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Jones, F. N.; Lu, D.4. Polym. frepr. (Am. Chem. Soc., Div. Polym. Chem.) 1985,26(1),264-265. Keller, T. M. J. folym. Sci., folym. Chem. Ed. 1984,22, 2719. Kingston, 6. H.; Garey, J. J.; Hellwig, W. B. Anal. Chem. 1969,4 7 . 86-89. Odian, G. Principles offolymerization, 2nd ed.; Wiley: New York, 1981; pp 91-92. Overberger, C. G.; Lu, C. X. J. folym. Sci., Polym. Left. Ed. 1984,22,193. Rempp, P.; Lutz, P.; Masson, P.; Franta, E. Makromol. Chem., Suppl. 1984, 8, 3. Webster, 0,W,; Hertier, W, R,; Sogah, D, y,; Farnham, W, 6 , ; RajanBabu, T.V. J. Am. Chem. SOC. 1983, 105, 5706-5708. Webster, 0. W.; Hertler, W. R.; Sogah, D. Y.; Farnham, W. B.; RajanBabu. T.V. J. Macromol. Sci., Chem. 1984,A27, 943-960. Wiiiams' "; Ibrahim,Rev. lg8l* 8 7 3 Zalipsky, s.; Gilon, c.;Zilkha, A. J . Macromol. SCi., Chem. 1984,A27, 839.
Literature Cited AMa, T.; Sanuke, K.; Inoue, S. Macromolecules 1985, 78,1049-1057. Blllmeyer. F. W., Jr. Textbook of Polymer Science, 3rd ed.; Wiley: New York, 1984; p 30. Collins, E. A.; Bares, J.; Billmeyer, F. W., Jr. Experiments in Polymer Science; Wiley: New York, 1973; pp 362-366. c' D' Prepr' (Am' Div' 1985,26(2),7-8. Hassner, A.; Krepsl, L. R.: Alexanian. V. Tetrahedron 1978,3 4 , 2069. Hirai, H.; NaRo, K.; Hamasaki, T.; Goto, M.; Koinuma, H. Makromol. Chem. 1984, 185, 2347-2359. Holmberg, K.; Hansen, B. Acta Chem. Scand., Ser. 8 : 1979,3 3 , 410-412. Holmberg, K,; Johansson, J,-A, proceedings of the 8th ~nternationa/conference on Organic Coatings Science and Technology; Amerlcan Chemical Societv: Washinaton. DC. 1982: D 225. Holmberg, K.; Johaisson, J.-A. Org.'Coat. 1984,6, 23.
Received f o r review October 7 , 1985 Accepted March 21, 1986
Synthesis of Statistical Networks with Liquid Polybutadiene and Telechelic Bis(hydrogenosilyl) Coupling Agents Gllbert Friedmann, Agus Nuryanto, and Jean Brossas Institut Charles Sadron (CRM-EAHP) (CNRS-ULP), 67083 Strasbourg Cedex, France
The synthesis of statistical networks using 1,2-polybutadiene as a liquid precursor and cross-linking agents operative through hydrosilylation of the pendent double bonds is described. These linking agents are telechelic siloxane and silane carrying two dimethylsilyl groups. According to the coupling agent ideal type networks could be obtained. They are characterized by the percentage of extractable polymer, the swollen degree by weight, and the uniaxial compression modulus. The networks obtained exhibit strong adhesion properties on various substrates such as glass and metal. They can be used as adhesive in the preparation of composite materials in the presence of fillers such as glass fibers and carbone fibers.
