mechanical and physical properties of 2, 2'-bis (4

148 Dental Materials Journal 6 (2): 148-155, 1987

Mechanical and Physical Properties of 2, 2'-Bis (4-Methacryloxy Polyethoxyphenyl) Propane Polymers

Minoru KAWAGUCHI, Tadao FUKUSHIMA and Takashi HORIBE

Department of Dental Materials and Devices, Fukuoka Dental College, 700Ta, Sawara-ku, Fukuoka 814-01, Japan

Received on July 24, 1987Accepted on September 30, 1987

Five types of BisMPEPP monomers with different side chain lengths were prepared from a commercial BisMPEPP monomer mixture in order to investigate the structural effect on the mechanical and physical

properties of their polymers. The mechanical properties (transverse strength, elastic modulus, compressive strength, and Knoop hardness) decreased with increasing the side chain lengths of BisMPEPP monomers, but the water sorption value increased. There were no significant differences between the diametral tensile strength of each polymer. BisGMA polymer showed higher values for elastic modulus (in dry conditions) and Knoop hardness (in dry and wet conditions) than BisMPEPP polymers. The decrease in the mechanical

properties of BisGMA polymer in water was larger than those of the others. It was found that the mechanical and physical properties of these polymers largely depended on their structural nature, especially the segmen-tal mobility of their side chains.

Key words: Physical properties, Dimethacrylate, BisGMA

INTRODUCTION

Aromatic dimethacrylates such as BisGMA and 2, 2'-bis (4-methacryloxy polyethoxy-

phenyl) propane (BisMPEPP) have been used as base monomers for most commercial composite resins1-4). These aromatic dimethacrylates consist of a hard segment containing

a bisphenol backbone and two soft segments containing ethylene oxide or methylene units.

The mechanical and physical properties of dental composites are mainly dependent on the

base monomer structure. However, the relationship between the chemical structure and

physical properties of these polymers is unknown. Therefore, further systematic investiga-tions are required to develop new dimethacrylate monomers which have superior mechanical

and physical properties to the dimethacrylate monomers currently employed.

The purpose of this study was to investigate the relationship between the side chain

lengths of various BisMPEPP monomers and the mechanical and physical properties of their

polymers.

MATERIALS AND METHODS

Preparation of BisMPEPP monomers

Five types of BisMPEPP monomers were isolated from commercial BisMPEPP mono-

mer mixture* using column chromatography (silicagel; Lobar type C**, eluent; benzene/

ethyl acetate, 90/10 in weight). The isolated BisMPEPP monomers were identified by IR,

* D-4E, Shin-Nakamura Chemical Co., LTD., Wakayama, Japan

** LiChroprep Si 60, Merck, Darmstadt, Germany

PHYSICAL PROPERTIES OF BISMPEPP POLYMERS 149

NMR, and elementary analyses. BisGMA was synthesized from bisphenol A diglycidyl ether

and methacrylic acid5). The viscosity of BisMPEPP monomers was determined with a

viscometer*** at 20•Ž.

Preparation of test specimens

Each BisMPEPP monomer with 1mol% benzoyl peroxide was polymerized in rectangu-

lar aluminium molds with the ends covered by glass plates or in glass tubes with the top

covered by a glass plate at 110•Ž for 8h. These polymer plates and rods were cut using a

low-speed diamond saw # and subsequently polished with SiC paper (400, 600 and 1000 grit) to

make the specimens suitable for measurement. Each specimen was divided into two groups.

One group was kept at 37•Ž in a desiccator for 30 days and the other was immersed in

distilled water at 37•Ž for 30 days.

Measurement of mechanical strength

Transverse strength and elastic modulus were measured on ten bar specimens (2•~2•~30

mm) by three-point bending test with a universal testing machine ##. The length between the

supports was 20mm. Elastic modulus was calculated from the transverse deflection at 2kg

load. The cross-head speed was 1mm/min.

Compressive strength tests were made with eight cylindrical specimens (4mm in diame-

ter and 6mm long) at a cross-head speed of 1mm/min. The proportional limits on the

compressive test were determined as •gcompressive strength•h because the specimens showed

a large plastic deformation when tested.

