This research work was devoted to the synthesis of hydroxyapatite nanoparticles with initiating centres
in polymer shell. Marcroinitiators comprised by heterofunctional copolymers containing either pendant
peroxidic groups or benzoin pieces attached to the backbone chain were used as surface modifiers of
hydroxyapatite. Their use in the stage of synthesis of the mineral particles makes possible a control over
size and the surface properties of particles. The effect of copolymer nature and its concentration, as well as
the synthesis conditions on hydroxyapatite particle size and the copolymer adsorption value was studied.
Both types of functional groups namely peroxide and benzoin in structure of copolymers immobilized at the
hydroxyapatite surface were used for initiation of polymerization processes at elevated temperature (in the
first case) or under UV-irradiation (in another case). These techniques of bioceramics modification allowed
to form polymer compatibilizing layer of proper structure and thickness bonded with the mineral particles
that enhanced compatibility of mineral filler and polymer matrix of different nature and as a result obtaining
composite materials with improved physico-mechanical properties.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3544

Bukartyk, N.M.

Chobit, M.R.

Shevchuk, O.M.

Tokarev, V.S.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 4, 04FCNF07(4pp) (2012)   2304-1862/2012/1(4)04FCNF07(4) 04FCNF07-1  2012 Sumy State University Synthesis of Hydroxyapatite Nanoparticles with Initiating Centres in Polymer Shell  O.M. Shevchuk*, M.R. Chobit, N.M. Bukartyk, G.O. Ogar, V.S. Tokarev  Lviv Polytechnic National University, 12, S. Bandery Str., 79052 Lviv, Ukraine  (Received 20 June 2012; published online 24 August 2012)  This research work was devoted to the synthesis of hydroxyapatite nanoparticles with initiating cen-tres in polymer shell. Marcroinitiators comprised by heterofunctional copolymers containing either pen-dant peroxidic groups or benzoin pieces attached to the backbone chain were used as surface modifiers of hydroxyapatite. Their use in the stage of synthesis of the mineral particles makes possible a control over size and the surface properties of particles. The effect of copolymer nature and its concentration, as well as the synthesis conditions on hydroxyapatite particle size and the copolymer adsorption value was studied. Both types of functional groups namely peroxide and benzoin in structure of copolymers immobilized at the hydroxyapatite surface were used for initiation of polymerization processes at elevated temperature (in the first case) or under UV-irradiation (in another case). These techniques of bioceramics modification allowed to form polymer compatibilizing layer of proper structure and thickness bonded with the mineral particles that enhanced compatibility of mineral filler and polymer matrix of different nature and as a result obtain-ing composite materials with improved physico-mechanical properties.  Keywords: Hydroxyapatite, Nanoparticles, Macroinititor of radical polymerization, Peroxide, Photoinitia-tor, Polymer composite.    PACS numbers: 81.16.Be, 82.35.Np   ______________ * oshevch@polynet.lviv.ua 1. INTRODUCTION  Hydroxyapatite (HA) attracts much attention as a bone substitute material in orthopedics and stomatolo-gy due to its biocompatibility and bone bonding ability [1], while its wide usage is hindered by its low mechan-ical properties [2]. This problem can be solved via ap-plying composite materials on the basis of HA and pol-ymers (including bioactive polymers). However such composites usually possess insufficient biological activi-ty because their filling degree with mineral particles is rather low (mostly less as 50%vol.). The problem arisen at obtaining of highly filled composites is caused by a poor adhesion between polymer matrix and hydrophilic surface of bioceramics resulting in delamination at the phase boundary and consequently in deterioration of the composite material mechanical properties. Surface modification of mineral particle by polymers of diverse nature is one of the known technique used for compatibilization of the components in composite. Silanes, isocyanates, polyacids, and vinyl polymers are used to modify HA surface [3, 4]. Graft-polymerization initiated by the initiators immobilized beforehand at the filler surface is another method for formation of thin compatibilizing layers [5, 6]. This method allows to control the thickness of polymer layer, its functionality, and structure via changing the monomer nature and process conditions. Heterofunctional copolymers con-taining peroxidic and other initiating centres (so called macroinitiators) synthesized in Lviv Polytechnic Na-tional University can be adsorbed irreversibly on the surface of minerals and initiate graft-polymerization of vinyl monomer; this combination is a powerful instru-ment for design of polymer composites [7]. This work is devoted to study of the processes of ob-taining the HA nanoparticles with functionalized poly-mer shell using two techniques: 1) adsorption modifica-tion of HA nanoparticles with macroinitiators; 2) for-mation of thin polymer layer on the surface of HA via graft-polymerization of vinyl monomers initiated by macroinitiators previously adsorbed on its surface.  