Homopolymers preparation

The true value of the chloropolymer (I) lies in its use as an intermediate for the synthesis of a wide variety of polytorgano-phosphazenes) as shown in Figure 1. The nature and size of the substituent attached to the phosphorus plays a dominant roll in determining the properties of the polyphosphazene. Homopolymers prepared from I, in which the R groups are the same or, if different, similar in molecular size, tend to be semi-crystalline thermoplastics. If two or more different substituents are introduced, the resulting polymers are generally amorphous elastomers. (See Figure 1.)... 

The structures of the dimethylsiloxane block copolymers and respective parent homopolymers prepared for use as positive, bilevel resist materials are shown in Figure 1. Most copolymers were synthesized with >10 wt % silicon. The selection of PDMSX block length and novolac chemical composition proved to be the two most critical variables in achieving adequate resolution. 

Figure 2. Sephacryl S-400 (PBS) chromatographic profiles of polyNIPAAM homopolymers prepared in various reaction solvents.

Of all of the AB benzocyclobutene maleimide homopolymers prepared, 114a appeared to have the best combination of thermal and mechanical properties as well as ease of fabrication (Table 21). This monomer/polymer was used as a... 

The physical properties of polyallomers are generally intermediate between those of the homopolymers prepared from the same monomers, but frequently represent a better balance of properties than blends of the homopolymers. This is illustrated by comparing the properties of a propylene-ethylene polyallomer containing 2.5% ethylene with polypropylene, high-density polyethylene, and a blend of 5% high-density polyethylene and 95% polypropylene. 

Block copolymers were also produced by oxidizing mixtures of the two homopolymers. A summary of the effect of polymerization conditions on the structures of polymers prepared using equimolar amounts of the two monomers is presented in Table III. The preformed blocks used in these examples were a DMP homopolymer prepared with a diethylamine-cuprous bromide catalyst and a DPP polymer prepared with tetramethyl-butanediamine-cuprous bromide at 60°C. Each had an average degree of polymerization of approximately 50 units. 

The authors demonstrated that polyvinyl chloride segments of these graft and block copolymers are more stable than PVC homopolymers prepared according to traditional ways. These last ways lead to disproportionation reactions giving unsaturations at the ends of polymers and these ends are responsible for the poor thermal stability of the polymers. In the present method, termination occurring essentially by transfer reaction, no unsaturations are observed and the authors showed an improvement in stability of the PVC segments of about 20 °C (Scheme 39). 

The morphology of a polyethylene blend (a homopolymer prepared from ethylene is a blend of species with different molar mass) after crystallisation is dependent on the blend morphology of the molten system before crystallisation and on the relative tendencies for the different molecular species to crystallise at different temperatures. The latter may lead to phase separation (segregation) of low molar mass species at a relatively fine scale within spherulites this is typical of linear polyethylene. Highly branched polyethylene may show segregation on a larger scale, so-called cellulation. Phase separation in the melt results in spherical domain structures on a large scale. 

Silica supported chromium catalysts that polymerize ethylene to polyethylene with as many as 12 methyl branches/1000 carbon atoms have been reported. The small amount of branching observed in the ethylene homopolymers prepared by these supported chromocene catalysts was attributed to a chain isomerization process (a) Karol, F. J. Karapinka, G. L. Wu,... 

The homopolymer, prepared by polymerization in liquid ammonia with sodium initiator at-77 °C, is insoluble in acetone, but it is soluble in dimethylformamide. When it is formed with lithium in liquid ammonia, at -75 °C, the molecular weight of the product increases with monomer concentration and decreases with initiator concentration. If, however, potassium initiates the reaction rather than lithium, the molecular weight is independent of the monomer concentration. " " Polymethaciylonitrile prepared with n-butyllithium in toluene or in dioxane is crystalline and insoluble in solvents like acetone. When polymerized in petroleum ether with /i-butyllithium, methacrylonitrile forms a living polymer. Highly crystalline polymethacrylonitrile can also be prepared with beryllium and magnesium alkyls in toluene over a wide range of temperatures. 

Homopolymers Prepared With Bifunctional Initiators. Warzelhan et al. showed that the syndiotactic content of PMMA was significantly lowered (from 58 to 20%) in going from a monofunctional to a bifunctional sodium initiator in THF at low temperatures. 

It has been observed that in carbocationic copolymerization the molecular weight of the resulting copolymer is always lower than that of the individual homopolymers prepared imder identical conditions (179). This was explained by the high tr/ p ratio of the favored cross-propagation step (reaction of the most reactive chain end with the monomer giving the most stable carbenium ion), compared to the respective homopolymerization tr/ p ratios (173). 

The photochemically initiated polymerization and copolymerization of VF were also carried out in a continuous flow cylindrical reactor at room temperature and under pressures of up to 30x10 Pa in order to achieve higher yields and to control the polymerization conditions [483]. From F-NMR analysis it turned out that the homopolymers prepared with the help of UV light were of higher regularity and contained less head-to-head addition than commercial PVF prepared at high temperatures. 

Cytop is a cyclic homopolymer prepared by cyclopolymerization of perfluoro(4-vinyloxy-1-butene) (IV), which is synthesized by the following multistep process (Scheme 16.4) [3]. The monomer is a colorless liquid and its boiling point is 65°C. 

The products were fractionated by successive extraction with a series of solvents and the solubility behaviors were compared with that of the corresponding homopolymers prepared under the same conditions. A typical result of the fractionation of the PB sample is listed in Table 3. It can be seen from the result that the solubility of the PB sample is much different from that of a mixture of the two homopolymers. It is worthy to mention that the propylene homopolymer was completely dissolved after extracting by boiling toluene, but the fractions of xylene extract and residual of the PB sample still contain propylene units 38.0 and 45.2 mol%, respectively. Furthermore, the IR spectra of all the fractions except the ether-soluble fraction exhibit the absorption band of trans-1,4 polybutadiene crystalline at 770 cm and absorption band of polypropylene crystalline at 841 cm as shown in Fig.8, indicating the presence of long butadiene-butadiene sequences and long propylene-propylene sequences. 

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