Tongyin Yu

Phase separation in blends of homopolymer and graft copolymer based on styrene and butadiene

A series of blends of homopolystyrene and styrene-g-butadiene copolymer with different combinations of molecular weights of the copolymer and graft polystyrene segments have been prepared. Phase separation behaviour of the blends has been examined by electron microscopy. The results reveal a regular change of morphology of the blends with the relative molecular weights of the free and graft polystyrene chains. The observed relationships between compatibility of the homopolymer and copolymer and the relative molecular weight are generally in agreement with that observed previously in homopolymer-block copolymer blends. Taking the inherent polydispersity of the molecular weight of the component polymers into account, some peculiarities of the morphologies of the blends have been explained.

Phase separation in polymer blends comprising copolymers: 6. Effect of molecular architecture of block copolymers

Abstract To study the effect of the molecular architecture of a copolymer on its miscibility with corresponding homopolymers a series of block copolymers of styrene and isoprene with diblock, triblock and four-arm star architectures have been prepared and the morphologies of the blends of the copolymers and polyisoprene with different molecular weights have been examined by electron microscopy. The results show that miscibility varies in the sequence diblock>triblock>four-arm star copolymers. This sequence is in the opposite direction to the variation of the architectural complexity of the block copolymers, i.e. the more complex is molecular architecture, the greater is conformation restriction in microdomain formation and the less is solubility of homopolymer in corresponding domains.

Phase separation in polymer blends comprising copolymers: 7. Statistical theory of block copolymer-homopolymer systems

Abstract The miscibility of a homopolymer in corresponding domains of a copolymer predicted by Meiers theory is far less than found experimentally. In this paper, a density gradient model is suggested for describing the segment distribution of the bound and free chains in block copolymer-homopolymer systems. Using this model, Helfands theory, which has been successful in explaining microphase separation of block copolymers, is extended to polymer blends of homopolymer and corresponding block copolymer with lamellar structure. The calculated free energy of mixing of the system shows that the predicted miscibility is much larger than that obtained by Meiers theory and is in good agreement with the main known experimental results. In particular, on the basis of the present theory, homopolymer can be expected to be solubilized by corresponding blocks in the whole composition range provided that the molecular weight of the former is less than that of the latter.

Controllable specific interactions and miscibility in polymer blends: 3. Non-radiative energy transfer fluorescence studies

Abstract Polymer blends of poly(methyl acrylate) and modified polystyrene (PS(OH)) with introduced strong proton-donating hydroxyl groups have been studied by non-radiative energy transfer fluorescence. As the content of hydroxyl in PS(OH) increases from 0 to 1.6 mol%, the efficiency of energy transfer increases gradually. This modification corresponds to the morphological change observed by transmission electron microscopy (TEM) from the completely phase-separated state to the single-phase state. Blends with hydroxyl contents in PS(OH) > 7 mol% show much higher efficiency of energy transfer than miscible blends, indicating a certain structural change which cannot be detected by TEM. The effect of the formation rate of the toluene cast films on morphology and the effect of chromophore concentration on efficiency of energy transfer are also discussed.

Phase separation in polymer blends comprising copolymers: 4. Polycarbonate/polystyrene ABCP system

Abstract An AB-crosslinked copolymer (ABCP) with polycarbonate as A-chain and polystyrene as B-chain was prepared and characterized. A series of blends of the ABCP and homopolystyrene fractions with different molecular weights were prepared and examined by electron microscopy. The results show that the miscibility between the homopolymer and the like chains in the copolymer is limited even if the molecular weight of the former is much less than that of the latter. Considering the relatively large miscibility in diblock copolymer/homopolymer blends and the limited miscibility in ABCP/homopolymer-A blends reported in literature, this study leads to an argument that the molecular architecture of a copolymer is an important factor governing its miscibility with homopolymer. The relatively complicated architecture of ABCPs causing more restriction to the chain conformation might be one of the main reasons for its low miscibility with homopolymers.

The synthesis and characterization of polyethylene succinamide (polyamide 24)

SummaryThe current paper presents the synthesis of a new polyamide, polyethylene succinamide (polyamide 24), via interfacial and solution-solid phase polycondensation. The resulting product was characterized by means of elementary analysis, infrared spectrometry, 1H-nuclear magnetic resonance, intrinsic viscosity and differential carolimetry. The effects of polymerization conditions on molecular weight of the product and the solubility of polyamide 24 in a number of commonly used solvents were also studied.

Polycondensation kinetics of poly(phenylene ether sulphone)

Abstract The synthesis of poly(phenyl ether sulphone) (from the potassium salts of 4,4′-dihydroxydiphenyl sulphone and 4,4′-dichlorodiphenyl sulphone or 4-chloro-4′-hydroxydiphenyl sulphone) was found to have different reaction kinetics according to the route used. By discriminating between rate constants (between monomer/monomer, monomer/polymer, polymer/polymer) a set of multi-parameter kinetic equations is obtained. Experimental and simulated values of the individual rate constants were in good agreement (for both the reaction rate and molecular weight distribution). The polycondensation reaction can be analysed, in terms of the component reactions.

Controllable specific interactions and miscibility in polymer blends: 4. Effect of hydrogen bonding density in interpenetrating polymer networks

Sequential interpenetrating polymer networks (IPNs) composed of poly(butyl acrylate) as the first network and modified polystyrene containing proton-donor hydroxyl groups [PS(OH)] as the second network are studied by d.s.c., transmission electron microscopy and dynamic mechanical analysis. The apparent miscibility between the components increases considerably as the hydroxyl content in PS(OH) increases. However, differing from the corresponding blends of the linear polymers, for which ∼2mol% hydroxyl introduced into PS(OH) leads to complete miscibility, the IPNs always show two-phase structures even when the hydroxyl content in PS(OH) is as high as 30 mol%.

Phase separation in polymer blends comprising copolymers: 5. Polyisoprenepoly(isoprene-g-styrene) copolymer system

Abstract As part of a programme of research into miscibility in polymer blends comprising copolymers, this paper presents the morphology of blends of polyisoprene and poly(isoprene- g -styrene) with complicated but well defined structure. The graft copolymers were prepared by polymerization of styrene initiated by metallated polyisoprene backbone and were fully characterized. All the studied blends of copolymers and polyisoprene of different molecular weights exhibit macrophase separation even when the molecular weight of the homo PI is apparently less than that of the PI segments between neighbourning junction points in the copolymers. The results provide support for the argument that the molecular architecture of a copolymer is an important factor governing its miscibility with corresponding homopolymers. Besides, it is observed that the copolymer with higher proportion of polystyrene shows apparent solubilization in polystyrene matrix of high molecular weight and solubilization varies predictably with the addition of low molecular weight polyisoprene.

Interpenetrating polymer networks with controllable intermolecular hydrogen bonding

SummaryThe effect of introducing simultaneously crosslinking and intermolecular hydrogen bonding into blends of poly(styrene) and poly(butyl acrylate) on miscibility was studied by DSC, TEM and IR. Incorporation of strong proton-donor groups into PS apparently promotes its miscibility with PBA due to hydrogen bonding. Single phase IPN can be prepared but much higher content of the proton-donor is needed in comparison with the corresponding blend without crosslinking. The interlocking structure of the networks appears unfavourable to forming real miscible IPNs.