2. EXPERIMENTAL  2.1 Materials   Peroxide-containing macroinitiator (PMI) was syn-thesized via radical copolymerization of peroxidic mon-omer 5-tert-butylperoxy-5-methyl-1-hexene-3-yne (PM) with maleic anhydride (MA) in ethyl acetate as de-scribed elsewhere [7].   m = 50,4% mol, n = 49,6% mol  Polymeric macrophotoinitiator (MPI) was obtained in accordance with [8] by attaching benzoin molecules to previously synthesized copolymer of methylmeth-acrylate with maleic anhydride (Fig. 1):    Fig. 1 – Scheme of MPI synthesis  O.M. SHEVCHUK, M.R. CHOBIT, N.M. BUKARTYK, ET AL. PROC. NAP 1, 04FCNF07 (2012)   04FCNF07-2 2.2 Synthesis   HA nanoparticles were obtained using sol-gel meth-od as described in [9] in accordance with the reaction:   10CaCl2 + 6(NH4)3PO4 + 2NH4OH  Ca10(PO4)6(OH)2 + 20NH4Cl  Adsorption of PMI and MPI onto HA surface was carried out from ethyl acetate solution at their different concentrations (T  298 K). Grafting of polymer layers onto the surface of perox-idized HA was carried out via radical polymerization of corresponding monomers in dioxane initiated by perox-ide fragments of PMI immobilized at the HA surface. No additional initiator was added to the system. The process was carried out in the sealed dilatometers; magnetic stirrer was used for stirring reaction mixture.  Photopolymerization of the composition on the basis of polyester resin PE-246, oligoesteracrylate TGM-3, photosensitizer eozine H, aerosile and HA nanoparti-cles with MPI adsorbed shell was carried out under UV-irradiation (DRT-400 mercury-quartz lamp, dis-tance to photopolymeric composite film was 10cm, T  298 K, HA nanoparticle concentration – 2.8 %).   2.3 Analysis  The content of PM links as well as the content of adsorbed PMI at the surface of HA was determined using the results of chromatographic analysis of PM thermal decomposition products in accordance with known method [9]. The content of adsorbed PMI was determined gravimetrically.  Kinetics of graft polymerization was studied by dila-tometric method. Additionally, gravimetric and gas-chromatography studies were performed. Photopoly-merization kinetics was controlled by content of gel-fraction in composite. The structure of the HA nanoparticles was deter-mined from X-ray diffraction analysis (XRD) data (“DRON-30”, CoKα irradiation) using Scherrer equa-tion. The hardness of photocured films was studied with the aid of M-3 pendulum device. Molecular weight of polystyrene (pSt) and polymethylmethacrylate (pMMA) was estimated via determination of their intrinsic viscosity in benzene and acetone. Thermogravimetric analysis of HA nanoparticles with grafted pMMA shell was carried out with the aid of "Q-1500D" derivatograph.   3. RESULTS AND DISCUSSION   Two approaches were realized to obtain HA nano-particles with functionalized polymer shell: 1) Sol-gel synthesis of HA nanoparticles in water solution in the presence of PMI; 2) PMI or MPI adsorption at the sur-face of mineral nanoparticles synthesized beforehand. The structure of obtained hydroxyapatite was proved by X-ray diffraction analysis data (Fig. 2).  Obtained data witnesses that the HA nanocrystals synthesized have an elongated shape with the size of about 9  18 nm in the case of the synthesis via ordi-nary technique and 5  14 nm if the synthesis was car-ried out in the PMI presence. Evidently, PMI macro-molecules while adsorbing at the surface of the seeds of HA crystalline phase restricted their growth serving in such a way as an exotemplate. Hence, the use of PMI during HA synthesis allowed to control the size and size distribution of synthesized nanoparticles.    Fig. 2 – XRD spectra of HA samples: 1) etalon; 2) HA nanoparticles synthesized via standard technique; 3) HA nanoparticles synthesized in the presence of PMI  The study of PMI adsorption at the surface of nano-HA synthesized via ordinary technique revealed its extremely high adsorption capacity A = 136 mg/g, that was connected with high specific surface area of the HA nanoparticles synthesized which was equal to 170-180 m2/g. At the same time the amount of PMI ad-sorbed in the case of HA particle nucleation in the presence of 25 % PMI was much higher reaching 182 mg/g that can be explained by greater specific sur-face of HA particles in the later case (Ssp  290 m2/g).  