystyrene (CMCPS) microsphereswere prepared. This method is environmentally friendlybecause of no cancerogenic toxicity of BCMB. Besides,this method is also more economical because of the lowcost of BCMB. The chloromethylation reaction of thegrafted particles PSt/SiO2 also was performed and thecomposite particles CMPS/SiO2 were obtained. The com-posite particle CMPS/SiO2 well combine the chemicalmodificability of chloromethylated polystyrene with theexcellent mechanical property and thermal stability of silicagel, so it is a kind of chloromethylated polystyrene particles
with high performance. During the process in preparingCMCPS microspheres and CMPS/SiO2 particles, alongwith the increase of chlorine content, Friedel–Crafts cross-linking reaction will occur. To prepare the chloromethylatedparticles with high chlorine content and without obviouscross-linking, the suitable reaction conditions need to becontrolled, such as reaction time and the used amount ofBCMB, solvent, and catalyst. The reaction should becarried out at lower temperatures (about 20°C) because ofthe sensitivity of Friedel–Crafts reaction to temperature.
References
1. Wang Y, Zhang G-H-, Yan H-S et al (2006) Tetrahedron 62:4948–4953
2. Arunan C, Nagaraj R, Rajasekharan Pillai VN (2000) Peptides21:773–777
3. Xu M-C, Ou Zh-Z, Shi Z-Q et al (2001) React Funct Polym48:85–95
4. Masuda T, Kitahara K-I, Aikawa Y, Arai S (2002) J Chromatogr A961:89–96
5. Jain VK, Pandya RA, Pillai SG, Shrivastav PS (2006) Talanta70:257–266
6. Mondal BC, Das AK (2002) React Funct Polym 53:45–527. Marquès G, Bourdelande JL, Valiente M (1999) React Funct
Polym 41:77–898. Maurya MR, Kumar M, Sikarwar S (2006) React Funct Polym
66:808–8189. Moghadam M, Tangestaninejad S, Mirkhani V et al (2005)
Bioorganic Med Chem 13:2901–290510. Sophiamma PN, Sreekumar K (1997) React Funct Polym 35:169–17711. Kedem M, Margel S (2002) J Polym Sci A Polym Chem 40:1342–
135212. Khan AA, Abdelaal MY, Ali MM, Abdel-Latiff EH (1998)
Polymer 40:233–24113. Jang BB, Lee K, Kwon WJ, Suh J (1999) J Polym Sci A Polym
Chem 37:3169–317714. Jang BB, Lee K, Kwon WJ, Suh J (1999) J Polym Sci A Polym
Chem 37:3169–317715. Carre EL, Lewis N, Ribas C, Wells A (2000) Org Process Res
Dev 4:606–61016. Kavaklı C, Özvatan N, Tuncel SA, Salih B (2002) Anal Chim
Acta 464:313–32217. Unsal E, Bahar T, Tuncel M, Tuncel A (2000) J Chromatogr A
898:167–17718. Shen Y-L, Yang Y-F, Gao B-J, Zhu Y (2007) Acta Polymerica
Sinica 6:531–537 (in Chinese)19. Shen Y-L, Yang Y-F, Gao B-J, Li G (2007) Chem J Chin Univ 28
(3):559–565 (in Chinese)20. Gao B-J, Wang R-X, Jiu H-F, Kong D-L (2006) J Appl Polym Sci
102:5808–5817
Colloid Polym Sci (2008) 286:553–561 561