Diametral tensile strength was measured on seven cylindrical specimens (4mm in

diameter and 4mm long) at a crosshead speed of 2.5mm/min. Knoop hardness measurement

was made on the polished surface of the specimen (10•~10•~2mm) with 200g load for 30s.

Amount of acetone and water sorption

Five cylindrical specimens (4mm in diameter and 10mm long) were immersed in 37•Ž

acetone for 14 days. The amount of acetone sorption was determined from differences in

weight, measured before and after immersing. Three disc specimens (20mm in diameter and

1mm thickness) were immersed in 37•Ž water for 30 days. The amount of water sorption was

determined from differences in weight, measured before and after immersing.

The date were analyzed with Scheffe's test for multiple comparisons between means at

the significant level of 0.05.

RESULTS

The structure and physical properties of BisMPEPP monomers are shown in Fig. 1 and

Table 1, respectively. The isolated BisMPEPP monomers (MEP-1, 2, MEP-2, 2, MEP-1, 3,

and MEP-2, 3) were viscous liquid except for crystalline MEP-1, 1. The viscosity of these

BisMPEPP monomers were considerably lower than that of BisGMA.

The IR spectra assignments, NMR chemical schifts, and elemental analyses of these

BisMPEPP monomers were listed in Table 2, 3, and 4, respectively. The 1R and NMR

*** Viscotester VT-02 , RION Co., Tokyo, Japan# Isomet , Buehler, Evanston, IL, USA

## IS-5000, Shimazu Co., Ltd., Kyoto, Japan

150 M. KAWAGUCHI, T. FUKUSHIMA and T. HORIBE

MEP-1, 1

MEP-1, 2

MEP-2, 2

MEP-1, 3

MEP-2, 3

Bis GMA

Fig. 1 Structural formulas of BisMPEPP monomers and BisGMA .

spectra were consistent with assigned structure of each monomer. The elemental analyses

were also reasonably consistent with the chemical formula assigned to them .Transverse strength and elastic modulus of BisMPEPP polymers are given in Table 5.

Transverse strength decreased with increasing the side chain lengths of BisMPEPP mono-

mers. Statistical analyses indicated that the transverse strength of BisMPEPP polymers

with relatively shorter side chains (MEP-1, 1 and MEP-1 , 2) were higher than those with longer side chains. There was no significant difference (p>0.05) between the transverse


Table 1 Physical characteristics of BisMPEPP monomers

Table 2 Infrared spectra assignments (cm-1) of BisMPEPP monomers

Table 3 NMR chemical schifts (ppm) of BisMPEPP monomers

(run in CDCl3)

Table 4 Elemental analyses for BisMPEPP monomers

strength of MEP-2, 2, MEP-2, 3, and BisGMA polymers. The elastic modulus of BisMPEPP

polymers decreased with increasing their side chain lengths. BisGMA polymer showed the

highest elastic modulus in dry conditions. In wet conditions, however, BisGMA polymer


showed an approximate 8.5% decline in elastic modulus. This decrease was the highest in

the study.

Table 5 Transverse strength and elastic modulus of BisMPEPP polymers

Bars indicate values of no statistical significances (SD in parentheses).

The compressive and diametral tensile strength, and Knoop hardness of BisMPEEP

polymers are shown in Table 6. The compressive strength decreased with increasing the side chain lengths in both dry and wet conditions, although there was no statistically significant

difference between MEP-1, 1 and MEP-1, 2, BisGMA polymer had a compressive strength of

71.4MPa in dry conditions, whereas it showed the lowest value of 56.2MPa in wet conditions.

The diametral tensile strength of BisGMA polymer (37.2MPa in dry conditions and 28.7MPa

in wet conditions) was relatively lower than that of BisMPEPP polymers. There was no

significant difference between the diametral tensile strength of each BisMPEPP polymer in

both dry and wet conditions. There was statistically significant difference (p<0.05) between

the Knoop hardness value of each BisMPEPP polymer.