The dependence of PMI adsorption value and corre-sponding thickness of reactive polymer layer on the concentration of initial reagents at synthesis of nano-HA is shown in Table 1. A decrease of concentrations of both calcium chloride and triammonium phosphate in reaction mixture brought about an increase in the val-ues of irreversible PMI adsorption. This phenomenon is obviously caused by rise of the HA overall surface ac-cessible for PMI macromolecules due to diminishing of HA particle size.  Table 1 – Dependence of the PMI adsorption value (A) and the content of peroxide group [Oact] on the HA surface on syn-thesis conditions of nano-HA (CPMI  10 % with respect to HA).  CCaCl2, % C(NH4)3PO4, % А, mg/g [Oact], % 2.50 2.00 56.9 0.30 0.83 0.66 70.1 0.37  MPI adsorption at the surface of HA nanoparticles from ethyl acetate and methanol solutions was studied (Fig. 3). Importantly the adsorption isotherms of MMA-MA copolymer did not differ from MPI isotherms. So, the conclusion was drown that an introduction of ben-zoin pieces into the structure of this copolymer do not influence on the character of adsorbate macromolecule interaction with adsorbent surface.  SYNTHESIS OF HYDROXYAPATITE NANOPARTICLES… PROC. NAP 1, 04FCNF07 (2012)   04FCNF07-3   Fig 3 – Isotherms of MPI and MMA-co-MA adsorption onto HA in different solvents  The characteristic transition of the adsorption curves from a sharp rise to saturation took place at copolymer concentration of about 0.5 % and further increase in its concentration did not give an essential gain in adsorption value. We supposed that formation of ionic bonds due to interaction of carboxylic groups of copolymer macromolecules reached the interface firstly with the basic groups at the HA surface should shield the adsorbing centres making a barrier for their chemi-cal interaction with other MPI macromolecules reach-ing the particles later. Chemical bonding hindered also conformational changes in the MPI macromolecules at the surface and consequently rearrangement of adsorp-tion layer.  The surface modification of HA by PMI allowed to initiate polymerization of vinyl monomers in order to create compatibilizing polymer layer of certain nature and controlled thickness on the surface. Obtained data witnessed that radical polymerization of styrene and methyl methacylate initiated from the HA nanoparticle surface by peroxide groups of the PMI immobilized pro-ceeded with quite high rates up to high conversions (85%) (Fig. 4, 5, Table 2). Kinetic curves of this process had rather ordinary shapes typical for a common radical polymerization, while this process had some features caused evidently by the presence in the system of solid highly dispersed phase as well as by immobilization of the initiator at the phase boundary. Reaction order with respect to initiator (n) was close to 1 that is much higher than value predicted for radical polymerization (typically n  0.5). We supposed that in spite of low overall con-centration of peroxide groups in this system, fixation of PMI macromolecules in adsorption layers caused a sharp increase of concentration of initiating centres in reaction zone. Under these conditions the main part of growing polymer chains were terminated via chain transfer reactions to peroxidic and other functional groups of immobilized PMI. This leaded to an increase of reaction order to the values higher than 0.5.  Table 2 – Characteristics of MMA polymerization initiated from the surface of peroxidized HA.   T, K CO-O, mole/l Wpol 105, mole/(l s) kpol 104, l0,5/(mole0,5 s) Ea, kJ/mol MWpMMA, g/mole 353 0.012 1.9 5.8 80.6 85400 358 0.012 3.2 9.7 56800 363 0.012 4.4 13.4 27700 363 0.006 1.9 13.2 16600 363 0.024 7.0 13.2 32800  Another feature consisted in an increase of pMMA molecular weight with rising concentration of perox-idized HA in the system  in contrast to typical regulari-ties, while the temperature enhancement caused its diminishing (Table 2). The explanation could be as fol-lows. The polymerization occurred mainly in the area close to the surface of HA nanoparticles where chain termination reactions were suppressed as a result of diffusion control. Thus, HA concentration enhancement caused an enlargement of area of this reaction zone that was a reason for a rise of pMMA average molecu-lar weight. The rates of styrene polymerization initiated from the HA surface peroxidized were lower than in case of methyl methacrylate (Fig. 5). This coincided with the literature data [10] reporting on higher ratio of the con-stants of chain growth and termination (kp/ko0.5) for MMA as compared to styrene.      