Linear polymers unsaturation

An alternative route to cross-linking is to start with a linear polymer and then cross-link the molecules by tying the molecule through some reactive group. For example, it is possible to cross-link unsaturated polyesters by an addition polymerisation across the double bond as shown schematically in Figure 2.12. 

Recently it has been shown that anionic functionalization techniques can be applied to the synthesis of macromonomers — macromolecular monomers — i.e. linear polymers fitted at chain end with a polymerizable unsaturation, most commonly styrene or methacrylic ester 69 71). These species in turn provide easy access to graft copolymers upon radical copolymerization with vinylic or acrylic monomers. 

PTEE is a linear polymer of the addition type, formed by polymerisation of the unsaturated monomer tetrafluoroethylene, CF2=Cp2. Despite the fact... 

The species IA, IB, IC represent the chain-propagating ester molecules, stabilised by styrene, and they are equivalent from the point of view of the polymerisation. At the end of the polymerisation, the now unstabilised ester II reacts with its own kind to give the indanyl ion III and a saturated linear polymer IV. It is also in equilibrium with unsaturated polymer V, and it reacts with acid and/or V to give the polymer with indanyl end groups VI. This is equivalent to the transfer reaction with monomer which gives the indanyl end groups [23]. The oligostyryl ion VII can only be present in very small concentration, as it is much less stable than the other SD ions which co-exist with ion III [7] these other SD ions have been omitted from the scheme so as not to complicate it unnecessarily. 

Ring-opening polymerization is different from the addition and condensation polymerizations described so far. It does not produce byproducts (e.g., water) as polycondensation does, and there is no unsaturated double bond in the monomers to lead to additional polymerization. However, some similarities do exist. Ringopening polymerization is initiated by the opening of a cyclic structure in the monomers and followed by polyaddition. As a result, a linear polymer with a chemical composition identical to that of the monomer is obtained. 

Linear polymers of DVB, with unsaturated groups in the main chain, have been obtained by the CF3SO3H- or AcClCVinitiated polymerization in benzene or CH2C12 [Eq. (2)] [3]. 

ADMET polymerization is performed on a,co-dienes to produce strictly linear polymers with unsaturated polyethylene backbones, as shown in Scheme 2. This step-growth polymerization is a thermally neutral process driven by the release of a small molecule condensate, ethylene [16-20]. Ring-opening metathesis polymerization (ROMP) is widely used to polymerize cyclic olefins and is performed with the same catalysts as in ADMET polymerizations. 

The nature and number of the terminal groups, the type of bonds, the presence of aromatic cycles and carbonate groups in the unsaturated ester molecule, as well as other structural features affect polymer flammability. The slope of the straight lines increases from methacrylate to acrylate polymers. Thus, for polymers of alkylene glycol dimethacrylates it is 2,82x 10 kJ/kg, for polymers with carbonate bonds 2.86 X 10 -2.9 X 10 kJ/kg for acrylic polymers it is somewhat higher, 3.27 x 10 kJ per kg. Linear polymers, e.g. PMMA, PE, etc. have a smaller slope corresponding to... 

As further shown, polymer chain scission or side scission of many linear polymers takes place through this mechanism. At higher temperatures (600-900° C) this type of reaction is also common for small molecules, which explains in some cases the formation of unsaturated or aromatic hydrocarbons from larger aliphatic ones. 

Crystalline inclusion compounds containing unsaturated monomers are effective reactive systems for the production of linear polymers (1-6). This process belongs to the wider class of solid state polymerization, but possesses some specific features which make it worthy of a separate description. Throughout this article, the polymerization in inclusion compounds will be referred to as "inclusion polymerization" (other names currently used in the scientific literature are channel, canal or tunnel polymerization), and the terms "clathrate" will be used as synonymous with "inclusion compound". When there is no risk of confusion, the more general term of "adduct" will be used for clathrate in principle a... 

Cataldo, F. On the action of polymers having unconjugated and cross or linearly conjugated unsaturations chemistry technological aspects. Polym. Deg. Stab. 2001, 73, 511. 

The product obtained in the polymerization of 4-methyl-l,6-heptadiene is a linear polymer containing no residual unsaturation. What is its chemical structure ... 

