Downloaded by CHINESE UNIV OF HONG KONG on June 28, 2016 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0239.ch005
5 Methacrylic-Allylic Interpenetrating Polymer Networks C. Rouf , S. Derrough , J.-J. André , J.-M. Widmaier , and G. C. Meyer 1
1
2
1
1
Institut Charles Sadron (CNRS-ULP), Ecole d'Application des Hauts Polymères, 4, rue Boussingault, 67000 Strasbourg, France Institut Charles Sadron (CNRS-ULP), Centre de Recherche sur les Macromolécules, 6, rue Boussingault, 67083 Strasbourg, France 1
2
Classically, the simultaneous synthesis utilized to obtain interpenetrating polymer networks requires noninterfering polymerization modes to achieve distinct networks that are held together by only physical entanglements. In the absence of different mechanisms, a single copolymer network is formed, except for monomers with quite different reactivity ratios. Specific initiators that decompose at two different temperatures were used in an in situ sequential process to combine methyl methacrylate and diallyl carbonate of bisphenol A; both monomers are polymerizable under free-radical conditions. The monomer-to-polymer conversions were followed by Fourier transform infrared spectroscopy, and the absence of grafting between networks was deduced from electron spin resonance experiments.
INTERPENETRATING POLYMER NETWORKS ( I P N S ) are a special type of poly
mer blend (1-3) insofar as they are a combination of two or more polymers in network form. Therefore, IPNs require specific methods of mixing due to their cross-linked nature. Three basic techniques are described in the liter ature: latex blending (4-9), sequential polymerization (10-13), and simul taneous polymerization (14-17). Classically, simultaneous polymerization signifies that all the reactants of both systems are mixed together prior to initiation, but it does not give any information about the formation processes of the final networks. Several authors have tried to be more explicit in the definition: Fox et al. (18, 19) introduced the expression "sequential timing" in simultaneous IPNs, which specifies the interval of time between the onset 0065-2393/94/0239-0143$06.00/0 © 1994 American Chemical Society
Klempner et al.; Interpenetrating Polymer Networks Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
Downloaded by CHINESE UNIV OF HONG KONG on June 28, 2016 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0239.ch005
144
INTERPENETRATING POLYMER NETWORKS
of the two independent reactions. In another approach, the simultaneous mixing of all the precursors is called in situ by Meyer and co-workers (20-22), and after this step, the initiation of both systems at once leads to " i n situ simultaneous" IPNs (23), whereas the complete conversion of one system before the onset of the second yields " i n situ sequential" IPNs. The expression " i n situ sequential" is used hereafter, instead of simultaneous I P N . In in situ IPNs, the reaction mechanisms that lead to the final networks must be different [e.g., polycondensation and free-radical polymerization (24-32)]; otherwise A B cross-linked polymers, which are quite different in behavior from IPNs, would be formed. However, if for some reason, two monomers that both polymerize by a free-radical mechanism must be com bined as i n situ IPNs, there exists an alternative means by which intersystem reactions may be avoided; namely, when the two monomers have quite different reactivities toward free radicals. This situation may occur with vinyl or acrylic C = C double bonds and allylic C = C double bonds, respectively. The allylie C = C double bonds are about 100 times less reactive than acrylic or methacrylic bonds (33). Additionally, cross-finking of a diallylic monomer takes place at the end of polymerization and requires a temperature higher than for a (meth)acrylic polymerization (34-38). Furthermore, the use of two initiators, each specific to one system, leads to the elaboration of an entirely radical process of obtaining in situ sequential IPNs based on methyl methacrylate and diallyl carbonate of bisphenol A ( D A C B A ) . First, cross-finked poly(methyl methacrylate) ( P M M A ) is formed at a moderate temperature. Then, by just increasing the temperature after completion of the first polymerization, the formation of the allylic network follows. The specificity of the initiators toward their respective monomers was established by refractive index measurements. The kinetics of network forma tion was followed by Fourier transform infrared (FTIR) spectroscopy, and the nature of the propagating radicals during polymerization was determined by electron spin resonance (ESR) spectroscopy.
Experimental Details The monomers, methyl methacrylate (MMA; Merck), 1,1,1-trimethylol propane trimethacrylate (TRIM; Degussa), diallyl carbonate of bisphenol A (DACBA; Pittsburgh Plate Glass Co.; see Chart I), were dried over molecular sieves, but not otherwise purified. The initiators, azobisisobutyronitrile (AIBN) and i-butylperoxy isononanoate (TBPIN) (Chart I), were used as received. The free-radical polymerization was carried out in the bulk. The monomer mixture was prepared by weighing the required amount of M M A , T R I M , DACBA, A I B N , and TBPIN, stirring thoroughly in a dry nitrogen atmosphere, and pouring into a glass mold to yield 3-mm-thick plates. A I B N and TBPIN were added in the amount of 1 and 3% by weight, respectively. The concentration of T R I M was 5 % by weight
Klempner et al.; Interpenetrating Polymer Networks Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
5.
ROUF ET AL.
145
Methacrylic-Allylic IPNs
O—-C—O
CH —CH=CH 2
2
Downloaded by CHINESE UNIV OF HONG KONG on June 28, 2016 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0239.ch005
diallyl carbonate of bisphenol A (DACBA)
Cfl
3
CH —