Fig. 4 – Temperature effect on kinetics of the MMA polymeri-zation initiated by PMI immobilized at the HA nanoparticles Fig. 5 – Dependence of St polymerization kinetics on the concentration of immobilized peroxide groups in the system   O.M. SHEVCHUK, M.R. CHOBIT, N.M. BUKARTYK, ET AL. PROC. NAP 1, 04FCNF07 (2012)   04FCNF07-4    Fig. 6 – Derivatograms of PMI (a), HA modified by PMI (b), HA after MMA graft polymerization  For St polymerization the influence of dispersed HA surface on both the process kinetics and physico-chemical characteristics of polymer obtained was very similar to that for MMA polymerization, indeed the order with respect to initiator was higher than 0.5 and pSt molecular weight increased with the rise of perox-idized HA concentration. At the same time pSt molecu-lar weights were higher than for pMMA; this fact is explained by difference in mechanisms of the chain termination reaction attributed to these monomers namely recombination for St and mainly disproportion-ation for MMA.  Comparison of derivatographic curves of PMI, HA nanoparticles modified by PMI, and HA nanoparticles with grafted pMMA layer (Fig. 6) showed that in con-trast to the latter, two first samples demonstrated exo-thermic effects on DTA curves in the range of 440-458 K attributed to decomposition of peroxidic groups. That means peroxidic fragments decomposed almost completely at the surface of HA nanoparticles modified during the graft polymerization process; and this phe-nomenon could be explained by essentially higher de-cay rates of PMI immobilized at solid surface as com-pared to this process in solution. Absence of active per-oxidic groups (being the free radical sources) in sam-ples of HA nanoparticles with grafted pMMA made them a good candidates for the use as an orthopedic material. Nano-hydroxyapatite surface-modified by MPI was used for obtaining the polyester composites capable of curing at room temperature under UV-irradiation. The synthesized MPI itself as well as immobilized at the surface of nanoparticles appeared to be more effective photoinitiator comparing to initial benzoin (Fig. 7). Immobilization of photoinitiating groups on the HA nanoparticles enhanced properties of photocomposites as compared with a low-molecular photoinitiator benzo-ine and MPI on its base. Faster hardening and more as twice higher hardness of composite with MPI immobi-lized was observed, evidently due to better compatibil-ity and more even distribution of the surface-modified HA nanoparticles in the polymer matrix. On the other hand filling of polyester composites by HA nanoparti-cles should improve their biocompatibility.    Fig. 7 – Effect of the photoinitiator nature on hardening kinetics of photopolymer composite film: benzoine (1); MPI (2); MPI immobilized on HA nanoparticles (3)   4. CONCLUSIONS   The method of the synthesis of nano-hydroxyapatite from a water salt solution in the presence of macroin-itiators was elaborated that allowed simultaneously to control over size and to modify the surface of nanopar-ticles. Immobilization of the macroinitiators containing either peroxidic groups or benzoin pieces in their struc-ture made possibility to carry out the radical graft polymerization initiated from the surface of modified nanoparticles and to design the structure and thick-ness of polymer shell bonded to the surface of nanopar-ticles. As a result improvements in physico-mechanical properties of filled polymer composites on the basis of nano-hydroxyapatite were achieved.   REFERENCES  1. R.W. Arcis, A. Lopez-Macibe, M. Toledano, E. Osorio, Den-tal Mat. 18, 49 (2002). 2. K.R.St. John, L.D. Zardiackas, R.C. Terry, J Appl Bio-mater, 6, 89 (1995).  3. C. Kunze, T. Freier, E. Helwig, Biomater. 24, 967 (2003). 4. Q. Liu, J.R. de Wijn, C.A. van Blitterswijk, J. Biomed. Mater. Res. 40, 257 (1998).  5. O.M. Shevchuk, N.M. Bukartyk, R.O. Moncibovych, V.S. Tokarev, Vopr. Khim. i Khim. Tehn. 4, 125 (2007). 6. O. Shybanova, S. Voronov, O. Bednarska, M. Stamm, Yu. Medvedevskikh, V. Tokarev, Macromol. Symp. 164, 211 (2001). 7. Voronov, V. Tokarev, K. Oduola, Yu. Lastukhin, J. Appl. Polym. Sci. 76,1217 (2000). 8. G.O. Ogar, L.V. Dolynska, V.S. Tokarev, Visnuk LPNU. 700, 353 (2011). 9. V.P. Vasilyev, L.S. Glus, S.P. Gubar, Visnuk LPNU. 191, 24 (1985). 10. G.S. Bagdasariyan, Theory of radical polymerization (Mos-cow: Nauka: 1966). 

