Monomer structural effects

Organic peroxide-aromatic tertiary amine system is a well-known organic redox system 1]. The typical examples are benzoyl peroxide(BPO)-N,N-dimethylani-line(DMA) and BPO-DMT(N,N-dimethyl-p-toluidine) systems. The binary initiation system has been used in vinyl polymerization in dental acrylic resins and composite resins [2] and in bone cement [3]. Many papers have reported the initiation reaction of these systems for several decades, but the initiation mechanism is still not unified and in controversy [4,5]. Another kind of organic redox system consists of organic hydroperoxide and an aromatic tertiary amine system such as cumene hydroperoxide(CHP)-DMT is used in anaerobic adhesives [6]. Much less attention has been paid to this redox system and its initiation mechanism. A water-soluble peroxide such as persulfate and amine systems have been used in industrial aqueous solution and emulsion polymerization [7-10], yet the initiation mechanism has not been proposed in detail until recently [5]. In order to clarify the structural effect of peroxides and amines including functional monomers containing an amino group, a polymerizable amine, on the redox-initiated polymerization of vinyl monomers and its initiation mechanism, a series of studies have been carried out in our laboratory. 

Polyester synthesis was carried out hy insertion-dehydration of glycols into polyanhydrides using lipase CA as catalyst (Scheme 6). The insertion of 1,8-octanediol into poly(azelaic anhydride) took place at 30-60°C to give the corresponding polyester with molecular weight of several thousands. Effects of the reaction parameters on the polymer yield and molecular weight were systematically investigated. The dehydration reachon also proceeded in water. The reaction behaviors depended on the monomer structure and reaction media. 

Effect of Monomer Structure on Synergistic Effects with UV Grafting. 

Assuming that all B groups have the same reactivity, the chemical reaction giving rise to a branched molecule is identical to the reaction resulting in a linear polymer. Statistically this will eventually result in a hyperbranched polymer. However, dependent on the chemical structure of the monomer, steric effects might favor the growth of linear polymers. Computer simulations of of ABX-monomer condensation and AB -monomers co-condensed with B-functional... 

In order to establish the effect of varying monomer structure on dynamic mechanical results, three films were cured as thin sheets under identical conditions. No significant differences appear in the Rheovibron plots (Figure 3). Thus the mechanical properties (and by inference, such properties as strength and toughness) appear to be insensitive to monomer structure. The dynamic mechanical properties should be regarded as influenced primarily by the network connectivity and extent of cure. 

A further study of the aggregation state of PhLi in etheral solvents has resolved signals for the ipso carbon which firmly establish the tetramer and dimer structures in diethylether, and the dimer and monomer structures in THF. The effects of polar additives such as THF, DME, dioxolane, 2,5-dimethyltetrahydrofuran, TMEDA, PMDTA, HMTTA, HMPA, DMPU, and 12-crown-6 to solutions of PhLi in diethylether and/or THE have been studied by low-temperature multinuclear techniques. 

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 ... 

In the overview of structure-property relationships that follows, it should be borne in mind tliat these comparisons are (wherever possible) for those materials where hydrogen has been replaced with fluorine. Cases in the literature where dramatically different monomer structures are used for the fluorinated and unfluorinated polyimides cannot easily be interpreted for effects of fluorine, although such comparisons are often casually made in the literature anyway. For instance, to ascribe die property differences in PMDA-ODA and 6FDA-0DA to fluorine substitution is of little value toward understanding the effect of fluorine, though this is often die extent to which data are available. 

Generally speaking, at least in theory, one attractive aspect of cation radical polymerization, from a commercial standpoint, is that either catalysts or monomer cation radicals can be generated electrochemically. Such an approach deserves special treatment. The scope of cation radical polymerization appears likely to be very substantial. A variety of cation radical pericyclic reaction types can potentially be applied, including cyclobutana-tion, Diels-Alder addition, and cyclopropanation. The monomers most effectively employed in the cation radical context are diverse and distinct from those that dominate standard polymerization methods (i.e., vinyl monomers). Consequently, the obtained polymers are structurally distinct from those available via conventional methods, although the molecular masses observed thus far are still modest. Further development in this area would be promising. 

Fukuoka T, Uyama H, Kobayashi S (2004) Effect of phenolic monomer structure of precursor polymers in oxidative coupling of enzymatically synthesized polyphenols. Macromolecules 37 5911-5915... 

Polymerization is influenced by the physical structure and phase of the monomer and polymer. It proceeds in the monomer, and the chemical configuration of the macromolecules formed depends on whether the monomer is a liquid, vapor, or solid at the moment of polymerization. The influence of structural phenomena is evident in the polymerization of acrylic monomer either as liquids or liquid crystals. Supermolecular structures are formed in solid- and liquid-state reactions during and simultaneously with polymerization. Structural effects can be studied by investigating the nucleation effect of the solid phase of the newly formed polymer as a nucleation reaction by itself and as nuclei for a specific supermolecular structure of a polymer. Structural effects are demonstrated also using macromo-lecular initiators which influence the polymerization kinetics and mechanism. 

According to this classification, the polymerization type can usually be easily determined. The structure of the initiator, the manner of its reaction with the monomer, the effects of the medium and last, but not least, sensitive spectroscopic or resonance methods usually, but not always, provide sufficiently convincing information. We know systems containing radical ions. Several years ago it was sometimes assumed that stereospecific polymerizations (now classified as coordination polymerizations) proceed by a radical or cationic mechanism. 

All structural effects decreasing the heat of polymerization are cumulated in a-methylstyrene resonance of the double bond with the aromatic ring, —CH3 hyperconjugation stabilizing the monomer, and polymer destabilizing 1,1-disubstitution. The same is true of methacrylic acid and of all its derivatives (AHlc between 54 and 59kJmol-1) and partly even of vinylidene chloride (AHlc = 75.4 kJ mol-1). 

A complete mechanistic picture of a polymerization should include structures of the active species participating in all elementary reactions (initiation, propagation, transfer, and termination), a mechanism (in the organic chemist s sense) of all of these reactions with a special emphasis on propagation which is responsible for the construction of nearly the entire macromolecule (except end groups), and an explanation of various structural effects in the monomer, active centers, additives, medium, etc., which affect rates, molecular weights, and MWDs. 

The similarities outlined, if valid, should mean that the rates of the many reactions indicated should be governed by some balance of the same list of structural influences relating monomer structure to reactivity, and the effect of the nature of the reaction medium. The following guiding principles are outlined briefly. More detailed discussions of factors affecting the rates of carbonyl additions, as well as mechanistic details, are given in several references [13—15] and in later sections of this chapter. 

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