Monomers and Homopolymers

While the ROP of five-membered cycUc carbonates is thermodynamically unfavorable and results in a poly(ether carbonate) via decarboxylation of part of the monomer [37], six-, seven- and higher-membered cyclic carbonates and dicarbonates [38-45] were polymerized to obtain polycarbonates without ether sequences. Several 2,2-disubstituted trimethylene carbonate and spirocarbonate monomers were prepared and polymerized in order to tune the polymer properties highly crystalline materials or materials with variable Tg-values were obtained [46-56]. 

As mentioned above, since the ROP of cyclic carbonates is an equilibrium reaction, six-membered cychc carbonates show a strong substitution effect on the equihbrium monomer concentration. The anionic ROP of l,3-dioxan-2-one (2) and 5,5-disubstituted l,3-dioxan-2-ones (10, 11, 12, 14) in THF solution using potassium tert-butoxide as initiator revealed an increasing monomer concentration at 

Polycarbonates with diethylene or triethylene glycol moieties were obtained by ROP of the corresponding cyclic dicarbonates 37 and 38. These polymers are crystalline and hydrophilic, and suitable for the preparation of amphiphilic copolymers [78]. 

Despite the typical behavior of five-membered cycUc carbonates to result in polyether carbonates upon polymerization at higher temperatures (T 150°C), five-membered cyclic carbonates derived from methyl-4,6-0-benzylidene-glucopy-ranoside (39) [79] and 1,2-O-isopropylidene-D-xylofuranose (40) [80] were polymerized at temperatures below 70 °C, without any eUmination of carbon dioxide, to produce polycarbonates. The polymerization of 39 was carried out with 1,8 diaz-abicyclo [5.4.0]undec-7-ene (DBU) or potassium tert-butoxide, while that of 40 was performed with potassium tert-butoxide or yttrium isopropoxide as initiator. After removal of the protection groups, the carbohydrate polymers with carbonate main-chain linkages were obtained. 

Bifunctional cyclic carbonates with two six-membered rings, as for example bis(5-ethyl-2-oxo-l,3-dioxan-5-yl)methylether (41), are used for the preparation of thermosetting aliphatic polycarbonates. These crosslinked polymers are degradable and have great potential for the preparation of delivery systems in agrochemical and medical applications [81]. 

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Pauluhn, J., Eidmann, P. and Mohr, U., Respiratory hypersensitivity in guinea pigs sensitized to 1,6-hexamethylene diisocyanate (HDI) Comparison of results obtained with the monomer and homopolymers of HDI. Toxicology, 171, 147, 2002. 

Table 18. Properties of AB-benzocyclobutene/alkene monomers and homopolymers...

Several different AB maleimide benzocyclobutenes were prepared and Table 21 lists these monomers and homopolymers along with their thermal and... 

NIPAAm-g-fPTFE plate or DMA-g-fPTFE plates were washed with cool water or with water and 50% y/w) methanol to remove monomers and homopolymers. DMA-g-fPTFE plate were soaked in a NaOH solution of pH12 for deprotonating grafted dimethylamino groups of PDMA chains. 

Free radical copolymerization is the most commonly used method to synthesize hydrogel from vinyl monomers. The ionic or neutral monomers and the cross-linking agents are copolymerized in bulk, in solution, or in suspension. The reaction is normally initiated with chemical initiator, heat, or radiation, e.g. UV light or gamma ray. After polymerization the hydrogels need to be washed with water in order to remove the residual monomers and homopolymers not incorporated into the network. 

In homopolymers all tire constituents (monomers) are identical, and hence tire interactions between tire monomers and between tire monomers and tire solvent have the same functional fonn. To describe tire shapes of a homopolymer (in the limit of large molecular weight) it is sufficient to model tire chain as a sequence of connected beads. Such a model can be used to describe tire shapes tliat a chain can adopt in various solvent conditions. A measure of shape is tire dimension of tire chain as a function of the degree of polymerization, N. If N is large tlien tire precise chemical details do not affect tire way tire size scales witli N [10]. In such a description a homopolymer is characterized in tenns of a single parameter tliat essentially characterizes tire effective interaction between tire beads, which is obtained by integrating over tire solvent coordinates. 

