Type I polymers

The pulp of this cactus contains an arabinogalactan type I polymer with the ability to stimulate phagosytosis. The galactose units are 1,4-linked with... 

An interesting example of the application of the theory is a prediction of a new route to polyamantane by polymerization of -quinodi-methane 121h The first step would be n-n overlapping interaction. The HO and LU of quinodimethane are indicated in Fig. 7.40 a. The mode of n HO-LU interaction and the possible structure of polyamantane derived therefrom (Type I polymer) can be seen in Fig. 7.40b. On the other hand, the direction of the hybridization change would be controlled by the a-n interaction. The nodal property of n HO and a LU of the monomeric unit are as shown in Fig. 7.40 c, so that the hybridized states of carbon atoms might change into the form illustrated in Fig. 7.40d to lead to the Type II polymer. 

In subsequent treatment, a condensation polymer formed from a monomer of the type A-B will be referred to as type I polymer and the polymerization will be called type I condensation, while a polymer formed from a mixture of A—A and B—B type monomers will be termed a type IIpolymer and the process referred to as type II condensation. 

All molecules containing an even number of units will necessarily be of type IIAB, while those containing an odd number of units will be of type IIAA or IIBB. In a stoichiometric mixture in which the numbers of A—A and B—B units are exactly equal, there will be as many even-x molecules (i.e., molecules with even number of units) as odd-x molecules (i.e., molecules with odd number of units), and the latter will be equally divided between types IIAA and IIBB. The molecular weight distribution given in the previous section for type I polymers (made from A—B monomers) applies here also only the alternation of end groups as described above will occur between successive even and odd values of x. 

Excited-state processes in polymer materials strongly depend on their electronic and structural properties. There are several types of polymers that are capable of energy transfer and migration. A polymer with a saturated backbone and pendant chromo-phores such as naphthalene, anthracene, and commercial dyes can be described as type I polymer [11], In some cases, the chromophore has also been incorporated as a component of the polymer backbone repeat unit or covalently linked to the polymer as a terminal end group. Typically, introduction of the chromophore is achieved through premodification of the monomers or postfunctionalization of the polymers. 

The photophysics of type I polymers is very similar to that of the corresponding small-molecule substituent chromophores that they contain. The polymer can be described as an inert scaffold that restricts the movement and relative distance of the chromophores. As a result, the photophysics of these polymers can be strongly affected by the conformation of the polymer backbone and, to a lesser extent, by the aggregation of the polymers. The basic photophysics and energy migration processes of this type of fluorescent polymers have been studied extensively by Guillet and Webber over the past two decades and have been summarized elsewhere [1,11]. 

Scheme 7.36 Synthetic scheme for the polymerization of norbornene and its derivatives via free radical polymerization (FRP), ring-opening metathesis polymerization (ROMP), and vinyl addition polymerization (VAP) techniques. Polymers I, II, and III are isomers that differ in their enchainment and physical properties. Co- and terpolymerization of norbornene and derivatives of norbornene with other alicyclic monomers such as maleic anhydride, methyltetracyclododecene carboxylic acid, etc. are also successfully synthesized with this scheme. (Note that 2, 3- and 2,7-enchainments of repeating units are reported in type I polymers. °°)...

Mass spectra of the type IPFPE sample with (n) = S. (a) Ionization at 273.3 run yields predominantly parent ions of the type I PFPE, which are indicated by the filled circles, (b) Ionization at 274.4 run favors ionization of the type B polymers present as an impurity in the sample (crosses) and van der Waals dimers of the type I polymers (open circles). Peaks due to these two components of the mass spectrum are not visible in panel A. The parent masses of the type I polymer are again indicated by the filled circles. 

During formation of MMCs various thermodynamic side efiects driven by a thermodynamically favoured terms can occur. This includes conformational changes, modification of functional groups and also macrochain breakage. Examples of conformational changes are chain transformation in poly(oxyethylene)-transition metal complexes [61,62], double helix model of poly(oxyethylene)-alkali metal ion complexes [63], conformational modifications of poly(2-vinylpyridine) or poly(amidoamines) during complex formation [64,65], and others. Important to mention here is that chain destruction can occur in type I polymers during their formation [3,66,67]. 

An other relevant class of type I polymers is given by polyimides [59-65]. As compared with polymethacrilates they show higher Tg and, in general, better time stability of NLO performances. The synthetic route to polyimides is versatile. They can be obtained by polymerization between bis-anhydrides and amino-chromophores. High performances are obtained using bis-phthalic anhydrides such as 3,3, 4,4 -oxydiphthalic anhydride (ODRA) or 4,4 -(hexafluoro-isopropylidene)diphthalic anhydride (6FDA). 

Those Haslam noted of Type (ii) include Vitis spp., Sorghum spp., and Vac-cinium oxycoccus. Further studies on the grape show that the leaves have a Type (i) polymer, and the Type (ii) are widespread in the Leguminosae - in Vida sativa, Lotus spp., Trifolium arvense, and Onobrychis vidifolia (36). Others include Vacdnium, Photinia spp, and Chaenomeles spedosa (L. J. Porter, unpublished results) and also apparently is almost the universal type in conifer barks (Pinus, Podocarpus, Pseudotsuga) (66, L. J. Porter, unpublished results). 

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