Polymerization thermally induced

Hepuzer et al. [91] have used the photoinduced homolytical bond scission of ACPB to produce styrene-based MAIs. These compounds were in a second thermally induced polymerization transferred into styrene-methacrylate block copolymers. However, as Scheme 24 implies, benzoin radicals are formed upon photolysis. In the subsequent polymerization they will react with monomer yielding nonazofunctionalized polymer. The relatively high amount of homopolymer has to be separated from the block copolymer formed after the second, thermally induced polymerization step. 

Marvel et al. described [41] the polymerization of 5,6-dibromocyclohexa-1,3-diene (16) to poly(5,6-dibromo-l,4-cyclohcx-2-ene) 17 followed by a thermally induced, solid state elimination of HBr on the formation of PPP 1. The products, however, display some indications for several types of structural defects (incomplete cyclization, crosslinking). 

The facile, photoinduced valence isomerization of ethyl 1//-azepine-l-carboxylate to ethyl 2-azabicyclo[3.2.0]hepta-3,6-diene-2-carboxylatehas been studied as a potential solar energy storage system.101102 Unfortunately, the system proved to be inefficient due to build up of polymeric material during the thermally induced, exothermic retro-reaction. 

The problem of the thermally induced polymerization reaction of partially or completely substituted cyclophosphazenes has been considered in the past by several authors [355-357], and more recently by H. R. AUcock [358]. This is because of the ease of synthesizing these substrates, the possibihty of preparing structurally regulated poly(organophosphazenes), and the lack of any additional nucleophilic substitution processes on the poly(organophosphazenes) obtained by the ROP process of fully saturated trimers. 

Polymeric forms have also been reported. One example, which also includes germanium heteroatoms terminating the chain, is the oligomer (RO)Ge(RO)2Co(RO)2Co(RO)2Ge(OR), (97) where each Co center is surrounded by four bridging tert-butoxide ions.416 These form via a photochemically induced labile solvent complex, or else through thermally induced substitution... 

O. Herzberg, M. Epple. Formation of Polyesters by Thermally Induced Polymerization Reactions of Molecular Solids. Eur. J. Inorg. Chem. 2001, 1395-1406. 

Under the DSC conditions (N, scanning rate = 10°C/min), it is apparent that the decomposition processes are occurring at a much faster rate at or near the temperature at which cure is taking place in all the pure dlcyanate samples. Both BADCy and THIOCy showed small exotherms (onset at 277°C and 226°C and peak at 308°C and 289°C, respectively). Their major decompositions began about 251°C and 246°C, respectively, as observed by TGA. On the contrary, all the 1 1 BCB/dlcyanate blends displayed the expected thermal transitions. Besides initial Tg s (20-28°C) and Tm s (171-183°C), all samples showed small exotherms in their DSC scans with maxima at 147-151°C. This is attributable to the thermally-induced crystallization in the mixtures, which also led to some initial phase separation. The polymerization exotherms are consistent with the typical temperature ranges for the known benzocyclobutene-based systems (onset 229-233°C max. 259-266°C). 

The synthesis and proposed cure mechanisms of this resin are described in reference 2. While the cure mechanism of the BCB terminated resin is not yet known, it is speculated that it reacts via one of two different routes. Initially the strained four member ring of the benzocyclobutene undergoes a thermally Induced ring opening. The opened rings then react with one another by a linear type addition to form a network type of structure or by cycloaddition to form linear polymer chains. An Illustration of the proposed polymerization mechanism of benzocyclobutene (BCB) terminated resins is shown below. 

The Diels Alder reaction, involving the [4 + 2]-cycloaddition of an unsaturated group (di-enophile) to a 1,3-diene, has been studied for the synthesis of ladder polymers, such as the reaction of 2-vinyl-l,3-butadiene with benzoquinone [Bailey, 1972] (Eq. 2-247). Related polymerizations are those utilizing the [2 + 2]-cycloaddition reaction [Dilling, 1983]. While [4 + 2]-cycloaddition reactions are thermally induced, [2 + 2]-cycloaddition reactions are... 

