Unperturbed Chain Dimensions of Stereoirregular 1, 4-Polybutadiene and 1, 4-Polyisoprene

Abstract

ABSTRACT:The characteristic ratios of stereoirregular 1, 4-polybutadiene and I, 4-polyisoprene chains have been theoretically investigated by the Monte Carlo procedure in accordance with the model proposed by Mark. It was pointed out that the presence of discrete cis units in trans-rich chains significantly reduces the characteristic ratio while that of discrete trans units in cis-rich chains has little effect on the characteristic ratio.KEY WORDS Characteristic Ratio / Chain Statistics / l, 4-Polybutadiene / 1, 4-Polyisoprene / Stereoirregular Polymer / Monte Carlo Chain/ In recent years a great deal of attention has been paid to the effect of stereochemical configuration on the conformational statistical mechanical properties of polymer chains. The dependence of characteristic ratio <R/)/nt2, in which <R/) is the unperturbed end-to-end length, n the degree of polymerization, and / the bond length per structural unit, on the tacticity, i.e., sequence distribution of stereoisomers, has been investigated by several authors. Such studies have been carried out for asymmetric vinyl chains, 1 ' 2 o, L-copolypeptides, 1 , 3 and o, L-polylactic acid. 4Many studies have already been published of random chain conformations of 1, 4-polyisoprene in which the double bonds are either all in trans or cis form. Allegra, et al., 5 ' 6 derived unperturbed end-to-end length of cis-I, 4-polybutadiene. Mark investigated the unperturbed endto-end length and its temperature coefficient for cis-I, 4-polybutadiene and cis-1, 4-polyisoprene. 8 Further, Ishikawa and Nagai 9 ' 10 discussed the unperturbed end-to-end length and stress-optical coefficient for these four kinds of stereoregular diene-polymers.Although stereoregular polymers are not classified as copolymer in usual sense, these can be treated as such by considering each stereoisomer as a molecular species which is experimentally * To whom correspondence should be addressed. 500 separable. In fact, some trials 11 -14 have been done to correlate the sequence distribuiton of stereoisomers with chain configuration of stereoirregular polymers.An investigation concerned with sequence distribution of trans and cis units has been reported by Berger, et al., 15 with a polybutadiene chain whose trans content varied from O to 95 % . The relation between the characteristic ratio and trans-cis arrangement for rubberlike hydrocarbon polymers containing double bonds were also reported by Wall 16 and Markovitz.17 With the use of a very simple model they simply assumed the distribution of cis and trans units to be random and moreover free rotation to be allowed only around the single bonds.

Effects of Asymmetric Molecular Architecture on Chain Stretching and Dynamics in Miktoarm Star Copolymers

“…However, with changes in PI molecular weight for the PSPI 2 polymers, the values of T Δε HN ϕ PI –1 are constant but vary among the PS 2 PI 2 polymers. The variations in T Δε HN ϕ PI –1 among the PS 2 PI 2 samples in Figure can be explained through another parameter that characterizes local constraints on chain conformations, the characteristic ratio ( C ∞ ∼ ⟨ R 2 ⟩/ M w,PI , which for PI homopolymer is 4.8) . Assuming g = 1 for the PSPI 2 and PS 2 PI 2 polymers, rearranging eq shows that T Δε n ϕ PI –1 ∼ ⟨ R 2 ⟩/ M w,PI .…”

“…The variations in TΔε HN ϕ PI −1 among the PS 2 PI 2 samples in Figure 5 can be explained through another parameter that characterizes local constraints on chain conformations, the characteristic ratio (C ∞ ∼ ⟨R 2 ⟩/M w,PI , which for PI homopolymer is 4.8). 76 Assuming g = 1 for the PSPI 2 and PS 2 PI 2 polymers, rearranging eq 3 shows that TΔε n ϕ PI −1 ∼ ⟨R 2 ⟩/M w,PI . The increase in PI molecular weight from the 16k 2 −9k 2 copolymer to the 16k 2 − 24k 2 copolymer brings about an increase in interfacial energy due to the change from spherical PI domains to lamellar morphology, which is offset with an increase in PI stretching energy in the PI spheres due to osmotic constraints.…”