Solid-state products, lead polymers

The electrical conductivity in the solid state is determined by the product of the carrier concentration and the carrier mobility. In conjugated polymers both entities are material dependent and, i.e., are different for electrons and holes. Electrons or holes placed on a conjugated polymer lead to a relaxation of the surrounding lattice, forming so-called polarons which can be positive or negative. Therefore, the conductivity, o, is the sum of both the conductivity of positive (P+) and negative polarons (P ) ... 

Janssen et al. [144] focused their work on ozonization of polyvinyl lactam, grafting with hydrophilic methacrylic monomers for applications in the field of contact lenses and other products used in the medical domain. The most studied polymer remains the poly-N-vinyl pyrrolidone which is ozonized either in solid state or in aqueous solution. This activation step leads to three hydroperoxides per chain but also to chain scissions. The resulting product is formulated with different mixtures of methacrylic and dimethacrylic monomers to graft them onto activated polymer by UV initiation. Using dimethacrylic monomers lead to perfect cross-linked polymers presenting excellent resistance to solvents. Unfortunately, the mechanisms of action of ozone onto polyvinyl lactams do not seem to have been studied in detail. 

One of the best-studied solid-state reactions is the photopolymerization of distyrylpyrazine (9) and related compounds to give crystalline polymers containing cyclobutane rings (Scheme 10). This reaction is reminiscent of Schmidt s early work on cinnamic acids, although the presence of two double bonds per monomer can lead to oligomeric or polymeric rather than solely dimeric products. The four-center reaction of 9, and other related polymerizations, have been reviewed in detail by Hasegawa, who has played a central role in the study of these systems... 

The solid state reactivity of butadiene derivatives has first been investigated by G.N.J. Schmidt and coworkers (1-1). They observed for a number of 1,4-disubstituted compounds that exposure to UV light leads to the formation of dimers according to a (2 2]-cycloaddition reaction. The structure of the dimers was found to be strictly related to the monomer arrangement in the crystal lattice. Oligomers or polymers could only be obtained as side products. 

However, the most interesting products could be obtained upon the radiolysis of butadiene derivatives included in a host matrix ( - ) For a number of monomers with a non-centrosymmetric molecular structure it could be demonstrated that y-irradiation leads to stereoregular, optically active polymers in a direct asymmetric induction. Especially these studies indicate that apart from polymerization in solution using optically active catalyst systems (A), the solid state polymerization represents a suitable method to obtain stereoregular polybutadienes. 

Recent work in our laboratory showed that the reaction can be extended to higher conjugated acetylenes. There is substantial evidence to assume that the solid state photopolymerization of octatriin-l,6-diol (VIII) leads not to polymer IX with a polyconjugated backbone and two conjugated triple bonds per base unit but to the "normal polymerization product X (22). 

Inserting the guest into the host can sometimes improve the selectivity of its reactions. The polymerization of 1,3-butadiene in urea crystals preferentially leads to the crystalline 1,4-trails polymer.55 Such solid-state reactions can improve the selectivity in many reactions.56 If performed with a chiral diol, the reaction can give products with high enantioselectivity (7.3). 

Wegner, however, established that radiation-induced solid-state polymerization of BCMO leads to a polymer morphology, which is incompatible with the so-called topochemical polymerization, i.e., a process in which monomer molecules are transformed into polymer without destruction of the crystal lattice 36). Electron microscopy, X-ray analysis and electron diffraction studies, have shown that polymerization starts at the edges and imperfections of the monomer crystals and that amorphous polymer is formed initially. Further transition from the amorphous state leads to the thermodynamically unstable monoclinic p-form. Density measurements indicate that the polymer is only 45-50% crystalline. The density of the amorphous poly-BCMO is 1.368 g/cm3 the density calculated for the crystalline polymer from crystallographic data of the p-form is 1.456 g/cm3. The density of the product of the radiation-induced solid-state polymerization is 1.41 g/cm3 36). 

For example, twin-screw extruders with 80 tons/hr throughput and injection (100,000 kN) molding presses with shot size of 100 liters of polymer are available. Composites where the matrix is a polymer blend that comprises six different polymers have been introduced. Gas and multiple injection processes, melt-core technology, solid-state forming, microcellular foams all lead to new products with advanced performance. The polymer industry is becoming increasingly sophisticated. 

Therefore, it is not surprising that this cascaded process opens the door to products with combinations of properties so far not known [48-50]. It is important to underline that with this process design the polymer generated in all three polymerization reactors is finely divided in the final polymer particle. Each catalyst primary particle is enveloped with the polymer from reactors 1, 2, and 3. With this in-situ blend it is possible to obtain a homogeneous melt in the granulation facility this is necessary to exploit the full potential of the product in the solid state. Mechanical blending of such three types of polyethylenes would never lead to a homogeneous melt. 

Polymer Pyrolysis Derived SiC Fibers (PP-fibers) As shown 1976 by Yajima [54], pSiC fibers with a smaller diameter (8-30 pm) and without a central core can be manufactured by solid state pyrolysis of a polycarbosilane (PCS) precursor fiber. The melt-spun PCS fiber is first cured at 200°C in air to produce a thin layer to protect from melting later on, then heated up in inert atmosphere to 1500°C to convert the PCS in crystalline pSiC. The steps leading to the production of SiC can be summarized as follows ... 

---