Synthesis of Hydroxyapatite Nanoparticles with Initiating Centres in Polymer Shell

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 4, 04FCNF07(4pp) (2012) 
 
 
2304-1862/2012/1(4)04FCNF07(4) 04FCNF07-1  2012 Sumy State University 
Synthesis of Hydroxyapatite Nanoparticles with Initiating Centres in Polymer Shell 
 
O.M. Shevchuk*, M.R. Chobit, N.M. Bukartyk, G.O. Ogar, V.S. Tokarev 
 
Lviv Polytechnic National University, 12, S. Bandery Str., 79052 Lviv, Ukraine 
 
(Received 20 June 2012; published online 24 August 2012) 
 
This research work was devoted to the synthesis of hydroxyapatite nanoparticles with initiating cen-
tres in polymer shell. Marcroinitiators comprised by heterofunctional copolymers containing either pen-
dant peroxidic groups or benzoin pieces attached to the backbone chain were used as surface modifiers of 
hydroxyapatite. Their use in the stage of synthesis of the mineral particles makes possible a control over 
size and the surface properties of particles. The effect of copolymer nature and its concentration, as well as 
the synthesis conditions on hydroxyapatite particle size and the copolymer adsorption value was studied. 
Both types of functional groups namely peroxide and benzoin in structure of copolymers immobilized at the 
hydroxyapatite surface were used for initiation of polymerization processes at elevated temperature (in the 
first case) or under UV-irradiation (in another case). These techniques of bioceramics modification allowed 
to form polymer compatibilizing layer of proper structure and thickness bonded with the mineral particles 
that enhanced compatibility of mineral filler and polymer matrix of different nature and as a result obtain-
ing composite materials with improved physico-mechanical properties. 
 
Keywords: Hydroxyapatite, Nanoparticles, Macroinititor of radical polymerization, Peroxide, Photoinitia-
tor, Polymer composite. 
 
  PACS numbers: 81.16.Be, 82.35.Np 
 
 
______________ 
* oshevch@polynet.lviv.ua 
1. INTRODUCTION 
 
Hydroxyapatite (HA) attracts much attention as a 
bone substitute material in orthopedics and stomatolo-
gy due to its biocompatibility and bone bonding ability 
[1], while its wide usage is hindered by its low mechan-
ical properties [2]. This problem can be solved via ap-
plying composite materials on the basis of HA and pol-
ymers (including bioactive polymers). However such 
composites usually possess insufficient biological activi-
ty because their filling degree with mineral particles is 
rather low (mostly less as 50%vol.). The problem arisen 
at obtaining of highly filled composites is caused by a 
poor adhesion between polymer matrix and hydrophilic 
surface of bioceramics resulting in delamination at the 
phase boundary and consequently in deterioration of 
the composite material mechanical properties. 
Surface modification of mineral particle by polymers 
of diverse nature is one of the known technique used 
for compatibilization of the components in composite. 
Silanes, isocyanates, polyacids, and vinyl polymers are 
used to modify HA surface [3, 4]. Graft-polymerization 
initiated by the initiators immobilized beforehand at 
the filler surface is another method for formation of 
thin compatibilizing layers [5, 6]. This method allows to 
control the thickness of polymer layer, its functionality, 
and structure via changing the monomer nature and 
process conditions. Heterofunctional copolymers con-
taining peroxidic and other initiating centres (so called 
macroinitiators) synthesized in Lviv Polytechnic Na-
tional University can be adsorbed irreversibly on the 
surface of minerals and initiate graft-polymerization of 
vinyl monomer; this combination is a powerful instru-
ment for design of polymer composites [7]. 
This work is devoted to study of the processes of ob-
taining the HA nanoparticles with functionalized poly-
mer shell using two techniques: 1) adsorption modifica-
tion of HA nanoparticles with macroinitiators; 2) for-
mation of thin polymer layer on the surface of HA via 
graft-polymerization of vinyl monomers initiated by 
macroinitiators previously adsorbed on its surface. 
 
