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Polymer International
Polym Int 49:184±188 (2000)
Novel magnetic polyethylene nanocomposites
produced by supported nanometre magnetic
Ziegler–Natta catalyst
Li Wang,* Lin-Xian Feng and Tao Xie
Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, 310027, People’s Republic of China
Abstract: This paper describes the preparation of novel magnetic polyethylene nanocomposites using a
nanometre magnetic Ziegler±Natta catalyst. It was found that novel magnetic polyethylene nanocomposites can be obtained according to the following four steps: (1) preparation of nanometre
magnetic particles; (2) reaction between AlR3 and hydroxyls on the surface of nanometre magnetic
particles to form anchor points ÐAlR2; (3) addition of TiCl4, Ti being coordinated to anchor points on
the surface of nanometre magnetic particles to form polymerization active centres; (4) ethylene
polymerization being carried out in situ on the surface of the nanometre magnetic particles to produce
novel magnetic polyethylene nanocomposites. It is found that the activity of ethylene polymerization is
essentially unaffected by polymerization temperature and polymerization time.
# 2000 Society of Chemical Industry
Keywords: ethylene polymerization; Ziegler±Natta catalyst; magnetic polyethylene nanocomposite; nanometre
magnetic particle
INTRODUCTION
Many papers have been published about ole®n
polymerization catalysed by supported Ziegler±Natta
catalyst since the discoveries by Ziegler's group in
1953 and by Natta's group in 1954. A large number of
supported Ziegler±Natta catalysts, particularly suitable for the preparation of polyethylene, polypropylene
and copolymer of ethylene and propylene, have been
discovered and developed.1±13
Recently, there have been obvious trends in audio
equipment, of®ce automation equipment and homeuse electric appliances to move towards smaller size,
lighter weight, more accurate shape, thinner construction and longer use period. In order to reach these
objectives, novel polymer magnetic materials, which
form one of the most exciting active areas and have
attracted much attention. Polymer magnetic materials
are mainly classed as `structure type' and `®lling type'.
The former are still far from practical industrial
production, and although the latter (polymer magnets
of the ®lling type, such as plastic magnets in most
cases) have been used and studied,14±16 there are many
disadvantages. Generally, it is dif®cult to compound
ferrite powder ®llers with polymers; it is especially
dif®cult to disperse homogeneously the nanometre
ferrite particles in polyole®n because of the selfgathering effect of nanometre ferrite powder ®llers,
and also because of the difference between nanometre
ferrite particle ®llers and polyole®ns in terms of density
and polarity. Therefore, owing to the chemical
stability and the low water-absorption of polyole®ns
and the easier processing and excellent properties of
the resultant magnetic polyole®n nanocomposites,
magnetic polyole®n nanocomposites such as magnetic
polyethylene nanocomposites with nanometre ferrite
particles in a polyethylene matrix are attracting
researchers' attention.
In this paper, some novel magnetic Ziegler±Natta
catalysts were prepared, and a new method was
developed to make magnetic polyole®n nanocomposites. Novel magnetic polyole®n nanocomposites,
especially magnetic polyethylene nanocomposites
were obtained through in situ coordination polymerization on the surface of nanometre magnetic particles.
EXPERIMENTAL
Materials
Polymerization-grade ethylene and propylene (from
the Zhen-hai Petroleum Chemical Plant) were puri®ed
before polymerization by passing through four
Ê molecular sieves and a hexane
columns with 4 A
solution containing 10 wt% triethylaluminium to
remove residual traces of moisture. Petroleum ether
(bp 90±120 °C) of analytical reagent grade was
Ê molecular sieves before use.
distilled or dried by 4 A
* Correspondence to: Li Wang, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic
of China
Contract/grant sponsor: National Natural Science Foundation of China
Contract/grant sponsor: Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Commission
(Received 5 May 1999; revised version received 12 July 1999; accepted 21 October 1999)
# 2000 Society of Chemical Industry. Polym Int 0959±8103/2000/$17.50
184
Novel magnetic polyethylene nanocomposites
Other chemicals (research grade) were obtained
commercially.
Preparation of nanometer magnetic particles,
nanometer magnetic catalysts and magnetic
polyolefin nanocomposites
The nanometer particles CrxFe3ÿxO4 (when x = 0,
Fe3O4) have been prepared and studied extensively by
many authors.2,10,17±19 Typically, in an N2 atmosphere, 1 M Fe3‡, 1 M Fe2‡ and 0.7 M Cr3‡ solutions
were mixed. Then a 3 M NaOH solution was added
dropwise to the above solution, and the resultant
precipitate was washed and collected. The particle
diameters and particle diameter distribution of the
resultant magnetic particles were measured with a
Malvern Autosizer 2C instrument. The amount of
ÐOH groups was determined through measuring the
amount of CH3CH3 released according to the reaction
In a typical preparation procedure for nanometre
magnetic catalyst and polymerization, a weighed
sample of 12 g nanometre magnetic particles was
suspended in 40 ml anhydrous petroleum ether and
stirred in a two-necked ¯ask under nitrogen atmosphere. A stoichiometric quantity of organoaluminium
compound (for example AlEt3 at Al/OH > 1:1) was
introduced into the ¯ask and the mixture stirred
continuously for 0.5 h. The slurry was ®ltered off and
the solid was washed with anhydrous petroleum ether.