The polymerization proceeds under photo- [49,50],X-ray [51], and y-ray [52] irradiation in the dark in vacuo, in air, or even in water or organic solvent as the dispersant (nonsolvent) for the crystals, similar to the solid-state polymerization of diacetylene compounds [ 12]. The process of topochemical polymerization of 1,3-diene monomers is also independent of the environment surrounding the crystals. Recently, the thermally induced topochemical polymerization of several monomers with a high decomposition and melting point was confirmed [53]. The polymer yield increases as the reaction temperature increases during the thermal polymerization. IR and NMR spectroscopies certified that the polymers obtained from the thermally induced polymerization in the dark have a stereoregular repeating structure identical to those of the photopolymers produced by UV or y-ray irradiation. 

Figure 4.3 Scheme illustrating the development of immobilized ionic liquids by thermally induced free radical polymerization of vinyl-substituted imidazolium-based monocationic and dicationic monomers. 

Organic-silica hybrid materials have been used for multi-photon microfabrication. These include the acrylate-functionalized oligosiloxanes known as ORMOCERs, which have been polymerized by radical processes using conventional IP radical iniatitors, such as c.2 [221,234]. Commercial poly(dimethylsiloxane)-based resists containing vinyl and Si-H functionalities use two different 2PA-induced processes hydrosilylation catalyzed by the photodecomposition products of Cp PtMes (Cp = ti -methylcyclopentadienyl) and radical initiation by c.4 (Fig. 13) [235]. The former process was complicated by thermally-induced polymerization. 

Experimentally, fN is determined as a function of temperature T, solvent composition x, and degree of polymerization N fN = F xp(T, x, N) here Fexp stands for the experimentally obtained functional form. On the other hand, statistical-mechanical formulations allow fN to be expressed in terms of s, a, and N fN = Flhcor(s, a, N), where Fth denotes a theoretical function. Then it should be possible from a comparison of F p and Flheor to determine s and a as functions of T and x. How can this be achieved Since the pioneering work of Zimm et al. (17) in 1959 various methods have been proposed. Typical approaches are outlined below for the experimental situation in which a thermally induced helix-coil transition is observed. For most of the proposed methods such transition curves must be available for a series of samples of different N. Preferably, these samples ought to be sharp in molecular weight distribution and cover as wide a range of N as possible. 

The well known thermally induced isomerization of an isoimide to an imide was the chemistry selected to test the concept. A series of high molecular weight polyisoimides was prepared based on PMDA and pendent aromatic diamines that on thermal treatment would exhibit the required geometry for reinforcement. Polymerizations of the diamines with PMDA were carried out in DMAC (10% by weight) at room temperature in a dry nitrogen atmosphere. Subsequent cyclodehydration of the polyamic acid to the corresponding polyisoimide was... 

A histamine selective MIP chemosensor, based on impedimetric transduction, has been devised [136]. Its preparation involved immobilization of the histamine imprinted MIP particles in apoly[2-methoxy-5-(3,7-dimethyloctyloxy)-l-4-pheny-lene vinylene] (OCiCi0-PPV) film deposited on aluminium electrodes. Preparation of these particles comprised thermally induced co-polymerization of MAA (functional monomer), EGDMA (cross-linker) and AIBN (initiator) in the presence of histamine. This film efficiently rebound histamine in the presence of histidine and... 

The concept of using the functional groups of electrode surfaces themselves to attach reagents by means of covalent bonding offers synthetic diversity and has been developed for mono- and multi-layer modifications. The electrode surface can be activated by reagents such as organosilanes [5] which can be used to covalently bond electroactive species to the activated electrode surface. Recently, thermally induced free-radical polymerization reactions at the surfaces of silica gel have been demonstrated [21]. This procedure has been applied to Pt and carbon electrode surfaces. These thermally initiated polymer macromolecules have the surface Of the electrode as one of their terminal groups. Preliminary studies indicate that the... 

After a brief discussion of the notion of molecular topology and the analogy principle as related to topology/reactivity relationships more recent developments in the field of reactivity indices for polynuclear benzenoid hydrocarbons are reviewed. Reaction mechanisms and correlations of reactivity indices with rates of electrophilic substitution and Diels-Alder reactions, thermally induced polymerization, and biochemical transformations of benzenoid hydrocarbons are discussed. 

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