Introduction We have prepared statistical networks using liquid polybutadiene as a liquid precursor with bis(hydrogenosily1) compounds as coupling agents. Our targets are the synthesis of thermosetting polymers for composites, with good mechanical properties; the possibility of cross-linking a t room temperature, with a short duration of the crosslinking reaction; and the increase of adhesivity of polymers on blends such as glass fibers or carbon fibers. We have chosen the hydrosilylation reaction (Sommer et al., 1947; Speier et al., 1956) of the double bonds as the principal reaction for the networks synthesis. The mechanism of this addition reaction was described by Chalk and Harrod (1965)and Chalk (1971).The networks were characterized by classical techniques: extractable material, swollen degree by weight, and uniaxial compression. The properties of the networks were studied toward the adhesive properties (Friedmann et al., 1985)and toward the possibility of preparing composite materials. A. Starting Materials. The precursors used are liquid polybutadiene samples (PB) of molecular weight in the range 20o(t8000. They are constituted of 1,2type structure (75%-85%) and of 1,4cis and trans (25%-15%). The coupling agents used are (a) 1,1,3,3-tetramethyldisiloxane, M i , a commercial product from Wacker Chemie; (b) 1,1,3,3,5,5,7,7,9,9,ll,ll-dodecamethylhexasiloxane, M'D4M', whose synthesis is described by Chaumont, 1981; (c) 1,4-bis(dimethylsilyl)benzene,Ar(SiH),; (d) 1,6-bis(dimethylsilyl)hexane, R(SiH),;and (e) telechelic bis(di0196-432118611225-0389$01.5010
methylsilyl)polybutadiene, PB(SiH),). The synthesis of c, d, and e has been described by Friedmann et al. (1985). B. Network Synthesis. The synthesis is carried out with the polybutadiene type liquid precursors (PB) in the presence of linking agents carrying hydrogenosilyl groups at both ends (Friedmann and Brossas, 1984). We have obtained three types of networks (Friedmann and Brossas, 1983): A type, polybutadiene + linking agents; B type, self-cross-linking of telechelic bis(dimethy1sily1)polybutadiene; and C type, cross-linking of telechelic bis(dimethylsily1)polybutadiene and a linking agent. The networks were prepared in bulk at 60-70 "C. The appropriate amount of cross-linker was taken so that the ratio Rt of pendent double bonds to silane hydride groups was equal to a predetermined value R, = [no. of pendent double bonds] / [no. of SiH groups]. The cross-linking reaction was carried out in the presence of chloroplatinic acid (H2PtCl6,6 H20) (Wagner and Strother, 1952). The concentration of H,PtCI, was taken so that the molar ratio C = C/Pt was near lo5. The reaction could be achieved at ambient temperature, but this needs too much catalyst: C = C/Pt must be near lo3.
Results and Discussion A. Characterization of the Network. 1. CrossLinking Yield. The cross-linking of polybutadiene with
0 1986 American Chemical Society
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3
rF(Fi$
,
I
I I
1
2
3
4
5
6
Rt
Figure 1. Extractable polymer as a function of the ratio R, = number of pendent double bonds/number of Si-H groups.
1 2 3 4 5 6 Rt Figure 2. Variation of the swollen degree by weight G3as a function of R,.
coupling agents is studied by IR spectroscopy following the disappearance of Si-H vibration of the different coupling agents at 2100 cm-‘. We have defined the cross-linking index cy = [SiH], [SiH],/[Si HI,. We obtained a plateau after 22-24 h. In these conditions CY = 0.90, and we can conclude that the network is formed after 24 h of cross-linking. 2. Ratio R,. R , = [F]/[SiH]. If the molecular weight of the coupling agent is M, and its weight, X,,and if the weight of the liquid polybutadiene is Y, and its percentage of 1,2 structure is 2, we have for the R, values
R, = YZ(Mc/54)2X 3. Extractable Polymer. We have defied in each case the percentage PEas soluble polymer weight/dry network weight. The different PEvalues are given in Figure 1. We observe for the same value of R, and for the same molecular weight of precursor PB that the percentage of extractable polymer depends on the coupling agent in this order (Friedmann and Brossas, 1984): Mp’ > M’D4M’ > Ar(SiH)2. We have analyzed the fraction of extractable polymer. In the case of M2’ and M’D4M’, the extractable polymer shows in ‘H NMR saturated hydrocarbon structures for the skeleton. The singlet signals at 6 = 0.2 are due to the hydrogen of the -CH3 groups bound to silicon atoms: Si(CH3)2or -O-Si(CH3),. The multiplet due to H-Sifunction has disappeared. This observation implies the addition of the linking agent on two neighboring double bonds on the same chain, giving polymers with loops along the chains called festoon polymers. 4. Swollen Degree by Weight G3. For each coupling agent and for several molecular weights of liquid prepolymers (2000, 3000, 4000, 5000, and 8000), we have compared the swollen degree by weight G 3 equal to the weight of swollen gel/weight of dry gel (Figure 2). The swollen degree by weight for the same molecular weight of precursor PB for each value of R, is set in the following order: M i > M’D4M’ > Ar(SiH),. When R, = 1, the network swollen degree by weight is low, G3 = 1.5, or even null for Ar(SiH), as a linking agent. 5. Uniaxial Compression Modulus EG. We have determined the elasticity modulus E G on the dry gel. We have plotted E G as a function of cross-linking reaction time. We observe that the elasticity modulus reaches a plateau after 22 h (Le., when 90% of the pendent double bonds have reacted at 70 “C). This plateau is in agreement with the results obtained by IR spectrometry for the kinetic study of the network formation.