Then 40 ml of a solution of anhydrous petroleum ether
and TiCl4 (1 ml) was introduced into the ¯ask
containing the nanometre magnetic particles which
had reacted with the organoaluminium compound.
The resultant slurry was stirred for another 1 h. After
that, the resultant slurry was ®ltered and washed until
no Ti was detected by spectrophotography; it was then
dried and used as a supported nanometre magnetic
catalyst. The polymerization was carried out at atmospheric pressure in a 200 ml reaction ¯ask provided with
a stirrer, as described elsewhere.1±3 70 ml of anhydrous
petroleum ether was introduced into the reactor under
nitrogen and thermostated at a set temperature.
Ethylene was rapidly bubbled through the stirred
solvent; then the organoaluminium compound and 1 g
supported nanometre magnetic catalyst with an appropriate Al/Ti ratio were added successively to the
reaction mixture. After polymerization was ®nished,
the resultant product was washed several times with
ethanol, and dried overnight in a vacuum oven (about
3 mmHg) at 60 °C.
RESULTS AND DISCUSSION
The new route to prepare magnetic polyethylene
nanocomposites through in situ coordination polymerPolym Int 49:184±188 (2000)
Scheme 1. Preparation of CrxFe3ÿxO4.
ization on the surface of nanometre magnetic particles
can be divided into the following four steps.
The preparation of nanometre magnetic particles
(step 1) is shown in Scheme 1.
The nanometre Fe3O4 and CrxFe3ÿxO4 (x = 0, ie
Fe3O4) particles have been prepared and studied
extensively by many authors.2,17±20 Chemical coprecipitation methods based on the precipitation
principle of Fe2‡ and Fe3‡ in basic solution have long
been used for practical preparation of nanometre
Fe3O4 particles. Usually, the reaction temperature,
reaction time, ratio of Fe2‡/Fe3‡ and pH play key roles
in this process. The results of XRD and particle size
distribution show that nanometre magnetic Fe3O4 and
CrxFe3ÿxO4 particles with narrow particle size distribution can be obtained.2,20,21 The typical particles
prepared have a mean diameter of 10±20 nm with
saturation magnetization ss = 55.2 eum gÿ1 for Fe3O4
(preparation conditions: pH 13, T = 50 °C, 1 h) and
ss = 52 eum gÿ1 for CrxFe3ÿxO4 (preparation conditions: pH 11, T = 80 °C, 40 min). The size distribution
of CrxFe3ÿxO4 particles is shown in Fig 1. The
diameter of the resultant particle was about 30 nm.
The amount of ÐOH groups on CrxFe3ÿxO4 was
approximately 0.45 mmol gÿ1.
The reaction between AlR3 and hydroxyls on the
surface of the nanometre magnetic particles to form
anchoring points ÐAlEt2 (step 2) is shown in Scheme
2, which has been investigated extensively.6,7 Usually
the organoaluminium compounds are added at a ratio
of Al/OH > 1 in order to remove OH completely and to
Figure 1. Nanometre magnetic CrxFe3ÿxO4 particles with narrow particle
size distribution (reaction temperature T = 80°C, reaction time t = 40min
and pH 11).
185
L Wang, L-X Feng, T Xie
Table 1. Influence of the kind of organic aluminium compound on Ti load
Organic aluminium
compound
Ti (%)
Scheme 2. Reaction between AlR3 and hydroxyls on CrxFe3ÿxO4.
form anchoring points. Many organic aluminium
compounds such as Al2Et3Cl3, AlEt2Cl, AlEt3 and
Al(iBu)3 can be used for forming anchor point
ÐOAlR2, but AlEt3 is the most common.
For step 3, as shown in Scheme 3, TiCl4 is added at
a ratio of Ti/Al > 1; then the excess TiCl4 is washed
out. It is found that the Ti content loaded on
CrxFe3ÿxO4 is 2.8±2.9% depending on the kind of
organic aluminium compound, as shown in Table 1.
However, it remains a challenging task to elucidate the
exact anchor point structure and the exact Ti coordination structure on the surface of the support.