Table 6 Compressive and diametral tensile strength, and Knoop hardness of BisMPEPP polymers

Bars indicate values of no statistical significances (SD in parentheses).

Acetone and water sorption values for BisMPEPP polymers were shown in Table 7.

The acetone sorption value for BisMPEPP polymers increased with increasing their side

chain lengths. There was statistically significant difference between the water sorption value

for each BisMPEPP polymer. The water sorption values for BisMPEPP polymers slightly

increased with increasing the side chain lengths. BisGMA polymer showed relatively higher

water sorption value than BisMPEPP polymers.


Table 7 Acetone, and water sorption values for BisMPEPP polymers

SD in parenthese

DISCUSSION

The majority of base monomers in dental restorative resins have consisted of various

dimethacrylates. The structure and composition of base monomers and polymerization

system affect the physical properties of the cured resins6). BisGMA is capable of producing

a strong and stiffer polymer because of its rigid bisphenol backbone7). However, highly

viscous BisGMA requires diluent monomers to achieve a suitable viscosity when incorporated

with fillers. Although triethyleneglycol dimethacrylate is commonly used as a diluent

monomer for the BisGMA-based monomer system, it could increase the water sorption value

of cured resins8). Therefore, low-viscosity aromatic dimethacrylate monomers would be

desirable for the base monomer system in dental restorative resins.The viscosity of BisMPEPP monomers (except for MEP-1, 1) was considerably lower

than that of BisGMA. This would be due to the absence of highly polar hydroxy groups in

their side chains and their large segmental mobility. Additionally, increasing the segmental

mobility can improve the toughness of the polymers. As shown in the results, lengthening the

side chains resulted in decreasing the transverse and compressive strength, elastic modulus,

and Knoop hardness of the BisMPEPP polymers. On the other hand, there was no obviuos

difference between the diametral tensile strength of the BisMPEPP polymers. This could be

explained by a relatively large plastic deformation that occurred in this test.

Hirasawa, et al.2) reported that a restorative resin based on the oligomeric BisMPEPP

showed a relatively low water sorptin value and a high transverse strength, but its compres-

sive strength was lower than that of the other commercially available materials. Price9)

reported that increasing the length and flexibility of the side chains of cross-linking agents led

to an increase in the impact resistance of PMMA resin. He observed that the cross-linking

agent (MEP-1, 1) increased the impact resistance at higher concentration (up to 50vol%).

These results suggested that the introducing of dimethacrylate monomer having relatively

longer and flexible side chains to the resin system improved the toughness of cured resins.

However, an increase of the segmental mobility of the monomers may be accompanied by an

increase in creep value. It is considered, therefore, that using BisMPEPP-based restorative

composite resins should be avoided in molar restorations which are subjected to so much

stress by occluding. However, they would be adequate to apply anterior and crown and

bridge resin restorations.

On the other hand, BisGMA polymer showed a brittle nature. Its elastic modulus of 334.4


MPa in dry conditions was the highest in this study. In wet conditions, however, BisGMA

polymer showed a higher decrease in mechanical properties. These results could be explained

by a relatively higher water sorptin value for BisGMA polymer. In addition, the acetone

sorption value of BisGMA polymer was considerably higher than that of BisMPEPP poly-

mers. These findings suggested that the higher polarity of BisGMA reduced its segmental

mobility which largely effects polymerization reaction. BisGMA could not form an effective

cross-linked polymer10-12)

The present results indicated that the mechanical and physical properties of these

aromatic dimethacrylate polymers were much dependent on their structural nature. Espe-

cially, the segmental mobility of their side chains affected the properties of the resultant

polymers.

CONCLUSIONS

Mechanical and physical properties of five types of BisMPEPP monomers with different

side chain lengths and BisGMA polymers were measured in order to investigate the relation-

ship between the chemical structure and the physical properties.

There were statistically significant differences between the mechanical properties,

except for diametral tensile strength, of BisMPEPP monomers with shorter side chains and

with longer side chains. Transverse and compressive strength, elastic modulus, and Knoop

hardness of BisMPEPP polymers decreased with increasing the side chain lengths . There

was no significant difference between the diametral tensile strength of each BisMPEPP

polymer. Water and scetone sorption value increased with increasing the side chain lengths.