When both and T2 are greater than 1, the copolymer becomes blocky ia nature. When and T2 are much greater than 1, homopolymers of each monomer are formed and the resulting material is usually a polymer blend of some copolymer and homopolymer. Type II ... 

The successful development of eye contact lenses led in turn to a demand for soft contact lenses. Such a demand was eventually met by the preparation of copolymers using a combination of an acrylic ester monomer such as methyl methacrylate, a cross-linkable monomer such as a dimethacrylate, and a monomer whose homopolymer is soluble or highly swollen in water such as N-vinyl pyrrolidone. Such copolymers swell in water (hence the term hydrophilic), the degree of swelling being controlled by the specific type and amount of the monomers used. In use the lens is swollen to equilibrium in water, a typical soft lens having a water content of about 75%. 

Mixtures of monomers can be used to balance properties. This is possible due to the ease of copolymer formation via free-radical polymerization. The glass transition temperature of acrylic copolymers can be predicted from the weight fraction of the component monomers and the glass transition temperatures of the respective homopolymers [20]. Eq. 3 (commonly known as the Fox equation) is reported ... 

More recently, the copolymerization of ethyl cyanoacrylate with other 1,1 disubstituted electron deficient monomers and the effect of the monomers on adhesive properties have been studied. Monomers, such as diethyl methylene-malonate (DEMM), 8, were prepared [6,7]. Their homopolymers and copolymers... 

Grafting efficiency is determined from the total conversion of monomer into homopolymer and graft copolymer and is expressed as ... 

Polymers are classified according to their chemical structures into homopolymers, copolymers, block copolymers, and graft copolymers. In a graft copolymer, sequences of one monomer are grafted onto a backbone of the other monomer and can be represented as follows ... 

R is a low-molecular weight radical or hydrogen atom. A and B are monomers. The homopolymer (B)m arises from initiation by small radicals R and also by radiolysis of the monomer B. 

To avoid homopolymer formation, it is necessary to ensure true molecular contact between the monomer and the polymer. Even if this is initially established, it needs to be maintained during the radiation treatment while the monomer is undergoing conversion. Several methods are used for minimizing the homopolymer formation. These include the addition of metal cations, such as Cu(II) and Fe(II). However, by this metal ion technique, both grafting and homopolymerization are suppressed to a great extent, thus permitting reasonable yield of graft with little homopolymer contamination by the proper selection of the optimum concentration of the inhibitor [83,90,91]. 

The homopolymers of styrene and acrylonitrile were not soluble In the acetonitrile mobile phase. Calibration factors thus had to be derived from a combination of literature data and experimental measurements. To calibrate the UV detector for polystyrene, 254 nm absorbance of both monomer and polymer was measured with a conventional spectrophotometer, using chloroform... 

Published refractive index data for the mobile phase, polystyrene, polyacrylonitrile, and the two monomers were used to calculate refractive index detector calibrations for the two homopolymers. The published data were used to determine relationship between refractive index increments of monomer and corresponding homopolymer. Chromatographic refractometer calibrations for the two homopelymers were then calculated from experimentally measured calibration data for the two monomers. 

The transition temperatures that are combined in Figure 2 show the disappearance of crystallinity in the copolymers as the Ter and Tm flow together moving away from either homopolymer. This reflects the random distribution of monomer units in these copolymers. If the copolymer reactions had given homopolymer mixtures, there would be two separate crystalline melting temperatures. In addition, the 13C NMR indicates that the copolymer products contain a random distribution of C5 and C8 units and that the resulting double bonds are cis from the C8 monomer and largely trans from the C5 monomer (52). 

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