Step 4 in Scheme 4 shows that ethylene is polymerized in situ on the surface of nanometre magnetic
particles to produce the magnetic polyethylene nanocomposite.
The polymerization characteristics of the resultant
Al2Et3Cl3
AlEt2Cl
AlEt3
Al(iBu)3
2.81
2.96
2.82
2.82
supported magnetic-particle/AlEt3/TiCl4 nanometre
magnetic catalyst are roughly the same as those
described previously.1±3 Several features are worth
noting. First, the polymerization activity is essentially
unaffected by the polymerization time within 1 h as
shown in Fig 3, and is also essentially unaffected by the
Al/Ti ratio as shown in Figs 2 and 4. Secondly, it was
also found that the polymerization activity is essentially unaffected by the polymerization temperature
within the range 30±60 °C. This is not surprising.
Generally, supported Ziegler±Natta catalysts are less
temperature sensitive, less time sensitive and less Al/Ti
ratio sensitive at low Al/Ti ratio than soluble catalysts.
One would expect the temperature-insensitivity,
time-insensitivity and Al/Ti ratio-insensitivity of a
catalytic system made of supported magnetic-particles, AlEt3 and TiCl4 to stem from the supported state
of the active centres. A more stable polymerization rate
is bene®cial to form a dense ®lm covering the nanometre magnetic particle. The saturation magnetization
ss of the resultant magnetic polyethylene nanocomposites virtually depends on the content of nanometre
magnetic particles; for example nanocomposite: con-
Scheme 3. Ti coordinating to an anchor
point on the surface of nanometre
magnetic particles to form
polymerization active centres.
Scheme 4. In situ ethylene
polymerization on the surface of
nanometre magnetic particles to
produce magnetic polyethylene
nanocomposite.
186
Polym Int 49:184±188 (2000)
Novel magnetic polyethylene nanocomposites
Figure 2. Influence of Al/Ti on activity (Fe3O4/AlEt3/TiCl4 catalytic system).
decrease in their ss,19 especially for nanometre
particles. H2O adsorbed on the surface of magnetic
particles was completely removed and the surface was
covered by a dense polymer layer in this preparation
route. Therefore the resultant magnet is stable, even if
it is exposed to air for a long period. In addition, the
advantage preventing the magnet from being corroded
was evident for the resultant plastic magnets prepared
by this route, because the nanometre magnetic
particles were covered by a dense polymer layer.
However, owing to nanometre lever homogeneity
which could not be obtained by any other method
until now, the resultant product is easy to process
compared to common blend plastic magnets.
Moreover, we also investigated a rare earth magnetic
particle AlEt3/TiCl4 catalytic system instead of the
Fe3O4 (or CrxFe3ÿxO4)/AlEt3/TiCl4 catalytic system to
obtain a series of magnetic polyethylene nanocomposites, and these results will be published separately.
It is worth mentioning that by using a mixture of
ethylene and propylene as monomers (such as
ethylene:propylene = 1:3), magnetic rubber containing
nanometre magnetic particles can also be prepared via
the same route. However, this provides a step towards
preparing a series of new functional polymer materials,
for example conductive polymers and optic polymers,
containing nanometre particles.
CONCLUSIONS
Figure 3. Influence of time on activity (Fe3O4/AlEt3/TiCl4 catalytic system).
A new method for preparing a supported nanometer
magnetic Ziegler±Natta catalyst has been developed.
Novel magnetic polyethylene nanocomposites can be
obtained according to the following four steps: step 1,
preparation of nanometre magnetic particles; step 2,
reaction between AlR3 and hydroxyls on the surface of
nanometre magnetic particles to form anchor points
ÐAlR2; step 3, addition of TiCl4, Ti being coordinated to anchor points on the surface of nanometre
magnetic particles, to form the polymerization active
centres; step 4, ethylene polymerization in situ on the
surface of nanometre magnetic particles to produce
novel magnetic polyethylene nanocomposites. It is
found that the activity of ethylene polymerization is
unaffected by polymerization temperature and polymerization time, using these nanometre magnetic
catalysts.
ACKNOWLEDGEMENTS
Figure 4. Influence of Al/Ti on activity [(CrxFe3ÿxO4)/AlEt3/TiCl4 catalytic
system].
taining 75.3% magnetic particles had ss = 39 eum/gÿ1,
whilst those containing 72% magnetic particles had
ss = 37 eum/gÿ1. It was found that the adsorption of
H2O on the surface of magnetic particles causes a
Polym Int 49:184±188 (2000)
This work was supported by the National Natural
Science Foundation of China and was sponsored by
the Scienti®c Research Foundation for Returned
Overseas Chinese Scholars, State Education Commission.
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Polym Int 49:184±188 (2000)
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