BisGMA polymer showed higher values for elastic modulus (in dry conditions) and Knoop

hardness (in dry and wet conditions) than BisMPEPP polymers. However , BisGMA polymer

showed a large decrease in the mechanical properties in wet conditions.

REFERENCES

1) Ruyter, I.E. and SjƒÓvik, I.J.: Composition of dental composite materials, Acta Odontol Scand 39 (3):

133-146, 1981.

2) Hirasawa, T., Hirano, S., Hirabayashi, S., Harashima, I., Nasu, I. and Kurosawa, T .: Mechanical

properties of microfilled composite resins, J Japan Soc Dent Appar Mat 22 (59): 187-195, 1981. (in

Japanese)

3) Vankerckhoven, H., Lambrechts, P., Van Beylen, M. and Vanherle, G.: Characterization of composite

resins by NMR and TEM, J Dent Res 60 (12): 1957-1965, 1981 .

4) Ruyter, I.E. and ƒ³ysaed, H.: Composites for use in posterior teeth: Composition and conversion , J Biomed Matey Res 21 (1): 11-23,1987.

5) Allard, D., Fontanille, M. and Prud'homme, R.E.: Synthesis and properties of miscible epoxy/acrylic

interpenetrating polymer networks, J Polym Sci Polym Chem Ed 22 (12): 3827-3842, 1984.

6) Ruyter, I.E.: Monomer systems and polymerization, In: Posterior composite resin dental restorative

materials, Vanherle, G. and Smith, D.C., Eds., P. Szulic Publishing Co., Utrecht , 1985, pp. 109-135.7) Bowen, R.L.: Compatibility of various materials with oral tissues. I: The components in composite

restoratives, J Dent Res 58 (5): 1493-1503,1979.

8) Dulik, D., Bernier, R. and Brauer, G.M.: Effect of diluent monomer on the physical properties of

BisGMA-based composites, J Dent Res 60 (6): 983-989, 1981.

9) Price, C.A.: The effect of cross-linking agents on the impact resistance of a linear poly (methyl


methacrylate) denture base polymer, J Dent Res 65 (7): 987-992, 1986.10) Vankerckhoven, H., Lambrechts, P., Van Beylen, M., Davidson, C.L. and Vanherle, G.: Unreacted

methacrylate groups on the surfaces of composite resins, J Dent Res 61 (6): 791-795, 1982.11) Konishi, R.N. and Turner, D.T.: Deformation and fracture of dentinal adhesive resins, Dent Mater 1

(2): 43-47, 1985.12) Ferracane, J.L. and Greener, E.H.: The effect of resin formulation on the degree of conversion and

mechanical properties of dental restorative resins, J Biomed Matey Res 20 (1): 121-131, 1986.

224

2, 2'-Bis (4-methacryloxy polyethoxyphenyl) propane重合体の理工学的性質

川口稔,福島忠男,堀部隆

福岡歯科大学歯科理工学教室

側鎮長の異なるビスフェノール系ジメタクリレート,

2, 2'-bis (4-methacryloxy polyethoxyphenyl) propane

(BisMPEPP)モノマー5種について,側鎮構造と重合体

の物性との相関を検討する目的で,モノマーの粘度と重

合体の機械的性質の測定を行った。BisMPEPPモノマー

はBisGMAに比較して,著しく低粘性を示した。各Bis-

MPEPP重合体の曲げ強さ,弾性係数,圧縮強さおよび硬

さは側鎮長の増大にともない低下したが,アセトン吸収

率および吸水量は増大する傾向を示した。BisGMA重合

体は脆性に富み,dryでの弾性係数,dryおよびwetでの

硬さはBisMPEPP重合体を上まわる値を示したが,吸

水による機械的性質の低下率はBisMPEPP重合体を上

まわる値を示した。

mechanical and physical properties of 2, 2'-bis (4

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