Initial achievements in this field were carried out by Kobayashi as early as 1978. Copolymerization of 71 with acrylonitrile produced linear polymers 72 (Scheme 10.14), which are soluble in polar aprotic solvents, that were assayed for different Michael additions. In general, good conversions were obtained, but enantioselec-tivities were always below 60% ee [204-206]. In a related approach by Oda, different spacers were introduced between the polyacrylonitrile backbone and the chiral fragment, which resulted in an increase of selectivity up to 65% ee [207]. Addition of thiol groups in PS-DVB resins to the double bond allowed the preparation of the corresponding insoluble polymers 73, which were assayed by Hodge for the addition of thiols to unsaturated ketones and nitrostyrene. Again, selectivities were... 

The polymerisation of DVF was first investigated by two independent research groups (2-7) who reported that soluble polymers could readily be obtained using free radical and cationic initiators. These authors proposed that cyclopolymerisation had occurred with the formation of linear polymers having three-carbon bridged ferrocene units (I), and some acyclic units (II), in the chain. Evidence for structure (I) as the predominant unit in the polymer chain was provided by the low level of vinyl unsaturation detectable by NMR or infrared spectroscopy and the observation that bands attributable to a bridged ferrocene (8) were to be found in the infrared spectra of these polymers. 

Whereas monoallyl derivatives sdeld thermoplastic polymers, allyl esters containing two or more unsaturated groups yield thermosetting resins. Thus, monoallyl esters of unsaturated acids, e.g., allyl acrylate, allyl methacrylate, allyl crotonate, and allyl itaconate, and diallyl esters of dibasic acids, e.g., diallyl oxalate, diallyl phthalate, and diallyl itaconate, yield thermoset resins, which generally combine solvent resistance, toughness, hardness, transparency, and heat resistance. The cross-linking tendency of the allyl esters makes them useful in copolymerization wherein they impart these properties to normally linear polymers. 

It was observed that up to about 25% conversion, the polymerization of diallyl o-phthalate is linear with time and initiator concentration. As the process continues, a cross-linked gel forms. The polymer formed up to 25% conversion has a melting point of about 90°C, is soluble, and is less unsaturated than would be expected for a linear polymer. Therefore, it was presumed that the prepolymers consisted of a main chain with a number of short branches [30]. 

By the photoreduction of H2PtCl6 in the presence of unsaturated surfactants (7 types), Pt clusters covered by polymeric micelles were obtained and further polymerized by UV radiation or by y-irradiation [290]. The formed clusters protected by polymerized micelles exhibited greater catalytic activity during the photochemical synthesis of H2 in the presence of EDTA/Ru(bpy)j /MV /Pt in aqueous solution than those clusters protected by linear polymers. The use of non-ionic surfactants resulted in the best catalytic activity. 

Linear polymers made of symmetrical unsaturated monomers, such as polyethylene and polyvinylidene chloride, crystallize easily. Asymmetric linear polymers such as polypropylene (PP) crystallize only if the configuration is regular, so isotactic and syndiotactic PP can crystallize, while atactic PP is amorphous. 

Polymers are normally classified into four main architectural types linear (which includes rigid rod, flexible coil, cyclic, and polyrotaxane structures) branched (including random, regular comb-like, and star shaped) cross-linked (which includes the interpenetrating networks (IPNs)) and fairly recently the dendritic or hyperbranched polymers. I shall cover in some detail the first three types, but as we went to press very little DM work has been performed yet on the hyperbranched ones, which show some interesting properties. (Compared to linear polymers, solutions show a much lower viscosity and appear to be Newtonian rather than shear thinning [134].) Johansson [135] compares DM properties of some hyperbranched acrylates, alkyds. and unsaturated polyesters and notes that the properties of his cured resins so far are rather similar to conventional polyester systems. 

Addition polymerization, also included in the modem term chain-growth polymerization, is a process in which unsaturated monomer units (those containing at least one double or triple carbon-carbon bond) are joined together one at a time to produce a linear polymer. Addition polymerization can he visualized as threading beads (monomers) on a string one by one. The resulting polymer contains only the small molecule which polymerizes the repeat unit found in the monomers and no by-products are formed. The simplest useful addition polymer is polyethylene which can be described as ... 

Natnrally ocenrring rabher is a linear polymer of isoprme nnits linked 1,4, and because the chain is unsaturated, two forms are found. Natural rubber is the cis form it has low crystallinity, = 200 K and = 301 K, whereas the trans form, called gutta-percha, or balata, has medium crystallinity with = 200 K and = 347 K. 

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