2. EXPERIMENTAL 
 
2.1 Materials  
 
Peroxide-containing macroinitiator (PMI) was syn-
thesized via radical copolymerization of peroxidic mon-
omer 5-tert-butylperoxy-5-methyl-1-hexene-3-yne (PM) 
with maleic anhydride (MA) in ethyl acetate as de-
scribed elsewhere [7]. 
 
 
m = 50,4% mol, n = 49,6% mol 
 
Polymeric macrophotoinitiator (MPI) was obtained 
in accordance with [8] by attaching benzoin molecules 
to previously synthesized copolymer of methylmeth-
acrylate with maleic anhydride (Fig. 1): 
 
 
 
Fig. 1 – Scheme of MPI synthesis 
 O.M. SHEVCHUK, M.R. CHOBIT, N.M. BUKARTYK, ET AL. PROC. NAP 1, 04FCNF07 (2012) 
 
 
04FCNF07-2 
2.2 Synthesis  
 
HA nanoparticles were obtained using sol-gel meth-
od as described in [9] in accordance with the reaction:  
 
10CaCl2 + 6(NH4)3PO4 + 2NH4OH  
Ca10(PO4)6(OH)2 + 20NH4Cl 
 
Adsorption of PMI and MPI onto HA surface was 
carried out from ethyl acetate solution at their different 
concentrations (T  298 K). 
Grafting of polymer layers onto the surface of perox-
idized HA was carried out via radical polymerization of 
corresponding monomers in dioxane initiated by perox-
ide fragments of PMI immobilized at the HA surface. 
No additional initiator was added to the system. The 
process was carried out in the sealed dilatometers; 
magnetic stirrer was used for stirring reaction mixture.  
Photopolymerization of the composition on the basis 
of polyester resin PE-246, oligoesteracrylate TGM-3, 
photosensitizer eozine H, aerosile and HA nanoparti-
cles with MPI adsorbed shell was carried out under 
UV-irradiation (DRT-400 mercury-quartz lamp, dis-
tance to photopolymeric composite film was 10cm, 
T  298 K, HA nanoparticle concentration – 2.8 %).  
 
2.3 Analysis 
 
The content of PM links as well as the content of 
adsorbed PMI at the surface of HA was determined 
using the results of chromatographic analysis of PM 
thermal decomposition products in accordance with 
known method [9]. The content of adsorbed PMI was 
determined gravimetrically.  
Kinetics of graft polymerization was studied by dila-
tometric method. Additionally, gravimetric and gas-
chromatography studies were performed. Photopoly-
merization kinetics was controlled by content of gel-
fraction in composite. 
The structure of the HA nanoparticles was deter-
mined from X-ray diffraction analysis (XRD) data 
(“DRON-30”, CoKα irradiation) using Scherrer equa-
tion. 
The hardness of photocured films was studied with 
the aid of M-3 pendulum device. 
Molecular weight of polystyrene (pSt) and 
polymethylmethacrylate (pMMA) was estimated via 
determination of their intrinsic viscosity in benzene 
and acetone. 
Thermogravimetric analysis of HA nanoparticles 
with grafted pMMA shell was carried out with the aid 
of "Q-1500D" derivatograph.  
 
3. RESULTS AND DISCUSSION  
 
Two approaches were realized to obtain HA nano-
particles with functionalized polymer shell: 1) Sol-gel 
synthesis of HA nanoparticles in water solution in the 
presence of PMI; 2) PMI or MPI adsorption at the sur-
face of mineral nanoparticles synthesized beforehand. 
The structure of obtained hydroxyapatite was 
proved by X-ray diffraction analysis data (Fig. 2).  
Obtained data witnesses that the HA nanocrystals 
synthesized have an elongated shape with the size of 
about 9  18 nm in the case of the synthesis via ordi-
nary technique and 5  14 nm if the synthesis was car-
ried out in the PMI presence. Evidently, PMI macro-
molecules while adsorbing at the surface of the seeds of 
HA crystalline phase restricted their growth serving in 
such a way as an exotemplate. Hence, the use of PMI 
during HA synthesis allowed to control the size and 
size distribution of synthesized nanoparticles. 
 
