Gel formation by chain-crosslinking photopolymerization of methyl methacrylate and ethylene glycol dimethacrylate

Abstract Photoinitiated free-radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate has been investigated in toluene at a monomer concentration of 35 w/v%. The photoinitiators used were benzoin, benzoin benzoin methyl ether, benzoin ethyl ether and 2,2-dimethoxy-2-phenyl-acetophenone. Conversion of monomer and pendant vinyl groups and the size of the pregel polymers were measured as a function of the reaction time up to the onset of macrogelation. Approximately 30% of the pendant vinyl groups were found to be consumed by cyclization reactions. The fraction of units in cycles is independent of the EGDM concentration. As a result of the cyclization reactions, the accessibility of the radical centres and pendant vinyl groups for other polymer molecules is strongly reduced. Consequently, both termination and crosslinking reactions are controlled by the segmental diffusion of the polymer radicals. Calculations indicate a 1–2 orders of magnitude decrease in the average reactivity of pendant vinyls for intermolecular reactions compared to the monomeric vinyls. This drastic decrease in pendant reactivity is mainly responsible for the delay in the gel point. Contrary to gelation theories, the size distribution curves of the pregel polymers change from monomodal to bimodal distributions as polymerization proceeds. This finding confirms the coagulation-type gelation mechanism of compact primary particles and indicates the shape polydispersity of the pregel polymers.

[1]  C. Bowman,et al.  Reaction Kinetics and Volume Relaxation during Polymerizations of Multiethylene Glycol Dimethacrylates , 1995 .

[2]  Douglas R. Miller,et al.  A New Derivation of Post Gel Properties of Network Polymers , 1976 .

[3]  C. Macosko,et al.  A new derivation of average molecular weights of nonlinear polymers. , 1976, Macromolecules.

[4]  Paul J. Flory,et al.  Molecular Size Distribution in Three Dimensional Polymers. I. Gelation1 , 1941 .

[5]  K. Horie,et al.  Photocrosslinking of polymers containing cinnamoyl groups: The change in polymer coil dimension during the reaction in solution , 1986 .

[6]  O. Okay,et al.  Pendant vinyl group reactivity during the free-radical copolymerization of methyl methacrylate and ethylene glycol dimethacrylate , 1994 .

[7]  I. Skeist.  Copolymerization; the composition distribution curve. , 1946, Journal of the American Chemical Society.

[8]  G. Odian,et al.  Principles of polymerization , 1981 .

[9]  P. Flory.  Principles of polymer chemistry , 1953 .

[10]  C. Bowman,et al.  Kinetic Gelation model predictions of crosslinked polymer network microstructure , 1994 .

[11]  H. Boots,et al.  Inhomogeneity during the photopolymerization of diacrylates: d.s.c. experiments and percolation theory , 1984 .

[12]  José M. Asua,et al.  Modeling Gelation and Sol Molecular Weight Distribution in Emulsion Polymerization , 1995 .

[13]  Masayoshi Okubo,et al.  Makromol Chem-Macromol Symp , 1990 .

[14]  O. Okay,et al.  Cyclization and Reduced Pendant Vinyl Group Reactivity during the Free-Radical Crosslinking Polymerization of 1,4-Divinylbenzene , 1995 .

[15]  O. Okay,et al.  Free-radical crosslinking copolymerization: Effect of cyclization on diffusion-controlled termination at low conversion , 1995 .

[16]  R. Whitney,et al.  Molecular size and gel formation in branched poly(methyl methacrylate) copolymers , 1980 .

[17]  W. Stockmayer.  Theory of Molecular Size Distribution and Gel Formation in Branched Polymers II. General Cross Linking , 1944 .

[18]  Paul J. Flory,et al.  Molecular Size Distribution in Three Dimensional Polymers. II. Trifunctional Branching Units , 1941 .

[19]  O. Okay.  Kinetic modelling of network formation and properties in free-radical crosslinking copolymerization , 1994 .

[20]  O. Okay.  Styrene‐divinylbenzene copolymers, V. Inhomogeneity in the structure and the average degree of swelling , 1987 .

[21]  Ashok C. Shah,et al.  Studies of dimethylacrylates as crosslinkers for styrene , 1978 .

[22]  O. Okay.  Gel properties in free radical crosslinking copolymerization: A kinetic approach , 1994 .

[23]  N. Peppas,et al.  Kinetic modeling of copolymerization/cross-linking reactions , 1986 .

[24]  W. Funke,et al.  Crosslinking mechanism in radical polymerization of tetrafunctional monomers , 1979 .

[25]  Walter H. Stockmayer,et al.  Theory of Molecular Size Distribution and Gel Formation in Branched‐Chain Polymers , 1943 .

[26]  Foster Dee Snell,et al.  Encyclopedia of Industrial Chemical Analysis , 1975 .

[27]  C. Macosko,et al.  Cyclization and reduced reactivity of pendant vinyls during the copolymerization of methyl methacrylate and ethylene glycol dimethacrylate , 1988 .

[28]  C. Decker.  Photoinitiated Curing of Multifunctional Monomers , 1993, Chimia (Basel).

[29]  S. P. Pappas,et al.  Benzoin ether photoinitiated polymerization (1) , 1975 .

[30]  O. Okay.  Kinetics of gelation in free radical crosslinking copolymerization , 1994 .

[31]  O. Okay,et al.  Critical properties for gelation in free-radical crosslinking copolymerization , 1995 .

[32]  J. Ebdon.  Developments in polymerization , 1991 .

[33]  H. Inagaki,et al.  Free-radical copolymerization. 3. Determination of rate constants of propagation and termination for styrene/methyl methacrylate system. A critical test of terminal-model kinetics , 1985 .

[34]  Shiping Zhu,et al.  Radical concentrations in free radical copolymerization of MMA/EGDMA , 1990 .

[35]  Dietrich Stauffer,et al.  Computer simulation of kinetics of gelation by addition polymerization in a solvent , 1984 .

[36]  A. Hamielec,et al.  Modeling of network formation in free radical polymerization , 1989 .

[37]  Kristi S. Anseth,et al.  Kinetic evidence of reaction diffusion during the polymerization of multi(meth)acrylate monomers , 1994 .

[38]  I. Capek,et al.  Kinetic investigation of the dispersion polymerization of N,N′‐methylenebis(acrylamide) in the presence of various emulsifiers , 1990 .

[39]  A. Hounslow,et al.  The radical polymerization of dimethacrylate monomers—the use of NMR spectrometry to follow the development of network structure , 1989 .

[40]  C. Walling.  Gel Formation in Addition Polymerization1 , 1945 .