Side-chain homopolymers

Many studies on side-chain modifications in PF were initially based on the idea of excimer formation, resulting in the green emission during LED operation or in solid-state PL on annealing PF films. This resulted in several proposed strategies for the design of fluorene side-chain homopolymers, where bulky substituents at position 9 of the fluorene moiety should sterically prevent (hinder) interchain interaction and thus improve the stability of blue emission. 

P8 M is not the only polymer forming the isotropic smectic phase. To date, we have observed formation of that phase for a half-dozen chiral polymethacrylates and polysiloxanes. Table 5.1 summarizes the chemical structure and phase behavior of synthesized side-chain homopolymers, which carry chirally substituted side chains derived from asymmetric esters of terephthalic acid and hydroquinone. Such a structure with alternating orientation of carboxylic link groups seems to favour the formation of the IsoSm phase, whereas isomeric derivatives of p-hydroxybenzoic acid, where all carboxylic links have the same orientation, form only conventional Sm A and Sm C phases. Molar mass of all the synthesized homo- and copoly(meth)acrylates is within the range of 1 to 2-10 g mol the poiysilox-anes have the average degree of polymerization, p 35. 

Fig. 2. Ultimate tensile strength of starch- -poly(methyl acrylate) from Dennenberg et al. as functions of poly-(methyl acrylate) content and molecular weight of the grafted side chains. Homopolymer is retained in the samples.

Side-chain homopolymers based on poly(meth)acrylic derivatives (Fig. 16.14a) have been also widely studied (Andruzzief al., 1999 Rodriguez et al, 2005, 2006). When a suitable flexible spacer mediates between the main chain and the chromophore, these side chain polymers tend to exhibit thermotropic hquid crystalline properties, which favor cooperative chromophores motion during photoorientation and lead to more stable anisotropic optical properties. The azobenzene chromophore strongly influences a material s photoresponse. As a representative example, Ikeda... 

As shown in Table 3, the glass-transition temperatures of the amorphous straight-chain alkyl vinyl ether homopolymers decrease with increasing length of the side chain. Also, the melting points of the semicrystalline poly(alkyl vinyl ether)s increase with increasing side-chain branching. 

This combination of monomers is unique in that the two are very different chemically, and in thek character in a polymer. Polybutadiene homopolymer has a low glass-transition temperature, remaining mbbery as low as —85° C, and is a very nonpolar substance with Htde resistance to hydrocarbon fluids such as oil or gasoline. Polyacrylonitrile, on the other hand, has a glass temperature of about 110°C, and is very polar and resistant to hydrocarbon fluids (see Acrylonitrile polymers). As a result, copolymerization of the two monomers at different ratios provides a wide choice of combinations of properties. In addition to providing the mbbery nature to the copolymer, butadiene also provides residual unsaturation, both in the main chain in the case of 1,4, or in a side chain in the case of 1,2 polymerization. This residual unsaturation is useful as a cure site for vulcanization by sulfur or by peroxides, but is also a weak point for chemical attack, such as oxidation, especially at elevated temperatures. As a result, all commercial NBR products contain small amounts ( 0.5-2.5%) of antioxidant to protect the polymer during its manufacture, storage, and use. 

Short chain branching is negligible with Ziegler and Phillips homopolymers although it is possible to introduce deliberately up to about seven ethyl side chains per 1000 carbon atoms in the Ziegler polymers. 

In 2003, the van Hest group produced elastin-based side-chain polymers [123]. This research was motivated by the demonstration of the occurrence of an inverse temperature transition in a single repeat of VPGVG [124]. A methacrylate-functionalized VPGVG was synthesized and used as a monomer to perform atom transfer radical polymerization (ATRP) to produce homopolymers (Fig. 16b) or... 

Fig. 16 Various type of elastin-based side-chain polymers (a) ABA block copolymer produced via ATRP, (b) homopolymer produced via ATRP, (c) homopolymer produced via RAFT polymerization...

Another interesting feature pertains to the melting points cited for the polymers having m — 6-9. The side chains are now long enough to crystallize themselves, which is apparently the reason that formation of mesophases is suppressed. Such side-chain crystallization has also been involved in polysilane homopolymers... 

The poly(5-fnethyl-l, 4-hexadiene) fiber pattern (Figure 6) gave an identity period of 6.3 A, indicating a 3 isotactic helix structure. The X-ray diffraction pattern was not very sharp, which may be due to the difficulty of the side chain with a double bond to fit in a crystalline lattice. The crystallinity was determined to be 15% using the Hermans and Weidinger method (27). A Chloroform-soluble fraction free from catalyst residues showed no improvement in the sharpness of the X-ray diffraction pattern. These data show that the configuration of the 1,2-polymerization units in the homopolymer of 5-methyl-1,4-hexadiene is isotactic. 

Macromolecules have also been specifically designed and synthesized for use as emulsifiers for lipophilic materials and as stabilizers in the colloidal dispersion of lipophilic, hydrocarbon polymers in C02. We have demonstrated the amphiphilicity of fluorinated acrylate homopolymers, such as PFOA, which contain a lipophilic, acrylate like backbone and C02-philic, fluorinated side chains (see Fig. 3) [103]. It has been demonstrated that a homopolymer which physically adsorbs to the surface of a polymer colloid prevents agglomeration by the presence of loops and tails (see Fig. 4) [113]. The synthesis of this type of... 

The properties of alkyl acrylate homopolymers vary accordingly to the number of carbon atoms in the alkyl radical. As the number of carbon atoms increases the Tg decreases from room temperature to well below 0 °C until the number exceeds 10. However, as the carbons in the side chain increase oil resistance decreases. When carbon atoms in the alkyl radical are replaced by oxygen, oil resistance improves. 

Preferential Screw Sense Homopolymers with Enantiopure Chiral Side Chains... 

---