3001
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,
‘,
‘
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. - _- - - - _- _- - _ - - - - _- - - _ _ ------
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1 2 3 4 5 Rt Figure 3. Variation of the uniaxial compression modulus EG as a function of R,.
We have compared EG for M i , M’D4M’, Ar(SiH)2and for different R, values (Figure 3). We observe that the variations of E G for each value of R, and for the same prepolymer are EG(M2’) < EG(M’D4M’) < E G Ar(SiH),. For R, = 1,fin= 3000 and EG = 166 N/cm2 (M,’), EG = 336 N/cm2 (M’D4M’), and EG = 900 N/cm2 Ar(SiH),. If we compare the elasticity modulus of networks prepared from a telechelic polybutadiene and a nontelechelic polybutadiene for R, = 1, with the same coupling agent Ar(SiH), the differences are very small: E G = 900 N/cm2 = 3000) and E G = 952 for nontelechelic polybutadiene N/cm2 for telechelic polybutadiene (fin= 3500). The Si-H function on the chain ends does not increase the elasticity modulus very sharply. The predominant effect on the elasticity modulus is given by the nature of the coupling agent. For example, = 3500) for the same liquid telechelic polybutadiene the elasticity modulus with Ar(SiH)2for each value of R, ( R = 1, 2, 4, 6)is 2 times those obtained with M,’.
(an
(an
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 3, 1986 391
Table I network type B A,C A,C A,C C C
linking agent PB(Si-H)z R(Si-H), hl2' Ar(Si-H), Ar(Si-H), Ar (Si-H)
F , daN/cm2 15 60 70 100 65 80
substrate glass/glass glass/glass glass/glass glass/glass glass/Al glass/Al
6. Elastic Chain Determination. We have determined the molecular weight M, of the elastic chains between two cross-links using the equation p o = network density Mc,exptl = p,,RoT/EC
Networks with M2'. For the different molecular weights M,, = 2000,3000, and 5000 of the polybutadiene and for R, = 1,we obtained M,,,,,] = 1500. This value does not correspond to the following theoretical values: Mc,theorl of the molecular weight between two cross-links on the polybutadiene backbone, M, 40 (R, = 1);or Mc,$heor] of the coupling agent M i , M, = 200. The only value which corresponds to I\;ln,exptl = 1500 is that of a polybutadiene chain with seven loops (M, of a loop = 200) between two cross-links. Networks with M'D4M'. For different molecular weights of the liquid polybutadiene (U, = 2000,3000,5000, and 8000) we obtained 739 C Mc,exptl C 916. With this coupling agent the average number of loops between two cross-links is around 1.2-1.5, i.e., one or two loops per elastic chain. Networks with Ar(SiH),. In this case, I\;lc,exptl= 277. This value is in good agreement with those calculated from the coupling agent, Mc,theorl = 260. We have no loops along the polybutadiene chains between two cross-links. All the chains are effective chains for the networks. A t all events ( M i , M'D4M', Ar(SiH),) > &&,tor], and we can conclude that we have no entanglements. With Ar(SiH), ( R , = 1)the networks behave ideally according to Flory's theory: the ratio of the theoretical number of elastic chains ve,theorl/the experimental number of elastic chains v,,,~,,' N 1. We also have plotted Q3 as a function of V,,the~r/-~'~, and Qs is a linear function with an intercept equal to 0. B. Application of Networks. These liquid mixtures are used as adhesive compounds and used for composite, syntactic foam, liquid metal, etc. 1. Physical Properties of Networks, Type C. The following are properties of telechelic polybutadiene with (Ar(SiH)& without blends: hardness, shore D, 75; density, 0.96; Q3 (R, = 11, 1.07; extractable polymer, 0; compression modulus, 10 N/mm2; Young modulus, 80 N/mm2; thermal stability (ATD), 250 "C; optical property, transparent; tenacity at break, 34 N/mm2; elongation at break, 3.3%; and Tg, 66 "C. 2. Adhesion. The adhesion properties have been measured by F, the mean shear resistance strength. F' varies with the network density and with the structure of the linking agent. The material obtained is transparent. (See Table I.) Composite Materials with Long Glass Fibers and with Carbon Fibers. The Young modulus E has been
determined for different filler contents of the networks PB(Si-H), + Ar(Si-H),. The results obtained confirm the relation E = VfEf V,E,
+
We have obtained a straight line that practically goes through the origin, which confirms the absence of defects. The modulus varies between 44 X lo3 and 140 x lo3 N/mm2 for volume filler contents in carbon fibers in the range 12%-40%, respectively, and between 9 and 45 X lo3 N/mm2 for volume filler contents in glass fibers between 12% and 60%. 3. Syntactic Foams. Since the networks prepared with P B and Ar(Si-H), possess good adhesion properties on glass, they have been used as adhesives for glass microspheres (0.d. I50 pm) in order to prepare syntactic foams (filler content in hollow beads 25% by wt; R, = 1; 80 "C; cross-linking time = 24 h). Their physical and mechanical properties are density = 0.51; uniaxial compression, modulus 1320 N/mm2, tenacity a t break 33 N/mm2, elongation 3.5%; hydrostatic compression, tenacity at break 46 N/mm2, water absorption 1.6% (under 200 bars/8 days).
Conclusions Hydrosilylation of the pendent double bonds of liquid polybutadiene samples with telechelic linking agents carrying two hydrogenosilyl type groups leads to statistical networks whose properties vary with the R, ratio and with the nature of the linking agent. Cross-linking takes place in the absence of solvent a t temperature 1. 60 "C. The network formed exhibits an ideal behavior at R, = 1when the linking agents are of the Ar(Si-H):! type. These networks can be used in composite materials through flow or molding (the moduli are of the order of magnitude of those obtained with epoxy type resins); syntactic foams whose properties are in an interesting range for technical applications; and adhesion for glass/ glass assemblies. We can say that our process presents several advantages such as low viscosity for molding; network reactions that are very easy to check (it is possible to increase the temperature of network formation to decrease the time to obtain the networks); good transparency of the sealant; and good adhesion on glass. Registry No. PB, 9003-17-2; M i , 3277-26-7; MDIM', 995-82-4; Ar(SiH)z, 2488-01-9; R(SiH)2, 2639-49-8; Al, 7429-90-5.
Literature Cited Chalk, A. J.; Harrod, J. F. J. Am. Cbem. SOC. 1985, 8 7 , 16. Chalk, A . J. Ann. Acad. Scl. N . Y . 1971, 772, 533. Chaumont, P. Thesis, Strasbourg, 1981. Friedmann, G.; Herz, H.; Brossas, J. Polym. Bull. (Berlin) 1982, 6, 251. Friedmann, G.; Brossas, J. Polym. Bull. (Berlin) 1983, 70, 2830. Fr. Patent 8219745, Nov 1982. Friedmann, G.; Brossas, J. Po/ym. Bull. (Berlin) 1984, 7 7 , 25. Friedmann, G.; Brossas, J. Eur. Polym. J. 1984, 12, 1151. Friedmann, G.; Brossas. J.; Widmaier, J. M. J. Appl. Polym. Scl. 1985, 30, 755. Sommer, L. H.; Pietrusza, E. W.; Whitmore, F. C. J. Am. Cbem. SOC. 1947, 69, 188. Speier, J. L.; Zimmermann, R.;Webster, J. A. J. Am. Cbem. SOC. 1858, 78, 2278. Wagner, G. H.;Strother, C. 0. Br. Patent 670617, April 1952.
Received for reuiew July 25, 1985 Accepted January 28, 1986
