Poly copolymers comonomer composition

Deviations are also observed in some copolymerizations where the copolymer formed is poorly soluble in the reaction medium [Pichot and Pham, 1979 Pichot et al., 1979 Suggate, 1978, 1979]. Under these conditions, altered copolymer compositions are observed if one of the monomers is preferentially adsorbed by the copolymer. Thus for methyl methacrylate (M1 )-/V-vinylcarbazole (M2) copolymerization, r — 1.80, r2 = 0.06 in benzene but r — 0.57, > 2 0.75 in methanol [Ledwith et al., 1979]. The propagating copolymer chains are completely soluble in benzene but are microheterogeneous in methanol. /V-vinylcarba-zole (NVC) is preferentially adsorbed by the copolymer compared to methyl methacrylate. The comonomer composition in the domain of the propagating radical sites (trapped in the precipitating copolymer) is richer in NVC than the comonomer feed composition in the bulk solution. NVC enters the copolymer to a greater extent than expected on the basis of feed composition. Similar results occur in template copolymerization (Sec. 3-10d-2), where two monomers undergo copolymerization in the presence of a polymer. Thus, acrylic acid-2-hydroxyethylmethacrylate copolymerization in the presence of poly(V-vinylpyrrolidone) results in increased incorporation of acrylic acid [Rainaldi et al., 2000]. 

Thermodynamic equations are formulated for the isomorphic behavior of A-B type random copolymer systems, in which both A and B comonomer units are allowed to cocrystallize in the common lattices analogous to, or just the same as, those of the corresponding homopolymers poly(A) or poly(B). It is assumed that, in the lattice of poly (A), the B units require free energy relative to the A units and vice versa. On the basis of the derived thermodyn-amie equations, phase diagrams are proposed for the A-B random copolymers with cocrystallization. The melting point versus comonomer composition curve predicted by this diagram is very consistent with that experimentally observed for the P(3HB-co-3HV) copolymers, as shown in Fig. 21.1. It is suggested that the minor comonomer unit with a less bulky structure cocrystallize thermodynamically simpler than that with a more bulky structure. 

Preformed particles are incorporated into the epoxy matrix by simple mechanical mixing. The dispersibility of the particles can be improved by 1) introducing crosslinking into the shell or 2) using comonomer-like acrylonitrile or GMA, which increases the interfacial adhesion by polar or chemical interaction [96, 97]. Quan and co-workers [98] reported that for poly (butadiene-co-styrene) core poly (methyl methacrylate) (PMMA) shell particles, the cluster size reduces from 3-5 pm to 1-3 pm as a result of using 5 wt% crosslinker (divinyl benzene). They also found that the cluster size could be further reduced to 1-2 pm by using a methyl methacrylate-acrylonitrile (MMA-AN) or methyl methacrylate-glycidyl methacrylate (MMA-GMA) copolymer shell composition. 

Recently, Choo and Way mouth performed the copolymerization of ethylene with 1,5-HD using various metallocene catalysts (12, 13, 14, Figure 19.2). 1,5-HD cyclopolymerized exclusively to give MCP units in the copolymers, with only traces of uncyclized 1,2-inserted 1,5-HD. The diaste-reoselectivity of the cyclocopolymerization favored the formation of 1,3-cyclopentane rings for metallocenes (74% trans for 12, 81% trans for 13, and 66% trans for 14). For metallocenes 12 and 14, the ethylene/1,5-HD copolymerization yielded copolymers with similar comonomer compositions and sequence distributions to those observed for ethylene/1-hexene copolymerization with these catalysts. On the other hand, the copolymers derived from metallocene 13 showed very different compositions and sequence distributions. At comparable comonomer feed ratios, the poly(ethylene-c -l,5-HD)s were enriched in the 1,5-HD comonomer and deficient in ethylene as compared to the analogous polymers prepared from ethylene and 1-hexene. The copolymerization behavior of 13 provided support for a dual-site alternating mechanism for 1,5-HD incorporation, wherein one coordination site of the active catalyst center is highly selective for the initial 1,2-inserion of 1,5-HD and the other site is selective for cyclization. 

The properties of smart polymers, which are important for biotechnological and medical applications, often can be controlled not only by the comonomer composition, but also by the polymer architecture. For example, block copolymers with a thermosensitive smart part consisting of poly(NIPAAM) do not separate from aqueous solutions in the same manner as random copolymers do. In particular, a reversible gel rather than a concentrated polymer phase is formed in response to an increase in temperature. Osmb-lilm copolymers with poly(NIPAAM)-grafts show a faster and more pronounced response to changes in temperature as compared to random copolymers. ... 

The maximum rates of crystallisation of the more common crystalline copolymers occur at 80—120°C. In many cases, these copolymers have broad composition distributions containing both fractions of high VDC content that crystallise rapidly and other fractions that do not crystallise at all. Poly(vinyhdene chloride) probably crystallises at a maximum rate at 140—150°C, but the process is difficult to foUow because of severe polymer degradation. The copolymers may remain amorphous for a considerable period of time if quenched to room temperature. The induction time before the onset of crystallisation depends on both the type and amount of comonomer PVDC crystallises within minutes at 25°C. 

Nonetheless, one cannot exclude the probability of a successful combination of these prerequisites (as was the case with poly[(NiPAAm-co-GMA)-g-PEO considered above]) that will allow us to obtain, using the chemical colouring approach, the protein-like HP-copolymers with a dense hydrophobic core wrapped by the hydrophilic shell. Such a shell should be capable of efficiently protecting the temperature-responsive macromolecules against pronounced interchain hydrophobic interactions and precipitation at temperatures significantly higher than those at which the copolymers of the same total monomer composition—but with a non-protein-like primary sequence of comonomer units—are in the soluble state. 

Polymerization Results. A batch polymerization of MMA-MAA comonomer was analyzed for the determination of the reactivity ratios of the two monomers. The change in the ratio of the copolymer composition determined by GC was plotted against conversion as shown in Figure 1. Similarly, the calculated curves for some assumed reactivity ratios are also shown in the same Figure. The optimum values of the reactivity ratio for the emulsion poly-... 

The copolymer composition is a function of the comonomers reactivities. For example, the carborane concentration in a poly (diene-co-acryloyloxymethyl carborane) is higher than that of the carborane monomer in the initial solution 20>. Chloroprene, which has a higher reactivity than the other monomers, is an exception. 

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