Effect of Monomer Structure

Consider the effect of monomer structure on the enthalpy of polymerization. The AH values for ethylene, propene, and 1-buene are very close to the difference (82-90 kJ mol 1) between the bond energies of the re-bond in an alkene and the a-bond in an alkane. The AH values for the other monomers vary considerably. The variations in AH for differently substituted ethy-lenes arise from any of the following effects  

Differences in the resonance stabilization of monomer and polymer due to differences in conjugation or hyperconjugation. 

Steric strain differences in the monomer and polymer arising from bond angle deformation, bond stretching, or interactions between nonbonded atoms. 

Differences in hydrogen bonding or dipole interactions in the monomer and polymer. 

Many substituents stabilize the monomer but have no appreciable effect on polymer stability, since resonance is only possible with the former. The net effect is to decrease the exothermicity of the polymerization. Thus hyperconjugation of alkyl groups with the C=C lowers AH for propylene and 1-butene polymerizations. Conjugation of the C=C with substituents such as the benzene ring (styrene and a-methylstyrene), and alkene double bond (butadiene and isoprene), the carbonyl linkage (acrylic acid, methyl acrylate, methyl methacrylate), and the nitrile group (acrylonitrile) similarly leads to stabilization of the monomer and decreases enthalpies of polymerization. When the substituent is poorly conjugating as in vinyl acetate, the AH is close to the value for ethylene. 

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Effect of Monomer Structure on Synergistic Effects with UV Grafting. 

The effect of monomer structure on reactivity (polymeriza-bility) and on presence of "side reactions," that is, those reactions that interfere with chain growth, for example, termination, transfer, and rearrangement. This factor is relevant to both mechanisms. 

Discuss the effect of monomer structure on the thermodynamics of the free-radical polymerization process. 

Dudowicz J, Freed KF (1991) Effect of monomer structure and compressibility on the properties of multicomponent polymer blends and solutions 1. Lattice cluster theory of compressible systems. Macromolecules 24 5076-5095... 

Yuan, J.Y. and Pan, C.Y. (2001) The effects of monomer structure of cyclic ketene acetals on the behavior of controlled radical ring-opening polymerization. Chiru J. Polym. Sci.,... 

To account for the effect of monomer structure on the tacticity of the polymer, Natta et al. (1963b) presented the following interpretation. Complexing of the monomer with catalyst was thought to occur with only one double bond, even for both isomeric 1,3-pentadienes which afford cis-1,4-polydiene. The idea of coordination of two double bonds was rejected for steric reasons. This cis isomer (LXXI) of 1,3-pentadiene should be too hindered in the cis conformation for double coordination. Furthermore, if double coordination of the tram isomer (LXXII) is evoked to explain the stereochemical results, then butadiene, which is even less hindered, should polymerize by 1,4-addition. 

Electronic arguments were used to explain the effect of monomer structure. In the example of butadiene, (LXXIII) and (LXXIV), primary carbonium ion character occurs at C-4,... 

To study the effects of monomer structures and reaction conditions on liquid crystallinity and crystallization, a series of homopolymers and copolymers were synthesized. Their monomer compositions are ANA, ABA, AAA/IA, ANA/AAA/IA, and ABA/AAA/IA. The chemical stmctures of these monomers are shown in Figure 2.18. 

In order to discern between the effects of monomer structure and viscosity on the polymerization kinetics, a two-component system, triethylene glycol dimethacrylate (TEGDM, I) and 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]-propane bis-GMA, n) [25], was investigated and the rate coefficients were estimated. 

M.B. Saeed, Mao-Sheng Zhan (2006) Effects of monomer structure and imidization degree on mechanical properties and viscoelastic behavior of thermoplastic polyimide films. European Polymer Journal. 42 1844-1854. 

Weng WG, Li Z, Jamiestui AM, Rowan SJ (2009) Effect of monomer structure on the gelation of a class of metallo-supramolecular polymers. Soft Matter 5 4647-4657... 

Guymon CA, Hoggan EN, Clark NA, Rieker TP, Walba DM, Bowman CN (1997) Effect of monomers structure on their organization and polymerisation in a smectic liquid crystal. Science 275 57-59... 

The thermodynamic characteristics AG, AH, and AS of pol ntnerization are important to an imderstanding of the effect of monomer structure on polymerization AG, AH, and AS are the differences in free energy, enthalpy, and entropy, respectively, between 1 mol of monomer and 1 mol of polymer repeating imits. 

A few papers which have been published deal with this problem for a limited number of plasma polymers only. Therefore, the current study was undertaken to estimate the surface free energies of plasma polymer films deposited from numerous organoslllcon and hydrocarbon monomers, and in particular, the effect of monomer structure on the dispersion and polar components of their surface energy. 

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