 
 
Fig. 2 – XRD spectra of HA samples: 1) etalon; 2) HA 
nanoparticles synthesized via standard technique; 3) HA 
nanoparticles synthesized in the presence of PMI 
 
The study of PMI adsorption at the surface of nano-
HA synthesized via ordinary technique revealed its 
extremely high adsorption capacity A = 136 mg/g, that 
was connected with high specific surface area of the HA 
nanoparticles synthesized which was equal to 170-
180 m2/g. At the same time the amount of PMI ad-
sorbed in the case of HA particle nucleation in the 
presence of 25 % PMI was much higher reaching 
182 mg/g that can be explained by greater specific sur-
face of HA particles in the later case (Ssp  290 m2/g).  
The dependence of PMI adsorption value and corre-
sponding thickness of reactive polymer layer on the 
concentration of initial reagents at synthesis of nano-
HA is shown in Table 1. A decrease of concentrations of 
both calcium chloride and triammonium phosphate in 
reaction mixture brought about an increase in the val-
ues of irreversible PMI adsorption. This phenomenon is 
obviously caused by rise of the HA overall surface ac-
cessible for PMI macromolecules due to diminishing of 
HA particle size. 
 
Table 1 – Dependence of the PMI adsorption value (A) and 
the content of peroxide group [Oact] on the HA surface on syn-
thesis conditions of nano-HA (CPMI  10 % with respect to HA). 
 
CCaCl2, % C(NH4)3PO4, % А, mg/g [Oact], % 
2.50 2.00 56.9 0.30 
0.83 0.66 70.1 0.37 
 
MPI adsorption at the surface of HA nanoparticles 
from ethyl acetate and methanol solutions was studied 
(Fig. 3). Importantly the adsorption isotherms of MMA-
MA copolymer did not differ from MPI isotherms. So, 
the conclusion was drown that an introduction of ben-
zoin pieces into the structure of this copolymer do not 
influence on the character of adsorbate macromolecule 
interaction with adsorbent surface. 
 SYNTHESIS OF HYDROXYAPATITE NANOPARTICLES… PROC. NAP 1, 04FCNF07 (2012) 
 
 
04FCNF07-3 
 
 
Fig 3 – Isotherms of MPI and MMA-co-MA adsorption onto 
HA in different solvents 
 
The characteristic transition of the adsorption 
curves from a sharp rise to saturation took place at 
copolymer concentration of about 0.5 % and further 
increase in its concentration did not give an essential 
gain in adsorption value. We supposed that formation 
of ionic bonds due to interaction of carboxylic groups of 
copolymer macromolecules reached the interface firstly 
with the basic groups at the HA surface should shield 
the adsorbing centres making a barrier for their chemi-
cal interaction with other MPI macromolecules reach-
ing the particles later. Chemical bonding hindered also 
conformational changes in the MPI macromolecules at 
the surface and consequently rearrangement of adsorp-
tion layer.  
The surface modification of HA by PMI allowed to 
initiate polymerization of vinyl monomers in order to 
create compatibilizing polymer layer of certain nature 
and controlled thickness on the surface. Obtained data 
witnessed that radical polymerization of styrene and 
methyl methacylate initiated from the HA nanoparticle 
surface by peroxide groups of the PMI immobilized pro-
ceeded with quite high rates up to high conversions 
(85%) (Fig. 4, 5, Table 2). 
Kinetic curves of this process had rather ordinary 
shapes typical for a common radical polymerization, 
while this process had some features caused evidently 
by the presence in the system of solid highly dispersed 
phase as well as by immobilization of the initiator at 
the phase boundary. Reaction order with respect to 
initiator (n) was close to 1 that is much higher than 
value predicted for radical polymerization (typically 
n  0.5). We supposed that in spite of low overall con-
centration of peroxide groups in this system, fixation of 
PMI macromolecules in adsorption layers caused a 
sharp increase of concentration of initiating centres in 
reaction zone. Under these conditions the main part of 
growing polymer chains were terminated via chain 
transfer reactions to peroxidic and other functional 
groups of immobilized PMI. This leaded to an increase 
of reaction order to the values higher than 0.5. 
 
Table 2 – Characteristics of MMA polymerization initiated 
from the surface of peroxidized HA.  
 
T, 
K 
CO-O, 
mole/l 
Wpol 105, 
mole/(l s) 
kpol 104, 
l0,5/(mole0,5 s) 
Ea, 
kJ/mol 
MWpMMA, 
g/mole 
353 0.012 1.9 5.8 
80.6 
85400 
358 0.012 3.2 9.7 56800 
363 0.012 4.4 13.4 27700 
363 0.006 1.9 13.2 16600 
363 0.024 7.0 13.2 32800 
 
Another feature consisted in an increase of pMMA 
molecular weight with rising concentration of perox-
idized HA in the system  in contrast to typical regulari-
ties, while the temperature enhancement caused its 
diminishing (Table 2). The explanation could be as fol-
lows. The polymerization occurred mainly in the area 
close to the surface of HA nanoparticles where chain 
termination reactions were suppressed as a result of 
diffusion control. Thus, HA concentration enhancement 
caused an enlargement of area of this reaction zone 
that was a reason for a rise of pMMA average molecu-
lar weight. 
The rates of styrene polymerization initiated from 
the HA surface peroxidized were lower than in case of 
methyl methacrylate (Fig. 5). This coincided with the 
literature data [10] reporting on higher ratio of the con-
stants of chain growth and termination (kp/ko0.5) for 
MMA as compared to styrene.  
 
  
 
Fig. 4 – Temperature effect on kinetics of the MMA polymeri-
zation initiated by PMI immobilized at the HA nanoparticles 
Fig. 5 – Dependence of St polymerization kinetics on the 
concentration of immobilized peroxide groups in the system 
 
 O.M. SHEVCHUK, M.R. CHOBIT, N.M. BUKARTYK, ET AL. PROC. NAP 1, 04FCNF07 (2012) 
 
 
04FCNF07-4 
  
 
Fig. 6 – Derivatograms of PMI (a), HA modified by PMI (b), HA after MMA graft polymerization 
 
For St polymerization the influence of dispersed HA 
surface on both the process kinetics and physico-
chemical characteristics of polymer obtained was very 
similar to that for MMA polymerization, indeed the 
order with respect to initiator was higher than 0.5 and 
pSt molecular weight increased with the rise of perox-
idized HA concentration. At the same time pSt molecu-
lar weights were higher than for pMMA; this fact is 
explained by difference in mechanisms of the chain 
termination reaction attributed to these monomers 
namely recombination for St and mainly disproportion-
ation for MMA.  
Comparison of derivatographic curves of PMI, HA 
nanoparticles modified by PMI, and HA nanoparticles 
with grafted pMMA layer (Fig. 6) showed that in con-
trast to the latter, two first samples demonstrated exo-
thermic effects on DTA curves in the range of 440-
458 K attributed to decomposition of peroxidic groups. 
That means peroxidic fragments decomposed almost 
completely at the surface of HA nanoparticles modified 
during the graft polymerization process; and this phe-
nomenon could be explained by essentially higher de-
cay rates of PMI immobilized at solid surface as com-
pared to this process in solution. Absence of active per-
oxidic groups (being the free radical sources) in sam-
ples of HA nanoparticles with grafted pMMA made 
them a good candidates for the use as an orthopedic 
material. 
Nano-hydroxyapatite surface-modified by MPI was 
used for obtaining the polyester composites capable of 
curing at room temperature under UV-irradiation. The 
synthesized MPI itself as well as immobilized at the 
surface of nanoparticles appeared to be more effective 
photoinitiator comparing to initial benzoin (Fig. 7). 
Immobilization of photoinitiating groups on the HA 
nanoparticles enhanced properties of photocomposites 
as compared with a low-molecular photoinitiator benzo-
ine and MPI on its base. Faster hardening and more as 
twice higher hardness of composite with MPI immobi-
lized was observed, evidently due to better compatibil-
ity and more even distribution of the surface-modified 
HA nanoparticles in the polymer matrix. On the other 
hand filling of polyester composites by HA nanoparti-
cles should improve their biocompatibility. 
 
 
 
Fig. 7 – Effect of the photoinitiator nature on hardening 
kinetics of photopolymer composite film: benzoine (1); MPI 
(2); MPI immobilized on HA nanoparticles (3)  
 
4. CONCLUSIONS  
 
The method of the synthesis of nano-hydroxyapatite 
from a water salt solution in the presence of macroin-
itiators was elaborated that allowed simultaneously to 
control over size and to modify the surface of nanopar-
ticles. Immobilization of the macroinitiators containing 
either peroxidic groups or benzoin pieces in their struc-
ture made possibility to carry out the radical graft 
polymerization initiated from the surface of modified 
nanoparticles and to design the structure and thick-
ness of polymer shell bonded to the surface of nanopar-
ticles. As a result improvements in physico-mechanical 
properties of filled polymer composites on the basis of 
nano-hydroxyapatite were achieved.  
 
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Synthesis of Hydroxyapatite Nanoparticles with Initiating Centres in Polymer Shell

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